Effect of sputtering parameters on structural and photocatalytic properties of N-doped TiO(2) films

Nitrogen-doped titanium oxide (N-TiO(2)) films deposited on unheated glass slides at various flow rates of N(2) in an atmosphere of Ar and O(2) gas mixture by direct current sputtering technique were investigated. The Ti2p, O1s and N1s spectra by X-ray photoelectron spectroscopy (XPS) verified N-substitution into TiO(2) lattice which is responsible for the band gap narrowing. The oxygen total ratio (r(OT)) in the gas mixture had profound influence on the photocatalytic properties of the N-doped films. At a ratio of r(OT) less than or equal to 0.18, heterogeneous phases, such as titanium oxynitride (TiN(x)O(y)) and titanium nitride (TiN), with low crystallinity were formed in the TiO(2) lattice, showing low photocatalytic activity. On the other hand, the N-TiO(2) films prepared at r(OT) greater than or equal to 0.20 were found to have improved photocatalytic activity on methylene blue degradation under visible-light irradiation at wavelengths longer than 500 nm, due to the substitutional N ions in the TiO(2) lattice.