Mechanical and electronic properties of monolayer and bilayer phosphorene under uniaxial and isotropic strains

Abstract

The mechanical and electronic properties of both the monolayer and bilayer phosphorenes under either isotropic or uniaxial strain have been systematically investigated using first-principles calculations. It is interesting to find that: 1) Under a large enough isotropic tensile strain, the monolayer phosphorene would lose its pucker structure and transform into a flat hexagonal plane, while two inner sublayers of the bilayer phosphorene could be bonded due to its interlayer distance contraction. 2) Under the uniaxial tensile strain along a zigzag direction, the pucker distance of each layer in the bilayer phosphorene can exhibit a specific negative Poisson's ratio. 3) The electronic properties of both the monolayer and bilayer phosphorenes are sensitive to the magnitude and direction of the applied strains. Their band gaps decrease more rapidly under isotropic compressive strain than under uniaxial strain. Also, their direct-indirect band gap transitions happen at the larger isotropic tensile strains compared with that under uniaxial strain. 4) Under the isotropic compressive strain, the bilayer phosphorene exhibits a transition from a direct-gap semiconductor to a metal. In contrast, the monolayer phosphorene initially has the direct-indirect transition and then transitions to a metal. However, under isotropic tensile strain, both the bilayer and monolayer phosphorene show the direct-indirect transition and, finally, the transition to a metal. Our numerical results may open new potential applications of phosphorene in nanoelectronics and nanomechanical devices by external isotropic strain or uniaxial strain along different directions.

Strain effects on borophene: ideal strength, negative Possion’s ratio and phonon instability

“…An adventitious strain is almost unavoidable experimentally, therefore, it is highly desirable to explore the mechanical properties of borophene.For 2D materials, the ideal tensile strength [10,11], is a crucial mechanical parameter which fundamentally characterizes the nature of the chemical bonding and the elastic limit of the single-or few-layer thin films. So far, the elastic limit of many 2D materials, such as graphene [12][13][14], h-BN [15][16][17][18][19], MoS 2 [20-24], black phosphorene (BP) [25][26][27][28], and silicone [29][30][31][32][33], have been characterized by the ideal tensile stress and critical strain. Compared to these materials, monolayer borophene is a stiffer material because of a higher Young's Modulus [7].…”

Molecular Structure and Dynamics of Water on Pristine and Strained Phosphorene: Wetting and Diffusion at Nanoscale

“…Recent computational studies based on the density functional theory (DFT) showed that a single-layer phosphorene could actualize tensile strain (stretching) up to 0.54 while maintaining its original P-P bond and “two-sublayer” (non-planar) structure2728. It has also been demonstrated that all the electrical29303132, optical3334, thermoelectric353637 and mechanical273038 properties of phosphorene could be modified upon mechanical strain. The puckered structure of phosphorene brings anisotropy and negative Poisson’s ratio2735.…”

Flexible Device Applications of 2D Semiconductors

“…Due to the buckled structure of phosphorene, the direction and type of applied mechanical strain would affect the magnitude of bandgap modulation, induce a direct–indirect gap transition, and significantly modulate the effective mass of both electrons and holes in phosphorene, through changing bond lengths and bond angles under various strain conditions . Biaxial strain can tune the optical band gap of monolayer phosphorene by 1.5 eV and the exciton energy, which is useful in designing optoelectronics .…”