Rutherford backscattering and channeling studies of Mg and Fe diffusion at the interface of γ-Fe2O3(001)/MgO(001)

Abstract

We have investigated the crystalline quality of an epitaxially-grown γ-Fe2O3(001) film on MgO(001) substrate along with Mg and Fe inter-diffusion using Rutherford backscattering spectrometry (RBS) and channeling experiments. The channeling effect in the film appears to be reduced compared to an ideal single crystal, with the minimum yield for Fe determined to be in the range 16-18%. Growth at a substrate temperature of 450 °C promotes limited Mg out-diffusion into the film. Subsequent appealing results in further Mg out-diffusion, which increases in extent with increasing temperature. A minimum of 4 at.% Mg was detected throughout the film at temperatures below the onset of Fe in-diffusion, which was found to be 800 °C. This impurity cation concentration is comparable to the native vacancy concentration in γ-Fe2O3 (4.8 at.%), suggesting that Mg occupies cation vacancy sites, as already established by Auger electron diffraction measurements for this system. The Mg concentration in the film was 8 at.%, while the associated Fe concentration in the substrate was 3.4 at.% after annealing at 800 °C. Moreover, these cation impurities were uniformly distributed throughout the film and substrate, with the fraction of substitution in both cases >90% at lower temperatures.