Producing oxygen-rich WO3 thin films by post-deposition thermal annealing

Abstract

Non-stoichiometric oxygen-rich monoclinic tungsten oxide (WO3+x) thin films have been produced by RF sputtering on SiO2 substrates. The films were annealed at temperatures between 300 °C and 700 °C for 4 h in a pure oxygen atmosphere after deposition. The crystal structure and chemical composition of the films were studied in detail via grazing incidence x-ray diffraction (GIXRD), Rutherford backscattering spectrometry (RBS), energy dispersive x-ray spectroscopy (EDX) and Raman spectroscopy. Their surface properties were analyzed by atomic force microscopy (AFM) and scanning electron microscopy (SEM). Optical properties were accessed via ellipsometry. Results indicate that the annealing procedure relaxes the crystal structure and increases the surface roughening. An increase of bandgap, surface texturization and fragments of a triclinic phase are observed as consequences.