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

Beta-gallium oxide (β-Ga2O3) has emerged as a highly promising ultrawide bandgap semiconductor with unique advantages, capturing significant attention. The presence of point and extended defects in β-Ga2O3 plays a crucial role in shaping the performance of devices based on this material, as they can either decrease or increase the net doping. However, the field has been lacking direct and detailed experimental information about the atomic-level structure of these defects. Bridging this knowledge gap is crucial to establish connections between the measured material properties and the observed atomic structure of defects in β-Ga2O3. To address this, atomic scale scanning transmission electron microscopy (STEM) was employed in this research to investigate the formation and impact of point and extended defects in β-Ga2O3. In the earlier works, we have used quantitative analysis of atomic and nanoscale defects from STEM images to understand the formation of various types of defects in β-Ga2O3, such as interstitial-divacancy complexes and planar defects. Furthermore, phase transformations in (AlxGa1−x)2O3, directly correlating them with Al incorporation into the lattice, were also extensively studied. Based on the findings, we began to tackle bigger scientific questions regarding the fundamental atomic scale mechanisms driving the phase transition from the β phase to the γ phase in Ga2O3. Additionally, it was also required to gain a deeper understanding of the effects of defect incorporation, such as by Sn doping, Al alloying, Si ion implantation, and Ir metal diffusion, on this phase transformation process. In order to address these questions, an atomic scale investigation was conducted to examine the effect of ion implantation on β-Ga2O3 materials, aiming to unravel the atomic scale mechanism behind structural changes, lattice relaxation, and phase transformation in Si-implanted β- Ga2O3 as a function of Si dose. Furthermore, by combining the secondary ion mass spectrom (open full item for complete abstract)

Committee: Jinwoo Hwang (Advisor); Ezekiel Johnston-Halperin (Committee Member); Siddharth Rajan (Committee Member); Hongping Zhao (Committee Member) Subjects: Materials Science

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

Lithium niobate (LN) has attracted significant interest over the past few decades as a potential platform for next generation nonlinear optical devices, high speed optical interconnects and modulators, and quantum light sources. Sub-micrometer thick lithium niobate on insulator (LNOI) is a promising integrated photonic platform that provides optical field confinement and high optical nonlinearity useful for state-of-the-art electro-optic modulators, wavelength converters, and acousto-optical devices. With fabrication foundry technologies enabling realization of low loss LNOI waveguides, devices fabricated using LNOI substrates and have been able to achieve record high harmonic generation efficiencies, and low insertion and propagation losses.Fabrication of LNOI on a silicon substrate through ion-slicing is advantageous for enabling velocity matching between microwave and optical copropagating fields in electro-optic modulators and for electronic-photonic integration but is challenging because of debonding and cracking due to thermal expansion coefficient mismatch between silicon and LN. Moreover, current techniques to pattern low loss waveguides with smooth sidewalls in LNOI rely on chemical mechanical polishing and electron beam lithography. Chemical mechanical polishing can result in film etching thickness variations, while electron beam lithography is not suited for high throughput production.Lastly, current schemes for fiber to chip edge coupling rely on the use of specialty optical fibers, such as lensed fibers, and there is a requirement for an efficient packaging solution that can utilize standard single mode cleaved optical fibers. Fabrication of thin film lithium niobate on insulator on a silicon handle wafer is achieved via ion-slicing, informed by structural modeling, and facilitated by accommodating for dissimilar wafer bows using a bonding apparatus. Structural finite element analysis of strain energy and stress, due to thermal expansion coefficient (open full item for complete abstract)

Committee: Ronald Reano (Advisor); Patrick Roblin (Committee Member); Robert Lee (Committee Member); Fernando Teixeira (Committee Member) Subjects: Electrical Engineering; Electromagnetics; Engineering; Nanotechnology; Optics

Doctor of Philosophy, The Ohio State University, 1978, Graduate School

Committee: Not Provided (Other) Subjects: Physics

MS, University of Cincinnati, 2013, Engineering and Applied Science: Electrical Engineering

Since the dawn of the field of superconductivity, advances in the field tended to come in the most unexpected fashion. With the ability to condense Helium to its liquid state and the subsequent groundbreaking measurements by Onnes, the field progressed with the cataloguing of the critical transition temperatures of solid metals and subsequently binary compounds. Theoretical explanations from Meissner and Ochsenfeld, Josephson, London, Abrikosov, Ginzberg and Landau, and Bardeen, Cooper, and Schreiffer provided the groundwork in understanding necessary to explain the observed phenomena and predict what could lead to higher measured values of transition properties. Further significant development did not arise until Bednorz and Mueller speculated on a copper-oxide system, which later provided for the fundamental breakthrough of YBCO by Chu and associates.

Committee: Andrew Steckl Ph.D. (Committee Chair); Timothy J. Haugan Ph.D. (Committee Member); Punit Boolchand Ph.D. (Committee Member) Subjects: Electrical Engineering

Doctor of Philosophy, University of Toledo, 2006, Physics

The direct-band-gap semiconductor CdTe is an important material for fabricating high efficiency, polycrystalline thin-film solar cells in a heterojunction configuration. The outstanding physical properties of this material such as its good band-gap match to the solar spectrum, ease of fabrication of stoichiometric films, and easy grain boundary passivation make it an important candidate for large area, thin-film solar cells. However, there are several poorly understood processing steps that are commonly utilized in cell fabrication. One of these is a CdCl2 treatment near 400C in the presence of oxygen, which can improve the cell efficiency a factor of two or more. Another factor is the role of copper in cell performance. In high performance CdS/CdTe thin-film solar cells, copper is usually included in the fabrication of low-resistance back contacts to obtain heavy p-type doping of the absorber CdTe at the contact. However, most of the copper is not electrically active. For example, secondary ion mass spectroscopy (SIMS) on typical CdTe cells has shown Cu concentrations of 1019 atoms/cm3 and even higher, although capacitance-voltage (C-V) measurements indicate typical ionized acceptor levels on the order of 1014 /cm3. Thus, there is great interest in the location and role of this inactive copper in CdTe photovoltaic (PV) devices. In this thesis, I will describe results obtained on magnetron-sputtered CdTe films that were diffused with copper following the procedure used for creating a cell back contact. Extended x-ray absorption fine structure (EXAFS) measurements identified the chemical environment of the majority of the copper and show major differences depending on whether the CdTe film has been treated with chloride prior to the Cu diffusion. Photoluminescence of CdTe crystals doped with two elements, Cl and P were studied individually. I have identified band-to-band transitions, free-to-bound transitions and bound-exciton lines related to these species. Through (open full item for complete abstract)

Committee: Alvin Compaan (Advisor) Subjects: Physics, Condensed Matter

Doctor of Philosophy, The Ohio State University, 2009, Integrated Biomedical Sciences

Ultra high molecular weight polyethylene (UHMWPE) is the material of choice for use as a bearingsurface in the majority of total joint replacements. Polyethylene wear and the osteolysis that occurs secondary to the debris particles continue to be the most important factors limiting the long term success of joint arthroplasties. This study was designed to explore the potential benefits of ion implanted UHMWPE. Our first goal was to “label” UHMWPE by mechanically implanting copper [Cu] through a two-step technique of surface coating with elemental Cu followed immediately by Xenon [Xe+] ion bombardment. This technique modifies only one surface or specific area of a polyethylene specimen. After successfully labeling one surface of a PE specimen, analysis of wear debris particles will allow computation of the relative amounts of particles released from the labeled and unlabelled surfaces. Sixty UHMWPE disks were mounted for implantation in a Z-100 implanter with Xe at a beam energy of approximately 100 keV, and a beam current of 0.65 mA (particle). The entire assembly including the specimens were treated with a 300 angstrom layer of copper applied by plasma vapor deposition followed immediately by a dose of Xe+ ions. Additional experiments void of copper pretreatment allowed for ion modified positive controls of Xe only bombardment to be produced. During our investigation we found a marked improvement of wear characteristics for the ion modified UHMWPE specimens. Before we could continue with our localization goal it was necessary to determine the extent of this increased wear resistance. Therefore a secondary goal became the development of a protocol for measuring this change in surface behavior. Three wear testing experiments were conducted with a multi-motion pin-on-disk wear simulator. The magnitudes of debris wear were measured at three distinct time intervals for comparison between samples. Group iii means were analyzed using a one way analysis of variance and a Du (open full item for complete abstract)

Committee: Alan Litsky M.D.Sc.D. (Advisor); John Olesik Ph.D. (Committee Member); William Brantley Ph.D. (Committee Member); Thomas DeMaria Ph.D. (Committee Member); Hooshang Hemami Ph.D. (Other) Subjects: Biomedical Research

Master of Science (M.S.), University of Dayton, 2011, Electro-Optics

InSb p-n junction detectors from bulk crystals are commonly utilized for mid-wave infrared (MWIR) focal-plane arrays (FPAs) because of their high quantum efficiency and well-established fabrication methods. The doping profiles of these detector structures are commonly defined by thermal diffusion techniques because it is an economical and repeatable fabrication process. The resulting impurity profiles have a characteristic shape determined by Fick's diffusion laws. In order to realize structures that are more complicated than simple PN junctions, like APDs, alternative methods of introducing and controlling impurities need to be developed, especially when high and low doping concentrations at specific depths beneath the surface are needed. Another technique that could maintain similar cost effectiveness and repeatability as thermal diffusion while providing greater control over the doping profile is ion implantation. This is well-developed for silicon, but less developed for InSb. Accurate modeling of the doping profile shapes and depth are important for transitioning detector designs to properly functioning devices. SRIM modeling software is used to predict the doping profiles of implanted Be ions into n-type InSb substrates. To test the accuracy of this software, implantations of varying energy were performed. After implantation, the doping profiles of these samples were measured using secondary ion mass spectrometry (SIMS) before and after a rapid thermal anneal. It was found that Be ions do not diffuse within the repeatability tolerance of the SIMS measurement technique. The SIMS results also revealed a highly oxidized InSb surface. This oxidized surface should be considered during the fabrication process. Spreading resistance profile measurement is made on an annealed Be implanted sample. P on N carrier concentration is verified by this measurement which suggests successful activation during anneal. A process for fabricating InSb photodiodes with ion implantati (open full item for complete abstract)

Committee: Andrew Sarangan PhD (Committee Chair); Thomas Nelson PhD (Committee Member); John Scheihing (Committee Member); Qiwen Zhan PhD (Committee Member) Subjects: Electrical Engineering; Optics; Physics; Solid State Physics

Doctor of Philosophy (Ph.D.), University of Dayton, 2010, Materials Engineering

Silicon nitride and WC-Co cermet tools are used for metal forming processes including extrusion and drawing. These materials are used to make tool dies which are exposed to deformation caused by friction and wear. Surface treatments such as ion implantation, laser blazing and coating have been found to improve surface properties, to optimize tribological behavior between the metal and die, as well as to extend service life of the tool dies. Early detection and continuous monitoring processes by non destructive testing (NDT) methods are needed in order to ensure the functionality of the wear process and extend the tool service life. Acoustic emission is one of the promising NDT methods for this application. The surface treatment chosen for this investigation was ion implantation. Three types of wear resistant materials with and without surface treatment were selected for this project; silicon nitride and two tungsten carbides (6% Cobalt and 10% Cobalt). This investigation was conducted using a pin-on-disk device for wear/friction tests of the selected materials with lubrication and/or without lubrication against both a stainless steel disk and an aluminum disk. The acoustic emissions generated during the experiments were recorded and analyzed. The results of this investigation showed that the ion implantation improved the tribological properties of the materials and reduced acoustic emission and coefficient of friction. A linear relationship between the average amplitude of the acoustic emission and the coefficient of friction of the tested materials was found. The investigation demonstrated that the acoustic emission method could be used to monitor the wear/friction processes.

Committee: Norbert Meyendorf (Committee Chair); Daniel Eylon (Committee Member); Norman Hecht (Committee Member); Paul Murray (Committee Member); Gerald Shaughnessy (Committee Member) Subjects: Engineering; Materials Science