Caracterização de filmes finos nanoestruturados de WOx obtidos por evaporação térmica

Abstract

Tungsten oxides (WOx) constitute a class of semiconductors with a potential application in photovoltaic cells due to the structural and chemical properties. One of these oxides’ peculiarities is related to tungsten’s capacity of reaching oxidation number between +VI and –II, which associated to the modifications in the surface and morphology enable the fabrication of electrochromic and optoelectronic devices. In this paper, thin films of tungsten oxide were obtained through thermal evaporation, varying the experimental conditions: types of substrate (silicon covered with gold, nominated Au/Si or glass covered with tin-doped indium oxide, nominated ITO/glass), time of deposition (t) and temperature of substrate (Ts). Chemical composition was evaluated on the surface and in depth. It was also evaluated the effect of the deposition parameters about the type of the films’ structuring and crystalline structure. The increase of the temperature of substrate affects directly the thickness of the WOx films, which have near 200 nm when obtained in higher Ts (600 °C). It was verified a matrix totally covered with tungsten oxide for the films deposited over ITO/glass and formation of grains with a diameter up to 800 nm for samples obtained in Au/Si substrate. The films obtained over substrate Au/Si are crystalline and exhibit predominantly hexagonal phase (h-WO3). For films obtained in ITO/glass substrate it is observed a mixture between elements, developing a crystalline phase rhombohedral.