Cheung Lok Ying Teresa = 竹炭模板上形成的二氧化硅與碳化硅納米線及其表徵 / 張樂影. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2006. / Includes bibliographical references. / Text in English; abstracts in English and Chinese. / Cheung Lok Ying Teresa = Zhu tan mo ban shang xing cheng de er yang hua gui yu tan hua gui na mi xian ji qi biao zheng / Zhang Leying. / ABSTRACT --- p.i / 摘要 --- p.iii / ACKNOWLEDGEMENTS --- p.v / TABLE OF CONTENTS --- p.vii / LIST OF FIGURE CAPTIONS --- p.xi / LIST OF TABLE CAPTIONS --- p.xv / Chapter Chapter 1 --- Introduction / Chapter 1.1. --- Biomineralization process --- p.1 / Chapter 1.2. --- Structures in biological matters --- p.2 / Chapter 1.2.1. --- Bone --- p.2 / Chapter 1.2.2. --- Wood --- p.3 / Chapter 1.3. --- Biomorphic products and their potential applications --- p.4 / Chapter 1.3.1 --- Environment conscious products --- p.4 / Chapter 1.3.2 --- Properties --- p.5 / Chapter 1.3.3 --- Carbide and oxide composites --- p.5 / Chapter 1.4 --- Common fabrication approaches --- p.6 / Chapter 1.4.1 --- Gaseous infiltration --- p.7 / Chapter 1.4.2 --- Liquid infiltration --- p.7 / Chapter 1.4.3 --- Sol-gel method --- p.8 / Chapter 1.5 --- Growth of nanowires --- p.8 / Chapter 1.5.1 --- Vapor-liquid-solid (VLS) mechanism --- p.9 / Chapter 1.5.2 --- Solution-liquid-solid (SLS) mechanism --- p.9 / Chapter 1.5.3 --- Vapor-solid (VS) mechanism --- p.10 / Chapter 1.6 --- Goals of the project --- p.10 / Chapter 1.6.1 --- Feedbacks on previous works --- p.10 / Chapter 1.6.2 --- Our breakthrough approach --- p.11 / Chapter 1.7 --- Thesis layout --- p.12 / References --- p.13 / Figures --- p.17 / Chapter Chapter 2 --- Samples preparation and characterization methods / Chapter 2.1 --- Materials selections --- p.22 / Chapter 2.1.1 --- Selection of materials for biomorphic substrate --- p.22 / Chapter 2.1.2 --- Selection of solution for infiltration --- p.23 / Chapter 2.2 --- Samples preparation --- p.24 / Chapter 2.2.1 --- Pyrolysis of raw bamboo --- p.24 / Chapter 2.2.2 --- Infiltration of reactants --- p.25 / Chapter 2.2.3 --- Sintering conditions --- p.26 / Chapter 2.3 --- Characterization methods --- p.26 / Chapter 2.3.1 --- Scanning electron microscopy (SEM) and energy dispersive x-ray spectroscopy (EDS) --- p.27 / Chapter 2.3.2 --- Transmission electron microscopy (TEM) and EDS --- p.27 / Chapter 2.3.3 --- High-resolution transmission electron microscopy (HRTEM) --- p.27 / Chapter 2.3.4 --- X-ray diffraction (XRD) --- p.28 / Chapter 2.3.5 --- X-ray photoelectron spectroscopy (XPS) --- p.28 / Chapter 2.3.6 --- Fourier transform infrared spectroscopy (FTIR) --- p.29 / Chapter 2.4 --- Conclusions --- p.29 / References --- p.30 / Figures --- p.31 / Tables --- p.33 / Chapter Chapter 3 --- Bamboo biomorphic substrates / Chapter 3.1 --- Overview --- p.34 / Chapter 3.2 --- Volumetric shrinkage and weight loss --- p.34 / Chapter 3.3 --- General morphology --- p.35 / Chapter 3.4 --- Intrinsic impurities --- p.35 / Chapter 3.5 --- Structures --- p.36 / References --- p.38 / Figures --- p.39 / Chapter Chapter 4 --- Silica / Chapter 4.1 --- Overview --- p.43 / Chapter 4.2 --- Thermal analyses --- p.44 / Chapter 4.2.1 --- Raw biomorphic substrates --- p.44 / Chapter 4.2.2 --- Infiltrated biomorphic substrates --- p.45 / Chapter 4.3 --- Experiments --- p.46 / Chapter 4.4 --- Characterization in general --- p.47 / Chapter 4.4.1 --- General morphologies --- p.47 / Chapter 4.4.2 --- Tips of the SiO2 nanowires --- p.48 / Chapter 4.5 --- Effects of sintering duration --- p.48 / Chapter 4.6 --- Effects of sintering temperature --- p.49 / Chapter 4.6.1 --- "Different temperatures, held for one hour" --- p.50 / Chapter 4.6.2 --- "Different temperatures, held for ten hours" --- p.50 / Chapter 4.7 --- Growth mechanisms --- p.52 / Chapter 4.8 --- Summary --- p.54 / References --- p.56 / Figures --- p.58 / Tables --- p.75 / Chapter Chapter 5 --- Silicon carbide / Chapter 5.1 --- Overview --- p.76 / Chapter 5.2 --- Experiments --- p.77 / Chapter 5.3 --- Characterization in general --- p.78 / Chapter 5.3.1 --- General morphologies --- p.78 / Chapter 5.3.2 --- Stacking faults and twinning --- p.79 / Chapter 5.3.3 --- Tips of the SiC nanowires --- p.81 / Chapter 5.4 --- Growth mechanisms --- p.82 / Chapter 5.5 --- Summary --- p.83 / References --- p.84 / Figures --- p.87 / Chapter Chatper 6 --- Conclusions and future works / Chapter 6.1 --- Main results of this projects --- p.101 / Chapter 6.2 --- Future works --- p.103 / References --- p.104

Neste trabalho foram investigadas estruturas de diodos Schottky de carbeto de silício (SiC) com potencial uso em detectores de energia de partículas carregadas. Para tanto, foram fabricados diodos Schottky de SiC do tipo Metal-Isolador-Semicondutor (MIS). Uma estrutura MIS é considerada uma vez que o SiC sempre forma em sua superfície uma fina camada de oxicarbeto de silício (SiCxOy) nativo, de difícil remoção por ataques químicos. Foi desenvolvido um modelo modificado da teoria de Emissão Termiônica (TE), de modo a levar em conta o óxido nativo e/ou finas camadas dielétricas inseridas entre metal e semicondutor nas estruturas de diodos Schottky. Foram fabricadas estruturas alumínio/dielétrico/silício para caracterização dos dielétricos utilizados. Foram depositados os dielétricos de SiO2, TiO2, HfO2 e Al2O3 entre o metal Ni e o semicondutor de SiC, variando as espessuras de 1 a 8 nm. As espessuras depositadas foram confirmadas por Elipsometria espectral e Reflectometria de raio X, anteriormente à deposição por sputtering do contato Schottky de Ni. Após a deposição e o tratamento térmico do Ni, as estruturas de diodos Schottky foram caracterizadas eletricamente por meio de medidas de Corrente-Tensão (I-V) e Capacitância-Tensão (C-V), variando a temperatura de medida. Foi observado que a presença de uma fina camada dielétrica entre metal e semicondutor aumenta artificialmente a Altura da Barreira Schottky (SBH), diminuindo a corrente reversa quando o diodo é polarizado reversamente. Por meio do modelo modificado da TE, foi calculada uma espessura variando de 0.18 – 0.20 nm para o oxicarbeto de silício presente nos diodos estudados. As SBH reais foram extraídas por meio das medidas de I-V, variando-se a temperatura. Foram obtidos os valores da SBH de 1.39, 1.32 e 1.26 V, para os dielétricos TiO2, Al2O3, HfO2 e com 1 nm de espessura nominal cada, respectivamente. Para esses, o fator de idealidade calculado ficou próximo de 1. Espessuras de dielétricos acima de 4 nm começam a apresentar características de capacitores Metal-Óxido-Semicondutor e não de diodos Schottky. Por fim, reportamos as estruturas de Ni/Al2O3/4H-SiC/Ni e Ni/HfO2/4H-SiC/Ni, com 1 nm de dielétrico depositado, para uso como detector de partículas alfa no experimento de Espectrometria de Retroespalhamento Rutherford (RBS). Ambos os detectores apresentaram corrente reversa menor que 70 nA.cm-2 e resolução em energia de 76 keV, para polarização reversa de 40 V. / In the present work, silicon carbide (SiC) Schottky diodes with potential use in energy particle detectors were investigated. Metal-Insulator-Semiconductor (MIS) SiC Schottky diodes were fabricated. The MIS structures are considered because SiC always forms a thin native silicon oxycarbide (SiCxOy) layer in its surface that is difficult to remove by chemical means. A modified Thermionic Emission theory (TE) was developed to take into account the native oxide and/or thin dielectric layers present between metal and semiconductor in Schottky diodes. Aluminum/dielectric/silicon structures were fabricated for the dielectric characterization. SiO2, TiO2, HfO2 and Al2O3 dielectrics were deposited between Ni and SiC, with thicknesses varying from 1 to 8 nm. The deposited dielectrics layers thicknesses were confirmed by Ellipsometry spectra and X ray reflectometry before deposition of Ni Schottky contacts by sputtering. After Ni deposition and annealing, the Schottky diodes were electrically characterized by Current-Voltage (I-V) and Capacitance-Voltage measurements, varying the temperature. A thin dielectric layer present between metal and semiconductor artificially augments the Schottky Barrier Height (SBH) and lowers the reverse current when the diodes are reverse biased. A 0.18 – 0.20 nm of SiCxOy layer was inferred for the diodes using the modified TE. The real SBH was extracted from the I-V measurements and presented values of 1.39, 1.32 and 1.26 V for the diodes with 1 nm of TiO2, Al2O3 and HfO2, respectively. For these, an ideality factor close to 1 was calculated. Diodes with thicker (>4 nm) dielectrics layers shows Metal-Oxide-Semiconductor capacitors behavior. Ni/Al2O3/4H-SiC/Ni and Ni/HfO2/4H-SiC/Ni structures with 1 nm of dielectric layer thickness were used in Rutherford Backscattering Spectrometry experiments. Both detectors presented reverse current lower than 70 nA.cm-2 and energy resolution of 76 keV, when applied 40 V reverse bias.

Nesta dissertação discorremos acerca do crescimento e caracterização de filmes finos de carbeto de silício amorfo hidrogenado (a-Si1-xCx:H), crescidos pelo método de deposição química de vapor assistida por plasma (PECVD) no regime de baixa densidade de potência a partir de misturas de silano e metano. Foram analisadas e correlacionadas as propriedades ópticas, morfológicas e composicionais de filmes depositados em diferentes condições de fluxo de silano e concentração de metano. Os resultados não apenas confirmaram dados anteriores obtidos em filmes de a-Si1-xCx:H similares, mas possibilitaram uma melhor compreensão das características deste material. Para a obtenção de um composto de alto gap, alto conteúdo de carbono, química e morfologicamente homogêneo é necessário utilizar baixos fluxos de silano e alta concentração de metano, condições de deposição conhecidas como regime de \"plasma faminto por silano\". Neste regime são crescidos filmes com Eg > 3 eV, x > 0,5, maior concentração de ligações Si-C, concentração de hidrogênio de 50 at.%, menor proporção de radicais CH3 e menor densidade de poros. / In this work we describe the growth and characterization of hydrogenated amorphous silicon carbide (a-Si1-xCx:H) thin films deposited by plasma enhanced chemical vapor deposition (PECVD) in the low power density regime from mixtures of silane and methane. The optical, morphological and compositional properties of films deposited under different silane flow and methane concentration were analyzed and correlated. The results not only confirmed previous data obtained on similar a-Si1-xCx:H films, but improved the comprehension of their characteristics. In order to obtain a compound with high optical gap, high carbon content, chemically and morphologically homogeneous, it is necessary to work with low silane flow and high methane concentration; deposition conditions known as \"silane starving plasma\" regime. In this regime, films with Eg > 3 eV, x > 0.5, higher concentration of Si-C bonds, hydrogen concentration of 50 at.%, smaller proportion of CH3 radicals and smaller density of pores are produced.

by Li, Kowk Cheung = 利用木材製作具有生物形態的碳化矽 / 李國彰. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2008. / Includes bibliographical references. / Abstracts in English and Chinese. / by Li, Kwok Cheung = Li yong mu cai zhi zuo ju you sheng wu xing tai de tan hua xi / Li Guozhang. / Abstract --- p.i / 摘要 --- p.iii / Acknowledgements --- p.v / Table of contents --- p.vi / List of figure captions --- p.x / List of table captions --- p.xiv / Chapter Chapter 1 --- Introduction / Chapter 1.1 --- Biomorphic products and their potential applications --- p.1 / Chapter 1.2 --- Structures and mechanical behaviors of wood --- p.1 / Chapter 1.3 --- Characteristics and applications of SiC --- p.2 / Chapter 1.4 --- Common methods of producing biomorphic SiC from wood --- p.2 / Chapter 1.4.1 --- Chemical vapor deposition --- p.3 / Chapter 1.4.2 --- Melt infiltration --- p.3 / Chapter 1.4.3 --- Sol-gel process --- p.4 / Chapter 1.5 --- Carbothermal reduction process of silica --- p.5 / Chapter 1.6 --- Objectives of present work --- p.5 / Chapter 1.6.1 --- Comments on the previous works --- p.5 / Chapter 1.6.2 --- Current approaches --- p.6 / References --- p.8 / Chapter Chapter 2 --- Experimental procedures / Chapter 2.1 --- Wood biotemplates --- p.10 / Chapter 2.1.1 --- Balsa --- p.10 / Chapter 2.1.2 --- Flame tree --- p.10 / Chapter 2.2 --- Sol Gel process --- p.11 / Chapter 2.2.1 --- Precursor --- p.11 / Chapter 2.2.2 --- Reaction mechanisms --- p.11 / Chapter 2.2.3 --- "Effects of pH, temperature, and environment" --- p.12 / Chapter 2.3 --- Preparation of biomorphic SiC / Chapter 2.3.1 --- HC1 pretreatment --- p.13 / Chapter 2.3.2 --- Infiltration of silica via sol gel process --- p.13 / Chapter 2.3.2.1 --- Balsa --- p.14 / Chapter 2.3.2.2 --- Flame tree --- p.15 / Chapter 2.3.3 --- Sintering --- p.15 / Chapter 2.3.4 --- Removal of carbon --- p.15 / Chapter 2.4 --- Characterization methods --- p.16 / Chapter 2.4.1 --- Scanning electron microscope and energy dispersive x-ray spectroscopy --- p.16 / Chapter 2.4.2 --- X-ray diffractometry --- p.16 / Chapter 2.4.3 --- Differential thermal analysis --- p.16 / Chapter 2.4.4 --- Compressive strength analysis --- p.17 / Chapter 2.5 --- Summary --- p.17 / References --- p.18 / Figures --- p.19 / Chapter Chapter 3 --- Results and discussions / Chapter 3.1 --- Balsa --- p.21 / Chapter 3.1.1 --- HC1 pretreatment --- p.21 / Chapter 3.1.2 --- Infiltration behaviors --- p.21 / Chapter 3.1.2.1 --- By the standard method --- p.21 / Chapter 3.1.2.2 --- Modified sol-gel process --- p.21 / Chapter 3.1.3 --- SiC products --- p.22 / Chapter 3.1.3.1 --- Volumetric shrinkage and weight loss --- p.22 / Chapter 3.1.3.2 --- Compositions --- p.23 / Chapter 3.1.3.3 --- Morphology and structure --- p.24 / Chapter 3.1.4 --- Optimal infiltration conditions --- p.25 / Chapter 3.2 --- Flame tree --- p.25 / Chapter 3.2.1 --- HC1 pretreatment --- p.26 / Chapter 3.2.2 --- Infiltration behaviors --- p.26 / Chapter 3.2.3 --- SiC products --- p.26 / Chapter 3.2.3.1 --- Volumetric shrinkage and weight loss --- p.26 / Chapter 3.2.3.2 --- Composition --- p.27 / Chapter 3.2.3.3 --- Morphology and structure --- p.27 / Chapter 3.3 --- Mechanisms for the formation of SiC cell walls --- p.30 / Chapter 3.4 --- Compressive strength --- p.31 / Chapter 3.5 --- Summary --- p.34 / References --- p.35 / Tables --- p.36 / Figures --- p.38 / Appendix --- p.65 / Chapter Chapter 4 --- Conclusions and future works / Chapter 4.1 --- Summary --- p.67 / Chapter 4.2 --- Suggestions for future work --- p.68 / References --- p.70

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

Due to the low current ratings of the currently available silicon carbide (SiC) switches they cannot be employed in high-power converters. Thus, it is necessary to parallel-connect several switches in order to reach higher current ratings. This paper presents an investigation of parallel-connected normally-on SiC junction field effect transistors. There are four crucial parameters affecting the effectiveness of the parallel-connected switches. However, the pinch-off voltage and the reverse breakdown voltage of the gates seem to be the most important parameters which affect the switching performance of the devices. In particular, the spread in these two parameters might affect the stable off-state operation of the switches. The switching performance and the switching losses of a pair of parallel-connected devices having different reverse breakdown voltages of the gates is investigated by employing three different gate-driver configurations. It is experimentally shown that using a single gate-driver circuit the switching performance of the parallel-connected devices is almost identical, while the total switching losses are lower compared to the other two configurations. / <p>QC 20121116</p>

Laser Chemical Vapor Deposition (LCVD) is a process by which reagent gases are thermally activated to react by means of a laser focused on a substrate. The reaction produces a ceramic or metallic deposit. This investigation focuses on the use of LCVD as a method for producing laminated composites, specifically carbon/silicon carbide laminates. The laminates that were produced were examined using scanning electron microscopy (SEM) and electron dispersive spectroscopy (EDS) to determine composition. Deposit geometrical characteristics such as laminate thickness and volcano depth as well as deposit morphology were also determined using SEM. Another subset of experiments was performed for the purpose of simultaneously depositing carbon and silicon carbide, ie., codeposition.

Ultrathin graphite films, with thickness from 1-30 atomic layers, are grown on the Si-terminated and C-terminated faces of 6H-SiC and 4H-SiC via thermal desorption of silicon in an ultrahigh vacuum (UHV) chamber or in a high-vacuum RF furnace. Graphite LEED patterns and atom-resolved STM images on graphite films prove that epitaxial growth is achieved on both faces of the SiC substrate. The thickness of graphite films is estimated with modeling the Si:C Auger peak intensities. Through LEED and STM investigations of monolayer graphite grown on the Si-face of SiC(0001) surface, we show the existence of a SiC 6R3*6R3 reconstructed layer between graphite films and the SiC substrate. The complicated LEED patterns can be interpreted partially by the kinematic scattering of the interfacial layer and the 6*6 surface corrugation. Further scanning tunneling spectroscopy (STS) measurements indicate that the graphite films remain continuous over the steps between domains. Carbon nanotubes and carbon nanocaps cover about 40% of the graphitized C-face of SiC. The remaining areas are flat graphite films. Graphite ribbons were made through E-beam lithography. After the lithography process, the graphitic features remain on flat region underneath HSQ residues.

In the past several years, epitaxial graphene on silicon carbide has been transformed from an academic curiosity of social scientists to a leading candidate material to replace silicon in post-CMOS electronics. This has come with rapid development of growth technologies, improved understanding of epitaxial graphene on the polar faces of silicon carbide, and new device fabrication techniques. The contributions of this thesis include refinement and improved understanding of graphene growth on the silicon- and carbon-faces in the context of managed local silicon partial pressure, high-throughput epitaxial graphene thickness measurement and uniformity characterization by ellipsometry, observations of nearly ideal graphene band structures on rotationally stacked carbon-face multilayer epitaxial graphene, presentation of initial experiments on localized in situ chemical modification of epitaxial graphene for an alternate path to semiconducting behavior, and novel device fabrication methods to exploit the crystal structure of the silicon carbide substrate. The latter is a particularly exciting foray into three dimensional patterning of the substrate that may eliminate the critical problem of edge roughness in graphene nanoribbons.

<p>Silicon carbide rectifiers are commercially available since 2001, and MESFET switches are expected to enter the market within a year. Moreover, three inch SiC wafers can be purchased nowadays without critical defects for the device performance and four inch substrate wafers are announced for the year 2005. Despite this tremendous development in SiC technology, the reliability issues like device degradation or high channel mobility still remain to be solved.</p><p>This thesis focuses on SiC surface passivation and termination, a topic which is very important for the utilisation of the full potential of this semiconductor. Three dielectrics with high dielectric constants, Al2O3, AlN and TiO2, were deposited on SiC with different techniques. The structural and electrical properties of the dielectrics were measured and the best insulating layers were then deposited on fully processed and well characterised 1.2 kV 4H SiC PiN diodes. For the best Al2O3 layers, the leakage current was reduced to half its value and the breakdown voltage was extended by 0.5 kV, reaching 1.6 kV, compared to non passivated devices.</p><p>As important as the proper choice of dielectric material is a proper surface preparation prior to deposition of the insulator. In the thesis two surface treatments were tested, a standard HF termination used in silicon technology and an exposure to UV light from a mercury lamp. The second technique is highly interesting since a substantial improvement was observed when UV light was used prior to the dielectric deposition. Moreover, UV light stabilized the surface and reduced the leakage current by a factor of 100 for SiC devices after 10 Mrad γ ray exposition. The experiments indicate also that the measured leakage currents of the order of pA are dominated by surface leakage.</p>