Reactive R.F. magnetron sputtering deposition of WO3 thin films

Thin films of tungsten trioxide (WO3) have been deposited by reactive R.F. magnetron sputtering in view of exploiting their gas sensing properties. Their surface structure, morphology and chemical composition were analysed by electron spectroscopy for chemical analysis (ESCA), atomic force microscopy (AFM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). In a first stage, WO3 films deposited on various substrates (glass, MgO (0 0 1), α-Al2O3 (0 0 0 1) and SiO2/Si) were compared and it appeared that the best suited film surface morphology for gas sensing applications have been obtained on SiO2/Si substrates. The TEM patterns of as-deposited films exhibit nanocrystallite features. The films are then stabilised by annealing in dry air. The influence of the deposition parameters (temperature, oxygen partial pressure in the plasma) upon the microstructure and surface morphology of these films has been evidenced by AFM and SEM. TEM and ESCA analyses showed that such a process yields to WO3 monoclinic phase with a chemical composition slightly deficient in oxygen.