Enhanced visible light adsorption of heavily nitrogen doped TiO₂ thin film via ion beam assisted deposition

Nitrogen doping is widely used to enhance the visible light absorption of TiO₂ by narrowing the bandgap. It is recognized that this modification is sensitively affected by the spatial distribution of anion doping. In order to explore the effects of nitrogen distributions in TiO₂, we synthesized nitrogen-doped TiO₂ thin films via the ion-beam assisted deposition (IBAD) technique and calcinations in NH₃ atmosphere. The morphology and crystal structure of these thin films were characterized by scanning electron microscope and X-ray diffraction respectively. The chemical states and spatial distributions of nitrogen in the TiO₂ were investigated by X-ray photoelectron spectroscopy. The nitrogen can be heavily and uniformly doped in anatase thin film by the IBAD technique with the N/Ti atomic ratio ranging from 61.3 to 51.9 %, much higher than that calcinated at 500 °C under NH₃ atmosphere, which fluctuated from 23.2 to 4.5 %. The time-dependent depth profile of the N 1s spectrum shows that the doped nitrogen in the TiON thin film synthesized via IBAD distributes from the surface to the inner layer. Compared to the traditional calcinations synthesized methods, the as-synthesized TiON thin film, shows a much higher absorption in the visible-light range. Its light absorbance spectrum extends to over 700 nm, covering most of the visible-light region.