“Step-up” versus “step-down” scattering asymmetry in the neutralization of H− on free-electron vicinal metal surfaces

The charge transfer between H− and a free-electron vicinal metallic surface is studied using a wave-packet propagation method. We apply a statistical Thomas–Fermi–von Weizsäcker model with a local density approximation for the exchange-correlation energy to compute the ground-state electronic structure of the substrate. The long-range image charge effects in the electron transfer are included on a phenomenological level. We obtain the ion-survival probability from a rate equation for a set of realistic scattering trajectories of projectiles that are incident with a kinetic energy of 50 eV. Our calculations reveal a pronounced substrate orientation dependence of the charge transfer dynamics expressed in a “left-right” (or “step-up–step-down”) scattering asymmetry in the final ion-survival probability, which is caused by an enhancement of electron loss on the outgoing part of those ion trajectories which approach steps from below.