Wechselwirkung hochgeladener Ionen mit Oberflächen

The interaction of highly charged ions approaching a surfaces probes the response of the surface to very strong Coulomb fields. The projectile can easily pull many electrons from the surface. It can act like a powerful vacuum cleaner for surface electrons. Many unusual features can be observed: among them are the formation of "hollow atoms", an exotic multiply excited highly unstable atomic system with only sparsely populated inner shells. Another is a highly efficient soft sputtering process. The gentle impact of a single multiply charged ion at very low velocities can eject hundreds of atoms from the surface forming impact crates and blisters. Our research focused on the microscopic understanding of this processes: We have shown that soft sputtering of alkali-haloginide surfaces such as LiF is predominantly caused by the formation of a large number of self-trapped holes due to the "vacuum cleaner" effect. These self-trapped holes remain localized in the vicinity of the surface for a sufficient amount of time such that a large number of surface atoms can be ejected. Soft sputtering may hold the promise to selectively ablate surface material in a controlled manner for surface modification on a nanoscale. Microscopic surfaces of microcapillaries can serve to control the ion-surface interaction. Unlike macroscopic surfaces, the final impact of the approaching ion at the surface can be suppressed and, instead, a near-miss collisions results. This allows spectroscopic studies of hollow atoms in flight. During the project period we performed first calculations for the interactions of ions with the internal surfaces of microcapillaries. Predictions for the charge state as well as the excited state distributions are found to be in good agreement with first measurements.