Structural phase transitions of phosphorene induced by applied strains

The effects of normal compressive strain and in-plane strain on the structures of phosphorene have been investigated by using first-principles calculations. It is quite intriguing to find that a structural transformation from pristine Z-phosphorene to a new A-phosphorene occurs under the normal compressive strain of epsilon = 48% or the anisotropic biaxial in-plane strain of epsilon(x) = -16% and epsilon(y) = 54%. In the extreme case where the pucker structure is flattened into a plane, the phosphorene structure is quite unstable at finite temperatures, transforming into another new H-phosphorene phase. The anisotropic structure of A-phosphorene gives rise to its direction-dependent mechanical properties whereas H-phosphorene exhibits isotropic mechanical properties. Both A-phosphorene and H-phosphorene are semiconductors with indirect band gaps of about 0.42 and 1.94 eV that use the Perdew-Burke-Ernzerhof exchange-correlation functional, respectively. The electronic properties of the two new phases are found to be sensitive to the magnitude and direction of the applied strains, which offer an effective method to modulate them in future device engineering.