Direct atomic structure determination of epitaxially grown films:Gd2O3on GaAs(100)

Abstract

We have used coherent bragg rod analysis (COBRA) to investigate the atomic structure of an epitaxial ${\mathrm{Gd}}_{2}{\mathrm{O}}_{3}$ 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 ${\mathrm{Gd}}_{2}{\mathrm{O}}_{3}$ film layers is different from that of cubic bulk ${\mathrm{Gd}}_{2}{\mathrm{O}}_{3}$ and resembles the stacking order of Ga and As layers in GaAs. Furthermore, in the first few ${\mathrm{Gd}}_{2}{\mathrm{O}}_{3}$ layers, Gd atoms are displaced to positions right above the Ga and As positions in the substrate, and they relax towards bulk ${\mathrm{Gd}}_{2}{\mathrm{O}}_{3}$ positions with increasing distance from the interface.