STRUCTURE INVESTIGATIONS OF XE-ADSORBATE LAYERS BY SPIN-POLARIZED LOW-ENERGY-ELECTRON DIFFRACTION .1. (ROOT-3X-ROOT-3)R30-DEGREES-XE PT(111)

The (root 3 x root 3)R30 degrees Xe layer on Pt(111) is studied by spi n-polarized low-energy electron diffraction (SPLEED). In the experimen t spin-polarized electrons from a GaAs photoemission source are scatte red at the target, and the spin-dependent intensities are measured in different diffracted beams. Corresponding calculations are performed u sing a relativistic LEED program. Measurements and calculations show s trong contributions from multiple scattering between the substrate and the adlayer. The scattering contributions from the substrate are foun d to dominate the general structure of asymmetry and intensity profile s of integer order beams. In adsorbate-induced beams the contributions from the substrate are significantly weaker but nevertheless clearly present. The integer-order beams as well as the adsorbate-induced beam s are suitable for structure investigations. Comparing measurements an d calculations by means of r-factor analysis, we determine the local a dsorption geometry. The Xe atoms are adsorbed in domains of fee and hc p hollow sites on the Pt(111) surface with identical domain size proba bility and random distribution of the domains. The distance between th e adsorbate layer and the topmost substrate layer is found to be 4.2+/ -0.1 Angstrom. Measurements and calculations agree very well in genera l.