The predicted structure and charge, kinetic and thermal properties of holey graphyne. The synthesis route and the band structure are also shown.Carbon has two naturally occurring allotropes, diamond and graphite, and numerous other allotropes, such as graphene, fullerene, and nanotubes, which are revolutionizing nanotechnology. These materials, however, typically have a zero-bandgap electronic structure, limiting some applications. Two more recent allotropes, graphdiyne and graphyne, which can adopt geometries different from the typical hexagonal atomic arrangement, are generating new interest because of their potential semiconducting properties.
Now researchers from the Institute of Basic Science (IBS) and Sungkyunkwan University in South Korea, and the University of Puerto Rico in the USA report the synthesis of a novel, two-dimensional, single-crystalline ‘holey’ graphyne in a bottom-up approach via a two-solvent system through a coupling reaction [Liu et al., Matter (2022), https://doi.org/10.1016/j.matt.2022.04.033]. The researchers, led by Do Hyun Ryu and Hyoyoung Lee, were intrigued by a molecule called dibenzocyclooctadiyne, which comprises two aromatic benzene rings connected by two bent acetylenic linkages to create a highly strained eight-membered ring.
“This exciting molecule inspired us to design and synthesize the new carbon allotrope, holey graphyne,” explains Lee. “To synthesize holey graphyne, we used the interface method between two immiscible liquids.”
The new two-dimensional allotrope is composed of a mixture of six- and eight-membered carbon rings, in a departure from the highly ordered hexagonal sheets of graphene. The six-membered rings of graphyne possess alternating single and double bonds, leading to sp2 hybridized carbon atoms, while those in the eight-membered rings are sp hybridized. Theoretical calculations indicate that graphyne is a p-type semiconductor with a direct bandgap of around 1.1 eV and possesses high carrier mobility. Moreover, the highly crystalline sheets of holey graphyne are stable thermally, kinetically, and mechanically.
“This new discovery not only demonstrates the first synthesis of the ultrathin crystalline holey graphyne but also introduces a new concept for the design and synthesis of such a new type of 2D carbon allotrope,” says Lee.
The researchers believe that the material’s attractive semiconducting properties could be useful in optoelectronics, energy harvesting, gas separation, catalysis, water remediation, sensing and energy-related applications. The team are now working on the synthesis of larger area, defect-free holey graphyne.
“[We hope] that the future application of holey graphyne in the semiconductor industry will pave the wave for a new generation of electronics beyond the silicon age,” adds Lee.