Exploring planar and nonplanar siligraphene: a first-principles study

摘要

Siligraphenes (g-SiCn and g-SinC) 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-SiCn is planar whereas g-SinC is nonplanar. Based on first-principles calculations, we have explored the planarity and nonplanarity for g-SiCn and g-SinC (n = 3, 5, and 7). It is found that the silicene-like g-Si5C and g-Si7C, though buckled, are actually energetically quite close to their planar counterpart. We found a new high buckled g-Si7C, which is much more stable and looks disordered. g-SiC7, though accepted to be planar, is identified to be nonplanar in fact. We focused on the widely studied g-SiC7 to illustrate the difference induced by planarity and nonplanarity. The total energy calculation and phonon spectrum show that the nonplanar g-SiC7 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-SiC7 has valley-contrasting Berry curvatures, suggesting potential application of siligraphene in valleytronics. The planar and nonplanar g-SiC7 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.