An atomic vacancy was produced at the surface by bombarding it with 40 to 80eV beams of Ar ions, and its structure was examined by means of scanning tunnelling microscopy and atomic force microscopy. The atomic vacancy was imaged as a surface protrusion by scanning tunnelling microscopy, while it was transparent to atomic force microscopy. These contradictory results were explained by a vacancy-induced enhancement of the partial charge density of states at C atoms near to the vacancy. The charge enhancement could occur over tens of surrounding C atoms in the case of multi-atom vacancies.

J.R.Hahn, H.Kang, S.Song, I.C.Jeon: Physical Review B, 1996, 53[4], R1725-8