Formation of an intercalation-like system by intercalation of C-60 molecules underneath a graphite monolayer on Ni(111)

The intercalation of C-60 molecules underneath a monolayer of graphite (MG) adsorbed on Ni(111) has been investigated by means of high resolution elec tron energy loss spectroscopy (HREELS) and angle resolved photoemission (PE ). Deposition of a thick layer of C-60 onto the MG/Ni(111) surface with sub sequent annealing to 600-700 K leads to a partial intercalation of C-60 mol ecules underneath MG, i.e. formation of areas with intercalated C60 molecul es and some initial MG/Ni(111) areas without intercalation. A number of int eresting features in the HREEL and PE spectra can be ascribed to the areas with intercalated C60: Stiffening of the phonon modes up to values characte ristic for pristine graphite, shift of the C-60 valence band states towards lower binding energies, and the appearance of a sharp structure close to t he Fermi level. All these features can be explained assuming a modification (weakening) of the 'substrate-overlayer' interaction caused by the interca lation of C-60. (C) 2000 Elsevier Science B.V. All rights reserved.