Photoemission, autoionization, and x-ray-absorption spectroscopy of ultrathin-filmC60on Au(110)

The occupied and unoccupied electronic states of ${\mathrm{C}}_{60}$ have been studied for single monolayer and multilayer coverages on Au(110). Only the electronic structure of the first layer, which is chemisorbed, is changed by the interaction with the substrate, due to hybridization with the possibility of charge transfer. There is no measurable bonding interaction with the second layer, which has essentially the same electronic structure as the thick film. The unoccupied electronic states below the ionization level are shown to be largely localized around the ${\mathrm{C}}_{60}$ molecule. The energy levels of the molecules not in direct contact with the substrate are referenced to the vacuum level.