Modification of Solid Surfaces by Slow Highly Charged Ions: Effects of Highly Confined Excitation

Due to their high amount of potential energy highly charged ions induce various changes in morphology and electronic structure of solid surfaces [1,2]. The potential energy which is the sum of the ionization energies of all removed electrons, is released on a very small localized area of a few nm2 and in very short times of tens of fs. Hence the power density deposited into the surface can reach values of up to 1014 Wcm−2 depending on the ions incident charge state. The changes in surface topology depend strongly on the electronic excitation in the surface and its lateral and longitudinal confinement. Focus of our investigations is the interaction of slow HCIs with surfaces that have a high confinement of excitation. Such surfaces are mainly all kind of insulators, but also samples with an additional confinement due to a layered structure. In this case the electron transfer between different layers is suppressed and the interacting system becomes quasi two dimensional. Investigations were performed at the Rossendorf Two Source Facility, an ion beam facility consisting of two sources: a 14.5 GHz ECR ion source and an Electron Beam Ion Source, the Dresden EBIT [3]. Ions of both sources are decelerated by a common deceleration unit to suppress kinetic effects during ion surface interaction. The combination of these both sources offers ions of various charge states (up to q = 44 for Xe), species (He, Ne, Ar, Xe, C, N, O) and kinetic energies (<q · 100 eV to q · 25 keV). We present scanning probe microscopy studies of surface modifications induced by single ion impacts. HOPG, MICA and ultra thin SiO2 layers were irradiated with ions of argon (charge states q = 1...16) and xenon (charge states q = 1...40). The diameter and the height of created nano structures wer e investigated in dependence on the ion charge state for both ion species. Additional to SPM investigations Raman spectroscopy of HOPG before and after irradiation was performed to get information about structural changes induced by the HCI impact.