Dangling Bond States, Edge Magnetism, and Edge Reconstruction in Pristine and B/N-Terminated Zigzag Graphene Nanoribbons

Recently it was reported that the edges of the pristine zigzag graphene nanoribbons (ZGNRs) tend to be reconstructed as a result of the instability induced by the dangling bonds of edge carbon atoms [see, e.g., PRL 101, 115502(2008), PRL 101, 096402(2008), PRE 80, 073401(2009)). The edge reconstruction brings significant changes to the ZGNRs, such as insulator-metal transition and suppression of the edge magnetism. In this work, the dangling bond states, edge magnetism, and edge reconstruction in pristine and B/N-terminated zigzag graphene nanoribbons are investigated by density functional theory calculations. It is found that a big difference is observed in the edge magnetism of the pristine and B/N-terminated ZGNRs and it arises from the different features of the dangling bond states in these systems. Interestingly, electron (N) doping can stabilize the edges, while hole (B) doping cannot, which also originates from the different features of the dangling bond states. Finally, when the effects of the dangling bond states are removed by H passivation, either in pristine ZGNRs or in B/N-terminated ZGNRs, no edge reconstruction occurs. The mechanism of electron doping or H passivation can be helpful in situations where the properties intrinsic of the zigzag edge shape are to be utilized and thus the spontaneous reconstruction process is to be avoided.