Introduction of nitrogen with controllable configuration into graphene via vacancies and edges

Doping with nitrogen in controllable configurations is very valuable to tailor the properties of graphene. Here we report density-functional theory calculations of chemical reactions of ammonia, a widely used nitrogen source, at vacancies and edges of graphene, through which we explore strategies to achieve N-doped graphene with optimized properties. We show that at different defects, ammonia reacts to form nitrogen impurities in distinct configurations, i.e. graphitic-N at single vacancies, pyridinic- or pyrrolic-N at divacancies, pyrrolic-N at armchair edges, and N in a four-member ring at zigzag edges. Moreover, different nitrogen-related defect configurations introduce distinct changes in the electronic structure of graphene. By calculating the core level shift of C-1s electrons, we find configuration-dependent redistribution of electrons around the N-dopant. A discussion of how to achieve optimized doping and enhanced chemical reactivity in experiments is included.