ATOMIC-COLLISIONS WITH INHOMOGENEOUS SOLID-SURFACES - MULTIPLE-SCATTERING FROM SURFACE-DEFECTS AND MIXED OVERLAYERS

We employ the multiple-scattering expansion of the transition operator to evaluate the role of multiple collisions in elastic scattering of atoms from adsorbates on solid surfaces at superthermal energies (E gr eater than or similar to 0.1 eV). The adsorbate-surface system is trea ted as a rigid-body model in the present work. Mixed-species periodic overlayers are considered as well as two-layer systems simultaneously involving periodic and non-periodic configurations. The calculated sca ttering patterns show rich structure due to the interference between w aves scattered from different adsorbates. The enhanced sensitivity pro vided by wavevectors k greater than or similar to 10 angstrom-1 could be exploited for surface characterization by scattering experiments. W e find that the single-collision approximation qualitatively reproduce s the trends of the intensity with respect to final angles. Double-col lision terms are evaluated with the pole approximation and found to pl ay an important role in large transfers of parallel momentum.