Author's personal copy In situ observations of the nucleation and growth of atomically sharp graphene bilayer edges

Using in situ transmission electron microscopy, we observed the nucleation and growth of graphene bilayer edges (BLE) with ‘‘fractional nanotube’’-like structure from the reaction of graphene monolayer edges (MLEs). Most BLEs showed atomically sharp zigzag or armchair crystallographic facets in contrast to the atomically rough MLEs with irregular shapes, suggesting that the BLEs are much more stable and crystallographically anisotropic. Our direct observations and theoretical studies (geometric models and ab initio calculations) provide important clues for tailoring the edge structure and transport properties of multi-layer