Materials science and engineering

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Laser Powder Bed Fusion of Ti-6Al-4V: A Round Robin Analysis of Powder Reuse and Process By-Products
(2026-04-20) Montelione, Alexander; Arola, Dwayne D; Mamidala, Ramulu
Metal Additive Manufacturing (AM) provides immense value as a manufacturing method to produce high complexity parts for stress-critical applications. Metal AM though Powder Bed Fusion (PBF) technologies can produce fully dense metal parts with mechanical properties on par with wrought counterparts, and with geometries unachievable with conventional manufacturing methods. Widespread adoption of this technology requires thorough understanding of the contributors to part variability, and robust machine and part qualification.This dissertation evaluates the effects of powder reuse in L-PBF over the course of ten builds, split into two phases. The study presents a novel approach to powder reuse through a “round robin” style study involving six independent participants following the same operational procedure and, importantly, starting with the same lot of plasma-atomized grade 5 Ti-6Al-4V metal powder. Important metrics of powder quality are monitored throughout the study and compared to mechanical properties of the metal produced over time and between participants. Several categories of variability are considered, including intra-build (referring to variability that arises within individual builds), inter-build (variability that arises from one build to another on the same machine), and inter-machine (variability that arises between different machines run under the same nominal conditions). Byproducts of the L-PBF process, including spatter and metal vapor condensate, are investigated and characterized as important components of variability in powder quality. Phase I of the study involved six builds performed by six participants. Samples of powder were taken prior to each build and analyzed to characterize the particle size distribution, morphology, bulk chemistry, and flowability. The mean particle size of the powder as well as its flowability increased slightly with reuse at all sites, whereas the powder chemistry did not change appreciably over the six builds conducted. Quasi-static mechanical properties of the metal produced from the reused powder were found to correlate with carbon and aluminum content, but not with reuse number. In Phase II of the study, three of the original six participants continued with an additional four builds. Powder was again collected, analyzed, and compared between partners and against Phase I. Extended reuse was found to not intensify the trends observed in Phase I, and instead many of the measured properties stayed at, or returned to, nominal values. Powder chemistry did not change over Phase I or Phase II, although variability was observed between partners. The mean particle size of the powder samples, which had increased in Phase I, decreased back to nominal values.
Towards High-Efficiency and High-Brightness Perovskite Quantum Dot Light-Emitting Diodes
(2026-04-20) Shen, Gillian; Ginger, David S
Metal-halide perovskite quantum dots show immense promise for future display and single-photonemission applications owing to their unique properties for optoelectronics applications, including their high defect tolerance, high photoluminescence quantum yields, facile processibility, and ease of spectral tunability. My work focuses on the integration of such perovskite quantum dots into quantum dot light-emitting diodes (QLEDs), including optimizing strategies for achieving higher brightness with an attention to interlayer, architecture, and ligand design. As rapid and exciting developments continue to unfold in the field of photovoltaics, there is an increasing need to translate the developments and lessons from the photovoltaics space into making more efficient, bright, and stable light-emitting diodes. In this work, I develop a deeper understanding of how interfacial modifiers of great relevance in photovoltaics can also lead to exciting performance gains in QLEDs. The use of a phosphonic acid hole-injecting interface material allows us modify the work function of the indium tin oxide (ITO) interface, thereby allowing us to achieve device brightnesses far exceeding what had previously been demonstrated for perovskite QLEDs, enabling brightness levels that were previously only attainable by 3-dimensional perovskite emitters. We explore the mechanisms underlying the superior brightness that can be achieved in QLEDs with the use of such interfacial modifiers. My second major advancement in the field involves the use of the carbazole phosphonic acid species as a ligand candidate binding to surface sites of the quantum dots in the active layer. The use of the species both as a ligand candidate and as an interfacial modifier enables us to achieve surface passivation and energy level modification directly in the quantum dot layer to enable improved charge injection balance throughout the device. Finally, I develop a Bayesian toolkit for the efficient characterization of single photon emitters (SPE) for rapid and robust screening of SPE’s for single photon purity and character. I explore Lasso regularization and Bayesian noise reduction techniques and contrast the Bayesian approach to least squares (?2) or maximum log likelihood estimation for predicting g2(0) values. This is accompanied by a single photon emitter simulator, enabling the user to generate simulated g2(?) traces to match observed experimental emitter behavior and noise levels, while also running statistical confidence interval tests on the estimation protocols. This tool contributes to the streamlining of experimental workflows in assessing the single photon character of single photon emitters such as quantum dots and defects in diamond in a high-throughput fashion, or when the data may be signal-to-noise limited.
Applications of Asymmetric Rowland Geometries in Hard X-ray Spectroscopies
(2026-04-20) Gironda, Anthony Joseph; Seidler, Gerald T
Hard X-ray spectroscopy is widely used to characterize all states of matter in contemporary and relevant materials systems including but not limited to life sciences, catalyst materials, batteries and energy storage materials, pharmaceuticals, nuclear fuel and waste, and fossil fuels. At the core of these spectroscopy techniques is the measurement of X-ray absorption fine structure (XAFS), and the secondary process of X-ray fluorescence.Both laboratory and synchrotron hard X-ray spectroscopies demand the use of high-resolution spectrometers to analyze scattered or fluorescing photons. In the laboratory, spectrometers are required for the measurement of both XAFS and X-ray emission spectroscopy (XES). At synchrotron light sources, advanced photon-in/photon-out techniques such as high energy resolution fluorescence detection X-ray absorption spectroscopy (HERFD-XAS), resonant inelastic X-ray scattering (RIXS) / resonant XES, and X-ray Raman Scattering (XRS) all require the use of a spectrometer to analyze outgoing photons. Across all of these disciplines, the state-of-the-art for large collection solid angles and point-focusing geometries for efficient data collection at high resolution rely on the same diffractive optic: the spherically bent crystal analyzer (SBCA). The employment of SBCAs for high energy resolution photon analysis across this suite of spectroscopy techniques are in the same symmetric geometry. The work within this dissertation details the characterization, commissioning, and application of asymmetric Rowland geometries of SBCAs to XAFS/XES, HERFD, and XRS. I propose that this is an overlooked and underutilized modality for spectrometer design and that it frequently enables improved energy resolution and a massively increased energy range for photon analysis; addressing the two largest shortcomings of SBCAs in conventional symmetric geometries. Most importantly, the use of SBCAs in asymmetric Rowland geometries can drastically reduce the number of unique optics required for a sufficient analysis energy range. I detail the applications of this geometry in the design and construction of three separate spectrometers (laboratory XAFS/XES, synchrotron HERFD, synchrotron XRS), and in all three cases we find that it is lowering the resource barrier required for these techniques. The relevance of these developments for materials science research is substantial, and some representative applications are discussed and presented.
Research on High-Durability Siloxane-Coated Vanadium Pentoxide Cathodes for Aqueous Zinc-Ion Batteries
(2026-04-20) Chen, Liming; Cao, Guozhong
Aqueous zinc-ion batteries (AZIBs) are promising for large-scale storage due to low cost, inherent safety, and long cycle life. Among AZIB cathodes, hydrated vanadium pentoxide (VOH) cathode combines high theoretical capacity with a hydrated layered framework that provides open Zn2+ diffusion pathways and elastic accommodation. However, the application of VOH in AZIB remains hindered by issues such as vanadium dissolution, albeit slow and small, leading to capacity fade. This work introduces a self-assembly monolayer (SAM) of methyltri-n-butoxysilane (MTBOS) through an atomic layer of silicon oxide covalently anchored on the surface of VOH that shields vanadium cations from leaching by aqueous electrolyte, enabling ultralong cycle life, retaining excellent storage capacity and reaction and transport kinetics. The methyl ligand anchored to atomic layer of silica through covalent bond C-Si and Si–O–Si cross-linked silica layer attached to VOH through Si–O–V bonds. The SAM of MTBOS passivates the interface and enhances the structural integrity of VOH, while remains ion-permissive. The VOH with SAM (SVOH) yields fast Zn2+ kinetics and remarkable longevity, achieving ~89% capacity retention after 6000 cycles at a current density of 5 A g−1.
Separator Effects on Lithium Plating and Stripping Reversibility and Performance of High-Voltage Lithium metal batteries
(2026-04-20) Zhu, Boyu; Liu, Jun
Polyolefin separators play a central role in regulating ion transport and interfacial stability inlithium metal batteries, yet their performance can vary markedly across testing environments. In this study, Celgard 2400 and Celgard 2500 polypropylene separators, the Celgard 2325 trilayer separator, and a Nanoshel polyethylene separator were systematically compared in CR2032 cells under controlled assembly conditions with fixed electrolyte volume and consistent cell hardware through both Li|Cu plating/stripping tests and high-voltage NMC811|Li full-cell cycling. In Li|Cu cells, all separators exhibited high coulombic efficiency, but a reproducible separator dependence emerged, with cells using Celgard 2400 and Celgard 2500 polypropylene separators showing higher efficiency than those using the polyethylene separator and Celgard 2400 delivering the highest average value. Replicate statistics further indicated small yet measurable scatter, highlighting that instrument precision can contribute to apparent fluctuations when efficiencies approach unity. In contrast, separator ranking changed in full cells cycled between 2.8 and 4.4 V, where the polyethylene separator provided the highest capacity retention, coulombic efficiency closest to unity, and the most stable long-term cycling behavior, while Celgard 2325 trilayer separator exhibited the poorest durability with pronounced late-cycle instability. These findings indicate that separator performance is not universal but depends strongly on the battery chemistry and operating conditions.
3D Chitosan-Based Microenvironments to Regulate Cellular Fate For Tissue Engineering and Drug Screening Applications
(2026-04-20) Zhou, Yang; Zhang, Miqin
Conventional two-dimensional (2D) cell culture systems fail to recapitulate the spatial organization, mechanical cues, and biochemical complexity of native tissues, limiting their predictive value in disease modeling, drug discovery, and regenerative medicine. Although three-dimensional (3D) culture platforms improve physiological relevance, widely used matrices such as Matrigel remain xenogeneic, compositionally undefined, mechanically unstable, and poorly suited for scalable manufacturing or clinical translation. These limitations underscore the need for tunable, xeno-free biomaterial systems capable of not only supporting cells structurally but actively regulating cellular plasticity and tissue morphogenesis.This dissertation advances a microenvironment engineering strategy based on tunable 3D chitosan-based porous scaffolds designed to function as active regulators of cell fate. Cellular plasticity—the ability of cells to alter phenotype, transcriptional programs, or lineage identity in response to environmental cues—plays a central role in cancer progression, stem cell reprogramming, and tissue development. The central hypothesis of this work is that precisely engineered 3D scaffold architectures can modulate mechanical, spatial, and biochemical signals to control cellular state transitions while maintaining translational feasibility. To establish this framework, freeze-drying–based fabrication strategies were systematically investigated to define how processing parameters—including polymer concentration, solution depth, mold geometry, freezing temperature, freezing direction, and cooling rate—govern pore size, anisotropy, and mechanical properties. By linking thermal gradients and ice crystal dynamics to scaffold microstructure, an integrated design framework was developed to enable predictable customization of 3D microenvironments tailored to specific biological applications. Building on this architectural foundation, three major applications were pursued. First, tunable chitosan–hyaluronic acid porous scaffolds were developed as high-throughput platforms for glioblastoma modeling and drug screening. Controlled modulation of pore size and structural organization revealed that scaffold architecture regulates tumor cell morphology, gene expression, phenotypic heterogeneity, and therapeutic response, demonstrating that 3D microenvironmental cues directly influence cancer cell plasticity. Second, a virus-free nanoparticle–scaffold system was engineered by integrating polymeric gene delivery nanoparticles with a 3D chitosan microenvironment. This platform significantly enhanced human induced pluripotent stem cell (hiPSC) reprogramming efficiency and enabled a continuous, selection-free workflow. Transcriptomic analyses revealed that 3D scaffold culture reshapes transcriptional programs by suppressing inflammatory and extracellular matrix–associated pathways while promoting chromatin remodeling and pluripotency networks, thereby facilitating controlled cell-state transitions and improving reprogramming stability. Third, a xeno-free chitosan–alginate scaffold was developed to support hiPSC-derived epithelial–mesenchymal recombination for dental organoid formation and early tooth regeneration. The scaffold enabled coordinated epithelial–mesenchymal interactions, progressive odontogenic differentiation, and mineralized matrix deposition in vitro. Following orthotopic implantation, cell-laden scaffolds supported early tooth-like tissue organization and localized mineral formation, demonstrating the potential of engineered 3D scaffolds to guide hard tissue morphogenesis. Collectively, this work establishes design principles for engineering 3D porous scaffolds as active regulators of cellular plasticity across disease modeling, cell reprogramming, and regenerative tissue formation. By integrating scaffold architecture control, gene delivery technologies, and organoid-based regeneration within a unified microenvironment engineering framework, this dissertation provides a translationally relevant strategy for next-generation biomaterial platforms in biomedical engineering.
On Rate-Limiting Mechanisms in Nickel Manganese Cobalt and Lithium Iron Phosphate Cathodes: The Interplay of Low and High Current Constraints
(2026-04-20) Brischetto, Martin; Yang, Jihui
Lithium-ion batteries lie at the heart of the energy transition away from fossil fuels. They allow us to store intermittent renewable energy and dispatch it on demand in the form of electricity. Mobile applications of lithium-ion batteries, such as in electric vehicles, require high energy densities as the battery needs to propel its own mass, in addition to that of the rest of the car. Much work has been devoted towards this end, with current commercial state-of-the-art lithium-ion batteries reaching energy densities of 200-300 Wh/kg. However, The United States Department of Energy has set the ambitious goal of developing a cell with energy density above 500 Wh/kg that can cycle for more than 1000 cycles and costs less than $60/kWh . Increasing the energy density of a cell often involve trade-offs with respect to cycling stability, discharge rate, and cost. Understanding these trade-offs is crucial. In this dissertation, we develop a physics-based framework for characterizing and understanding discharge curves, rate performance data, and their relationship to the physical rate-limiting mechanisms evolving within the cell. With these models in mind, we assemble the largest, highest resolution, and highest quality rate performance data set of its kind available in literature; consisting of 58 LiNi_(0.6)Mn_(0.2)Co_(0.2)O_2 and 86 LiFePO_4 lithium metal anode cells, across five loadings and three porosities, discharged through a densely staggered series of galvanostatic discharge currents. We identify four different rate-limiting mechanisms that play a role in the capacity underutilization observed in LiNi_(0.6)Mn_(0.2)Co_(0.2)O_2 and LiFePO_4 cathodes. At low currents, LiNi_(0.6)Mn_(0.2)Co_(0.2)O_2 cathodes are limited by the ionic solid-diffusion in the active particles, while LiFePO_4 cathodes are limited by the phase transformation rate of the active particles. We find that the sharp capacity drop at high currents is generally caused by the growing Ohmic and charge-transfer potentials, and not by the ionic liquid-diffusion limits often ascribed to it. The ionic liquid-diffusion limits emerge in the thickest and most dense of cathodes, and requires a very low threshold voltage to be visible beyond the Ohmic/charge- transfer limit. The experimental data points to an optimal dense cathode thickness of 140-160 um and our modeling suggests that the optimal thickness for cells with porous anodes would be much smaller. Overall, this work provides a broad and nuanced framework for understanding the design considerations in Lithium-ion cells.
Electrochemical and Chemical Pathways for Resource Recovery Utilizing Seawater Resources
(2026-04-20) Robinson, Alexander J.; Subban, Chinmayee V
Oceans are a largely underutilized resource for energy and mineral resources. Developing technology, methods, and materials to responsibly harvest and utilize the diverse resources of the ocean could aid our national security and boost domestic production of critical minerals. Work performed in this thesis explores direct extraction of minerals from seawater and the utilization of seawater produced materials for resource recovery. Direct mineral extraction from seawater encompassed two projects split into separate chapters including: (i) an investigation of how pulsed voltage profiles can be used to alter Ca/Mg composition of calcareous electrodeposits in seawater for applications in corrosion prevention and carbon mineralization; and (ii) survey and synthesis of sorbents for selective Sr recovery from seawater to support domestic production of SrFe magnets as replacement strategy for certain applications of rare-earth containing magnets. Seawater produced materials, namely a waste acid stream was used to:(iii) economically produce Ni-metal and Ni-alloy from domestically sourced olivine minerals; and (iv) to perform a proof-of-concept extraction of Al from anorthosite. In chapter 2, the investigation of pulsed voltage profiles on calcareous electrodeposits found that providing a pulsed voltage between -0.8V and -1.2 V vs. SCE between 1-100 Hz produced more CaCO3 relative to Mg(OH)2 than the baseline case of a constant voltage at -0.8V. The formed deposits were also denser and provided better coverage than the deposits formed at a constant voltage at -1.2V which primarily consisted of Mg(OH)2. The most CaCO3-rich deposits were obtained under 10 Hz frequency and 10% duty cycle conditions for the voltage window investigated. While pulsing the voltage increases the amount of CaCO3 deposited, the energy required per gram of CaCO3 is significantly higher (14.5x) when compared to the base case of applying a constant voltage of -0.8V vs SCE. Further optimization of pulse conditions and system configuration could improve selectivity for carbonate deposits without compromising precipitation rates. In chapter 3, the synthesis of a Sr selective ion-exchange sorbent composed of barium silicate is investigated to increase its performance. The synthesis optimizations include altering the total volume of reactants in the hydrothermal reactor and varying the physical form of barium introduced into the system. Initial experiments show that limiting reaction volume to 30 mL provides the best Sr/Ca selectivity while using a solid source of barium provides better absorption performance. Further experiments characterizing and assessing sorbent performance are ongoing. In chapter 4, a waste acid generated by bipolar membrane electrodialysis technology is used to leach olivine for the purposes of extracting nickel. The waste acid was shown to leach nickel from olivine at a 37% increased rate over equal strength commercial HCl at room temperature. Treating this leachate with alkalinity to increase the pH to remove dissolved Si and the majority of dissolved iron resulted in retaining the majority of dissolved Ni (65%) and Mg (84%). This enriched solution is used for Ni-metal recovery via electroplating and demonstrated that the formed deposits is a FeNi alloy with a 43.4 wt% of Ni. Preliminary assessment indicates an overall economic benefit from recovering nickel from olivine using the proposed method and may increase further upon process optimization and changes in supply and demand of nickel. In chapter 5, a process for the extraction of Al from anorthosite utilizing oxalate chemistry is developed and explored for its feasibility. We found that leaching the anorthosite sample in 0.4 M HCl removes >95% of the Al from the sample and that applying oxalate to the leachate allows for the selective extraction and recovery of ~70% of the original Al. Economic cost-benefit shows a production cost of $1.07/kg alumina, about 2.5-3.5x more expensive than the Bayer process. Future optimizations and process refinement can bring this cost down while providing an Al extraction pathway with significantly less waste.
Controlling Crystallization of Two-dimensional Materials at Solid-liquid Interfaces
(2026-02-05) Xia, Ying; De Yoreo, James J.; Liu, Jun
Two-dimensional (2D) materials have been widely explored in biological, quantum, and energy-related applications due to their unique chemical, physical, and mechanical properties. The novel properties and their technological potential have driven the development of numerous synthesis strategies for 2D materials over the past decades. However, current synthesis strategies still rely heavily on practitioner expertise and trial-and-error (Edisonian) approaches. In this work, we propose solid–liquid interfaces as a powerful platform for controlling interfacial energies and structures, which can subsequently be used to direct the growth of 2D materials. This approach leverages the symmetry-breaking and 2D confinement effects of the interfaces. The overarching goal is to establish scientific design principles that enable adaptive control over the structures, phases, and crystallographic orientations of 2D materials, as well as to access stable or metastable 2D phases that cannot be synthesized in bulk solution. By tuning parameters such as intermolecular interactions, molecule–substrate interactions, entropic contributions, and external electric fields (E-fields), the structure of the solid-liquid interface can be modulated; thereby leading to variations in the interfacial energy landscapes that determine the stability of phases, the thermodynamic barrier to their nucleation, and the kinetics of desolvation and attachment. In this way, nucleation, growth, and assembly of 2D materials at interfaces can be precisely controlled. To test the hypothesis, a set of projects were chosen to individually investigate the various factors governing interfacial free energies. In the first project, patchy proteins, L-rhamnulose-1-phosphate aldolase (RhuA), with tunable interactions, shapes, and electrostatic patchiness, were selected as a model system to understand the effects of molecule-molecule interactions, the entropic drivers related to shape complementarity, and external E-fields. Using in-situ AFM, we observed the 2D assembly of distinct phases of β-cyclodextrin (CD) and azobenzene (Azo) modified RhuA (CDRhuA and AzoRhuA, respectively) at mica-water interfaces, as well as the transitions between them. For AzoRhuA, the presence of appropriate long functional groups and weak inter-protein interactions enables the formation of multiple polymorphs and between which phase transitions occur via two distinct pathways. However, when functional groups become excessively long or bulky, as with CDRhuA, densely packed alternating structures emerge via an unusual assembly pathway involving protein adsorption and reconfiguration. In this system, entropy related to shape complementarity dominate the assembly outcome. To probe the balance of forces governing these behaviors, we performed coarse-grained (CG) simulations in which we varied the relative contributions of protein-substrate interactions and protein-protein interactions, including both enthalpic and entropic forces. The simulations reveal that formation of the alternating pattern depends on a delicate balance between enthalpy and entropy, with the entropy of the bulky CD side groups and RhuA main bodies serving as the dominant driving force among the combined contributions. Finally, because the site-modified proteins possess intrinsic dipole moments, they provide an opportunity to study how coupling between external E-fields and the protein dipoles biases the thermodynamics and kinetics of nucleation. Moreover, the coupling between the E-field and the protein dipole moment might be a “knob” to manipulate the enthalpic term in the free energy to enable the controllable competition between system entropy and enthalpy. In the second project, we investigated the assembly of a peptide known to form 2D crystalline films on MoS2 on three representative van der Waals (vdW) substrates: WS2, MoS2, and highly oriented pyrolytic graphite (HOPG) to explore the effects of molecule-substrate interactions on assembly. Using in-situ AFM, we found that assembly of the model system, MoSBP1 peptides (YSATFTY), is substrate-dependent, resulting in multilayers on WS2, monolayers on MoS2, and multiple coexisting phases on HOPG. On WS2, the higher negative charge, strong long-range forces, and extensive hydration layering appear to promote multilayer stacking. In contrast, MoS2 has stronger short-range interactions with the peptides but much weaker long-range interactions and hydration structure, which may favor monolayer formation. Molecular dynamics simulations predict a corresponding switch from monolayer to multilayer aggregates of the adsorbed monomers, reflected in their relative mobilities. On hydrophobic HOPG, peptides bind most strongly and remain as monomers with high surface mobility. The peptide dimers comprising the basic unit of the crystals are more compact on HOPG, which has a smaller lattice constant than WS2 or MoS2, suggesting strain contributes to stabilizing multiple phases. Together, these results provide mechanistic insights into how surface charge, hydration structure, and lattice structures of vdW substrates govern peptide assembly. We also found that differences in strain and electronic states of twisted vdW materials may influence the epitaxial relationship between substrates and peptides. In the third project, the knowledge gained from the model systems was applied to control the interfacial energy of the substrate-electrolytes and Zn-electrolyte interfaces using additives, addressing an application-driven challenge: the suppression of zinc dendrites in batteries. We used the in-situ electrochemical (EC) AFM to directly observe the interfacial evolution during Zn electrodeposition and polymer adsorption on Cu substrates in the presence of varying concentrations of ZnSO4 and polyethylene oxide (PEO), one of the simplest and most widely used polymers. Contrary to previous literature assumptions which emphasize the binding to the growing Zn crystal surfaces or Zn2+ ions, our results demonstrate that PEO smooths Zn films by promoting nucleation of (002)-oriented Zn platelets through interactions with the Cu substrate. Density functional theory simulations support this finding by showing that PEO adsorption on Cu modifies the interfacial energy of Zn/Cu/electrolyte interfaces, favoring the stabilization of Zn (002) on the Cu substrate, as well as confines Zn electrodeposition to a narrow near-surface region. These findings elucidate a novel design principle for electrode smoothing, emphasizing the importance of substrate selection paired with polymer additives that exhibit an attractive interaction with the substrate, but minimal interaction with growing crystals, offering a mechanistic perspective for improved battery performance. Building on this principle and our established platforms for studying complex electrochemical interfaces, we further examined how polymer chemical structures and anions in solutions influence polymer-induced electrode flattening using sequence-defined peptoids as a model system.
Insights of the Nanoscale Compositional Variations in Dental Enamel Revealed by Statistical Atom Probe Tomography
(2026-02-05) Grimm, Jack Robert; Arola, Dwayne D; Devaraj, Arun
Dental enamel is a critical tissue in the body, acting as the primary surface for mastication as well as serving an aesthetic role in a smile. Enamel is also an inspirational material from a materials science perspective, as it endures decades in a challenging and complex oral environment whilst being subjected to cyclic loads. For these reasons, it is worthwhile to develop a thorough understanding of the microstructural and compositional features that provide this tissue its longevity, and how those features can be altered as a function of location within the tooth, age, or external factors such as disease or lifestyle choices. This dissertation is concerned with exploring the composition of the hydroxyapatite nanocrystals that constitute enamel at the smallest scale, elucidating where changes take place at a nanometric level and providing a perspective as to how those changes occur. Atom probe tomography (APT) is a powerful tool that is well suited to this investigation. Over the past decade, APT has had a significant impact on the study of enamel structure, however small sample sizes and inconsistent use of parameters have limited its ability to make rigorous comparisons between samples from distinct locations, age groups, or conditions. To address these issues, we have developed a routine for atom probe data analysis which enables more granular and robust statistical tests to provide a measure of confidence when comparing multiple groups. The routine is strengthened by complimentary analysis with other techniques such as TEM and Raman spectroscopy. Applied to human enamel from young and senior age groups, this routine reveals an enrichment of fluorine with age in the outer shell of nanocrystals, but not in the nanocrystal core or the intergranular space between nanocrystals. This reflects the culmination of decades of cyclical de- and re-mineralization during which fluorine is incorporated into the nanocrystal shells, though the nanocrystals themselves become slightly smaller and the separation between them slightly larger. The routine described above was also applied to “aprismatic” crocodilian enamel (i.e. without rods), complimenting a broader investigation of the sharp gradient in mechanical properties, composition, and nanocrystal morphology that arises at the outermost enamel surface. Parameter selection during atom probe experimentation and choices made during analysis can have a substantial impact on the reported results. In pursuit of improved accuracy, precision, and repeatability for these and future experiments, this dissertation also includes a systematic exploration of the parameter space for atom probe experiments on synthetic hydroxyapatite. As part of this, we present a facile and automated approach to ranging of the mass-to-charge spectrum, from which the composition is derived. The significance of the wavelength of the laser pulse used during APT is also studied, with evidence indicating that hydroxyapatite is photoionized by the deep ultraviolet wavelength laser which comes equipped on the newest generation of commercial laser pulsed atom probe systems. Finally, this dissertation incorporates the developments described above to compare inner enamel from primary, young, and senior age groups, with a particular focus on the presence of nanoscale organic precipitates that reside between some nanocrystals. Statistical analysis of these precipitates allows for the confident differentiation between organic (e.g., CO) and inorganic (e.g., CO2H) carbon-containing signals in atom probe reconstructions, which can then be applied to better understand the variations in both mineral and organic components between age groups. Additionally, retention of some precipitates after exposure of the enamel to a prolonged bleaching solution indicates that these organic features can be occluded by mineral and thus are resistant to change under attack by external threats. Altogether, this research advances both our understanding of dental enamel as well as the measurement science required to explore nanoscale features in this and other material systems. We envision that future investigations will be able to delve deeper into specific conditions of global and clinical concern, such as aging populations, environmental exposures, caries, molar-incisal hypomineralization, and amelogenesis imperfecta.
Scaling Synthesis of Sulfur Cathode Materials: an Analysis of Sulfur Distribution to Achieve High Performing Lithium-Sulfur Batteries
(2026-02-05) Ng, Wilson Shi Jie; Xiao, Jie
As a promising candidate for next-generation high performance lithium batteries, lithium-sulfur (Li-S) technology has been widely explored in academia. With a wide variety of cathode materials validated, the next step towards practical development is to be able to scale up their production while maintaining consistent quality. This thesis, in collaboration with the Pacific Northwest National Laboratory (PNNL), focuses on the reproduction of a nitrogen-doped Ketjen Black/sulfur (NKB/S) composite material developed at PNNL with the goal of producing batches at a consistent quality before scaling up. During the material and electrochemical validation of the material, it was found that, while very similar to the standard NKB/S produced at PNNL, a major quality difference was found in the sulfur content distribution across particle sizes. Sulfur distribution in the usable 25-90µm NKB/S was found to consistently have 2-4% extra wt.% sulfur than the target, while the material <25µm were missing almost an equivalent amount of sulfur. Theories behind this phenomenon and further validations are discussed and proposed.
Development of Fabrication Process for Twisted Rhombohedral Trilayer-Bilayer Graphene Transport Devices
(2026-02-05) Mastel, Isaac; Yankowitz, Matthew
This work presents the development and refinement of a fabrication methodology for twisted rhombohedral trilayer-bilayer graphene (tRTBG) transport devices. The tRTBG system is predicted to host flat electronic bands with high Chern numbers at twist angles of 1.1°~1.4°, promoting highly correlated, potentially fractionalized topological phases. This methodology covers parameters for exfoliation, identification, isolation, and stacking of graphene and hexagonal Boron Nitride flakes into van der Waals heterostructures via AFM and polymer-based dry transfer techniques, as well as modified PC/PDMS transfer slide properties. The resulting heterostructures are patterned into devices using electron-beam lithography, reactive ion etching, and Cr/Au metal evaporation. We find that increased O2 plasma cleaning and baking times of SiO2 wafers prior to and during exfoliation promotes the generation of large, pristine flakes with regions of both bilayer and trilayer graphene. Four devices were successfully fabricated using this methodology, and initial 4K transport measurements confirm functional operation and reveal features consistent with the predicted tRTBG band structure, including a displacement field-dependent band gap at ν = 0 and a resistive bump within the range 0<ν<1, suggestive of emergent states at millikelvin temperatures. This methodology provides a reproducible route for the fabrication of tRTBG devices and establishes the foundation for future work aimed at more thorough characterization of the underlying physics of this system.
Nanocharacterization of Composite Adhesive Bonding Systems
(2026-02-05) Olander, Rita Jeannine Taitano Johnson; Flinn, Brian D
University of WashingtonAbstract Nanocharacterization of Composite Adhesive Bonding Systems Rita Jeannine Taitano Johnson Olander Chair of the Supervisory Committee: Brian D. Flinn Department of Materials Science and Engineering This research was directed toward understanding the fundamental science behind polymer matrix-adhesive interactions in adhesively bonded composite aircraft materials. Nanoindentation and nanochemical techniques were used to characterize various regions of adhesively bonded carbon fiber/epoxy composite samples including the matrix resin, adhesive, and bondline mixing zones (interface/interphase). Adhesive regions in cobonded systems were found to have distinct nanomechanical properties. Regions with a higher degree of comingling between adhesive and resin materials, in general, were found to have higher nanomechanical properties unique from the bulk materials. Nanochemical techniques were also shown to be capable of identifying changes in the chemical constituents within cobond system bondline regions. Nano-dynamic mechanical analysis (nanoDMA) methodology was developed and validated through model-based controlled mixtures to directly characterize bondline regions within various bond architectures. NanoDMA measurements overall have good agreement with traditional Tg methods. NanoDMA and the model-based system evaluation indicates that the TgTan(δ) in comingled regions may be estimated for certain systems with Reuss Rule of Mixtures. However, some adhesives show a 3rd order dependence on the volume of adhesive within the comingled region and a baseline characterization curve should be generated for each system. A composite adhesive bonding system baseline with controlled high temperature exposures above and below the anticipated adhesive’s glass transition temperature were characterized to assess high temperature effects on nanomechanical properties. This was then compared to systems with long-term on-aircraft time temperature and stress exposures (scrapped parts), and systems with on-ground, outdoor environmental exposures. When baseline cobond system coupons were conditioned at higher temperatures for short durations, subtle increases in nanomechanical properties were observed, suggesting additional crosslinking at higher temperatures. Exposure below anticipated Tg show that a “post-cure” effect may occur while exposure above Tg show some indications of degradation. Despite subtle changes in the nanomechanical properties, the bonding systems showed long-term thermal exposure stability at temperatures below Tg without any indication of degradation. Overall, implementation of nanomechanical characterization provides value in identifying initial and environmental exposure compatibility of materials within adhesively bonded systems. Combined with other techniques, these methods may significantly reduce the barriers for developing new bonding systems for use in the aerospace industry. Further investigation is recommended to correlate nanomechanical properties to chemical and marco-mechanical properties traditionally used in assessment of bonding systems.
Evaluation of Cavitation Abrasive Surface Finishing as a Surface Treatment for Metal Produced Through Laser Powder Bed Fusion
(2026-02-05) Petram, Rohin; Arola, Dwayne; Mamidala, Ramulu
Laser powder bed fusion (L-PBF) has emerged as a highly viable method for manufacturing metal structural components across various industries. However, the inherently rough surfaces and complex morphologies of L-PBF components, particularly those with vertical, upskin, and downskin orientations, necessitate post processing treatments to improve surface finish and integrity. Additionally, heat treatments used to control microstructure and mechanical properties often produce a surface oxide layer that requires removal. In this investigation, cavitation abrasive surface finishing (CASF) was employed to improve the surface quality and remove the oxide layer of LPBF Ti6Al4V components, with specific attention to how build orientation, presence of alpha case, and line of sight effected the ability of CASF to improve the surface texture, introduce residual stress, and remove material. Results showed that CASF reduced the average surface roughness from approximately 5 to 20 μm in the as-built condition (depending on orientation) to as low as 4 μm. The process also imparted compressive residual stresses up to 600 MPa and was capable of removing the alpha case from direct line-of-sight surfaces. Despite these improvements, treatment uniformity varied with surface orientation. downskin surfaces, characterized by higher initial roughness and more extensive coverage of partially fused powder particles were the most challenging to treat. Even after CASF, these surfaces achieved significantly lower compressive residual stress, apparently due to shielding effects of particles that limit cavitation impact. Overall, CASF demonstrated strong potential as a non-chemical alternative for post processing LPBF titanium components, offering both surface smoothing and beneficial compressive stress. However, optimization of treatment parameters is needed to improve uniformity across orientations and to further assess the fatigue performance of treated surfaces.
A High-Throughput Microfluidic Platform for Targeted Drug Delivery and Multiplex Analysis at the Single Cancer Stem Cell Level
(2026-02-05) Xue, Jiaheng; Yang, Quansan
Cancer stem cells (CSCs) drive tumor initiation, therapy resistance, and relapse, but traditional bulk assays and multi-well screens average heterogeneous populations and obscure the behavior of rare CSCs. This dissertation reports the design and fabrication of a high-throughput microfluidic platform that enables gradient drug delivery and multiplex analysis at single-CSC resolution. Through iterative engineering of several chip architectures, we developed a final device that integrates microstructures for deterministic single-cell capture, a microchannel network that generates stable spatial drug gradients, and a multi-electrode array compatible with fluorescence imaging and label-free electrical measurements such as impedance spectroscopy. Using model CSC populations, we demonstrate robust single-cell trapping, long-term on-chip culture, and reproducible gradient exposure, and show that the resulting single-cell datasets reveal pronounced heterogeneity in drug response within nominally identical treatment groups. This platform provides a practical foundation for future integration with high-content imaging, multi-omics analysis, and patient-derived samples.
Probing and Manipulating Novel Electronic States in Graphene Multilayers
(2026-02-05) Ma, Xuetao; Yankowitz, Matthew; Chu, Jiun-Haw
The pursuit of understanding, manipulating, and engineering quantum materials has opened new avenues for exploring exotic states of matter. Among these materials, graphene multilayers represent a rapidly emerging platform in which the electronic properties can be drastically tuned through artificial control of stacking configurations. These systems provide a unique opportunity to investigate a wide range of correlated and topological phases, including (Quantum) anomalous Hall effects, fractional quantum Hall states, and unconventional superconductivity. Their versatility offers an exciting pathway for advancing both fundamental science and future technologies in quantum information and materials engineering. This dissertation presents a comprehensive study of the electronic transport properties of graphene multilayers and the development of novel experimental techniques to manipulate their quantum states. First, we revisit the transport behavior of monolayer, Bernal bilayer, and twisted bilayer graphene across a range of twist angles, uncovering new and unexpected phenomena. Building on these findings, we introduce two complementary tuning approaches designed for cryogenic transport measurements: the application of high pressure using a diamond anvil cell and the precise control of in-plane uniaxial strain. These techniques open access to previously unexplored regimes, enabling detailed studies of symmetry breaking, electronic correlations, and topological transitions. The insights gained from these measurements deepen our understanding of the ground states in graphene multilayers and demonstrate their potential as a versatile platform for exploring strongly correlated and topological quantum phases.
Design of Thermoformable Composites and Advanced Manufacturing: Linking Processing, Microstructure, and Service Life Performance
(2026-02-05) Parker, Mallory; Arola, Dwayne D; Roumeli, Eleftheria
Engineered materials continue to evolve at incredible rates, serving an expansive range of consumer, industrial, and research needs. Composites, specifically polymer composites, offer lightweight alternatives with nearly unlimited combinations of constituents for both niche and broad applications. In parallel, advanced manufacturing techniques expand to accommodate precise control over these novel materials. For instance, additive manufacturing (AM) has revolutionized the rapid production of component parts since the commercialization of stereolithography in the 1980s and is now hailed for design freedom in complex structures and low material waste. Originally conceived for polymers, all classes of materials are now being exploited and produced in tandem with additive processes to push the possibilities of engineered micro- and macro-structures. In the case of AM, as well as other manufacturing techniques, there is an opportunity to thoughtfully design multifunctional materials, especially composites, in which each element can provide specific functions for targeted applications. Bulk material properties are induced through careful selection of the matrix reinforcement elements and further property tuning can stem from refinement of component manufacturing parameters, such as production temperature or post-process treatment. However, despite being crucial towards the improvement of composite design, developing the interconnected knowledge for each composite system and/or manufacturing technique can be exhaustive. Through two unique composite systems, this research investigates the relationship between manufacturing parameters, microstructural elements, and physical performance to conclude generalizable correlations for future iterations. In the first system, we analyze a continuous carbon fiber reinforced polyphenylene sulfide filament for fused filament fabrication. Here, we characterize two generations of filament designs and modify print tooling in attempt to maximize composite mechanical performance and potential service life/reliability. While still stronger (in tension) than all commercially available polymer composite filaments, we find that the stiffness of carbon fibers combined with the severe deposition angle of current commercial 3D printers leads to inherent process induced defects, which reduce strength and reliability. We can begin to alleviate these defects with improvements to initial composite morphology and the extruder nozzle design. In the second system, we utilize a sustainable feedstock, algae, as a potential matrix platform for biodegradable biocomposites. A deep investigation into algal biomatter transformation informs our correlation between its thermomechanical manufacturing (hot-pressing) and mechanical/chemical properties. We explore the complete life cycle of our biocomposites, from feedstock composition to changes during thermomechanical processing and ultimately end-of-life degradation. That knowledge informs intentional manipulation of the service life in a targeted product application. While vastly different material systems, the findings from these efforts will provide both researchers and manufacturers critical and diverse knowledge as to how production processes influence the manufacturability and resulting mechanical behavior of both synthetic and natural composite structures. Armed with informed cause and effect, we can then lead production of a new generation of advanced composite materials.
Chitosan-Based Biomaterials for Renewal and Differentiation of Human Neural Stem Cells
(2025-10-02) James, Matthew; Zhang, Miqin
Human neural stem cells (hNSCs) are critical for regenerative medicine and disease modeling due to their self-renewal and ability to differentiate into neurons, astrocytes, and oligodendrocytes. These traits make hNSCs ideal for repairing neural tissue and studying neurodegenerative disorders like Alzheimer's and Parkinson's, which are increasingly prevalent in aging populations and carry significant socioeconomic costs. Stem cell-based strategies offer transformative potential for therapeutic development and mechanistic studies. However, hNSC applications are hindered by current in vitro culture systems. Conventional 2D platforms, often using murine-derived extracellular matrix (ECM) coatings like Geltrex or Matrigel, fail to mimic the brain's 3D microenvironment. These materials are not chemically defined or xeno-free, posing regulatory and safety challenges for clinical translation. Cells grown on such substrates require extensive testing to meet current Good Manufacturing Practice (cGMP) standards, increasing costs and complexity. Moreover, 2D systems lack physiological relevance, contributing to the high failure rate of drug candidates in clinical trials. This dissertation addresses these challenges through a systematic exploration of chitosan-based biomaterials as a versatile, next-generation platform for hNSC expansion, maintenance, differentiation, and disease modeling. Chitosan, a biocompatible and biodegradable polysaccharide derived from chitin, closely mimics the glycosaminoglycans in the brain's ECM, offering a biomimetic substrate for neural cell culture. Its ability to be processed under mild conditions into various morphologies, such as films, scaffolds, or hydrogels, and chemically modified to tune mechanical and biological properties makes it an ideal candidate for advanced stem cell engineering applications.The research began with the fabrication and characterization of composite thin films made from chitosan, alginate, and hyaluronic acid. These films were designed to optimize key parameters, including surface hydrophilicity, mechanical stiffness, nanoscale topography, and electrostatic interactions with hNSCs. By systematically varying polymer ratios, we found that pure chitosan films provided the most supportive environment for maintaining hNSC multipotency over a 4-day culture period, as evidenced by sustained expression of stemness markers (SOX2, nestin, Ki67, and SOX1) assessed via an alamarBlue assay, immunocytochemistry, and flow cytometry. These findings established pure chitosan as the foundational material for subsequent 3D scaffold development. To address the limitations of 2D cultures and enable scalable production of functional stem cells, we designed 3D porous chitosan scaffolds optimized for dynamic culture conditions. Using an orbital shaker model to simulate perfusion and mechanical agitation, we demonstrated that these scaffolds maintained structural integrity under fluid shear stress while supporting hNSC viability and function. The porous architecture facilitated enhanced nutrient and oxygen diffusion, promoting physiologically relevant cell–cell and cell–matrix interactions. Compared to static 2D controls, these scaffolds significantly improved hNSC proliferation and multipotency, as measured by alamarBlue assay, live/dead staining, and SOX2, nestin, SOX1, and PAX6 staining. This system supported long-term culture of hNSCs (over 21 days). Scaffolds with higher chitosan content (e.g., 4% w/v) exhibited superior mechanical resilience, making them well-suited for bioprocessing applications in large-scale cell manufacturing. Recognizing the need for controlled, scalable stem cell production, we developed a custom, modular bioreactor system capable of supporting both macro- and microscale cultures. The bioreactor featured real-time, in-line monitoring of critical parameters, pH, dissolved oxygen, and CO₂, using integrated sensors connected to a microcontroller-based interface for precise environmental control. This system supported the culture of hNSCs for 7 days, as well as other cell types such as suspension-grown T cells and adherent tumor cell lines, demonstrating its broad applicability. The use of cost-effective, off-the-shelf components enhances the system's accessibility for academic research and its potential for adoption in translational settings, such as cGMP-compliant cell production facilities. We then investigated chitosan scaffolds as a platform for directing hNSC differentiation into cortical neurons. Various surface modifications, including Geltrex coatings, medium conditioning with neurotropic factors (e.g., BDNF, GDNF), and pre-seeding techniques, were evaluated for their impact on lineage commitment. Pre-seeded scaffolds outperformed 2D controls, achieving higher neuronal yields and faster differentiation (within 14 days), with reduced astrocytic phenotypes, as confirmed by flow cytometry, immunocytochemistry, RT-qPCR analyses. These results highlight the scaffolds' ability to create a 3D microenvironment that closely mimics in vivo neural development. To validate the platform's translational potential, we cultured human induced pluripotent stem cell (hiPSC)-derived neural progenitors from healthy donors and Alzheimer's disease (AD) patients on aligned porous chitosan scaffolds. These scaffolds supported the formation of functional 3D neural networks, with AD-derived cultures exhibiting disease-specific hallmarks, including amyloid-beta peptide accumulation and dysregulated tau-related gene expression (e.g., MAPT, PSEN1). These phenotypes were quantified using ELISA and RNA sequencing, confirming the platform's utility as a scalable, physiologically relevant model for neurodegenerative disease research and preclinical drug screening. In conclusion, chitosan-based biomaterials offer a chemically defined, xeno-free, and scalable solution to key challenges in hNSC culture, differentiation, and disease modeling. By meeting cGMP regulatory standards and enabling the transition from static cultures to dynamic bioreactor systems, these platforms support both research and therapeutic applications. This work advances the field of regenerative medicine and provides a robust, biomimetic tool for studying neurodegenerative disease mechanisms, paving the way to produce high-quality, clinically relevant neural cells.
Obscure Variables in Battery Research: Impacts of Spacer Thickness and Slurry Formulation Protocols
(2025-10-02) Gao, Maxwell; Liu, Jun
While much battery research focuses on new materials and full-cell designs, early-stage battery evaluation still relies on small, lab-scale coin cells, where often-overlooked factors can significantly affect test results. This work investigates two critical yet underexamined aspects of electrode performance: cell pressure and slurry formulation. First, the impact of spacer thickness, and thus internal cell pressure, on the electrochemical performance of sodium-ion coin cells is examined using hard carbon anodes. Findings show that insufficient compression leads to unstable contact, reduced capacity, and greater variability, while greater compression promotes higher capacity and greater cycle stability. Theories explaining these findings are discussed. Second, the optimization process of aqueous slurry mixing for hard carbon electrodes is presented. The sources of particle agglomeration and slurry inconsistency are found, ultimately developing a reliable protocol that improves coating uniformity and slurry stability.
Novel Demonstrations of Optical Refrigeration in Enzymes and Polystyrene and TEM Imaging of Novel Fluoride Microstructures
(2025-08-01) Gariepy, Rachel; Pauzauskie, Peter J.
This work focuses on novel demonstrations of optical cooling in structures that have not beencooled via laser refrigeration previously. The primary study was focused on investigating the possibility of optical refrigeration being powerful enough to cool enzymes attached to the surface of the cooling crystals, with potential applications in biochemical techniques requiring thermocycling, such as the polymerase chain reaction. Another study focused on the potential development of radiation balanced whispering gallery mode lasers through use of cooling nanoparticles deposited on the surface is also presented. Finally, transmission electron microscopy work that helped to uncover novel microstructures in common rare earth- doped fluoride materials that would not have been discovered without use of the instrument. Chapter 1 presents an introduction to the concepts of optical refrigeration and the ther- mometry techniques used to track the temperatures of our optical refrigeration materials. The parameters that must be carefully balanced to attain optimal laser refrigeration are in- troduced and discussed in detail. The two primary methods of thermometry and the concepts that underlie them are also presented. Chapter 2 introduces the idea of optical refrigeration of enzymes by describing the tech- nique we hope it may eventually be applied to, that being the polymerase chain reaction. Data is presented showing the development of a synthetic technique for covalently attaching a test enzyme, horseradish peroxidase, to the surface of the cooling ytterbium-doped yttrium lithium fluoride crystals. It is shown that the enzymes remain functional while attached to the crystals and that the enzymatic reaction product is not generated by any source other than the bound enzymes. A data collection apparatus and method are designed in order to obtain comparable enzymatic reaction rate data across heating, cooling, and control con- ditions from a single confirmed cooling crystal coated with the enzymes, and experiments using this setup and method can repeatedly show reaction rate increase during heating trials, reaction rate decrease during cooling trials, and control trials landing in between them. This is the first demonstration of optical refrigeration of enzymes. Chapter 3 involves cooling experiments using polystyrene resonators coated with ytterbium- doped upconverting nanoparticles with the goal of creating a radiation balanced microlaser as well as provide an improved substrate for single molecule biophysics. Multiple thermom- etry methods are used to probe the temperatures reached at the surface of the microspheres and their surrounding environment. It is found that local cooling of the crystals at the sur- face of the crystals is possible, but overall cooling of the local environment is not achieved. However, the coated spheres demonstrate significantly reduced heating when compared to identical uncoated spheres of the same diameter. Chapter 4 largely departs from the subjects of the rest of this dissertation and moves to electron microscopy of novel structures synthesized within the Pauzauskie group. The two structures presented are of porous α phase sodium yttrium fluoride crystals and core-shell calcium fluoride crystals referred to as mandala structures. Data generated from multiple advanced techniques are presented, including elemental maps from energy-dispersive x-ray spectroscopy and three dimensional tomographic reconstructions. Hypotheses describing the possible reasons for growth of these unusual structures are presented and potential future applications for these crystals are discussed.

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