Defect configuration, not nitrogen content, governs the mechanical integrity of nitrogen-doped graphene: a molecular dynamics study

Abstract

The mechanical reliability of nitrogen-doped graphene is often attributed to its nitrogen content, yet nitrogen occurs in chemically distinct configurations whose individual mechanical roles, and whose interactions with other defects, remain unresolved. Here, molecular dynamics simulations of uniaxial tension are used to separate the contributions of nitrogen chemistry, missing atoms, and defect arrangement to the strength and fracture of graphene. Three size-matched defects, a graphitic-nitrogen cluster, a void, and a pyridinic-nitrogen cluster, are compared so that two controlled contrasts isolate the effects of edge chemistry and of the vacancy independently. The graphitic cluster leaves the mechanical properties essentially unchanged (a strength reduction of <1 %), whereas the void degrades the ultimate strength by ~23 % and the pyridinic cluster, which combines the same vacancy with edge nitrogen, is the most damaging (~30 %), failing abruptly from its nitrogen-decorated rim rather than through the damage-tolerant process of the bare void. The mechanical impact of a nitrogen cluster is therefore governed by whether it carries vacancies, not by nitrogen itself. When a nitrogen cluster and a void coexist, their interaction is controlled by orientation relative to the load: in-line defects interact negligibly and fail at the more severe member, whereas side-by-side defects couple through overlapping stress fields and weaken the sheet progressively as they approach, an interaction that persists to separations of ~80 {\AA}. These results establish that the mechanical integrity of nitrogen-modified graphene is determined by the configuration of defects, the bonding environment of nitrogen, and the arrangement of coexisting defects relative to the load, rather than by nitrogen content or defect density alone, thereby providing a basis for defect-tolerant design.