STM-HREELS INVESTIGATION OF C-60 ON CU(111)

Using an STM/HREELS system, we have investigated the relationship betw een the surface morphology and vibrational modes of C-60 adsorbed on C u(111). At 300K, C-60 is mobile on the Cu(111) terrace, but is more st rongly bound at the step edge. Therefore, any C-60 which adsorbs on th e terrace will migrate to the step edge where it is immobilized. Thus for very low coverages, the C-60 preferentially adsorbs at the step ed ge. Adsorption of the molecule on metal surfaces results in a signific ant amount of charge transfer from the substrate to the C-60 molecule. Two of the four tl, infrared active modes are predicted by theory to shift to lower frequency as the amount of charge transfer increases. H owever, only a softening of the lowest frequency tl,mode was observed. Furthermore, no further shifting of the frequency of this mode was se en for very low coverages, indicating that any additional charge trans fer at the step edge is smaller than one electron per C-60 molecule.