Layer dependent optical properties of γ-graphyne

Abstract

Stacking two-dimensional (2D) materials vertically provides a distinct platform for creating hybrid materials with adjustable properties. Based on this research study, density functional theory (DFT) was complemented by including van der Waals density function, where γ-graphyne and stacking structures (monolayer, bilayer, tri-layer and bulk forms) were systematically considered. According to our findings, AB stacking is more stable than AA-stacking, with an electrical bandgap that changes depending on the stacking configuration. We found a new two-dimensional (2D) carbon allotrope based on the AB-stacked configuration, which goes beyond conventional van der Waals (vdW) homogeneous stacking. The AB-stacked configuration represents a structurally optimized arrangement with distinct electronic characteristics compared to other stacking forms. Interestingly, tri-layer γ-graphyne can also be used to create various 2D carbon allotropes with unique carbon networks. We observed that bulk γ-graphyne exhibits either semiconductor or metallic behavior, depending on the stacking arrangement. Additionally, the interlayer vdW interactions cause a redshift in the optical absorption peaks for bulk γ-graphyne compared to the monolayer, with notable differences in the spectra for various stacking configurations below 1 eV. These results highlight few-layer γ-graphyne's encouraging potential for developing carbon-based nanoelectronics. Additionally, this introduces a novel approach for designing new two-dimensional carbon allotropes by vertically stacking graphyne with acetylene linkages.