Surface nitrogen functionality for the enhanced field emission of free-standing few-layer graphene nanowalls

The effects of nitrogen functionalization on the field emission properties of vertically aligned few-layer graphene (FLG) nanowall thin films are investigated. Lowered work function and enhanced electron emission property are observed after ammonia plasma treatment. The turn-on field (defined at 10 mu Acm(-2)) is found to be decreased from 6.5 to 4.6 V mu m(-1). Additionally, more stable emission with fluctuation less than 5% is obtained after surface N-functionalization. The electron configuration of nitrogen in FLG edge is proposed to be amine (C-NH2) terminal configuration. Nitrogen doping could significantly increases the pi density states near the Fermi level. The maximum upward shift of E-F is determined to be similar to 0.23 eV by low-energy XPS measurements, which mainly accounts for the lower turn-on electric field. Meanwhile, nitrogen functionalization would minimize surface desorption and accounts for more uniform work function distribution. Finally, the nonlinear characteristics of Fowler-Nordheim plots could be understood by thermionic-field emission process. (C) 2016 Elsevier B.V. All rights reserved.