Living on the edge: A nanographene molecule adsorbed across gold step edges

The unusual adsorption geometry of the large graphene-like polycyclic aromatic hydrocarbon hexa-peri-hexabenzocoronene (HBC) across kinks on the stepped vicinal Au(11 12 12) surface has been studied by synchrotron radiation X-ray photoelectron diffraction (XPD) and scanning tunneling microscopy (STM). By a combination of the two techniques a complete characterisation of the adsorption behaviour is achieved, yielding information on preferential adsorption sites (STM) and molecular orientation (XPD). At low coverage (<0.15 ML) HBC adsorbs across kink sites in fcc-stacking regions with its axis rotated by 19° with respect to the step edge normal direction and the polyaromatic disc tilted by 12° relative to the (1 1 1) terraces of the substrate. Furthermore, a small fraction of HBCs adsorbs across straight step edges. The possible exploitation of the characteristic step- and kink-adsorption of molecular derivates of HBC in supramolecular architectures is exemplified at the example of the adsorption of a HBC-derivative on the same substrate.