Mears, Kristian Luke; (2021) The Synthesis and Reactivity of Mixed-Metal Precursors towards Oxide Materials. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

This work is concerned with the synthesis of precursors to aluminium and gallium oxide thin films, and the subsequent aerosol-assisted chemical vapour deposition (CVD) of the corresponding oxide films. Investigations into precur- sor formation for mixed-metal oxide thin films, specifically those containing copper and either aluminium or gallium is also discussed. The synthesis of aminoenoate pro-ligands with varying steric demand, referred to as (HAMEX), where X = iPr, isopropyl; Dip, 2,6-diisopropylphenyl at the N-position was carried out. These pro-ligands were converted to their corre- sponding lithium salts in a metathesis reaction with relevant metal trichlo- ride. These reactions lead to the isolation of a library of aluminium or gallium amidoenoate complexes with the general formula {MCl2(AMEX)}, {MCl(AMEX)2}, M = Al, Ga; X = iPr, Dip. The reactivity of the metal-amidoenoate chlorides was investigated via reac- tions aiming to convert the chloride to a hydride. Various reagents were used with partial success including the isolation of an aluminium hydride species, {AlH(AMEDip)2}. Where the conversion route to the hydride was unsuccess- ful, other reactive alkyl groups were installed, leading to the isolation of the complexes {GaMe2(AMEiPr)} and {GaMe2(AMEDip)}. A selection of the Gp 13 amidoenoates were used to deposit the corresponding oxide material (α-Al2O3 and β-Ga2O3) using aerosol-assisted chemical vapour deposition. The films deposited had excellent element ratios and were not oxygen deficient after post-deposition annealing at 1000◦C. Despite likely carbon/chlorine contamination, band gap calculations showed that the de- posited materials had a band gap value of > 3.1 eV and hence, were optically transparent. A synthetic investigation into mixed-metal precursors containing copper and either aluminium or gallium was carried out. Two routes were taken in order to probe these systems. The first route explored connecting the metals via bridging heteroatoms including chlorides and hydrides. The second route at- tempted to directly bond the Gp 13 metal with a copper centre. Significant findings include that depending on the ligands at the metal centres, a variety of synthetic outcomes are possible. These included the formation of tetrakis- salts, main-group hydride species and formally bonded {Cu–Al} and {Cu–Ga} complexes.

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