First-principles study of Stone-Wales defects in monolayer and Bernal-stacked hexagonal boron nitride

Recently, Stone-Wales (SW) defects gradually attracted people's research interest because of their unique properties. The theoretical research indicated that the SW defect in hexagonal boron nitride (h-BN) can lead to new defect levels in bandgap, making h-BN apply in ultraviolet emitters. However, the SW defect is always observed in graphene and rarely observed in h-BN in the experiments. Here, we confirmed the SW defects are not easily formed in h-BN under thermodynamic conditions by first-principles calculations. Specifically, the monolayer h-BN with SW defect (h-BN-SW) has the weak bond strength, dynamic stability and high-temperature thermal stability, facilitating the healing of SW defects under high-temperature conditions and the role of hydrogen. Additionally, we found the SW defect in AB stacked h-BN (AB-h-BN) have good mechanical stability, dynamic stability and thermodynamic stability than h-BN-SW, especially for AB-h-BN-2SW (2SW defects formed in upper and lower layer of AB-h-BN, respectively), which can meet the requirements for its application in electronic devices. Even under thermodynamic conditions, the formation of SW defects is extremely challenging. Electron beam irradiation technology provides a window for the generation of SW defects in h-BN. This offers opportunities for the introduction and control of SW defects, while also creating potential for their application in electronic devices. Moreover, we found that the absorption peak broadens, and a new absorption peak appears with the generation of SW defects, which is mainly induced by the decrease of bandgap and the generation of defect levels. Our research can provide theoretical guidance at atomic scale for designing and applying h-BN with SW defect in the experiments.