X-ray diffraction study on size effects in epitaxial magnetite thin films on MgO(001)

Epitaxial ultrathin iron oxide films of different thicknesses were grown by reactive molecular beam epitaxy in 10-6 mbar oxygen atmosphere on MgO(001) single crystal substrates at room temperature. Afterwards, the films were studied by x-ray diffraction, x-ray reflectivity and x-ray photoelectron spectroscopy to provide information regarding film structure as well as chemical composition of the films. Except for a very thin interface layer of subnanometre thickness, the iron oxide films have magnetite stoichiometry and structure and Mg does not diffuse from the substrate into the iron oxide film. The interface layer has a wuestite structure as determined by kinematic diffraction analysis. The magnetite films exhibit very homogeneous thickness while the vertical lattice constant decreases gradually towards its bulk value.