Interplay of covalent bonding and correlation effects at molecule–metal contacts

We compare photoelectron spectra (PES) and theoretical densities-of-states of C60/Al(1 1 1), C60/Al(1 1 0) and C60/Al(1 0 0). The splitting observed on all three surfaces is attributed to final state charging. This splitting can also be used to improve estimates of the charging energy U of adsorbed molecules and as a criterion for the existence of strong covalent bonding to the electrode. Au exhibits weak bonding in available data, whereas Ag(1 0 0), with measurable charge transfer, appears qualitatively similar to Al.