Researchers in the US, Germany, Singapore and Spain have developed a new technique to image grain boundary defects in graphene by analysing how surface plasmons are reflected and scattered by the defects. The study reveals that the boundaries, which act as electronic barriers around 10–20 nm in size, are responsible for the low electron mobility observed in graphene grown by chemical vapour deposition. These barriers might be used as tuneable “plasmon reflectors” and “phase retarders” in plasmonic circuits made of graphene in the future. Grain boundaries in graphene Graphene, a single atomic layer of sp2-hybridized carbon arranged in a honeycomb lattice, is a promising material for making molecular electronic devices of the future thanks to its unique electronic and mechanical properties that include extremely high electrical conductivity and exceptional strength. Defect-free graphene has the best mechanical and electronic properties but current techniques to synthesize graphene sheets large enough to use in applications invariably produce grain boundary defects. Such defects (which can be likened to the seams in patchwork quilts, made of pieces of fabric that have been sewn together) are notoriously difficult to characterize using conventional microscopy techniques such as transmission electron or optical microscopy that provide only limited information. These

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