2D BN-biphenylene: structure stability and properties tenability from a DFT perspective.

Abstract

With state-of-the-art density functional theory and ab initio molecular dynamics, we explored the BN-analog of a recently synthesized 2D biphenylene sheet. Its dynamical, thermal, and mechanical stability has been confirmed with phonon spectrum calculations, ab initio molecular dynamics (AIMD), and Born criteria, and its synthesis feasibility has been ascertained in terms of cohesive energy. The phonon spectrum and AIMD results show all positive frequencies and negligible variations in structure (bond length), kinetic and total energy for 5 ps, respectively. Having found this stable BN-BPh, we have analyzed its electronic, mechanical, optical, and vibration properties. Electronic property results (density of states and band structure) show that the BN-equivalent of metallic BPh has a large band gap of 3.12 eV and 4.48 eV with the PBE and HSE06 DFT functionals, respectively, similar to the graphene BN-equivalent (hBN) with a band gap of 6.1 eV. The mechanical strength of BN-BPh is close to that of BPh with a difference of ∼15 N m-1 and ∼10 N m-1 along the x- and y-directions, and its Young's modulus indicates that BN-BPh is stiffer than BN-graphyne. The optical absorption coefficient of BN-BPh shows a first peak at 4.48 eV (3.12 eV) with the HSE06 (PBE) functional. Infrared and Raman spectrum intensity and irreducible representation are computed, and the first IR (Raman) peak is found at 1300 cm-1 (1000 cm-1) for BN-BPh. Finally, substitutions of external atoms such as P, Al, As, C, Li, Mg, S, and Si for B and N atoms in BN-BPh tune its electronic properties to semiconducting, semi-metallic, and even metallic. Considering its mechanical, optical, and band gap tunability, BN-BPh might be useful in electronic, optical, and spintronics devices, even in high-pressure environments.