Scalable synthesis and characterization of multilayer $\gamma$-graphyne, new carbon crystals with a small direct bandgap

TL;DR

This paper reports the scalable synthesis and detailed characterization of multilayer γ-graphyne, a new carbon allotrope with a small direct bandgap, demonstrating its potential as a semiconducting material.

Contribution

The study introduces a novel scalable synthesis method for multilayer γ-graphyne and provides comprehensive experimental characterization aligning with theoretical predictions.

Findings

γ-graphyne is a 0.48 eV bandgap semiconductor

The material exhibits a hexagonal a-axis spacing of 6.88 Å

Thermally stable up to 240°C with a specific crystal structure

Abstract

$\gamma$-Graphyne is the most symmetric sp2/sp1 allotrope of carbon, which can be viewed as graphene uniformly expanded through insertion of two-carbon acetylenic units between all the aromatic rings. To date, synthesis of bulk $\gamma$-graphyne has remained a challenge. We here report the synthesis of multilayer $\gamma$-graphyne through crystallization-assisted irreversible cross-coupling polymerization. Comprehensive characterization of this new carbon phase is described, including synchrotron X-ray diffraction, electron diffraction, lateral force microscopy, Raman and infrared spectroscopy, and cyclic voltammetry. Experiments indicate that $\gamma$-graphyne is a 0.48 eV bandgap semiconductor, with a hexagonal a-axis spacing of 6.88 {\AA} and an interlayer spacing of 3.48 {\AA}, which is consistent with theoretical predictions. The observed crystal structure has an aperiodic sheet stacking. The material is thermally stable up to 240 $^\circ$C but undergoes a transformation at higher temperatures. While conventional 2D polymerizations and reticular chemistry rely on error correction through reversibility, we demonstrate that a periodic covalent lattice can be synthesized under purely kinetic control. The reported methodology is scalable and inspires extension to other allotropes of the graphyne family.