Effect of deposition conditions and doping on the structure, optical properties and photocatalytic activity of d.c. magnetron sputtered TiO2 thin films
The main topic of this thesis was to investigate the relationship between the microstructure and the photocatalytic activity of TiO2 thin films, with respect to the catalytic breakdown of volatile organic compounds. TiO2 thin films were deposited by d.c. magnetron sputtering from sub-stoichiometric, ceramic TiO2 targets. The as deposited films were found to be amorphous, as determined by x-ray diffraction (XRD), and a post deposition anneal treatment was needed to crystallize the films in the anatase phase. The physical properties and photocatalytic activity of the as deposited as well as the annealed films were studied. The thin film porosity, as determined from the refractive index, was found to be influenced by the deposition conditions and to be a major factor controlling the photocatalytic activity of the thin films, together with the thin film crystallinity. A second topic of this thesis was to study the effect of additives on the microstructure and properties of the TiO2 thin films. Doped TiO2 thin films were prepared by d.c. magnetron sputtering from sub-stoichiometric, ceramic M2O3/ TiO2 mixed oxide targets (M = Fe, Nd, V) and by ion implantation of TiO2 thin films with Fe and Nd. The deposition conditions of the thin films were fixed and the effect of the additive concentration in the target as well as the ion dose during implantation on the thin film properties were studied. For the ceramic TiO2 as well as the mixed oxide targets the sputtering behavior in Ar and Ar/ O2 atmosphere was determined which allowed to control the thin film deposition process. Since stoichiometric thin films could be deposited without the addition of O2 to the sputter gas, the thin films used for further characterization were deposited in a pure Ar atmosphere. In order to determine the photocatalytic activity of the thin films towards the breakdown of volatile organic substances in air, a dedicated batch reactor for testing of thin films in a controlled atmosphere was designed and characterized. As a measure for the photocatalytic activity of the thin films, the initial breakdown rate of ethanol during UV illumination was used.
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