Charge exchange in low-energy ion-surface scattering

Charge exchange between low-energy projectiles and solid materials is explored for systems in which there is overlap between the ionization level and the surface bands. Time-of-flight spectroscopy is used to measure the charge state and kinetic energy distributions of scattered and recoiled atomic particles. Alkali ions scattered from alkali and halogen adatoms have larger neutralization probabilities than for scattering from the substrate, indicating that they both have positively charged regions at the top, which is surprising for the negatively charged halogen adsorbates. Because of strong overlap, Na+ ions scattered from Au nanocrystals neutralize by interaction with the quantum-confined states. Charge exchange in symmetric systems was investigated by measurements of the charge state of Al emitted from clean Al(100) by direct recoil induced by 5 keV Xe+ ions. The neutralization of recoiled Al is basically consistent with a resonant process resulting from the overlap of the Al atomic and solid states. (C) 2004 Elsevier Ltd. All rights reserved.