Influence of argon flow rate on TiO2 photocatalyst film deposited by dc reactive magnetron sputtering

Titanium oxide films were deposited at different argon flow rates by dc reactive magnetron sputtering. A lower oxygen flow rate threshold could be achieved at a higher argon flow rate. The substrate temperature was approximately 130 °C after 5 h deposition. The deposited TiO2 films were of the anatase phase with a (220) preferred orientation. The crystallite sizes of the films were 17.7, 15.3 and 13.5 nm for the films deposited at argon flow rates of 5.66, 9.91 and 14.15 ml/min, respectively. Fine nano-crystalline TiO2 with nano-sized holes among the crystalline particles were shown in the SEM images. The XPS spectra of the Ti2p and O1s regions showed that the titanium in the TiO2 film was Ti4+ and the oxygen was composed of O2− in TiO2 and H2O. The deposited TiO2 films exhibited quantum size effects and their band edges had a significant blue shift to lower wavelength region. Compared with the film deposited at argon flow rate of 5.66 ml/min, the UV-visible transmittance increased less than 5% and the reflectance decreased more than 10% below the wavelength of 400 nm for the film deposited at argon flow rate of 14.15 ml/min. The photocatalytic activity was enhanced when the argon flow rate increased, owing to more light being absorbed and more electrons and holes being generated.