by Mok Wing Keung. / Parallel title in Chinese characters. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1992. / Includes bibliographical references (leaves 149-154). / Acknowledgement --- p.i / Abstract --- p.ii / Table Of Contents --- p.iii / List Of Figures --- p.v / List Of Tables --- p.ix / List Of Plates --- p.x / Chapter Chapter One --- Introduction / Chapter 1.1 --- General introduction --- p.1 / Chapter 1.2 --- Gallium arsenide --- p.4 / Chapter 1.2.1 --- Basic facts --- p.4 / Chapter 1.2.2 --- Band structure --- p.6 / Chapter 1.2.3 --- Production of GaAs --- p.9 / Chapter 1.3 --- Ion implantation --- p.11 / Chapter 1.3.1 --- Principle of ion implantation --- p.11 / Chapter 1.3.2 --- Basic facts --- p.17 / Chapter 1.3.3 --- Radiation damage and annealing --- p.21 / Chapter 1.4 --- Optical measurements --- p.27 / Chapter 1.4.1 --- Basic facts --- p.27 / Chapter 1.4.2 --- Optical reflectance --- p.29 / Chapter 1.4.3 --- Oxide overlayer --- p.39 / Chapter Chapter Two --- Experimental / Chapter 2.1 --- Sample preparation --- p.42 / Chapter 2.2 --- Ion implantation --- p.46 / Chapter 2.2.1 --- Implantation parameters --- p.46 / Chapter 2.2.2 --- Computer modeling of implantation profiles --- p.48 / Chapter 2.3 --- Annealing --- p.57 / Chapter 2.3.1 --- Conventional annealing --- p.57 / Chapter 2.3.2 --- Rapid thermal annealing --- p.61 / Chapter 2.4 --- Optical reflectance measurement --- p.69 / Chapter 2.4.1 --- Principle of measurement --- p.69 / Chapter 2.4.1.1 --- Relative reflectance measurement --- p.71 / Chapter 2.4.1.2 --- Absolute reflectance measurement --- p.79 / Chapter 2.4.2 --- Error estimation and data reduction --- p.82 / Chapter 2.4.2.1 --- Error estimation --- p.84 / Chapter 2.4.2.2 --- Data reduction --- p.86 / Chapter 2.5 --- Optical microscopy and photoluminescence --- p.90 / Chapter Chapter Three --- Results And Discussion / Chapter 3.1 --- Surface morphology --- p.93 / Chapter 3.2 --- Optical reflectance measurement --- p.101 / Chapter 3.2.1 --- Reflectance spectrum --- p.101 / Chapter 3.2.1.1 --- Reference mirror --- p.101 / Chapter 3.2.1.2 --- Crystalline GaAs --- p.104 / Chapter 3.2.1.3 --- Implanted GaAs before annealing --- p.108 / Chapter 3.2.1.4 --- Conventional annealed GaAs --- p.115 / Chapter 3.2.1.5 --- Rapid thermal annealed GaAs (proximity) --- p.120 / Chapter 3.2.2 --- Extraction of optical constants --- p.128 / Chapter 3.2.2.1 --- Oxide overlayer --- p.128 / Chapter 3.2.2.2 --- Dielectric function --- p.132 / Chapter 3.3 --- Photoluminescence results --- p.143 / Chapter Chapter Four --- Conclusions And Suggestions For Further Work --- p.147 / References --- p.149

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Physics, 1981. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE. / Vita. / Includes bibliographical references. / by Paolo Rava. / Ph.D.

by Chan Kwok Wai. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1997. / Includes bibliographical references (leaves 93-95). / ACKNOWLEDGEMENT --- p.i / ABSTRACT --- p.ii / LIST OF SYMBOLS --- p.iii / LIST OF FIGURES --- p.v / LIST OF TABLES --- p.vi / Chapter CHAPTER ONE --- INTRODUCTION --- p.1 / Chapter CHAPTER TWO --- SURVEYS ON ION IMPLANTATION DAMAGE STUDY --- p.6 / Chapter 2.1 --- Introduction --- p.6 / Chapter 2.1.1 --- Basic Theory --- p.7 / Chapter 2.1.2 --- Amorphization --- p.9 / Chapter 2.1.3 --- Amorphous Layer Regrowth --- p.10 / Chapter 2.1.4 --- Point Defect Sources --- p.11 / Chapter 2.1.5 --- Types of Extended Defects --- p.11 / Chapter 2.2 --- Nature of Point Defects --- p.15 / Chapter 2.2.1 --- Important Parameters --- p.15 / Chapter 2.2.2 --- Vacancy Centers in Semiconductor --- p.16 / Chapter 2.2.3 --- Self-interstitial in Silicon --- p.17 / Chapter 2.2.4 --- Distribution of Excess Point Defects --- p.18 / Chapter 2.2.5 --- Energy Level of Defect Species --- p.19 / Chapter CHAPTER THREE --- EXPERIMENTAL METHOD --- p.21 / Chapter 3.1 --- Experimental --- p.21 / Chapter 3.2 --- Spreading Resistance Profiling --- p.25 / Chapter CHAPTER FOUR --- MODELING OF SPREADING RESISTANCE PROFILES OF ION-IMPLANTED DAMAGE IN SILICON --- p.29 / Chapter 4.1 --- Introduction --- p.29 / Chapter 4.2 --- Basic equation --- p.30 / Chapter 4.3 --- Formation of Model --- p.34 / Chapter CHAPTER FIVE --- RESULTS AND DISCUSSION --- p.37 / Chapter 5.1 --- Results --- p.37 / Chapter 5.2 --- Discussion --- p.55 / Chapter CHAPTER SIX --- CONCLUSION AND SUGGESTIONS OF FURTHER WORK --- p.58 / Chapter 6.1 --- Conclusion --- p.58 / Chapter 6.2 --- Suggestions of further work --- p.59 / APPENDIX A --- p.60 / APPENDIX B / SPREADING RESISTIVITY PROFILES --- p.62 / REFERENCE --- p.93

Filmes finos de TiO2 e N:TiO2, e multicamadas TiO2/N:TiO2 foram crescidos sobre substratos de aço AISI 316 e Si(100), por meio da técnica de deposição química de organometálicos em fase vapor (MOCVD). Foram produzidos filmes com diferentes espessuras, nas temperaturas de 400 e 500°C. Os filmes foram caracterizados utilizando-se técnicas de difração de raios X (DRX), espectroscopia de fotoelétrons excitados por raios x (XPS) e microscopia eletrônica de varredura (MEV). A resistência à corrosão foi avaliada por meio de testes de polarização potenciodinâmica em eletrólito 3,5%p NaCl. Filmes não dopados, crescidos a 400°C, apresentaram TiO2 anatase, enquanto que os crescidos a 500°C apresentaram a fase rutilo, além de anatase. Nos filmes dopados com nitrogênio (7,29 e 8,29 at% a 400 e 500°C, respectivamente), em ambas as temperaturas, houve a formação de TiO2 anatase, bem como de fases contendo nitrogênio. Os filmes de TiO2 crescidos a 400°C ofereceram melhor proteção contra a corrosão que os crescidos a 500°C. Filmes crescidos a 500°C apresentaram estrutura colunar, que representa alto nível de porosidade, enquanto que os filmes crescidos a 400°C apresentaram estrutura mais densa. A dopagem não foi eficiente para proteger o substrato contra corrosão, provavelmente devido à formação das fases contendo nitrogênio. Os resultados para os testes com filmes compostos por multicamadas sugerem que aqueles com mais interfaces apresentam melhor resistência à corrosão. O processo de corrosão das amostras se inicia na superfície do filme, que está em contato com o meio agressivo, originando pites, que permitem ao meio corrosivo acessar o substrato metálico. O metal é atacado e dissolvido sob o filme, e resulta na delaminação do filme. / TiO2 and N-doped TiO2 (N:TiO2) thin films, and TiO2/N:TiO2 multilayered films were grown on AISI 316 steel substrates, and Si (100) by using metallorganic chemical vapor deposition (MOCVD) technique. The growth of the films was carried out at 400 and 500°C, and films with different thicknesses and structures were obtained. Titanium dioxide films were produced by using only titanium isopropoxide IV as both titanium and oxygen sources. In order to obtain N:TiO2 films, NH3 was also added to the system. The films were characterized by using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM) The corrosion resistance was evaluated by potentiodynamic polarization tests in a 3.5wt% NaCl electrolyte. TiO2 undoped films, grown at 400°C, presented anatase, while those grown at 500°C showed the rutile phase, besides anatase. For nitrogendoped films (7.29 and 8.29 at% at 400 and 500°C, respectively), at both temperatures, TiO2 anatase was formed, as well as nitrogen-containing phases. TiO2 films grown at 400°C provided better protection against corrosion than those grown at 500°C. Films grown at 500°C showed a columnar structure, which represents a high level of porosity, while the films grown at 400°C presented a denser structure. Doping was not efficient to protect the substrate against corrosion, probably due to the formation of nitrogen containing phases. The corrosion results for tests with multilayered films suggest that those with more interfaces present better resistance to corrosion. The corrosion of the samples starts at the surface of the films, which is in contact with the aggressive medium, causing pitting in this film, which allows the corrosive medium to reach the metallic substrate. The metal is attacked and dissolved under the film, and results in film delamination.

Two-dimensional (2D) transition metal dichalcogenides (TMDs) with intrinsic band gaps are considered to be prospective alternatives for graphene in the applications of emerging nano-semiconductor devices. As a significant member of the TMDs family, WSe₂ with superior optical properties attracts increasing attention, especially in the optoelectronics. In this thesis, the electronic and mechanical properties of 2D WSe₂ have been studied experimentally and theoretically. Firstly, the fabrication of substrate-supported and suspended pre-patterned WSe₂ FETs with the low-cost optical lithography and vapour HF etching technology have been realised. The subsequent electrical measurement of the fabricated WSe₂ FETs indicates that the WSe₂/dielectric interface can affect the electrical performance of 2D WSe₂ negatively. To gain more insights on the impact of field-effect on 2D WSe₂, first-principle calculations have been conducted in this research to study the evolutions of the crystal structure, electronic band structure, conductive channel size, and electrical transport property of WSe2 under various levels of field-effect. Furthermore, a layer thinning and chemical doping method of 2D WSe₂ by vapour XeF₂ exposure featured with good air-stability, scalability, and controllability has been developed to enable the layer engineering of 2D WSe₂ and integration of 2D WSe₂ to logic circuits, solar cells, and light-emitting diodes (LED). The thinning and doping mechanism has been investigated with a combination of Raman spectroscopy, photoluminescence (PL) spectroscopy, and Xray photoelectron spectroscopy (XPS) characterization techniques. Afterwards, the inplane elastic properties (including the Young's modulus, breaking strain, and etc.) of 2D WSe₂ have been measured with nanoindentation experiments implemented by atomic force microscopy (AFM). The results prove the suitability of 2D WSe₂ in the applications of flexible devices and nanoelectromechanical systems (NEMS) operating in the audio resonance frequency, such as acoustic sensors and loudspeakers. To provide a comprehensive understanding of the strain engineering of 2D WSe₂, the strain induced variations of the crystal structure, electronic band structure, and electrical transport property of 2D WSe₂ have been further studied with first-principle calculations, which paves the way for the performance tuning of 2D WSe₂ devices via strain and applications of 2D WSe₂ in strain sensors.

CdTe/CdS thin film solar cells are the most promising cost-effective solar cells. The goal of this project is to improve the performance for CdS/CdTe devices by improving the open circuit voltage Voc and current density Jsc. Efforts focused on increasing the Voc, which include increasing the doping concentration by introducing Phosphorus and Antimony, finding and testing new back contact materials, and varying the ambient of CSS CdTe. In addition, the effect of Zn2SnO4 on the cells' performance was also studied. Electrical characterization of the thin films and completed devices were carried out by Current-Voltage (J-V), Capacitance-Voltage (C-V), and Spectral Response (SR) measurements. Structural/chemical characterization was done by SEM, XRD and EDS analysis. The ambient of CSS CdTe affects the growth rate, the grain size and electronic properties of CdTe. The N2/O2 mixture with varied ratio (N2/O2=9/1, 7/3, 5/5 and 1/9) was used in this study. The cells' performance and the net carrier concentration were studied as a function of the N2/O2 ratio. The net carrier concentration increases with the increasing O2 concentration. The extrinsic impurities (P and Sb) were incorporated into CdTe layer. Phosphorus was directly introduced into CSS CdTe source. The Sb was incorporated into CdTe by a diffusion process. The effects of the annealing parameters, the excess Sb on CdTe surface, the CdCl2 treatment and the depth of Sb in CdTe were studied. Higher doping concentration up to 1016 cm-3 has been achieved, however, Voc is still in the range of 830 mV.

Metal-organic nanotubular (MON) materials have garnered significant attention in the recent years not only due to the aesthetic architecture but also due to the interesting chemical and physical properties that have been reported for these compounds. The number of MONs reported in the literature are limited compared to metal organic frameworks due to synthetic challenges and difficulties in crystal engineering. These types of materials are of interest given their one-dimensional channels that lead to their potential application in advanced membrane technologies. In Forbes group, a uranium-based metal-organic nanotube (UMON) was synthesized using zwitterionic like iminodiacetic acid (IDA) as the ligand. IDA ligand chelates to the U(VI) metal center in a tridentate fashion and doubly protonated IDA linker connects the neighboring uranyl moieties until it forms hexameric macrocycles. These macrocycles stack into a nanotubular array due to supramolecular interactions. Single crystal X-ray diffraction studies displayed there are two crystallographically unique water molecules that can be removed reversibly at 37 °C. UMON indicated selectivity to water, the selectivity of this material was analyzed using solvents with different polarities, sizes, and shapes. In the current body of work, dehydrated UMON crystallites were exposed to these solvents (in liquid and vapor phase) and studied using TGA coupled FTIR set up, confirming the highly selective nature of UMON. Kinetic studies were also conducted using an in-house built vapor adsorption setup confirmed the water uptake rate of the nanotube depends on the humidity of the environment. Uptake rates were estimated using a simple kinetic model and indicated enhanced hydration compared to other porous materials. One of the hypotheses regarding the interesting properties of UMON is that the uranium metal center might play a central role in the selectivity of this material. To test this hypothesis, a similar uranium based metal-organic nanotube containing 2,6-pyridine dicarboxylic acid (UPDC) as the ligand was synthesized and its properties were compared to that of the UMON material. UPDC did display some selectivity based upon size exclusion but did not exhibit the same selectivity to water that is observed for UMON. Different transition metals were also incorporated into the nanotubular structures to determine the influence of dopants on the observable properties. Only small amounts of transition metal dopants were incorporated into the structure, but it increased the stability under high humid environment. Attempts to incorporate transition metal dopants in the UPDC led to the formation of novel chain structures.

<p> </p><p>Organic semiconductors are prime candidates for thermoelectric applications, because one can maximize the dimensionless figure of merit ZT (by maximizing the Seebeck coefficient and electrical conductivity) while simultaneously minimizing the thermal conductivity. In this work, we explore a few materials and try to find their thermoelectric characteristics. For the n-leg of the thermogenerator, we studied a modified fullerene (PCBM) which is doped with TDAE vapor. For the p-leg, we studied PEDOT and found the TDAE dedoping level at which the figure of merit is maximized.</p>

Graphene, a one-atom-thick sheet of hexagonally packed carbon atoms, is a novel material with high electron mobility due to its unique linear and gapless electronic band structure. Its broadband absorption and unusual doping properties, along with superb mechanical flexibility make graphene of promising application in optoeletronic devices such as solar cell, ultrafast photodetectors, and terahertz modulators. How- ever, the current performance of graphene-based devices is quite unacceptable owning to serious limitations by its inherently small absorption cross section and low quan- tum efficiency. Fortunately, nanoscale optical antennas, consisting of closely spaced, coupled metallic nanoparticles, have fascinating optical response since the collective oscillation of electrons in them, namely surface plasmons, can concentrate light into a subwavelength regime close to the antennas and enhance the corresponding field considerably. Given that optical antenna have been applied in various areas such as subwavelength optics, surface enhanced spectroscopies, and sensing, they are also able to assist graphene to harvest visible and near-infrared light with high efficiency. Moreover, the efficient production of hot electrons due to the decay of the surface plasmons can be further implemented to modulate the properties of graphene. Here we choose plasmonic oligomers to serve as optical antenna since they pos- sess tunable Fano resonances, consisting of a transparency window where scattering is strongly suppressed but absorption is greatly enhanced. By placing them in di- rect contact with graphene sheet, we find the internal quantum efficiency of hybrid antenna-graphene devices achieves up to 20%. Meanwhile, doping effect due to hot electron is also observed in this device, which can be used to optically tune the elec- tronic properties of graphene.

Organic semiconductors are prime candidates for thermoelectric applications, because one can maximize the dimensionless figure of merit ZT (by maximizing the Seebeck coefficient and electrical conductivity) while simultaneously minimizing the thermal conductivity. In this work, we explore a few materials and try to find their thermoelectric characteristics. For the n-leg of the thermogenerator, we studied a modified fullerene (PCBM) which is doped with TDAE vapor. For the p-leg, we studied PEDOT and found the TDAE dedoping level at which the figure of merit is maximized.