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 N-2 (F-N2) 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 F-N2 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 similar to 500 nm from the absorption edge of similar to 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 F-N2 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. (c) 2005 Elsevier B.V. All rights reserved.