Graphyne-based carbon allotropes with tunable properties: From Dirac fermion to semiconductor

•We study α-graphyne and carbon foams based on first-principles calculations.•α-Graphyne has linear energy-momentum dispersion relations.•The Dirac fermion characteristics are preserved in AA stacking mode not in AB.•There are some exceptional properties of these 3D carbon foams.•The materials not only enrich the databases but also find new applications.

Inserting acetylenic bonds into the framework of graphene leads to a novel carbon allotrope family named as graphyne and graphdiyne, one of the graphyne, has been synthesized. Here, we focus on the graphyne with all the covalent bonds of graphene being replaced by sp2–sp…sp–sp2 linkages (α-graphyne) and its three-dimensional (3D) derivatives. We predicted that regardless of the length of the acetylenic linkages, α-graphyne has linear energy-momentum dispersion relations which cross at the Dirac point characterized by Dirac fermion, similar to graphene. The Fermi velocity is also comparable to graphene. The Dirac fermion characteristics are preserved in the multi-layered α-graphyne with AA stacking mode, where the AB stacking mode leads to a parabolic dispersion relation at the K point. We also proposed that α-graphyne may convert to more stable 3D porous structures whose energies are even comparable to diamond. More interestingly, some exceptional properties of these carbon foams, such as lower hardness, tunable electronic properties ranging from metal to semiconductor, and strong adsorption in the visible light region have been predicted from first-principles calculations. The realization of these novel graphyne-based carbon materials may not only enrich the databases of carbon allotrope family but also find applications in wide-range fields, such as electronic devices, shape-selective catalysts, molecular sieves, and solar cells.