Auxetic properties of a newly proposed γ-graphyne-like material

Journal of the American Chemical Society, 2022

γ-Graphyne is the most symmetric sp 2 /sp 1 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 γ-graphyne has remained a challenge. We here report the synthesis of multilayer γ-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 γ-graphyne is a 0.48 eV bandgap semiconductor, with a hexagonal a-axis spacing of 6.88 Å and an interlayer spacing of 3.48 Å, which is consistent with theoretical predictions. The observed crystal structure has an aperiodic sheet stacking. The material is thermally stable up to 240 °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.

ACS Omega

In the present investigation, we have proposed a novel form of two-dimensional (2D) carbon allotropes with the aid of first-principle density functional theory-based calculations. The carbon polymorph is mainly composed of carbon pentagons (cp) and acetylenic linkers and hence named cp-graphyne. This 2D material is energetically more preferable than the rest of the semimetals of graphyne family, including graphdiyne monolayer. Close inspection of lattice dynamics and thermal and mechanical properties demonstrates the excellent dynamic, thermal, and mechanical stabilities of cpgraphyne. Interestingly, cp-graphyne exhibits a semimetallic nature and possesses double distorted Dirac points in the electronic band spectrum. The Fermi velocities (v f) of cp-graphyne are highly anisotropic and are predicted to be in the range of 1.50−8.20 × 10 5 m/s. Furthermore, the analysis of structural and electronic properties of the cp-graphyne bilayer discloses the presence of self-doped Dirac-like points nearer to the Fermi level in the electronic spectrum.

RSC Advances, 2015

In this study, two novel forms of two-dimensional (2D) carbon frameworks (named as coro-graphene (CG) and circumcoro-graphyne (CCG)) were designed with the help of First-Principles Density Functional Theory based calculations using the PBE-GGA level of theory employing a plane wave basis set. Both CG and CCG exhibit the space group p6/mmm which is akin to that of graphene. The dynamical stability of CG and CCG was analyzed by performing phonon mode analysis and molecular dynamics simulations. Interestingly, the CG shows a narrow band gap. Anisotropic Dirac cones in the proximity of the Fermi level are observed in the case of CCG. The band gap and other associated features of these novel 2D materials are sensitive to the external strain and hole/electron doping (B/N doping).

Designing new 2D systems with tunable properties is an important subject for science and technology. Starting from graphene, we developed an algorithm to systematically generate 2D carbon crystals belonging to the family of graphdiynes (GDYs) and having different structures and sp/sp 2 carbon ratios. We analyze how structural and topological effects can tune the relative stability and the electronic behavior, to propose a rationale for the development of new systems with tailored properties. A total of 26 structures have been generated, including the already known polymorphs such as α-, β-, and γ-GDY. Periodic density functional theory calculations have been employed to optimize the 2D crystal structures and to compute the total energy, the band structure, and the density of states. Relative energies with respect to graphene have been found to increase when the values of the carbon sp/sp 2 ratio increase, following however different trends based on the peculiar topologies present in the crystals. These topologies also influence the band structure, giving rise to semiconductors with a finite band gap, zero-gap semiconductors displaying Dirac cones, or metallic systems. The different trends allow identifying some topological effects as possible guidelines in the design of new 2D carbon materials beyond graphene.

arXiv (Cornell University), 2023

Graphyne is a two-dimensional carbon allotrope of graphene. Its structure is composed of aromatic rings and/or carbon-carbon bonds connected by one or more acetylene chains. As some graphynes present the most of the excellent properties of graphene and non-null bandgap, they have been extensively studied. Recently, Kanegae and Fonseca reported calculations of four elastic properties of 70 graphynes, ten members of the seven families of graphynes [Carbon Trends 7, 100152 (2022)]. They showed that the acetylene chain length dependence of these properties can be simply modelled by a serial association of springs. Here, based on those results, we present the density dependence of these properties and show that the elastic moduli, E, of graphyne are less dependent on density, ρ, than porous cellular materials with an exponent of E ~ ρ n , smaller than 2. We discuss the results in terms of the shape of the pores of the graphyne structures.

Structural Chemistry, 2014

Based on first principle calculation using generalized gradient approximation, we report electronic properties of graphyne and its related structures (graphdiyne, graphyne-3, graphyne-4). Boron and nitrogen atoms are systematically substituted into the position of carbon atom and the corresponding changes of the properties are reported. All the structures are found to be direct band gap semiconductors with band gap depending on the concentration and position of the doping material. Our band structure calculation clearly shows that the band gap can be tuned by B-N doping and the spin-polarized calculation depicts the nonmagnetic nature of these structures. The possibility of modulating the band gap provides flexibility for its use in nanoelectronic devices. Projected density of state (PDOS) analysis shed insights on the bonding nature of these novel materials, whereas from the view point of Crystal Orbital Hamilton Population (-COHP) analysis, the nature of chemical bonding between neighbouring atoms and the orbital participating in bonding and antibonding have been explored in details. Keywords Graphyne Á Stability Á Electronic band gap Á Density of states Á-COHP analysis Electronic supplementary material The online version of this article (

The Journal of Physical Chemistry C, 2013

On the basis of first-principles calculations, we present exotic geometrical and electronic properties in hydrogenated graphyne, a 2D material of sp−sp 2 hybrid carbon networks. Hydrogen atoms adsorbed onto sp-bonded carbon atoms can form both sp 2 -and sp 3 -hybridized bonds and can exist in three different geometries: in-plane, out-ofplane, and oblique-plane; this is in sharp contrast to hydrogenated graphene, which has only one hydrogenation geometry. The band gaps of hydrogenated graphyne can vary by ∼3 eV as the geometry changes. We also find that change in the hydrogen concentration allows a large band-gap tuning of ∼5 eV. Unlike hydrogenated graphene, in which H atoms show a tendency to cluster, H atoms tend to be dispersed in graphyne, making band-gap tuning feasible. These exotic properties in hydrogenated graphyne indicate that the band gap of hydrogenated graphyne can be tailored for new device applications. Furthermore, the composite of fully hydrogenated graphyne is C 1 H 1.75 , which has a hydrogen-to-carbon ratio greater than that of graphane (C 1 H 1 ). This large hydrogen capacity (∼13 wt % H) suggests that graphyne also can be used as a high-capacity hydrogen storage material.

Nanotechnology, Science and Applications

Plenty of new two-dimensional materials including graphyne, graphdiyne, graphone, and graphane have been proposed and unveiled after the discovery of the "wonder material" graphene. Graphyne and graphdiyne are two-dimensional carbon allotropes of graphene with honeycomb structures. Graphone and graphane are hydrogenated derivatives of graphene. The advanced and unique properties of these new materials make them highly promising for applications in next generation nanoelectronics. Here, we briefly review their properties, including structural, mechanical, physical, and chemical properties, as well as their synthesis and applications in nanotechnology. Graphyne is better than graphene in directional electronic properties and charge carriers. With a band gap and magnetism, graphone and graphane show important applications in nanoelectronics and spintronics. Because these materials are close to graphene and will play important roles in carbon-based electronic devices, they deserve further, careful, and thorough studies for nanotechnology applications.

The Journal of Chemical Physics

Graphynes can be structurally envisioned as 2D extensions to graphene, whereby linearly bonded carbon linkages increase the distance between trigonal carbon nodes. Many graphynes have been predicted to exhibit a Dirac-like semimetallic (SEM) graphenic electronic structure, which could potentially make them competitive with graphene for applications. Currently, most graphynes remain as attractive synthetic targets, and their properties are still unconfirmed. Here, we demonstrate that the electronic structure of hexagonal α-graphyne is analogous to that of biaxially strained graphene. By comparison with accurate quantum Monte Carlo results on strained graphene, we show that the relative energetic stability of electronic states in this correlated 2D system can be captured by density functional theory (DFT) calculations using carefully tailored hybrid functionals. Our tuned hybrid DFT approach confirms that α-graphyne has a low energy correlated Mott-like antiferromagnetic insulating (A...

ACS applied materials & interfaces, 2018

Graphynes and graphdiynes are generic names for families of two-dimensional carbon allotropes, where acetylenic groups connect benzenoid-like hexagonal rings, with the coexistence of sp and sp hybridized carbon atoms. The main differences between graphynes and graphdiynes are the number of acetylenic groups (one and two for graphynes and graphdiynes, respectively). Similarly to graphene nanoscrolls, graphyne and graphdiynes nanoscrolls are nanosized membranes rolled into papyrus-like structures. In this work we studied through molecular dynamics simulations, using reactive potentials, the structural and thermal (up to 1000 K) stability of α,β,γ-graphyne and α,β,γ-graphdiyne scrolls. Our results demonstrate that stable nanoscrolls can be created for all the structures studied here, although they are less stable than corresponding graphene scrolls. This can be elucidated as a result of the higher graphyne/graphdiyne structural porosity in relation to graphene, and as a consequence, th...