PREPARATION AND CHARACTERIZATION OF ULTRA-THIN IRON-OXIDE FILMS ON A MO(100) SURFACE

The synthesis and characterization of ultra-thin films of iron and iron oxides on a Mo(100) surface, have been carried out under ultrahigh vacuum conditions in the 100-1500 K substrate temperature range. The oxides were prepared by both post-oxidation of pure Fe ultra-thin films and by evaporating Fe onto the Mo surface in oxygen ambient (in situ oxidation). The characterization of the iron oxide films, with respect to the chemical states and composition, was made using X-ray photoelectron spectroscopy as well as temperature programmed desorption. By varying the molybdenum substrate temperature and the oxygen background pressure during either the post-or the in situ oxidation process, oxide films consisting of virtually pure phases of Fe2O3 and FeO can be successfully obtained as well as intermediate phases including Fe3O4. In addition, discrete phase changes were found corresponding to the reduction of Fe2O3 to Fe3O4 at similar to 550 K and Fe3O4 to FeO at similar to 750 K by means of thermally induced oxygen loss.