Structural Change of the Rutile–TiO2(110) Surface During the Photoinduced Wettability Conversion

The surface structural change of the rutile–TiO2(110) during the UV-light-induced wettability conversion was studied with atomic resolution using the X-ray crystal truncation rod (CTR) scattering method. We confirmed that an atomic-scale surface structural change occurs during the UV-light irradiation by using time-resolved CTR profile measurements. Quantitative structural analysis on static CTR data, which were measured before and after the conversion, shows that on the hydrophobic (nonphotoirradiated) surface the five-coordinated Ti atom is covered with an O atom likely in a form of water molecule, for which the bridging O atom is not likely hydroxylated, and that large atomic positional fluctuations occur on the hydrophilic (photoirradiated) surface possibly due to the photoinduced proton transfer from the intact water molecule to the bridging oxygen atom. The resulting surface OH groups might be active sites for water adsorption to make the surface superhydrophilic.