▎ 摘　　要

Recent experiments have shown that gap opening and work function modulating in graphenes have been obtained by substituting C atoms with B or N atoms. Especially, some efforts have been set on the fabrication of semiconducting graphene nanocomposites. Here we propose an island-shaped graphene-BN nanocomposite for potential applications as field-emission electron sources. The field emission mechanism of the graphene-BN has been investigated by using density functional theory calculations. Our results show that graphene has a high level of emission currents with a low external electric field. The combination of BN nanocage and graphene makes use of the curvature effect and the nitrogenation that induce local charge enhancement. The presence of an BN nanocage allows for an important enhancement of the field emission properties. The graphene-BN nanofabrication perhaps leads to a unique hybrid platform consisting of graphene and nonmetal, paving the way in future field-emission electron sources.