Molten regolith electrolysis (MRE) is a promising in situ resource utilization process that produces both metals and O2 through the direct electrolysis of molten lunar regolith (dirt), in support of a permanent human presence on the Moon. However, MRE requires an operational temperature of 1600\u00b0C, involves contact with corrosive molten regolith, and causes an oxidizing atmosphere during electrolysis. These conditions prevent the usage of many refractory materials due to rapid degradation. Moreover, there are additional challenges associated with MRE, such as bubble detachment and O2 collection at the anode.
\r\n\r\nIn this thesis, a hollow anode design, composed of an oxygen-conducting yttria-stabilized zirconia (YSZ) shell and a platinum current collector, is presented to address the challenges of MRE. Research is performed to evaluate the performance of YSZ electrolytes and containment materials in the extreme MRE environment and identify the mechanisms governing their degradation. From these experiments, a laboratory-scale MRE cell is designed and fabricated to support hollow anode testing. Electrolysis experiments with lunar regolith simulants successfully demonstrate sustained oxygen production for up to 12 hours. Extended testing with a degradation mitigation strategy further increases O2 production efficiencies and enables cumulative operation of 40 hours, establishing design life estimates for YSZ hollow anodes and guidelines for integration into industrial-scale MRE systems.
\r\n\r\nA previously unreported Sc2O3-rich phase, silicon aluminum scandate (SAS), is discovered while performing materials compatibility testing. The crystal structure of SAS is solved using microcrystal electron diffraction, and its material properties are characterized. These results indicate that SAS is an entropy-stabilized oxide with potential applications as a thermally insulating, refractory oxide material.
\r\n\r\nUltimately, the work presented demonstrates the feasibility of YSZ hollow anodes for MRE and expands the understanding of ceramic behavior in molten oxide environments. The successful production of O2 with a hollow anode provides a foundation for scaling MRE toward industrial operation on the lunar surface, while the discovery of SAS highlights the potential for uncovering new oxide materials in extreme environments.
", "doi": "10.7907/41bv-7696", "publication_date": "2026", "thesis_type": "phd", "thesis_year": "2026" }, { "id": "thesis:17716", "collection": "thesis", "collection_id": "17716", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:10072025-232922980", "primary_object_url": { "basename": "mchaffie_daniel_2026_redacted.pdf", "content": "final", "filesize": 43106664, "license": "other", "mime_type": "application/pdf", "url": "/17716/2/mchaffie_daniel_2026_redacted.pdf", "version": "v7.0.0" }, "type": "thesis", "title": "Computational and Data-Driven Discovery of Li Solid-State Electrolytes: From Representation to Experimental Realization", "author": [ { "family_name": "McHaffie", "given_name": "Daniel Brendan", "orcid": "0000-0002-7265-7584", "clpid": "McHaffie-Daniel-Brendan" } ], "thesis_advisor": [ { "family_name": "See", "given_name": "Kimberly", "orcid": "0000-0002-0133-9693", "clpid": "See-Kimberly" } ], "thesis_committee": [ { "family_name": "Faber", "given_name": "Katherine T.", "orcid": "0000-0001-6585-2536", "clpid": "Faber-K-T" }, { "family_name": "Atwater", "given_name": "Harry Albert", "orcid": "0000-0001-9435-0201", "clpid": "Atwater-H-A" }, { "family_name": "Bernardi", "given_name": "Marco", "orcid": "0000-0001-7289-9666", "clpid": "Bernardi-Marco" }, { "family_name": "See", "given_name": "Kimberly", "orcid": "0000-0002-0133-9693", "clpid": "See-Kimberly" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "Improvements in energy storage are required to facilitate the transition to renewable energy and the electrification of transport. Lithium-ion batteries (LIBs) are a promising solution, but the current leading chemistry, consisting of a layered oxide cathode and a graphite anode separated by a liquid electrolyte, has been optimized to near-theoretical limits. Replacing the graphitic carbon with Li metal would significantly improve energy density but the instability of the Li metal-electrolyte interface introduces performance and safety challenges. Using a solid-state electrolyte (SSE) to construct an all-solid-state battery (ASSB) could mitigate these issues. However, an ideal SSE material has yet to be identified.
\r\n \r\nThousands of known Li-containing materials have not yet been evaluated as SSEs. Data-driven methods could prioritize materials for experimental study but have historically lacked sufficient data and optimal representations. Chapter 2 presents the largest structure-ionic conductivity database to date and uses semi-supervised learning to determine the highest-performing descriptors. From ~26,000 Li-containing materials, 212 candidates are identified and screened using semi-empirical and first-principles calculations. Li3BS3 exhibits ionic conductivity above 10-3 S cm-1 with defect engineering through substitution and mechanical milling.
\r\n \r\nChapter 3 explores Cl, Al, and Si substitution in Li3BS3 to reveal mechanisms of ionic conductivity enhancement. At low substitution levels, conductivity improvements are driven by disordered environments from reduced crystallinity and microstructural effects. For Cl and Al, higher substitution generates fully amorphous phases with ionic conductivity above 10-4 S cm-1. Sufficient Si substitution produces novel crystalline phases with conductivities exceeding 10-3 S cm-1.
\r\n \r\nPrevious approaches, such as that in Chapter 2, could not represent disordered compounds, excluding much of the training data and candidate materials. This is particularly significant given the importance of disorder highlighted in Chapters 2 and 3 and the prevalence of disorder in known superionic conductors. Chapter 4 implements a transfer-learned graph representation compatible with disordered structures. A larger database is curated and used to train models for screening all known Li-containing materials. Experimental validation of superionic conductivity in an identified candidate demonstrates the utility of this graph-based approach for discovering experimentally relevant, high-performance materials.
", "doi": "10.7907/fn7h-vz84", "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", "primary_object_url": { "basename": "Yingjin Wang_2026_Thesis.pdf", "content": "final", "filesize": 5924868, "license": "other", "mime_type": "application/pdf", "url": "/18514/5/Yingjin Wang_2026_Thesis.pdf", "version": "v8.0.0" }, "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:18643", "collection": "thesis", "collection_id": "18643", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05262026-225330605", "primary_object_url": { "basename": "gorske_thesis.pdf", "content": "final", "filesize": 9253119, "license": "other", "mime_type": "application/pdf", "url": "/18643/2/gorske_thesis.pdf", "version": "v5.0.0" }, "type": "thesis", "title": "In-Situ Synchrotron Studies of Microstructural Effects on Brittle Fracture", "author": [ { "family_name": "Gorske", "given_name": "Sara Frances", "orcid": "0000-0002-1329-962", "clpid": "Gorske-Sara-Frances" } ], "thesis_advisor": [ { "family_name": "Faber", "given_name": "Katherine T.", "orcid": "0000-0001-6585-2536", "clpid": "Faber-K-T" } ], "thesis_committee": [ { "family_name": "Bhattacharya", "given_name": "Kaushik", "orcid": "0000-0003-2908-5469", "clpid": "Bhattacharya-K" }, { "family_name": "Fultz", "given_name": "Brent T.", "orcid": "0000-0002-6364-8782", "clpid": "Fultz-B-T" }, { "family_name": "Voorheese", "given_name": "Peter", "orcid": "0000-0003-2769-392X", "clpid": "Voorhees-Peter-W" }, { "family_name": "Faber", "given_name": "Katherine T.", "orcid": "0000-0001-6585-2536", "clpid": "Faber-K-T" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "Brittle fracture, despite having been mathematically described more than a century ago, has remained a difficult topic of experimental and computational study. While the end states of brittle materials which have failed via fracture have been characterized using post-mortem fractography, sequential focused-ion beam studies, and tomography, the intermediate stages of brittle crack growth are difficult to study due to the unstable and fast nature of crack propagation. As a result, only partial characterization of a full crack front in a brittle material has been achieved, via two-dimensional studies or in simple systems that lack the complexity of most materials used in real-world applications. Presented in this thesis is a novel method of studying brittle cracks and their interaction with material microstructures using a combination of high-energy synchrotron X-ray radiation, precise loading, and a geometry capable of achieving stable crack growth, the double-cleavage drilled compression geometry. Cracks in two materials, a glass-ceramic with an alkali-aluminosilicate matrix and cubic crystals, and polycrystalline aluminum oxynitride, are characterized using this method. Full three-dimensional reconstructions of cracks at multiple loading steps are obtained via X-ray micro-computed tomography; the sizes, orientations, and strains of grains in the surrounding microstructures are characterized using both near-field and far-field high-energy diffraction microscopy; and the relationship between the crack paths and the microstructures is explored, elucidating behavior such as crack deflection in the presence of residual stress, intergranular versus transgranular crack motion through grains, and crack arrest after extension. Individual grain orientations and mechanical states are not found to be predictive as to whether a grain will crack in a certain manner, but average and cumulative properties for ensembles of grains around and ahead of the crack front have a significant effect on the length to which it extends and the fracture toughness.", "doi": "10.7907/2d9j-a075", "publication_date": "2026", "thesis_type": "phd", "thesis_year": "2026" }, { "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:17276", "collection": "thesis", "collection_id": "17276", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05272025-224848756", "type": "thesis", "title": "Mechanical Characterization of Irregular Architected Two-Phase Materials", "author": [ { "family_name": "Fox", "given_name": "Chelsea Brae", "orcid": "0009-0002-6612-8309", "clpid": "Fox-Chelsea-Brae" } ], "thesis_advisor": [ { "family_name": "Daraio", "given_name": "Chiara", "orcid": "0000-0001-5296-4440", "clpid": "Daraio-C" } ], "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": "Fu", "given_name": "Xiaojing", "orcid": "0000-0001-7120-704X", "clpid": "Fu-Xiaojing" }, { "family_name": "Faber", "given_name": "Katherine T.", "orcid": "0000-0001-6585-2536", "clpid": "Faber-K-T" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "Architected materials offer a wide range of mechanical properties through the choice of their constitutive materials and the design of their structure. Periodic architected materials are the most widely studied and used in practical applications, as their repeating unit cells are easy to design, fabricate, and analytically model, but these materials are only a small subset of the possible design space. Irregular architected materials, which are aperiodic but not necessarily stochastic, offer a way to achieve a wider design space of mechanical properties.
\r\n\r\nIn this thesis, we explore the design space of irregular architected materials and relate structural irregularity to the mechanical properties using measures of topology and geometry. We show that these measures of irregularity can be used to spatially and temporally control the mechanical response across linear and non-linear regimes, including fracture and dynamic impact, and we show that irregularity leads to improved mechanical properties when compared with periodic equivalents. To generate the irregular architected materials, we use a virtual growth algorithm, which imitates the stochastic growth process of biological structures by assembling a finite set of building blocks according to local connectivity rules. By varying the building blocks and connectivity rules, we show how to achieve a wide range of structures with varying degrees of irregularity all the way up to fully periodic structures. This thesis primarily focuses on the fabrication and characterization of additively manufactured two-phase polymer composites, but the design methods and irregular structure characterizations are material-agnostic, opening up a wide design space for future architected materials which use irregularity to achieve excellent mechanical performances.
", "doi": "10.7907/58vg-9217", "publication_date": "2025", "thesis_type": "phd", "thesis_year": "2025" }, { "id": "thesis:17264", "collection": "thesis", "collection_id": "17264", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05222025-165729471", "primary_object_url": { "basename": "pham_kim_2024_thesis-final.pdf", "content": "final", "filesize": 41860246, "license": "other", "mime_type": "application/pdf", "url": "/17264/1/pham_kim_2024_thesis-final.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Application of Ultrafast Spectroscopy Techniques to Probe Correlated Ion Hopping Mechanisms in Solid-State Ion Conductors", "author": [ { "family_name": "Pham", "given_name": "Kim Hoang", "orcid": "0000-0003-4053-6363", "clpid": "Pham-Kim-Hoang" } ], "thesis_advisor": [ { "family_name": "Cushing", "given_name": "Scott K.", "orcid": "0000-0003-3538-2259", "clpid": "Cushing-Scott-K" }, { "family_name": "See", "given_name": "Kimberly", "orcid": "0000-0002-0133-9693", "clpid": "See-Kimberly" } ], "thesis_committee": [ { "family_name": "Blake", "given_name": "Geoffrey A.", "orcid": "0000-0003-0787-1610", "clpid": "Blake-G-A" }, { "family_name": "Stoltz", "given_name": "Brian M.", "orcid": "0000-0001-9837-1528", "clpid": "Stoltz-B-M" }, { "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": "Cushing", "given_name": "Scott K.", "orcid": "0000-0003-3538-2259", "clpid": "Cushing-Scott-K" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "Superionic conductors, or solid-state ion conductors that surpass the ionic con- ductivity of its liquid counterpart, can enable more energy dense batteries, robust artificial ion pumps, and optimized fuel cells. The mechanisms enabling superionic conductivity still remain elusive, though many-body correlations between the mi- grating ions, lattice vibrational modes, and charge screening clouds have all been posited to greatly enhance ionic conduction. Most spectroscopic techniques cannot directly probe and validate the role of such correlations due to their inability to transiently resolve these ultrafast dynamics occurring at picosecond timescales. In this work, we develop an ultrafast technique that measures the time-resolved change in impedance while a light source ranging from UV to THz frequencies selectively excites an ion-coupled correlation. The technique is used to compare the relative changes in impedance of a solid-state Li\u207a conductor Li0.5La0.5TiO3 (LLTO) before and after light excitation to elucidate the role of charge screening clouds, optical phonons, and acoustic phonons on ion migration. From our techniques, we deter- mine that electronic screening and rocking phonon-mode interactions significantly dominate the ion migration pathway of LLTO compared to acoustic phonons. Al- though we only present one case study, our technique can extend to O\u00b2\u207b, H\u207a, or other charge carrier transport phenomena where ultrafast correlations control transport. Furthermore, the temporal relaxation of the measured impedance can distinguish ion transport effects caused by many-body correlations, optical heating, correlation, and memory behavior.", "doi": "10.7907/825x-r459", "publication_date": "2025", "thesis_type": "phd", "thesis_year": "2025" }, { "id": "thesis:17097", "collection": "thesis", "collection_id": "17097", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:03272025-184257192", "type": "thesis", "title": "Investigation and Control of the Electrode/Electrolyte Interface in Electrochemical Systems", "author": [ { "family_name": "Lee", "given_name": "Brian Chansol", "orcid": "0000-0002-0898-0838", "clpid": "Lee-Brian-Chansol" } ], "thesis_advisor": [ { "family_name": "See", "given_name": "Kimberly", "orcid": "0000-0002-0133-9693", "clpid": "See-Kimberly" } ], "thesis_committee": [ { "family_name": "Agapie", "given_name": "Theodor", "orcid": "0000-0002-9692-7614", "clpid": "Agapie-T" }, { "family_name": "Cushing", "given_name": "Scott K.", "orcid": "0000-0003-3538-2259", "clpid": "Cushing-Scott-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" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "In electrochemical reactions, the electrode/electrolyte interface is of vital importance, as no reactivity occurs in the bulk electrode or the electrolyte. Often, the interface can be the difference between a successful reaction and a failure. In this thesis, we present three works wherein the electrode/electrolyte interface is studied and controlled to drive desired electrochemical reactivity. A Mg-In alloy is employed for Mg metal batteries to prevent Mg dendrite growth, which can cause cell shorting and failure. By coating the surface of Mg metal electrodes with the Mg-In alloy, the nucleation of Mg dendrites is suppressed and instead the Mg electroalloys into the surface alloy upon reduction, significantly increasing the cell life time. Next, the Li-intercalation material LiTiS\u2082 is studied for use in organic reductive electrosynthesis as counter anodes. Traditional metal sacrificial counter anodes are known to cause issues such as surface passivation, chemical reactivity, and cross-plating at the working electrode, which is deleterious to the desired organic reactivity. It is found that LiTiS\u2082 surface is less reactive in organic electrolytes, reducing both passivation and chemical reactivity. Further, Li\u207a de-intercalated from LiTiS\u2082 oxidation is found to be less susceptible to cross-plating than Zn, a common sacrificial anode. Finally, the effect of electrode material on the electrochemical reduction of \u1d57BuI is studied. Using electrochemical characterization, it is found that the reduction is catalyzed on Au and Ag through adsorption of the initial substrate, as well as the adsorption of the reactive intermediate tBu radical. The catalysis of \u1d57BuI reduction can have meaningful consequences for organic reactivity, driving the desirable generation of the carbanion nucleophile from alkyl halide reactants.", "doi": "10.7907/fz2d-pe37", "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:16440", "collection": "thesis", "collection_id": "16440", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05302024-015407649", "primary_object_url": { "basename": "Zachery_Iton_Caltech_Thesis_2024_V2.pdf", "content": "final", "filesize": 56370845, "license": "other", "mime_type": "application/pdf", "url": "/16440/1/Zachery_Iton_Caltech_Thesis_2024_V2.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Superionic Conduction of Next-Generation Mobile Ions in Solids Enabled by Coordinating Ligands", "author": [ { "family_name": "Iton", "given_name": "Zachery William Benjamin", "orcid": "https://orcid.org/0000-0002-2226-9006", "clpid": "Iton-Zachery-William-Benjamin" } ], "thesis_advisor": [ { "family_name": "See", "given_name": "Kimberly", "orcid": "0000-0002-0133-9693", "clpid": "See-Kimberly" } ], "thesis_committee": [ { "family_name": "Faber", "given_name": "Katherine T.", "orcid": "0000-0001-6585-2536", "clpid": "Faber-K-T" }, { "family_name": "Atwater", "given_name": "Harry Albert", "orcid": "0000-0001-9435-0201", "clpid": "Atwater-H-A" }, { "family_name": "Greer", "given_name": "Julia R.", "orcid": "0000-0002-9675-1508", "clpid": "Greer-J-R" }, { "family_name": "See", "given_name": "Kimberly", "orcid": "0000-0002-0133-9693", "clpid": "See-Kimberly" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "Advancements in battery technologies are a critical step towards meeting the growing demand for sustainable energy storage solutions. The development of next-generation battery technologies using \"beyond-Li\" ions, like Na\u207a, K\u207a, Mg\u00b2\u207a, Ca\u00b2\u207a, Zn\u00b2\u207a, and Al\u00b3\u207a, could potentially offer improved performance, safety, and cost-effectiveness over traditional lithium-ion systems. However, the realization of next-generation battery technology based on \"beyond-Li\" mobile ions is limited, in part, due to a lack of understanding of solid state conduction of next-generation ions, which governs ion transport in electrodes, interphases, and solid electrolytes. \u201cBeyond-Li\u201d ions tend to have relatively low mobility in solids due to: (1) the larger ionic radii (Na\u207a, K\u207a, Ca\u00b2\u207a), which limit the accessible migration pathways, or (2) higher charge densities (Mg\u00b2\u207a, Zn\u00b2\u207a Al\u00b3\u207a), which results in strong electrostatic interactions within the solid.
\r\n \r\nThis work discusses several structure-property relationships and structural modifications that are hypothesized to lead to facile conduction of next-generation working ions. A notable discovery is the superionic conductivity of ZnPS3 after exposure to humid environments. Water is introduced into the grain boundaries, thereby enabling Zn\u00b2\u207a ions from the material to migrate and conduct freely in the network of adsorbed water. The introduction of water leads to potential H\u207a, therefore a methodology for decoupling the contributions of Zn\u00b2\u207a and H\u207a in mixed ionic conducting solids using ion-selective EIS, transference number measurements, and deposition experiments is established.
\r\n \r\nFurther extending this approach, superionic conductivity of other next-generation ions in electronically-insulating inorganic solids is achieved by leveraging the established ion exchange/intercalation mechanism of MPS3 (M = Cd, Mn) materials. The mobile cations that are introduced are coordinated with H2O ligands which simultaneously increase the size of the bottlenecks within the migration pathway and screen the charge-dense ions resulting in high mobilities. Potential applications can be extended to water-incompatible systems by replacing the water ligands with aprotic molecules.
\r\n \r\nThese insights contribute significantly to the understanding and development of next-generation battery technologies, representing an important step toward the development of more sustainable and efficient energy storage solutions.
", "doi": "10.7907/fwyd-2w86", "publication_date": "2024", "thesis_type": "phd", "thesis_year": "2024" }, { "id": "thesis:16242", "collection": "thesis", "collection_id": "16242", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:11082023-043634180", "primary_object_url": { "basename": "thesis v2.5 Chen-Hsuan Lu.pdf", "content": "final", "filesize": 11189287, "license": "other", "mime_type": "application/pdf", "url": "/16242/16/thesis v2.5 Chen-Hsuan Lu.pdf", "version": "v7.0.0" }, "type": "thesis", "title": "Strategic Advances in 2D Materials: Low-Temperature Plasma-Enhanced Chemical Vapor Deposition Growth of Graphene and Complementary Insights into MoS\u2082", "author": [ { "family_name": "Lu", "given_name": "Chen-Hsuan", "orcid": "0000-0002-4802-1332", "clpid": "Lu-Chen-Hsuan" } ], "thesis_advisor": [ { "family_name": "Yeh", "given_name": "Nai-Chang", "orcid": "0000-0002-1826-419X", "clpid": "Yeh-Nai-Chang" } ], "thesis_committee": [ { "family_name": "Fabe", "given_name": "Katherine T.", "orcid": "0000-0001-6585-2536", "clpid": "Faber-K-T" }, { "family_name": "Falso", "given_name": "Joseph", "orcid": "0000-0003-3183-9864", "clpid": "Falson-Joseph" }, { "family_name": "Goddard", "given_name": "William A., III", "orcid": "0000-0003-0097-5716", "clpid": "Goddard-W-A-III" }, { "family_name": "Yeh", "given_name": "Nai-Chang", "orcid": "0000-0002-1826-419X", "clpid": "Yeh-Nai-Chang" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "This thesis explores the intricate details of the plasma-enhanced chemical vapor deposition (PECVD) technique for growing graphene on various substrates at low temperatures. The research begins by finely optimizing the PECVD growth conditions to produce high-quality graphene on copper ink, which can potentially be used in a wide range of flexible electronics and Internet of Things (IoT) devices. The study also showcases that PECVD is an effective technique for growing graphene directly on electroplated copper over polyimide substrates, which greatly improves the resilience and environmental stability of copper circuits.
\r\n\r\nFurthermore, the research investigates the possibility of using PECVD to grow graphene on gold, which can be a game-changer in anti-corrosion applications and increase the longevity of gold electrode-based biosensors. The study also makes a significant breakthrough by growing nanocrystalline multilayer graphene on silver in a single step, which demonstrates exceptional oxidation resistance and opens new opportunities for hybrid graphene-silver plasmonic technologies.
\r\n\r\nLastly, the thesis examines the potential and complexities of using electrodeposited (ED) copper foil as a graphene growth substrate, showing significant transformations in the properties of the ED copper foil post PECVD process. Towards the latter part of this work, attention is briefly shifted to explore the unique dipole ordering properties of monolayer molybdenum disulfide (MoS2) single crystals, which are synthesized using high-temperature chemical vapor deposition (CVD) and are van der Waals materials like graphene. Although not the main focus, this inclusion offers valuable insights into contrasting attributes and functionalities of graphene and MoS2, especially in areas like high-density data storage and non-volatile memories, and also compares the status of synthesis methods of these two types of van der Waals materials.
\r\n\r\nAlongside these investigations, the thesis also touches upon the prospects of both large-area PECVD graphene growth and interfacial graphene growth, identifying future paths for research and innovation. This comprehensive study highlights the versatility of low-temperature PECVD for graphene synthesis and provides insights that may reshape research and applications in flexible electronics, biosensing, and beyond. The findings of this research therefore pave ways for researchers, technology developers, and businesses to explore realistic technological applications of graphene and two-dimensional materials in various industries.
", "doi": "10.7907/cetf-ns02", "publication_date": "2024", "thesis_type": "phd", "thesis_year": "2024" }, { "id": "thesis:16490", "collection": "thesis", "collection_id": "16490", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:06032024-223707990", "primary_object_url": { "basename": "Final Thesis - MS.pdf", "content": "final", "filesize": 11000714, "license": "other", "mime_type": "application/pdf", "url": "/16490/1/Final Thesis - MS.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Exploring Thermal Photonics for Sustainability: From Selective Solar Absorbers to Terrestrial Radiative Cooling", "author": [ { "family_name": "Su", "given_name": "Magel Powei", "orcid": "0000-0003-4898-5024", "clpid": "Su-Magel-Powei" } ], "thesis_advisor": [ { "family_name": "Atwater", "given_name": "Harry Albert", "orcid": "0000-0001-9435-0201", "clpid": "Atwater-H-A" } ], "thesis_committee": [ { "family_name": "Faber", "given_name": "Katherine T.", "orcid": "0000-0001-6585-2536", "clpid": "Faber-K-T" }, { "family_name": "Nadj-Perge", "given_name": "Stevan", "orcid": "0000-0002-2394-9070", "clpid": "Nadj-Perge-S" }, { "family_name": "Minnich", "given_name": "Austin J.", "orcid": "0000-0002-9671-9540", "clpid": "Minnich-A-J" }, { "family_name": "Atwater", "given_name": "Harry Albert", "orcid": "0000-0001-9435-0201", "clpid": "Atwater-H-A" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "Photonic materials for thermal emission control have attracted much attention in sustainable technologies where energy and heat management are highly desirable. Controlling the frequency dependency of emissivity enables passive suppression or enhancement of thermal emission which can be used to exploit thermodynamically favorable conditions.
\r\n\r\nIn Part I, we present the development of a selective solar absorber which suppresses thermal emission for efficient conversion of solar energy into thermal energy. Our absorber uses an ultrathin metal layer and an antireflective coating to suppress thermal emission and enhance solar absorption, respectively. Furthermore, we constructed a novel scalable photothermal reactor which utilizes the selective solar absorber for thermocatalytic processes. Thermochemical processes provide a sustainable alternative for fuel synthesis compared to traditional industrial methods, and catalyzed processes operate at reduced temperatures and pressures allowing them to be powered solely by direct solar thermal energy. Using sunlight, we synthesized C\u2086 \u2013 C\u2082\u2084 carbon chain length olefins from ethylene gas with Ni-catalyzed ethylene oligomerization, demonstrating a vital step for direct CO\u2082 to sustainable aviation fuel synthesis.
\r\n\r\nIn Part II, we present silicon oxide and silicon nitride bilayer laminate nanoparticle films as scalable efficient daytime terrestrial radiative coolers which couple enhanced thermal emission with the cold background of space. We show experimentally that laminate nanoparticle films deposited from a nonthermal plasma are well described by effective medium mixing models, and their fill fraction tunability enables them to spectrally match more efficiently to the atmospheric transmission window than conventional dense laminate thin films. During this process, we realized a need for directly measuring thermal emission in a controlled ambient to facilitate inter-comparisons between radiative cooling performances. In response, we constructed a new instrument for direct spectrally and angularly resolved radiative emission measurements, providing a new avenue to study the thermal emission behavior of photonic materials.
", "doi": "10.7907/rrf2-4979", "publication_date": "2024", "thesis_type": "phd", "thesis_year": "2024" }, { "id": "thesis:16457", "collection": "thesis", "collection_id": "16457", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:06012024-040012207", "type": "thesis", "title": "Freeze-Cast Porous Ceramics: Tailoring Chemistry and Porosity for Functionality", "author": [ { "family_name": "Quinn", "given_name": "Laura Katherine", "orcid": "0000-0002-6112-028X", "clpid": "Quinn-Laura-Katherine" } ], "thesis_advisor": [ { "family_name": "Faber", "given_name": "Katherine T.", "orcid": "0000-0001-6585-2536", "clpid": "Faber-K-T" } ], "thesis_committee": [ { "family_name": "See", "given_name": "Kimberly", "orcid": "0000-0002-0133-9693", "clpid": "See-Kimberly" }, { "family_name": "Gray", "given_name": "Harry B.", "orcid": "0000-0002-7937-7876", "clpid": "Gray-H-B" }, { "family_name": "Kornfield", "given_name": "Julia A.", "orcid": "0000-0001-6746-8634", "clpid": "Kornfield-J-A" }, { "family_name": "Faber", "given_name": "Katherine T.", "orcid": "0000-0001-6585-2536", "clpid": "Faber-K-T" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "Porous ceramics have been created and utilized in applications ranging from the automotive industry to biomedical research, with the chemical and pore characteristics of these ceramic structures crucial to their function and design. In this work, these intertwined factors are explored for a variety of applications by controlling the chemistry through precursor preparation and heat treatments, and the porosity controlled through freeze casting, a tunable and facile pore-forming technique yielding a range of pore sizes and morphologies. First, shape memory and superelastic behaviors in ceria-doped zirconia are observed by creating porous honeycomb structures that can accommodate the volume change of the martensitic transformation enabling such performance. By controlling dopant concentration, powder morphology, and freezing rate, the martensitic transformation is tracked over multiple cycles and collection volumes in these bulk-scale, polycrystalline zirconia ceramics. Next, transparent porous model sediments are created through heat treatments of freeze-cast synthetic cryolite (Na3AlF6) powder. Fluorescent beads the same size as many bacterial cells are visualized in a range of pore morphologies over both depth and time, and these porous ceramics are deployed in a sedimentary environment and the imaging of the microbial communities contained within and are found to colonize the porous cryolite structures. Alternate porous habitats for bacterial colonization are further created using materials such as iron oxides and carbon nanotubes to produce structures that can act both as electron acceptors and as microbial habitats. Finally, thermally anisotropic Si-based porous ceramics are developed with a potential use in optical devices. Using two contrasting preceramic polymers and both traditional and UV-assisted freeze-casting techniques, porous SiOC is produced from preceramic polymers with differing carbon contents. Together, these examples explore how the chemistry and porosity of porous ceramics can be manipulated to affect the chemical, optical, mechanical, and thermal properties of ceramic structures to best suit the intended function.", "doi": "10.7907/nj6y-4315", "publication_date": "2024", "thesis_type": "phd", "thesis_year": "2024" }, { "id": "thesis:16450", "collection": "thesis", "collection_id": "16450", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05302024-193052659", "primary_object_url": { "basename": "Pedro Guzman PhD Thesis 2024.pdf", "content": "final", "filesize": 8827433, "license": "other", "mime_type": "application/pdf", "url": "/16450/1/Pedro Guzman PhD Thesis 2024.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Developments in M\u00f6ssbauer Spectrometry: From Instrumentation to High Pressure Studies on Spins and Phonons", "author": [ { "family_name": "Guzman", "given_name": "Pedro", "orcid": "0000-0002-9726-8315", "clpid": "Guzman-Pedro" } ], "thesis_advisor": [ { "family_name": "Fultz", "given_name": "Brent T.", "orcid": "0000-0002-6364-8782", "clpid": "Fultz-B-T" } ], "thesis_committee": [ { "family_name": "Faber", "given_name": "Katherine T.", "orcid": "0000-0001-6585-2536", "clpid": "Faber-K-T" }, { "family_name": "Falson", "given_name": "Joseph", "orcid": "0000-0003-3183-9864", "clpid": "Falson-Joseph" }, { "family_name": "Scott", "given_name": "Valerie", "orcid": "0000-0002-0267-9833", "clpid": "Scott-Valerie" }, { "family_name": "Fultz", "given_name": "Brent T.", "orcid": "0000-0002-6364-8782", "clpid": "Fultz-B-T" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "The well-established technique of 57Fe M\u00f6ssbauer spectrometry is used to investigate the local chemical environment in iron-containing materials. This technique relies on the recoil-free emission and absorption of \u03b3-rays by resonant nuclei within a solid. The key component of a M\u00f6ssbauer spectrometer is the velocity Doppler drive, which modulates the energy of the incident \u03b3-rays to detect the hyperfine structure of resonant nuclei. Since the 1970s, the conventional velocity Doppler drive has been constructed using a pair of electromagnetic coils, one for power and the second for feedback. An alternative M\u00f6ssbauer spectrometer was developed, utilizing an amplified piezoelectric actuator as the Doppler velocity drive under feedback control. The actuator, driven with a quadratic displacement waveform, produced a linear velocity profile and was optimized using measurements from a laser Doppler vibrometer (LDV). In transmission geometry, 57Fe M\u00f6ssbauer spectra of \u03b1-iron display minimal peak distortions, enabling M\u00f6ssbauer spectrometry in applications requiring compact size and low mass, such as geochemical studies on the Moon, Mars, or asteroids.
\r\n\r\nSynchrotron radiation is used for numerous experimental techniques, including X-ray diffraction (XRD), nuclear resonant inelastic X-ray scattering (NRIXS), and nuclear forward scattering (NFS), also known as synchrotron M\u00f6ssbauer spectrometry. Diamond-anvil cells, capable of reaching high pressures at various temperatures, combined with synchrotron experimental methods, provide the means to investigate the vibrational, magnetic, and thermophysical properties of materials. Measurements on 57Fe55Ni45 were conducted using synchrotron XRD, NRIXS, and NFS under various pressures and temperatures. XRD measurements at 298 K and 392 K under pressures up to 20 GPa confirmed a pressure-induced Invar effect between 7 GPa and 13 GPa, where the coefficient of thermal expansion is nearly zero. NFS measurements revealed a decrease in the magnetic moment of 57Fe under pressure, indicating an increase in magnetic entropy. The 57Fe phonon density of states (DOS) was measured with NRIXS from which a phonon entropy was extracted. Using thermodynamic Maxwell relations, magnetic and phonon contributions to thermal expansion were determined, demonstrating that the low thermal expansion in the pressure-induced Invar region stems from a competition between the thermal expansion from spins and from phonons.
", "doi": "10.7907/hyry-q484", "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: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:16186", "collection": "thesis", "collection_id": "16186", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:09222023-185858765", "primary_object_url": { "basename": "Bernal_Choban_Thesis.pdf", "content": "final", "filesize": 39913083, "license": "other", "mime_type": "application/pdf", "url": "/16186/1/Bernal_Choban_Thesis.pdf", "version": "v5.0.0" }, "type": "thesis", "title": "Atomic Dynamics in Solids and Liquids from Inelastic Neutron Scattering", "author": [ { "family_name": "Bernal-Choban", "given_name": "Camille Marie", "orcid": "0000-0001-7550-3153", "clpid": "Bernal-Choban-Camille-Marie" } ], "thesis_advisor": [ { "family_name": "Fultz", "given_name": "Brent T.", "orcid": "0000-0002-6364-8782", "clpid": "Fultz-B-T" } ], "thesis_committee": [ { "family_name": "Faber", "given_name": "Katherine T.", "orcid": "0000-0001-6585-2536", "clpid": "Faber-K-T" }, { "family_name": "Falson", "given_name": "Joseph", "orcid": "0000-0003-3183-9864", "clpid": "Falson-Joseph" }, { "family_name": "Granroth", "given_name": "Garrett", "orcid": "0000-0002-7583-8778", "clpid": "Granroth-Garrett" }, { "family_name": "Fultz", "given_name": "Brent T.", "orcid": "0000-0002-6364-8782", "clpid": "Fultz-B-T" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "As temperature increases, atomic scale disorder, or entropy, drives the thermophysical properties of materials. One way it does this is by passing heat through materials in the form of vibrations. In solids, vibrational motions are called phonons, and their behaviors are used to predict macroscopic properties such as thermal expansion and thermal conductivity. Vibrational dynamics also exist in liquids but are traditionally less studied. Other forms of entropy include configurational and electronic entropy, which also evolve with temperature. Configurational changes in solids are often small, but in liquids, the prominence of diffusion makes this contribution significant. This dissertation addresses these atomistic components of entropy in two studies, one on bcc chromium and the other on the melting of monatomic systems.
\r\n\r\nIn the first study, phonon densities of states (DOS) of body-centered cubic chromium were measured by time-of-flight inelastic neutron scattering (INS) at temperatures up to 1493 K. Density functional theory calculations with both quasi-harmonic (QH) and anharmonic (AH) methods were performed at temperatures above the Neel temperature. Features in the phonon DOS decrease in energy (soften) substantially with temperature. A Born-von Karman analysis using fits to the experimental DOS reveals a softening of almost 17% of the high transverse phonon branch between 330 and 1493 K. The low transverse branch changes by approximately half this amount. The AH calculations capture the observed behavior of the two transverse phonon branches, but the QH calculations give some inverted trends. Vibrational entropies from phonons and electrons are obtained, and their sum is in excellent agreement with the entropy of chromium obtained by calorimetry, indicating that above 330 K, no explicit temperature-dependent magnetic contributions are necessary.
\r\n\r\nThe second investigation delves into the latent heat of melting, defined as TmΔSfus where Tm is the melting temperature and ΔSfus is the entropy of fusion. At the scale of atoms and electrons, ΔSfus has components from changes of atom configurations, atom vibrations, and thermal excitations of electrons. New data analyses were developed for inelastic neutron scattering to obtain changes in vibrational spectra upon melting. Combining these INS experiments with computational work using thermodynamic integration and molecular dynamics, components of ΔSfus were obtained for a total of six elements, Ge, Si, Bi, Sn, Pb, Li. Upon melting, there is always a positive change of configurational entropy, ΔSconfig. A baseline value of ΔSconfig=1.2kB/atom, approximately the value for Richard's rule, corresponds to zero change in the vibrational part of the entropy of fusion, ΔSvib. Elements having values of ΔSfus\r\nthat depart from this value of Richard's rule have both an additional ΔSvib and an additional ΔSconfig. Surprisingly, the extra ΔSconfig is close to 77% of ΔSvib, for both positive and negative deviations from Richard's rule. This implies a correlation between the change in the number of basins in a potential energy landscape and the change in the inverse of their curvature upon melting.
", "doi": "10.7907/3nv3-g144", "publication_date": "2024", "thesis_type": "phd", "thesis_year": "2024" }, { "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:15259", "collection": "thesis", "collection_id": "15259", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:06012023-173549089", "type": "thesis", "title": "Experimental Study on the Thermodynamic Interactions of Phonons and Magnetism in Fe Systems", "author": [ { "family_name": "H\u00e4geli Lohaus", "given_name": "Stefan P.", "orcid": "0000-0002-4430-3834", "clpid": "H\u00e4geli-Lohaus-Stefan-P-H\u00e4geli" } ], "thesis_advisor": [ { "family_name": "Fultz", "given_name": "Brent T.", "orcid": "0000-0002-6364-8782", "clpid": "Fultz-B-T" } ], "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": "Alp", "given_name": "Esen E.", "clpid": "Alp-Esen-E" }, { "family_name": "Scott", "given_name": "Valerie", "clpid": "Scott-Valerie" }, { "family_name": "Fultz", "given_name": "Brent T.", "orcid": "0000-0002-6364-8782", "clpid": "Fultz-B-T" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "The macroscopic thermophysical behavior of materials is governed by their atomic level excitations and how they store heat. Most of the thermal energy excites oscillations of the atoms, quantized as phonons, but in magnetic materials a considerable amount of heat is also absorbed by fluctuations of the electronic spins. This thesis explores the thermodynamics of phonons and magnetic spins in Fe-systems: we investigate the coupling between these excitations in Fe, Fe-Ni, and Fe-C, quantify their size dependency in nanocrystalline in Ni\u2083Fe, and assess their individual roles in the anomalous thermal expansion of Fe-Ni Invar.
\r\n \r\nMost materials expand when heated due to enhanced atomic oscillations. However, in 1895 C.E. Guillaume combined Fe and Ni to discover a material with near-zero thermal expansion, called Invar. This discovery was awarded the 1920 Physics Nobel Prize and sparked thousands of scientific investigations. Since the anomalous Invar effect is associated with magnetism, nearly all studies have focused on the electronic and spin structure of Fe-Ni. But phonons are needed to complete the picture, and to date, the anomalous Invar behavior is not fully understood. Here, we explore a method for measuring thermal expansion that is capable of isolating contributions from phonons and spins. Since the thermal energy of materials is related to entropy, the thermal expansion can be indirectly determined through individual entropic contributions by using a Maxwell relation. The phonon and magnetic entropies were measured by combining two nuclear resonant x-ray scattering techniques, with samples under pressure in diamond-anvil cells. We show that the Invar behavior stems from a competition between phonons and spins, that oppose each other for near-zero thermal expansion. A spin-phonon coupling improves the precision of this cancellation, extending the range of Invar behavior.
\r\n \r\nSuch a coupling of phonons and spin was also observed in pure Fe and Fe\u2083C cementite, as their phonon energies correlate to the change in magnetization. This motivated us to develop a magnetic quasi-harmonic model for Fe and Fe\u2083C, which accounts well for the deviation of phonon energies from pure volumetric effects of the conventional quasi-harmonic approximation.
\r\n\r\nThe thermodynamics of materials is also affected by the size of their crystallites. We determined the size effects on the heat absorption by phonons, electrons, and spins in nanocrystalline Ni\u2083Fe. All excitations become enhanced in the nanomaterial. In particular, the redistribution of spectral weights amplifies the phonon entropy. This helps stabilize the nanostructure against the enthalpy from its extra grain boundaries. However, the nanostructure is meta-stable, and the grains will grow into their bulk counterpart when diffusion is enabled at elevated temperatures.
", "doi": "10.7907/5sb5-fm96", "publication_date": "2023", "thesis_type": "phd", "thesis_year": "2023" }, { "id": "thesis:15254", "collection": "thesis", "collection_id": "15254", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:06012023-020314168", "primary_object_url": { "basename": "Meier_Thesis_Final_v2.pdf", "content": "final", "filesize": 2204784, "license": "other", "mime_type": "application/pdf", "url": "/15254/1/Meier_Thesis_Final_v2.pdf", "version": "v9.0.0" }, "type": "thesis", "title": "Inorganic Phototropism: Emergent Properties Directing Growth of Mesostructured Semiconductors", "author": [ { "family_name": "Meier", "given_name": "Madeline Claire", "orcid": "0000-0003-1608-0810", "clpid": "Meier-Madeline-Claire" } ], "thesis_advisor": [ { "family_name": "Lewis", "given_name": "Nathan Saul", "orcid": "0000-0001-5245-0538", "clpid": "Lewis-N-S" } ], "thesis_committee": [ { "family_name": "Gray", "given_name": "Harry B.", "orcid": "0000-0002-7937-7876", "clpid": "Gray-H-B" }, { "family_name": "Faber", "given_name": "Katherine T.", "orcid": "0000-0001-6585-2536", "clpid": "Faber-K-T" }, { "family_name": "Blake", "given_name": "Geoffrey A.", "orcid": "0000-0003-0787-1610", "clpid": "Blake-G-A" }, { "family_name": "Lewis", "given_name": "Nathan Saul", "orcid": "0000-0001-5245-0538", "clpid": "Lewis-N-S" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "Nature exhibits emergent growth phenomena where in neighboring features result in ensemble effects that direct the overall growth morphologies. Plants, such as palm trees, display phototropism where-in the crown grows toward the time weighted average position of the sun to optimize solar collection. A methodology, known as inorganic phototropic growth, utilizes a similar mechanism with the incident illumination during electrochemical deposition directing the growth of mesostructured semiconductors. This photoelectrochemical deposition process, generates highly anisotropic, periodic lamellar features resulting in the capability to fabricate nanostructured features over macroscopic areas. The process is lithography-free and uses no templates or directing agents of any kind and relies solely on the incident illumination to direct semiconductor growth. In this thesis, the nanophotonic phenomena and emergent synergistic absorption that drives the inorganic phototropic growth process was investigated using unconstrained and confined susbtrates. Additionally, the impact of inclined, off-normal incident illumination on the evolution of structure morphology was investigated for patterned and isotropic substrates revealing the mechanism behind the non-monotonic relationship between incident angle and observed out-of-plane orientation for unconstrained substrates.
", "doi": "10.7907/rqwq-tv81", "publication_date": "2023", "thesis_type": "phd", "thesis_year": "2023" }, { "id": "thesis:16102", "collection": "thesis", "collection_id": "16102", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:06092023-230729474", "primary_object_url": { "basename": "Chun-Wei Vince Wu_Thesis_Final_Version.pdf", "content": "final", "filesize": 6438611, "license": "other", "mime_type": "application/pdf", "url": "/16102/1/Chun-Wei Vince Wu_Thesis_Final_Version.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Freeze Casting - from Battery Separators to Ceramic Scaffolds", "author": [ { "family_name": "Wu", "given_name": "Chun-Wei Vince", "orcid": "0009-0002-4509-9713", "clpid": "Wu-Chun-Wei-Vince" } ], "thesis_advisor": [ { "family_name": "Faber", "given_name": "Katherine T.", "orcid": "0000-0001-6585-2536", "clpid": "Faber-K-T" } ], "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": "Kornfield", "given_name": "Julia A.", "orcid": "0000-0001-6746-8634", "clpid": "Kornfield-J-A" }, { "family_name": "Liu", "given_name": "Hansan", "clpid": "Liu-Hansan" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "Freeze casting is a versatile pore-forming technique which allows tunability of pore structures including pore size, size distribution, morphology, and alignment in various material systems. It is that versatility that makes freeze casting a prospective candidate for fabrication of porous components used in a wide range of fields, ranging from biomaterials to supercapacitors. This work explores freeze casting as the processing route to fabricate battery separators and ceramic scaffolds.
\r\n\r\nThe first part of this study assesses the feasibility of tape/freeze casting, a combination of tape casting and freeze casting, in fabricating battery separators for sodium-ion batteries. Poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) is chosen as the separator material due to its chemical inertness in battery environments, and dioxane is selected as the solvent for PVDF-HFP owing to its dendritic crystal structure and the absence of demixing upon freezing the solution. PVDF-HFP membranes fabricated by a bi-directional tape/freeze casting with dioxane exhibit through-thickness, directionally aligned pore structures. Although PVDF-HFP is shown to surpass reference separators in electrolyte affinity and electrochemical performance, composite strategies are designed to provide enhanced mechanical and electrochemical properties.
\r\n\r\nFirstly, the effects of alumina, a reinforcing agent introduced via ball milling with dioxane to form suspensions prior to tape/freeze casting, are examined. Composite PVDF- HFP/Al2O3 membranes show similar microstructures to their polymer counterpart, with enhanced resistance to thermal shrinkage, elastic modulus, electrolyte uptake, and ionic conductivity. Moreover, coin cells made with composite membranes deliver better rate performance and cycling stability than those with polymer membranes and filter paper reference materials.
\r\n\r\nSecondly, an alternative route to incorporate inorganic reinforcing elements into PVDF- HFP membranes is found through a co-solvent process. Silica particles from a sol-gel reaction of tetraethoxysilane (TEOS) are introduced into PVDF-HFP membranes via a co- solvent method in conjunction with dimethyl sulfoxide (DMSO). The tape/freeze-cast PVDF-HFP membranes fabricated with DMSO alone exhibit directionally aligned pores, while a hierarchical pore morphology with circular pores on the aligned pore walls is observed in composite membranes fabricated with TEOS, and hence, silica additions.\r\nComposite PVDF-HFP/SiO\u2082 membranes outperform their unreinforced polymer counterpart in terms of elastic modulus, thermal stability, electrolyte affinity, and ionic conductivity, along with capacity retention and cycling performance when assembled into coin cells.
\r\n\r\nThe final portion of this study evaluates the capability of freeze casting for highly permeable ceramic scaffolds using a polymethylsiloxane preceramic polymer with tert- butyl alcohol (TBA), a solvent creating prismatic pores without side arms that affords high permeability. A double-sided freeze-casting configuration results in more controlled freezing of the polymer solutions in comparison with the conventional single-sided counterpart, and hence a more aligned pore structure is obtained. Further improvement in pore alignment accompanied by an eight-fold increase in water permeability is realized by templating the substrate in freeze-casting molds.
", "doi": "10.7907/ghvz-q712", "publication_date": "2023", "thesis_type": "phd", "thesis_year": "2023" }, { "id": "thesis:15279", "collection": "thesis", "collection_id": "15279", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:06022023-055053747", "type": "thesis", "title": "Complex Charge Compensation Mechanisms in Lithium-Rich Chalcogenide Cathodes", "author": [ { "family_name": "Zak", "given_name": "Joshua Joseph", "orcid": "0000-0003-3793-7254", "clpid": "Zak-Joshua-Joseph" } ], "thesis_advisor": [ { "family_name": "See", "given_name": "Kimberly", "orcid": "0000-0002-0133-9693", "clpid": "See-Kimberly" } ], "thesis_committee": [ { "family_name": "Cushing", "given_name": "Scott K.", "orcid": "0000-0003-3538-2259", "clpid": "Cushing-Scott-K" }, { "family_name": "Giapis", "given_name": "Konstantinos P.", "orcid": "0000-0002-7393-298X", "clpid": "Giapis-K-P" }, { "family_name": "Faber", "given_name": "Katherine T.", "orcid": "0000-0001-6585-2536", "clpid": "Faber-K-T" }, { "family_name": "Hadt", "given_name": "Ryan G.", "orcid": "0000-0001-6026-1358", "clpid": "Hadt-Ryan-G" }, { "family_name": "See", "given_name": "Kimberly", "orcid": "0000-0002-0133-9693", "clpid": "See-Kimberly" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "Lithium-ion batteries have revolutionized the world by enabling long-lasting portable electronics, electrified transportation, and grid storage solutions for renewable energy implementation. However, current commercialized technologies are limited by the one electron transfer per transition metal paradigm utilized by cathode materials that operate with an intercalation-based charge storage mechanism. Finding ways to increase the charge storage capabilities of the cathode into the multielectron regime has long been a focus of research efforts, and involvement of structural anions in the redox has been demonstrated as a promising way to accomplish multielectron storage. Layered lithium-rich oxide materials have been shown to afford dramatic improvements to overall storage capacity but are plagued by complex mechanisms and unwanted side reactions that lead to poor cycling stability and characterization difficulties. This thesis expands upon previous understanding of oxide-based anion redox materials and extends the exploration into sulfide and selenide systems, which allow the study of anion redox without the side processes that affect oxides. First, a dynamic charge compensation mechanism of late group metal-poor, lithium-rich oxide, Li2Ru0.3Mn0.7O3, is uncovered and found to involve an irreversible anion oxidation that leads to involvement of redox states on transition metals previously thought to be unavailable. Second, active electrolyte additives are explored as a method of stabilizing the cathode-electrolyte interface of anion redox material, Li2RuO3. Third, reversible anion redox is demonstrated in alkali-rich sulfides, Li2FeS2 and LiNaFeS2, and proven to occur through oxidation of sulfides (S2-) to persulfides ([S2]2-). Understanding of the structural ramifications of anion oxidation in Li2FeS2 is further expanded through computational and experimental methods. Fourth, the role of metal-anion covalency is systematically investigated through anion substitution of Li2FeS2 with S2-, highlighting the importance of a holistic understanding of changes to the electronic and physical structure of anion redox materials to predict long-term performance. Finally, detailed perspectives and future outlooks on sulfur redox in lithium battery systems are offered with an exhaustive survey of thermodynamically stable binary and ternary persulfide materials.
", "doi": "10.7907/1k50-3811", "publication_date": "2023", "thesis_type": "phd", "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:15017", "collection": "thesis", "collection_id": "15017", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:08312022-141029875", "primary_object_url": { "basename": "CChari_Thesis_CompleteVersion.pdf", "content": "final", "filesize": 13690059, "license": "other", "mime_type": "application/pdf", "url": "/15017/2/CChari_Thesis_CompleteVersion.pdf", "version": "v5.0.0" }, "type": "thesis", "title": "Degradation of Ceramic Surfaces and its Mitigation: From Electric Propulsion to Cultural Heritage", "author": [ { "family_name": "Chari", "given_name": "Celia S.", "orcid": "0000-0001-6404-4203", "clpid": "Chari-Celia-S" } ], "thesis_advisor": [ { "family_name": "Faber", "given_name": "Katherine T.", "orcid": "0000-0001-6585-2536", "clpid": "Faber-K-T" } ], "thesis_committee": [ { "family_name": "Fultz", "given_name": "Brent T.", "orcid": "0000-0002-6364-8782", "clpid": "Fultz-B-T" }, { "family_name": "Ravichandran", "given_name": "Guruswami", "orcid": "0000-0002-2912-0001", "clpid": "Ravichandran-G" }, { "family_name": "Rossman", "given_name": "George Robert", "orcid": "0000-0002-4571-6884", "clpid": "Rossman-G-R" }, { "family_name": "McEnerney", "given_name": "Bryan W.", "orcid": "0000-0003-0869-0686", "clpid": "McEnerney-B-W" }, { "family_name": "Faber", "given_name": "Katherine T.", "orcid": "0000-0001-6585-2536", "clpid": "Faber-K-T" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "Ceramics have played an evolving role throughout human history, with the earliest known fired clay figurines dating back to 29,000-25,000 BCE in what is today the Czech Republic. Such examples of porous, low-fired potteries transitioned into vitreous and heat-resistant porcelain with the advancements of kiln technologies, which steadily grew to reach temperatures up to 1270 \u00b0C by the time of the Song Dynasty (960-1279 CE). In the modern-age, furnaces technologies have become exceedingly more sophisticated, reaching ultra-high temperatures of up to 3000 \u00b0C with dedicated calibration systems. With the advancement of firing technologies came the advancement of materials processing methods, which have transformed the role of ceramics in everyday applications: from ceramic fibers used in tennis racquets, to ceramics used in space shuttle tiles and even in artificial joints. Indeed, ceramics are candidate solutions to the most stringent material problems faced today, including high-temperature applications like electric propulsion and turbine engine systems. However, in order to improve the long-term use and sustainability of ceramics, it is essential to evaluate both their performance and their eventual degradation from mechanical wear and chemical erosion.
\r\n\r\nThis work explores the processing-microstructure-performance relationship of ceramics to better understand the performance and degradation mechanisms of ceramic surfaces. This relationship is investigated using a series of material case studies, including (i) advanced high-temperature ceramics composed of h-BN rich composites, and (ii) historic ceramics, ranging from low-fired pottery to porcelain. Details are provided for the design and manufacturing of novel high-performing ceramics, while simultaneously referring to ceramics of the past to understand how their surfaces have altered over their lifetime. Highlights of this work include the innovative use of carbothermic reactions to create h-BN surface layers for electric propulsion; self-healing strategies from AlN/BN composites; DFT-supported analysis of pottery corrosion in acidic soils; and nanoscale processing of historic porcelain glazes. These analyses provide us with an opportunity to learn from materials of the past to create more sustainable materials for the future, with an emphasis on ways of mitigating degradation by controlling processing conditions and environmental exposures.
", "doi": "10.7907/22st-q436", "publication_date": "2023", "thesis_type": "phd", "thesis_year": "2023" }, { "id": "thesis:15161", "collection": "thesis", "collection_id": "15161", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05102023-041835603", "type": "thesis", "title": "Droplet Control in Aqueous and Hydrocarbon Fluids: Long, End-Associative Polymers Dictate Fluid Behavior Under Elongational Flows", "author": [ { "family_name": "Learsch", "given_name": "Robert Whitson", "orcid": "0000-0001-6329-5879", "clpid": "Learsch-Robert-Whitson" } ], "thesis_advisor": [ { "family_name": "Kornfield", "given_name": "Julia A.", "orcid": "0000-0001-6746-8634", "clpid": "Kornfield-J-A" } ], "thesis_committee": [ { "family_name": "Faber", "given_name": "Katherine T.", "orcid": "0000-0001-6585-2536", "clpid": "Faber-K-T" }, { "family_name": "Troian", "given_name": "Sandra M.", "orcid": "0000-0003-1224-6377", "clpid": "Troian-S-M" }, { "family_name": "Nelson", "given_name": "Chris W.", "clpid": "Nelson-Chris-W" }, { "family_name": "Kornfield", "given_name": "Julia A.", "orcid": "0000-0001-6746-8634", "clpid": "Kornfield-J-A" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "Modifying elongational flows seen in sprayed mists, turbulent flows, and droplet spreading and retraction following impact, is of interest in diverse industries, including agriculture and aviation. Long flexible polymers (with fully extended lengths 1 to 10 \u00b5m) modify the elongational flow behavior of a fluid to which they are added. At low concentrations (1 to 10% of their overlap concentrations), their effect is mild under shear flow (shear viscosity increases < 50%), but dramatic under elongational flows (extensional viscosity increases \u2265 300).
\r\n\r\nThese long polymers are not widely used in practice because they degrade under strong flows, such as passing through pumps and filters, that typically precede spray. Pairwise end-associative polymers can overcome this limitation. Pulling apart non-covalent associative bonds under such strong flow conditions relieves the tension along the polymer backbone. The pairwise end-associative polymers that are effective in mist control and drag reduction are individually short enough to avoid chain scission in flows that would break long covalent polymers, yet long enough that 6 to 8 associative polymers connected end-to-end create supermolecules that are as effective as their long covalent counterparts.
\r\n\r\nThis thesis systematically compares the effect of long covalent and long end-associative polymers on the fluid\u2019s extensional flow properties and the polymers' performance in controlling droplet impact and spray breakup. To measure the elongational flow properties, I implemented and enhanced the Dripping onto Substrate Extensional Rheometry (DoSER) technique (Chapter 2) and applied it to long covalent polymers (Chapter 3) and to end-to-end associative polymers (Chapter 4). Preparing solutions in which the polymers negligibly affect the interfacial tension (< 10%) allows us to explore the relationship between extensional flow properties and droplet impact (Chapter 5) and spray (Chapter 6).
\r\n\r\nBy combining the quantitative measurements of extensional viscosity and extensional relaxation time with the corresponding behavior in impact and spray, I correlate the structure of polymers to the solution behavior in droplet rebound and spray breakup. This work has the potential to reduce pesticide contamination of soil, water, and air from agricultural sprays and fire hazard associated with hydrocarbon lubricants.
", "doi": "10.7907/zkpd-bq33", "publication_date": "2023", "thesis_type": "phd", "thesis_year": "2023" }, { "id": "thesis:14457", "collection": "thesis", "collection_id": "14457", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:12222021-065913893", "primary_object_url": { "basename": "Thesis_Orland_Bateman_final_record-14458.pdf", "content": "final", "filesize": 5958689, "license": "other", "mime_type": "application/pdf", "url": "/14457/10/Thesis_Orland_Bateman_final_record-14458.pdf", "version": "v5.0.0" }, "type": "thesis", "title": "Design and Application of Novel Membrane Materials", "author": [ { "family_name": "Bateman", "given_name": "Orland Christopher Lycurgue", "orcid": "0000-0002-6985-494X", "clpid": "Bateman-Orland-Christopher-Lycurgue" } ], "thesis_advisor": [ { "family_name": "Kornfield", "given_name": "Julia A.", "orcid": "0000-0001-6746-8634", "clpid": "Kornfield-J-A" }, { "family_name": "Diallo", "given_name": "Mamadou S.", "clpid": "Diallo-Mamadou-S" } ], "thesis_committee": [ { "family_name": "Faber", "given_name": "Katherine T.", "orcid": "0000-0001-6585-2536", "clpid": "Faber-K-T" }, { "family_name": "Brady", "given_name": "John F.", "orcid": "0000-0001-5817-9128", "clpid": "Brady-J-F" }, { "family_name": "Wang", "given_name": "Zhen-Gang", "orcid": "0000-0002-3361-6114", "clpid": "Wang-Zhen-Gang" }, { "family_name": "Diallo", "given_name": "Mamadou S.", "clpid": "Diallo-Mamadou-S" }, { "family_name": "Kornfield", "given_name": "Julia A.", "orcid": "0000-0001-6746-8634", "clpid": "Kornfield-J-A" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "Membrane technology is uniquely suited to meet the growing need for more sustainable processes due to membranes\u2019 tailorable selectivity and energy efficiency. Efforts to further improve membrane performance and modify them for new applications have found success in academic studies with a versatile class of membranes known as mixed-matrix membranes (MMM). Mixed-matrix membranes combine the strength and controlled morphology of semicrystalline polymeric membranes with superior functionality of a separate material dispersed in the polymer matrix. The strength and toughness of the resulting membranes depends on polymer morphology, including degree of crystallinity and pore structure. Control of the membrane morphology is achieved by kinetically trapping a partially phase separated state, for example, using Nonsolvent Induced Phase Separation (NIPS) to drive liquid-liquid and solid-liquid demixing. However, the processes used to control the polymer morphology are influenced by the functional particles and can result in novel morphologies. In Chapter 2, we used a promising strategy for stably incorporating functional polymeric particles in a structural polymer matrix to investigate the role of the particles during NIPS. The interplay of functional polymeric particle loading and nonsolvent induced phase separation are examined using x-ray diffraction (to deduce the crystal morph adopted by polyvinylidene difluoride, PVDF) and scanning electron microscopy (to observe membrane morphology and the size and distribution of functional particles). We found that the interaction between nonsolvent and functional particles enables a shift in crystal phase usually not attainable with our solvent.
\r\n\r\nIn addition to studying the fundamentals underlying MMM formation, we investigated two applications for novel membrane materials: purification of therapeutic antibodies and size-selective particle capture. Purification of proteins for medical use requires several chromatographic steps in order to produce solutions of sufficient purity. For many years, the gold standard in the field was resin-based packed bed chromatography; however, more recently membrane chromatography has gained prevalence due to its faster processing time, lower cost, and low operating pressure. With these advantages come the drawbacks of low binding capacity and a sensitivity to the concentration of salt ions in the solution. To address these two drawbacks, we investigated the chromatographic abilities of a modified MMM, in Chapter 3, and a novel membrane material comprising an MMM-ceramic composite, in Chapter 4. We discovered that the performance of the modified MMM is dependent on crosslinker chemistry and crosslink density. Upon optimization, the modified membrane demonstrated a binding capacity consistent with the upper range of available literature values as well as reduced sensitivity to salt. In addition, the development of the novel MMM-ceramic composite enables the use of a broader range of polymer matrix compositions for membrane chromatography.
\r\n\r\nCapture of pathogens from complex fluids, such as blood, has received substantial attention due to rising rates of sepsis and antibiotic resistance. \tIn Chapter 5, we pursued the capture of pathogens from model fluids using the size-based separation capabilities of dendritic ceramic membranes. We found that interactions between the ceramic surface and the suspended particles played a significant role in membrane performance.
", "doi": "10.7907/9w23-ax66", "publication_date": "2022", "thesis_type": "phd", "thesis_year": "2022" }, { "id": "thesis:14932", "collection": "thesis", "collection_id": "14932", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:06012022-214247822", "type": "thesis", "title": "Oxidative and Internal Stress Effects of Dopants in Multilayer Yb\u2082Si\u2082O\u2087 Environmental Barrier Coatings", "author": [ { "family_name": "Herren", "given_name": "Benjamin Riley", "orcid": "0000-0002-6011-710", "clpid": "Herren-Benjamin-Riley" } ], "thesis_advisor": [ { "family_name": "Faber", "given_name": "Katherine T.", "orcid": "0000-0001-6585-2536", "clpid": "Faber-K-T" } ], "thesis_committee": [ { "family_name": "Fultz", "given_name": "Brent T.", "orcid": "0000-0002-6364-8782", "clpid": "Fultz-B-T" }, { "family_name": "Ravichandran", "given_name": "Guruswami", "orcid": "0000-0002-2912-0001", "clpid": "Ravichandran-G" }, { "family_name": "Almer", "given_name": "Jonathan D.", "orcid": "0000-0002-1900-2271", "clpid": "Almer-Jonathan-D" }, { "family_name": "Lee", "given_name": "Kang N.", "orcid": "0000-0003-1215-0228", "clpid": "Lee-Kang-N" }, { "family_name": "Faber", "given_name": "Katherine T.", "orcid": "0000-0001-6585-2536", "clpid": "Faber-K-T" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "One of the best approaches to improving the efficiency of turbine engines is to increase their operating temperatures. A revolutionary improvement toward this goal will be the replacement of structural metallic components with silicon-based ceramic-matrix composites (CMCs). However, corrosive chemistries in combustion engines necessitate chemical protection of the structural material. Environmental Barrier Coatings (EBCs) are designed for this purpose through thermomechanical and chemical compatibility with the system. High-temperature, humid oxidation of the EBC bondcoat, a silicon layer which adheres the topcoat to the substrate, remains a critical failure mode EBC systems.
\r\n\r\nThis work studies the effects of chemical modifications on bondcoat oxidation during steam cycling in a current state-of-the-art EBC (Yb\u2082Si\u2082O\u2087/Si), and the implications for the durability of the system. Chemically modified EBCs have been shown to decrease oxide growth by more than 85 percent after 1000 hours of steam cycling. Post-exposure analyses are used to investigate the effects of chemistry on thermal oxide thickness and microstructure. Synchrotron X-ray scattering at the Advanced Photon Source, Argonne National Laboratory, is used to observe internal strains, connected to oxidation and chemistry through microstructure. Compared internal stresses, oxidation, and microstructure between baseline and modified EBCs promote the effectiveness of topcoat chemical modifications as they may apply to EBC durability. Microindentation, nanoindentation, and ongoing beam-bending experiments are also used to assess EBC interface toughness in a baseline EBC system. Additionally, a custom induction furnace has been designed and tested for in-situ steam cycling at the synchrotron. Traits facilitating the use of the custom furnace at the synchrotron make for convenient steam-cycling and other exposures in conventional laboratory settings, as well, with enhanced customizability and flexibility.
", "doi": "10.7907/4cm0-8e79", "publication_date": "2022", "thesis_type": "phd", "thesis_year": "2022" }, { "id": "thesis:13994", "collection": "thesis", "collection_id": "13994", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:11062020-163041829", "primary_object_url": { "basename": "Arai_Noriaki_2020.pdf", "content": "final", "filesize": 39528493, "license": "other", "mime_type": "application/pdf", "url": "/13994/14/Arai_Noriaki_2020.pdf", "version": "v5.0.0" }, "type": "thesis", "title": "Freeze Casting of Ceramics: Pore Design from Solidification Principles", "author": [ { "family_name": "Arai", "given_name": "Noriaki", "orcid": "0000-0002-3040-2997", "clpid": "Arai-Noriaki" } ], "thesis_advisor": [ { "family_name": "Faber", "given_name": "Katherine T.", "orcid": "0000-0001-6585-2536", "clpid": "Faber-K-T" } ], "thesis_committee": [ { "family_name": "Fultz", "given_name": "Brent T.", "orcid": "0000-0002-6364-8782", "clpid": "Fultz-B-T" }, { "family_name": "Kornfield", "given_name": "Julia A.", "orcid": "0000-0001-6746-8634", "clpid": "Kornfield-J-A" }, { "family_name": "Johnson", "given_name": "William L.", "clpid": "Johnson-W-L" }, { "family_name": "Faber", "given_name": "Katherine T.", "orcid": "0000-0001-6585-2536", "clpid": "Faber-K-T" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "Freeze casting is a porous material processing method which allows the creation of directionally aligned pores by the solidification process. Pores are generated by sublimation of solidified crystals which reject suspending particles or dissolved solutes during freezing. Although freeze-cast ceramics have been identified for applications such as filtration and bioceramics, the lack of understanding of the process often results in a discrepancy between the desired pore structure and the fabricated structures.
\r\n\r\nSince solidification is the foundation upon which freeze casting is built, this work seeks to understand the solidification process, especially the growth and time evolution of dendrites. To understand the dendritic growth process, two solidification parameters, freezing front velocity and temperature gradient, are independently controlled to investigate the effects of each parameter. Dendritic pore size changes with solidification parameters and shows good agreement with dendrite growth theory. The theory of constitutional supercooling serves as a guide to control pore morphology between dendritic pores and cellular pores. Furthermore, dendrite growth under the effects of the gravitational force is investigated by changing the solidification direction with respect to the gravity direction. Convection changes the degree of constitutional supercooling, and results in different pore sizes as well as pore morphology.
\r\n\r\nTime evolution of dendrites through isothermal coarsening is investigated. During the coarsening of dendrites, they are transformed to cylinder-like crystals, which yield honeycomb-like structures. Moreover, dendrite size changes linearly with the cube root of coarsening time. Both findings are well-established phenomena in alloy solidification. Further comparison with alloy systems are achieved with tomography-based analysis where similar microstructural evolution with alloy system is demonstrated.
\r\n\r\nBased upon the understanding of underlying solidification principles in freeze casting, three applications are explored. First, the freeze-cast structure is designed to improve shape-memory properties. Processing variables are controlled such that shape-memory porous zirconia can enable martensitic phase transformations and shape deformation without fracture. Other applications utilize unique pore space. Dendritic pores are investigated for size-based filtration to preferentially capture small particles. Flow-through experiments and in-situ observation by confocal microscopy confirm that pores created by secondary dendrites capture small particles. Finally, honeycomb-like structures are filled with functional microgels to create a ceramic/polymer composite as an application for membrane chromatography. The fabricated composite demonstrates advantages such as mechanical stability during the fluid flow.
", "doi": "10.7907/3rmr-cz93", "publication_date": "2021", "thesis_type": "phd", "thesis_year": "2021" }, { "id": "thesis:14042", "collection": "thesis", "collection_id": "14042", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:12242020-000539491", "type": "thesis", "title": "Customized Porosity in Ceramic Composites via Freeze Casting", "author": [ { "family_name": "Kuo", "given_name": "Claire Taijung", "orcid": "0000-0002-3720-968X", "clpid": "Kuo-Claire-Taijung" } ], "thesis_advisor": [ { "family_name": "Faber", "given_name": "Katherine T.", "orcid": "0000-0001-6585-2536", "clpid": "Faber-K-T" } ], "thesis_committee": [ { "family_name": "Fultz", "given_name": "Brent T.", "orcid": "0000-0002-6364-8782", "clpid": "Fultz-B-T" }, { "family_name": "Kornfield", "given_name": "Julia A.", "orcid": "0000-0001-6746-8634", "clpid": "Kornfield-J-A" }, { "family_name": "Johnson", "given_name": "William L.", "clpid": "Johnson-W-L" }, { "family_name": "Faber", "given_name": "Katherine T.", "orcid": "0000-0001-6585-2536", "clpid": "Faber-K-T" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "Freeze casting is a facile pore-forming technique for ceramics as it affords great tunability in pore structure including size, morphology, wall thickness, tortuosity, and alignment. Nevertheless, similar to any other pore-forming techniques, it has limitations in terms of the range of accessible properties. For example, a porous lamellar structure is highly permeable but easily fractures, while the dendritic structure is the opposite. This research seeks to provide strategies used with freeze casting to achieve a combination of properties that go beyond the current limitations and create optimized pore structures with a specific focus on three properties: strength, permeability, and surface area.
\r\n\r\nSuch strategies utilize two composite material principles. First, particle reinforcement was implemented to optimize the mechanical and transport properties. Second, surface area was increased with hierarchical design for enhanced capture or catalysis applications. To optimize the mechanical and transport properties, we reinforced high-permeability lamellar structures with reinforcement fillers of silicon carbide (SiC) whiskers and carbon nanotubes (CNTs). The two fillers afford two different mechanisms of reinforcement: structural and material reinforcement.
\r\n\r\nAdditions of 30 vol.% SiC whiskers increased the compressive strength by 325% at a small expense in permeability. Shear failure, common in lamellar structures, was prevented by the interwall bridges produced via particle engulfment during freezing. These bridges were demonstrated by the change in microstructure, stress-strain behavior, and fracture surfaces. A 2D in-situ solidification experiment was conducted to observe solidification and particle engulfment directly. We proposed a modified engulfment model to account for the complexity stemming from high-aspect ratio particles and non-planar freezing fronts. Reasonable agreement was found between the model, the simulation based on the model, and the experimental values from the freeze-casting and 2D-solidification experiments.
\r\n\r\nFreeze-casting with CNTs was explored as an alternative reinforcement strategy, but one which maintains the original pore structure. CNTs were pushed aside by the freezing front to pore walls due to their small diameters for low CNT concentration composites (<4.5 wt.%) such that the original pore structures remained. The compressive strength increased, albeit by smaller percentages (118% for 4.3 wt.%) than those with SiC whiskers. The increase was attributed to the toughening of pore walls with no diminishing effect on permeability. In addition, CNTs changed the electrical conductivity by ten orders of magnitude with the addition of 8.2 wt.% of the reinforcement.
\r\n\r\nFinally, conformal coatings via self-assembly of block copolymers (BCP) were produced by infiltration into a freeze-cast lamellar structure and significantly increased the surface area of the underlying scaffold. A bimodal pore size distribution with nanometer-size pores from the BCP self-assembly and micron-size pores from freeze casting was observed. An increase in compressive strengths was achieved with the introduction of pore hierarchy while retaining permeability of the macroporous structure due to enlarged lamellar spacings from the infiltration process.
", "doi": "10.7907/88p1-5v79", "publication_date": "2021", "thesis_type": "phd", "thesis_year": "2021" }, { "id": "thesis:14042", "collection": "thesis", "collection_id": "14042", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:12242020-000539491", "type": "thesis", "title": "Customized Porosity in Ceramic Composites via Freeze Casting", "author": [ { "family_name": "Kuo", "given_name": "Claire Taijung", "orcid": "0000-0002-3720-968X", "clpid": "Kuo-Claire-Taijung" } ], "thesis_advisor": [ { "family_name": "Faber", "given_name": "Katherine T.", "orcid": "0000-0001-6585-2536", "clpid": "Faber-K-T" } ], "thesis_committee": [ { "family_name": "Fultz", "given_name": "Brent T.", "orcid": "0000-0002-6364-8782", "clpid": "Fultz-B-T" }, { "family_name": "Kornfield", "given_name": "Julia A.", "orcid": "0000-0001-6746-8634", "clpid": "Kornfield-J-A" }, { "family_name": "Johnson", "given_name": "William L.", "clpid": "Johnson-W-L" }, { "family_name": "Faber", "given_name": "Katherine T.", "orcid": "0000-0001-6585-2536", "clpid": "Faber-K-T" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "Freeze casting is a facile pore-forming technique for ceramics as it affords great tunability in pore structure including size, morphology, wall thickness, tortuosity, and alignment. Nevertheless, similar to any other pore-forming techniques, it has limitations in terms of the range of accessible properties. For example, a porous lamellar structure is highly permeable but easily fractures, while the dendritic structure is the opposite. This research seeks to provide strategies used with freeze casting to achieve a combination of properties that go beyond the current limitations and create optimized pore structures with a specific focus on three properties: strength, permeability, and surface area.
\r\n\r\nSuch strategies utilize two composite material principles. First, particle reinforcement was implemented to optimize the mechanical and transport properties. Second, surface area was increased with hierarchical design for enhanced capture or catalysis applications. To optimize the mechanical and transport properties, we reinforced high-permeability lamellar structures with reinforcement fillers of silicon carbide (SiC) whiskers and carbon nanotubes (CNTs). The two fillers afford two different mechanisms of reinforcement: structural and material reinforcement.
\r\n\r\nAdditions of 30 vol.% SiC whiskers increased the compressive strength by 325% at a small expense in permeability. Shear failure, common in lamellar structures, was prevented by the interwall bridges produced via particle engulfment during freezing. These bridges were demonstrated by the change in microstructure, stress-strain behavior, and fracture surfaces. A 2D in-situ solidification experiment was conducted to observe solidification and particle engulfment directly. We proposed a modified engulfment model to account for the complexity stemming from high-aspect ratio particles and non-planar freezing fronts. Reasonable agreement was found between the model, the simulation based on the model, and the experimental values from the freeze-casting and 2D-solidification experiments.
\r\n\r\nFreeze-casting with CNTs was explored as an alternative reinforcement strategy, but one which maintains the original pore structure. CNTs were pushed aside by the freezing front to pore walls due to their small diameters for low CNT concentration composites (<4.5 wt.%) such that the original pore structures remained. The compressive strength increased, albeit by smaller percentages (118% for 4.3 wt.%) than those with SiC whiskers. The increase was attributed to the toughening of pore walls with no diminishing effect on permeability. In addition, CNTs changed the electrical conductivity by ten orders of magnitude with the addition of 8.2 wt.% of the reinforcement.
\r\n\r\nFinally, conformal coatings via self-assembly of block copolymers (BCP) were produced by infiltration into a freeze-cast lamellar structure and significantly increased the surface area of the underlying scaffold. A bimodal pore size distribution with nanometer-size pores from the BCP self-assembly and micron-size pores from freeze casting was observed. An increase in compressive strengths was achieved with the introduction of pore hierarchy while retaining permeability of the macroporous structure due to enlarged lamellar spacings from the infiltration process.
", "doi": "10.7907/88p1-5v79", "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:14211", "collection": "thesis", "collection_id": "14211", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05312021-211620881", "primary_object_url": { "basename": "Buabthong_thesis_Final.pdf", "content": "final", "filesize": 14890977, "license": "other", "mime_type": "application/pdf", "url": "/14211/1/Buabthong_thesis_Final.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Stability and Protective Coatings of Semiconductor Electrodes for Solar Fuel Devices", "author": [ { "family_name": "Buabthong", "given_name": "Pakpoom (Pai)", "orcid": "0000-0001-5538-138X", "clpid": "Buabthong-Pakpoom-Pai" } ], "thesis_advisor": [ { "family_name": "Lewis", "given_name": "Nathan Saul", "orcid": "0000-0001-5245-0538", "clpid": "Lewis-N-S" } ], "thesis_committee": [ { "family_name": "Gray", "given_name": "Harry B.", "orcid": "0000-0002-7937-7876", "clpid": "Gray-H-B" }, { "family_name": "Faber", "given_name": "Katherine T.", "orcid": "0000-0001-6585-2536", "clpid": "Faber-K-T" }, { "family_name": "Goddard", "given_name": "William A., III", "orcid": "0000-0003-0097-5716", "clpid": "Goddard-W-A-III" }, { "family_name": "Lewis", "given_name": "Nathan Saul", "orcid": "0000-0001-5245-0538", "clpid": "Lewis-N-S" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "Climate change and increasing global energy consumption drive the need for clean and renewable alternatives to fossil fuels. Photoelectrochemical solar fuel devices offer a potential solution to capture and store clean and renewable solar energy in chemical bonds. Nevertheless, degradation of semiconductor electrodes is one of the major impediments to the implementation of practical stable solar fuels systems.
\r\n\r\nerein, we investigate the corrosion mechanisms and the corrosion kinetics of CdTe and ZnTe cathodes under the conditions for hydrogen-evolution reaction in strong acid and strong alkaline media. The effects of catalyst over-layer on CdTe\u2019s and ZnTe\u2019s corrosion pathways are discussed as well as potential protective coatings for ZnTe cathodes. Then, we address the original physical pinhole defects in amorphous a TiO\u2082 grown by atomic-layer deposition (ALD) on GaAs anodes. In addition, we explore new pinhole formation during electrochemical experiments and provide simulation for the propagation of the corroding GaAs substrate after new exposure to the electrolyte through microscopic pinholes. Finally, we develop a fabrication procedure for GaAs micro-island structures to provide defect isolation on the a TiO\u2082 film. The micro-island structures combined with dissolution measurements of the ALD a TiO\u2082 films were used to study the distribution and the evolution of pinholes from pre-existing defect spots in the protective coatings.
", "doi": "10.7907/dx7s-fh20", "publication_date": "2021", "thesis_type": "phd", "thesis_year": "2021" }, { "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:13994", "collection": "thesis", "collection_id": "13994", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:11062020-163041829", "primary_object_url": { "basename": "Arai_Noriaki_2020.pdf", "content": "final", "filesize": 39528493, "license": "other", "mime_type": "application/pdf", "url": "/13994/14/Arai_Noriaki_2020.pdf", "version": "v5.0.0" }, "type": "thesis", "title": "Freeze Casting of Ceramics: Pore Design from Solidification Principles", "author": [ { "family_name": "Arai", "given_name": "Noriaki", "orcid": "0000-0002-3040-2997", "clpid": "Arai-Noriaki" } ], "thesis_advisor": [ { "family_name": "Faber", "given_name": "Katherine T.", "orcid": "0000-0001-6585-2536", "clpid": "Faber-K-T" } ], "thesis_committee": [ { "family_name": "Fultz", "given_name": "Brent T.", "orcid": "0000-0002-6364-8782", "clpid": "Fultz-B-T" }, { "family_name": "Kornfield", "given_name": "Julia A.", "orcid": "0000-0001-6746-8634", "clpid": "Kornfield-J-A" }, { "family_name": "Johnson", "given_name": "William L.", "clpid": "Johnson-W-L" }, { "family_name": "Faber", "given_name": "Katherine T.", "orcid": "0000-0001-6585-2536", "clpid": "Faber-K-T" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "Freeze casting is a porous material processing method which allows the creation of directionally aligned pores by the solidification process. Pores are generated by sublimation of solidified crystals which reject suspending particles or dissolved solutes during freezing. Although freeze-cast ceramics have been identified for applications such as filtration and bioceramics, the lack of understanding of the process often results in a discrepancy between the desired pore structure and the fabricated structures.
\r\n\r\nSince solidification is the foundation upon which freeze casting is built, this work seeks to understand the solidification process, especially the growth and time evolution of dendrites. To understand the dendritic growth process, two solidification parameters, freezing front velocity and temperature gradient, are independently controlled to investigate the effects of each parameter. Dendritic pore size changes with solidification parameters and shows good agreement with dendrite growth theory. The theory of constitutional supercooling serves as a guide to control pore morphology between dendritic pores and cellular pores. Furthermore, dendrite growth under the effects of the gravitational force is investigated by changing the solidification direction with respect to the gravity direction. Convection changes the degree of constitutional supercooling, and results in different pore sizes as well as pore morphology.
\r\n\r\nTime evolution of dendrites through isothermal coarsening is investigated. During the coarsening of dendrites, they are transformed to cylinder-like crystals, which yield honeycomb-like structures. Moreover, dendrite size changes linearly with the cube root of coarsening time. Both findings are well-established phenomena in alloy solidification. Further comparison with alloy systems are achieved with tomography-based analysis where similar microstructural evolution with alloy system is demonstrated.
\r\n\r\nBased upon the understanding of underlying solidification principles in freeze casting, three applications are explored. First, the freeze-cast structure is designed to improve shape-memory properties. Processing variables are controlled such that shape-memory porous zirconia can enable martensitic phase transformations and shape deformation without fracture. Other applications utilize unique pore space. Dendritic pores are investigated for size-based filtration to preferentially capture small particles. Flow-through experiments and in-situ observation by confocal microscopy confirm that pores created by secondary dendrites capture small particles. Finally, honeycomb-like structures are filled with functional microgels to create a ceramic/polymer composite as an application for membrane chromatography. The fabricated composite demonstrates advantages such as mechanical stability during the fluid flow.
", "doi": "10.7907/3rmr-cz93", "publication_date": "2021", "thesis_type": "phd", "thesis_year": "2021" }, { "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:11759", "collection": "thesis", "collection_id": "11759", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:08092019-151803660", "primary_object_url": { "basename": "MacDonaldKimberley2020thesis.pdf", "content": "final", "filesize": 78530454, "license": "other", "mime_type": "application/pdf", "url": "/11759/1/MacDonaldKimberley2020thesis.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Three-Dimensional Quantitative Visualization for Mechanics of Discontinuous Materials", "author": [ { "family_name": "Mac Donald", "given_name": "Kimberley Ann", "orcid": "0000-0003-4512-9740", "clpid": "Mac-Donald-Kimberley-Kimberley-Ann" } ], "thesis_advisor": [ { "family_name": "Ravichandran", "given_name": "Guruswami", "clpid": "Ravichandran-G" } ], "thesis_committee": [ { "family_name": "Hunt", "given_name": "Melany L.", "clpid": "Hunt-M-L" }, { "family_name": "Andrade", "given_name": "Jose E.", "clpid": "Andrade-J-E" }, { "family_name": "Faber", "given_name": "Katherine T.", "clpid": "Faber-K-T" }, { "family_name": "Ravichandran", "given_name": "Guruswami", "clpid": "Ravichandran-G" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "The complexity and multiscale nature of material microstructures introduces significant intricacies to many mechanics problems for which we do not have a full theoretical understanding. Under loading, these microstructures can introduce significant nonlinearities that cannot be described sufficiently by current theories and models. This leads us to consider experiments we could perform to improve our understanding of such effects. This thesis describes the design of experiments exploring two aspects of material microstructure effects: (i) crack propagation and renucleation in soft brittle polymers and (ii) interparticle forces in granular materials.
\r\n\r\nFirst, experimental and analysis methods are developed to study fracture mechanics in soft brittle polymers with the goal of developing a more detailed understanding of the effects of microstructural heterogeneities on crack propagation and renucleation in three-dimensions. To better understand these processes, experiments on crack propagation in thin soft polymers using confocal microscopy images are conducted. Traditional metrics associated with crack propagation including stress intensity factor (SIF, K) and energy release rate (ERR, G) are calculated by direct measurement of the crack tip opening displacement (CTOD, \u03b4t) on the sub-millimeter scale. Errors in these calculations are comparable to those reported in the literature for more traditional fracture experiment geometries. Fluorescent speckle images are captured using confocal microscopy imaging, a fast and low cost 3D optical imaging technique, to study crack geometry during propagation. Images of renucleation events are also captured allowing investigation of factors contributing to slow crack roughening observed by earlier researchers. The goal of this study is to provide an experimental method to enhance understanding of crack interactions with microstructural heterogeneities and of renucleation events, which can significantly improve our ability to design material toughness.
\r\n\r\nTo begin to understand the effects of engineered microstructural heterogeneities such as inclusions in materials, we must be able to produce such engineered systems and understand the interparticle interactions. To this end, a method to manufacture volumetrically speckled spheres in-house with controlled diameters was developed. Additionally, an experimental method combining confocal microscopy with digital volume correlation (DVC) was also used to study interparticle force transmission in 3D. Analysis of an in-plane 2D projection of volumetric surface data shows that three-dimensional effects play a significant role in the deformation of granular assemblies. Study of a single grain in 3D demonstrates progress in experimental capabilities and highlights the need for more studies to validate existing numerical models and theories for granular matter. Analysis of particle scale deformations and strains with the Granular Element Method (GEM) allows us to determine interparticle forces and understand the development and evolution of force chains in a granular assembly under a wide variety of loading conditions. These experiments can also lead to development of new understanding of the effects of inclusions on material properties, processes, and damage evolution.
", "doi": "10.7907/0M4F-FG13", "publication_date": "2020", "thesis_type": "phd", "thesis_year": "2020" }, { "id": "thesis:13574", "collection": "thesis", "collection_id": "13574", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:11122019-171331857", "type": "thesis", "title": "Fracture and Toughening of Brittle Structures with Designed Anisotropy", "author": [ { "family_name": "Brodnik", "given_name": "Neal Ryan", "orcid": "0000-0002-4426-5997", "clpid": "Brodnik-Neal-Ryan" } ], "thesis_advisor": [ { "family_name": "Faber", "given_name": "Katherine T.", "clpid": "Faber-K-T" }, { "family_name": "Ravichandran", "given_name": "Guruswami", "clpid": "Ravichandran-G" } ], "thesis_committee": [ { "family_name": "Bhattacharya", "given_name": "Kaushik", "clpid": "Bhattacharya-K" }, { "family_name": "Faber", "given_name": "Katherine T.", "clpid": "Faber-K-T" }, { "family_name": "Ravichandran", "given_name": "Guruswami", "clpid": "Ravichandran-G" }, { "family_name": "Greer", "given_name": "Julia R.", "clpid": "Greer-J-R" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "Despite good thermal and chemical properties, the use of ceramic materials in structural applications is limited by their inherently brittle nature. Efforts have been made to improve the toughness of ceramics through composite design, but recent developments in net shape processing such as additive manufacturing have significantly expanded this design space. Where composite topologies and morphologies were previously limited by material composition and thermodynamics, tools like 3D printing now allow for the design of composite structures of nearly any shape or arrangement.
\r\n\r\nThis work seeks to understand how these processing advances might be utilized to improve the toughness of brittle composites by exploring how previously inaccessible anisotropic inclusion structures might influence fracture behavior. The study begins with the evaluation of printed photopolymer structures as model brittle materials. First, printed structures are used to explore how elastic contrast between inclusions and matrix can affect crack propagation and improve toughness. Here, anisotropy presents an opportunity to achieve similar toughness to isotropic structures at smaller volume fractions by virtue of topologies that only exhibit toughening only in a singular direction, but require significantly less material to do so. Next, the effect of anisotropic voids is explored as a means of controlling crack nucleation and growth. With consideration of both compliance and directional propagation, a \"fracture diode\" that exhibits controlled, predictable fracture 100% of the time can be realized.
\r\n\r\nAfter exploring brittle polymers, ceramics systems with similar toughness and higher stiffness are considered. First, a model layered system of mica is explored, where wedge splitting can be used achieve stable crack growth. This allows for the evaluation of how changes in compliance can improve the interlayer toughness without directly interacting with the crack. Finally, this study extends further into ceramics by exploring silicon oxycarbide (SiOC) truss structures and truss elements produced from 3D printed preceramic polymers. In addition to considering the material itself, changes in truss structure are explored as a means of changing deformation mode, and by consequence, failure strength. These model experiments suggest that if trusses are compatible, they can be interchanged to control failure of the bulk structure.
\r\n\r\nThis study demonstrates how designed heterogeneities with anisotropic structure can be used to both enhance the toughness of brittle composites as well achieve a greater degree of control over both crack nucleation and propagation in brittle systems where predicting failure is otherwise difficult. Looking forward, new processing tools like additive manufacturing present major opportunities for expanding the design space of brittle composites to achieve higher toughness and better fracture control than previously available. These new techniques may be able to expand the mechanical viability of ceramics, and make them better suited to mechanically demanding applications in the future.
", "doi": "10.7907/ET0C-MK61", "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: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: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:11390", "collection": "thesis", "collection_id": "11390", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:02112019-143327096", "primary_object_url": { "basename": "Weadock_Nicholas_2019_Final.pdf", "content": "final", "filesize": 25632235, "license": "other", "mime_type": "application/pdf", "url": "/11390/1/Weadock_Nicholas_2019_Final.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Addressing Thermodynamic Inefficiencies of Hydrogen Storage in Transition Metal Hydrides", "author": [ { "family_name": "Weadock", "given_name": "Nicholas Joseph", "orcid": "0000-0002-1178-7641", "clpid": "Weadock-Nicholas-Joseph" } ], "thesis_advisor": [ { "family_name": "Fultz", "given_name": "Brent T.", "orcid": "0000-0002-6364-8782", "clpid": "Fultz-B-T" } ], "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": "See", "given_name": "Kimberly", "orcid": "0000-0002-0133-9693", "clpid": "See-Kimberly" }, { "family_name": "Fultz", "given_name": "Brent T.", "orcid": "0000-0002-6364-8782", "clpid": "Fultz-B-T" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "Transition metal hydrides (MH) are an attractive class of materials for several energy technologies. Primary benefits include their large volumetric storage capacity (often exceeding that of liquid hydrogen) and capability to absorb and desorb hydrogen for hundreds of cycles. In this thesis, we set out to understand two of the thermodynamic inefficiencies of MH: the pressure hysteresis associated with hydrogen absorption and desorption and the corrosion and dissolution of high capacity MH alloys in high pH electrolyte environments.
\r\n\r\nThe volume change associated with hydriding transitions can exceed 10%, and a macroscopic nucleation barrier resulting from coherency strains has been proposed as the origin of the pressure hysteresis. We investigated this hypothesis for the palladium-hydrogen system. The hysteresis and phase transformation characteristics of bulk and nanocrystalline PdH were characterized with coupled in situ X-ray diffraction and pressure composition isotherm measurements. Size effects are observed in the total hydrogen uptake and hydrogen solubility in the hydride phases. Experimentally determined hysteresis energies were found to be comparable to the misfit strain between the Pd and PdH phases and much larger than the energy for dislocation formation. Theoretical predictions of pressure hysteresis overestimate the experimentally measured hysteresis, and we suggest methods of accommodation which could explain the discrepancy. Finally, we propose that an effect of the nucleation barrier is to split the coherent spinodal phase diagram and introduce directionally dependent phase boundaries.
\r\n\r\nWe report a successful development of Ti29V62-xNi9Crx (x = 0, 6, 12) body-centered cubic (BCC) MH electrodes for MH batteries by addressing vanadium corrosion and dissolution in potassium hydroxide electrolytes. The effectiveness of a limited oxygen environment and vanadate ion addition against corrosion are compared to the effects of Cr substitution. By identifying oxygen as the primary source of corrosion and eliminating oxygen with an Ar-purged cell, the Cr-free alloy electrode achieved a maximum capacity of 594 mAh/g, double the capacity of commercial AB5 MH electrodes. With modified coin cells suppressing oxygen evolution, the cycle stability of the Ti29V62Ni9 alloy electrode was greatly improved with either vanadate ion additions to the electrolyte or Cr-substitution in the alloy. Both approaches lead to reversible capacity of 500 mAh/g for 200 cycles.
", "doi": "10.7907/ANY4-VA70", "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:11727", "collection": "thesis", "collection_id": "11727", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:06082019-133053987", "primary_object_url": { "basename": "TanWeiLin2019-Final.pdf", "content": "final", "filesize": 18201661, "license": "other", "mime_type": "application/pdf", "url": "/11727/1/TanWeiLin2019-Final.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Polycrystalline Perovskite Ferroelectrics: Microstructural Origins of the Macroscale Electromechanical Response", "author": [ { "family_name": "Tan", "given_name": "Wei Lin", "orcid": "0000-0001-6855-8340", "clpid": "Tan-Wei-Lin" } ], "thesis_advisor": [ { "family_name": "Kochmann", "given_name": "Dennis M.", "clpid": "Kochmann-D-M" }, { "family_name": "Faber", "given_name": "Katherine T.", "clpid": "Faber-K-T" } ], "thesis_committee": [ { "family_name": "Bhattacharya", "given_name": "Kaushik", "clpid": "Bhattacharya-K" }, { "family_name": "Kochmann", "given_name": "Dennis M.", "clpid": "Kochmann-D-M" }, { "family_name": "Faber", "given_name": "Katherine T.", "clpid": "Faber-K-T" }, { "family_name": "Rossman", "given_name": "George Robert", "clpid": "Rossman-G-R" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "Ferroelectrics are a class of electromechanically coupled materials which possess an electric dipole polarization that can be permanently reoriented by applied electric and mechanical stress fields. Their reorientable polarization results in complex, nano- to micrometer scale domain structures whose evolution under electric and mechanical stress fields alters the material's overall time-dependent electrical and viscoelastic properties. To understand domain structure evolution, in-situ microscopy of domain switching processes in ferroelectric thin films, single crystals and nanoparticles have been well-studied in the past. However, domain evolution in bulk polycrystals is less well understood as their local stress and electric field environment differs from thin specimens.
\r\n\t\r\nThis work seeks to understand ferroelectric domain evolution in bulk ferroelectric perovskite polycrystals using a combination of a recently-developed electromechanical characterization technique, Broadband Electromechanical Spectroscopy (BES), and theoretical-computational predictions. A constitutive material model for polycrystalline ferroelectrics is first developed and applied to simulate barium titanate single crystals and polycrystals. Simulated polarization, strain and energy dissipation hysteresis curves show good qualitative agreement to experimental data and demonstrate that macroscale properties can be efficiently predicted from microscale physics to some extent.
\r\n\t\r\nThe microstructural origins of fatigue behavior in bulk polycrystalline lead zirconate titanate (PZT) are investigated using a combination of macroscale electrical and viscoelastic property characterization via BES, and scanning electron microscopy (SEM) imaging of microstructure. The evolution of electrical and viscoelastic properties during bipolar electrical fatigue show differences in the effects of electrical vs. mechanical fatigue processes, and the latter is verified through SEM imaging and measurement of microcracks.
\r\n\t\r\nFinally, the same electromechanical BES characterizations are performed on specimens of bulk polycrystalline barium titanate (BT). Results reveal stark qualitative differences in electrical and viscoelastic responses from PZT despite both materials being perovskite ferroelectrics. A growth vs. nucleation hypothesis is proposed to explain the observed results, guided by preliminary imaging of domain microstructure.
\r\n\t\r\nIn summary, the BES is a powerful tool to elucidate domain switching processes within bulk ferroelectric specimens, while a computational method which bridges the micro- and macroscale further adds to the diagnostic toolbox of understanding bulk ferroelectric domain switching mechanisms. This opens the pathway to designing future applications which make use of the unique electrical and viscoelastic properties of ferroelectric switching.
", "doi": "10.7907/J2W5-XA95", "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: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:11137", "collection": "thesis", "collection_id": "11137", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:07272018-145200158", "type": "thesis", "title": "Unconventional Approaches to Structured Semiconductors", "author": [ { "family_name": "Thompson", "given_name": "Jonathan Ross", "clpid": "Thompson-Jonathan-Ross" } ], "thesis_advisor": [ { "family_name": "Lewis", "given_name": "Nathan Saul", "clpid": "Lewis-N-S" } ], "thesis_committee": [ { "family_name": "Faber", "given_name": "Katherine T.", "clpid": "Faber-K-T" }, { "family_name": "Gray", "given_name": "Harry B.", "clpid": "Gray-H-B" }, { "family_name": "Johnson", "given_name": "William Lewis", "clpid": "Johnson-W-L" }, { "family_name": "Lewis", "given_name": "Nathan Saul", "clpid": "Lewis-N-S" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "The function of semiconductor devices is intrinsically tied to their structure. While there are already myriad techniques in use today to fabricate an extreme diversity of devices, new processes are regularly developed to make the production of previously unrealizable structures, and consequently devices, possible.
\r\n\r\nThis dissertation deals with several unconventional approaches to generating ordered semiconductor structures. One chapter discusses a novel technique to measure the various forces that impede the alignment of randomly dispersed microstructures. The technique made it possible to both determine the magnitude of the interactions that the particles must overcome in order to be organized into a useful structure and assess the functional form of the forces that the microstructure is experiencing, thereby giving insight into the physical origin of said forces.
\r\n\r\nThe following chapter deal with the spontaneous structure formation seen in photoelectrodeposited semiconductor films. One chapter investigates how the natural tendency of these films to form oriented, high aspect ratio structures can be coupled to the geometry of the substrate on which they are grown. This work demonstrates that extremely straight, high aspect ratio structures can be grown over macroscopic areas by making simple modifications of the substrate.
\r\n\r\nThe final chapter characterizes the iridescence that these films exhibit. A simple physical explanation for the origin of the coloration is posited and verified. Then the information gleaned about the optical response of these films is used to generate vibrant, colorful patterns on electrode using consumer electronics.
", "doi": "10.7907/YW6M-H367", "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: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:10851", "collection": "thesis", "collection_id": "10851", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05062018-164727269", "type": "thesis", "title": "Performance and Stability Optimization of Solar Fuel Devices", "author": [ { "family_name": "Zhou", "given_name": "Xinghao", "orcid": "0000-0001-9229-7670", "clpid": "Zhou-Xinghao" } ], "thesis_advisor": [ { "family_name": "Lewis", "given_name": "Nathan Saul", "clpid": "Lewis-N-S" } ], "thesis_committee": [ { "family_name": "Lewis", "given_name": "Nathan Saul", "clpid": "Lewis-N-S" }, { "family_name": "Faber", "given_name": "Katherine T.", "clpid": "Faber-K-T" }, { "family_name": "Goddard", "given_name": "William A., III", "clpid": "Goddard-W-A-III" }, { "family_name": "Johnson", "given_name": "William Lewis", "clpid": "Johnson-W-L" } ], "local_group": [ { "literal": "JCAP" }, { "literal": "div_eng" } ], "abstract": "Fossil fuels enabled the Industrial Revolution, and have been the most important power for promoting the world's economic growth ever since. However, burning fossil fuels have also been causing severe air pollution, and global warming is also related to excessive use of fossil fuels. Solar energy is considered to be the largest renewable clean energy resource. The principal problems of solar energy are low energy concentration and intermittency. Storing solar energy in chemical bonds, similar to photosynthesis in nature, is a possible way to overcome these two problems. Carbon-free chemicals, like hydrogen gas produced by solar-driven water splitting, or carbon-neutral chemicals, like methane, ethylene, formic acid, carbon monoxide, etc. produced from solar-driven CO2 reduction, are all promising clean fuels for solar storage, as they feature high energy/power intensity, are easy and cheap to store and transport, and have direct interface with existing infrastructures.
\r\n\r\nIn this thesis, we focus on improving the efficiency and stability of the solar-driven fuel generation devices, which consist of (photo-)anode and (photo-)cathode. For the anode part, cobalt oxide Co3O4 ultrathin (2 nm) films by atomic layer deposition (ALD) were deposited onto silicon photoanode prior to deposition of thick nickel oxide (NiOx) layers. The photovoltage of the photoanode increased from 200 mV to 580 mV after including the interfacial Co3O4 layer, and the anode was stable in 1.0 M KOH(aq) for 1700 hours, which was equivalent to one year of operation in the field at a maximum photocurrent density of 30 mA/cm2 assuming a 20% solar capacity factor. Furthermore, the non-uniform sputtered (NiOx) layer of the n-Si/SiOx/Co3O4/NiOx photoanode was removed, and the 2 nm Co3O4 film was thickened to 50 nm, and the stability of n-Si/SiOx/50 nm-Co3O4 was improved to 2500 hours with lower efficiency decay rate. For the cathode part, an optimized Pd/C nanoparticle coated Ti mesh cathode exhibited < 100 mV overpotential at 8.5 mA/cm2 current density, and > 94% Faradaic efficiency for the reduction of 1 atm of CO2(g) to formate in 2.8 M KHCO3. A solar-driven CO2 reduction (CO2R) cell was constructed with this cathode, showing 10% solar-to-fuels conversion efficiency.
\r\n\r\nThis thesis can be divided into three parts. The first part discusses importance of solar fuels, as well as gives an introduction of solar-fuel generators. The second part includes Chapter II and Chapter III, which deal with performance improvement of silicon photoanode with ALD Co3O4 thin films. The third part is Chapter IV, in which we study the cathode for CO2 reduction to formate, and demonstrate a 10% efficiency solar-driven CO2 reduction cell with the cathode.
", "doi": "10.7907/SSNP-XW29", "publication_date": "2018", "thesis_type": "phd", "thesis_year": "2018" }, { "id": "thesis:10546", "collection": "thesis", "collection_id": "10546", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:10262017-091901955", "type": "thesis", "title": "Development of Ferromagnetic Metallic Glasses into Low Loss Power Transformer Cores", "author": [ { "family_name": "Floyd", "given_name": "Michael Cameron Dawley", "clpid": "Floyd-Michael-Cameron-Dawley" } ], "thesis_advisor": [ { "family_name": "Johnson", "given_name": "William Lewis", "clpid": "Johnson-W-L" } ], "thesis_committee": [ { "family_name": "Johnson", "given_name": "William Lewis", "clpid": "Johnson-W-L" }, { "family_name": "Schwab", "given_name": "Keith C.", "clpid": "Schwab-K-C" }, { "family_name": "Demetriou", "given_name": "Marios D.", "clpid": "Demetriou-M-D" }, { "family_name": "Greer", "given_name": "Julia R.", "clpid": "Greer-J-R" }, { "family_name": "Faber", "given_name": "Katherine T.", "clpid": "Faber-K-T" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "Currently, 3% of energy losses in the U.S. electrical grid occur at power transformers. With a transition to Metglas, transformer efficiency could be increased, but is Metglas the best replacement material for power transformers?
\r\n\r\nWith this in mind we develop a Fe-based metallic glass for its glass forming ability and soft magnetic properties. During this development we identify a redox reaction of boron oxide by Si during melt fluxing of the Fe-based glass, which promotes an unexpected exchange of Si and B in the alloy. Taking this reaction into account, a unique optimization strategy is implemented, enabling oxide purification of the melt coupled with a significant but predictable shift in composition. This leads to an optimized Fe-based glass demonstrating a global peak in glass forming ability. Following boron oxide fluxing in the high temperature melt, alloy with composition Fe57.5Co20.2Si10.2B2.05P10.05 transforms to Fe57Co19.2Si6.8B7.4P9.6, and increases its critical rod diameter from 1 mm to 5 mm. The alloy also demonstrates excellent soft ferromagnetic performance characterized by a magnetic saturation of 1.53 T.
\r\n\r\nWhile developing the above alloy, we also analyzed the effect of varying thickness of a Fe68Mo4Ni3Co5Si1P11.5C5B2.5 transformer core as a function of frequency to discover if there was a minimum in the losses. We did not find a single minimum, but found that the optimal thickness exhibits a logarithmic dependency on frequency. This dependence suggests the optimal thickness of a core ranges from 100\u2212400\u03bcm, instead of in the < 50\u03bcm range currently used. These larger optimal thicknesses are unexpected if anomalous losses are not considered, but the dominance of the anomalous losses at low frequencies, or for thin samples, validates the need for thicker power transformers. While other amorphous metals and casting techniques will yield varying results, the logarithmic dependence on frequency and the 100\u2212400\u03bcm optimal thickness range should be broadly applicable.
\r\n", "doi": "10.7907/Z9QF8R27", "publication_date": "2018", "thesis_type": "phd", "thesis_year": "2018" }, { "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:10961", "collection": "thesis", "collection_id": "10961", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05292018-140812451", "primary_object_url": { "basename": "Kang_Stephen_2018.pdf", "content": "final", "filesize": 2900674, "license": "cc_by_nc_sa", "mime_type": "application/pdf", "url": "/10961/1/Kang_Stephen_2018.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Charge Transport Analysis Using the Seebeck Coefficient-Conductivity Relation", "author": [ { "family_name": "Kang", "given_name": "Stephen Dongmin", "orcid": "0000-0002-7491-7933", "clpid": "Kang-Stephen-Dongmin" } ], "thesis_advisor": [ { "family_name": "Snyder", "given_name": "G. Jeffrey", "orcid": "0000-0003-1414-8682", "clpid": "Snyder-G-J" } ], "thesis_committee": [ { "family_name": "Faber", "given_name": "Katherine T.", "orcid": "0000-0001-6585-2536", "clpid": "Faber-K-T" }, { "family_name": "Minnich", "given_name": "Austin J.", "orcid": "0000-0002-9671-9540", "clpid": "Minnich-A-J" }, { "family_name": "Bernardi", "given_name": "Marco", "orcid": "0000-0001-7289-9666", "clpid": "Bernardi-Marco" }, { "family_name": "Snyder", "given_name": "G. Jeffrey", "orcid": "0000-0003-1414-8682", "clpid": "Snyder-G-J" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "Charge transport properties like electrical conductivity or the Seebeck coefficient are defined phenomenologically from near-equilibrium thermodynamics, while the analysis or modeling of them often involves a physical model based on mechanistic principles. In other words, physical models connect microscopic and physical parameters to phenomenological and experimental properties. One of the challenges is that the complexity of solid state requires many physical parameters, whereas the measurable properties which help to determine those parameters are limited. The interrelations of measured properties are very important to overcome this challenge, but this aspect is not well recognized in conventional analysis themes. In this thesis, the concept of using a phenomenological transport function is devised to help combine a collection of measurements into an intermediate level of phenomenology, relevant for Fermion transport but not dependent on a particular physical model. This phenomenological transport function can be determined by examining the electrical conductivity, the Seebeck coefficient, and potentially the Lorenz number. Because the phenomenological transport function combines information from a set of multiple measurable properties, a direct comparison to the transport function of a physical model serves as a strong test for the model.
\r\n\r\nParticular usefulness comes from extracting transport functions from the Seebeck coefficient-conductivity relation, especially in doped semiconductors. This approach is applied to contrast CeO2-x and n-type SrTiO3 as narrow and dispersive transport function materials, each consistent with polaron and band conduction, respectively. In band conductors such as SrTiO3 and Mg3Sb2, the approach is used to test and refute previous claims about the scattering mechanism and find consistency with deformation potential scattering in both cases. In conducting polymers, which do not resemble any other type of conventional conductors, the Seebeck-conductivity relation reveals a qualitative disagreement with the commonly cited Mott's models. For the case of Cu2Se, a peculiar band conductor which shows anomalies in the Hall measurement of the high temperature phase and also in other transport properties at the phase transition, the transport function approach is applied as a workaround for modeling. On the practical side, for thermoelectric applications, the transport function approach is used to characterize material quality factors for both majority carrier conduction and bipolar conduction. Finally, experimental efforts for improving the accuracy and applicability of Seebeck measurements is discussed.
", "doi": "10.7907/ZAQP-MN67", "publication_date": "2018", "thesis_type": "phd", "thesis_year": "2018" }, { "id": "thesis:10952", "collection": "thesis", "collection_id": "10952", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05282018-024934056", "primary_object_url": { "basename": "Avellar_Louisa_2018.pdf", "content": "final", "filesize": 12288291, "license": "other", "mime_type": "application/pdf", "url": "/10952/14/Avellar_Louisa_2018.pdf", "version": "v7.0.0" }, "type": "thesis", "title": "Observations of Failure Phenomena in Periodic Media", "author": [ { "family_name": "Avellar", "given_name": "Louisa Taylor", "orcid": "0000-0003-1299-5343", "clpid": "Avellar-Louisa-Taylor" } ], "thesis_advisor": [ { "family_name": "Ravichandran", "given_name": "Guruswami", "clpid": "Ravichandran-G" } ], "thesis_committee": [ { "family_name": "Bhattacharya", "given_name": "Kaushik", "clpid": "Bhattacharya-K" }, { "family_name": "Faber", "given_name": "Katherine T.", "clpid": "Faber-K-T" }, { "family_name": "Daraio", "given_name": "Chiara", "clpid": "Daraio-C" }, { "family_name": "Ravichandran", "given_name": "Guruswami", "clpid": "Ravichandran-G" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "New manufacturing techniques, such as 3D printing, allow for greater control over material properties and can be used to create custom heterogeneous materials. Heterogeneities can be leveraged to increase fracture toughness by redistributing the stresses, such as due to an elastic heterogeneity, or by impeding crack propagation, such as the renucleation at a material interface or edge of a void. The goal of this research is to study the mechanisms by which heterogeneities work to make composite materials more resistant to fracture than either of the individual base materials.
\r\n\r\nThe influence of heterogeneities on the deformation and fracture of 3D printed fracture specimens is investigated. Brick-like heterogeneities are studied in compact tension and plate specimens with soft, stiff, and void heterogeneities. Horizontally layered heterogeneities are studied in compact tension specimens. The specimens are manufactured using a printer capable of printing multiple materials. The specimens are loaded until failure, and full-field displacement and strain data are collected using digital image correlation. The evolution of resistance to fracture is quantified by the energy release rate and fracture toughness values calculated using load, load-point displacement measurements, and crack extension data determined from images of the specimen. Both in soft specimens with stiff heterogeneities and in stiff specimens with soft heterogeneities, stresses are observed to be higher in the stiffer material. Fracture toughness is observed to increase in the presence of stiff inclusions and voids, although in the case of voids this is due to the crack terminating at the edge of the void and renucleating at the other edge.
\r\n\r\nThe effects of interfaces on crack propagation in periodic media are experimentally studied. Comparative experiments on two proposed heterogeneity architectures aim to separate the effects of elastic deformation caused by heterogeneous inclusions in a composite from the effects of passing through an interface during crack propagation. The first, 'stripe' specimens, alternate equal width stripes perpendicular to the plane of the crack. The second, 'cross' specimens, have the same stripe pattern but with a narrow strip of one of the constituent materials in the plane of crack propagation. The 'cross' is wide enough to contain the crack to an area without material interfaces but thin enough that its overall effect on elastic deformation is minimal. Specimens are manufactured from two polymers using polyjet 3D printing. Energy release rate for fracture is calculated from load and displacement measurements. Digital image correlation is used to study strain and stress fields during crack propagation. While the stress fields during crack propagation appear similar, the fracture toughness in the 'stripe' specimens was found to be higher than that of the 'cross' specimens, indicating that fracture toughness is enhanced by renucleation at the interfaces. Additionally, the amount of enhancement was observed to depend on the width of the heterogeneous layers.
\r\n\r\nThe interaction between the cohesive zone and elastic stiffness heterogeneity in the peeling of an adhesive tape from a rigid substrate is examined experimentally and with finite element simulations. It is understood that elastic stiffness heterogeneities can greatly enhance the adhesion of a tape without changing the properties of the interface. However, in peeling experiments performed on pressure sensitive adhesive tapes with both an elastic stiffness heterogeneity and a substantial cohesive zone, muted adhesion enhancement was observed. It is proposed that the cohesive zone acts to smooth out the effect of the discontinuity at the edge of the elastic stiffness heterogeneities, suppressing their effect on peel force enhancement. The results of numerical simulations show that the peel force enhancement depends on the strength of the adhesive and the size of the cohesive zone.
", "doi": "10.7907/8N81-MV74", "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:11046", "collection": "thesis", "collection_id": "11046", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:06082018-081351539", "type": "thesis", "title": "Understanding the Origin of Glass Forming Ability in Metallic Glasses", "author": [ { "family_name": "Hoff", "given_name": "Andrew Taylor", "clpid": "Hoff-Andrew-Taylor" } ], "thesis_advisor": [ { "family_name": "Johnson", "given_name": "William Lewis", "clpid": "Johnson-W-L" } ], "thesis_committee": [ { "family_name": "Fultz", "given_name": "Brent T.", "clpid": "Fultz-B-T" }, { "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 Lewis", "clpid": "Johnson-W-L" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "The glass forming ability of metallic glasses has been one of their most studied yet least understood properties. Crystal nucleation in a recently development Ni-based metallic glass was studied by undercooling in a DSC under a variety of conditions and showed stochastic very deep undercooling behavior. The glass forming ability of a family of Ni-based alloys was analyzed and was found to depend only on two experimentally accessible factors, the reduced glass transition temperature and the liquid fragility. Neutron scattering experiments showed that in two model glass formers vibrational entropy had essentially no change through the glass transition, demonstrating that the change in entropy through the glass transition is due almost entirely to configurational entropy. The configurational enthalpy of a pair of recently developed Pt-based metallic glasses show almost no change in the undercooled liquid between the liquidus and TTT-nose, demonstrating the inability of current models to explain the thermodynamics of supercooled liquids. ", "doi": "10.7907/Z7Y5-0B62", "publication_date": "2018", "thesis_type": "phd", "thesis_year": "2018" }, { "id": "thesis:9907", "collection": "thesis", "collection_id": "9907", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:08292016-233907648", "primary_object_url": { "basename": "Murialdo_Maxwell_FullThesis (Final Complete).pdf", "content": "final", "filesize": 25505593, "license": "other", "mime_type": "application/pdf", "url": "/9907/85/Murialdo_Maxwell_FullThesis (Final Complete).pdf", "version": "v5.0.0" }, "type": "thesis", "title": "Anomalous Thermodynamics of Nonideal Gas Physisorption on Nanostructured Carbons", "author": [ { "family_name": "Murialdo", "given_name": "Maxwell Robert", "clpid": "Murialdo-Maxwell-Robert" } ], "thesis_advisor": [ { "family_name": "Fultz", "given_name": "Brent T.", "orcid": "0000-0002-6364-8782", "clpid": "Fultz-B-T" } ], "thesis_committee": [ { "family_name": "Fultz", "given_name": "Brent T.", "orcid": "0000-0002-6364-8782", "clpid": "Fultz-B-T" }, { "family_name": "Bernardi", "given_name": "Marco", "orcid": "0000-0001-7289-9666", "clpid": "Bernardi-Marco" }, { "family_name": "Faber", "given_name": "Katherine T.", "orcid": "0000-0001-6585-2536", "clpid": "Faber-K-T" }, { "family_name": "Goddard", "given_name": "William A., III", "orcid": "0000-0003-0097-5716", "clpid": "Goddard-W-A-III" }, { "family_name": "Johnson", "given_name": "William Lewis", "clpid": "Johnson-W-L" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "Mesoporous and microporous adsorbents play critical roles in gas storage and separation applications. This thesis describes previously unexplored anomalous thermodynamics in the field of gas physisorption and their impact on energy relevant gases including methane, ethane, krypton and carbon dioxide. Physisorption occurs when an adsorbent induces gas molecules to form a locally densified layer at its surface due to physical interactions. This increases gas storage capacity over pure compression and its efficacy is dependent on the surface area of the adsorbent and the isosteric heat of adsorption. The isosteric heat of adsorption is the molar change in the enthalpy of the adsorptive species upon adsorption and serves as a measure of adsorbent-adsorbate binding strength.
\r\n\r\nUnlike conventional adsorbate-adsorbent systems, which have isosteric heats of adsorption that decrease with surface loading, zeolite-templated carbon is shown to have isosteric heats of methane, ethane and krypton adsorption that increase with surface loading. This is a largely beneficial effect that can enhance gas storage and separation. The unique nanostructure and uniform pore periodicity of the zeolite-templated carbon promote lateral interactions among the adsorbed molecules that cause the isosteric heats of adsorption to increase with loading. These results have been tested and corroborated by developing robust fitting techniques and thermodynamics analyses. The anomalous thermodynamics are shown to result from cooperative adsorbate-adsorbate interactions among the nonideal species and are modeled with an Ising-type model.
\r\n\r\nAs a second theme of this thesis, the study of nonideal gas adsorption has enabled the development of a Generalized Law of Corresponding States for Physisorption. A predictive understanding of high-pressure physisorption on a variety of adsorbents would facilitate the further development of tailored adsorbents and adsorption analysis. Prior attempts at developing a predictive understanding, however, have been hindered by nonideal gas effects.
\r\n\r\nBy approaching physisorption from both empirical and fundamental perspectives, a Generalized Law of Corresponding States for Physisorption was established that accounts for a number of nonideal effects. This new Law of Corresponding States allows one to predict adsorption isotherms for a variety of classical gases from data measured with a single gas. In brief: \"At corresponding conditions on the same adsorbent, classical gases physisorb to the same fractional occupancy.\"
\r\n\r\nCorresponding conditions are met when the reduced variables of each nonideal gas are equivalent, and fractional occupancy gives the fraction of occupied adsorption sites. This Law of Corresponding States for Physisorption is determined using monolayer, BET and Dubinin-Polanyi adsorption theories along with measured adsorption isotherms across a number of conditions and adsorbents. Furthermore, the anomalous cooperative adsorbate-adsorbate interactions discussed in this thesis are shown to be consistent with the Generalized Law of Corresponding States for Physisorption.
\r\n", "doi": "10.7907/Z9GH9FXM", "publication_date": "2017", "thesis_type": "phd", "thesis_year": "2017" }, { "id": "thesis:10288", "collection": "thesis", "collection_id": "10288", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:06052017-162306037", "type": "thesis", "title": "An Investigation of Nonstoichiometric Oxides for Solar-Driven Thermochemical Fuel Production", "author": [ { "family_name": "Ignatowich", "given_name": "Michael Joseph", "orcid": "0000-0002-0097-664X", "clpid": "Ignatowich-Michael-Joseph" } ], "thesis_advisor": [ { "family_name": "Haile", "given_name": "Sossina M.", "clpid": "Haile-S-M" } ], "thesis_committee": [ { "family_name": "Wang", "given_name": "Zhen-Gang", "clpid": "Wang-Zhen-Gang" }, { "family_name": "Faber", "given_name": "Katherine T.", "clpid": "Faber-K-T" }, { "family_name": "Ravichandran", "given_name": "Guruswami", "clpid": "Ravichandran-G" }, { "family_name": "Haile", "given_name": "Sossina M.", "clpid": "Haile-S-M" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "In order to realize energy independence and substantially combat global climate change, renewable and sustainable energy technologies must be developed. Solar energy is the most readily abundant, and if converted into a chemical fuel, could be stored and transported easily. Solar-driven thermochemical cycling is a method of chemical fuel production that shows great promise, but current state-of-the-art systems have very low efficiencies. This work discusses new reactor designs and cycling techniques using nonstoichiometric oxides that will enable more efficient solar to fuel energy conversion. Practical aspects of the reactor design are explored \u2013 specifically, thermochemical expansion of the reactive oxide, and morphologies aimed at enhancing the reaction kinetics. Additionally, doped fluorite- and perovskite-structured materials are evaluated for thermodynamic behavior and in-situ thermochemical cycling performance. Oxide morphology and new doped compounds show little improvement over previously established neat ceria due to thermodynamic limitations. The thermodynamic limit is explored in new reactor geometries and is shown to demonstrate significantly more efficient fuel production. Finally, different nonstoichiometry thermodynamics are explored to provide guidance for further material exploration, as well as applicable methodologies.
", "doi": "10.7907/Z92805PM", "publication_date": "2017", "thesis_type": "phd", "thesis_year": "2017" }, { "id": "thesis:10266", "collection": "thesis", "collection_id": "10266", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:06042017-165228124", "type": "thesis", "title": "Effective Toughness of Heterogeneous Materials", "author": [ { "family_name": "Hsueh", "given_name": "Chun-Jen", "orcid": "0000-0001-6522-4505", "clpid": "Hsueh-Chun-Jen" } ], "thesis_advisor": [ { "family_name": "Bhattacharya", "given_name": "Kaushik", "clpid": "Bhattacharya-K" } ], "thesis_committee": [ { "family_name": "Ravichandran", "given_name": "Guruswami", "clpid": "Ravichandran-G" }, { "family_name": "Faber", "given_name": "Katherine T.", "clpid": "Faber-K-T" }, { "family_name": "Daraio", "given_name": "Chiara", "clpid": "Daraio-C" }, { "family_name": "Bourdin", "given_name": "Blaise", "clpid": "Bourdin-B" }, { "family_name": "Bhattacharya", "given_name": "Kaushik", "clpid": "Bhattacharya-K" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "Composite materials are widely used because of their extraordinary performance. It is understood that the heterogeneity / microstructure can dramatically affect the effective behavior of materials. Although there is a well-developed theory for this relation in elasticity, there is no similar theory in fracture mechanics. Therefore, we use theoretical, numerical, and experimental approaches to study the relationship between heterogeneity / microstructure and the effective fracture behavior in this thesis.
\r\n\r\nWe use the surfing boundary condition, a boundary condition that ensures the macroscopic steady crack growth, and then define the effective toughness of heterogeneous materials as the peak energy release rate during crack propagation. We also use the homogenization theory to prove that the effective J-integral in heterogeneous materials is well defined, and that it can be calculated by the homogenized stress and strain field.
\r\n\r\nIn order to study the relationship between heterogeneities and effective toughness, we first use the semi-analytical method under the assumption of small elastic contrast to study selected examples. For strong heterogeneities, we use the phase field fracture method to study the crack propagation numerically. We then optimize the microstructure with respect to effective stiffness and effective toughness in a certain class of microgeometries. We show that it is possible to significantly enhance toughness without significant loss of stiffness. We also design materials with asymmetric toughness.
\r\n\r\nWe develop a new experimental configuration that can measure the effective toughness of specimens with arbitrary heterogeneities. We confirm through preliminary tests that the heterogeneities can enhance the effective toughness.
\r\n\r\nBesides study the effective toughness of heterogeneous materials, we also study a model problem of peeling a thin sheet from a heterogeneous substrate. We develop a methodology to systematically optimize microstructure.
", "doi": "10.7907/Z9HH6H49", "publication_date": "2017", "thesis_type": "phd", "thesis_year": "2017" }, { "id": "thesis:9991", "collection": "thesis", "collection_id": "9991", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:12082016-154933538", "primary_object_url": { "basename": "Small_Molecule_Catalysis_SJIJohnson_Final.pdf", "content": "final", "filesize": 17748756, "license": "other", "mime_type": "application/pdf", "url": "/9991/60/Small_Molecule_Catalysis_SJIJohnson_Final.pdf", "version": "v7.0.0" }, "type": "thesis", "title": "Computational Investigation of Small Molecule Catalysis by Cobalt, Rhodium, and Iridium Molecular Catalysts ", "author": [ { "family_name": "Johnson", "given_name": "Samantha Jo Iva", "orcid": "0000-0001-6495-9892", "clpid": "Johnson-Samantha-Jo-Iva" } ], "thesis_advisor": [ { "family_name": "Goddard", "given_name": "William A., III", "clpid": "Goddard-W-A-III" } ], "thesis_committee": [ { "family_name": "Goddard", "given_name": "William A., III", "clpid": "Goddard-W-A-III" }, { "family_name": "Gray", "given_name": "Harry B.", "clpid": "Gray-H-B" }, { "family_name": "Faber", "given_name": "Katherine T.", "clpid": "Faber-K-T" }, { "family_name": "Greer", "given_name": "Julia R.", "clpid": "Greer-J-R" }, { "family_name": "Persson", "given_name": "Petter", "clpid": "Persson-Petter" } ], "local_group": [ { "literal": "Resnick Sustainability Institute" }, { "literal": "div_eng" } ], "abstract": "Global energy demands are predicted to increase through 2040. In the spirit of meeting these demands, work focusing on increasing the efficiency of existing energy technologies, as well as improving energy storage is necessary. This work takes a catalytic approach to these challenges, focusing on Co, Rh, and Ir catalysts with pincer and bipyridine ligands. Density functional theory (DFT) can be used in order to gain a deeper understanding of how these catalysts behave. In the realm of improving existing technologies, the mechanism for oxidation of methane to methanol by Phebox Ir (Phebox = bis(oxazolinyl)phenyl) is investigated with a focus on understanding how subtle substitutions to the ligand can help or hinder this reaction. It is shown that in this catalyst, two unwanted intermediates on the potential energy surface (an IrIV state leading to catalyst deactivation and an IrV state leading to over-oxidation) can potentially be avoided by adding trifluoromethyl groups to the ligand. For production of fuels from solar energy, two reactions are studied. Experimentally, CO2 reduction to formate by (POCOP)Ir (POCOP = C6H3-2,6-[OP(tBu)2]2) has been shown to selectively occur at moderate potentials. The mechanism by which this catalyst reduces CO2 is elucidated. In particular, the impressive product selectivity afforded this catalyst for formate over hydrogen production is rooted in kinetics: high barriers for protonation inhibit the creation of H2 adducts. In addition to this, substitutions to the ligand and metal center are investigated to further illuminate the relationship between kinetics and thermodynamics. Hydrogen evolution in Cp*Rh(bpy) (bpy = 2,2'-bipyridine, Cp* = pentamethylcyclopentadienyl) is investigated, centering on unexpected protonation at the Cp* ligand rather than the metal center. This state is on the path for hydrogen evolution in the case of using weak acids, but in the presence of strong acids, the path through the traditional hydride is most likely. Finally, the attachment of these catalysts to electrode surfaces is discussed with the aim of making molecular catalysts a more viable option in industry It is shown that chlorine present in the attachment process enables easy catalyst dissociation from the surface. Several non-halogen options are discussed as replacements. Throughout the thesis two themes emerge: the constant interaction between thermodynamics and kinetics to control mechanistic paths and products, and the ability of small modifications to have huge impacts on catalytic cycles. ", "doi": "10.7907/Z9TD9V9K", "publication_date": "2017", "thesis_type": "phd", "thesis_year": "2017" }, { "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:9718", "collection": "thesis", "collection_id": "9718", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05122016-150703449", "type": "thesis", "title": "Investigation of Capacitive Discharge Heating of Metallic Glasses", "author": [ { "family_name": "Kaltenboeck", "given_name": "Georg", "clpid": "Kaltenboeck-Georg" } ], "thesis_advisor": [ { "family_name": "Johnson", "given_name": "William Lewis", "clpid": "Johnson-W-L" } ], "thesis_committee": [ { "family_name": "Johnson", "given_name": "William Lewis", "clpid": "Johnson-W-L" }, { "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": "Goddard", "given_name": "William A., III", "orcid": "0000-0003-0097-5716", "clpid": "Goddard-W-A-III" }, { "family_name": "Demetriou", "given_name": "Marios D.", "clpid": "Demetriou-M-D" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "In recent years, the discovery of bulk metallic glasses with exceptional properties has generated much interest. One of their most intriguing features is their capacity for viscous flow above the glass transition temperature. This characteristic allows metallic glasses to be formed like plastics at modest temperatures. However, crystallization of supercooled metallic liquids in the best bulk metallic glass-formers is much more rapid than in most polymers and silicate glass-forming liquids. The short times to crystallization impairs experimentation on and processing of supercooled glass-forming metallic liquids. A technique to rapidly and uniformly heat metallic glasses at rates of 105 to 106 kelvin per second is presented. A capacitive discharge is used to ohmically heat metallic glasses to temperatures in the super cooled liquid region in millisecond time-scales. By heating samples rapidly, the most time-consuming step in experiments on supercooled metallic liquids is reduced orders of magnitude in length. This allows for experimentation on and processing of metallic liquids in temperature ranges that were previously inaccessible because of crystallization.
\r\n\r\nA variety of forming techniques, including injection molding and forging, were coupled with capacitive discharge heating to produce near net-shaped metallic glass parts. In addition, a new forming technique, which combines a magnetic field with the heating current to produce a forming force, was developed. Viscosities were measured in previously inaccessible temperature ranges using parallel plate rheometry combined with capacitive discharge heating. Lastly, a rapid pulse calorimeter was developed with this technique to investigate the thermophysical behavior of metallic glasses at these rapid heating rates.
", "doi": "10.7907/Z9251G5Z", "publication_date": "2016", "thesis_type": "phd", "thesis_year": "2016" }, { "id": "thesis:9718", "collection": "thesis", "collection_id": "9718", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05122016-150703449", "type": "thesis", "title": "Investigation of Capacitive Discharge Heating of Metallic Glasses", "author": [ { "family_name": "Kaltenboeck", "given_name": "Georg", "clpid": "Kaltenboeck-Georg" } ], "thesis_advisor": [ { "family_name": "Johnson", "given_name": "William Lewis", "clpid": "Johnson-W-L" } ], "thesis_committee": [ { "family_name": "Johnson", "given_name": "William Lewis", "clpid": "Johnson-W-L" }, { "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": "Goddard", "given_name": "William A., III", "orcid": "0000-0003-0097-5716", "clpid": "Goddard-W-A-III" }, { "family_name": "Demetriou", "given_name": "Marios D.", "clpid": "Demetriou-M-D" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "In recent years, the discovery of bulk metallic glasses with exceptional properties has generated much interest. One of their most intriguing features is their capacity for viscous flow above the glass transition temperature. This characteristic allows metallic glasses to be formed like plastics at modest temperatures. However, crystallization of supercooled metallic liquids in the best bulk metallic glass-formers is much more rapid than in most polymers and silicate glass-forming liquids. The short times to crystallization impairs experimentation on and processing of supercooled glass-forming metallic liquids. A technique to rapidly and uniformly heat metallic glasses at rates of 105 to 106 kelvin per second is presented. A capacitive discharge is used to ohmically heat metallic glasses to temperatures in the super cooled liquid region in millisecond time-scales. By heating samples rapidly, the most time-consuming step in experiments on supercooled metallic liquids is reduced orders of magnitude in length. This allows for experimentation on and processing of metallic liquids in temperature ranges that were previously inaccessible because of crystallization.
\r\n\r\nA variety of forming techniques, including injection molding and forging, were coupled with capacitive discharge heating to produce near net-shaped metallic glass parts. In addition, a new forming technique, which combines a magnetic field with the heating current to produce a forming force, was developed. Viscosities were measured in previously inaccessible temperature ranges using parallel plate rheometry combined with capacitive discharge heating. Lastly, a rapid pulse calorimeter was developed with this technique to investigate the thermophysical behavior of metallic glasses at these rapid heating rates.
", "doi": "10.7907/Z9251G5Z", "publication_date": "2016", "thesis_type": "phd", "thesis_year": "2016" }, { "id": "thesis:9801", "collection": "thesis", "collection_id": "9801", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05272016-161721247", "primary_object_url": { "basename": "Shing_Amanda_Thesis_2016.pdf", "content": "final", "filesize": 12770609, "license": "other", "mime_type": "application/pdf", "url": "/9801/1/Shing_Amanda_Thesis_2016.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Development of Zn-IV-Nitride Semiconductor Materials and Devices", "author": [ { "family_name": "Shing", "given_name": "Amanda M.", "clpid": "Shing-Amanda-M" } ], "thesis_advisor": [ { "family_name": "Lewis", "given_name": "Nathan Saul", "clpid": "Lewis-N-S" }, { "family_name": "Atwater", "given_name": "Harry Albert", "clpid": "Atwater-H-A" } ], "thesis_committee": [ { "family_name": "Faber", "given_name": "Katherine T.", "clpid": "Faber-K-T" }, { "family_name": "Gray", "given_name": "Harry B.", "clpid": "Gray-H-B" }, { "family_name": "Goddard", "given_name": "William A., III", "clpid": "Goddard-W-A-III" }, { "family_name": "Lewis", "given_name": "Nathan Saul", "clpid": "Lewis-N-S" }, { "family_name": "Atwater", "given_name": "Harry Albert", "clpid": "Atwater-H-A" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "This thesis details explorations of the materials and device fabrication of Zn-IV-Nitride thin-films. Motivation in studying this materials series originates from its analgous properties to the III-Nitride semiconductor materials and its potential applications in photonic devices such as solar cells, light emitting diodes, and optical sensors. Building off of initial fabrication work from Coronel, Lahourcade et al., ZnSnxGe1-xN2 thin-films have shown to be a non-phase-segregating, tunable alloy series and a possible earth-abundant alternative to InxGa1-xN alloys. This thesis discusses further developments in fabrication of ZnSnxGe1-xN2 alloys by three-target co-sputtering and molecular beam epitaxy, and the resulting structural and optoelectronic characterization. Devices from these developed alloys are also highlighted.
\r\n\r\nInitial fabrication was based on the reactive radio-frequency (RF) sputtering technique and was limited to two-target sources and produced nanocrystalline films. Progression to three-target reactive RF co-sputtering for ZnSnxGe1-xN2 (x < 1) alloys is presented, where three-target co-sputtered alloys follow the structural and optoelectronic trends of the initial alloy series. However, three-target co-sputtering further enabled synthesis of alloys having < 10% atomic composition (x < 0.4) of tin, exhibiting non-degenerate doping. The electronic structure of sputtered thin-film surfaces for the alloy series were also characterized by photoelectron spectroscopy to measure their work functions and relative band alignment for device implementation.
\r\n\r\nLow electronic mobilities, degenerate carrier concentrations, and limited photoresponse may stem from the defective and nanocrystalline nature of the sputtered films. To improve crystalline quality, films were grown by molecular beam epitaxy (MBE). MBE ZnSnxGe1-xN2 films on sapphire and GaN were epitaxially grown, overall displaying single-crystalline quality films, higher electronic mobilities, and lower carrier concentrations. Througout experimentation, devices from both sputter deposited and MBE ZnSnxGe1-xN2 alloys films were constructed. Attempts at solid-state and electrochemical devices are described. Devices exhibited some photoresponse, providing a positive outlook for employment of ZnSnxGe1-xN2 alloys in solar cells or photon sensors.
\r\n", "doi": "10.7907/Z94Q7RXJ", "publication_date": "2016", "thesis_type": "phd", "thesis_year": "2016" }, { "id": "thesis:9203", "collection": "thesis", "collection_id": "9203", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:10062015-165650934", "primary_object_url": { "basename": "SallyJuneTracy_Final2.pdf", "content": "final", "filesize": 25055753, "license": "other", "mime_type": "application/pdf", "url": "/9203/1/SallyJuneTracy_Final2.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Polaron Hopping in Olivine Phosphates Studied by Nuclear Resonant Scattering", "author": [ { "family_name": "Tracy", "given_name": "Sally June", "orcid": "0000-0002-6428-284X", "clpid": "Tracy-Sally-June" } ], "thesis_advisor": [ { "family_name": "Fultz", "given_name": "Brent T.", "clpid": "Fultz-B-T" } ], "thesis_committee": [ { "family_name": "Fultz", "given_name": "Brent T.", "clpid": "Fultz-B-T" }, { "family_name": "Rossman", "given_name": "George Robert", "clpid": "Rossman-G-R" }, { "family_name": "Johnson", "given_name": "William Lewis", "clpid": "Johnson-W-L" }, { "family_name": "Faber", "given_name": "Katherine T.", "clpid": "Faber-K-T" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "Valence fluctuations of Fe2+ and Fe3+ were studied in a solid solution of LixFePO4 by nuclear resonant forward scattering of synchrotron x rays while the sample was heated in a diamond-anvil pressure cell. The spectra acquired at different temperatures and pressures were analyzed for the frequencies of valence changes using the Blume-Tjon model of a system with a fluctuating Hamil- tonian. These frequencies were analyzed to obtain activation energies and an activation volume for polaron hopping. There was a large suppression of hopping frequency with pressure, giving an anomalously large activation volume. This large, positive value is typical of ion diffusion, which indicates correlated motions of polarons, and Li+ ions that alter the dynamics of both.
\r\n\r\nIn a parallel study of NaxFePO4, the interplay between sodium ordering and electron mobility was investigated using a combination of synchrotron x-ray diffraction and nuclear resonant scattering. Conventional Mossbauer spectra were collected while the sample was heated in a resistive furnace. An analysis of the temperature evolution of the spectral shapes was used to identify the onset of fast electron hopping and determine the polaron hopping rate. Synchrotron x-ray diffraction measurements were carried out in the same temperature range. Reitveld analysis of the diffraction patterns was used to determine the temperature of sodium redistribution on the lattice. The diffraction analysis also provides new information about the phase stability of the system. The temperature evolution of the iron site occupancies from the Mossbauer measurements, combined with the synchrotron diffraction results give strong evidence for a relationship between the onset of fast electron dynamics and the redistribution of sodium in the lattice.
\r\n\r\nMeasurements of activation barriers for polaron hopping gave fundamental insights about the correlation between electronic carriers and mobile ions. This work established that polaron-ion interactions can alter the local dynamics of electron and ion transport. These types of coupled processes may be common in many materials used for battery electrodes, and new details concerning the influence of polaron-ion interactions on the charge dynamics are relevant to optimizing their electrochemical performance.
", "doi": "10.7907/Z95H7D67", "publication_date": "2016", "thesis_type": "phd", "thesis_year": "2016" }, { "id": "thesis:8811", "collection": "thesis", "collection_id": "8811", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:04022015-231633336", "primary_object_url": { "basename": "KozachkovHenry2015Thesis.pdf", "content": "final", "filesize": 7371634, "license": "other", "mime_type": "application/pdf", "url": "/8811/1/KozachkovHenry2015Thesis.pdf", "version": "v7.0.0" }, "type": "thesis", "title": "Modifying Bulk Metallic Glasses: Composites and Configurational States", "author": [ { "family_name": "Kozachkov", "given_name": "Henry", "clpid": "Kozachkov-Henry" } ], "thesis_advisor": [ { "family_name": "Johnson", "given_name": "William Lewis", "clpid": "Johnson-W-L" }, { "family_name": "Hofmann", "given_name": "Douglas C.", "clpid": "Hofmann-D-C" } ], "thesis_committee": [ { "family_name": "Fultz", "given_name": "Brent T.", "clpid": "Fultz-B-T" }, { "family_name": "Johnson", "given_name": "William Lewis", "clpid": "Johnson-W-L" }, { "family_name": "Hofmann", "given_name": "Douglas C.", "clpid": "Hofmann-D-C" }, { "family_name": "Ravichandran", "given_name": "Guruswami", "clpid": "Ravichandran-G" }, { "family_name": "Faber", "given_name": "Katherine T.", "clpid": "Faber-K-T" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "Bulk metallic glasses (BMGs) maybe be considered to share some of the same inherent trade-offs as engineering ceramics. While BMGs typically exhibit high yield strengths, and while some have surprising fracture toughness, they exhibiting little to no tensile ductility, and fail in a brittle manner under uniaxial loading. Speaking broadly, there are two complimentary approaches to improving on these shortcomings: 1) create bulk metallic glass matrix composites (BMGMCs) and 2) improve the properties of a monolithic BMG. The structure of this thesis mirrors this division, with chapters 2-7 focusing on creating and processing amorphous metal matrix composites, and chapter 8 focusing on modifying the properties of a monolithic BGM by altering its configurational state through irradiation.", "doi": "10.7907/Z9JQ0XZ4", "publication_date": "2015", "thesis_type": "phd", "thesis_year": "2015" }, { "id": "thesis:8667", "collection": "thesis", "collection_id": "8667", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:10032014-161017442", "type": "thesis", "title": "Surface Activity and Bulk Defect Chemistry of Solid Oxide Fuel Cell Cathodes", "author": [ { "family_name": "Usiskin", "given_name": "Robert Ezra", "clpid": "Usiskin-Robert-Ezra" } ], "thesis_advisor": [ { "family_name": "Haile", "given_name": "Sossina M.", "clpid": "Haile-S-M" } ], "thesis_committee": [ { "family_name": "Haile", "given_name": "Sossina M.", "clpid": "Haile-S-M" }, { "family_name": "Fultz", "given_name": "Brent T.", "clpid": "Fultz-B-T" }, { "family_name": "Faber", "given_name": "Katherine T.", "clpid": "Faber-K-T" }, { "family_name": "Rossman", "given_name": "George Robert", "clpid": "Rossman-G-R" } ], "local_group": [ { "literal": "Resnick Sustainability Institute" }, { "literal": "div_eng" } ], "abstract": "In the first half of this thesis, a new robotic instrument called a scanning impedance probe is presented that can acquire electrochemical impedance spectra in automated fashion from hundreds of thin film microelectrodes with systematically varied properties. Results from this instrument are presented for three catalyst compositions that are commonly considered for use in state-of-the-art solid oxide fuel cell cathodes. For (La0.8Sr0.2)0.95MnO3+\u03b4 (LSM), the impedance spectra are well fit by a through-the-film reaction pathway. Transport rates are extracted, and the surface activity towards oxygen reduction is found to be correlated with the number of exposed grain boundary sites, suggesting that grain boundaries are more surface-active than grains. For La0.5Sr0.5CoO3-\u03b4 (LSC), the surface activity degrades ~50x initially and then stabilizes at a comparable activity to that of previously measured Ba0.5Sr0.5Co0.8Fe0.2O3-\u03b4 films. For Sr0.06Nb0.06Bi1.87O3 (SNB), an example of a doped bismuth oxide, the activity of the metal-SNB boundary is measured.
\r\n\r\nIn the second half of this thesis, SrCo0.9Nb0.1O3-\u03b4 is selected as a case study of perovskites containing Sr and Co, which are the most active oxygen reduction catalysts known. Several bulk properties are measured, and synchrotron data are presented that provide strong evidence of substantial cobalt-oxygen covalency at high temperatures. This covalent bonding may be the underlying source of the high surface activity.
\r\n", "doi": "10.7907/Z91N7Z3N", "publication_date": "2015", "thesis_type": "phd", "thesis_year": "2015" } ]