Inelastic energy loss and spectrum shape for medium energy He ions undergoing a large-angle single collision with Si(1 1 1)-√3x√3-Sb

The inelastic energy loss and the spectrum shape were measured for medium energy He ions undergoing a large-angle single collision with Sb atoms of the Si(1 1 1)-√3x√3-Sb structure. The electronic energy loss observed is consistent with the theoretical prediction based on the coupled-channel method which allows a dynamically-curved projectile trajectory. The He+ ions emerging from the surface at a grazing angle lose an energy additionally owing to an interaction with the surface expressed by plasmon excitation and single electron excitation. The energy spectrum after a large-angle collision takes a pronounced asymmetric profile, which is approximated by an asymmetric Gaussian or asymmetric Gaussian-Lorentzian distribution. The asymmetric nature is enhanced for grazing emergence from the surface, attributed to an ion-surface interaction