Oxidation of epitaxial Fe films monitored by x-ray reflectivity

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Abstract
We have studied the oxidation of thin epitaxial Fe(100) films on MgO(100) with and without an Au(100) protecting cap by x-ray reflectivity measurements. The oxidation was carried out under atmospheric conditions between 20 δC and 200 δC. The results are compared to the oxidation of Fe(110) oriented films on Al2O3(1120) substrates with an Au(111) cap. Auger electron spectroscopy before and after oxidation was carried out for sublimentary chemical information of the surface. For the uncovered Fe films we observe smoothly growing oxide films at the surface during oxidation at elevated temperatures. As expected, the Au(100) cap serves as an effective shield against oxidation, while the Au(111) cap, surprisingly, does not. In the case of Au/Fe/Al203, we find Fe2O3 formation at the surface of the Au layer at 200 δC. The different behavior of Au(100) and Au(111) is discussed in terms of stacking faults and/or domain structure occurring in the latter case during epitaxial growth.