Interaction of multiple charged ions with solid surfaces

The observation of the decay of inner-shell vacancies can serve as an excellent probe of the neutralization of multicharged ions during their approach to a metal surface. Several recent experiments that have measured electrons emitted during this neutralization are discussed. Measurements of the total electron yield for incident ions with inner-shell vacancies first showed marked differences from the yield observed for lower charge states and indicated the need for further investigations. Measurements of the emitted electron energy distributions have led to a qualitative understanding of the timescales of the neutralization process. For incident ions with high enough energies, projectile inner-shell vacancies have been observed to survive the neutralization process above the surface and then to be transferred to target atoms in close collisions. The inner-shell reactions occuring in such close collisions are analogous to those that have been observed in ion-atom and ion-foil collisions. Recent measurements of angular distributions of the electrons emitted due to the decay of target vacancies created during the interaction show evidence of the projectile penetrating several layers below the surface. (author)