Energy loss in medium-energy ion scattering: A combined theoretical and experimental study of the model system Y on Si(111)

The energy-loss spectrum associated with scattering of 100 keV H+ ions from Y atoms on Si(111) has been investigated both experimentally and theoretically. Measurements were made from Y overlayers, and from the Si(111)(1×1) two-dimensional silicide phase formed by Y on this surface, in various scattering geometries and with different surface preparations. Theoretical simulations were conducted based on calculations of the energy loss experienced in specific ion trajectories through the surface, using coupled-channel calculations to describe inner-shell ionization and excitation as a function of impact parameter. The experimental results indicate that additional broadening contributions arise from surface inhomogeneity and roughness, but for near-normal incident and outgoing trajectories the theory and experiment agree quite well. The calculations show that, even for the ideal two-dimensional silicide phase in which the Y atoms lie just below the surface, significant energy loss arises from interaction of the ions with surrounding Si atoms, leading to a complete loss of intensity at zero energy loss.