Threshold and Efficiency for Pore Formation in 1nm Thick Carbon Nanomembranes by Slow Highly Charged Ions

The perforation of 1nm thick carbon nanomembranes by slow highly charged ions is studied with respect to their pore formation efficiency. It is found that a threshold in potential energy of the highly charged ions of about 10keV must be exceeded in order to form round pores with diameters of a few nm. Above this energy threshold the efficiency for a single ion to form a pore increases from 70% to nearly 100% with increasing charge state. These findings are verified by two independent methods, namely the analysis of individual membranes stacked together during irradiation and the detailed analysis of exit charge state spectra utilizing an electrostatic analyzer.