SCANNING PROBE MICROSCOPY AND TUNNELING MEASUREMENTS OF POLYCRYSTALLINE TIN OXIDE-FILMS

Polycrystalline SnO2 films fabricated by thermal evaporation of tin an d isothermal oxidation at 500 degrees C in pure oxygen have been studi ed by atomic force microscopy and scanning tunnelling microscopy. Topo graphic images revealed that individual grains have a polyhedral micro structure consisting of facets intersecting at depressions surrounded by terrace-step features. These may be the result of the anisotropic o xidation of tin. Ambient tunnelling current-voltage characteristics me asured from individual grains ate strongly rectifying, suggesting that the Fermi level is being pinned by surface states within the bandgap. The surface states are due mainly to chemisorbed oxygen species from air.