STM-HREELS Investigation of C60 on Cu(111)

Abstract

Using an STM/HREELS system, we have investigated the relationship between the surface morphology and vibrational modes of C 60 adsorbed on Cu(111). At 300K, C 60 is mobile on the Cu(111) terrace, but is more strongly bound at the step edge. Therefore, any C 60 which adsorbs on the terrace will migrate to the step edge where it is immobilized. Thus for very low coverages, the C 60 preferentially adsorbs at the step edge. Adsorption of the molecule on metal surfaces results in a significant amount of charge transfer from the substrate to the C 60 molecule. Two of the four t 1u infrared active modes are predicted by theory to shift to lower frequency as the amount of charge transfer increases. However, only a softening of the lowest frequency t 1u mode was observed. Furthermore, no further shifting of the frequency of this mode was seen for very low coverages, indicating that any additional charge transfer at the step edge is smaller than one electron per C 60 molecule.