Versatile mechanical properties of novel g-SiCx monolayers from graphene to silicene: a first-principles study

Abstract

Recently, a series of graphene-like binary monolayers (g-SiCx), where Si partly substitutes the C positions in graphene, have been obtained by tailoring the band gaps of graphene and silicene that have made them a promising material for application in opto-electronic devices. Subsequently, evaluating the mechanical properties of g-SiCx has assumed great importance for engineering applications. In this study, we quantified the in-plane mechanical properties of g-SiCx (x = 7, 5, 3, 2 and 1) monolayers (also including graphene and silicene) based on density function theory. It was found that the mechanical parameters of g-SiCx, such as the ideal strength, Young’s modulus, shear modulus, Poisson’s ratio, as well as fracture toughness, are overall related to the ratio of Si–C to C–C bonds, which varies with Si concentration. However, for g-SiC7 and g-SiC3, the mechanical properties seem to depend on the structure because in g-SiC7, the C–C bond strength is severely weakened by abnormal stretching, and in g-SiC3, conjugation structure is formed. The microscopic failure of g-SiCx exhibits diverse styles depending on the more complex structural deformation modes introduced by Si substitution. We elaborated the structure-properties relationship of g-SiCx during the failure process, and in particular, found that the structural transformation of g-SiC3 and g-SiC is due to the singular symmetry of their structure. Due to the homogeneous phase, all the g-SiCx investigated in this study preserve rigorous isotropic Young’s moduli and Poisson’s ratios. With versatile mechanical performances, the family of g-SiCx may facilitate the design of advanced two-dimensional materials to meet the needs for practical mechanical engineering applications. The results offer a fundamental understanding of the mechanical behaviors of g-SiCx monolayers.