Group-III nitride materials are increasingly important, because of their semiconducting properties and bandgaps tuneable across a wide range from the infrared to ultraviolet. They are of particular interest for optoelectronic and power electronic applications. The studies on nitride materials are comprehensive, and one way to categorise them is based on the scale of the material, namely: (a) 3D bulk materials, for example the development of 3D bulk nitride substrate; (b) epitaxial layers, for example GaN/InGaN 2D quantum well based light emitting diodes (LEDs); (c) 1D nitride nanowires and (d) 0D quantum dots, for example InGaN quantum dot based single photon sources. This thesis uses a multimicroscopy concept to investigate various group-III nitride nanowires and hillocks. Multiple different microscopy techniques were applied to the same specific nanostructure or defect. This allows the properties of the materials of interest to be linked directly to the nanostructures or defects, providing a more complete picture of the samples that have been studied. The multiple microscopy techniques used to conduct the work in this thesis include (scanning) transmission electron microscopy ((S)TEM), cathodoluminescence (CL), focused ion beam (FIB) and atomic force microscopy (AFM). Specifically, AFM was used to characterise the morphology of the sample on a sub-nanometer scale. The crystalline structures were characterised using (S)TEM, and the in-situ energy dispersive X-ray spectroscopy (EDS) was used to conduct compositional analysis of the selected sites. CL was used to reveal the optoelectronic properties by analysing the emission wavelengths of the materials, excited by the electron beam. FIB was the technique used to prepare site-specific samples to be measured in (S)TEM. A detailed explanation of these characterisation techniques was also included. In the context of the studies on nitride materials, nitride nanowires and their heterostructures are a particular research focus. They combine the unique properties of III-nitride materials together with the advantages induced by the nanowire geometry. This thesis explores three different nanowire systems: a GaN nanowire structure incorporating a GaN/Sc$_x$Ga$_{1-x}$N axial heterostructure grown by molecular beam epitaxy (MBE); GaN/InGaN core-shell nanowires fabricated by a hybrid approach combining metalorganic vapour phase epitaxy (MOVPE) and dry etching techniques; and AlGaN nanowires on free standing AlGaN substrates fabricated by MBE and inductively coupled plasma (ICP) etching. The optoelectronic properties, compositions and structures of these nanowires were studied in detail. Moreover, a comprehensive review on the properties, growth methods and applications of group-III nitride nanowires is also included in this thesis. Apart from nanowires, a lot of effort has been focusing on the improvement of the quality of epitaxial layers of GaN and its alloys, and they currently have an even wider perspective than nitride nanowires. The understanding of defects within the epitaxial layers is crucial in order to mitigate the their adverse effects, leading to the increased emphasis on defect analysis. Hillocks are a type of defects found on GaN epilayers, which are less well studied than other defects such as dislocations and stacking faults. As a consequence, the formation mechanisms of hillocks remain controversial. In this context, after a review on the past studies on GaN hillocks, this thesis also investigates two types of hillocks, i.e. hillocks on GaN p-i-n diodes and hillocks on GaN grown on patterned sapphire substrates (PSS). Their nanoscale structures, properties and formation mechanisms are studied.

L’objectif de cette thèse est de développer un réseau de nanofils GaAs (coeur) / oxyde (coquille) pour la photoélectrolyse de l'eau. Pour cela, la géométrie des nanofils GaAs a été d’abord optimisée en ajustant différents paramètres expérimentaux de la croissance auto-catalysée de ces nanofils par Épitaxie par Jets Moléculaires. Nous avons ensuite étudié systématiquement l'oxydation de surface des nanofils GaAs et son effet négatif sur la croissance de la coquille. Nous avons donc développé une méthode dite d'encapsulation / désencapsulation d'une couche d'arsenic (As) amorphe qui protège les facettes des NFs de l'oxydation. Une étude physico-chimique a montré l'effet bénéfique d'une telle méthode sur la croissance de la coquille. La croissance d'une coquille de SrTiO3 sur des nanofils de GaAs a ensuite été réalisée. Des caractérisations approfondies de la croissance de la coquille de SrTiO3 sur les NFs de GaAs ont été réalisées. La plus grande partie de la structure pérovskite SrTiO3 était en relation d'épitaxie avec le réseau cristallin de GaAs. La dernière partie de cette thèse concerne l’utilisation de tels réseaux de nanofil GaAs / oxyde pour les dispositifs PEC où l'oxyde sert de couche de passivation. L'influence du dopage et de la morphologie des nanofils GaAs a d'abord été étudiée. Les propriétés des réseaux de nanofils de GaAs / SrTiO3 et de GaAs / TiO2 servant de photoélectrodes dans des dispositifs PEC sont étudiées. / The objective of this PhD is to develop the network of GaAs (core) / oxide (shell) nanowires for solar water splitting. The geometry of the GaAs nanowires was firstly optimized by adjusting different experimental parameters of the self-catalyzed growth of these nanowires by molecular beam epitaxy. We then systematically studied the surface oxidation of the GaAs nanowires and its negative effect on the growth of the shell. We have therefore developed a method called the arsenic (As) capping / decapping method that protects the facets of nanowires from the oxidation. A physico-chemical study has shown the beneficial effect of such a method on the growth of the shell. The growth of a SrTiO3 shell on GaAs nanowires was then performed. In-depth characterizations of SrTiO3 shell growth on GaAs nanowires were carried out. Most of the SrTiO3 perovskite structure was in epitaxial relationship with the GaAs crystalline lattice. The last part of this thesis concerns the application of such GaAs / oxide nanowire networks to PEC devices where the oxide serves as a passivation layer. The influence of the doping and the morphology of GaAs nanowires was first studied. The properties of GaAs / SrTiO3 and GaAs / TiO2 nanowire networks used as photoelectrodes in PEC devices are finally studied.

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Jiao Yang. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2005. / Includes bibliographical references (leaves 85-87). / Abstracts in English and Chinese. / Abstract --- p.i / 摘要 --- p.ii / Acknowledgement --- p.iii / Table of Content --- p.iv / List of Figures --- p.ix / List of Tables --- p.xiv / Chapter Chapter 1 --- Introduction --- p.1 / Chapter Chapter 2 --- Background of the Pseudo One-dimensional Si Crystal Growth --- p.5 / Chapter 2.1 --- Vapor-liquid-solid (VLS) Mechanism --- p.5 / Chapter 2.2 --- Oxide-assisted-growth (OAG) Mechanism --- p.8 / Chapter 2.3 --- Solid-liquid-solid Mechanism --- p.10 / Chapter Chapter 3 --- Instrumentation --- p.12 / Chapter 3.1 --- Deposition Apparatus --- p.12 / Chapter 3.2 --- Scanning Electron Microscope (SEM) --- p.14 / Chapter 3.2.1 --- Principle of SEM --- p.14 / Chapter 3.2.2 --- Electron-specimen Interactions in SEM --- p.14 / Chapter 3.2.3 --- Imaging by Secondary Electron --- p.15 / Chapter 3.2.4 --- Elemental Analysis by Energy Dispersive X-ray --- p.16 / Chapter 3.3 --- Transmission Electron Microscope (TEM) --- p.18 / Chapter 3.3.1 --- Principle of the TEM --- p.18 / Chapter 3.3.2 --- Electron Specimen Interaction in TEM --- p.18 / Chapter 3.3.3 --- Electron Diffraction --- p.19 / Chapter 3.3.4 --- Contrast --- p.20 / Chapter 3.3.5 --- X-ray Microanalysis --- p.22 / Chapter 3.3.6 --- Energy-loss Spectrum and Element Distribution Image (elemental mapping) --- p.22 / Chapter 3.4 --- Scanning TEM (STEM) --- p.23 / Chapter Chapter 4 --- Synthesis of SiNWs Using Si Wafer and H2 --- p.31 / Chapter 4.1 --- Experiment --- p.31 / Chapter 4.2 --- Morphologies and Microstructures of the As-synthesized Nanowires --- p.32 / Chapter 4.2.1 --- Morphologies and Microstructures of the Nanowires Synthesized Using SiO Powder as the Starting Material (control experiment) --- p.32 / Chapter 4.2.2 --- Morphologies and Microstructures of the Nanowires Synthesized Using Smashed Si Wafers as the Source Material --- p.34 / Chapter 4.3 --- Discussions --- p.36 / Chapter 4.3.1 --- Growth Mechanism of the Modified SiNW Synthesis Method (use smashed Si wafer) --- p.36 / Chapter 4.3.1.1 --- Comparison with the OAG --- p.36 / Chapter 4.3.1.2 --- Yield Dependence on the Surface Area of the Si Wafer --- p.37 / Chapter 4.3.1.3 --- The Importance of H2 --- p.37 / Chapter 4.3.2 --- Advantages of the Modified Method --- p.38 / Chapter 4.3.2.1 --- Stable and Low Supersaturation Level (in comparison with the conventional OAG method using SiO powder) --- p.38 / Chapter 4.3.2.2 --- A Possible Method to Achieve SiNW Doping --- p.39 / Chapter Chapter 5 --- One-dimensional Au-Si Heterojunctions ´ؤ Microstructure and Phase Evolution under Electron Beam Irradiation --- p.48 / Chapter 5.1 --- Experiment --- p.48 / Chapter 5.2 --- Microstructure Analysis of the As-synthesized One-dimensional Au-Si Heterojunctions --- p.49 / Chapter 5.3 --- The Au Flow and Phase Evolution of the Au-Si Heteroj unctions under the Electron Beam Irradiation --- p.51 / Chapter 5.3.1 --- The Phenomenon --- p.51 / Chapter 5.3.2 --- The Mechanisms --- p.52 / Chapter 5.4 --- Conclusions --- p.55 / Chapter Chapter 6 --- A General Route to Fabricate One-dimensional Metal-Si Heteroj unctions --- p.65 / Chapter 6.1 --- Experiment --- p.65 / Chapter 6.2 --- Common Morphology Descriptions (SEM) --- p.66 / Chapter 6.3 --- 1D Au-Si Heterojunctions --- p.66 / Chapter 6.3.1 --- General Morphologies --- p.66 / Chapter 6.3.2 --- Effect of the Au Film Thickness on the Yield and Diameter of the Nanowire Products --- p.68 / Chapter 6.4 --- 1D Cu-Si Heterojunctions --- p.68 / Chapter 6.5 --- 1D Au-SiO2 Heterojunctions --- p.69 / Chapter 6.6 --- 1D Zn-SiO2 Heterojunctions --- p.70 / Chapter 6.7 --- Result of the Control Experiments --- p.70 / Chapter 6.8 --- Discussions --- p.70 / Chapter 6.8.1 --- General Mechanism of the 1D Si-metal Heterojunction Formation --- p.70 / Chapter 6.8.2 --- Source of the Si (vapor source and supersaturation control) --- p.71 / Chapter 6.8.3 --- Source of Metal --- p.72 / Chapter 6.8.4 --- Effect of the Reductive Atmosphere --- p.73 / Chapter Chapter 7 --- Conclusions --- p.83 / Reference --- p.85

Liang, Hui = 纳米线器件的制备和表征 / 梁慧. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2011. / Includes bibliographical references (leaves 45-48). / Abstracts in English and Chinese. / Liang, Hui = Na mi xian qi jian de zhi bei he biao zheng / Liang Hui. / Chapter Chapter 1 --- Nanowire-based devices --- p.1 / Chapter 1.1 --- Introduction --- p.1 / Chapter 1.1.1 --- Properties of various nanowires --- p.2 / Chapter 1.1.2 --- Nanowire growth methods --- p.3 / Chapter 1.1.3 --- Introduction to EBL --- p.4 / Chapter 1.1.4 --- Properties of nanowire and the arrays and related devices --- p.6 / Chapter Chapter 2 --- Experimental --- p.9 / Chapter 2.1 --- Nanowire preparation --- p.9 / Chapter 2.1.1 --- ZnS nanowire growth --- p.9 / Chapter 2.1.2 --- Sb2S3 nanowire growth --- p.10 / Chapter 2.2 --- Device fabrication --- p.10 / Chapter 2.2.1 --- Single-nanowire device --- p.10 / Chapter 2.2.2 --- Multiple-nanowire device --- p.17 / Chapter 2.2.3 --- Silicon device --- p.17 / Chapter 2.3 --- Characterizations --- p.18 / Chapter 2.3.1 --- Morphological and structural characterizations of the nanowires --- p.18 / Chapter 2.3.2 --- Two-probe measurements --- p.18 / Chapter 2.3.3 --- Four-probe measurements --- p.19 / Chapter Chapter 3 --- Results and Discussion --- p.21 / Chapter 3.1 --- Optimal factors for sample preparation --- p.21 / Chapter 3.1.1 --- Trial of spin coating --- p.21 / Chapter 3.1.2 --- Trial of Coating thickness --- p.21 / Chapter 3.1.3 --- Trial of e-beam lithography --- p.22 / Chapter 3.1.4 --- Trial of dosage --- p.23 / Chapter 3.1.5 --- Trial of development time --- p.26 / Chapter 3.2 --- Electrical Properties of devices made --- p.28 / Chapter 3.2.1 --- UV-visible response of single ZnS nanowire devices --- p.28 / Chapter 3.2.2 --- The optoelectronic characteristics of single Sb2S3 nanowire devices --- p.32 / Chapter 3.2.3 --- The optoelectronic characteristics of multiple-nanowire devices --- p.35 / Chapter 3.2.4 --- Temperature dependent resistance and magnetoresistance of the silicon device --- p.41 / Chapter Chapter 4 --- Conclusions --- p.44 / Chapter Chapter 5 --- References --- p.45

Zhuang, Junping = 單根納米線的軸向局域的光學性質 / 庄俊平. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2011. / Includes bibliographical references. / Abstracts in English and Chinese. / Zhuang, Junping = Dan gen na mi xian de zhu xiang ju yu de guang xue xing zhi / Zhuang Junping. / Acknowledgement --- p.I / Abstract --- p.II / 摘要 --- p.IV / Contents --- p.i / List of Figures --- p.iv / List of Tables --- p.viii / Abbreviations --- p.ix / Chapter Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Background --- p.1 / Chapter 1.2 --- ZnSe Semiconductor Nanowires --- p.2 / Chapter 1.3 --- Carrier Dynamics in Semiconductor Nanowires --- p.3 / Chapter 1.3.1 --- Carrier Relaxation --- p.3 / Chapter 1.3.2 --- Surface Effects on Carrier Recombination --- p.7 / Chapter 1.4 --- Principle ofTCSPC Technique --- p.9 / Chapter 1.5 --- Motivations and Works --- p.10 / References --- p.12 / Chapter Chapter 2 --- Experiments --- p.17 / Chapter 2.1 --- Growth of ZnSe Nanowires --- p.17 / Chapter 2.2 --- Measurements with Electron Microscopes --- p.17 / Chapter 2.3 --- Measurements by a Laser Scanning Microscope --- p.18 / Chapter 2.3.1 --- Experimental Setup --- p.18 / Chapter 2.3.2 --- Settings of Measurements --- p.23 / References --- p.25 / Chapter Chapter 3 --- Methods of Analysis --- p.26 / Chapter 3.1 --- Luminescence Intensity --- p.26 / Chapter 3.1.1 --- Intensity Detected by PMT --- p.27 / Chapter 3.1.2 --- Intensity Detected by SPAD --- p.28 / Chapter 3.2 --- Lifetime Histogram --- p.29 / Chapter 3.2.1 --- Pixel Binning --- p.29 / Chapter 3.2.2 --- Lifetime Fitting --- p.32 / References --- p.33 / Chapter Chapter 4 --- Results and Discussion --- p.34 / Chapter 4.1 --- "Morphology, Structure and Composition of As-Grown Nanowires" --- p.34 / Chapter 4.2 --- Cathodoluminescence of Individual ZnSe Nanowires --- p.36 / Chapter 4.3 --- Photoluminescence of ZnSe Nanowires --- p.36 / Chapter 4.4 --- Luminescence of Individual Nanowires --- p.39 / Chapter 4.4.1 --- Luminescence of As-Grown Nanowires --- p.39 / Chapter 4.4.2 --- Nonlinear Optical Properties --- p.42 / Chapter 4.5 --- Luminescence Lifetimes of Individual Nanowires --- p.47 / Chapter 4.5.1 --- Power Dependence --- p.48 / Chapter 4.5.2 --- Chemical Environments --- p.53 / Chapter 4.5.3 --- Concentration of Ammonium Sulfide Solution --- p.56 / Chapter 4.6 --- Axially Resolved Luminescence Lifetimes --- p.60 / Chapter 4.6.1 --- Axially Resolved 2D Decay Diagrams --- p.60 / Chapter 4.6.2 --- Axially Resolved Luminescence Lifetimes --- p.62 / Chapter 4.6.3 --- (TNBE) and T1 of DL Emission --- p.69 / References --- p.72 / Chapter Chapter 5 --- Conclusions --- p.76 / Appendix A --- p.79 / Chapter A.1 --- Laser Beam Diameter and Spatial Resolution --- p.79 / Chapter A.2 --- Instrument Response Function of TCSPC module --- p.81 / Chapter A.3 --- Photo-Injection --- p.82 / Chapter A.3.1 --- Two-Photon Excitation by Pulse Laser --- p.82 / Chapter A.3.2 --- One-Photon Excitation by CW UV Laser --- p.84 / Chapter A.4 --- Lifetime Distributions --- p.85 / References --- p.86 / Appendix B Supporting Data --- p.87

Tao, Yin = 納米線在液晶中的動力學 / 陶寅. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2010. / Includes bibliographical references. / Abstracts in English and Chinese. / Tao, Yin = Na mi xian zai ye jing zhong de dong li xue / Tao Yin. / Abstract --- p.I / 摘要 --- p.III / Acknowledgement --- p.IV / List of Figures --- p.VIII / List of Tables --- p.XV / Chapter Chapter 1 --- Introduction --- p.1 / Chapter 1.1. --- Background --- p.1 / Chapter 1.2. --- Review of Liquid Crystals --- p.2 / Chapter 1.2.1. --- Basic concepts --- p.2 / Chapter 1.2.2. --- Physical Properties of liquid crystals --- p.5 / Chapter 1.3. --- Manipulation of nanowires in suspensions --- p.8 / Chapter 1.3.1. --- Longitudinal Anchoring of liquid crystals --- p.8 / Chapter 1.3.2. --- Dielectrophoretic force and torque --- p.12 / Chapter 1.3.3. --- Measurement of conductivity --- p.15 / Chapter 1.4. --- Our motivation and work --- p.17 / Reference --- p.19 / Chapter Chapter 2 --- Experiments --- p.22 / Chapter 2.1. --- Nematic Liquid Crystal Cell Design and Fabrication --- p.22 / Chapter 2.1.1. --- Parallel Plate Capacitor like Liquid Crystal Cell --- p.22 / Chapter 2.1.2. --- In-Plane Switching Liquid Crystal Cell --- p.23 / Chapter 2.2. --- Filling of liquid crystals and dispersing nanowires --- p.28 / Chapter 2.3. --- Measurements --- p.30 / Chapter 2.3.1. --- Measurement of alignment and reorientation of the nanowires --- p.30 / Chapter 2.3.2. --- Measurements of the optical transmittance of liquid crystal cell --- p.31 / Chapter 2.4. --- Experimental Procedures --- p.33 / Chapter 2.4.1. --- Study of the relaxation of liquid crystals and nanowires --- p.33 / Chapter 2.4.2. --- Study of response of liquid crystals and nanowires to applied E field --- p.34 / Reference --- p.35 / Chapter Chapter 3 --- Numerical simulations of the motion of liquid crystals --- p.36 / Chapter 3.1. --- Leslie-Ericsson equation --- p.36 / Chapter 3.2. --- Response and relaxation of liquid crystals --- p.39 / Chapter 3.2.1. --- Parallel plate capacitor like liquid crystal cells --- p.39 / Chapter 3.2.2. --- In-plane switching liquid crystal cells --- p.45 / Reference --- p.49 / Chapter Chapter 4 --- Method of analysis --- p.50 / Chapter 4.1. --- Deduction of the orientation of nanowires --- p.50 / Chapter 4.1.1. --- Parallel plate capacitor like liquid crystal cell --- p.50 / Chapter 4.1.2. --- In-plane switching liquid crystal cells --- p.52 / Chapter 4.2. --- Methods of curve fitting to experimental data --- p.54 / Chapter 4.2.1. --- Procedures of fitting the curves of transmission --- p.54 / Chapter 4.2.2. --- Procedures of fitting the curves of angle β (t) and φ (t)…… --- p.57 / Reference --- p.64 / Chapter Chapter 5 --- Results and discussion --- p.65 / Chapter 5.1. --- Study of the relaxation of nanowires and liquid crystals --- p.65 / Chapter 5.1.1. --- Dependence on the length of nanowires --- p.65 / Chapter 5.1.2. --- Dependence on the temperature of liquid crystals --- p.82 / Chapter 5.2. --- Study of the responses of nanowires and liquid crystals to E field --- p.89 / Chapter 5.2.1. --- Dependence on the applied E field --- p.89 / Chapter 5.2.2. --- Dependence on the length of nanowires --- p.112 / Chapter 5.2.3. --- Dependence on the temperature of liquid crystal --- p.116 / Reference --- p.122 / Chapter Chapter 6 --- Conclusions --- p.123 / Appendix 1 --- p.125 / Appendix 2 --- p.132

Thesis (M.E.E.)--University of Delaware, 2006. / Principal faculty advisor: Balaji Panchapakesan, Dept. of Electrical and Computer Engineering. Includes bibliographical references.

The interaction of laser radiation with a material can excite coherent lattice vibration. The observation of such periodic motion of the atoms in the lattice provides information on the properties of the material. In the present work a femtosecond pump-probe technique was applied for studies of acoustic vibrations in nanoparticles and nanowires, and coherent optical phonons in thin films. The elastic properties of spherical Ag nanoparticles and Ag and Bi nanowires were studied in a dual-color femtosecond pump-probe experiment. The results of the period determinations of the acoustic vibrations, obtained from the time-domain measurements with low intensity pump pulses, together with the information about the size of the particles, were used to determine the elastic constants of the materials. Also changes in the measured acoustical response of the Ag nanowires under high intensity laser excitation were studied. In addition the coherent optical phonon excitation in a Bi film was studied in a femtosecond pump-probe experiment. A red-shift of the phonon frequency at the high photoexcitation density was observed. To separate the effect of the lattice softening and the lattice anharmonicity the excitation with two pump pulses was employed. Numerical simulations, which took into account the evolution of the spatial inhomogeneity of the excitation density, were carried out and compared to the experimental results.

The use of nanostructures has become very common throughout high-tech industries. In order to enhance the applicability of Shape Memory Alloys (SMAs) in systems such as Nano-Electromechanical Systems, the phase transformation behavior of SMA nanostructures should be explored. The primary focus of this work is on the fabrication of metallic nanowires and the characterization of the phase transformation of SMA nanowires. Various metallic nanowires are fabricated through the use of the mechanical pressure injection method. The mechanical pressure injection method is a template assisted nanowire fabrication method in which an anodized aluminum oxide (AAO) template is impregnated with liquid metal. The fabrication procedure of the AAO templates is analyzed in order to determine the effect of the various fabrication steps. Furthermore, metallic nanowires are embedded into polymeric nano bers as a means to incorporate nanowires within other nanostructures. The knowledge obtained through the analysis of the AAO template fabrication guides the fabrication of SMA nanowires of various diameters. The fabrication of SMA nanowires with di fferent diameters is accomplished through the fabrication of AAO templates of varying diameters. The phase transformation behavior of the fabricated SMA nanowires is characterized through transmission electron microscopy. By analyzing the fabricated SMA nanowires, it is found that none of the fabricated SMA nanowires exhibit a size eff ect on the phase transformation. The lack of a size e ffect on the phase transition of SMA nanowires is contrary to the results for SMA nanograins, nanocrystals, and thin films, which all exhibit a size eff ect on the phase transformation. The lack of a size eff ect is further studied through molecular dynamic simulations. These simulations show that free-standing metallic nanowires will exhibit a phase transformation when their diameters are sufficiently small. Furthermore, the application of a constraint on metallic nanowires will inhibit the phase transformation shown for unconstrained metallic nanowires. Therefore, it is concluded that free-standing SMA nanowires will exhibit a phase transformation throughout the nanoscale, but constrained SMA nanowires will reach a critical size below which the phase transformation is inhibited.