A theoretical study on the design, structure, and electronic properties of novel forms of graphynes

Abstract

α-, β-, γ- and 6,6,12-graphynes are well established one-atom-thick two-dimensional (2D) materials in the graphyne family. These 2D sheets have been mainly designed by incorporating an acetylenic linker (−C≡C−) in graphene with different ratios. The graphdiynes and their higher order 2D architectures have also been studied to elucidate the effect of length of linker (−C≡C–C≡C−) on the structure–property relationship. In the present investigation, we have modeled the three novel analogues of α-graphyne by increasing the acetylenic linkers and expanding the sp² network. The structure, stability, and electronic properties of novel forms of graphyne architectures were examined by using the computational methods within the framework of density functional theory (DFT). The molecular dynamics simulations show that only one system is thermodynamically stable and rule out the existence of other two newly designed systems. The electronic structure calculations reveal that, the stable 2D sheet exhibit semimetallic Dirac point features. Further, the semimetallic carbon sheet has massless Dirac Fermions (m* = 0.014 m0) akin to those of γ-graphyne and graphdiyne. The predicted Fermi velocity (v_f(K→M) = 7.13 × 10⁵ m/s) of the novel 2D sheet is higher than that of α-graphyne and close to that of graphene. Furthermore, the electronic properties of armchair and zigzag nanoribbons of stable 2D sheet have also been investigated. Interestingly, one of the zigzag nanoribbons shows linear band dispersion (Dirac point) in the proximity of the Fermi level, and others exhibit semiconducting to metallic properties.