Switchable supramolecular assemblies on graphene.

We studied the self-assembly of trimesic acid on single- and few-layer graphene supported by SiO2 substrates. A scanning tunneling microscope operated under ambient conditions was utilized to image supramolecular networks of trimesic acid at liquid-graphene interfaces. Trimesic acid can self-assemble into large-scale, highly ordered adlayers on graphene surfaces. Phase transition of the trimesic acid adlayer from a close-packed structure to a porous chicken-wire structure was observed by changing from single- to few-layer graphene, which was attributed to the modulation of molecule-graphene interactions by the layer number of graphene. The guest-induced phase transition of trimesic acid by complexation with coronene on single-layer graphene further confirms that supramolecular networks on graphene can be rationally tailored with sub-nanometer resolution by balancing between intermolecular vs. molecule-graphene interactions. We further investigated the effects of trimesic acid adlayers on the electronic transport properties of graphene transistors. The adsorption of trimesic acid induces p-doping and defects in the adlayers cause scattering of charge carriers in single-layer graphene.