A COMPUTER STUDY OF THE ENERGY-LOSS SPECTRUM OF 100 KEV H+ AT A W(111) SURFACE

The computer simulation code ACOCT has been applied to analyze the experimental energy loss spectrum of 100 keV H+ on a W(111) surface obtained by proton energy loss spectroscopy in a glancing-scattering geometry. The ACOCT code is based on the binary collision approximation, and the electronic energy loss is estimated by the impact-parameter-dependent formula, i.e., the Oen-Robinson local model. The influence of the anisotropic thermal vibration of a surface atom and of the surface contraction to the energy loss spectrum of 100 keV He+ at a W(111) surface have been investigated. It is found that a W(111) surface has a contraction of 5-25 pm and that the Oen-Robinson model can predict the main feature of the proton energy loss if its collision number is large enough. The vacancy at the topmost layer is found not to be sensitive to the energy loss spectrum in a glancing-scattering geometry. © 1990.