MBE-growth of iron and iron oxide thin films on MgO(100), using NO2, NO, and N2O as oxidising agents

We have made a study of the use of NO2 as the source of oxygen in the MBE-growth of iron oxides thin films. It is found that NO2 is a much more efficient oxidising agent than molecular O-2. As indicated by Mossbauer spectroscopy, performed on Fe-57 probe layers, NO2 is not only capable of forming stoichiometric magnetite Fe3O4, but also ail non-stoichiometric Fe3-deltaO4 phases. Even the metastable maghemite phase gamma-Fe2O3 (Fe3-deltaO4 with delta = 1/3) can be formed. All iron oxides grow layer-by-layer-like, as indicated by strong RHEED intensity oscillations. When small doses of NO2 are used, new wustite Fe1-xO and Fe3O4 phases are formed. In contrast to the Fe3-deltaO4 films, these phases have nitrogen incorporated into the crystal lattice. Similar compounds are obtained when NO is used as the source of oxygen. The use of N2O does not lead to the formation of iron oxides. It does, however, alter the growth mode of Fe on MgO(100). Whereas Fe deposited under UHV conditions forms 3D islands, the N2O acts as a surfactant and induces 2D layer-by-layer growth.