Thesis (Ph. D.)--University of Missouri-Columbia, 2007. / The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on October 16, 2007) Vita. Includes bibliographical references.

Thesis (Ph. D.)--Oregon Graduate Center, 1987.

Thesis (Ph.D.)--University of Nebraska-Lincoln, 2009. / Title from title screen (site viewed October 15, 2009). PDF text: xiii, 146 p. : ill. (some col.) ; 14 Mb. UMI publication number: AAT 3358962. Includes bibliographical references. Also available in microfilm and microfiche formats.

Thesis (Ph. D.)--Virginia Polytechnic Institute and State University, 1993. / Vita. Abstract. Includes bibliographical references (leaves 146-156). Also available via the Internet.

Thesis (Ph. D.)--Virginia Polytechnic Institute and State University, 1994. / Vita. Abstract. Includes bibliographical references (leaves 89-90). Also available via the Internet.

abstract: This thesis discusses the use of low temperature microwave anneal as an alternative technique to recrystallize materials damaged or amorphized due to implantation techniques. The work focuses on the annealing of high-Z doped Si wafers that are incapable of attaining high temperatures required for recrystallizing the damaged implanted layers by microwave absorption The increasing necessity for quicker and more efficient processing techniques motivates study of the use of a single frequency applicator microwave cavity along with a Fe2O3 infused SiC-alumina susceptor/applicator as an alternative post implantation process. Arsenic implanted Si samples of different dopant concentrations and implantation energies were studied pre and post microwave annealing. A set of as-implanted Si samples were also used to assess the effect of inactive dopants against presence of electrically active dopants on the recrystallization mechanisms. The extent of damage repair and Si recrystallization of the damage caused by arsenic and Si implantation of Si is determined by cross-section transmission electron microscopy and Raman spectroscopy. Dopant activation is evaluated for the As implanted Si by sheet resistance measurements. For the same, secondary ion mass spectroscopy analysis is used to compare the extent of diffusion that results from such microwave annealing with that experienced when using conventional rapid thermal annealing (RTA). Results show that compared to susceptor assisted microwave annealing, RTA caused undesired dopant diffusion. The SiC-alumina susceptor plays a predominant role in supplying heat to the Si substrate, and acts as an assistor that helps a high-Z dopant like arsenic to absorb the microwave energy using a microwave loss mechanism which is a combination of ionic and dipole losses. Comparisons of annealing of the samples were done with and without the use of the susceptor, and confirm the role played by the susceptor, since the samples donot recrystallize when the surface heating mechanism provided by the susceptor is not incorporated. Variable frequency microwave annealing was also performed over the as-implanted Si samples for durations and temperatures higher than the single frequency microwave anneal, but only partial recrystallization of the damaged layer was achieved. / Dissertation/Thesis / M.S. Materials Science and Engineering 2011

Solid oxide fuel cells (SOFCs) convert chemical energy directly into electrical energy, leading to significantly higher conversion efficiencies. The oxygen reduction reaction (ORR) at the cathode is often the rate-controlling step in the electrochemical reactions occurring in the SOFCs. Strontium doped lanthanum cobalt ferrite (LSCF) is a widely used cathode material due to its high electronic and ionic conductivity, and reasonable oxygen surface exchange coefficient. However, LSCF can have long-term stability issues such as surface segregation of Sr during SOFC operation, which can adversely affect the electrochemical performance. Thus, understanding the nature of the Sr surface segregation phenomenon, and how it is affected by the composition of LSCF, strain, and the CO2 in the gas phase at the cathode, are critical. In this research, heteroepitaxial thin films of La1-x SrxCo0.2Fe0.8O3- with various Sr contents (x = 0.4, 0.3, 0.2) were deposited by Pulsed Laser Deposition (PLD) on single crystal NdGaO3, SrTiO3 and GdScO3 substrates, leading to different strains in the films. The extent of Sr segregation at the film surface was quantified using the synchrotron-based total reflection X-ray fluorescence (TXRF) technique, and by Atomic Force Microscopy (AFM). The microstructure and the electronic structure of the Sr-rich phases formed on the surface were investigated by scanning/transmission electron microscopy (S/TEM) and hard X-ray photoelectron spectroscopy (HAXPES), respectively. These studies revealed that the surface phases consisted of SrO covered with a capping layer of SrCO3. The presence of CO2 in the atmosphere was found to enhance the kinetics of Sr surface segregation in LSCF. The extent of Sr segregation was found to be a function of the Sr content in bulk. Lowering the Sr content from 40% to 30% reduced the surface segregation, but further lowering the Sr content to 20% increased the segregation. The strains of LSCF thin films on various substrates were measured using high-resolution X-ray diffraction (HRXRD) and the Sr surface segregation was found to be reduced with compressive strain and enhanced with tensile strain present within the thin films. A model was developed correlating the Sr surface segregation with Sr content and strain effects to explain the experimental results.

Lanthanum chromite (LaCrO3), Lanthanum manganite (LaMnO3) and 40% strontium doped lanthanum cobalt iron oxide, La0.6Sr0.4Co0.2Fe0.8O3 (LSCF-6428) are perovskite oxides which are widely used as interconnect or cathode materials in solid oxide fuel cells(SOFCs) due to their high electrical conductivity, good oxygen reduction kinetics, and good chemical stability. The solid state reaction route is the most commonly used method for synthesis of these materials. However, the solid state reaction method usually involves long-time mixing and high synthesis temperature (typically, >1200 ºC), which makes it time-consuming and costly. Molten salt synthesis, which occurs at much lower temperatures (350 ºC – 550 ºC) can offer better particle size and compositional control and reduced energy usage during materials synthesis. In this study, LaCrO3, LaMnO3, and LSCF were synthesized in a molten salt eutectic of LiCl-KCl. A range of reaction temperature from 370 ºC to 600 ºC was investigated. It was found that a pure LaMnO3 perovskite phase can be formed at as 400 ºC using the molten salt method and that LSCF powders were successfully synthesized at 500 ºC. When forming LaCrO3 using the molten salt method, LaOCl was also formed at or above 400 ºC. The X-ray diffraction (XRD) results show this is an attractive alternative route of synthesis to decrease the reaction temperature. Both Scanning Electron Microscopy (SEM) images and XRD patterns for LaCrO3 showed that only cubic structures were formed at low temperature (400 ºC and 450 ºC) and then hexagonal structures started to appear at temperatures above 500 ºC. The molten salt synthesis method was then used to prepare core-shell structures with LaCrO3 or LSCF particles as the core and LaMnO3 as the shell. Core-shell structures were characterized by Scanning Electron Microscopy (SEM), Scanning Transmission Electron Microscope (STEM) and Energy Dispersive X-ray Spectroscopy (EDS). It was found that the expected core-shell structures were successfully formed with the overall cubic structures. Therefore, the molten salt synthesis method is a feasible method to decrease the operation temperature and form the core-shell structure.

abstract: The goal of this work is to develop low cost and highly efficient hybrid solar cells based on semiconductor nanoparticles (NPs). Hybrid solar cells have been demonstrated to take advantages of both inorganic and organic semiconductors by employing simple soluble process. In order to improve the power conversion efficiency (PCE), the bulk heterojunction (BHJ) of cadmium selenide (CdSe) tetrapods (TPs) and poly (3-hexylthiophene) (P3HT) are introduced as an electron acceptor and donor, respectively. The dimension of CdSe TPs and the 3D spatial distribution of CdSe TPs:P3HT photoactive blends are investigated to improve optical and electrical properties of photovoltaic devices. Hybrid solar cells having long-armed CdSe TPs and P3HT establish higher PCE of 1.12% when compared to device employing short-armed TPs of 0.80%. The device performance are improved by using longer armed CdSe TPs, which aids in better percolation connectivity and reduced charge hopping events, thus leading to better charge transport. The device architecture of hybrid solar cells is examined to assist vertical phase separation (VPS). Improvement of VPS in hybrid solar cells using CdSe TPs:P3HT photoactive blends is systematically manipulated by solution processed interfacial layers, resulting in enhanced device performance. Multi-layered hybrid solar cells assist better light absorption, efficient charge carrier transport, and increase of the surface contact area. In this work, hole transport assisting layer (HTAL)/BHJ photoactive layer (BPL)/electron transport assisting layer (ETAL) or HTAL/BPL/ETAL (HBE) multi-layered structure is introduced, similarly to p-type layer/intermixed photoactive layer/n-type layer (p-i-n) structure of organic photovoltaic devices. To further control the improvement of the device performance, the effects of nano-scale morphology from solvents having different boiling points, the various shapes of semiconductor NPs, and the emergence of blending NPs are demonstrated. The formation of favorable 3D networks in photoactive layer is attributed to enhance the efficient charge transport by the optimized combination of semiconductor NPs in polymer matrix. / Dissertation/Thesis / Ph.D. Materials Science and Engineering 2012

abstract: Lithium-ion batteries can fail and catch fire when overcharged, exposed to high temperatures or short-circuited due to the highly flammable organic liquid used in the electrolyte. Using inorganic solid electrolyte materials can potentially improve the safety factor. Additionally, nanostructured electrolyte materials may further enhanced performance by taking advantage of their large aspect ratio. In this work, the synthesis of two promising nanostructured solid electrolyte materials was explored. Amorphous lithium niobate nanowires were synthesized through the decomposition of a niobium-containing complex in a structure-directing solvent using a reflux method. Lithium lanthanum titanate was obtained via solid state reaction with titanium oxide nanowires as the titanium precursor, but the nanowire morphology could not be preserved due to high temperature sintering. Hyperbranched potassium lanthanum titanate was synthesized through hydrothermal route. This was the first time that hyperbranched nanowires with perovskite structure were made without any catalyst or substrate. This result has the potential to be applied to other perovskite materials. / Dissertation/Thesis / M.S. Materials Science and Engineering 2012