Institut des Sciences Moléculaires d'Orsay, CNRS, Université Paris Sud, 91405 Orsay, France.
Phys Chem Chem Phys. 2013 Apr 14;15(14):4939-46. doi: 10.1039/c3cp42591f.
Scanning Tunneling Microscopy (STM), Scanning Tunneling Spectroscopy (STS), and manipulation studies were performed on an ordered self-assembled monolayer (SAM) of N,N'-bis(1-hexylheptyl)perylene-3,4:9,10-bis(dicarboximide) molecules on epitaxial graphene on hexagonal silicon carbide - SiC(0001). Four novel aspects of the molecular SAM on graphene are presented. Molecules adsorb in both armchair and zig-zag configurations, giving rise to six orientations of the molecular layer with respect to the underlying substrate. The interaction between the molecules and the graphene surface shifts the LUMO towards the Fermi level, inducing a charge transfer and the opening of a band gap in the graphene, with the LUMO inside. This decouples the LUMO from the surface rendering it invisible in the dI/dV spectroscopy. The HOMO only becomes visible at short tip-surface distances, as its energy lies within the band gap of the SiC substrate. Finally, the observed molecular defects are very particular, being composed exclusively of molecular dimers. These molecular dimers have a stronger interaction with the graphene than other molecules.
在六方氮化硼上外延生长的碳化硅（0001）衬底上的石墨烯上，对 N,N'-双（1-己基庚基）苝-3,4:9,10-双（二羧酸酰亚胺）分子的有序自组装单层（SAM）进行了扫描隧道显微镜（STM）、扫描隧道光谱（STS）和操纵研究。本文提出了分子 SAM 在石墨烯上的四个新特性。分子以扶手椅和锯齿形两种构型吸附，导致分子层相对于基底有六种取向。分子与石墨烯表面的相互作用将 LUMO 推向费米能级，导致石墨烯中的电荷转移和带隙打开，而 LUMO 在内部。这将 LUMO 与表面分离，使其在 dI/dV 光谱中不可见。HOMO 仅在短的针尖-表面距离处可见，因为其能量位于 SiC 衬底的带隙内。最后，观察到的分子缺陷非常特殊，仅由分子二聚体组成。这些分子二聚体与石墨烯的相互作用比其他分子更强。
