Low energy ion irradiations in material research

The ion beam centre (IBC) of the Helmholtz-Zentrum Dresden-Rossendorf is an European leading user facility primarily dedicated to research and application of ion beam techniques in materials science. The IBC comprises various ion beam facilities (accelerators, ion beam implanters, plasma-based ion beam equipment, focused / highly-charged ion facilities) which provide a wide energy range between 100 eV and 60 MeV. Besides these facilities, structural analysis (electron microscopy and spectroscopy, X-ray scattering techniques) and sample or device processing (under clean-room conditions) are part of the IBC to deliver a “complete” user service.
Special focus of the IBC is material research with low energy ions. Irradiations of surfaces with low energy ions can induce the formation of patterns with periodicities in the range of tens to hundreds of nanometers. At off-normal angle of incidence between 50° and 70° to the surface normal ripple patterns oriented perpendicular to the ion beam direction are observed. At normal incidence or for incidence angles smaller than 50° smoothing dominates on elemental materials, like Si and Ge. However, in contrast to irradiations at room temperature pattern formation is observed at normal ion incidence irradiations performed at temperatures above the recrystallization temperature of the material. Depending on the surface orientation checkerboard patterns with two-fold, three-fold, or six-fold symmetry reflecting the crystal structure of the irradiated surface are formed (Fig. 1).
Moreover, low energy highly charged ions are used to create nanostructures on surfaces and in thin membranes by single ion impacts. In this case the release of the potential energy of the ions leads to a local phase transformation of the material. Currently a new facility for highly charged ions is developed to enable controlled single ion implantation with a positioning accuracy of a few nanometers only.