▎ 摘　　要

The aim of this paper is to improve the field emission properties of graphene-carbon nanotube composites by doping nitrogen atom. The electronic structure and field emission mechanism of the composite have been investigated by first principle methods. Compared to pristine graphene-carbon nanotube composite, work functions and ionization potentials with ten different doping positions decrease drastically as well as energy gap, which illustrates the enhancement of field emission properties. In this study, the most preferable doping position (doping position 2) can be inferred. Due to the doping of nitrogen atom, coupled electron states is generated, more electrons aggregate at the doping position. All results suggest that the field emission properties of graphene-carbon nanotube composite can be improved by doping nitrogen atom. The work we have done is significant for obtaining better, electron sources with less energies, our investigation will provide a theoretical reference for the design and manufacture of new field emission devices. (C) 2015 Elsevier Ltd. All rights reserved.