Investigation of thin films of mixed oxides for gas-sensing applications

Recently, the thin films of some mixed metal oxides (Mo, Ti, Sn, W, etc.) have been indicated as very promising materials for gas-sensing applications. Nevertheless, there is still a significant lack of experimental information on these compounds, where the surface properties can be defined not only by their chemical composition but also by the nanosized morphology of the films. In this study we report the results of XPS investigations of Mo-Ti, Mo-Sn and Mo-W oxides. The films of mixed oxides with different composition ratios were prepared by sol-gel and magnetron sputtering techniques. The gas sensitivity of the films at different temperatures was studied by measuring the electrical response to typical gases. Selected-area XPS depth profiling of the samples was carried out by using cyclic Ar+ sputtering. The separation of different chemical species of the same element and quantitative analysis of experimental depth profiles enabled us to reveal completely the chemical composition of the films investigated. In such a way, the samples of mixed oxides, prepared by two different techniques and annealed at different temperatures (450-700°C), were characterized and compared.