Browsing by Subject "Boron compounds"
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Item Adventures in main group chemistry: from molecules to materials(2008-05) Findlater, Michael; Cowley, Alan H.Three synthetic methods have been explored for the preparation of several novel boron-substituted amidinates and guanidinates. The extension of heterocumulene insertion chemistries to boron-aryl, boron-metallocene and boron-transition metal moieties has also been achieved and the mechanism of such insertions is addressed via density functional theory modeling techniques. The reactivity of these complexes is also explored, mainly through halide abstraction methodologies to generate boron cations, which are potent Lewis Acids and may be useful in promoting organic transformations or in the polymerization of ethylene. The synthesis and characterization of the elusive monomeric low valent carbenoid boron(I), a compound with a formal lone pair located upon the boron center, has been lacking. The suitability of the guanidinate ligand system to support such a species is also discussed and a combined experimental and theoretical approach to this highly topical problem is also presented. Thirdly, the use of photovoltaics (devices which convert solar energy directly into electricity) as an alternative source of energy outwith fossil fuel technologies is a rapidly growing area of interest. Initial efforts to use a novel approach, which incorporates inorganic nanocrystals wired into a conducting polymer matrix, are also presented. Successful synthetic approaches to the gallium, aluminum and indium monomeric precursors suitable for electropolymerization were developed. These compounds proved to be effective starting points for the generation of conducting polymers with embedded III/VI (Ga₂S₃) nanocrystals with further studies currently underway as to their III/V (InP, GaAs) compatriots. Finally, a retrospective of projects that may best be described in terms of the moniker "Loose Ends and Future Directions" will be presented. The aim of which will be to serve as a useful guidepost for further studies in the fields and topics discussed.Item Synthesis and characterization of group 13 & 15 complexes supported by N,N'-bidentate ligands(2007-12) Lu, Zheng, 1973-; Cowley, Alan H.The first example of an N,N'-chelated [beta]-diketiminato phosphenium salt has been isolated by careful tuning of both the ligand architecture and the electronic characteristics of the phosphorus containing moiety. Using a two-electron reduction approach, the first example of a phosphinidene valence isomer has been isolated and structurally characterized. The mechanism of formation of this valence isomer was elucidated via Density Functional Theory (DFT) calculations. These calculations revealed that the formation of this valence isomer involves the intermediacy of a triplet diradical. In turn, the triplet diradical decays by two further steps to generate the observed product. A cationic phosphinous acid has been prepared via the hydrolysis of a cationic phosphenium complex in basic solution. DFT calculations reveals that the introduction of a positive charge stabilizes the phosphinous acid form. Two N,C-bonded phosphenium cation salts have also been obtained, the crystal structures of which reveal that the formation of these compounds involves C-H activation of a methyl group on the [beta]-diketiminate ligand. Three synthetic methods, namely halide abstraction, aluminum/boron halide exchange process and salt metathesis, have been explored for the preparation of boron cations supported by [beta]-diketiminate ligands. The first structurally characterized boron cation supported by a [beta]-diketiminate ligand has been isolated as its [Al₂Cl₇]⁻ salt. A Ga-Fe organometallic complex supported by a [beta]-diketiminate ligand has also been synthesized via salt metathesis reaction and fully characterized. Finally, several bisamidinate supported boron complexes have been synthesized and structurally characterized. Such complexes may have applications as bifunctional catalysts or as building blocks for novel polymers.Item Ultra-shallow junction formation : co-implantation and rapid thermal annealing(2002-08) Li, Hong-jyh; Banerjee, SanjayBoron diffusion and activation in the presence of co-implanted species are studied experimentally and theoretically (ab initio Molecular Dynamics simulations and SUPREM diffusion process simulator) in this dissertation. Simulation results imply that B diffusion and activation in the presence of coimplanted species can be affected through both the electronic and strain compensation effects and the theoretical prediction is consistent with experimental data. In the presence of co-implanted species, the electronic bonding between B and the co-implant species makes it energetically unfavorable for B to migrate when it comes close to the co-implant species. The bonding can be characterized by the electronegativity difference between B and the coimplanted species. The strain effect, on the other hand, indicates that B tends to stay close to the larger co-implant species (In, for example) so that the strain caused by the size misfit of In and Si can be compensated by the smaller B atom. In order to have both the above factors be effective in B diffusion reduction, we need to increase the concentration of the co-implant species in order to maximize the B diffusion reduction with the co-implant technique. Experiments on B diffusion and activation in the presence of Al, Ga, In, Ge, F and C, with or without capping layers (oxide, nitride or Si), are conducted in this research. Those species are incorporated into Si either by ion implantation or Chemical Vapor Deposition (CVD) process. Boron and co-implant diffusion and activation is studied Rapid Thermal Annealing (RTA) for various process parameters such as ramp-up rate, soak time and peak temperature. Fundamental studies on the interaction of B, defects and the co-implanted species are also included in this dissertation.