Hydrogen Distribution and Electronic Structure of TiO2(110) Hydrogenated with Low-Energy Hydrogen Ions

The rutile TiO2 surface irradiated by hydrogen ions at 0.5 keV was investigated by ultraviolet photoemission spectroscopy, X-ray photoemission spectroscopy, and nuclear reaction analysis. With hydrogen irradiation, an in-gap state (IGS) was formed at ∼0.8 eV below the Fermi level, and the bands were downward bent by 0.5 eV. The H depth profile showed a maximum at about 1 nm, extending to ∼30 nm with an average concentration of 5.6 at. %. Upon annealing at 673 K, the IGS intensity was reduced and H with a coverage of 1.4 monolayer remained in the near-surface region, suggesting stable H occupation of subsurface sites. After an O2 dose to the H-irradiated surface, although the IGS intensity was substantially reduced, the hydrogen distribution was found to be unchanged.