Nano Lett.http://doi.org/hsm (2012)

Graphene electronic devices can take advantage of the very high conductivity of this single layer of carbon atoms. But how is the current actually distributed in a graphene flake of finite size? According to Jungseok Chae and co-authors there is a strong current enhancement at the edges. They used a scanning gate microscope to monitor the variation of current induced by a gate voltage applied locally on the surface of a graphene transistor. Nothing remarkable occurs when no charges are present in the flake, but a considerable enhancement is evident when either holes or electrons are there. The team explained the observation by the opening of a conduction band induced by zigzag edges, which is significant regardless of the flake size, but can be dominant in very narrow ones. The results could therefore be important for the design of devices based on graphene nanoribbons, typically only a few tens of nanometres wide.