XPS analysis of N-doped TiO2 nanotube array

Abstract

TiO2 is a promising photoactive material but just in the UV region. One of many approaches that are proposed in order to achieve the TiO2 activity in the visible region is doping of TiO2 with nonmetals, such as F, C, S, N. Among them, nitrogen atom has similar atomic size as oxygen atom and small ionization energy. Because of that there are many publications with nitrogen doping, but many questions are still open. The aim of this study is XPS investigation of nature of N-doping TiO2 nanotubes. Highly ordered nanotubes were prepared by anodization of titanium foil in HF/CH3COOH electrolyte. As-anodized amorphous nanotubes were annealed in NH3 atmosphere, where time of heat treatments was varied. Optical responses of undoped and N-doped TiO2 films were investigated by UV-Vis DRS. The XPS results revealed three N1s peaks: ~ 396, ~ 399 and ~ 401 eV, that describe substitutional and interstitial nature of nitrogen in TiO2 films. Longer time of annealing decreases total amount of nitrogen and that is in correlation with optical measurement.