Study of photocatalytic activity of $TiO2$ thin films prepared in various $Ar∕O2$ ratio and sputtering gas pressure

In this study, various transparent $TiO2$ films were deposited on unheated glass-slide substrates by dc reactive sputtering technique. For one set of samples the ratio of Ar to $O2$ $(GR)$ was varied from 9:1 to 6:4 for a fixed sputtering pressure of $0.8Pa$⁠, while for another set of samples the total working pressure was varied from $0.2to0.8Pa$ for a fixed $GR$ of 7:3. The crystallographic and optical properties of $TiO2$ films were investigated in detail. The photocatalytic activity was evaluated by the measurement of decomposition of methanol under UV-visible irradiation. The structure of the $TiO2$ films, prepared with various $GR$⁠, varied from amorphous to different crystalline phases. Similarly sputtering pressure variation induced change of crystalline phase and crystallinity of $TiO2$ films. The crystallinity improved greatly with decreasing sputtering pressure. The average transmittances of all of the $TiO2$ films were almost constant for wavelengths in the range of $900–380nm$ for $GR$-varied thin films. The optical transmission edge of the $TiO2$ films deposited at various sputtering pressure shifts toward low wavelength with higher sputtering pressure. The as-deposited $TiO2$ films successfully photocatalyzed methanol to $CO2$ and $H2O$⁠, measured by Fourier transform infrared spectrometer. The decomposition efficiency of $TiO2$ films increased with increasing sputtering pressure. However, the photocatalytic efficiency of $TiO2$ films prepared at different $GR$ did not show any regular dependence. The high photocatalytic activity of the sample prepared with $GR=7:3$ at sputtering pressure of $0.8Pa$ was tried to be explained by the effect of surface morphology and pure anatase crystalline phase.