Nanodots formation with slow highly charged ions

We have been developing a compact electron beam ion source with a high-T-c superconductor as a solenoid magnet, which can be operated at liquid nitrogen temperature, and can deliver slow highly-charged ions as high as q = 42. With this ion source together with other ion sources, nanodot formation processes were studied for a highly oriented pyrolytic graphite (HOPG) plate as a target. The impact site was observed with both the scanning tunnelling microscope (STM) mode and non-contact atomic force microscope (NCAFM) mode. It was found that protrusion-like dots were observed for both modes at the same position, and one HCI induced one dot. The dot size (diameter) and height were observed to be more or less the same for both modes, i.e, an HCI impact induces topographic modification on the HOPG surface. The dot size and height were measured as functions of the charge state (q = 8-46) and the kinetic energy (E = 1 - 300 keV) of highly-charged ions. It was found that the dot size increased linearly with the charge state, although the dependence on the kinetic energy was very weak if any.