We have performed the scanning tunneling microscopy (STM) and scanning tunneling spectroscopy measurements of the oxide nanofilms formed on stainless steel at 450 degreesC in oxygen partial pressures (p') of 1 X 10(-7) and 1 X 10(-9) Torr. The STM observations reveal that the films grown at p' of 10(-7) Torr consist of grains varying from 40 to 120 Angstrom in size, while the films grown at p' of 10(-9) Torr consist of grains of about 400 Angstrom. We also show that the native oxide layers of stainless steel surfaces exhibit subgrain structures with grains of size in the range 30-60 Angstrom. The current-voltage characteristics allow us to identify iron oxides, in the films grown at p' of 10(-7) Torr, Fe3O4, and Fe2O3, whereas the films grown at p' of 10(-9) Torr are pure Cr2O3. We thus conclude that oxidation at p' of 10(-9) Torr develops complete Cr2O3 films with large grains, while oxidation at p' of 10(-7) Torr develops iron-rich oxide films with small grains. (C) 2003 American Vacuum Society.