Observation of charge enhancement induced by graphite atomic vacancy: A comparative STM and AFM study

An atomic vacancy is produced on a graphite surface by bombarding it with low-energy (40-80 eV) beams of Ar⁺ ions, and its structure is examined by scanning tunneling microscopy (STM) and atomic force microscopy (AFM). The atomic vacancy is imaged as a surface protrusion in STM, while it is transparent in AFM. These two contradictory results are explained by the vacancy-induced enhancement of the partial charge density of states at the carbon atoms near the vacancy. The charge enhancement can occur over tens of the surrounding carbon atoms for multiatom vacancy.