The surface defects which were produced by single-ion impacts of highly-charged Ar ions (charge state of up to 8) were investigated by using scanning tunnelling microscopy and atomic force microscopy. The defect appeared to be a protrusion in scanning tunnelling microscopic images, but appeared flat in atomic force microscopy images. On the basis of these contrasting images, the defects were concluded to be due to an increase, in the local charge density of states at the surface, which was caused by C-atom sputtering. The average defect size increased markedly with the charge state of the incident Ar ions. This was attributed to an enhancement of potential sputtering, due to the Coulomb repulsion between surface holes which were generated by the neutralization of highly charged Ar ions.

K.Mochiji, S.Yamamoto, H.Shimizu, S.Ohtani, T.Seguchi, N.Kobayashi: Journal of Applied Physics, 1997, 82[12], 6037-40