Angular dependence of energy loss in scattering of slow highly charged Ar ions from a Au surface

We have studied the energy loss of slow (velocity upsilon approximate to 0. 06 a.u.) highly charged Ar9+ ions scattered at large angles from a clean Au (1 1 1) single crystal surface. The influence of the scattering geometry on the energy loss has been investigated for different incidence angles (5 de grees less than or equal to psi less than or equal to 37.5 degrees) and sca ttering angles (30 degrees less than or equal to theta less than or equal t o 75 degrees). At large angles (psi = 37.5 degrees, theta = 75 degrees), th e main peak in the measured energy spectrum agrees well with the position e xpected for binary elastic scattering. With decreasing incidence angle a sh ift of the "binary peak" to lower energy is observed, and for decreasing sc attering angles, a shift of the binary peak to higher energy than calculate d by kinematics is found. The additional energy loss seen at small psi (psi = 5 degrees) is interpreted by inelastic energy loss. A model calculation which combines s rate-equation description of Auger cascades, recapture to the surface with a Firsov type model and image charge acceleration during i on-surface interaction is used to describe the data. (C) 1999 Elsevier Scie nce B.V. All rights reserved.