Flat optics based on subwavelength metasurfaces has emerged as a powerful tool for compact and versatile wavefront control, enabling advances in imaging, sensing, displays, and communications. However, the functionality of single-layer metasurfaces is fundamentally limited by the finite degrees of freedom available in a single optical interaction. The growing demand for multifunctionality has motivated innovations in more complex designs involving multilayered structures. While cascaded or multilayer metasurfaces provide this additional design freedom, their realization through conventional top-down lithography is hindered by fabrication complexity and alignment challenges. Additive manufacturing, in particular two-photon lithography, has recently been explored to realize inverse-designed multilayered metaoptics, but such demonstrations have remained largely polymeric. High-index materials fabricated through TPL are still constrained to homogeneous lattices with uniform features. These challenges underscore the importance of alternative fabrication strategies that can expand the design space of multilayer and volumetric structures.
\r\n\r\nIn this dissertation, we establish a bottom-up platform for volumetric metaoptics based on nanoscale additive manufacturing (nano-AM) of TiO2. In Chapter 2, we develop a two-photon lithography framework that overcomes calcination-induced defects, enabling uniformly shrunk TiO2 lattices with lateral dimensions exceeding 90 \u03bcm and thicknesses up to 20 \u03bcm. In Chapter 3, we validate this platform by demonstrating metalenses operating at \u03bb = 4.5 \u03bcm with numerical aperture (NA) up to 0.74. In Chapter 4, we introduce heterogeneous multilayer stacking---achievable in a single lithography step---as a strategy to decouple phase, group delay, and higher-order dispersion control using simple cylindrical unit cells without height constraints. We experimentally realize broadband achromatic metalenses with NA = 0.25 and 0.49, exhibiting near-constant focal lengths across \u03bb = 4-5 \u03bcm. In Chapter 5, we further explore multifunctionality by demonstrating polarization-splitting metalenses and an inverse-designed color router, both fabricated in TiO2. Collectively, this work establishes nanoscale additive manufacturing of high-index oxides as a versatile route to functional multilayer and heterogeneous architectures, complementing existing polymer-based and subtractive approaches, and demonstrating new pathways toward compact, multifunctional, and volumetric optical devices.
", "doi": "10.7907/nyfd-tj09", "publication_date": "2026", "thesis_type": "phd", "thesis_year": "2026" }, { "id": "thesis:17678", "collection": "thesis", "collection_id": "17678", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:09132025-054711849", "primary_object_url": { "basename": "Shaker_Sammy_2026.pdf", "content": "final", "filesize": 307026680, "license": "other", "mime_type": "application/pdf", "url": "/17678/1/Shaker_Sammy_2026.pdf", "version": "v7.0.0" }, "type": "thesis", "title": "3D Vat Photopolymerization of Microarchitected Magnetic Metal Alloys for Chemotherapy Capture Filters", "author": [ { "family_name": "Shaker", "given_name": "Sammy", "orcid": "0000-0003-1751-4908", "clpid": "Shaker-Sammy" } ], "thesis_advisor": [ { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "thesis_committee": [ { "family_name": "Shapiro", "given_name": "Mikhail G.", "orcid": "0000-0002-0291-4215", "clpid": "Shapiro-M-G" }, { "family_name": "Kornfield", "given_name": "Julia A.", "orcid": "0000-0001-6746-8634", "clpid": "Kornfield-J-A" }, { "family_name": "Guttman", "given_name": "Mitchell", "orcid": "0000-0003-4748-9352", "clpid": "Guttman-M" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "local_group": [ { "literal": "div_bbe" } ], "abstract": "Primary liver cancer constitutes an object of concern for communities across the globe. With the majority of new diagnoses of the most common subtype of primary liver cancer, hepatocellular carcinoma, inoperable at diagnosis, the standard of care revolves around the use of liver-directed therapies to treat tumors. The most popular therapy is termed transarterial chemoembolization, wherein the unique anatomy of the liver is exploited to deliver chemotherapy and embolic agents selectively to a large tumor, leading to tumor cell death and improved survival for patients. However, the chemotherapeutics used in this procedure have toxic effects on organs outside of the liver, and are as such dose-restricted on the basis of these side effects. In order to increase the amount of drug used and thus increase the chance of tumor cell death, chemotherapy capture devices are necessary. While some materials have been developed for this application, these devices regularly suffer from such restrictions as passive capture mechanisms necessitating the design of devices with poor hemodynamics or the use of immunogenic materials such as heteroDNA. Magnetic nanoparticles conjugated to chemotherapeutics as well as magnetic nanoparticle chemotherapy capture agents, delivered with the chemotherapeutics, present a potential way out of this conundrum, but the application of these materials requires the design of magnetic capture devices with favorable hemodynamic and magnetic properties. Architected magnetic metal devices can potentially provide the sought after solution to these difficulties, but techniques to such devices with high spatial resolution are lacking. An additive manufacturing technique that can provide high spatial resolution utilizes vat photopolymerization in tandem with thermal processing to produce well-resolved metal lattices that can provide for this ongoing need.
\r\n\r\nThis thesis applies this technique to the synthesis of magnetic lattices for particle capture. Lattices are synthesized in iron, nickel-iron, and copper-nickel-iron compositions and characterized structurally and magnetically. Simulations of particle capture in these lattices under various conditions are performed. In addition, attempts at particle capture are described and methods of characterization of particle capture are discussed. This technique is also explored with regards to the synthesis of iron-nickel and iron-cobalt lattices and the characterization of the resultant products is discussed and evaluated. Finally, a modification to this technique is used to generate metal-carbon microcomposites with unusual magnetic properties when compared with their counterparts synthesized using the unmodified procedure.
", "doi": "10.7907/gc1t-5869", "publication_date": "2026", "thesis_type": "phd", "thesis_year": "2026" }, { "id": "thesis:18514", "collection": "thesis", "collection_id": "18514", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:04272026-182608505", "type": "thesis", "title": "Additive Manufacturing and Characterization of Micro-Architected Lithium-ion Battery Electrodes", "author": [ { "family_name": "Wang", "given_name": "Yingjin", "orcid": "0009-0002-1239-3422", "clpid": "Wang-Yingjin" } ], "thesis_advisor": [ { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "thesis_committee": [ { "family_name": "Faber", "given_name": "Katherine T.", "orcid": "0000-0001-6585-2536", "clpid": "Faber-K-T" }, { "family_name": "Ravichandran", "given_name": "Guruswami", "orcid": "0000-0002-2912-0001", "clpid": "Ravichandran-G" }, { "family_name": "See", "given_name": "Kimberly", "orcid": "0000-0002-0133-9693", "clpid": "See-Kimberly" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "Electrode structure is closely coupled with mechanical behavior, ion transport, and reaction uniformity during battery operation. In addition to conventional slurry-cast electrodes, emerging fabrication approaches provide new opportunities to study and design electrode architectures. This thesis investigates lithium-ion battery electrodes through two complementary perspectives related to the electrode structure: micro-scale mechanical characterization to elucidate degradation mechanisms and additive manufacturing of three-dimensional (3D) micro-architected electrodes to investigate structure-transport relationships.
\r\n\r\nIn Chapters 2 and 3, the mechanical behavior of lithium-ion battery electrodes was investigated using nanoindentation and micro-pillar compression experiments. State-of-charge-dependent mechanical properties of electroplated LiCoO2 (LCO) cathodes were quantified, revealing a decreasing tendency in elastic modulus and hardness during delithiation, which is attributed to the expansion of LCO layered structure. Fracture toughness distribution across the electrode thickness was analyzed to understand how structural heterogeneity contributes to the mechanical property landscape. In addition, we studied the deformation of lithium-based composite anodes, confirming that the Li/Na composite anode exhibits higher deformability at the electrode-electrolyte interface, which enhances interfacial contact.
\r\n\r\nThe interconnected pore structure and large surface-to-volume ratio of 3D architected battery electrodes render them promising for enhancing electrochemical performance via more efficient ionic transport. In Chapters 4 and 5, we develop a hydrogel infusion additive manufacturing (HIAM)-based approach to fabricate micro-architected LiFePO4 (LFP)/C composite electrodes with feature sizes down to 18 \u00b5m. The concomitant formation of carbon within the lattice enhances the mechanical strength, which preserves shape integrity of the 3D structure during cell assembly and function. We designed electrodes with different geometries, including tilted cubes, honeycombs, and triply periodic minimal surfaces (TPMS), to probe the influence of geometric factors on electrochemical performance under various charge-discharge rates. We propose an experimentally informed electrochemical model that demonstrates the roles of Li+ transport in the electrolyte and Li+ diffusion in the electrode in determining the utilization of active materials. This work introduces a versatile manufacturing platform for printing 3D battery components and provides insights into structure optimization for high-performance rechargeable batteries.
", "doi": "10.7907/tkgq-7c28", "publication_date": "2026", "thesis_type": "phd", "thesis_year": "2026" }, { "id": "thesis:17120", "collection": "thesis", "collection_id": "17120", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:03312025-221040469", "primary_object_url": { "basename": "PhD Thesis_SLee.pdf", "content": "final", "filesize": 40115968, "license": "other", "mime_type": "application/pdf", "url": "/17120/7/PhD Thesis_SLee.pdf", "version": "v5.0.0" }, "type": "thesis", "title": "Multiscale Design, Fabrication, and Mechanical Analysis of Structural Hierarchies in Functional Materials", "author": [ { "family_name": "Lee", "given_name": "Seola", "orcid": "0000-0002-4538-0890", "clpid": "Lee-Seola" } ], "thesis_advisor": [ { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "thesis_committee": [ { "family_name": "Ravichandran", "given_name": "Guruswami", "orcid": "0000-0002-2912-0001", "clpid": "Ravichandran-G" }, { "family_name": "Daraio", "given_name": "Chiara", "orcid": "0000-0001-5296-4440", "clpid": "Daraio-C" }, { "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" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "Hierarchical structuring has emerged as a powerful strategy in functional material design to enhance mechanical performance and impart functional properties across multiple scales. In architected materials, leveraging tessellated multiscale geometrical features enables unconventional properties such as ultra-low density and high energy absorption. Similarly, in functional polymers, rational design of molecular chemistries and polymer microstructures allows for tunable mechanical properties and stimuli-responsive behaviors. However, a substantial knowledge gap persists in understanding how multiscale interactions connect to determine the macroscale performance of these materials. This gap arises from challenges in scalable fabrication, multiscale characterization, and limited mechanistic insight from theory and simulations. To address these challenges, this thesis presents a comprehensive approach that integrates scalable fabrication, multiscale characterization, and theoretical modeling to develop hierarchical materials with tunable functionalities. Specifically, we (1) demonstrate scalable fabrication of hierarchical materials using additive manufacturing, (2) investigate the bulk mechanical responses by tuning the smallest level in hierarchical design, and (3) perform multiscale studies to bridge the gap between unit-level interactions and macroscale performance.
\r\n\r\nIn the first study, we explore the role of structural hierarchies in architected polymeric materials for enhanced energy dissipation. Using metasurface-based holographic lithography, we fabricate nano-architected polymeric sheets and demonstrate how geometrical parameters for unit cell design such as relative density and beam aspect ratio influence stiffness, energy dissipation, and deformation modes. These findings highlight the significance of hierarchical structuring in enhancing mechanical performance and establish design principles for scalable manufacturing. In the second study, we focus on dynamic polymers and examine how dynamic crosslinking at the molecular level influences macroscale material responses. A single-step stereolithography approach is developed to tune molecular-level controls in the material. Through multiscale modeling and experimental characterizations, we reveal how dynamic bonding mechanisms govern stiffness, stretchability, and fracture energy. The results underscore the significance of multiscale interactions in tuning mechanical behavior and suggest a pathway for designing materials with programmable responses. In the final study, we build on these insights by integrating molecular-level controls with nonlinear structural responses such as buckling and shape transformations. The central premise is that molecular interactions dictate local responsiveness, while structural geometries can amplify or suppress these responses through localized deformation or stress redistribution. As a demonstration, we explore how tailored viscoelasticity and controlled instabilities can determine the buckling mode of a structural beam. This synergistic interplay highlights the potential of the materials requiring programmed reconfigurability, shape morphing, and stimuli-responsive properties.
\r\n\r\nThe findings presented in this thesis offer a robust framework for bridging molecular-level design with macro-scale performance through scalable fabrication and characterization strategies. By expanding the design space of material-level behavior, this work lays the groundwork for developing next-generation materials with enhanced functionality, adaptability, and intelligence for applications such as soft robotics, healthcare, and sustainable materials.
", "doi": "10.7907/1ee0-bc98", "publication_date": "2025", "thesis_type": "phd", "thesis_year": "2025" }, { "id": "thesis:17290", "collection": "thesis", "collection_id": "17290", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05292025-003646523", "primary_object_url": { "basename": "tran_thomas_2025.pdf", "content": "final", "filesize": 20060046, "license": "other", "mime_type": "application/pdf", "url": "/17290/1/tran_thomas_2025.pdf", "version": "v5.0.0" }, "type": "thesis", "title": "Microstructural and Mechanical Characterization of Additively Manufactured Binary Metallic Alloys", "author": [ { "family_name": "Tran", "given_name": "Thomas Tuan", "orcid": "0009-0003-7034-9486", "clpid": "Tran-Thomas-Tuan" } ], "thesis_advisor": [ { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "thesis_committee": [ { "family_name": "Faber", "given_name": "Katherine T.", "orcid": "0000-0001-6585-2536", "clpid": "Faber-K-T" }, { "family_name": "Ravichandran", "given_name": "Guruswami", "orcid": "0000-0002-2912-0001", "clpid": "Ravichandran-G" }, { "family_name": "Nelson", "given_name": "Hosea M.", "orcid": "0000-0002-4666-2793", "clpid": "Nelson-H-M" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "Hydrogel infusion-based additive manufacturing (HIAM) is a chemically versatile solid-state processing pathway that allows 3D structuring of ceramics and metals with micro-scale precision. Using controlled thermal treatments of 3D-printed metal ion-infused gels, this process generates intricate microstructures which are heavily influenced by the kinetics of gas-solid reactions and their subsequent phase evolution. This work seeks to refine our understanding of the process-structure-property relationships in HIAM-produced alloys and provide general insights for AM-enabled alloy development and microstructure design using metal oxide reduction.
\r\n\r\nThrough HIAM, we demonstrate the arbitrary alloying of CuxNi1-x binary alloys, where systematic characterization of microstructures down to the atomic scale revealed that reduction, or the lack thereof, drove the formation of chemically homogeneous alloy grains with numerous annealing twins and entrapped unreduced oxide nano-inclusions, resulting in a hierarchical two-phase composite. These features appear to elevate the average nanoindentation hardnesses by up to four times that of bulk annealed CuxNi1-x and lead to a composition dependence on the scaling of the \u201csmaller is stronger\u201d size effect in uniaxial micropillar compressions. This compositional dependence of hardness and deformation mechanisms arises from changes in reduction kinetics which influence the density of inclusions and voids developed by HIAM processing. As a result, HIAM demonstrates the capability to fabricate heterogeneous alloy systems as a result of their oxide reduction pathways, which are revealed by thermogravimetry experiments and kinetic analysis.
", "doi": "10.7907/ej4t-7e95", "publication_date": "2025", "thesis_type": "phd", "thesis_year": "2025" }, { "id": "thesis:17059", "collection": "thesis", "collection_id": "17059", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:03132025-055626664", "primary_object_url": { "basename": "thesis_WenxinZhang.pdf", "content": "final", "filesize": 13336993, "license": "other", "mime_type": "application/pdf", "url": "/17059/18/thesis_WenxinZhang.pdf", "version": "v10.0.0" }, "type": "thesis", "title": "Advanced Nano Manufacturing Enables Probing Fundamental Mechanical Behaviors of Materials", "author": [ { "family_name": "Zhang", "given_name": "Wenxin", "orcid": "0000-0002-6318-0622", "clpid": "Zhang-Wenxin" } ], "thesis_advisor": [ { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "thesis_committee": [ { "family_name": "Ravichandran", "given_name": "Guruswami", "orcid": "0000-0002-2912-0001", "clpid": "Ravichandran-G" }, { "family_name": "Pellegrino", "given_name": "Sergio", "orcid": "0000-0001-9373-3278", "clpid": "Pellegrino-S" }, { "family_name": "Faber", "given_name": "Katherine T.", "orcid": "0000-0001-6585-2536", "clpid": "Faber-K-T" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "The trend of miniaturization has revolutionized modern technologies, with micro- and nanoscale materials driving transformative advancements in high-tech industries and scientific discovery. Among the various properties and applications enabled at these small scales, nanomechanical properties play a fundamental role, underpinning the integrity and functionality of any structures or systems. However, despite advancements in both conventional and emerging micro- and nano-manufacturing strategies, there has remained a lack of direct \u201cbottom-up\u201d experimental pathways to fabricate and probe the mechanical responses of submicron-sized monolithic nano-specimens with unconventional microstructures and/or 3D nano-architectures with submicron-sized features, particularly for non-carbon materials.
\r\n\r\nIn this work, I will present novel nano-fabrication and manufacturing strategies and their applications in addressing these nanomechanical challenges through three key studies. In Chapter 2, the deformation characteristic of organic ice is studied via cryogenic micro-compression and molecular dynamics simulations, providing insights into a benzene-ring re-orientation-mediated densification deformation route and offering new insights into planetary geology for celestial bodies such as Titan. In Chapter 3, we experimentally unveiled unprecedented two-regime size effects in additively manufactured metallic nanopillars with hierarchical microstructures, revealing a nanocrystallinity-, nanoporosity-mediated plasticity mechanism through atomistic insights. In Chapter 4, we extended this nano-manufacturing approach to explore nanoporosity-driven deformation behaviors in nano-architected metals with in situ experiments and finite element analysis. Together, these studies not only elucidate previously unprobed fundamental small-scale mechanical behaviors but also lay the groundwork for developing an advanced micro-to-nanoscale manufacturing platform, enabling complex systems and functional applications such as energy storage, biomedical microrobots, nanophotonics, and beyond, which I will briefly discuss in Chapter 5 as an outlook with a few examples from metal/oxide nanocomposites to interpenetrated pyrolytic carbon microarchitectures.
", "doi": "10.7907/fxq3-7817", "publication_date": "2025", "thesis_type": "phd", "thesis_year": "2025" }, { "id": "thesis:16163", "collection": "thesis", "collection_id": "16163", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:08212023-211243186", "type": "thesis", "title": "Additive Manufacturing of 3D Micro-Architected Materials for Device Applications", "author": [ { "family_name": "Deng", "given_name": "Weiting", "orcid": "0000-0003-0984-8027", "clpid": "Deng-Weiting" } ], "thesis_advisor": [ { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "thesis_committee": [ { "family_name": "Gao", "given_name": "Wei", "orcid": "0000-0002-8503-4562", "clpid": "Gao-Wei" }, { "family_name": "Gharib", "given_name": "Morteza", "orcid": "0000-0003-0754-4193", "clpid": "Gharib-M" }, { "family_name": "Faber", "given_name": "Katherine T.", "orcid": "0000-0001-6585-2536", "clpid": "Faber-K-T" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "Natural cellular biomaterials typically consist of hard and soft constituent materials that are hierarchically ordered to achieve outstanding mechanical properties, e.g., light weight, mechanical resilience, multi-functionality, etc. Architected materials are a new class of engineered materials with meticulously controlled internal structures that produce properties that differ from or exceed those of their constituent materials. Recent developments in additive manufacturing offer an extraordinary opportunity to rationally design the structure and chemical composition of architected materials to optimize properties and functionalities for a wide range of device applications. Here we first present a framework that combines an artificial intelligence tool and two-photon lithography in order to design and fabricate optimal porous structure with the desired anisotropic mechanical properties. The biomimetic and extremely tunable natural of the structures generated by the framework enables the great potential to be used as the bone scaffold design strategy which meets the requirements of complex anisotropic and heterogeneous mechanical properties of the vivo environment. The designed the architectures are meticulously verified by in situ Nanomechanics. These theory-informed experiments revealed close agreement between experimental data and artificial intelligence-predicted stiffness anisotropy, which opens a pathway for uncovering previous unattainable design space of elasticity vs. 3D architecture mapping in quantifiable and deterministic way. Besides, we explore the structural and material effects of additively manufactured microrobots which is powered by external physical fields for complex therapeutic assignments. The excellent movability and controllability permit the microrobots to be used as minimal invasive instruments for precise application in healthcare. The synergistically optimized microstructures and chemical composition enables the microrobots great potential to be applied to in vivo clinical applications.", "doi": "10.7907/74dt-4442", "publication_date": "2024", "thesis_type": "phd", "thesis_year": "2024" }, { "id": "thesis:16212", "collection": "thesis", "collection_id": "16212", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:10222023-023442759", "primary_object_url": { "basename": "Villafuerte_Fernando_2024.pdf", "content": "final", "filesize": 16747509, "license": "other", "mime_type": "application/pdf", "url": "/16212/1/Villafuerte_Fernando_2024.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Additive Manufacturing of Batteries and IR-Active Microparticles: Polyborane-Based Electrolytes for Solid State Batteries and Additively Manufactured, TiN-Coated Microbridges", "author": [ { "family_name": "Villafuerte", "given_name": "Fernando Joaquin", "orcid": "0000-0003-0958-7111", "clpid": "Villafuerte-Fernando-Joaquin" } ], "thesis_advisor": [ { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "thesis_committee": [ { "family_name": "Fultz", "given_name": "Brent T.", "orcid": "0000-0002-6364-8782", "clpid": "Fultz-B-T" }, { "family_name": "Faber", "given_name": "Katherine T.", "orcid": "0000-0001-6585-2536", "clpid": "Faber-K-T" }, { "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" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "Advances in additive manufacturing (AM) processes are continuously opening up the material design space, providing scientists with opportunities to explore the relationship between structure, processing, and materials properties in new contexts. The first project presented in this thesis presents the design and refinement of a novel, polyborane-based solid electrolyte, whose design and investigation were motivated by the advent of additively manufactured, 3D electrodes, which could play a pivotal role in enabling next-generation batteries that can store more energy without sacrificing power. The first iteration of this electrolyte was synthesized by hydroborating polybutadiene with 9-borabicyclo(3.3.1)nonane (9-BBN). The resultant poly(9-BBN) was then reacted with precise amounts of n-butyllithium (n-BuLi), an organolithium reagent, to create the final polymer electrolyte. The polymer electrolyte films were assembled into a custom apparatus for impedance measurements, and though found to be ionically conductive, these measurements were not consistent, even within films made from the same batch of polymer in solution.
\r\n\r\nThis necessitated the modification of the electrolyte into a UV-cured version, which was achieved by hydroboration of polybutadiene using 9-BBN. The resulting poly(9BBN)-co-polybutadiene is treated with lithium tert-butoxide (LiOtBu) and crosslinked to produce a precursor resin, which is then drop cast onto PTFE spacers, UV-cured for 5 minutes, dried, and assembled into coin cells for electrochemical impedance spectroscopy (EIS) and into pans for differential scanning calorimetry (DSC). The ionic conductivity of the PBEs as measured by EIS as a function of molar salt ratio, r = molLi/molB, does not track with their measured glass transition temperatures, Tg or the activation energies, Ea, extracted from fitting the Vogel-Tammann-Fulcher (VTF) equation to the conductivity data. Beyond r = 0.33, values for Tg and Ea demonstrate insensitivity to increasing concentration, while conductivity continues to change with concentration and reaches a maximum at r = 0.75. Moreover, measurement of ionic conductivity of control PBE films without boron on the polybutadiene backbone confirms that the presence of Lewis-acidic boron groups is necessary for ionic solvation and conduction. Further analysis that compared the PBEs to a well-studied PEO-based electrolyte in the literature through the calculation of a reduced conductivity to control for polymer viscosity and segmental motion revealed that PBEs obtain optimal conductivity at higher salt concentrations than PEO, and that their ionic conductivities are far below that of PEO. We posit that we are observing a mechanism of ionic conduction in a glassy regime partially decoupled from the relaxation of the polymer host. We attribute these effects to the strong interaction between the Lewis-acidic boron centers and the strongly Lewis-basic tert-butoxide anions, which limits ionic conductivity by suppressing motion of the anions and presenting a large activation barrier for motion of Li+, which is optimized at high concentrations where the distance between the boron-anion centers is sufficiently small to increase the probability of a hopping event from one center to another.
\r\n\r\nNanorods fashioned from noble metals are ideal for maximizing extinction of electromagnetic radiation, which is necessary for plasmonically active materials in numerous applications, from contrast agents for biological imaging to effective obscurants. Key challenges that prevent nanorods from being employed for these technological applications include the prohibitively expensive cost of Au and Ag, their lack of requisite thermal and chemical stability, and the limitations in resolution and attainable feature sizes produced by existing wet chemistry techniques. The second project in this thesis focuses on the development of an AM process to create arrays of TiN-coated microbridges with lengths of 4.749 microns, cross-sections with dimensions of 0.692 by 2.256 microns, and effective aspect ratios of 3.368, that are capable of attenuating light reflected from a TiN-coated sapphire substrate by more than 80% in the mid-infrared (mid-IR), as measured by Fourier Transform Infrared (FTIR) spectroscopy. FTIR spectroscopy measurements further reveal attenuation of light transmitted through the same TiN-coated structures by up to 35% in the near- to mid-IR. These results indicate a promising pathway for AM of plasmonically active microparticles with broad reflectance and transmittance attenuation of light in the near- and mid-IR.
", "doi": "10.7907/jc8h-gs34", "publication_date": "2024", "thesis_type": "phd", "thesis_year": "2024" }, { "id": "thesis:16356", "collection": "thesis", "collection_id": "16356", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:04162024-184348195", "primary_object_url": { "basename": "Sun_Yuchun_2024.pdf", "content": "final", "filesize": 59124352, "license": "other", "mime_type": "application/pdf", "url": "/16356/230/Sun_Yuchun_2024.pdf", "version": "v5.0.0" }, "type": "thesis", "title": "3D Micro-Architected Materials for Batteries", "author": [ { "family_name": "Sun", "given_name": "Yuchun", "orcid": "0000-0002-7028-3523", "clpid": "Sun-Yuchun" } ], "thesis_advisor": [ { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "thesis_committee": [ { "family_name": "Faber", "given_name": "Katherine T.", "orcid": "0000-0001-6585-2536", "clpid": "Faber-K-T" }, { "family_name": "See", "given_name": "Kimberly", "orcid": "0000-0002-0133-9693", "clpid": "See-Kimberly" }, { "family_name": "West", "given_name": "William C.", "orcid": "0000-0001-6417-8930", "clpid": "West-W-C" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "local_group": [ { "literal": "Resnick Sustainability Institute" }, { "literal": "div_eng" } ], "abstract": "Additive manufacturing (AM) enables three-dimensional micro-patterning of battery electrode materials, permitting complex structural designs beyond those of traditional slurry electrodes. We demonstrate two novel AM approaches for architecting electrode materials in lithium-ion batteries. First, we introduce a process for fabricating 3D micro-architected cathodes utilizing gel infusion additive manufacturing, and demonstrate this technique with lithium cobalt oxide (LCO). This method combines VP-based 3D printing with subsequent ion infusion and calcination processes. It starts with the printing of a blank organogel structure using a customized acrylate-based photoresin. This organogel is then converted into a hydrogel, infused with lithium and cobalt precursors, and finally subjected to calcination to form the LCO structure. This technique achieves 3D micro-architected LCO lattices with beam diameters of 45 \u03bcm, and maintains the designed architecture with tunable microstructures. By fabricating 3D micro-architected LiNi0.33Mn0.33Co0.33O2 (NMC111) through a very similar process, we demonstrate the potential for this gel infusion additive manufacturing method to engineer a variety of cathode materials for lithium-ion batteries in 3D.
\r\n\r\nWe also develop a fabrication method to create 3D lithium anodes supported by micro-architected carbon scaffold. By pyrolyzing 3D printed polymer microlattices, mechanically robust carbon electrodes are produced. Their micro-scale features and flexible structural control make them suitable as scaffolds for lithium-metal anodes. Surface functionalization and lithium electrodeposition are explored for dense lithium nucleation and uniform epitaxial growth on the carbon framework, resulting in micro-architected lithium/carbon anodes. With the rapid development of high-resolution AM techniques in recent decades, these approaches to additively manufacture cathode and anode materials provide promising pathways to build batteries with customizable 3D designs, and pursue higher energy and power densities for different applications.
", "doi": "10.7907/y6bt-xb40", "publication_date": "2024", "thesis_type": "phd", "thesis_year": "2024" }, { "id": "thesis:16124", "collection": "thesis", "collection_id": "16124", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:06202023-173615207", "primary_object_url": { "basename": "Senior Thesis.pdf", "content": "final", "filesize": 77257140, "license": "other", "mime_type": "application/pdf", "url": "/16124/1/Senior Thesis.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Manufacturing 3-D Lithium-Ion Batteries with Interpenetrating Lattice Electrodes", "author": [ { "family_name": "Zou", "given_name": "Fangyu Nathan", "clpid": "Zou-Fangyu-Nathan" } ], "thesis_advisor": [ { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "thesis_committee": [ { "family_name": "None", "given_name": "None" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "3-D lithium-ion batteries have been proven to exhibit a higher energy density while minimizing power loss compared to the standard, layer-by-layer constructed 2-D lithium-ion batteries. This thesis explores the implementation of additive manufacturing in the process of constructing the proposed 3-D battery due to its capability of architecting materials with high accuracy and tunability. A 3-D lithium-ion battery backbone was created using a 2-step process, in which the first step 3-D printed the overall structure as a polymer, and the second step sputtered gold onto the polymer for conductive properties. The 3-D printed battery backbone consisted of two interpenetrating lattices made of post-cured PR48 resin that would serve as the anode and cathode, while the electrolyte would fill the space between the two electrodes. During the sputtering process, the polymer structure was rotated 6 times to guarantee that the sputtering will be conformal throughout the lattice. Electrodeposition was used to generate a LiCoO2 anode and a Li cathode. The electrodeposition of the lithium cobalt oxide cathode onto the lattice structure was proven to be unsuccessful due to the low thermal stability and high reactivity of the 3-D printed polymer when submerged into the electrolyte, consisting of KOH at 260 \u00b0C. Results indicate that the uniform electrodeposition of the lithium anode onto the lattice structure was successful using a 1s on, 1s off pulse current for a 60-minute duration. Using a titanium and gold layer proved to increase the uniformity of the coating. However, due to the failure of the lithium cobalt oxide electrodeposition, a different backbone structure may need to be considered. Having two separate structures serving as the anode and cathode (and later combining them into one structure) as opposed to both electrodes being on one structure may be beneficial. This allows for the cathode to be altered without altering both electrodes, allowing more flexibility to coat the structure with lithium cobalt oxide.", "doi": "10.7907/t8n9-wj51", "publication_date": "2023", "thesis_type": "senior_major", "thesis_year": "2023" }, { "id": "thesis:16057", "collection": "thesis", "collection_id": "16057", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:06022023-145117270", "primary_object_url": { "basename": "Thesis_Caltech_Thesis_LaTeX_Template__with_logo____Amylynn_Chen (1).pdf", "content": "final", "filesize": 15428051, "license": "other", "mime_type": "application/pdf", "url": "/16057/1/Thesis_Caltech_Thesis_LaTeX_Template__with_logo____Amylynn_Chen (1).pdf", "version": "v4.0.0" }, "type": "thesis", "title": "3D in situ Chemical Synthesis: Additive Manufacturing of Functional Polymeric Materials via Vat Photo-polymerization", "author": [ { "family_name": "Chen", "given_name": "Amylynn C.", "orcid": "0000-0002-8112-5862", "clpid": "Chen-Amylynn-C" } ], "thesis_advisor": [ { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "thesis_committee": [ { "family_name": "Gao", "given_name": "Wei", "orcid": "0000-0002-8503-4562", "clpid": "Gao-Wei" }, { "family_name": "Faber", "given_name": "Katherine T.", "orcid": "0000-0001-6585-2536", "clpid": "Faber-K-T" }, { "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" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "As additively manufacturing gains popularity in rapid-prototyping, manufacturing and customized production, there is a continuous demand in seeking for new materials with advanced functionalities to satisfy the wide range of applications in aerospace, construction, optics, actuation, dentistry, biomedical practices and even food industry. Vat photopolymerization (VP), a light-enabled AM technique, is particularly promising due to its ability to achieve good surface quality, high resolution, and large volumetric throughput. The vast majority of materials obtained by VP are covalently-crosslinked thermosets with nondegradable carbon backbones. This highly crosslinked molecular structure gives rise to stiff and brittle materials, limiting the structural functionality in desired applications.
\r\n\r\nThis thesis explores a variety of molecular structures for new VP photopolymers: a) dynamically-crosslinked compliant polymer, b) interpenetrating network (IPN) hydrogel, and c) covalently-crosslinked polymer with labile group (ex. ester) insertion to polymer backbone. With the dynamic crosslinking system, we demonstrate tunable mechanical behaviors of the metal-coordinated supramolecular polymers. These materials display a range of failure strain of 450% - 940% and ultimate tensile strength of 12.4 - 2.2 MPa with varying resin compositions. To incorporate multifunctionality, we design thermoresponsive IPN hydrogels by fabricating a hydrophilic host polymer network via VP and a subsequent formation a thermoresponsive 2nd network (poly(N-Isopropylacrylamide)). The architected IPNs consistently display strong polymer-liquid phase separation behavior and a tunable water release behavior with volumetric shrinkage between 30% and 70% upon heating at 50oC. Finally, to promote the degradability of the acylate-based photoresin, we demonstrated successful incorporation for ester functional groups into the polymer backbone via radical ring opening polymerization of cyclic ketene acetals. The obtained polymer undergoes 84% mass loss within 7 hours under hydrolytic degradation condition. Overall, we demonstrated VP as a powerful technique to achieve one-pot synthesis and fabrication of functional materials. Our explorations on the development of degradable photopolymers, thermoresponsive double-network hydrogels, and metal-coordinated supramolecular polymers provide valuable insights into the impact of resin formulation on mechanical properties. From analyzing the molecular weight of 3DP materials to finetuning of phase separation behavior and degradability, we demonstrate that VP provides a new platform to inspire advanced photoresin design strategies for desirable mechanical performance.
", "doi": "10.7907/ca3e-rc06", "publication_date": "2023", "thesis_type": "phd", "thesis_year": "2023" }, { "id": "thesis:14970", "collection": "thesis", "collection_id": "14970", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:07112022-193425820", "primary_object_url": { "basename": "GALLIVAN_Rebecca_2023_Thesis_Corrected.pdf", "content": "final", "filesize": 64223386, "license": "cc_by_nd", "mime_type": "application/pdf", "url": "/14970/23/GALLIVAN_Rebecca_2023_Thesis_Corrected.pdf", "version": "v9.0.0" }, "type": "thesis", "title": "The Role of Boundaries and Other Microstructural Features on Emergent Mechanical and Mechanically-Coupled Phenomena at the Nanoscale", "author": [ { "family_name": "Gallivan", "given_name": "Rebecca Anne", "orcid": "0000-0001-6516-2180", "clpid": "Gallivan-Rebecca-Anne" } ], "thesis_advisor": [ { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "thesis_committee": [ { "family_name": "Falson", "given_name": "Joseph", "orcid": "0000-0003-3183-9864", "clpid": "Falson-Joseph" }, { "family_name": "Faber", "given_name": "Katherine T.", "orcid": "0000-0001-6585-2536", "clpid": "Faber-K-T" }, { "family_name": "Fultz", "given_name": "Brent T.", "orcid": "0000-0002-6364-8782", "clpid": "Fultz-B-T" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "As nanotechnology continues to advance, the need for smaller, structurally complex materials has grown. However, these microscopic (10\u2076) and nanoscopic (10\u2079) structures often display unexpected changes in mechanical properties as compared to their macroscopic counterparts. Nanomechanical studies investigating size-effects in stiffness, strength, recoverability, ductility, and fracture, reveal an intimate interplay between the breakdown in continuum behavior and the energetic landscape of microstructural mechanisms. Additive manufacturing opens new opportunities to explore this microstructure-mechanics relationship as it enables the micro- and nano-scale production of novel materials and microstructures. While existing studies on structural and functional materials highlight the unique size-scale behavior, a large gap remains in our understanding of the complex relationship between microstructure and material performance. This work investigates the interactions and mechanisms that give rise to emergent nanoscale phenomena. With microstructural characterizations, we demonstrate the role of boundaries and interfaces on mechanical and mechanically-coupled behavior in (1) dense nanowire arrays, (2) nano-architected nanocrystalline zinc oxide, and (3) highly-twinned additively manufactured metallic systems. This work provides critical insights into the mechanisms underlying the observed emergent phenomena and further opens our fundamental intuition for microstructure-mechanics relationships in materials at the nanoscale.", "doi": "10.7907/gv3v-9k07", "publication_date": "2023", "thesis_type": "phd", "thesis_year": "2023" }, { "id": "thesis:14963", "collection": "thesis", "collection_id": "14963", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:06242022-190238579", "primary_object_url": { "basename": "Moestopo_Caltech_Thesis_Final.pdf", "content": "final", "filesize": 51975787, "license": "other", "mime_type": "application/pdf", "url": "/14963/12/Moestopo_Caltech_Thesis_Final.pdf", "version": "v8.0.0" }, "type": "thesis", "title": "Design, Fabrication, and Mechanical Analysis of Intertwined and Frictional Micro-Architected Materials", "author": [ { "family_name": "Moestopo", "given_name": "Widianto Putra", "orcid": "0000-0002-7617-4280", "clpid": "Moestopo-Widianto-Putra" } ], "thesis_advisor": [ { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "thesis_committee": [ { "family_name": "Pellegrino", "given_name": "Sergio", "orcid": "0000-0001-9373-3278", "clpid": "Pellegrino-S" }, { "family_name": "Bhattacharya", "given_name": "Kaushik", "orcid": "0000-0003-2908-5469", "clpid": "Bhattacharya-K" }, { "family_name": "Asimaki", "given_name": "Domniki", "orcid": "0000-0002-3008-8088", "clpid": "Asimaki-D" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "Natural biomaterials, e.g., shells, bone, and wood, are typically comprised of hard and soft constituent materials that are hierarchically ordered to achieve mechanical resilience, light weight, and multifunctionality. Advanced fabrication techniques have enabled the creation of precisely architected materials with exceptional mechanical properties unattainable by their constituent materials, yet they are often designed with fully interconnected structural members whose junctions are detrimental to their performance because they serve as stress concentrations for damage accumulation and lower mechanical resilience. Most studies have also focused on understanding the stretching, bending, and buckling of the structural members, while explorations toward contact interactions within structural members remain limited. We address these challenges by (i) introducing a new three-dimensional (3D) hierarchical architecture in which fibers are interwoven to construct effective beams, (ii) introducing the concept of knots into the hierarchical architecture framework, and (iii) developing a model to study the effects of structural element length scale on the energy dissipation capability of a frictional architected material.
\r\n\r\nWe first explore the effective lattice response of hierarchical woven microlattices, and we demonstrate the superior ability of woven architectures to achieve high tensile and compressive strains via smooth reconfiguration of woven microfibers in the effective beams and junctions without failure events. We study how fiber topology and constituent materials influence the mechanical behaviors of hierarchical intertwined structures, and we compare our results with theory. Our study reveals that knot topology allows a new regime of deformation capable of shape-retention, leading to increased absorbed energy and failure strain compared to structures with woven topology. Agreements between experimental results and a model for long overhand knots suggest that the model can aid the optimization of the mechanical performance of microwoven materials. We then adapt classical contact mechanics and adhesion models to explore the influence of the size of structural elements in a frictional architected material on its energy dissipation capability. Our model shows that the energy dissipation capability of our frictional architected material can be significantly increased when it is scaled down from the mm-scale to the sub-micron length scale.
\r\n\r\nOur 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. The unique tightening mechanism introduced by knotted topology unlocks new ways to create shape-reconfigurable, highly extensible, and extremely energy-absorbing bulk, 3D architected materials with mechanical properties that can be tuned not only by their geometries and bulk properties, but also by the surface interactions experienced by the structural elements. Lastly, our modeling work shows the potential of creating highly dissipative architected materials with shape-retention capability via carefully architected structural elements.
", "doi": "10.7907/ycqd-1f27", "publication_date": "2023", "thesis_type": "phd", "thesis_year": "2023" }, { "id": "thesis:16067", "collection": "thesis", "collection_id": "16067", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:06022023-223752519", "primary_object_url": { "basename": "AndrewFriedmanThesis.pdf", "content": "final", "filesize": 14702200, "license": "other", "mime_type": "application/pdf", "url": "/16067/1/AndrewFriedmanThesis.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Scalable Fabrication of Micro-Architected Water Filtering Membranes", "author": [ { "family_name": "Friedman", "given_name": "Andrew Collin", "clpid": "Friedman-Andrew-Collin" } ], "thesis_advisor": [ { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "thesis_committee": [ { "family_name": "Wang", "given_name": "Zhen-Gang", "orcid": "0000-0002-3361-6114", "clpid": "Wang-Zhen-Gang" }, { "family_name": "Shapiro", "given_name": "Mikhail G.", "orcid": "0000-0002-0291-4215", "clpid": "Shapiro-M-G" }, { "family_name": "Giapis", "given_name": "Konstantinos P.", "orcid": "0000-0002-7393-298X", "clpid": "Giapis-K-P" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "Polymer-based filtration devices are predominantly mass manufactured via mechanical spinning or electrospinning of heated polymer materials or fiberglass to create a randomly oriented fibrous network. This technique, while effective at producing materials necessary for traditional filtering applications, fails to afford control over morphology, both macro- and microscopically. The filtering material produced often relies exclusively on its randomly assembled porosity (and occasionally on its surface charge) to capture materials from filtered fluids but provides little means for targeted analyte capture without bulk surface coating or functionalization. This thesis seeks to demonstrate a unique approach to filtration membrane manufacture via a novel high-throughput holographic lithography and contact lithography process in the visible spectrum that utilizes a customized negative-tone photoresist inherently capable of localized surface modification.
\r\n\r\nThis thesis first describes the development of a large-scale holographic lithography process, from conceptualization to implementation, and demonstrates its efficacy by examining produced materials. A phase metasurface mask is utilized to produce a periodic intensity distribution of incident photons. This mask is irradiated at 0.23-0.25 W via linear raster scanning of a 2.2 mm diameter 532 nm laser at 1.5 mm/s and a scan offset of 0.4 mm to produce a homogeneous exposure profile in visible-light sensitized SU-8 negative-tone photoresist. Subsequent photoresist development results in 30\u201340 \u00b5m-thick nano-architected sheets with 2.1 \u00d7 2.4 cm\u00b2 lateral dimensions and ~500 nm-wide struts organized in layered 3D brick-and-mortar-like patterns to result in ~50\u201370% porosity. Scanning electron micrographs of cross-sectioned materials reveal how pattern morphology varies with cure depth, and furthermore how the lack of complete porosity disqualifies this material for application as a membrane filter.
\r\n\r\nThis thesis subsequently focuses on the development of a novel glycidyl methacrylate (GMA)-based negative-tone photoresist for implementation in the previously described lithography system to produce materials more amenable to functional membrane filter production. GMA is polymerized with a photo-caged aminated monomer, 2-((((2-nitrobenzyl)oxy)carbonyl)amino)ethyl 2-methyloxirane-2-carboxylate (ONBAMA) via free radical polymerization (FRP) and atom-transfer radical polymerization (ATRP) to produce ~30 kDa statistical co-polymers at an 85:15 monomer ratio, respectively. These linear co-polymers are then mixed with a photoacid generator (PAG) to produce a 532 nm sensitized negative-tone photoresist. Pre- and post-exposure bake temperatures are selected via glass-transition temperature identification (~62 \u00b0C) with differential scanning calorimetry (DSC) experiments, and cure depth varying with optical exposure dose is examined via establishment of contrast curves. The photoresist is then utilized in the previously described lithography system to produce square arrays of ~25 um circular holes, and the resulting films are characterized via optical and scanning electron microscopy.
\r\n\r\nThis thesis concludes with an examination of the poly(GMA-rand-ONBAMA) films implemented as water-permeable filtration membranes. Efficacy of surface functionalization and solution capture explored via amine deprotection and subsequent tagging with fluorescein isothiocyanate (FITC) dye. The presence and intensity uniformity of tagged samples are examined via confocal microscopy. Transmission of water is justified analytical examination and phenomenologically demonstrated via droplet loading of supported membranes with methylene blue-dyed water. Results are preliminary but indicate potential application of manufactured films as water filters.
\r\n\r\nIn summary, this thesis provides a foundation for the development of nano- and micro-architected materials at large scale and details its implementation for the design and preliminary testing of a GMA-based photoresist for water filtering membrane manufacture. Future research on optimizing photoresist design for mechanical stability could enable utilization of similar membranes for protein capture from biological fluids for use in diagnostic tools and assay automation.
", "doi": "10.7907/rktj-2v55", "publication_date": "2023", "thesis_type": "phd", "thesis_year": "2023" }, { "id": "thesis:14953", "collection": "thesis", "collection_id": "14953", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:06062022-211326081", "primary_object_url": { "basename": "Saccone_Max_Thesis_2022.pdf", "content": "final", "filesize": 54345211, "license": "other", "mime_type": "application/pdf", "url": "/14953/1/Saccone_Max_Thesis_2022.pdf", "version": "v5.0.0" }, "type": "thesis", "title": "Vat Photopolymerization Additive Manufacturing of Functional Materials: from Batteries to Metals and Alloys", "author": [ { "family_name": "Saccone", "given_name": "Max Anthony", "orcid": "0000-0003-3846-2908", "clpid": "Saccone-Max-Anthony" } ], "thesis_advisor": [ { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "thesis_committee": [ { "family_name": "Manthiram", "given_name": "Karthish", "orcid": "0000-0001-9260-3391", "clpid": "Manthiram-Karthish" }, { "family_name": "See", "given_name": "Kimberly", "orcid": "0000-0002-0133-9693", "clpid": "See-Kimberly" }, { "family_name": "Kornfield", "given_name": "Julia A.", "orcid": "0000-0001-6746-8634", "clpid": "Kornfield-J-A" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "local_group": [ { "literal": "Resnick Sustainability Institute" }, { "literal": "div_chem" } ], "abstract": "In recent years, additive manufacturing (AM), also known as 3D printing, has emerged as a uniquely powerful tool for rapid prototyping and for creating complex, high value structures. Vat polymerization (VP) is an AM technique which forms parts through light-initiated polymerization, capable of achieving both high resolution and high throughput. While VP has been utilized to fabricate a wide variety of polymeric materials, fabricating functional materials such as ceramics, metals, and inorganic composites has remained a challenge. This thesis focuses on developing fabrication methods for a range of functional materials, from battery active materials to metals and ceramics, via vat polymerization additive manufacturing, taking advantage of chemical reactions within an AM part after fabrication to form target materials in situ.
\r\n\r\nWe demonstrate the use of emulsions to introduce aqueous active material precursors into organic photopolymer resins to create architected lithium sulfide/carbon composites for use as lithium-sulfur battery cathodes. Such architected cathode materials are promising for mitigating mechanical degradation in high volume-change battery materials such as the sulfur cathode. We additionally performed nanome- chanical experiments on lithium sulfide powders to determine how lithium sulfide yields, deforms, and fails in the context of volume-change-induced stress during battery cycling. Because lithium sulfide is present as a discharge product in all lithium sulfur batteries, these nanomechanical particle compressions have bearing on the entire field, beyond the realm of 3D architected cathodes.
\r\n\r\nWe additionally demonstrate the use of organogel templates to streamline the AM process by enabling the fabrication of many materials starting with a single resin composition, followed by infiltration of appropriate metal precursors and post-processing heat treatment to convert the polymer/precursor matrix to the target metal via calcination and reduction reactions. We fabricate and characterize copper, nickel, silver, cobalt, cupronickel alloys, tungsten, and more to highlight the wide-ranging versatility of achievable materials and microstructures.
", "doi": "10.7907/v3cn-8h28", "publication_date": "2022", "thesis_type": "phd", "thesis_year": "2022" }, { "id": "thesis:14219", "collection": "thesis", "collection_id": "14219", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:06012021-150444627", "primary_object_url": { "basename": "Edwards_Bryce_2021_final.pdf", "content": "final", "filesize": 21680369, "license": "other", "mime_type": "application/pdf", "url": "/14219/1/Edwards_Bryce_2021_final.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Mechanical Investigations: Experimental Fracture Techniques and Frozen Small-Molecule Organics", "author": [ { "family_name": "Edwards", "given_name": "Bryce Walker", "orcid": "0000-0002-2393-5488", "clpid": "Edwards-Bryce-Walker" } ], "thesis_advisor": [ { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "thesis_committee": [ { "family_name": "Faber", "given_name": "Katherine T.", "orcid": "0000-0001-6585-2536", "clpid": "Faber-K-T" }, { "family_name": "Johnson", "given_name": "William Lewis", "clpid": "Johnson-W-L" }, { "family_name": "Ravichandran", "given_name": "Guruswami", "orcid": "0000-0002-2912-0001", "clpid": "Ravichandran-G" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "Fracture of architected lattices: Three-dimensional diamond, kagome, and octet lattices were prepared for validation of a standard compact tension fracture experiment at two different length scales. Solid polymer lattices were written via two-photon lithography at the microscale, and solid polymer lattices are printed via digital light processing at the macroscale. Several of the macrolattices were pyrolyzed into carbon lattices to yield a brittle material for testing. The scaling laws of fracture toughness with relative density are explored, and this offers one of the first experimental studies of a fully 3D kagome lattice.
\r\n\r\nMechanical properties of solid benzene: We explore the mechanical properties and deformation of 10 um-sized cuboid-shaped solid benzene crystals made by freezing directly onto a liquid-nitrogen-cooled sample stage and compressed quasi-statically to 10% strain at 125 K with an in-situ nanomechanical instrument inside a Scanning Electron Microscope (SEM). Cryo-Transmission Electron Microscopy (cryo-TEM) and diffraction of frozen benzene confirms the orthorhombic crystal structure of benzene. Compressive contact pressure-strain response generated from load-displacement data suggests the deformation mechanism to occur via densification, with a loading modulus of 9 GPa, slightly larger than that of other small molecules composed of aromatic rings, such as naphthalene and biphenyl. Molecular dynamics (MD) simulations of experimentally equivalent compressions of 10-30 nm benzene samples of the same crystal structure and geometry along the principal lattice directions at 10-30 K suggest densification could, initially, occur by local amorphization of the compressed region. The discovered deformation mechanism, stiffness, and strength of benzene at 125 K can inform our understanding of geological processes on cold planetary bodies. For example, the surface of Saturn\u2019s moon Titan is teeming with solid organics at an ambient temperature of 95 K; this work will have significant impact on designing in-situ sampling tools for future missions to Titan and to substantiate speculative surface compositions.
", "doi": "10.7907/8f8y-5h58", "publication_date": "2021", "thesis_type": "phd", "thesis_year": "2021" }, { "id": "thesis:14131", "collection": "thesis", "collection_id": "14131", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05012021-183915976", "primary_object_url": { "basename": "Narita_Kai_2021.pdf", "content": "final", "filesize": 9041369, "license": "other", "mime_type": "application/pdf", "url": "/14131/28/Narita_Kai_2021.pdf", "version": "v8.0.0" }, "type": "thesis", "title": "3D Architected Battery Electrodes for Exploring Battery Kinetics from Nano to Millimeter", "author": [ { "family_name": "Narita", "given_name": "Kai", "orcid": "0000-0002-3867-8234", "clpid": "Narita-Kai" } ], "thesis_advisor": [ { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "thesis_committee": [ { "family_name": "Bhattacharya", "given_name": "Kaushik", "orcid": "0000-0003-2908-5469", "clpid": "Bhattacharya-K" }, { "family_name": "Faber", "given_name": "Katherine T.", "orcid": "0000-0001-6585-2536", "clpid": "Faber-K-T" }, { "family_name": "See", "given_name": "Kimberly", "orcid": "0000-0002-0133-9693", "clpid": "See-Kimberly" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "The ability to design a particular geometry of porous electrodes at multiple length scales in a lithium-ion battery can significantly and positively influence battery performance because it enables control over kinetics and trajectories of ion and electron transport. None of the existing methods of engineering electrode structure is capable of creating 3D architected electrodes designed with independent and flexible form-factors at multiscale that are also resilient against cell packaging pressure. In addition, battery kinetics coupled at multiscale from ion transport in an electrolyte to solid electrolyte interphase (SEI) growth has only been studied by numerical simulations, but has never been experimentally explored.
\r\n\r\nIn this thesis, we demonstrate an additive manufacturing technique to engineer porous electrode structure in 3D and explore battery kinetics at multiscale. First, we develop 3D architected carbon electrodes, whose structural factors are independently controlled and whose dimensions span microns to centimeters, using digital light processing and pyrolysis.\r\nThese free-standing lattice electrodes are disordered graphitic carbon composed of several stacked graphitic layers that are mechanically robust. Galvanostatic cycling using these architected carbon electrodes showed sloping capacity, typically observed in pyrolyzed carbon electrodes. We discuss the modified rate performance of the 3D architected carbon electrodes in the framework of ion transport kinetics in the electrode vs. electrolyte and overpotential, enabled by controlling structural factors of battery electrodes, including porosity, surface morphology, electrode thickness, and beam diameter, whose length scales range from nano to millimeter.
\r\n\r\nWe then explore battery kinetics associated with SEI using deterministic, mechanically resilient, and thick 3D architected carbon electrodes, which allow us to study the formation, structure-resistance relationship, and position-dependent growth of SEI by combining the newly developed in operando DC-based technique and post-characterization using secondary ion mass spectroscopy. The amount of Li in SEI agrees with capacity losses, and the amount of F in SEI showed a strong linear correlation with SEI resistance evolutions. The position-dependent SEI growth was experimentally explored; the Li amount in SEI along the electrode thickness agrees with the simulation results in prior work, but the F amount in SEI showed the opposite tendency, suggesting modeling of multilayer SEI is necessary to predict precisely battery aging especially for thick electrodes. Our work demonstrates the use of 3D architected electrodes as a model system to explore multiscale kinetics in Li-ion batteries.
", "doi": "10.7907/dr3b-2d27", "publication_date": "2021", "thesis_type": "phd", "thesis_year": "2021" }, { "id": "thesis:14093", "collection": "thesis", "collection_id": "14093", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:02232021-081136982", "primary_object_url": { "basename": "Zhang_Haolu_2021.pdf", "content": "final", "filesize": 29820010, "license": "other", "mime_type": "application/pdf", "url": "/14093/1/Zhang_Haolu_2021.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Microstructure-Enabled Plasticity in Nano-to-Microscale Materials", "author": [ { "family_name": "Zhang", "given_name": "Haolu Jane", "orcid": "0000-0002-2871-5169", "clpid": "Zhang-Haolu-Jane" } ], "thesis_advisor": [ { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "thesis_committee": [ { "family_name": "Bhattacharya", "given_name": "Kaushik", "orcid": "0000-0003-2908-5469", "clpid": "Bhattacharya-K" }, { "family_name": "Pellegrino", "given_name": "Sergio", "orcid": "0000-0001-9373-3278", "clpid": "Pellegrino-S" }, { "family_name": "James", "given_name": "Richard D.", "clpid": "James-Richard-D" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "Microstructure-governed damage resistance in materials enables a variety of functional applications, such as durable biomedical implants and robust product packaging. For example, the refined phase compatibility qualifies NiTi for artery stents, while carbon fiber reinforced polymers improve structural strength in aerospace engineering. As the overall size of industrial applications continue to decrease, it has become increasingly apparent that when a material's external structural size and internal microstructural size become comparable, its mechanical behavior starts to deviate from that of bulk, such as the smaller-is-stronger size-effect in metals. This elucidation necessitates the characterization of materials at lengthscales relevant to their internal microstructure to guarantee accuracy in the design of real-world applications.
\r\n\r\nThis thesis aims at deciphering the microstructure-mechanics relationship for materials at lengthscales bridging the gap between 1nm and 1\u00b5m, with shape memory ceramics, scorpion shells, and jellyfish biogel as sample systems. We use electron and x-ray diffraction to characterize microstructures such as twinning, defects, and fiber organization, while revealing strength, toughness, and other deformation mechanisms through in-situ nanomechanical experiments. We show improved shape recovery in an otherwise brittle ceramic by tuning its phase compatibility at the nanoscale and reveal unprecedented smaller-is-stronger size-dependence for its twinning-induced plasticity. We then unveil competing fiber orientations in Scorpion shells that follow fiber-mechanics principles and demonstrate a combined poroelasticity/viscoelasticity constitutive relation in jellyfish that explains their self-healing behavior. The correlation between microstructure and mechanical behavior unveils unique damage mitigation and energy dissipation techniques in both brittle ceramics and natural biomaterials at each order of lengthscale, paving the road to designing macroscopic materials with hierarchical mechanical behavior and improved plasticity.
", "doi": "10.7907/0zvc-tc14", "publication_date": "2021", "thesis_type": "phd", "thesis_year": "2021" }, { "id": "thesis:14048", "collection": "thesis", "collection_id": "14048", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:01082021-041336404", "type": "thesis", "title": "Stimuli Responsive Micro-Architected Materials", "author": [ { "family_name": "Elliott", "given_name": "Luizetta Vadimovna", "orcid": "0000-0002-6411-0239", "clpid": "Elliott-Luizetta-Vadimovna" } ], "thesis_advisor": [ { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "thesis_committee": [ { "family_name": "Gao", "given_name": "Wei", "orcid": "0000-0002-8503-4562", "clpid": "Gao-Wei" }, { "family_name": "Gharib", "given_name": "Morteza", "orcid": "0000-0003-0754-4193", "clpid": "Gharib-M" }, { "family_name": "Daraio", "given_name": "Chiara", "orcid": "0000-0001-5296-4440", "clpid": "Daraio-C" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "Shape memory polymers (SMPs) respond to heat by generating programmable movement useful in devices that require substantial deformation and operate at transient temperatures, including stents, embolization coils, and robotic grippers. Transitioning these materials to the microscale can result in expanded potential applications, such as clot removal from retinal vasculature, neural probe delivery, and responsive metamaterials. To achieve these goals, shape transformation must occur in SMPs with complex 3D geometries and nanoscale features.
\r\n\r\nThis thesis describes the synthesis and sculpting of a benzyl methacrylate-based SMP into 3D structures with <800nm characteristic critical dimensions via two photon lithography. The glass transition based shape memory mechanism of these materials is explored through dynamic nanomechanical analysis of 8\u00b5m-diameter cylindrical pillars, which revealed the initiation of a tunable glass transition at 60\u00b0C not present in highly crosslinked materials. Shape memory programming of the characterized pillars as well as complex 3D architectures, including flowers with 500nm thick petals and cubic lattices with 2.5\u00b5m unit cells and overall dimensions of 4.5\u00b5m x 4.5\u00b5m x 10\u00b5m, demonstrated an 86 +/- 4% characteristic shape recovery ratio. These results reveal a pathway towards SMP devices with nanoscale features and arbitrary 3D geometries changing shape in response to temperature.
\r\n\r\nThis thesis subsequently focuses on a particular potential application for such materials: neural probes designed for deployment in primate brains. Architected shape memory structures have the potential to create favorable long-term recording environments through softening triggered by biological conditions, deployment to beyond tissue damage during initial electrode positioning, and architectural features designed for optimal scaffold-tissue interactions. This thesis addresses one of the barriers to the deployment of such structures: the high loading during centimeter scale insertions required for primate brain targeting is incompatible with buckling free-insertion of low stiffness and/or cross sectional area probes required for minimizing the foreign body response.
\r\n\r\nLamb brain tissue model experiments with 280\u00b5m diameter platinum coated carbon fiber probes demonstrate that 59+/- 3% of the work during 3cm probe insertion is attributable to friction, suggesting that friction reduction is a favorable approach to load minimization. A phosphorylcholine-based ~100nm low friction coating is used to reduce the shear stress at the probe-brain interface by 20+/-7 %, demonstrating a facile method for friction reduction that has minimal impacts on probe cross sectional area. Surgical validation of probe insertion in a porcine head model reveals that these probes are suitable for whole brain penetration of brains at the primate scale (~10\u00b2g). These results show that loading requirements during whole brain penetration can be reduced through addressing the contribution of friction and introduce a viable vehicle for recording electrode delivery to large scale brains.
\r\n\r\nIn summary, this thesis provides the foundation for developing stimuli responsive microscale devices and materials and, in the case of deep brain neural recording, the building blocks for the design of an integrated shape memory/ low friction carbon fiber electrode delivery device. Future research on the scalable fabrication of architected shape memory polymers could enable the widespread application of such materials.
", "doi": "10.7907/bnfv-9c75", "publication_date": "2021", "thesis_type": "phd", "thesis_year": "2021" }, { "id": "thesis:13599", "collection": "thesis", "collection_id": "13599", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:12032019-200437699", "primary_object_url": { "basename": "Citrin_Michael_2019.pdf", "content": "final", "filesize": 29185593, "license": "other", "mime_type": "application/pdf", "url": "/13599/13/Citrin_Michael_2019.pdf", "version": "v8.0.0" }, "type": "thesis", "title": "Nanomechanical Properties of Electrodeposited Li and Fabrication of 3D Architected Cathodes for Li-Based Batteries", "author": [ { "family_name": "Citrin", "given_name": "Michael Andrew", "orcid": "0000-0001-8183-5437", "clpid": "Citrin-Michael-Andrew" } ], "thesis_advisor": [ { "family_name": "Greer", "given_name": "Julia R.", "clpid": "Greer-J-R" } ], "thesis_committee": [ { "family_name": "Faber", "given_name": "Katherine T.", "clpid": "Faber-K-T" }, { "family_name": "Johnson", "given_name": "William Lewis", "clpid": "Johnson-W-L" }, { "family_name": "Rossman", "given_name": "George Robert", "clpid": "Rossman-G-R" }, { "family_name": "Greer", "given_name": "Julia R.", "clpid": "Greer-J-R" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "Advancements in the active materials of Li-based batteries provide a promising route to significantly improve electrochemical performance. Li metal has a 10x increase in gravimetric capacity compared to conventional graphite anodes and can be utilized with a solid electrolyte. However, current solid-state Li metal anode batteries cannot reliably cycle large amounts of Li due to chemical and mechanical degradation at the solid electrolyte / Li interface. One key factor in the failure of solid electrolytes is the dearth of mechanical data on Li at the relevant length scales and microstructures to solid-state batteries. The initial stages of Li formation at the solid electrolyte / Li interface also require further exploration to help improve the performance of solid-state Li batteries.
\r\n\r\nIn the first part of the thesis, we will discuss the methods used to investigate Li electrodeposited in-situ in a scanning electron microscope (SEM) chamber from a thin film solid-state battery. We probed the formation of this Li and found preferential growth at the domain boundaries of the surface of the cell, corroborated by electrochemical simulations. Cryogenic electron microscopy was determined to be the optimal method for examining the microstructure of Li and was utilized to reveal the single crystalline microstructure of Li pillars. Uniaxial compression experiments were performed on single crystalline Li pillars that grew from these batteries. We found that Li pillars with diameters of 360-759 nm first deformed elastically, then yielded and flowed plastically, with an average yield stress of 16.0 \u00b1 6.82 MPa, 24x stronger than bulk polycrystalline Li. The mechanical results are discussed in the framework of dislocation starvation and nucleation, in addition to thermally activated deformation processes.
\r\n\r\nNext generation battery systems may also utilize 3D electrodes to allow for both high energy (large mass loading) and power densities (small diffusion lengths). The last section of the thesis investigates the fabrication of 3D architected LiCoO2 structures and their performance as Li-ion battery cathodes. Using a novel hydrogel photoresin with relevant salt contents, the structures were fabricated using digital light processing and calcination. The electrochemical performance of the architected cathodes was examined and the electrodes exhibited a relatively high areal capacity up to \u223c8 mAh/cm2 and a capacity retention of 82% after 100 cycles.
", "doi": "10.7907/YD18-8N08", "publication_date": "2020", "thesis_type": "phd", "thesis_year": "2020" }, { "id": "thesis:13819", "collection": "thesis", "collection_id": "13819", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:06122020-164731280", "primary_object_url": { "basename": "schwacke_miranda_2020_thesis.pdf", "content": "final", "filesize": 3336053, "license": "other", "mime_type": "application/pdf", "url": "/13819/1/schwacke_miranda_2020_thesis.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Mechanical Properties and Characterization of Nanocrystalline Ni and Ni Solid Solutions", "author": [ { "family_name": "Schwacke", "given_name": "Miranda Lee", "clpid": "Schwacke-Miranda-Lee" } ], "thesis_advisor": [ { "family_name": "Greer", "given_name": "Julia R.", "clpid": "Greer-J-R" } ], "thesis_committee": [ { "family_name": "None", "given_name": "None" } ], "local_group": [ { "literal": "Senior Undergraduate Thesis Prize" }, { "literal": "div_eng" } ], "abstract": "In this work we investigate the mechanical properties of nanocrystalline Ni and Ni solid solutions made by both traditional fabrication methods (through a literature review) and by a newly developed chemical-derivation method (through experimental characterization and nanoindentaiton testing). Chapter 1 consists of a review of the current literature on nanocrystalline Ni. It focuses specifically on\r\nhow the grain size of these materials is related to hardness through the Hall-Petch relationship and at grain sizes past the Hall-Petch breakdown. Given the number of apparent deviations from the Hall-Petch relationship found in the literature, in Chapter 2 we consider factors other than grain size which can impact hardness, including additives, annealing, and texture. Chapter 3 provides a description of\r\nour own experimental methods and results, including sample fabrication, grain size measurement, and nanoindentation. The hardness and reduced modulus of our nanocrystalline Ni samples are calculated to be 56 MPa and 1.76 GPa, respectively. These values are very low compared to what is described in the literature. Chapter 4 presents models for the hardness and Young\u2019s modulus of nanocrystalline materials as functions of porosity, impurity content, and other factors which might cause anomalously low values. However, we find that these models are unable to account for the values we have observed. Chapter 5 includes a discussion of future work which should be done in order to better understand the deformation occurring in chemically-derived nanocrystalline Ni and how it differs from what is described in the literature.", "doi": "10.7907/j8rq-5c26", "publication_date": "2020", "thesis_type": "senior_major", "thesis_year": "2020" }, { "id": "thesis:13966", "collection": "thesis", "collection_id": "13966", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:09252020-152536826", "primary_object_url": { "basename": "Kwong_Anthony_2020.pdf", "content": "final", "filesize": 4947657, "license": "other", "mime_type": "application/pdf", "url": "/13966/1/Kwong_Anthony_2020.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Mechanical Properties of Small-Scale Sputtered Metallic Glasses", "author": [ { "family_name": "Kwong", "given_name": "Anthony Herman Fu-Hao", "orcid": "0000-0001-6389-1443", "clpid": "Kwong-Anthony-Herman-Fu-Hao" } ], "thesis_advisor": [ { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "thesis_committee": [ { "family_name": "Faber", "given_name": "Katherine T.", "orcid": "0000-0001-6585-2536", "clpid": "Faber-K-T" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" }, { "family_name": "Johnson", "given_name": "William Lewis", "clpid": "Johnson-W-L" }, { "family_name": "Falson", "given_name": "Joseph", "orcid": "0000-0003-3183-9864", "clpid": "Falson-Joseph" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "Sputtered metallic glasses (MGs) represent a unique class of materials because their nonperiodic arrangements are far from equilibrium. This microstructure gives rise to their exceptional mechanical properties; for example, experiments and simulations on the deformation of small-scale sputtered Zr-based MGs demonstrate their exceptional compressive and tensile strengths in excess of 1 GPa and exceptional tensile ductility of ~150%.
\r\n\r\nWe report a new property that emerges in sputtered MGs: age-induced strengthening. We measured the compressive strengths of cylindrical pillars with diameters between 300 nm to 1.1 \u03bcm, which were carved from a 5 \u03bcm-thick sputtered Zr\u2013Ni\u2013Al thin film that was aged in a nitrogen environment for three years. Nanomechanical experiments revealed that the aged samples had a stiffness of 91 \u00b1 4 GPa and a yield strength of 2.7 \u00b1 0.2 GPa for all cylinder sizes, which represents a nearly 43% increase in yield strength and a 31% increase in the elastic modulus compared to equivalently sized as-sputtered samples. We also observed nano-sized induced failure suppression: samples with diameters below 600 nm deformed smoothly and noncatastrophically. Those with larger diameters deformed via a series of observable and detectable shear bands that propagated to the surfaces. Molecular dynamics (MD) simulations of uniaxial compression of chemically equivalent Zr\u2013Ni\u2013Al MG nanowires revealed that the underlying physics of enhanced strengths involves the evolution of local disorder that can be quantified in the number of fivefold atomic bonds. The average amount of fivefold bonding increased systematically with energetic relaxation and the maximum compressive stress. Dynamic mechanical analysis (DMA) revealed the presence of hydrides within the MG. Hydrogen diffusion into the host matrix resulted in an increase in the local volume such that more\u2013mobile atoms (i.e., Ni and Al) can redistribute and relax into a more\u2013energetically favorable configuration.
\r\n\r\nExperiments and simulations in this work demonstrate that sputtered MGs strength by 43% when solely aged for three years, i.e., without any accompanying annealing or mechanical treatment, which originates from atomic-level microstructural relaxation in these materials. This provides a useful foundation for simple design of advanced materials whose mechanical properties can be predicted and prescribed a priori using physical principles of atomic-level relaxation.
", "doi": "10.7907/4nv1-1f26", "publication_date": "2020", "thesis_type": "phd", "thesis_year": "2020" }, { "id": "thesis:13777", "collection": "thesis", "collection_id": "13777", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:06042020-112316408", "primary_object_url": { "basename": "Yee_Daryl_2020.pdf", "content": "final", "filesize": 71411927, "license": "other", "mime_type": "application/pdf", "url": "/13777/51/Yee_Daryl_2020.pdf", "version": "v6.0.0" }, "type": "thesis", "title": "Additive Manufacturing of 3D Functional Materials: From Surface Chemistry to Combustion-Derived Materials", "author": [ { "family_name": "Yee", "given_name": "Daryl Wei Liang", "orcid": "0000-0002-4114-6167", "clpid": "Yee-Daryl-Wei-Liang" } ], "thesis_advisor": [ { "family_name": "Greer", "given_name": "Julia R.", "clpid": "Greer-J-R" } ], "thesis_committee": [ { "family_name": "Faber", "given_name": "Katherine T.", "clpid": "Faber-K-T" }, { "family_name": "Grubbs", "given_name": "Robert H.", "clpid": "Grubbs-R-H" }, { "family_name": "Johnson", "given_name": "William Lewis", "clpid": "Johnson-W-L" }, { "family_name": "Greer", "given_name": "Julia R.", "clpid": "Greer-J-R" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "Over the past decade, additive manufacturing has emerged as one of the most powerful manufacturing tools available today. Vat photopolymerization techniques, in particular, are especially promising as they are capable of achieving high resolutions and throughputs. However, the vast majority of materials that are compatible with them only have structural functionality. The fabrication of functional materials still remains a challenge in the field: functional polymers often require a complex multi-step synthesis. Ceramics-based photoresins are limited in composition and are challenging to use or synthesize. Metals have also been hardly explored with vat photopolymerization techniques.
\r\n\r\nThis thesis explores methods of fabricating functional materials with vat photopolymerization. We develop accessible techniques for the fabrication of functional polymers, ceramics, metals, and multimaterials at a variety of length scales, from sub-micron to centimeter scales. On the polymer front, we first explore how surface coatings can be an accessible method of introducing chemical functionality to a material. In particular, we demonstrate the surface coating of genomic DNA on an architected polymeric structure and show how it can be used as a drug capture device to reduce off-target toxicity in chemotherapy. We also explore the use of click chemistry, the thiol-Michael reaction in particular, in the facile synthesis of acrylate monomers with a variety of functional groups. We demonstrate the compatibility of these functionalized monomers with two-photon lithography and highlight some potential applications of these functional polymers structures.
\r\n\r\nIn the fabrication of ceramics and metals, we present a novel technique called photopolymer complex synthesis that combines solution combustion synthesis with vat photopolymerization to enable their fabrication. We illustrate the use of this technique by first fabricating piezoelectric zinc oxide architected structures with sub-micron features using two-photon lithography. Following that, we fabricate lithium cobalt oxide structures using digital light processing printing and highlight their use as architected lithium-ion battery cathodes. Lastly, we show how photopolymer complex synthesis can be expanded to fabricate metal and multimaterial architected structures. Our work highlights the use of polymer chemistry and materials science in expanding the range of materials that are compatible with vat photopolymerization, with the vision of democratizing the fabrication of advanced functional materials and enabling the production of previously impossible 3D devices.
", "doi": "10.7907/ya58-cn88", "publication_date": "2020", "thesis_type": "phd", "thesis_year": "2020" }, { "id": "thesis:13639", "collection": "thesis", "collection_id": "13639", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:02122020-151048251", "primary_object_url": { "basename": "Ng_Ryan_2020.pdf", "content": "final", "filesize": 20979784, "license": "other", "mime_type": "application/pdf", "url": "/13639/1/Ng_Ryan_2020.pdf", "version": "v7.0.0" }, "type": "thesis", "title": "Nanophotonic Phenomena in Dielectric Photonic Crystals", "author": [ { "family_name": "Ng", "given_name": "Ryan Cecil", "orcid": "0000-0002-0527-9130", "clpid": "Ng-Ryan-Cecil" } ], "thesis_advisor": [ { "family_name": "Greer", "given_name": "Julia R.", "clpid": "Greer-J-R" } ], "thesis_committee": [ { "family_name": "Faraon", "given_name": "Andrei", "clpid": "Faraon-A" }, { "family_name": "Shapiro", "given_name": "Mikhail G.", "clpid": "Shapiro-M-G" }, { "family_name": "Brady", "given_name": "John F.", "clpid": "Brady-J-F" }, { "family_name": "Greer", "given_name": "Julia R.", "clpid": "Greer-J-R" } ], "local_group": [ { "literal": "Kavli Nanoscience Institute" }, { "literal": "div_chem" } ], "abstract": "Photonic crystals are periodic optical nanostructures with varying dielectric constant that allow light flow to be controlled and manipulated much in a similar way to electrons within a semiconductor crystal. These nanostructures tend to have a spatially varying refractive index on the order of the wavelength of light to be manipulated. 1D and 2D photonic crystals have already garnered significant attention in the realm of thin-film optics, while 3D photonic crystals have been thus far limited in application, due to difficulties in fabrication and a lack of available materials for fabrication.
\r\n\r\nIn this work, we first explore 1D and 2D photonic crystals based on the concept of a guided mode resonance, which manifests as a narrow near-unity resonance in reflection or transmission that arise from the coupling of an incident wave into a leaky waveguide mode via a grating vector that is subsequently re-radiated. Such a resonance is well-suited for multi- and hyper- spectral filtering applications in the infrared. We designed a platform consisting of amorphous Si arrays embedded in SiO2 in simulation and experiment for application as narrow stopband filters. We present the tunability of the spectral characteristics of the resonance in these arrays through variation of array geometric parameters in simulation and experiment. Guided mode resonance designs often consider only the case of an infinite array, where the leaky waveguide mode can propagate laterally for hundreds of periods, allowing for this mode to eventually scatter out of the array giving rise to the characteristic narrow near-unity rapid spectral variations of a GMR. With an insufficient number of periods, the quality factor and thus the optical filtering performance is greatly diminished. Thus, we further extend our analysis to compact periodic arrays of finite size, which are required for high spatial resolution snapshot imaging, and introduce array designs that operate under finite size limitations in the near-infrared.
\r\n\r\nWe then transition to 3D photonic crystals, exploring the use of an additive manufacturing process to directly fabricate nanocrystalline rutile TiO2 with ~100 nm resolution. Though TiO2 was chosen as the model material, the key to this work is that a similar process can be used to print many different materials, enabling future applications of 3D photonic crystals. The focus here is the additive manufacturing of high index materials such as TiO2, and its potential for photonic applications is demonstrated by characterizing the optical band gap of 3D PhC TiO2 structures printed with this method. We present a system where the ability to print high refractive index 3D photonic crystals would be useful, by studying 3D polymer-germanium core-shell structures that should exhibit all-angle negative refraction in the mid-infrared regime.
", "doi": "10.7907/ZP30-F550", "publication_date": "2020", "thesis_type": "phd", "thesis_year": "2020" }, { "id": "thesis:13722", "collection": "thesis", "collection_id": "13722", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05252020-134146453", "primary_object_url": { "basename": "Thesis Draft_v1.3.pdf", "content": "final", "filesize": 32451964, "license": "other", "mime_type": "application/pdf", "url": "/13722/12/Thesis Draft_v1.3.pdf", "version": "v5.0.0" }, "type": "thesis", "title": "Additive Manufacturing of 3D Nano-Architected Metals and Ceramics", "author": [ { "family_name": "Vyatskikh", "given_name": "Andrey", "orcid": "0000-0002-6917-6931", "clpid": "Vyatskikh-Andrey" } ], "thesis_advisor": [ { "family_name": "Greer", "given_name": "Julia R.", "clpid": "Greer-J-R" } ], "thesis_committee": [ { "family_name": "Shapiro", "given_name": "Mikhail G.", "clpid": "Shapiro-M-G" }, { "family_name": "Faber", "given_name": "Katherine T.", "clpid": "Faber-K-T" }, { "family_name": "Gao", "given_name": "Wei", "clpid": "Gao-Wei" }, { "family_name": "Greer", "given_name": "Julia R.", "clpid": "Greer-J-R" } ], "local_group": [ { "literal": "Resnick Sustainability Institute" }, { "literal": "Rosen Bioengineering Center" }, { "literal": "div_eng" } ], "abstract": "Additive manufacturing (AM) represents a set of manufacturing processes that create complex 3D parts out of polymers, metals, and ceramics. AM of metals and ceramics is widely used to produce parts for aerospace, automotive, and medical applications. At the micro- and nano-scales, AM is poised to become the enabling technology for efficient 3D microelectromechanical systems (MEMS), 3D micro-battery electrodes, 3D electrically small antennae, micro-optical components, and photonics. Today, the minimum feature size for most commercially available metal and ceramic AM is limited to ~20-50 \u03bcm. Currently, no established processes can reliably produce complex 3D metal and ceramic parts with sub-micron features.
\r\n\r\nIn this thesis, we first demonstrate a nanoscale metal AM process that can produce ~300 nm features out of nanocrystalline, nanoporous nickel using synthesized hybrid organic-inorganic materials, two-photon lithography, and pyrolysis. We study microstructure and mechanical properties of as-fabricated nickel architectures and compare their structural strength to established AM processes. We then show how this process can be extended to other metals and metalloids, including Mg, Ge, Si, and Ti.
\r\n\r\nThis study extends further into nanoscale AM of transparent, high refractive index materials for micro-optics and photonic crystals. We develop an AM process to 3D print fully dense nanocrystalline rutile titanium dioxide (TiO\u2082) with feature dimensions down to ~120 nm. We carefully study and model the relationship between feature dimensions and process parameters to achieve a <2% variation in critical dimensions. We then use this understanding of the process to fabricate and study 3D dielectric photonic crystals with a full photonic bandgap in the infrared.
\r\n\r\nFinally, a microscale AM process of titanium dioxide is demonstrated for photocatalytic water treatment. We show how synthesized hybrid organic-inorganic materials can be applied for stereolithography to print TiO\u2082 architectures with 100 \u03bcm features. We use the developed 3D printing process to investigate the effect of 3D architecture on the efficiency of photocatalytic water treatment.
\r\n\r\nThis work establishes a versatile and efficient pathway to create three-dimensional nano-architected metals and ceramics and to investigate their properties for applications in 3D MEMS, micro-optics, photonics, and photocatalysis.
\r\n", "doi": "10.7907/pdz2-dd59", "publication_date": "2020", "thesis_type": "phd", "thesis_year": "2020" }, { "id": "thesis:13775", "collection": "thesis", "collection_id": "13775", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:06032020-220309895", "primary_object_url": { "basename": "Salzman_Erika_thesis.pdf", "content": "final", "filesize": 1786322, "license": "other", "mime_type": "application/pdf", "url": "/13775/1/Salzman_Erika_thesis.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Functional Acrylate Resins for Shape Memory Polymer Microarchitectures", "author": [ { "family_name": "Salzman", "given_name": "Erika Emmanuelle", "orcid": "0000-0002-2995-7864", "clpid": "Salzman-Erika-Emmanuelle" } ], "thesis_advisor": [ { "family_name": "Greer", "given_name": "Julia R.", "clpid": "Greer-J-R" } ], "thesis_committee": [ { "family_name": "None", "given_name": "None" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "Shape memory polymers (SMPs) are materials that can undergo programmable shape change in response to a specific stimulus. The ability to undergo this reliable, three-dimensional shape change makes SMPs promising smart materials for applications like biomedical stents and sutures. However, to access areas like blood vessels in the eye, these materials must be fabricated with micron or submicron resolution. In this work, benzyl methacrylate-based, heat-responsive SMP microstructures were fabricated using two-photon lithography in a variety of three-dimensional designs. The effects of different fabrication conditions on the structures were studied, and Raman spectroscopy was used to probe network properties, including degree of polymerization.
\r\n\r\nThe resin was also chemically functionalized prior to polymerization with BOC-protected amine groups via the thiol-Michael addition reaction, which allows for attachment of other useful functional groups to the surface of the structures. This chemistry was utilized for attachment of a dye as well as gold nanoparticles. When exposed to laser light, these nanoparticles can undergo localized surface plasmon resonance and serve as heat generators. The theoretical feasibility of using this heating technique to induce shape change in SMP microstructures is examined in this work.
", "doi": "10.7907/8870-1x03", "publication_date": "2020", "thesis_type": "senior_major", "thesis_year": "2020" }, { "id": "thesis:11235", "collection": "thesis", "collection_id": "11235", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:10162018-124906600", "type": "thesis", "title": "Small-Scale Deformation and Fracture of Hard Biomaterials", "author": [ { "family_name": "Tertuliano", "given_name": "Ottman Aeman", "orcid": "0000-0003-0524-3944", "clpid": "Tertuliano-Ottman-Aeman" } ], "thesis_advisor": [ { "family_name": "Greer", "given_name": "Julia R.", "clpid": "Greer-J-R" } ], "thesis_committee": [ { "family_name": "Faber", "given_name": "Katherine T.", "clpid": "Faber-K-T" }, { "family_name": "Johnson", "given_name": "William Lewis", "clpid": "Johnson-W-L" }, { "family_name": "Ravichandran", "given_name": "Guruswami", "clpid": "Ravichandran-G" }, { "family_name": "Greer", "given_name": "Julia R.", "clpid": "Greer-J-R" } ], "local_group": [ { "literal": "Kavli Nanoscience Institute" }, { "literal": "div_eng" } ], "abstract": "Structural materials engineering often aims to realize materials that are simultaneously strong, tough, and lightweight \u2014 a combination classically considered mutually exclusive. Natural composite materials such as bone exhibit a combination of these properties far exceeding that of their constituents, a feat generally credited to their hierarchical structure \u2014 all the way down the nanoscale. To date, a quantitative description of how this property combination arises in such microstructurally complex materials has remained elusive due to challenges in experimentally isolating and probing the salient deformation and toughening mechanisms at the micro and nanometer scales \u2014 length scales on the order the constituents of many natural composites.
\r\n\r\nIn this thesis, we first investigate the site-specific nanoscale structure of human bone using transmission electron microscopy. We show the presence of previously undiscovered disordered arrangement of collagen and mineral \u2014 alongside a well known ordered structure \u2014 within the trabecular architecture of bone. We perform micro- and nano-mechanical compression experiments to probe strength and deformation of each of these microstructures, revealing a size-dependent strength of bone attributed to the limited number of failure-initiating critical defects (e.g pores) in the small-scale samples relative to macro-scale tissue.
\r\n\r\nUnlike experiments for investigating strength at small-scales, fracture experiments are standardized for the macroscale. To address this, we developed an in situ SEM/nanoindenter methodology that enables 3-point bending fracture experiments with observation and measurement of crack growth and toughening behavior at nano and micrometer scales. Using this technique, we discuss the crack initiation and growth toughness arising primarily from the underlying fibril microstructure in bone. In the context of a crack growth resistance, we describe a transition in the toughening behavior of bone originating from different levels of hierarchy. Given its versatility, this experimental technique establishes a platform for understanding the coupling between structure and fracture behavior of micron-sized materials.
", "doi": "10.7907/CAPE-5661", "publication_date": "2019", "thesis_type": "phd", "thesis_year": "2019" }, { "id": "thesis:11595", "collection": "thesis", "collection_id": "11595", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:06012019-140706232", "type": "thesis", "title": "Adaptive and Reconfigurable Architected Materials Driven by Electrochemistry", "author": [ { "family_name": "Xia", "given_name": "Xiaoxing", "orcid": "0000-0003-1255-3289", "clpid": "Xia-Xiaoxing" } ], "thesis_advisor": [ { "family_name": "Greer", "given_name": "Julia R.", "clpid": "Greer-J-R" } ], "thesis_committee": [ { "family_name": "Faber", "given_name": "Katherine T.", "clpid": "Faber-K-T" }, { "family_name": "Greer", "given_name": "Julia R.", "clpid": "Greer-J-R" }, { "family_name": "Johnson", "given_name": "William L.", "clpid": "Johnson-W-L" }, { "family_name": "Daraio", "given_name": "Chiara", "clpid": "Daraio-C" } ], "local_group": [ { "literal": "Kavli Nanoscience Institute" }, { "literal": "div_eng" } ], "abstract": "Architected materials are a new class of engineered materials with carefully controlled internal structures that give rise to properties that differ from or surpass those of their constituent materials. Recent advances in additive manufacturing provide an extraordinary opportunity to rationally design the structure and the chemical composition of architected materials across multiple length scales to optimize properties and functionalities for a variety of applications. These functional architected materials are capable of decoupling critical trade-offs, such as strength vs. density, to reach new regions of the material property space, and enabling exotic properties that rarely exist in classical materials such as negative refraction and negative thermal expansion.
\r\n\r\nThis thesis probes into the dynamic behaviors of architected materials undergoing electrochemical reactions and aims to provide an in-depth understanding of the underlying mechanisms as well as design principles generalizable for other functional architected material systems. We developed novel fabrication methods based on two-photon lithography and various physical and chemical post-processing techniques to create architected materials with multi-level design freedom including feature sizes, structural geometries, and material compositions, which resonates with the multi-faceted challenges in electrochemical systems. We demonstrated that architected materials provide a new platform to design battery electrodes that could accommodate the large volumetric changes associated with conversion-based electrode materials, while decoupling the longstanding trade-off between active material loading and transport kinetics in batteries. Furthermore, we presented a new class of electrochemically reconfigurable architected materials that could transform their structures in a programmable, reversible and non-volatile fashion, which provide new vistas for designing mechanical metamaterials with tunable phononic bandgaps and deployable micro-devices for biomedical applications.
\r\n\r\nThe multi-scale and multi-physics nature of these electrochemically driven architected materials prompted us to develop a toolset of (1) in situ SEM and optical microscopy to visualize the dynamic responses, (2) coupled chemo-mechanical finite element analysis to reconstruct detailed mechanical evolution as electrochemical reactions proceed, and (3) a statistical mechanics framework to capture the transient interactions between coupled mechanical instabilities. Using these tools, we investigated lithiation-induced cooperative beam buckling in tetragonal Si microlattices: from the deformation mechanisms of individual beams and the cooperative coupling between buckling directions of neighboring beams to the lithiation rate-dependent distribution of ordered buckling domains separated by distorted domain boundaries. Results indicate that local defects and stochastic energy fluctuations play a critical role in the dynamic response of architected materials in a way analogous to that during phase transformations of classical materials. These connections have profound implications on how we could understand and design architected materials by drawing inspiration from established theories in materials science.
\r\n", "doi": "10.7907/Q092-P711", "publication_date": "2019", "thesis_type": "phd", "thesis_year": "2019" }, { "id": "thesis:11690", "collection": "thesis", "collection_id": "11690", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:06052019-161606954", "type": "thesis", "title": "Fabrication, Mechanical Characterization, and Modeling of 3D Architected Materials upon Static and Dynamic Loading", "author": [ { "family_name": "Portela G.", "given_name": "Carlos Mauricio", "orcid": "0000-0002-2649-4235", "clpid": "Portela-G-Carlos-M" } ], "thesis_advisor": [ { "family_name": "Greer", "given_name": "Julia R.", "clpid": "Greer-J-R" }, { "family_name": "Kochmann", "given_name": "Dennis M.", "clpid": "Kochmann-D-M" } ], "thesis_committee": [ { "family_name": "Ravichandran", "given_name": "Guruswami", "clpid": "Ravichandran-G" }, { "family_name": "Daraio", "given_name": "Chiara", "clpid": "Daraio-C" }, { "family_name": "Greer", "given_name": "Julia R.", "clpid": "Greer-J-R" }, { "family_name": "Kochmann", "given_name": "Dennis M.", "clpid": "Kochmann-D-M" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "Architected materials have been ubiquitous in nature, enabling unique properties that are unachievable by monolithic, homogeneous materials. Inspired by natural processes, man-made three-dimensional (3D) architected materials have been reported to enable novel mechanical properties such as high stiffness- and strength-to-density ratios, extreme resilience, or high energy absorption. Furthermore, advanced fabrication techniques have enabled architected materials with feature sizes at the nanometer-scale, which exploit material size effects to approach theoretical bounds. However, most architected materials have relied on symmetry, periodicity, and lack of defects to achieve the desired mechanical response, resulting in sub-optimal mechanical response under the presence of inevitable defects. Additionally, most of these nano- and micro-architected materials have only been studied in the static regime, leaving the dynamic parameter space unexplored.
\r\n\r\nIn this work, we address these issues by: (i) proposing numerical and theoretical tools that predict the behavior of architected materials with non-ideal geometries, (ii) presenting a pathway for scalable fabrication of tunable nano-architected materials, and (iii) exploring the response of nano- and micro-architected materials under three types of dynamic loading. We first explore lattice architectures with features at the micro- and millimeter scales and provide an extension to the classical stiffness scaling laws, enabled by reduced-order numerical models and experiments at both scales. After discussing the effect of nodes (i.e., junctions) on the mechanical response of lattice architectures, we propose alternative node-less geometries that eliminate the stress concentrations associated with nodes to provide extreme resilience. Using natural processes such as spinodal decomposition, we present pathways to fabricate a version of these materials with samples sizes on the order of cubic centimeters while achieving feature sizes on the order of tens of nanometers. In the dynamic regime, we design, fabricate, and test micro-architected materials with tunable vibrational band gaps through the use of architectural reconfiguration and local resonance. Lastly, we present methods to fabricate carbon-based materials at the nano- and centimeter scales and test them under supersonic impact and blast conditions, respectively. Our work provides explorations into pathways that could enable the use of nano- and micro-architected materials for applications that go beyond small-volume, quasi-static mechanical regimes.
", "doi": "10.7907/75S6-SB32", "publication_date": "2019", "thesis_type": "phd", "thesis_year": "2019" }, { "id": "thesis:11092", "collection": "thesis", "collection_id": "11092", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:06252018-172548450", "type": "thesis", "title": "Microstructure and Small-Scale Deformation of Al\u2080.\u2087CoCrFeNi High-Entropy Alloy", "author": [ { "family_name": "Giwa", "given_name": "Adenike Monsurat", "orcid": "0000-0002-1229-7505", "clpid": "Giwa-Adenike-Monsurat" } ], "thesis_advisor": [ { "family_name": "Greer", "given_name": "Julia R.", "clpid": "Greer-J-R" } ], "thesis_committee": [ { "family_name": "Johnson", "given_name": "William Lewis", "clpid": "Johnson-W-L" }, { "family_name": "Faber", "given_name": "Katherine T.", "clpid": "Faber-K-T" }, { "family_name": "Greer", "given_name": "Julia R.", "clpid": "Greer-J-R" }, { "family_name": "Goddard", "given_name": "William A., III", "clpid": "Goddard-W-A-III" } ], "local_group": [ { "literal": "Kavli Nanoscience Institute" }, { "literal": "div_eng" } ], "abstract": "Novel engineering materials are continuously being designed for structural applications, particularly for improved mechanical properties such as high strength, enhanced ductility, and great thermal stability. High entropy alloys (HEAs) as an emerging material can be distinguished from other metal systems as a five-or-more-component alloy in which the constituents are in equiatomic or near equiatomic proportions, thereby maximizing the configurational entropy.
\r\n\r\nThis thesis is focused on understanding the microstructure of an aluminum-containing HEA in relation to its small-scale mechanical properties. Physical phenomena such as size-effect, slip sizes, temperature effect, crystallographic orientation effect, influence of interface, and small perturbations in atom motions are studied.
\r\n\r\nUniaxial compression experiments were conducted on nanopillars fabricated from the individual phases (i.e. Face Centered Cubic (FCC) and Body Cubic Centered (BCC) present in the Al0.7CoCrFeNi HEA. 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 law exponent m in \u03c4y \u03b1 D-m for the BCC phase was \u2212 0.28, which is lower than that of most pure BCC metals, and the FCC phase had m = \u2212 0.66, which is equivalent to most pure FCC metals. These results are discussed in the framework of nano-scale plasticity and the intrinsic lattice resistance through the interplay of the internal (microstructural) and external (dimensional) size effects.
\r\n\r\nIn addition to higher stresses observed at cryogenic temperature in both phases, the microstructural analysis of the deformed pillar via Transmission Electron Microscopy (TEM) showed that FCC pillars undergo deformation by planar-slip dislocation activities even at temperatures of 40 K. Bulk FCC HEAs have been studied to deform via twinning mechanism at low temperatures. The BCC phase, however, confirms dislocation\u2013driven plasticity and twinning at 40 K. These results are explained from the intrinsic nature of the dislocation structure of both phases at low temperatures.
\r\n\r\nThe effect of an 'interphase' in micron-sized HEA pillars was studied from different orientation configurations of the BCC | FCC phases. Slip transmission across the phases was observed in high symmetry orientation combination of both phases. Configurations having a mixture of both low and high symmetry orientations vary in deformation mechanisms. We explain these findings in relation to crystal orientation effect of the combining half pillars, competing plastic mechanisms, dislocation \u2013 boundary interactions and how these findings correlate with their mechanical response.
\r\n\r\nAlso, we conducted dynamic mechanical analysis on the FCC and BCC HEA nanopillars to reveal their damping properties. Higher storage modulus and damping factor values were observed in FCC and BCC the nanopillars. Storage Moduli in the nano-sized HEAs are a factor of 2 greater than both bulk BCC and FCC HEA counterparts. The difference is due to greater surface contribution of the external atoms in the small-sized HEAs.
", "doi": "10.7907/PSWX-RY20", "publication_date": "2019", "thesis_type": "phd", "thesis_year": "2019" }, { "id": "thesis:11347", "collection": "thesis", "collection_id": "11347", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:01182019-105653047", "primary_object_url": { "basename": "Lifson_Max_2019.pdf", "content": "final", "filesize": 49397814, "license": "other", "mime_type": "application/pdf", "url": "/11347/1/Lifson_Max_2019.pdf", "version": "v5.0.0" }, "type": "thesis", "title": "Electromechanical Properties of 3D Multifunctional Nano-Architected Materials", "author": [ { "family_name": "Lifson", "given_name": "Max Louis", "orcid": "0000-0002-0382-182X", "clpid": "Lifson-Max-Louis" } ], "thesis_advisor": [ { "family_name": "Greer", "given_name": "Julia R.", "clpid": "Greer-J-R" } ], "thesis_committee": [ { "family_name": "Faber", "given_name": "Katherine T.", "clpid": "Faber-K-T" }, { "family_name": "Johnson", "given_name": "William Lewis", "clpid": "Johnson-W-L" }, { "family_name": "Burdick", "given_name": "Joel Wakeman", "clpid": "Burdick-J-W" }, { "family_name": "Greer", "given_name": "Julia R.", "clpid": "Greer-J-R" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "In this thesis, we explore the fabrication and characterization of 3D architected multifunctional materials in three different categories: varied density for tailored mechanical response, stiff ultra low-k dielectric materials, and direct laser writing of piezoelectric structures at the micron scale. The density of an architected material plays a large role in determining its effective Young\u2019s modulus, strength, and deformation behavior. The first section of this work explores the effect of incorporating two density regions into hollow nanolattices, which results in two distinct mechanical response regions for horizontal interfaces and a combined varying response for a diagonal interface. The second section of this work describes low dielectric constant (low-k) materials, which have gained increasing popularity because of their critical role in developing faster, smaller, and higher performance devices. We report the fabrication of 3D nanoarchitected hollow-beam alumina dielectrics with a k value of 1.06 - 1.10 at 1 MHz that is stable over the voltage range of -20 to 20 V and a frequency range of 100 kHz to 10 MHz, with an effective Young\u2019s modulus of 30 MPa, a 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 x 10-5K-1 up to 800\u00b0 C. Finally, we report the fabrication of monolithic piezoelectric ZnO structures of arbitrary shape via a polymer complex route. We have confirmed the microstructure using XRD, TEM, and SAED, and have observed its electromechanical response using a novel in-situ experiment.
", "doi": "10.7907/D0AD-4T88", "publication_date": "2019", "thesis_type": "phd", "thesis_year": "2019" }, { "id": "thesis:10441", "collection": "thesis", "collection_id": "10441", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:09202017-020239229", "primary_object_url": { "basename": "ThesisNi.pdf", "content": "final", "filesize": 9379631, "license": "other", "mime_type": "application/pdf", "url": "/10441/1/ThesisNi.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Probing Microplastic Deformation in Metallic Materials", "author": [ { "family_name": "Ni", "given_name": "Xiaoyue", "orcid": "0000-0002-1822-1122", "clpid": "Ni-Xiaoyue" } ], "thesis_advisor": [ { "family_name": "Greer", "given_name": "Julia R.", "clpid": "Greer-J-R" }, { "family_name": "Adhikari", "given_name": "Rana", "clpid": "Adhikari-R" } ], "thesis_committee": [ { "family_name": "Johnson", "given_name": "William Lewis", "clpid": "Johnson-W-L" }, { "family_name": "Faber", "given_name": "Katherine T.", "clpid": "Faber-K-T" }, { "family_name": "Dahmen", "given_name": "Karin A.", "clpid": "Dahmen-Karin-A" }, { "family_name": "Greer", "given_name": "Julia R.", "clpid": "Greer-J-R" }, { "family_name": "Adhikari", "given_name": "Rana", "clpid": "Adhikari-R" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "Metallic materials deform through discrete displacement bursts that are commonly associated with abrupt dislocation activities, i.e. avalanches, during plastic flow. Dislocations might be active prior to the textbook yielding, but it is unclear whether these activities can be discerned as smaller strain events, i.e. microplasticity. Novel experimental approaches involving nanomechanical experiments are developed to detect and to quantify microplastic deformation that occurs during compression of micron- and sub-micron sized single crystalline copper nano-pillars. The experiment, focusing on metals\u2019 pre-yield regime, reveals an evolving dissipation component in the storage and loss moduli that likely corresponds to a smooth transition from perfect elasticity to avalanche-dominated plastic deformation. This experimental investigation is corroborated by mesoscopic plasticity simulations, which apply to a minimal model that combines fast avalanche dynamics and slow relaxation processes of dislocations. The model's predictions are consistent with the microscopic experiments and provide constitutive relationship predicting microplastic crackling noise being upconverted by small stress perturbations. Another experimental investigation on unload-reload cyclic behavior of copper nano-pillars post yielding shows a decaying microplastic hysteresis with emergent power laws and scaling features, which signifies an ever-explored reversible-to- irreversible transitions in metal deformation, as seen in other nonequilibrium systems. To study microplasticity in macroscopic metallic samples, an instrument is custom-built based on Michelson interferometer and achieves unprecedented high displacement noise resolution of 10\u221214m/\u221aHz in the frequency range of 10 \u2013 1000 Hz. The macroscopic experiment has resolved a driving-modulated microplastic noise in bulk cantilever steel samples under nominal elastic loading. The characteristics of the noise resemble those of the microplastic noise predicted from the micromechanical simulations developed from microscopic experiments.", "doi": "10.7907/F38W-6N47", "publication_date": "2018", "thesis_type": "phd", "thesis_year": "2018" }, { "id": "thesis:11076", "collection": "thesis", "collection_id": "11076", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:06122018-094549478", "primary_object_url": { "basename": "Mateos_Arturo_2018.pdf", "content": "final", "filesize": 128167927, "license": "other", "mime_type": "application/pdf", "url": "/11076/15/Mateos_Arturo_2018.pdf", "version": "v5.0.0" }, "type": "thesis", "title": "Tensile Failure and Fracture of Three-Dimensional Brittle Nanolattices", "author": [ { "family_name": "Mateos Arrieta", "given_name": "Arturo Jos\u00e9", "orcid": "0000-0002-9306-3531", "clpid": "Mateos-Arrieta-Arturo-Jos\u00e9" } ], "thesis_advisor": [ { "family_name": "Greer", "given_name": "Julia R.", "clpid": "Greer-J-R" } ], "thesis_committee": [ { "family_name": "Ravichandran", "given_name": "Guruswami", "clpid": "Ravichandran-G" }, { "family_name": "Faber", "given_name": "Katherine T.", "clpid": "Faber-K-T" }, { "family_name": "Pellegrino", "given_name": "Sergio", "clpid": "Pellegrino-S" }, { "family_name": "Greer", "given_name": "Julia R.", "clpid": "Greer-J-R" } ], "local_group": [ { "literal": "Kavli Nanoscience Institute" }, { "literal": "GALCIT" }, { "literal": "div_eng" } ], "abstract": "The emergence of a new class of cellular solids, i.e., nano- and micro-architected materials, poses the question of whether they can be characterized as a continuum solid. Extensive research has shown that these ultralight and strong structural metamaterials are particularly attractive for mechanically-demanding applications; yet their susceptibility to flaws, fracture behavior, and discrete-continuum duality remains relatively unexplored. In the course of this work, we report the fabrication and tensile-to-failure response of three-dimensional ceramic nanolattices, comprised of 50nm-thick alumina tubes that are arranged into periodic 5um-wide octet-truss unit cells, with and without pre-fabricated through-thickness center notches oriented at different angles to the loading direction. In-situ uniaxial tensile experiments revealed that for all notch orientations, failure always initiated at the notch root, as would be in a monolithic material, with the tube walls at nodal junctions fracturing first, followed by instantaneous crack propagation through the discrete lattice architecture along nodal planes orthogonal to the loading direction. Measured tensile strength of 27.4 MPa was highest for the unnotched samples and decreased systematically with the increase of notch orientation to its minimum of 7.2 MPa in the orthogonally-notched samples. We found the specific tensile strength of hollow-tube octet alumina nanolattices to be 4 times higher than what has been reported for architected and bulk materials at similar low densities. Three-dimensional finite element simulations closely reproduce the observed failure mechanism and trends in failure strength. A direct comparison is made between the experimental measurements, finite element simulations, and predictions of linear elastic fracture mechanics for a self-similar monolithic tensile samples made out of an ideally-brittle solid. Results are in good agreement with the scaling of failure strengths from classical mode I fracture criteria and suggest that trajectory of crack propagation can be adequately explained by considering the connectivity of the lattice architecture. These findings imply that the continuum nature of nano-architected materials offers predictability of failure stresses, which helps enable the development of advanced materials through informed architectural design.", "doi": "10.7907/AZXG-NB17", "publication_date": "2018", "thesis_type": "phd", "thesis_year": "2018" }, { "id": "thesis:10617", "collection": "thesis", "collection_id": "10617", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:12242017-060345135", "primary_object_url": { "basename": "Maggi-2018.pdf", "content": "final", "filesize": 9300158, "license": "other", "mime_type": "application/pdf", "url": "/10617/1/Maggi-2018.pdf", "version": "v5.0.0" }, "type": "thesis", "title": "Three-Dimensional Nano-Architected Materials as Platforms for Designing Effective Bone Implants", "author": [ { "family_name": "Maggi", "given_name": "Alessandro", "clpid": "Maggi-Alessandro" } ], "thesis_advisor": [ { "family_name": "Greer", "given_name": "Julia R.", "clpid": "Greer-J-R" } ], "thesis_committee": [ { "family_name": "Ravichandran", "given_name": "Guruswami", "clpid": "Ravichandran-G" }, { "family_name": "Daraio", "given_name": "Chiara", "clpid": "Daraio-C" }, { "family_name": "Burdick", "given_name": "Joel Wakeman", "clpid": "Burdick-J-W" }, { "family_name": "Shapiro", "given_name": "Mikhail G.", "clpid": "Shapiro-M-G" }, { "family_name": "Greer", "given_name": "Julia R.", "clpid": "Greer-J-R" } ], "local_group": [ { "literal": "Kavli Nanoscience Institute" }, { "literal": "GALCIT" }, { "literal": "div_eng" } ], "abstract": "The growing world population coupled with longer human life expectancy warrants the need for better medical implant development. Recent advances in lithographic techniques have opened the door to a variety of approaches to tackle the aforementioned issue. However, several scientific hurdles must be overcome before patients can use fully synthetic and effective implants.
\r\n\r\nIdentifying the optimal material, porosity, and mechanical properties of the scaffold to induce cell functionality are key obstacles. Limitations in established fabrication techniques have hindered the ability to fully understand cell behavior on 3D substrates. 3D printing is limited to feature sizes that are at least one order of magnitude larger than a single cell (~10\u03bcm); electrospinning is able to yield features that are on the same scale as cells, but its stochastic nature leads to scaffolds with poor mechanical properties; salt leeching doesn\u2019t allow for control of pore size and distribution which have detrimental effects on nutrient diffusion and cell ingrowth, thereby thwarting the formation of functional tissue.
\r\n\r\nMuch effort has been made to create a suitable platform for regenerating a relatively less complex organ, such as bone, yet the inability to fully understand cell mechanics on 3D scaffolds has curbed the fabrication of effective bone implants.
\r\n\r\nThe first part of this thesis focuses on the suitability of nanoarchitected materials as 3D platforms for bone-tissue growth. We employed two-photon lithography to create polymeric and hydroxyapatite-coated 3D nanolattices to explore scaffold biocompatibility and material effects on osteoblast attachment and growth. Our experiments showed that the unit cell geometry, tetrakaidekahedron, and size, 25\u03bcm, were adequate for cell attachment and infiltration, which are hallmark signs of biocompatibility. Our study also corroborated previous findings that mammalian cells respond differently to different materials that they come in contact with. To isolate structural effects, we fabricated nanolattices coated with a uniform 20nm-thick outermost layer of TiO2. These nanolattices, which had fixed porosity and unit cell size (25\u03bcm) while they varied in structural stiffness (~2-9MPa) were used to explore the influence of scaffold properties on the viability of osteoblasts in a microenvironment similar to that of natural bone. Upon growing osteogenic cells on the nanolattices, significant cell attachment and presence of various calcium phosphate species, which are commonly found in natural bone, were observed. These findings suggest that 3-dimensional nano-architected materials can be used as effective scaffolds for bone cell growth and proliferation.
\r\n\r\nThe second part of the thesis investigates the effects of nanolattice structural stiffness and loading conditions on osteoblast behavior. We fabricated nanolattices with stiffness ranging from ~0.7MPa to 100MPa. Experiments done by seeding osteoblast-like cells on these nanolattices revealed that both stress fiber concentration and bioapatite deposition were higher on the most compliant nanolattice, (0.7 MPa) by ~20% and ~40% respectively. These results provide insights into cell behavior in 3D microenvironments which can lead to a better understanding of stress shielding at the cellular level. Preventing stress shielding by creating scaffolds with structural stiffness and porosity that enhances osteoblasts activity could lead to the creation of effective implants with improved mechanical stability which ultimately improves osteointegration.
\r\n\r\nIn addition to investigating static cell-scaffold interactions we took advantage of the nanolattices tunability to study the effects of dynamic loading on cell behavior. Bone adaptation is driven by dynamic, rather than static loading, however there is still wide controversy on whether stress, strain or loading frequency plays the most significant role in bone remodeling, which drives bone healing.
\r\n\r\nIn order to understand cell sensitivity to varying loads, displacements and frequencies, we fabricated hollow TiO2 nanolattices with stiffness ranging from ~0.7-35MPa which were populated with osteoblast-like cells and subjected to cyclic compression to either a constant stress or strain. After seeding SAOS-2 cells on the nanolattices for 12 days different dynamic loading conditions were tested: (1) cyclic uniaxial compressions to strains ranging from ~0.3-2% strain were carried out to investigate the effects of strain magnitude on cell behavior. (2) Cyclic uniaxial compressions to stresses spanning from ~0.02-1MPa were performed to explore the role of stress magnitude on the cells\u2019 stress fibers formation. (3) The nanolattices were cyclically loaded at different frequencies, ~0.1-3Hz, while maintaining stress and strain constant, which provided insights into how loading frequency affects osteoblasts behavior.
\r\n\r\nCell activity, which was measured by monitoring f-actin and vinculin fluorescence intensity, revealed increased fluorescence in those cells that were mechanically stimulated as opposed to those that were statically grown on the nanolattices regardless of loading condition. Cell response was most drastically affected by varying the loading frequency. A ~30% increase in f-actin fluorescence was observed in the cells grown on the nanolattices that were loaded at ~3Hz compared to those that were grown on the nanolattices that were cyclically compressed at ~0.1Hz.
\r\n\r\nThe last part of this thesis is focused on developing a three-dimensional architected capacitor that could be used as a strain gauge to further our understanding of cell mechanics in 3D. We took advantage of the mechanical tunability of the nanolattices to fabricate a 3D parallel-plate capacitor with a basal capacitance of ~280fF and able to sense forces as low as ~30\u03bcN. This work points to nano-architected materials as promising candidates for ideal platforms to investigate more realistic cellular conditions which can immensely benefit the field of tissue engineering.
", "doi": "10.7907/Z947482K", "publication_date": "2018", "thesis_type": "phd", "thesis_year": "2018" }, { "id": "thesis:10876", "collection": "thesis", "collection_id": "10876", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05112018-154344223", "type": "thesis", "title": "Design, Fabrication, and Characterization of 3D Nanolattice Photonic Crystals for Bandgap and Refractive Index Engineering", "author": [ { "family_name": "Chernow", "given_name": "Victoria Fay", "orcid": "0000-0001-5405-1928", "clpid": "Chernow-Victoria-Fay" } ], "thesis_advisor": [ { "family_name": "Greer", "given_name": "Julia R.", "clpid": "Greer-J-R" } ], "thesis_committee": [ { "family_name": "Atwater", "given_name": "Harry Albert", "clpid": "Atwater-H-A" }, { "family_name": "Rossman", "given_name": "George Robert", "clpid": "Rossman-G-R" }, { "family_name": "Painter", "given_name": "Oskar J.", "clpid": "Painter-O" }, { "family_name": "Greer", "given_name": "Julia R.", "clpid": "Greer-J-R" } ], "local_group": [ { "literal": "Kavli Nanoscience Institute" }, { "literal": "div_eng" } ], "abstract": "Three-dimensional (3D) photonic crystals (PhCs) have been the focus of ever-increasing interest in the scientific community given their potential to impact areas spanning energy conversion to analyte sensing. These architected materials are defined by a refractive index that is spatially modulated with a period comparable to that of the electromagnetic wavelength. As a result, constructive and destructive interference due to multiple scattering gives rise to a band structure for photons which may contain gaps. Both bands and bandgaps can be engineered to specifically manipulate light propagation by 3D PhCs. In this work we explore the effect of lattice architecture, finite-size effects, and material constraints on stopband position and emergence of band dispersion phenomena like negative refraction. We show that uniaxial mechanical compression can be used to stably and reversibly tune stopband position in 3D polymer nanolattice PhCs with octahedron unit-cell geometry. We then explore how lattice architecture, namely the differences in 3D cubic space group and finite size effects impact experimentally observable stopbands, and assess the degree to which the stopband behavior of real PhCs can be adequately described by the photonic band structure for an infinite, ideal PhC. Finally, we discuss the design, fabrication, and characterization of a core-shell 3D nanolattice PhC which exhibits an effective negative refractive index in the mid-infrared range.
", "doi": "10.7907/FK5P-FA29", "publication_date": "2018", "thesis_type": "phd", "thesis_year": "2018" }, { "id": "thesis:11037", "collection": "thesis", "collection_id": "11037", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:06072018-140534228", "type": "thesis", "title": "Cathode Design for High Energy Molten Salt Lithium-Oxygen Batteries", "author": [ { "family_name": "Tozier", "given_name": "Dylan Douglas", "orcid": "0000-0001-9489-8824", "clpid": "Tozier-Dylan-Douglas" } ], "thesis_advisor": [ { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "thesis_committee": [ { "family_name": "Fultz", "given_name": "Brent T.", "orcid": "0000-0002-6364-8782", "clpid": "Fultz-B-T" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" }, { "family_name": "Johnson", "given_name": "William Lewis", "clpid": "Johnson-W-L" }, { "family_name": "See", "given_name": "Kimberly", "orcid": "0000-0002-0133-9693", "clpid": "See-Kimberly" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "State of the art commercial lithium ion batteries use cathodes such as lithium cobalt oxide which rely on insertion and removal of lithium ions from a host material. However, insertion cathode materials are limited in their capacity, and replacing them with a cathode that employs growth and dissolution of new phases could significantly increase a battery\u2019s energy density. For example, oxygen and sulfur cathodes have been widely researched to this end, with both cases involving the growth of a lithium-rich compound on a current collector/catalyst support.
\r\n\r\nWe begin by describing the effect of using a molten salt electrolyte in a lithium-oxygen battery. In particular, we focus on how the electrochemical performance and discharge product, lithium peroxide, differ from that of a traditional organic electrolyte. In addition, we discuss the enhanced peroxide solubility in a molten salt and its implications for lithium peroxide growth and coulombic efficiency. Finally, we address the cell death of a galvanostatically cycled battery.
\r\n\r\nWe then introduce a similar phase-forming conversion chemistry, whereby a molten nitrate salt serves as both an active material and the electrolyte. Molten nitrate salts were previously studied as an active material in a primary lithium battery where lithium oxide irreversibly forms as nitrate reduces to nitrite. We will describe how the use of a nanoparticle heterogeneous catalyst allows the reversible growth and dissolution of micron-scale lithium oxide crystals in this system.
\r\n\r\nAfter introducing these molten salt lithium batteries, we address the effect of cathode geometry on electrochemical performance. In particular, we note that the growth of such large, solid phase species on the surface of the catalyst support imposes new design restrictions when optimizing a cathode for energy density. As a proof of concept, we design and implement an architected electrode with large pore volume and relatively small surface area, comparing it with the more typical geometries of thin films and nanoparticles.
", "doi": "10.7907/TG0K-8776", "publication_date": "2018", "thesis_type": "phd", "thesis_year": "2018" }, { "id": "thesis:10624", "collection": "thesis", "collection_id": "10624", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:01082018-142110350", "primary_object_url": { "basename": "Final thesis Shi Luo.pdf", "content": "final", "filesize": 5695075, "license": "other", "mime_type": "application/pdf", "url": "/10624/1/Final thesis Shi Luo.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Microstructural Effects on Diffusion and Mechanical Properties in Different Material Systems", "author": [ { "family_name": "Luo", "given_name": "Shi", "clpid": "Luo-Shi" } ], "thesis_advisor": [ { "family_name": "Greer", "given_name": "Julia R.", "clpid": "Greer-J-R" } ], "thesis_committee": [ { "family_name": "Goddard", "given_name": "William A., III", "clpid": "Goddard-W-A-III" }, { "family_name": "Faber", "given_name": "Katherine T.", "clpid": "Faber-K-T" }, { "family_name": "Daraio", "given_name": "Chiara", "clpid": "Daraio-C" }, { "family_name": "Greer", "given_name": "Julia R.", "clpid": "Greer-J-R" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "Material microstructures is a very broad subject that encompasses most of the field of materials science. Advances in materials characterization and small scale mechanical experiments have brought about progress in the understanding of microstructural features and mechanisms down to the nanometer scale. In contrast to bulk features and properties, the small length scale of these microstructures lead to many interesting properties, and often requires a material-by-material, and even localized region-by-region study. While a thorough understanding of microstructural effects even in one material system is way beyond the scope of this thesis, there are nonetheless many common themes and properties that link together microstructures and their effects on different materials, especially in terms of mechanical properties.
\r\n\r\nIn this thesis, the effects of microstructural features such as grain boundaries, surface modification and structural hierarchy are investigated using two sample material systems: Cu-In-Ga-Se (CIGS) thin films and marine diatom frustules. We find that grain structures (or a lack there of) play a major role in both systems, and lead to differences in material stiffness, strength, and diffusion of species. The latter is also significantly affected by material defects across length scales, exemplified in CIGS by both microscopic voids and pores, and atomic scale like substitutional point defects. On the other hand, in diatoms, a low flaw density combined with an effective hierarchical design can propel the mechanical property of relatively simple ingredients like amorphous silica, to achieve extraordinary mechanical strength. We will conclude by showcasing that we can generalize some of these knowledge on microstructural effects across material systems, to help designing manmade structures that fully capture the material-level and structural-level properties of natural marine diatoms.
", "doi": "10.7907/Z90G3HBV", "publication_date": "2018", "thesis_type": "phd", "thesis_year": "2018" }, { "id": "thesis:9977", "collection": "thesis", "collection_id": "9977", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:11062016-104329889", "type": "thesis", "title": "The Catalytic and Mechanical Properties of Lithium Battery Electrodes", "author": [ { "family_name": "Xu", "given_name": "Chen", "orcid": "0000-0002-9427-0161", "clpid": "Xu-Chen" } ], "thesis_advisor": [ { "family_name": "Greer", "given_name": "Julia R.", "clpid": "Greer-J-R" } ], "thesis_committee": [ { "family_name": "Greer", "given_name": "Julia R.", "clpid": "Greer-J-R" }, { "family_name": "Fultz", "given_name": "Brent T.", "clpid": "Fultz-B-T" }, { "family_name": "Faber", "given_name": "Katherine T.", "clpid": "Faber-K-T" }, { "family_name": "Miller", "given_name": "Thomas F.", "clpid": "Miller-T-F" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "The mass adoption of electric vehicles warrants higher energy densities at lower costs. Novel chemistries such as Li-S or Li-air, high energy density anodes such as lithium (Li) metal are some of the ways to address the aforementioned issue. However, many scientific challenges must be overcome in order to achieve the successful commercialization of these batteries. For Li-air, poor cyclability and low coulumbic efficiency are key obstacles. The search for cathode materials that exhibit high capacity, low discharge/charge overpotential and chemical stability over many cycles is a major area of interest in the field. On the anode side, the application of Li metal is stumped by uncontrollable dendrite growth during the charging, and existing methods such as pulsed charging, physical suppression, and additives in the electrolyte have only had alleviating effects.
\r\n\r\nThe first part of this thesis investigates the suitability of various materials as Li-air cathodes. We fabricated 3-dimensional architected electrodes using a variety of materials including Au, Ni, Ti, LaCoO3 (LCO), LaNiO3 (LNO), and LaNi0.5Co0.5O3 (LNCO). Their performances in capacity, overpotential, and cyclability were assessed using galvanostatic battery testing methods. The reaction products were investigated using spectroscopic techniques such as FTIR and Raman. Our experiments corroborated recent findings that even trace moisture contamination can dramatically influence discharge product composition and morphology. Furthermore, Ni nanoparticles may serve as a carbon substitute in investigating the properties of non-conductive catalysts under specific potential windows. By incorporation the perovskites into a Ni based conductive mesh, we found the oxygen reduction reaction capability of the three materials to be ranked as LCO>LNCO>LNO, and the chemical stability ranked as LCO>LNO>LNCO. The instability of DMSO due to chemical reactions with discharge products is observed and discussed in the context of the solution-mediated mechanism of Li2O2 growth. The second part of the thesis investigates the nano-mechanical properties of Li (bcc), as a function of size, temperature, and crystal grain orientation. At room temperature the power law exponent of the strength vs. size log-log plot is -0.68, while at 90\u00b0C this value is increased to -1.00. A factor of 3 decrease in the yield strength at 90\u00b0C is observed, and the morphology of deformation was found to transition from localized slip planes to homogeneous barreling. Our collaborators at Carnegie Mellon University calculated the elastic constants of Li from 78 K to 440 K (melting temperature of Li is 453 K), and is found to be within reasonable agreement with existing experimental data where applicable (78 -300 K). We proceeded to calculate the elastic and shear moduli of single crystal Li as a function of temperature and orientation. We found that due to the extreme anisotropy of Li, there is a factor of ~4 difference between the strongest and weakest orientation of both the elastic and shear moduli. Our findings are discussed in the context of Li anodes, where we highlight the importance of taking into consideration the size-effect and anisotropy when designing solid electrolytes, or modeling dendrite growth behavior.
\r\n", "doi": "10.7907/Z9XG9P4W", "publication_date": "2017", "thesis_type": "phd", "thesis_year": "2017" }, { "id": "thesis:10634", "collection": "thesis", "collection_id": "10634", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:01102018-104101666", "primary_object_url": { "basename": "McCormick Place_AP_2017.pdf", "content": "final", "filesize": 20399745, "license": "other", "mime_type": "application/pdf", "url": "/10634/1/McCormick Place_AP_2017.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Differential Bandgap Solar Cell Analysis", "author": [ { "family_name": "Place", "given_name": "Alexander Patrick Mccormick", "clpid": "Place-Alexander-Patrick-McCormick" } ], "thesis_advisor": [ { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "thesis_committee": [ { "family_name": "None", "given_name": "None" } ], "local_group": [ { "literal": "div_pma" } ], "abstract": "This thesis proposes and analyzes a new solar cell design. The base electrode of the new\r\nphotovoltaic is composed of several electrically isolated nanolattices suspended on top of\r\neach other. Doped semiconductors are then deposited onto the beams of this electrode,\r\nforming isolated p-n junctions. The deposition thicknesses of one of the doped\r\nsemiconductors is varied along the height of the device, creating a multi-junction solar cell.\r\nThe charge ca rrier dynamics in an amorphous silicon- and germanium-based device are\r\nsimulated, and the efficiency is found to be a factor of four greater than a conventional\r\nplanar structure with similar parameters. The main components of this photovoltaic's\r\nfabrication process are developed and analyzed. Specifically, suspended and electrically\r\nisolated lattice electrodes made of carbon are built. The electrical conductivity of the\r\ncarbon is shown to be similar to that of indium-tin oxide. The electrode material is\r\ndetermined to be a mix of amorphous and glassy carbon. Different methods of radiofrequency\r\nsputter deposition are used to deposit spatially dependent layer thicknesses of\r\nsemiconductors onto the lattice beams. The spatial dependence is shown to be\r\napproximately linearly dependent on the height dimension of the lattice.", "doi": "10.7907/K524-AZ81", "publication_date": "2017", "thesis_type": "senior_major", "thesis_year": "2017" }, { "id": "thesis:9924", "collection": "thesis", "collection_id": "9924", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:09132016-104159178", "primary_object_url": { "basename": "RachelLiontas_2017_Thesis.pdf", "content": "final", "filesize": 6382336, "license": "other", "mime_type": "application/pdf", "url": "/9924/59/RachelLiontas_2017_Thesis.pdf", "version": "v12.0.0" }, "type": "thesis", "title": "Controlling Deformability in Metallic Glass Nanopillars and Nanolattices", "author": [ { "family_name": "Liontas", "given_name": "Rachel", "orcid": "0000-0001-9925-9466", "clpid": "Liontas-Rachel" } ], "thesis_advisor": [ { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "thesis_committee": [ { "family_name": "Brady", "given_name": "John F.", "orcid": "0000-0001-5817-9128", "clpid": "Brady-J-F" }, { "family_name": "Johnson", "given_name": "William Lewis", "clpid": "Johnson-W-L" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" }, { "family_name": "Arnold", "given_name": "Frances Hamilton", "orcid": "0000-0002-4027-364X", "clpid": "Arnold-F-H" } ], "local_group": [ { "literal": "Kavli Nanoscience Institute" }, { "literal": "div_chem" } ], "abstract": "Metallic glasses offer desirable mechanical properties, including high strength, hardness, and elasticity. In bulk, they suffer from catastrophic failure upon mechanical loads. However, ductility may emerge upon (1) reducing the characteristic dimension of the metallic glass to the nanoscale or (2) irradiating the metallic glass. These two methods of controlling metallic glass deformability are investigated through a host of mechanical experiments on metallic glass nanopillars and nanolattices before and after irradiation. The mechanical experiments are conducted inside a scanning electron microscope to allow simultaneous mechanical loading and visualization of nanoscale deformation behavior.
\r\n\r\nSuch experiments reveal that helium irradiation of electrodeposited Ni73P27 metallic glass tensile nanopillars increases plasticity by a factor of two with no sacrifice in strength. Other tensile experiments on Zr-Ni-Al metallic glass nanopillars in as-sputtered and annealed states reveal substantial ductility, highly dependent upon both the nanopillar size and processing conditions. Molecular dynamics simulations, transmission electron microscopy, and synchrotron x-ray diffraction are used to explain the observed mechanical behavior through changes in free volume and short-range order.
\r\n\r\nLarger nanolattice structures are fabricated to contain hollow beams of metallic glass, with beam wall thicknesses in the nanoscale size range that may allow proliferation of the beneficial \u201csmaller is more ductile\u201d size effect observed in metallic glass nanopillars. Compression experiments on Zr-Ni-Al metallic glass nanolattices reveal enhanced deformability as the nanolattice wall thickness is reduced and upon irradiation. This work points to metallic glass nanolattices as promising candidates for radiation-intensive applications and demonstrates that by fabricating the metallic glass in a nanolattice architecture the beneficial nanoscale size effect in deformability can be preserved.
\r\n", "doi": "10.7907/Z9028PHX", "publication_date": "2017", "thesis_type": "phd", "thesis_year": "2017" }, { "id": "thesis:9759", "collection": "thesis", "collection_id": "9759", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05252016-155624343", "primary_object_url": { "basename": "Chen_David_2016_Caltech_Thesis.pdf", "content": "", "filesize": 9910115, "license": "other", "mime_type": "application/pdf", "url": "/9759/1/Chen_David_2016_Caltech_Thesis.pdf", "version": "v1.0.0" }, "type": "thesis", "title": "Atomic-Level Structure and Deformation in Metallic Glasses", "author": [ { "family_name": "Chen", "given_name": "David Zhaoyue", "orcid": "0000-0001-5732-5015", "clpid": "Chen-David-Zhaoyue" } ], "thesis_advisor": [ { "family_name": "Greer", "given_name": "Julia R.", "clpid": "Greer-J-R" } ], "thesis_committee": [ { "family_name": "Greer", "given_name": "Julia R.", "clpid": "Greer-J-R" }, { "family_name": "Johnson", "given_name": "William Lewis", "clpid": "Johnson-W-L" }, { "family_name": "Goddard", "given_name": "William A., III", "clpid": "Goddard-W-A-III" }, { "family_name": "Miller", "given_name": "Thomas F.", "clpid": "Miller-T-F" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "Metallic glasses (MGs) are a relatively new class of materials discovered in 1960\r\nand lauded for its high strengths and superior elastic properties. Three major obstacles\r\nprevent their widespread use as engineering materials for nanotechnology and\r\nindustry: 1) their lack of plasticity mechanisms for deformation beyond the elastic\r\nlimit, 2) their disordered atomic structure, which prevents effective study of their\r\nstructure-to-property relationships, and 3) their poor glass forming ability, which\r\nlimits bulk metallic glasses to sizes on the order of centimeters. We focused on\r\nunderstanding the first two major challenges by observing the mechanical properties\r\nof nanoscale metallic glasses in order to gain insight into its atomic-level structure\r\nand deformation mechanisms. We found that anomalous stable plastic flow emerges\r\nin room-temperature MGs at the nanoscale in wires as little as ~100 nanometers\r\nwide regardless of fabrication route (ion-irradiated or not). To circumvent experimental\r\nchallenges in characterizing the atomic-level structure, extensive molecular\r\ndynamics simulations were conducted using approximated (embedded atom\r\nmethod) potentials to probe the underlying processes that give rise to plasticity in\r\nnanowires. Simulated results showed that mechanisms of relaxation via the sample\r\nfree surfaces contribute to tensile ductility in these nanowires. Continuing with characterizing\r\nnanoscale properties, we studied the fracture properties of nano-notched\r\nMGnanowires and the compressive response of MG nanolattices at cryogenic (~130\r\nK) temperatures. We learned from these experiments that nanowires are sensitive\r\nto flaws when the (amorphous) microstructure does not contribute stress concentrations,\r\nand that nano-architected structures with MG nanoribbons are brittle at low\r\ntemperatures except when elastic shell buckling mechanisms dominate at low ribbon\r\nthicknesses (~20 nm), which instead gives rise to fully recoverable nanostructures regardless\r\nof temperature. Finally, motivated by understanding structure-to-property\r\nrelationships in MGs, we studied the disordered atomic structure using a combination\r\nof in-situ X-ray tomography and X-ray diffraction in a diamond anvil cell\r\nand molecular dynamics simulations. Synchrotron X-ray experiments showed the\r\nprogression of the atomic-level structure (in momentum space) and macroscale volume\r\nunder increasing hydrostatic pressures. Corresponding simulations provided\r\ninformation on the real space structure, and we found that the samples displayed\r\nfractal scaling (rd ∝ V, d < 3) at short length scales (< ~8 \u00c5), and exhibited a\r\ncrossover to a homogeneous scaling (d = 3) at long length scales. We examined\r\nthis underlying fractal structure of MGs with parallels to percolation clusters and\r\ndiscuss the implications of this structural analogy to MG properties and the glass\r\ntransition phenomenon.", "doi": "10.7907/Z95Q4T2B", "publication_date": "2016", "thesis_type": "phd", "thesis_year": "2016" }, { "id": "thesis:9058", "collection": "thesis", "collection_id": "9058", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:07132015-150843708", "primary_object_url": { "basename": "MontemayorThesis.pdf", "content": "", "filesize": 88804608, "license": "other", "mime_type": "application/pdf", "url": "/9058/1/MontemayorThesis.pdf", "version": "v1.0.0" }, "type": "thesis", "title": "Fabrication, Characterization, And Deformation of 3D Structural Meta-Materials ", "author": [ { "family_name": "Montemayor", "given_name": "Lauren Christine", "clpid": "Montemayor-Lauren-Christine" } ], "thesis_advisor": [ { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "thesis_committee": [ { "family_name": "Ravichandran", "given_name": "Guruswami", "orcid": "0000-0002-2912-0001", "clpid": "Ravichandran-G" }, { "family_name": "Ortiz", "given_name": "Michael", "orcid": "0000-0001-5877-4824", "clpid": "Ortiz-M" }, { "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" } ], "local_group": [ { "literal": "Kavli Nanoscience Institute" }, { "literal": "GALCIT" }, { "literal": "div_eng" } ], "abstract": "Current technological advances in fabrication methods have provided pathways to creating architected structural meta-materials similar to those found in natural organisms that are structurally robust and lightweight, such as diatoms. Structural meta-materials are materials with mechanical properties that are determined by material properties at various length scales, which range from the material microstructure (nm) to the macro-scale architecture (\u03bcm \u2013 mm). It is now possible to exploit material size effect, which emerge at the nanometer length scale, as well as structural effects to tune the material properties and failure mechanisms of small-scale cellular solids, such as nanolattices. \r\nThis work demonstrates the fabrication and mechanical properties of 3-dimensional hollow nanolattices in both tension and compression. Hollow gold nanolattices loaded in uniaxial compression demonstrate that strength and stiffness vary as a function of geometry and tube wall thickness. Structural effects were explored by increasing the unit cell angle from 30\u00b0 to 60\u00b0 while keeping all other parameters constant; material size effects were probed by varying the tube wall thickness, t, from 200nm to 635nm, at a constant relative density and grain size. In-situ uniaxial compression experiments reveal 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 3-dimensional architected meta-materials and highlight the importance of material, geometric, and microstructural effects in small-scale mechanics. \r\nThis work also explores the flaw tolerance of 3D hollow-tube alumina kagome nanolattices with and without pre-fabricated notches, both in experiment and simulation. Experiments demonstrate that the hollow kagome nanolattices in uniaxial tension always fail at the same load when the ratio of notch length (a) to sample width (w) is no greater than 1/3, with no correlation between failure occurring at or away from the notch. For notches with (a/w) > 1/3, the samples fail at lower peak loads and this is attributed to the increased compliance as fewer unit cells span the un-notched region. Finite element simulations of the kagome tension samples show that the failure is governed by tensile loading for (a/w) < 1/3 but as (a/w) increases, bending begins to play a significant role in the failure. This work explores the flaw sensitivity of hollow alumina kagome nanolattices in tension, using experiments and simulations, and demonstrates that the discrete-continuum duality of architected structural meta-materials gives rise to their flaw insensitivity even when made entirely of intrinsically brittle materials.\r\n", "doi": "10.7907/Z9D21VH2", "publication_date": "2016", "thesis_type": "phd", "thesis_year": "2016" }, { "id": "thesis:9735", "collection": "thesis", "collection_id": "9735", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05232016-115645913", "primary_object_url": { "basename": "LucasMeza_Thesis_Final.pdf", "content": "final", "filesize": 22363609, "license": "other", "mime_type": "application/pdf", "url": "/9735/48/LucasMeza_Thesis_Final.pdf", "version": "v7.0.0" }, "type": "thesis", "title": "Design, Fabrication, and Mechanical Property Analysis of 3D Nanoarchitected Materials", "author": [ { "family_name": "Meza", "given_name": "Lucas Rosendo", "orcid": "0000-0003-0250-2621", "clpid": "Meza-Lucas-Rosendo" } ], "thesis_advisor": [ { "family_name": "Greer", "given_name": "Julia R.", "clpid": "Greer-J-R" } ], "thesis_committee": [ { "family_name": "Ravichandran", "given_name": "Guruswami", "clpid": "Ravichandran-G" }, { "family_name": "Kochmann", "given_name": "Dennis M.", "clpid": "Kochmann-D-M" }, { "family_name": "Pellegrino", "given_name": "Sergio", "clpid": "Pellegrino-S" }, { "family_name": "Greer", "given_name": "Julia R.", "clpid": "Greer-J-R" } ], "local_group": [ { "literal": "Kavli Nanoscience Institute" }, { "literal": "div_eng" } ], "abstract": "Recent developments in micro- and nanoscale 3D fabrication techniques have enabled the creation of materials with a controllable nanoarchitecture that can have structural features spanning 5 orders of magnitude from tens of nanometers to millimeters. These fabrication methods in conjunction with nanomaterial processing techniques permit a nearly unbounded design space through which new combinations of nanomaterials and architecture can be realized. In the course of this work, we designed, fabricated, and mechanically analyzed a wide range of nanoarchitected materials in the form of nanolattices made from polymer, composite, and hollow ceramic beams. Using a combination of two-photon lithography and atomic layer deposition, we fabricated samples with periodic and hierarchical architectures spanning densities over 4 orders of magnitude from \u03c1=0.3-300kg/m3 and with features as small as 5nm. Uniaxial compression and cyclic loading tests performed on different nanolattice topologies revealed a range of novel mechanical properties: the constituent nanoceramics used here have size-enhanced strengths that approach the theoretical limit of materials strength; hollow aluminum oxide (Al2O3) nanolattices exhibited ductile-like deformation and recovered nearly completely after compression to 50% strain when their wall thicknesses were reduced below 20nm due to the activation of shell buckling; hierarchical nanolattices exhibited enhanced recoverability and a near linear scaling of strength and stiffness with relative density, with E\u221d\u03c11.04 and \u03c3y\u221d\u03c11.17 for hollow Al2O3 samples; periodic rigid and non-rigid nanolattice topologies were tested and showed a nearly uniform scaling of strength and stiffness with relative density, marking a significant deviation from traditional theories on \u201cbending\u201d and \u201cstretching\u201d dominated cellular solids; and the mechanical behavior across all topologies was highly tunable and was observed to strongly correlate with the slenderness \u03bb and the wall thickness-to-radius ratio t/a of the beams. These results demonstrate the potential of nanoarchitected materials to create new highly tunable mechanical metamaterials with previously unattainable properties.", "doi": "10.7907/Z9154F1K", "publication_date": "2016", "thesis_type": "phd", "thesis_year": "2016" }, { "id": "thesis:8774", "collection": "thesis", "collection_id": "8774", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:02242015-173330087", "primary_object_url": { "basename": "thesis final revised.pdf", "content": "final", "filesize": 37069880, "license": "other", "mime_type": "application/pdf", "url": "/8774/1/thesis final revised.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Strength, Deformation and Fracture in Metallic Nanostructures", "author": [ { "family_name": "Gu", "given_name": "Xun Wendy", "clpid": "Gu-Xun-Wendy" } ], "thesis_advisor": [ { "family_name": "Greer", "given_name": "Julia R.", "clpid": "Greer-J-R" } ], "thesis_committee": [ { "family_name": "Greer", "given_name": "Julia R.", "clpid": "Greer-J-R" }, { "family_name": "Haile", "given_name": "Sossina M.", "clpid": "Haile-S-M" }, { "family_name": "Wang", "given_name": "Zhen-Gang", "clpid": "Wang-Zhen-Gang" }, { "family_name": "Kochmann", "given_name": "Dennis M.", "clpid": "Kochmann-D-M" } ], "local_group": [ { "literal": "Kavli Nanoscience Institute" }, { "literal": "div_chem" } ], "abstract": "An understanding of the mechanics of nanoscale metals and semiconductors is necessary for the safe and prolonged operation of nanostructured devices from transistors to nanowire- based solar cells to miniaturized electrodes. This is a fascinating but challenging pursuit because mechanical properties that are size-invariant in conventional materials, such as strength, ductility and fracture behavior, can depend critically on sample size when materials are reduced to sub- micron dimensions. In this thesis, the effect of nanoscale sample size, microstructure and structural geometry on mechanical strength, deformation and fracture are explored for several classes of solid materials. Nanocrystalline platinum nano-cylinders with diameters of 60 nm to 1 \u03bcm and 12 nm sized grains are fabricated and tested in compression. We find that nano-sized metals containing few grains weaken as sample diameter is reduced relative to grain size due to a change from deformation governed by internal grains to surface grain governed deformation. Fracture at the nanoscale is explored by performing in-situ SEM tension tests on nanocrystalline platinum and amorphous, metallic glass nano-cylinders containing purposely introduced structural flaws. It is found that failure location, mechanism and strength are determined by the stress concentration with the highest local stress whether this is at the structural flaw or a microstructural feature. Principles of nano-mechanics are used to design and test mechanically robust hierarchical nanostructures with structural and electrochemical applications. 2-photon lithography and electroplating are used to fabricate 3D solid Cu octet meso-lattices with micron- scale features that exhibit strength higher than that of bulk Cu. An in-situ SEM lithiation stage is developed and used to simultaneously examine morphological and electrochemical changes in Si-coated Cu meso-lattices that are of interest as high energy capacity electrodes for Li-ion batteries.", "doi": "10.7907/Z91J97NV", "publication_date": "2015", "thesis_type": "phd", "thesis_year": "2015" }, { "id": "thesis:8841", "collection": "thesis", "collection_id": "8841", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:04302015-143917971", "primary_object_url": { "basename": "zachary_aitken_2015_thesis.pdf", "content": "final", "filesize": 3688241, "license": "other", "mime_type": "application/pdf", "url": "/8841/1/zachary_aitken_2015_thesis.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Effect of Microstructural Interfaces on the Mechanical Response of Crystalline Metallic Materials", "author": [ { "family_name": "Aitken", "given_name": "Zachary Howard", "clpid": "Aitken-Zachary-Howard" } ], "thesis_advisor": [ { "family_name": "Greer", "given_name": "Julia R.", "clpid": "Greer-J-R" } ], "thesis_committee": [ { "family_name": "Ravichandran", "given_name": "Guruswami", "clpid": "Ravichandran-G" }, { "family_name": "Goddard", "given_name": "William A., III", "clpid": "Goddard-W-A-III" }, { "family_name": "Kochmann", "given_name": "Dennis M.", "clpid": "Kochmann-D-M" }, { "family_name": "Greer", "given_name": "Julia R.", "clpid": "Greer-J-R" } ], "local_group": [ { "literal": "Kavli Nanoscience Institute" }, { "literal": "div_eng" } ], "abstract": "Advances in nano-scale mechanical testing have brought about progress in the understanding of physical phenomena in materials and a measure of control in the fabrication of novel materials. In contrast to bulk materials that display size-invariant mechanical properties, sub-micron metallic samples show a critical dependence on sample size. The strength of nano-scale single crystalline metals is well-described by a power-law function, \u03c3\u03b1D-n, where D is a critical sample size and n is a experimentally-fit positive exponent. This relationship is attributed to source-driven plasticity and demonstrates a strengthening as the decreasing sample size begins to limit the size and number of dislocation sources. A full understanding of this size-dependence is complicated by the presence of microstructural features such as interfaces that can compete with the dominant dislocation-based deformation mechanisms. In this thesis, the effects of microstructural features such as grain boundaries and anisotropic crystallinity on nano-scale metals are investigated through uniaxial compression testing. We find that nano-sized Cu covered by a hard coating displays a Bauschinger effect and the emergence of this behavior can be explained through a simple dislocation-based analytic model. Al nano-pillars containing a single vertically-oriented coincident site lattice grain boundary are found to show similar deformation to single-crystalline nano-pillars with slip traces passing through the grain boundary. With increasing tilt angle of the grain boundary from the pillar axis, we observe a transition from dislocation-dominated deformation to grain boundary sliding. Crystallites are observed to shear along the grain boundary and molecular dynamics simulations reveal a mechanism of atomic migration that accommodates boundary sliding. We conclude with an analysis of the effects of inherent crystal anisotropy and alloying on the mechanical behavior of the Mg alloy, AZ31. Through comparison to pure Mg, we show that the size effect dominates the strength of samples below 10 \u03bcm, that differences in the size effect between hexagonal slip systems is due to the inherent crystal anisotropy, suggesting that the fundamental mechanism of the size effect in these slip systems is the same.", "doi": "10.7907/Z9C24TCP", "publication_date": "2015", "thesis_type": "phd", "thesis_year": "2015" }, { "id": "thesis:8235", "collection": "thesis", "collection_id": "8235", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05142014-151151819", "primary_object_url": { "basename": "Nisha_Mohan_2014.pdf", "content": "final", "filesize": 4550555, "license": "other", "mime_type": "application/pdf", "url": "/8235/1/Nisha_Mohan_2014.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Extracting Material Response from Simple Mechanical Tests on Hardening-Softening-Hardening Viscoplastic Solids", "author": [ { "family_name": "Mohan", "given_name": "Nisha", "clpid": "Mohan-Nisha" } ], "thesis_advisor": [ { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "thesis_committee": [ { "family_name": "Kochmann", "given_name": "Dennis M.", "orcid": "0000-0002-9112-6615", "clpid": "Kochmann-D-M" }, { "family_name": "Ortiz", "given_name": "Michael", "orcid": "0000-0001-5877-4824", "clpid": "Ortiz-M" }, { "family_name": "Ravichandran", "given_name": "Guruswami", "orcid": "0000-0002-2912-0001", "clpid": "Ravichandran-G" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" } ], "local_group": [ { "literal": "GALCIT" }, { "literal": "div_eng" } ], "abstract": "Compliant foams are usually characterized by a wide range of desirable mechanical properties. These properties include viscoelasticity at different temperatures, energy absorption, recoverability under cyclic loading, impact resistance, and thermal, electrical, acoustic and radiation-resistance. Some foams contain nano-sized features and are used in small-scale devices. This implies that the characteristic dimensions of foams span multiple length scales, rendering modeling their mechanical properties difficult. Continuum mechanics-based models capture some salient experimental features like the linear elastic regime, followed by non-linear plateau stress regime. However, they lack mesostructural physical details. This makes them incapable of accurately predicting local peaks in stress and strain distributions, which significantly affect the deformation paths. Atomistic methods are capable of capturing the physical origins of deformation at smaller scales, but suffer from impractical computational intensity. Capturing deformation at the so-called meso-scale, which is capable of describing the phenomenon at a continuum level, but with some physical insights, requires developing new theoretical approaches.
\r\n\r\nA fundamental question that motivates the modeling of foams is \u2018how to extract the intrinsic material response from simple mechanical test data, such as stress vs. strain response?\u2019 A 3D model was developed to simulate the mechanical response of foam-type materials. The novelty of this model includes unique features such as the hardening-softening-hardening material response, strain rate-dependence, and plastically compressible solids with plastic non-normality. Suggestive links from atomistic simulations of foams were borrowed to formulate a physically informed hardening material input function. Motivated by a model that qualitatively captured the response of foam-type vertically aligned carbon nanotube (VACNT) pillars under uniaxial compression [2011,\u201cAnalysis of Uniaxial Compression of Vertically Aligned Carbon Nanotubes,\u201d J. Mech.Phys. Solids, 59, pp. 2227\u20132237, Erratum 60, 1753\u20131756 (2012)], the property space exploration was advanced to three types of simple mechanical tests: 1) uniaxial compression, 2) uniaxial tension, and 3) nanoindentation with a conical and a flat-punch tip. The simulations attempt to explain some of the salient features in experimental data, like
\r\n1) The initial linear elastic response.
\r\n2) One or more nonlinear instabilities, yielding, and hardening.
The model-inherent relationships between the material properties and the overall stress-strain behavior were validated against the available experimental data. The material properties include the gradient in stiffness along the height, plastic and elastic compressibility, and hardening. Each of these tests was evaluated in terms of their efficiency in extracting material properties. The uniaxial simulation results proved to be a combination of structural and material influences. Out of all deformation paths, flat-punch indentation proved to be superior since it is the most sensitive in capturing the material properties.
", "doi": "10.7907/MMTW-FF91", "publication_date": "2014", "thesis_type": "phd", "thesis_year": "2014" }, { "id": "thesis:7112", "collection": "thesis", "collection_id": "7112", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05312012-162830014", "primary_object_url": { "basename": "Final_Thesis.pdf", "content": "final", "filesize": 32125998, "license": "other", "mime_type": "application/pdf", "url": "/7112/1/Final_Thesis.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Deformation Mechanisms in Nanoscale Single Crystalline Electroplated Copper Pillars", "author": [ { "family_name": "Jennings", "given_name": "Andrew Tynes", "clpid": "Jennings-Andrew-Tynes" } ], "thesis_advisor": [ { "family_name": "Greer", "given_name": "Julia R.", "clpid": "Greer-J-R" } ], "thesis_committee": [ { "family_name": "Johnson", "given_name": "William Lewis", "clpid": "Johnson-W-L" }, { "family_name": "Fultz", "given_name": "Brent T.", "clpid": "Fultz-B-T" }, { "family_name": "Kochmann", "given_name": "Dennis M.", "clpid": "Kochmann-D-M" }, { "family_name": "Greer", "given_name": "Julia R.", "clpid": "Greer-J-R" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "Scientific research in nanotechnology has enabled advances in a diverse range of applications, such as: electronics, chemical sensing, and cancer treatment. In order to transition these nanotechnology-driven innovations out of the laboratory and into real-world applications, the resilience and mechanical reliability of nanoscale structures must be well understood in order to preserve functionality under real-world operating environments. Understanding the mechanical properties of nanoscale materials is especially important because several authors have shown that single crystalline metal pillars produced through focused-ion-beam milling have unique properties when the pillar diameter, D, approaches nanotechnology-relevant dimensions. The strength, \u03c3, of these pillars is size-dependent and is well described through a power-law relation showing that smaller is stronger: \u03c3\u221dD^(-n), where n is the exponent and is found to be 0.5\u2264n\u22641.0 in face-centered-cubic metals. In this work, the fundamental deformation mechanisms governing the size-dependent mechanical properties are investigated through uniaxial compression and tension tests of electroplated single crystalline copper pillars with diameters between 75 nm and 1000 nm. At larger pillar diameters, D >125 nm, these copper pillars are shown to obey a similar size-dependent regime, demonstrating that the \u201csmaller is stronger\u201d phenomenon is a function of the pillar microstructure, as opposed to the fabrication route. Furthermore, the dominant dislocation mechanism in this size-dependent regime is shown to be the result of single-arm, or spiral, sources. At smaller pillar diameters, D\u2264125 nm, a strain-rate-dependent mechanism transition is observed through both the size-strength relation and also quantitative, experimental measures of the activation volume. This new deformation regime is characterized by a size-independent strength and is governed by surface dislocation nucleation, a thermally activated mechanism sensitive to both temperature and strain-rate. Classical, analytical models of surface source-nucleation are shown to be insufficient to describe either the quantitative strength or the nucleation site preference. As a result, a combination of atomistic chain-of-states simulations and semi-analytical continuum models are developed in order to achieve a realistic, intuitive understanding of surface nucleation processes. ", "doi": "10.7907/6128-HG61", "publication_date": "2012", "thesis_type": "phd", "thesis_year": "2012" }, { "id": "thesis:6454", "collection": "thesis", "collection_id": "6454", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05262011-141718914", "primary_object_url": { "basename": "PhDthesis_Hutchens-S-B_2011(embedded-movies).pdf", "content": "final", "filesize": 64256089, "license": "other", "mime_type": "application/pdf", "url": "/6454/2/PhDthesis_Hutchens-S-B_2011(embedded-movies).pdf", "version": "v6.0.0" }, "type": "thesis", "title": "Deformation Behavior and Mechanical Analysis of Vertically Aligned Carbon Nanotube (VACNT) Bundles", "author": [ { "family_name": "Hutchens", "given_name": "Shelby Brooke", "orcid": "0000-0003-0349-1792", "clpid": "Hutchens-Shelby-Brooke" } ], "thesis_advisor": [ { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" }, { "family_name": "Wang", "given_name": "Zhen-Gang", "orcid": "0000-0002-3361-6114", "clpid": "Wang-Zhen-Gang" } ], "thesis_committee": [ { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" }, { "family_name": "Wang", "given_name": "Zhen-Gang", "orcid": "0000-0002-3361-6114", "clpid": "Wang-Zhen-Gang" }, { "family_name": "Daraio", "given_name": "Chiara", "orcid": "0000-0001-5296-4440", "clpid": "Daraio-C" }, { "family_name": "Flagan", "given_name": "Richard C.", "orcid": "0000-0001-5690-770X", "clpid": "Flagan-R-C" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "Vertically aligned carbon nanotubes (VACNTs) serve as integral components in a variety of applications including MEMS devices, energy absorbing materials, dry adhesives, light absorbing coatings, and electron emitters, all of which require structural robustness. It is only through an understanding of VACNT\u2019s structural mechanical response and local constitutive stress-strain relationship that future advancements through rational design may take place. Even for applications in which the structural response is not central to device performance, VACNTs must be sufficiently robust and therefore knowledge of their microstructure-property relationship is essential. This thesis first describes the results of in situ uniaxial compression experiments of 50 micron diameter cylindrical bundles of these complex, hierarchical materials as they undergo unusual deformation behavior. Most notably they deform via a series of localized folding events, originating near the bundle base, which propagate laterally and collapse sequentially from bottom to top. This deformation mechanism accompanies an overall foam-like stress-strain response having elastic, plateau, and densification regimes with the addition of undulations in the stress throughout the plateau regime that correspond to the sequential folding events. Microstructural observations indicate the presence of a strength gradient, due to a gradient in both tube density and alignment along the bundle height, which is found to play a key role in both the sequential deformation process and the overall stress-strain response. Using the complicated structural response as both motivation and confirmation, a finite element model based on a viscoplastic solid is proposed. This model is characterized by a flow stress relation that contains an initial peak followed by strong softening and successive hardening. Analysis of this constitutive relation results in capture of the sequential buckling phenomenon and a strength gradient effect. This combination of experimental and modeling approaches motivates discussion of the particular microstructural mechanisms and local material behavior that govern the non-trivial energy absorption via sequential, localized buckle formation in the VACNT bundles.", "doi": "10.7907/BPW6-Z145", "publication_date": "2011", "thesis_type": "phd", "thesis_year": "2011" } ]