Doctor of Philosophy, Case Western Reserve University, 0, EECS - Electrical Engineering

Timely characterization of the hemostatic system at the point-of-care/point-of-injury (POC/POI) is clinically important in traumatically injured and critically ill patients to guide therapeutic interventions and improve survival outcomes. This work advances the development of a microfluidic dielectric sensor, termed ClotChip, as a platform technology for POC/POI assessment of whole blood coagulation by enhancing its readout characteristics to precisely identify a range of blood coagulation disorders, including dysfunctions in fibrin formation and fibrinolysis. Specifically, two new distinct readout parameters in the ClotChip readout curve, namely, lysis time (LT) and maximum lysis rate (MLR) are identified and shown to be sensitive to the fibrinolytic status in whole blood. LT identifies the time that it takes from the onset of coagulation for the fibrin clot to mostly dissolve in the blood sample during fibrinolysis, whereas MLR captures the rate of fibrin clot lysis. A third new parameter, Smax, is also identified that represents the maximum permittivity slope and is shown to be sensitive to fibrin-polymerization defects during clot formation. These findings are validated through correlative measurements with rotational thromboelastometry (ROTEM) – a clinical, viscoelastic-based, global assay of blood coagulation. This work also includes the development of next-generation miniaturized dielectric coagulometry featuring multiple channels with bioreagent-functionalized electrodes that uniquely and specifically elicit differential responses from the multifactorial process of blood coagulation. Specifically, a microfluidic sensor is developed with physisorption of tissue factor and aprotinin on the electrode surfaces to probe the fibrinolytic function. The dual-coated microsensor can detect the hemostatic rescue in the hyperfibrinolytic profile of whole blood coagulation induced by tissue plasminogen activator as well as the hemostatic dysfunction due to concurrent pl (open full item for complete abstract)

Committee: Pedram Mohseni Dr. (Advisor) Subjects: Biomedical Engineering; Electrical Engineering; Engineering

Master of Sciences, Case Western Reserve University, 2022, Macromolecular Science and Engineering

Power electronics have been heavily developed, with polymer film capacitors as one of the key components in power electronics. Poly(ethylene 2,6-naphthalate) (PEN) possesses the potential to be the next generation polymer film capacitor for application in the induction motor system of electric vehicles (EVs) because of its high temperature rating. Furthermore, as a result of its ability to be processed into biaxially oriented PEN (BOPEN) via tenter-line processing, BOPEN films can be both thin and uniform. In this study, the dielectric and insulating property of BOPEN is studied at different high temperatures that simulate the harsh environment in which the DC-link capacitors operate. Based on the AC/DC breakdown strength analyses and lifetime measurement, BOPEN can still operate well in high-temperature environments, even as high as 150 °C. The relationship between the semicrystalline structure of BOPEN and the insulating properties has also been studied in this thesis. Utilizing thermal annealing to increase the crystallinity (both primary and secondary crystals) and the rigid amorphous fraction, the dielectric performance of BOPEN in high-temperature environment can be even better.

Committee: Zhu Lei (Advisor) Subjects: Energy; Engineering; Experiments; Film Studies; Materials Science; Polymers

Doctor of Philosophy, Case Western Reserve University, 2020, EECS - Electrical Engineering

This project has developed a microfluidic sensor for comprehensive assessment of human whole blood hemostasis using miniaturized broadband dielectric spectroscopy. In particular, first, a Gen-1 microfluidic sensor for dielectric coagulometry, termed ClotChip, has been developed. The sensor employs a three-dimensional (3D), parallel-plate, capacitive sensing structure with a floating electrode integrated into a microfluidic channel. Using an impedance analyzer, the sensor is shown to measure the real part of complex relative dielectric permittivity of human whole blood in a frequency range of 10kHz to 100MHz using <10 μL of it. The temporal variation of dielectric permittivity at 1MHz is taken as the ClotChip readout featuring a time to reach a permittivity peak parameter, Tpeak, which corresponds to the onset of CaCl2-initiated coagulation of the blood sample. Next, a biocompatible version of the sensor (Gen-2), fabricated entirely out of PMMA, has been developed. The readout of the Gen-2 sensor features a time to reach a permittivity peak, Tpeak, as well as a maximum change in permittivity after the peak, Δεr,max, as two distinct parameters of the sensor readout that are respectively sensitive towards detecting non-cellular (i.e., coagulation factor) and cellular (i.e., platelet) abnormalities in the hemostatic process. The sensor performance has been benchmarked against standard coagulation assays like rotational thromboelastometry (ROTEM) and Light Transmission Aggregometry (LTA) to evaluate the utility of its readout parameters in capturing the clotting dynamics using ex vivo modified blood samples. Tpeak exhibited very strong positive correlations with the ROTEM clotting time (CT) parameter, whereas Δεr,max exhibited strong positive correlation both with the ROTEM maximum clot firmness (MCF) parameter and the LTA. Finally, clinical studies with blood samples from patients suffering from a variety of coagulation defects, on factor replacement therapy and on d (open full item for complete abstract)

Committee: Pedram Mohseni (Advisor); Anirban Sen Gupta (Committee Member); Umut Gurkan (Committee Member); Philip Feng (Committee Member); Michael Suster (Committee Member) Subjects: Biomedical Engineering; Electrical Engineering; Engineering

Doctor of Philosophy (Ph.D.), University of Dayton, 2015, Materials Engineering

Single and multilayer films of nitrogen-doped hafnium oxide and aluminum oxide were fabricated up to 1 µm thick using pulsed DC reactive magnetron sputtering. The relationship between material properties and dielectric performance was investigated for wide temperature capacitor applications. A thorough characterization of the material and dielectric properties of single layer, nitrogen-doped aluminum oxide and nitrogen-doped hafnium oxide films was performed, including morphology, roughness, grain size, composition, dielectric constant, dissipation factor, leakage current, and breakdown strength. The dielectric properties of the films were also characterized across a temperature range of -50 to 200 °C to investigate temperature stability as well as the conduction mechanisms that led to dielectric loss and breakdown in a capacitor at elevated temperatures. Following characterization of the single layer films, multilayer films of two, three, and five layers were constructed and compared to the single layer films to see how the dielectric properties of the films changed with the addition of multiple dielectric interfaces. The dielectric properties of the films were found to improve significantly when additional dielectric/dielectric interfaces were present. Increasing the number of layers was found to considerably reduce leakage current and dissipation factor while increasing the breakdown strength by up to 75%. An investigation of the conduction mechanism of the films indicated that although the same conduction processes were occurring in both the single and multilayer films (Poole-Frenkel conduction and Schottky emission), the manner in which the conduction occurred changed as well as the temperature at which the conduction mechanism began to dominate, ultimately prolonging the breakdown of the dielectric. The results suggest that the layered architecture of the films aids in the dissipation of runaway charges at the dielectric/dielectric interface that lead to de (open full item for complete abstract)

Committee: Terry Murray (Committee Chair); Joseph Merrett (Advisor); Andrey Voevodin (Committee Member); Norman Hecht (Committee Member); Donald Klosterman (Committee Member) Subjects: Materials Science

Doctor of Philosophy, The Ohio State University, 2015, Electrical and Computer Engineering

For satellite communications, traditional phased array antennas could offer advantages over reflector antennas such as increased functionality, conformality, and no feed blockage. However, phased array systems are complex and expensive and, thus, not commonly used for satellites. Indeed, many applications (radar, electronic warfare, communications, etc.) would greatly benefit from less expensive phased array systems. Thus, much effort has been invested into addressing these challenges. This dissertation aims to greatly improve the feasibility of traditional phased arrays by eliminating the array backend (the main source of cost and complexity). Specifically, we introduce a traveling wave array (TWA) concept using a single feedline whose propagation constant can be controlled to enable scanning. This is done using a small mechanical movement (<100mil) to adjust the feedline propagation constant. In this manner, the phase delivered to each element can be altered, enabling scanning. Of importance, beam steering is achieved with only one feed and one small mechanical movement (for any size linear array) without using individual phase shifters. Four specific TWA implementations are presented: 1) parallel plate waveguide (PPW) array, 2) trapezoidal wedge coplanar stripline (TWCPS) array, 3) vertical PPW array, and 4) metal PPW array. Each of these three TWAs is comprised of a 20+ element linear array with stable realized gain and low side lobe level (SLL) across -25°≤θ≤25° scanning range. This dissertation describes the design procedure for each TWA, including element, feed, termination, and aperture excitation. Fabrication procedures and challenges are provided. Fabrication for these unique TWA geometries is found to be a key challenge for the concept. Prototype measurements are compared to simulations. The dissertation culminates in the metal PPW array which overcomes many of the challenges encountered by the previous designs. The array achieves st (open full item for complete abstract)

Committee: John Volakis (Advisor); Chi-Chih Chen (Advisor); Christopher Baker (Committee Member) Subjects: Electrical Engineering; Electromagnetics; Engineering

Master of Science, University of Akron, 2006, Physics

Dielectric materials have been widely used in electronic industry. Recently an oxide ceramic CaCu3Ti4O12 (denoted as CCTO) is reported to be very promising because it possesses a very high dielectric constant. However, further research on its dielectric properties indicates that this material has a high dielectric loss, which seriously blocks its practical application. In this work, pure CCTO ceramic, and two series of CCTO derivatives, i.e., “CCTO + CaTiO3” and “CCTO + MnO2” ceramics were prepared, and their phase assemblies, structure, dielectric properties, and conducting properties are studied. The relaxation mechanism was investigated for CCTO and its derivatives. It is for the first time revealed that the relaxation time follows the Vogel-Fulcher relation instead of the Arrhenius relation.

Committee: Ang Chen (Advisor) Subjects:

Master of Science in Electrical Engineering (MSEE), Wright State University, 2024, Electrical Engineering

This study examines the aging effects of GaN HEMTs, focusing on the CG2H40010 device under conditions that mimic the high-power, high-frequency environments of wireless communication systems. With the increasing adoption of GaN technology in RF applications, understanding its degradation mechanisms under CW stress and modulated signal characterization is essential for predicting device lifetime and ensuring performance standards for modern communication systems. RFALT was employed to stress the device using CW signals, while key performance metrics, such as gain compression, gate leakage, ACP, and EVM, were assessed using W-CDMA signals to replicate real-world dynamic stresses. The findings reveal that CW stress accelerates thermal and electrical degradation in GaN HEMTs, while W-CDMA characterization highlights the impact of complex modulation on linearity and spectral containment. Degradation mechanisms such as ohmic contact wear and dielectric failure significantly affect performance, especially under high peak-to-average ratio conditions. This research underscores the importance of combining CW-based RFALT with modulation-specific testing to evaluate device reliability comprehensively. By addressing thermal management, enhancing dielectric materials, and employing linearization techniques, these insights pave the way for optimizing GaN HEMTs to meet the stringent requirements of 5G and future wireless communication systems.

Committee: Yan Zhuang Ph.D. (Advisor); Weisong Wang Ph.D. (Committee Member); Marian K. Kazimierczuk Ph.D. (Committee Member) Subjects: Electrical Engineering; Electromagnetics

Doctor of Philosophy, Case Western Reserve University, 2025, Chemical Engineering

Direct air capture (DAC) of CO2 is a keystone technology in global plans to mitigate climate change. While the existing materials capable of performing this difficult separation can absorb high amounts of CO2 from air, the heat required to regenerate them for reuse imposes an immense energy tax. With projected energy demands for DAC exceeding 120 petajoules per year by 2030 (nearly the total annual electricity consumption of Ireland), more efficient materials and processes are vital to reaching net zero CO2 emissions. Ionic liquids (ILs) – salts that melt below 100 ˚C – are a class of solvents with exceptional tunability and negligible volatility, making them excellent candidate materials for DAC. However, a major barrier to the implementation of ILs in DAC is their high viscosity, limiting the diffusion rate of CO2. Through fundamental property characterization, spectroscopic investigation, and lab-scale performance analysis, this thesis seeks to build the scientific foundation for leveraging the advantages of ILs while mitigating their weaknesses by creating composite materials with ILs, enabling high performance DAC sorbents that can be regenerated using dielectric heating (the same heating mechanism as a kitchen microwave). We first explore the complex role that hydrogen bonding plays in CO2 binding mechanisms when diluting amino acid ILs with ethylene glycol to lower their viscosity. We reveal through collaborative study with computational chemists that hydrogen bonding can limit the interactions between amine binding sites, preventing their deactivation and resulting in maintained gravimetric capacity upon dilution. Next, we demonstrate the first successful regeneration of an IL by microwave irradiation. We reveal through finite element modeling that experimental trends in heating rate when varying frequency and material are highly dependent on the geometry of the system. Finally, we investigate the formation of composites between an IL and a metal organic (open full item for complete abstract)

Committee: Burcu Gurkan (Advisor); Christine Duval (Committee Member); Michelle Kidder (Committee Member); Pavel Fileviez-Perez (Committee Member); Rohan Akolkar (Committee Member) Subjects: Chemical Engineering

PHD, Kent State University, 2024, College of Arts and Sciences / Materials Science Graduate Program

The discovery of ferroelectric nematic liquid crystal (FNLC) was envisioned by Born already in 1916, but it was only 100 years later that Nishikawa et. al. and Chen et. al reported macroscopic polarization of 5-6 μC/cm^2 on newly synthesized highly polar (dipole moment of ~ 10 Debye) rod-shape molecules called DIO and RM734. Large number of researchers also reported very large ε~10^4 dielectric permittivity at 1 kHz. Our group began investigating FNLCs in 2020 on chiral RM734 and RT10011 synthesized by Prof Twieg in the Department of Chemistry and Biochemistry at KSU. Since then, supported by an NSF grant Twieg and his students synthesized over 100 FNLC materials that we have been characterizing by measuring their novel physical properties. My role in this group was to measure the ferroelectric polarization, dielectric permittivity , electro-optical properties and electric field-induced shift of phase transitions of newly synthesized FNLC materials. For this I have explored several ways to deduce the magnitude of the ferroelectric polarization using several geometries, learned dielectric spectroscopy, characterized the phase sequences of the materials using polarized optical microscopy (POM). After introduction and description of the experimental techniques I used, I will describe my experimental results in four chapters. Firstly, I will give a detailed analysis of about fifty FNLC materials that I have received to determine their phase sequences and the temperature dependencies of the ferroelectric polarization. I found that the measured polarization of materials with isotropic-nematic-ferroelectric nematic phase sequence has polarization that can be explained by their molecular dipoles, a large number of FNLC materials with direct isotropic-ferroelectric nematic transition, the measured polarization values are too high to explain based on the magnitude of their dipole moments. I will discuss possible reasons for these discrepancies. (open full item for complete abstract)

Committee: Antal Jákli (Advisor) Subjects: Materials Science

Doctor of Philosophy, The Ohio State University, 2024, Chemistry

Investigating dielectric behavior in inhomogeneous systems remains an open question, despite significant progress with homogeneous systems like the continuum. This work shifts the paradigm, interpreting dielectric behavior through a molecular picture instead of a continuum one. Our investigation focuses on water's dielectric behavior near a spherical ion—a model widely applicable to biological processes and electrokinetics. We demonstrate that the total bound charge near an ion is identical for both continuum and molecular systems. While polarization charge density is confined to an infinitely thin layer in continuum systems, it distributes within a finite range near the ion in molecular systems. We derive the formulations of dielectric properties in terms of polarization charge density compatible with both continuum and molecular solvents. Furthermore, we critically discuss a theoretical approach to interfacial dielectric constant that was recently proposed and underscore the necessity of appropriate treatment of dielectric properties under periodic boundary conditions. Building on dielectric behavior, we explore ion solvation through molecular dynamics simulations. We propose a theoretical methodology for correcting the finite size effect inherent in the periodic boundary condition, without employing Ewald summation. This correction leads to a free energy value and the corresponding Born radius for an infinite system aligning with existing literatures. Through simulations and our methodology, we provide a physical interpretation of the Born radius in molecular systems. We unveil unique overcompensations from alternating charge layers near the ion, which converge to the Born radius further from the ion. It has been observed that the Born radius in molecular systems is smaller than the radius where solvent molecules begin to appear. To interpret this smaller Born radius, we utilize a simple model for cumulative bound charge, where (open full item for complete abstract)

Committee: Sherwin Singer (Advisor); Alexander Sokolov (Committee Member); Steffen Lindert (Committee Member) Subjects: Chemistry; Physical Chemistry

Master of Science in Materials Science and Engineering (MSMSE), Wright State University, 2023, Materials Science and Engineering

The persistent demand for flexible and wearable electronic components in healthcare, aerospace, media, and transit applications has led to a significant shift from traditional electronics processes to printed electronics. Printed electronics are anticipated to establish itself as the industry's dominant force due to their enhanced flexibility, rapid prototyping capabilities, and seamless integration with everyday objects. They are cost-effective and have the scalable option for large-scale production because additive manufacturing techniques are used. Among the various printing methods available, inkjet printing has recently gained popularity for printing electronics, especially capacitors that require precise and complex structures on different substrates. Inkjet printing relies on micro dispensing additive technology, where liquid phase materials are dispensed using the drop on demand (DOD) technique with conductive nanoparticle inks. Researchers have made several attempts to fabricate fully inkjet-printed composite capacitors and have discovered that the permittivity value of the composite increases compared to a polymer. This suggests that using composites as the dielectric material in a capacitor can potentially increase the capacitance value. However, despite the discussion on various composite dielectric materials, there is a scarcity of information on the use of BaTiO3/SU-8 dielectric materials for capacitor applications. To address this gap, the objective of this study is to formulate BaTiO3/SU-8 ink suitable for inkjet printing and develop a printing process for layered metal insulator metal (MIM) structures. The formulated BaTiO3/SU-8 ink is employed to print the dielectric material, while nano silver ink is used for the two electrodes, enabling the fabrication of the capacitor in a single step. The study takes into account volume and speed jetting parameters as well as waveform to achieve optimal and uniform liquid phase material inkjet printing on the s (open full item for complete abstract)

Committee: Ahsan Mian Ph.D. (Committee Co-Chair); Hong Huang Ph.D. (Committee Co-Chair); Daniel Young Ph.D. (Committee Member) Subjects: Engineering; Materials Science; Mechanical Engineering; Nanoscience; Nanotechnology

Doctor of Philosophy, The Ohio State University, 2023, Electrical and Computer Engineering

Beta-phase gallium oxide (β-Ga2O3), with its ultrawide band gap energy (~4.8 eV), high predicted breakdown field strength (6-8 MV/cm), controllable n-type doping and availability of large area, melt-grown, differently oriented native substrates, has spurred substantial interest for future applications in power electronics and ultraviolet optoelectronics. The ability to support bandgap engineering by alloying with Al2O3 also extends β-(AlxGa1-x)2O3 based electronic and optoelectronic applications into new regime with even higher critical field strength that is currently unachievable from SiC-, GaN- or AlxGa1-xN- (for a large range of alloy compositions) based devices. However, the integration of β-(AlxGa1-x)2O3 alloys into prospective applications will largely depend on the epitaxial growth of high quality materials with high Al composition. This is considerably important as higher Al composition in β-(AlxGa1-x)2O3/Ga2O3 heterojunctions can gain advantages of its large conduction band offsets in order to simultaneously achieve maximized mobility and high carrier density in lateral devices through modulation doping. However, due to the relative immaturity of β-(AlxGa1-x)2O3 alloy system, knowledge of the synthesis and fundamental material properties such as the solubility limits, band gaps, band offsets as well as the structural defects and their influence on electrical characteristics is still very limited. Hence, this research aims to pursue a comprehensive investigation of synthesis of β-(AlxGa1-x)2O3 thin films via metal organic chemical vapor deposition (MOCVD) growth methods, building from the growth on mostly investigated (010) β-Ga2O3 substrate to other orientations such as (100), (001) and (-201), as well as exploring other polymorphs, such as alpha (α) and kappa (κ) phases of Ga2O3 and (AlxGa1-x)2O3 to provide a pathway for bandgap engineering of Ga2O3 using Al for high performance device applications. Using a wide range of material characterization techniqu (open full item for complete abstract)

Committee: Hongping Zhao (Advisor); Siddharth Rajan (Committee Member); Steven A. Ringel (Committee Member); Sanjay Krishna (Committee Member) Subjects: Condensed Matter Physics; Electrical Engineering; Engineering; Materials Science; Nanoscience; Nanotechnology; Physics

Doctor of Philosophy, The Ohio State University, 2023, Materials Science and Engineering

In many scientific and engineering fields, the physical properties of materials can become a vital factor that limits the development of technologies or opens a new pathway to emerging applications. The study of ultrashort laser interaction with solid materials is no different. While the material damage induced by ultra-intense laser pulses has become the principal bottleneck in advances of high power laser technology, the highly localized nature of laser ablation can also expand the toolbox for high-precision material manufacturing. Moreover, few-cycle pulses can make ultrafast optical switching possible, which can be orders of magnitude faster than state-of-the-art electronic switches. In this thesis, with the assist of extensive experiments, a comprehensive computational model is proposed to study the mechanisms of ultrashort laser induced excitation and damage in dielectric materials. First, to capture the dynamic interplay of physical processes during the laser and thin-film material interaction, I wrote a two-dimensional finite difference in time domain (FDTD) multi-physical model incorporating the electromagnetic wave propagation, strong-field Keldysh photoionization theory, impact ionization, Drude-Lorentz model, etc. The simulation results for bulk fused silica and femtosecond laser pulses at varying durations and fluences agree well with the measurements. Then I modeled the laser interactions with multi-layer dielectric (MLD) mirrors and gratings designed for broadband pulses and predicted the laser induced damage thresholds (LIDTs). Next, laser damage experiments and computational modeling were performed to study the laser induced damage in the MLD mirrors and gratings designed for femtosecond laser pulses at 2-micron wavelength. The LIDTs measured by the experiments are consistent with the modeling results. I also observed the blister formation in both gratings and mirrors at fulences below the ablation threshold. The inner structure of the blisters w (open full item for complete abstract)

Committee: Enam Chowdhury (Advisor); Wolfgang Windl (Committee Member); Gregory Lafyatis (Other); Steve Niezgoda (Committee Member); Roberto Myers (Committee Member) Subjects: Materials Science; Physics

MS, Kent State University, 2023, College of Arts and Sciences / Department of Physics

LIQUID CRYSTALSLIQUID CRYSTALSThe present work studied the physical properties of a nematic LC material compound RT11165. The recently discovered ferroelectric nematic phase that carries a non-zero dipole moment exhibits in this material. Experimentally we used the Freedericksz transition method in the nematic phase by measuring the light intensity through a planar nematic layer as a function of the amplitude and frequency of an applied voltage. The threshold voltage shows dependence on the frequency. In addition, the dielectric anisotropy and the splay elastic constant K11 are measured. The dielectric anisotropy indicates critical behavior at high frequencies relatively low as cooling toward the NF phase, while at low frequencies, it shows strong positive dielectric permittivity. Also, the dielectric spectroscopy shows two molecular relaxation modes detected at low frequency and temperature in the perpendicular component of the dielectric permittivity, and the strength of the relaxation frequency was found to be decreased. In contrast, it increases rapidly and smoothly in the parallel component.

Committee: James Gleeson Dr (Advisor) Subjects: Physics

Doctor of Philosophy, Case Western Reserve University, 2023, Macromolecular Science and Engineering

Polymer film capacitors are suitable for capacitive energy storage in the expanding market of electric vehicles and high-speed trains, as their advantages of high electric breakdown, long lifetime, and high ripple current tolerance. The state-of-the-art polymer capacitor material is biaxially oriented polypropylene (BOPP), due to its ultralow loss, long operating lifetime, and high breakdown strength. However, its temperature rating of ~85 °C limits its application in electric vehicles since the ambient temperature, where DC-link capacitors are installed, is around 140 °C. Multilayer technology has proved its potential to achieve high energy density, high breakdown strength, and high-temperature rating simultaneously. These multilayer films (MLFs) are composed of a high temperature/low loss polymer and a high dielectric constant polymer. Under extreme conditions (e.g., high electric fields and high temperatures), an important loss mechanism of AC electronic conduction occurs in MLF capacitors by homocharge injection at the metal electrode/polymer interfaces and subsequently charge recombination, leading to heat generation. In this dissertation, this mechanism was studied for high temperature polycarbonate (HTPC)/poly(vinylidene fluoride) (PVDF) MLFs with either HTPC (MLF@HTPC) or PVDF (MLF@PVDF) as the outer skin layers. Based on DC/AC breakdown strength, DC lifetime measurements, and electric displacement-electric field loop analysis on metal electrode/MLF/metal electrode capacitor devices, it is concluded that the charge injection can be largely minimized when aluminum is used as the metal electrode material and HTPC is used as skin layers. In addition, the Tg effect of three PC MLFs was also studied by dielectric breakdown, lifetime, and leakage current measurements. From the experimental results, we conclude that charge injection was largely reduced with HTPC MLFs, leading to significantly enhanced insulation properties with high breakdown strength and l (open full item for complete abstract)

Committee: Lei Zhu (Committee Chair); Geneviève Sauvé (Committee Member); Gary Wnek (Committee Member); Eric Baer (Committee Member) Subjects: Energy; Plastics

Master of Science in Materials Science and Engineering (MSMSE), Wright State University, 2023, Materials Science and Engineering

Electronics in different applications, such as in medical imaging devices, radar systems, communication transmitters, and optical drives, often require various power and signal lines to be integrated at board level. In such cases, different lines may cross over one another in three-dimensional space for efficient electronic integration. Crossovers are usually achieved by adding additional layers to a PCB. However, these additional layers increase the cost, weight, and complexity of the component. By creating a process and structure to offer board-level heterogenous integration, these factors may be reduced. RF-DC crossovers were designed and additively manufactured using an aerosol jet printer. Benzocyclobutene (BCB), a thermally curable dielectric material, and Norland Electronic Adhesive 121 (NEA), a UV curable dielectric ink, were printed as crossover materials on boards containing an RF transmission line. Electroninks 615 (EI-615), a conductive silver ink, was printed on the crossover's surface to complete the DC circuit trace. Two different toolpath designs were explored to serve for the digital printing of the crossover structure. A network analyzer was used to measure the scattering parameters (S12 and S21) across the RF transmission line in X-band (8-12 GHz). A thermal camera was used to capture the heat spread across the crossover region. The printed ramp design resulted in a more gradual slope as expected, requiring a single print of the conductive trace while the steep pad design required tilting of the crossover and multiple printing sessions. The NEA 121 and BCB showed no significant changes in the S21 parameter as DC power increased; however, slight coupling occurred in both. The largest S21 difference recorded at 10 GHz was 0.339 dB. The BCB crossovers exhibited higher power handling than the NEA 121 crossovers, reaching up to 6.93 W. The maximum breakdown temperature occurred at 273.0°C in the NEA 121 and at 248.6°C in the BCB crossovers.

Committee: Ahsan Mian Ph.D. (Advisor); Daniel Young Ph.D. (Committee Member); Emily Heckman Ph.D. (Committee Member) Subjects: Electrical Engineering; Engineering; Materials Science

Doctor of Philosophy, The Ohio State University, 2023, Physics

Wide bandgap semiconductors (WBGS) are an exceptionally important class of materials for next-generation microelectronics that exhibit a diverse set of physical phenomena spanning piezo- and ferroelectricity, ferromagnetism, superconductivity, and 2-dimensional electron and hole gases. Oxide and nitride WBGS are particularly well-positioned to accelerate the advancement of renewable energy technologies and improve power electronic efficiencies and life-cycle costs. The identification and capacity for control of optically and electrically active point defects are central in transitioning these materials from research laboratory to practical applications. This dissertation investigates the optoelectronic property-structure relationship of native point defects in wide bandgap semiconductors. By combining spatially resolved cathodoluminescence spectroscopy and surface photovoltage spectroscopy (SPS) with surface sensitive x-ray photoelectron spectroscopy (XPS), native anionic point defects and cation defect complexes are identified in ternary ZnGeN2 and binary ScN. The control and refinement of these defects with material growth is essential for coherent integration with complementary GaN architectures. Direct control of point defects on the nanoscale is demonstrated in oxide semiconducting Ga2O3 vertical devices and ZnO nanowire structures by applying electric fields to stimulate the migration of intrinsic defect species. Redistribution of oxygen vacancies (VO) in high power Ga2O3 is demonstrated for the first time by nanoscale hyperspectral imaging after strong reverse biasing while manipulation of oxygen vacancies in suspended ZnO nanowires is selectively driven by applied bias through nanoscale contacts. The density of positively charged interfacial VO is tuned via electric fields to control Schottky barrier heights and reversibly convert metal-ZnO interfaces between Ohmic and Schottky behavior, highlighting the need to consider intrinsic point defect migration i (open full item for complete abstract)

Committee: Leonard Brillson (Advisor); Ciriyam Jayaprakash (Committee Member); Andrew Heckler (Committee Member); Jay Gupta (Committee Member) Subjects: Physics

Doctor of Philosophy, The Ohio State University, 2022, Chemistry

Perovskite-based materials provide an exemplary platform to explore fundamental structure-property relationships. The relative simplicity of the perovskite crystal structure and a plethora of interesting properties related to purposes such as optoelectronics, multiferroics, and superconductivity, has sparked immense research interest. For halide perovskite variants, research has focused primarily on APbX3 (A = Cs+, CH3NH3+, NH2CHNH2+; X = Cl−, Br−, I−) perovskites for photovoltaic applications. One of the most impressive features of the halide perovskite is the ease of chemical substitution, which has resulted in a wide variety of structural variations. Halide perovskite materials containing transition metals offer a broader range of applications due to the possibility of diamagnetic and paramagnetic electronic configurations. Here we explore halide perovskite derivatives containing transition metals to understand the optical and magnetic properties that arise in low dimensional crystal structures. Following the first introductory chapter, Chapter 2 looks to expand on the known compositional space of the (CH3NH3)2M′MʺX6 halide double perovskites by introducing Rh3+ at the Mʺ site. Here, we synthesized (CH3NH¬3)2M′RhX6 (M′ = Na+, Ag+; X = Cl−, Br−) and looked to understand the optical properties that arise from the one-dimensional chain structure of these hexagonal 2H perovskite variants. This sets the foundation for Chapter 3, which explores two-dimensional layered perovskites containing the Ag–Rh–X inorganic framework. By replacing CH3NH3+ with a bulky organic cation, the crystal structure transitions from one-dimensional chains to two-dimensional layers. The optical properties are further explored in comparison to the previously studied hexagonal perovskites. Changes in the absorption spectra are explained by changes in the octahedral connectivity and ability of orbitals to hybridize. Chapter 4 focuses on the structural phase transitions and magnetic propertie (open full item for complete abstract)

Committee: Patrick Woodward (Advisor); Yiying Wu (Committee Member); Joshua Goldberger (Committee Member) Subjects: Chemistry; Materials Science

Doctor of Philosophy (Ph.D.), University of Dayton, 2022, Electrical and Computer Engineering

In this dissertation, Fresnel coefficients are examined for electromagnetic (EM) propagation across an achiral/chiral (ACC) boundary, and thereafter extended to cases involving slab-type resonator structures. An important factor to be noted is that while the numerical results presented in this research are accurate to the limits of our assumptions, one feature of a chiral material not taken into consideration in the early stages of work is the presence of dielectric losses. It turns out that a chiral (meta) material is usually also lossy via a complex dielectric permittivity. In the research presented in several chapters of this dissertation, the chiral dielectric has been assumed to be lossless, whereby all three material parameters (permittivity, permeability and chirality) are assumed to be real. Towards the latter chapters, dielectric losses are taken into account to make the results more compatible with practical cases. The results presented are aimed at observing the effects of loss on both the propagated fields themselves as decaying vectors, as well as on the amplitude and phase characteristics of the relevant Fresnel coefficients (amplitude as well as power or intensity). As is well known, upon both transmission and reflection from a chiral interface, the incident plane (specifically perpendicularly or s-polarized) wave transforms into two modes (right circular polarization (RCP) and left circular polarization (LCP)), propagating non-collinearly and collinearly for the transmitted and reflected modes respectively. This work focuses on certain anomalous properties pertinent to the chirality itself which provide novel insights into chiral materials. The dissertation highlights anomalies relative to the emergence of Brewster effects, tunability of Brewster angles and critical angles via the (dimensionless) chirality coefficient (κ ) over specific bands, total internal reflection (TIR), non-complementarity, mode evanescence, and also possible effective ne (open full item for complete abstract)

Committee: Monish Chatterjee (Advisor); Partha Banerjee (Committee Member); John Loomis (Committee Member); Youssef Raffoul (Committee Member) Subjects: Electrical Engineering; Electromagnetics; Energy; Materials Science; Optics

Master of Science in Electrical Engineering, University of Dayton, 2021, Electrical and Computer Engineering

Over the past decade, Additive Manufacturing (AM) has advanced as a novel manufacturing technique used to develop rapid prototypes for custom and complex geometries and multilayer devices in many different industries. Recent advances in emerging technologies such as dual-extrusion FDM 3D printing, along with newly introduced conductive polymer filament materials, have created the potential to use low-cost, readily available 3D printing methods to fabricate electronic devices on-the-fly in remote environments. This study explores the use of Protopasta conductive filament and various common thermoplastic filament materials (PLA, PP, PC) and an Ultimaker s5 Pro dual-extrusion FDM printer with high-resolution 0.25 mm diameter print nozzles to fabricate a fully-fused 50 mm x 50 mm plate capacitor. A maximum capacitance of 328 pF was measured with a 0.25 mm thick dielectric layer of extruded PLA. This demonstrates a 215% increase in capacitance when compared to measurements for a similar plate capacitor constructed with wrought sheet aluminum (104 pF) using the same dielectric material and thickness. An EVAL-AD5940 impedance analyzer was used to measure the capacitance with PLA, PP, and PC dielectric layers at 1 kHz, 5 kHz, 7.5 kHz, and 10 kHz. From these measurements, the dielectric constant of each material was calculated for a dielectric thickness of 1 mm, as follows: 1 kHz (PLA: 3.00, PP: 2.96, PC: 3.00); 5 kHz (PLA: 2.83, PP: 2.74, PC: 2.83); 7.5 kHz (PLA: 2.82, PP: 2.76, PC: 2.910; and 10 kHz (PLA: 2.39, PP: 2.63, PC: is 2.99).

Committee: Amy Neidhard-Doll Ph.D., P.E. (Committee Chair); Carrie Bartsch Ph.D. (Committee Member); Guru Subramanyam Ph.D. (Committee Member); Vamsy Chodavarapu Ph.D., P.E. (Committee Member) Subjects: Electrical Engineering; Engineering