**Anisotropic mechanical strength, negative Poisson's ratio and fracture
mechanism of borophene with defects**

VT Pham and TH Fang, THIN SOLID FILMS, 709, 138197 (2020).

DOI: 10.1016/j.tsf.2020.138197

In this work, we used molecular dynamics simulations to study the effect of vacancy defects and impurity defects on the tensile properties of monolayer borophene under uniaxial tension. The effects of the number of point defects and defect angle on the fracture behavior and the tensile properties were investigated under different tensile strains along the zigzag direction and armchair direction. Furthermore, the impact of temperature on their mechanical properties has been analyzed and discussed. We find that borophene has anisotropic properties, Young's modulus of the borophene nanosheet at 1 K is 165.03 Nm(-1) in the zigzag direction and 390.02 Nm(-1) in the armchair direction. The borophene has a negative Poisson's ratio in the direction perpendicular to the atomic plane. The mechanical strength and the ultimate strain of borophene decrease as increasing the temperature. Moreover, the stress concentration around the vacancy defect leads to the initial crack formed at the vacancy position and the reduction of the fracture strength. If increasing the dimension of the vacancies projected onto the direction, which is perpendicular to the tensile direction, the fracture strength, fracture strain, and Young's modulus will decrease. Besides, the mechanical strength of borophene is reduced by the substitutional C atoms defects. With the angle defect of theta = 60 degrees the fracture of nanosheet which has C impurity defects easier occurs than the angle defect of theta = 0 degrees in both zigzag and armchair tensile directions.

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