ENERGETIC FULLERENE INTERACTIONS WITH SI CRYSTAL-SURFACES

The interaction of fullerene molecules with silicon crystal surfaces is modelled using molecular dynamics. The results are compared to similar interactions with graphite surfaces. In contrast to the results for graphite, it is found that the molecule rarely reflects intact from the surface. When reflection does occur it is always at near grazing incidence with impact energies less than 300 eV. At normal incidence and similar energies the molecule remains intact, but becomes embedded in the surface layers of the Si lattice. Grazing incidence (congruent-to 75-80-degrees to the surface normal) at energies of a few hundred eV results in the C60 molecule becoming trapped in the surface binding potential. The molecule can roll across the surface for up to one revolution before coming to rest. At energies of greater than congruent-to 500 eV, at grazing incidence, the molecule breaks up on impact with the majority of the constituent atoms reflected. Normal incidence with impact energies in excess of 1 keV leads to disintegration of the C60 molecule and sputtering from the crystal, with the ejection of atoms and larger Si(x)C(y) molecules. This is especially evident at energies greater than 4 keV where high-energy deposition near die impact point creates a crater surrounded by a hot disordered region from which Si atoms can be thermally ejected for times up to the order of 1 ps.