In-situ x-ray diffraction studies on post-deposition vacuum-annealing of ultra-thin iron oxide films

A maghemite (γ-Fe2O3) film of 8.3 nm thickness is epitaxially grown on MgO(001) single crystal substrate by reactive molecular beam epitaxy. Chemical composition and crystal structure of the surface was studied by x-ray photoelectron spectroscopy and low energy electron diffraction, respectively. Afterwards the sample was moved to a heating cell for in situ x-ray diffraction experiments on the post-deposition annealing process in high-vacuum to study structural phase transitions of the iron oxide film. The iron oxide film is reduced with increasing temperature. This reduction occurs in two steps that are accompanied by structural transitions. The first step is a reduction from γ-Fe2O3 to Fe3O4 at 360 °C and the second step is the reduction from Fe3O4 to FeO at 410 °C.