The Ideal Tensile Strength and Phonon Instability of Borophene

TL;DR

This study uses first-principle calculations to analyze the mechanical strength, critical strain, and phonon stability of borophene, revealing its high tensile strength, low critical strain, and unique negative Poisson's ratio.

Contribution

It provides the first detailed computational analysis of borophene's mechanical properties, including tensile strength, failure mechanisms, and phonon instability.

Findings

Borophene withstands tensile stress up to 20.26 N/m in one direction.

Critical strain in borophene is as low as 8%, the lowest among 2D materials.

Applying strain in the b direction induces a negative Poisson's ratio.

Abstract

Very recently, two-dimensional(2D) boron sheets (borophene) with rectangular structure has been grown successfully on single crystal Ag(111) substrates.The fabricated boroprene is predicted to have unusual mechanical properties. We performed first-principle calculations to investigate the mechanical properties of the monolayer borophene, including ideal tensile strength and critical strain. It was found that monolayer borophene can withstand stress up to 20.26 N/m and 12.98 N/m in a and b directions, respectively.However, its critical strain was found to be small. In a direction, the critical value is only 8%, which, to the best of our knowledge, is the lowest among all studied 2D materials.Our numerical results show that the tensile strain applied in b direction enhances the bucking height of borophene resulting in an out-of-plane negative Poisson's ratio, which makes the boron sheet show superior mechanical flexibility along b direction.The failure mechanism and phonon instability of monolayer borophene were also explored.