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

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.