Rare-gas thermal desorption from flat and stepped platinum surfaces: Lateral interactions and the influence of dimensionality

High-resolution thermal-desorption data are presented for xenon desorption from flat Pt(111) and stepped Pt(997) surfaces. Analysis of the experimental data and comparison with detailed lattice-gas models which are able to describe different adsorption sites on the stepped surface reveal similar xenon single-particle binding energies of 253 meV and 264 meV on Pt(111) and on the terraces of a Pt(997) surface, respectively. The extracted corresponding lateral interactions are attractive and again of similar value (pairwise attraction of 11 meV). However, for terrace desorption different kinetics are observed: On the flat (111) surface desorption is zero order over a wide range of coverage, due to equilibrium between adsorbate condensate and two-dimensional gas, whereas on the stepped surface terrace desorption is near first order. We interpret the changed desorption kinetics as a consequence of the finite size of the (111) terraces in one direction on the stepped surface, i.e., as an influence of dimensionality on adlayer statistics. On the basis of the lattice-gas model we demonstrate the influence of different terrace widths. For adsorption on Pt(997) we find complete xenon step decoration before terrace adsorption starts with a binding energy of about 400 meV and a pairwise repulsion of about 16 meV. Completion of the step decoration is accompanied by a work function change of 0.47 eV which might explain the observed repulsion as due to dipole-dipole interaction along the steps.