STM studies of HCl-induced surface damage on highly oriented pyrolytic graphite

Scanning tunneling microscopy (STM) with atomic scale resolution has been applied to study surface defects in highly oriented pyrolytic graphite (HOPG) which have been produced by impact of 150 eV singly and multiply charged Ar ions (charge state up to 9+). The most prominent surface defects axe protrusions. Their area density is in good agreement with the applied ion dose, implying that about every single ion impact causes one protrusion. A (root3 x root3) R 30 degrees surface reconstruction, as characteristic for interstitial defects in HOPG, is observed in the vicinity of most defects. As the most remarkable result we find that the measured size of the hillocks (mean diameter and height) increases with projectile charge state.