Electronic structure at the C-60/metal interface: An angle-resolved photoemission and first-principles study

High-resolution angle-resolved photoemission reveals a complex electronic structure at the interface between a highly ordered C-60 monolayer and the Cu(111) surface. The Shockley-type surface state of the clean substrate is pushed to higher energies by the overlayer and strongly couples to intramolecular C-60 phonons. A second interface state with a bandwidth spanning the entire HOMO-LUMO gap disperses with the periodicity of the C-60 superstructure. Density functional theory calculations indicate that this state is due to strong hybridization of molecular orbitals and substrate electronic states at the C-60/metal interface. This finding sheds light on the issue of self-doping in molecular layers on metal surfaces.