Scanning tunneling microscopy and spectroscopy of tungsten oxide thin films in air

Scanning tunneling spectroscopy and microscopy investigations have been carried out in air on thermally evaporated tungsten oxide thin films deposited onto silicon substrates. The films have been submitted to thermal annealing at different temperatures and for different times. The microscopy images show strong effects of recrystallization and different grain sizes depending on the thermal treatment. The spectroscopic data exhibit a rectifying characteristics and the comparison between the topographic and current images allows a better understanding of the sample morphology in relation to the electrical behavior. X-ray photoelectron spectroscopy valence band measurements have evidenced a structure near the Fermi level, which has been assigned to a structural oxygen deficiency of the deposited films, which is also observed in the conductance curve of some samples. (C) 1999 American Vacuum Society. [S0734-2101(99)05204-5].