Nanostructure formation due to impact of highly charged ions on mica

Muscovite mica was irradiated with slow highly charged Arq+ (charge state q = 12, 16) and Xeq+ (q = 23, 27) ions in a kinetic energy range of 150-216 keV and subsequently observed by contact mode atomic force microscopy. Surprisingly, on samples irradiated with Xe ions nano-sized hillock-like structures were found well below the charge state threshold reported in earlier experimental investigations. However, the structures found are not the result of a true topographic surface modification induced by the ion bombardment, because the absence of these nanostructures in tapping mode images and the dependence of the detected structures on scan conditions points towards a surface modification which manifests itself only in frictional forces and therefore in height measurement artifacts. Furthermore the generated defects are not stable but can be erased by continuous scanning.