The interaction of slow highly charged ions with carbon nano membranes

The ability of highly charged ions to induce various kinds of nanostructures at solid surfaces was intensively investigated within recent years [1-6]. Whether these nanostructures were hillocks, craters or of caldera type they all had one thing in common: a pronounced dependency of their size on the projectiles potential energy and to a minor extend on their velocity. Thus by tuning the incident ions charge state the size of nanostructures can be precisely adjusted.
The mechanisms of nano structuring by HCI impact were intensively investigated and especially for insulating surfaces of alkali and earth alkali halide crystals plausible models could be derived from extensive experimental studies [1-4]. Thereby it turned out that the confinement of initial excitations induced by the relaxing projectile as well as the coupling of electronic excitations to the phononic system of the target play a major role in the formation of nanostructures [5]. A strong local confinement of electronic excitation is not exclusively present in insulators, but can also be achieved by reducing the dimensions of the interaction volume.
In the present contribution we will show recent results of investigations on the nano structure formation by HCIs on 1nm thick freestanding carbon nano membranes (CNMs). We could successfully demonstrate the ability of HCI to create nano pores in CNMs with a diameter of a few nm, which is controllable by the projectile’s charge state [6].
Besides these findings the use of a 2D material as a target offers another unique opportunity that was not available in all previous investigations on bulk materials: the chance to have a look onto the projectile after transmission through the surface.
We could access the HCIs charge exchange and energy transfer to the surface during interaction by observing its energy and charge state distribution by means of an electrostatic analyzer (Fig.1). As a result of these investigations we will present energy loss and charge spectra of low energy (4keV...135keV) Xenon ions of
various charge states (q=5+...30+) when passing through CNMs as well as through freestanding sheets of graphene. A microscopic model to explain the experimental findings with special emphasis on the non-equilibrium charge state dependent energy loss of HCIs will be presented and discussed.

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et al., Appl. Phys. Lett. 102, 063112 (2013)