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

Abstract

The (root 3 x root 3)R30 degrees Xe layer on Pt(111) is studied by spin-polarized low-energy electron diffraction (SPLEED). In the experiment spin-polarized electrons from a GaAs photoemission source are scattered at the target, and the spin-dependent intensities are measured in different diffracted beams. Corresponding calculations are performed using a relativistic LEED program. Measurements and calculations show strong contributions from multiple scattering between the substrate and the adlayer. The scattering contributions from the substrate are found to dominate the general structure of asymmetry and intensity profiles 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 beams are suitable for structure investigations. Comparing measurements and calculations by means of r-factor analysis, we determine the local adsorption geometry. The Xe atoms are adsorbed in domains of fee and hcp hollow sites on the Pt(111) surface with identical domain size probability and random distribution of the domains. The distance between the adsorbate layer and the topmost substrate layer is found to be 4.2+/-0.1 Angstrom. Measurements and calculations agree very well in general.