New evaluation of fullerene molecules on Si(111)-(7 × 7) reconstructed structure using non-contact scanning non-linear dielectric microscopy

Fullerene (C ₆₀) molecules on an Si(111)-(7 × 7) surface have been investigated using non-contact scanning non-linear dielectric microscopy (NC-SNDM) under an ultra-high vacuum. The topography, the interface between the C ₆₀ molecule and Si adatoms, and the internal structure of the C ₆₀ molecules were successfully investigated. For ∼ 0 ML and ∼ 0.4 ML coverage, both phase reversal sites and sites without phase reversal could be observed in the first order phase (θ1) image. On the other hand, for 1 ML coverage, phase reversal could not be identified. These results indicate that charge transfer only occurred from Si adatoms to C ₆₀ molecules at three-fold symmetric sites on the Si(111)-(7 × 7) surface, and the electric dipole moment is reflected in the electronic state of the C ₆₀ molecules. The internal structure of C ₆₀ molecules was clearly observed in topography by the second order amplitude (A ₂) feedback signal for 1 ML coverage, reflecting the LDOS originating from the t _1u orbital.