Nano-hillock formation on CaF2 due to individual slow Au-cluster impacts

Ion-irradiation and the induced nanostructuring was found, over the last century, to be a very powerful technique for surface modifications on a vast amount of different materials. Especially the formation of nanostructures by strong electronic excitation mediated by slow highly charged ions and swift heavy ions received lots of interest in recent years. The ionic crystal CaF2 was a model system for the underlying processes. In our investigations we reveal the formation of nano-hillocks by slow individual Au-cluster-irradiation on CaF2(111) surface that were found to be very similar to nano-hillocks in former studies with highly charged ions. We show that the high energy density directly transferred to the atomic lattice of the target leads to the same hillock-like structures as in case of indirect energy transfer for slow highly charged ions.