High-resolution photoelectron spectroscopy studies on WO₃ films modified by Ag addition

In this work, WO3 films loaded with different amounts of Ag atoms, prepared by screen-printing onto Si substrates and annealed in air at 300 and 600 °C, were investigated. Atomic force microscopy micrographs showed that the films are nano-particulate with increasing final grain size on increasing the annealing temperature and/or Ag loading level. The observation of a Raman band near 930 cm−1, whose intensity increased on increasing the level of Ag loading for the samples annealed at 600 °C, suggests the intercalation of Ag into WO3 tunnels; this is supported by the presence of a peak at 32 eV binding energy in the high-resolution x-ray photoelectron (XP) spectra. From the analysis of the W 4f core level XP spectra it was also observed that when the level of Ag loading increases, the component in the spectra associated to surface defects decreased; as the measured concentration of Ag in the films is 1.8 higher then the nominal one when the samples are annealed at 600 °C, the XPS observations strongly suggest that the Ag atoms migrate to the surface of the WO3 grains, localizing at defect sites.