Interplay between nitrogen dopants and native point defects in graphene

To understand the interaction between nitrogen dopants and native point\ndefects in graphene, we have studied the energetic stability of N-doped\ngraphene with vacancies and Stone-Wales (SW) defect by performing the density\nfunctional theory calculations. Our results show that N substitution\nenergetically prefers to occur at the carbon atoms near the defects, especially\nfor those sites with larger bond shortening, indicating that the defect-induced\nstrain plays an important role in the stability of N dopants in defective\ngraphene. In the presence of monovacancy, the most stable position for N dopant\nis the pyridinelike configuration, while for other point defects studied (SW\ndefect and divacancies) N prefers a site in the pentagonal ring. The effect of\nnative point defects on N dopants is quite strong: While the N doping is\nendothermic in defect-free graphene, it becomes exothermic for defective\ngraphene. Our results imply that the native point defect and N dopant attract\neach other, i.e., cooperative effect, which means that substitutional N dopants\nwould increase the probability of point defect generation and vice versa. Our\nfindings are supported by recent experimental studies on the N doping of\ngraphene. Furthermore we point out possibilities of aggregation of multiple N\ndopants near native point defects. Finally we make brief comments on the effect\nof Fe adsorption on the stability of N dopant aggregation.\n