Magnetite Fe_3-δO₄: A stoichiometry and structure analysis of MBE grown thin films using NO₂ as the oxidizing source

Epitaxial single crystalline films of iron oxides have been grown on MgO(100) substrates by means of MBE. Natural Fe or ⁵⁷Fe was evaporated from alumina crucibles, and oxidized simultaneously with a dosed flux of NO₂. The resulting oxide layers have been characterized in situ with RHEED, LEED, XPS, and AES. RHEED intensity oscillations, observed during deposition of the oxides, indicate a layer-by-layer growth for all substrate temperatures between 373 and 673 K. A stoichiometry analysis with CEMS, performed ex situ, shows that it is straightforward to prepare both the stable magnetite Fe₃O₄ and the metastable maghemite γ-Fe₂O₃ phases. Moreover, also all solid solutions in between these two extreme phases, i.e. Fe_3-δO₄ with 0<δ<1/3, could be formed. Ion beam channelling has been used to examine the epitaxy of the films. It was found that the films grow coherent on MgO(100).