Ultra-thin MoS2 irradiated with highly charged ions

Single MoS2 layers exfoliated on KBr have been irradiated with highly charged Xe ions, i.e. with Xe35+ and Xe40+. By atomic force microscopy (AFM) we identified pits and hillocks induced by single ion impacts. The latter ones appear on single layer and bulk-like MoS2 after both irradiations, whereas their diameter and height apparently depend on the charge state q and layer number. By comparison of contact mode and tapping mode AFM measurements we deduce that these ion induced defects are topographical hillocks accompanied by an enhanced friction. In contrast to this, pit-like structures were only observed on single layer MoS2 irradiated with q = 40. Taking into account the well known ion induced pit formation on KBr due to defect mediated sputtering, we deduce that pit formation takes place in the substrate and not in the MoS2 layer.