Materials Science & Engineering
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Item INVESTIGATION AND ENGINEERING OF HfZrO2 INTERFACES FOR FERROELECTRIC BASED NEUROMORPHIC DEVICES(2024) Pearson, Justin Seth; Takeuchi, Ichiro; Najmaei, Sina; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This dissertation describes the study of ferroelectric hafnium zirconium oxide (HZO) and its integration into ferroelectric field effect transistors (FeFET). Ferroelectric HZO is uniquely situated for energy efficient, non-volatile memory applications such as FeFETs due to its CMOS compatibility and ferroelectricity at scaled thicknesses less than 10 nm[1]. This work covers material growth of HZO via atomic layer deposition (ALD), as well as electrode metallization (W and Pt) via sputtering and electron beam physical vapor deposition, to optimize ferroelectricity in capacitive structures. Preliminary results show Pt-based devices were sufficient in producing ferroelectric HZO, but had issues in electrode degradation at high thermal processing > 450 °C. In contrast, HZO capacitors in W devices showed drastic improvement in the ferroelectric response reaching remnant polarization values > 40 μC/cm2. To integrate into a FET structure, gate dielectrics (Al2O3 and HfO2) and the 2D semiconductor tungsten diselenide (WSe2) are introduced to the HZO stack. Material and electrical characterization was performed and gave indication of challenges such as: low remnant polarization (<10 μC/cm2), surface roughness (> 20 nm), and high trap characteristics in FeFET modulation. Electrical characterization was performed via variable pulsing, high frequency cycling, current vs voltage, capacitance vs voltage, and polarization vs voltage testing. Challenges such as low remnant polarization, leaky dielectrics, and surface roughness are identified through transmission electron microscopy, atomic force microscopy, and electrical characterization. These challenges were addressed by altering the growth conditions, scaling the thickness of each material, and thermally processing within the bounds of material stability. Upon integration of these various materials into FETs, the challenges of reliability, stochasticity, and consistency were evaluated on through various means of electrically testing such as, variable pulsing, high frequency cycling, current vs voltage, capacitance vs voltage, and polarization vs voltage. A greater depth of understanding of fundamental aspects of these device architectures is required to untangle the complex electrical characteristics of the fabricated devices. Characterization of material properties is performed by transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). Throughout the studies performed in this dissertation, the phase landscape of HZO was investigated on inert Ti/Pt electrodes. While the ferroelectric nature of the HZO was sufficiently explored at CMOS compatible temperatures, yielding remanent polarization values of 20 μC/cm2 and demonstrating multi state memory within Ferroelectric field effect devices (3.5 order of magnitude conductivity change), due to the phase landscape evolution under thermal processing. Higher temperatures were found to be incompatible with the electrode choice as the interdiffusion and breakdown resulted in poor device performance. W electrode HZO capacitors were then used to study the higher temperature ferroelectric devices as well as incorporate scaling of the ferroelectric films to better match the needs of modern device architectures. The optimal ferroelectric films were found to have remanent polarization values > 40 μC/cm2 and when implemented in a FEFET were able to demonstrate a memory window of 6.3 volts, allowing for a large range of modulation for neuromorphic devices.Item Insulating Materials for an Extreme Environment in a Supersonically Rotating Fusion Plasma(2024) Schwartz, Nick Raoul; Koeth, Timothy W; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Fusion energy has long been sought as the “holy grail” of energy sources. One of the most critical remaining challenges in fusion is that of plasma-facing materials, even denoted by the National Academies of Science. The materials challenge is particularly acute for centrifugal mirrors, an alternative concept to the industry-standard tokamak that may offer a more efficient scheme with a faster path to development. The centrifugal mirror incorporates supersonic rotation into a conventional magnetic mirror scheme, providing three primary benefits: (1) increased confinement, (2) suppression of instabilities, and (3) plasma heating through shear flow. However, this rotation, which is driven by an axial magnetic field and a radial electric field, requires the magnetic field lines to terminate on electrically insulating surfaces to avoid “shorting” the plasma. This unique requirement presents a novel materials challenge: the insulator must not only resist irradiation and thermal damage, but also be an excellent electrical insulator and thermal conductor that can be actively cooled. To address this materials challenge, the Centrifugal Mirror Fusion Experiment (CMFX) was developed at the University of Maryland. CMFX serves as a test bed for electrically insulating materials in a fusion environment, as well as a proof-of-concept for the centrifugal mirror scheme. To guide the design of future power plants and better understand the neutronand ion flux on the insulators, a zero-dimensional (0-D) scoping tool, called MCTrans++, was developed. This software, discussed in Chapter 2, demonstrates the ability to rapidly model experimental parameter sets in CMFX and predict the scaling to larger devices, informing material selection and design. Assuming the engineering challenges have been met, the centrifugal mirror has been demonstrated as a promising scheme for electricity production via fusion energy. One of the key aspects to the operation of CMFX is the high voltage system. This system, discussed in Chapter 3, was developed in incremental stages, beginning with a 20 kV, then 50 kV pulsed power configuration, and finally culminating in a 100 kV direct current power supply to drive rotation at much higher voltages, creating an extreme environment for materials testing. This work identified hexagonal boron nitride (hBN) as a promising insulator material. Computational modeling (Chapter 4) demonstrated hBN’s superior resistance to ion-irradiation damage compared to other plasma-facing materials. Additionally, fusion neutrons are crucial for assessing both material damage and power output. Chapter 5 details the neutronics for CMFX, including 3He proportional counters, which have been installed on CMFX to measure neutron production. In parallel, Monte Carlo computational methods were used to predict neutron transport and material damage in the experiment. Ultimately, a materials test stand was installed on CMFX to expose electrically insulating materials to high energy fusion plasmas (Chapter 6). Comparative analysis of hBN and silicon carbide after exposure revealed superior performance of hBN as a plasma-facing material. Two primary erosion mechanisms were identified by surface morphology and roughness measurements: grain ejection and sputtering, both more pronounced in silicon carbide. This work advances our understanding of insulating material behavior in fusion environments and paves the way for the development of the next-generation centrifugal mirror fusion reactors. Chapter 7 discusses conclusions and proposes future work. In particular this section suggests some changes that may allow CMFX to operate at much higher voltages, unlocking higher plasma density and temperature regimes for further material testing.Item HIGH-THROUGHPUT COMBINATORIAL EXPLORATION OF QUANTUM MATERIALS AND DEVICES FOR SPINTRONIC AND TOPOLOGICAL COMPUTING APPLICATIONS(2024) Park, Jihun; Takeuchi, Ichiro; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This doctoral dissertation aims to explore via high-throughput methodologies heavy-element-based quantum materials and devices for spintronic and topological computing applications. It is organized into three parts: (1) the development of spin wave devices based on magnetic insulators for magnon spintronics, (2) the search for spin-triplet superconductors based on Bi alloys (Bi–Ni and Bi–Pd) for superconducting spintronics, and (3) fabricating Josephson junctions based on topological insulators for topological quantum computing.The first part of this dissertation is to develop spin wave devices based on acoustically driven ferromagnetic resonance (ADFMR) using magnetic materials, including yttrium iron garnet (YIG). Spintronic devices based on ferromagnetic metals entail Joule heating and energy loss due to the moving of charge carriers. On the other hand, spin waves can be used without resistive losses. ADFMR is an efficient platform for generating and detecting spin waves via magneto-elastic coupling. While numerous ADFMR studies in ferromagnetic metals have been reported, there is no such report on magnetic insulators. This is due to (1) thermal degradation of piezoelectric substrates (e.g., LiNbO3) during the film crystallization (T > 800°C for YIG), (2) reaction between substrate and film materials, and (3) low ADFMR signals due to intrinsically low magnetostriction. The first part of this thesis attempts to address these issues to achieve YIG ADFMR devices by utilizing rapid thermal annealing to minimize thermal damage, a SiO2 buffer layer to avoid unwanted chemical reactions during crystallization, and a time-gating method for enhanced signal-to-noise ratio. YIG thin films deposited via pulsed laser deposition and crystallized by rapid thermal annealing show decent ferromagnetic behavior. YIG devices show exotic angle- and field-dependent absorption features, indicative of ADFMR. The observed ADFMR pattern is consistent with simulations. This result indicates the first demonstration of ADFMR in magnetic insulators. The second part of this work performs combinatorial synthesis of Bi–Ni and Bi–Pd alloys, which possibly show spin-triplet superconductivity. Such spin-triplet Cooper pairing would allow field-controllable spin polarization in superconductors, enabling superconducting spintronic applications. Furthermore, this type of device possibly provides evidence of superconducting pairing symmetries. In Bi–Ni spread study, Bi3Ni acts as a superconducting host material, where the superconductivity is identified to be varied according to two competing mechanisms: carrier doping and impurity scattering. These results can provide useful guidance in studying superconducting materials with stoichiometric defects. In the Bi–Pd spread films, two superconducting phases are identified with maximum Tc of 3.1 and 3.7 K, corresponding to BiPd and Bi2Pd phases, respectively. With Bi2Pd thin films, spin injection devices are fabricated and characterized. The Bi2Pd spin injection device showed unusual pair-breaking behavior where the superconductivity of Bi2Pd is destroyed significantly by unpolarized current injection. These superconducting spintronic studies demonstrate prompt device exploration via combinatorial methods, efficiently providing insight into spin-triplet superconductivity and its applications. Lastly, this dissertation aims to fabricate topological Josephson junctions based on Yb6/SmB6/Yb6 trilayers. SmB6 is a topological insulator characterized by a robust insulating bulk state and topological surface states. Superconducting proximity effects on the topological surface states can generate topological superconductivity, which can be utilized for fault-tolerant topological quantum computing. This dissertation addresses challenges in fabricating topological Josephson devices. With statistical analysis, device failure mechanisms are identified and addressed, allowing for improved design and fabrication. The improved devices showed Josephson junction-like behavior. The junction characterization revealed that 100% of measured samples showed Josephson features with prominent statistical reproducibility, possibly induced by the Klein effect. The dependence of SmB6 dimensions on the junction behavior is also investigated, along with possible proposed scenarios. These results demonstrate that the combinatorial approaches allow for efficient and prompt investigation of novel quantum materials and devices, facilitating phase diagram studies, materials screening, and stoichiometric controls.Item Dataset for "Resistance of Boron Nitride Nanotubes to Radiation-Induced Oxidation" as published in The Journal of Physical Chemistry C(2024) Chao, Hsin-Yun (Joy); Nolan, Adelaide M.; Hall, Alex T.; Golberg, Dmitri; Park, Cheol; Yang, Wei-Chang David; Mo, Yifei; Sharma, Renu; Cumings, JohnItem Scalable Rapid Fabrication of Low-Cost, High-Performance, Sustainable Thermal Insulation Foam for Building Energy Efficiency(2024) Siciliano, Amanda Pia; Hu, Liangbing; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Bio-based thermal insulation materials offer a promising path towards energy savings in the buildings sector. However, these materials face competitiveness challenges against conventional petroleum-based alternatives due to issues with inferior insulation performance, poor compressive strength, and limited manufacturing scalability. Various fabrication methods such as freeze drying, thermal bonding, and chemical treatment have been proposed to enhance the material’s internal structure by introducing additional pores, creating a more complex path for heat transfer, and improving insulation efficiency. Despite advancements, the manufacturing scalability of these methods and their integration into industrial production remain unachieved.This thesis aims to bridge the gap between laboratory experiments and large-scale production by developing low-cost, sustainable cellulose-based thermal insulation. By investigating both aqueous and non-aqueous-based processing strategies, this work proposes several different fabrication techniques, leading to significant savings in energy, time, and cost. Establishing a comprehensive understanding of the interactions among the fabrication process, insulation foam, manufacturing scalability, and intended product application is imperative. This understanding accounts for variations in processing parameters (e.g., pretreatments, binders, temperature, time) and their impact on the insulation foam’s internal structure and overall performance. By examining the relationship between processing parameters and material structure, this thesis not only advances the fundamental understanding necessary for optimizing fabrication but also provides strategic guidance for selecting and designing scalable bio-based thermal insulation foams. Studying and characterizing commercially viable methods that seamlessly integrate with current industrial infrastructures is crucial for facilitating the transition from small-scale laboratory experimentation to large-scale industrial production. Through various technical strategies, this work illustrates how our understanding can be utilized to offer direction for fabrication method selection, design, and processing, ultimately optimizing the scalable rapid fabrication of low-cost, high-performance sustainable thermal insulation materials for building energy efficiency.Item INTERFACES IN THIN-FILM SOLID-STATE BATTERIES(2024) Castagna Ferrari, Victoria; Rubloff, Gary GWR; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The lack of a diagnostics approach to monitor interface kinetics in solid-state batteries (SSBs) results in an incomplete knowledge of the mechanisms affecting device performance. In this study, a new protocol for process control of SSB interface formation and their evolution during operation is presented. Thin-film SSBs and diagnostic test devices that are composed by a permutation of isolated layers were simultaneously fabricated using sequential sputtering deposition and in-situ patterning using shadow masks. Physics-based electric circuit models were designed for deconvolution of impedance profiles, which enabled an evaluation of bulk properties and space-charge layers at interfaces individually and during operation under different states-of-charge. Relative permittivity values of fundamental battery components (cathode, electrolyte and anode) were calculated as a function of the frequency and the applied voltage. Interfacial impedances, as well as space-charge layers formed at heterojunctions during charge and discharge processes, were successfully deconvoluted using the diagnostic test devices and electric circuit modeling. The cathode-electrolyte interphase was kinetically stable under a voltage window of 0 – 3.6 V vs Cu, and it had an estimated ionic conductivity of the order of 10-9 S/cm, hence it is a localized limiting factor for Li+ transfer. The anode-electrolyte interphase was thermodynamically stable upon completion of the fabrication process, but it became kinetically unstable during charge and discharge cycles. Hence, the proposed diagnostics protocol enlightened the necessity of implementing interfacial engineering on these interphases in the future for improvement of cyclability and stability of SSBs and ionic devices.Item DIRECT INK WRITING SOLID-STATE LI+ CONDUCTING CERAMICS FOR NEXT GENERATION LITHIUM METAL BATTERIES(2024) Godbey, Griffin Luh; Wachsman, Eric D; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The global pursuit of safer and higher-capacity energy storage devices emphasizes the crucial link between the microstructures of electrochemically active materials and overall battery performance. The emergence of solid-state electrolytes featuring multi-layered, variable porosity microstructures presents fresh opportunities for developing the next generation of rechargeable batteries. However, this advancement also brings forth novel challenges in terms of device integration and operation. In this dissertation, solid-state Li-ion conducting electrolytes were 3D printed to enhance the performance of porous electrolyte layers within porous-dense-porous trilayer systems.LLZO-based garnet electrolyte scaffolds were fabricated via 3D printing using direct ink writing (DIW), facilitating the generation of scaffolds with minimal tortuosity and constriction in comparison to previous porous scaffolds manufactured through tape casting. Rheological techniques, including stress and time sweep tests, were employed to characterize the DIW inks and discern their conformal and self-supporting properties. The analysis focused on ink characteristics critical for Direct Ink Writing (DIW), emphasizing properties essential for achieving high aspect ratio printing and minimal constriction in 3D structures. Drawing from this ink research, two distinct 3D architectures, columns and grids, were fabricated. Column structures were utilized in assembling Li-NMC622 and Li-SPAN cells, with detailed discussions highlighting improvements in printing and sintering outcomes. Notably, NMC622, characterized by larger particle sizes, demonstrated complete infiltration within 3D printed porous networks, yielding a promising specific capacity of 169.9 mAh/g with minimal capacity fade. Further optimization involved integrating a porous 3D scaffold to facilitate SPAN infiltration in Li-SPAN cells, resulting in a specific capacity of 1594 mAh/g, albeit with significant capacity fade. The Li-S was implemented into a grid structure achieving 763 mAh/gS with less than 0.25% capacity loss over 16 cycles. Lastly, comprehensive morphology analysis was conducted to evaluate the effectiveness of our optimal DIW structures and to inform future enhancements of such cells.Item Interface Diagnostics Platform for Thin-Film Solid-State Batteries(2024-08-28) Ferrari, Victoria Castagna; Stewart, David Murdock; Rubloff, GaryThis dataset comprises electorchemical impedance spectroscopy measurements from thin film batteries comprised of LiV2O5, LiPON, and Si. The data is associated with a manuscript that describes the methodology and analysis of the data and conclusions we draw from it in complete detail. (At the time of submission, the manuscript was set to be submitted to a peer reviewed journal.) The data herein is intended to be used to model equivalent circuits for each material and the charge transfer interfaces throughout the device in order to construct the model of the full battery. The demonstrated methods to build from simple materials to a complex device are novel in the field and we hope this data and process will be used by other researchers to develop more robust analysis of batteries across academic labs and industry.Item Flame retardant biogenic building insulation materials from hemp fiber(Wiley, 2023-12-27) Jadhav, Porus Sunil; Sarkar, Arpita; Zhu, Long; Ren, ShenqiangBiogenic thermal insulation materials are in high demand because of its carbon-sequestration nature. However, high flammability, moisture condensation, and relatively high thermal conductivity of biogenic material are major concerns for sustainable building applications. In this study, we report the fire-retardant cellulose xerogel insulation nanocomposites derived from hemp fiber recycling and silica xerogel, in which the boric acid treatment improves its fire retardancy. The as-prepared materials show a low thermal conductivity of 31.3 mW/m K, high flexural modulus of 665 MPa, hydrophobicity with the water contact angle of 115°, and fire retardancy with 30% weight loss over a period of burning time 10 min. Overall, this work provides an effective method for the synthesis of fire-retardant biogenic thermal insulation materials and shows a promising way for next-generation bio-based insulation materials.Item Mitigating Electronic Conduction in Ceria-Based Electrolytes via External Structure Design(Wiley, 2023-12-22) Robinson, Ian A.; Huang, Yi-Lin; Horlick, Samuel A.; Obenland, Jonathan; Robinson, Nicholas; Gritton, J. Evans; Hussain, A. Mohammed; Wachsman, Eric D.Doped ceria electrolytes are the state of the art low-temperature solid oxide electrolytes because of their high ionic conductivity and good material compatibility. However, cerium tends to reduce once exposed to reducing environments, leading to an increase in electronic conduction and a decrease in efficiency. Here, the leakage current is mitigated in ceria-based electrolytes by controlling the defect chemistry through an engineered cathode side microstructure. This functional layer effectively addresses the problematic electronic conduction issue in ceria-based electrolytes without adding significant ohmic resistance and increases the ionic transference to2- number to over 0.93 in a thin 20 µm ceria-based electrolyte at 500 °C, compared to a of to2- 0.8 for an unmodified one. Based on this design, solid oxide fuel cells (SOFCs) are further demonstrated with the remarkable peak power density of 550 mW at 500 °C and excellent stability for over 2000 h. This approach enables a potential breakthrough in the development of ceria-based low-temperature solid oxide electrolytes.