Charge state of ∼1 to 50 keV ions after passing through graphene and ultrathin carbon foils

Abstract

Carbon foils have been used reliably for many decades in space plasma instrumentation to detect ions and energetic neutral atoms (ENA). When these particles pass through a foil, secondary electrons are emitted on both sides. Those electrons are used for coincidence detection and/or timing signals. Ultrathin carbon foils are also used to convert an ENA into an ion for further analysis. The interaction of particles with carbon foils also includes unwanted effects such as energy straggling and angular scattering, both of which scale with foil thickness. Therefore, it has always been a goal to use foils as thin as practically possible. The foils used in space are usually made of amorphous carbon of roughly a hundred atomic layers. Graphene can be made much thinner, even down to a single atomic layer, and is therefore a natural candidate for this kind of application. We evaluate one aspect of the interaction of particles with foils: charge exchange. We show the first measurements of exit charge state distributions of ~1 to 50 keV ions passing through self-supported graphene foils. We compare the charge state fraction of exiting particles with state-of-the-art amorphous carbon foils. © 2014 The Authors.