Vibrational modes of c6o fullerene on si(111)7×7 surface: estimation of charge transfer from silicon dangling bonds to c₆₀ molecules

We have investigated vibrational modes of C₆₀ monolayer film adsorbed on the Si(111)7 × 7 surface using high-resolution electron-energy-loss spectroscopy in combination with scanning tunneling microscopy. The differences in energies and in oscillator strengths from a thick C₆₀ film (i.e., bulk C₆₀) are discussed in terms of the charge transfer from silicon dangling bonds to C₆₀ molecules. The amount of charge transfer is estimated to be 1 ± 1 electron(s) compared with the infrared absorption spectra of alkaline-doped C₆₀ fullerides and with the weak electron- molecular-vibration coupling calculation.