Interaction of C₆₀ with silicon dangling bonds on the Si(111)-(7 × 7) surface

We report here the measurements of vibrational excitation spectra of C₆₀ molecules adsorbed on Si(111)-(7 × 7) and H-terminated Si(111)-δ(7 × 7) surfaces using high-resolution electron energy loss spectroscopy. Upon adsorption of C₆₀ on Si(111)-(7 × 7), a shift to a lower energy is measured for the ν₁ and ν₄ vibrational modes, but no indication of softening is observed on the H-terminated Si(111)-δ(7 × 7) surface. These results show that the C₆₀ molecules interact strongly with the dangling bonds of adatom on the (7 × 7) structure. From the softening of the vibrational modes, the amount of charge transfer is estimated to be (3 ± 1) electrons per C₆₀ molecule on the Si(111)-(7 × 7).