The interconnected pore structure and large surface-to-volume ratio of three-dimensional (3D) architected battery electrodes enable enhanced electrochemical performance through improved ionic transport. We developed a hydrogel infusion additive manufacturing (HIAM)-based approach to fabricate microarchitected LiFePO4 (LFP)/C composite electrodes with feature dimensions of 18 μm, delivering a specific capacity of 160 mAh/g at C/10. Electrodes with tilted cube, honeycomb, and triply periodic minimal surface (TPMS) geometries were designed to probe geometric effects on electrochemical performance under various rates. Material characterization revealed homogeneous formation of LFP particles (201 ± 67 nm) within the lattices, while the concomitantly formed carbon network provided mechanical support and enabled high-fidelity architecture. An experimentally informed electrochemical model identified electrolyte Li+ transport and solid-state Li+ diffusion as the dominant factors governing active material utilization. This work introduces a versatile manufacturing platform for 3D battery components and provides insights into structure optimization for high-performance rechargeable batteries.
", "doi": "10.1021/acsenergylett.6c00372", "issn": "2380-8195", "publisher": "American Chemical Society", "publication": "ACS Energy Letters", "publication_date": "2026-05-04", "pages": "acsenergylett.6c00372" }, { "id": "authors:04nsx-jg275", "collection": "authors", "collection_id": "04nsx-jg275", "cite_using_url": "https://authors.library.caltech.edu/records/04nsx-jg275", "type": "article", "title": "Nanoporosity-driven deformation of additively manufactured nano-architected metals", "author": [ { "family_name": "Zhang", "given_name": "Wenxin", "orcid": "0000-0002-6318-0622", "clpid": "Zhang-Wenxin" }, { "family_name": "Li", "given_name": "Zhi", "orcid": "0000-0003-2399-379X" }, { "family_name": "Gao", "given_name": "Huajian", "orcid": "0000-0002-8656-846X" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "3D printing methods for small-scale metals enable a unique 10–100 nm dimensional niche where functional feature sizes, critical microstructural detail and atomic-level defects converge, challenging conventional hierarchical relationships and carrying significant nanomechanical implications. We introduce a metal nano-printing system combining two-photon lithography, hydrogel infusion-based additive manufacturing and in situ mechanical experiments on 3D nano-architected Ni, achieving ~100 nm critical dimensions, ~10 nm surface roughness, and a broad range of geometries (periodic vs. non-periodic; beam-based vs. shell-based) with superior specific strengths of ~100 MPa·g − 1·cm3 enabled by an unambiguous smaller is stronger size effect. Experiments identify concentrated-porosity regions as primary deformation-initiation sources and quantify their distribution as input for physics-informed, multiscale finite-element simulations that accurately predict size-dependent mechanical properties governed by nanoporosity-driven deformation. This work integrates experimental and computational approaches for the fabrication, characterization, and evaluation of nano- and micro-architected metals for nanotechnology and nanoscale manufacturing systems.
", "doi": "10.1038/s41467-026-69845-8", "issn": "2041-1723", "publisher": "Nature Publishing Group", "publication": "Nature Communications", "publication_date": "2026-02-28" }, { "id": "authors:cc6vh-gx897", "collection": "authors", "collection_id": "cc6vh-gx897", "cite_using_url": "https://authors.library.caltech.edu/records/cc6vh-gx897", "type": "article", "title": "Micro-Architected Lithium Cobalt Oxide", "author": [ { "family_name": "Sun", "given_name": "Yuchun", "orcid": "0000-0002-7028-3523" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "Advancements in additive manufacturing (AM) enable the precise engineering of micro\u2010architected electrodes with enhanced electrochemical and mechanical properties. Existing AM approaches for fabricating lithium\u2010ion battery cathodes rely on extrusion\u2010based direct ink\u2010writing, which is usually limited to 150–200 µm resolution, or vat photopolymerization (VP) 3D printing with metal salt solution, which is limited in material choices due to the complicated photoresin design and printing parameter optimization. A gel infusion AM technique is introduced to fabricate micro\u2010architected cathodes, using lithium cobalt oxide (LCO) as a model prototype, which utilizes VP 3D printing with a \"blank\" photoresin to circumvent these limitations. The synthesized micro\u2010architected LCO electrodes are free\u2010standing and binder\u2010free, with beam diameters below 50 µm and tunable microstructure and mechanical resilience. The nanoindentation modulus of differently oriented LCO grains varies between 148.4 and 286.6 GPa, with no grain boundary weakening. This electrode gives a reversible capacity of 122–142 mAh g−1 (11.3–13.2 mAh cm−2) up to a current density of 28 mA g−1 (2.6 mA cm−2). This method is adaptable for a broad range of cathode materials, which opens a promising pathway to fabricate micro\u2010architected electrodes with fully controllable form factors, versatile material choices, and micro\u2010sized resolution for future energy storage solutions.
", "doi": "10.1002/advs.202513312", "issn": "2198-3844", "publisher": "Wiley-VCH GmbH", "publication": "Advanced Science", "publication_date": "2025-10-08", "pages": "e13312" }, { "id": "authors:0e3vd-afq85", "collection": "authors", "collection_id": "0e3vd-afq85", "cite_using_url": "https://authors.library.caltech.edu/records/0e3vd-afq85", "type": "article", "title": "Multiscale Microstructural and Mechanical Characterization of Cu\u2013Ni Binary Alloys Reduced During Hydrogel Infusion\u2010Based Additive Manufacturing (HIAM)", "author": [ { "family_name": "Tran", "given_name": "Thomas T.", "orcid": "0009-0003-7034-9486" }, { "family_name": "Gallivan", "given_name": "Rebecca A.", "orcid": "0000-0001-6516-2180" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "AbstractHydrogel infusion\u2010based additive manufacturing (HIAM) is a chemically versatile solid\u2010state processing pathway that allows 3D structuring of ceramics and alloys with micro\u2010scale precision. Using thermal treatments of 3D\u2010printed metal ion\u2010infused gels, this process generates intricate microstructures throughout their complex phase evolution. Through investigation of the HIAM\u2010produced CuxNi1-x alloy system, substantial grain growth after reduction is shown to drive the formation of numerous annealing twins and entrap unreduced oxide nano\u2010inclusions, resulting in hierarchical composite microstructures. These features appear to elevate the average nanoindentation hardnesses by up to four times that of bulk annealed CuxNi1-x. Uniaxial compression of micropillars milled from individual grains reveals composition dependence on the scaling of the \"smaller is stronger\" size effect. This compositional dependence of deformation mechanisms arises from changes in reduction kinetics which influence the density of inclusions and voids developed by the HIAM process. This work highlights the rich microstructural landscape accessible to HIAM\u2010produced alloys and provides a useful pathway for the characterization and tuning of superior mechanical performance in additively manufactured alloys.
", "doi": "10.1002/smll.202501320", "issn": "1613-6810", "publisher": "Wiley-VCH GmbH", "publication": "Small", "publication_date": "2025-09-11", "series_number": "36", "volume": "21", "issue": "36", "pages": "e01320" }, { "id": "authors:ds788-kw182", "collection": "authors", "collection_id": "ds788-kw182", "cite_using_url": "https://authors.library.caltech.edu/records/ds788-kw182", "type": "article", "title": "Interface morphogenesis with a deformable secondary phase in solid-state lithium batteries", "author": [ { "family_name": "Yoon", "given_name": "Sun Geun", "orcid": "0000-0002-6222-8962" }, { "family_name": "Vishnugopi", "given_name": "Bairav S." }, { "family_name": "Nelson", "given_name": "Douglas Lars", "orcid": "0000-0003-3429-0547" }, { "family_name": "Yong", "given_name": "Adrian Xiao Bin", "orcid": "0000-0002-0691-2380" }, { "family_name": "Wang", "given_name": "Yingjin", "orcid": "0009-0002-1239-3422", "clpid": "Wang-Yingjin" }, { "family_name": "Sandoval", "given_name": "Stephanie Elizabeth", "orcid": "0000-0002-0895-5237" }, { "family_name": "Thomas", "given_name": "Talia A.", "orcid": "0000-0003-0508-6045" }, { "family_name": "Cavallaro", "given_name": "Kelsey Anne", "orcid": "0000-0002-5066-9883" }, { "family_name": "Shevchenko", "given_name": "Pavel", "orcid": "0000-0002-7847-472X" }, { "family_name": "Alsa\u00e7", "given_name": "Elif P\u0131nar", "orcid": "0000-0002-4255-9676" }, { "family_name": "Wang", "given_name": "Congcheng", "orcid": "0000-0002-9156-2310" }, { "family_name": "Singla", "given_name": "Aditya", "orcid": "0000-0003-4229-605X" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" }, { "family_name": "Ertekin", "given_name": "Elif" }, { "family_name": "Mukherjee", "given_name": "Partha P." }, { "family_name": "McDowell", "given_name": "Matthew T.", "orcid": "0000-0001-5552-3456" } ], "abstract": "The complex morphological evolution of lithium metal at the solid-state electrolyte interface limits performance of solid-state batteries, leading to inhomogeneous reactions and contact loss. Inspired by biological morphogenesis, we developed an interfacial self-regulation concept in which a deformable secondary phase dynamically aggregates at the interface in response to local electro-chemo-mechanical stimuli, enhancing contact. The stripping of a lithium electrode that contains 5 to 20 mole % electrochemically inactive sodium domains causes spontaneous sodium accumulation across the interface, with the sodium deforming to attain intimate electrical contact without blocking lithium transport. This process, characterized with operando x-ray tomography and electron microscopy, mitigates voiding and improves cycling at low stack pressures. The counterintuitive strategy of adding electrochemically inactive alkali metal to improve performance demonstrates the utility of interfacial self-regulation for solid-state batteries.", "doi": "10.1126/science.adt5229", "issn": "0036-8075", "publisher": "American Association for the Advancement of Science", "publication": "Science", "publication_date": "2025-06-05", "series_number": "6751", "volume": "388", "issue": "6751", "pages": "1062-1068" }, { "id": "authors:v9pxv-1f534", "collection": "authors", "collection_id": "v9pxv-1f534", "cite_using_url": "https://authors.library.caltech.edu/records/v9pxv-1f534", "type": "article", "title": "Morphological Heterogeneity Impact of Film Solid-State Cathode on Utilization and Fracture Dynamics", "author": [ { "family_name": "Park", "given_name": "Se Hwan", "orcid": "0000-0001-5579-0765" }, { "family_name": "Juarez-Yescas", "given_name": "Carlos", "orcid": "0000-0003-4509-6547" }, { "family_name": "Naik", "given_name": "Kaustubh G." }, { "family_name": "Wang", "given_name": "Yingjin", "orcid": "0009-0002-1239-3422", "clpid": "Wang-Yingjin" }, { "family_name": "Luo", "given_name": "Yuting" }, { "family_name": "Puthusseri", "given_name": "Dhanya" }, { "family_name": "Kwon", "given_name": "Patrick" }, { "family_name": "Vishnugopi", "given_name": "Bairav S." }, { "family_name": "Shyam", "given_name": "Badri" }, { "family_name": "Yang", "given_name": "Heng" }, { "family_name": "Cook", "given_name": "John" }, { "family_name": "Okasinski", "given_name": "John" }, { "family_name": "Chuang", "given_name": "Andrew C.", "orcid": "0000-0003-0295-381X" }, { "family_name": "Xiao", "given_name": "Xianghui" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" }, { "family_name": "Mukherjee", "given_name": "Partha P." }, { "family_name": "Zahiri", "given_name": "Beniamin", "orcid": "0000-0003-0508-6416" }, { "family_name": "Braun", "given_name": "Paul V.", "orcid": "0000-0003-4079-8160" }, { "family_name": "Hatzell", "given_name": "Kelsey B.", "orcid": "0000-0002-5222-7288" } ], "abstract": "Structural heterogeneity in solid-state batteries can impact the material utilization and fracture mechanisms. Crystallographically oriented LiCoO2 film cathodes serve as a model electrode system for exploring how void distribution contributes to stress relief and buildup during cycling. Real- and reciprocal-space operando and ex situ synchrotron-based experiments are utilized to understand structural changes across multiple length scales that contribute to stress generation and fracture. Nanotomography uncovers a depth-dependent porosity variation in the pristine electrode and highlights the preferential fracture in regions of lower porosity during delithiation. Energy-dispersive X-ray diffraction and three-dimensional (3D) X-ray absorption near-edge spectroscopy (XANES) reveal the underutilization of cathode material in these regions. 3D XANES also confirms preferential delithiation near the subgrain boundaries. Chemo-mechanical modeling coupled with site-specific mechanical characterization demonstrates how stress accumulation in dense regions of the electrode leads to fracture and underutilization of active material. Our findings reveal the importance of material design to alleviate stress in small-volume changing cathodes.
", "doi": "10.1021/acsnano.5c06799", "issn": "1936-0851", "publisher": "American Chemical Society", "publication": "ACS Nano", "publication_date": "2025-06-04" }, { "id": "authors:cnjbq-19d54", "collection": "authors", "collection_id": "cnjbq-19d54", "cite_using_url": "https://authors.library.caltech.edu/records/cnjbq-19d54", "type": "article", "title": "Multiphoton 3D lithography", "author": [ { "family_name": "Skliutas", "given_name": "Edvinas" }, { "family_name": "Merkininkait\u0117", "given_name": "Greta", "orcid": "0000-0003-4894-3414" }, { "family_name": "Maruo", "given_name": "Shoji", "orcid": "0000-0002-6589-1225" }, { "family_name": "Zhang", "given_name": "Wenxin", "clpid": "Zhang-Wenxin" }, { "family_name": "Chen", "given_name": "Wenyuan", "clpid": "Chen-Wenyuan" }, { "family_name": "Deng", "given_name": "Weiting", "orcid": "0000-0003-0984-8027", "clpid": "Deng-Weiting" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" }, { "family_name": "Freymann", "given_name": "Georg von", "orcid": "0000-0003-2389-5532" }, { "family_name": "Malinauskas", "given_name": "Mangirdas", "orcid": "0000-0002-6937-4284" } ], "abstract": "Multiphoton 3D lithography (MP3DL) is a mesoscale additive manufacturing technique (product dimensions range from nanometres to centimetres) that uses confined non-linear light–matter interactions to produce 3D structures. The use of ultrafast pulsed lasers to induce photocrosslinking enables rapid optical 3D printing of diverse materials ranging from pure organic natural resins to fully inorganic amorphous and crystalline ceramics. MP3DL allows for the direct writing of unrestricted, true free-form geometries, reaching 100 nm feature size and millimetre-scale object dimensions; further, the dose dependence of the photomodification depth (degree of conversion) allows for 3D greyscale and 4D patterning. The throughput of the technique is constantly improving with the recent development of novel light sources, synthesis of special materials and novel exposure strategies. In this Primer, we introduce the photophysical principles behind the technique, describe experimental methods, highlight the milestones achieved, review promising applications and discuss reproducibility, limitations and upcoming optimizations. Finally, we provide an outlook on future trends and the potential to exploit artificial intelligence for mesoscale multi-material 4D advanced additive manufacturing.
", "doi": "10.1038/s43586-025-00386-y", "issn": "2662-8449", "publisher": "Nature Publishing Group", "publication": "Nature Reviews Methods Primers", "publication_date": "2025-03-13", "series_number": "1", "volume": "5", "issue": "1", "pages": "15" }, { "id": "authors:3gkmd-rqq82", "collection": "authors", "collection_id": "3gkmd-rqq82", "cite_using_url": "https://authors.library.caltech.edu/records/3gkmd-rqq82", "type": "article", "title": "Imaging-guided bioresorbable acoustic hydrogel microrobots", "author": [ { "family_name": "Han", "given_name": "Hong", "orcid": "0000-0002-2852-8662", "clpid": "Han-Hong" }, { "family_name": "Ma", "given_name": "Xiaotian", "orcid": "0009-0000-8357-9916", "clpid": "Ma-Xiaotian" }, { "family_name": "Deng", "given_name": "Weiting", "orcid": "0000-0003-0984-8027", "clpid": "Deng-Weiting" }, { "family_name": "Zhang", "given_name": "Junhang", "orcid": "0000-0002-7847-3102" }, { "family_name": "Tang", "given_name": "Songsong", "orcid": "0000-0003-4699-6563", "clpid": "Tang-Songsong" }, { "family_name": "Pak", "given_name": "On Shun", "orcid": "0000-0003-1510-7049" }, { "family_name": "Zhu", "given_name": "Lailai", "orcid": "0000-0002-3443-0709" }, { "family_name": "Criado-Hidalgo", "given_name": "Ernesto", "orcid": "0000-0001-9086-9129", "clpid": "Criado-Hidalgo-Ernesto" }, { "family_name": "Gong", "given_name": "Chen", "orcid": "0000-0002-6262-704X" }, { "family_name": "Karshalev", "given_name": "Emil", "orcid": "0000-0001-7802-6153", "clpid": "Karshalev-Emil" }, { "family_name": "Yoo", "given_name": "Jounghyun", "orcid": "0000-0003-4253-2382" }, { "family_name": "You", "given_name": "Ming", "clpid": "You-Ming" }, { "family_name": "Liu", "given_name": "Ann", "orcid": "0000-0002-0908-3506", "clpid": "Liu-Ann" }, { "family_name": "Wang", "given_name": "Canran", "orcid": "0000-0003-3297-9041", "clpid": "Wang-Canran" }, { "family_name": "Shen", "given_name": "Hao K.", "orcid": "0000-0003-2687-0736", "clpid": "Shen-Hao-K" }, { "family_name": "Patel", "given_name": "Payal N.", "clpid": "Patel-Payal-N" }, { "family_name": "Hays", "given_name": "Claire L.", "orcid": "0009-0006-9312-9816", "clpid": "Hays-Claire-L" }, { "family_name": "Gunnarson", "given_name": "Peter J.", "orcid": "0000-0002-4437-5379", "clpid": "Gunnarson-Peter-J" }, { "family_name": "Li", "given_name": "Lei", "orcid": "0000-0001-6164-2646", "clpid": "Li-Lei" }, { "family_name": "Zhang", "given_name": "Yang", "orcid": "0000-0002-4533-4325", "clpid": "Zhang-Yang" }, { "family_name": "Dabiri", "given_name": "John Oluseun", "orcid": "0000-0002-6722-9008", "clpid": "Dabiri-J-O" }, { "family_name": "Wang", "given_name": "Lihong V.", "orcid": "0000-0001-9783-4383", "clpid": "Wang-Lihong-V" }, { "family_name": "Shapiro", "given_name": "Mikhail G.", "orcid": "0000-0002-0291-4215", "clpid": "Shapiro-M-G" }, { "family_name": "Wu", "given_name": "Di", "orcid": "0000-0002-6848-668X", "clpid": "Wu-Di" }, { "family_name": "Zhou", "given_name": "Qifa", "orcid": "0000-0003-1527-3020" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" }, { "family_name": "Gao", "given_name": "Wei", "orcid": "0000-0002-8503-4562", "clpid": "Gao-Wei" } ], "abstract": "Micro- and nanorobots excel in navigating the intricate and often inaccessible areas of the human body, offering immense potential for applications such as disease diagnosis, precision drug delivery, detoxification, and minimally invasive surgery. Despite their promise, practical deployment faces hurdles, including achieving stable propulsion in complex in vivo biological environments, real-time imaging and localization through deep tissue, and precise remote control for targeted therapy and ensuring high therapeutic efficacy. To overcome these obstacles, we introduce a hydrogel-based, imaging-guided, bioresorbable acoustic microrobot (BAM) designed to navigate the human body with high stability. Constructed using two-photon polymerization, a BAM comprises magnetic nanoparticles and therapeutic agents integrated into its hydrogel matrix for precision control and drug delivery. The microrobot features an optimized surface chemistry with a hydrophobic inner layer to substantially enhance microbubble retention in biofluids with multiday functionality and a hydrophilic outer layer to minimize aggregation and promote timely degradation. The dual-opening bubble-trapping cavity design enables a BAM to maintain consistent and efficient acoustic propulsion across a range of biological fluids. Under focused ultrasound stimulation, the entrapped microbubbles oscillate and enhance the contrast for real-time ultrasound imaging, facilitating precise tracking and control of BAM movement through wireless magnetic navigation. Moreover, the hydrolysis-driven biodegradability of BAMs ensures its safe dissolution after treatment, posing no risk of long-term residual harm. Thorough in vitro and in vivo experimental evidence demonstrates the promising capabilities of BAMs in biomedical applications. This approach shows promise for advancing minimally invasive medical interventions and targeted therapeutic delivery.", "doi": "10.1126/scirobotics.adp3593", "issn": "2470-9476", "publisher": "American Association for the Advancement of Science", "publication": "Science Robotics", "publication_date": "2024-12", "series_number": "97", "volume": "9", "issue": "97" }, { "id": "authors:3zjzt-sfj07", "collection": "authors", "collection_id": "3zjzt-sfj07", "cite_using_url": "https://authors.library.caltech.edu/records/3zjzt-sfj07", "type": "article", "title": "Molecular control via dynamic bonding enables material responsiveness in additively manufactured metallo-polyelectrolytes", "author": [ { "family_name": "Lee", "given_name": "Seola", "orcid": "0000-0002-4538-0890", "clpid": "Lee-Seola" }, { "family_name": "Walker", "given_name": "Pierre J.", "orcid": "0000-0001-8628-6561" }, { "family_name": "Velling", "given_name": "Seneca J.", "orcid": "0000-0002-4670-8923", "clpid": "Velling-Seneca-J" }, { "family_name": "Chen", "given_name": "Amylynn", "orcid": "0000-0002-8112-5862", "clpid": "Chen-Amylynn" }, { "family_name": "Taylor", "given_name": "Zane W.", "orcid": "0000-0002-9326-6873" }, { "family_name": "Fiori", "given_name": "Cyrus J.B.M", "orcid": "0009-0009-2926-8522" }, { "family_name": "Gandhi", "given_name": "Vatsa", "orcid": "0000-0002-6752-113X", "clpid": "Gandhi-Vatsa" }, { "family_name": "Wang", "given_name": "Zhen-Gang", "orcid": "0000-0002-3361-6114", "clpid": "Wang-Zhen-Gang" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "Metallo-polyelectrolytes are versatile materials for applications like filtration, biomedical devices, and sensors, due to their metal-organic synergy. Their dynamic and reversible electrostatic interactions offer high ionic conductivity, self-healing, and tunable mechanical properties. However, the knowledge gap between molecular-level dynamic bonds and continuum-level material properties persists, largely due to limited fabrication methods and a lack of theoretical design frameworks. To address this critical gap, we present a framework, combining theoretical and experimental insights, highlighting the interplay of molecular parameters in governing material properties. Using stereolithography-based additive manufacturing, we produce durable metallo-polyelectrolytes gels with tunable mechanical properties based on metal ion valency and polymer charge sparsity. Our approach unveils mechanistic insights into how these interactions propagate to macroscale properties, where higher valency ions yield stiffer, tougher materials, and lower charge sparsity alters material phase behavior. This work enhances understanding of metallo-polyelectrolytes behavior, providing a foundation for designing advanced functional materials.
", "doi": "10.1038/s41467-024-50860-6", "pmcid": "PMC11316739", "issn": "2041-1723", "publisher": "Nature Publishing Group", "publication": "Nature Communications", "publication_date": "2024-08-10", "series_number": "1", "volume": "15", "issue": "1", "pages": "6850" }, { "id": "authors:ppkg1-d8j60", "collection": "authors", "collection_id": "ppkg1-d8j60", "cite_using_url": "https://authors.library.caltech.edu/records/ppkg1-d8j60", "type": "monograph", "title": "Solid-state cathode heterogeneity impact on utilization and fracture dynamics", "author": [ { "family_name": "Park", "given_name": "Se Hwan", "orcid": "0000-0001-5579-0765" }, { "family_name": "Yescas", "given_name": "Carlos Juarez", "orcid": "0000-0003-4509-6547" }, { "family_name": "Naik", "given_name": "Kaustubh" }, { "family_name": "Wang", "given_name": "Yingjin", "orcid": "0009-0002-1239-3422", "clpid": "Wang-Yingjin" }, { "family_name": "Luo", "given_name": "Yuting" }, { "family_name": "Puthusseri", "given_name": "Dhanya", "orcid": "0000-0002-8594-2683" }, { "family_name": "Kwon", "given_name": "Patrick" }, { "family_name": "Vishnugopi", "given_name": "Bairav S.", "orcid": "0009-0002-6357-9358" }, { "family_name": "Shyam", "given_name": "Badri", "orcid": "0009-0001-0345-0977" }, { "family_name": "Yang", "given_name": "Heng" }, { "family_name": "Cook", "given_name": "John", "orcid": "0000-0002-2886-3276" }, { "family_name": "Okasinki", "given_name": "John" }, { "family_name": "Chaung", "given_name": "Andrew" }, { "family_name": "Xiao", "given_name": "Xianghui", "orcid": "0000-0002-7142-3452" }, { "family_name": "Greer", "given_name": "Julia", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" }, { "family_name": "Mukherjee", "given_name": "Partha P.", "orcid": "0000-0001-7900-7261" }, { "family_name": "Zahiri", "given_name": "Beniamin", "orcid": "0000-0003-0508-6416" }, { "family_name": "Braun", "given_name": "Paul", "orcid": "0000-0003-4079-8160" }, { "family_name": "Hatzell", "given_name": "Kelsey", "orcid": "0000-0002-5222-7288" } ], "abstract": "Structural heterogeneity in solid-state batteries can impact material utilization and fracture mechanisms. Dense crystallographically oriented lithium cobalt oxide cathodes serve as a model electrode system for exploring how density variability contributes to stress relief and build up during cycling. Real- and reciprocal-space operando and ex-situ synchrotron based experiments are utilized to understand structural changes across multiple length scales contribute to stress generation and fracture. Nanotomography uncovers a depth-dependent porosity variation in the pristine electrode and highlights preferential fracture in regions of lower porosity during delithiation. Energy-dispersive X-ray diffraction and 3D X-ray absorption near-edge spectroscopy (XANES) reveal the underutilization of cathode material in these regions. 3D XANES also confirms preferential delithiation near the subgrain boundaries. Chemo-mechanical modeling coupled with site-specific mechanical characterization demonstrate how stress accumulation in dense regions of the electrode leads to fracture and underutilization of active material. Our findings reveal the importance of materials design to alleviate stress in small-volume changing cathodes.", "doi": "10.26434/chemrxiv-2024-0hdbp", "publisher": "ChemRxiv", "publication_date": "2024-04-25" }, { "id": "authors:nes99-dsd87", "collection": "authors", "collection_id": "nes99-dsd87", "cite_using_url": "https://authors.library.caltech.edu/records/nes99-dsd87", "type": "article", "title": "Approaching Standardization: Mechanical Material Testing of Macroscopic Two\u2010Photon Polymerized Specimens", "author": [ { "family_name": "Koch", "given_name": "Thomas", "orcid": "0000-0003-2801-3113", "clpid": "Koch-Thomas" }, { "family_name": "Zhang", "given_name": "Wenxin", "orcid": "0000-0002-6318-0622", "clpid": "Zhang-Wenxin" }, { "family_name": "Tran", "given_name": "Thomas T.", "orcid": "0009-0003-7034-9486", "clpid": "Tran-Thomas-T" }, { "family_name": "Wang", "given_name": "Yingjin", "clpid": "Wang-Yingjin" }, { "family_name": "Mikitisin", "given_name": "Adrian", "orcid": "0000-0002-4789-2144", "clpid": "Mikitisin-Adrian" }, { "family_name": "Puchhammer", "given_name": "Jakob", "orcid": "0009-0004-4464-8375", "clpid": "Puchhammer-Jakob" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" }, { "family_name": "Ovsianikov", "given_name": "Aleksandr", "orcid": "0000-0001-5846-0198", "clpid": "Ovsianikov-Aleksandr" }, { "family_name": "Chalupa\u2010Gantner", "given_name": "Franziska", "orcid": "0000-0001-7161-4171", "clpid": "Chalupa\u2010Gantner-Franziska" }, { "family_name": "Lunzer", "given_name": "Markus", "orcid": "0000-0002-8052-6517", "clpid": "Lunzer-Markus" } ], "abstract": "Two-photon polymerization (2PP) is becoming increasingly established as additive manufacturing technology for microfabrication due to its high-resolution and the feasibility of generating complex parts. Until now, the high resolution of 2PP is also its bottleneck, as it limited throughput and therefore restricted the application to the production of microparts. Thus, mechanical properties of 2PP materials can only be characterized using nonstandardized specialized microtesting methods. Due to recent advances in 2PP technology, it is now possible to produce parts in the size of several millimeters to even centimeters, finally permitting the fabrication of macrosized testing specimens. Besides suitable hardware systems, 2PP materials exhibiting favorable mechanical properties that allow printing of up-scaled parts are strongly demanded. In this work, the up-scalability of three different photopolymers is investigated using a high-throughput 2PP system and low numerical aperture optics. Testing specimens in the cm-range are produced and tested with common or even standardized material testing methods available in conventionally equipped polymer testing labs. Examples of the characterization of mechanical, thermo-mechanical, and fracture properties of 2PP processed materials are shown. Additionally, aspects such as postprocessing and aging are investigated. This lays a foundation for future expansion of the 2PP technology to broader industrial application.
\nNatural porous materials have exceptional properties—for example, light weight, mechanical resilience, and multi-functionality. Efforts to imitate their properties in engineered structures have limited success. This, in part, is caused by the complexity of multi-phase materials composites and by the lack of quantified understanding of each component's role in overall hierarchy. This challenge is twofold: 1) computational. because non-periodicity and defects render constructing design guidelines between geometries and mechanical properties complex and expensive and 2) experimental. because the fabrication and characterization of complex, often hierarchical and non-periodic 3D architectures is non-trivial.
\nAdvances in nanoscale additive manufacturing (AM) offer great opportunities to expand nanotechnologies; however, the size effects in these printed remain largely unexplored. Using both in situ nanomechanical and electrical experiments and molecular dynamics (MD) simulations, this study investigates additively manufactured nano-architected nanocrystalline ZnO (nc-ZnO) with \u223c7 nm grains and dimensions spanning 0.25\u20134 \u03bcm. These nano-scale ceramics are fabricated through printing and subsequent burning of metal ion-containing hydrogels to produce oxide structures. Electromechanical behavior is shown to result from random ordering in the microstructure and can be modeled through a statistical treatment. A size effect in the failure behavior of AM nc-ZnO is also observed and characterized by the changes in deformation behavior and suppression of brittle failure. MD simulations provide insights to the role of grain boundaries and grain boundary plasticity on both electromechanical behavior and failure mechanisms in nc-ZnO. The frameworks developed in this paper extend to other AM nanocrystalline materials and provide quantification of microstructurally-drive limitations to precision in materials property design.
", "doi": "10.1088/1361-6528/ad0984", "issn": "0957-4484", "publisher": "IOP Publishing", "publication": "Nanotechnology", "publication_date": "2024-02-05", "series_number": "6", "volume": "35", "issue": "6", "pages": "065706" }, { "id": "authors:97csb-6dg75", "collection": "authors", "collection_id": "97csb-6dg75", "cite_using_url": "https://authors.library.caltech.edu/records/97csb-6dg75", "type": "article", "title": "Carbon-Related Quantum Emitter in Hexagonal Boron Nitride with Homogeneous Energy and 3-Fold Polarization", "author": [ { "family_name": "Zhong", "given_name": "Ding", "orcid": "0000-0003-3149-2071", "clpid": "Zhong-Ding" }, { "family_name": "Gao", "given_name": "Shiyuan", "orcid": "0000-0002-9069-5306", "clpid": "Gao-Shiyuan" }, { "family_name": "Saccone", "given_name": "Max", "orcid": "0000-0003-3846-2908", "clpid": "Saccone-Max" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" }, { "family_name": "Bernardi", "given_name": "Marco", "orcid": "0000-0001-7289-9666", "clpid": "Bernardi-Marco" }, { "family_name": "Nadj-Perge", "given_name": "Stevan", "orcid": "0000-0002-2394-9070", "clpid": "Nadj-Perge-S" }, { "family_name": "Faraon", "given_name": "Andrei", "orcid": "0000-0002-8141-391X", "clpid": "Faraon-A" } ], "abstract": "Most hexagonal boron nitride (hBN) single-photon emitters (SPEs) studied to date suffer from variable emission energy and unpredictable polarization, two crucial obstacles to their application in quantum technologies. Here, we report an SPE in hBN with an energy of 2.2444 ± 0.0013 eV created via carbon implantation that exhibits a small inhomogeneity of the emission energy. Polarization-resolved measurements reveal aligned absorption and emission dipole orientations with a 3-fold distribution, which follows the crystal symmetry. Photoluminescence excitation (PLE) spectroscopy results show the predictability of polarization is associated with a reproducible PLE band, in contrast with the non-reproducible bands found in previous hBN SPE species. Photon correlation measurements are consistent with a three-level model with weak coupling to a shelving state. Our ab initio excited-state calculations shed light on the atomic origin of this SPE defect, which consists of a pair of substitutional carbon atoms located at boron and nitrogen sites separated by a hexagonal unit cell.
\nStudies on mechanical size effects in nanosized metals unanimously highlight both intrinsic microstructures and extrinsic dimensions for understanding size-dependent properties, commonly focusing on strengths of uniform microstructures, e.g., single-crystalline/nanocrystalline and nanoporous, as a function of pillar diameters, D. We developed a hydrogel infusion-based additive manufacturing (AM) technique using two-photon lithography to produce metals in prescribed 3D-shapes with \u223c100 nm feature resolution. We demonstrate hierarchical microstructures of as-AM-fabricated Ni nanopillars (D \u223c 130\u2013330 nm) to be nanoporous and nanocrystalline, with d \u223c 30\u201350 nm nanograins subtending each ligament in bamboo-like arrangements and pores with critical dimensions comparable to d. In situ nanocompression experiments unveil their yield strengths, \u03c3, to be \u223c1\u20133 GPa, above single-crystalline/nanocrystalline counterparts in the D range, a weak size dependence, \u03c3 \u221d D^(\u20130.2), and localized-to-homogenized transition in deformation modes mediated by nanoporosity, uncovered by molecular dynamics simulations. This work highlights hierarchical microstructures on mechanical response in nanosized metals and suggests small-scale engineering opportunities through AM-enabled microstructures.
", "doi": "10.1021/acs.nanolett.3c02309", "issn": "1530-6984", "publisher": "American Chemical Society", "publication": "Nano Letters", "publication_date": "2023-09-13", "series_number": "17", "volume": "23", "issue": "17", "pages": "8162-8170" }, { "id": "authors:8p3x0-j0875", "collection": "authors", "collection_id": "8p3x0-j0875", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20230207-904098000.2", "type": "article", "title": "Chemo-mechanical-microstructural coupling in the tarsus exoskeleton of the scorpion Scorpio palmatus", "author": [ { "family_name": "Zhang", "given_name": "Haolu", "orcid": "0000-0002-2871-5169", "clpid": "Zhang-Haolu" }, { "family_name": "Kellersztein", "given_name": "Israel", "orcid": "0000-0002-8838-818X", "clpid": "Kellersztein-Israel" }, { "family_name": "Freychet", "given_name": "Guillaume", "orcid": "0000-0001-8406-798X", "clpid": "Freychet-Guillame" }, { "family_name": "Zhernenkov", "given_name": "Mikhail", "orcid": "0000-0003-3604-0672", "clpid": "Zhernenkov-Mikhail" }, { "family_name": "Wagner", "given_name": "H. Daniel", "clpid": "Wagner-H-Daniel" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "The multiscale structure of biomaterials enables their exceptional mechanical robustness, yet the impact of each constituent at their relevant length scale remains elusive. We used SAXD analysis to expose the intact chitin-fiber architecture within the exoskeleton on a scorpion's claw, revealing varying orientations, including Bouligand and unidirectional regions different from other arthropod species. We uncovered the contribution of individual components' constituent behavior to its mechanical properties from the micro- to the nanoscale. At the microscale, in-situ micromechanical experiments were used to determine site-specific stiffness, strength, and failure of the biocomposite due to fiber orientation, while metal-crosslinking of proteins is characterized via fluorescence maps. At the constituent level, combined with FEA simulations, we uncovered the behavior of fiber-matrix deformation with fiber diameter <53.7 nm and protein modulus in the range 1.4-11 MPa. The unveiled microstructure-mechanics relationship sheds light on the evolved structural functionalities and constituents' interactions within the scorpion cuticle.", "doi": "10.1016/j.actbio.2023.01.038", "issn": "1742-7061", "publisher": "Elsevier", "publication": "Acta Biomaterialia", "publication_date": "2023-04-01", "volume": "160", "pages": "176-186" }, { "id": "authors:k4erg-qg433", "collection": "authors", "collection_id": "k4erg-qg433", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20230314-846094500.86", "type": "article", "title": "Metasurface\u2010Enabled Holographic Lithography for Impact\u2010Absorbing Nanoarchitected Sheets", "author": [ { "family_name": "Kagias", "given_name": "Matias", "orcid": "0000-0003-0435-6672", "clpid": "Kagias-Matias" }, { "family_name": "Lee", "given_name": "Seola", "clpid": "Lee-Seola" }, { "family_name": "Friedman", "given_name": "Andrew C.", "clpid": "Friedman-Andrew-C" }, { "family_name": "Zheng", "given_name": "Tianzhe", "orcid": "0000-0001-7058-5196", "clpid": "Zheng-Tianzhe" }, { "family_name": "Veysset", "given_name": "David", "orcid": "0000-0003-4473-1983", "clpid": "Veysset-David" }, { "family_name": "Faraon", "given_name": "Andrei", "orcid": "0000-0002-8141-391X", "clpid": "Faraon-A" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "Nanoarchitected materials represent a class of structural meta-materials that utilze nanoscale features to achieve unconventional material properties such as ultralow density and high energy absorption. A dearth of fabrication methods capable of producing architected materials with sub-micrometer resolution over large areas in a scalable manner exists. A fabrication technique is presented that employs holographic patterns generated by laser exposure of phase metasurface masks in negative-tone photoresists to produce 30\u201340 \u00b5m-thick nanoarchitected sheets with 2.1 \u00d7 2.4 cm\u00b2 lateral dimensions and \u2248500 nm-wide struts organized in layered 3D brick-and-mortar-like patterns to result in \u224850\u201370% porosity. Nanoindentation arrays over the entire sample area reveal the out-of-plane elastic modulus to vary between 300 MPa and 4 GPa, with irrecoverable post-elastic material deformation commencing via individual nanostrut buckling, densification within layers, shearing along perturbation perimeter, and tensile cracking. Laser induced particle impact tests (LIPIT) indicate specific inelastic energy dissipation of 0.51\u20132.61 MJ kg\u207b\u00b9, which is comparable to other high impact energy absorbing composites and nanomaterials, such as Kevlar/poly(vinyl butyral) (PVB) composite, polystyrene, and pyrolized carbon nanolattices with 23% relative density. These results demonstrate that holographic lithography offers a promising platform for scalable manufacturing of nanoarchitected materials with impact resistant capabilities.", "doi": "10.1002/adma.202209153", "issn": "0935-9648", "publisher": "Wiley", "publication": "Advanced Materials", "publication_date": "2023-03-29", "series_number": "13", "volume": "35", "issue": "13", "pages": "Art. No. 2209153" }, { "id": "authors:f0x2g-qbt33", "collection": "authors", "collection_id": "f0x2g-qbt33", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20230310-60798000.1", "type": "article", "title": "Knots are not for naught: Design, properties, and topology of hierarchical intertwined microarchitected materials", "author": [ { "family_name": "Moestopo", "given_name": "Widianto P.", "orcid": "0000-0002-7617-4280", "clpid": "Moestopo-Widianto-P" }, { "family_name": "Shaker", "given_name": "Sammy", "orcid": "0000-0003-1751-4908", "clpid": "Shaker-Sammy" }, { "family_name": "Deng", "given_name": "Weiting", "orcid": "0000-0003-0984-8027", "clpid": "Deng-Weiting" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "Lightweight and tough engineered materials are often designed with three-dimensional hierarchy and interconnected structural members whose junctions are detrimental to their performance because they serve as stress concentrations for damage accumulation and lower mechanical resilience. We introduce a previously unexplored class of architected materials, whose components are interwoven and contain no junctions, and incorporate micro-knots as building blocks within these hierarchical networks. Tensile experiments, which show close quantitative agreements with an analytical model for overhand knots, reveal that knot topology allows a new regime of deformation capable of shape retention, leading to a ~92% increase in absorbed energy and an up to ~107% increase in failure strain compared to woven structures, along with an up to ~11% increase in specific energy density compared to topologically similar monolithic lattices. Our exploration unlocks knotting and frictional contact to create highly extensible low-density materials with tunable shape reconfiguration and energy absorption capabilities.", "doi": "10.1126/sciadv.ade6725", "pmcid": "PMC9995035", "issn": "2375-2548", "publisher": "American Association for the Advancement of Science", "publication": "Science Advances", "publication_date": "2023-03-10", "series_number": "10", "volume": "9", "issue": "10", "pages": "eade6725" }, { "id": "authors:qzjpk-eg930", "collection": "authors", "collection_id": "qzjpk-eg930", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20230202-569057000.1", "type": "article", "title": "Enabling Durable Ultralow-k Capacitors with Enhanced Breakdown Strength in Density-Variant Nanolattices", "author": [ { "family_name": "Kim", "given_name": "Min-Woo", "clpid": "Kim-Min-Woo" }, { "family_name": "Lifson", "given_name": "Max L.", "orcid": "0000-0002-0382-182X", "clpid": "Lifson-Max-L" }, { "family_name": "Gallivan", "given_name": "Rebecca", "orcid": "0000-0001-6516-2180", "clpid": "Gallivan-Rebecca-A" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" }, { "family_name": "Kim", "given_name": "Bong-Joong", "orcid": "0000-0002-5335-4342", "clpid": "Kim-Bong-Joong" } ], "abstract": "Ultralow-k materials used in high voltage devices require mechanical resilience and electrical and dielectric stability even when subjected to mechanical loads. Existing devices with organic polymers suffer from low thermal and mechanical stability while those with inorganic porous structures struggle with poor mechanical integrity. Recently, 3D hollow-beam nanolattices have emerged as promising candidates that satisfy these requirements. However, their properties are maintained for only five stress cycles at strains below 25%. Here, we demonstrate that alumina nanolattices with different relative density distributions across their height elicit a deterministic mechanical response concomitant with a 1.5\u20133.3 times higher electrical breakdown strength than nanolattices with uniform density. These density-variant nanolattices exhibit an ultralow-k of \u22481.2, accompanied by complete electric and dielectric stability and mechanical recoverability over 100 cyclic compressions to 62.5% strain. We explain the enhanced insulation and long-term cyclical stability by the bi-phase deformation where the lower-density region protects the higher-density region as it is compressed before the higher-density region, allowing to simultaneously possess high strength and ductility like composites. This study highlights the superior electrical performance of the bi-phase nanolattice with a single interface in providing stable conduction and maximum breakdown strength.", "doi": "10.1002/adma.202208409", "issn": "0935-9648", "publisher": "Wiley", "publication": "Advanced Materials", "publication_date": "2023-02-09", "series_number": "6", "volume": "35", "issue": "6", "pages": "Art. No. 2208409" }, { "id": "authors:4adpq-0fp16", "collection": "authors", "collection_id": "4adpq-0fp16", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20230202-570644000.3", "type": "article", "title": "Metasurface\u2010Enabled Holographic Lithography for Impact\u2010Absorbing Nano\u2010Architected Sheets", "author": [ { "family_name": "Kagias", "given_name": "Matias", "orcid": "0000-0003-0435-6672", "clpid": "Kagias-Matias" }, { "family_name": "Lee", "given_name": "Seola", "clpid": "Lee-Seola" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" }, { "family_name": "Friedman", "given_name": "Andrew C.", "clpid": "Friedman-Andrew-C" }, { "family_name": "Zheng", "given_name": "Tianzhe", "orcid": "0000-0001-7058-5196", "clpid": "Zheng-Tianzhe" }, { "family_name": "Faraon", "given_name": "Andrei", "orcid": "0000-0002-8141-391X", "clpid": "Faraon-A" }, { "family_name": "Veysset", "given_name": "David", "orcid": "0000-0003-4473-1983", "clpid": "Veysset-David" } ], "abstract": "Nano-architected materials represent a class of structural meta-materials that utilze nanoscale features to achieve unconventional material properties such as ultra-low density and high energy absorption. A dearth of fabrication methods capable of producing architected materials with sub-micron resolution over large areas in a scalable manner exists. We present a fabrication technique that employs holographic patterns generated by laser exposure of phase metasurface masks in negative-tone photoresists to produce 30 to 40 micrometer thick nano-architected sheets with 2.1 x 2.4 cm\u00b2 lateral dimensions and approximately 500 nm wide struts organized in layered 3D brick-and-mortar-like patterns to result in approximately 50 to 70% porosity. Nanoindentation arrays over the entire sample area reveal the out-of-plane elastic modulus to vary between 300 MPa and 4 GPa, with irrecoverable post-elastic material deformation commencing via individual nano-strut buckling, densification within layers, shearing along perturbation perimeter, and tensile cracking. Laser induced particle impact tests (LIPIT) indicate specific inelastic energy dissipation of 0.51-2.61 MJ kg\u207b\u00b9, which is comparable to other high-impact energy absorbing composites and nanomaterials, such as Kevlar/polyvinyl butyral (PVB) composite, polystyrene, and pyrolized carbon nanolattices with 23% relative density. These results demonstrate that holographic lithography offers a promising platform for scalable manufacturing of nano-architected materials with impact resistant capabilities.", "doi": "10.1002/adma.202209153", "issn": "0935-9648", "publisher": "Wiley", "publication": "Advanced Materials", "publication_date": "2023-02-02", "pages": "Art. No. 2209153" }, { "id": "authors:92xgd-h0w81", "collection": "authors", "collection_id": "92xgd-h0w81", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20230125-514337900.7", "type": "article", "title": "Deformation characteristics of solid-state benzene as a step towards understanding planetary geology", "author": [ { "family_name": "Zhang", "given_name": "Wenxin", "orcid": "0000-0002-6318-0622", "clpid": "Zhang-Wenxin" }, { "family_name": "Zhang", "given_name": "Xuan", "orcid": "0000-0002-6155-6825", "clpid": "Zhang-Xuan" }, { "family_name": "Edwards", "given_name": "Bryce W.", "clpid": "Edwards-Bryce-W" }, { "family_name": "Zhong", "given_name": "Lei", "clpid": "Zhong-Lei" }, { "family_name": "Gao", "given_name": "Huajian", "orcid": "0000-0002-8656-846X", "clpid": "Gao-Huajian" }, { "family_name": "Malaska", "given_name": "Michael J.", "orcid": "0000-0003-0064-5258", "clpid": "Malaska-Michael-J" }, { "family_name": "Hodyss", "given_name": "Robert", "orcid": "0000-0002-6523-3660", "clpid": "Hodyss-Robert-P" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "Small organic molecules, like ethane and benzene, are ubiquitous in the atmosphere and surface of Saturn's largest moon Titan, forming plains, dunes, canyons, and other surface features. Understanding Titan's dynamic geology and designing future landing missions requires sufficient knowledge of the mechanical characteristics of these solid-state organic minerals, which is currently lacking. To understand the deformation and mechanical properties of a representative solid organic material at space-relevant temperatures, we freeze liquid micro-droplets of benzene to form ~10 \u03bcm-tall single-crystalline pyramids and uniaxially compress them in situ. These micromechanical experiments reveal contact pressures decaying from ~2 to ~0.5\u2009GPa after ~1 \u03bcm-reduction in pyramid height. The deformation occurs via a series of stochastic (~5-30\u2009nm) displacement bursts, corresponding to densification and stiffening of the compressed material during cyclic loading to progressively higher loads. Molecular dynamics simulations reveal predominantly plastic deformation and densified region formation by the re-orientation and interplanar shear of benzene rings, providing a two-step stiffening mechanism. This work demonstrates the feasibility of in-situ cryogenic nanomechanical characterization of solid organics as a pathway to gain insights into the geophysics of planetary bodies.", "doi": "10.1038/s41467-022-35647-x", "pmcid": "PMC9792550", "issn": "2041-1723", "publisher": "Nature Publishing Group", "publication": "Nature Communications", "publication_date": "2022-12-26", "volume": "13", "pages": "Art. No. 7949" }, { "id": "authors:mgzme-mkf79", "collection": "authors", "collection_id": "mgzme-mkf79", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20221026-429882000.2", "type": "article", "title": "Additive manufacturing of micro-architected metals via hydrogel infusion", "author": [ { "family_name": "Saccone", "given_name": "Max A.", "orcid": "0000-0003-3846-2908", "clpid": "Saccone-Max-A" }, { "family_name": "Gallivan", "given_name": "Rebecca A.", "orcid": "0000-0001-6516-2180", "clpid": "Gallivan-Rebecca-A" }, { "family_name": "Narita", "given_name": "Kai", "orcid": "0000-0002-3867-8234", "clpid": "Narita-Kai" }, { "family_name": "Yee", "given_name": "Daryl W.", "orcid": "0000-0002-4114-6167", "clpid": "Yee-Daryl-Wei-Liang" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "Metal additive manufacturing (AM) enables the production of high value and high performance components with applications from the aerospace to biomedical fields. Layer-by-layer fabrication circumvents the geometric limitations of traditional metalworking techniques, allowing topologically optimized parts to be made rapidly and efficiently. Existing AM techniques rely on thermally initiated melting or sintering for part shaping, a costly and material-limited process. We report an AM technique that produces metals and alloys with microscale resolution via vat photopolymerization (VP). 3D-architected hydrogels are infused with metal precursors, then calcined and reduced to convert the hydrogel scaffolds into miniaturized metal replicas. This approach represents a paradigm shift in VP; the material is selected only after the structure is fabricated. Unlike existing VP strategies, which incorporate target materials or precursors into the photoresin during printing, our method does not require re-optimization of resins and curing parameters for different materials, enabling quick iteration, compositional tuning, and the ability to fabricate multimaterials. We demonstrate AM of metals with critical dimensions of ~40 \u00b5m that are challenging to fabricate using conventional processes. Such hydrogel-derived metals have highly twinned microstructures and unusually high hardness, providing a pathway to create advanced metallic micromaterials.", "doi": "10.1038/s41586-022-05433-2", "pmcid": "PMC9713131", "issn": "0028-0836", "publisher": "Nature Publishing Group", "publication": "Nature", "publication_date": "2022-12-22", "series_number": "7941", "volume": "612", "issue": "7941", "pages": "685-690" }, { "id": "authors:4dr2m-bc398", "collection": "authors", "collection_id": "4dr2m-bc398", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20221017-767512000.2", "type": "article", "title": "Fracture resistance of 3D nano-architected lattice materials", "author": [ { "family_name": "Maurizi", "given_name": "Marco", "orcid": "0000-0002-4304-1000", "clpid": "Maurizi-Marco" }, { "family_name": "Edwards", "given_name": "Bryce W.", "clpid": "Edwards-Bryce-W" }, { "family_name": "Gao", "given_name": "Chao", "orcid": "0000-0003-4023-0970", "clpid": "Gao-Chao" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" }, { "family_name": "Berto", "given_name": "Filippo", "orcid": "0000-0001-9676-9970", "clpid": "Berto-Filippo" } ], "abstract": "Exploiting small scale material effects and structural topology, nano-architected lattices represent a recent novel class of mechanical metamaterials, which exhibit unprecedented combination of mechanical properties. Together with scarce resistance to fracture and catastrophic failure, understanding of the fracture characteristics and properties of 3D nano-architected lattices still represents a limiting factor for the design and realization of future engineering applications. Here, using a combination of in-situ tensile fracture experiments and finite element simulations, we first show the possibility to reach stable crack growth in nano-architected materials harnessing only the intrinsic plastic toughening mechanism. Exploring the effect of lattice topology on the fracture properties, we then demonstrate similar performance between the octet and 3D kagome architecture (along one direction). Based on the experimental and numerical results, a power-scaling law of normalized crack initiation toughness with relative density \u03c1\u0305 (i.e., fraction of material per unit volume) K_(IC)/\u03c3\u1d67\n\u221aL \u221d \u03c1\u0305^(1.11), \u03c1\u0305^(1.17\u22121.27) is exhibited by the octet and 3D kagome topology, respectively, given the yield strength \u03c3\u1d67 and the unit cell size L. Owing to the combination of the parent material's size effect and plasticity (3D-printed photo-resist polymer), the fracture initiation toughness (considering \u03c3\u1d67) of our octet nano-architected lattices is 8 times that of previously realized macroscopic octet titanium structures. After crack initiation, the two architectures manifest rising (in average 18%) fracture resistance curves (i.e., R-curves), without catastrophic failure. In addition, we find that the fracture toughness of architected lattices, measured by means of compact tension specimens, seems not to be dependent on the sample's thickness, forcing to re-think the plain strain toughness definition for this class of materials. Our results uncover the basic fracture characteristics of 3D architected materials exhibiting stable crack growth, providing insights for the design of light-weight, tough materials, with implications for future macro-scaled structural applications.", "doi": "10.1016/j.eml.2022.101883", "issn": "2352-4316", "publisher": "Elsevier", "publication": "Extreme Mechanics Letters", "publication_date": "2022-10", "volume": "56", "pages": "Art. No. 101883" }, { "id": "authors:bdn0b-vrr31", "collection": "authors", "collection_id": "bdn0b-vrr31", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20220729-722279000", "type": "article", "title": "Tailoring the Desorption Behavior of Hygroscopic Gels for Atmospheric Water Harvesting in Arid Climates", "author": [ { "family_name": "Lu", "given_name": "Hengyi", "clpid": "Lu-Hengyi" }, { "family_name": "Shi", "given_name": "Wen", "clpid": "Shi-Wen" }, { "family_name": "Zhang", "given_name": "James H.", "clpid": "Zhang-James-H" }, { "family_name": "Chen", "given_name": "Amylynn C.", "clpid": "Chen-Amylynn-C" }, { "family_name": "Guan", "given_name": "Weixin", "clpid": "Guan-Weixin" }, { "family_name": "Lei", "given_name": "Chuxin", "clpid": "Lei-Chuxin" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" }, { "family_name": "Boriskina", "given_name": "Svetlana V.", "clpid": "Boriskina-Svetlana-V" }, { "family_name": "Yu", "given_name": "Guihua", "orcid": "0000-0002-3253-0749", "clpid": "Yu-Guihua" } ], "abstract": "The ubiquitous nature of atmospheric moisture makes it a significant water resource available at any geographical location. Atmospheric water harvesting (AWH) technology, which extracts moisture from ambient air to generate clean water, is a promising strategy to realize decentralized water production. The high water uptake exhibited by salt-based sorbents makes them attractive for AWH, especially in low relative humidity (RH) environments. Salt-based sorbents often have relatively high desorption heat, rendering water release an energy-intensive process. We proposed a hygroscopic gel, PAM hydrogel controlled incorporated with LiCl, capable of effective moisture harvesting from arid environments. The interactions between the hydrophilic hydrogel network and the captured water enable the PAM-LiCl to accumulate more free and weakly-bonded water molecules, significantly lowering the desorption heat compared with conventional neat salt sorbents. Benefiting from the affinity for swelling of the polymer backbones, the developed PAM-LiCl achieves a high water uptake of ca. 1.1 g/g at 20% RH with fast sorption kinetics of ca. 0.008 g g\u207b\u00b9 min\u207b\u00b9 and further demonstrates a daily water yield up to ca. 7 g/g at this condition. These findings provide a new pathway for synthesis of materials with efficient water absorption/desorption properties, to reach energy-efficient water release for AWH in arid climates.", "doi": "10.1002/adma.202205344", "issn": "0935-9648", "publisher": "Wiley", "publication": "Advanced Materials", "publication_date": "2022-09-15", "series_number": "37", "volume": "34", "issue": "37", "pages": "Art. No. 2205344" }, { "id": "authors:1zjqe-qa974", "collection": "authors", "collection_id": "1zjqe-qa974", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20220707-978178000", "type": "article", "title": "Responsive materials architected in space and time", "author": [ { "family_name": "Xia", "given_name": "Xiaoxing", "orcid": "0000-0003-1255-3289", "clpid": "Xia-Xiaoxing" }, { "family_name": "Spadaccini", "given_name": "Christopher M.", "orcid": "0000-0002-7074-1459", "clpid": "Spadaccini-Christopher-M" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "Rationally designed architected materials have attained previously untapped territories in materials property space. The properties and behaviours of architected materials need not be stagnant after fabrication; they can be encoded with a temporal degree of freedom such that they evolve over time. In this Review, we describe the variety of materials architected in both space and time, and their responses to various stimuli, including mechanical actuation, changes in temperature and chemical environment, and variations in electromagnetic fields. We highlight the additive manufacturing methods that can precisely prescribe complex geometries and local inhomogeneities to make such responsiveness possible. We discuss the emergent physics phenomena observed in architected materials that are analogous to those in classical materials, such as the formation and behaviour of defects, phase transformations and topologically protected properties. Finally, we offer a perspective on the future of architected materials that have a degree of intelligence through mechanical logic and artificial neural networks.", "doi": "10.1038/s41578-022-00450-z", "pmcid": "PMC9208549", "issn": "2058-8437", "publisher": "Nature Publishing Group", "publication": "Nature Reviews Materials", "publication_date": "2022-09", "series_number": "9", "volume": "7", "issue": "9", "pages": "683-701" }, { "id": "authors:egxk9-42588", "collection": "authors", "collection_id": "egxk9-42588", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20220502-202342151", "type": "article", "title": "Additive manufacturing of 3D batteries: a perspective", "author": [ { "family_name": "Narita", "given_name": "Kai", "orcid": "0000-0002-3867-8234", "clpid": "Narita-Kai" }, { "family_name": "Saccone", "given_name": "Max A.", "orcid": "0000-0003-3846-2908", "clpid": "Saccone-Max-A" }, { "family_name": "Sun", "given_name": "Yuchun", "orcid": "0000-0002-7028-3523", "clpid": "Sun-Yuchun" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "Additive manufacturing (AM) enables the fabrication of battery materials with complex geometries. When battery components can take arbitrary form factors, opportunities emerge for creating electrode configurations with improved power density, reduced weight, and excellent mechanical stability. We provide a perspective on recent progress in AM of 3D batteries, discussing relevant techniques, materials, designs, and applications. We highlight advantages and limitations associated with battery electrodes fabricated by direct ink writing, fused deposition modeling, vat photopolymerization, and selective laser sintering. Additionally, we discuss optimal geometries and compatible materials for anode, cathode, and electrolyte of fully 3D batteries. To increase transparency and utility in the field, we suggest a standardized set of reporting metrics for 3D batteries. Finally, we identify key opportunities for implementation where 3D batteries can provide critical advantages such as shape conformability and the ability to serve as multifunctional or structural components.", "doi": "10.1557/s43578-022-00562-w", "issn": "0884-2914", "publisher": "Springer", "publication": "Journal of Materials Research", "publication_date": "2022-05", "series_number": "9", "volume": "37", "issue": "9", "pages": "1535-1546" }, { "id": "authors:2z24p-cd948", "collection": "authors", "collection_id": "2z24p-cd948", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20211112-211025694", "type": "article", "title": "Dispersion Mapping in 3-Dimensional Core\u2013Shell Photonic Crystal Lattices Capable of Negative Refraction in the Mid-Infrared", "author": [ { "family_name": "Chernow", "given_name": "Victoria F.", "orcid": "0000-0001-5405-1928", "clpid": "Chernow-Victoria-F" }, { "family_name": "Ng", "given_name": "Ryan C.", "orcid": "0000-0002-0527-9130", "clpid": "Ng-Ryan-C" }, { "family_name": "Peng", "given_name": "Siying", "orcid": "0000-0002-1541-0278", "clpid": "Peng-Siying" }, { "family_name": "Atwater", "given_name": "Harry A.", "orcid": "0000-0001-9435-0201", "clpid": "Atwater-H-A" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "Engineering of the dispersion properties of a photonic crystal (PhC) opens a new paradigm for the design and function of PhC devices. Exploiting the dispersion properties of PhCs allows control over wave propagation within a PhC. We describe the design, fabrication, and experimental observation of photonic bands for 3D PhCs capable of negative refraction in the mid-infrared. Band structure and equifrequency contours were calculated to inform the design of 3D polymer\u2013germanium core\u2013shell PhCs, which were fabricated using two-photon lithography direct laser writing and sputtering. We successfully characterized a polymer\u2013Ge core\u2013shell lattice and mapped its band structure, which we then used to calculate the PhC refraction behavior. An analysis of wave propagation revealed that this 3D core\u2013shell PhC refracts light negatively and possesses an effective negative index of refraction in the experimentally observed region. These results suggest that architected nanolattices have the potential to serve as new optical components and devices across infrared frequencies.", "doi": "10.1021/acs.nanolett.1c02851", "issn": "1530-6984", "publisher": "American Chemical Society", "publication": "Nano Letters", "publication_date": "2021-11-10", "series_number": "21", "volume": "21", "issue": "21", "pages": "9102-9107" }, { "id": "authors:qtrkx-j6330", "collection": "authors", "collection_id": "qtrkx-j6330", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20210428-140642160", "type": "article", "title": "Supersonic impact resilience of nanoarchitected carbon", "author": [ { "family_name": "Portela", "given_name": "Carlos M.", "orcid": "0000-0002-2649-4235", "clpid": "Portela-Carlos-M" }, { "family_name": "Edwards", "given_name": "Bryce W.", "clpid": "Edwards-Bryce-W" }, { "family_name": "Veysset", "given_name": "David", "orcid": "0000-0003-4473-1983", "clpid": "Veysset-David" }, { "family_name": "Sun", "given_name": "Yuchen", "clpid": "Sun-Yuchen" }, { "family_name": "Nelson", "given_name": "Keith A.", "orcid": "0000-0001-7804-5418", "clpid": "Nelson-Keith-A" }, { "family_name": "Kochmann", "given_name": "Dennis M.", "orcid": "0000-0002-9112-6615", "clpid": "Kochmann-D-M" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "Architected materials with nanoscale features have enabled extreme combinations of properties by exploiting the ultralightweight structural design space together with size-induced mechanical enhancement at small scales. Apart from linear waves in metamaterials, this principle has been restricted to quasi-static properties or to low-speed phenomena, leaving nanoarchitected materials under extreme dynamic conditions largely unexplored. Here, using supersonic microparticle impact experiments, we demonstrate extreme impact energy dissipation in three-dimensional nanoarchitected carbon materials that exhibit mass-normalized energy dissipation superior to that of traditional impact-resistant materials such as steel, aluminium, polymethyl methacrylate and Kevlar. In-situ ultrahigh-speed imaging and post-mortem confocal microscopy reveal consistent mechanisms such as compaction cratering and microparticle capture that enable this superior response. By analogy to planetary impact, we introduce predictive tools for crater formation in these materials using dimensional analysis. These results substantially uncover the dynamic regime over which nanoarchitecture enables the design of ultralightweight, impact-resistant materials that could open the way to design principles for lightweight armour, protective coatings and blast-resistant shields for sensitive electronics.", "doi": "10.1038/s41563-021-01033-z", "issn": "1476-1122", "publisher": "Nature Publishing Group", "publication": "Nature Materials", "publication_date": "2021-11", "series_number": "11", "volume": "20", "issue": "11", "pages": "1491-1497" }, { "id": "authors:kysrv-r5s17", "collection": "authors", "collection_id": "kysrv-r5s17", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20210917-215613610", "type": "article", "title": "Failure Mechanisms in Vertically Aligned Dense Nanowire Arrays", "author": [ { "family_name": "Gallivan", "given_name": "Rebecca A.", "orcid": "0000-0001-6516-2180", "clpid": "Gallivan-Rebecca-A" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "Nanowires are an increasingly prevalent class of nanomaterials in composites and devices, with arrays and other complex geometries used in various applications. Little investigation has been done regarding the mechanical behavior of micron-sized nanowire structures. We conduct in situ microcompression experiments on vertically aligned dense microbundles of 300 nm diameter single-crystalline zinc oxide nanowires to gain insights into their structural failure. Experiments demonstrate that bundles containing approximately 10\u2013130 nanowires experience two failure regimes: (1) localized noncatastrophic interfacial splitting and (2) global structural failure. Utilizing Weibull statistics and experimental results, we develop a technique for analyzing flaw distribution and use it to predict the expected range of bundle failure stress. This analysis provides guidelines for nanowire arrays' susceptibility to failure, sensitivity to flaw size, interfacial interactions of constituents, and degree of alignment. This work develops insights to understand and predict fundamental failure mechanisms in highly aligned, dense structures.", "doi": "10.1021/acs.nanolett.1c01944", "issn": "1530-6984", "publisher": "American Chemical Society", "publication": "Nano Letters", "publication_date": "2021-09-22", "series_number": "18", "volume": "21", "issue": "18", "pages": "7542-7547" }, { "id": "authors:mqqt0-z3g68", "collection": "authors", "collection_id": "mqqt0-z3g68", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20210623-141714887", "type": "article", "title": "3D-Printed Drug Capture Materials Based on Genomic DNA Coatings", "author": [ { "family_name": "Yee", "given_name": "Daryl W.", "orcid": "0000-0002-4114-6167", "clpid": "Yee-Daryl-Wei-Liang" }, { "family_name": "Hetts", "given_name": "Steven W.", "clpid": "Hetts-Steven-W" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "The toxic side effects of chemotherapy have long limited its efficacy, prompting expensive and long-drawn efforts to develop more targeted cancer therapeutics. An alternative approach to mitigate off-target toxicity is to develop a device that can sequester chemotherapeutic agents from the veins that drain the target organ before they enter systemic circulation. This effectively localizes the chemotherapy to the target organ, minimizing any hazardous side effects. 3D printing is ideal for fabricating these devices, as the geometric control afforded allows us to precisely dictate its hemodynamic performance in vivo. However, the existing materials compatible with 3D printing do not have drug-binding capabilities. Here, we report the stable coating of genomic DNA on a 3D-printed structure for the capture of doxorubicin. Genomic DNA is an effective chemotherapeutic-agent capture material due to the intrinsic DNA-targeting mechanism of action of these drugs. Stable DNA coatings were achieved through a combination of electrostatic interactions and ultraviolet C (UVC, 254 nm) cross-linking. These UVC cross-linked DNA coatings were extremely stable\u2014leaching on average 100 pg of genomic DNA per mm2 of 3D-printed structure over a period of 30 min. In vitro studies of these materials in phosphate buffered saline and human serum demonstrated that they were able to capture, on average, 72 and 60 ng of doxorubicin per mm\u00b2 of structure, respectively. The stability and efficacy of these genomic DNA-coated 3D-printed materials represent a significant step forward towards the translation of these devices to clinical applications for the potential improvement of chemotherapy treatment.", "doi": "10.1021/acsami.1c05209", "issn": "1944-8244", "publisher": "American Chemical Society", "publication": "ACS Applied Materials and Interfaces", "publication_date": "2021-09-08", "series_number": "35", "volume": "13", "issue": "35", "pages": "41424-41434" }, { "id": "authors:v1j0j-w5x68", "collection": "authors", "collection_id": "v1j0j-w5x68", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20210409-123059226", "type": "article", "title": "Understanding and mitigating mechanical degradation in lithium\u2013sulfur batteries: additive manufacturing of Li\u2082S composites and nanomechanical particle compressions", "author": [ { "family_name": "Saccone", "given_name": "Max A.", "orcid": "0000-0003-3846-2908", "clpid": "Saccone-Max-A" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "Lithium\u2013sulfur batteries are poised to outcompete lithium-ion batteries in key sectors such as transportation and grid storage due to the low cost and high theoretical energy density of sulfur as a cathode material. Widespread implementation of this technology is hindered by significant degradation during cycling, including mechanical failure via cracking or detachment of insulating lithium sulfide (Li\u2082S) from the conductive matrix in the cathode, causing irreversible capacity fade. We developed a technique to additively manufacture Li\u2082S composites to fabricate rationally designed cathodes and demonstrate the utility of a three dimensionally architected Li\u2082S composite cathode in a battery. We additionally measure the yet unknown material properties and deformation mechanisms of Li\u2082S powders via in situ scanning electron microscope (SEM) nanomechanical experiments. Measuring these mechanical properties is a first step towards understanding the process of mechanical degradation and is necessary to enable the rational design of high energy density, long-cycling, and mechanically robust sulfur cathodes.", "doi": "10.1557/s43578-021-00182-w", "issn": "0884-2914", "publisher": "Materials Research Society", "publication": "Journal of Materials Research", "publication_date": "2021-09", "series_number": "18", "volume": "36", "issue": "18", "pages": "3656-3666" }, { "id": "authors:k1gmw-nbr60", "collection": "authors", "collection_id": "k1gmw-nbr60", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20201216-152241391", "type": "article", "title": "Three\u2010dimensional chemical reactors: in situ materials synthesis to advance vat photopolymerization", "author": [ { "family_name": "Yee", "given_name": "Daryl W.", "orcid": "0000-0002-4114-6167", "clpid": "Yee-Daryl-Wei-Liang" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "Vat photopolymerization (VP) is one of the most remarkable additive manufacturing techniques today and has been used for a variety of applications, from materials research to product manufacturing. The main challenge with VP is the limited choice of compatible materials, which motivates significant interest in VP materials development. We provide a brief overview of the materials that are currently accessible via VP and highlight recent advances in the field. We also provide perspective on expanding the library of materials compatible with VP using in situ materials synthesis.", "doi": "10.1002/pi.6165", "issn": "0959-8103", "publisher": "Society of Chemical Industry", "publication": "Polymer International", "publication_date": "2021-07", "series_number": "7", "volume": "70", "issue": "7", "pages": "964-976" }, { "id": "authors:cfvz2-bqj12", "collection": "authors", "collection_id": "cfvz2-bqj12", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20210514-114309275", "type": "article", "title": "All-day fresh water harvesting by microstructured hydrogel membranes", "author": [ { "family_name": "Shi", "given_name": "Ye", "orcid": "0000-0002-5228-1604", "clpid": "Shi-Ye" }, { "family_name": "Ilic", "given_name": "Ognjen", "clpid": "Ilic-Ognjen" }, { "family_name": "Atwater", "given_name": "Harry A.", "orcid": "0000-0001-9435-0201", "clpid": "Atwater-H-A" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "Solar steam water purification and fog collection are two independent processes that could enable abundant fresh water generation. We developed a hydrogel membrane that contains hierarchical three-dimensional microstructures with high surface area that combines both functions and serves as an all-day fresh water harvester. At night, the hydrogel membrane efficiently captures fog droplets and directionally transports them to a storage vessel. During the daytime, it acts as an interfacial solar steam generator and achieves a high evaporation rate of 3.64\u2009kg\u2009m\u207b\u00b2 h\u207b\u00b9 under 1 sun enabled by improved thermal/vapor flow management. With a homemade rooftop water harvesting system, this hydrogel membrane can produce fresh water with a daily yield of ~34\u2009L\u2009m\u207b\u00b2 in an outdoor test, which demonstrates its potential for global water scarcity relief.", "doi": "10.1038/s41467-021-23174-0", "pmcid": "PMC8121874", "issn": "2041-1723", "publisher": "Nature Publishing Group", "publication": "Nature Communications", "publication_date": "2021-05-14", "volume": "12", "pages": "Art. No. 2797" }, { "id": "authors:yr3d4-szb92", "collection": "authors", "collection_id": "yr3d4-szb92", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20210122-082128326", "type": "article", "title": "Nanofibril-mediated fracture resistance of bone", "author": [ { "family_name": "Tertuliano", "given_name": "Ottman", "orcid": "0000-0003-0524-3944", "clpid": "Tertuliano-Ottman" }, { "family_name": "Edwards", "given_name": "Bryce W.", "clpid": "Edwards-Bryce-W" }, { "family_name": "Meza", "given_name": "Lucas R.", "orcid": "0000-0003-0250-2621", "clpid": "Meza-Lucas-R" }, { "family_name": "Deshpande", "given_name": "Vikram S.", "orcid": "0000-0003-3899-3573", "clpid": "Deshpande-Vikram-S" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "Natural hard composites like human bone possess a combination of strength and toughness that exceeds that of their constituents and of many engineered composites. This augmentation is attributed to their complex hierarchical structure, spanning multiple length scales; in bone, characteristic dimensions range from nanoscale fibrils to microscale lamellae to mesoscale osteons and macroscale organs. The mechanical properties of bone have been studied, with the understanding that the isolated microstructure at micro- and nano-scales gives rise to superior strength compared to that of whole tissue, and the tissue possesses an amplified toughness relative to that of its nanoscale constituents. Nanoscale toughening mechanisms of bone are not adequately understood at sample dimensions that allow for isolating salient microstructural features, because of the challenge of performing fracture experiments on small-sized samples. We developed an in-situ three-point bend experimental methodology that probes site-specific fracture behavior of micron-sized specimens of hard material. Using this, we quantify crack initiation and growth toughness of human trabecular bone with sharp fatigue pre-cracks and blunt notches. Our findings indicate that bone with fatigue cracks is two times tougher than that with blunt cracks. In-situ data-correlated electron microscopy videos reveal this behavior arises from crack-bridging by nanoscale fibril structure. The results reveal a transition between fibril-bridging (~1\u00b5m) and crack deflection/twist (~500\u00b5m) as a function of length-scale, and quantitatively demonstrate hierarchy-induced toughening in a complex material. This versatile approach enables quantifying the relationship between toughness and microstructure in various complex material systems and provides direct insight for designing biomimetic composites.", "doi": "10.1088/1748-3190/abdd9d", "issn": "1748-3182", "publisher": "IOP", "publication": "Bioinspiration and Biomimetics", "publication_date": "2021-05", "series_number": "3", "volume": "16", "issue": "3", "pages": "Art. No. 035001" }, { "id": "authors:b0m1k-j5036", "collection": "authors", "collection_id": "b0m1k-j5036", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20201209-163844443", "type": "article", "title": "Stimuli Responsive Shape Memory Microarchitectures", "author": [ { "family_name": "Elliott", "given_name": "Luizetta V.", "orcid": "0000-0002-6411-0239", "clpid": "Elliott-Luizetta-V" }, { "family_name": "Salzman", "given_name": "Erika E.", "orcid": "0000-0002-2995-7864", "clpid": "Salzman-Erika-E" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "Shape memory polymers (SMPs) respond to heat by generating programmable movement in devices that require substantial deformation and operate at transient temperatures, including stents and embolization coils. To enable their use in small\u2010scale applications like retinal vasculature stenting, shape transformations must occur in SMPs with complex 3D geometries with nanoscale features. This work describes the synthesis and sculpting of a benzyl methacrylate\u2010based SMP into 3D structures with <800 nm characteristic critical dimensions via two photon lithography. Dynamic nanomechanical analysis of 8 \u00b5m\u2010diameter cylindrical pillars reveal the initiation of this SMP's glass transition at 60 \u00b0C. Shape memory programming of the characterized pillars as well as complex 3D architectures, including flowers with 500 nm thick petals and cubic lattices with 2.5 \u00b5m unit cells and overall dimensions of 4.5 \u00b5m \u00d7 4.5 \u00b5m \u00d7 10 \u00b5m, demonstrate an 86 +/\u2212 4% characteristic shape recovery ratio. These results reveal a pathway toward SMP devices with nanoscale features and arbitrary 3D geometries changing shape in response to temperature.", "doi": "10.1002/adfm.202008380", "issn": "1616-301X", "publisher": "Wiley", "publication": "Advanced Functional Materials", "publication_date": "2021-02-24", "series_number": "9", "volume": "31", "issue": "9", "pages": "Art. No. 2008380" }, { "id": "authors:xm906-8ve82", "collection": "authors", "collection_id": "xm906-8ve82", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20201204-110355287", "type": "article", "title": "Thermal Stability of Thin Au Films Deposited on Salt Whiskers", "author": [ { "family_name": "Almog", "given_name": "Ehud", "clpid": "Almog-Ehud" }, { "family_name": "Derkach", "given_name": "Vadim", "orcid": "0000-0003-0039-281X", "clpid": "Derkach-Vadim" }, { "family_name": "Sharma", "given_name": "Amit", "clpid": "Sharma-Amit" }, { "family_name": "Novick-Cohen", "given_name": "Amy", "orcid": "0000-0001-6709-5030", "clpid": "Novick-Cohen-Amy" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" }, { "family_name": "Rabkin", "given_name": "Eugen", "orcid": "0000-0001-5545-1261", "clpid": "Rabkin-Eugen" } ], "abstract": "Thin metal films deposited on patterned or rough substrates play an increasing role in microelectronics, sensing, catalysis, and other areas of nanotechnology. However, the thermal stability and solid state dewetting of thin metal films with complex three-dimensional architecture is still poorly understood. In this work we employed a model system of nanocrystalline Au thin films deposited on prismatic single crystalline KCl whiskers to study the solid state dewetting of thin films in a three-dimensional setting. The arrays of KCl whiskers were grown on porous substrates under well-defined humidity and temperature conditions. Single crystalline prismatic KCl whiskers with a very high aspect ratio, [001] axis and {100} side facets were obtained. The whiskers were coated with thin conformal Au films of 20-30 nm in thickness. The annealing of these core-shell whiskers at the temperature of 350oC resulted in solid state dewetting of the Au film, with the dewetting processes occurring much faster along the whisker edges than on the side facets. The orientation relationships between Au and KCl were determined by employing similarly prepared thin Au films deposited on the flat KCl (100) substrates. Inspired by our experimental results, we developed a numerical model describing the curvature-gradient driven and surface diffusion-controlled growth of a hole in the thin film deposited on a curved substrate. The model predicted the growth of anisotropic elliptical holes elongated along the whisker axis. We discuss the experimental results in terms of the proposed model, indicating the importance of the change in orientation relationship between the Au grains and KCl whisker along the whisker edges.", "doi": "10.1016/j.actamat.2020.116537", "issn": "1359-6454", "publisher": "Elsevier", "publication": "Acta Materialia", "publication_date": "2021-02-15", "volume": "205", "pages": "Art. No. 116537" }, { "id": "authors:fzmmp-kya50", "collection": "authors", "collection_id": "fzmmp-kya50", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20201109-112630307", "type": "article", "title": "3D Architected Carbon Electrodes for Energy Storage", "author": [ { "family_name": "Narita", "given_name": "Kai", "orcid": "0000-0002-3867-8234", "clpid": "Narita-Kai" }, { "family_name": "Citrin", "given_name": "Michael A.", "orcid": "0000-0001-8183-5437", "clpid": "Citrin-Michael-A" }, { "family_name": "Yang", "given_name": "Heng", "orcid": "0000-0001-7431-932X", "clpid": "Yang-Heng" }, { "family_name": "Xia", "given_name": "Xiaoxing", "orcid": "0000-0003-1255-3289", "clpid": "Xia-Xiaoxing" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "The ability to design a particular geometry of porous electrodes at multiple length scales in a lithium\u2010ion battery can significantly and positively influence battery performance because it enables control over distribution of current and potential and can enhance ion and electron transport. 3D architecturally designed carbon electrodes are developed, whose structural factors are independently controlled and whose dimensions span micrometers to centimeters, using digital light processing and pyrolysis. These free\u2010standing lattice electrodes are comprised of monolithic glassy carbon beams, are lightweight, with a relative density of 0.1\u20130.35, and mechanically robust, with a maximum precollapse stress of 27 MPa, which facilitates electrode recycling. The specific strength is 101 kN m kg\u207b\u00b9, comparable to that of 6061 aluminum alloy. These carbon electrodes can reach a mass loading of 70 mg cm\u207b\u00b2 and an areal capacity of 3.2 mAh cm\u207b\u00b2 at a current density of 2.4 mA cm\u207b\u00b2. It is demonstrated that this approach allows for independent design of structural factors, i.e., beam diameter, electrode thickness, and surface morphology, enabling control over Li\u2010ion transport length, overpotential and battery performance, not available for slurry\u2010based electrodes. This multiscale approach to design of electrodes may open substantial performance\u2010enhancing capabilities for solid\u2010 and liquid\u2010state batteries, flow batteries, and fuel cells.", "doi": "10.1002/aenm.202002637", "issn": "1614-6832", "publisher": "Wiley", "publication": "Advanced Energy Materials", "publication_date": "2021-02-04", "series_number": "5", "volume": "11", "issue": "5", "pages": "Art. No. 2002637" }, { "id": "authors:fxwgn-j3h40", "collection": "authors", "collection_id": "fxwgn-j3h40", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20201111-131428787", "type": "article", "title": "Hydrogel-Based Additive Manufacturing of Lithium Cobalt Oxide", "author": [ { "family_name": "Yee", "given_name": "Daryl W.", "orcid": "0000-0002-4114-6167", "clpid": "Yee-Daryl-Wei-Liang" }, { "family_name": "Citrin", "given_name": "Michael A.", "orcid": "0000-0001-8183-5437", "clpid": "Citrin-Michael-A" }, { "family_name": "Taylor", "given_name": "Zane W.", "orcid": "0000-0002-9326-6873", "clpid": "Taylor-Zane-W" }, { "family_name": "Saccone", "given_name": "Max A.", "orcid": "0000-0003-3846-2908", "clpid": "Saccone-Max-A" }, { "family_name": "Tovmasyan", "given_name": "Victoria L.", "orcid": "0000-0001-8202-5057", "clpid": "Tovmasyan-Victoria-L" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "3D multicomponent metal oxides with complex architectures can enable previously impossible energy storage devices, particularly lithium\u2010ion battery (LIB) electrodes with fully controllable form factors. Existing additive manufacturing approaches for fabricating 3D multicomponent metal oxides rely on particle\u2010based or organic\u2013inorganic binders, which are limited in their resolution and chemical composition, respectively. In this work, aqueous metal salt solutions are used as metal precursors to circumvent these limitations, and provide a platform for 3D printing multicomponent metal oxides. As a proof\u2010of\u2010concept, architected lithium cobalt oxide (LCO) structures are fabricated by first synthesizing a homogenous lithium and cobalt nitrate aqueous photoresin, and then using it with digital light processing printing to obtain lithium and cobalt ion containing hydrogels. The 3D hydrogels are calcined to obtain micro\u2010porous self\u2010similar LCO architectures with a resolution of \u2248100 \u00b5m. These free\u2010standing, binder\u2010 and conductive additive\u2010free LCO structures are integrated as cathodes into LIBs, and exhibit electrochemical capacity retention of 76% over 100 cycles at C/10. This facile approach to fabricating 3D LCO structures can be extended to other materials by tailoring the identity and stoichiometry of the metal salt solutions used, providing a versatile method for the fabrication of multicomponent metal oxides with complex 3D architectures.", "doi": "10.1002/admt.202000791", "pmcid": "PMC8115722", "issn": "2365-709X", "publisher": "Wiley", "publication": "Advanced Materials Technologies", "publication_date": "2021-02", "series_number": "2", "volume": "6", "issue": "2", "pages": "Art. No. 2000791" }, { "id": "authors:gv9y9-7q819", "collection": "authors", "collection_id": "gv9y9-7q819", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20201208-105037703", "type": "article", "title": "Size-dependence of zirconia-based ceramics via deformation twinning", "author": [ { "family_name": "Zhang", "given_name": "H.", "orcid": "0000-0002-2871-5169", "clpid": "Zhang-Haolu-Jane" }, { "family_name": "Gu", "given_name": "H.", "clpid": "Hu-H" }, { "family_name": "Jetter", "given_name": "J.", "orcid": "0000-0003-2725-8426", "clpid": "Jetter-Justin" }, { "family_name": "Quandt", "given_name": "E.", "orcid": "0000-0002-2314-5179", "clpid": "Quandt-Eckhard" }, { "family_name": "James", "given_name": "R. D.", "orcid": "0000-0001-6019-6613", "clpid": "James-Richard-D" }, { "family_name": "Greer", "given_name": "J. R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "Contrary to the dislocation-driven 'smaller-is-stronger' size-effect in nanocrystals, the size-dependence of strength in deformation twinning, another carrier of plasticity, still lacks universal understanding. Deformation twinning enables pseudoplastic strain of >5% in a shape memory ceramic (ZrHfO\u2084)_x (YTaO\u2084)_(1\u2212x). We use diffraction methods, microstructure analysis, and in-situ nanomechanical experiments to uncover contributing factors to the competition between twinning and slip in these submicron-sized ionic crystals, revealing power-law scaling of strength with size for both mechanisms. The significant twinning size-dependence was found to follow a superimposed power-law with exponent of -1, identical to that in metals. These findings unveil the universality of the superimposed power-law size-effect for twinning in single-crystals and provide new insights on deformability of ceramics and microstructure-driven nano-plasticity.", "doi": "10.1016/j.eml.2020.101124", "issn": "2352-4316", "publisher": "Elsevier", "publication": "Extreme Mechanics Letters", "publication_date": "2021-01", "volume": "42", "pages": "Art. No. 101124" }, { "id": "authors:cf0jy-8fe49", "collection": "authors", "collection_id": "cf0jy-8fe49", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20210506-135655817", "type": "article", "title": "Energy-based approach for failure assessment of 3D architectured materials", "author": [ { "family_name": "Maurizi", "given_name": "Marco", "clpid": "Maurizi-Marco" }, { "family_name": "Edwards", "given_name": "Bryce", "clpid": "Edwards-Bryce-W" }, { "family_name": "Greer", "given_name": "Julia", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" }, { "family_name": "Berto", "given_name": "Filippo", "clpid": "Berto-Filippo" } ], "abstract": "3D architectured materials with features at the micro-/nano-scale can attain extreme mechanical properties, overcoming the tradeoff between lightness, strength and damage tolerance. The combination of the material size effect and the geometry (architecture) gives rise to peculiar mechanical behaviors, often found in biological systems. Despite stiffness and strength have been widely investigated for a large variety of geometries, fracture properties, such as fracture toughness, of 3D cellular materials have not been deeply studied yet. Here, we re-adapt an energy-based approach, called averaged strain energy density (ASED), to assess the failure of 3D nanolattices. An octet geometry characterizes the unit cell of the periodic cellular material adopted in this work, without loss of generality. By exploiting of preliminary experimental results on a compact tension (CT) specimen, with smallest features at the nano-scale, a finite element model is created to assess its failure (first beam to fracture) under mode 1, employing the energy criterion. The structural control volume, i.e. the volume around the notch where the strain energy is averaged, is assumed to be a portion of a square cuboid centered at the notch/crack tip, cut by the notch flanks, and with semi-length of the edge equal to the unit cell size, being the zone of highest and steepest strain energy density concentration and gradient, respectively. Based on this energy criterion, the fracture toughness is determined as a function of the relative density (\u03c1) and unit cell length (L), in agreement with the classical power-law behavior, i.e. \u221aL\u03c1^(\u2212d). Preliminary experimental and numerical results seem to be in agreement, however, further research is needed to face the problem of modeling the fracture of such materials.", "doi": "10.1016/j.prostr.2020.11.046", "issn": "2452-3216", "publisher": "Elsevier", "publication": "Procedia Structural Integrity", "publication_date": "2020-12-01", "volume": "28", "pages": "2181-2186" }, { "id": "authors:49075-e8b03", "collection": "authors", "collection_id": "49075-e8b03", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20200713-102704003", "type": "article", "title": "From ion to atom to dendrite: Formation and nanomechanical behavior of electrodeposited lithium", "author": [ { "family_name": "Citrin", "given_name": "Michael A.", "orcid": "0000-0001-8183-5437", "clpid": "Citrin-Michael-A" }, { "family_name": "Yang", "given_name": "Heng", "orcid": "0000-0001-7431-932X", "clpid": "Yang-Heng" }, { "family_name": "Nieh", "given_name": "Simon K.", "clpid": "Nieh-Simon-K" }, { "family_name": "Berry", "given_name": "Joel", "clpid": "Berry-Joel" }, { "family_name": "Gao", "given_name": "Wenpei", "orcid": "0000-0002-2776-2676", "clpid": "Gao-Wenpei" }, { "family_name": "Pan", "given_name": "Xiaoqing", "orcid": "0000-0002-0965-8568", "clpid": "Pan-Xiaoqing" }, { "family_name": "Srolovitz", "given_name": "David J.", "orcid": "0000-0001-6038-020X", "clpid": "Srolovitz-David-J" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "Development of high energy density solid-state batteries with Li metal anodes has been limited by uncontrollable growth of Li dendrites in liquid and solid electrolytes (SEs). This, in part, may be caused by a dearth of information about mechanical properties of Li, especially at the nano- and microlength scales and microstructures relevant to Li batteries. We investigate Li electrodeposited in a commercial LiCoO\u2082/LiPON/Cu solid-state thin-film cell, grown in situ in a scanning electron microscope equipped with nanomechanical capabilities. Experiments demonstrate that Li was preferentially deposited at the LiPON/Cu interface along the valleys that mimic the domain boundaries of underlying LiCoO\u2082 (cathode). Cryogenic electron microscopy analysis of electrodeposited Li revealed a single-crystalline microstructure, and in situ nanocompression experiments on nano-pillars with 360\u2013759 nm diameters revealed their average Young's modulus to be 6.76 \u00b1 2.88 GPa with an average yield stress of 16.0 \u00b1 6.82 MPa, ~24x higher than what has been reported for bulk polycrystalline Li. We discuss mechanical deformation mechanisms, stiffness, and strength of nano-sized electrodeposited Li in the framework of its microstructure and dislocation-governed nanoscale plasticity of crystals, and place it in the parameter space of existing knowledge on small-scale Li mechanics. The enhanced strength of Li at small scales may explain why it can penetrate and fracture through much stiffer and harder SEs than theoretically predicted.", "doi": "10.1557/mrs.2020.148", "issn": "0883-7694", "publisher": "Materials Research Society", "publication": "MRS Bulletin", "publication_date": "2020-11", "series_number": "11", "volume": "45", "issue": "11", "pages": "891-904" }, { "id": "authors:tx6b1-2bd50", "collection": "authors", "collection_id": "tx6b1-2bd50", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20200825-095728096", "type": "article", "title": "Pushing and Pulling on Ropes: Hierarchical Woven Materials", "author": [ { "family_name": "Moestopo", "given_name": "Widianto P.", "orcid": "0000-0002-7617-4280", "clpid": "Moestopo-W-P" }, { "family_name": "Mateos", "given_name": "Arturo J.", "orcid": "0000-0002-9306-3531", "clpid": "Mateos-A-J" }, { "family_name": "Fuller", "given_name": "Ritchie M.", "clpid": "Fuller-R-M" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" }, { "family_name": "Portela", "given_name": "Carlos M.", "orcid": "0000-0002-2649-4235", "clpid": "Portela-C-M" } ], "abstract": "Hierarchy in natural and synthetic materials has been shown to grant these architected materials properties unattainable independently by their constituent materials. While exceptional mechanical properties such as extreme resilience and high deformability have been realized in many human\u2010made three\u2010dimensional (3D) architected materials using beam\u2010and\u2010junction\u2010based architectures, stress concentrations and constraints induced by the junctions limit their mechanical performance. A new hierarchical architecture in which fibers are interwoven to construct effective beams is presented. In situ tension and compression experiments of additively manufactured woven and monolithic lattices with 30 \u00b5m unit cells demonstrate the superior ability of woven architectures to achieve high tensile and compressive strains (>50%)\u2014without failure events\u2014via smooth reconfiguration of woven microfibers in the effective beams and junctions. Cyclic compression experiments reveal that woven lattices accrue less damage compared to lattices with monolithic beams. Numerical studies of woven beams with varying geometric parameters present new design spaces to develop architected materials with tailored compliance that is unachievable by similarly configured monolithic\u2010beam architectures. Woven hierarchical design offers a pathway to make traditionally stiff and brittle materials more deformable and introduces a new building block for 3D architected materials with complex nonlinear mechanics.", "doi": "10.1002/advs.202001271", "pmcid": "PMC7578876", "issn": "2198-3844", "publisher": "Wiley", "publication": "Advanced Science", "publication_date": "2020-10-21", "series_number": "20", "volume": "7", "issue": "20", "pages": "2001271" }, { "id": "authors:0p0wv-pb268", "collection": "authors", "collection_id": "0p0wv-pb268", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20200924-144351561", "type": "article", "title": "Miniaturization of a-Si guided mode resonance filter arrays for near-IR multi-spectral filtering", "author": [ { "family_name": "Ng", "given_name": "Ryan C.", "orcid": "0000-0002-0527-9130", "clpid": "Ng-Ryan-C" }, { "family_name": "Garcia", "given_name": "Juan C.", "clpid": "Garcia-Juan-C" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" }, { "family_name": "Fountaine", "given_name": "Katherine T.", "orcid": "0000-0002-0414-8227", "clpid": "Fountaine-K-T" } ], "abstract": "Sub-wavelength periodic arrays exhibit narrow near-unity reflection bands that arise from guided mode resonances. These resonances have extremely high quality factor (i.e., narrow band features) and are ideal for filtering applications. A high quality factor requires many periods, causing large lateral footprints that limit an imaging system's spatial resolution. We present a 1D ultra-thin (<100\u2009nm) compact finite design of seven periods of amorphous Si slabs with subwavelength periodicity surrounded by Al mirrors, which allow the finite array to approximate an infinite array and enabling a small footprint (\u223c5\u2009\u03bcm), for near-infrared applications (\u03bb = 800\u20132000\u2009nm). We demonstrate spectral tunability (amplitude, bandwidth, and peak location) via geometric parameter variation and demonstrate the performance of these filters both in experiment and in simulation. This work miniaturizes guided-mode resonance filters, previously limited by extremely large footprints, while being relatively cheap and simple to fabricate compared to many existing designs.", "doi": "10.1063/5.0024302", "issn": "0003-6951", "publisher": "American Institute of Physics", "publication": "Applied Physics Letters", "publication_date": "2020-09-14", "series_number": "11", "volume": "117", "issue": "11", "pages": "Art. No. 111106" }, { "id": "authors:axqhj-kwv80", "collection": "authors", "collection_id": "axqhj-kwv80", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20200817-092018098", "type": "article", "title": "Julia Greer answers questions about additive manufacturing", "author": [ { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "Professor Julia R Greer is a materials scientist at the California Institute of Technology. Her group focuses on designing, fabricating and characterising micro- and nano-architected materials using 3D lithography, nanofabrication, and additive manufacturing (AM) techniques for a multitude of applications ranging from biological devices to damage-tolerant fabrics.", "doi": "10.1038/s41467-020-17723-2", "issn": "2041-1723", "publisher": "Nature Publishing Group", "publication": "Nature Communications", "publication_date": "2020-08-17", "volume": "11", "pages": "Art. No. 3993" }, { "id": "authors:en5rw-zab75", "collection": "authors", "collection_id": "en5rw-zab75", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20200302-140842584", "type": "article", "title": "Effect of temperature on small-scale deformation of individual face-centered-cubic and body-centered-cubic phases of an Al_(0.7)CoCrFeNi high-entropy alloy", "author": [ { "family_name": "Giwa", "given_name": "Adenike M.", "clpid": "Giwa-A-M" }, { "family_name": "Aitken", "given_name": "Zachary H.", "clpid": "Aitken-Z-H" }, { "family_name": "Liaw", "given_name": "Peter K.", "clpid": "Liaw-P-K" }, { "family_name": "Zhang", "given_name": "Yong-Wei", "clpid": "Zhang-Yong-Wei" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "High-entropy alloys (HEAs) represent an important class of structural materials because of their high strength, ductility, and thermal stability. Understanding the mechanical response of isolated phases of a FCC/BCC dual-phase HEA is integral to understanding the mechanical properties of these alloys in the bulk. We investigate the compressive response of single-crystalline cylinders with diameters between 400\u202fnm and 2\u202f\u03bcm excised from individual grains within FCC and BCC phases of the dual-phase Al_(0.7)CoCrFeNi HEA at 295\u202fK, 143\u202fK, and 40\u202fK. We observed a \"smaller is stronger\" size effect in the yield strength as a function of pillar diameter, D, of both alloy phases for all temperatures, with a power-law exponent, m, decreasing with temperature for the FCC phase, and remaining constant for all temperatures in the BCC phase. We found reduced work-hardening rates and more extensive strain bursts during deformation at lower temperatures in all samples. We performed molecular dynamics simulations of similar FCC and BCC HEA compression that displayed deformation dominated by dislocation slip at all temperatures. We discussed theories of low-temperature strengthening in HEAs, compared them to our experimental data and assessed how they manifest in the observed temperature-dependent size effect and work-hardening.", "doi": "10.1016/j.matdes.2020.108611", "issn": "0264-1275", "publisher": "Elsevier", "publication": "Materials and Design", "publication_date": "2020-06", "volume": "191", "pages": "Art. No. 108611" }, { "id": "authors:53cbk-4y539", "collection": "authors", "collection_id": "53cbk-4y539", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20200427-132503609", "type": "article", "title": "Additive Manufacturing of High-Refractive-Index, Nanoarchitected Titanium Dioxide for 3D Dielectric Photonic Crystals", "author": [ { "family_name": "Vyatskikh", "given_name": "Andrey", "orcid": "0000-0002-6917-6931", "clpid": "Vyatskikh-A" }, { "family_name": "Ng", "given_name": "Ryan C.", "orcid": "0000-0002-0527-9130", "clpid": "Ng-Ryan-C" }, { "family_name": "Edwards", "given_name": "Bryce", "clpid": "Edwards-Bryce" }, { "family_name": "Briggs", "given_name": "Ryan M.", "clpid": "Briggs-R-M" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "Additive manufacturing at small scales enables advances in micro- and nanoelectromechanical systems, micro-optics, and medical devices. Materials that lend themselves to AM at the nanoscale, especially for optical applications, are limited. State-of-the-art AM processes for high-refractive-index materials typically suffer from high porosity and poor repeatability and require complex experimental procedures. We developed an AM process to fabricate complex 3D architectures out of fully dense titanium dioxide (TiO\u2082) with a refractive index of 2.3 and nanosized critical dimensions. Transmission electron microscopy (TEM) analysis proves this material to be rutile phase of nanocrystalline TiO\u2082, with an average grain size of 110 nm and <1% porosity. Proof-of-concept woodpile architectures with 300\u2013600 nm beam dimensions exhibit a full photonic band gap centered at 1.8\u20132.9 \u03bcm, as revealed by Fourier-transform infrared spectroscopy (FTIR) and supported by plane wave expansion simulations. The developed AM process enables advances in 3D MEMS, micro-optics, and prototyping of 3D dielectric PhCs.", "doi": "10.1021/acs.nanolett.0c00454", "issn": "1530-6984", "publisher": "American Chemical Society", "publication": "Nano Letters", "publication_date": "2020-05-13", "series_number": "5", "volume": "20", "issue": "5", "pages": "3513-3520" }, { "id": "authors:a9h6j-n4r40", "collection": "authors", "collection_id": "a9h6j-n4r40", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20200608-101206169", "type": "patent", "title": "DNA-functionalized scaffolds for drug capture applications", "author": [ { "family_name": "Schulz", "given_name": "Michael D.", "orcid": "0000-0001-8499-6025", "clpid": "Schulz-M-D" }, { "family_name": "Blumenfeld", "given_name": "Carl M.", "clpid": "Blumenfeld-C-M" }, { "family_name": "Grubbs", "given_name": "Robert H.", "orcid": "0000-0002-0057-7817", "clpid": "Grubbs-R-H" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" }, { "family_name": "Yee", "given_name": "Daryl Wei Liang", "orcid": "0000-0002-4114-6167", "clpid": "Yee-Daryl-Wei-Liang" } ], "abstract": "This disclosure is directed to structured compositions, including DNA-functionalized scaffolds, for drug capture, and methods and devices for sequestering chemotherapeutics from physiological fluids using the functionalized scaffolds.", "publisher": "U.S. Patent Office", "publication_date": "2020-05-12" }, { "id": "authors:3rcma-cvw49", "collection": "authors", "collection_id": "3rcma-cvw49", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20200304-130419102", "type": "article", "title": "Extreme mechanical resilience of self-assembled nanolabyrinthine materials", "author": [ { "family_name": "Portela", "given_name": "Carlos M.", "orcid": "0000-0002-2649-4235", "clpid": "Portela-C-M" }, { "family_name": "Vidyasagar", "given_name": "A.", "clpid": "Vidyasagar-A" }, { "family_name": "Kr\u00f6del", "given_name": "Sebastian", "orcid": "0000-0002-9218-8578", "clpid": "Kr\u00f6del-S" }, { "family_name": "Weissenbach", "given_name": "Tamara", "clpid": "Weissenbach-T" }, { "family_name": "Yee", "given_name": "Daryl W.", "orcid": "0000-0002-4114-6167", "clpid": "Yee-Daryl-Wei-Liang" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" }, { "family_name": "Kochmann", "given_name": "Dennis M.", "orcid": "0000-0002-9112-6615", "clpid": "Kochmann-D-M" } ], "abstract": "Low-density materials with tailorable properties have attracted attention for decades, yet stiff materials that can resiliently tolerate extreme forces and deformation while being manufactured at large scales have remained a rare find. Designs inspired by nature, such as hierarchical composites and atomic lattice-mimicking architectures, have achieved optimal combinations of mechanical properties but suffer from limited mechanical tunability, limited long-term stability, and low-throughput volumes that stem from limitations in additive manufacturing techniques. Based on natural self-assembly of polymeric emulsions via spinodal decomposition, here we demonstrate a concept for the scalable fabrication of nonperiodic, shell-based ceramic materials with ultralow densities, possessing features on the order of tens of nanometers and sample volumes on the order of cubic centimeters. Guided by simulations of separation processes, we numerically show that the curvature of self-assembled shells can produce close to optimal stiffness scaling with density, and we experimentally demonstrate that a carefully chosen combination of topology, geometry, and base material results in superior mechanical resilience in the architected product. Our approach provides a pathway to harnessing self-assembly methods in the design and scalable fabrication of beyond-periodic and nonbeam-based nano-architected materials with simultaneous directional tunability, high stiffness, and unsurpassed recoverability with marginal deterioration.", "doi": "10.1073/pnas.1916817117", "pmcid": "PMC7084143", "issn": "0027-8424", "publisher": "National Academy of Sciences", "publication": "Proceedings of the National Academy of Sciences of the United States of America", "publication_date": "2020-03-17", "series_number": "11", "volume": "117", "issue": "11", "pages": "5686-5693" }, { "id": "authors:aazds-bja13", "collection": "authors", "collection_id": "aazds-bja13", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20200311-151707535", "type": "book_section", "title": "Scalable fabrication of nano-architected materials using 3D interference lithography with metasurfaces at visible wavelengths (Conference Presentation)", "book_title": "Photonic and Phononic Properties of Engineered Nanostructures X", "author": [ { "family_name": "Pearson", "given_name": "Phillippe", "clpid": "Pearson-Phillippe" }, { "family_name": "Kamali", "given_name": "Seyedeh Mahsa", "orcid": "0000-0002-6968-811X", "clpid": "Kamali-S-M" }, { "family_name": "Afshinmanesh", "given_name": "Farzaneh", "clpid": "Afshinmanesh-F" }, { "family_name": "Navrazhnykh", "given_name": "Luizetta", "clpid": "Navrazhnykh-L" }, { "family_name": "Ng", "given_name": "Ryan", "orcid": "0000-0002-0527-9130", "clpid": "Ng-Ryan-C" }, { "family_name": "Faraon", "given_name": "Andrei", "orcid": "0000-0002-8141-391X", "clpid": "Faraon-A" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "contributor": [ { "family_name": "Adibi", "given_name": "Ali", "clpid": "Adibi-A" }, { "family_name": "Lin", "given_name": "Shawn-Yu", "clpid": "Lin-Shawn-Yu" }, { "family_name": "Scherer", "given_name": "Axel", "clpid": "Scherer-A" } ], "abstract": "Nano-architected materials have the potential to be adopted in several areas including photonic devices and structural materials. We present a 3D interference lithography technique with dielectric metasurfaces at visible wavelengths that allows patterning of thick epoxide films over areas on the order of 10 cm^2 with 100 nm resolution. By leveraging the ability of the metasurface to control the amplitude and phase of a wavefront, complex near-field 3D interference patterns can be designed. Pyrolysis of 3D patterned SU-8 produces a carbon-based material with sub-100 nm features and enhanced mechanical properties.", "doi": "10.1117/12.2555112", "isbn": "9781510633414", "publisher": "Society of Photo-optical Instrumentation Engineers (SPIE)", "place_of_publication": "Bellingham, WA", "publication_date": "2020-03-10", "pages": "Art. No. 112890I" }, { "id": "authors:2cpyz-tn319", "collection": "authors", "collection_id": "2cpyz-tn319", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20200219-080014830", "type": "conference_item", "title": "Genomic DNA coated 3D printed devices for chemotherapy", "author": [ { "family_name": "Yee", "given_name": "Daryl W.", "orcid": "0000-0002-4114-6167", "clpid": "Yee-Daryl-Wei-Liang" }, { "family_name": "Grubbs", "given_name": "Robert Howard", "orcid": "0000-0002-0057-7817", "clpid": "Grubbs-R-H" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "Since the discovery of chemotherapy, researchers around the world have been actively developing new and more effective chemotherapeutic agents to better treat cancer. Traditionally, chemotherapeutic agents work by interfering with cell division. However, by virtue of their mechanism of action, healthy normal cells can also be targeted and destroyed. \n\nAs a result, while chemotherapy is an effective way of managing cancer, the resulting side effects limits its use. One approach currently taken to reduce these side effects is to deliver the chemotherapy drugs directly to the tumor. While this has been effective in reducing systemic toxicity, more can be done to improve this. Ideally, a device that could sequester any unreacted chemotherapy agents could be installed \"downstream\" of the tumor prior to them entering systemic circulation. Such drug-capture materials have yet to be realized due to the difficulty in achieving materials that have the right surface chem. and geometry for blood flow. Working together with medical doctors, computational fluid dynamics experts, and material chemists, we demonstrate the fabrication of DNA coated 3D printed materials that can be used to capture doxorubicin, a commonly used DNA-targeting chemotherapy agent. We discuss the concept behind the device, the use of 3D printed materials as an ideal substrate, and the chemistries considered in drug binding. To achieve scalability of these devices, we developed a method of coating cheaply available genomic DNA to these materials, a departure from commonly used synthetic DNA. The efficacy of these coated materials were demonstrated in PBS, where we obsd. a marked decrease in doxorubicin concn. over a period of 20 min, highlighting the viability of this as a method of drug capture. We also discuss the in-vitro stability of these DNA coatings, with approx. 400 pg of DNA lost/mm\u00b2 of coated material over 30 min in PBS at 37 C.", "publisher": "Caltech Library", "publication_date": "2020-03" }, { "id": "authors:dmw04-ch108", "collection": "authors", "collection_id": "dmw04-ch108", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20200219-152722407", "type": "conference_item", "title": "Additive manufacturing of functional materials via photopolymer complex synthesis", "author": [ { "family_name": "Yee", "given_name": "Daryl W.", "orcid": "0000-0002-4114-6167", "clpid": "Yee-Daryl-Wei-Liang" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "Additive manufg. is one of the most powerful manufg. tools available today, due to its potential in fabricating a wide variety of materials at resolns. ranging from nanometers to meters. In particular, significant advances have been made in polymeric 3D printing, with recent work showing the fabrication of polymers with unique properties, such as self-healing, stimuli-responsive behaviors, and etc. However, there is still a dearth of techniques for the printing of multifunctional metal oxides and metals. Conventional methods involve: a) the patterning of slurries contg. a metal oxide/metal powder, with a subsequent debinding and sintering step, b) printing with inorg.-org. polymers, followed by a similar thermal treatment, or c) the use of a high-powered laser to fuse metal oxide/metal powder together. However, these techniques have difficulties with issues ranging from inhomogeneous dispersion of particles in slurries, challenging synthesis of inorg.-org. resists, to cost of equipment resp. In this presentation, a new technique, called \"Photopolymer Complex Synthesis,\" that addresses some of the challenges above, is demonstrated. Aq. metal-ion contg. photoresins are prepd. and used with photolithog., in conjunction with post-processing techniques to fabricate architected metal oxide or metal structures. These photopolymer systems are facile to prep. and can be modified to fabricate various multifunctional complex metal oxides or alloys. As examples of this technique, we fabricate and characterized zinc oxide (ZnO) and lithium cobalt oxide (LCO) architected structures with sub-micron and sub-millimetre features resp. Compression of the ZnO structures resulted in an electromech. response, and electrochem. cycling of the LCO structures showed efficient performance as a lithium ion battery cathode. We also demonstrate the fabrication and characterization of metal structures made from copper and cupronickel alloys. Our work highlights the use of polymer chem. and materials science in expanding the range of materials that can be made via additive manufg.", "publisher": "Caltech Library", "publication_date": "2020-03" }, { "id": "authors:f1nez-zp243", "collection": "authors", "collection_id": "f1nez-zp243", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20200219-073958165", "type": "conference_item", "title": "Durable, low-voltage electroactive polymers formed from polyionic complexes", "author": [ { "family_name": "Learsch", "given_name": "Robert", "clpid": "Learsch-R" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "Development for refreshable braille devices has recently shifted to electroactive polymers (EAP). This paradigm benefits from greater precision, smaller size, and lower cost assocd. with modern electronics, opening the door for higher resoln. and less expensive devices. Displays with resoln. finer than required to display braille characters will enable representation of non-text information such as figures, tables, or diagrams. However, adoption of EAPs for responsive displays has encountered problems such as high required field strength (kV/cm), insufficient pressure (2 kPa generated), and poor durability. This work presents a new type of electroactive polymers, based on poly ionic complexes. In contrast to previously reported electroactive polymers, these gels do not rely on a solvent bath, respond to a field that is on the order of V/cm, and expand in a direction parallel to the applied elec. field. Ultimately, the expansion is driven by electrostatic interactions: The polyionic gels are overall charge neutral, however, when an elec. field of sufficient strength is applied, the ionic bonds are broken and the polycation is drawn towards the plate. This reveals the charged backbone of both the polyanions and the polycations, which causes the repeat units to repel one another and the gel to expand. This mechanism is confirmed using cyclic voltammetry and impedance spectroscopy. With the understanding of the mechanism, the gels are made to expand rapidly and tolerate 100s of cycles. These properties are controlled through the identity of the ionic repeat units and further tuning the crosslinking and processing of the gels. The ionic crosslinks within the gel impart desirable qualities such as self-healing and high toughness a through a cooperative effect, yielding durable gels that are the much stronger than their component parts. The low power requirements and resilient nature of these EAPs make them attractive for use as refreshable braille displays. This methodol. could be adapted to other actuators such as soft robotic joints or grippers.", "publisher": "Caltech Library", "publication_date": "2020-03" }, { "id": "authors:8wpv6-ph027", "collection": "authors", "collection_id": "8wpv6-ph027", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20200219-092943939", "type": "conference_item", "title": "3D printable polyelectrolyte complexes with versatile mechanical, responsive, and self-healing properties", "author": [ { "family_name": "Yee", "given_name": "Daryl W.", "orcid": "0000-0002-4114-6167", "clpid": "Yee-Daryl-Wei-Liang" }, { "family_name": "Taylor", "given_name": "Zane W.", "clpid": "Taylor-Z-W" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "Additive manufg. has been at the forefront of manufg. in the past decade, due to its ability to overcome geometric limitations inherent with traditional manufg. processes. Photolithog. 3D printing processes, in particular, have been of significant interest due to the resoln. of features that can be achieved using these techniques. However, a large fraction of photolithog.-compatible materials are highly crosslinked brittle polymers, which places an inherent limit on their applications. Recent work in the field have endeavored to address this by making compliant polymers, but these elastomeric photoresins often require high temps. during printing, are highly viscous, or require an involved synthesis. In addn., these compliant polymers typically only have structural purposes and exhibit no other functionality. To incorporate both mech. compliance and stimuli-responsive behavior, we turned to supramol. polymers. Supramol. polymers are classes of polymers that have reversible non-covalent interactions between monomers/polymer chains. These dynamic bonds, such as hydrogen bonding, electrostatic interactions, and etc., allow for a variety of emergent material properties such as self-healing, and shape changing capabilities. In this work, we demonstrate the facile 3D printing of polyelectrolyte complexes (PECs) via projection-microstereolithog. PECs are a class of supramol. polymers that have ionizable functional groups that can form a complex with other oppositely charged compds. We developed a versatile and simple PEC photoresin using in-situ polymn. of acrylic acid in the presence of metal cation crosslinkers. The resulting materials displayed upwards of ~300 % strain and a failure stress of ~4 MPa, as detd. using D638 Std. V tensile testing. 3D printed architectures of this material were shown to exhibit self-healing capabilities and other solvent-dependent behaviors, with properties being easily modified by the choice of metal cation crosslinking species. The versatility and simplicity of this system introduces a large parameter space for 3D printing of self-healable and responsive supramol. polymers with tunable properties.", "publisher": "Caltech Library", "publication_date": "2020-03" }, { "id": "authors:26bbc-pvx51", "collection": "authors", "collection_id": "26bbc-pvx51", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20200219-132634139", "type": "conference_item", "title": "3D printing of recyclable dynamic covalent boronate ester-based polymers", "author": [ { "family_name": "Chen", "given_name": "Amylynn", "clpid": "Chen-Amylynn" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" }, { "family_name": "Yee", "given_name": "Daryl W.", "orcid": "0000-0002-4114-6167", "clpid": "Yee-Daryl-Wei-Liang" }, { "family_name": "Ko", "given_name": "Jeong Hoon", "clpid": "Ko-Jeong-Hoon" } ], "abstract": "The development of 3D printing or additive manufg. has grown rapidly in the past decade, which calls for more sustainable photoresins to accommodate the increasing demand of the future 3D printed products. In particular, stereolithog. (SLA) 3D printing have been demonstrated as an efficient method to produce high-accuracy and isotropic parts using either com. available or custom-made photoresins with fine features and smooth surface finish. Herein, we demonstrate a new method to print boronate-ester contg. polymer in 3D by locally activating a photobase using an SLA system. Because the lack of toxicity and the ability to anticipate reversible dynamic covalent bonding, boronic acid-contg. macromols. have been utilized in nos. of biomedical applications, such as mol. sensing, thermoresponsive hydrogels, drug delivery, and cell capture and release; however, their potentials in 3D printing has not yet been explored. In our study, we have incorporated a polymer derived from 3-acrylamidophenylboronic acid and a tetra-1,2 diol functionalized mol. to demonstrate the recyclability of the 3D printed materials. In our system, upon photoactivation the photobase increase the local pH to be great than its pKa, the boronic acids then form boronate ester with 1,2-diols to create a highly crosslinked network. This esterification process can also be reversed once being exposed to an acidic environment. We have performed mech. characterization on the bulk boronate ester-based polymers and show the feasibility of purifying and reusing the depolymd. materials in the proceeding printing cycles.", "publisher": "Caltech Library", "publication_date": "2020-03" }, { "id": "authors:4q75g-zkp05", "collection": "authors", "collection_id": "4q75g-zkp05", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20191030-100227426", "type": "conference_item", "title": "Supersonic Impact on Carbon Nano-architected Materials", "author": [ { "family_name": "Portela", "given_name": "Carlos", "orcid": "0000-0002-2649-4235", "clpid": "Portela-C-M" }, { "family_name": "Edwards", "given_name": "Bryce", "clpid": "Edwards-Bryce-W" }, { "family_name": "Veysset", "given_name": "David", "clpid": "Veysset-D" }, { "family_name": "Sun", "given_name": "Yuchen", "clpid": "Sun-Yuchen" }, { "family_name": "Nelson", "given_name": "Keith", "clpid": "Nelson-K-A" }, { "family_name": "Kochmann", "given_name": "Dennis", "orcid": "0000-0002-9112-6615", "clpid": "Kochmann-D-M" }, { "family_name": "Greer", "given_name": "Julia", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "[no abstract]", "publisher": "Caltech Library", "publication_date": "2019-10" }, { "id": "authors:e2khd-x3542", "collection": "authors", "collection_id": "e2khd-x3542", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20200220-131819577", "type": "article", "title": "Three-dimensional architected materials and structures: Design, fabrication, and mechanical behavior", "author": [ { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" }, { "family_name": "Deshpande", "given_name": "Vikram S.", "orcid": "0000-0003-3899-3573", "clpid": "Deshpande-V-S" } ], "abstract": "The integration of materials and architectural features at multiple length scales into structural mechanics has shifted the paradigm of structural design toward optimally engineered structures, which resulted in, for example, the Eiffel Tower. This structural revolution paved the way for the development of computational design approaches used in modern-day construction. Similar principles are now being applied to the design and manufacture of architected materials with a suite of properties determined a priori and attained through multiscale approaches. These new material classes potentially offer breakthrough advances in almost every branch of technology: from ultra-lightweight and damage-tolerant structural materials to safe and efficient energy storage, biomedical devices, biochemical, and micromechanical sensors and actuators, nanophotonic devices, and textiles. When reduced to the microscale, such materials embody the characteristics of both the constituent material, which brings the effects of its microstructure and ensuing properties at the relevant characteristic length scales, as well as the structure, which is driven by architected design. This issue gives an overview of the current state of the art of this new class of materials.", "doi": "10.1557/mrs.2019.232", "issn": "0883-7694", "publisher": "Materials Research Society", "publication": "MRS Bulletin", "publication_date": "2019-10", "series_number": "10", "volume": "44", "issue": "10", "pages": "750-757" }, { "id": "authors:01sgx-9ch27", "collection": "authors", "collection_id": "01sgx-9ch27", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190626-134011804", "type": "article", "title": "Structural color three-dimensional printing by shrinking photonic crystals", "author": [ { "family_name": "Liu", "given_name": "Yejing", "clpid": "Liu-Yejing" }, { "family_name": "Wang", "given_name": "Hao", "clpid": "Wang-Hao" }, { "family_name": "Ho", "given_name": "Jinfa", "orcid": "0000-0001-6884-4785", "clpid": "Ho-Jinfa" }, { "family_name": "Ng", "given_name": "Ryan C.", "orcid": "0000-0002-0527-9130", "clpid": "Ng-Ryan-C" }, { "family_name": "Ng", "given_name": "Ray J. H.", "clpid": "Ng-Ray-J-H" }, { "family_name": "Hall-Chen", "given_name": "Valerian H.", "clpid": "Hall-Chen-V-H" }, { "family_name": "Koay", "given_name": "Eleen H. H.", "clpid": "Koay-E-H-H" }, { "family_name": "Dong", "given_name": "Zhaogang", "orcid": "0000-0002-0929-7723", "clpid": "Dong-Zhaogang" }, { "family_name": "Liu", "given_name": "Hailong", "clpid": "Liu-Hailong" }, { "family_name": "Qiu", "given_name": "Cheng-Wei", "orcid": "0000-0002-6605-500X", "clpid": "Qiu-Cheng-Wei" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" }, { "family_name": "Yang", "given_name": "Joel K. W.", "orcid": "0000-0003-3301-1040", "clpid": "Yang-Joel-K-W" } ], "abstract": "The coloration of some butterflies, Pachyrhynchus weevils, and many chameleons are notable examples of natural organisms employing photonic crystals to produce colorful patterns. Despite advances in nanotechnology, we still lack the ability to print arbitrary colors and shapes in all three dimensions at this microscopic length scale. Here, we introduce a heat-shrinking method to produce 3D-printed photonic crystals with a 5x reduction in lattice constants, achieving sub-100-nm features with a full range of colors. With these lattice structures as 3D color volumetric elements, we printed 3D microscopic scale objects, including the first multi-color microscopic model of the Eiffel Tower measuring only 39\u2009\u00b5m tall with a color pixel size of 1.45\u2009\u00b5m. The technology to print 3D structures in color at the microscopic scale promises the direct patterning and integration of spectrally selective devices, such as photonic crystal-based color filters, onto free-form optical elements and curved surfaces.", "doi": "10.1038/s41467-019-12360-w", "pmcid": "PMC6761189", "issn": "2041-1723", "publisher": "Nature Publishing Group", "publication": "Nature Communications", "publication_date": "2019-09-25", "volume": "10", "pages": "Art. No. 4340" }, { "id": "authors:2jjeb-8h075", "collection": "authors", "collection_id": "2jjeb-8h075", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190701-140145897", "type": "article", "title": "Electrochemically Reconfigurable Architected Materials", "author": [ { "family_name": "Xia", "given_name": "Xiaoxing", "orcid": "0000-0003-1255-3289", "clpid": "Xia-Xiaoxing" }, { "family_name": "Afshar", "given_name": "Arman", "clpid": "Afshar-A" }, { "family_name": "Yang", "given_name": "Heng", "orcid": "0000-0001-7431-932X", "clpid": "Yang-Heng" }, { "family_name": "Portela", "given_name": "Carlos M.", "orcid": "0000-0002-2649-4235", "clpid": "Portela-C-M" }, { "family_name": "Kochmann", "given_name": "Dennis M.", "orcid": "0000-0002-9112-6615", "clpid": "Kochmann-D-M" }, { "family_name": "Di Leo", "given_name": "Claudio V.", "orcid": "0000-0002-3410-6677", "clpid": "Di-Leo-C-V" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "Architected materials can actively respond to external stimuli\u2014such as mechanical forces, hydration and magnetic fields\u2014by changing their geometries and thereby achieve novel functionalities. Such transformations are usually binary and volatile because they toggle between 'on' and 'off' states and require persistent external stimuli. Here we develop three-dimensional silicon-coated tetragonal microlattices that transform into sinusoidal patterns via cooperative beam buckling in response to an electrochemically driven silicon-lithium alloying reaction. In situ microscopy reveals a controllable, non-volatile and reversible structural transformation that forms multiple ordered buckling domains separated by distorted domain boundaries. We investigate the mechanical dynamics of individual buckling beams, cooperative coupling among neighbouring beams, and lithiation-rate-dependent distributions of domain sizes through chemo-mechanical modelling and statistical mechanics analysis. Our results highlight the critical role of defects and energy fluctuations in the dynamic response of architected materials. We further demonstrate that domain boundaries can be programmed to form particular patterns by pre-designing artificial defects, and that a variety of reconfigurational degrees of freedom can be achieved through micro-architecture design. This framework enables the design, fabrication, modelling, behaviour prediction and programming of electrochemically reconfigurable architected materials, and could open the way to beyond-intercalation battery electrodes, tunable phononic crystals and bio-implantable devices.", "doi": "10.1038/s41586-019-1538-z", "issn": "0028-0836", "publisher": "Nature Publishing Group", "publication": "Nature", "publication_date": "2019-09-12", "series_number": "7773", "volume": "573", "issue": "7773", "pages": "205-213" }, { "id": "authors:zb235-xyx64", "collection": "authors", "collection_id": "zb235-xyx64", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190923-155209595", "type": "article", "title": "Tuning crystallographic compatibility to enhance shape memory in ceramics", "author": [ { "family_name": "Jetter", "given_name": "Justin", "orcid": "0000-0003-2725-8426", "clpid": "Jetter-J" }, { "family_name": "Gu", "given_name": "Hanlin", "clpid": "Gu-Hanlin" }, { "family_name": "Zhang", "given_name": "Haolu", "clpid": "Zhang-Haolu" }, { "family_name": "Wuttig", "given_name": "Manfred", "clpid": "Wuttig-M" }, { "family_name": "Chen", "given_name": "Xian", "clpid": "Chen-Xian" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" }, { "family_name": "James", "given_name": "Richard D.", "orcid": "0000-0001-6019-6613", "clpid": "James-R-D" }, { "family_name": "Quandt", "given_name": "Eckhard", "clpid": "Quandt-E" } ], "abstract": "The extraordinary ability of shape-memory alloys to recover after large imposed deformation motivates efforts to transpose these properties onto ceramics, which would enable practical shape-memory properties at high temperatures and in harsh environments. The theory of mechanical compatibility was utilized to predict promising ceramic candidates in the system (Y_(0.5)Ta_(0.5)O_2)_(1−x)−(Zr_(0.5)Hf_(0.5)O_2)_x, 0.6< x < 0.85. When these compatibility conditions are met, a reduction in thermal hysteresis by a factor of 2.5, a tripling of deformability, and a 75% enhancement in strain recovery within the shape-memory effect was found. These findings reveal that predicting and optimizing the chemical composition of ceramics to attain improved crystallographic compatibility is a powerful tool for enabling and enhancing their deformability that could ultimately lead to a highly reversible oxide ceramic shape-memory material.
", "doi": "10.1103/physrevmaterials.3.093603", "issn": "2475-9953", "publisher": "American Physical Society", "publication": "Physical Review Materials", "publication_date": "2019-09", "series_number": "9", "volume": "3", "issue": "9", "pages": "093603" }, { "id": "authors:9a8ws-7jf11", "collection": "authors", "collection_id": "9a8ws-7jf11", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190625-161755810", "type": "article", "title": "Additive Manufacturing of 3D-Architected Multifunctional Metal Oxides", "author": [ { "family_name": "Yee", "given_name": "Daryl W.", "orcid": "0000-0002-4114-6167", "clpid": "Yee-Daryl-Wei-Liang" }, { "family_name": "Lifson", "given_name": "Max L.", "orcid": "0000-0002-0382-182X", "clpid": "Lifson-Max-L" }, { "family_name": "Edwards", "given_name": "Bryce W.", "clpid": "Edwards-Bryce-W" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "Additive manufacturing (AM) of complex three\u2010dimensional (3D) metal oxides at the micro\u2010 and nanoscales has attracted considerable attention in recent years. State\u2010of\u2010the\u2010art techniques that use slurry\u2010based or organic\u2013inorganic photoresins are often hampered by challenges in resin preparation and synthesis, and/or by the limited resolution of patterned features. A facile process for fabricating 3D\u2010architected metal oxides via the use of an aqueous metal\u2010ion\u2010containing photoresin is presented. The efficacy of this process, which is termed photopolymer complex synthesis, is demonstrated by creating nanoarchitected zinc oxide (ZnO) architectures with feature sizes of 250 nm, by first patterning a zinc\u2010ion\u2010containing aqueous photoresin using two\u2010photon lithography and subsequently calcining them at 500 \u00baC. Transmission electron microscopy (TEM) analysis reveals their microstructure to be nanocrystalline ZnO with grain sizes of 5.1 \u00b1 1.6 nm. In situ compression experiments conducted in a scanning electron microscope show an emergent electromechanical response: a 200 nm mechanical compression of an architected ZnO structure results in a voltage drop of 0.52 mV. This photopolymer complex synthesis provides a pathway to easily create arbitrarily shaped 3D metal oxides that could enable previously impossible devices and smart materials.", "doi": "10.1002/adma.201901345", "pmcid": "PMC8063598", "issn": "0935-9648", "publisher": "Wiley", "publication": "Advanced Materials", "publication_date": "2019-08-16", "series_number": "33", "volume": "31", "issue": "33", "pages": "Art. No. 1901345" }, { "id": "authors:gy0ka-jca61", "collection": "authors", "collection_id": "gy0ka-jca61", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190715-080054791", "type": "article", "title": "Recoverable electrical breakdown strength and dielectric constant in ultra-low k nanolattice capacitors", "author": [ { "family_name": "Kim", "given_name": "Min-Woo", "clpid": "Kim-Min-Woo" }, { "family_name": "Lifson", "given_name": "Max L.", "orcid": "0000-0002-0382-182X", "clpid": "Lifson-M-L" }, { "family_name": "Rebecca", "given_name": "Gallivan A.", "clpid": "Rebecca-G-A" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" }, { "family_name": "Kim", "given_name": "Bong-Joong", "orcid": "0000-0002-5335-4342", "clpid": "Kim-Bong-Joong" } ], "abstract": "The dielectric reliability of low-k materials during mechanical deformation attracts tremendous attention, owing to the increasing demand for thin electronics to meet the ever-shrinking form factor of consumer products. However, the strong coupling between dielectric/electric and mechanical properties limits the use of low-k dielectrics in industrial applications. We report the leakage current and dielectric properties of a nanolattice capacitor during compressive stress cycling. Electrical breakdown measurements during the stress cycling, combined with a theoretical model and in situ mechanical experiments, provide insights to key breakdown mechanisms. Electrical breakdown occurs at nearly 50% strain, featuring a switch-like binary character, correlated with a transition from beam bending and buckling to collapse. Breakdown strength appears to recover after each cycle, concomitant with nanolattice's shape recovery. The compressive displacement at breakdown decreases with cycling due to permanently buckled beams, transforming the conduction mechanism from Schottky to Poole\u2013Frankel emission. Remarkably, our capacitor with 99% porosity, k \u223c 1.09, is operative up to 200 V, whereas devices with 17% porous alumina films breakdown upon biasing based on a percolation model. Similarly with electrical breakdown, the dielectric constant of the capacitor is recoverable with five strain cycles and is stable under 25% compression. These outstanding capabilities of the nanolattice are essential for revolutionizing future flexible electronics.", "doi": "10.1021/acs.nanolett.9b02282", "issn": "1530-6984", "publisher": "American Chemical Society", "publication": "Nano Letters", "publication_date": "2019-08-14", "series_number": "8", "volume": "19", "issue": "8", "pages": "5689-5696" }, { "id": "authors:m4gqq-g9352", "collection": "authors", "collection_id": "m4gqq-g9352", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190517-100134758", "type": "article", "title": "Theoretical strength and rubber-like behaviour in micro-sized pyrolytic carbon", "author": [ { "family_name": "Zhang", "given_name": "Xuan", "orcid": "0000-0002-6155-6825", "clpid": "Zhang-Xuan" }, { "family_name": "Zhong", "given_name": "Lei", "clpid": "Zhong-Lei" }, { "family_name": "Mateos", "given_name": "Arturo", "clpid": "Mateos-A-J" }, { "family_name": "Kudo", "given_name": "Akira", "orcid": "0000-0002-0830-5509", "clpid": "Kudo-Akira" }, { "family_name": "Vyatskikh", "given_name": "Andrey", "orcid": "0000-0002-6917-6931", "clpid": "Vyatskikh-A" }, { "family_name": "Gao", "given_name": "Huajian", "orcid": "0000-0002-8656-846X", "clpid": "Gao-Huajian" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" }, { "family_name": "Li", "given_name": "Xiaoyan", "orcid": "0000-0002-2953-9267", "clpid": "Li-Xiaoyan" } ], "abstract": "The creation of materials with a combination of high strength, substantial deformability and ductility, large elastic limit and low density represents a long-standing challenge, because these properties are, in general, mutually exclusive. Using a combination of two-photon lithography and high-temperature pyrolysis, we have created micro-sized pyrolytic carbon with a tensile strength of 1.60\u2009\u00b1\u20090.55\u2009GPa, a compressive strength approaching the theoretical limit of ~13.7\u2009GPa, a substantial elastic limit of 20\u201330% and a low density of ~1.4\u2009g\u2009cm^(\u22123). This corresponds to a specific compressive strength of 9.79\u2009GPa\u2009cm^3\u2009g^(\u22121), a value that surpasses that of nearly all existing structural materials. Pillars with diameters below 2.3\u2009\u03bcm exhibit rubber-like behaviour and sustain a compressive strain of ~50% without catastrophic failure; larger ones exhibit brittle fracture at a strain of ~20%. Large-scale atomistic simulations reveal that this combination of beneficial mechanical properties is enabled by the local deformation of 1\u2009nm curled graphene fragments within the pyrolytic carbon microstructure, the interactions among neighbouring fragments and the presence of covalent carbon\u2013carbon bonds.", "doi": "10.1038/s41565-019-0486-y", "issn": "1748-3387", "publisher": "Nature Publishing Group", "publication": "Nature Nanotechnology", "publication_date": "2019-08", "series_number": "8", "volume": "14", "issue": "8", "pages": "762-769" }, { "id": "authors:8qmdj-8xs26", "collection": "authors", "collection_id": "8qmdj-8xs26", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180910-144259345", "type": "article", "title": "Yield precursor dislocation avalanches in small crystals: the irreversibility transition", "author": [ { "family_name": "Ni", "given_name": "Xiaoyue", "clpid": "Ni-Xiaoyue" }, { "family_name": "Zhang", "given_name": "Haolu", "clpid": "Zhang-Haolu" }, { "family_name": "Liarte", "given_name": "Danilo B.", "clpid": "Liarte-D-B" }, { "family_name": "McFaul", "given_name": "Louis W.", "clpid": "McFaul-L-W" }, { "family_name": "Dahmen", "given_name": "Karin A.", "clpid": "Dahmen-K-A" }, { "family_name": "Sethna", "given_name": "James P.", "clpid": "Sethna-J-P" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "The transition from elastic to plastic deformation in crystalline metals shares history dependence and scale-invariant avalanche signature with other nonequilibrium systems under external loading such as colloidal suspensions. These other systems exhibit transitions with clear analogies to work hardening and yield stress, with many typically undergoing purely elastic behavior only after \"training\" through repeated cyclic loading; studies in these other systems show a power-law scaling of the hysteresis loop extent and of the training time as the peak load approaches a so-called reversible-to-irreversible transition (RIT). We discover here that deformation of small crystals shares these key characteristics: yielding and hysteresis in uniaxial compression experiments of single-crystalline Cu nano- and micropillars decay under repeated cyclic loading. The amplitude and decay time of the yield precursor avalanches diverge as the peak stress approaches failure stress for each pillar, with a power-law scaling virtually equivalent to RITs in other nonequilibrium systems.", "doi": "10.1103/PhysRevLett.123.035501", "issn": "0031-9007", "publisher": "American Physical Society", "publication": "Physical Review Letters", "publication_date": "2019-07-19", "series_number": "3", "volume": "123", "issue": "3", "pages": "Art. No. 035501" }, { "id": "authors:2q6yr-aag28", "collection": "authors", "collection_id": "2q6yr-aag28", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190318-133734983", "type": "article", "title": "Lightweight, flaw-tolerant, and ultrastrong nanoarchitected carbon", "author": [ { "family_name": "Zhang", "given_name": "Xuan", "orcid": "0000-0003-1548-8021", "clpid": "Zhang-Xuan" }, { "family_name": "Vyatskikh", "given_name": "Andrey", "orcid": "0000-0002-6917-6931", "clpid": "Vyatskikh-Andrey" }, { "family_name": "Gao", "given_name": "Huajian", "orcid": "0000-0002-8656-846X", "clpid": "Gao-Huajian" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" }, { "family_name": "Li", "given_name": "Xiaoyan", "orcid": "0000-0002-2953-9267", "clpid": "Li-Xiaoyan" } ], "abstract": "It has been a long-standing challenge in modern material design to create low-density, lightweight materials that are simultaneously robust against defects and can withstand extreme thermomechanical environments, as these properties are often mutually exclusive: The lower the density, the weaker and more fragile the material. Here, we develop a process to create nanoarchitected carbon that can attain specific strength (strength-to-density ratio) up to one to three orders of magnitude above that of existing micro- and nanoarchitected materials. We use two-photon lithography followed by pyrolysis in a vacuum at 900 \u00b0C to fabricate pyrolytic carbon in two topologies, octet- and iso-truss, with unit-cell dimensions of \u223c2 \u03bcm, beam diameters between 261 nm and 679 nm, and densities of 0.24 to 1.0 g/cm^3. Experiments and simulations demonstrate that for densities higher than 0.95 g/cm^3 the nanolattices become insensitive to fabrication-induced defects, allowing them to attain nearly theoretical strength of the constituent material. The combination of high specific strength, low density, and extensive deformability before failure lends such nanoarchitected carbon to being a particularly promising candidate for applications under harsh thermomechanical environments.", "doi": "10.1073/pnas.1817309116", "pmcid": "PMC6452738", "issn": "0027-8424", "publisher": "National Academy of Sciences", "publication": "Proceedings of the National Academy of Sciences of the United States of America", "publication_date": "2019-04-02", "series_number": "14", "volume": "116", "issue": "14", "pages": "6665-6672" }, { "id": "authors:j6htj-tdq25", "collection": "authors", "collection_id": "j6htj-tdq25", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190225-072508371", "type": "conference_item", "title": "Stimuli responsive microscale architectures: Two-photon lithography with shape memory polymers", "author": [ { "family_name": "Luizetta", "given_name": "Navrazhnykh", "clpid": "Luizetta-N" }, { "family_name": "Greer", "given_name": "Julia", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "3D architectures with nearly arbitrary geometry and features on the submicron scale can be fabricated using direct laser writing, which gives rise to unique combinations of properties, such as high strength-to-wt. ratios and superior mech. resilience of micro- and nanolattices. Inducing a shape transformation of the constituent solid that comprises such architected materials in response to external stimuli could lead to a controllable and substantial change in the mech. response of the structure. One class of such solids is shape memory polymers, in which crosslinked elastomer shape memory networks can be deformed in the rubbery state and maintain the deformed shape when cooled to the glassy state. The original shape is then recovered in response to heat. We developed a benzyl methacrylate-based resist that can be polymd. into such networks via direct laser writing. We then conducted a suite of dynamic mech. anal. (DMA) nanomech. expts. at 22\u00b0C to 90\u00b0C on individual microscale pillars, which measured their storage and loss moduli, to det. glass transition temp. We obsd. a shape memory phenomenon in all fabricated 3D architectures with submicron features and arbitrary geometries. Programming was accomplished by first deforming the samples at 77\u00b0C and cooling them to glassy state at 30\u00b0C. After load removal, the structures remained deformed until heated to 90\u00b0C, when they recovered >95% of the original height.", "publisher": "Caltech Library", "publication_date": "2019-04" }, { "id": "authors:qda6z-t9873", "collection": "authors", "collection_id": "qda6z-t9873", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190325-091433064", "type": "conference_item", "title": "3D printing of multifunctional metal oxides via a novel photopolymer system", "author": [ { "family_name": "Yee", "given_name": "Daryl W.", "orcid": "0000-0002-4114-6167", "clpid": "Yee-Daryl-Wei-Liang" }, { "family_name": "Lifson", "given_name": "Max L.", "orcid": "0000-0002-0382-182X", "clpid": "Lifson-M-L" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "In recent years, 3D printing of ceramics has become a significant area of interest as it has the potential to remove the geometrical limitations assocd. with the current state of the art of ceramic processing. In particular, processes involving photolithog. are esp. promising due to the high resoln. and small feature sizes achievable.These photolithog. systems typically consist of photosensitive slurries, where fine powders of the desired ceramic of choice are dispersed in a photosensitive org. binder. By selectively exposing certain parts of the slurry, a green body can be made. A subsequent high temp. treatment then burns off the org. binder and sinters together the remaining ceramic powders into a dense ceramic part.The advantages of these systems are that it's simple and versatile - as long as the desired ceramic can be\nobtained in powder form and can be dispersed in the binder, the slurry can be obtained and the part 3D printed. However, the slurry often has to have a high loading of ceramic particles, which increases the viscosity and refractive index of the slurry, making it difficult to print with. In this presentation, a new photopolymer system that circumvents the problems of powder loading is demonstrated. As an example of this technique, we demonstrate the printing of zinc oxide (ZnO) architected structures. ZnO is traditionally deposited as films and can only be made 3D via a multistep process that involves depositing a thick layer of ZnO and then using an ion-mill to cut out the structure desired. Here, we show a two-step process to fabricate monolithic ZnO structures out of any arbitary design. Characterization of these structures\nverify that the structures are indeed zinc oxide. Compression of these materials also results in a voltage response, showing the piezoelec. behavior of these structures.", "publisher": "Caltech Library", "publication_date": "2019-04" }, { "id": "authors:xajeg-7q935", "collection": "authors", "collection_id": "xajeg-7q935", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190318-074827498", "type": "conference_item", "title": "Genomic DNA functionalized 3D printed architected materials for drug capture", "author": [ { "family_name": "Yee", "given_name": "Daryl", "orcid": "0000-0002-4114-6167", "clpid": "Yee-Daryl-Wei-Liang" }, { "family_name": "Krishnamoorthy", "given_name": "Sankarganesh", "clpid": "Krishnamoorthy-Sankarganesh" }, { "family_name": "Grubbs", "given_name": "Robert Howard", "orcid": "0000-0002-0057-7817", "clpid": "Grubbs-R-H" }, { "family_name": "Hetts", "given_name": "Steven", "clpid": "Hetts-S-W" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "Since the discovery of chemotherapy in the beginning of the 20th century, researchers around the world have been\nactively developing new and more effective chemotherapeutic agents to better treat cancer. Traditionally,\nchemotherapeutic agents work by interfering with cell division. However, by virtue of their mechanism of action, healthy\nnormal cells can also be targeted and destroyed. As a result, while chemotherapy is an effective way of managing\ncancer, the resulting side effects limits its use. One approach currently taken to reduce these side effects is to deliver the\nchemotherapy drugs directly to the tumor via transarterial chemoembolization, or other similar procedures. While this\nhas been effective in reducing systemic toxicity, more can be done to improve this. Ideally, a device that could sequester\nany unreacted chemotherapy agents could be installed \"downstream\" of the tumor prior to them entering systemic\ncirculation. Such drug-capture materials have yet to be realized due to the difficulty in achieving materials that have the\nright surface chem. and geometry for blood flow. Here, we report the fabrication of DNA functionalized 3D printed porous\nmaterials that can be used to capture doxorubicin, a commonly used DNA-targeting chemotherapy agent. We discuss\nthe concept behind the device, the use of 3D printed materials as an ideal substrate, and the chemistries considered in\ndrug binding. To achieve scalability of these devices, we developed a method of functionalizing the surface with cheaply\navailable genomic DNA to these materials, a departure from commonly used synthetic DNA. We characterize the\nsurface of the structure and verify the binding of DNA to the surface via XPS, EDS and the use of chem. assays. The\nefficacy of these functionalized materials were demonstrated in PBS, where we obsd. a >70% redn. in doxorubicin\nconcn. over a period of 10 min, highlighting the viability of this as a method of drug capture.", "publisher": "Caltech Library", "publication_date": "2019-04" }, { "id": "authors:5hxj8-1q081", "collection": "authors", "collection_id": "5hxj8-1q081", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190514-124438045", "type": "book_section", "title": "Additive manufacturing of titanium dioxide for dielectric photonic crystals", "author": [ { "family_name": "Vyatskikh", "given_name": "Andrey", "orcid": "0000-0002-6917-6931", "clpid": "Vyatskikh-A" }, { "family_name": "Ng", "given_name": "Ryan C.", "orcid": "0000-0002-0527-9130", "clpid": "Ng-Ryan-C" }, { "family_name": "Edwards", "given_name": "Bryce", "clpid": "Edwards-Bryce" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "contributor": [ { "family_name": "von Freymann", "given_name": "Georg", "clpid": "von-Freymann-G" }, { "family_name": "Schoenfeld", "given_name": "Winston V.", "clpid": "Shoenfeld-W-V" }, { "family_name": "Rumpf", "given_name": "Raymond C.", "clpid": "Rumpf-R-C" } ], "abstract": "Fabrication of 3D dielectric photonic crystals in the visible and in the infrared range typically requires sub-micron structural features and high-refractive index materials. We developed a template-free additive manufacturing (AM) process based on direct laser writing (DLW) that can create complex 3D architectures out of titania (TiO_2) with ~100 nm resolution. In this process, we synthesize hybrid organic-inorganic materials that contain titanium clusters coordinated with acrylic ligands to prepare a photoresist that is amenable to two-photon lithography (TPL). We sculpt a pre-ceramic architecture using TPL and then pyrolyze in air at 900\u00b0C to remove the organic constituents to produce a replica of the original structure with ~70% reduced linear dimensions. Energy-Dispersive Spectroscopy (EDS) and Raman spectroscopy confirm the constituent solid to consist predominantly out of rutile titania.\nWe demonstrate this process by fabricating titania woodpile structures with lateral dimensions of 70 \u00d7 70 \u03bcm and lateral periodicities between 1.0 and 1.3 \u03bcm. Fourier Transform Infrared (FTIR) spectroscopy reveals passive tuning of the reflectance peak between 1.7 and 2.3 \u03bcm, which agrees with Plane Wave Expansion simulations. This titania AM process offers a promising pathway to efficiently fabricate complex 3D nano-architectures out of a high-index material for 3D dielectric photonic crystals in the visible and the infrared.", "doi": "10.1117/12.2507076", "publisher": "Society of Photo-optical Instrumentation Engineers (SPIE)", "publication_date": "2019-03-04" }, { "id": "authors:j4e0h-qvq52", "collection": "authors", "collection_id": "j4e0h-qvq52", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190114-082742867", "type": "article", "title": "Polarization-Independent, Narrowband, Near-IR Spectral Filters via Guided Mode Resonances in Ultrathin a-Si Nanopillar Arrays", "author": [ { "family_name": "Ng", "given_name": "Ryan C.", "orcid": "0000-0002-0527-9130", "clpid": "Ng-Ryan-C" }, { "family_name": "Garcia", "given_name": "Juan C.", "clpid": "Garcia-J-C" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" }, { "family_name": "Fountaine", "given_name": "Katherine T.", "orcid": "0000-0002-0414-8227", "clpid": "Fountaine-K-T" } ], "abstract": "We report the optical properties obtained through experiments, simulation, and theory of ultrathin (<0.1\u03bb), amorphous Si nanopillar arrays embedded in a thin film of SiO_2 designed for narrowband filtering for multi- and hyperspectral imaging in the near-infrared. The fabricated nanopillar arrays are square-packed with subwavelength periodicity, heights of \u223c100 nm, and a radius-to-spacing ratio, r/a, of \u223c0.2. Specular reflection measurements at normal incidence demonstrate that these arrays behave as narrow stopband filters in the near-infrared (\u03bb = 1300\u20131700 nm) and attain \u223c90% reflectivity in band and a full width at half-maximum as low as 20 nm. Using a combination of full-wave simulations and theory, we demonstrate that these narrowband filtering properties arise from efficient grating coupling of light into guided modes of the array because the nanopillar arrays serve as photonic crystal slabs. This phenomenon is known as a guided mode resonance. We discover that the spectral location of these resonances is passively tunable by modifying array geometry and is most sensitive to nanopillar spacing. Theoretical photonic crystal slab band diagrams accurately predict the spectral locations of the observed resonance and provide physical insights into and support the guided mode resonance formulation. This work demonstrates that these ultrathin all-dielectric nanopillar arrays have advantages over existing hyperspectral filter designs because they are polarization independent, do not suffer from material absorption loss, and have significant implications for minimizing imaging device size.", "doi": "10.1021/acsphotonics.8b01253", "issn": "2330-4022", "publisher": "American Chemical Society", "publication": "ACS Photonics", "publication_date": "2019-02-20", "series_number": "2", "volume": "6", "issue": "2", "pages": "265-271" }, { "id": "authors:17502-gmt30", "collection": "authors", "collection_id": "17502-gmt30", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20181213-132119156", "type": "article", "title": "Discrete\u2010Continuum Duality of Architected Materials: Failure, Flaws, and Fracture", "author": [ { "family_name": "Mateos", "given_name": "Arturo J.", "clpid": "Mateos-A-J" }, { "family_name": "Huang", "given_name": "Wei", "clpid": "Huang-Wei" }, { "family_name": "Zhang", "given_name": "Yong\u2010Wei", "clpid": "Zhang-Yong\u2010Wei" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "3D nano\u2010 and micro\u2010architected materials are resilient under compression; their susceptibility to flaws and fracture remain unexplored. This work reports the fabrication and tensile\u2010to\u2010failure response of hollow alumina nanolattices arranged into 5 \u00b5m octet\u2010truss unit cells. Some specimens contained through\u2010thickness center notches oriented at different angles to the loading direction, with a length\u2010over\u2010sample\u2010width ratio of 0.45. In situ tensile experiments reveal that for all orientations, failure initiates at the notch root, followed by instantaneous crack propagation along lattice planes orthogonal to extension. A tensile strength of 27.4 \u00b1 0.7 MPa is highest for unnotched samples and decreases as notch orientation varies from 0\u00b0 to 90\u00b0 to its minimum, 7.2 \u00b1 0.4 MPa; their specific tensile strength is \u22484 \u00d7 higher than that for all other low\u2010density materials. Finite element simulations reproduce observed strengths and failure mechanisms: initial cracks always initiate at the nodal junctions with highest stress concentrations by tearing of alumina walls at the nodes. Subsequent crack propagation shifts maximum stress concentration to the nodes along lattice plane orthogonal to the loading direction. A modified analytical fracture model based on the effective notch length predicts tensile strengths consistent with experiments. These findings imply that continuum fracture mechanics can predict failure in nano\u2010architected materials, which helps develop advanced materials through informed architectural design.", "doi": "10.1002/adfm.201806772", "issn": "1616-301X", "publisher": "Wiley", "publication": "Advanced Functional Materials", "publication_date": "2019-02-01", "series_number": "5", "volume": "29", "issue": "5", "pages": "Art. No. 1806772" }, { "id": "authors:7522e-pm611", "collection": "authors", "collection_id": "7522e-pm611", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190122-090637615", "type": "article", "title": "Computationally efficient design of directionally compliant metamaterials", "author": [ { "family_name": "Shaw", "given_name": "Lucas A.", "clpid": "Shaw-Lucas-A" }, { "family_name": "Sun", "given_name": "Frederick", "clpid": "Sun-Frederick" }, { "family_name": "Portela", "given_name": "Carlos M.", "orcid": "0000-0002-2649-4235", "clpid": "Portela-Carlos-M" }, { "family_name": "Barranco", "given_name": "Rodolfo I.", "clpid": "Barranco-Rodolfo-I" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" }, { "family_name": "Hopkins", "given_name": "Jonathan B.", "orcid": "0000-0003-4752-746X", "clpid": "Hopkins-Jonathan-B" } ], "abstract": "Designing mechanical metamaterials is overwhelming for most computational approaches because of the staggering number and complexity of flexible elements that constitute their architecture\u2014particularly if these elements don't repeat in periodic patterns or collectively occupy irregular bulk shapes. We introduce an approach, inspired by the freedom and constraint topologies (FACT) methodology, that leverages simplified assumptions to enable the design of such materials with ~6 orders of magnitude greater computational efficiency than other approaches (e.g., topology optimization). Metamaterials designed using this approach are called directionally compliant metamaterials (DCMs) because they manifest prescribed compliant directions while possessing high stiffness in all other directions. Since their compliant directions are governed by both macroscale shape and microscale architecture, DCMs can be engineered with the necessary design freedom to facilitate arbitrary form and unprecedented anisotropy. Thus, DCMs show promise as irregularly shaped flexure bearings, compliant prosthetics, morphing structures, and soft robots.", "doi": "10.1038/s41467-018-08049-1", "pmcid": "PMC6336888", "issn": "2041-1723", "publisher": "Nature Publishing Group", "publication": "Nature Communications", "publication_date": "2019-01-17", "volume": "10", "pages": "Art. No. 291" }, { "id": "authors:t90mb-tcj22", "collection": "authors", "collection_id": "t90mb-tcj22", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180622-095714454", "type": "article", "title": "Bio\u2010Mimicked Silica Architectures Capture Geometry, Microstructure, and Mechanical Properties of Marine Diatoms", "author": [ { "family_name": "Luo", "given_name": "Shi", "clpid": "Luo-Shi" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "The authors create life\u2010sized synthetic replicas of marine diatom coscinodiscus sp frustules out of cyclohexyl polyhedral oligomeric silsesquioxanes (POSS). The authors demonstrate that these synthetic structures have biosilica\u2010like amorphous atomic\u2010level microstructure and mechanical attributes similar to those of a natural diatom. In situ beam bending and fracture experiments on micron\u2010sized excised sections of natural and synthetic diatoms reveal similarities in their mechanical properties: a Young's modulus of 20.2 \u00b1 2.6 GPa and a fracture toughness of 0.78\u2009\u00b1\u20090.10\u2009MPa\u2009m^(\u22121/2) for the synthetic materials; those of natural diatoms are 36.4 \u00b1 8.3 GPa and 1.05 \u00b1 0.08 MPa mm^(\u22121/2), respectively. In situ single edge notched beam (SENB) bending fracture experiments reveal that fracture behavior of the natural and synthetic specimens is virtually indistinguishable and is characterized by the same brittle failure and crack\u2010arresting behavior enabled by the double\u2010wall geometry. Their fracture toughness is comparable to that of fully dense silica, which suggests that the natural diatoms' frustule maintains its mechanical resilience even at <50% of the weight attained through multi\u2010scale architecture. The demonstrated ability to fabricate a synthetic hard biomaterial that is virtually indistinguishable from its natural counterpart while capturing its complex architecture, microstructure, and mechanical properties provides a powerful platform for investigating the specific role of each geometrical feature at every relevant length scale in the often sophisticated, multi\u2010scale hierarchical construct of hard biomaterials, and provides a robust pathway for property optimization.", "doi": "10.1002/adem.201800301", "issn": "1438-1656", "publisher": "Wiley", "publication": "Advanced Engineering Materials", "publication_date": "2018-09", "series_number": "9", "volume": "20", "issue": "9", "pages": "Art. No. 1800301" }, { "id": "authors:0v1br-pjm64", "collection": "authors", "collection_id": "0v1br-pjm64", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180719-105749681", "type": "article", "title": "Ultralow Thermal Conductivity and Mechanical Resilience of Architected Nanolattices", "author": [ { "family_name": "Dou", "given_name": "Nicholas G.", "orcid": "0000-0001-8199-5588", "clpid": "Dou-Nicholas-G" }, { "family_name": "Jagt", "given_name": "Robert A.", "clpid": "Jagt-R-A" }, { "family_name": "Portela", "given_name": "Carlos M.", "orcid": "0000-0002-2649-4235", "clpid": "Portela-C-M" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" }, { "family_name": "Minnich", "given_name": "Austin J.", "orcid": "0000-0002-9671-9540", "clpid": "Minnich-A-J" } ], "abstract": "Creating materials that simultaneously possess ultralow thermal conductivity, high stiffness, and damage tolerance is challenging because thermal and mechanical properties are coupled in most fully dense and porous solids. Nanolattices can fill this void in the property space because of their hierarchical design and nanoscale features. We report that nanolattices composed of 24- to 182-nm-thick hollow alumina beams in the octet-truss architecture achieved thermal conductivities as low as 2 mW m^(\u20131) K^(\u20131) at room temperature while maintaining specific stiffnesses of 0.3 to 3 MPa kg^(\u20131) m^3 and the ability to recover from large deformations. These nanoarchitected materials possess the same ultralow thermal conductivities as aerogels while attaining specific elastic moduli that are nearly 2 orders of magnitude higher. Our work demonstrates a general route to realizing multifunctional materials that occupy previously unreachable regions within the material property space.", "doi": "10.1021/acs.nanolett.8b01191", "issn": "1530-6984", "publisher": "American Chemical Society", "publication": "Nano Letters", "publication_date": "2018-08-08", "series_number": "8", "volume": "18", "issue": "8", "pages": "4755-4761" }, { "id": "authors:6r5gp-fna97", "collection": "authors", "collection_id": "6r5gp-fna97", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180620-151712137", "type": "article", "title": "Impact of node geometry on the effective stiffness of non-slender three-dimensional truss lattice architectures", "author": [ { "family_name": "Portela", "given_name": "Carlos M.", "orcid": "0000-0002-2649-4235", "clpid": "Portela-C-M" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" }, { "family_name": "Kochmann", "given_name": "Dennis M.", "orcid": "0000-0002-9112-6615", "clpid": "Kochmann-D-M" } ], "abstract": "Three-dimensional (3D), lattice-based micro- and nano-architected materials can possess desirable mechanical properties that are unattainable by homogeneous materials. Manufacturing these so-called structural metamaterials at the nano- and microscales typically results in non-slender architectures (e.g., struts with a high radius-to-length ratio r\u2215l), for which simple analytical and computational tools are inapplicable since they fail to capture the effects of nodes at strut junctions. We report a detailed analysis that quantifies the effect of nodes on the effective Young's modulus (E\u2217) of lattice architectures with different unit cell geometries through (i) simple analytical constructions, (ii) reduced-order computational models, and (iii) experiments at the milli- and micrometer scales. The computational models of variable-node lattice architectures match the effective stiffness obtained from experiments and incur computational cost that are three orders-of-magnitude lower than alternative, conventional methods. We highlight a difference in the contribution of nodes to rigid versus non-rigid architectures and propose an extension to the classical stiffness scaling laws of the form E\u2217\u221dC_1(r\u2215l)\u03b1+C_2(r\u2215l)^\u03b2, which holds for slender and non-slender beam-based architectures, where constants C_1 and C_2 change with lattice geometry. We find the optimal scaling exponents for rigid architectures to be \u03b1=2 and \u03b2=4, and \u03b1=4 and \u03b2=6 for non-rigid architectures. These analytical, computational, and experimental results quantify the specific contribution of nodes to the effective stiffness of beam-based architectures and highlight the necessity of incorporating their effects into calculations of the structural stiffness. This work provides new, efficient tools that accurately capture the mechanics and physics of strut junctions in 3D, beam-based architected materials.", "doi": "10.1016/j.eml.2018.06.004", "issn": "2352-4316", "publisher": "Elsevier", "publication": "Extreme Mechanics Letters", "publication_date": "2018-07", "volume": "22", "pages": "138-148" }, { "id": "authors:jqx4p-9he65", "collection": "authors", "collection_id": "jqx4p-9he65", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180308-103302974", "type": "article", "title": "Additive Manufacturing of Polymer-Derived Titania for One-Step Solar Water Purification", "author": [ { "family_name": "Vyatskikh", "given_name": "Andrey", "orcid": "0000-0002-6917-6931", "clpid": "Vyatskikh-A" }, { "family_name": "Kudo", "given_name": "Akira", "orcid": "0000-0002-0830-5509", "clpid": "Kudo-Akira" }, { "family_name": "Delalande", "given_name": "St\u00e9phane", "clpid": "Delalande-S" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "Solar disinfection of drinking water (SODIS) is an approach for water purification widely used in households with limited access to fresh water. SODIS relies on microorganism inactivation triggered by sunlight energy in the UV spectrum and requires processing times of up to 48\u202fhr. Water treatment rate is drastically increased by using photocatalytic materials, such as TiO_2, which can harvest sunlight to promote generation of reactive oxygen species (ROS) that inactivate bacteria within few hours. One main challenge that impedes the insertion of photocatalysts in most water treatment approaches is the need to populate the catalyst particles on a three-dimensional (3D) structure with a high-surface area that is stable under water flow.", "doi": "10.1016/j.mtcomm.2018.02.010", "issn": "2352-4928", "publisher": "Elsevier", "publication": "Materials Today Communications", "publication_date": "2018-06", "volume": "15", "pages": "288-293" }, { "id": "authors:dq0k2-q0g62", "collection": "authors", "collection_id": "dq0k2-q0g62", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20200414-144926046", "type": "article", "title": "Additive Manufacturing of Nano- and Microarchitected Materials", "author": [ { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" }, { "family_name": "Park", "given_name": "Jiwoong", "clpid": "Park-Jiwoong" } ], "abstract": "Creating materials with a suite of designed properties is one of key challenges in our society. Solving this grand challenge will open pathways to create entirely new classes of materials, whose properties are determined a priori and are attained through a multiscale physically informed approach. These new material classes will offer breakthrough advances in almost every branch of manufacturing and technology from ultralightweight and damage-tolerant structural materials to safe and efficient energy storage, biomedical devices, biochemical and micromechanical sensors and actuators, nanophotonic devices, and textiles.", "doi": "10.1021/acs.nanolett.8b00724", "issn": "1530-6984", "publisher": "American Chemical Society", "publication": "Nano Letters", "publication_date": "2018-04-11", "series_number": "4", "volume": "18", "issue": "4", "pages": "2187-2188" }, { "id": "authors:t660r-08w66", "collection": "authors", "collection_id": "t660r-08w66", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180227-083635588", "type": "article", "title": "Irradiation Enhances Strength and Deformability of Nano-Architected Metallic Glass", "author": [ { "family_name": "Thompson", "given_name": "Rachel L.", "clpid": "Thompson-R-L" }, { "family_name": "Wang", "given_name": "Yongqiang", "clpid": "Wang-Yongqiang" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "The quest for radiation-damage tolerant materials has found good candidates in nanoporous metals, whose abundance of free surfaces provides ample sinks for radiation-induced defects, as well as in metallic glasses, whose characteristic failure via shear banding can be alleviated by irradiation. This type of catastrophic failure in metallic glass can also be suppressed by reducing their dimensions to the nanoscale. To combine the beneficial effects of resilience against irradiation in materials containing many free surfaces and nano-sized metallic glasses, the authors fabricate Zr\u2013Ni\u2013Al metallic glass nano-architecture and irradiate them with 12 MeV Ni^(4+) ions. These 3D nanolattices are composed of hollow beams of sputtered metallic glass with beam wall thicknesses \u224810\u2013100\u2009nm, with a relative density of \u22485%, which renders them to be 20 times lighter than their bulk-level counterparts. The authors find that the thickest-walled nanolattices, those with a median wall thickness of \u224888\u2009nm, are able to withstand irradiation without significant contraction; all other substantially shrunk; and collapsed upon irradiation. In situ nanomechanical experiments on the irradiated samples compressed inside a scanning electron microscope (SEM) reveal substantial improvement in mechanical response upon irradiation, with an average increase in yield strength of 35.7% and a significant enhancement in deformability. Enhanced deformability upon irradiation is apparent from the nanolattices' accommodation of larger strains before any kind of failure, as well as the presence of smaller strain bursts and stress drops throughout the stress\u2013strain response. The irradiated nanolattices are largely intact after compression, with in situ SEM videos demonstrating a layer-by-layer like collapse in the irradiated nanolattices in contrast to the catastrophic failure with complete destruction of the failed layers observed in equivalent as-fabricated samples. This work points to nano-architected metallic glasses being a promising candidate for creating ultra-lightweight, radiation tolerant materials, and irradiation as a promising technique for improving the mechanical response of metallic glass nanolattices with stiffness on the order of 250\u2009MPa.", "doi": "10.1002/adem.201701055", "issn": "1438-1656", "publisher": "Wiley Verlag", "publication": "Advanced Engineering Materials", "publication_date": "2018-04", "series_number": "4", "volume": "20", "issue": "4", "pages": "Art. No. 1701055" }, { "id": "authors:vkn8b-h4814", "collection": "authors", "collection_id": "vkn8b-h4814", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180129-083003785", "type": "article", "title": "High-Strength Nanotwinned Al Alloys with 9R Phase", "author": [ { "family_name": "Li", "given_name": "Qiang", "clpid": "Li-Qiang" }, { "family_name": "Xue", "given_name": "Sichuang", "clpid": "Xue-Sichuang" }, { "family_name": "Wang", "given_name": "Jian", "clpid": "Wang-Jian" }, { "family_name": "Shao", "given_name": "Shuai", "orcid": "0000-0002-9525-6310", "clpid": "Shao-Shuai" }, { "family_name": "Kwong", "given_name": "Anthony H.", "clpid": "Kwong-Aanthony-H" }, { "family_name": "Giwa", "given_name": "Adenike", "clpid": "Giwa-A-M" }, { "family_name": "Fan", "given_name": "Zhe", "clpid": "Fan-Zhe" }, { "family_name": "Liu", "given_name": "Yue", "clpid": "Liu-Yue" }, { "family_name": "Qi", "given_name": "Zhimin", "clpid": "Qi-Zhimin" }, { "family_name": "Ding", "given_name": "Jie", "orcid": "0000-0002-3584-6140", "clpid": "Ding-Jie" }, { "family_name": "Wang", "given_name": "Han", "clpid": "Wang-Han-Materials-Science" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" }, { "family_name": "Wang", "given_name": "Haiyan", "clpid": "Wang-Haiyan" }, { "family_name": "Zhang", "given_name": "Xinghang", "clpid": "Zhang-Xinghang" } ], "abstract": "Light-weight aluminum (Al) alloys have widespread applications. However, most Al alloys have inherently low mechanical strength. Nanotwins can induce high strength and ductility in metallic materials. Yet, introducing high-density growth twins into Al remains difficult due to its ultrahigh stacking-fault energy. In this study, it is shown that incorporating merely several atomic percent of Fe solutes into Al enables the formation of nanotwinned (nt) columnar grains with high-density 9R phase in Al(Fe) solid solutions. The nt Al\u2013Fe alloy coatings reach a maximum hardness of \u22485.5 GPa, one of the strongest binary Al alloys ever created. In situ uniaxial compressions show that the nt Al\u2013Fe alloys populated with 9R phase have flow stress exceeding 1.5 GPa, comparable to high-strength steels. Molecular dynamics simulations reveal that high strength and hardening ability of Al\u2013Fe alloys arise mainly from the high-density 9R phase and nanoscale grain sizes.", "doi": "10.1002/adma.201704629", "issn": "0935-9648", "publisher": "Wiley", "publication": "Advanced Materials", "publication_date": "2018-03-15", "series_number": "11", "volume": "30", "issue": "11", "pages": "Art. No. 1704629" }, { "id": "authors:6b2fz-sz096", "collection": "authors", "collection_id": "6b2fz-sz096", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190827-112057275", "type": "book_section", "title": "Fabrication and characterization of a three-dimensional core-shell photonic-crystal lattice capable of negative refraction in the mid-infrared (Conference Presentation)", "book_title": "Photonic and Phononic Properties of Engineered Nanostructures VIII", "author": [ { "family_name": "Chernow", "given_name": "Victoria F.", "clpid": "Chernow-V-F" }, { "family_name": "Ng", "given_name": "Ryan C.", "orcid": "0000-0002-0527-9130", "clpid": "Ng-Ryan-C" }, { "family_name": "Peng", "given_name": "Siying", "orcid": "0000-0002-1541-0278", "clpid": "Peng-Siying" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "contributor": [ { "family_name": "Adibi", "given_name": "Ali", "clpid": "Adibi-A" }, { "family_name": "Lin", "given_name": "Shawn-Yu", "clpid": "Lin-Shawn-Yu" }, { "family_name": "Scherer", "given_name": "Axel", "clpid": "Scherer-A" } ], "abstract": "Interest in negative refraction has been motivated by the possibility of creating a \"superlens\" as proposed by Pendry (Phys. Rev. Lett. 85, 3966 (2000)). This theoretical work showed that a material capable of negative refraction amplifies evanescent waves and allows this material to act as a lens with a resolution not limited by working wavelength. Although theory and some experiments have shown that certain metamaterials and photonic crystals (PhCs) can act as superlenses, realistic demonstration of negative refraction in the optical and infrared range remains a challenge. This is because most metamaterials employ lossy metal elements and most PhC structures found to exhibit negative refraction are made of positive index dielectric materials and are two-dimensional. Subwavelength imaging of a 3D object requires a 3D PhC capable of negative refraction. Inspired by the numerical simulations of Luo, et. al. (Appl. Phys. Lett. 81, 2352 (2002)), we demonstrate the fabrication and characterization of a 500nm-diameter polymer core, 250nm-thick Germanium shell 3D photonic crystal lattice that exhibits negative refraction in the mid-infrared, centered around 8\u00b5m. This 3D photonic crystal resembles a BCC lattice of air cubes in dielectric media and was fabricated using two-photon lithography direct laser writing of an acrylic polymer resin scaffold followed by RF sputtering of Ge. The band structure of the lattice was mapped using FTIR spectroscopy reflectance measurements, and negative refraction was observed using far-field IR transmission imaging.", "doi": "10.1117/12.2290697", "isbn": "9781510615670", "publisher": "Society of Photo-Optical Instrumentation Engineers (SPIE)", "place_of_publication": "Bellingham, WA", "publication_date": "2018-03-14", "pages": "Art. No. 105410N" }, { "id": "authors:yvsbe-ndy09", "collection": "authors", "collection_id": "yvsbe-ndy09", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180413-160844730", "type": "conference_item", "title": "Genomic DNA functionalized 3D printed materials for drug capture", "author": [ { "family_name": "Yee", "given_name": "Daryl", "orcid": "0000-0002-4114-6167", "clpid": "Yee-Daryl-Wei-Liang" }, { "family_name": "Schulz", "given_name": "Michael", "orcid": "0000-0001-8499-6025", "clpid": "Schulz-M-D" }, { "family_name": "Blumenfeld", "given_name": "Carl", "clpid": "Blumenfeld-C-M" }, { "family_name": "Grubbs", "given_name": "Robert", "orcid": "0000-0002-0057-7817", "clpid": "Grubbs-R-H" }, { "family_name": "Greer", "given_name": "Julia", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "Since the discovery of nitrogen mustard as an effective anti-cancer agent in the 1940s, and consequently, the concept of\nchemotherapy, researchers around the world have been actively developing new and more effective chemotherapeutic agents\nto better treat cancer. Traditionally, chemotherapeutic agents work by interfering with cell division. However, by virtue of their\nmechanism of action, healthy normal cells can also be targeted and destroyed. As a result, while chemotherapy is an effective\nway of managing cancer, the resulting side effects limits its use. One approach currently taken to reduce these side effects is\nto deliver the chemotherapy drugs directly to the tumor via transarterial chemoembolization, or other similar procedures.\nWhile this has been effective in reducing systemic toxicity, more can be done to improve this. Ideally, a device that could\nsequester any unreacted chemotherapy agents could be installed \"downstream\" of the tumor prior to them entering systemic\ncirculation. Such drug-capture materials have yet to be realized. We report the synthesis of genomic DNA\nfunctionalized 3D printed materials that can be used to capture doxorubicin, a commonly used chemotherapy agent. The\nefficacy of these materials highlight the possibility of utilizing them in a device that can be deployed in the body for drug\ncapture.", "publisher": "Caltech Library", "publication_date": "2018-03" }, { "id": "authors:q37rg-8r635", "collection": "authors", "collection_id": "q37rg-8r635", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190110-080648684", "type": "book_section", "title": "Fabrication of ultra-thin si nanopillar arrays for polarization-independent spectral filters in the near-IR", "book_title": "Photonic and Phononic Properties of Engineered Nanostructures VIII", "author": [ { "family_name": "Ng", "given_name": "Ryan C.", "orcid": "0000-0002-0527-9130", "clpid": "Ng-Ryan-C" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" }, { "family_name": "Fountaine", "given_name": "Katherine T.", "orcid": "0000-0002-0414-8227", "clpid": "Fountaine-K-T" } ], "contributor": [ { "family_name": "Adibi", "given_name": "Ali", "clpid": "Adibi-A" }, { "family_name": "Lin", "given_name": "Shawn-Yu", "clpid": "Lin-S-Y" }, { "family_name": "Scherer", "given_name": "Axel", "clpid": "Scherer-A" } ], "abstract": "Sub-wavelength arrays have garnered significant interest for many potential optoelectronics applications. We fabricated sub-wavelength silicon nanopillar arrays with a ratio of radius, r and a center-to-center distance, a, of r/a \u2248 0.2 that were fully embedded in SiO_2 for narrow stopband filters that are compact and straightforward to fabricate compared to conventional Bragg stack reflectors. These arrays are well-suited for hyperspectral filtering applications in the infrared. They are ultra-thin (<0.1\u03bb), polarization-independent, and attain greater efficiencies enabled by low loss compared to plasmonic-based designs. The choice of Si as the nanopillar material stems from its low cost, high index of refraction, and a band gap of 1.1 eV near the edge of the visible.\nThese arrays exhibit narrow near-unity reflectivity resonances that arise from coupling of an incident wave into a leaky waveguide mode via a grating vector that is subsequently reradiated, also known as guided mode resonances (GMRs). Simulations reveal reflectivities of >99% with full width at half maxima (FWHM) of \u22480.01 \u03bcm. We demonstrate a fabrication route for obtaining nanopillar arrays that exhibit these GMRs. We experimentally observed a GMR with an amplitude of ~0.8 for filter arrays fabricated on silicon on insulator (SOI) substrates, combined with Fabry-Perot interference that stems from the underlying silicon layer.", "doi": "10.1117/12.2286804", "isbn": "9781510615670", "publisher": "Society of Photo-optical Instrumentation Engineers (SPIE)", "place_of_publication": "Bellingham, WA", "publication_date": "2018-02-21", "pages": "Art. No. 105411D" }, { "id": "authors:g2nqq-42g09", "collection": "authors", "collection_id": "g2nqq-42g09", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180206-130051890", "type": "article", "title": "Additive manufacturing of 3D nano-architected metals", "author": [ { "family_name": "Vyatskikh", "given_name": "Andrey", "orcid": "0000-0002-6917-6931", "clpid": "Vyatskikh-Andrey" }, { "family_name": "Delalande", "given_name": "St\u00e9phane", "clpid": "Delalande-St\u00e9phane" }, { "family_name": "Kudo", "given_name": "Akira", "orcid": "0000-0002-0830-5509", "clpid": "Kudo-Akira" }, { "family_name": "Zhang", "given_name": "Xuan", "orcid": "0000-0002-6155-6825", "clpid": "Zhang-Xuan" }, { "family_name": "Portela", "given_name": "Carlos M.", "orcid": "0000-0002-2649-4235", "clpid": "Portela-Carlos-M" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "Most existing methods for additive manufacturing (AM) of metals are inherently limited to ~20\u201350\u2009\u03bcm resolution, which makes them untenable for generating complex 3D-printed metallic structures with smaller features. We developed a lithography-based process to create complex 3D nano-architected metals with ~100\u2009nm resolution. We first synthesize hybrid organic\u2013inorganic materials that contain Ni clusters to produce a metal-rich photoresist, then use two-photon lithography to sculpt 3D polymer scaffolds, and pyrolyze them to volatilize the organics, which produces a >90\u2009wt% Ni-containing architecture. We demonstrate nanolattices with octet geometries, 2\u2009\u03bcm unit cells and 300\u2013400-nm diameter beams made of 20-nm grained nanocrystalline, nanoporous Ni. Nanomechanical experiments reveal their specific strength to be 2.1\u20137.2\u2009MPa\u2009g^(\u22121)\u2009cm^3, which is comparable to lattice architectures fabricated using existing metal AM processes. This work demonstrates an efficient pathway to 3D-print micro-architected and nano-architected metals with sub-micron resolution.", "doi": "10.1038/s41467-018-03071-9", "pmcid": "PMC5807385", "issn": "2041-1723", "publisher": "Nature Publishing Group", "publication": "Nature Communications", "publication_date": "2018-02-09", "volume": "9", "pages": "Art. No. 593" }, { "id": "authors:gkrwe-g7533", "collection": "authors", "collection_id": "gkrwe-g7533", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20171107-134955226", "type": "article", "title": "Enabling Simultaneous Extreme Ultra Low-k in Stiff, Resilient, and Thermally Stable Nano-Architected Materials", "author": [ { "family_name": "Lifson", "given_name": "Max L.", "orcid": "0000-0002-0382-182X", "clpid": "Lifson-M-L" }, { "family_name": "Kim", "given_name": "Min-Woo", "clpid": "Kim-Min-Woo" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" }, { "family_name": "Kim", "given_name": "Bong-Joong", "orcid": "0000-0002-5335-4342", "clpid": "Kim-Bong-Joong" } ], "abstract": "Low dielectric constant (low-k) materials have gained increasing popularity because of their critical role in developing faster, smaller, and higher performance devices. Their practical use has been limited by the strong coupling among mechanical, thermal, and electrical properties of materials and their dielectric constant; a low-k is usually attained by materials that are very porous, which results in high compliance, that is, silica aerogels; high dielectric loss, that is, porous polycrystalline alumina; and poor thermal stability, that is, Sr-based metal\u2013organic frameworks. We report the fabrication of 3D nanoarchitected hollow-beam alumina dielectrics which k is 1.06\u20131.10 at 1 MHz that is stable over the voltage range of \u221220 to 20 V and a frequency range of 100 kHz to 10 MHz. This dielectric material can be used in capacitors and is mechanically resilient, with a Young's modulus of 30 MPa, a yield strength of 1.07 MPa, a nearly full shape recoverability to its original size after >50% compressions, and outstanding thermal stability with a thermal coefficient of dielectric constant (TCK) of 2.43 \u00d7 10^(-5) K^(-1) up to 800 \u00b0C. These results suggest that nanoarchitected materials may serve as viable candidates for ultra low-k materials that are simultaneously mechanically resilient and thermally and electrically stable for microelectronics and devices.", "doi": "10.1021/acs.nanolett.7b03941", "issn": "1530-6984", "publisher": "American Chemical Society", "publication": "Nano Letters", "publication_date": "2017-12-13", "series_number": "12", "volume": "17", "issue": "12", "pages": "7737-7743" }, { "id": "authors:8zt06-95b70", "collection": "authors", "collection_id": "8zt06-95b70", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170828-140820883", "type": "article", "title": "Reexamining the mechanical property space of three-dimensional lattice architectures", "author": [ { "family_name": "Meza", "given_name": "Lucas R.", "orcid": "0000-0003-0250-2621", "clpid": "Meza-L-R" }, { "family_name": "Phlipot", "given_name": "Gregory P.", "clpid": "Phlipot-G-P" }, { "family_name": "Portela", "given_name": "Carlos M.", "orcid": "0000-0002-2649-4235", "clpid": "Portela-C-M" }, { "family_name": "Maggi", "given_name": "Alessandro", "clpid": "Maggi-A" }, { "family_name": "Montemayor", "given_name": "Lauren C.", "clpid": "Montemayor-L-C" }, { "family_name": "Comella", "given_name": "Andre", "clpid": "Comella-A" }, { "family_name": "Kochmann", "given_name": "Dennis M.", "orcid": "0000-0002-9112-6615", "clpid": "Kochmann-D-M" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "Lightweight materials that are simultaneously strong and stiff are desirable for a range of applications from transportation to energy storage to defense. Micro- and nanolattices represent some of the lightest fabricated materials to date, but studies of their mechanical properties have produced inconsistent results that are not well captured by existing lattice models. We performed systematic nanomechanical experiments on four distinct geometries of solid polymer and hollow ceramic (Al_2O_3) nanolattices. All samples tested had a nearly identical scaling of strength (\u03c3y) and Young's modulus (E) with relative density (\u03c1\u00af), ranging from \u03c3y\u221d\u03c1\u00af1.45 to \u03c1\u00af1.92 and E\u221d\u03c1\u00af1.41 to \u03c1\u00af1.83, revealing that changing topology alone does not necessarily have a significant impact on nanolattice mechanical properties. Finite element analysis was performed on solid and hollow lattices with structural parameters beyond those realized experimentally, enabling the identification of transition regimes where solid-beam lattices diverge from existing analytical theories and revealing the complex parameter space of hollow-beam lattices. We propose a simplified analytical model for solid-beam lattices that provides insight into the mechanisms behind their observed stiffness, and we investigate different hollow-beam lattice parameters that give rise to their aberrant properties. These experimental, computational and theoretical results uncover how architecture can be used to access unique lattice mechanical property spaces while demonstrating the practical limits of existing beam-based models in characterizing their behavior.", "doi": "10.1016/j.actamat.2017.08.052", "issn": "1359-6454", "publisher": "Elsevier", "publication": "Acta Materialia", "publication_date": "2017-11", "volume": "140", "pages": "424-432" }, { "id": "authors:gv245-j5f57", "collection": "authors", "collection_id": "gv245-j5f57", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170919-085010063", "type": "article", "title": "Three-Dimensional Nano-Architected Scaffolds with Tunable Stiffness for Efficient Bone Tissue Growth", "author": [ { "family_name": "Maggi", "given_name": "Alessandro", "orcid": "0000-0001-9438-7258", "clpid": "Maggi-Alessandro" }, { "family_name": "Li", "given_name": "Hanqing", "clpid": "Li-Hanqing" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "The precise mechanisms that lead to orthopedic implant failure are not well understood; it is believed that the micromechanical environment at the bone-implant interface regulates structural stability of an implant. In this work, we seek to understand how the 3D mechanical environment of an implant affects bone formation during early osteointegration. We employed two-photon lithography (TPL) direct laser writing to fabricate 3-dimensional rigid polymer scaffolds with tetrakaidecahedral periodic geometry, herewith referred to as nanolattices, whose strut dimensions were on the same order as osteoblasts' focal adhesions (\u223c2\u03bcm) and pore sizes on the order of cell size, \u223c10\u03bcm. Some of these nanolattices were subsequently coated with thin conformal layers of Ti or W, and a final outer layer of 18nm-thick TiO_2 was deposited on all samples to ensure biocompatibility. Nanomechanical experiments on each type of nanolattice revealed the range of stiffnesses of 0.7-100 MPa.\nOsteoblast-like cells (SAOS-2) were seeded on each nanolattice, and their mechanosensitve response was explored by tracking mineral secretions and intracellular f-actin and vinculin concentrations after 2, 8 and 12 days of cell culture in mineralization media.\nExperiments revealed that the most compliant nanolattices had \u223c20% more intracellular f-actin and \u223c40% more Ca and P secreted onto them than the stiffer nanolattices, where such cellular response was virtually indistinguishable.\nWe constructed a simple phenomenological model that appears to capture the observed relation between scaffold stiffness and f-actin concentration. This model predicts a range of optimal scaffold stiffnesses for maximum f-actin concentration, which appears to be directly correlated with osteoblast-driven mineral deposition.\nThis work suggests that three-dimensional scaffolds with titania-coated surfaces may provide an optimal microenvironment for cell growth when their stiffness is similar to that of cartilage (\u223c0.5-3MPa). These findings help provide a greater understanding of osteoblast mechanosensitivity and may have profound implications in developing more effective and safer bone prostheses.\nStatement of Significance:\nCreating prostheses that lead to optimal bone remodeling has been a challenge for more than two decades because of a lack of thorough knowledge of cell behavior in three-dimensional (3D) environments. Literature has shown that 2D substrate stiffness plays a significant role in determining cell behavior, however, limitations in fabrication techniques and difficulties in characterizing cell-scaffold interactions have limited our understanding of how 3D scaffolds' stiffness affects cell response.\nThe present study shows that scaffold structural stiffness affects osteoblasts cellular response. Specifically this work shows that the cells grown on the most compliant nanolattices with a stiffness of 0.7MPa expressed \u223c20% higher concentration of intracellular f-actin and secreted \u223c40% more Ca and P compared with all other nanolattices. This suggests that bone scaffolds with a stiffness close to that of cartilage may serve as optimal 3D scaffolds for new synthetic bone graft materials.", "doi": "10.1016/j.actbio.2017.09.007", "pmcid": "PMC5663471", "issn": "1742-7061", "publisher": "Elsevier", "publication": "Acta Biomaterialia", "publication_date": "2017-11", "volume": "63", "pages": "294-305" }, { "id": "authors:sdap6-w9k84", "collection": "authors", "collection_id": "sdap6-w9k84", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170912-140307884", "type": "conference_item", "title": "Materials for drug capture: An approach for removing off-target chemotherapy from the bloodstream", "author": [ { "family_name": "Schulz", "given_name": "Michael", "orcid": "0000-0001-8499-6025", "clpid": "Schulz-M-D" }, { "family_name": "Blumenfeld", "given_name": "Carl", "clpid": "Blumenfeld-C-M" }, { "family_name": "Yee", "given_name": "Daryl", "orcid": "0000-0002-4114-6167", "clpid": "Yee-Daryl-Wei-Liang" }, { "family_name": "Greer", "given_name": "Julia", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" }, { "family_name": "Hetts", "given_name": "Steven", "clpid": "Hetts-S-W" }, { "family_name": "Grubbs", "given_name": "Robert", "orcid": "0000-0002-0057-7817", "clpid": "Grubbs-R-H" } ], "abstract": "The systemic, off-target toxicity of chemotherapy is a well-known problem in oncol. In an effort to overcome this challenge, many approaches have been developed to deliver chemotherapy directly and exclusively the tumor. One of these approaches is transarterial chemoembolization (TACE), a procedure in which chemotherapy is introduced via catheter directly into the artery supplying the tumor. Despite this site-specific delivery, a portion of the chemotherapy dose still enters systemic circulation and causes off-target damage. To address this issue, we are developing materials and devices that are capable of capturing this residual chemotherapy from the blood stream. The ultimate goal is to construct a device that can be\ndeployed via catheter \"downstream\" from the tumor, enabling excess chemotherapy to be sequestered before entering systemic circulation. Our approach uses DNA-functionalized surfaces, which enable the capture of DNA-targeting chemotherapy drugs. In order to improve the cost and scalability of this system, we developed simple methods of covalently attaching genomic DNA to a variety of surfaces. We have further demonstrated that this approach is capable of sequestering doxorubicin, cisplatin, and epirubicin-three common chemotherapy agents-from soln. at clin. relevant concns. The efficacy of these materials was demonstrated in PBS, human serum, whole blood, and initial in vivo studies. Moreover, the kinetics of drug capture are rapid: We obsd. >95% redn. of doxorubicin concn. in human serum in <10 min. The efficacy of these materials indicates that drug capture is indeed a viable strategy for mitigating the harmful side-effects assocd. with chemotherapy.", "publisher": "Caltech Library", "publication_date": "2017-08" }, { "id": "authors:yg36n-5df94", "collection": "authors", "collection_id": "yg36n-5df94", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170908-091500055", "type": "article", "title": "Deformation of Crystals: Connections with Statistical Physics", "author": [ { "family_name": "Sethna", "given_name": "James P.", "clpid": "Sethna-J-P" }, { "family_name": "Bierbaum", "given_name": "Matthew K.", "clpid": "Bierbaum-M-K" }, { "family_name": "Dahmen", "given_name": "Karin A.", "clpid": "Dahmen-K-A" }, { "family_name": "Goodrich", "given_name": "Carl P.", "clpid": "Goodrich-C-P" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" }, { "family_name": "Hayden", "given_name": "Lorien X.", "clpid": "Hayden-L-X" }, { "family_name": "Kent-Dobias", "given_name": "Jaron P.", "clpid": "Kent-Dobias-J-P" }, { "family_name": "Lee", "given_name": "Edward D.", "clpid": "Lee-E-D" }, { "family_name": "Liarte", "given_name": "Danilo B.", "clpid": "Liarte-D-B" }, { "family_name": "Ni", "given_name": "Xiaoyue", "clpid": "Ni-Xiaoyue" }, { "family_name": "Quinn", "given_name": "Katherine N.", "clpid": "Quinn-K-N" }, { "family_name": "Raju", "given_name": "Archishman", "clpid": "Raju-A" }, { "family_name": "Rocklin", "given_name": "D. Zeb", "clpid": "Rocklin-D-Z" }, { "family_name": "Shekhawat", "given_name": "Ashivni", "clpid": "Shekhawat-A" }, { "family_name": "Zapperi", "given_name": "Stefano", "clpid": "Zapperi-S" } ], "abstract": "We give a bird's-eye view of the plastic deformation of crystals aimed at the statistical physics community, as well as a broad introduction to the statistical theories of forced rigid systems aimed at the plasticity community. Memory effects in magnets, spin glasses, charge density waves, and dilute colloidal suspensions are discussed in relation to the onset of plastic yielding in crystals. Dislocation avalanches and complex dislocation tangles are discussed via a brief introduction to the renormalization group and scaling. Analogies to emergent scale invariance in fracture, jamming, coarsening, and a variety of depinning transitions are explored. Dislocation dynamics in crystals challenge nonequilibrium statistical physics. Statistical physics provides both cautionary tales of subtle memory effects in nonequilibrium systems and systematic tools designed to address complex scale-invariant behavior on multiple length scales and timescales.", "doi": "10.1146/annurev-matsci-070115-032036", "issn": "1531-7331", "publisher": "Annual Reviews", "publication": "Annual Review of Materials Research", "publication_date": "2017-07", "volume": "47", "pages": "217-246" }, { "id": "authors:he55e-7bc71", "collection": "authors", "collection_id": "he55e-7bc71", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170526-084814693", "type": "article", "title": "3D nano-architected metallic glass: Size effect suppresses catastrophic failure", "author": [ { "family_name": "Liontas", "given_name": "Rachel", "clpid": "Liontas-R" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "We investigate the mechanical behavior of 3D periodically architected metallic glass nanolattices, constructed from hollow beams of sputtered Zr-Ni-Al metallic glass. Nanolattices composed of beams with different wall thicknesses are fabricated by varying the sputter deposition time, resulting in nanolattices with median wall thicknesses of \u223c88 nm, \u223c57 nm, \u223c38 nm, \u223c30 nm, \u223c20 nm, and \u223c10 nm. Uniaxial compression experiments conducted inside a scanning electron microscope reveal a transition from brittle, catastrophic failure in thicker-walled nanolattices (median wall thicknesses of \u223c88 and \u223c57 nm) to deformable, gradual, layer-by-layer collapse in thinner-walled nanolattices (median wall thicknesses of \u223c38 nm and less). As the nanolattice wall thickness is varied, large differences in deformability are manifested through the severity of strain bursts, nanolattice recovery after compression, and in-situ images obtained during compression experiments. We explain the brittle-to-deformable transition that occurs as the nanolattice wall thickness decreases in terms of the \"smaller is more deformable\" material size effect that arises in nano-sized metallic glasses. This work demonstrates that the nano-induced failure-suppression size effect that emerges in small-scale metallic glasses can be proliferated to larger-scale materials by the virtue of architecting.", "doi": "10.1016/j.actamat.2017.05.019", "issn": "1359-6454", "publisher": "Elsevier", "publication": "Acta Materialia", "publication_date": "2017-07", "volume": "133", "pages": "393-407" }, { "id": "authors:fex7a-4jt57", "collection": "authors", "collection_id": "fex7a-4jt57", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170525-140501296", "type": "article", "title": "Osteogenic cell functionality on 3-dimensional nano-scaffolds with varying stiffness", "author": [ { "family_name": "Maggi", "given_name": "Alessandro", "clpid": "Maggi-A" }, { "family_name": "Allen", "given_name": "Jessica", "clpid": "Allen-J" }, { "family_name": "Desai", "given_name": "Tejal", "orcid": "0000-0003-3409-9208", "clpid": "Desai-T-A" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "Creating implants that lead to optimal bone remodeling has been a challenge for more than two decades because of a lack of thorough knowledge of cell behavior in three-dimensional (3D) environments Limitations in traditional fabrication techniques and difficulties in characterizing cell-scaffold interactions have limited our understanding of how factors like scaffold pore size and distribution, as well as stiffness affect cell response.\nTo date, cellular activity on 3D substrates with stiffness ranging from a few kPa to hundreds of MPa has been investigated extensively (Cui et al., 2009; Fu et al., 2011; Hulbert et al., 1970; Hollinger et al., 1996; Johnson and Herschler, 2011; Karageorgiou and Kaplan, 2005). Fabrication limitations have restricted scaffolds with strut dimensions on the order of a few microns, a size comparable to the dimensions of osteoblasts, to have compressive moduli ranging from 10 kPa to 200 kPa, which has limited our understanding of how scaffolds stiffness affects mineral deposition. Cell viability and functionality on 3D scaffolds with compressive moduli in the MPa range and with strut dimensions on the order of a few microns have not yet been reported. We employed two-photon lithography to create periodic 3D nano-architectures with \u223c99% porosity, \u223c2 \u03bcm strut diameters, and \u223c2\u20139 MPa structural stiffness to explore the influence of scaffold properties on the viability of osteoblasts in a microenvironment similar to that of natural bone. These nanolattices were made out of a polymeric core coated with different materials and had unit cells with tetrakaidecahedral geometry and a 25 \u03bcm pore size. The unit cells were tessellated in space to form a lattice with lateral dimensions of 200\u00d7200 \u03bcm and a height of 50 \u03bcm. Some of the polymer nanolattices were coated with a conformal 120 nm-thick layer of SiO_2, others were coated with 120 nm of Ti. All nanolattices had a \u223c20 nm-thick outermost layer of TiO_2. Osteogenic cells were grown on the nanolattices for 28 days and the resulting cell morphology and depositions were characterized via scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and Raman spectroscopy. These analyses revealed significant cell attachment and the presence of hydroxyapatite (Ca_(10)(PO_4)_6(OH)_2), tricalcium phosphate (Ca_3(PO_4)_2) and metaphosphates ([Ca_2(P_2O_7)]n), chemical species normally found in natural bone. Such osteogenic functionality suggests that 3-dimensional nano-architected materials can be used as effective scaffolds for cell growth and proliferation, which could eventually lead to the generation of better bone implants.", "doi": "10.1016/j.eml.2017.01.002", "issn": "2352-4316", "publisher": "Elsevier", "publication": "Extreme Mechanics Letters", "publication_date": "2017-05", "volume": "13", "pages": "1-9" }, { "id": "authors:wjn00-h8306", "collection": "authors", "collection_id": "wjn00-h8306", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170221-153709555", "type": "article", "title": "Functionalized 3D Architected Materials via Thiol-Michael Addition and Two-Photon Lithography", "author": [ { "family_name": "Yee", "given_name": "Daryl W.", "orcid": "0000-0002-4114-6167", "clpid": "Yee-Daryl-Wei-Liang" }, { "family_name": "Schulz", "given_name": "Michael D.", "orcid": "0000-0001-8499-6025", "clpid": "Schulz-Michael-D" }, { "family_name": "Grubbs", "given_name": "Robert H.", "orcid": "0000-0002-0057-7817", "clpid": "Grubbs-R-H" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "Fabrication of functionalized 3D architected materials is achieved by a facile method using functionalized acrylates synthesized via thiol-Michael addition, which are then polymerized using two-photon lithography. A wide variety of functional groups can be attached, from Boc-protected amines to fluoroalkanes. Modification of surface wetting properties and conjugation with fluorescent tags are demonstrated to highlight the potential applications of this technique.", "doi": "10.1002/adma.201605293", "pmcid": "PMC5529122", "issn": "0935-9648", "publisher": "Wiley", "publication": "Advanced Materials", "publication_date": "2017-04-25", "series_number": "16", "volume": "29", "issue": "16", "pages": "Art. No. 1605293" }, { "id": "authors:rhdd8-vpw91", "collection": "authors", "collection_id": "rhdd8-vpw91", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170414-085644069", "type": "article", "title": "Probing Microplasticity in Small-Scale FCC Crystals via Dynamic Mechanical Analysis", "author": [ { "family_name": "Ni", "given_name": "Xiaoyue", "clpid": "Ni-Xiaoyue" }, { "family_name": "Papanikolaou", "given_name": "Stefanos", "clpid": "Papanikolaou-S" }, { "family_name": "Vajente", "given_name": "Gabriele", "orcid": "0000-0002-7656-6882", "clpid": "Vajente-G" }, { "family_name": "Adhikari", "given_name": "Rana X.", "orcid": "0000-0002-5731-5076", "clpid": "Adhikari-R-X" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "In small-scale metallic systems, collective dislocation activity has been correlated with size effects in strength and with a steplike plastic response under uniaxial compression and tension. Yielding and plastic flow in these samples is often accompanied by the emergence of multiple dislocation avalanches. Dislocations might be active preyield, but their activity typically cannot be discerned because of the inherent instrumental noise in detecting equipment. We apply alternate current load perturbations via dynamic mechanical analysis during quasistatic uniaxial compression experiments on single crystalline Cu nanopillars with diameters of 500 nm and compute dynamic moduli at frequencies 0.1, 0.3, 1, and 10 Hz under progressively higher static loads until yielding. By tracking the collective aspects of the oscillatory stress-strain-time series in multiple samples, we observe an evolving dissipative component of the dislocation network response that signifies the transition from elastic behavior to dislocation avalanches in the globally preyield regime. We postulate that microplasticity, which is associated with the combination of dislocation avalanches and slow viscoplastic relaxations, is the cause of the dependency of dynamic modulus on the driving rate and the quasistatic stress. We construct a continuum mesoscopic dislocation dynamics model to compute the frequency response of stress over strain and obtain a consistent agreement with experimental observations. The results of our experiments and simulations present a pathway to discern and quantify correlated dislocation activity in the preyield regime of deforming crystals.", "doi": "10.1103/PhysRevLett.118.155501", "issn": "0031-9007", "publisher": "American Physical Society", "publication": "Physical Review Letters", "publication_date": "2017-04-14", "series_number": "15", "volume": "118", "issue": "15", "pages": "Art. No. 155501" }, { "id": "authors:avtjc-s1r31", "collection": "authors", "collection_id": "avtjc-s1r31", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170524-162636343", "type": "book_section", "title": "Computational modeling in design of endovascular Chemofilter device for removing toxins from blood", "book_title": "2017 IEEE Great Lakes Biomedical Conference (GLBC)", "author": [ { "family_name": "Maani", "given_name": "Nazanin", "clpid": "Maani-N" }, { "family_name": "Yee", "given_name": "Daryl", "orcid": "0000-0002-4114-6167", "clpid": "Yee-Daryl-Wei-Liang" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" }, { "family_name": "Nosonovsky", "given_name": "Micheal", "clpid": "Nosonovsky-M" }, { "family_name": "Hetts", "given_name": "Steven W.", "clpid": "Hetts-S-W" }, { "family_name": "Rayz", "given_name": "Vitaliy L.", "clpid": "Rayz-V-L" } ], "abstract": "Intra-arterial chemotherapy delivery (IAC) for treating cancer can lead to significant cardiac toxicity due to the drainage of excess drug to the systemic circulation. A catheter-based Chemofilter device temporarily inserted into the veins downstream of the tumor can remove chemotherapy drugs out of the blood stream right after these drugs have had their effect on the tumor. In this research, computational modeling is used to design the Chemofilter and optimize its hemodynamics performance.", "doi": "10.1109/GLBC.2017.7928894", "isbn": "978-1-5090-6358-1", "publisher": "IEEE", "place_of_publication": "Piscataway, NJ", "publication_date": "2017-04" }, { "id": "authors:rxz9q-apa82", "collection": "authors", "collection_id": "rxz9q-apa82", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170502-095652517", "type": "conference_item", "title": "Genomic DNA functionalized architected materials fabricated via two-photon lithography for drug capture", "author": [ { "family_name": "Yee", "given_name": "Daryl", "orcid": "0000-0002-4114-6167", "clpid": "Yee-Daryl-Wei-Liang" }, { "family_name": "Schulz", "given_name": "Michael D.", "orcid": "0000-0001-8499-6025", "clpid": "Schulz-M-D" }, { "family_name": "Blumenfeld", "given_name": "Carl", "clpid": "Blumenfeld-C-M" }, { "family_name": "Grubbs", "given_name": "Robert H.", "orcid": "0000-0002-0057-7817", "clpid": "Grubbs-R-H" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "Two photon lithog. has recently emerged as one of the most powerful tools for fabricating structures with\nvirtually any geometry. This architectural versatility renders these 3D polymer structures useful for many\ntechnol. applications, including drug delivery and tissue engineering. While significant headway has been made\nin understanding the physics of the two-photon process and the mech. properties of these architected structures, making these structures have the right functional groups still remains a challenge. This is esp. important if we want to utilize these structures for biomedical applications, as it is often necessary to have\ncontrol over the chem. functionality on the surface and/or in the vol. of these 3D materials. In this talk, we describe a facile method of fabricating functional architected materials via the use of a functional acrylate monomer synthesized via the thiol -Michael addn. We then demonstrate the application of this by fabricating amine-functionalized structures which are then post-functionalized with genomic DNA for use as a drug capture device.", "publisher": "Caltech Library", "publication_date": "2017-04" }, { "id": "authors:7xk0d-7gz70", "collection": "authors", "collection_id": "7xk0d-7gz70", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170518-104629829", "type": "book_section", "title": "Designing core-shell 3D photonic crystal lattices for negative refraction", "book_title": "Photonic and Phononic Properties of Engineered Nanostructures VII", "author": [ { "family_name": "Chernow", "given_name": "Victoria F.", "clpid": "Chernow-V-F" }, { "family_name": "Ng", "given_name": "Ryan C.", "orcid": "0000-0002-0527-9130", "clpid": "Ng-Ryan-C" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "contributor": [ { "family_name": "Adibi", "given_name": "Ali", "clpid": "Adibi-A" }, { "family_name": "Lin", "given_name": "Shawn-Yu", "clpid": "Lin-Shawn-Yu" }, { "family_name": "Scherer", "given_name": "Axel", "clpid": "Scherer-A" } ], "abstract": "We use a plane wave expansion method to define parameters for the fabrication of 3-dimensional (3D) core-shell photonic crystals (PhCs) with lattice geometries that are capable of all-angle negative refraction (AANR) in the midinfrared centered around 8.0 \u03bcm. We discuss the dependence of the AANR frequency range on the volume fraction of solid within the lattice and on the ratio of the low index core material to the high index shell material. Following the constraints set by simulations, we fabricate two types of nanolattice PhCs: (1) polymer core-germanium shell and (2) amorphous carbon core-germanium shell to enable experimental observation of 3D negative refraction and related dispersion phenomena at infrared and eventually optical frequencies.", "doi": "10.1117/12.2251545", "isbn": "9781510606654", "publisher": "Society of Photo-Optical Instrumentation Engineers (SPIE)", "place_of_publication": "San Francisco, CA", "publication_date": "2017-02-20", "pages": "Art. No. 101120G" }, { "id": "authors:njgwv-nbf18", "collection": "authors", "collection_id": "njgwv-nbf18", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170720-091304564", "type": "book_section", "title": "Light-emitting nanolattices with enhanced brightness", "book_title": "Light-Emitting Diodes: Materials, Devices, and Applications for Solid State Lighting XXI", "author": [ { "family_name": "Ng", "given_name": "Ryan C.", "orcid": "0000-0002-0527-9130", "clpid": "Ng-Ryan-C" }, { "family_name": "Mandal", "given_name": "Rajib", "clpid": "Mandal-R" }, { "family_name": "Anthony", "given_name": "Rebecca J.", "clpid": "Anthony-R-J" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "contributor": [ { "family_name": "Kim", "given_name": "Jong Kyu", "clpid": "Kim-Jong-Kyu" }, { "family_name": "Krames", "given_name": "Michael R.", "clpid": "Krames-M-R" }, { "family_name": "Tu", "given_name": "Li-Wei", "clpid": "Tu-Li-Wei" }, { "family_name": "Strassburg", "given_name": "Martin", "clpid": "Strassburg-M" } ], "abstract": "Three-dimensional (3D) photonic crystals have potential in solid state lighting applications due to their advantages over conventional planar thin film devices. Periodicity in a photonic crystal structure enables engineering of the density of states to improve spontaneous light emission according to Fermi's golden rule. Unlike planar thin films, which suffer significantly from total internal reflection, a 3D architectured structure is distributed in space with many non-flat interfaces, which facilitates a substantial enhancement in light extraction. We demonstrate the fabrication of 3D nano-architectures with octahedron geometry that utilize luminescing silicon nanocrystals as active media with an aluminum cathode and indium tin oxide anode towards the realization of a 3D light emitting device. The developed fabrication procedure allows charge to pass through the nanolattice between two contacts for electroluminescence. These initial fabrication efforts suggest that 3D nano-architected devices are realizable and can reach greater efficiencies than planar devices.", "doi": "10.1117/12.2250081", "isbn": "978-1-5106-0689-0", "publisher": "Society of Photo-Optical Instrumentation Engineers (SPIE)", "place_of_publication": "Bellingham, WA", "publication_date": "2017-02-16", "pages": "Art. No. 101241E" }, { "id": "authors:7azcc-mbe81", "collection": "authors", "collection_id": "7azcc-mbe81", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20161025-111520333", "type": "article", "title": "Enhanced strength and temperature dependence of mechanical properties of Li at small scales and its implications for Li metal anodes", "author": [ { "family_name": "Xu", "given_name": "Chen", "orcid": "0000-0002-9427-0161", "clpid": "Xu-Chen-MatSci" }, { "family_name": "Ahmad", "given_name": "Zeeshan", "clpid": "Ahmad-Zeeshan" }, { "family_name": "Aryanfar", "given_name": "Asghar", "orcid": "0000-0002-8890-077X", "clpid": "Aryanfar-Asghar" }, { "family_name": "Viswanathan", "given_name": "Venkatasubramanian", "clpid": "Viswanathan-Venkatasubramanian" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "Most next-generation Li ion battery chemistries require a functioning lithium metal (Li) anode. However, its application in secondary batteries has been inhibited because of uncontrollable dendrite growth during cycling. Mechanical suppression of dendrite growth through solid polymer electrolytes (SPEs) or through robust separators has shown the most potential for alleviating this problem. Studies of the mechanical behavior of Li at any length scale and temperature are limited because of its extreme reactivity, which renders sample preparation, transfer, microstructure characterization, and mechanical testing extremely challenging. We conduct nanomechanical experiments in an in situ scanning electron microscope and show that micrometer-sized Li attains extremely high strengths of 105 MPa at room temperature and of 35 MPa at 90 \u00b0C. We demonstrate that single-crystalline Li exhibits a power-law size effect at the micrometer and submicrometer length scales, with the strengthening exponent of \u22120.68 at room temperature and of \u22121.00 at 90 \u00b0C. We also report the elastic and shear moduli as a function of crystallographic orientation gleaned from experiments and first-principles calculations, which show a high level of anisotropy up to the melting point, where the elastic and shear moduli vary by a factor of \u223c4 between the stiffest and most compliant orientations. The emergence of such high strengths in small-scale Li and sensitivity of this metal's stiffness to crystallographic orientation help explain why the existing methods of dendrite suppression have been mainly unsuccessful and have significant implications for practical design of future-generation batteries.", "doi": "10.1073/pnas.1615733114", "pmcid": "PMC5224391", "issn": "0027-8424", "publisher": "National Academy of Sciences", "publication": "Proceedings of the National Academy of Sciences of the United States of America", "publication_date": "2017-01-03", "series_number": "1", "volume": "114", "issue": "1", "pages": "57-61" }, { "id": "authors:xvz0e-ccg60", "collection": "authors", "collection_id": "xvz0e-ccg60", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170105-164637698", "type": "article", "title": "Evidence for exceptional low temperature ductility in polycrystalline magnesium processed by severe plastic deformation", "author": [ { "family_name": "Figueiredo", "given_name": "Roberto B.", "clpid": "Figueiredo-R-B" }, { "family_name": "Sabbaghianrad", "given_name": "Shima", "clpid": "Sabbaghianrad-S" }, { "family_name": "Giwa", "given_name": "Adenike", "clpid": "Giwa-A" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" }, { "family_name": "Langdon", "given_name": "Terence G.", "clpid": "Langdon-T-G" } ], "abstract": "An investigation was conducted to examine the mechanical behavior and microstructure evolution during deformation of ultrafine-grained pure magnesium at low temperatures within the temperature range of 296\u2013373 K. Discs were processed by high-pressure torsion until saturation in grain refinement. Dynamic hardness testing revealed a gradual increase in strain rate sensitivity up to m \u2248 0.2. High ductility was observed in the ultrafine-grained magnesium including an exceptional elongation of \u223c360% in tension at room temperature and stable deformation in micropillar compression. Grain coarsening and an increase in frequency of grain boundaries with misorientations in the range 15\u00b0\u201345\u00b0 occurred during deformation in tension. The experimental evidence, when combined with an analysis of the deformation behavior, suggests that grain boundary sliding plays a key role in low strain rate deformation of pure magnesium when the grain sizes are at and below \u223c5 \u03bcm.", "doi": "10.1016/j.actamat.2016.09.054", "issn": "1359-6454", "publisher": "Elsevier", "publication": "Acta Materialia", "publication_date": "2017-01-01", "volume": "122", "pages": "322-331" }, { "id": "authors:7vw5s-81y27", "collection": "authors", "collection_id": "7vw5s-81y27", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170104-164339438", "type": "article", "title": "Ordering and dimensional crossovers in metallic glasses and liquids", "author": [ { "family_name": "Chen", "given_name": "David Z.", "clpid": "Chen-David-Z" }, { "family_name": "An", "given_name": "Qi", "orcid": "0000-0003-4838-6232", "clpid": "An-Qi" }, { "family_name": "Goddard", "given_name": "William A., III", "orcid": "0000-0003-0097-5716", "clpid": "Goddard-W-A-III" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "The atomic-level structures of liquids and glasses are amorphous, lacking long-range order. We characterize the atomic structures by integrating radial distribution functions (RDF) from molecular dynamics (MD) simulations for several metallic liquids and glasses: Cu_(46)Zr_(54), Ni_(80)Al_(20), Ni_(33.3)Zr_(66.7), and Pd_(82)Si_(18). Resulting cumulative coordination numbers (CN) show that metallic liquids have a dimension of d=2.55\u00b10.06 from the center atom to the first coordination shell and metallic glasses have d=2.71\u00b10.04, both less than 3. Between the first and second coordination shells, both phases crossover to a dimension of d=3, as for a crystal. Observations from discrete atom center-of-mass position counting are corroborated by continuously counting Cu glass- and liquid-phase atoms on an artificial grid, which accounts for the occupied atomic volume. Results from Cu grid analysis show short-range d=2.65 for Cu liquid and d=2.76 for Cu glass. Cu grid structures crossover to d=3 at \u03be \u223c 8\u00c5 (\u223c3 atomic diameters). We study the evolution of local structural dimensions during quenching and discuss its correlation with the glass transition phenomenon.", "doi": "10.1103/PhysRevB.95.024103", "issn": "2469-9950", "publisher": "American Physical Society", "publication": "Physical Review B", "publication_date": "2017-01-01", "series_number": "2", "volume": "95", "issue": "2", "pages": "Art. No. 024103" }, { "id": "authors:2rtf6-pb168", "collection": "authors", "collection_id": "2rtf6-pb168", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20161107-113303591", "type": "article", "title": "Exceptional resilience of small-scale Au_(30)Cu_(25)Zn_(45) under cyclic stress-induced phase transformation", "author": [ { "family_name": "Ni", "given_name": "Xiaoyue", "clpid": "Ni-Xiaoyue" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" }, { "family_name": "Bhattacharya", "given_name": "Kaushik", "orcid": "0000-0003-2908-5469", "clpid": "Bhattacharya-K" }, { "family_name": "James", "given_name": "Richard D.", "orcid": "0000-0001-6019-6613", "clpid": "James-R-D" }, { "family_name": "Chen", "given_name": "Xian", "clpid": "Chen-Xian" } ], "abstract": "Shape memory alloys that produce and recover from large deformation driven by martensitic transformation are widely exploited in biomedical devices and micro-actuators. Generally their actuation work degrades significantly within first a few cycles, and is reduced at smaller dimensions. Further, alloys exhibiting unprecedented reversibility have relatively small superelastic strain, 0.7%. These raise the questions of whether high reversibility is necessarily accompanied by small work and strain, and whether high work and strain is necessarily diminished at small scale. Here we conclusively demonstrate that these are not true by showing that Au_(30)Cu_(25)Zn_(45) pillars exhibit 12 MJ m^(\u22123) work and 3.5% superelastic strain even after 100,000 phase transformation cycles. Our findings confirm that the lattice compatibility dominates themechanical behavior of phase-changing materials at nano to micron scales, and points a way for smart micro-actuators design having the mutual benefits of high actuation work and long lifetime.", "doi": "10.1021/acs.nanolett.6b03555", "issn": "1530-6984", "publisher": "American Chemical Society", "publication": "Nano Letters", "publication_date": "2016-12-14", "series_number": "12", "volume": "16", "issue": "12", "pages": "7621-7625" }, { "id": "authors:76hkv-kk416", "collection": "authors", "collection_id": "76hkv-kk416", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20160630-153358460", "type": "article", "title": "The nanocomposite nature of bone drives its strength and damage resistance", "author": [ { "family_name": "Tertuliano", "given_name": "Ottman", "clpid": "Tertuliano-O" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "In human bone, an amorphous mineral serves as a precursor to the formation of a highly substituted nanocrystalline apatite. However, the precise role of this amorphous mineral remains unknown. Here, we show by using transmission electron microscopy that 100\u2013300\u2009nm amorphous calcium phosphate regions are present in the disordered phase of trabecular bone. Nanomechanical experiments on cylindrical samples, with diameters between 250\u2009nm and 3,000\u2009nm, of the bone's ordered and disordered phases revealed a transition from plastic deformation to brittle failure and at least a factor-of-2\u2009higher strength in the smaller samples. We postulate that this transition in failure mechanism is caused by the suppression of extrafibrillar shearing in the smaller samples, and that the emergent smaller-is-stronger size effect is related to the sample-size scaling of the distribution of flaws. Our findings should help in the understanding of the multi-scale nature of bone and provide insights into the biomineralization process.", "doi": "10.1038/nmat4719", "issn": "1476-1122", "publisher": "Nature Publishing Group", "publication": "Nature Materials", "publication_date": "2016-11", "series_number": "11", "volume": "15", "issue": "11", "pages": "1195-1202" }, { "id": "authors:494cf-mfa97", "collection": "authors", "collection_id": "494cf-mfa97", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20160815-090908420", "type": "article", "title": "Substantial tensile ductility in sputtered Zr-Ni-Al nano-sized metallic glass", "author": [ { "family_name": "Liontas", "given_name": "Rachel", "clpid": "Liontas-R" }, { "family_name": "Jafary-Zadeh", "given_name": "Mehdi", "clpid": "Jafary-Zadeh-M" }, { "family_name": "Zeng", "given_name": "Qiaoshi", "clpid": "Zeng-Qiaoshi" }, { "family_name": "Zhang", "given_name": "Yong-Wei", "clpid": "Zhang-Yong-Wei" }, { "family_name": "Mao", "given_name": "Wendy L.", "clpid": "Mao-Wendy-L" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "We investigate the mechanical behavior and atomic-level structure of glassy Zr-Ni-Al nano-tensile specimens with widths between 75 and 215 nm. We focus our studies on two different energy states: (1) as-sputtered and (2) sputtered then annealed below the glass transition temperature (T_g). In-situ tensile experiments conducted inside a scanning electron microscope (SEM) reveal substantial tensile ductility in some cases reaching >10% engineering plastic strains, >150% true plastic strains, and necking down to a point during tensile straining in specimens as wide as \u223c150 nm. We found the extent of ductility depends on both the specimen size and the annealing conditions. Using molecular dynamics (MD) simulations, transmission electron microscopy (TEM), and synchrotron x-ray diffraction (XRD), we explain the observed mechanical behavior through changes in free volume as well as short- and medium-range atomic-level order that occur upon annealing. This work demonstrates the importance of carefully choosing the metallic glass fabrication method and post-processing conditions for achieving a certain atomic-level structure and free volume within the metallic glass, which then determine the overall mechanical response. An important implication is that sputter deposition may be a particularly promising technique for producing thin coatings of metallic glasses with significant ductility, due to the high level of disorder and excess free volume resulting from the sputtering process and to the suitability of sputtering for producing thin coatings that may exhibit enhanced size-induced ductility.", "doi": "10.1016/j.actamat.2016.07.050", "issn": "1359-6454", "publisher": "Elsevier", "publication": "Acta Materialia", "publication_date": "2016-10-01", "volume": "118", "pages": "270-285" }, { "id": "authors:66t8m-05s45", "collection": "authors", "collection_id": "66t8m-05s45", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20160815-085245379", "type": "article", "title": "In Situ Lithiation\u2013Delithiation of Mechanically Robust Cu\u2013Si Core\u2013Shell Nanolattices in a Scanning Electron Microscope", "author": [ { "family_name": "Xia", "given_name": "Xiaoxing", "orcid": "0000-0003-1255-3289", "clpid": "Xia-Xiaoxing" }, { "family_name": "Di Leo", "given_name": "Claudio V.", "orcid": "0000-0002-3410-6677", "clpid": "Di-Leo-C-V" }, { "family_name": "Gu", "given_name": "X. Wendy", "clpid": "Gu-X-Wendy" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "Nanoarchitected Cu\u2013Si core\u2013shell lattices were fabricated via two-photon lithography and tested as mechanically robust Li-ion battery electrodes which accommodate \u223c250% Si volume expansion during lithiation. The superior mechanical performance of the nanolattice electrodes is directly observed using an in situ scanning electron microscope, which allows volume expansion and morphological changes to be imaged at multiple length scales, from single lattice beam to the architecture level, during electrochemical testing. Finite element modeling of lithiation-induced volume expansion in a core\u2013shell structure reveals that geometry and plasticity mechanisms play a critical role in preventing damage in the nanolattice electrodes. The two-photon lithography-based fabrication method combined with computational modeling and in situ characterization capabilities would potentially enable the rational design and fast discovery of mechanically robust and kinetically agile electrode materials that independently optimize geometry, feature size, porosity, surface area, and chemical composition, as well as other functional devices in which mechanical and transport phenomena are important.", "doi": "10.1021/acsenergylett.6b00256", "issn": "2380-8195", "publisher": "American Chemical Society", "publication": "ACS Energy Letters", "publication_date": "2016-09-09", "series_number": "3", "volume": "1", "issue": "3", "pages": "492-499" }, { "id": "authors:zc963-5n416", "collection": "authors", "collection_id": "zc963-5n416", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170711-073658776", "type": "article", "title": "Microstructure and small-scale size effects in plasticity of individual phases of Al_(0.7)CoCrFeNi High Entropy alloy", "author": [ { "family_name": "Giwa", "given_name": "Adenike M.", "clpid": "Giwa-A-M" }, { "family_name": "Liaw", "given_name": "Peter K.", "clpid": "Liaw-P-K" }, { "family_name": "Dahmen", "given_name": "Karin A.", "clpid": "Dahmen-K-A" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "High Entropy alloys (HEAs) are solid solution alloys containing five or more principal elements in equal or near equal atomic percent (at %). We synthesized Al_(0.7)CoCrFeNi HEA by vacuum arc melting and homogenized it at 1250 \u00b0C for 50 h. The microstructure shows the presence of two phases: the Body-Centered Cubic (BCC: A2+B2) and the Face-Centered Cubic (FCC). Using the Focused Ion Beam, we fabricated single-crystalline cylindrical nano-pillars from each phase within individual grains in the Al_(0.7)CoCrFeNi HEA. These nano-pillars had diameters ranging from 400 nm to 2 \u03bcm and were oriented in the [324] direction for the FCC phase and in the [001] direction for the BCC phase. Uniaxial compression experiments revealed that the yield strength is 2.2 GPa for the 400 nm diameter samples in the BCC phase and 1.2 GPa for the equivalent diameter samples in the FCC phase. We observed the presence of a size-effect in both phases, with smaller pillars having substantially greater strengths compared with bulk and with larger-sized samples. The size-effect power exponent for the BCC phase was \u22120.28, which is lower than that of most pure BCC metals, and the FCC phase had the exponent of \u22120.66, equivalent to most pure FCC metals. We discuss these results in the framework of nano-scale plasticity and the intrinsic lattice resistance through the interplay of the internal (microstructural) and external (dimensional) size effects.", "doi": "10.1016/j.eml.2016.04.013", "issn": "2352-4316", "publisher": "Elsevier", "publication": "Extreme Mechanics Letters", "publication_date": "2016-09", "volume": "8", "pages": "220-228" }, { "id": "authors:mzs18-myv06", "collection": "authors", "collection_id": "mzs18-myv06", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20160615-160058302", "type": "article", "title": "An instrument to measure mechanical up-conversion phenomena in metals in the elastic regime", "author": [ { "family_name": "Vajente", "given_name": "G.", "orcid": "0000-0002-7656-6882", "clpid": "Vajente-G" }, { "family_name": "Quintero", "given_name": "E. A.", "clpid": "Quintero-E-A" }, { "family_name": "Ni", "given_name": "X.", "clpid": "Ni-X" }, { "family_name": "Arai", "given_name": "K.", "clpid": "Arai-K" }, { "family_name": "Gustafson", "given_name": "E. K.", "clpid": "Gustafson-E-K" }, { "family_name": "Robertson", "given_name": "N. A.", "clpid": "Robertson-N-A" }, { "family_name": "Sanchez", "given_name": "E. J.", "clpid": "Sanchez-E-J" }, { "family_name": "Greer", "given_name": "J. R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" }, { "family_name": "Adhikari", "given_name": "R. X.", "orcid": "0000-0002-5731-5076", "clpid": "Adhikari-R-X" } ], "abstract": "Crystalline materials, such as metals, are known to exhibit deviation from a simple linear relation between strain and stress when the latter exceeds the yield stress. In addition, it has been shown that metals respond to varying external stress in a discontinuous way in this regime, exhibiting discrete releases of energy. This crackling noise has been extensively studied both experimentally and theoretically when the metals are operating in the plastic regime. In our study, we focus on the behavior of metals in the elastic regime, where the stresses are well below the yield stress. We describe an instrument that aims to characterize non-linear mechanical noise in metals when stressed in the elastic regime. In macroscopic systems, this phenomenon is expected to manifest as a non-stationary noise modulated by external disturbances applied to the material, a form of mechanical up-conversion of noise. The main motivation for this work is for the case of maraging steel components (cantilevers and wires) in the suspension systems of terrestrial gravitational wave detectors. Such instruments are planned to reach very ambitious displacement sensitivities, and therefore mechanical noise in the cantilevers could prove to be a limiting factor for the detectors' final sensitivities, mainly due to non-linear up-conversion of low frequency residual seismic motion to the frequencies of interest for the gravitational wave observations. We describe here the experimental setup, with a target sensitivity of 10^(\u221215) m/\u221aHz in the frequency range of 10\u20131000 Hz, a simple phenomenological model of the non-linear mechanical noise, and the analysis method that is inspired by this model.", "doi": "10.1063/1.4953114", "issn": "0034-6748", "publisher": "American Institute of Physics", "publication": "Review of Scientific Instruments", "publication_date": "2016-06", "series_number": "6", "volume": "87", "issue": "6", "pages": "Art. No. 065107" }, { "id": "authors:6crj1-hpw46", "collection": "authors", "collection_id": "6crj1-hpw46", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20160601-065255489", "type": "article", "title": "Cross-Split of Dislocations: An Athermal and Rapid Plasticity Mechanism", "author": [ { "family_name": "Kositski", "given_name": "Roman", "clpid": "Kositski-Roman" }, { "family_name": "Kovalenko", "given_name": "Oleg", "clpid": "Kovalenko-Oleg" }, { "family_name": "Lee", "given_name": "Seok-Woo", "orcid": "0000-0001-6752-5694", "clpid": "Lee-Seok-Woo" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" }, { "family_name": "Rabkin", "given_name": "Eugen", "orcid": "0000-0001-5545-1261", "clpid": "Rabkin-Eugen" }, { "family_name": "Mordehai", "given_name": "Dan", "orcid": "0000-0001-8523-7362", "clpid": "Mordehai-Dan" } ], "abstract": "The pathways by which dislocations, line defects within the lattice structure, overcome microstructural obstacles represent a key aspect in understanding the main mechanisms that control mechanical properties of ductile crystalline materials. While edge dislocations were believed to change their glide plane only by a slow, non-conservative, thermally activated motion, we suggest the existence of a rapid conservative athermal mechanism, by which the arrested edge dislocations split into two other edge dislocations that glide on two different crystallographic planes. This discovered mechanism, for which we coined a term \"cross-split of edge dislocations\", is a unique and collective phenomenon, which is triggered by an interaction with another same-sign pre-existing edge dislocation. This mechanism is demonstrated for faceted \u03b1-Fe nanoparticles under compression, in which we propose that cross-split of arrested edge dislocations is resulting in a strain burst. The cross-split mechanism provides an efficient pathway for edge dislocations to overcome planar obstacles.", "doi": "10.1038/srep25966", "pmcid": "PMC4869067", "issn": "2045-2322", "publisher": "Nature Publishing Group", "publication": "Scientific Reports", "publication_date": "2016-05-17", "volume": "6", "pages": "Art. No. 25966" }, { "id": "authors:9vf2k-ars41", "collection": "authors", "collection_id": "9vf2k-ars41", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20160406-102411816", "type": "conference_item", "title": "Fractal arrangement of atomic structures in metallic glasses", "author": [ { "family_name": "Chen", "given_name": "D.", "clpid": "Chen-D" }, { "family_name": "Shi", "given_name": "C.", "clpid": "Shi-C" }, { "family_name": "An", "given_name": "Q.", "orcid": "0000-0003-4838-6232", "clpid": "An-Qi" }, { "family_name": "Zeng", "given_name": "Q.", "clpid": "Zeng-Q" }, { "family_name": "Mao", "given_name": "W.", "clpid": "Mao-W" }, { "family_name": "Goddard", "given_name": "W.", "orcid": "0000-0003-0097-5716", "clpid": "Goddard-W-A-III" }, { "family_name": "Greer", "given_name": "Julia", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "Understanding and properly describing at.-level structure in metallic glasses and other amorphous materials\nrepresents a long-standing and significant scientific problem. Metallic glasses have been shown to exhibit\nanomalous non-cubic scaling in vol. with respect to their first diffraction peak position, , with a power law\nexponent in the range of \u223c2.3-2.5. This range of exponent values is characteristic of fractals, and, in contrast\nto crystals, where the exponent is always 3, suggests that the at. structure in metallic glasses may be\nfractal. However, the nature of this underlying fractal structure is ambiguous. Our in-situ x-ray tomog.\nmeasurements of the sample vol. along with corresponding x-ray diffraction data shows a shift in this power law\nexponent with measurements of the second diffraction peak, . We also show a crossover in the scaling behavior\nfrom exponent \u223c2.5 (fractal) to \u223c3 (homogeneous) that occurs at the second and third nearest neighbor\npositions, , in the real space radial distribution functions as a function of hydrostatic pressure for three distinct\nsimulated metallic glasses. These results are explained using continuum percolation theory where the at.\nstructure has a correlation length, . Expts., simulations, and theory on multiple glass compns. all corroborate\nthat the at. structure is well described by a specific class of fractal, the percolation cluster, demonstrating a\nunifying picture of how long-range structure may organize without order in metallic glasses. The long-range\nstructural detail afforded by this model may have significant implications on the phys. properties of glasses as\nwell as the origin of the glass transition phenomenon.", "publisher": "Caltech Library", "publication_date": "2016-03" }, { "id": "authors:9by64-d9j62", "collection": "authors", "collection_id": "9by64-d9j62", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20160125-140843363", "type": "article", "title": "Suppression of surface recombination in CuInSe_2 (CIS) thin films via Trioctylphosphine Sulfide (TOP:S) surface passivation", "author": [ { "family_name": "Luo", "given_name": "Shi", "clpid": "Luo-Shi" }, { "family_name": "Eisler", "given_name": "Carissa", "orcid": "0000-0002-5755-5280", "clpid": "Eisler-C-N" }, { "family_name": "Wong", "given_name": "Tsun-Hsin", "clpid": "Wong-Tsun-Hsin" }, { "family_name": "Xiao", "given_name": "Hai", "orcid": "0000-0001-9399-1584", "clpid": "Xiao-Hai" }, { "family_name": "Lin", "given_name": "Chuan-En", "clpid": "Lin-Chuan-En" }, { "family_name": "Wu", "given_name": "Tsung-Ta", "clpid": "Wu-Tsung-Ta" }, { "family_name": "Shen", "given_name": "Chang-Hong", "clpid": "Shen-Chang-Hong" }, { "family_name": "Shieh", "given_name": "Jia-Min", "clpid": "Shieh-Jia-Min" }, { "family_name": "Tsai", "given_name": "Chuang-Chuang", "clpid": "Tsai-Chuang-Chuang" }, { "family_name": "Liu", "given_name": "Chee-Wee", "clpid": "Liu-Chee-Wee" }, { "family_name": "Atwater", "given_name": "Harry A.", "orcid": "0000-0001-9435-0201", "clpid": "Atwater-H-A" }, { "family_name": "Goddard", "given_name": "William A., III", "orcid": "0000-0003-0097-5716", "clpid": "Goddard-W-A-III" }, { "family_name": "Lee", "given_name": "Jiun-Haw", "clpid": "Lee-Jiun-Haw" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "CuInSe_2 (CIS) solar cells are promising candidates for thin film photovoltaic applications, one key limitation in their performance is surface recombination in these thin films. We demonstrate that passivating CIS films with Trioctylphosphine Sulfide (TOP:S) solution increases photoluminescence (PL) intensity by a factor of \u223c30, which suggests that this passivation significantly reduces surface recombination. X-ray photoelectron spectroscopy (XPS) reveals that TOP:S forms both \u2013S and \u2013P bonds on the CIS film surface, which leads to a \u223c4-fold increase in the surface Na peak intensity. This value is significantly higher than what would be expected from high temperature annealing alone, which has been linked to improvements in surface morphology and device efficiency in CIGS solar cells. We use Energy-Dispersive X-ray Spectroscopy (EDS) to measure the solid-state transport of Na within CIS films with and without passivation. EDS spectra on CIS film cross-sections reveals a saddle-shaped Na profile in the as-fabricated films and a concentration gradient towards the film surface in the passivated films, with 20% higher surface Na content compared with the unpassivated films. We employ Hybrid (B3PW91) Density Functional Theory (DFT) to gain insight into energetics of Na defects, which demonstrate a driving force for Na diffusion from bulk towards the surface. DFT Calculations with TOP:S-like molecules on the same surfaces reveal a \u223c 1eV lower formation energy for the Na_(Cu) defect. The experiments and computations in this work suggest that TOP:S passivation promotes Na diffusion towards CIS film surfaces and stabilizes surface Na defects, which leads to the observed substantial decrease in surface recombination.", "doi": "10.1016/j.actamat.2016.01.021", "issn": "1359-6454", "publisher": "Elsevier", "publication": "Acta Materialia", "publication_date": "2016-03", "volume": "106", "pages": "171-181" }, { "id": "authors:wqgkc-ytf88", "collection": "authors", "collection_id": "wqgkc-ytf88", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20160208-125648420", "type": "article", "title": "Microstructure provides insights into evolutionary design and resilience of Coscinodiscus sp. frustule", "author": [ { "family_name": "Aitken", "given_name": "Zachary H.", "clpid": "Aitken-Zachary-H" }, { "family_name": "Luo", "given_name": "Shi", "clpid": "Luo-Shi" }, { "family_name": "Reynolds", "given_name": "Stephanie N.", "clpid": "Reynolds-Stephanie-N" }, { "family_name": "Thaulow", "given_name": "Christian", "clpid": "Thaulow-Christian" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "We conducted in situ three-point bending experiments on beams with roughly square cross-sections, which we fabricated from the frustule of Coscinodiscus sp. We observe failure by brittle fracture at an average stress of 1.1 GPa. Analysis of crack propagation and shell morphology reveals a differentiation in the function of the frustule layers with the basal layer pores, which deflect crack propagation. We calculated the relative density of the frustule to be \u223c30% and show that at this density the frustule has the highest strength-to-density ratio of 1,702 kN\u22c5m/kg, a significant departure from all reported biologic materials. We also performed nanoindentation on both the single basal layer of the frustule as well as the girdle band and show that these components display similar mechanical properties that also agree well with bending tests. Transmission electron microscopy analysis reveals that the frustule is made almost entirely of amorphous silica with a nanocrystalline proximal layer. No flaws are observed within the frustule material down to 2 nm. Finite element simulations of the three-point bending experiments show that the basal layer carries most of the applied load whereas stresses within the cribrum and areolae layer are an order of magnitude lower. These results demonstrate the natural development of architecture in live organisms to simultaneously achieve light weight, strength, and exceptional structural integrity and may provide insight into evolutionary design.", "doi": "10.1073/pnas.1519790113", "pmcid": "PMC4776537", "issn": "0027-8424", "publisher": "National Academy of Sciences", "publication": "Proceedings of the National Academy of Sciences of the United States of America", "publication_date": "2016-02-23", "series_number": "8", "volume": "113", "issue": "8", "pages": "2017-2022" }, { "id": "authors:f25dn-3qb53", "collection": "authors", "collection_id": "f25dn-3qb53", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20160208-092709587", "type": "article", "title": "Insensitivity to Flaws Leads to Damage Tolerance in Brittle Architected Meta-Materials", "author": [ { "family_name": "Montemayor", "given_name": "L. C.", "clpid": "Montemayor-L-C" }, { "family_name": "Wong", "given_name": "W. H.", "clpid": "Wong-W-H" }, { "family_name": "Zhang", "given_name": "Y.-W.", "clpid": "Zhang-Y-W" }, { "family_name": "Greer", "given_name": "J. R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "Cellular solids are instrumental in creating lightweight, strong, and damage-tolerant engineering materials. By extending feature size down to the nanoscale, we simultaneously exploit the architecture and material size effects to substantially enhance structural integrity of architected meta-materials. We discovered that hollow-tube alumina nanolattices with 3D kagome geometry that contained pre-fabricated flaws always failed at the same load as the pristine specimens when the ratio of notch length (\u0251) to sample width (w) is no greater than 1/3, with no correlation between failure occurring at or away from the notch. Samples with (\u0251/w)\u2009>\u20090.3, and notch length-to-unit cell size ratios of (\u0251/l)\u2009>\u20095.2, failed at a lower peak loads because of the higher sample compliance when fewer unit cells span the intact region. Finite element simulations show that the failure is governed by purely tensile loading for (\u0251/w)\u2009<\u20090.3 for the same (\u0251/l); bending begins to play a significant role in failure as (\u0251/w) increases. This experimental and computational work demonstrates that the discrete-continuum duality of architected structural meta-materials may give rise to their damage tolerance and insensitivity of failure to the presence of flaws even when made entirely of intrinsically brittle materials.", "doi": "10.1038/srep20570", "pmcid": "PMC4738344", "issn": "2045-2322", "publisher": "Nature Publishing Group", "publication": "Scientific Reports", "publication_date": "2016-02-03", "volume": "6", "pages": "Art. No. 20570" }, { "id": "authors:2whmw-5jr13", "collection": "authors", "collection_id": "2whmw-5jr13", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20151103-104811137", "type": "article", "title": "Tunable Microfibers Suppress Fibrotic Encapsulation via Inhibition of TGF\u03b2 Signaling", "author": [ { "family_name": "Allen", "given_name": "Jessica", "clpid": "Allen-Jesscia" }, { "family_name": "Ryu", "given_name": "Jubin", "clpid": "Ryu-Jubin" }, { "family_name": "Maggi", "given_name": "Alessandro", "clpid": "Maggi-A" }, { "family_name": "Flores", "given_name": "Bianca", "clpid": "Flores-B" }, { "family_name": "Greer", "given_name": "Julia", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" }, { "family_name": "Desai", "given_name": "Tejal", "orcid": "0000-0003-3409-9208", "clpid": "Desai-T-A" } ], "abstract": "Fibrotic encapsulation limits the efficacy and lifetime of implantable biomedical devices. Microtopography has shown promise in the regulation of myofibroblast differentiation, a key driver of fibrotic encapsulation. However, existing studies have not systematically isolated the requisite geometric parameters for suppression of myofibroblast differentiation via microtopography, and there has not been in vivo validation of this technology to date. To address these issues, a novel lamination method was developed to afford more control over topography dimensions. Specifically, in this study we focus on fiber length and its effect on myofibroblast differentiation. Fibroblasts cultured on films with microfibers exceeding 16 \u03bcm in length lost the characteristic morphology associated with myofibroblast differentiation, while shorter microfibers of 6 \u03bcm length failed to produce this phenotype. This increase in length corresponded to a 50% decrease in fiber stiffness, which acts as a mechanical cue to influence myofibroblast differentiation. Longer microfiber films suppressed expression of myofibroblast specific genes (\u03b1SMA, Col1\u03b12, and Col3\u03b11) and TGF\u03b2 signaling components (TGF\u03b21 ligand, TGF\u03b2 receptor II, and Smad3). 16 \u03bcm long microfiber films implanted subcutaneously in a mouse wound-healing model generated a substantially thinner fibrotic capsule and less deposition of collagen in the wound bed. Together, these results identify a critical feature length threshold for microscale topography-mediated repression of fibrotic encapsulation. This study also demonstrates a simple and powerful strategy to improve surface biocompatibility and reduce fibrotic encapsulation around implanted materials.", "doi": "10.1089/ten.TEA.2015.0087", "pmcid": "PMC5802271", "issn": "1937-3341", "publisher": "Mary Ann Liebert", "publication": "Tissue Engineering Part A", "publication_date": "2016-01-15", "series_number": "1-2", "volume": "22", "issue": "1-2", "pages": "142-150" }, { "id": "authors:kyrzx-29p78", "collection": "authors", "collection_id": "kyrzx-29p78", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20160705-130213482", "type": "monograph", "title": "Percolation structure in metallic glasses and liquids", "author": [ { "family_name": "Chen", "given_name": "David Z.", "clpid": "Chen-David-Z" }, { "family_name": "An", "given_name": "Qi", "orcid": "0000-0003-4838-6232", "clpid": "An-Qi" }, { "family_name": "Goddard", "given_name": "William A., III", "orcid": "0000-0003-0097-5716", "clpid": "Goddard-W-A-III" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "The atomic-level structures of liquids and glasses are similar, obscuring any structural basis for the glass transition. To delineate structural differences between them, we characterized the atomic structures using the integrated radial distribution functions (RDF) from molecular dynamics (MD) simulations for several metallic liquids and glasses: Cu_(46)Zr_(54), Ni_(80)Al_(20),\nNi_(33.3)Zr_(66.7), and Pd_(82)Si_(18). We find that the integrated RDF leads to cumulative coordination numbers (CN) that are similar for all four metallic glasses and for all four liquids, but are consistently different between the liquid and glass phases. We find that metallic liquids have a fractal dimension of df = 2.54 \u00b1 0.06 from the center atom to the first coordination shell whereas the metallic glasses have d_f = 2.66 \u00b1 0.04, which suggests the development of weak ordering during the glass transition. Beyond the second coordination shell, the CN indicates a dimension of d = 3 as for a crystal. Crossovers in dimension from d_f~2.54-2.66 to d = 3 between the first and second coordination shells imply an underlying percolation structure in metallic liquids and glasses.", "doi": "10.48550/arXiv.1601.02057", "publication_date": "2016-01-09" }, { "id": "authors:8erwj-a7w25", "collection": "authors", "collection_id": "8erwj-a7w25", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180302-142244426", "type": "book_section", "title": "Size-Dependent Plasticity of Single Crystalline Metallic Nanostructures", "book_title": "Encyclopedia of Nanotechnology", "author": [ { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "contributor": [ { "family_name": "Bhushan", "given_name": "Bharat", "clpid": "Bhushan-B" } ], "abstract": "\"Size-dependent plasticity\" here refers to the strength of metallic samples being a strong function of their size when their dimensions are reduced to the micron and below scales. The notion of reduced sample size applies to all three dimensions, i.e., stand-alone, or one-dimensional\n(1D) nano and microstructures rather than thin films (2D), where only their thicknesses are reduced to nano- and micro-scales, or to the small-scale deformation volumes within a bulk matrix (3D) as would be the case during nanoindentation experiments, for example.", "doi": "10.1007/978-94-017-9780-1", "isbn": "978-94-017-9779-5", "publisher": "Springer", "place_of_publication": "Dordrecht", "publication_date": "2016", "pages": "3713-3719" }, { "id": "authors:6ra9w-8ya71", "collection": "authors", "collection_id": "6ra9w-8ya71", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170711-072842008", "type": "article", "title": "Surface roughness imparts tensile ductility to nanoscale metallic glasses", "author": [ { "family_name": "Adibi", "given_name": "Sara", "clpid": "Adibi-S" }, { "family_name": "Branicio", "given_name": "Paulo S.", "clpid": "Branicio-P-S" }, { "family_name": "Liontas", "given_name": "Rachel", "clpid": "Liontas-R" }, { "family_name": "Chen", "given_name": "David Z.", "clpid": "Chen-David-Z" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" }, { "family_name": "Srolovitz", "given_name": "David J.", "clpid": "Srolovitz-D-J" }, { "family_name": "Joshi", "given_name": "Shailendra P.", "clpid": "Joshi-S-P" } ], "abstract": "Experiments show an intriguing brittle-to-ductile transition on size reduction on nanoscale metallic glasses (MGs). Here we demonstrate that such phenomena is linked to a fundamental characteristic size effect in the failure mode under tensile loading. Large-scale molecular dynamics simulations reveal that nanoscaled MGs with atomistically smooth surfaces exhibit catastrophic failure via sharp, localized shear band propagation. In contrast, nanosized specimens with surface imperfections exhibit a clear transition from shear banding to necking instability above a critical roughness ratio of \u2008\u03be \u223c 1/20, defined as the ratio between the average surface imperfection size and sample diameter. The observed brittle-to-ductile transition that emerges in nanosized MGs deformed at room temperature can be strongly attributed to this roughness argument. In addition, the results suggest that the suppression of brittle failure may be scale-free and be realizable on length scales much beyond those considered here, provided the threshold roughness ratio is exceeded. The fundamental critical roughness ratio demonstrated sheds light on the complex mechanical behavior of amorphous metals and has implications for the application of MGs in nano- and micro-devices.", "doi": "10.1016/j.eml.2015.08.004", "issn": "2352-4316", "publisher": "Elsevier", "publication": "Extreme Mechanics Letters", "publication_date": "2015-12", "volume": "5", "pages": "88-95" }, { "id": "authors:hf2g8-37e70", "collection": "authors", "collection_id": "hf2g8-37e70", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20151201-141224356", "type": "article", "title": "Universal Quake Statistics: From Compressed Nanocrystals to Earthquakes", "author": [ { "family_name": "Uhl", "given_name": "Jonathan T.", "clpid": "Uhl-Jonathan-T" }, { "family_name": "Pathak", "given_name": "Shivesh", "orcid": "0000-0001-7279-8195", "clpid": "Pathak-Shivesh" }, { "family_name": "Schorlemmer", "given_name": "Danijel", "orcid": "0000-0003-3969-1059", "clpid": "Schorlemmer-Danijel" }, { "family_name": "Liu", "given_name": "Xin", "orcid": "0000-0003-0049-5210", "clpid": "Liu-Xin" }, { "family_name": "Swindeman", "given_name": "Ryan", "clpid": "Swindeman-Ryan" }, { "family_name": "Brinkman", "given_name": "Braden A. W.", "orcid": "0000-0002-2572-8861", "clpid": "Brinkman-Braden-A-W" }, { "family_name": "LeBlanc", "given_name": "Michael", "clpid": "LeBlanc-Michael" }, { "family_name": "Tsekenis", "given_name": "Georgios", "orcid": "0000-0002-9156-7840", "clpid": "Tsekenis-Georgios" }, { "family_name": "Friedman", "given_name": "Nir", "orcid": "0000-0002-9678-3550", "clpid": "Friedman-Nir" }, { "family_name": "Behringer", "given_name": "Robert", "orcid": "0000-0003-2499-2182", "clpid": "Behringer-Robert" }, { "family_name": "Denisov", "given_name": "Dmitry", "clpid": "Denisov-Dmitry" }, { "family_name": "Schall", "given_name": "Peter", "clpid": "Schall-Peter" }, { "family_name": "Gu", "given_name": "Xiaojun", "clpid": "Gu-Xiaojun" }, { "family_name": "Wright", "given_name": "Wendelin J.", "orcid": "0000-0001-6493-6025", "clpid": "Wright-Wendelin-J" }, { "family_name": "Hufnagel", "given_name": "Todd", "orcid": "0000-0002-6373-9377", "clpid": "Hufnagel-Todd" }, { "family_name": "Jennings", "given_name": "Andrew", "clpid": "Jennings-Andrew-T" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" }, { "family_name": "Liaw", "given_name": "P. K.", "clpid": "Liaw-P-K" }, { "family_name": "Becker", "given_name": "Thorsten", "orcid": "0000-0002-5656-4564", "clpid": "Becker-Thorsten" }, { "family_name": "Dresen", "given_name": "Georg", "orcid": "0000-0002-3737-2858", "clpid": "Dresen-Georg" }, { "family_name": "Dahmen", "given_name": "Karin A.", "clpid": "Dahmen-Karin-A" } ], "abstract": "Slowly-compressed single crystals, bulk metallic glasses (BMGs), rocks, granular materials, and the earth all deform via intermittent slips or \"quakes\". We find that although these systems span 12 decades in length scale, they all show the same scaling behavior for their slip size distributions and other statistical properties. Remarkably, the size distributions follow the same power law multiplied with the same exponential cutoff. The cutoff grows with applied force for materials spanning length scales from nanometers to kilometers. The tuneability of the cutoff with stress reflects \"tuned critical\" behavior, rather than self-organized criticality (SOC), which would imply stress-independence. A simple mean field model for avalanches of slipping weak spots explains the agreement across scales. It predicts the observed slip-size distributions and the observed stress-dependent cutoff function. The results enable extrapolations from one scale to another, and from one force to another, across different materials and structures, from nanocrystals to earthquakes.", "doi": "10.1038/srep16493", "pmcid": "PMC4647222", "issn": "2045-2322", "publisher": "Nature Publishing Group", "publication": "Scientific Reports", "publication_date": "2015-11-17", "volume": "5", "pages": "Art. No. 16493" }, { "id": "authors:hfd0t-xz645", "collection": "authors", "collection_id": "hfd0t-xz645", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150918-110856646", "type": "article", "title": "Fractal atomic-level percolation in metallic glasses", "author": [ { "family_name": "Chen", "given_name": "David Z.", "clpid": "Chen-David-Z" }, { "family_name": "Shi", "given_name": "Crystal Y.", "clpid": "Shi-Crystal-Y" }, { "family_name": "An", "given_name": "Qi", "orcid": "0000-0003-4838-6232", "clpid": "An-Qi" }, { "family_name": "Zeng", "given_name": "Qiaoshi", "clpid": "Zeng-Qiaoshi" }, { "family_name": "Mao", "given_name": "Wendy L.", "clpid": "Mao-Wendy-L" }, { "family_name": "Goddard", "given_name": "William A., III", "orcid": "0000-0003-0097-5716", "clpid": "Goddard-W-A-III" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "Metallic glasses are metallic alloys that exhibit exotic material properties. They may have fractal structures at the atomic level, but a physical mechanism for their organization without ordering has not been identified. We demonstrated a crossover between fractal short-range (<2 atomic diameters) and homogeneous long-range structures using in situ x-ray diffraction, tomography, and molecular dynamics simulations. A specific class of fractal, the percolation cluster, explains the structural details for several metallic-glass compositions. We postulate that atoms percolate in the liquid phase and that the percolating cluster becomes rigid at the glass transition temperature.", "doi": "10.1126/science.aab1233", "issn": "0036-8075", "publisher": "American Association for the Advancement of Science", "publication": "Science", "publication_date": "2015-09-18", "series_number": "6254", "volume": "349", "issue": "6254", "pages": "1306-1310" }, { "id": "authors:dgtwx-cmb47", "collection": "authors", "collection_id": "dgtwx-cmb47", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150909-102806332", "type": "article", "title": "Resilient 3D hierarchical architected metamaterials", "author": [ { "family_name": "Meza", "given_name": "Lucas R.", "orcid": "0000-0003-0250-2621", "clpid": "Meza-Lucas-R" }, { "family_name": "Zelhofer", "given_name": "Alex J.", "orcid": "0000-0002-8064-2876", "clpid": "Zelhofer-Alex-J" }, { "family_name": "Clarke", "given_name": "Nigel", "clpid": "Clarke-Nigel" }, { "family_name": "Mateos", "given_name": "Arturo J.", "orcid": "0000-0002-9306-3531", "clpid": "Mateos-Arturo-J" }, { "family_name": "Kochmann", "given_name": "Dennis M.", "orcid": "0000-0002-9112-6615", "clpid": "Kochmann-D-M" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "Hierarchically designed structures with architectural features that span across multiple length scales are found in numerous hard biomaterials, like bone, wood, and glass sponge skeletons, as well as manmade structures, like the Eiffel Tower. It has been hypothesized that their mechanical robustness and damage tolerance stem from sophisticated ordering within the constituents, but the specific role of hierarchy remains to be fully described and understood. We apply the principles of hierarchical design to create structural metamaterials from three material systems: (i) polymer, (ii) hollow ceramic, and (iii) ceramic\u2013polymer composites that are patterned into self-similar unit cells in a fractal-like geometry. In situ nanomechanical experiments revealed (i) a nearly theoretical scaling of structural strength and stiffness with relative density, which outperforms existing nonhierarchical nanolattices; (ii) recoverability, with hollow alumina samples recovering up to 98% of their original height after compression to \u226550% strain; (iii) suppression of brittle failure and structural instabilities in hollow ceramic hierarchical nanolattices; and (iv) a range of deformation mechanisms that can be tuned by changing the slenderness ratios of the beams. Additional levels of hierarchy beyond a second order did not increase the strength or stiffness, which suggests the existence of an optimal degree of hierarchy to amplify resilience. We developed a computational model that captures local stress distributions within the nanolattices under compression and explains some of the underlying deformation mechanisms as well as validates the measured effective stiffness to be interpreted as a metamaterial property.", "doi": "10.1073/pnas.1509120112", "pmcid": "PMC4577192", "issn": "0027-8424", "publisher": "National Academy of Sciences", "publication": "Proceedings of the National Academy of Sciences of the United States of America", "publication_date": "2015-09-15", "series_number": "37", "volume": "112", "issue": "37", "pages": "11502-11507" }, { "id": "authors:8n5tc-30g93", "collection": "authors", "collection_id": "8n5tc-30g93", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20151015-154153188", "type": "article", "title": "Polymer lattices as mechanically tunable 3-dimensional photonic crystals operating in the infrared", "author": [ { "family_name": "Chernow", "given_name": "V. F.", "clpid": "Chernow-V-F" }, { "family_name": "Alaeian", "given_name": "H.", "clpid": "Alaeian-H" }, { "family_name": "Dionne", "given_name": "J. A.", "orcid": "0000-0001-5287-4357", "clpid": "Dionne-J-A" }, { "family_name": "Greer", "given_name": "J. R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "Broadly tunable photonic crystals in the near- to mid-infrared region could find use in spectroscopy, non-invasive medical diagnosis, chemical and biological sensing, and military applications, but so far have not been widely realized. We report the fabrication and characterization of three-dimensional tunable photonic crystals composed of polymer nanolattices with an octahedron unit-cell geometry. These photonic crystals exhibit a strong peak in reflection in the mid-infrared that shifts substantially and reversibly with application of compressive uniaxial strain. A strain of \u223c40% results in a 2.2\u2009\u03bcm wavelength shift in the pseudo-stop band, from 7.3\u2009\u03bcm for the as-fabricated nanolattice to 5.1\u2009\u03bcm when strained. We found a linear relationship between the overall compressive strain in the photonic crystal and the resulting stopband shift, with a \u223c50\u2009nm blueshift in the reflection peak position per percent increase in strain. These results suggest that architected nanolattices can serve as efficient three-dimensional mechanically tunable photonic crystals, providing a foundation for new opto-mechanical components and devices across infrared and possibly visible frequencies.", "doi": "10.1063/1.4930819", "issn": "0003-6951", "publisher": "American Institute of Physics", "publication": "Applied Physics Letters", "publication_date": "2015-09-07", "series_number": "10", "volume": "107", "issue": "10", "pages": "Art. No. 101905" }, { "id": "authors:gzjb1-52690", "collection": "authors", "collection_id": "gzjb1-52690", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150824-125516097", "type": "article", "title": "Size Effect Suppresses Brittle Failure in Hollow Cu_(60)Zr_(40) Metallic Glass Nanolattices Deformed at Cryogenic Temperatures", "author": [ { "family_name": "Lee", "given_name": "Seok-Woo", "orcid": "0000-0001-6752-5694", "clpid": "Lee-Seok-Woo" }, { "family_name": "Jafary-Zadeh", "given_name": "Mehdi", "clpid": "Jafary-Zadeh-M" }, { "family_name": "Chen", "given_name": "David Z.", "clpid": "Chen-David-Z" }, { "family_name": "Zhang", "given_name": "Yong-Wei", "clpid": "Zhang-Yong-Wei" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "To harness \"smaller is more ductile\" behavior emergent at nanoscale and to proliferate it onto materials with macroscale dimensions, we produced hollow-tube Cu_(60)Zr_(40) metallic glass nanolattices with the layer thicknesses of 120, 60, and 20 nm. They exhibit unique transitions in deformation mode with tube-wall thickness and temperature. Molecular dynamics simulations and analytical models were used to interpret these unique transitions in terms of size effects on the plasticity of metallic glasses and elastic instability.", "doi": "10.1021/acs.nanolett.5b01034", "issn": "1530-6984", "publisher": "American Chemical Society", "publication": "Nano Letters", "publication_date": "2015-09", "series_number": "9", "volume": "15", "issue": "9", "pages": "5673-5681" }, { "id": "authors:v8btg-y9z80", "collection": "authors", "collection_id": "v8btg-y9z80", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150625-115224109", "type": "article", "title": "Mechanical Response of Hollow Metallic Nanolattices: Combining Structural and Material Size Effects", "author": [ { "family_name": "Montemayor", "given_name": "L. C.", "clpid": "Montemayor-L-C" }, { "family_name": "Greer", "given_name": "J. R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "Ordered cellular solids have higher compressive yield strength and stiffness compared to stochastic foams. The mechanical properties of cellular solids depend on their relative density and follow structural scaling laws. These scaling laws assume the mechanical properties of the constituent materials, like modulus and yield strength, to be constant and dictate that equivalent-density cellular solids made from the same material should have identical mechanical properties. We present the fabrication and mechanical properties of three-dimensional hollow gold nanolattices whose compressive responses demonstrate that strength and stiffness vary as a function of geometry and tube wall thickness. All nanolattices had octahedron geometry, a constant relative density, \u03c1\u2009\u223c\u20095%, a unit cell size of 5\u201320 \u03bcm, and a constant grain size in the Au film of 25\u201350 nm. Structural effects were explored by increasing the unit cell angle from 30 deg to 60 deg while keeping all other parameters constant; material size effects were probed by varying the tube wall thickness, t, from 200 nm to 635 nm, at a constant relative density and grain size. In situ uniaxial compression experiments revealed an order of magnitude increase in yield stress and modulus in nanolattices with greater lattice angles, and a 150% increase in the yield strength without a concomitant change in modulus in thicker-walled nanolattices for fixed lattice angles. These results imply that independent control of structural and material size effects enables tunability of mechanical properties of three-dimensional architected metamaterials and highlight the importance of material, geometric, and microstructural effects in small-scale mechanics.", "doi": "10.1115/1.4030361", "issn": "0021-8936", "publisher": "American Society Mechanical Engineers", "publication": "Journal of Applied Mechanics", "publication_date": "2015-07", "series_number": "7", "volume": "82", "issue": "7", "pages": "Art. No. 071012" }, { "id": "authors:hmk33-8rg06", "collection": "authors", "collection_id": "hmk33-8rg06", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150518-150949548", "type": "article", "title": "Three-Dimensional Au Microlattices as Positive Electrodes for Li\u2013O_2 Batteries", "author": [ { "family_name": "Xu", "given_name": "Chen", "orcid": "0000-0002-9427-0161", "clpid": "Xu-Chen-MatSci" }, { "family_name": "Gallant", "given_name": "Betar M.", "clpid": "Gallant-B-M" }, { "family_name": "Wunderlich", "given_name": "Phillip U.", "clpid": "Wunderlich-P-U" }, { "family_name": "Lohmann", "given_name": "Timm", "clpid": "Lohmann-T" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "We demonstrate the feasibility of using a 3-dimensional gold microlattice with a periodic porous structure and independently tunable surface composition as a Li\u2013O_2 battery cathode. The structure provides a platform for studying electrochemical reactions in architected Li\u2013O_2 electrodes with large (300 \u03bcm) pore sizes. The lack of carbon and chemical binders in these Au microlattices enabled the investigation of chemical and morphological processes that occur on the surfaces of the microlattice during cycling. Li\u2013O_2 cells with Au microlattice cathodes were discharged in 0.5 M lithium-bis(trifluoromethane)sulfonamide (LiTFSI) in a 1,2-dimethoxyethane (DME) electrolyte, with lithium metal foil as the anode. SEM analysis of microlattice cathodes after first discharge revealed the presence of toroidal-shaped 500\u2013700 nm particles covering the surface of the electrode, which disappeared upon subsequent charging. Raman and FTIR spectroscopy analysis determined these particulates to be Li_2O_2. The morphology of discharge products evolved with cycling into micrometer-sized clusters of arranged \"platelets\", with a higher amount of side reaction products such as Li_2CO_3 and LiOH. This work shows that properly designed 3-dimensional architected materials may provide a useful foundation for investigating fundamental surface electrochemistry while simultaneously enabling mechanical robustness and enhancing the surface area over a factor of 30 compared with a thin film with the same foot print.", "doi": "10.1021/acsnano.5b00443", "issn": "1936-0851", "publisher": "American Chemical Society", "publication": "ACS Nano", "publication_date": "2015-06", "series_number": "6", "volume": "9", "issue": "6", "pages": "5876-5883" }, { "id": "authors:3en75-zmq24", "collection": "authors", "collection_id": "3en75-zmq24", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150429-103132238", "type": "article", "title": "Tailoring of Interfacial Mechanical Shear Strength by Surface Chemical Modification of Silicon Microwires Embedded in Nafion Membranes", "author": [ { "family_name": "Gallant", "given_name": "Betar M.", "clpid": "Gallant-B-M" }, { "family_name": "Gu", "given_name": "X. Wendy", "clpid": "Gu-X-W" }, { "family_name": "Chen", "given_name": "David Z.", "clpid": "Chen-D-Z" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" }, { "family_name": "Lewis", "given_name": "Nathan S.", "orcid": "0000-0001-5245-0538", "clpid": "Lewis-N-S" } ], "abstract": "The interfacial shear strength between Si microwires and a Nafion membrane has been tailored through surface functionalization of the Si. Acidic (\u2212COOH-terminated) or basic (\u2212NH_2-terminated) surface-bound functionality was introduced by hydrosilylation reactions to probe the interactions between the functionalized Si microwires and hydrophilic ionically charged sites in the Nafion polymeric side chains. Surfaces functionalized with SiO_x, Si\u2013H, or Si\u2013CH_3 were also synthesized and investigated. The interfacial shear strength between the functionalized Si microwire surfaces and the Nafion matrix was quantified by uniaxial wire pull-out experiments in an in situ nanomechanical instrument that allowed simultaneous collection of mechanical data and visualization of the deformation process. In this process, an axial load was applied to the custom-shaped top portions of individual wires until debonding occurred from the Nafion matrix. The shear strength obtained from the nanomechanical measurements correlated with the chemical bond strength and the functionalization density of the molecular layer, with values ranging from 7 MPa for Si\u2013CH3 surfaces to \u223c16\u201320 MPa for oxygen-containing surface functionalities. Hence surface chemical control can be used to influence the mechanical adhesion forces at a Si\u2013Nafion interface.", "doi": "10.1021/acsnano.5b00468", "issn": "1936-0851", "publisher": "American Chemical Society", "publication": "ACS Nano", "publication_date": "2015-05", "series_number": "5", "volume": "9", "issue": "5", "pages": "5143-5153" }, { "id": "authors:tjmqr-khd83", "collection": "authors", "collection_id": "tjmqr-khd83", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150507-104158137", "type": "article", "title": "Slip statistics of dislocation avalanches under different loading modes", "author": [ { "family_name": "Maa\u00df", "given_name": "R.", "clpid": "Maa\u00df-R" }, { "family_name": "Wraith", "given_name": "M.", "clpid": "Wraith-M" }, { "family_name": "Uhl", "given_name": "J. T.", "clpid": "Uhl-J-T" }, { "family_name": "Greer", "given_name": "J. R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" }, { "family_name": "Dahmen", "given_name": "K. A.", "clpid": "Dahmen-K-A" } ], "abstract": "Slowly compressed microcrystals deform via intermittent slip events, observed as displacement jumps or stress drops. Experiments often use one of two loading modes: an increasing applied stress (stress driven, soft), or a constant strain rate (strain driven, hard). In this work we experimentally test the influence of the deformation loading conditions on the scaling behavior of slip events. It is found that these common deformation modes strongly affect time series properties, but not the scaling behavior of the slip statistics when analyzed with a mean-field model. With increasing plastic strain, the slip events are found to be smaller and more frequent when strain driven, and the slip-size distributions obtained for both drives collapse onto the same scaling function with the same exponents. The experimental results agree with the predictions of the used mean-field model, linking the slip behavior under different loading modes.", "doi": "10.1103/PhysRevE.91.042403", "issn": "1539-3755", "publisher": "American Physical Society", "publication": "Physical Review E", "publication_date": "2015-04", "series_number": "4", "volume": "91", "issue": "4", "pages": "Art. No. 042403" }, { "id": "authors:dgd95-pby45", "collection": "authors", "collection_id": "dgd95-pby45", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150611-100019960", "type": "book_section", "title": "A new approach to wind energy: Opportunities and challenges", "book_title": "Physics of Sustainable Energy III (PSE III)", "author": [ { "family_name": "Dabiri", "given_name": "John O.", "orcid": "0000-0002-6722-9008", "clpid": "Dabiri-J-O" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" }, { "family_name": "Koseff", "given_name": "Jeffrey R.", "clpid": "Koseff-J-R" }, { "family_name": "Moin", "given_name": "Parviz", "orcid": "0000-0002-0491-7065", "clpid": "Moin-Parviz" }, { "family_name": "Peng", "given_name": "Jifeng", "clpid": "Peng-Jifeng" } ], "contributor": [ { "family_name": "Knapp", "given_name": "R. H.", "clpid": "Knapp-R-H" }, { "family_name": "Levi", "given_name": "B. J.", "clpid": "Levi-B-J" }, { "family_name": "Kammer", "given_name": "D. M.", "clpid": "Kammer-D-M" } ], "abstract": "Despite common characterizations of modern wind energy technology as mature, there remains a persistent disconnect between the vast global wind energy resource\u2014which is 20 times greater than total global power consumption\u2014and the limited penetration of existing wind energy technologies as a means for electricity generation worldwide. We describe an approach to wind energy harvesting that has the potential to resolve this disconnect by geographically distributing wind power generators in a manner that more closely mirrors the physical resource itself. To this end, technology development is focused on large arrays of small wind turbines that can harvest wind energy at low altitudes by using new concepts of biology-inspired engineering. This approach dramatically extends the reach of wind energy, as smaller wind turbines can be installed in many places that larger systems cannot, especially in built environments. Moreover, they have lower visual, acoustic, and radar signatures, and they may pose significantly less risk to birds and bats. These features can be leveraged to attain cultural acceptance and rapid adoption of this new technology, thereby enabling significantly faster achievement of state and national renewable energy targets than with existing technology alone. Favorable economics stem from an orders-of-magnitude reduction in the number of components in a new generation of simple, mass-manufacturable (even 3D-printable), vertical-axis wind turbines. However, this vision can only be achieved by overcoming significant scientific challenges that have limited progress over the past three decades. The following essay summarizes our approach as well as the opportunities and challenges associated with it, with the aim of motivating a concerted effort in basic and applied research in this area.", "doi": "10.1063/1.4916168", "isbn": "9780735412941", "publisher": "American Institute of Physics", "place_of_publication": "Melville, NY", "publication_date": "2015-03-30", "pages": "51-57" }, { "id": "authors:vds4b-7ez34", "collection": "authors", "collection_id": "vds4b-7ez34", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141208-085540326", "type": "article", "title": "The effect of size, orientation and alloying on the deformation of AZ31 nanopillars", "author": [ { "family_name": "Aitken", "given_name": "Zachary H.", "clpid": "Aitken-Z-H" }, { "family_name": "Fan", "given_name": "Haidong", "clpid": "Fan-Haidong" }, { "family_name": "El-Awady", "given_name": "Jaafar A.", "clpid": "El-Awady-J-A" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "We conducted uniaxial compression of single crystalline Mg alloy, AZ31 (Al 3% wt. and Zn 1% wt.) nanopillars with diameters between 300\u20135000 nm with two distinct crystallographic orientations: (1) along the [0001] c-axis and (2) at an acute angle away from the c-axis, nominally oriented for basal slip. We observe single slip deformation for sub-micron samples nominally oriented for basal slip with the deformation commencing via a single set of parallel shear offsets. Samples compressed along the c-axis display an increase in yield strength compared to basal samples as well as significant hardening with the deformation being mostly homogeneous. We find that the \"smaller is stronger\" size effect in single crystals dominates any improvement in strength that may have arisen from solid solution strengthening. We employ 3D-discrete dislocation dynamics (DDD) to simulate compression along the [0001] and [1122] directions to elucidate the mechanisms of slip and evolution of dislocation microstructure. These simulations show qualitatively similar stress strain signatures to the experimentally obtained stress-strain data. Simulations of compression parallel to the [1122] direction reveal the activation and motion of only -type dislocations and virtually no dislocation junction formation. Computations of compression along [0001] show the activation and motion of both and dislocations along with a significant increase in the formation of junctions corresponding to the interaction of intersecting pyramidal planes. Both experiments and simulation show a size effect, with a differing exponent for basal and pyramidal slip. We postulate that this anisotropy in size effect is a result of the underlying anisotropic material properties only. We discuss these findings in the context of the effective resolved shear stress relative to the unit Burgers vector for each type of slip, which reveal that the mechanism that governs size effect in this Mg-alloy is equivalent in both orientations.", "doi": "10.1016/j.jmps.2014.11.014", "issn": "0022-5096", "publisher": "Elsevier", "publication": "Journal of the Mechanics and Physics of Solids", "publication_date": "2015-03", "volume": "76", "pages": "208-223" }, { "id": "authors:ya419-wkr75", "collection": "authors", "collection_id": "ya419-wkr75", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150217-082419354", "type": "article", "title": "Ductility and work hardening in nano-sized metallic glasses", "author": [ { "family_name": "Chen", "given_name": "D. Z.", "clpid": "Chen-D-Z" }, { "family_name": "Gu", "given_name": "X. W.", "clpid": "Gu-X-Wendy" }, { "family_name": "An", "given_name": "Q.", "orcid": "0000-0003-4838-6232", "clpid": "An-Qi" }, { "family_name": "Goddard", "given_name": "W. A., III", "orcid": "0000-0003-0097-5716", "clpid": "Goddard-W-A-III" }, { "family_name": "Greer", "given_name": "J. R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "In-situ nano-tensile experiments on 70\u2009nm-diameter free-standing electroplated NiP metallic glass nanostructures reveal tensile true strains of \u223c18%, an amount comparable to compositionally identical 100\u2009nm-diameter focused ion beam samples and \u223c3 times greater than 100\u2009nm-diameter electroplated samples. Simultaneous in-situ observations and stress-strain data during post-elastic deformation reveal necking and work hardening, features uncharacteristic for metallic glasses. The evolution of free volume within molecular dynamics-simulated samples suggests a free surface-mediated relaxation mechanism in nano-sized metallic glasses.", "doi": "10.1063/1.4907773", "issn": "0003-6951", "publisher": "American Institute of Physics", "publication": "Applied Physics Letters", "publication_date": "2015-02-09", "series_number": "6", "volume": "106", "issue": "6", "pages": "Art. No. 061903" }, { "id": "authors:77qaz-3rq58", "collection": "authors", "collection_id": "77qaz-3rq58", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20210202-135442294", "type": "book_section", "title": "Size Effects in Nanomaterials and Their Use in Creating Architectured Structural Metamaterials", "book_title": "The Nano\u2010Micro Interface: Bridging the Micro and Nano Worlds", "author": [ { "family_name": "Lee", "given_name": "Seok-Woo", "orcid": "0000-0001-6752-5694", "clpid": "Lee-Seok-Woo" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "contributor": [ { "family_name": "Van de Voorde", "given_name": "Marcel", "clpid": "Van-de-Voorde-Marcel" }, { "family_name": "Werner", "given_name": "Matthias", "clpid": "Werner-Matthias" }, { "family_name": "Fecht", "given_name": "Hans\u2010J\u00f6rg", "clpid": "Fecht-Hans\u2010J\u00f6rg" } ], "abstract": "With the increasing use of nanotechnology, mechanical properties of nano\u2010sized crystals with different initial microstructures are being had been actively investigated. Especially, the size effects on mechanical properties, especially strength and toughness, have attracted significant interest since those would be the most important parameters for the design of mechanically reliable devices such as micro\u2010electro\u2010mechanical systems (MEMS). For the past decade, the small\u2010scale mechanical testing community has unraveled the fundamental mechanisms that govern the size effects in mechanical behavior, and the present time is just around the corner to turning toward a scalable engineered structures consisting of nanoscale components, a scalable three\u2010dimensional architecture metamaterials where our knowledge on small\u2010scale plasticity should be incorporated. This chapter overviews some of the size effects that arise in the mechanical behavior of materials at small length scales and then discusses how these nanomechanical effects can be applied towards the fabrication of useful structural ....", "doi": "10.1002/9783527679195.ch28", "isbn": "9783527679195", "publisher": "Wiley", "place_of_publication": "Weinheim", "publication_date": "2015-01-31", "pages": "583-598" }, { "id": "authors:6jj8a-bev79", "collection": "authors", "collection_id": "6jj8a-bev79", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20140908-085350716", "type": "article", "title": "Independence of Slip Velocities on Applied Stress in Small Crystals", "author": [ { "family_name": "Maa\u00df", "given_name": "R.", "clpid": "Maa\u00df-R" }, { "family_name": "Derlet", "given_name": "P. M.", "clpid": "Derlet-P-M" }, { "family_name": "Greer", "given_name": "J. R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "Directly tracing the spatiotemporal dynamics of intermittent plasticity at the micro- and nanoscale reveals that the obtained slip dynamics are independent of applied stress over a range of up to \u223c400 MPa, as well as being independent of plastic strain. Whilst this insensitivity to applied stress is unexpected for dislocation plasticity, the stress integrated statistical properties of both the slip size magnitude and the slip velocity follow known theoretical predictions for dislocation plasticity. Based on these findings, a link between the crystallographic slip velocities and an underlying dislocation avalanche velocity is proposed. Supporting dislocation dynamics simulations exhibit a similar regime during microplastic flow, where the mean dislocation velocity is insensitive to the applied stress. Combining both experimental and modeling observations, the results are discussed in a framework that firmly places the plasticity of nano- and micropillars in the microplastic regime of bulk crystals.", "doi": "10.1002/smll.201400849", "issn": "1613-6810", "publisher": "Wiley", "publication": "Small", "publication_date": "2015-01-21", "series_number": "3", "volume": "11", "issue": "3", "pages": "341-351" }, { "id": "authors:e45vs-m7832", "collection": "authors", "collection_id": "e45vs-m7832", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20140915-083240514", "type": "article", "title": "Mechanisms of Failure in Nanoscale Metallic Glass", "author": [ { "family_name": "Gu", "given_name": "X. Wendy", "clpid": "Gu-X-Wendy" }, { "family_name": "Jafary-Zadeh", "given_name": "Mehdi", "clpid": "Jafary-Zadeh-M" }, { "family_name": "Chen", "given_name": "David Z.", "clpid": "Chen-David-Z" }, { "family_name": "Wu", "given_name": "Zhaoxuan", "clpid": "Wu-Zhaoxuan" }, { "family_name": "Zhang", "given_name": "Yong-Wei", "clpid": "Zhang-Yong-Wei" }, { "family_name": "Srolovitz", "given_name": "David J.", "clpid": "Srolovitz-D-J" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "The emergence of size-dependent mechanical strength in nanosized materials is now well-established, but no fundamental understanding of fracture toughness or flaw sensitivity in nanostructures exists. We report the fabrication and in situ fracture testing of \u223c70 nm diameter Ni\u2013P metallic glass samples with a structural flaw. Failure occurs at the structural flaw in all cases, and the failure strength of flawed samples was reduced by 40% compared to unflawed samples. We explore deformation and failure mechanisms in a similar nanometallic glass via molecular dynamics simulations, which corroborate sensitivity to flaws and reveal that the structural flaw shifts the failure mechanism from shear banding to cavitation. We find that failure strength and deformation in amorphous nanosolids depend critically on the presence of flaws.", "doi": "10.1021/nl5027869", "issn": "1530-6984", "publisher": "American Chemical Society", "publication": "Nano Letters", "publication_date": "2014-10", "series_number": "10", "volume": "14", "issue": "10", "pages": "5858-5864" }, { "id": "authors:3axy1-xz436", "collection": "authors", "collection_id": "3axy1-xz436", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20140909-170521846", "type": "article", "title": "Strong, lightweight, and recoverable three-dimensional ceramic nanolattices", "author": [ { "family_name": "Meza", "given_name": "Lucas R.", "orcid": "0000-0003-0250-2621", "clpid": "Meza-L-R" }, { "family_name": "Das", "given_name": "Satyajit", "clpid": "Das-Satyajit" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "Ceramics have some of the highest strength- and stiffness-to-weight ratios of any material but are suboptimal for use as structural materials because of their brittleness and sensitivity to flaws. We demonstrate the creation of structural metamaterials composed of nanoscale ceramics that are simultaneously ultralight, strong, and energy-absorbing and can recover their original shape after compressions in excess of 50% strain. Hollow-tube alumina nanolattices were fabricated using two-photon lithography, atomic layer deposition, and oxygen plasma etching. Structures were made with wall thicknesses of 5 to 60 nanometers and densities of 6.3 to 258 kilograms per cubic meter. Compression experiments revealed that optimizing the wall thickness-to-radius ratio of the tubes can suppress brittle fracture in the constituent solid in favor of elastic shell buckling, resulting in ductile-like deformation and recoverability.", "doi": "10.1126/science.1255908", "issn": "0036-8075", "publisher": "American Association for the Advancement of Science", "publication": "Science", "publication_date": "2014-09-11", "series_number": "6202", "volume": "345", "issue": "6202", "pages": "1322-1326" }, { "id": "authors:pch7r-dmf38", "collection": "authors", "collection_id": "pch7r-dmf38", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20140811-094735112", "type": "article", "title": "Effects of Helium Implantation on the Tensile Properties and Microstructure of Ni\u2087\u2083P\u2082\u2087 Metallic Glass Nanostructures", "author": [ { "family_name": "Liontas", "given_name": "Rachel", "clpid": "Liontas-R" }, { "family_name": "Gu", "given_name": "X. Wendy", "clpid": "Gu-X-Wendy" }, { "family_name": "Fu", "given_name": "Engang", "clpid": "Fu-Engang" }, { "family_name": "Wang", "given_name": "Yonqiang", "clpid": "Wang-Yonqiang" }, { "family_name": "Li", "given_name": "Nan", "clpid": "Li-Nan" }, { "family_name": "Mara", "given_name": "Nathan", "clpid": "Mara-Nathan" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "We report fabrication and nanomechanical tension experiments on as-fabricated and helium-implanted 130 nm diameter Ni\u2087\u2083P\u2082\u2087 metallic glass nanocylinders. The nanocylinders were fabricated by a templated electroplating process and implanted with He+ at energies of 50, 100, 150, and 200 keV to create a uniform helium concentration of 3 atom % throughout the nanocylinders. Transmission electron microscopy imaging and through-focus analysis reveal that the specimens contained 2 nm helium bubbles distributed uniformly throughout the nanocylinder volume. In situ tensile experiments indicate that helium-implanted specimens exhibit enhanced ductility as evidenced by a 2-fold increase in plastic strain over as-fabricated specimens with no sacrifice in yield and ultimate tensile strengths. This improvement in mechanical properties suggests that metallic glasses may actually exhibit a favorable response to high levels of helium implantation.", "doi": "10.1021/nl502074d", "issn": "1530-6984", "publisher": "American Chemical Society", "publication": "Nano Letters", "publication_date": "2014-09", "series_number": "9", "volume": "14", "issue": "9", "pages": "5176-5183" }, { "id": "authors:c3nv0-3ze19", "collection": "authors", "collection_id": "c3nv0-3ze19", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20140911-092057079", "type": "article", "title": "Deformation of as-fabricated and helium implanted 100 nm-diameter iron nano-pillars", "author": [ { "family_name": "Landau", "given_name": "Peri", "clpid": "Landau-P" }, { "family_name": "Guo", "given_name": "Qiang", "clpid": "Guo-Qiang" }, { "family_name": "Hosemann", "given_name": "Peter", "clpid": "Hosemann-P" }, { "family_name": "Wang", "given_name": "Yongqiang", "clpid": "Wang-Yongqiang" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "\u3008101\u3009-oriented cylindrical single crystalline Fe samples with diameters of 100 nm and heights of 1 \u03bcm were implanted with 0.36\u00b10.06 at% helium throughout their gauge sections. Uniaxial deformation experiments revealed a 40% higher yield and ultimate strengths in tension and a 25% higher yield strength and flow stress at 10% plastic strain in compression for implanted samples compared with as-fabricated ones. Observed tension\u2013compression asymmetry in implanted pillars was attributed to the non-planarity of screw dislocation cores and to twinning-antitwinning deformation typical of bcc metals and the interaction between dislocations and He bubbles. Compressive stress\u2013strain data in both sets of samples had three distinct regimes: (1) elastic loading followed by (2) discrete strain bursts during plastic flow with significant hardening up to strains of 5%, and (3) \"steady state\" discrete plasticity characterized by nearly-constant average flow stress. Each regime is discussed and explained in terms of competition in the rates of dislocation multiplication and dislocation annihilation.", "doi": "10.1016/j.msea.2014.06.052", "issn": "0921-5093", "publisher": "Elsevier", "publication": "Materials Science and Engineering A", "publication_date": "2014-08-26", "volume": "612", "pages": "316-325" }, { "id": "authors:9e98p-p7430", "collection": "authors", "collection_id": "9e98p-p7430", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20140811-150537796", "type": "conference_item", "title": "Hierarchical 3D nano-architectures for biomimetics, batteries, and lightweight structural materials", "author": [ { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "Creation of extremely strong yet ultra-light materials can be achieved by capitalizing on the hierarchical design of 3-dimensional nano-architectures. Such structural metamaterials exhibit superior thermomech. properties at extremely low mass densities (lighter than aerogels), making these solid foams ideal for many scientific and technol. applications. The dominant deformation mechanisms in such \"meta-materials\", where individual constituent size (nanometers to microns) is comparable to the characteristic microstructural length scale of the constituent solid, are essentially unknown. To harness the lucrative properties of 3-dimensional hierarchical nanostructures, it is crit. to assess mech. properties at each relevant scale while capturing the overall structural complexity. We present the fabrication of 3-dimensional nano-lattices whose constituents vary in size from several nanometers to tens of microns to millimeters. We discuss the deformation and mech. properties of a range of nano-sized solids with different microstructures deformed in an in-situ nanomech. instrument. Attention is focused on the interplay between the internal crit. microstructural length scale of materials and their external limitations in revealing the phys. mechanisms which govern the mech. deformation, where competing material- and structureinduced size effects drive overall properties. We focus on the deformation and failure in metallic, ceramic, and glassy nano structures and discuss size effects in nanomaterials in the framework of mechanics and physics of defects. Specific discussion topics include: nano-mech. expts. on nano structures extd. from particular phases and contg. specific boundaries and interfaces, flaw sensitivity in fracture of nano structures, and the creation of hollow nano-lattices for applications in biomedical devices, ultra lightwt. Li-ion batteries, and damage-tolerant cellular solids.", "publisher": "Caltech Library", "publication_date": "2014-08" }, { "id": "authors:5bdq4-59484", "collection": "authors", "collection_id": "5bdq4-59484", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20140714-082203208", "type": "article", "title": "Strength, stiffness, and microstructure of Cu(In,Ga)Se_2 thin films deposited via sputtering and co-evaporation", "author": [ { "family_name": "Luo", "given_name": "Shi", "clpid": "Luo-Shi" }, { "family_name": "Lee", "given_name": "Jiun-Haw", "clpid": "Lee-Jiun-Haw" }, { "family_name": "Liu", "given_name": "Chee-Wee", "clpid": "Liu-Chee-Wee" }, { "family_name": "Shieh", "given_name": "Jia-Min", "clpid": "Shieh-Jia-Min" }, { "family_name": "Shen", "given_name": "Chang-Hong", "clpid": "Shen-Chang-Hong" }, { "family_name": "Wu", "given_name": "Tsung-Ta", "clpid": "Wu-Tsung-Ta" }, { "family_name": "Jang", "given_name": "Dongchan", "orcid": "0000-0002-2814-9734", "clpid": "Jang-Dongchan" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "This work examines Cu(In,Ga)Se_2 thin films fabricated by (1) selenization of pre-sputtered Cu-In-Ga and (2) co-evaporation of each constituent. The efficiency disparity between films deposited via these two methods is linked to differences in morphology and microstructure. Atomic force microscopy and scanning electron microscopy show that selenized films have rougher surfaces and poor adhesion to molybdenum back contact. Transmission electron microscopy and electron energy loss spectroscopy revealed multiple voids near the Mo layer in selenized films and a depletion of Na and Se around the voids. Residual stresses in co-evaporated films were found to be \u223c1.23\u2009GPa using wafer curvature measurements. Uniaxial compression experiments on 500\u2009nm-diameter nanopillars carved out from co-evaporated films revealed the elastic modulus of 70.4\u2009\u00b1\u20096.5\u2009GPa. Hertzian contact model applied to nanoindentation data on selenized films revealed the indentation modulus of 68.9\u2009\u00b1\u200912.4\u2009GPa, which is in agreement with previous reports. This equivalence of the elastic moduli suggests that microstructural differences manifest themselves after the yield point. Typical plastic behavior with two distinct failure modes is observed in the extracted stress-strain results, with the yield strength of 640.9\u2009\u00b1\u200913.7\u2009MPa for pillars that failed by shearing and 1100.8\u2009\u00b1\u200977.8\u2009MPa for pillars that failed by shattering.", "doi": "10.1063/1.4890086", "issn": "0003-6951", "publisher": "American Institute of Physics", "publication": "Applied Physics Letters", "publication_date": "2014-07-07", "series_number": "1", "volume": "105", "issue": "1", "pages": "Art. No. 011907" }, { "id": "authors:0j06h-f8p33", "collection": "authors", "collection_id": "0j06h-f8p33", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20140822-102914643", "type": "article", "title": "Fabrication and Deformation of Metallic Glass Micro-Lattices", "author": [ { "family_name": "Rys", "given_name": "Jan", "clpid": "Rys-J" }, { "family_name": "Valdevit", "given_name": "Lorenzo", "clpid": "Valdevit-L" }, { "family_name": "Schaedler", "given_name": "Tobias A.", "clpid": "Schaedler-T-A" }, { "family_name": "Jacobsen", "given_name": "Alan J.", "clpid": "Jacobsen-A-J" }, { "family_name": "Carter", "given_name": "William B.", "clpid": "Carter-W-B" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "Recent progress in micro- and nanofabrication techniques enables the creation of hierarchically architected microlattices with dimensional control over six orders of magnitude, from centimeters down to nanometers. This hierarchical control facilitates the exploration of opportunities to exploit nano-sized material effects in structural materials. In this work, we present the fabrication, characterization, and properties of hollow metallic glass NiP microlattices. The wall thicknesses, deposited by electroless plating, were varied from \u224860\u2009nm up to 600\u2009nm, resulting in relative densities spanning from 0.02 to 0.2%. Uniaxial quasi-static compression tests revealed two different regimes in deformation: (i) Structures with a wall thickness above 150\u2009nm failed by catastrophic failure at the nodes and fracture events at the struts, with significant micro-cracking and (ii) Lattices whose wall thickness was below 150\u2009nm failed initially via buckling followed by significant plastic deformation rather than by post-elastic catastrophic fracture. This departure in deformation mechanism from brittle to deformable exhibited by the thin-walled structures is discussed in the framework of brittle-to-ductile transition emergent in nano-sized metallic glasses.", "doi": "10.1002/adem.201300454", "issn": "1438-1656", "publisher": "Wiley Verlag", "publication": "Advanced Engineering Materials", "publication_date": "2014-07", "series_number": "7", "volume": "16", "issue": "7", "pages": "889-896" }, { "id": "authors:cfbwd-nvh18", "collection": "authors", "collection_id": "cfbwd-nvh18", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20140603-101604423", "type": "article", "title": "Cold-temperature deformation of nano-sized tungsten and niobium as revealed by in-situ nano-mechanical experiments", "author": [ { "family_name": "Lee", "given_name": "Seok-Woo", "orcid": "0000-0001-6752-5694", "clpid": "Lee-Seok-Woo" }, { "family_name": "Cheng", "given_name": "YinTong", "clpid": "Cheng-YinTong" }, { "family_name": "Ryu", "given_name": "Ill", "clpid": "Ryu-Ill" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "We constructed and developed an in-situ cryogenic nanomechanical system to study small-scale mechanical behavior of materials at low temperatures. Uniaxial compression of two body-centered-cubic (bcc) metals, Nb and W, with diameters between 400 and 1300 nm, was studied at room temperature and at 165 K. Experiments were conducted inside of a Scanning Electron Microscope (SEM) equipped with a nanomechanical module, with simultaneous cooling of sample and diamond tip. Stress-strain data at 165 K exhibited higher yield strengths and more extensive strain bursts on average, as compared to those at 298 K. We discuss these differences in the framework of nano-sized plasticity and intrinsic lattice resistance. Dislocation dynamics simulations with surface-controlled dislocation multiplication were used to gain insight into size and temperature effects on deformation of nano-sized bcc metals.", "doi": "10.1007/s11431-014-5502-8", "issn": "1674-7321", "publisher": "Springer", "publication": "Science China Technological Sciences", "publication_date": "2014-04", "series_number": "4", "volume": "57", "issue": "4", "pages": "652-662" }, { "id": "authors:tpc4g-zq075", "collection": "authors", "collection_id": "tpc4g-zq075", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20140417-075457299", "type": "article", "title": "Nanoframe Catalysts", "author": [ { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "The catalytic properties of materials depend strongly on their microscopic structure, with the atomic-level chemistry and structure directly influencing the activity and durability of the catalyst. However, these microscopic properties can be difficult to understand and control. Furthermore, most efficient catalysts contain substantial amounts of precious metals, rendering them prohibitively expensive. The search for efficient, inexpensive catalysts has, therefore, been challenging. On page 1339 of this issue, Chen et al. (1) report the synthesis of a new class of electrocatalysts built from platinum-nickel nanocrystals. Their Pt_3Ni nanoframes have more than 22 times the catalytic activity of conventional platinum/carbon catalysts at 0.9 V, yet contain about 85% less precious metal.", "doi": "10.1126/science.1251865", "issn": "0036-8075", "publisher": "American Association for the Advancement of Science", "publication": "Science", "publication_date": "2014-03-21", "series_number": "6177", "volume": "343", "issue": "6177", "pages": "1319-1320" }, { "id": "authors:tkkh5-96902", "collection": "authors", "collection_id": "tkkh5-96902", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20140424-104958021", "type": "conference_item", "title": "Effects of helium implantation on tensile properties and microstructure of amorphous nickel phosphorous metallic glasses", "author": [ { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" }, { "family_name": "Liontas", "given_name": "Rachel", "clpid": "Liontas-R" }, { "family_name": "Gu", "given_name": "Wendy", "clpid": "Gu-X-Wendy" }, { "family_name": "Wang", "given_name": "Yongqiang", "clpid": "Wang-Yongqiang" }, { "family_name": "Li", "given_name": "Nan", "clpid": "Li-Nan" }, { "family_name": "Fu", "given_name": "Engang", "clpid": "Fu-Engang" }, { "family_name": "Mara", "given_name": "Nathan", "clpid": "Mara-Nathan" } ], "abstract": "Nuclear reactions generate insol. helium, which forms nano-sized bubbles that can lead to swelling and embrittlement of\nirradiated materials. Innovative structural materials must be created and utilized to enable new-generation nuclear reactors to\nwithstand harsh thermomech. environments and to suppress helium-induced embrittlement. One family of candidate structural\nmaterials is metallic glasses, which offer high elastic limit and strength, corrosion resistance, and potential for improved ductility\nupon irradn. A significant detriment in their use for structural applications is catastrophic failure under tensile loadsWe use\ntemplated electron-beam lithog. and electro-deposition to fabricate 100 nm-diam. amorphous Ni-P metallic glass cylindrical\nnano-tensile specimens. Earlier studies in our group demonstrated the emergence of brittle-to-ductile transition in nano-sized\nmetallic glasses upon tension, with useful ductility in excess of 20% in some cases. In this work we explore the effects of\nHelium implantation into already-ductile nano-sized metallic glasses. Helium was implanted uniformly into each sample at a\nconcn. of 3 at% at 25\u00b0C and at 280\u00b0C to result in the bubble sizes between 2-3nm and \u223c10nm. In-situ uniaxial tension expts.\nrevealed that He-ion implantation increased available plastic strain in the nano-metallic glass tensile specimens by a factor of\n2 and maintained the high strength of \u223c2.1 GPa. We discuss these promising results in the framework of microstructural and\ndefect response to ion irradn. in metallic glasses.", "publisher": "Caltech Library", "publication_date": "2014-03" }, { "id": "authors:hkyz6-w6p45", "collection": "authors", "collection_id": "hkyz6-w6p45", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20131223-110132955", "type": "article", "title": "Mechanical characterization of hollow ceramic nanolattices", "author": [ { "family_name": "Meza", "given_name": "Lucas R.", "orcid": "0000-0003-0250-2621", "clpid": "Meza-L-R" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "In the analysis of complex, hierarchical structural meta-materials, it is critical to understand the mechanical behavior at each level of hierarchy in order to understand the bulk material response. We report the fabrication and mechanical deformation of hierarchical hollow tube lattice structures with features ranging from 10 nm to 100 \u03bcm, hereby referred to as nanolattices. Titanium nitride (TiN) nanolattices were fabricated using a combination of two-photon lithography, direct laser writing, and atomic layer deposition. The structure was composed of a series of tessellated regular octahedra attached at their vertices. In situ uniaxial compression experiments performed in combination with finite element analysis on individual unit cells revealed that the TiN was able to withstand tensile stresses of 1.75 GPa under monotonic loading and of up to 1.7 GPa under cyclic loading without failure. During the compression of the unit cell, the beams bifurcated via lateral-torsional buckling, which gave rise to a hyperelastic behavior in the load\u2013displacement data. During the compression of the full nanolattice, the structure collapsed catastrophically at a high strength and modulus that agreed well with classical cellular solid scaling laws given the low relative density of 1.36 %. We discuss the compressive behavior and mechanical analysis of the unit cell of these hollow TiN nanolattices in the context of finite element analysis in combination with classical buckling laws, and the behavior of the full structure in the context of classical scaling laws of cellular solids coupled with enhanced nanoscale material properties.", "doi": "10.1007/s10853-013-7945-x", "issn": "0022-2461", "publisher": "Springer", "publication": "Journal of Materials Science", "publication_date": "2014-03", "series_number": "6", "volume": "49", "issue": "6", "pages": "2496-2508" }, { "id": "authors:r9eb8-7m270", "collection": "authors", "collection_id": "r9eb8-7m270", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20140619-094937686", "type": "article", "title": "Design and Fabrication of Hollow Rigid Nanolattices via Two-Photon Lithography", "author": [ { "family_name": "Montemayor", "given_name": "Lauren C.", "clpid": "Montemayor-L-C" }, { "family_name": "Meza", "given_name": "Lucas R.", "orcid": "0000-0003-0250-2621", "clpid": "Meza-L-R" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "This paper presents the design and fabrication of 3-dimensional hollow metallic nanolattices using 2-photon lithography, shown in the figure. The ability to fabricate structures of any geometry, with resolution down to 150\u2009nm, provides opportunities to engineer structures spanning multiple length scales with potential to capitalize on combined structural and material size effects for use in many technological applications.", "doi": "10.1002/adem.201300254", "issn": "1438-1656", "publisher": "Wiley Verlag", "publication": "Advanced Engineering Materials", "publication_date": "2014-02", "series_number": "2", "volume": "16", "issue": "2", "pages": "184-189" }, { "id": "authors:c2mxa-12s05", "collection": "authors", "collection_id": "c2mxa-12s05", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130726-075320969", "type": "article", "title": "Grain Boundary Sliding in Aluminum Nano-Bi-Crystals Deformed at Room Temperature", "author": [ { "family_name": "Aitken", "given_name": "Zachary H.", "clpid": "Aitken-Z-H" }, { "family_name": "Jang", "given_name": "Dongchan", "orcid": "0000-0002-2814-9734", "clpid": "Jang-Dongchan" }, { "family_name": "Weinberger", "given_name": "Christopher R.", "clpid": "Weinberger-C-R" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "Room-temperature uniaxial compressions of 900-nm-diameter aluminum bi-crystals,\neach containing a high-angle grain boundary with a plane normal inclined at 24\u00b0 to\nthe loading direction, revealed frictional sliding along the boundary plane to be the\ndominant deformation mechanism. The top crystallite sheared off as a single unit in\nthe course of compression instead of crystallographic slip and extensive dislocation\nactivity, as would be expected. Compressive stress strain data of deforming nano\nbicrystals was continuous, in contrast to single crystalline nano structures that show a\nstochastic stress strain signature, and displayed a peak in stress at the elastic limit of\n\u223c176 MPa followed by gradual softening and a plateau centered around \u223c125 MPa.\nAn energetics-based physical model, which may explain observed room-temperature\ngrain boundary sliding, in presented, and observations are discussed within the\nframework of crystalline nano-plasticity and defect microstructure evolution.", "doi": "10.1002/smll.201301060", "issn": "1613-6810", "publisher": "Wiley", "publication": "Small", "publication_date": "2014-01-15", "series_number": "1", "volume": "10", "issue": "1", "pages": "100-108" }, { "id": "authors:wmv15-f3m73", "collection": "authors", "collection_id": "wmv15-f3m73", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20140116-093552385", "type": "article", "title": "Deformation response of ferrite and martensite in a dual-phase steel", "author": [ { "family_name": "Ghassemi-Armaki", "given_name": "H.", "clpid": "Ghassemi-Armaki-H" }, { "family_name": "Maa\u00df", "given_name": "R.", "clpid": "Maa\u00df-R" }, { "family_name": "Bhat", "given_name": "S. P.", "clpid": "Bhat-S-P" }, { "family_name": "Sriram", "given_name": "S.", "clpid": "Sriram-S" }, { "family_name": "Greer", "given_name": "J. R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" }, { "family_name": "Kumar", "given_name": "K. S.", "clpid": "Kumar-K-S" } ], "abstract": "Deformation response of ferrite and martensite in a commercially produced dual-phase sheet steel with a nominal composition of 0.15% C\u20131.45% Mn\u20130.30% Si (wt.%) was characterized by nanoindentation and uniaxial compression of focused ion beam-milled cylindrical micropillars (1\u20132 \u03bcm diameter). These experiments were conducted on as-received and pre-strained specimens. The average nanoindentation hardness of ferrite was found to increase from \u223c2 GPa in the as-received condition to \u223c3.5 GPa in the specimen that had been pre-strained to 7% plastic tensile strain. Hardness of ferrite in the as-received condition was inhomogeneous: ferrite adjacent to ferrite/martensite interface was \u223c20% harder than that in the interior, a feature also captured by micropillar compression experiments. Hardness variation in ferrite was reversed in samples pre-strained to 7% strain. Martensite in the as-received condition and after 5% pre-strain exhibited large scatter in nanoindentation hardness; however, micropillar compression results on the as-received and previously deformed steel specimens demonstrated that the martensite phase in this steel was amenable to plastic deformation and rapid work hardening in the early stages of deformation. The observed microscopic deformation characteristics of the constituent phases are used to explain the macroscopic tensile deformation response of the dual-phase steel.", "doi": "10.1016/j.actamat.2013.10.001", "issn": "1359-6454", "publisher": "Elsevier", "publication": "Acta Materialia", "publication_date": "2014-01", "volume": "62", "pages": "197-211" }, { "id": "authors:2ajbx-zk885", "collection": "authors", "collection_id": "2ajbx-zk885", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20131220-135618467", "type": "article", "title": "Microstructure versus Flaw: Mechanisms of Failure and Strength in Nanostructures", "author": [ { "family_name": "Gu", "given_name": "X. Wendy", "clpid": "Gu-X-Wendy" }, { "family_name": "Wu", "given_name": "Zhaoxuan", "clpid": "Wu-Zhaoxuan" }, { "family_name": "Zhang", "given_name": "Yong-Wei", "clpid": "Zhang-Yong-Wei" }, { "family_name": "Srolovitz", "given_name": "David J.", "clpid": "Srolovitz-D-J" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "Understanding failure in nanomaterials is critical for the design of reliable structural materials and small-scale devices with nanoscale components. No consensus exists on the effect of flaws on fracture at the nanoscale, but proposed theories include nanoscale flaw tolerance and maintaining macroscopic fracture relationships at the nanoscale with scarce experimental support. We explore fracture in nanomaterials using nanocrystalline Pt nanocylinders with prefabricated surface notches created using a \"paused\" electroplating method. In situ scanning electron microscopy (SEM) tension tests demonstrate that the majority of these samples failed at the notches, but that tensile failure strength is independent of whether failure occurred at or away from the flaw. Molecular dynamics simulations verify these findings and show that local plasticity is able to reduce stress concentration ahead of the notch to levels comparable with the strengths of microstructural features (e.g., grain boundaries). Thus, failure occurs at the stress concentration with the highest local stress whether this is at the notch or a microstructural feature.", "doi": "10.1021/nl403453h", "issn": "1530-6984", "publisher": "American Chemical Society", "publication": "Nano Letters", "publication_date": "2013-11-13", "series_number": "11", "volume": "13", "issue": "11", "pages": "5703-5709" }, { "id": "authors:kqzec-qyy94", "collection": "authors", "collection_id": "kqzec-qyy94", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20131010-081524348", "type": "article", "title": "Small-scale plasticity: Insights into dislocation avalanche velocities", "author": [ { "family_name": "Maa\u00df", "given_name": "Robert", "clpid": "Maa\u00df-R" }, { "family_name": "Derlet", "given_name": "Peter M.", "clpid": "Derlet-P-M" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "We report direct measurements of displacement jump velocities in deforming nano- and microcrystals. These velocities exhibit large scatter and no correlation with plastic strain, crystal size or applied stress. Statistical analysis for the displacement jump velocities shows a cubic power-law decay, with a shoulder at low velocities. Our results indicate that the collective motion of dislocations in the deforming crystals is dominated by statistical fluctuations within the internal stresses, rather than by a mobility law that depends on the externally applied stress.", "doi": "10.1016/j.scriptamat.2013.07.005", "issn": "1359-6462", "publisher": "Elsevier", "publication": "Scripta Materialia", "publication_date": "2013-10", "series_number": "8", "volume": "69", "issue": "8", "pages": "586-589" }, { "id": "authors:mehad-gq046", "collection": "authors", "collection_id": "mehad-gq046", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20131204-145203712", "type": "article", "title": "Local Relative Density Modulates Failure and Strength in Vertically Aligned Carbon Nanotubes", "author": [ { "family_name": "Pathak", "given_name": "Siddhartha", "clpid": "Pathak-S" }, { "family_name": "Mohan", "given_name": "Nisha", "clpid": "Mohan-N" }, { "family_name": "Decolvenaere", "given_name": "Elizabeth", "clpid": "Decolvenaere-E" }, { "family_name": "Needleman", "given_name": "Alan", "clpid": "Needleman-A" }, { "family_name": "Bedewy", "given_name": "Mostafa", "clpid": "Bedewy-M" }, { "family_name": "Hart", "given_name": "A. John", "orcid": "0000-0002-7372-3512", "clpid": "Hart-A-J" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "Micromechanical experiments, image analysis, and theoretical modeling revealed that local failure events and compressive stresses of vertically aligned carbon nanotubes (VACNTs) were uniquely linked to relative density gradients. Edge detection analysis of systematically obtained scanning electron micrographs was used to quantify a microstructural figure-of-merit related to relative local density along VACNT heights. Sequential bottom-to-top buckling and hardening in stress\u2013strain response were observed in samples with smaller relative density at the bottom. When density gradient was insubstantial or reversed, bottom regions always buckled last, and a flat stress plateau was obtained. These findings were consistent with predictions of a 2D material model based on a viscoplastic solid with plastic non-normality and a hardening\u2013softening\u2013hardening plastic flow relation. The hardening slope in compression generated by the model was directly related to the stiffness gradient along the sample height, and hence to the local relative density. These results demonstrate that a microstructural figure-of-merit, the effective relative density, can be used to quantify and predict the mechanical response.", "doi": "10.1021/nn402710j", "issn": "1936-0851", "publisher": "American Chemical Society", "publication": "ACS Nano", "publication_date": "2013-10", "series_number": "10", "volume": "7", "issue": "10", "pages": "8593-8604" }, { "id": "authors:rfpm8-8c750", "collection": "authors", "collection_id": "rfpm8-8c750", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130930-130210956", "type": "article", "title": "Fabrication and deformation of three-dimensional hollow ceramic nanostructures", "author": [ { "family_name": "Jang", "given_name": "Dongchan", "orcid": "0000-0002-2814-9734", "clpid": "Jang-Dongchan" }, { "family_name": "Meza", "given_name": "Lucas R.", "orcid": "0000-0003-0250-2621", "clpid": "Meza-L-R" }, { "family_name": "Greer", "given_name": "Frank", "clpid": "Greer-F" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "Creating lightweight, mechanically robust materials has long\nbeen an engineering pursuit. Many siliceous skeleton species\u2014\nsuch as diatoms, sea sponges and radiolarians\u2014have remarkably\nhigh strengths when compared with man-made materials\nof the same composition, yet are able to remain lightweight\nand porous1\u20137. It has been suggested that these properties\narise from the hierarchical arrangement of different structural\nelements at their relevant length scales8,9. Here, we report the\nfabrication of hollow ceramic scaffolds that mimic the length\nscales and hierarchy of biological materials. The constituent\nsolids attain tensile strengths of 1.75 GPa without failure\neven after multiple deformation cycles, as revealed by in situ\nnanomechanical experiments and finite-element analysis. We\ndiscuss the high strength and lack of failure in terms of stress\nconcentrators at surface imperfections and of local stresses\nwithin the microstructural landscape. Our findings suggest that\nthe hierarchical design principles offered by hard biological organisms\ncan be applied to create damage-tolerant lightweight\nengineering materials.", "doi": "10.1038/nmat3738", "issn": "1476-1122", "publisher": "Nature Publishing Group", "publication": "Nature Materials", "publication_date": "2013-10", "series_number": "10", "volume": "12", "issue": "10", "pages": "893-898" }, { "id": "authors:d194w-20b13", "collection": "authors", "collection_id": "d194w-20b13", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20140213-094643087", "type": "article", "title": "Nanometallic Glasses: Size Reduction Brings Ductility, Surface State Drives Its Extent", "author": [ { "family_name": "Chen", "given_name": "D. Z.", "clpid": "Chen-D-Z" }, { "family_name": "Jang", "given_name": "D.", "orcid": "0000-0002-2814-9734", "clpid": "Jang-Dongchan" }, { "family_name": "Guan", "given_name": "K. M.", "clpid": "Guan-K-M" }, { "family_name": "An", "given_name": "Q.", "orcid": "0000-0003-4838-6232", "clpid": "An-Qi" }, { "family_name": "Goddard", "given_name": "W. A., III", "orcid": "0000-0003-0097-5716", "clpid": "Goddard-W-A-III" }, { "family_name": "Greer", "given_name": "J. R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "We report tensile experiments on Ni_(80)P_20 metallic glass samples fabricated via a templated electroplating process and via focused ion beam milling, which differed only in their surface energy states: Ga-ion-irradiated and as-electroplated. Molecular dynamics simulations on similar Ni_(80)Al_20 systems corroborate the experimental results, which suggest that the transition from brittle to ductile behavior is driven by sample size, while the extent of ductility is driven by surface state.", "doi": "10.1021/nl402384r", "issn": "1530-6984", "publisher": "American Chemical Society", "publication": "Nano Letters", "publication_date": "2013-09-11", "series_number": "9", "volume": "13", "issue": "9", "pages": "4462-4468" }, { "id": "authors:p1eb8-c5q05", "collection": "authors", "collection_id": "p1eb8-c5q05", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20131202-083351205", "type": "article", "title": "Cryogenic nanoindentation size effect in [0 0 1]-oriented face-centered cubic and body centered cubic single crystals", "author": [ { "family_name": "Lee", "given_name": "Seok-Woo", "orcid": "0000-0001-6752-5694", "clpid": "Lee-Seok-Woo" }, { "family_name": "Meza", "given_name": "Lucas", "orcid": "0000-0003-0250-2621", "clpid": "Meza-L-R" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "Cryogenic nanoindentation experiments performed on [0 0 1]-oriented single crystalline Nb, W, Al, and Au in an in situ nanomechanical instrument with customized cryogenic testing capability revealed temperature dependence on nanoindentation size effect. The Nix-Gao model, commonly used to capture indentation size effect at room temperature, does not take into account thermal effects and hence is not able to explain these experimental results where both hardness at infinite indentation depth and characteristic material length scale were found to be strong functions of temperature. Physical attributes are critically examined in the framework of intrinsic lattice resistance and dislocation cross-slip probability.", "doi": "10.1063/1.4820585", "issn": "0003-6951", "publisher": "American Institute of Physics", "publication": "Applied Physics Letters", "publication_date": "2013-09-02", "series_number": "10", "volume": "103", "issue": "10", "pages": "Art. No. 101906" }, { "id": "authors:r87kn-q1893", "collection": "authors", "collection_id": "r87kn-q1893", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20131016-131137084", "type": "conference_item", "title": "Mechanics and physics of nano solids in designing 3D hierarchical meta materials", "author": [ { "family_name": "Greer", "given_name": "Julia", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "This presentation will be given by the ACS Nano Letters Young Investigator Award recipient.", "publisher": "Caltech Library", "publication_date": "2013-09" }, { "id": "authors:8h4cv-bpd86", "collection": "authors", "collection_id": "8h4cv-bpd86", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130826-132327179", "type": "article", "title": "Nanotwinned metals: It's all about imperfections", "author": [ { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "Experiments and simulations show that coherent twin boundaries, commonly believed to be perfect, are riddled\nwith kinks and other defects.", "doi": "10.1038/nmat3721", "issn": "1476-1122", "publisher": "Nature Publishing Group", "publication": "Nature Materials", "publication_date": "2013-08", "series_number": "8", "volume": "12", "issue": "8", "pages": "689-690" }, { "id": "authors:559rt-42q79", "collection": "authors", "collection_id": "559rt-42q79", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130729-080552163", "type": "monograph", "title": "Flaw-driven Failure in Nanostructures", "author": [ { "family_name": "Gu", "given_name": "X. Wendy", "clpid": "Gu-X-Wendy" }, { "family_name": "Wu", "given_name": "Zhaoxuan", "clpid": "Wu-Zhaoxuan" }, { "family_name": "Zhang", "given_name": "Yong-Wei", "clpid": "Zhang-Yong-Wei" }, { "family_name": "Srolovitz", "given_name": "David J.", "clpid": "Srolovitz-D-J" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "Understanding failure in nanomaterials is critical for the design of reliable structural materials and small-scale devices that have components or microstructural elements at the nanometer length scale. No consensus exists on the effect of flaws on fracture in bulk nanostructured materials or in nanostructures. Proposed theories include nanoscale flaw tolerance and maintaining macroscopic fracture relationships at the nanoscale with virtually no experimental support. We explore fracture mechanisms in nanomaterials via nanomechanical experiments on nanostructures with pre-fabricated surface flaws in combination with molecular dynamics simulations. Nanocrystalline Pt cylinders with diameters of ~120 nm with intentionally introduced surface notches were created using a template-assisted electroplating method and tested in uniaxial tension in in-situ SEM. Experiments demonstrate that 8 out of 12 samples failed at the notches and that tensile failure strengths were ~1.8 GPa regardless of whether failure occurred at or away from the flaw. These findings suggest that failure location was sensitive to the presence of flaws, while strength was flaw-insensitive. Molecular dynamics simulations support these observations and show that incipient plastic deformation commences via nucleation and motion of dislocations in concert with grain boundary sliding. We postulate that such local plasticity reduces stress concentration ahead of the flaw to levels comparable with the strengths of intrinsic microstructural features like grain boundary triple junctions, a phenomenon unique to nano-scale solids that contain an internal microstructural energy landscape. This mechanism causes failure to occur at the weakest link, be it an internal inhomogeneity or a surface feature with a high local stress.", "doi": "10.48550/arXiv.1307.3182", "publisher": "California Institute of Technology", "publication_date": "2013-07-11" }, { "id": "authors:v8rv3-88m27", "collection": "authors", "collection_id": "v8rv3-88m27", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20131203-110109054", "type": "article", "title": "Uniaxial Tension of a Class of Compressible Solids With Plastic Non-Normality", "author": [ { "family_name": "Mohan", "given_name": "Nisha", "clpid": "Mohan-N" }, { "family_name": "Cheng", "given_name": "Justine", "clpid": "Cheng-Justine" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" }, { "family_name": "Needleman", "given_name": "Alan", "clpid": "Needleman-A" } ], "abstract": "Motivated by a model that qualitatively captured the response of vertically aligned carbon nanotube (VACNT) pillars in uniaxial compression, we consider the uniaxial tensile response of a class of compressible elastic-viscoplastic solids. In Hutchens et al. [\"Analysis of Uniaxial Compression of Vertically Aligned Carbon Nanotubes,\" J. Mech. Phys. Solids, 59, pp. 2227\u20132237 (2011), Erratum 60, 1753\u20131756 (2012)] an elastic viscoplastic constitutive relation with plastic compressibility, plastic non-normality, and a hardening-softening-hardening hardness function was used to model experimentally obtained uniaxial compression data of cylindrical VACNT micropillars. Complex deformation modes were found in uniaxial compression, which include a sequential buckling-like collapse of the type seen in experiments. These complex deformation modes led to the overall stress-strain signature of the pillar not being of the same form as the input material hardness function. A fundamental question that motivates exploring the deformation of this class of materials\u2014both experimentally and theoretically\u2014is how to extract the intrinsic material response from simple tests. In this study we explore the relation between the input material response and the overall stress strain behavior in uniaxial tension using the constitutive framework of Hutchens et al. A simple one-dimensional analysis reveals the types of instability modes to be expected. Dynamic, finite deformation finite element calculations are carried out to explore the dependence of diffuse necking, localized necking, and propagating band deformation modes on characteristics of the hardness function. Attention is devoted to uncovering implications for obtaining intrinsic material properties of complex hierarchical structures; for example, vertically aligned carbon nanotubes (VACNTs), from uniaxial tension experiments.", "doi": "10.1115/1.4024179", "issn": "0021-8936", "publisher": "American Society Mechanical Engineers", "publication": "Journal of Applied Mechanics", "publication_date": "2013-07", "series_number": "4", "volume": "80", "issue": "4", "pages": "Art. No. 040912" }, { "id": "authors:xvp2h-pcy22", "collection": "authors", "collection_id": "xvp2h-pcy22", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130712-075812593", "type": "article", "title": "Buckling-driven delamination of carbon nanotube forests", "author": [ { "family_name": "Abadi", "given_name": "Parisa Pour Shahid Saeed", "clpid": "Abadi-P-P-S-S" }, { "family_name": "Hutchens", "given_name": "Shelby B.", "clpid": "Hutchens-S-B" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" }, { "family_name": "Cola", "given_name": "Baratunde A.", "clpid": "Cola-B-A" }, { "family_name": "Graham", "given_name": "Samuel", "clpid": "Graham-S" } ], "abstract": "We report buckling-driven delamination of carbon nanotube (CNT) forests from their growth substrates when subjected to compression. Macroscale compression experiments reveal local delamination at the CNT forest-substrate interface. Results of microscale flat punch indentations indicate that enhanced CNT interlocking at the top surface of the forest accomplished by application of a metal coating causes delamination of the forest from the growth substrate, a phenomenon not observed in indentation of as-grown CNT forests. We postulate that the post-buckling tensile stresses that develop at the base of the CNT forests serve as the driving force for delamination.", "doi": "10.1063/1.4802080", "issn": "0003-6951", "publisher": "American Institute of Physics", "publication": "Applied Physics Letters", "publication_date": "2013-06-04", "series_number": "22", "volume": "102", "issue": "22", "pages": "Art. No. 223103" }, { "id": "authors:v5qz6-wje09", "collection": "authors", "collection_id": "v5qz6-wje09", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130506-072038332", "type": "article", "title": "Fatigue deformation of microsized metallic glasses", "author": [ { "family_name": "Jang", "given_name": "Dongchan", "orcid": "0000-0002-2814-9734", "clpid": "Jang-Dongchan" }, { "family_name": "Maa\u00df", "given_name": "Robert", "clpid": "Maa\u00df-R" }, { "family_name": "Wang", "given_name": "Gongyao", "clpid": "Wang-Gongyao" }, { "family_name": "Liaw", "given_name": "Peter K.", "clpid": "Liaw-Peter-K" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "Metallic glasses typically exhibit high strength and a high elastic limit but suffer from poor fatigue resistance. This work demonstrates that 1.6 micron diameter Zr-based metallic glass samples subjected to compressive fatigue cycling did not fail after 40 \u00d7 10^6 cycles. The fatigue endurance limit was shown to increase to more than 110% of bulk yield strength under compression\u2013compression and up to 90% under bending; those of the same material with macroscopic dimensions are typically at 50% of bulk yield strength.", "doi": "10.1016/j.scriptamat.2012.12.011", "issn": "1359-6462", "publisher": "Elsevier", "publication": "Scripta Materialia", "publication_date": "2013-05", "series_number": "10", "volume": "68", "issue": "10", "pages": "773-776" }, { "id": "authors:a3x67-5fm11", "collection": "authors", "collection_id": "a3x67-5fm11", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130614-153115852", "type": "article", "title": "Solid-state dewetting of thin iron films on sapphire substrates controlled by grain boundary diffusion", "author": [ { "family_name": "Kovalenko", "given_name": "O.", "clpid": "Kovalenko-O" }, { "family_name": "Greer", "given_name": "J. R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" }, { "family_name": "Rabkin", "given_name": "E.", "clpid": "Rabkin-E" } ], "abstract": "The initial stages of solid-state dewetting of 25 nm-thick Fe films on basal plane-oriented sapphire substrates were found to occur via nucleation and growth of through-thickness craters within the film. The rims along these voids were not elevated, in contrast to commonly observed void growth mechanisms. Instead, the material that was consumed during the crater expansion was absorbed by several isolated grains in its vicinity but not adjacent to it. These grains transformed into faceted hillocks that protruded above the original film surface at later stages. A thin film dewetting model is proposed, in which the self-diffusion of Fe atoms along the grain boundaries transports the mass from the expanding cavities to the hillocks and determines the kinetics of this dilation. The grain boundary self-diffusion coefficients of Fe that were estimated based on the experimentally determined crater expansion rates and the proposed model agreed well with the literature.", "doi": "10.1016/j.actamat.2013.01.062", "issn": "1359-6454", "publisher": "Elsevier", "publication": "Acta Materialia", "publication_date": "2013-05", "series_number": "9", "volume": "61", "issue": "9", "pages": "3148-3156" }, { "id": "authors:txx6w-8f419", "collection": "authors", "collection_id": "txx6w-8f419", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130507-103249946", "type": "article", "title": "Compressive response of vertically aligned carbon nanotube films gleaned from in situ flat-punch indentations", "author": [ { "family_name": "Pathak", "given_name": "Siddhartha", "clpid": "Pathak-S" }, { "family_name": "Mohan", "given_name": "Nisha", "clpid": "Mohan-N" }, { "family_name": "Abadi", "given_name": "Parisa Pour Shahid Saeed", "clpid": "Abadi-P-P-S-S" }, { "family_name": "Graham", "given_name": "Samuel", "clpid": "Graham-S" }, { "family_name": "Cola", "given_name": "Baratunde A.", "clpid": "Cola-B-A" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "We report the mechanical behavior of vertically aligned carbon nanotube films, grown on Si substrates using atmospheric pressure chemical vapor deposition, subjected to in situ large displacement (up to 70 \u03bcm) flat-punch indentations. We observed three distinct regimes in their indentation stress\u2013strain curves: (i) a short elastic regime, followed by (ii) a sudden instability, which resulted in a substantial rapid displacement burst manifested by an instantaneous vertical shearing of the material directly underneath the indenter tip by as much as 30 \u03bcm, and (iii) a positively sloped plateau for displacements between 10 and 70 \u03bcm. In situ nanomechanical indentation experiments revealed that the shear strain was accommodated by an array of coiled carbon nanotube \"microrollers,\" providing a low-friction path for the vertical displacement. Mechanical response and concurrent deformation morphologies are discussed in the foam-like deformation framework with a particular emphasis on boundary conditions.", "doi": "10.1557/jmr.2012.366", "issn": "0884-2914", "publisher": "Materials Research Society", "publication": "Journal of Materials Research", "publication_date": "2013-04-14", "series_number": "7", "volume": "28", "issue": "7", "pages": "984-997" }, { "id": "authors:s0ffq-7pj43", "collection": "authors", "collection_id": "s0ffq-7pj43", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130423-150025688", "type": "article", "title": "Modeling dislocation nucleation strengths in pristine metallic nanowires under experimental conditions", "author": [ { "family_name": "Jennings", "given_name": "Andrew T.", "clpid": "Jennings-A-T" }, { "family_name": "Weinberger", "given_name": "Christopher R.", "clpid": "Weinberger-C-R" }, { "family_name": "Lee", "given_name": "Seok-Woo", "orcid": "0000-0001-6752-5694", "clpid": "Lee-Seok-Woo" }, { "family_name": "Aitken", "given_name": "Zachary H.", "clpid": "Aitken-Z-H" }, { "family_name": "Meza", "given_name": "Lucas R.", "orcid": "0000-0003-0250-2621", "clpid": "Meza-L-R" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "The nature of dislocation sources in small-scale metals is critical to understanding and building models of size-dependent crystalline strength at the nanoscale. Pre-existing dislocations with one pinning point can be readily described as truncated Frank\u2013Read sources, and modeling their operation strengths is straightforward. In contrast, simple and accurate models describing surface dislocation nucleation processes remain elusive. Here, we develop a computationally simple model of heterogeneous dislocation nucleation from free surfaces by combining a continuum description of the nucleation process with the atomistic inputs where accuracy is critical. This model is used to derive the upper strength limits of single-crystalline face-centered cubic nanopillars as a function of size, material and crystal orientation for uniaxial compression and tension. The output parameter space of this model is critically compared against direct atomistic simulations, as well as experiments on tension of pristine gold nanowires and compression of copper nanopillars to highlight its virtues and limitations.", "doi": "10.1016/j.actamat.2012.12.044", "issn": "1359-6454", "publisher": "Elsevier", "publication": "Acta Materialia", "publication_date": "2013-04", "series_number": "6", "volume": "61", "issue": "6", "pages": "2244-2259" }, { "id": "authors:d9rnq-jys11", "collection": "authors", "collection_id": "d9rnq-jys11", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130424-105427771", "type": "article", "title": "Emergence of enhanced strengths and Bauschinger effect in conformally passivated copper nanopillars as revealed by dislocation dynamics", "author": [ { "family_name": "Lee", "given_name": "Seok-Woo", "orcid": "0000-0001-6752-5694", "clpid": "Lee-Seok-Woo" }, { "family_name": "Jennings", "given_name": "Andrew T.", "clpid": "Jennings-A-T" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "The ability to precisely control the surface state of a nanostructure may offer a pathway towards tuning the mechanical properties of small-scale metallic components. In our previous work [Jennings et al., Acta Mater. 60 (2012) 3444\u20133455], single-crystalline Cu nanopillars were conformally coated with a 5\u201325 nm thick layer of TiO_2/Al_2O_3. Uniaxial compression tests revealed two key findings associated with these passivated samples: (i) \u223c80% higher strengths as compared with the uncoated samples of the same diameter, 200 nm; and (ii) Bauschinger effect-like hysteresis during unloading\u2013reloading segments. Dislocation dynamics simulations of uniaxially compressed 200 nm diameter Cu nanopillars with coated surfaces revealed the contribution of dislocation multiplication, pinning, and pile-up processes to the experimentally observed enhancement in pillar strength. They further helped explain the transition of plasticity mechanisms from dislocation multiplication via the operation of single-arm dislocation sources to dislocation nucleation from the crystal-coating interface. Hysteresis in stress\u2013strain data is discussed in the framework of dislocation structure evolution during unloading\u2013reloading cycles in experiments and simulations.", "doi": "10.1016/j.actamat.2012.12.008", "issn": "1359-6454", "publisher": "Elsevier", "publication": "Acta Materialia", "publication_date": "2013-04", "series_number": "6", "volume": "61", "issue": "6", "pages": "1872-1885" }, { "id": "authors:ww57w-rh354", "collection": "authors", "collection_id": "ww57w-rh354", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130424-111159482", "type": "article", "title": "Nanostructure and surface effects on yield in Cu nanowires", "author": [ { "family_name": "Wu", "given_name": "Z. X.", "clpid": "Wu-Z-X" }, { "family_name": "Zhang", "given_name": "Y. W.", "clpid": "Zhang-Y-W" }, { "family_name": "Jhon", "given_name": "M. H.", "clpid": "Jhon-M-H" }, { "family_name": "Greer", "given_name": "J. R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" }, { "family_name": "Srolovitz", "given_name": "D. J.", "clpid": "Srolovitz-D-J" } ], "abstract": "The yield strengths of nanomaterials are highly sensitive to their internal and surface structures. However, it is difficult to identify a priori which structural feature will govern plastic yield. We employ very large scale molecular dynamics simulations to explicitly identify the relevant yield mechanisms for Cu nanowires with four distinct, experimentally realizable nanostructures: single crystal (SC), nanotwinned single crystal (NTSC), nanocrystal (NC) and nanotwinned nanocrystal (NTNC). By characterizing the deformation at the yield point on the atomic scale, our simulations elucidate the effects of surface defects, nanotwins and grain boundaries on the commencement of yield and reveal several critically important features of the yielding process. First, the initial yields in all nanowires occur via dislocation nucleation at different characteristic nanostructural features. SC and NTSC nanowires yield via dislocation nucleation from surfaces or surface defects, while NC and NTNC nanowires yield via dislocation nucleation from grain boundary triple junctions. Second, our simulations highlight the relative potency of stress concentrators arising from different imperfections in modulating the yield strength of nanowires. Grain boundary triple junctions are as effective as surface defects at acting as stress concentrators. However, the higher density of triple junctions in NC and NTNC nanowires renders these structures considerably weaker than their SC and NTSC counterparts. Third, the presence of nanotwins only marginally enhances the yield strength of nanocrystalline Cu nanowires, which is in line with experimental observation in NTNC Cu nanowires but contrary to that in bulk ultrafine-grain nanotwinned Cu. The reason for this divergent behavior is that in nanowires yield strength is governed by dislocation nucleation from triple junctions in contrast to dislocation propagation in the bulk. Finally, excellent agreement is obtained between the relative yield strengths, stress\u2013strain behavior and dislocation nucleation conditions of nanowires in our simulations and existing experimental data. This suggests that our predicted atomistic processes controlling yield in our simulations may also control yield in experiments.", "doi": "10.1016/j.actamat.2012.11.053", "issn": "1359-6454", "publisher": "Elsevier", "publication": "Acta Materialia", "publication_date": "2013-04", "series_number": "6", "volume": "61", "issue": "6", "pages": "1831-1842" }, { "id": "authors:nwffg-f8b31", "collection": "authors", "collection_id": "nwffg-f8b31", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130412-141442900", "type": "article", "title": "The Effect of He Implantation on the Tensile Properties and Microstructure of Cu/Fe Nano-Bicrystals", "author": [ { "family_name": "Landau", "given_name": "Peri", "clpid": "Landau-P" }, { "family_name": "Guo", "given_name": "Q.", "clpid": "Guo-Qiang" }, { "family_name": "Hattar", "given_name": "K.", "clpid": "Hattar-K" }, { "family_name": "Greer", "given_name": "J. R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "In situ uniaxial tensile experiments on as-fabricated and helium-implanted 100 nm-diameter Cu/Fe bicrystals unearth the effect of individual face-centred-cubic/body-centred-cubic (fcc-bcc) interfaces on improving radiation-damage tolerance and helium absorption. Arrays of nanotensile specimens, each containing a single Cu grain in the bottom half and a single Fe grain on top, were fabricated by templated electron-beam lithography and electrodeposition. Helium is implanted at 200 keV to a dose of 10^(14) ion/cm^2 nominally into the interface region. High-resolution, site-specific transmission electron microscopy (TEM) and through-focus analysis reveal that the interfaces are nonplanar and contain \u22485 nm-spaced He bubbles with diameters of 1\u20132 nm. Nanomechanical experimental results show that the irradiated samples exhibit yield and ultimate tensile strengths more than 60% higher than the as-fabricated ones, while they retain comparable ductility. Tensile failure always occurs gradually, along the interfaces, with no noticeable shape localization. The absence of brittle failure in He-irradiated metals might be explained, in part, by the inability of the small He bubbles to serve as sufficient stress concentrators for cracking. In addition, the non-orthogonal orientation of the interfaces with respect to the loading axes results in the development of both normal- and shear-stress components. Tensile loading along the pillar axes may cause those interfacial regions subjected to normal stresses to detach, while the inclined regions, subjected to shear, to carry plastic deformation until final fracture.", "doi": "10.1002/adfm.201201776", "issn": "1616-301X", "publisher": "Wiley", "publication": "Advanced Functional Materials", "publication_date": "2013-03-13", "series_number": "10", "volume": "23", "issue": "10", "pages": "1281-1288" }, { "id": "authors:91wk8-4wn65", "collection": "authors", "collection_id": "91wk8-4wn65", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20121115-151311708", "type": "article", "title": "Helium Implantation Effects on the Compressive Response of Cu Nanopillars", "author": [ { "family_name": "Guo", "given_name": "Qiang", "clpid": "Guo-Qiang" }, { "family_name": "Landau", "given_name": "Peri", "clpid": "Landau-P" }, { "family_name": "Hosemann", "given_name": "Peter", "clpid": "Hosemann-P" }, { "family_name": "Wang", "given_name": "Yongqiang", "clpid": "Wang-Yongqiang" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "A fabrication methodology for 120 nm-diameter, <111>-oriented single crystalline Cu nanopillars which are uniformly implanted with helium is described. Uniaxial compression experiments reveal that their yield strength is 30% higher than that of their unimplanted counterparts. This study sheds light on the fundamental understanding of the deformation mechanism of irradiated metallic nanocrystals, and has important implications for the interplay between irradiation-induced defects and the external sample dimensions in the nanoscale.", "doi": "10.1002/smll.201201614", "issn": "1613-6810", "publisher": "Wiley", "publication": "Small", "publication_date": "2013-03-11", "series_number": "5", "volume": "9", "issue": "5", "pages": "691-696" }, { "id": "authors:bemew-mh433", "collection": "authors", "collection_id": "bemew-mh433", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130222-094935317", "type": "article", "title": "Emergence of film-thickness- and grain-size-dependent elastic\n properties in nanocrystalline thin films", "author": [ { "family_name": "Lian", "given_name": "Jie", "clpid": "Lian-Jie" }, { "family_name": "Lee", "given_name": "Seok-Woo", "orcid": "0000-0001-6752-5694", "clpid": "Lee-Seok-Woo" }, { "family_name": "Valdevit", "given_name": "Lorenzo", "clpid": "Valdevit-L" }, { "family_name": "Baskes", "given_name": "Michael I.", "clpid": "Baskes-M-I" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "Molecular dynamics simulations of nanocrystalline Ni revealed that the in-plane Young's modulus of 2.2 nm grained Ni film with \u223c10 grains across its thickness was only 0.64% smaller than that of bulk, while it dropped to 24.1% below bulk value for \u223c1 grain across film. This size dependence arises from the increased number of more compliant grains adjacent to the free surface. Simulations of nanocrystalline diamond revealed that the anharmonicity of the potential curve determined the sensitivity of the Young's modulus to variations in the sample size.", "doi": "10.1016/j.scriptamat.2012.10.031", "issn": "1359-6462", "publisher": "Elsevier", "publication": "Scripta Materialia", "publication_date": "2013-03", "series_number": "5", "volume": "68", "issue": "5", "pages": "261-264" }, { "id": "authors:syjms-ybr47", "collection": "authors", "collection_id": "syjms-ybr47", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130125-090536086", "type": "article", "title": "The mechanical behavior and deformation of bicrystalline nanowires", "author": [ { "family_name": "Tucker", "given_name": "Garritt J.", "clpid": "Tucker-G-J" }, { "family_name": "Aitken", "given_name": "Zachary H.", "clpid": "Aitken-Z-H" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" }, { "family_name": "Weinberger", "given_name": "Christopher R.", "clpid": "Weinberger-C-R" } ], "abstract": "The competition between free surfaces and internal grain boundaries as preferential sites for dislocation nucleation during plastic deformation in aluminum bicrystalline nanowires is investigated using molecular dynamics simulations at room temperature. A number of nanowires containing various minimum energy interfaces are studied under uniaxial compression at a constant applied strain rate to provide a broad, inclusive look at the competition between the two types of sources. In addition, we conduct a detailed study on the role of the grain boundaries to act as a source, sink, or obstacle for lattice dislocations, as a function of grain boundary structure. This work compares the behavior of bicrystalline nanowires containing both random high-angle boundaries and a series of symmetric tilt grain boundaries to further elucidate the effect of interface structure on its behavior. The results show that grain boundaries in nanowires can be preferred nucleation sites for dislocations and twin boundaries, in addition to efficient sinks and pinning points for migrating dislocations. Plastic deformation behavior at high imposed strains is linked to the underlying deformation processes, such as twinning, dislocation pinning, or dislocation exhaustion/starvation. We also detail some important reactions between lattice dislocations and grain boundaries observed in the simulations, along with the activation of a single-arm source. This work suggests that the cooperation of numerous mechanisms and the structure of internal grain boundaries are crucial in understanding the deformation of bicrystalline nanowires.", "doi": "10.1088/0965-0393/21/1/015004", "issn": "0965-0393", "publisher": "IOP", "publication": "Modelling and Simulation in Materials Science and Engineering", "publication_date": "2013-01", "series_number": "1", "volume": "21", "issue": "1", "pages": "Art. No. 015004" }, { "id": "authors:d8bx9-mpp70", "collection": "authors", "collection_id": "d8bx9-mpp70", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130523-135329186", "type": "book_section", "title": "Size-Dependent Strength in Single-Crystalline Metallic Nanostructures", "book_title": "Nano and Cell Mechanics: Fundamentals and Frontiers", "author": [ { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "contributor": [ { "family_name": "Espinosa", "given_name": "Horacia D.", "clpid": "Espinosa-H-D" }, { "family_name": "Bao", "given_name": "Gang", "clpid": "Bao-Gang" } ], "abstract": "The emergence of a substantial body of literature focusing on uniaxial compression experiments of micro- and nano-sized single-crystalline cylindrical papers has unambiguously demonstrated that, at these scales, the sample dimensions dramatically affect crystalline strength (for reviews, see [1-3]). In most of these experimental studies, cylindrical pillars with diameters ranging from ~ 100 nm up to several micrometers were fabricated, largely by the use of the focused ion beam (FIB) method, with some non-FIB-based methods as well, and were subsequently compressed in a nanoindenter with a custom-made flat punch indenter tip. More recently, small-scale mechanical behavior has also been explored through uniaxial tensile experiments, usually performed inside of in-situ scanning electron microscopes (SEM)- or transmission electron microscopes (TEM)-with the custom-built mechanical deformation instruments by a small number of research groups [3-6]. Intriguingly, the results of all of these reports for single-crystalline metals with a variety of crystal structures - face-centered cubic (fcc), body-centered cubic (bcc), hexagonal close-packed (hcp), and tetragonal -show power-law dependence between flow stress and pillar diameter. Further, within the fcc family, the slopes of all metals tested converge on a unique value of approximately -0.6 [1-3,7] (see Figure 7.1), which is not the case for all other crystals.", "doi": "10.1002/9781118482568.ch7", "isbn": "9781118460399", "publisher": "John Wiley & Sons, Ltd.", "place_of_publication": "Chichester, West Sussex", "publication_date": "2013", "pages": "163-190" }, { "id": "authors:yjctt-pny76", "collection": "authors", "collection_id": "yjctt-pny76", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130107-104520272", "type": "article", "title": "Size-Dependent Deformation of Nanocrystalline Pt Nanopillars", "author": [ { "family_name": "Gu", "given_name": "X. Wendy", "clpid": "Gu-X-Wendy" }, { "family_name": "Loynachan", "given_name": "Colleen N.", "clpid": "Loynachan-C-N" }, { "family_name": "Wu", "given_name": "Zhaoxuan", "clpid": "Wu-Zhaoxuan" }, { "family_name": "Zhang", "given_name": "Yong-Wei", "clpid": "Zhang-Yong-Wei" }, { "family_name": "Srolovitz", "given_name": "David J.", "clpid": "Srolovitz-D-J" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "We report the synthesis, mechanical properties, and deformation mechanisms of polycrystalline, platinum nanocylinders of grain size d = 12 nm. The number of grains across the diameter, D/d, was varied from 5 to 80 and 1.5 to 5 in the experiments and molecular dynamics simulations, respectively. An abrupt weakening is observed at a small D/d, while the strengths of large nanopillars are similar to bulk. This \"smaller is weaker\" trend is opposite to the \"smaller is stronger\" size effect in single crystalline nanostructures. The simulations demonstrate that the size-dependent behavior is associated with the distinct deformation mechanisms operative in interior versus surface grains.", "doi": "10.1021/nl3036993", "issn": "1530-6984", "publisher": "American Chemical Society", "publication": "Nano Letters", "publication_date": "2012-11-13", "series_number": "12", "volume": "12", "issue": "12", "pages": "6385-6392" }, { "id": "authors:bmzv0-9jg88", "collection": "authors", "collection_id": "bmzv0-9jg88", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170404-082920837", "type": "book_section", "title": "Nanoindentation and Nano-Compresion Testing of Ni_3Al Precipitates", "book_title": "Superalloys 2012", "author": [ { "family_name": "Gan", "given_name": "B.", "clpid": "Gan-Bin" }, { "family_name": "Murakami", "given_name": "H.", "clpid": "Murakami-H" }, { "family_name": "Maa\u00df", "given_name": "R.", "clpid": "Maa\u00df-R" }, { "family_name": "Meza", "given_name": "L.", "orcid": "0000-0003-0250-2621", "clpid": "Meza-L-R" }, { "family_name": "Greer", "given_name": "J. R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" }, { "family_name": "Ohmura", "given_name": "T.", "clpid": "Ohmura-T" }, { "family_name": "Tin", "given_name": "S.", "clpid": "Tin-Sammy" } ], "contributor": [ { "family_name": "Huron", "given_name": "Eric S.", "clpid": "Huron-E-S" } ], "abstract": "[no abstract]", "doi": "10.1002/9781118516430.ch9", "isbn": "9780470943205", "publisher": "Wiley", "place_of_publication": "Hoboken, NJ", "publication_date": "2012-10-02", "pages": "83-91" }, { "id": "authors:kcv76-gwg98", "collection": "authors", "collection_id": "kcv76-gwg98", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20121115-093146533", "type": "article", "title": "Exploring Deformation Mechanisms in Nanostructured Materials", "author": [ { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" }, { "family_name": "Jang", "given_name": "Dongchan", "orcid": "0000-0002-2814-9734", "clpid": "Jang-Dongchan" }, { "family_name": "Gu", "given_name": "X. Wendy", "clpid": "Gu-X-Wendy" } ], "abstract": "Useful properties of structural materials generally depend on their bulk microstructure. For centuries, improvements in structural materials relied heavily on processing, which in turn determined the resulting microstructure and properties. Materials sciences are entering an era in which specific properties of a material are obtained not only from its processing but also by controlling of the architecture of its constituents, often with sub-micron dimensions. To utilize this newly achievable nanoscale engineering precision in structural applications, it is imperative to quantify the deformation processes at each relevant scale, with special attention focusing on the importance of internal and external heterogeneities, for example grain boundaries, bi-material interfaces, phase boundaries, etc., on mechanical loading. It has been shown for single crystals that yield (and fracture) strengths increase with power-law dependence on sample size reduction when the micron scale is reached, and therefore, can no longer be inferred from bulk response or from the literature. Although these studies provide a powerful foundation for fundamental deformation processes operating at small scales, they are far from representing real materials used in structural applications, whose microstructure is often complex, containing boundaries and interfaces. Both homogeneous (i.e. grain and twin boundaries) and heterogeneous (i.e. phase and precipitate\u2013matrix boundaries) interfaces in size-limited features are crucial aspects of the structural reliability of most modern materials. They are also of particular importance to damage initiation. This article provides a comprehensive overview of the state-of-the-art experimental and computational methods used to investigate mechanical behavior and microstructural evolution in small-scale metallic systems, deformation of which depends on intricate interactions of defects with internal interfaces and with free surfaces. Attention is focused on the effects of multiple grain boundaries spanning the sample volume (nanocrystalline and polycrystalline metals). This overview sheds light on the relative importance of intrinsic versus extrinsic length scale limitations on deformation mechanisms in nanostructured metals, which has significant implications for the development of new materials with tunable mechanical properties.", "doi": "10.1007/s11837-012-0438-6", "issn": "1047-4838", "publisher": "Springer", "publication": "JOM - Journal of the Minerals, Metals and Materials Society", "publication_date": "2012-10", "series_number": "10", "volume": "64", "issue": "10", "pages": "1241-1252" }, { "id": "authors:1pp60-wb048", "collection": "authors", "collection_id": "1pp60-wb048", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20120716-152217289", "type": "article", "title": "Deformation mechanisms in nanotwinned metal nanopillars", "author": [ { "family_name": "Jang", "given_name": "Dongchan", "orcid": "0000-0002-2814-9734", "clpid": "Jang-Dongchan" }, { "family_name": "Liao", "given_name": "Xiaoyan", "clpid": "Liao-Xiaoyan" }, { "family_name": "Gao", "given_name": "Huajian", "orcid": "0000-0002-8656-846X", "clpid": "Gao-Huajian" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "Nanotwinned metals are attractive in many applications because they simultaneously demonstrate high strength and high ductility, characteristics that are usually thought to be mutually exclusive. However, most nanotwinned metals are produced in polycrystalline forms and therefore contain randomly oriented twin and grain boundaries making it difficult to determine the origins of their useful mechanical properties. Here, we report the fabrication of arrays of vertically aligned copper nanopillars that contain a very high density of periodic twin boundaries and no grain boundaries or other microstructural features. We use tension experiments, transmission electron microscopy and atomistic simulations to investigate the influence of diameter, twin-boundary spacing and twin-boundary orientation on the mechanical responses of individual nanopillars. We observe a brittle-to-ductile transition in samples with orthogonally oriented twin boundaries as the twin-boundary spacing decreases below a critical value (~3\u20134 nm for copper). We also find that nanopillars with slanted twin boundaries deform via shear offsets and significant detwinning. The ability to decouple nanotwins from other microstructural features should lead to an improved understanding of the mechanical properties of nanotwinned metals.", "doi": "10.1038/NNANO.2012.116", "issn": "1748-3387", "publisher": "Nature Publishing Group", "publication": "Nature Nanotechnology", "publication_date": "2012-09", "series_number": "9", "volume": "7", "issue": "9", "pages": "594-601" }, { "id": "authors:qevv1-n2e27", "collection": "authors", "collection_id": "qevv1-n2e27", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20121010-070312238", "type": "article", "title": "Statistics of Dislocation Slip Avalanches in Nanosized Single Crystals Show Tuned Critical Behavior Predicted by a Simple Mean Field Model", "author": [ { "family_name": "Friedman", "given_name": "Nir", "orcid": "0000-0002-9678-3550", "clpid": "Friedman-N" }, { "family_name": "Jennings", "given_name": "Andrew T.", "clpid": "Jennings-A-T" }, { "family_name": "Tsekenis", "given_name": "Georgios", "clpid": "Tsekenis-G" }, { "family_name": "Kim", "given_name": "Ju-Young", "clpid": "Kim-Ju-Young" }, { "family_name": "Tao", "given_name": "Molei", "clpid": "Tao-Molei" }, { "family_name": "Uhl", "given_name": "Jonathan T.", "clpid": "Uhl-J-T" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" }, { "family_name": "Dahmen", "given_name": "Karin A.", "clpid": "Dahmen-K-A" } ], "abstract": "We show that slowly sheared metallic nanocrystals deform via discrete strain bursts (slips), whose size distributions follow power laws with stress-dependent cutoffs. We show for the first time that plasticity reflects tuned criticality, by collapsing the stress-dependent slip-size distributions onto a predicted scaling function. Both power-law exponents and scaling function agree with mean-field theory predictions. Our study of 7 materials and 2 crystal structures, at various deformation rates, stresses, and crystal sizes down to 75 nm, attests to the universal characteristics of plasticity.", "doi": "10.1103/PhysRevLett.109.095507", "issn": "0031-9007", "publisher": "American Physical Society", "publication": "Physical Review Letters", "publication_date": "2012-08-30", "series_number": "9", "volume": "109", "issue": "9", "pages": "Art. No. 095507" }, { "id": "authors:d592s-bbf69", "collection": "authors", "collection_id": "d592s-bbf69", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20121011-101015825", "type": "article", "title": "Deformation of plastically compressible hardening-softening-hardening solids", "author": [ { "family_name": "Needleman", "given_name": "A.", "clpid": "Needleman-A" }, { "family_name": "Hutchens", "given_name": "S. B.", "clpid": "Hutchens-S-B" }, { "family_name": "Mohan", "given_name": "N.", "clpid": "Mohan-N" }, { "family_name": "Greer", "given_name": "J. R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "Motivated by a model of the response of vertically aligned carbon nanotube (VACNT) pillars in uniaxial compression, we consider the deformation of a class of compressible elastic-viscoplastic solids with a hardening-softening-hardening variation of flow strength with plastic strain. In previous work (Hutchens et al. 2011) a constitutive relation was presented and used to model the response of VACNT pillars in axisymmetric compression. Subsequently, it was found that due to a programming error the constitutive relation presented in the paper (Hutchens et al. 2011) was not the one actually implemented. In particular, the plastic flow rule actually used did not satisfy plastic normality. Here, we present the constitutive formulation actually implemented in the previous work (Hutchens et al. 2011). Dynamic, finite deformation, finite element calculations are carried out for uniaxial compression, uniaxial tension and for indentation of a \"half-space\" by a conical indenter tip. A sequential buckling-like deformation mode is found in compression when there is plastic non-normality and hardening-softening-hardening. The same material characterization gives rise to a L\u00fcders band-like deformation mode in tension. When there is a deformation mode with a sharp front along mesh boundaries, the overall stress-strain response contains high frequency oscillations that are a mesh artifact. The responses of non-softening solids are also analyzed and their overall stress-strain behavior and deformation modes are compared with those of hardening-softening-hardening solids. We find that indentation with a sharp indenter tip gives a qualitatively equivalent response for hardening and hardening-softening-hardening solids.", "doi": "10.1007/s10409-012-0117-4", "issn": "0567-7718", "publisher": "Springer Verlag", "publication": "Acta Mechanica Sinica", "publication_date": "2012-08", "series_number": "4", "volume": "28", "issue": "4", "pages": "1115-1124" }, { "id": "authors:rrpk0-sg284", "collection": "authors", "collection_id": "rrpk0-sg284", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20120405-082105826", "type": "article", "title": "Ultrahigh Strength of Dislocation-Free Ni_3Al Nanocubes", "author": [ { "family_name": "Maa\u00df", "given_name": "Robert", "clpid": "Maa\u00df-R" }, { "family_name": "Meza", "given_name": "Lucas", "orcid": "0000-0003-0250-2621", "clpid": "Meza-L-R" }, { "family_name": "Gan", "given_name": "Bin", "clpid": "Gan-Bin" }, { "family_name": "Tin", "given_name": "Sammy", "clpid": "Tin-Sammy" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "Individual Ni_3Al nanocubes under pressure are investigated by comparing the compressive strength of both dislocation-free and irradiated Ni3Al nanocubes. The results are dicussed in light of the size-dependent and size-independent strength of face-centered cubic (fcc) nanocrystals in the framework of dislocation nucleation at free surfaces. This study sheds more light on the understanding of fundamental deformation mechanisms and size-affected strength in dislocation-free metallic nanocrystals.", "doi": "10.1002/smll.201102603", "issn": "1613-6810", "publisher": "Wiley", "publication": "Small", "publication_date": "2012-06-25", "series_number": "12", "volume": "8", "issue": "12", "pages": "1869-1875" }, { "id": "authors:h52ra-tt269", "collection": "authors", "collection_id": "h52ra-tt269", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20120621-133116661", "type": "article", "title": "In Situ Nanomechanical Measurements of Interfacial Strength in Membrane-Embedded Chemically Functionalized Si Microwires for Flexible Solar Cells", "author": [ { "family_name": "Cho", "given_name": "Clara J.", "clpid": "Cho-Clara-J" }, { "family_name": "O'Leary", "given_name": "Leslie", "clpid": "O'Leary-L-E" }, { "family_name": "Lewis", "given_name": "Nathan S.", "orcid": "0000-0001-5245-0538", "clpid": "Lewis-N-S" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "Arrays of vertically aligned Si microwires embedded in polydimethylsiloxane (PDMS) have emerged as a promising candidate for use in solar energy conversion devices. Such structures are lightweight and concurrently demonstrate competitive efficiency and mechanical flexibility. To ensure reliable functioning under bending and flexing, strong interfacial adhesion between the nanowire and the matrix is needed. In situ uniaxial tensile tests of individual, chemically functionalized, Si microwires embedded in a compliant PDMS matrix reveal that chemical functionality on Si microwire surfaces is directly correlated with interfacial adhesion strength. Chemical functionalization can therefore serve as an effective methodology for accessing a wide range of interfacial adhesion between the rigid constituents and the soft polymer matrix; the adhesion can be quantified by measuring the mechanical strength of such systems.", "doi": "10.1021/nl3014007", "issn": "1530-6984", "publisher": "American Chemical Society", "publication": "Nano Letters", "publication_date": "2012-06-13", "series_number": "6", "volume": "12", "issue": "6", "pages": "3296-3301" }, { "id": "authors:j9vsn-2m052", "collection": "authors", "collection_id": "j9vsn-2m052", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20120611-111342071", "type": "article", "title": "Effects of morphology on the micro-compression response of carbon nanotube forests", "author": [ { "family_name": "Abadi", "given_name": "Parisa Pour Shahid Saeed", "clpid": "Abadi-P-P-S-S" }, { "family_name": "Hutchens", "given_name": "Shelby B.", "clpid": "Hutchens-S-B" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" }, { "family_name": "Cola", "given_name": "Baratunde A.", "clpid": "Cola-B-A" }, { "family_name": "Graham", "given_name": "Samuel", "clpid": "Graham-S" } ], "abstract": "This study reports the mechanical response of distinct carbon nanotube (CNT) morphologies as\nrevealed by flat punch in situ nanoindentation in a scanning electron microscope. We find that the\nlocation of incipient deformation varies significantly by changing the CNT growth parameters. The\ninitial buckles formed close to the growth substrate in 70 and 190 \u00b5m tall CNT forests grown with low\npressure chemical vapor deposition (LPCVD) and moved to ~100 \u00b5m above the growth substrate when\nthe height increased to 280 \u00b5m. Change of the recipe from LPCVD to CVD at pressures near\natmospheric changed the location of the initial buckling event from the bottom half to the top half of\nthe CNT forest. Plasma pretreatment of the catalyst also resulted in a unique CNT forest morphology\nin which deformation started by bending and buckling of the CNT tips. We find that the vertical\ngradients in CNT morphology dictate the location of incipient buckling. These new insights are critical\nin the design of CNT forests for a variety of applications where mechanical contact is important.", "doi": "10.1039/c2nr30474k", "issn": "2040-3372", "publisher": "Royal Society of Chemistry", "publication": "Nanoscale", "publication_date": "2012-06-07", "series_number": "11", "volume": "4", "issue": "11", "pages": "3373-3380" }, { "id": "authors:002w8-sgs03", "collection": "authors", "collection_id": "002w8-sgs03", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20120530-101424817", "type": "article", "title": "Suppression of Catastrophic Failure in Metallic Glass\u2013Polyisoprene Nanolaminate Containing Nanopillars", "author": [ { "family_name": "Kim", "given_name": "Ju-Young", "clpid": "Kim-J-Y" }, { "family_name": "Gu", "given_name": "Xun", "clpid": "Gu-X-Wendy" }, { "family_name": "Wraith", "given_name": "Matt", "clpid": "Wraith-M" }, { "family_name": "Uhl", "given_name": "Jonathan T.", "clpid": "Uhl-J-T" }, { "family_name": "Dahmen", "given_name": "Karin A.", "clpid": "Dahmen-K-A" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "One considerable concern in metallic glass is enhancing ductility by suppressing catastrophic failure by the instantaneous propagation of shear bands. Compressed nanopillars with alternating CuZr metallic glass and polyisoprene nanolaminates exhibit >30% enhancement in plastic flow, as compared with monolithic glass, without sacrifice of strength. A suppression of stochastic strain burst signature in these metallic glass-polymer composites is reported, which is an undesirable characteristic ubiquitously present in monolithic metallic glass and in metallic glass-metal composites. The intermittent stochastic signature is quantified in each metallic glass-containing nanolaminate system by constructing histograms of burst size distributions and provide theoretical foundation for each behavior. The exceptional mechanical properties emergent in these MG-polymer nanolaminate composites are attributed to the combination of nanometer size-induced shear band suppression in metallic glasses and the damping capability of the polyisoprene layers.", "doi": "10.1002/adfm.201103050", "issn": "1616-301X", "publisher": "Wiley", "publication": "Advanced Functional Materials", "publication_date": "2012-05-09", "series_number": "9", "volume": "22", "issue": "9", "pages": "1972-1980" }, { "id": "authors:026sf-e0a35", "collection": "authors", "collection_id": "026sf-e0a35", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20120613-103523754", "type": "article", "title": "Higher compressive strengths and the Bauschinger effect in conformally passivated copper nanopillars", "author": [ { "family_name": "Jennings", "given_name": "A. T.", "clpid": "Jennings-A-T" }, { "family_name": "Gross", "given_name": "C.", "clpid": "Gross-C" }, { "family_name": "Greer", "given_name": "F.", "clpid": "Greer-F" }, { "family_name": "Aitken", "given_name": "Z. H.", "clpid": "Aitken-Z-H" }, { "family_name": "Lee", "given_name": "S.-W.", "clpid": "Lee-S-W" }, { "family_name": "Weinberger", "given_name": "C. R.", "clpid": "Weinberger-C-R" }, { "family_name": "Greer", "given_name": "J. R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "Our current understanding of size-dependent strength in nano- and microscale crystals is centered around the idea that the overall strength is determined by the stress required to propagate dislocation sources. The nature and type of these dislocation sources is the subject of extensive debate, however, one commonality amongst these theories is that the ability of the free surface to absorb dislocations is a necessary condition for transition to a source controlled regime. In this work we demonstrate that atomic layer deposition (ALD) of conformal 5\u201325 nm thick TiO_2/Al_(2)O_3 coatings onto electroplated single crystalline copper pillars with diameters ranging from 75 nm to 1 \u03bcm generally inhibits the ability of a dislocation to vanish at the free surface. Uniaxial compression tests reveal increased strength and hardening relative to uncoated pillars at equivalent diameters, as well as a notable recovery of plastic strain during unloading, i.e. the Bauschinger effect. Unlike previous reports, these coated pillars retained the stochastic signature in their stress\u2013strain curves. We explain these observations within the framework of a size-dependent strength theory based on a single arm source model, dislocation theory, and microstructural analysis by transmission electron microscopy.", "doi": "10.1016/j.actamat.2012.03.013", "issn": "1359-6454", "publisher": "Elsevier", "publication": "Acta Materialia", "publication_date": "2012-05", "series_number": "8", "volume": "60", "issue": "8", "pages": "3444-3455" }, { "id": "authors:c5krr-ave21", "collection": "authors", "collection_id": "c5krr-ave21", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20120427-133508396", "type": "article", "title": "A microstructurally motivated description of the deformation of vertically aligned carbon nanotube structures", "author": [ { "family_name": "Hutchens", "given_name": "Shelby B.", "clpid": "Hutchens-S-B" }, { "family_name": "Needleman", "given_name": "Alan", "clpid": "Needleman-A" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "Vertically aligned carbon nanotube's extreme compliance and mechanical energy absorption/dissipation capabilities are potentially promising aspects of their multi-functionality. Mathematical models have revealed that a hardening-softening-hardening material relation can capture the unique sequential, periodic buckling behavior displayed by vertically aligned carbon nanotubes under uniaxial compression. Yet the physical origins of these models remain unknown. We provide a microstructure-based motivation for such a phenomenological constitutive relation and use it to explore changes in structural response with nanotube volume fraction.", "doi": "10.1063/1.3697686", "issn": "0003-6951", "publisher": "American Institute of Physics", "publication": "Applied Physics Letters", "publication_date": "2012-03-19", "series_number": "12", "volume": "100", "issue": "12", "pages": "Art. No. 121910" }, { "id": "authors:2n82w-r5479", "collection": "authors", "collection_id": "2n82w-r5479", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20120420-100036179", "type": "article", "title": "Plasticity of indium nanostructures as revealed by synchrotron X-ray microdiffraction", "author": [ { "family_name": "Budiman", "given_name": "Arief Suriadi", "clpid": "Budiman-A-S" }, { "family_name": "Lee", "given_name": "Gyuhyon", "clpid": "Lee-Gyuhyon" }, { "family_name": "Burek", "given_name": "Michael J.", "clpid": "Burek-M-J" }, { "family_name": "Jang", "given_name": "Dongchan", "orcid": "0000-0002-2814-9734", "clpid": "Jang-Dongchan" }, { "family_name": "Han", "given_name": "Seung Min J.", "clpid": "Han-Seung-Min-J" }, { "family_name": "Tamura", "given_name": "Nobumichi", "orcid": "0000-0002-3698-2611", "clpid": "Tamura-Nobumichi" }, { "family_name": "Kunz", "given_name": "Martin", "clpid": "Kunz-M" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" }, { "family_name": "Tsui", "given_name": "Ting Y.", "clpid": "Tsui-Ting-Y" } ], "abstract": "Indium columnar structures with diameters near 1 \u03bcm were deformed by uniaxial compression at strain rates of approximately 0.01 and 0.001 s^(\u22121). Defect density evolution in the nanopillars was evaluated by applying synchrotron Laue X-ray microdiffraction (\u03bcSLXRD) on the same specimens before and after deformation. Results of the \u03bcSLXRD measurements indicate that the dislocation density increases as a result of mechanical deformation and is a strong function of strain rate. These results suggest that the rate of defect generation during the compression tests exceeds the rate of defect annihilation, implying that plasticity in these indium nanostructures commences via dislocation multiplication rather than nucleation processes. This is in contrast with the behaviors of other materials at the nanoscale, such as, gold, tin, molybdenum, and bismuth. A hypothesis based on the dislocation mean-free-path prior to the multiplication process is proposed to explain this variance.", "doi": "10.1016/j.msea.2012.01.017", "issn": "0921-5093", "publisher": "Elsevier", "publication": "Materials Science and Engineering A", "publication_date": "2012-03-15", "volume": "538", "pages": "89-97" }, { "id": "authors:ameq3-fts69", "collection": "authors", "collection_id": "ameq3-fts69", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20120420-144857331", "type": "article", "title": "Higher Recovery and Better Energy Dissipation at Faster Strain Rates in Carbon Nanotube Bundles: An in-Situ Study", "author": [ { "family_name": "Pathak", "given_name": "Siddhartha", "clpid": "Pathak-S" }, { "family_name": "Lim", "given_name": "Ee J.", "clpid": "Lim-Ee-J" }, { "family_name": "Abadi", "given_name": "Parisa Pour Shahid Saeed", "clpid": "Abadi-P-P-S-S" }, { "family_name": "Graham", "given_name": "Samuel", "clpid": "Graham-S" }, { "family_name": "Cola", "given_name": "Baratunde A.", "clpid": "Cola-B-A" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "We report mechanical behavior and strain rate dependence of recoverability and energy dissipation in vertically aligned carbon nanotube (VACNT) bundles subjected to quasi-static uniaxial compression. We observe three distinct regimes in their stress\u2013strain curves for all explored strain rates from 4 \u00d7 10^(\u20132) down to 4 \u00d7 10^(\u20134) /sec: (1) a short initial elastic section followed by (2) a sloped plateau with characteristic wavy features corresponding to buckle formation and (3) densification characterized by rapid stress increase. Load\u2013unload cycles reveal a stiffer response and virtually 100% recoverability at faster strain rates of 0.04/sec, while the response is more compliant at slower rates, characterized by permanent localized buckling and significantly reduced recoverability. We propose that it is the kinetics of attractive adhesive interactions between the individual carbon nanotubes within the VACNT matrix that governs morphology evolution and ensuing recoverability. In addition, we report a 6-fold increase in elastic modulus and gradual decrease in recoverability (down to 50%) when VACNT bundles are unloaded from postdensification stage as compared with predensification. Finally, we demonstrate energy dissipation capability, as revealed by hysteresis in load\u2013unload cycles. These findings, together with high thermal and electrical conductivities, position VACNTs in the \"unattained-as-of-to-date-space\" in the material property landscape.", "doi": "10.1021/nn300376j", "issn": "1936-0851", "publisher": "American Chemical Society", "publication": "ACS Nano", "publication_date": "2012-03", "series_number": "3", "volume": "6", "issue": "3", "pages": "2189-2197" }, { "id": "authors:cqay5-cnp92", "collection": "authors", "collection_id": "cqay5-cnp92", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20120504-111031921", "type": "article", "title": "Nanoshearing - Collective carbon nanotube micromechanics", "author": [ { "family_name": "Hutchens", "given_name": "Shelby B.", "clpid": "Hutchens-S-B" }, { "family_name": "Decolvenaere", "given_name": "Elizabeth", "clpid": "Decolvenaere-E" }, { "family_name": "Pathak", "given_name": "Siddhartha", "clpid": "Pathak-S" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "N/A", "doi": "10.1016/S1369-7021(12)70048-2", "issn": "1369-7021", "publisher": "Elsevier", "publication": "Materials Today", "publication_date": "2012-03", "series_number": "3", "volume": "15", "issue": "3", "pages": "127-127" }, { "id": "authors:rszw6-v6h16", "collection": "authors", "collection_id": "rszw6-v6h16", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20120302-094512909", "type": "article", "title": "Compressive properties of interface-containing Cu\u2013Fe nano-pillars", "author": [ { "family_name": "Guo", "given_name": "Qiang", "clpid": "Guo-Qiang" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "We report a focused-ion-beam-less fabrication route for producing 100 nm-diameter bi-material nano-pillars comprising single crystalline ~<110>-oriented Fe and ~<111>-oriented Cu. Uniaxial compression tests revealed that these pillars exhibit strengths around 1 GPa, without failure at the Cu\u2013Fe interface. The pillars represent a prototyped metal\u2013matrix nano-composite with highly\ncontrollable microstructure, high strengths, and strong metal\u2013metal interfaces. The isolation and engineering of a single interface in a single pillar allow for fundamental insights gained into their deformation mechanisms.", "doi": "10.1016/j.scriptamat.2011.11.008", "issn": "1359-6462", "publisher": "Elsevier", "publication": "Scripta Materialia", "publication_date": "2012-03", "series_number": "5", "volume": "66", "issue": "5", "pages": "272-275" }, { "id": "authors:18vk7-6hq65", "collection": "authors", "collection_id": "18vk7-6hq65", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20120104-143903753", "type": "article", "title": "Atomistic simulations and continuum modeling of dislocation\n nucleation and strength in gold nanowires", "author": [ { "family_name": "Weinberger", "given_name": "Christopher R.", "clpid": "Weinberger-C-R" }, { "family_name": "Jennings", "given_name": "Andrew T.", "clpid": "Jennings-A-T" }, { "family_name": "Kang", "given_name": "Keonwook", "clpid": "Kang-Keonwook" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "The strength of true metallic nanowires and nanopillars (diameters below 100 nm) is known to be higher than the strength of bulk metals and is most likely controlled by dislocation nucleation from free surfaces. Dislocation nucleation is a thermally activated process that is sensitive to both temperature and strain rate. However, most simulations rely on high strain rate molecular dynamics to investigate strength and nucleation, which is limited by short molecular dynamics time scales. In this work, the energetics of dislocation nucleation in gold nanowires are computed using atomistic simulations, and transition state theory is used to estimate the strength at experimental strain rates revealing detailed information outside the realm accessible to molecular dynamics simulations. This allows investigation into the competition between thermally activated dislocation nucleation and other failure mechanisms such as elastic and structural instabilities. Additionally, the mechanisms of dislocation nucleation are compared against analytical continuum models which allow a better understanding of the nucleation process including the effects of the wire surfaces. This study helps clarify and consolidate our understanding of the nature of dislocation nucleation in small structures.", "doi": "10.1016/j.jmps.2011.09.010", "issn": "0022-5096", "publisher": "Elsevier", "publication": "Journal of the Mechanics and Physics of Solids", "publication_date": "2012-01", "series_number": "1", "volume": "60", "issue": "1", "pages": "84-103" }, { "id": "authors:8atpc-mfp78", "collection": "authors", "collection_id": "8atpc-mfp78", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20111223-090231432", "type": "article", "title": "Crystallographic orientation and size dependence of tension\u2013compression asymmetry in molybdenum nano-pillars", "author": [ { "family_name": "Kim", "given_name": "Ju-Young", "clpid": "Kim-Ju-Young" }, { "family_name": "Jang", "given_name": "Dongchan", "orcid": "0000-0002-2814-9734", "clpid": "Jang-Dongchan" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "Uniaxial tension and compression experiments on [0 0 1] and [0 1 1] oriented molybdenum nano-pillars exhibit tension\u2013compression asymmetry, a difference in attained stresses in compression vs. tension, which is found to depend on crystallographic orientation and sample size. We find that (1) flow stresses become higher at smaller diameters in both orientations and both loading directions, (2) compressive flow stresses are higher than tensile ones in [0 0 1] orientation, and visa versa in [0 1 1] orientation, and (3) this tension\u2013compression asymmetry is in itself size dependent. We attribute these phenomena to the dependence of twinning vs. antitwinning deformation on loading direction, to the non-planarity of screw dislocation cores in Mo crystals, and to the possibly lesser role of screw dislocations in governing nano-scale plasticity compared with bulk Mo.", "doi": "10.1016/j.ijplas.2011.05.015", "issn": "0749-6419", "publisher": "Elsevier", "publication": "International Journal of Plasticity", "publication_date": "2012-01", "series_number": "1", "volume": "28", "issue": "1", "pages": "46-52" }, { "id": "authors:rpcnd-f5563", "collection": "authors", "collection_id": "rpcnd-f5563", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20120123-152313648", "type": "article", "title": "Continuum modeling of dislocation starvation and subsequent nucleation in nano-pillar compressions", "author": [ { "family_name": "J\u00e9rusalem", "given_name": "Antoine", "clpid": "J\u00e9rusalem-A" }, { "family_name": "Fern\u00e1ndez", "given_name": "Ana", "orcid": "0000-0001-6825-0426", "clpid": "Fern\u00e1ndez-A" }, { "family_name": "Kunz", "given_name": "Allison", "clpid": "Kunz-A" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "The mechanical behavior of single crystalline aluminum nano-pillars under uniaxial compression differs from bulk Al in that the former is characterized by a smoother transition from elasticity to plasticity. We propose an extension of the phenomenological model of dislocation starvation originally proposed in [Greer and Nix, Phys. Rev. B 73 (2006) 245410] additionally accounting for dislocation nucleation. The calibrated and validated continuum model successfully captures the intrinsic mechanisms leading to the transition from dislocation starvation to dislocation nucleation in fcc nano-pillars.", "doi": "10.1016/j.scriptamat.2011.10.009", "issn": "1359-6462", "publisher": "Elsevier", "publication": "Scripta Materialia", "publication_date": "2012-01", "series_number": "2", "volume": "66", "issue": "2", "pages": "93-96" }, { "id": "authors:vnqw9-1c432", "collection": "authors", "collection_id": "vnqw9-1c432", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20120106-091747290", "type": "article", "title": "Nanolaminates Utilizing Size-Dependent Homogeneous Plasticity of Metallic Glasses", "author": [ { "family_name": "Kim", "given_name": "Ju-Young", "clpid": "Kim-Ju-Young" }, { "family_name": "Jang", "given_name": "Dongchan", "orcid": "0000-0002-2814-9734", "clpid": "Jang-Dongchan" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "Homogeneous plasticity in metallic glasses is generally only observed at high temperatures or in very small structures (less than \u2248100 nm), so their applications for structural performance have been very limited. Here, nanolaminates with alternating layers of Cu_(50)Zr_(50) metallic glass and nanocrystalline Cu are synthesized and it is found that samples with an optimal composition of 112-nm-thick metallic-glass layers and 16-nm-thick Cu layers demonstrate a maximum strength of 2.513 GPa, a value 33% greater than that predicted by the rule-of-mixtures and 25% better than that of pure Cu_(50)Zr_(50) metallic glass. Furthermore, \u22484% strain at fracture is achieved, suppressing the instantaneous catastrophic failure often associated with metallic glasses. It is postulated that this favorable combination of high strength and deformability is caused by the size-dependent deformation-mode transition in metallic glasses, from highly localized plasticity, leading to immediate failure in larger samples to homogeneous extension in the smaller ones.", "doi": "10.1002/adfm.201101164", "issn": "1616-301X", "publisher": "Wiley", "publication": "Advanced Functional Materials", "publication_date": "2011-12-06", "series_number": "23", "volume": "21", "issue": "23", "pages": "4550-4554" }, { "id": "authors:05mkq-g4w85", "collection": "authors", "collection_id": "05mkq-g4w85", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20120312-110102686", "type": "article", "title": "Heterogeneous dislocation nucleation from surfaces and interfaces as governing plasticity mechanism in nanoscale metals", "author": [ { "family_name": "Jennings", "given_name": "Andrew T.", "clpid": "Jennings-A-T" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "We report the results of constant strain rate experiments on electroplated, single crystalline copper pillars with diameters between 75 and 525 nm. At slow strain rates, 10^(\u22123) s^(\u22121), pillar diameters with 150 nm and above show a size-dependent strength similar to previous reports. Below 150 nm, we find that the size effect vanishes as the strength transitions to a relatively size-independent regime. Strain rate sensitivity and activation volume are determined from uniaxial compression tests at different strain rates and corroborate a deformation mechanism change. These results are discussed in the framework of recent in situ transmission electron microscopy experiments observing two distinct deformation mechanisms in pillars and thin films on flexible substrates: partial dislocation nucleation from stress concentrations in smaller structures and single arm source operation in larger samples. Models attempting to explain these different size-dependent regimes are discussed in relation to these experiments and existing literature revealing further insights into the likely small-scale deformation mechanisms.", "doi": "10.1557/jmr.2011.338", "issn": "0884-2914", "publisher": "Materials Research Society", "publication": "Journal of Materials Research", "publication_date": "2011-11-22", "series_number": "22", "volume": "26", "issue": "22", "pages": "2803-2814" }, { "id": "authors:4ahsx-8cr72", "collection": "authors", "collection_id": "4ahsx-8cr72", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20111207-112803529", "type": "article", "title": "Ultralight Metallic Microlattices", "author": [ { "family_name": "Schaedler", "given_name": "T. A.", "clpid": "Schaedler-T-A" }, { "family_name": "Jacobsen", "given_name": "A. J.", "clpid": "Jacobsen-A-J" }, { "family_name": "Torrents", "given_name": "A.", "clpid": "Torrents-A" }, { "family_name": "Sorensen", "given_name": "A. E.", "clpid": "Sorensen-A-E" }, { "family_name": "Lian", "given_name": "J.", "clpid": "Lian-J" }, { "family_name": "Greer", "given_name": "J. R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" }, { "family_name": "Valdevit", "given_name": "L.", "clpid": "Valdevit-L" }, { "family_name": "Carter", "given_name": "W. B.", "clpid": "Carter-W-B" } ], "abstract": "Ultralight (<10 milligrams per cubic centimeter) cellular materials are desirable for thermal insulation; battery electrodes; catalyst supports; and acoustic, vibration, or shock energy damping. We present ultralight materials based on periodic hollow-tube microlattices. These materials are fabricated by starting with a template formed by self-propagating photopolymer waveguide prototyping, coating the template by electroless nickel plating, and subsequently etching away the template. The resulting metallic microlattices exhibit densities \u03c1 \u2265 0.9 milligram per cubic centimeter, complete recovery after compression exceeding 50% strain, and energy absorption similar to elastomers. Young's modulus E scales with density as E ~ \u03c1^2, in contrast to the E ~ \u03c1^3 scaling observed for ultralight aerogels and carbon nanotube foams with stochastic architecture. We attribute these properties to structural hierarchy at the nanometer, micrometer, and millimeter scales.", "doi": "10.1126/science.1211649", "issn": "0036-8075", "publisher": "American Association for the Advancement of Science", "publication": "Science", "publication_date": "2011-11-18", "series_number": "6058", "volume": "334", "issue": "6058", "pages": "962-965" }, { "id": "authors:jew0m-j5a38", "collection": "authors", "collection_id": "jew0m-j5a38", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20111025-072156444", "type": "article", "title": "Analysis of uniaxial compression of vertically aligned\n carbon nanotubes", "author": [ { "family_name": "Hutchens", "given_name": "Shelby B.", "clpid": "Hutchens-S-B" }, { "family_name": "Needleman", "given_name": "Alan", "clpid": "Needleman-A" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "We carry out axisymmetric, finite deformation finite element analyses of the uniaxial compression of cylindrical bundles of vertically aligned carbon nanotubes (VACNTs) firmly attached to a Si substrate. A compressible elastic\u2013viscoplastic constitutive relation with a piecewise, linear hardening\u2013softening\u2013hardening flow strength is used to model the material. Calculations are performed for VACNTs both with uniform properties and with axially graded properties. We show that, with uniform properties, sequential buckling initiates at the substrate and propagates away from it, in agreement with previous experimental findings. We investigate the dependence of the magnitude and wavelength of the buckles on characteristics of the function defining the flow strength. When a property gradient giving a more compliant response at the end opposite to the substrate is specified, we find that sequential buckling initiates at that end and propagates toward the substrate. Results of the analyses are compared with the experimental observations and capture many of the experimentally obtained stress\u2013strain and morphological features. The proposed model serves as a promising foundation for capturing the underlying energy absorption mechanisms in these systems. Comparison of the model predictions with the experimental results also suggests directions for model improvement.", "doi": "10.1016/j.jmps.2011.05.002", "issn": "0022-5096", "publisher": "Elsevier", "publication": "Journal of the Mechanics and Physics of Solids", "publication_date": "2011-10", "series_number": "10", "volume": "59", "issue": "10", "pages": "2227-2237" }, { "id": "authors:1zmzb-s4s81", "collection": "authors", "collection_id": "1zmzb-s4s81", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20111116-101311984", "type": "article", "title": "Catastrophic vs Gradual Collapse of Thin-Walled Nanocrystalline Ni Hollow Cylinders As Building Blocks of Microlattice Structures", "author": [ { "family_name": "Lian", "given_name": "Jie", "clpid": "Lian-Jie" }, { "family_name": "Jang", "given_name": "Dongchan", "orcid": "0000-0002-2814-9734", "clpid": "Jang-Dongchan" }, { "family_name": "Valdevit", "given_name": "Lorenzo", "clpid": "Valdevit-L" }, { "family_name": "Schaedler", "given_name": "Tobias A.", "clpid": "Schaedler-T-A" }, { "family_name": "Jacobsen", "given_name": "Alan J.", "clpid": "Jacobsen-A-J" }, { "family_name": "Carter", "given_name": "William B.", "clpid": "Carter-W-B" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "Lightweight yet stiff and strong lattice structures are attractive for various engineering applications, such as cores of sandwich shells and components designed for impact mitigation. Recent breakthroughs in manufacturing enable efficient fabrication of hierarchically architected microlattices, with dimensional control spanning seven orders of magnitude in length scale. These materials have the potential to exploit desirable nanoscale-size effects in a macroscopic structure, as long as their mechanical behavior at each appropriate scale \u2013 nano, micro, and macro levels \u2013 is properly understood. In this letter, we report the nanomechanical response of individual microlattice members. We show that hollow nanocrystalline Ni cylinders differing only in wall thicknesses, 500 and 150 nm, exhibit strikingly different collapse modes: the 500 nm sample collapses in a brittle manner, via a single strain burst, while the 150 nm sample shows a gradual collapse, via a series of small and discrete strain bursts. Further, compressive strength in 150 nm sample is 99.2% lower than predicted by shell buckling theory, likely due to localized buckling and fracture events observed during in situ compression experiments. We attribute this difference to the size-induced transition in deformation behavior, unique to nanoscale, and discuss it in the framework of \"size effects\" in crystalline strength.", "doi": "10.1021/nl202475p", "issn": "1530-6984", "publisher": "American Chemical Society", "publication": "Nano Letters", "publication_date": "2011-10", "series_number": "10", "volume": "11", "issue": "10", "pages": "4118-4125" }, { "id": "authors:bg6mz-8sp54", "collection": "authors", "collection_id": "bg6mz-8sp54", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20110906-090719350", "type": "article", "title": "Size effects in strength and plasticity of single-crystalline titanium micropillars with prismatic slip orientation", "author": [ { "family_name": "Sun", "given_name": "Qiaoyan", "clpid": "Sun-Qiaoyan" }, { "family_name": "Guo", "given_name": "Qiang", "clpid": "Guo-Qiang" }, { "family_name": "Yao", "given_name": "Xi", "clpid": "Yao-Xi" }, { "family_name": "Xiao", "given_name": "Lin", "clpid": "Xiao-Lin" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" }, { "family_name": "Sun", "given_name": "Jun", "clpid": "Sun-Jun" } ], "abstract": "We present results of uniaxial compression experiments on rectangular prismatic titanium micropillars loaded along [1120]. We find that flow stress increases significantly with decreasing pillar size down to 300 nm, with a slope of -0.5 on the log\u2013log scale. The strength of 300 nm pillars is 1040 MPa, reaching 16% of the theoretical strength of titanium. We observe wavy lines for samples with diameters greater than 1 \u00b5m. The critical resolved shear stress is inversely proportional to the sample size, consistent with dislocation source nucleation-controlled plasticity.", "doi": "10.1016/j.scriptamat.2011.05.033", "issn": "1359-6462", "publisher": "Elsevier", "publication": "Scripta Materialia", "publication_date": "2011-09", "series_number": "6", "volume": "65", "issue": "6", "pages": "473-476" }, { "id": "authors:zgs0y-btj79", "collection": "authors", "collection_id": "zgs0y-btj79", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20110912-113911247", "type": "article", "title": "Emergence of strain-rate sensitivity in Cu nanopillars: Transition from dislocation multiplication to dislocation nucleation", "author": [ { "family_name": "Jennings", "given_name": "Andrew T.", "clpid": "Jennings-A-T" }, { "family_name": "Li", "given_name": "Ju", "clpid": "Li-Ju" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "We demonstrate strain-rate sensitivity emerging in single-crystalline Cu nanopillars with diameters ranging from 75 up to 500 nm through uniaxial deformation experiments performed at different constant strain rates. In the range of pillar diameters and strain rates tested, we find that the size dependence of the pillar strength deviates from the ubiquitously observed power law to a relatively size-independent flow strength, markedly below the predicted theoretical strength for strain rates slower than 10^(\u22121) s^(\u22121). We find this transition diameter, D_t, to be a function of strain rate, where faster strain rates shift the transition diameter to smaller pillar diameters: D_t ~ 150 nm at 10^(\u22123) s^(\u22121) and D_t \u223c \u226475 nm at 10^(\u22121) s^(\u22121). We compute the activation volumes, \u03a9, as a function of pillar diameter at each strain rate and find that for pillar diameters below D_t, the activation volumes are relatively small, \u03a9 < 10b^3. This range agrees favorably with atomistic simulations for dislocation nucleation from a free surface. We postulate a plasticity mechanism transition from dislocation multiplication via the operation of truncated dislocation sources, also referred to as single-arm sources, in pillars with diameters greater than D_t to dislocation nucleation from the surface in the smaller samples.", "doi": "10.1016/j.actamat.2011.05.038", "issn": "1359-6454", "publisher": "Elsevier", "publication": "Acta Materialia", "publication_date": "2011-08", "series_number": "14", "volume": "59", "issue": "14", "pages": "5627-5637" }, { "id": "authors:q1440-sf167", "collection": "authors", "collection_id": "q1440-sf167", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20110608-112911849", "type": "article", "title": "Plasticity in small-sized metallic systems: Intrinsic versus extrinsic size effect", "author": [ { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" }, { "family_name": "De Hosson", "given_name": "Jeff Th. M.", "clpid": "De-Hosson-J-Th-M" } ], "abstract": "A material strength depends on its microstructure, which in turn, is controlled by an engineering process. Strengthening mechanisms like work hardening, precipitate, and grain boundary strengthening can alter the strength of a material in a predictive, quantitative manner and are readily linked to the deformation mechanism. This quantification strongly depends on the characteristic length scale of a particular microstructure, thereby dictating bulk material's strength as a function of, for example, grain or precipitate size, twin boundary spacing, or dislocation density. This microstructural, or intrinsic, size governs the mechanical properties and post-elastic material deformation at all sample dimensions, as the classical definition of \"ultimate tensile strength\" deems it to be \"an intensive property, therefore its value does not depend on the size of the test specimen.\" Yet in the last 5 years, the vast majority of uniaxial deformation experiments and computations on small-scale metallic structures unambiguously demonstrated that at the micron and sub-micron scales, this definition no longer holds true. In fact, it has been shown that in single crystals the ultimate tensile strength and the yield strength scale with external sample size in a power law fashion, sometimes attaining a significant fraction of material's theoretical strength, and exhibiting the now-commonly-known phenomenon \"smaller is stronger.\" Understanding of this \"extrinsic size effect\" at small scales is not yet mature and is currently a topic of rigorous investigations. As both the intrinsic (i.e. microstructural) and extrinsic (i.e. sample size) dimensions play a non-trivial role in the mechanical properties and material deformation mechanisms, it is critical to develop an understanding of their interplay and mutual effects on the mechanical properties and material deformation, especially in small-scale structures. This review focuses on providing an overview of metal-based material classes whose properties as a function of external size have been investigated and provides a critical discussion on the combined effects of intrinsic and extrinsic sizes on the material deformation behavior.", "doi": "10.1016/j.pmatsci.2011.01.005", "issn": "0079-6425", "publisher": "Elsevier", "publication": "Progress in Materials Science", "publication_date": "2011-08", "series_number": "6", "volume": "56", "issue": "6", "pages": "654-724" }, { "id": "authors:9967n-grw30", "collection": "authors", "collection_id": "9967n-grw30", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20110801-133052184", "type": "article", "title": "Plastic deformation of indium nanostructures", "author": [ { "family_name": "Lee", "given_name": "Gyuhyon", "clpid": "Lee-Gyuhyon" }, { "family_name": "Kim", "given_name": "Ju-Young", "clpid": "Kim-Ju-Young" }, { "family_name": "Burek", "given_name": "Michael J.", "clpid": "Burek-M-J" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" }, { "family_name": "Tsui", "given_name": "Ting Y.", "clpid": "Tsui-Ting-Y" } ], "abstract": "Mechanical properties and morphology of cylindrical indium nanopillars, fabricated by electron beam lithography and electroplating, are characterized in uniaxial compression. Time-dependent deformation and influence of size on nanoscale indium mechanical properties were investigated. The results show two fundamentally different deformation mechanisms which govern plasticity in these indium nanostructures. We observed that the majority of indium nanopillars deform at engineering stresses near the bulk values (Type I), with a small fraction sustaining flow stresses approaching the theoretical limit for indium (Type II). The results also show the strain rate sensitivity and flow stresses in Type I indium nanopillars are similar to bulk indium with no apparent size effects.", "doi": "10.1016/j.msea.2011.04.065", "issn": "0921-5093", "publisher": "Elsevier", "publication": "Materials Science and Engineering A", "publication_date": "2011-07-25", "series_number": "19-20", "volume": "528", "issue": "19-20", "pages": "6112-6120" }, { "id": "authors:z1e81-wfe42", "collection": "authors", "collection_id": "z1e81-wfe42", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20110624-095047405", "type": "article", "title": "Size effects in Al nanopillars: Single crystalline vs. bicrystalline", "author": [ { "family_name": "Kunz", "given_name": "Allison", "clpid": "Kunz-A" }, { "family_name": "Pathak", "given_name": "Siddhartha", "clpid": "Pathak-S" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "The mechanical behavior of bicrystalline aluminum nano-pillars under uniaxial compression reveals size effects, a stochastic stress\u2013strain signature, and strain hardening. Pillar diameters range from 400 nm to 2 \u03bcm and contain a single, non-sigma high angle grain boundary oriented parallel to the pillar axes. Our results indicate that these bicrystalline pillars are characterized by intermittent strain bursts and exhibit an identical size effect to their single crystalline counterparts. Further, we find that the presence of this particular grain boundary generally decreases the degree of work hardening relative to the single crystalline samples. These findings, along with transmission electron microscopy analysis, show that nano-pillar plasticity in the presence of a grain boundary is also characterized by dislocation avalanches, likely resulting from dislocation nucleation-controlled mechanisms, and that at these small length scales this grain boundary may serve as a dislocation sink rather than a dislocation source.", "doi": "10.1016/j.actamat.2011.03.065", "issn": "1359-6454", "publisher": "Elsevier", "publication": "Acta Materialia", "publication_date": "2011-06", "series_number": "11", "volume": "59", "issue": "11", "pages": "4416-4424" }, { "id": "authors:s8p2r-nx769", "collection": "authors", "collection_id": "s8p2r-nx769", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20110627-112106280", "type": "article", "title": "Effects of size on the strength and deformation mechanism in Zr-based metallic glasses", "author": [ { "family_name": "Jang", "given_name": "Dongchan", "orcid": "0000-0002-2814-9734", "clpid": "Jang-Dongchan" }, { "family_name": "Gross", "given_name": "Cameron T.", "clpid": "Gross-C-T" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "We report results of uniaxial compression tests on Zr_(35)Ti_(30)Co_(6)Be_(29) metallic glass nano-pillars with diameters ranging from ~1.6 \u03bcm to ~100 nm. The tested pillars have nearly vertical sidewalls, with the tapering angle lower than ~1\u00b0 (diameter >200 nm) or ~2\u00b0 (diameter ~100 nm), and with a flat pillar top to minimize the artifacts due to imperfect geometry. We report that highly-localized-to-homogeneous deformation mode change occurs at 100 nm diameter, without any change in the yield strength. We also find that yield strength depends on size only down to 800 nm, below which it remains at its maximum value of 2.6 GPa. Quantitative Weibull analysis suggests that the increase in strength cannot be solely attributed to the lower probability of having weak flaws in small samples \u2013 most likely there is an additional influence of the sample size on the plastic deformation mechanism.", "doi": "10.1016/j.ijplas.2010.09.010", "issn": "0749-6419", "publisher": "Elsevier", "publication": "International Journal of Plasticity", "publication_date": "2011-06", "series_number": "6", "volume": "27", "issue": "6", "pages": "858-867" }, { "id": "authors:awzm2-76633", "collection": "authors", "collection_id": "awzm2-76633", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20110712-113658723", "type": "article", "title": "Protocols for the Optimal Design of Multi-Functional Cellular Structures: From Hypersonics to Micro-Architected Materials", "author": [ { "family_name": "Valdevit", "given_name": "Lorenzo", "clpid": "Valdevit-L" }, { "family_name": "Jacobsen", "given_name": "Alan J.", "clpid": "Jacobsen-A-J" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" }, { "family_name": "Carter", "given_name": "William B.", "clpid": "Carter-W-B" } ], "abstract": "Cellular materials with periodic architectures have been extensively investigated over the past decade for their potential to provide multifunctional solutions for a variety of applications, including lightweight thermo-structural panels, blast resistant structures, and high-authority morphing components. Stiffer and stronger than stochastic foams, periodic cellular materials lend themselves well to geometry optimization, enabling a high degree of tailorability and superior performance benefits. This article reviews a commonly established optimal design protocol, extensively adopted at the macro-scale for both single and multifunctional structures. Two prototypical examples are discussed: the design of strong and lightweight sandwich beams subject to mechanical loads and the combined material/geometry optimization of actively cooled combustors for hypersonic vehicles. With this body of literature in mind, we present a motivation for the development of micro-architected materials, namely periodic multiscale cellular materials with overall macroscopic dimensions yet with features (such as the unit cell or subunit cell constituents) at the micro- or nano-scale. We review a suite of viable manufacturing approaches and discuss the need for advanced experimental tools, numerical models, and optimization strategies. In analyzing challenges and opportunities, we conclude that the technology is approaching maturity for the development of micro-architected materials with unprecedented combinations of properties (e.g., specific stiffness and strength), with tremendous potential impact on a number of fields.", "doi": "10.1111/j.1551-2916.2011.04599.x", "issn": "0002-7820", "publisher": "Wiley-Blackwell", "publication": "Journal of the American Ceramic Society", "publication_date": "2011-06", "series_number": "S1", "volume": "94", "issue": "S1", "pages": "S15-S34" }, { "id": "authors:qv87g-cvb27", "collection": "authors", "collection_id": "qv87g-cvb27", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180914-101019654", "type": "article", "title": "Measuring Graphene Piezoreisistance via In-Situ Nanoindentation", "author": [ { "family_name": "Huang", "given_name": "M.", "clpid": "Huang-Mingyuan" }, { "family_name": "Greer", "given_name": "J. R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "We report piezoresistance measurements of uniaxially strained graphene ribbons obtained by performing in-situ nanoindentation experiments on suspended graphene devices with simultaneous electrical measurements. We find the Young's modulus of graphene to be ~335 N/m, which is consistent with previous reports. We measure the gauge factor of graphene ribbons to be ~2, a value close to that predicted by a tight binding model.", "doi": "10.1149/1.3569914", "issn": "1938-6737", "publisher": "Electrochemical Society", "publication": "ECS Transactions", "publication_date": "2011-04-27", "series_number": "3", "volume": "35", "issue": "3", "pages": "211-216" }, { "id": "authors:1agjz-2ab46", "collection": "authors", "collection_id": "1agjz-2ab46", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20110429-104239248", "type": "article", "title": "Influence of Homogeneous Interfaces on the Strength of 500 nm\n Diameter Cu Nanopillars", "author": [ { "family_name": "Jang", "given_name": "Dongchan", "orcid": "0000-0002-2814-9734", "clpid": "Jang-Dongchan" }, { "family_name": "Cai", "given_name": "Can", "clpid": "Cai-Can" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "Interfaces play an important role in crystalline plasticity as they affect strength and often serve as obstacles to dislocation motion. Here we investigate effects of grain and nanotwin boundaries on uniaxial strength of 500 nm diameter Cu nanopillars fabricated by e-beam lithography and electroplating. Uniaxial compression experiments reveal that strength is lowered by introducing grain boundaries and significantly rises when twin boundaries are present. Weakening is likely due to the activation of grain-boundary-mediated processes, while impeding dislocation glide can be responsible for strengthening by twin boundaries.", "doi": "10.1021/nl2003076", "issn": "1530-6984", "publisher": "American Chemical Society", "publication": "Nano Letters", "publication_date": "2011-04-13", "series_number": "4", "volume": "11", "issue": "4", "pages": "1743-1746" }, { "id": "authors:b0xks-fy019", "collection": "authors", "collection_id": "b0xks-fy019", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190214-102139841", "type": "monograph", "title": "Future Missions to Titan: Scientific and Engineering Challenges", "author": [ { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" }, { "family_name": "Jackson", "given_name": "Jennifer M.", "orcid": "0000-0002-8256-6336", "clpid": "Jackson-J-M" }, { "family_name": "Lunine", "given_name": "Jonathan I.", "orcid": "0000-0003-2279-4131", "clpid": "Lunine-Jonathan-Irving" }, { "family_name": "Mojarradi", "given_name": "Mohammad", "clpid": "Mojarradi-M" } ], "abstract": "Saturn's largest moon, Titan, has been an enigma at every stage of its exploration. For three decades after the hazy atmosphere was discovered from the ground in the 1940s, debate ensued over whether it was a thin layer of methane or a dense shield of methane and nitrogen. Voyager 1 settled the matter in favor of the latter in 1980, but the details of the thick atmosphere discovered raised even more intriguing questions about the nature of the hidden surface, and the sources of resupply of methane to the atmosphere. The simplest possibility, that an ocean of methane and its major photochemical product ethane might cover the globe, was cast in doubt by Earth-based radar studies and then eliminated by Hubble Space Telescope and adaptive optics imaging in the near-infrared from large ground-based telescopes in the 1990s. These data, however, did not reveal the complexity of the surface that Cassini-Huygens would uncover beginning in 2004. A hydrological cycle appears to exist in which methane (in concert with ethane in some processes) plays the role on Titan that water plays on Earth.\nChannels likely carved by liquid methane and/or ethane, lakes and seas of these materials\u2014some rivaling or exceeding North America's Great Lakes in size\u2014vast equatorial dune fields of complex organics made high in the atmosphere and shaped by wind, and intriguing hints of geologic activity suggest a world with a balance of geologic and atmospheric processes that is the solar system's best analogue to Earth. Deep underneath Titan's dense atmosphere and active, diverse surface is an interior ocean discovered by Cassini and thought to be largely composed of liquid water.\nCassini-Huygens has provided spectacular data and has enabled us to glimpse the mysterious surface of Titan. However the mission will leave us with many questions that require future missions to answer. These include determining the composition of the surface and the geographic distribution of various organic constituents. Key questions remain about the ages of surface features, specifically whether cryovolcanism and tectonism are actively ongoing or are relics of a more active past. Ammonia, circumstantially suggested to be present by a variety of different kinds of Cassini-Huygens data, has yet to be seen. Is methane out-gassing from the interior or ice crust today? Are the lakes fed primarily by rain or underground methane-ethane aquifers (more properly, \"alkanofers\") and how often have heavy methane rains come to the equatorial region? We should investigate whether Titan's surface supported vaster seas of methane in the past, and whether complex self-organizing chemical systems have come and gone in the water volcanism, or even exist in exotic form today in the high latitude lakes. The presence of a magnetic field has yet to be established. A large altitude range in the atmosphere, from 400\u2013900 km in altitude, will remain poorly explored after Cassini. Much remains to be understood about seasonal changes of the atmosphere at all levels, and the long-term escape of constituents to space.\nOther than Earth, Titan is the only world in our solar system known to have standing liquids and an active \"hydrologic cycle\" with clouds, rains, lakes and streams. The dense atmosphere and liquid lakes on Titan's surface can be explored with airborne platforms and landed probes, but the key aspect ensuring the success of future investigations is the conceptualization and design of instruments that are small enough to fit on the landed probes and airborne platforms, yet sophisticated enough to conduct the kinds of detailed chemical (including isotopic), physical, and structural analyses needed to investigate the history and cycling of the organic materials. In addition, they must be capable of operating at cryogenic temperatures while maintaining the integrity of the sample throughout the analytic process. Illuminating accurate chemistries also requires that the instruments and tools are not simultaneously biasing the measurements due to localized temperature increases. While the requirements for these techniques are well understood, their implementation in an extremely low temperature environment with limited mass, power and volume is acutely challenging. No such instrument systems exist today.\nMissions to Titan are severely limited in both mass and power because spacecraft have to travel over a billion miles to get there and require a large amount of fuel, not only to reach Titan, but to maintain the ability to maneuver when they arrive. Landed missions have additional limitations, in that they must be packaged in a sealed aeroshell for entry into Titan's atmosphere. Increases in landed mass and volume translate to increased aeroshell mass and size, requiring even more fuel for delivery to Titan. Nevertheless, missions during which such systems and instruments could be employed range from Discovery and New Frontiers class in situ probes that might be launched in the next decade, to a full-up Flagship class mission anticipated to follow the Europa Jupiter System Mission. Capitalizing on recent breakthroughs in cryo-technologies and smart materials fabrication, we developed conceptual designs of sample acquisition systems and instruments capable of in situ operation under low temperature environments.\nThe study included two workshops aimed at brainstorming and actively discussing a broad range of ideas and associated challenges with landing instruments on Titan, as well as more focused discussions during the intervening part of the study period. The workshops each lasted ~4 days (Monday-Thursday/Friday), included postdoctoral fellows and students in addition to the core team members, and generated active engagement from the Caltech and JPL team participants, as well as from the outside institutions. During the workshops, new instruments and sampling methodologies were identified to handle the challenges of characterizing everything from small molecules in Titan's upper atmosphere to gross mixtures of high molecular weight complex organics in condensed phases, including atmospheric aerosols and \"organic sand\" in dunes, to highly dilute components in ices and lakes. To enable these advances in cryogenic instrumentation breakthroughs in a wide range of disciplines, including electronics, chemical and mechanical engineering, and materials science were identified.", "doi": "10.26206/5VKW-9021", "publication_date": "2011-03-01" }, { "id": "authors:z2zgp-3hq16", "collection": "authors", "collection_id": "z2zgp-3hq16", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20110329-092152539", "type": "article", "title": "Electronic-Mechanical Coupling in Graphene from in situ Nanoindentation Experiments and Multiscale Atomistic Simulations", "author": [ { "family_name": "Huang", "given_name": "Mingyuan", "clpid": "Huang-Mingyuan" }, { "family_name": "Pascal", "given_name": "Tod A.", "orcid": "0000-0003-2096-1143", "clpid": "Pascal-T-A" }, { "family_name": "Kim", "given_name": "Hyungjun", "orcid": "0000-0001-8261-9381", "clpid": "Kim-Hyungjun" }, { "family_name": "Goddard", "given_name": "William A., III", "orcid": "0000-0003-0097-5716", "clpid": "Goddard-W-A-III" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "We present the in situ nanoindentation experiments performed on suspended graphene devices to introduce homogeneous tensile strain,\n while simultaneously carrying out electrical measurements. We find that\n the electrical resistance shows only a marginal change even under\n severe strain, and the electronic transport measurement confirms that\n there is no band gap opening for graphene under moderate uniform\n strain, which is consistent with our results from the first-principles\n informed molecular dynamics simulation.", "doi": "10.1021/nl104227t", "issn": "1530-6984", "publisher": "American Chemical Society", "publication": "Nano Letters", "publication_date": "2011-03", "series_number": "3", "volume": "11", "issue": "3", "pages": "1241-1246" }, { "id": "authors:pp7ww-4qd02", "collection": "authors", "collection_id": "pp7ww-4qd02", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20110321-150812583", "type": "article", "title": "Size-induced weakening and grain boundary-assisted deformation in 60 nm grained Ni nanopillars", "author": [ { "family_name": "Jang", "given_name": "Dongchan", "orcid": "0000-0002-2814-9734", "clpid": "Jang-Dongchan" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "Nanocrystalline metals generally exhibit high strengths and good fatigue resistance Their strengthening scales with the inverse of grain\n size through square root dependence down to grain sizes of ~20 nm, representing the well-known Hall-Petch relation Here we show\n that in surface-dominated structures with sub-micron dimensions, i e\n nanopillars, 60 nm grained Ni-W alloys exhibit lower tensile strengths\n with decreasing pillar diameter, form shear bands and undergo\n mechanical twinning Moreover, there appears to be a transition in the\n deformation mechanism from dislocation-driven deformation in pillars\n with diameters larger than 100 nm to grain-boundary mediated\n deformation in pillars of 100 nm and below, including grain rotation\n and grain-boundary migration, processes previously observed only in\n grain sizes below 20 nm in materials of the same composition We\n postulate that the presence of free surfaces activates these\n grain-boundary mediated deformation processes at much larger grain\n sizes than observed before and results in lower attained strengths.", "doi": "10.1016/j.scriptamat.2010.09.010", "issn": "1359-6462", "publisher": "Elsevier", "publication": "Scripta Materialia", "publication_date": "2011-01", "series_number": "1", "volume": "64", "issue": "1", "pages": "77-80" }, { "id": "authors:tydxd-vq489", "collection": "authors", "collection_id": "tydxd-vq489", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20110331-103319686", "type": "article", "title": "Tensile deformation of electroplated copper nanopillars", "author": [ { "family_name": "Jennings", "given_name": "Andrew T.", "clpid": "Jennings-A-T" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "The results are presented of uniaxial tensile testing of single crystalline electroplated copper nanopillars with diameters between 75 nm and 165 nm fabricated without the use of a focused ion beam (FIB). The experiments were performed in an in situ nanomechanical instrument, SEMentor, and reveal that the pillars' ultimate tensile strengths follow a similar power law dependence on diameter as reported for microcompression studies on fcc metals fabricated with and without FIB. Further, these pillars are characterized by limited or non-existent initial homogeneous deformation, immediately followed by necking in the top portion of the pillar. The particular deformation attributes are discussed in the context of hardening by dislocation starvation. Site-specific transmission electron microscopy microstructural analysis of as-fabricated nanopillars indicates the presence of scarce twin boundaries in some specimens. We comment on the potential for mechanical effects due to the presence of twins.", "doi": "10.1080/14786435.2010.505180", "issn": "1478-6435", "publisher": "Taylor & Francis", "publication": "Philosophical Magazine", "publication_date": "2011", "series_number": "7-9", "volume": "91", "issue": "7-9", "pages": "1108-1120" }, { "id": "authors:6tyhv-65r52", "collection": "authors", "collection_id": "6tyhv-65r52", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20100803-153016422", "type": "article", "title": "In situ characterization of vertically oriented carbon nanofibers for three-dimensional nano-electro-mechanical device applications", "author": [ { "family_name": "Kaul", "given_name": "Anupama B.", "clpid": "Kaul-A-B" }, { "family_name": "Megerian", "given_name": "Krikor G.", "clpid": "Megerian-K-G" }, { "family_name": "Jennings", "given_name": "Andrew T.", "clpid": "Jennings-A-T" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "We have performed mechanical and electrical characterization of individual as-grown, vertically oriented carbon nanofibers (CNFs) using in situ techniques, where such high-aspect-ratio, nanoscale structures are of interest for three-dimensional (3D) electronics, in particular 3D nano-electro-mechanical-systems (NEMS). Nanoindentation and uniaxial compression tests conducted in an in situ nanomechanical instrument, SEMentor, suggest that the CNFs undergo severe bending prior to fracture, which always occurs close to the bottom rather than at the substrate\u2013tube interface, suggesting that the CNFs are well adhered to the substrate. This is also consistent with bending tests on individual tubes which indicated that bending angles as large as ~70\u00b0 could be accommodated elastically. In situ electrical transport measurements revealed that the CNFs grown on refractory metallic nitride buffer layers were conducting via the sidewalls, whereas those synthesized directly on Si were electrically unsuitable for low-voltage dc NEMS applications. Electrostatic actuation was also demonstrated with a nanoprobe in close proximity to a single CNF and suggests that such structures are attractive for nonvolatile memory applications. Since the magnitude of the actuation voltage is intimately dictated by the physical characteristics of the CNFs, such as diameter and length, we also addressed the ability to tune these parameters, to some extent, by adjusting the plasma-enhanced chemical vapor deposition growth parameters with this bottom-up synthesis approach.", "doi": "10.1088/0957-4484/21/31/315501", "issn": "0957-4484", "publisher": "IOP", "publication": "Nanotechnology", "publication_date": "2010-08-06", "series_number": "31", "volume": "21", "issue": "31", "pages": "Art. No. 315501" }, { "id": "authors:r59vc-3fs65", "collection": "authors", "collection_id": "r59vc-3fs65", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20100817-080847275", "type": "article", "title": "In situ Mechanical Testing Reveals Periodic Buckle Nucleation and Propagation in Carbon Nanotube Bundles", "author": [ { "family_name": "Hutchens", "given_name": "Shelby B.", "clpid": "Hutchens-S-B" }, { "family_name": "Hall", "given_name": "Lee J.", "clpid": "Hall-L-J" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "Uniaxial compression studies are performed on 50-\u00b5m-diameter bundles of nominally vertical, intertwined carbon nanotubes grown via chemical vapor deposition from a photolithographically defined catalyst. The inhomogeneous microstructure is examined, demonstrating density and tube orientation gradients, believed to play a role in the unique periodic buckling deformation mechanism. Through in situ uniaxial compression experiments it is discovered that the characteristic bottom-to-top sequential buckling proceeds by first nucleating on the bundle surface and subsequently propagating laterally through the bundle, gradually collapsing the entire structure. The effects of strain rate are explored, and storage and loss stiffnesses are analyzed in the context of energy dissipation.", "doi": "10.1002/adfm.201000305", "issn": "1616-301X", "publisher": "Wiley", "publication": "Advanced Functional Materials", "publication_date": "2010-07-23", "series_number": "14", "volume": "20", "issue": "14", "pages": "2338-2346" }, { "id": "authors:qr1xy-anp54", "collection": "authors", "collection_id": "qr1xy-anp54", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20110816-103614921", "type": "article", "title": "Nano-Electro-Mechanical Switches Derived from Carbon-Based Nanomaterials", "author": [ { "family_name": "Kaul", "given_name": "A. B.", "clpid": "Kaul-A-B" }, { "family_name": "Khan", "given_name": "A. R.", "clpid": "Khan-A-R" }, { "family_name": "Megerian", "given_name": "K. G.", "clpid": "Megerian-K-G" }, { "family_name": "Epp", "given_name": "L.", "clpid": "Epp-L" }, { "family_name": "Bagge", "given_name": "L.", "clpid": "Bagge-L" }, { "family_name": "Jennings", "given_name": "A. T.", "clpid": "Jennings-A-T" }, { "family_name": "Jang", "given_name": "D.", "orcid": "0000-0002-2814-9734", "clpid": "Jang-Dongchan" }, { "family_name": "Greer", "given_name": "J. R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "We provide an overview of our work where carbon-based nanostructures have been applied to two-dimensional (2D) planar and three-dimensional (3D) vertically-oriented nano-electro-mechanical (NEM) switches. In the first configuration, laterally oriented single-walled nanotubes (SWNTs) synthesized using thermal chemical vapor deposition (CVD) were implemented for forming bridge-type 2D NEMS switches, where switching voltages were on the order of a few volts. In the second configuration, vertically oriented carbon nanofibers (CNFs) synthesized using plasma-enhanced (PE) CVD have been explored for their potential application in 3D NEMS. We have performed nanomechanical measurements on such vertically oriented tubes using nanoindentation to determine the mechanical robustness of the CNFs. Electrostatic switching was demonstrated in the CNFs synthesized on refractory metallic nitride substrates, where a nanoprobe was used as the actuating electrode inside a scanning-electron-microscope. The switching voltages were determined to be in the tens of volts range and van der Waals interactions at these length scales appeared significant, suggesting such structures are promising for nonvolatile memory applications. A finite element model was also developed to determine a theoretical pull-in voltage which was compared to experimental results.", "issn": "1941-4900", "publisher": "American Scientific Publishers", "publication": "Nanoscience and Nanotechnology Letters", "publication_date": "2010-06", "series_number": "2", "volume": "2", "issue": "2", "pages": "163-169" }, { "id": "authors:q13r6-ek553", "collection": "authors", "collection_id": "q13r6-ek553", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20100625-110342947", "type": "article", "title": "Enhanced resistance of single-layer graphene to ion bombardment", "author": [ { "family_name": "Lopez", "given_name": "J. J.", "clpid": "Lopez-J-J" }, { "family_name": "Greer", "given_name": "F.", "clpid": "Greer-F" }, { "family_name": "Greer", "given_name": "J. R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "We report that single-layer graphene on a SiO_2/Si substrate withstands ion bombardment up to ~7\ntimes longer than expected when exposed to focused Ga^+ ion beam. The exposure is performed in\na dual beam scanning electron microscope/focused ion beam system at 30 kV accelerating voltage\nand 41 pA current. Ga^+ ion flux is determined by sputtering a known volume of hydrogenated\namorphous carbon film deposited via plasma-enhanced chemical vapor deposition.", "doi": "10.1063/1.3428466", "issn": "0021-8979", "publisher": "American Institute of Physics", "publication": "Journal of Applied Physics", "publication_date": "2010-05-15", "series_number": "10", "volume": "107", "issue": "10", "pages": "Art. No. 104326" }, { "id": "authors:kaanj-d0417", "collection": "authors", "collection_id": "kaanj-d0417", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20161107-143812276", "type": "book_section", "title": "Carbon-based nano-electro-mechanical systems", "book_title": "Micro- and Nanotechnology Sensors, Systems, and Applications II", "author": [ { "family_name": "Kaul", "given_name": "A. B.", "clpid": "Kaul-A-B" }, { "family_name": "Khan", "given_name": "A. R.", "clpid": "Khan-A-R" }, { "family_name": "Megerian", "given_name": "K. G.", "clpid": "Megerian-K-G" }, { "family_name": "Epp", "given_name": "L.", "clpid": "Epp-L" }, { "family_name": "LeDuc", "given_name": "H. G.", "clpid": "LeDuc-H-G" }, { "family_name": "Bagge", "given_name": "L.", "clpid": "Bagge-L" }, { "family_name": "Jennings", "given_name": "A. T.", "clpid": "Jennings-A-T" }, { "family_name": "Jang", "given_name": "D.", "orcid": "0000-0002-2814-9734", "clpid": "Jang-Dongchan" }, { "family_name": "Greer", "given_name": "J. R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "contributor": [ { "family_name": "George", "given_name": "Thomas", "clpid": "George-T" }, { "family_name": "Islam", "given_name": "M. Saif", "clpid": "Islam-" }, { "family_name": "Dutta", "given_name": "Achyut K.", "clpid": "Dutta-A-K" } ], "abstract": "We provide an overview of our work where carbon-based nanostructures have been applied to twodimensional (2D) planar and three-dimensional (3D) vertically-oriented nano-electro-mechanical (NEM) switches. In the first configuration, laterally oriented single-walled nanotubes (SWNTs) synthesized using thermal chemical vapor deposition (CVD) were implemented for forming bridge-type 2D NEMS switches, where switching voltages were on the order of a few volts. In the second configuration, vertically oriented carbon nanofibers (CNFs) synthesized using plasma-enhanced (PE) CVD have been explored for their potential application in 3D NEMS. We have performed nanomechanical measurements on such vertically oriented tubes using nanoindentation to determine the mechanical properties of the CNFs. Electrostatic switching was demonstrated in the CNFs synthesized on refractory metallic nitride substrates, where a nanoprobe was used as the actuating electrode inside a scanning-electron-microscope. The switching voltages were determined to be in the tens of volts range and van der Waals interactions at these length scales appeared significant, suggesting such structures are promising for nonvolatile memory applications. A finite element model was also developed to determine a theoretical pull-in voltage which was compared to experimental results.", "doi": "10.1117/12.851293", "isbn": "978-0-8194-8143-6", "publisher": "Society of Photo-Optical Instrumentation Engineers (SPIE)", "place_of_publication": "Bellingham, WA", "publication_date": "2010-05-05", "pages": "Art. No. 76790N" }, { "id": "authors:htdfw-xkt80", "collection": "authors", "collection_id": "htdfw-xkt80", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20100526-084624542", "type": "article", "title": "Microstructure versus Size: Mechanical Properties of Electroplated Single Crystalline Cu Nanopillars", "author": [ { "family_name": "Jennings", "given_name": "Andrew T.", "clpid": "Jennings-A-T" }, { "family_name": "Burek", "given_name": "Michael J.", "clpid": "Burek-M-J" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "We report results of uniaxial compression experiments on single-crystalline Cu nanopillars with nonzero initial dislocation densities produced without focused ion beam (FIB). Remarkably, we find the same power-law size-driven strengthening as FIB-fabricated face-centered cubic micropillars. TEM analysis reveals that initial dislocation density in our FIB-less pillars and those produced by FIB are on the order of 10^(14)\u2009\u2009m^(-2) suggesting that mechanical response of nanoscale crystals is a stronger function of initial microstructure than of size regardless of fabrication method.", "doi": "10.1103/PhysRevLett.104.135503", "issn": "0031-9007", "publisher": "American Physical Society", "publication": "Physical Review Letters", "publication_date": "2010-04-02", "series_number": "13", "volume": "104", "issue": "13", "pages": "Art. No. 135503" }, { "id": "authors:hab3b-g8s41", "collection": "authors", "collection_id": "hab3b-g8s41", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20100512-134911991", "type": "article", "title": "Tensile and compressive behavior of tungsten, molybdenum, tantalum and niobium at the nanoscale", "author": [ { "family_name": "Kim", "given_name": "Ju-Young", "clpid": "Kim-Ju-Young" }, { "family_name": "Jang", "given_name": "Dongchan", "orcid": "0000-0002-2814-9734", "clpid": "Jang-Dongchan" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "In situ nanomechanical tests are carried out to investigate the tensile and compressive behavior of <0 0 1>-oriented body-centered cubic (bcc) metals W, Mo, Ta and Nb with nanometer dimensions. We find that the strength of these metals exhibits strong size dependence. The compressive size effect in Nb, as evaluated by the log\u2013log slope of strength vs. nanopillar diameter, is \u22120.93, a factor of 2.1 greater than that for the other three metals W, Mo and Ta (\u22120.44). In tension, however, Ta and Nb show higher size effect slopes (\u22120.80 and \u22120.77) as compared with W and Mo (\u22120.58 and \u22120.43). We also report that while the yield strength of these metals is a strong function of size, the strain-hardening behavior does not present any size-dependent trends. We further discuss the effects of strain-rate on deformation behavior and provide transmission electron microscopy analysis of microstructural evolution in the same Mo nanopillar before and after compression.", "doi": "10.1016/j.actamat.2009.12.022", "issn": "1359-6454", "publisher": "Elsevier", "publication": "Acta Materialia", "publication_date": "2010-04", "series_number": "7", "volume": "58", "issue": "7", "pages": "2355-2363" }, { "id": "authors:gardc-kam73", "collection": "authors", "collection_id": "gardc-kam73", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20100305-133845582", "type": "article", "title": "Transition from a strong-yet-brittle to a stronger-and-ductile state by size reduction of metallic glasses", "author": [ { "family_name": "Jang", "given_name": "Dongchan", "orcid": "0000-0002-2814-9734", "clpid": "Jang-Dongchan" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "Amorphous metallic alloys, or metallic glasses, are lucrative engineering materials owing to their superior mechanical properties such as high strength and large elastic strain. However, their main drawback is their propensity for highly catastrophic failure through rapid shear banding, significantly undercutting their structural applications. Here, we show that when reduced to 100\u2009nm, Zr-based metallic glass nanopillars attain ceramic-like strengths (2.25\u2009GPa) and metal-like ductility (25%) simultaneously. We report separate and distinct critical sizes for maximum strength and for the brittle-to-ductile transition, thereby demonstrating that strength and ability to carry plasticity are decoupled at the nanoscale. A phenomenological model for size dependence and brittle-to-homogeneous deformation is provided.", "doi": "10.1038/nmat2622", "issn": "1476-1122", "publisher": "Nature Publishing Group", "publication": "Nature Materials", "publication_date": "2010-03", "series_number": "3", "volume": "9", "issue": "3", "pages": "215-219" }, { "id": "authors:yvmx1-18d08", "collection": "authors", "collection_id": "yvmx1-18d08", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20100308-111032384", "type": "article", "title": "Fabrication, structure and mechanical properties of indium nanopillars", "author": [ { "family_name": "Lee", "given_name": "Gyuhyon", "clpid": "Lee-Gyuhyon" }, { "family_name": "Kim", "given_name": "Ju-Young", "clpid": "Kim-Ju-Young" }, { "family_name": "Budiman", "given_name": "Arief Suriadi", "clpid": "Budiman-A-S" }, { "family_name": "Tamura", "given_name": "Nobumichi", "orcid": "0000-0002-3698-2611", "clpid": "Tamura-Nobumichi" }, { "family_name": "Kunz", "given_name": "Martin", "clpid": "Kunz-M" }, { "family_name": "Chen", "given_name": "Kai", "orcid": "0000-0002-3325-3536", "clpid": "Chen-Kai" }, { "family_name": "Burek", "given_name": "Michael J.", "clpid": "Burek-M-J" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" }, { "family_name": "Tsui", "given_name": "Ting Y.", "clpid": "Tsui-Ting-Y" } ], "abstract": "Solid and hollow cylindrical indium pillars with nanoscale diameters were prepared using electron beam lithography followed by the electroplating fabrication method. The microstructure of the solid-core indium pillars was characterized by scanning micro-X-ray diffraction, which shows that the indium pillars were annealed at room temperature with very few dislocations remaining in the samples. The mechanical properties of the solid pillars were characterized using a uniaxial microcompression technique, which demonstrated that the engineering yield stress is 9 times greater than bulk and is ~1/28 of the indium shear modulus, suggesting that the attained stresses are close to theoretical strength. Microcompression of hollow indium nanopillars showed evidence of brittle fracture. This may suggest that the failure mode for one of the most ductile metals can become brittle when the feature size is sufficiently small.", "doi": "10.1016/j.actamat.2009.10.042", "issn": "1359-6454", "publisher": "Elsevier", "publication": "Acta Materialia", "publication_date": "2010-02", "series_number": "4", "volume": "58", "issue": "4", "pages": "1361-1368" }, { "id": "authors:swbjm-pdr06", "collection": "authors", "collection_id": "swbjm-pdr06", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20100129-133838310", "type": "article", "title": "Fabrication and Microstructure Control of Nanoscale Mechanical Testing Specimens via Electron Beam Lithography and Electroplating", "author": [ { "family_name": "Burek", "given_name": "Michael J.", "clpid": "Burek-M-J" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "It has been demonstrated that the mechanical properties of materials change significantly when external dimensions are confined to the nanoscale. Currently, the dominant fabrication method for mechanical testing specimens with nanometer dimensions is by using focused ion beam (FIB) milling, which results in inevitable Ga+ induced damage to the microstructure. Here, we report a FIB-less fabrication technique to create arrays of vertically oriented gold and copper nanopillars based on patterning polymethylmethacrylate by electron beam lithography and subsequent electroplating into the prescribed template. This fabrication process is capable of producing a wide range of microstructures: from single crystals and nanotwinned, to bi-, poly-, and nanocrystalline mechanical testing specimens with diameters from 750 down to 25 nm with the diameter range below 100 nm previously inaccessible by FIB.", "doi": "10.1021/nl902872w", "issn": "1530-6984", "publisher": "American Chemical Society", "publication": "Nano Letters", "publication_date": "2010-01", "series_number": "1", "volume": "10", "issue": "1", "pages": "69-76" }, { "id": "authors:5y1wt-1yc68", "collection": "authors", "collection_id": "5y1wt-1yc68", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20100129-141942300", "type": "article", "title": "The in-situ mechanical testing of nanoscale single-crystalline nanopillars", "author": [ { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" }, { "family_name": "Kim", "given_name": "Ju-Young", "clpid": "Kim-Ju-Young" }, { "family_name": "Burek", "given_name": "Michael J.", "clpid": "Burek-M-J" } ], "abstract": "This article reviews recent studies on the mechanical properties of cylindrical metallic nanopillars subjected to uniaxial deformation. Remarkable strengths and very different mechanical properties arise due to the activation of unique deformation mechanisms operating in these nanoscale volumes. Effects of both size and microstructure are discussed.", "doi": "10.1007/s11837-009-0174-8", "issn": "1047-4838", "publisher": "Springer Boston", "publication": "JOM - Journal of the Minerals, Metals and Materials Society", "publication_date": "2009-12", "series_number": "12", "volume": "61", "issue": "12", "pages": "19-25" }, { "id": "authors:g0e9h-h5b42", "collection": "authors", "collection_id": "g0e9h-h5b42", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20091102-085834273", "type": "article", "title": "Tensile and compressive behavior of gold and molybdenum single crystals at the nano-scale", "author": [ { "family_name": "Kim", "given_name": "Ju-Young", "clpid": "Kim-Ju-Young" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "In situ mechanical tests were carried out to measure the tensile behavior of single-crystalline face-centered cubic (fcc) gold (Au) and body-centered cubic (bcc) molybdenum (Mo) nano-pillars with diameters between 250 and 1 \u03bcm, and to compare this with the compression results of these materials at the equivalent sizes. In Au, we observed similar tensile and compressive flow stresses at 10% strain although strain-hardening in tension is somewhat more pronounced than it is in compression. In Mo, the amount of strain-hardening in tension is significantly lower than that in compression, leading to a distinct tension\u2013compression asymmetry in the flow stress at ~5% strain. The dissimilarities between tensile and compressive behavior in both crystals are discussed in terms of sample geometry constraints and dislocation behavior in bcc crystals.", "doi": "10.1016/j.actamat.2009.07.027", "issn": "1359-6454", "publisher": "Elsevier", "publication": "Acta Materialia", "publication_date": "2009-10", "series_number": "17", "volume": "57", "issue": "17", "pages": "5245-5253" }, { "id": "authors:sny7w-ypm71", "collection": "authors", "collection_id": "sny7w-ypm71", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20091020-134039389", "type": "article", "title": "Emergence of New Mechanical Functionality in Materials via Size Reduction", "author": [ { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" }, { "family_name": "Jang", "given_name": "Dongchan", "orcid": "0000-0002-2814-9734", "clpid": "Jang-Dongchan" }, { "family_name": "Kim", "given_name": "Ju-Young", "clpid": "Kim-Ju-Young" }, { "family_name": "Burek", "given_name": "Michael J.", "clpid": "Burek-M-J" } ], "abstract": "Julia R. Greer received her S.B. in Chemical Engineering from the Massachusetts Institute of Technology (1997) and a Ph.D. in Materials Science from Stanford University, where she worked on the nanoscale plasticity of gold with W. D. Nix (2005). She also worked at Intel Corporation in Mask Operations (2000-03) and was a post-doctoral fellow at the Palo Alto Research Center (2005-07), where she worked on organic flexible electronics with R. A. Street. Greer is a recipient of TR-35, Technology Review's Top Young Innovator award (2008), a NSF CAREER Award (2007), a Gold Materials Research Society Graduate Student Award (2004), and an American Association of University Women Fellowship (2003). Julia joined Caltech's Materials Science department in 2007 where she is developing innovative experimental techniques to assess mechanical properties of nanometer-sized materials. One such approach involves the fabrication of nanopillars with different initial microstructures and diameters between 25 nm and 1 \u00b5m by using focused ion beam and electron-beam lithography microfabrication. The mechanical response of these pillars is subsequently measured in a custom-built in situ mechanical deformation instrument, SEMentor, comprising a scanning electron microscope and a nanoindenter.", "doi": "10.1002/adfm.200900854", "issn": "1616-301X", "publisher": "Wiley", "publication": "Advanced Functional Materials", "publication_date": "2009-09-23", "series_number": "18", "volume": "19", "issue": "18", "pages": "2880-2886" }, { "id": "authors:37ycb-arp49", "collection": "authors", "collection_id": "37ycb-arp49", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20101209-105858696", "type": "article", "title": "Insight into the deformation behavior of niobium single crystals under uniaxial compression and tension at the nanoscale", "author": [ { "family_name": "Kim", "given_name": "Ju-Young", "clpid": "Kim-Ju-Young" }, { "family_name": "Jang", "given_name": "Dongchan", "orcid": "0000-0002-2814-9734", "clpid": "Jang-Dongchan" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "Size-dependent deformation behavior of niobium single-crystalline samples 200\u2013900 nm in diameter is investigated by in situ\ncompression and tension testing. Stress\u2013strain curves in compression show discrete plastic flow associated with dislocation escapes\nat the surface. In tension, plastic flow is more continuous with pronounced strain hardening, and fracture occurs at the low true\nstrain of ~3%. Transmission electron microscopy analysis of the same 100 nm nanopillar before and after deformation provides\ninsights into dislocation activity during compression deformation.", "doi": "10.1016/j.scriptamat.2009.04.012", "issn": "1359-6462", "publisher": "Elsevier", "publication": "Scripta Materialia", "publication_date": "2009-08", "series_number": "3", "volume": "61", "issue": "3", "pages": "300-303" }, { "id": "authors:k18xa-j6r38", "collection": "authors", "collection_id": "k18xa-j6r38", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130710-154501417", "type": "book_section", "title": "In-Situ Investigation of Plasticity at Nano-Scale", "book_title": "Proceedings of the 9th Biennial Conference on Engineering Systems Design and Analysis", "author": [ { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" }, { "family_name": "Kim", "given_name": "Ju-Young", "clpid": "Kim-Ju-Young" }, { "family_name": "Brinckmann", "given_name": "Steffen", "clpid": "Brinckmann-S" } ], "abstract": "Mechanical behavior of crystals is dictated by dislocation motion in response to applied force. While it is extremely\ndifficult to directly observe the motion of individual dislocations, several correlations can be made between the\nmicroscopic stress-strain behavior and dislocation activity. Here, we present for the first time the differences observed\nbetween mechanical behavior in two fundamental types of crystals: face-centered cubic, fcc (Au, Cu, AI, Ni, etc.) and\nbody-centered cubic, bcc (W, Cr, Mo, Nb, etc.) with sub-micron dimensions subjected to in-situ micro-compression in\nSEM chamber. In a striking deviation from classical mechanics, there is a significant increase in strength as crystal size\nis reduced to 100nm; however in gold crystals (fcc) the highest strength achieved represents 44% of its theoretical\nstrength while in molybdenum crystals (bcc) it is only 7%. Moreover, unlike in bulk where plasticity commences in a\nsmooth fashion, both nano-crystals exhibit numerous discrete strain bursts during plastic deformation. These remarkable\ndifferences in mechanical response of fcc and bcc crystals to uniaxial micro-compression challenge the applicability of\nconventional strain-hardening to nano-scale crystals. We postulate that they arise from significant differences in\ndislocation behavior between fcc and bcc crystals at nanoscale and serve as the fundamental reason for the observed\ndifferences in their plastic deformation. Namely, dislocation starvation is the predominant mechanism of plasticity in\nnano-scale fcc crystals while junction formation and subsequent hardening characterize bcc plasticity, as confirmed by\nthe microstructural electron microscopy. Experimentally obtained stress-strain curves together with video frames during\ndeformation and cross-sectional TEM analysis are presented, and a statistical analysis of avalanche-like strain bursts is\nperformed for both crystals and compared with stochastic models.", "isbn": "978-0-7918-4835-7", "publisher": "American Society of Mechanical Engineers", "place_of_publication": "New York", "publication_date": "2009-07", "pages": "519-520" }, { "id": "authors:zmqqe-y6490", "collection": "authors", "collection_id": "zmqqe-y6490", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190516-124159002", "type": "book_section", "title": "High-throughput processes and structural characterization of single-nanotube based devices for 3D electronics", "book_title": "Micro- and Nanotechnology Sensors, Systems, and Applications", "author": [ { "family_name": "Kaul", "given_name": "A. B.", "clpid": "Kaul-A-B" }, { "family_name": "Megerian", "given_name": "K. G.", "clpid": "Megerian-K-G" }, { "family_name": "Baron", "given_name": "R. L.", "clpid": "Baron-R-L" }, { "family_name": "Jennings", "given_name": "A. T.", "clpid": "Jennings-A-T" }, { "family_name": "Jang", "given_name": "D.", "orcid": "0000-0002-2814-9734", "clpid": "Jang-Dongchan" }, { "family_name": "Greer", "given_name": "J. R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "contributor": [ { "family_name": "George", "given_name": "Thomas", "clpid": "George-T" }, { "family_name": "Islam", "given_name": "M. Saif", "clpid": "Islam-M-S" }, { "family_name": "Dutta", "given_name": "Achyut K.", "clpid": "Dutta-A-K" } ], "abstract": "We have developed manufacturable approaches to form single, vertically aligned carbon nanotubes, where the tubes are centered precisely, and placed within a few hundred nm of 1-1.5 \u03bcm deep trenches. These wafer-scale approaches were enabled by chemically amplified resists and inductively coupled Cryo-etchers to form the 3D nanoscale architectures. The tube growth was performed using dc plasmaenhanced chemical vapor deposition (PECVD), and the materials used for the pre-fabricated 3D architectures were chemically and structurally compatible with the high temperature (700 \u00b0C) PECVD synthesis of our tubes, in an ammonia and acetylene ambient. The TEM analysis of our tubes revealed graphitic basal planes inclined to the central or fiber axis, with cone angles up to 30\u00b0 for the particular growth conditions used. In addition, bending tests performed using a custom nanoindentor, suggest that the tubes are well adhered to the Si substrate. Tube characteristics were also engineered to some extent, by adjusting growth parameters, such as Ni catalyst thickness, pressure and plasma power during growth.", "doi": "10.1117/12.820723", "isbn": "9780819475848", "publisher": "Society of Photo-Optical Instrumentation Engineers (SPIE)", "place_of_publication": "Bellingham, WA", "publication_date": "2009-05-11", "pages": "Art. No. 73180B" }, { "id": "authors:mcd6p-9r458", "collection": "authors", "collection_id": "mcd6p-9r458", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20090904-103700120", "type": "article", "title": "Sample boundary effect in nanoindentation of nano and microscale surface structures", "author": [ { "family_name": "Lian", "given_name": "Jie", "clpid": "Lian-Jie" }, { "family_name": "Wang", "given_name": "Junian", "clpid": "Wang-Junian" }, { "family_name": "Kim", "given_name": "Yu-Young", "clpid": "Kim-Yu-Young" }, { "family_name": "Greer", "given_name": "Julia", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "Nanoindentation is a widely used technique to characterize mechanical properties of materials in small volumes. When the sample size is comparable to the indent size, the indentation-induced plastic zone can be affected by the sample boundary which may cause inaccurate interpretation of the mechanical properties. In this study, the sample boundary effect is investigated by performing experiments and atomistic simulations of nanoindentation into nano- and micro-scale Au pillars and bulk Au (0 0 1) surfaces. In experiments, a more compliant deformation is observed in pillar indentations compared to bulk Au. The elastic modulus decreases with increasing indent size over sample size ratio. Atomistic simulations are performed to gain insights on the mechanisms of pillar deformation and pillar boundary effect. The reduced modulus has a similar trend of decrease with increasing indent size over sample size ratio. Significantly different dislocation activities and dislocation interactions with the pillar boundary contribute to the lower value of the reduced modulus in the pillar indentation. The presence of the free surface would allow the dislocations to annihilate, causing a higher plastic recovery during the pillar unloading process.", "doi": "10.1016/j.jmps.2009.01.008", "issn": "0022-5096", "publisher": "Elsevier", "publication": "Journal of the Mechanics and Physics of Solids", "publication_date": "2009-05", "series_number": "5", "volume": "57", "issue": "5", "pages": "812-827" }, { "id": "authors:azn3d-39v97", "collection": "authors", "collection_id": "azn3d-39v97", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20090806-085230553", "type": "article", "title": "Strain rate effects in the mechanical response of polymer-anchored carbon nanotube foams", "author": [ { "family_name": "Misra", "given_name": "Abha", "clpid": "Misra-A" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" }, { "family_name": "Daraio", "given_name": "Chiara", "orcid": "0000-0001-5296-4440", "clpid": "Daraio-C" } ], "abstract": "Strain rate effects on the mechanical properties of carbon nanotube forests are studied, and several related interesting new phenomena are reported. Dense vertically aligned foam-like forests of carbon nanotubes are anchored on a thin, flexible polymer layer to provide structural stability, particularly at the higher strain rates. Permanent deformation and for the first time the delamination and crumbling of carbon nanotube walls is observed.", "doi": "10.1002/adma.200801997", "issn": "0935-9648", "publisher": "Wiley", "publication": "Advanced Materials", "publication_date": "2009-01-19", "series_number": "3", "volume": "21", "issue": "3", "pages": "334-338" }, { "id": "authors:zhq2b-25k49", "collection": "authors", "collection_id": "zhq2b-25k49", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20090807-123242532", "type": "article", "title": "Effects of sample geometry on the uniaxial tensile stress state at the nanoscale", "author": [ { "family_name": "Brinckmann", "given_name": "S.", "clpid": "Brinckmann-S" }, { "family_name": "Kim", "given_name": "J. -Y.", "clpid": "Kim-J-Y" }, { "family_name": "Jennings", "given_name": "A.", "clpid": "Jennings-A-T" }, { "family_name": "Greer", "given_name": "J. R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "Uniaxial compression of micro- and nanopillars is frequently used to elicit plastic size effects in single crystals. Uniaxial tensile experiments on nanoscale materials have the potential to enhance the understanding of the experimentally widely observed strength increase. Furthermore, these experiments allow for investigations into the in-strength and to help to study tension-compression asymmetry. The sample geometry might influence mechanical proper- ties, and to investigate this dependence, we demonstrate two methods of uniaxial nanotensile sample fabrication. We compare the experimentally obtained tensile stress-strain response for cylindrical and square nanopillars and provide finite element method simulation results and discuss the initiation of plastic yielding in these nanosamples.", "doi": "10.1615/IntJMultCompEng.v7.i3.20", "issn": "1543-1649", "publisher": "Begell House", "publication": "International Journal for Multiscale Computational Engineering", "publication_date": "2009", "series_number": "3", "volume": "7", "issue": "3", "pages": "187-194" }, { "id": "authors:k4ef4-f9751", "collection": "authors", "collection_id": "k4ef4-f9751", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:KIMapl08", "type": "article", "title": "Size-dependent mechanical properties of molybdenum nanopillars", "author": [ { "family_name": "Kim", "given_name": "Ju-Young", "clpid": "Kim-Ju-Young" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "We report the deformation behavior of single crystalline molybdenum nanopillars in uniaxial compression, which exhibits a strong size effect called the \"smaller is stronger\" phenomenon. We show that higher strengths arise from the increase in the yield strength rather than through postyield strain hardening. We find the yield strength at nanoscale to depend strongly on sample size and not on the initial dislocation density, a finding strikingly different from that of the bulk metal.", "doi": "10.1063/1.2979684", "issn": "0003-6951", "publisher": "American Institute of Physics", "publication": "Applied Physics Letters", "publication_date": "2008-09-08", "series_number": "10", "volume": "93", "issue": "10", "pages": "Art. No. 101916" }, { "id": "authors:17p27-rn313", "collection": "authors", "collection_id": "17p27-rn313", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:KIMam08", "type": "article", "title": "Evaluating plastic flow properties by characterizing indentation size effect using a sharp indenter", "author": [ { "family_name": "Kim", "given_name": "Ju-Young", "clpid": "Kim-Ju-Young" }, { "family_name": "Kang", "given_name": "Seung-Kyun", "clpid": "Kang-Seung-Kyun" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" }, { "family_name": "Kwon", "given_name": "Dongil", "clpid": "Kwon-Dongil" } ], "abstract": "The strain-hardening exponent, used in describing the plastic flow properties of materials, is evaluated from the characteristic length in the indentation size effect (ISE). A linear relationship is found between the strain-hardening exponent and the log of the ISE characteristic length for Ni and SCM21 (structural steel) samples with different plastic pre-strain values. These results are explained through the Taylor dislocation hardening model and a representative stress\u2013strain approach. A dimensionless function characterizing the plastic deformation using only parameters generally measurable by nanoindentation testing is also proposed. The feasibility of developing a\nunique dimensionless function is studied for 22 metals.", "doi": "10.1016/j.actamat.2008.02.049", "issn": "1359-6454", "publisher": "Elsevier", "publication": "Acta Materialia", "publication_date": "2008-08", "series_number": "14", "volume": "56", "issue": "14", "pages": "3338-3343" }, { "id": "authors:42xyq-cmr76", "collection": "authors", "collection_id": "42xyq-cmr76", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:BRIprl08", "type": "article", "title": "Fundamental Differences in Mechanical Behavior between Two Types of Crystals at the Nanoscale", "author": [ { "family_name": "Brinckmann", "given_name": "Stefan", "clpid": "Brinckmann-S" }, { "family_name": "Kim", "given_name": "Ju-Young", "clpid": "Kim-Ju-Young" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "We present differences in the mechanical behavior of nanoscale gold and molybdenum single crystals. A significant strength increase is observed as the size is reduced to 100 nm. Both nanocrystals exhibit discrete strain bursts during plastic deformation. We postulate that they arise from significant differences in the dislocation behavior. Dislocation starvation is the predominant mechanism of plasticity in nanoscale fcc crystals, while junction formation and hardening characterize bcc plasticity. A statistical analysis of strain bursts is performed as a function of size and compared with stochastic models.", "doi": "10.1103/PhysRevLett.100.155502", "issn": "0031-9007", "publisher": "American Physical Society", "publication": "Physical Review Letters", "publication_date": "2008-04-18", "series_number": "15", "volume": "100", "issue": "15", "pages": "Art. No. 155502" }, { "id": "authors:nzxfr-cx111", "collection": "authors", "collection_id": "nzxfr-cx111", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:GREapl08", "type": "article", "title": "Comment on \"Effects of focused ion beam milling on the nanomechanical behavior of a molybdenum-alloy single crystal\" Appl. Phys. Lett. 91, 111915 (2007)", "author": [ { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" }, { "family_name": "Espinosa", "given_name": "Horacio", "clpid": "Espinosa-H" }, { "family_name": "Ramesh", "given_name": "K. T.", "clpid": "Ramesh-K-T" }, { "family_name": "Nadgorny", "given_name": "Edward", "clpid": "Nadgorny-E" } ], "abstract": "While this article provides insight into differences in mechanics between Ga+-irradiated and \"pure\" surfaces of molybdenum, there are several statements that are either inaccurate or poorly stated. It is clear that when a surface is directly irradiated by orthogonal ion beam (0.07\u20130.21 mW), a focused ion beam (FIB) damage layer will likely form and affect the strength. However, this finding does not provide adequate foundation for raising the question of FIB-induced hardening in nanopillars, given the vast differences between these experiments and procedure used in pillar fabrication. These issues would cause considerable confusion and result in disservice to mechanical testing community if not clarified.", "doi": "10.1063/1.2889997", "issn": "0003-6951", "publisher": "American Institute of Physics", "publication": "Applied Physics Letters", "publication_date": "2008-03-03", "series_number": "9", "volume": "92", "issue": "9", "pages": "Art. No. 096101" }, { "id": "authors:699zk-kzw94", "collection": "authors", "collection_id": "699zk-kzw94", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170408-144528730", "type": "article", "title": "A search for evidence of strain gradient hardening in Au submicron pillars under uniaxial compression using synchrotron X-ray microdiffraction", "author": [ { "family_name": "Budiman", "given_name": "A. S.", "clpid": "Budiman-Arief-Suriadi" }, { "family_name": "Han", "given_name": "S. M.", "clpid": "Han-Seungmin" }, { "family_name": "Greer", "given_name": "J. R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" }, { "family_name": "Tamura", "given_name": "N.", "clpid": "Tamura-Nobumichi" }, { "family_name": "Patel", "given_name": "J. R.", "clpid": "Patel-Jamshed-R" }, { "family_name": "Nix", "given_name": "W. D.", "clpid": "Nix-William-D" } ], "abstract": "When crystalline materials are mechanically deformed in small volumes, higher stresses are needed for plastic flow. This has been called the \"smaller is stronger\" phenomenon and has been widely observed. Various size-dependent strengthening mechanisms have been proposed to account for such effects, often involving strain gradients. Here we report on a search for strain gradients as a possible source of strength for single-crystal submicron pillars of gold subjected to uniform compression, using a submicron white-beam (Laue) X-ray diffraction technique. We have found, both before and after uniaxial compression, no evidence of either significant lattice curvature or subgrain structure. This is true even after 35% strain and a high flow stress of 300 MPa were achieved during deformation. These observations suggest that plasticity here is not controlled by strain gradients or substructure hardening, but rather by dislocation source starvation, wherein smaller volumes are stronger because fewer sources of dislocations are available.", "doi": "10.1016/j.actamat.2007.10.031", "issn": "0956-7151", "publisher": "Elsevier", "publication": "Acta Metallurgica et Materialia", "publication_date": "2008-02", "series_number": "3", "volume": "56", "issue": "3", "pages": "602-608" }, { "id": "authors:1ay9h-dg218", "collection": "authors", "collection_id": "1ay9h-dg218", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:GREmsea08", "type": "article", "title": "Comparing the strength of f.c.c. and b.c.c. sub-micrometer pillars: Compression experiments and dislocation dynamics simulations", "author": [ { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" }, { "family_name": "Weinberger", "given_name": "Christopher R.", "clpid": "Weinberger-C-R" }, { "family_name": "Cai", "given_name": "Wei", "clpid": "Cai-Wei" } ], "abstract": "We compare mechanical strength of f.c.c. gold and b.c.c. molybdenum single crystal pillars of sub-micrometer diameter in uniaxial compression tests. Both crystals show an increase of flow stress with decreasing diameter, but the change is more pronounced in Au than in Mo. The ratio between the observed maximum flow stress and the theoretical strength is much larger in Au pillars than in Mo pillars. Dislocation dynamics simulations also reveal different dislocation behavior in these two metals. While in a f.c.c. crystal a dislocation loop nucleated from the surface simply moves on its glide plane and exits the pillar, in a b.c.c. crystal it can generate multiple new dislocations due to the ease of screw dislocations to change slip planes. We postulate that this difference in dislocation behavior is the fundamental reason for the observed difference in the plastic deformation behavior of f.c.c. and b.c.c. pillars.", "doi": "10.1016/j.msea.2007.08.093", "issn": "0921-5093", "publisher": "Elsevier", "publication": "Materials Science and Engineering A", "publication_date": "2007-10-15", "series_number": "1-2", "volume": "493", "issue": "1-2", "pages": "21-25" }, { "id": "authors:p2tsc-jcw29", "collection": "authors", "collection_id": "p2tsc-jcw29", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130710-152649934", "type": "article", "title": "Thermal cure effects on electrical performance of nanoparticle silver inks", "author": [ { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" }, { "family_name": "Street", "given_name": "Robert A.", "orcid": "0000-0001-6279-0552", "clpid": "Street-R-A" } ], "abstract": "Physical, electrical, and morphological properties of thermally annealed silver nanoparticle thin films are described. These solution-deposited nanoparticle thin films form highly conducting films at low curing temperatures via sintering due to the high surface area to volume ratio. Measured resistivity correlates with thickness decrease and densification, and can be explained by a simple geometrical model applicable to the sintering process. Consideration of the active sintering mechanisms provides the basis for a phenomenological model predicting optimal pathways to achieve desired electrical performance.", "doi": "10.1016/j.actamat.2007.07.040", "issn": "1359-6454", "publisher": "Elsevier", "publication": "Acta Materialia", "publication_date": "2007-10", "series_number": "18", "volume": "55", "issue": "18", "pages": "6345-6349" }, { "id": "authors:ktm8n-m0x08", "collection": "authors", "collection_id": "ktm8n-m0x08", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:GREjap07", "type": "article", "title": "Mechanical characterization of solution-derived nanoparticle silver ink thin films", "author": [ { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" }, { "family_name": "Street", "given_name": "Robert A.", "orcid": "0000-0001-6279-0552", "clpid": "Street-R-A" } ], "abstract": "Mechanical properties of sintered silver nanoparticles are investigated via substrate curvature and nanoindentation methods. Substrate curvature measurements reveal that permanent microstructural changes occur during initial heating while subsequent annealing results in nearly elastic behavior of the thinner films. Thicker films were found to crack upon thermal treatment. The coefficient of thermal expansion was determined from linear slopes of curvature curves to be 1.9\u00b10.097 ppm/\u00b0C, with elastic modulus and hardness determined via nanoindentation. Accounting for substrate effects, nanoindentation hardness and modulus remained constant for different film thicknesses and did not appear to be a function of annealing conditions. Hardness of 0.91 GPa and modulus of 110 GPa are somewhat lower than expected for a continuous nanocrystalline silver film, most likely due to porosity.", "doi": "10.1063/1.2735404", "issn": "0021-8979", "publisher": "American Institute of Physics", "publication": "Journal of Applied Physics", "publication_date": "2007-05-15", "series_number": "10", "volume": "101", "issue": "10", "pages": "Art. No. 103529" }, { "id": "authors:g383v-ax287", "collection": "authors", "collection_id": "g383v-ax287", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130710-153043195", "type": "article", "title": "Deformation at the nanometer and micrometer length scales: Effects of strain gradients and dislocation starvation", "author": [ { "family_name": "Nix", "given_name": "William D.", "clpid": "Nix-W-D" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" }, { "family_name": "Feng", "given_name": "Gang", "clpid": "Feng-Gang" }, { "family_name": "Lilleodden", "given_name": "Erica T.", "clpid": "Lilleodden-E-T" } ], "abstract": "Nanomechanical devices are certain to play an important role in future technologies. Already sensors and actuators based on MEMS technologies are common and new devices based on NEMS are just around the corner. These developments are part of a decade-long trend to build useful engineering devices and structures on a smaller and smaller scale. The creation of structures and devices calls for an understanding of the mechanical properties of materials at these small length scales. Here we examine some of the effects that arise when crystalline materials are mechanically deformed in small volumes. We show that indentation size effects at the micrometer scale can be understood in terms of the hardening associated with strain gradients and geometrically necessary dislocations, while indentation size effects at the nanometer scale involve the concepts of dislocation starvation and the nucleation of dislocations. We also describe uniaxial compression experiments on micrometer size pillars of single crystal gold and find surprisingly strong size effects, even though no significant strain gradients are present and the crystals are not initially dislocation free. We argue that these size effects are caused by dislocation starvation hardening, with dislocations leaving the crystal more quickly than they multiply and leading to the requirement of continual dislocation nucleation during the course of deformation. A new length scale for plasticity, the distance a dislocation travels before it creates another, arises naturally in this treatment. Hardening of crystals smaller than this characteristic size is expected to be dominated by dislocation starvation while crystals much larger than this size should exhibit conventional dislocation plasticity.", "doi": "10.1016/j.tsf.2006.01.030", "issn": "0040-6090", "publisher": "Elsevier", "publication": "Thin Solid Films", "publication_date": "2007-02-12", "series_number": "6", "volume": "515", "issue": "6", "pages": "3152-3157" }, { "id": "authors:65vkn-ycf33", "collection": "authors", "collection_id": "65vkn-ycf33", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20110630-091922277", "type": "article", "title": "Bridging the gap between computational and experimental length scales: A review on nanoscale plasticity", "author": [ { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "The results of both experimental studies and molecular dynamics simulations indicate that crystals exhibit strong size effects at the sub-micron scale: smaller is stronger. Until recently, experimental aspects of nano-scale deformation involved the effects of strain gradients, constraints of neighboring layers, grain boundaries, etc., which were key factors in observed size effects. Even without experimental constraints, many computational studies find that yield strength depends on sample size through a power relationship. Both experimental and computational results suggest that a fundamentally different plasticity mechanism might operate at the length scale of material's microstructure. In this work a brief review of some of these works is presented and compared with the results of our gold nanopillar micro-compression experiments, which were found to deform at nearly 50% of theoretical shear strength. To explain the observed size effect, we introduce our phenomenological model of hardening by dislocation starvation.", "issn": "1606-5131", "publisher": "Institute of Problems of Mechanical Engineering", "publication": "Reviews on Advanced Materials Science", "publication_date": "2006-11", "series_number": "1", "volume": "13", "issue": "1", "pages": "59-70" }, { "id": "authors:kmh1w-y4p75", "collection": "authors", "collection_id": "kmh1w-y4p75", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130710-151346908", "type": "article", "title": "Size effect in contact compression of nano- and microscale pyramid structures", "author": [ { "family_name": "Wang", "given_name": "Junlan", "clpid": "Wang-Junlan" }, { "family_name": "Lian", "given_name": "Jie", "clpid": "Lian-Jie" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" }, { "family_name": "Nix", "given_name": "William D.", "clpid": "Nix-W-D" }, { "family_name": "Kim", "given_name": "Kyung-Suk", "clpid": "Kim-Kyung-Suk" } ], "abstract": "An electrochemical etching approach was developed to fabricate self-similar nano- and microscale pyramid structures on single-crystal gold (1 0 0) surfaces. Using their unique self-similar characteristics, pyramids of (1 1 4) facets were compressed to study the length scale effects in the contact pressure and plastic deformation. At first, many pyramids were compressed simultaneously with a flat mica sheet to measure the ridge angle changes of the deformed pyramids with respect to the sizes of the flattened area. The ridge angle changes were scattered between approximately 2\u00b0 and 13\u00b0 for compression displacements of 50\u2013350 nm, in contrast to the perfect plasticity prediction of \u22124.7\u00b0. Then, individual pyramids isolated with a focused ion beam were compressed with a flat tip nanoindenter for displacements of approximately 10\u2013100 nm to obtain the relationship between the contact pressure and the compression depth. The plastic deformation-adjusted contact pressure evaluated by taking into account the initial 6\u201314 nm roundness offset of the pyramids is characterized by an initial increase up to approximately 2.5 GPa for a shallow compression depth within 10 nm followed by a gradual decay to approximately 450 MPa at a compression depth of 100 nm. This pressure seems to be still decaying towards an asymptotic value predicted by a continuum limit analysis. Given the size and self-similar nature of the pyramids, various mechanisms could possibly contribute to the observed scale dependence. The current study provides valuable experimental evidence for size-dependent material behavior at small length scales.", "doi": "10.1016/j.actamat.2006.04.030", "issn": "1359-6454", "publisher": "Elsevier", "publication": "Acta Materialia", "publication_date": "2006-09", "series_number": "15", "volume": "54", "issue": "15", "pages": "3973-3982" }, { "id": "authors:3maqb-7pr86", "collection": "authors", "collection_id": "3maqb-7pr86", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:GREprb06", "type": "article", "title": "Nanoscale gold pillars strengthened through dislocation starvation", "author": [ { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" }, { "family_name": "Nix", "given_name": "William D.", "clpid": "Nix-W-D" } ], "abstract": "It has been known for more than half a century that crystals can be made stronger by introducing defects into them, i.e., by strain-hardening. As the number of defects increases, their movement and multiplication is impeded, thus strengthening the material. In the present work we show hardening by dislocation starvation, a fundamentally different strengthening mechanism based on the elimination of defects from the crystal. We demonstrate that submicrometer sized gold crystals can be 50 times stronger than their bulk counterparts due to the elimination of defects from the crystal in the course of deformation.", "doi": "10.1103/PhysRevB.73.245410", "issn": "1098-0121", "publisher": "American Physical Society", "publication": "Physical Review B", "publication_date": "2006-06-15", "series_number": "24", "volume": "73", "issue": "24", "pages": "Art. No. 245410" }, { "id": "authors:24e07-55104", "collection": "authors", "collection_id": "24e07-55104", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130715-081458561", "type": "article", "title": "Effective Use of Focused Ion Beam (FIB) in Investigating Fundamental Mechanical Properties of Metals at the Sub-Micron Scale", "author": [ { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "abstract": "Recent advances in the 2-beam focused ion beams technology (FIB) have enabled researchers to\nnot only perform high-precision nanolithography and micro-machining, but also to apply these\nnovel fabrication techniques to investigating a broad range of materials' properties at the submicron\nand nano-scales. In our work, the FIB is utilized in manufacturing of sub-micron\ncylinders, or nano-pillars, as well as of TEM cross-sections to directly investigate plasticity of\nmetals at these small length scales. Single crystal nano-pillars, ranging in diameter between 300\nnm and 870 nm, were fabricated in the FIB from epitaxial gold films on MgO substrates and\nsubsequently compressed using a Nanoindenter fitted with a custom-fabricated diamond flat\npunch. We show convincingly that flow stresses strongly depend on the sample size, as some of\nour smaller specimens were found to plastically deform in uniaxial compression at stresses as\nhigh as 600 MPa, a value ~25 times higher than for bulk gold. We believe that these high\nstrengths are hardened by dislocation starvation. In this mechanism, once the sample is small\nenough, the mobile dislocations have a higher probability of annihilating at a nearby free surface\nthan of multiplying and being pinned by other dislocations.\n\n\nContrary to this, if the dislocations are trapped inside the specimen by a coating, the\nstrengthening mechanism is expected to be different. Here we present for the first time the\ncomparison of plastic deformation of passivated and unpassivated single crystal specimens at the\nsub-micron scale. The role of free surfaces is investigated by comparing stress results of both as-FIB'd,\nannealed, and alumina-passivated pillars. Preliminary results show that ALD-coated\npillars exhibit much higher flow stresses at equivalent sizes and strains compared with the\nuncoated samples. We also found that while FIB damage during pillar fabrication might account\nfor a small portion of the strength increase, it is not the major contributor.", "doi": "10.1557/PROC-983-0983-LL08-03", "issn": "0272-9172", "publisher": "Materials Research Society", "publication": "Materials Research Society symposia proceedings", "publication_date": "2006", "series_number": "1", "volume": "983", "issue": "1", "pages": "69-71" }, { "id": "authors:pes7c-v0586", "collection": "authors", "collection_id": "pes7c-v0586", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130710-144814692", "type": "article", "title": "Size dependence of mechanical properties of gold at the sub-micron scale", "author": [ { "family_name": "Greer", "given_name": "J. R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" }, { "family_name": "Nix", "given_name": "W. D.", "clpid": "Nix-W-D" } ], "abstract": "The results of both experimental studies and molecular dynamics simulations indicate that crystals exhibit strong size effects at the sub-micron scale. In experimental studies, the size effects are usually explained by strain gradients. By contrast, atomistic simulations suggest that the yield strength depends on the size even without strain gradients and scales with the sample size through a power relationship. Here we address these two different approaches to the size dependence of mechanical properties. Results of uniaxial compression experiments on gold single crystals at the sub-micron scale, without significant stress/strain gradients, are presented. The free-standing single-crystal Au cylinders are created by focused ion beam machining and are subsequently compressed using a nanoindenter fitted with a diamond flat punch. Compressive stresses and strains, as well as pillar stiffnesses, are determined from the test data. The experiments show that the flow stresses of these pillars increase significantly with decreasing pillar diameter, reaching several GPa for the smallest pillars. These high strengths appear to be controlled by dislocation starvation, which is unique to small crystals.", "doi": "10.1007/s00339-005-3204-6", "issn": "0947-8396", "publisher": "Springer", "publication": "Applied Physics A: Materials Science and Processing", "publication_date": "2005-05", "series_number": "8", "volume": "80", "issue": "8", "pages": "1625-1629" }, { "id": "authors:mxshx-cn478", "collection": "authors", "collection_id": "mxshx-cn478", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130710-145408467", "type": "article", "title": "Size dependence of mechanical properties of gold at the micron scale in the absence of strain gradients", "author": [ { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" }, { "family_name": "Oliver", "given_name": "Warren C.", "clpid": "Oliver-W-C" }, { "family_name": "Nix", "given_name": "William D.", "clpid": "Nix-W-D" } ], "abstract": "Classical laws of mechanics hold that mechanical properties are independent of sample size; however, results of experiments and molecular dynamics simulations indicate that crystals exhibit strong size effects at the sub-micron scale. In experimental studies, the size effect can be explained by strain gradients. Atomistic simulations suggest that the yield strength depends on the size even without strain gradients and scales with the sample size through a power relationship. We address these different approaches to the size dependence of mechanical properties. Results of uniaxial compression experiments on gold at the sub-micron scale, without stress/strain gradients, are presented here. Freestanding Au cylinders are created by two unique fabrication processes and subsequently compressed in the Nanoindenter with a flat punch. Compressive stress, strain, and stiffness of the pillars are determined. Test results indicate a significant flow stress increase, up to several GPa. These high strengths appear to be controlled by dislocation starvation, unique to small crystals.", "doi": "10.1016/j.actamat.2004.12.031", "issn": "1359-6454", "publisher": "Elsevier", "publication": "Acta Materialia", "publication_date": "2005-04", "series_number": "6", "volume": "53", "issue": "6", "pages": "1821-1830" } ]