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

Fullerene (C60) 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 C60 molecule and Si adatoms, and the internal structure of the C60 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 C60 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 C60 molecules. The internal structure of C60 molecules was clearly observed in topography by the second order amplitude (A2) feedback signal for 1 ML coverage, reflecting the LDOS originating from the t1u orbital.