Red shift in the light absorption threshold of anodic TiO2 films induced by nitrogen incorporation

Titanium foils were anodized in ammonium containing and ammonium free solutions in order to check the possibility of inducing nitrogen incorporation into anodic TiO2 films. XPS spectra confirmed the presence of O-Ti-N bonds on the surface of the anodic films prepared in ammonium biborate electrolytes. In order to evidence the effect of nitrogen incorporation on the light absorption threshold, photoelectrochemical behavior of as-anodized and high temperature annealed films as a function of the anodizing electrolyte composition were investigated. A photocurrent tail at energies lower than the mobility gap of TiO2 appeared for those films prepared in ammonium containing electrolytes which became more evident after thermal treatment. It is suggested that a red shift of the light absorption threshold of titanium oxide occurred due to nitrogen incorporation during film formation.