Reactively sputtered N-doped titanium oxide films as visible-light photocatalyst

Nitrogen-doped titanium oxide (TiOxNy) films were prepared by reactive magnetron sputtering of a titanium metal target in gas mixtures of argon, oxygen and nitrogen. Two types of nitrogen species are formed in the films following the fraction of N2 (FN2) in the reactive atmosphere. One is substitutional nitrogen in anatase titania phase and the other is nitrogen in TiN phase. In a large range of FN2 from 0 to 0.57, TiOxNy films in anatase structure with about 1.0–1.4 at.% substitutional nitrogen are produced and the films exhibit red shifts to ∼ 500 nm from the absorption edge of ∼ 380 nm of undoped TiO2. The nitrogen is readily doped in the films by energetic nitrogen ions in the plasma and the films exhibited photocatalytic properties under visible light. When excess nitrogen is supplied as the FN2 above 0.75, the resulting film contains 20.8 at.% of nitrogen with formation of TiN that makes the film opaque and destroys the photocatalytic activity largely.