Nitrogen–Nitrogen Bonds Undermine Stability of N‑Doped Graphene

Two-dimensional
alloys of carbon and nitrogen draw strong interest
due to prospective applications in nanomechanical and optoelectronic
devices. The stability of these chemical structures can vary greatly
as a function of chemical composition and structure. The present study
employs hybrid density functional theory and reactive molecular dynamics
simulations to elucidate how many nitrogen atoms can be incorporated
into the graphene sheet without destroying it. We conclude that (1)
the C/N = 56:29 structure and all nitrogen-poorer structures maintain
stability at 1000 K; (2) the stability suffers greatly in the presence
of N–N bonds; and (3) distribution of electron density depends
heavily on the structural pattern in the N-doped graphene. Our calculations
support the experimental efforts aimed at production of highly N-doped
graphene and generate important insights into the mechanisms of tuning
graphene mechanical and optoelectronic properties. The theoretical
prediction can be tested directly by chemical synthesis.