Reactive molecular beam epitaxy of iron oxide films: Strain, order, and interface properties

Abstract

Iron oxide films can show very different stoichiometries due to the flexibility of their Fe oxidation state (Fe2 /Fe3 ). This flexibility is accompanied by the formation of various single-crystalline phases (e.g., hematite, magnetite, maghemite, and wüstite) with different chemical and physical properties. Therefore, iron oxide films are of interest in different fields as heterogeneous catalysis or spintronics and a deeper understanding of the epitaxy of iron oxide films are of strong interest. Here, we report on systematic studies on the epitaxy of iron oxides on different metal and oxide substrates with focus on the growth on MgO(001) substrates due to its negligible lattice mismatch compared with different iron oxide phases. Surface-near stoichiometry and structure of the iron oxide films are especially studied by surface-sensitive techniques as photoelectron spectroscopy and low-energy electron diffraction, while the properties of bulk and buried interfaces are determined by X-ray diffraction and reflectivity using synchrotron radiation. Thus, detailed studies on strain and relaxation of epitaxial iron oxide films depending on film thickness and support properties are possible. Further, the distribution of Fe cations on different sublattices for the inverse spinel structure of Fe3O4 can be determined, and the influence of buffer layers is discussed. © 2018 Elsevier Inc. All rights reserved.