Surface Nanostructuring Induced by Slow Highly Charged Ions

Because of the large amount of potential energy that slow highly charged ions SHCIs carry with respect to their kinetic energy, the interaction of such ions with surfaces is characterized by interesting features and results in a pronounced modification of the surface and near-surface regions. The project aims to reach a better understanding of surface modifications induced at the surfaces of various materials by SHCIs. These studies are devoted mainly to solve the puzzle of observing hillocks in several insulating materials after irradiation with SHCIs, where one might expect craters rather than hillocks. The proposed materials are crystalline CaF2 and LiF. Both materials have many applications in various fields. For example CaF2 is a potential insulator in silicon based microelectronic devices. The ion induced surface nanostructures will be investigated using mainly in situ UHV scanning probe microscopy (AFM and STM). The measured features will be correlated to the measured ion-induced sputtering, where the quartz-crystal microbalance technique will be used for the detection of the sputtering yield. In addition, UV-Vis absorption spectroscopy of the ion irradiated crystals will be performed to observe the produced optical centers and their following aggregates. The results obtained from all these techniques are expected to give an explanation about the origin of these hillocks. The second part of the proposal is aiming to create 7x7 reconstruction of the silicon (111) surface which is only stable at exceptionally low pressures. Although this surface is considered as one of the most complicated surface structure, it has promising applications as it use as a pre-patterned template where nanostructures with well defined size and position can be inserted. To this goal the SHCIs will be used as a tool to create these defined nanostuctures. After irradiation with different ions, the surface will be investigated using STM (at constant current mode) as well as AFM (tapping mode). One of the most promised applications of this proposal is the using of ion bombardment in the ECR source at TU Wien as tool for the generation of ordered nanometer-scaled quantum dots on various surfaces. Both the first and the second part of the proposal will lead to the long term goal which is to understand and control the mechanisms of nanometer-scale structural transformations of semiconductor and insulator surfaces induced by SHCIs. This is expected to make a strong contribution to nanotechnological tools.