PhD, University of Cincinnati, 2007, Engineering : Electrical Engineering

This research studies an innovative micromagnetic method for electron beam control in the electron beam microcolumn. In order to realize the magnetic electron beam control in the electron beam microcolumn, three new micromachined magnetic devices have been designed, fabricated and characterized in this work. First, a magnetic microdeflector has been designed, fabricated, and characterized for the electron beam deflection/scanning in the EBMC. Experimental results showed that the developed magnetic microdeflector with a pole distances 0.5 mm linearly deflected the electron beam (280 eV) a distance of 0.21 mm with an electrical power of 3 mW. The realized magnetic microdeflector shows an excellent dynamic property with the reponse time of 25 ns for a step signal of 50 mA. The developed magnetic microdeflector has excellent capability of deflecting/scanning the electron beam in the electron beam microcolumn system with large scanning linearity and low power consumption. Second, a magnetic microstigmator has been designed, fabricated, and characterized for the electron beam astigmatism correction in the EBMC. Experimental results showed that the astigmatism of an electron beam (200 eV) was effectively corrected by the fabricated magnetic microstigmator with a low power consumption. Third, a magnetic microlens has been designed, simulated, fabricated, and tested for the electron beam focusing in an EBMC. The experimental results showed that, with a driving current of 150 mA, an electron beam of 1 keV was effectively focused by the developed magnetic microlens. Finally, the magnetic interference within the miniaturized magnetic electron beam control system consisting of the three developed magnetic devices has been modeled and simulated. The span range of the magnetic field distribution generated by each individual device has also been simulated and investigated. In summary, an innovative magnetic method for the electron beam control in the electron beam microcolumn has b (open full item for complete abstract)

Committee: Dr. Chong H. Ahn (Advisor) Subjects:

Doctor of Philosophy, The Ohio State University, 2011, Electrical and Computer Engineering

Chalcogenide glasses are amorphous, glassy, semiconducting materials containing S, Se, or Te as the primary components, with network modifiers such as Ge, As, Sb and Bi. They are of interest in photonics because of their low-loss transmission in the infrared, their large third order susceptibility, low two photon absorption at telecommunications wavelengths, and variety of bond rearrangement effects such as photoexpansion, photodarkening, electron beam induced deformation, and electron beam induced second harmonic generation. The large Kerr nonlinearities and large refractive indices of chalcogenide glasses enable compact integrated optical circuits capable of all-optical switching. In this thesis, electron beam induced deformations are explored as a way of fabricating optical waveguides in Ge0.2Se0.8 chalcogenide glasses because this is an etchless technique that potentially allows writing waveguides whose surface roughness is limited only by the roughness of the as-deposited film, allowing for a minimum of surface roughness scattering loss. Thin films (100 nm to several microns thick) of Ge0.2Se0.8 glass are deposited using pulsed laser deposition (PLD). Another option for depositing films, which has the advantage of being lower cost, is explored: spin coating. A process to deposit thin amorphous Ge-Se films using spin coating from amine-based solutions is developed. Mixing in an alcohol such as methanol in relatively small proportions (< 10 mol %) allows for the production of thicker films while maintaining stoichiometry. Films thicker than 1 μm and with surface roughness less than 1 nm RMS can be obtained in a single layer. Exposure to focused electron beams (generated in an electron beam lithography system) is investigated as a way to directly write waveguides into thin PLD Ge0.2Se0.8 films. These waveguides are mound-shaped and similar to rib waveguides. Electron beam parameter sweeps are run demonstrating a transition from mound formation to trench formati (open full item for complete abstract)

Committee: Ronald Reano PhD (Advisor); Betty Lise Anderson PhD (Committee Member); Fernando Teixeira PhD (Committee Member); Roberto Rojas-Teran PhD (Committee Member); Stewart Shapiro PhD (Committee Member) Subjects: Optics

Doctor of Philosophy, The Ohio State University, 2005, Electrical Engineering

In this dissertation we report on the structural quality of the GaAs/Ge interface for GaAs nucleation by solid source molecular beam epitaxy (MBE). Through feedback from these characterizations, optimized growth methods are established, demonstrating the ability to grow defect-free epitaxial GaAs films on Ge substrates. We also present data on the electrical activity associated with defects that result if the growth is not fully controlled. In theses studies we exploit a novel use of an electron beam induced current (EBIC) technique to show the electrical activity associated with anti-phase domains and inter-diffusion from regions as small as 100 nm. Integrating this GaAs MBE nucleation methodology on the SiGe graded substrates we show that the GaAs stoichiometry and material properties transfer without degradation from the higher threading dislocation density of the SiGe substrates. In these studies we show that fundamental defects such as; threading dislocation, anti-phase domains, and atomic inter-diffusion are controlled to a level that enables growth of extremely high quality GaAs device layers. Combined with the low TDD enabled by the SiGe graded buffer, record GaAs/Si minority carrier lifetimes in excess of 10 ns have been achieved. However, other larger scale defects are shown to have a limiting effect on large area device performance. One such morphological surface defect, known as the “bat”, is generated during the UHVCVD SiGe growth. The defect was comprehensively studied and results indicate that the impact on GaAs device performance was due to dislocation clusters in MBE device layers. Comparison analysis with GaAs overgrowth via metal organic chemical vapor deposition (MOCVD) demonstrated this growth method produced fully-operational large-area device structure. A model relating surface growth rates to an incomplete lattice-mismatch relaxation predicts the formation of these clusters. While challenges remain for monolithic III/V optoelectronic integrat (open full item for complete abstract)

Committee: Steven Ringel (Advisor) Subjects:

Master of Science, The Ohio State University, 2024, Electrical and Computer Engineering

Selective area epitaxy in III-V compound semiconductors has been used for decades in applications such as patterned quantum dots, strain blocking in metamorphic growth, and substrate removal. Recent work in integrated photonic structures, photonic crystal lasers, and metamaterials have led to a renewed interest in patterned and selective epitaxy. The ability to embed dielectric materials into an epitaxial layer or to create regions of complete selectivity (no growth) allow for flexibility in device design and monolithic integration. Advances in lithography and fabrication techniques offer opportunities to explore selective epitaxy and length scales that were not previously accessible. This work focuses on nanoscale selective epitaxy using hydrogen silsesquioxane (HSQ) as the dielectric mask. HSQ becomes a silicon oxide, nearly identical to SiO2, after electron beam exposure and development. HSQ patterns smaller than 20 nm wide, 90 nm tall on a 10 um grid on GaAs (100) offcut 6° toward the nearest (111)A were used in selective epitaxy by both molecular beam epitaxy (MBE) and organometallic chemical vapor deposition (MOCVD). Addionally, on-axis GaAs (100) substrates were used in MOCVD as a comparison to the 6° offcut. The grid lines were aligned to the [011] and [01¯1]. The goal of this work was to understand the interaction between the HSQ “nanowalls” and the epitaxy. The specific orientation of HSQ nanowalls had the most significant impact on local epilayer morphology for both MBE and MOCVD growths. Interestingly, the two growth methods yielded effectively opposite effects, with vast differences in epitaxial wetting, growth initiation/inhibition, lateral overgrowth, and type/number/propagation/direction of material imperfections. For both on-axis and off-cut substrates, the MOCVD growths possess highly faceted trenches along the [011] direction that effectively extend down to the substrate surface; no GaAs growth is observed over or adjacent to the HSQ lines. (open full item for complete abstract)

Committee: Tyler Grassman Ph. D. (Advisor); Steven Ringel Ph. D. (Committee Co-Chair) Subjects: Electrical Engineering; Materials Science

Master of Science, The Ohio State University, 1969, Graduate School

Committee: Not Provided (Other) Subjects:

Master of Science, The Ohio State University, 1970, Graduate School

Committee: Not Provided (Other) Subjects:

PhD, University of Cincinnati, 2024, Engineering and Applied Science: Mechanical Engineering

One of the largest sources of uncertainty in the calculation of stopping power ratios for use in proton radiotherapy is the measurement of Hounsfield Units (HU) for the determination of electron density. The primary source of this uncertainty is due to the relative difference in scatter between the patient and electron density calibration phantoms. In this dissertation, I will show how anatomy adaptive CT number to electron density calibration curves can improve the accuracy of stopping power ratio tabulations for proton radiation therapy dosimetry. We will generate new curves by measuring realistic (anthropomorphic) phantoms, fabricated using realistic tissue equivalent materials that accurately represent the internal structure and tissue types of the pelvis. The goal of this research is to use the new realistic anthropomorphic phantoms to evaluate how patient scatter affects measured electron density curves.

Committee: Henry Spitz Ph.D. (Committee Chair); Jay Kim Ph.D. (Committee Member); Michael Lamba Ph.D. (Committee Member); Bruce Mahoney (Committee Member); Peter Sandwall Ph.D M.A B.A. (Committee Member); Michael Alexander-Ramos Ph.D. (Committee Member); Sam Glover Ph.D. (Committee Member) Subjects: Nuclear Physics

Master of Science, The Ohio State University, 2020, Welding Engineering

High energy density welds are often used in critical applications involving a wide range of structural materials. In most cases, both laser and electron beam welding may be considered for these applications and the ability to use both processes to make comparable welds in terms of both weld profile and microstructure provides considerable process selection flexibility. In this study, autogenous, partial penetration welds on 304 SS, 304L SS, and Ti-6Al-4V were made using both fiber laser and electron beam processes. The main variables of interest, power and travel speed, were varied independently. Beam characterization was performed to determine parameters necessary for similar welding conditions between the two processes. Overfocused electron beams produced a more Gaussian distribution than underfocused beams. Laser beam characterization showed a slight increase in sharp spot size with increasing power, likely due to machine capabilities. Welds were made using sharp focus for laser welds and both a sharp, deflected beam and an overfocused beam for electron beam welds. Depth of penetration varied substantially between process conditions, but a similar trend between processes was observed when comparing area of the fusion zone, suggesting a similar melting efficiency. For defocused electron beam welds, increases in voltage yielded a dip in penetration for increasing power. This was likely due to complications with the machine or the diagnostic tool resulting in a narrower beam at lower voltages. A reduction in melting efficiency was observed in Ti-6Al-4V laser welds as compared to EB welds, likely due to vaporization effects, material properties, or both. Analysis of the depth of penetration for 304L and Ti-6Al-4V laser welds at varying powers and travel speed yielded predictive process maps. Stainless steel alloys showed consistent microstructures with work found in literature for pulsed laser welding. Limited metallographic analysis for Ti-6Al-4V welds was conducte (open full item for complete abstract)

Committee: John Lippold (Advisor); Boyd Panton (Advisor); Carolin Fink (Committee Member) Subjects: Materials Science

Doctor of Philosophy, The Ohio State University, 2020, Physics

Magnonics is a promising field revolving around using angular momentum – instead of charge – to transmit, store, and process information. Similar to organic based counterparts to inorganic electronics, magnonics provides the possibility to expand the application space of electronics. It can do this via reduced heating, nonlinear effects allowing for complex, unimaginable manipulations of microwave signals, and miniaturization of microwave components. In order to effectively study the properties of magnons, we need to find and characterize the best materials. For the transduction and transportation of information at microwave frequencies, low magnon loss materials are crucial to prevent the generation of spurious signals and maintain coherence. The two leaders of this low-loss criteria are YIG and V[TCNE]x. Two important factors have hindered the full success of these materials, however, difficulty patterning laterally at micron length scales and characterization and understanding of the damping and band structure within V[TCNE]x. In this dissertation, I explore successful methods for patterning these two low-loss materials and further characterize damping and band structure manipulations in V[TCNE]x. First I investigate patterning of YIG thin films. High-quality micron-scale YIG bars on GGG are achieved via the liftoff of magnetron sputtered YIG with a patterned bilayer of PMMA resists followed by an annealing step. The high quality of the patterned bars is assessed through x-ray diffraction, angle-dependent hysteresis,and angle-dependent FMR. These results advance the application space of YIG by introducing patterned YIG to the market, allowing for the creation of low-damping YIG features with manipulatable anisotropy fields and fine-tuned active areas for device creation. Second I investigate patterning of V[TCNE]x thin films. High-quality micron-scale V[TCNE]x features are achieved via liftoff of CVD grown V[TCNE]x with a patterned bilayer of PMMA resists. (open full item for complete abstract)

Committee: Ezekiel Johnston-Halperin (Advisor); Jay Gupta (Committee Member); Yuanming Lu (Committee Member); Louis DiMauro (Committee Member) Subjects: Physics

Master of Science in Renewable and Clean Energy Engineering (MSRCE), Wright State University, 2019, Renewable and Clean Energy

Due to the large band gap of β-Ga2O3 and recent improvements toward high quality native substrates and the ability to shallow dope epitaxial β-Ga2O3 it is an attractive material for applications in power electronic devices. Such devices require advances in the areas of thin film growth and carrier concentration control to deliver high mobility films appropriate for the device structures. Transmission electron microscopy (TEM) analysis can provide information concerning doping, crystal structure, and internal strain which will be valuable to assess the role of defects and impurities on the transport properties for feedback to optimize the bulk and epitaxial growth processes. The objective of this work is to fabricate high-quality TEM specimens with the help of dual-beam Focused Ion Beam/Scanning Electron Microscopy (FIB/SEM) to study the quality of Si-doped β-Ga2O3 homoepitaxial films grown by pulsed laser deposition and to analyze the nanoscale features in the films. Final thinning procedures were developed to enable observation of tensile strain attributed to the Si dopant level. These results are important for improving the thin film growth towards nanoscale device design and fabrication

Committee: Hong Huang Ph.D. (Advisor); Gregory Kozlowski Ph.D., D.Sc. (Committee Member); John Boeckl Ph.D. (Committee Member) Subjects: Materials Science; Mechanical Engineering

Doctor of Philosophy, The Ohio State University, 2018, Materials Science and Engineering

By making electron energy-loss spectroscopy (EELS) measurements in a scanning transmission electron microscope (STEM), the optoelectronic properties of a material can be determined with nanometer spatial resolution. Since these optoelectronic properties can be related to the electronic structure of a material, STEM-EELS can also probe the local bonding environment at the interface of two materials. Such measurements could be key in developing more efficient P3HT:PCBM bulk-heterojunction organic photovoltaics (OPVs) (P3HT = poly(3-hexylthiophene), PCBM = [6,6] phenyl C61 butyric acid methyl ester), as understanding the local electronic structure at P3HT/PCBM interfaces should provide insight into charge generation/transport. However, organic materials are extremely susceptible to beam-damage when placed under a high energy electron beam, making it difficult to use STEM-EELS to collect reliable data. It was demonstrated that, via a beam damage-minimization EELS acquisition method, reliable high-resolution valence-loss STEM-EELS data could be collected for electron beam-sensitive materials. Using this method, valence-loss EELS spectra were acquired (using an FEI Titan3 60-300 Image-Corrected S/TEM) for thin films of four OPV materials – P3HT, PCBM, CuPc (copper phthalocyanine), and C60. From these valence-loss spectra, the real (e1) and imaginary (e2) parts of the complex dielectric function were extracted and compared to similar spectra obtained via a technique that should not damage these organic materials (variable-angle spectroscopic ellipsometry, VASE), thus proving that the acquisition method developed was suitable for collecting reliable valence-loss EELS spectra of P3HT, PCBM, CuPc, and C60. Valence-loss EELS spectra were then collected for P3HT, PCBM, CuPc, and C60 using a Nion UltraSTEM 100 MC `HERMES' S/TEM. With this STEM, it was possible to collect valence-loss spectra with higher energy resolutions (35 meV) than what was achievable using the FEI T (open full item for complete abstract)

Committee: David McComb (Advisor); Tyler Grassman (Committee Member); Vicky Doan-Nguyen (Committee Member) Subjects: Materials Science

Doctor of Philosophy, University of Toledo, 2017, Electrical Engineering

Electrically conductive hair-like structures, referred to as whiskers, can bridge the gap between densely spaced electronic components. This can cause current leakage and short circuits resulting in significant losses and, in some cases, catastrophic failures in the automotive, aerospace, electronics and other industries since 1946. Detecting a metal whiskers (MWs) is often a challenging task because of their random growth nature and very small size (diameters can be less than 1 µm, lengths vary from 1µm to several millimeters). Many decades ago the industry introduced whisker mitigating Pb in the solders used to fabricate electric and electronic parts. In recent years, this changed because the European Union (EU) passed a legislation in 2006, called “Restriction of the use of Certain Hazardous Substances (RoHS) in Electrical and Electronic Equipment”, which requires a reduction and elimination of the use of Pb in technology. Thus, the issue of undesirable and unpredictable whiskers growth has returned and there is a renewed interest in the mechanisms of formation of these structures. None of the whisker growth models proposed to date are capable of answering consistently and universally why whisker grow in the first place and why Pb addition suppresses their growth. Understanding MW nucleation and growth mechanism are of significant interest to this project, since this would potentially allow the development of new accelerated-failure testing methods of electronic components to replace existing testing methods which are generally found to be unreliable. In particular, this research is intended to study the effects of electric fields on the whisker growth, which according to the recently developed electrostatic theory[1] of whisker growth, are of crucial importance. This theory proposes that the imperfections on metal surfaces can form small patches of net positive or negative electric charge leading to the formation of the anomalous electric field (E), which go (open full item for complete abstract)

Committee: Daniel Georgiev Dr. (Committee Chair); Vijay Devabhaktuni Dr. (Committee Member); Victor Karpov Dr. (Committee Member); Devinder Kaur Dr. (Committee Member); Anthony Johnson Dr. (Committee Member) Subjects: Aerospace Materials; Chemical Engineering; Condensed Matter Physics; Electrical Engineering; Engineering; Experiments; Materials Science; Metallurgy; Nanoscience; Nanotechnology; Physics; Plasma Physics; Solid State Physics; Theoretical Physics

Master of Sciences, Case Western Reserve University, 2017, Physics

The historical and current market trends for transparent conductive coating are considered. The metal oxide transparent conductive coatings are found to have all but reached their theoretical limits. In light of this background, a coating process that was developed for an electron-beam deposition chamber at VisiMax Technologies is described. The coating process is shown to be capable of depositing an ITO film that is on par with the protective coatings that are currently on the market. The protective coating market is investigated and found to be sufficiently large for a specialized thin film-coating firm to enter. The ITO film that was produced by this process had a sheet resistance of 62 ohm-squares and an average transmission through the visible range (400nm – 700nm) of 89.4%.

Committee: Edward Caner M.S. (Committee Chair); Ina Martin Ph.D. (Committee Member); Singer Kenneth Ph.D. (Committee Member) Subjects: Entrepreneurship; Physics

Master of Science in Engineering, Youngstown State University, 2017, Department of Mechanical, Industrial and Manufacturing Engineering

Powder bed-based EBM technology has been utilized for biomedical implant manufacturing. Anisotropic microstructure of the EBM built implant surface is closely related to wear and corrosion behavior during active biomechanical loadings. A series of experimental studies are performed in ambient and in simulated body fluids. Before the wear tests, local properties are characterized by depth-sensing nanoindentation technique to obtain mechanical properties due to surface anisotropy. Microscale (fretting) contact experiments are conducted using the pure titanium spherical head of instrumented nanoindenter as a well-characterized single asperity to apply controlled sliding contact motions on the EBM-built Ti6Al4V surfaces. Removed volume of the surface is measured to determine the influence of surface anisotropy, contact stress, and synovial environment effect on surface fatigue response. Experimental results indicate that the layer-by-layer fashion of the EBM-built part develops anisotropic microstructure and the microstructure leads to variable tribological properties. In ambient environment with controlled humidity (35%), the wear behavior of the EBM built Ti6Al4V displays a significant dependence on both build orientation and sliding motions. In phosphate buffer saline (PBS) solution, wear rate for most of the EBM built parts increase under the cyclic sliding contacts, while the surface anisotropy effect becomes less significant. The result implies electrochemical attack largely affects the wear of transversely developed parts. However, wear rate of millannealed Ti6Al4V decreases in PBS compared to the wear in ambient. Material removal rates in protein-hyaluronic acid solution are significantly reduced in all specimens and sliding directions. Presence of major components in synovial fluids improves lubricative effect under the same mechanical stimuli. In conclusion, the grain morphology and iv orientation significantly changes the tribological and electrochemical pe (open full item for complete abstract)

Committee: Jae Ryu PhD (Advisor); Guha Manogharan PhD (Committee Member); Virgil Solomon PhD (Committee Member); Brett Conner PhD (Committee Member); Hazel Marie PhD (Committee Member) Subjects: Mechanical Engineering

Doctor of Philosophy, The Ohio State University, 2017, Physics

Skyrmions are magnetic spin textures that have a non-zero topological winding number associated with them. They have attracted much interest recently since they can be as small as ~1 nm and could be the next generation of magnetic memory and logic. First, we grow epitaxial films of FeGe by molecular beam epitaxy and characterized the skyrmion properties. This had led us to image skyrmions in real-space with Lorentz transmission electron microscopy for the first time in the United States. Next, from an extensive series of thin and thick films, we have experimentally shown the existence of a magnetic surface state in FeGe and, consequently, any skyrmion material for the first time. Complementary theoretical calculations supported the existence of chiral bobbers—a surface state only predicted in 2015. Next, we fabricated for the first time a new class of skyrmion materials: B20 superlattices. These novel heterostructures of [FeGe/MnGe/CrGe] have now opened the door for tunable skyrmion systems with both Dresselhaus and Rashba Dzyaloshinskii-Moriya interactions. Additionally, we perform resonant soft x-ray scattering to image magnetic spin textures in reciprocal space for FeGe thin films in transmission. We have accomplished the removal of substrate and left an isolated single-crystal FeGe film. Lastly, SrO is grown on graphene as a crystalline, atomically smooth, and pinhole free tunnel barrier for spin injection.

Committee: Roland Kawakami (Advisor); Chris Hammel (Committee Member); Nandini Trivedi (Committee Member); John Beacom (Committee Member) Subjects: Physics

Master of Science, The Ohio State University, 2017, Electrical and Computer Engineering

Zinc oxide (ZnO) has emerged as a promising wide bandgap material (3.35eV at 300K) for use in next-generation nanoelectronics and photonics, with important piezoelectric, pyroelectric, sensing, and optoelectronic properties. ZnO has seen specific application in ultraviolet (UV) photodetectors, UV lasers [1], hydrogen gas sensors [2, 3], surface acoustic wave devices, piezoelectric generators [4], and transparent thin-film transistors for displays [5]. Various forms of ZnO nanostructures, such as nanobelts, nanobows, and nanowires, and have all attracted significant attention due to their ease of fabrication, remarkable relative surface area, and low-dimensional nature [6, 7]. Nanowires of ZnO in particular can exhibit pinch-off of electrical current with surface charge-sensitive depletion depths that are on the order of the wire radius [8, 9]. In bulk ZnO, defects have been shown to strongly affect the behavior of metal contacts, by modifying band bending and allowing trap-assisted tunneling transport through the metal-ZnO Schottky barrier [10]. The electronic impact of native point defects becomes critical at the nanoscale, since their physical properties can dominate charge carrier transport and especially electronic contact behavior. In order to control the distribution of defects at the metal-nanowire interface, various forms of surface modification were investigated. We report the in-situ fabrication of both Ohmic and Schottky platinum (Pt) metal contacts to single ZnO nanowires prepared by pulsed laser deposition (PLD) and carbothermal vapor phase transport, using Ga-ion surface modification and both furnace and electron beam annealing. A Ga focused ion beam (FIB) was operated at 30 keV to implant nanowire surfaces before metallization for production of Ohmic contacts, and at 5 keV to gently mill the defect-rich outer annulus, promoting formation of Schottky contacts. Electron beam induced deposition (EBID) was used to pattern Pt metal contacts to the wire (open full item for complete abstract)

Committee: Leonard Brillson (Advisor); Betty Lise Anderson (Committee Member) Subjects: Electrical Engineering

Doctor of Philosophy, University of Akron, 2017, Chemical Engineering

Corrosion of structure materials in light water reactors (LWRs) can be ultimately equally disastrous as the immediate attack and degradation of components, which arise from the formation and behavior of corrosion products[1]. Especially, stress corrosion cracking (SCC) can lead to unexpected sudden failure of normally ductile construction materials in LWRs. This study presents an investigation on the corrosion properties of interstitially hardened (IH) austenitic stainless steel 316L and nickel-based Inconel 718 by low temperature carburization/nitro-carburization (IH-C/IN-NC SS 316L/IN718), which are being developed for use in light water reactors, specifically, as a surface treatment for fuel cladding to increase accident tolerance during loss-of-coolant accidents. Microstructure and chemical composition of the oxides were characterized after long-term exposure test in simulated oxidizing BWR-NWC environment. Stress corrosion cracking susceptibility was investigated via slow strain rate test with different applied strain rate. After 500 hours exposure in the simulated environment, the oxides formed on IH-C SS 316L were identified as loosely packed spinel outer layer and nano-scale Ni enriched spinel inner layer with a relatively compact Cr-rich spinel intermediate layer. The proposed oxidation mechanisms were consistent with metal dissolution/oxide precipitation and solid-state growth mechanism. Whereas, their oxidation procedure might be modified due to the high concentration near-surface interstitial carbon, which had a high affinity with Cr. Duplex oxide structures were identified on both IH-C and IH-NC IN718 samples with distinct interface between the top single crystal spinel scales and inner fine polycrystal oxides. However, Cr enriched regions were observed at the bottom of the outer scales of both IH-C and IH-NC samples. While, IH-NC IN718 exhibited the smallest weight loss and thinnest oxide layer thickness. It was found from the study of cross (open full item for complete abstract)

Committee: Scott Lillard (Advisor); Zheng Jie (Committee Member); Rajeev Gupta (Committee Member); Gary Doll (Committee Member); Curtis Clemons (Committee Member); Gerald Young (Committee Member) Subjects: Chemical Engineering; Materials Science; Nuclear Engineering

MTEC, Kent State University, 2015, College of Aeronautics and Engineering

Development of a Low Energy Electron Accelerator System for Surface Treatments and Coatings N. PHANTKANKUM, Kent State University. – Treatment with ionizing radiation can modify the physical, chemical or biological properties of materials. By using this method one can obtain many beneficial effects such as surface treatment and coatings. Electron Beam Accelerators are durable and reliable equipment for these applications. The work described in this thesis was concerned with the simulation and design of the enclosure of a low energy electron accelerator. The focus of this work was on determining the construction of an appropriate enclosure for the accelerator, as well as determining and obtaining the appropriate dose in a sample. First, general information of the electron accelerator was studied and presented. To clarify how the design calculations were optimized for a low energy electron accelerator, the main quantities and units such as energy, beam current, power, and dose were reviewed. In order to obtain a more clear understanding of this thesis, radiation processing and how it can initiate biological and chemical changes in a material was studied and presented. These details were used in the simulation and design of the unit, and allowed for the correct parameters to be used when determining the appropriate enclosure properties and dose delivery. The hazards present during normal operation of the unit, which contribute to the requirements of the project, are also important. These were studied before simulating and designing the enclosure. PENELOPE Monte Carlo simulations were used to determine an appropriate shielding material type and its appropriate amount, as well as the expected dose under several conditions. Autodesk Inventor was used to create drawings and simulations for the mechanical design.

Committee: Roberto Uribe Ph.D. (Advisor); Darwin Boyd Ph.D. (Committee Member); John Duncan Ph.D. (Committee Member); Michael Fisch Ph.D. (Committee Member); Shin-Min Song Ph.D (Committee Member) Subjects: Radiation; Technology

Master of Science (MS), Ohio University, 2015, Physics and Astronomy (Arts and Sciences)

A trench-like structure has been observed after sub-monolayer Mn is deposited onto N-polar gallium nitride (GaN) surfaces. It is reminiscent of the well-documented formation of the vacancy line structures on Si(001) surfaces. However, little is known about what really causes this trench-like structure to form. Although it was previously hypothesized that it may be due to the Mn atoms, it may in fact be present before Mn deposition, and possibly caused by annealing or some other variations in the growth conditions. This study investigates the causes of the appearance of this trench-like structure on N-polar w-GaN surfaces by optimizing the growth recipe to obtain reproducible trench structures. Additionally, surface structure after Mn deposition onto w-GaN (0001 ¯) was observed and the role of the Mn was analyzed. In the current study, GaN samples were grown on sapphire (0001) substrates using ultra high vacuum molecular beam epitaxy (UHV-MBE). The growth was monitored using a reflection high energy electron diffraction (RHEED) system. For room temperature scanning tunneling microscopy (RT-STM) studies, the samples were transferred in-situ to the analysis chamber, where STM images were taken using a tungsten tip under a constant current condition. In the first attempt, the RHEED patterns of the GaN growth showed the well-known 3×3 reconstruction, which was further confirmed by atomic resolution STM. The sample was annealed at a high temperature range of ~ 600°C to 700°C but no trench-like structure was observed. Another GaN sample was grown under highly Ga-rich conditions and then annealed at a higher temperature, ~ 800°C, for ~ 6 minutes. These growth conditions resulted in the trench-like formation often appearing nearby the c(6×12) reconstruction. The trench-like structure is composed of two sub-units of the c(6×12) reconstruction because of the observable similarities between the trench-like formation and the c(6×12) reconstruction. After depositing ~ 0.15 (open full item for complete abstract)

Committee: Arthur Smith (Advisor) Subjects: Physics

Master of Sciences (Engineering), Case Western Reserve University, 2015, Materials Science and Engineering

In this study, a number of established additive manufacturing processes were evaluated for their suitability repairing high-pressure die cast tooling. The processes included in this study are laser hot wire (LHW), electron beam freeform fabrication (EBF3), gas metal arc welding (GMAW), Laser Engineered Net Shaping (LENS®), and direct metal deposition (DMD). To determine each process' suitability, blocks of maraging 250 steel were deposited on H-13 base metal. The results show that the maraging deposits are capable of providing good strength (>160 ksi), toughness (>15 ft-lbs), and hardness (45 HRC) for die tooling applications, but care must be taken to limit the occurrence of defects, particularly porosity. Of the processes tested, the LHW, DMD, and LENS® processes had the best balance of deposit properties. However, additional work will be required to optimize the processing parameters for each process.

Committee: David Schwam (Advisor); John Lewandowski (Committee Member); Gerhard Welsch (Committee Member) Subjects: Engineering; Materials Science; Metallurgy