First-principles study on a new carbon allotrope based on AA-stacked γ-graphyne

The versatile hybridization of carbon atoms gives rise to a variety of allotropes with varying carbon frameworks, providing an unprecedented platform for the design of novel carbon-based materials with intriguing properties. In this work, the structural and electronic properties of bilayer γ-graphyne with the AA stacking arrangement have been investigated through first-principles calculations. Based on the AA-stacked bilayer γ-graphyne, a new bilayer configuration with interfacial covalent bonding can be obtained, in addition to the typical van der Waals (vdW) stacks of two-dimensional (2D) materials. Correspondingly, the emergence of this new 2D carbon allotrope can be attributed to the absence of intralayer sp-hybridized acetylene bonds in each sublayer, leading to a purely sp²-hybridized carbon network with improved structural dynamical stability. Moreover, either the vdW force or interfacial covalent bonding is capable of significantly altering the electronic structure of bilayer γ-graphyne, exhibiting reduced band gaps compared to the single-layer counterpart. Additionally, the effect of biaxial strain on the structural and electronic properties of the new carbon allotrope, as well as its vdW homogeneous counterpart, has also been revealed. Thus, the results of this work demonstrate the great potential for efficient modulation of electronic properties in graphyne through vertical stacking, and also provide a promising avenue for developing novel 2D carbon allotropes based on the few-layer graphyne.