FORMATION OF ULTRATHIN FILMS OF IRON-OXIDE ON CU(110)

Ultrathin films of iron have been prepared on Cu(110) and the interact ion with oxygen studied with LEED and XPS. Chemical shifts of the Fe2p 3/2 XPS signal indicate that sub- to a few monolayer amounts of iron o n Cu(110) can be oxidized to FeO, then Fe3O4 or possibly gamma-Fe2O3. A mild annealing of a heavily oxidized iron overlayer leads to an appe arance of a new LEED pattern with hexagonal symmetry that is assigned to Fe3O4, though the possibility of gamma-Fe2O3 is not fully eliminate d. Another LEED pattern is observed for surfaces giving an Fe2p3/2 bin ding energy at 709.5 eV which is typical of an FeO overlayer. Annealin g the Fe3O4 overlayer up to 930 K converts both XPS and LEED features back to those assigned to FeO.