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Cadmium sulfide and cadmium selenide are important materials for applications such as photoconductive cells, photovoltaic cells and other electrooptical devices. Generally, these devices use single crystals. However, reasonable efficiencies have been observed by using polycrystalline films on conducting substrates, which are easier to make and provide considerable savings on materials and energy. Polycrystalline CdS/CdSe films have been made by sputtering and solution spraying, compound evaporation, chemical vapor deposition, and many others. A recent technique involves the electrochemical deposition of CdS and CdSe from nonaqueous solvents. Preparation of these films is based upon the cathodic deposition from a nonaqueous solution of a cadmium salt and elemental sulfur and/or selenium. Although the technique is simple, no mechanistic information is known to optimize the conditions in which films of controlled stoichiometry, doping and crystallinity are made. This research has the purpose to understand the mechanism of the formation of polycrystalline films of CdS and CdSe by electrochemical deposition in dimethylsulfoxide. This approach to the problem makes use of electrochemical techniques such as rotating ring disc electrode, linear scan voltammetry, high pressure liquid chromatography coupled with ultraviolet and electrochemical detection. By the rotating ring disc electrode technique, we have studied the kinetic parameters for the reduction of sulfur, selenium, cadmium, and the electroChemical formation of CdS and CdSe for temperatures from 25 - lOO°C. The results show that rates of initie.l electron transfer for the reduction of these species are moderately rapid, and secondly, that the reverse reaction is irreversible and involves additional steps. Studies of solubility of selenium with temperature reveal that its solubility is enhanced by the addition of sulfur. Understanding the electrochemical behavior of sulfur-selenium mixtures is of great importance to produce mixed semiconductive films with more adequate bandgaps for use with solar spectrum. Electrochemistry of sulfur-selenium mixtures are no different from that of sulfur alone. High pressure liquid chromatography separations with spectroscopic and electrochemical detectors have shown that sulfur solutions contain 86 and 87 fractions which are not electrochemically active.

Methyl-functionalized porous silica is of considerable interest as a low dielectric constant film for semiconductor devices. The structural development of these materials appears to affect their gelation behaviors and impact their mechanical properties and shrinkage during processing. 29Si solution NMR was used to follow the structural evolution of MTMS (methyltrimethoxysilane) polymerization to gelation or precipitation, and thus to better understand the species that affect these properties and gelation behaviors. The effects of pH, water concentration, type of solvents, and synthesis procedures (single step acid catalysis and two-step acid/base catalysis) on MTMS polymerization were discussed. The reactivity of silicon species with different connectivity and the extent of cyclization were found to depend appreciably on the pH value of the sol. A kinetic model is presented to treat the reactivity of both silicon species involved in condensations separately based on the inductive and steric effects of these silicon species. Extensive cyclization in the presence of acid, which was attributed to the steric effects among numerous reaction pathways for the first time, prevents MTMS gelation, whereas gels were obtained from the two-step method with nearly random condensations. The experimental degree of condensation (DC) at the gel point using the two-step procedure was determined to be 0.86, which is considerably higher than that predicted by the current accepted theories. Both chemical and physical origins of this high value were suggested. Aerogels dried by supercritical CO2 extraction were characterized by FTIR, 13C and 29Si solid-state NMR and nitrogen sorption. The existence of three residual groups (Si-OH, Si-OCH3, and Si-OC2H5) was confirmed, but their concentrations are very low compared to silica aerogels. The low concentrations of the residual groups, along with the presence of Si-CH3, make MTMS aerogels permanently hydrophobic. To enhance applicability, MTMS aerogels were successfully prepared that demonstrated shrinkage less than 10% after supercritical drying; proving that the rigidity of the gel network is not the sole factor, suggesting in the literature, to cause the huge shrinkage in many hybrid aerogels reported. An important finding of this work is that MTMS aerogels can be prepared without tedious solvent exchange and surface modification if the molar ratio of water/MTMS increases to 8, substantially reducing the cost of aerogel production. This result was attributed to MTMS's fully condensation and low concentrations of ring species.

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by Kwong-hung Tam = 低壓化學氣相沈積硅膜之電學特性 / 譚廣雄. / Thesis (M.Ph.)--Chinese University of Hong Kong, 1985 / Bibliography: leaves 102-105. / by Kwong-hung Tam = Di ya hua xue qi xiang chen ji gui mo zhi dian xue te xing / Tan Guangxiong.

Current leading thin-film solar cell technologies, i.e., cadmium telluride (CdTe) and copper indium gallium diselenide (CIGS), employ elements which are either toxic (Cd), or rare and/or expensive (In, Te, Ga, and Cd). The aim of this thesis is to investigate new, abundant, non-toxic p-type semiconductors for potential solar absorber application. Two ternary chalcogenides, Cu���PSe��� and CuTaS���, were selected for their attractive calculated optical absorption properties. Thin films of both materials were synthesized using physical vapor deposition (PVD) techniques in conjunction with post-deposition annealing. Cu���PSe��� appears promising for solar absorber applications, with a measured optical bandgap of 1.2 eV, an absorption coefficient (��) reaching 10��� cm�����, Hall mobilities of 19.8���30.3 cm��/V���s, and carrier concentrations of 3.3���4.9 10����� cm�����. Optical characterization of CuTaS��� thin-films showed a rapid turn-on of absorption, with �� exceeding 10��� cm����� within 0.5 eV of the bandgap. To date, reproducible synthesis of CuTaS��� thin films has been problematic. Moreover, these films are insulating and thus not yet appropriate for thin-film solar cell absorber applications. / Graduation date: 2013

Thesis (Ph. D.)--University of Missouri-Columbia, 1999. / Typescript. Vita. Includes bibliographical references (leaves 147-152). Also available on the Internet.

Thesis (Ph. D.)--Mississippi State University. Department of Electrical and Computer Engineering. / Title from title screen. Includes bibliographical references.

Thesis (M.S.) in Electrical Engineering--University of Maine, 2001. / Includes vita. Includes bibliographical references (leaves 128-129).

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