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 degrees 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 degrees C, suggests the intercalation of Ag into W03 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 degrees C, theXPS observations strongly suggest that the Ag atoms migrate to the surface of the WO3 grains, localizing at defect sites.