Edges bring new dimension to graphene nanoribbons.

Chemistry at the edges of saturated graphene nanoribbons can cause ribbons to leave the plane and form three-dimensional helical structures. Calculations, based on density functional theory and enabled by adopting helical symmetry, show that F-terminated armchair ribbons are intrinsically twisted in helices, unlike flat H-terminated strips. Twisting ribbons of either termination couple the conduction and valence bands, resulting in band gap modulation. This electromechanical response could be exploited in switches and sensor applications.