SURFACE TERMINATION OF EPITAXIAL NIAL ON GAAS(001) BY HIGH-ANGULAR-RESOLUTION X-RAY PHOTOELECTRON DIFFRACTION

We have utilized x-ray photoelectron diffraction at high kinetic energy and high angular resolution to investigate the surface-layer composition of epitaxial films of NiAl grown on GaAs(001) at 250°C. NiAl, which possesses a CsCl crystal structure and a lattice constant of nearly one-half that of GaAs, might be expected to terminate with either an Al or Ni layer on the surface. However, angle-resolved Al 2p and Ni 3p photoemission intensity measurements near grazing emission and quantitative comparison with theoretical scattering calculations strongly support a mixed-termination model. Optimal agreement between theory and experiment, as judged by R-factor analysis, indicates that the surface is composed of approximately 50 at. % Ni and 50 at. % Al. The sensitivity of the technique falls off at higher polar angles, largely because the Ni and Al sublattices possess the same symmetry. © 1990 The American Physical Society.