Oligothiophene Template Effects on Packings and Orientations of C60 Molecules on Ag(111) Surface

The packing conformations of sexithiophene (6T) and the orientations of the C-60 molecules on top of the preadsorbed 6T monolayer on Ag(111) surface have been investigated by the molecular dynamics simulations (on the basis of molecular mechanics) in conjunction with quantum mechanics calculations of the relative strength of intermolecular and interfacial interactions. It is demonstrated that the flat-lying oligothiophene (nT, n=4 and 6) monolayer is formed on the Ag(111) surface, and the arrangement of 6T molecules is more ordered than that in 4T film. It is also shown that the underlying 6T stripes make C-60 molecules aggregate in chainlike arrays on the 6T covered Ag(111) surface, showing significant template effects on the directed self-assembly of C-60 cages. For the absorbed C-60 molecule on the 6T prepatterned Ag(111) surface, four typical orientations, hexagon, pentagon, 6:6 bond, and 5:6 bond, are found to appear with populations of 26.3%, 2.7%, 37.5%, and 18.8%, respectively. When the deposition order is changed, the 6T stripes are shown to tilt with corrugation on the underlying C-60 carpet, revealing the important role of the deposition order in modulation of the ordered supramolecular nanostructures.