The electronic structure of the 3√3 x 3√3R30°-C60/Ge(111) system as measured by angle-resolved photoemission

We have investigated the close packed 3 root 3 x 3 root 3R30 degrees-C-60 monolayer on the Ge(111) surface using synchrotron radiation photoemission. No filling of the lowest unoccupied molecular orbital (LUMO) derived bands has been observed. The C 1s core level and the valence band photoemission spectra point to the presence of a localized covalent bond between the C-60 molecules and the Ge atoms. This bond induces the splitting of the C-60 highest occupied molecular orbital (HOMO) with a new feature appearing at about 2.3 eV. The Ge 3d core level spectra show the quenching of the surface features related to the adatoms/rest atoms complex, suggesting that the observed 3 root 3 x 3 root 3R30 degrees ordering is not due to a Ge(111) reconstruction induced by the C-60 adsorption. (C) 2000 Elsevier Science B.V. All rights reserved.