Charge transfer and structure inC60adsorption on metal surfaces

The charge state and structure of ${\mathrm{C}}_{60}$ monolayers deposited on Au(110), polycrystalline Ag, and Ni(110) have been investigated by electron-energy-loss spectroscopy and low-energy electron diffraction. The vibrational excitation spectra have been used to obtain a quantitative determination of the molecular charge state of the adsorbed ${\mathrm{C}}_{60}$ molecules. On both the Au(110) and Ag surfaces the charge transfer from the surface to the ${\mathrm{C}}_{60}$ is found to be (1±1) electrons and that on Ni(110) is (2±1) electrons. These estimates are supported by the metallic nature of the low-energy (0–7.5 eV) electronic excitations of the monolayers. For submonolayer coverages of ${\mathrm{C}}_{60}$, rectangular overlayer phases are observed on Ni(110) in contrast to the close-packed islands seen on the other metals. This difference in the low-coverage structure can be related to differing substrate-adsorbate interactions, directly reflected by the ${\mathrm{C}}_{60}$ charge state.