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

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