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 ≳ 0.1 eV). The adsorbatesurface system is treated 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 scattering patterns show rich structure due to the interference between waves scattered from different adsorbates. The enhanced sensitivity provided by wavevectors k ≳ 10 Å^-1 could be exploited for surface characterization by scattering experiments. We find that the single-collision approximation qualitatively reproduces the trends of the intensity with respect to final angles. Double-collision terms are evaluated with the pole approximation and found to play an important role in large transfers of parallel momentum.