First principles study of distributions of Si atoms and structures of siligraphene g-SiC<sub>7</sub>

Abstract

Siligraphene, as a composite of graphene and silicene, has attracted widespread attraction since it has many excellent properties that neither of graphene and silicene possesses. The properties of siligraphene are closely related to the distribution of Si atoms and its structure, but most of the current researches of siligraphene focus on the regular distribution of Si atoms and the planar structure with high symmetry. Therefore, we study in this work all possible Si atoms’ distributions with planar and nonplanar structures for siligraphene g-SiC<sub>7</sub> based on density functional theory. At first, 365 kinds of inequivalent Si atoms’ distributions in g-SiC<sub>7</sub> are selected out from the 35960 kinds of Si atoms’ distributions, and then for each inequivalent Si atoms’ distribution, a comparison of the stability between the planer and nonplanar structures is made. In terms of the Si distribution, the Si atoms tend to gather together to lower the energy. The more dispersed Si atoms’ distribution usually has appreciably higher energy. In terms of the planarity of the structures, it is found that there are many non-planar structures with significantly lower energy than the planar ones. For all possible Si atoms’ distributions, there are only 8 planar structures which are stable against out-of-plane perturbations. We further study the dynamic, thermodynamic and mechanical stability of the structures with the lowest energies and find that they are stable. The energy band calculation shows that two Dirac valleys still persist in the first Brillouin zone despite their appreciable structure deformation, and a considerable band gap is opened at the Dirac point. We calculate the Berry curvatures and find that the Berry curvatures at the inequivalent valleys are opposite, indicating that the system has valley degree of freedom. Our research shows that siligraphene is more likely to have a buckled structure and a more concentrated silicon atoms’ distribution, and the most stable structures have good electronic properties.