Nanostructure of photocatalytic TiO 2 films sputtered at temperatures below 200 °C

Abstract

The article reports on correlations between the process parameters of reactive pulsed dc magnetron sputtering, physical properties and the photocatalytic activity (PCA) of TiO 2 films sputtered at substrate surface temperature T surf ≤ 180 °C. Films were deposited using a dual magnetron system equipped with Ti (Ø50 mm) targets in Ar + O 2 atmosphere in oxide mode of sputtering. The TiO 2 films with highly photoactive anatase phase were prepared without a post-deposition thermal annealing. The decomposition rate of the acid orange 7 (AO7) solution during the photoactivation of the TiO 2 film with UV light was used for characterization of the film PCA. It was found that (i) the partial pressure of oxygen p O 2 and the total sputtering gas pressure p T are the key deposition parameters influencing the TiO 2 film phase composition that directly affects its PCA, (ii) the structure of sputtered TiO 2 films varies along the growth direction from the film/substrate interface to the film surface, (iii) ∼500 nm thick anatase TiO 2 films with high PCA were prepared and (iv) the structure of sputtered TiO 2 films is not affected by the substrate surface temperature T surf when T surf < 180 °C. The interruption of the sputtering process and deposition in long (tens of minutes) pulses alternating with cooling pauses has no effect on the structure and the PCA of TiO 2 films and results in a decrease of maximum value of T surf necessary for the creation of nanocrystalline nc-TiO 2 film. It was demonstrated that crystalline TiO 2 films with high PCA can be sputtered at T surf ≤ 130 °C. Based on obtained results a phase zone model of TiO 2 films was developed.