Resonance-enhanced inelastic He-atom scattering from subsurface optical phonons of Bi(111)

Helium-atom scattering angular distributions from Bi(111) show a number of selective-adsorption resonance features corresponding to three bound states of the He atom in the surface-averaged Bi(111) potential. They are well represented by a 3-9 potential with a potential depth of 8.3meV. The bound-state resonance enhancement of inelastic scattering is shown to provide the mechanism for the observation of subsurface optical phonons and for their comparatively large intensity.