Stable hydrogenated graphene edge types: Normal and reconstructed Klein edges

TL;DR

This paper reveals that hydrogenated Klein and reconstructed Klein edges are more stable than zigzag edges in graphene, unifying edge topology and impacting graphene growth and nanostructure formation.

Contribution

It introduces new stable hydrogenated Klein and reconstructed Klein edge structures, challenging the assumption that zigzag edges are most stable.

Findings

Klein edges are more stable than zigzag edges in certain orientations.

Stable edges consist of pairwise bonded C2H4 groups.

Including rippling favors CH3 edge groups for stability.

Abstract

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 structure along the <2-1-10> direction. Instead hydrogenated Klein and reconstructed Klein based edges are found to be energetically more favourable, 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 C2H4 edge groups, irrespective the edge orientation. When edge rippling is included, CH3 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 behaviour.