Improved optical response and photocatalysis for N-doped titanium oxide (TiO2) films prepared by oxidation of TiN

In order to improve the photocatalytic activity, N-doped titanium oxide (TiO2) films were obtained by thermal oxidation of TiN films, which were prepared on Ti substrates by ion beam assisted deposition (IBAD). The dominating rutile TiO2 phase was found in films after thermal oxidation. According to the results of X-ray photoelectron spectroscopy (XPS), the residual N atoms occupied O-atom sites in TiO2 lattice to form Ti–O–N bonds. UV–vis spectra revealed the N-doped TiO2 film had a red shift of absorption edge. The maximum red shift was assigned to the sample annealed at 750 8C, with an onset wavelength at 600 nm. The onset wavelength corresponded to the photon energy of 2.05 eV, which was nearly 1.0 eV below the band gap of pure rutile TiO2. The effect of nitrogen was responsible for the enhancement of photoactivity of N-doped TiO2 films in the range of visible light.