Ambient AFM investigation of nanostructures on CaF2 single crystals induced by slow highly charged Ar and Xe ions

Full text: Atomic force microscopy (AFM) is a convenient method to study nanostructures on insulating atomically flat surfaces. We have irradiated freshly cleaved CaF2 (111) surfaces with slow (v < 1 a.u.) highly charged ions from the Heidelberg Electron Beam Ion Trap facility, transferred the samples to Vienna and investigated them with our ambient AFM. This was feasible because - like for other ionic fluoride single crystals - ion-induced surface structures in CaF2 are known to be stable under atmospheric conditions at room temperature. Topographic AFM images show the generation of nanosized hillocks protruding from the surface. The number of hillocks per unit area stays in good agreement with the applied ion flux. We discuss the role of potential energy as well as compare our results with observations for swift heavy ion irradiations of CaF2 single crystals. (author)