Changes in the dipolar vibrational fingerprint of C upon 60 adsorption and K intercalation

The HREELS spectra of a C60 monolayer deposited on Ag 111.show evidences for a strong chemical bonding with the Ag substrate, accompanied by a charge transfer of about 1 electron per adsorbed molecule. K atom intercalation in the adsorbed layer allows an easy tuning of the C60 LUMO t1u.occupancy. The evolution of the C60 intramolecular vibrational spectrum upon K intercalation is studied by HREELS and discussed with particular emphasis on the two Ag Raman active. and four T1u IR active.modes. Both Ag modes exhibit at the interface dipolar activity explained by electron–phonon coupling. Upon K intercalation, the T1u modes show an evolution similar to what is observed in K- or Rb-doped bulk C60, allowing to identify C660y as the saturated phase. q2000 Elsevier Science B.V. All rights reserved.