Internal structure and two-dimensional order of monolayer C60 molecules on gold substrate

Monolayer coverages of C60 on a gold substrate have been studied using scanning tunneling microscopy. The images reveal various packing arrangements and reproducible intramolecular contrasts of the C60 molecules. We find that approximately every other carbon atom is highlighted on the π-electron surface of the molecule as a result of a preferential electron transfer from the gold substrate, in agreement with a theoretical analysis of the high-lying π-electron density of a C60 molecule adsorbed on metallic surfaces.