published_or_final_version / abstract / Physics / Master / Master of Philosophy

Zinc oxide (ZnO) is a promising material for ultra-violet optoelectronics applications due to its direct band gap and large exciton binding energy. Defect in semiconductor plays an important role in determining the optical and electrical properties. It is thus crucial to understand the defects‟ performance for realizing the device fabrication. Green luminescence (GL) having the peak at 2.4-2.5 eV is a defect related emission band commonly found in the luminescence spectra of many of the ZnO materials. Despite of the effort devoted for several decades, its origin and emission mechanism remain controversial. In this thesis, the origin of the GL emitted from the ZnO films grown by pulsed laser deposition (PLD) is studied using a comprehensive spectroscopic approach, including the Hall effect measurement, photoluminescence (PL), Raman spectroscopy, positron annihilation spectroscopy (PAS), and secondary ion mass spectroscopy (SIMS). ZnO thin films are grown by PLD method with the growth parameters (namely the substrate temperature and oxygen pressure during the growth) systemically varied. Annealing studies in argon atmosphere reveal the correlation between the free electron concentration and the hydrogen concentration in the samples. Two oxygen deficient defect related Raman modes are also identified and they anneal out after annealing at high temperature. We have investigated the introduction the GL systematically grown by different growth parameters, undergone different post-growth annealing treatment, and different methods of growth. Two kinds of GL’s are identified. The first kind of GLs has peak at 2.47 eV without the fine structure, and the other has the peak at 2.45 eV having the fine structure of separation of 0.07 eV. The GL with the fine structure is originated from the surficial region of the ZnO film. The GL without the fine structure is introduced after the annealing 900℃ irrespective of the initial growth conditions. PAS results show a strong correlation between the thermal introductions of a kind of Zn-vacancy and the GL without the fine structure. Moreover, a donor-acceptor-pair (DAP) emission is induced in the low temperature PL spectrum after the same annealing temperature of 900℃. The GL and the DAP emissions are thus associated with the involvement of the VZn. Furthermore by comparing the photon energies of the GL and DAP with the previous first principle calculated results, the GL is ascribed to the conduction band to the (-/2-) acceptor level of VZn, and the DAP involves the (0/-) acceptor level of VZn The presence of the conduction band to the (0/-) level transition is compatible with the results of the photoluminescence excitation (PLE) study. / published_or_final_version / Physics / Doctoral / Doctor of Philosophy

Kwong Kwan Wai = 氧化鋅基低維納米結構之生長與分析 / 鄺筠慧. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2004. / Includes bibliographical references (leaves 75-79). / Text in English; abstracts in English and Chinese. / Kwong Kwan Wai = Yang hua xin ji di wei na mi jie gou zhi sheng zhang yu fen xi / Guang Yunhui. / Acknowledgement --- p.i / Abstract --- p.ii / 摘要 --- p.iii / Table of Contents --- p.iv / List of Figures --- p.vii / Chapter Chapter 1 --- Introduction --- p.1 / Chapter Chapter 2 --- Background --- p.3 / Chapter Chapter 3 --- Instrumentation --- p.6 / Chapter 3.1 --- Tube furnace system --- p.6 / Chapter 3.2 --- X-ray Diffraction (XRD) --- p.8 / Chapter 3.3 --- Scanning Electron Microscopy (SEM) --- p.9 / Chapter 3.4 --- Transmission Electron Microscopy (TEM) --- p.12 / Chapter 3.4.1 --- General Review --- p.12 / Chapter 3.4.2 --- Low-magnification imaging --- p.14 / Chapter 3.4.3 --- Transmission electron diffraction (TED) --- p.14 / Chapter 3.4.4 --- High-resolution electron microscopy (HREM) --- p.15 / Chapter 3.4.5 --- Experimental --- p.15 / Chapter Chapter 4 --- Oxygen partial pressure effect on the morphology of ZnO nanostructures --- p.17 / Chapter 4.1 --- Introduction --- p.17 / Chapter 4.2 --- Experimental --- p.17 / Chapter 4.3 --- Results --- p.19 / Chapter 4.3.1 --- SEM study for general morphology --- p.21 / Chapter 4.3.2 --- TEM study for detailed microstructures of the tetrapods and the nanocombs --- p.28 / Chapter 4.3.2.1 --- Tetrapods --- p.28 / Chapter 4.3.2.2 --- Nanocombs --- p.29 / Chapter 4.4 --- Discussions --- p.34 / Chapter 4.4.1 --- Thermal reduction and oxidation to form ZnO --- p.34 / Chapter 4.4.2 --- Vapor-Solid (VS) growth mechanism of low-dimensional nanostructures --- p.34 / Chapter 4.4.3 --- The oxygen partial pressure effect on the morphology of the ZnO nanostructures --- p.35 / Chapter 4.4.4 --- Transition from tetrapod to nanocomb --- p.36 / Chapter 4.4.5 --- Decreasing size effect --- p.39 / Chapter Chapter 5 --- Self-assembly of periodical ZnO/C multilayers on Zn nanowire --- p.40 / Chapter 5.1 --- Introduction --- p.40 / Chapter 5.2 --- Experimental --- p.42 / Chapter 5.3 --- Results and Discussion --- p.46 / Chapter 5.3.1 --- Freshly synthesized Zn nanowires --- p.46 / Chapter 5.3.2 --- Introducing carbon into the Zn nanowires一Solid phase diffusion --- p.50 / Chapter 5.3.3 --- Introducing carbon into the Zn nanowires一Gas phase reaction --- p.52 / Chapter 5.3.3.1 --- Diffusion of the gas molecules through the ZnO sheath to the Zn/ZnO interface --- p.60 / Chapter 5.3.3.2 --- Chemical reaction(s) --- p.60 / Chapter 5.3.3.3 --- Phase separation of ZnO and C --- p.61 / Chapter 5.3.3.4 --- Self-organized multilayers --- p.62 / Chapter 5.3.3.5 --- Factors affecting SAM formation --- p.64 / Chapter 5.3.3.5.1 --- Crystallinity of original oxide sheath (series A) --- p.64 / Chapter 5.3.3.5.2 --- Temperature (series B) --- p.66 / Chapter 5.3.3.5.3 --- Gas molecules (series C) --- p.69 / Chapter Chapter 6 --- Conclusions --- p.72 / Appendix --- p.74 / References --- p.75

Hung Ngar Chun = 氧化鋅納米棒的生長和表徵 / 洪雅真. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2004. / Includes bibliographical references. / Text in English; abstracts in English and Chinese. / Hung Ngar Chun = Yang hua xin na mi bang de sheng zhang he biao zheng / Hong Yazhen. / Acknowledgements --- p.i / Abstract --- p.ii / 摘要 --- p.iii / List of Tables --- p.iv / List of Figures --- p.v / Table of contents --- p.vii / Chapter Chapter 1 --- Introduction / Chapter 1.1. --- Objectives --- p.1-1 / Chapter 1.2. --- Background --- p.1-1 / Chapter 1.2.1. --- Nanomaterials --- p.1-1 / Chapter 1.2.1.1. --- From three-dimensional to one-dimensional --- p.1-1 / Chapter 1.2.1.2. --- One-dimensional nanomaterials --- p.1-2 / Chapter 1.2.2. --- Characteristics and potential applications --- p.1-2 / Chapter 1.2.3. --- Growth mechanisms --- p.1-4 / Chapter 1.2.3.1. --- The VLS growth --- p.1-4 / Chapter 1.2.3.2. --- The VS growth --- p.1-5 / Chapter 1.2.4. --- ZnO --- p.1-6 / Chapter 1.2.4.1. --- Characteristics and potential applications --- p.1-6 / Chapter 1.2.4.2. --- Recent works performed by the others --- p.1-7 / Chapter 1.2.4.2.1. --- Different fabrication systems --- p.1-7 / Chapter 1.2.4.2.2. --- Different morphologies and shapes --- p.1-8 / Chapter 1.3. --- Our work --- p.1-9 / Chapter 1.3.1. --- Advantages of our fabrication method --- p.1-9 / Chapter 1.4. --- Thesis layout --- p.1-9 / References --- p.1-10 / Figures --- p.1-13 / Tables --- p.1-14 / Chapter Chapter 2 --- Methodology and Experiments / Chapter 2.1. --- Introduction --- p.2-1 / Chapter 2.2. --- The setup --- p.2-1 / Chapter 2.2.1. --- Preparation of substrate --- p.2-1 / Chapter 2.2.2. --- Chamber pressure and gas flow rate --- p.2-2 / Chapter 2.2.3. --- Heating profile --- p.2-2 / Chapter 2.3. --- The two important growth parameters --- p.2-3 / Chapter 2.3.1. --- Substrate compositions --- p.2-3 / Chapter 2.3.2. --- Temperature --- p.2-3 / Chapter 2.4. --- Methods of characterizations --- p.2-4 / Chapter 2.4.1. --- Morphology --- p.2-4 / Chapter 2.4.1.1. --- SEM --- p.2-4 / Chapter 2.4.1.2. --- TEM --- p.2-5 / Chapter 2.4.2. --- Phases and Microstructures --- p.2-5 / Chapter 2.4.2.1. --- XRD --- p.2-5 / Chapter 2.4.2.2. --- HRTEM --- p.2-5 / Chapter 2.4.3. --- Cathodoluminescence --- p.2-6 / References --- p.2-7 / Figures --- p.2-8 / Chapter Chapter 3 --- Results / Chapter 3.1. --- Introduction --- p.3-1 / Chapter 3.2. --- General Morphologies --- p.3-1 / Chapter 3.3. --- Microstructural analysis --- p.3-2 / Chapter 3.4. --- Samples sintered using substrate of different composition --- p.3-2 / Chapter 3.5. --- Samples sintered at different temperatures --- p.3-4 / Chapter 3.6. --- The cathodoluminescence of the ZnO nanorods --- p.3-4 / References --- p.3-6 / Figures --- p.3-7 / Chapter Chapter 4 --- Discussions / Chapter 4.1. --- Introduction --- p.4-1 / Chapter 4.2. --- Proposed growth model --- p.4-1 / Chapter 4.2.1. --- Chemical reactions --- p.4-1 / Chapter 4.2.2. --- Justification on the effect of residue oxygen and leakage --- p.4-2 / Chapter 4.2.3. --- Justification on the possibility of VLS growth --- p.4-3 / Chapter 4.2.4. --- Coarsening mechanisms --- p.4-3 / Chapter 4.2.4.1. --- Oswald Ripening --- p.4-4 / Chapter 4.2.4.2. --- Preferential growth direction --- p.4-4 / Chapter 4.3. --- The effects of substrate composition --- p.4-5 / Chapter 4.3.1. --- Roles of Si and Si02 --- p.4-5 / Chapter 4.4. --- The effects of temperature --- p.4-6 / Chapter 4.4.1. --- Range of sintering temperature --- p.4-6 / Chapter 4.4.2. --- Diameter of the rods --- p.4-7 / Chapter 4.4.3. --- Luminescence behavior --- p.4-7 / References --- p.4-10 / Figures --- p.4-11 / Chapter Chapter 5 --- Conclusions and future works

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Includes bibliographical references (p. 136-150).

Thesis (M.S.)--Oregon State University, 2010. / Printout. Includes bibliographical references (leaves 78-85). Also available on the World Wide Web.

published_or_final_version / Physics / Doctoral / Doctor of Philosophy

As a wide band gap semiconductor, Zinc Oxide (ZnO) has recently attracted considerable attention due to its wide applicability. Transition metal (TM) doped ZnO is one of the most intensive research field in the last decade because of its possible application in spintronics devices. The Co-implanted ZnO has been considered as one of the most promising candidate in the field of diluted magnetic semiconductor (DMS). In this study, the magnetic and structural properties of Co-implanted ZnO single crystal were investigated. ZnO single crystals were implanted with 100 keV-Co ions at 300K with a fluence of 1014cm-2and subsequently annealed at 750oC and 900oC respectively. The samples were studied by secondary ion mass spectrometry, X-ray diffraction, photoluminescence, X-ray photoemission spectroscopy and vibrating sample magnetometer. The as-implanted sample seemed to be phase pure while the spinel secondary phase ZnCo2O4 was present in 750oC and 900oC samples showed trace ofCo3O4,Zn0.52Co2.48O4 and metallic Co cluster. All the samples exhibited ferromagnetism at room temperature in low field region, and the magnetic moment was found to decrease and increase after the heat treatment. In high field region, typical paramagnetism was the dominating magnetic property. More than one ferromagnetic mechanism is involved to explain the experimental results. / published_or_final_version / Physics / Master / Master of Philosophy

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