Bloor, LG; (2012) On the Synthesis and Chemical Vapour Deposition of Group 13 Precursors Towards Metal Oxide Thin Films. Doctoral thesis , UCL (University College London).

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Abstract

Various routes towards novel chlorogallium bis(alkoxides) and heteroleptic gallium alkoxides have been investigated. Compounds of the type, [GaCl(OR2)2] and [Ga(OR2)2(OR’)] (R = CH2CH2NMe2, CH2CH2NEt2, CH2CH2CH2NMe2; R’ = Me, Et, iPr, tBu), were synthesised using air sensitive methods and analysed by a variety of techniques. The chlorogallium bis(alkoxides) showed diastereotopic NMR splitting and in depth 1H NMR studies and DFT calculations were carried out on [GaCl(OCH2CH2CH2NMe2)2] to investigate the in situ ring conversion mechanism. Thermogravimetric analysis was employed to study the decomposition characteristics of the compounds, which were then used as single-source precursors towards gallium oxide thin films using aerosol-assisted chemical vapour deposition (AACVD). Amorphous, transparent films of Ga2O3 were deposited at 450 °C onto glass and quartz substrates. Subsequent annealing at 1000 °C gave crystalline films. Nitrogen-doped indium oxide films were deposited by AACVD via the in situ reaction of [In{NtBu(SiMe3)}3] and three equivalents of HOCH2CH2NMe2. The resultant films had a range of morphologies depending on solvent and temperature employed during the deposition. The cubic phase In2O3 films deposited had band gaps of ~2.9 eV suggesting nitrogen incorporation. These films were tested on steel and titanium substrates for their visible light water-splitting properties. Films were tested for their hydrogen production but limited activity as a photocatalyst was observed in the visible region. However, In2O3 nanoparticles produced using a solvothermal method and Ti- and Ta-doped In2O3 thin films grown via AACVD were tested for their gas sensing properties. Sensors were tested against reducing oxidising gases. The In2O3 nanoparticles showed the highest response to all gases, in particular ethanol. In2O3:Ta also showed a significant response to ethanol and smaller responses to other gases. Overall, novel precursors have been used as single-source precursors to main group oxide thin films, which were deposited via AACVD. Photocatalytic and gas sensing applications of these films have been explored.

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