Synthesis, modelling and deposition of organic thin films

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Hairisha, Abulaiti
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University College Cork
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Organic and organic/inorganic hybrid thin film materials have various potential applications because they combine the distinct properties of organic and inorganic components. Molecular layer deposition (MLD) is a promising method to deposit high-quality uniform thin films composed of organic and organic/inorganic hybrid thin films. In this thesis, we use MLD to deposit acrylate based organic/inorganic hybrid thin films, which have many potential applications due to its strong adhesive properties. To achieve this goal, we simulate various precursors and their reactions for acrylate based MLD processes to find the most suitable precursors and to study the MLD reaction mechanism using density functional theory (DFT). The analysis based on DFT serves to facilitate and interpret the results from MLD experiments and various thin films characterization. We use computational techniques based on quantum chemical calculations to study the acrylate-based precursors and reactions for our MLD processes. We demonstrate acrylate-based hybrid organic/inorganic thin film growth on silicon (100) substrate with a new ABC-style MLD process employing trimethylaluminum (TMA), ethanolamine (EA) and vinyl methacrylate (VM) as precursors at the temperature of 70 to 150 °C. Appreciably uniform and smooth thin films were grown with thickness increasing linearly with MLD cycles. From the film thicknesses measured by SEM the maximum deposition rate of 1.7 Å per cycle was obtained for this MLD process. Surface morphology was investigated using AFM showing root-mean-square roughness of 8.9 Å. The hydrophilic property of the films increased with film thickness as identified by contact angle measurements. The structures predicted with DFT are consistent with the FTIR, Raman and XPS analysis, which show Al-N, N-Al-O and other chemical bonds in the thin films. The results from experiment and computation confirm that the proposed acrylate-based hybrid films were formed during the MLD process. As part of collaborative research project between CIC nanoGUNE and Tyndall, we also investigate the interactions of TMA and diethyl zinc (DEZ) with the organic functional groups –OH, –NH2 and –NO2 in the respective substituted phenyls, as well as their stability upon exposure to air. Secondly, we carry out DFT calculations to understand how DEZ and subsequently H2O react with Kevlar, and then find out how these structures influence Kevlar’s properties. We found that DEZ reacts with Kevlar so that fragments of DEZ form cross-links between chains of the Kevlar polymer. The original hydrogen bonds in Kevlar are replaced by stronger Zn-O and Zn-N bonds, which can explain the experimental finding that shows the ALD infiltrated kevlar remains its toughness when exposed to UV light.
Molecular layer deposition , Density functional theory , Organic thin films , Acrylates
Hairisha, A. 2017. Synthesis, modelling and deposition of organic thin films. PhD Thesis, University College Cork.