Th. 3e cycle--Sci. des matér.--Toulouse--I.N.P., 1984. N°: 198.

Th. doct.-ing.--Physico-chim. des matér.--Toulouse--I.N.P., 1980. N°: 79.

Th.--Sci.--Toulouse 3, 1981. N°: 1014.

Th. 3e cycle--Physico-chim. des matér.--Toulouse--I.N.P., 1978. N°: 27.

No description available.

This PhD thesis is focused on the development of novel catalysis with low-oxidation main group species, mainly based on the group 13 element gallium, a relatively abundant, inexpensive, and low-toxic metal. Gallium in its stable high-oxidation state ‘+III’ is a commonly used Lewis acid catalyst in organic synthesis. In contrast, gallium in its less stable low-oxidation state ‘+I’ is under-explored, but may display both acceptor and donor properties at a single site (ambiphilicity). Based on the hypothesis that potentially ambiphilic gallium(I) –oxidatively generated in situ from gallium(0) using a silver salt– may activate both basic and acidic reagents, various gallium(I)-catalyzed carbon–carbon bond formations have been developed. These include catalytic C–O and C–B bond activations of electrophiles (acetals and aminals) and pro-nucleophiles (allyl and allenyl boronates), respectively. Gallium(III) and other metal Lewis acids have proved to be ineffective. These results represent the first catalytic use of gallium(0) in organic synthesis and a rare example of gallium(I) catalysis. The identity of the gallium(I) catalyst and its regeneration have been confirmed by 71Ga NMR analysis, and a reactive allyl–Ga(I) intermediate has been detected for the first time. In combination with 11B NMR and HRMS analyses, an SN1 reaction mechanism has been proposed. Importantly, the potential for asymmetric gallium(I) catalysis has been demonstrated using a chiral silver co-catalyst (40% ee). This gallium(I) chemistry has proved to be applicable to the catalytic activation of other electrophiles, including ethers or aldehydes, and pro-nucleophiles such as boranes, silanes, or tin-based reagents. Finally, the potential of a related low-oxidation aluminium catalyst has been explored for C–C bond formation.

abstract: Nanowires are 1D rod-like structures which are regarded as the basis for future technologies. III-V nanowires have attracted immense attention because of their stability, crystal quality and wide use. In this work, I focus on the growth and characterization of III-V semiconductor nanowires, in particular GaP, InP and InGaP alloys. These nanowires were grown using a hot wall CVD(Chemical Vapor Deposition) setup and are characterized using SEM (Scanning Electron Microscope), EDX (Energy Dispersive X-ray Spectroscopy) and PL (Photoluminescence) techniques. In the first chapter, Indium Phosphide nanowires were grown using elemental sources (In and P powders). I consider the various kinds of InP morphologies grown using this method. The effect of source temperature on the stoichiometry and optical properties of nanowires is studied. Lasing behavior has been seen in InP nanostructures, showing superior material quality of InP. InGaP alloy nanowires were grown using compound and elemental sources. Nanowires grown using compound sources have significant oxide incorporation and showed kinky morphology. Nanowires grown using elemental sources had no oxide and showed better optical quality. Also, these samples showed a tunable alloy composition across the entire substrate covering more than 50% of the InGaP alloy system. Integrated intensity showed that the bandgap of the nanowires changed from indirect to direct bandgap with increasing Indium composition. InGaP alloy nanowires were compared with Gallium Phosphide nanowires in terms of PL emission, using InGaP nanowires it is possible to grow nanowires free of defects and oxygen impurities, which are commonly encountered in GaP nanowires. / Dissertation/Thesis / Masters Thesis Electrical Engineering 2016

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