Master of Science, University of Akron, 2022, Geology

Stresses in the upper crust are redistributed to the lower crust after earthquakes. Stresses released by seismic slip induce crystal-plastic deformation in the mid to lower crust, which is composed of foliated, heterogeneous feldspathic rocks that deform and transfer stress back to the upper crust. Current models for the strength of the crust are primarily based on flow laws determined from experimentally deformed homogeneous quartzites or other monophase rocks. However, heterogeneities such as foliation orientations and foliation intensities, which are known to cause anisotropy of rock strength under brittle conditions, may cause viscous anisotropy at high temperatures and pressures where crystal-plastic mechanisms are dominant. To investigate if heterogeneities like foliation orientation and foliation intensity cause viscous anisotropy, I deformed weakly foliated Westerly Granite and strongly foliated Gneiss Minuti in different orientations that maximize (foliation at 45 degrees to the compression direction) and minimize (foliation parallel and foliation perpendicular to the compression direction) the shear stresses on the dispersed, elongate biotite grains in the quartz-feldspar framework, which should be the weakest and strongest orientations, respectively. These rocks were chosen because they both have similar low biotite contents (7%) and compositions: Westerly Granite is composed of 22 vol% quartz, 26 vol% K-feldspar, 45 vol% albite, and 7 vol% biotite and Gneiss Minuti is composed of 29 vol% quartz, 10 vol% K-feldspar, 53 vol% plagioclase and 7 vol% biotite. Experiments were performed using a Griggs apparatus at a temperature (T) of 800°C, confining pressure (Pc) of 1.5 GPa, and strain rate of 1.6 x 10-6/s. Westerly Granite and Gneiss Minuti reached peak stresses of 920 (+/- 50 MPa) and 670 (+/- 75 MPa), respectively, and viscous anisotropy was minor with anisotropy coefficients of 1.1x and 1.2x, respectively. Westerly Granite contained microstructures like (open full item for complete abstract)

Committee: Caleb Holyoke (Advisor); Molly Witter-Shelleman (Committee Member); John Peck (Committee Member) Subjects: Geology

Doctor of Philosophy, The Ohio State University, 2019, Electrical and Computer Engineering

Beta-phase gallium oxide (β-Ga2O3) is attracting significant interest for high-power electronics and ultraviolet optoelectronics due to its ~4.8 eV wide bandgap, large predicted breakdown field, ability to support β-(Al1-xGax)2O3/Ga2O3 heterojunctions, and the availability of large area, melt-grown native substrates for homoepitaxial growth. There is also continued interest for space-based applications due to its predicted high radiation hardness compared to contemporary wide bandgap materials (III-nitrides and SiC). However, the integration of β-Ga2O3 into prospective applications will largely depend on device design innovations as well as the availability of high quality and low defect-density materials. This is considerably important as crystalline defects can adversely affect material properties critical to device operation, output power, threshold voltage, and carrier mobility by causing carrier compensation, scattering, and trapping effects. Defect-induced degradation can also dictate the entire behavior of β-Ga2O3 devices in their intended space-based applications where exposure to energetic radiation particles is typical, leading to introducing defect states in the bandgap. Furthermore, there is an intense need of understanding of metal/ β-Ga2O3 contact and interface properties to ensure large Schottky barrier height and low leakage current for high power operations. However, despite remarkable early progress, the underlying knowledge of metal contact properties, dopants, electrically active defects, and their role on material properties is still very limited. Hence, this research aims to pursue a comprehensive investigation of defects in β-Ga2O3 bandgap, building from the native β-Ga2O3 substrate to subsequent homoepitaxial layers. Using deep level transient and optical spectroscopy (DLTS/DLOS) techniques, experiments have been undertaken to understand the formation, physical structure, electronic, and optical properties of defects in β-Ga2O3 bandgap, wit (open full item for complete abstract)

Committee: Steven Ringel (Advisor); Wu Lu (Committee Member); Aaron Arehart (Committee Member) Subjects: Electrical Engineering

Master of Science (MS), Wright State University, 2011, Chemistry

The purpose of this work was to examine the effects of polished crystal-surface orientation and degree of solution undersaturation (Ωcalcite) on the dissolution kinetics of calcite as a means of improving our understanding of fundamental reactions that may influence the efficacy of CO2 sequestration in geological formations. Crystallographic surface orientations utilized in this study included ~ 1 cm2 areas of natural calcite specimens polished approximately parallel to the (104) plane, giving rise to surfaces with flat terraces with few steps, as well as fully kinked surfaces created by sectioning approximately parallel to the (001) plane. Results from inductively coupled plasma (ICP-OES) and vertical scanning interferometry (VSI) investigations revealed how crystallographic orientations of calcite with higher initial surface morphologies were associated with greater Ca2+ release, greater surface retreat, and therefore, greater initial transient dissolution rates than those with lower initial surface morphologies. However, both the ICP-OES and atomic force microscopy (AFM) results confirm that the effects of crystal orientation become minimal under long-term conditions since (1.) varyingly oriented calcite surfaces exhibited similar “steady” rates and (2.) orientations with high initial reactive site densities developed lower energy morphologies. Results from this study are significant for predicting long term calcite dissolution rates because they suggest the “steady” dissolution rate of any calcite surface with any degree of initial surface energy will be similar to that of a surface with natively low surface energy.

Committee: Steven Higgins PhD (Advisor); Steven Higgins PhD (Committee Chair); David Dolson PhD (Committee Member); Ioana Pavel PhD (Committee Member) Subjects: Chemistry

Doctor of Philosophy, Miami University, 2010, Geology and Environmental Earth Science

Understanding the crystal chemistry of actinides in nuclear waste forms is critical for the evaluation of the material's potential use and stability as solid state waste repositories. Because of the ability of apatite to incorporate lanthanides and actinides there is great interest in the phase as a solid nuclear waste form. However, the crystal chemistry of U and Th in the apatite structure is still poorly understood. This dissertation investigates the structural crystal chemical parameters in a variety of natural and synthetic apatites with substituent U and Th through the complimentary use of single crystal X-ray diffraction and X-ray absorption spectroscopy. 1) Site preference of U and Th in F, Cl, Sr apatites, investigated the site preference of U and Th and the structural response to these substituents in a series of synthetic fluor-, chlor-, and strontium-apatite crystals using single crystal X-ray diffraction. 2) Crystal chemistry of Th in fluorapatite, obtained quantitative information of the local structure of Th in both natural and synthetic fluorapatite by Extended X-ray absorption fine-structure spectroscopy (EXAFS). Understanding the mechanism of incorporation and the structural response of fluorapatite to Th is important in assessing the use of apatite as a possible host for tetravalent radionuclides and understanding the behavior of Th in geological systems where fluorapatite is present. 3) Orientation dependent polarized micro-XAS study of single crystal apatite, developed the technique/equipment to accommodate polarization effects of synchrotron radiation on single crystal apatites. A goniometer was designed for precise positioning of single crystals for microXAS data collection. Lattice orientation is determined from X-ray diffraction data and then can be applied to EXAFS data analysis. The outcome of this technique development will have application to many other studies with similar sample constraints.

Committee: John Rakovan PhD (Committee Chair); John Hughes PhD (Committee Member); Elisabeth Widom PhD (Committee Member); Hailiang Dong PhD (Committee Member); Stephen Wright PhD (Committee Member) Subjects: Mineralogy

Doctor of Philosophy, University of Akron, 2009, Polymer Science

One dimensionally (1D) confined crystallization based on semicrystalline diblock copolymers has been widely investigated for twenty years. Highly orientated lamellar samples, after large amplitude oscillation shear, provide the typical 1D confined environment to investigate crystallization behavior, such as crystal orientation and crystallization kinetics. However, inevitable defect generation, such as edge and screw dislocations during mechanical shear lead to “cross-talking” between grain boundaries and significantly affect the ideal 1D confinement crystallization kinetics by releasing the confinement. Meanwhile, the mechanism of the origin of specific crystal orientations (parallel or perpendicular) within the 1D confinement is still under debate. In this research, PS-b-PEO single crystals composed of one PEO nano-layer sandwiched by two PS glassy layers on the nanoscale were chosen as a template to investigate polymer crystallization in a 1D defect-free nanoscale confinement. Since the TgPS is higher than the TmPEO in such a “sandwich” lamellar structure, the PEO single crystal can be melted while keeping the PS layer in the vitrified state. The PEO blocks can be recrystallized between the two confining, glassy PS nano-layers at different re-crystallization temperatures, Trx, and monitored for different recrystallization behavior using electron diffraction (ED). Results indicate that the PEO block does not recrystallize until Trx = -5 °C, the limit of homogeneous nucleation. This observation confirms PEO recrystallization takes place in a defect-free confinement. Next, a puzzling ED pattern taken from PEO microcrystals grown at Trx > -5 °C via self-seeding was analyzed to be the result of the specific interaction between tethered PEO blocks having monoclinic symmetry and the glassy PS substrate. Two different inclined PEO microcrystals having an orthogonal relationship truly coexisting in the lamellar confinement during self-seeding were found. Furthermore, (open full item for complete abstract)

Committee: Stephen Z. D. Cheng Dr. (Advisor) Subjects: Materials Science; Polymers

Doctor of Philosophy, University of Akron, 2006, Polymer Engineering

Polyethylene has become an important commercial thermoplastic since its low density form was first produced in the 1930's by ICI. A high density form was synthesized in the 1950's by Ziegler and by Phillips Petroleum researchers. Ziegler catalyst based copolymers known as linear low density polyethylene was introduced in the 1970s. In recent years, new types of polyethylene have also been commercially available through the application of improved catalysts, notably metallocene catalysts. These include narrow composition distribution of ethylene copolymers with different types of comonomer and various comonomer contents. In this dissertation, we studied structure development during melt spinning, cold drawing and cold compression of such ethylene-octene copolymers with various octene contents and conventional linear low density polyethylene. One of our major concerns is to study the effects of comonomer contents on structure development in processing metallocene polyethylene copolymer. Another major concern is to compare these copolymers with conventional linear low density polyethylene. We began with the material characterization, which mainly include comonomer content and distribution, molecular weight and molecular weight distribution, isothermal and non-isothermal crystallization kinetics, melting behavior after annealing. The latter studies largely used differential scanning calorimetry (DSC). Subsequently, we studied structure development during melting spinning, cold drawing and cold compression of these materials, which mainly include the development of crystal structure, crystalline morphology, orientation factors and mechanical properties of filaments under different spinline stress and deformation ratio. The processed filaments were mainly characterized by wide angle x-ray diffraction (WAXD), small angle x-ray scattering (SAXS), scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and birefringence. We correlated the formation of str (open full item for complete abstract)

Committee: James White (Advisor) Subjects: