For this thesis niobium oxides (NbO [subscript x]) with the goal of obtaining phase pure epitaxial NbO₂ were grown under variable conditions by molecular beam epitaxy (MBE) on different substrates, mostly (111) oriented strontium titanate. The films were characterized by X-ray diffraction (XRD) and reflection high-energy electron diffraction (RHEED) and from that their epitaxial relationship to the substrate was determined. With X-ray photoelectron spectroscopy (XPS) the oxidation states and stoichiometry of the films were determined. Asymmetric NbO₂ Nb 3d core-level spectra are clearly seen for the first time in XPS. Additionally, the film thickness was measured by X-ray reflectivity (XRR). Judging from the XPS spectra and diffraction data the goal to grow epitaxial NbO₂ of high phase-purity was achieved. / text

The quaternary material system In[subscript x]Ga[subscript 1-x]As[subscript y]P[subscript 1-y] is an important material system for optoelectronic devices, specifically covering optimum fiber optic wavelengths. Among the limitations of using this material system concerning photodetector performance is generation of carriers due to material defects and impurities. This dissertation reports on the growth optimization of InGaAs using molecular-beam epitaxy for low-dark-current avalanche photodiodes through the study of the effects of the growth conditions on dark current. An optimum growth temperature of 545°C and arsenic beam equivalent pressure of 2x10⁻⁵ Torr was found for producing the lowest dark current density. Avalanche photodiodes were implemented with a dark current density 80 mA/cm² at 90% of the breakdown voltage.

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The microelectronics industry is driven by the need to produce smaller transistors at lower costs, and this requires an ever-changing approach to the chemistry involved in their fabrication. While photolithography has been able to keep pace with Moore’s law over the past four decades, alternative patterning technologies are now receiving increased attention to keep up with market demand. The first project describes work towards increasing the sensitivity of electron-beam resists by incorporating electron-withdrawing groups into the alpha position of methacrylates. After monomer design and synthesis, several polymers were synthesized that investigated the role of fluorine in the resists performance. G-values, electron-beam contrast curves, and EUV imaging showed that these fluorinated polymethacrylates outperformed current industrial resists. The next project deals with the design, synthesis, and evaluation of a resist that seeks to decouple chemical amplification from acid diffusion. While work was shown that a system comprised of a photo-labile polyphthalaldehyde and x novolak could achieve this process, the high dose required to image was problematic. An aliphatic dialdehyde was envisioned to account for these issues, but its synthesis was never achieved. A polyethylene glycol aldehyde was synthesized and polymerized, but its material properties did not perform the intended function. Ultimately, the stability of aliphatic aldehydes proved to be too unstable for this project to continue. While the synthesis was troublesome, a fundamental study of ceiling temperatures was undertaken. Numerical and analytical solutions were developed that describe the exact nature of the equilibrium constant on a living polymer system. These results were verified by a VT-NMR experiment, which accurately predicted the ceiling temperature of polythalaldehyde with a Van’t Hoff plot. Lastly, the self-assembly of block copolymers was investigated as a means to produce high resolution, high density nano-imprint lithography templates for bit patterned media. The first set of experiments involved synthesizing polymeric cross-linked surface treatments from substituted styrenes. The aryl substituent was shown to largely effect the surface energy, and after anionically synthesizing PS-b-PMMA, these materials were shown to effect block copolymer orientation. To produce a 3-D pattern of the self-assembled features, silicon was incorporated into one block to provide adequate etch resistance. Several monomers were investigated, and two, an isoprene and methacrylate analog, were successfully incorporated into two block copolymers. The silicon containing methacrylate derivative polymer was shown to successfully self-assemble in thin films under solvent annealing conditions. / text

The objective of this research is the evaluation of shear behavior of full-scale reinforced concrete T-beams strengthened with carbon fiber reinforced polymer (CFRP) sheets and CFRP anchors. Although the CRFP material has high tensile strength, premature failure due to debonding CFRP sheets prevents utilizing that strength. The use of CFRP anchors prevents this failure, so the CFRP sheets are able to reach ultimate strain. The current shear design is based on plasticity, which assumes that all steel (ductile material) stirrups, across the critical section yield at ultimate. However the strain in the CFRP (brittle material), is essential to estimate the shear contribution of CFRP. To evaluate the validity of CFRP strengthening for shear, 24 tests were conducted with several parameters including shear-span-to-depth ratio, depth of beams, different transverse reinforcement ratios, and the layout of CFRP strips. In addition, a simple shear behavior model was developed to explain the differences between ductile and brittle material. From test observation, the use of CFRP anchors resulted in U-wrap application to perform like continuous wrapping which implies that a CFRP strip reached rupture strain because the anchors prevented debonding failure. However, all FRP strips did not rupture simultaneously because the strain distribution across a critical crack was not uniform. The average strain across the critical crack was about 0.005. Therefore a conservative value of effective strain (0.004) was selected for design purposes. In addition, when a beam is strengthened with CFRP, interactions between the contributions of the CFRP, steel or concrete must be taken into account. Factors ka, ks, and kf were introduced in the proposed shear design equations. Factor ka reflects the change in the material contributions as the shear span to depth ratio (a/d ratio) changes in deep beams. Factors ks and kf account for the change in steel or CFRP shear contribution due to the change in the critical crack angle as well as the interactions between the steel and FRP transverse reinforcement. As the amount of either steel or FRP material increase, the efficiency of the other material decreases. / text

published_or_final_version / abstract / toc / Physics / Doctoral / Doctor of Philosophy

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Fresh produce is often touted for its many health benefits; however, various items have been linked to foodborne disease outbreaks. This is especially a concern for immune suppressed individuals who are classified as severely neutropenic (white blood cell count under 500 neutrophils/μL of blood). At this degree of suppression, many are urged to follow a restrictive diet that reduces the potential of exposure to microbial populations. Currently no processing technique is used to sanitize microorganisms from fresh produce. Electron beam (e-beam) irradiation is a non-thermal process that has been approved by the FDA to treat fresh foods and is able to eliminate bacteria. Another technology used to extend shelf life is modified atmosphere packaging (MAP). The objective of this study was to evaluate the use of e-beam irradiation at current FDA-approved doses (< 1 kGy) to determine whether bioburden on fresh fruits can be reduced while maintaining sensory quality. Aerobic plate count methods were employed to determine the bioburden of treatments over a 21 day storage period under both ambient and MAP conditions. A previously identified bacterial plate count benchmark of < 500 CFU/ gram will be used to determine the applicability of the e-beam treatment. A consumer study using a 9 point hedonic scale as well as instrumentation measuring color, texture, moisture content, total soluble solids and titratable acidity were used to compare the treated fruit to the control. E-beam consistently reduced the bioburden on strawberries, fresh-cut watermelon and significantly (p<0.05) for avocado samples. Avocado, grapes and watermelon showed potential to be labeled as clean foods (below 500 CFU/gram). Fruit firmness (as measured by deformation) was not negatively affected by e-beam treatment and was preserved over storage with MAP treatment. Color was not adversely affected by e-beam or MAP, except for avocados that were significantly more grey in the presence of O_(2). Most importantly, consumers rated e-beam and MAP treated samples as acceptable (score above 5) in qualities of color, odor, flavor and firmness. E-beam proved to be an effective tool in reducing bioburden at low doses while maintaining fruit quality.