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.