Scanning tunneling microscopy and atomic force microscopy study of graphite defects produced by bombarding with highly charged ions

The defects produced on a graphite surface by single ion impact using highly charged Ar ions (charge state q less than or equal to 8) is investigated by scanning tunneling microscopy (STM) and atomic force microscopy (AFM). The defect looks like a protrusion in the STM image, while it is flat in the AFM image. From these two contrasting images, the defects are considered to be due to the increase in the local charge density of state at the surface caused by carbon atom sputtering. The average value for the defect size increases remarkably with the charge state of incident Ar ions, This is explained by the enhancement of potential sputtering due to the Coulomb repulsion between surface holes which are generated by the neutralization of highly charged Ar ions. (C) 1997 American Institute of Physics.