Effects of nitrogen incorporation on the electronic structure of rutile-TiO2

By direct atomic nitrogen (N) doping, high concentration of N is incorporated into TiO2 and the doping effects are investigated. High resolution x-ray photoelectron spectroscopy core-level spectra indicate N substitution for O and formation of Ti–N bonds. Different Ti valent states are found at different N concentrations. Although the shape of the valence spectra changes significantly up on N doping, the band gap narrowing effect is insignificant. First-principles calculations confirm formation of Ti 3d gap states when N concentration exceeds 1 at. %, which leads to pinging of N 2p states in the band gap.