Edusi, C; (2014) Aerosol assisted chemical vapour deposition of titanium dioxide and tungsten oxide thin films. Doctoral thesis , UCL (University College London).

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Abstract

This thesis focuses on the Aerosol Assisted Chemical Vapour deposition (AACVD) of titanium dioxide (TiO2) thin films using titanum (IV) isopropoxide (TTIP) and also reports the deposition of tungsten oxide via AACVD using tungsten hexacarbonyl [W(CO)6] in different solvents including methanol and ethanol. Chapter 1 of this thesis gives an overview of TiO2, including its properties and functions and the motivation for this project. In chapter 2 brief descriptions are provided of the main characterisation techniques used throughout this thesis. The substrate and solvent effect on the phase of TiO2 obtained by AACVD is outlined in chapter 3 and 4. TiO2 was deposited via the AACVD of TTIP in different solvents including methanol, ethanol and other solvents. The films deposited showed some substrate dependent morphology and properties. In particular at 550°C the films on steel show needle and rod like particles. XRD and Raman spectra of the TiO2 films showed that on steel or titanium substrates only the rutile form could be obtained, whereas on glass either anatase, anatase-rutile mixtures or rutile could be obtained depending on substrate temperature. Using methanol as the carrier solvent produced exclusively the rutile films on steel and predominantly rutile on glass substrates while the use of the other solvents produced exclusively the anatase phase on the steel under the same conditions. TiO2 was also deposited by AACVD from a mixture of ethanol and methanol solvents. As little as 15% of methanol in ethanol produces rutile as the predominant phase. The photocatalytic properties and the hydrophilicity of the films deposited are also reported. X-ray absorption spectroscopy (XAS) was used to map across the surface of the TiO2 films deposited as described in chapter 5. The X-ray absorption near edge structure (XANES) was used to determine the phase of TiO2 present at each point on the substrate. The AACVD deposition tungsten oxide using tungsten hexacarbonyl (W(CO)6) in methanol and ethanol is reported in chapter 6. Preferred orientation was observed when using either ethanol or methanol as the carrier solvent. In chapter 7 insitu work was attempted to investigate the mechanism of the deposited titania and tungsten oxide films. A new reactor vessel was designed, constructed and tested to allow synchrotron radiation in and out using a kapton window. The XANES pattern recorded during in-situ deposition were not of high enough to resolve the mechanism. The in-situ work carried out has great potential in the growth study of thin film deposition and can in the future help control the phase and composition of deposited films to produce more desirable properties.

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