Thin film deposition of pure and doped TiO2 by RF magnetron sputtering for visible light photocatalytic and optoelectronic applications
Three different ways to dope nitrogen into TiO2 by means of RF reactive sputtering was compared, and the structural, optical, and photo-active performance of these materials were explored. First, multi-layered thin films of TiO2 and TiN were prepared by sputtering a titanium target and alternating oxygen and nitrogen reactive gases in the deposition chamber. The total thickness of each multi stack was kept constant while the overall composition of the films (TiN to TiO2 ratio) was varied between 5% and 30% and the number of TiN/TiO2 bi-layers was increased from 9 to 45. Secondly, we prepared N-TiO2 by introducing oxygen and nitrogen reactive gases simultaneously during the depositions. The ratio of oxygen to nitrogen was systematically changed in order to control the concentration of nitrogen incorporation into the films between 0% and 6%. Finally, we prepared TiN thin films and oxidized them at different temperatures and for several time intervals. X-ray photoelectron spectroscopy showed that nitrogen was successfully doped into all of the TiO2 films in substitutional and/or interstitial sites depending on the deposition conditions. The variance in the concentration and position of the nitrogen doping had a significant effect on the optical, structural and photoactive properties of the three types of N-TiO2 films. The parameters of sputtering deposition were optimized using both plasma diagnostics and Design of Experiments. This study has shown the desirable ability to control several important physical and chemical characteristics of N-TiO2 films, with considerable promise for many applications