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Observation of sub-20nm line-defects in graphene by friction force microscopy

Graphene films, produced by chemical vapor deposition (CVD) on copper foils, generally have a lot of line-defects, such as grain boundaries and nanogaps between adjacent graphene domains. We demonstrated to identify such 1-D defects with size less than 20 nanometers using friction force microscopy (FFM). These line defects can be clearly observed in friction force images, while no height variation in simultaneously collected topographic ones. The possible reasons for line defects imaging under FFM mode is also studied.