Molecular self-assembly controls graphene-edge configuration

A research team headed by Prof. Patrick Han and Prof. Taro Hitosugi at the Advanced Institute of Materials Research (AIMR), Tohoku University discovered a new bottom-up fabrication method that produces defect-free graphene nanoribbons (GNRs) with periodic zigzag-edge regions. This method, which controls GNR growth direction and length distribution, is a stepping stone towards future graphene-device fabrication by self-assembly.

Graphene, with its low dimensionality, high stability, high strength, and high charge-carrier mobility, promises to be a revolutionary material for making next-generation high-speed transistors. Moreover, graphene's properties are predicted to be directly controllable by its structure. For example, recent works have demonstrated that the bandgap of armchair GNRs is controlled by the ribbon width. However, the property-tailoring capabilities of other edge conformations (e.g., the zigzag edge is predicted by theory to have magnetic properties) have not been tested, because their defect-free fabrication remains a major challenge.

"Previous strategies in bottom-up molecular assemblies used inert substrates, such as gold or silver, to give molecules a lot of freedom to diffuse and react on the surface," says Han. "But this also means that the way these molecules assemble is completely determined by the intermolecular forces and by the molecular chemistry." Currently, there is no molecule that can assemble to produce zigzag-edge GNRs.