Reversible metamorphosis from Fe 3 O 4 to FeO of epitaxial iron oxide films grown on the Fe-p(1 × 1)O surface.

The reduction and oxidation of epitaxial Fe 3 O 4 films grown by reactive deposition on a Fe-p(1 × 1)O surface have been investigated by means of Auger electron spectroscopy (AES), low energy electron diffraction (LEED) and scanning tunneling microcopy (STM). The as-grown iron oxide samples display a square LEED pattern with a lattice constant compatible with a p(1 × 1) bulk terminated Fe 3 O 4 (001) surface. STM topographic images of Fe 3 O 4 are characterized by atomically flat terraces separated by highly oriented steps running along the (010) and (100) crystallographic directions of the substrate. Upon annealing at 800 K in an ultra-high vacuum, AES reveals that magnetite transforms to FeO. The sample exposes the (001) surface of the rock salt structure, with a lattice parameter close to that of bulk wüstite. The Fe 3 O 4 phase can be recovered by oxidation at 10 -6 mbar of molecular oxygen.