OXIDATION OF ULTRATHIN IRON LAYERS GROWN ON CU(111)

Oxidation of thin iron layers (<25 Angstrom) grown on a Cu(111) substr ate is studied at 300 K by Auger spectroscopy, LEED and RHEED. After a 250 L exposure of oxygen, iron is oxidized into Fe2O3 or Fe3O4. RHEED and LEED experiments gave evidence for the formation of a plane with hexagonal symmetry. The unit cell parameter of this plane is higher th an those observed in (111) close packed oxygen planes of the different bulk iron oxides. If the layer is thin (<3 Angstrom), iron is fully o xidized. For thicker layers, an iron underlayer exists. The thickness of the oxide cannot exceed 10 Angstrom.