Chemisorption of small fullerenes C-n (n=28,32,36,40,44,48,60) on the Si(001)-c(2x1) surface

We present a systematic first-principles study using density-functional theory on chemisorption of small fullerenes C-n (n=28,32,36,40,44,48,60) on the Si(001)-c(2x1) reconstructed surface. The most stable adsorption structures were identified and the size-dependent adsorption strength was calculated. Detailed analysis on the geometric and electronic structures indicates that fullerenes can be strongly anchored on the substrate. Unlike adsorption of small unsaturated organic molecules on Si surfaces, where adsorption on top of Si dimers was reported to be favored, the trench channel and the two adjacent Si dimer sites were found to be the energetically preferred binding sites for fullerenes. Our results indicate that the adsorption strength is largely determined by the local curvature of fullerene molecules near the binding sites, the geometric fitness between fullerenes and adsorption sites and the stability of fullerene electronic structures. In addition, charge transfer from the substrate to fullerenes was found to be relatively small due to the highly covalent nature of the C-Si bonds formed upon fullerene chemisorption.