Exploring planar and nonplanar siligraphene: a first-principles study

Siligraphenes (g-SiC(n) and g-Si(n)C) are a novel family of two dimensional materials derived from the hybrid of graphene and silicene, which are expected to have excellent properties and versatile applications. It is generally assumed that g-SiC(n) is planar whereas g-Si(n)C is nonplanar. Based on first-principles calculations, we have explored the planarity and nonplanarity for g-SiC(n) and g-Si(n)C (n = 3, 5, and 7). It is found that the silicene-like g-Si(5)C and g-Si(7)C, though buckled, are actually energetically quite close to their planar counterpart. We found a new high buckled g-Si(7)C, which is much more stable and looks disordered. g-SiC(7), though accepted to be planar, is identified to be nonplanar in fact. We focused on the widely studied g-SiC(7) to illustrate the difference induced by planarity and nonplanarity. The total energy calculation and phonon spectrum show that the nonplanar g-SiC(7) is very energetically favorable and dynamically stable. The buckling leads to a considerable change in band structure, but the Dirac cones and the energy gap are still preserved. It is further found that g-SiC(7) has valley-contrasting Berry curvatures, suggesting potential application of siligraphene in valleytronics. The planar and nonplanar g-SiC(7) have quite similar lattice thermal properties, which are close to those of graphene. Our calculations indicate the importance of examination of the planarity and nonplanarity in the study of siligraphene.