Linewidths in bound state resonances for helium scattering from Si(111)–(1 × 1)H

Abstract

Helium-3 spin-echo measurements of resonant scattering from the Si(111)–(1 × 1)H surface, in the energy range 4–14 meV, are presented. The measurements havehigh energy resolution yet they reveal bound state resonance features withuniformly broad linewidths. We show that exact quantum mechanical calculationsof the elastic scattering, using the existing potential for the helium/Si(111)–(1 × 1)H interaction, cannot reproduce the linewidths seen in the experiment. Furthercalculations rule out inelastic and other mechanisms that might give rise to losses from theelastic scattering channels. We show that corrugation in the attractive part of theatom–surface potential is the most likely origin of the experimental lineshapes.