SCANNING TUNNELING MICROSCOPY OF THE DAMAGE INDUCED BY ION-BOMBARDMENT ON A GRAPHITE SURFACE

We have used a scanning tunneling microscope to study the effects of ion bombardment on a freshly cleaved graphite surface. The large-scale images reveal the formation of small hillocks whose size is analyzed for ions of increasing masses, as C-12+, N-14+, S-32+, Ar-40+ and Xe-131+, and for various energies (from 5 to 40 keV). The volume of these defects is found to vary as the damage energy. It is therefore possible to predict the surface disorder by means of the damage distribution. Structural modifications on the atomic scale such as crystallites or square-root 3 X square-root 3 R30-degrees superstructures are also observed next to some hillocks. Since the classical models describe the surfaces bombarded with low doses as undamaged, these STM observations force us to reconsider this macroscopic description when only a few atoms are considered.