THE ATOMIC GEOMETRY OF THE GE(111) SURFACE AS A FUNCTION OF TEMPERATURE STUDIED BY PHOTOEMISSION AND PHOTOELECTRON DIFFRACTION

Photoelectron diffraction of the bulk and surface components of the Ge 3d core-level has been measured from the Ge(111)-c(2 x 8) reconstructed surface at room temperature and on the Ge(111)-(1 x 1) surface at 400-degrees-C. Calculations show good agreement with the results of recent X-ray diffraction work on the c(2 x 8) surface. Results for the (1 x 1) surface show no change in the short-range structure at the surface across the phase transition suggesting that the adatom-restatom building block structure accepted for the c(2 x 8) surface remains intact after the phase transition. This method of measuring the photoelectron diffraction from resolved surface core-levels provides a direct method for assigning these levels to specific species at the surface. In addition, significant variations in the branching ratios as a function of azimuthal angle have been found which are due to differences in the final state for the two spin-orbit components of the Ge 3d photoemission peak.