Transport of multiply and highly charged ions through nanoscale apertures in silicon nitride membranes

We report on experimental studies of the transport of multiply (Ar2,3+, 0.2–0.3 keV/u) and highly charged ions (Ar16+, Xe44+, 2–3 keV/u) through nanoscale apertures. Arrays of apertures with diameters of 50–200 nm and aspect ratios of 1.5:1–1:5 were formed in silicon nitride membranes by focused ion beam drilling in combination with ion beam assisted thin film deposition. The fraction of ions undergoing charge exchange is found to be in agreement with model predictions for low charge state ions, while it is much lower than expected for high charge state ions. We discuss results in relation to a classical over-the-barrier model and capillary guiding mechanisms.