Interaction of molecules on Si(1 0 0)

The interactions between pairs of C 60 molecules adsorbed upon the Si(1 0 0) surface have been studied via a series of DFT calculations. Configurations which have the fullerene cage located within the dimer trench bonded to four dimers (t4) have been investigated, as these have previously been found to be among the most stable for the C 60 molecule. These t4 configurations are explored with all possible pairs of fullerene configuration combinations considered. We have looked at two distinct groups of separation distances between the two C 60 molecules. These have the fullerene bonding sites as either adjacent to one another or separated by one Si surface dimer. Comparisons between the two groups confirm the trend of the combinations becoming more favourable at a greater fullerene separation. In the systems with adjacent bonding sites the combined pair of fullerenes were in general less favourable than the two isolated cases. At the longer fullerene separation distance this trend was reversed. The longer fullerene separation distance reflects the experimental separation observed by Moriarty et al. [P. Moriarty, Y.R. Ma, M.D. Upward, P.H. Beton, Surf. Sci. 407 (1998) 27].