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Graphene is considered to be a large aromatic molecule, the limiting case of the family of polycyclic aromatic hydrocarbons. This fascinating two-dimensional material has many potential applications, including fi eld effect transistors (FETs). However, the graphene sheets in these devices have irregular shapes and variable sizes, and contain various impurities and defects, which are undesirable for applications. Moreover, the bandgap of graphene is zero and, consequently, the on / off ratios of graphene FETs are small, making it diffi cult to build logic circuits. To overcome these diffi culties, we report here a bottom-up attempt to fabricate nanoscale graphene FETs. We synthesize structurally well-defi ned coronene molecules (consisting of 13 benzene rings) terminated with linker groups, bridge each molecule to source and drain electrodes through the linkers, measure conductance and demonstrate the FET behaviour of the molecule.
Van der Waals (vdW) forces act ubiquitously in condensed matter. Despite being weak on an atomic level, they substantially influence molecular and biological systems due to their long range and system-size scaling. The difficulty to isolate and measure vdW forces on a single-molecule level causes our present understanding to be strongly theory based. Here we show measurements of the attractive potential between differently sized organic molecules and a metal surface using an atomic force microscope. Our choice of molecules and the large molecule-surface separation cause this attraction to be purely of vdW type. The experiment allows testing the asymptotic vdW force law and its validity range. We find a superlinear growth of the vdW attraction with molecular size, originating from the increased deconfinement of electrons in the molecules. Because such non-additive vdW contributions are not accounted for in most first-principles or empirical calculations, we suggest further development in that direction.
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