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.