SCANNING TUNNELING MICROSCOPY OF DEFECTS INDUCED BY CARBON BOMBARDMENT ON GRAPHITE SURFACES

HOPG graphite samples are bombarded at room temperature with a 20 keV 12C+ ion beam and the surface topography is investigated by scanning tunneling microscopy (STM) for increasing doses. Lattice deformations and point defects are observed on the nanometer scale and several types of defects can be identified. The surface topography modifications appearing on the atomic scale are analyzed and theoretical damage calculations are done in order to associate the surface features after bombardment with the generation of the defects due to the ionic impact and subsequent cascade development. The experiments reported here show that the number of visible defects is not linearly dependent on the dose. Most of the defects observed by STM seem to result from interstitial migrations and lattice rearrangements following disorder generation by the cascade. It is also reported that the "atomic" resolution of the STM is lost when the graphite is supposed amorphous. © 1990.