Mixed Oxides for Gas Sensing: The Role of the Annealing Processes

The selective sublimation process (SSP) consists in the co-deposition of two metal oxides, and the subsequent annealing at appropriate temperatures, which forces diffusion towards film surface and sublimation of the most volatile compound. It demonstrated to be a suitable tool in the synthesis of thin layers with good sensing properties. Several mixed systems (MoO3-WO3, TiO2-WO3, TiO2-MoO3) have been synthesized via reactive sputtering on the basis of the SSP process and characterized from a compositional point of view. We developed a model based on diffusion equations to take into account both diffusion towards surface and sublimation of the dopant. The model has been successfully applied to a systematic study of the systems TiO2-WO3 and TiO2-MoO3. Experimental results exhibited a very good agreement with the model, and highlighted the importance of a proper choice of deposition and annealing parameters in order to obtain suitable layers for gas sensing.