▎ 摘　　要

Graphene has demonstrated excellent field emission performance, however, the emitted-current shows irreversible decline. The cause of this decline has not been clearly studied or thoroughly identified, which limits application of graphene as field emitters. In this work, accompanied by the decay of emission currents, the damage to few-layer graphene sheets was observed for the first time by introducing a plate-needle-type setup. The low turn-on field show excellent emission ability. The thinnest regions at the edges of graphene sheets, which have high emission efficiency, are the first to be destroyed. Thus, the graphene sheets become shortened and show thicker serrated edges because of thermally assisted field evaporation induced by the local heating effect of the currents, resulting in the degradation of emission ability. In contrast to the damage, changes in the Raman features of the graphene sheets are not visible, indicating that the graphene structure is retained in the remaining graphene sheets and only the morphology is changed, which renders the phi unchanged. This work provides the first direct and credible evidence that the degradation of emission performance is derived from damage to the graphene sheets, which leads to changes in their geometry and determines the beta. (C) 2017 Elsevier Ltd. All rights reserved.