Structural and Electronic Decoupling of C₆₀ from Epitaxial Graphene on SiC

Abstract

We have investigated the initial stages of growth and the electronic structure of C(60) molecules on graphene grown epitaxially on SiC(0001) at the single-molecule level using cryogenic ultrahigh vacuum scanning tunneling microscopy and spectroscopy. We observe that the first layer of C(60) molecules self-assembles into a well-ordered, close-packed arrangement on graphene upon molecular deposition at room temperature while exhibiting a subtle C(60) superlattice. We measure a highest occupied molecular orbital-lowest unoccupied molecular orbital gap of ∼3.5 eV for the C(60) molecules on graphene in submonolayer regime, indicating a significantly smaller amount of charge transfer from the graphene to C(60) and substrate-induced screening as compared to C(60) adsorbed on metallic substrates. Our results have important implications for the use of graphene for future device applications that require electronic decoupling between functional molecular adsorbates and substrates.

van der Waals interactions mediating the cohesion of fullerenes on graphene

“…These findings are consistent with the recent observation made by Cho et al. 14 The detail in the inset of Fig. 1(a) shows submolecular resolution, which suggests the adsorbed molecules on SLG are all equally oriented.…”

“…Charge transfer from the surface to a C 60 is negligible, amounting to ≈0.03 electrons/C 60 , which has been suggested recently. 14 Interestingly, when we perform the total energy calculations without the vdW interactions (E DFT ), all four structures result about the same energy (with differences less than 3 meV/C 60 ) and therefore the orientation of the molecules in the islands on the surface would not have any particular preference under our experimental conditions. The introduction of the vdW interaction results in a considerable reduction of the C 60 -SLG distance (d vdW compared to d DFT ).…”

“…In particular, the width of the gap between the highest occupied and lowest unoccupied states of a C 60 is likely to be overestimated. 14 So far, we have pointed out the dominance of vdW intermolecular attraction between the C 60 molecules on SLG. Due to a distinct decay and strength of this force one can expect a qualitatively different dynamical behavior of the molecules in this system.…”

“…In contrast to these studies, we found a much weaker interaction of the C 60 with the SLG grown on 6H-SiC(0001), which lead us to a workbench to discuss the origin of the bonding mechanism in weakly interacting systems. Very recently a study of a very similar system appeared, 14 which characterizes the basic behavior of the C 60 on a graphene layer at 6H-SiC(0001) near to one monolayer coverage and studies its electronic properties based on scanning tunneling spectroscopy.…”

Nanoelectrical analysis of single molecules and atomic-scale materials at the solid/liquid interface

“…Figure 4b shows a well-resolved dI /dV spectrum (acquired over the sites indicated in the in situ STM image, Fig. 4a) with a distinctive line shape resembling the energy spectrum of graphene, similar to previous STS observations of graphene on non-metallic substrates [51][52][53] . The minimum in each of the directly measured spectral curves corresponds to the charge-neutral Dirac point (E D ) located at positive bias energy slightly above the Fermi level.…”