Microstructural characterization of a titanium-tungsten oxide gas sensor

Thin films of Ti-W-O were prepared from a W-Ti alloy target by rf magnetron sputtering in reactive atmosphere. Analysis devoted to investigate the microstructural properties of this material was carried out in order to explain the origin for the high sensing performance of a W-Ti-oxide gas sensor. Scanning and transmission electron microscopy techniques showed that after annealing the film consists of a polycrystalline layer, isostructural to tetragonal WO3, over which crystallites of pure WO3 are dispersed. The WO3 crystallites are insulated from each other and do not enter into the process of conduction of the layer. It was shown that Ti is soluted in the tetragonal WO3 lattice of the underlying layer. This layer exhibits fine granularity, which is an optimal feature for materials suited to gas sensing.