Vibrational modes of C₆₀ fullerene on Si(100)2x1 surface

We have measured coverage and scattering angle dependences on the electron energy loss by vibrational excitations of C₆₀ on the Si(100)2x1 surface using a high-resolution spectrometer. If C₆₀ is evaporated 5 Å (approximately half a monolayer) on Si(100), a strong energy loss peak appears at 65 meV, and weak peaks and shoulders at 72, 144, and 175 meV. In the 12 Å thick film, additional weak peaks at 96, 160, and 189 meV become more apparent. Intensities of these peaks are comparable to those of thick films measured by infra-red absorption and by Raman scattering spectroscopies. These results suggest appreciable interactions between C₆₀ and the dangling bonds of Si surface.