Electronic and optical characterisation of TiO2 films deposited from ceramic targets

The deposition of stoichiometric TiO2 films for abrasion resistant V2O5/TiO2 anatase catalysts was investigated. DC magnetron sputtering from ceramic oxide targets in an argon/oxygen atmosphere was chosen as deposition technique. Smaller amounts of oxygen gas proved necessary to achieve stoichiometry in the deposited layers, than during deposition processes involving metal targets. TiO2 layers were prepared with different oxygen mole fractions and the influence upon electronic and optical properties was investigated. Surface XPS measurements showed that stoichiometry is obtained for low oxygen mole fractions, while for higher oxygen contributions, Ti3+ species are increasingly present. This departure from stoichiometry was ascribed to active resputtering of the deposited layer by O ions. Due to the higher sputter yield of oxygen as compared to titanium, this resputtering resulted in the observed reduction. From optical transmission measurements, the refractive index was found to decrease with increasing oxygen mole fraction, while the band gap increased considerably. Post-deposition annealing in oxygen improved the crystallinity of the layers. The refractive index and optical band gap were both reduced by this treatment and the oxygen deficiency of the layers was in general seen to decrease. (C) 2001 Elsevier Science B.V. All rights reserved.