Preparation and microstructural characterization of nanosized Mo:TiO2 and Mo-W-O thin films by sputtering: tailoring of composition and porosity by thermal treatment

Nanosized Mo doped TiO2 and mixed W–Mo oxide thin films were deposited via RF-magnetron sputtering, in either reactive or inert atmosphere, to study the influence of the plasma gas on the film growth. Mixed targets (Ti (97 at.%)–Mo (3 at.%) and W (12 at.%)–Mo (88 at.%)) were used for the purpose. Thermal treatments were performed to promote structural and chemical changes. Experimental evidences highlighted the dependence of structural, morphological and compositional evolution of the films on the annealing temperature. In particular, coalescence inhibition to titania nanograins induced by Mo was observed in the Mo doped TiO2 films. The different volatility of WO3 and MoO3 in the W–Mo mixed oxides greatly affected the evolution of the film through annealing. This method proved useful to tailor the composition and porosity of the layers. Mo doped TiO2 films were tested as chemoresistive sensors towards ethanol; mixed W–Mo oxide were found to respond to CO.