Mechanical Anisotropy and Phase Transition in Black Phosphorus

Black phosphorus (BP), a puckered 2D allotrope of phosphorus, has shown high carrier mobility and surface area to mass/volume ratio in recent research. Because of this, BP has seen much interest from industries such as electronics, photonics, biomedical applications, linear polarizers, and plasmonics. Due to its unique orthorhombic lattice structure, BP has also shown incredible in-plane anisotropy in thermal, electrical, optical, and phonon properties. Additionally, BP presents novel properties such as a tunable bandgap and thickness-dependent charge-carrier mobility. Using Density Functional Theory (DFT) simulations, we investigate the mechanistic basis of BP's anisotropic properties under different loading conditions spanning both linear and nonlinear regimes of mechanical deformation. Our results suggest a unique anisotropic behavior of BP, where a phase transition occurs when strain is applied in the zigzag direction at Ɛ = 24.79%. Apart from this, analyzing the mechanical properties of the layer and its changed electronic characteristics with increasing strain, we obtain the fundamental insights that govern the unique behavior of BP. Thus, we discuss possible applications of BP in electronics and optics.