Charge transfer in single and multiple scattering events at metal surfaces: a wavepacket study of theNa + /Cu(100) system

Abstract

Resonant neutralization of hyperthermal energyNa + ions impinging on Cu(100) surfaces is studied, focusing on two specific collision events: onein which the projectile is reflected off the surface, the other in which the incident atompenetrates the outer surface layers initiating a series of scattering processes, within thetarget, and coming out together with a single surface atom. A semi-empiricalmodel potential is adopted that embeds: (i) the electronic structure of the sample,(ii) the central field of the projectile, and (iii) the contribution of the Cu atomejected in multiple scattering events. The evolution of the ionization orbital of thescattered atom is simulated, backwards in time, using a wavepacket propagationalgorithm. The output of the approach is the neutralization probability, obtained byprojecting the time-reversed valence wavefunction of the projectile onto the initiallyfilled conduction band states. The results are in agreement with available datafrom the literature (Keller et al 1995 Phys. Rev. Lett. 75 1654) indicating that themotion of surface atoms, exiting the targets with kinetic energies of the order of afew electronvolts, plays a significant role in the final charge state of projectiles.