Mechanical properties and deformation mechanisms of two-dimensional borophene under different loadings

Abstract

Two-dimensional (2D) borophene has attracted widespread research interest in condensed matter physics and materials science because of its rich physical and chemical properties. However, the mechanical properties and deformation mechanisms of borophene under different loadings are still unclear and not thoroughly investigated. In this work, the tensile, shear, and nanoindentation failure processes of borophene are simulated via molecular dynamics method to obtain the key mechanical parameters of borophene. The mechanical response and deformation mechanism of borophene under different loads are analyzed from the change of B—B bond length with the strain/indentation depth. The results show that the tensile mechanical properties of borophene exhibit significant anisotropic characteristics, with the Young's modulus and strength along the armchair direction being much higher than those along the zigzag direction. However, the anisotropy of the shear mechanical properties of borophene is not significant. This phenomenon can be attributed to the different contributions of the strong B—B σ bonds and weak multi-center bonds in borophene when they are stretched in different directions. It is also found that borophene exhibits different mechanical responses under spherical indentation and cylindrical indentation. The force at failure of the borophene under spherical indentation is much lower than the value under cylindrical one, and the intrinsic mechanical parameters of borophene under spherical indentation cannot be estimated accurately because of the anisotropic characteristics of borophene. However, under cylindrical indentation, borophene exhibits similar anisotropic characteristics to those under tension, and the mechanical parameters such as Young's modulus can be measured accurately, which are consistent with those obtained under tension. In addition, the effects of the borophene indentation model and spherical/cylindrical indenter size, the loading rate and temperature on the mechanical parameters of borophene are also studied systematically. The results indicate that the Young’s modulus of borophene from spherical indentation is highly estimated when <i>a</i>/<i>R</i> <15 but not sensitive when <i>a</i>/<i>R</i> >15, while the results from cylindrical indentation are hardly affected by the values of <i>L</i>/<i>R</i> and <i>W</i>/<i>L</i>. The Young's modulus of borophene slightly decreases with temperature increasing, while the loading rate has almost no influence on the value of Young's modulus of borophene. These findings are expected to provide important guidelines for realizing the practical applications of borophene based micro/nano electromechanical systems.