Photoemission Study of N-Doped TiO2(110) with NH3

High-resolution photoemission spectroscopy using synchrotron radiation was employed to understand the bonding state of N incorporated into a reduced TiO2(110)-1 x 1 surface. N-doping into TiO2(110) was accomplished both by dosing NH3 at elevated temperatures (800 K) and by using a NHx+ ion implantation method onto TiO2(110) at room temperature. Our results indicate that the N-doped TiO2(110) obtained after final annealing to 900 K contains N species incorporated into the subsurface region of TiO2 substitutionally replacing the lattice O2-. Interestingly, we find that some of the N species are found to have a direct N-H bond (NH species). The valence band indicates that the band-gap state related to the Ti 3d state is enhanced with increasing subsurface N species, which explains an attractive interaction between N species and defects with a charge in the Ti 3d state, such as reduced Ti3+ species and oxygen vacancies.