First-Principles Study of Square-Octagon Lines Defects in Monolayer Hexagonal Boron Nitride

Abstract

We study line square-octagon (4 vertical bar 8) defects in monolayer hexagonal boron nitride from first-principles. The defect formation energies are calculated both for symmetric and asymmetric defect structures. The calculated defect formation energies of the asymmetric defect structures, involving only the B-N bonds, are around 1.71 similar to 1.86 eV per 4 vertical bar 8 defect, whereas those of symmetric defect structures, involving all the B-N, B-B, and N-N bonds, are around 5.62 similar to 5.65 eV per 4 vertical bar 8 defect. The energy barrier for the slip of the BN atomic chain, calculated from the nudged elastic band method, is about 7.5 eV per 4 vertical bar 8 defect.