published_or_final_version / Physics / Doctoral / Doctor of Philosophy

Because of their high surface area (and hence, increased reactivity) nanocrystals can be used as reactive precursors in the low-temperature synthesis of solid state materials. When nanocrystals are used as reactants, the temperatures needed for diffusion between them can be significantly lower than for bulk-scale reactions—often at temperatures attainable using solution-based techniques. In the following work, two synthetic strategies are defined and developed for accessing metal oxides, borates and phosphides using nanocrystalline precursors and solution-mediated techniques. Broadly, the strategies involve either 1) the formation of a nano-sized precursor in solution which is post-annealed after isolation to form a target metal oxide or borate or 2) the solution-mediated diffusion of phosphorus into a nanocrystalline metal to form target metal phosphides. To form multi-metal oxides using the first strategy, metal oxide nanoparticle precursors are mixed in stoichiometric ratios in solution to form a nanocomposite. After isolation, the nanocomposite is annealed in air at 700-800 °C to form target ternary metal oxides, including Y2Ti2O7, Eu2Ti2O7, NiTiO3, Zn2SnO4 and CuInO2. As a variation of this method, rare earth borate nanoparticle precursors can be formed in solution by the reaction of RE3+ with NaBH4. After isolation, annealing in air at 700-800 °C crystallizes a range of REBO3 and Al3RE(BO3)4 powders. Using solution-based techniques, metal phosphides can be formed by the reaction of pre-formed metal nanocrystals with trioctylphosphine (TOP), which acts as a mild phosphorus-source, at 300-370 °C. A range of transition metal phosphide nanocrystals are accessible using this strategy, including the polyphosphides PdP2, AgP2 and Au2P3. Furthermore, shape and size of the metal phosphide product can be influenced by the shape and size of the metal precursor, allowing for the templated-design of nanostructured metal phosphides. The utility of this technique is not limited to the nano-regime. Bulk-scale metal powders, wires, foils, thin films and nanostructured metals can be converted to metal phosphides using analogous reactions with hot TOP. The two-fold purpose of this work is to extend these solution-mediated nanocrystal-based synthetic strategies to new classes of materials, and to compliment the existing library of low-temperature methods for making solid state materials.

Because of their high surface area (and hence, increased reactivity) nanocrystals can be used as reactive precursors in the low-temperature synthesis of solid state materials. When nanocrystals are used as reactants, the temperatures needed for diffusion between them can be significantly lower than for bulk-scale reactions—often at temperatures attainable using solution-based techniques. In the following work, two synthetic strategies are defined and developed for accessing metal oxides, borates and phosphides using nanocrystalline precursors and solution-mediated techniques. Broadly, the strategies involve either 1) the formation of a nano-sized precursor in solution which is post-annealed after isolation to form a target metal oxide or borate or 2) the solution-mediated diffusion of phosphorus into a nanocrystalline metal to form target metal phosphides. To form multi-metal oxides using the first strategy, metal oxide nanoparticle precursors are mixed in stoichiometric ratios in solution to form a nanocomposite. After isolation, the nanocomposite is annealed in air at 700-800 °C to form target ternary metal oxides, including Y2Ti2O7, Eu2Ti2O7, NiTiO3, Zn2SnO4 and CuInO2. As a variation of this method, rare earth borate nanoparticle precursors can be formed in solution by the reaction of RE3+ with NaBH4. After isolation, annealing in air at 700-800 °C crystallizes a range of REBO3 and Al3RE(BO3)4 powders. Using solution-based techniques, metal phosphides can be formed by the reaction of pre-formed metal nanocrystals with trioctylphosphine (TOP), which acts as a mild phosphorus-source, at 300-370 °C. A range of transition metal phosphide nanocrystals are accessible using this strategy, including the polyphosphides PdP2, AgP2 and Au2P3. Furthermore, shape and size of the metal phosphide product can be influenced by the shape and size of the metal precursor, allowing for the templated-design of nanostructured metal phosphides. The utility of this technique is not limited to the nano-regime. Bulk-scale metal powders, wires, foils, thin films and nanostructured metals can be converted to metal phosphides using analogous reactions with hot TOP. The two-fold purpose of this work is to extend these solution-mediated nanocrystal-based synthetic strategies to new classes of materials, and to compliment the existing library of low-temperature methods for making solid state materials.

Thesis (Ph. D.)--University of Hong Kong, 1999. / Includes bibliographical references (leaf 110).

Not available / text

Thesis (Ph. D.)--University of Texas at Austin, 2005. / Vita. Includes bibliographical references.

This dissertation describes the preparation and application of a novel class of hydroprocessing catalysts, transition metal phosphides. Concentration was placed on molybdenum and tungsten monophosphides because of the importance of these elements in standard sulfidic hydrotreating catalysts. Transition metal phosphides exist over a wide range of stoichiometry, and their properties have a great deal of variation, ranging from phosphorus poor compounds with metallic electrical properties to phosphorus rich compounds with semiconducting or insulating properties. The x-ray diffraction patterns of the phosphides studied here were unchanged under the conditions of catalytic hydroprocessing, demonstrating their stability toward the hydroprocessing conditions and allowing study of their intrinsic catalytic properties. Materials were prepared in bulk form, supported on alumina, and supported on silica. The mechanism of hydrodenitrogenation on MoP/SiO2 and WP/SiO2 catalysts was investigated by comparison of hydrodenitrogenation reactions of pyridine, piperidine, n-pentylamine, tert-pentylamine, and neo-pentylamine. / Ph. D.

abstract: Nanowires are 1D rod-like structures which are regarded as the basis for future technologies. III-V nanowires have attracted immense attention because of their stability, crystal quality and wide use. In this work, I focus on the growth and characterization of III-V semiconductor nanowires, in particular GaP, InP and InGaP alloys. These nanowires were grown using a hot wall CVD(Chemical Vapor Deposition) setup and are characterized using SEM (Scanning Electron Microscope), EDX (Energy Dispersive X-ray Spectroscopy) and PL (Photoluminescence) techniques. In the first chapter, Indium Phosphide nanowires were grown using elemental sources (In and P powders). I consider the various kinds of InP morphologies grown using this method. The effect of source temperature on the stoichiometry and optical properties of nanowires is studied. Lasing behavior has been seen in InP nanostructures, showing superior material quality of InP. InGaP alloy nanowires were grown using compound and elemental sources. Nanowires grown using compound sources have significant oxide incorporation and showed kinky morphology. Nanowires grown using elemental sources had no oxide and showed better optical quality. Also, these samples showed a tunable alloy composition across the entire substrate covering more than 50% of the InGaP alloy system. Integrated intensity showed that the bandgap of the nanowires changed from indirect to direct bandgap with increasing Indium composition. InGaP alloy nanowires were compared with Gallium Phosphide nanowires in terms of PL emission, using InGaP nanowires it is possible to grow nanowires free of defects and oxygen impurities, which are commonly encountered in GaP nanowires. / Dissertation/Thesis / Masters Thesis Electrical Engineering 2016

by Won Hon Kit. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1997. / Includes bibliographical references (leaves 66-70). / by Won Hon Kit. / Acknowledgment --- p.i / Abstract --- p.ii / Chapter Chapter1 --- Introduction --- p.1 / Chapter 1.1 --- Uniqueness of ZnxCd/1-x Se --- p.1 / Chapter 1.2 --- The Choice of OMVPE --- p.1 / Chapter 1.3 --- Epilayer Relaxation in Heteroepitaxy --- p.2 / Chapter 1.4 --- The Most Suitable Substrate --- p.4 / Chapter Chapter2 --- Experimental Procedures --- p.6 / Chapter 2.1 --- Degreasing and Etching --- p.6 / Chapter 2.2 --- Preheating --- p.6 / Chapter 2.3 --- OMVPE Growth --- p.6 / Chapter Chapter3 --- Characterization --- p.9 / Chapter 3.1 --- X-ray Diffraction --- p.9 / Chapter 3.2 --- EDX Spectroscopy --- p.13 / Chapter 3.3 --- Optical Reflectance --- p.15 / Chapter Chapter4 --- Data Analysis --- p.20 / Chapter 4.1 --- Control of Composition --- p.20 / Chapter 4.2 --- Structural Quality and Epilayer Relaxation --- p.22 / Chapter 4.3 --- Critical Point Energies --- p.24 / Chapter 4.4 --- Refractive Index and Extinction coefficient --- p.26 / Chapter Chapter5 --- Conclusions --- p.28 / List of Figures --- p.30 / Reference --- p.66

by Lee Wai Lok. / x and 1-x are in title are subscript. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1996. / Includes bibliographical references (leaves [67]-[70]). / by Lee Wai Lok. / Abstract --- p.i / Chapter Chapter1 --- Introduction --- p.1-1 / Chapter 1.1 --- Epitaxial Growth --- p.1-2 / Chapter 1.1.1 --- Background of Epitaxy --- p.1-2 / Chapter 1.1.2 --- Operating Principle of OMVPE --- p.1-2 / Chapter 1.1.3 --- Problems in Heteroepitaxy --- p.1-3 / Chapter 1.2 --- Basic Requirements of a Semiconductor Laser --- p.1-3 / Chapter 1.3 --- Our work --- p.1-4 / Chapter Chapter2 --- OMVPE Growth --- p.2-1 / Chapter 2.1 --- Our OMVPE System Design --- p.2-1 / Chapter 2.1.1 --- Growth Environment --- p.2-2 / Chapter 2.1.2 --- Susceptor Temperature Control --- p.2-2 / Chapter 2.1.3 --- Reactor Pressure Control --- p.2-2 / Chapter 2.1.4 --- MO Vapor Handling Control --- p.2-2 / Chapter 2.1.4.1 --- MO Flow Control --- p.2-3 / Chapter 2.1.4.2 --- Flow Path Selection --- p.2-3 / Chapter 2.1.5 --- Cabinet with Air Extraction --- p.2-3 / Chapter 2.1.6 --- Chemical Scrubber --- p.2-4 / Chapter 2.2 --- System Calibration --- p.2-4 / Chapter 2.3 --- Materials Used --- p.2-5 / Chapter 2.3.1 --- Precursor Materials --- p.2-5 / Chapter 2.3.2 --- Hydrogen Gas --- p.2-5 / Chapter 2.3.3 --- Nitrogen Gas --- p.2-6 / Chapter 2.3.4 --- Substrate --- p.2-6 / Chapter 2.4 --- Fabrication Conditions --- p.2-6 / Chapter Chapter3 --- Characterization --- p.3-1 / Chapter 3.1 --- X-ray Diffraction --- p.3-1 / Chapter 3.2 --- EDX Spectroscopy --- p.3-2 / Chapter 3.3 --- Optical Reflectance --- p.3-4 / Chapter Chapter4 --- Data Analysis --- p.4-1 / Chapter 4.1 --- ZnSe/GaAs(100) --- p.4-1 / Chapter 4.1.1 --- Structural Analysis --- p.4-1 / Chapter 4.1.2 --- Stoichiometry --- p.4-2 / Chapter 4.1.3 --- Growth Rate --- p.4-3 / Chapter 4.1.4 --- Energies of Critical Points --- p.4-3 / Chapter 4.1.5 --- Reflectance --- p.4-4 / Chapter 4.2 --- ZnCdSe/InP(100) --- p.4-5 / Chapter 4.2.1 --- Structural Analysis --- p.4-5 / Chapter 4.2.1.1 --- Structural Quality --- p.4-5 / Chapter 4.2.1.2 --- Crystal Structure --- p.4-5 / Chapter 4.2.1.3 --- Lattice Parameter --- p.4-8 / Chapter 4.2.2 --- Composition Range --- p.4-8 / Chapter 4.2.3 --- Degree of Relaxation --- p.4-9 / Chapter 4.2.4 --- Comparison to Prior Art --- p.4-10 / Chapter 4.2.5 --- Growth Rate --- p.4-11 / Chapter 4.2.6 --- Energies of Critical Points --- p.4-12 / Chapter Chapter5 --- Conclusions --- p.5-1 / Appendix A Calculation of the actual MO Mass Flow --- p.6-1 / Appendix B Interpretation of in-plane Lattice Parameter --- p.6-3 / Appendix C Structure Factor of Wurtzite Lattice --- p.6-4 / References --- p.7-1