STM imaging, spectroscopy and manipulation of a self-assembled PTCDI monolayer on epitaxial graphene

다국어 초록 (Multilingual Abstract)

<P>Scanning Tunneling Microscopy (STM), Scanning Tunneling Spectroscopy (STS), and manipulation studies were performed on an ordered self-assembled monolayer (SAM) of <I>N</I>,<I>N</I>′-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 d<I>I</I>/d<I>V</I> 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.</P>

<P>Graphic Abstract</P><P>Scanning tunneling microscopy and spectroscopy studies of a self-assembled hexyl heptyl PTCDI monolayer on epitaxial graphene reveal molecules adsorbed in two configurations. Charge transfer induces band gap opening in graphene and decouples the LUMO.
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