Chemical vapor deposition of alumina-based thin films
Fahlman, Bradley Dean
Barron, Andrew R.
Doctor of Philosophy
Deposition of highly conformal alumina thin films onto various substrates was carried out by hydrolysis of AlH3(NMe2Et) in a hot-wall atmospheric pressure chemical vapor deposition (APCVD) system. Optimum growth conditions were at 165°C with a AlH3(NMe 2Et):H2O ratio of less than 1:25. Films were characterized by SEM, microprobe and electrical conductivity measurements. Deposition of hermetic coatings onto ZnS EL-phosphor particles was accomplished in a simple fluidized-bed APCVD reactor. Chromium-doped alumina (ruby) thin films were deposited onto sapphire substrates using a mixture of Al(acac)3 and Cr(acac)3 precursors with added oxygen sources. APCVD with water vapor resulted in smooth films that were visibly colored following thermal annealing. Substituting water vapor with [Me2Al(mu-OiPr)]2 in vacuo increased growth rates and produced films with improved color homogeneity. The observed intensity of the ruby fluorescence was found to increase with post-deposition annealing. The sublimation enthalpies for a variety of metal beta-diketonate compounds were determined using thermogravimetric analysis. Replacing methyl groups with CF3 units increased the volatility of the particular complex in the order acac < tfac < hfac. The refinement of the Al:Cr site occupancy in mixed AlxCr y(acac)3 crystals was accomplished by various methods. Refinement of occupancy with common displacement parameters and refinement of both occupancy and displacement parameters were found to agree with WDS data within experimental error for all crystals studied. A facile chalcogenide exchange is observed for the reaction of [( tBu)Ga(mu3-Te)]4 with elemental sulfur or selenium, resulting in the stoichiometric formation of the appropriate cubane, [(tBu)Ga(mu3-E)]4 (E = S, Se), and metallic tellurium. The rate of the chalcogenide exchange is dependent not only on the chalcogen, but also the allotropic form of the chalcogen. The exchange reaction is proposed to be heterogeneous in nature and involves the opening of the cubane core. The reaction of [(R)Ga(mu3-Te)] 4 with an oxygen source ultimately produces the galloxane nonamer or hexamer, depending on the size of the alkyl group. Density functional theory (DFT) calculations supported the experimental observations and mechanistic proposals for chalcogenide exchange reactions. The intermediate species formed during sequential oxygen exchanges are predicted to have extremely distorted and relatively unstable structures allowing for the rearrangement to larger galloxane cages.
Inorganic chemistry; Chemical engineering