Stability of Edges and Extended Defects on Boron Nitride and Graphene Monolayers: The Role of Chemical Environment

We perform ab initio calculations that indicate that the relative stability of antiphase boundaries (APBs) with armchair and zigzag chiralities in monolayer boron nitride (BN) is strongly dependent on the chemical potentials of boron (B) and nitrogen (N) in the synthesis process. For a realistic interval of chemical potentials, ranging from gas-phase to solid-state sources, a stoichiometric armchair APB with tetragons and octagons in its core and no homopolar bonds (N–N or B–B) is found to be the most stable in the intrinsic region of the chemical-potential interval, while for N-rich (B-rich) environments a zigzag-oriented boundary with a core consisting of hexagons only, containing N–N (B–B) bonds is found to be the most stable. Zigzag boundaries with core structures consisting of pentagons and octagons, containing homopolar bonds, are also considered in both undoped and carbon-doped forms. We find that at the typical temperatures of BN–nanostructure synthesis several of these zigzag boundaries should co...