Graphynes
The word graphyne denotes a variety of all-carbon 2D structures containing linear groups with a triple bond, like in alkyne chains, linking subunits made of sp2 C. Different forms have been proposed, originally named α, β, and γ. The structure of these three graphynes can be derived from graphene by substitution of an acetylenic group C≡C for every carbon bond, for two thirds of the bonds and one third of the bonds, respectively. Both form has a hexagonal unit cell composed of 8, 16, and 12 atoms. Although different strategies have been proposed to synthesize graphyne [1], no sample were available by the time this page was written. By contrast, graphdiyne has been successfuly synthesized in 2010.
The three forms α, β, and γ of graphyne are illustrated in the above figure from left to right. The triple bond is represented in black. Atomic parameters of the three structures are given in the Table [2], where a is the lattice parameter, l1 is the length of the bond between a triply-coordinated atom and a doubly-coordinated atom, l2 is the length of the bond between two doubly-coordinated atoms, l3 is the length of the bond between two triply-coordinated atoms, N is the number of carbon atoms per unit area.
| a (nm) | l1 (nm) | l2 (nm) | l3 (nm) | N (at/nm2) | |
|---|---|---|---|---|---|
| alpha | 0.699 | 0.140 | 0.123 | -- | 18.90 |
| beta | 0.951 | 0.142 | 0.122 | 0.140 | 23.00 |
| gamma | 0.689 | 0.143 | 0.122 | 0.141 | 29.15 |
| graphene | 0.246 | -- | -- | 0.142 | 38.18 |
Both α- and β-graphyne are zero-gap semiconductor, the band structure of α-graphyne sharing many common features with that of graphene (Dirac cones pinned at the K and K' points of the First-Brillouin zone) [3]. By contrast, γ-graphyne is a semiconductor with a direct band gap of 1.45 eV located at the M point of the First-Brillouin zone [2].
- "Synthesis and properties of annulenic subunits of graphyne and graphdiyne nanoarchitectures" M.M Haley, Pure Appl. Chem. 80 (2008), 519-532 [DOI: 10.1351/pac200880030519].
- "Theoretical Raman fingerprints of α, β, and γ-graphyne" V.N. Popov and Ph. Lambin, Phys. Rev. B 88 (2013) 075427 [DOI: 10.1103/PhysRevB.88.075427].
- "Competition for graphene: graphynes with direction-dependent Dirac cones" D. Malko, C. Neiss, F. Viñes, and A. Görling, Phys. Rev. Lett. 108 (2012) 086804 [DOI: 10.1103/PhysRevLett.108.086804].