The role of nitrogen doping on the development of visible light-induced photocatalytic activity in thin TiO₂ films grown on glass by chemical vapour deposition

A brief review of the findings of a range of studies aimed at describing the influence of the N-doping of TiO₂ thin films and particles on possible visible light-induced photoactivity is presented. By way of a new approach to the direct growth of N-doped TiO₂ thin films, the physical and photochemical effects of the addition of ammonia during atmospheric chemical vapour deposition (CVD) growth of TiO₂ are described. It is found that the addition of ammonia to the CVD reactive gas mixture causes a dramatic change in film morphology and a reduction in growth rates. In addition, it is found that although we have clear evidence for the incorporation of β-substitutional N atoms within the growing film, there is no evidence of any appreciable photocatalytic activity of the doped TiO₂ films when irradiated with visible light. In fact the degradation in film morphology results in a decrease in conventional UV-induced photoactivity as compared to that for an undoped film. These findings are discussed in terms of the findings of other studies of N-doped TiO₂ films that have been reported.