Hydrophilic properties of hydro-oxygenated TiOx films prepared by plasma enhanced chemical vapor deposition

The hydrophilicity of the hydro-oxygenated amorphous TiOx (a-TiOx:OH) films, in which the dangling bonds at defects were inactivated by the termination with OH groups, was investigated. The a-TiOx:OH films were prepared by plasma enhanced chemical vapor deposition method. It was found that the a-TiOx:OH films, which showed good hydrophilicity at as-deposited state, recovered the initial hydrophilicity by UV light irradiation even if it deteriorated during long storage in dark. The recovery of hydrophilicity by UV light irradiation was recognized both in ambient air and in O2. Photo-response to the electrical conductivity of the a-TiOx:OH films was getting worse along with increase in O2 pressure, suggesting the consumption of the photo-excited carriers by O2 molecules during UV light irradiation. Considering the electron-withdrawing property of O2 molecules, it is deduced that the photo-excited electrons easily reacted with O2 to result in O2− species, which have strong oxidation power. These imply that the recovery of the hydrophilicity for the a-TiOx:OH films was achieved by the decomposition of hydrophobic adsorbates on the film surface during UV light irradiation. Moreover, it is supposed that for the a-TiOx:OH films, O2 molecules play an important role for recovering the hydrophilicity under UV light irradiation.