Graphene is expected to be rather insensitive to ionizing particle radiation. We demonstrate that single layers of exfoliated graphene sustain significant damage from irradiation with slow highly charged ions. We have investigated the ion induced changes of graphene after irradiation with highly charged ions of different charge states (q = 28-42) and kinetic energies (E kin = 150-450 keV). Atomic force microscopy images reveal that the ion induced defects are not topographic in nature but are related to a significant change in friction. To create these defects, a minimum charge state is needed. In addition to this threshold behaviour, the required minimum charge state as well as the defect diameter show a strong dependency on the kinetic energy of the projectiles. From the linear dependency of the defect diameter on the projectile velocity we infer that electronic excitations triggered by the incoming ion in the above-surface phase play a dominant role for this unexpected defect creation in graphene. PACS numbers:The bombardment of surfaces with highly charged ions (HCI) offers an elegant way to deposit a large amount of energy into a very small volume and to study the behaviour of solid matter under such extreme conditions. In contrast to singly charged ions, HCI store a considerable amount of potential energy E pot (defined as the energy to remove the electrons from the initial atom to infinity). Upon impact they trigger significant electronic excitations in the near surface region, which can result in a variety of nanoscaled structural modifications [1]. For two dielectric materials, CaF 2 and KBr, the dependency of the structural surface modification on the charge state q and the kinetic energy E kin of the projectile was investigated in great detail [2][3][4] and could be explained in terms of different phase transitions and defect agglomeration mechanisms, respectively. In the case of CaF 2 , the good agreement with model calculations based on a twotemperature-model [3] suggests, that the transfer of the primary electronic excitation to the lattice by electronphonon-coupling is the origin of the structural modifications. For conductive materials, however, the situation is less clear as experimental evidence is sparse [5,6] and inconclusive. One way to investigate the fundamental interaction mechanisms of HCI with conductive targets is to use crystalline graphite. It can be used either in its bulk form (highly oriented pyrolytic graphite, HOPG) or in its two-dimensional (2D) form, graphene. Chemically identical, graphene shows superior electronic and heat transfer properties. As a consequence, it has even been proposed that graphene should be virtually transparent to energetic ions [7].In this paper we show, that graphene sustains significant damage even by individual HCI impacts. We demonstrate that HCI irradiation can be used to create regions of enhanced friction, which we attribute to chemical changes of the graphene lattice and whose size can be easily controlled. We present evidence that this damage is...

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The layout of a new instrument designed to study the interaction of highly charged ions with surfaces, which consists of an ion source, a beamline including charge separation and a target chamber, is presented here. By varying the charge state and impact velocity of the projectiles separately, the dissipation of potential and kinetic energy at or below the surface can be studied independently. The target chamber offers the use of tunable metal-insulator-metal devices as detectors for internal electronic excitation, a timeof-flight system to study the impact induced particle emission and the possibility to transfer samples in situ to a UHV scanning probe microscope. Samples and detectors can be prepared in situ as well. As a first example data on graphene layers on SrTiO3 which have been irradiated with Xe36+ are presented. Key words: highly charged ions, sputtering, AFM, grapheneComment: 4 pages, 4 figures, conference proceeding to 17th Internat. Workshop for Ion Surf. Collision

The generation of hot charge carriers within a solid bombarded by charged particles is investigated using biased thin film metal-insulator-metal (MIM) devices. For slow, highly charged ions approaching a metal surface the main dissipation process is electronic excitation of the substrate, leading to electron emission into the vacuum and internal electron emission across the MIM junction. In order to gain a deeper understanding of the distribution and transport of the excited charge carriers leading to the measured device current, we compare ion induced and electron induced excitation processes in terms of absolute internal emission yields as well as their dependence on the applied bias voltage.

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