POINT-DEFECT FORMATION ON GRAPHITE SURFACE INDUCED BY ION IMPACT AT ENERGIES NEAR PENETRATION THRESHOLD

It is shown that point defects are predominantly generated by irradiating low energy noble gas ions onto a graphite(0001) surface. Scanning tunneling microscopic images of the graphite surface irradiated with 50 eV Ar+ ions show a structure corresponding to a point defect in which only one or two surface atoms are displaced. The process of ion penetration and trapping into the graphite is investigated as a function of ion energy in the range of 1-500 eV. Trapping efficiency rapidly increases with ion energy in the threshold region (10-100 eV), and leads to a saturation for higher energies. The penetration and trapping mechanism is discussed in relation to defect formation on the surface.