Enhanced effect of vacuum-deposited SiO_(2) overlayer on photo-induced hydrophilicity of TiO_(2) film

摘要

Photo-induced hydrophilicity of SiO_(2)/TiO_(2) multilayer film prepared by using the vacuum deposition method was investigated by means of water contact angle measurement. Using black light irradiation of the films centering at a wavelength of 365 nm, an extreme photo-induced hydrophilicity was achieved when the TiO_(2) film was covered by SiO_(2) overlayer ranging from 10 to 20 nm in thickness. These multilayer films exhibited much more extreme hydrophilicity than the TiO_(2) film without SiO_(2) overlayer. The surface analyses revealed that the enhanced photo-induced hydrophilic surface of the multilayer films exhibited an improved photo-catalytic activity towards decomposition of organic substances on their surfaces. It was found that significant growth of the SiOH group occurred in the uppermost surface of the SiO_(2) overlayer of the multilayer films through the depth profile measurement of TOF-SIMS. This result suggests that the photo-generated reactive species such as hole created in the TiO_(2) film may transmit the SiO_(2) layer to reach the surface. The enhanced photo-induced hydrophilicity of the films can be explained by a synergetic effect of the improved photo-catalytic activity of the multilayer film and the stable hydrophilicity of SiO_(2) itself.