Crystallinity and photocatalytic activity of TiO2 films deposited by reactive sputtering with radio frequency substrate bias

TiO2 films with thicknesses of 400–460 nm were deposited on the unheated non-alkali glass by radio frequency (rf) reactive magnetron sputtering using a Ti metal target. Depositions were carried out using a 3-in. 1000 G magnetron cathode with various rf substrate bias voltages (Vsb, dc component of self bias) of 10–80 V under total gas pressure of 1.0 or 3.0 Pa. The oxygen flow ratio [O2/(O2 + Ar)] and rf sputtering power were kept constant at 60% and 200 W, respectively. Photocatalytic activity on photoinduced oxidative decomposition of acetaldehyde (CH3CHO) of the TiO2 films showed a clear tendency to decrease with the increase in the Vsb during the deposition. Most of the films consisted of the mixture of anatase and rutile polycrystalline portions. It was confirmed that the rutile phase content increased and anatase phase content decreased markedly with increasing Vsb, where the crystallinity of anatase phase was much higher than that of rutile phase.