MOLECULAR-DYNAMICS SIMULATION OF A CARBON CLUSTER ION IMPACTING ON A CARBON SURFACE

High-density irradiation effects were studied by molecular dynamics si mulations of fullerene (C-60) impacting on a carbon surface. When a C- 60 ion with the incident energy of nearly 200 eV per atom impacts on t he solid surface, an effect termed 'clearing-way (CW) effect' occurs. This effect is due to the high energy density and coherency of inciden t atoms. The penetration depth of C-60 is deeper than that of the carb on monomer (C-1) with 200 eV because of the CW effect, but shallower t han that of the carbon monomer with 12 keV (200 eV per atom x 60). Thi s result is attributed to a second effect termed 'multiple-collision ( MC) effect'. This effect is caused by a large number of collisions bet ween the incident and surface atoms that occur at the impact, and thes e collisions transfer the larger component of the momenta of the clust er to the lateral direction, unlike the monomer ion impact. Therefore, the penetration depth is proportional to the cube root of the inciden t energy, and the stopping power is magnified compared with the carbon monomer. When the incident energy of the cluster increases, both the cross-section of the impact and the number of collisions decrease, the MC effect is reduced and the behavior of incident atoms becomes simil ar to that of the monomer ions. On the contrary, when the incident ene rgy of a cluster is less than the threshold energy of implantation, a cluster dissociates on the solid surface without implantation and the MC effect does not occur. It is shown that the range of incident energ y where C-60 shows a non-linear impact effect is from about 100 eV per atom to 2 keV per atom. (C) 1998 Elsevier Science S.A. All rights res erved.