Stabilizing the Zigzag Edge: Graphene Nanoribbons with Sterically Constrained Terminations

The zigzag edge of a graphene nanoribbon is predicted to support a spin-polarized edge state. However, this edge state only survives under a pure sp(2) termination, and it is difficult to produce thermodynamic conditions that favor a pure sp(2) termination of a graphene edge, since the edge carbons generally prefer to bond to two hydrogen atoms in sp(3) hybridization, rather than one hydrogen, as sp(2). We describe how to use the steric effects of large, bulky ligands to modify the thermodynamics of edge termination and favor the sp(2) edge during, e. g., chemical vapor deposition. Ab initio calculations demonstrate that these alternative terminations can support robust edge states across a broad range of thermodynamic conditions. This method of exploiting steric crowding effects along the one-dimensional edge of a two-dimensional system may be a general way to control edge reconstructions across a range of emerging single-layer systems.