Tight binding studies of exohedral silicon doped C 60

Abstract

We study the exohedral doping of C 60 fullerenes by silicon atoms. The structural properties and stability of C 60Si m aggregates, with m in the range 1–15, are investigated using a non-orthogonal tight binding model. For each cluster size an extensive set of possible configurations has been considered in order to increase the likelihood of determining the lowest energy structure. Each configuration was then minimised using the conjugate gradients algorithm. We find that for cluster sizes up to C 60Si 5 the trend is for Si atoms to aggregate, forming a monolayer on the C 60 surface, while for C 60Si m with m equal to 5 and beyond the trend changes towards the formation of three dimensional Si clusters attached to the fullerene surface. For m⩾8 the additional Si atoms place themselves on the Si already present, and not directly on the buckyball surface. We have also conducted dynamical simulations of cluster fragmentation, which indicate that when the fragmentation of C 60Si m takes place, it generates two homonuclear pieces, i.e., a Si m cluster and the C 60 fullerene, which remains intact, in agreement with photofragmentation experiments.