Positional and Orientational Templating of C60 Molecules on the Ag/Pt(111) Strain-Relief Pattern

We report on the site-specific nucleation of small C-60 molecular clusters on the strain-relief pattern formed by two monolayers of Ag on Pt(111) as well as on the orientational ordering within a molecular monolayer formed on this same template surface. Small triangular patches, which are characteristic of the strain-relief pattern, are found to be the most favorable sites for trapping single molecules. The reason for this site specificity seems to reside in a higher adsorption energy of the C60 molecules in these patches. This is different from the previously reported case of metal (Ag) deposition where diffusion barriers and therefore kinetic reasons play the major role in the confinement of the metal adatoms in hexagonal patches of the strain-relief pattern, where they form nanoislands [Brune, H., et al. Nature 1998, 394, 451]. Here, for organic molecules, the small triangular patches are definitely the nucleation centers of two-dimensional islands covering the surface up to the full monolayer coverage. The particular pinning of the molecular monolayer in these patches imposes specific orientations for the molecules, whereas anywhere else on the surface the orientational order is strongly perturbed due to intrinsic irregularities of the strain-relief pattern.