Nitrogen-Doped Graphene on Copper: Edge-Guided Doping Process and Doping-Induced Variation of Local Work Function

The synthesis of nitrogen-doped single-layer graphene has been achieved on the copper surface by using the nitrogen-containing sole precursor azafullerene. The synthesis process, doping properties, and doping-induced variation of local work function of graphene have been investigated on the atomic scale by combining scanning tunneling microscopy/spectroscopy, X-ray photoelectron spectroscopy measurements, and density functional theory calculations. Most nitrogen dopants are at the edges of graphene islands and the graphene domain boundaries with the pyridinic configuration. Graphitic nitrogen dopants arrange into curved lines within graphene islands after multiple growth cycles, which results from a doping process guided by the edges of graphene islands. The doping-induced variation of local work function of the graphene surface has been measured on the atomic scale by using scanning tunneling spectroscopy measurements. We find that the local work function strongly depends on the atomic bonding configuration and concentration of nitrogen dopants. The local work function decreases for graphitic nitrogen doping but increases for pyridinic nitrogen doping. This work provides new atomic-scale insights into the synthesis of heteroatom-doped graphene from sole precursors as well as the strong correlations between nitrogen doping and the local work function of the graphene layer.