Hydrogenated graphene edges are assumed to be either armchair, zigzag, or a combination of the two. We show that the zigzag is not the most stable fully hydrogenated edge structure along the $\langle 2\overline{1}\overline{1}0\rangle$ direction. Instead hydrogenated Klein and reconstructed Klein based edges are found to be energetically more favorable, with stabilities approaching that of armchair edges. These new structures “unify” graphene edge topology, the most stable flat hydrogenated graphene edges always consisting of pairwise bonded C${}_2$H${}_4$ edge groups, irrespective of the edge orientation. When edge rippling is included, CH${}_3$ edge groups are most stable. These new fundamental hydrogen-terminated edges have important implications for graphene edge imaging and spectroscopy, as well as mechanisms for graphene growth, nanotube cutting, and nanoribbon formation and behavior.

• Received 29 May 2013

DOI:https://doi.org/10.1103/PhysRevB.88.094106