Effect of oxygen and nitrogen concentration of nitrogen doped TiOx film as photocatalyst prepared by reactive sputtering Original Research Article

The N-doped TiOx films were prepared by radio-frequency (RF) magnetron reactive sputtering of Ti target in a mixed gas of Ar, O2 and N2. The effects of varying oxygen and nitrogen flow ratios on the physical properties and photocatalytic properties with defect formation energies using DFT calculations were investigated, and the photocatalytic ability was evaluated by decomposition of NO gas. The photocatalytic properties as well as other film properties such as lattice parameters, grain sizes, surface atomic contents, surface doping configurations, and optical properties strongly depend on the gas flow ratios. The N-doping configuration in TiO2 is significantly affected by the oxygen concentration in sputtering, based on the XPS and the defect formation energy results. Also, the visible light photocatalysis of N-doped TiOx film requires a certain range of oxygen and nitrogen concentrations in the sputtering process. The substitutional N-doped TiO2 has weak photocatalysis compared with the interstitial N (or NOx)-doped TiO2, suggesting that the interstitial N (NOx)-doping states with the oxygen deficiency are more effective for photocatalysis than the substitutional N-doping states with the oxygen deficiency, probably due to the variation in the number and location of the impurity levels (active recombination sites) in the energy band gap.