X-ray absorption and emission spectroscopy of TiO2 thin films with modified anionic sublattice

Abstract

Crystallographic and optical properties as well as electronic structure of titanium dioxide thin films with modified anionic sublattice, i.e., non-stoichiometric, undoped and nitrogen doped thin films of TiO2−x and TiO2−x:N, were studied by means of X-ray diffraction, optical spectrophotometry, X-ray absorption and emission spectroscopy. We demonstrate that TiO2−x films undergo a gradual evolution of the crystallographic structure accompanied by the progressive change in interatomic distances with the preserved local symmetry and nearly unchanged effective 3d charge of Ti ions. At a certain degree of oxygen deficit an abrupt change in all the properties studied can be seen. Amorphisation, possible Ti precipitation and increased optical absorption over the visible range correlates well with a significantly higher 3d band occupancy derived from XES for TiO2−x. Thin films of TiO2−x:N demonstrate gradual evolution of the local structure and charge redistribution upon increased level of nitrogen doping.