Nano-hillock formation on CaF2due to individual slow Au-cluster impacts.

We present a direct way to generate hillock-like nanostructures on CaF2(111) ionic crystals by kinetic energy deposition upon Au-cluster irradiation.In the past, the formation of similar nanostructures has been observed for bothslow highly charged ions and swift heavy ions. However, in these cases, potentialenergy deposition of highly charged ions or the electronic energy loss of fast heavyions, respectively, first leads to strong electronic excitation of the target materialbefore the excitation energy is transferred to the lattice by efficient electron-phonon coupling. We now show that the kinetic energy deposited by slow singleAu-clusters directly in the lattice of CaF2(111) leads to the production of nano-hillocks very similar to those found with slow highly charged and swift heavyions, with heights between 1-2 nm. Our results are in good agreement withprevious cluster irradiation studies regarding energy deposition and hence nano-structuring of surfaces, and we present Au-cluster irradiation as novel tool to finetune nanostructure formation.