Direct atomic structure determination of epitaxially grown films: Gd₂O₃ on GaAs(100)

We have used coherent bragg rod analysis (COBRA) to investigate the atomic structure of an epitaxial Gd₂O₃ film grown on a (100) GaAs substrate. COBRA is a method to directly obtain the structure of systems periodic in two dimensions by determining the complex scattering factors along the substrate-defined Bragg rods. The system electron density and atomic structure are obtained by Fourier transforming the complex scattering factors into real space. The results show that the stacking order of the Gd₂O₃ film layers is different from that of cubic bulk Gd₂O₃ and resembles the stacking order of Ga and As layers in GaAs. Furthermore, in the first few Gd₂O₃ layers, Gd atoms are displaced to positions right above the Ga and As positions in the substrate, and they relax towards bulk Gd₂O₃ positions with increasing distance from the interface.