Hydrophilicity of hydro-oxygenated amorphous TiOx films prepared by plasma enhanced chemical vapor deposition

Hydrophilicity of the amorphous TiOx thin films, which were prepared by plasma enhanced chemical vapor deposition, was investigated in connection with the electrical conductivity measurements in various gas media. In vacuum, the photoexcited current of the obtained films was 7 orders higher than the dark one, in spite of the amorphous state. This suggests that the dangling bonds at defects in the films were inactivated by the termination with OH groups, which was observed by the FT-IR spectra. Hence, we refer to the obtained films as hydro-oxygenated amorphous TiOx (a-TiO x:OH) films in analogy with a-Si:H. In oxygen atmosphere, the photoexcited current of the a-TiOxOH films drastically decreased, suggesting that the photoexcited carriers were consumed preferably by oxygen in ambient air. UV light irradiation in oxygen atmosphere also recovered the film hydrophilicity. It is well known that .O2- species, which would be generated by UV light irradiation in oxygen atmosphere, have strong oxidation power. Thus, it is deduced that the hydrophilicity of the a-TiO x:OH films was recovered by the photo-catalytic decomposition of hydrophobic adsorbates on the film surface.