Drosos, C; (2017) Chemical vapour deposition of thin film metal oxides on glass: exploring methods toward enhanced functionality. Doctoral thesis , UCL (University College London).

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Abstract

This thesis describes the optimization of the synthesis of thin films from various precursors within a novel APCVD setup. Since, the latter was essential to be built for the needs of the current project, fine tuning deposition parameters, e.g. temperature flow rates, as well as screening precursors with the ability to block the stainless-steel lines were monitored. Moreover, volatility of precursors, decomposition and deposition temperature profiles were examined thoroughly. A novel APCVD pre – reactor was established. Several steps included such as, DMADV (Define-Measure-Analyse-Design-Verify) methodology to increase the end product’s ability to produce results that would meet industrial standards. A key objective of the project was to elucidate the temperature profiles related to composition and decomposition of various materials (precursors, dopants, oxidants). A large list of materials was covered such as, titanium (IV) isopropoxide, tert-butylamine, niobium (V) ethoxide, vanadyl acetylacetonate, ammonium tungsten, iron (0) pentacarbonyl, tungsten hexacarbonyl, dimethyl sulfide (DMS) and vanadium oxytriisopropoxide. The optimisation of the pre-reaction system allows us to optimise deposition temperature, pressure and growth rate much faster and with better accuracy. A brief example of the latter, would be the evaluation of the deposition and decomposition process of the proposed precursor. The temperature profile of each precursor may contribute to a better screening of the chemical process. Our goal was to check on certain process parameters what would each precursor result after each experiment. Eventually, the outcome helped us to understand whether a reaction might produce powders during or after the experimental process, contributing to a safer and faster industrial procedure. The objective in forming TiO 2 coatings was to deposit barrier layers that reduce ion migration from the surface of glass bottles during a caustic wash. An additional function of these coatings was to prevent skunking in beer (anti-skunking coatings) or light struck flavour (LSF), is the result of a complex photocatalysed chemical change not yet fully understood mechanistically. This can be inhibited by reducing UV and short wavelength visible light transmittance. Moreover, in terms of industrial application of thin films of TiO 2 , low friction coatings can inhibit breakages, increase production line speed and ease additives removal. Self-cleaning surfaces would ease the wash process and finally, coloured coatings can increase aesthetics. As for Fe 2 O 3 coatings the main objectives were mainly to produce anti – skunking coatings. Investigating a range of precursors gave us the opportunity to test both the capabilities of the pre – reactor in order to ensure parameters found from the APCVD pre – reactor is comparable with those used in the industrial scale APCVD reactor. Finally, using a newly developed technique, a modified APCVD reactor and a molecular beam mass spectrometer were used in tandem to investigate the deposition of titanium dioxide in order to better understand the decomposition reactions that occur inside the reactor chamber. Monitoring chemical reactions during APCVD allowed us to gain a unique insight into the decomposition mechanism for several precursors at a range of conditions (mass flow rate, temperature etc) and can assist industry form new synthetic pathways or optimise existing routes. A two – way function of the newly founded system was established; film throughput alongside with screening of the chemical synthesis with in – situ with the Mass Spectrometer. Dibutoxydiacetoxy silane (DBDAS), a precursor for the deposition of SiO 2 thin films was passed through the reactor - spectrometer system in order to better understand the deposition mechanism. Additionally, TTIP and TiCl 4 vapour phases were examined and analysed by the mass spectrometer, in – situ during decomposition and the formation of thin films for the first time.

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