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Layered metal sulfides MoS2 and WS2 exhibit highly anisotropic surface chemistry. Adsorption of molecules is stronger on the atomic layer edges than on atomic planes. The edges are catalytically active in the petroleum hydrodesulfurization, while the layer planes are inert. Dispersing MoS2 and WS2 on the nanometer scale can also lead to the onset of photocatalytic properties due to the bandgap tuning by quantum confinement. In this work, we aim at determining how the adsorption on surface sites is altered for the nanoparticles compared to the bulk sulfides (micron-sized particles). A comparative study of the MoS2 and WS2 nanoparticles and bulk materials is done by attempting the adsorption of small molecules (N2, CO, acetone, and acetonitrile) to probe the surface sites. MoS2 and WS2 nanoparticles were synthesized by thermal decomposition of the metal hexacarbonyls in presence of sulfur in high-boiling solvents. The size range is 5-30 nm from Transmission Electron Microscopy. Transmission Infrared Spectroscopy was used to monitor the spectra of the probe molecules. A dedicated experimental setup has been constructed that consists of a high-vacuum chamber with a base pressure of 5×10-7 Torr. At the lowest achievable temperature of the sample (-145°C), N2, CO, and acetone were found to not adsorb strongly enough to be retained in vacuum on these materials. Acetonitrile was found to adsorb on these materials at -145°C and to desorb between -90°C and -50°C. The nanomaterial samples adsorbed significantly more acetonitrile than the corresponding bulk sulfides, as judged by the infrared signals intensity. Qualitatively, adsorbed acetonitrile species on nanodispersed and bulk sulfides are the same. It is likely that most of the adsorbed acetonitrile observed is physisorbed as ice or adsorbed on the sulfur-terminated terraces. At the final stages of desorprtion, distinctly different adsorbed species are seen whose CN stretching IR bands are shifted to higher frequencies. It is likely that these minority species are at monolayer or submonolayer coverages. The exact nature of the species requires further studies. / Department of Chemistry

The research presented in this dissertation focuses on chiral BINOL metal phosphatephosphoric acid catalyzed enantioselective additions of phosphorus and sulfur nucleophiles to imines and epoxides. In chapter 2, we reported a new method to synthesize chiral amino phosphine oxides. The reaction combines N-substituted imines and diphenylphosphine oxide catalyzed by chiral magnesium 9-antryl phosphate. A wide variety of aliphatic and aromatic aldimines substituted by electron neutral benzhydryl or dibenzocycloheptene groups were excellent substrates for the addition reaction. The imines protected with dibenzocycloheptene protecting group provided better enantioselectivity than those protected with benzhydryl group, while both imines gave comparable yields. Also, the substituted diphenylphosphine oxides were excellent nucleophiles obtaining chiral α-amino phosphine oxides in good yields and enantioselectivities. In chapter 3, we reported the first catalytic asymmetric method to prepare enantioenriched N,S-acetals catalyzed TRIP phosphoric acids. The reaction combined N-acyl imines with thiols to generate products in excellent yield and enantioselectivity. Electron-rich and electron-deficient aromatic N-acyl imines were excellent substrate for the addition reaction. A wide range of aliphatic and aromatic thiols obtained the N,S-acetals in excellent yields and enantioselectivities. The TRIP phosphoric acid was found to be an extremely efficient catalyst for the transformation, resulting in asymmetric induction at extremely low catalyst loading. In chapter 4, a highly enantioselective method for desymmetrization of meso-epoxides using thiols catalyzed by substituted BINOL lithium phosphate is reported. This is the first example of epoxide activation using metal phosphate is reported. Various five and six membered aliphatic cyclic meso-epoxides were excellent substrates for the desymmetrization reaction; aromatic acyclic epoxides also reacted with excellent yield and asymmetric induction. Similarly electron rich and electron deficient aromatic thiols obtained the β-hydroxyl sulfides in excellent yields and enantioselectivities.

This thesis contains primarily a study of CdTe/CdS heterojunction solar cells^ chiefly using photoluminescence spectroscopy. These solar cells show a good potential for commercial power generation in the near Aiture and are of interest to several major companies. A vital but little understood step in the manufacturing process is: annealing the cells in the presence of chlorine prior to back contact application. Studies are performed on a selection of thin film CdTe/CdS cells subjected to CdCl(_2) anneals of different duration. A chemical bevel etch was used to study the spectra at different depths into the sample and laser intensity arid sarhple temperature variations to identify the mechanisms behind the observed photoluminescence peaks. Evidence was found for the CdCl(_2) anneal promoting sulphur diffusion and subsequent grain boundary passivation in the CdTe, leading to increased minority carrier lifetimes and device efficiencies Attempts to obtain electroluminescence from the CdTe/CdS solar cells were madei By using current pulses electroluminescence was obtained in the 780-850nm range with discernible spectral features. Photoluminescence (PL) studies were also performed on a single crystal of CdTe grown to an unprecedented size of approx. 5 cm diameter at Durham university by a multi-tube seeded vapour method of crystal growth. Much higher resolution spectra were: obtained for this than for the solar cells. Several peaks were identified arid the mechanisms responsible were theorised. By taking slices of the crystal boule the PL spectra at different points-throughout the bulk of the crystal were determined. A series of high quality ion-implanted CdTe crystals were also studied! by intensity and temperature dependent PL in order to obtain a better understanding of the effects of known concentrations of known impurities on the PL spectra of CdTe. Specific PL features associated with certain dopants were observed.

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No description available.

Thesis (Ph.D.)--McMaster University (Canada), 1992. / Source: Dissertation Abstracts International, Volume: 54-02, Section: B, page: 0696.

Thesis (Ph.D.)--York University, 2006. Graduate Programme in Chemistry. / Typescript. Includes bibliographical references. Also available on the Internet. MODE OF ACCESS via web browser by entering the following URL: http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pqdiss&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&rft_dat=xri:pqdiss:NR19763

Thesis (Ph.D.)--Ohio University, November, 2006. / Title from PDF t.p. Includes bibliographical references.

Thesis (Ph. D.)--University of Washington, 2000. / Vita. Includes bibliographical references (leaves 239-244).