A New Facility for In-Situ Characterization of Slow Highly Charged Ion Modifications of Various Materials

The interaction of highly charged ions (HCI) with materials has been studied intensively in the last years. On various materials local topographic modifications at the ion’s impact site could be identified by means of atomic force microscopy (AFM). The type of the modifications, commonly known as nano-structures, varies from pit-like (KBr, PMMA) to craters (TiO2) and hillock-like structures on CaF2 and others ([1, 2]). Most of the recent studies were performed under ex-situ conditions, meaning the target material was transported under ambient conditions from the place of irradiation to an AFM or scanning tunneling microscope. We present a new experimental set-up for in-situ investigations on HCI induced nano-structures. The set-up is based on an assembly of a Dresden-EBIT (Electron Beam Ion Trap) ion source and an Omicron ultra-high-vacuum-AFM. Samples can be mounted in the AFM and analyzed by means of AFM and STM before, during and after the irradiation with HCI. Samples can be heated in-vacuum to prepare clean surfaces before irradiation. The EBIT delivers highly charged ions with Xe charge states up to q=40+, which can be decelerated to kinetic energies
of only 10 eV·q. Figure 1 shows a drawing of the set-up. The dimensions of the set-up are small compared to other HCI facilities. The EBIT is mounted in a high voltage cave and so a negative potential can be applied, while the AFM chamber is kept on ground potential. The final kinetic energy of the ions is defined by the difference of the extraction potential (respective to ground) and the target potential (ground) by Efinal kin = (Uext − Ubeamline) · q. A lens system focusses the beam onto the target with a beam diameter of less than 1 mm.