Threshold and efficiency for perforation of 1 nm thick carbon nanomembranes with slow highly charged ions

Cross-linking of a self-assembled monolayer of 1,1'-biphenyl-4-thiol by low\nenergy electron irradiation leads to the formation of a carbon nanomembrane, which\nis only 1nm thick. Here we study the perforation of these freestanding membranes by\nslow highly charged ion irradiation with respect to the pore formation yield. It is found\nthat a threshold in potential energy of the highly charged ions of about 10 keV must be\nexceeded in order to form round pores with tunable diameters in the range of 5 - 15 nm.\nAbove this energy threshold the efficiency for a single ion to form a pore increases from\n70% to nearly 100% with increasing charge state. These findings are verified by two\nindependent methods, namely the analysis of individual membranes stacked together\nduring irradiation and the detailed analysis of exit charge state spectra utilizing an\nelectrostatic analyzer.