Carbyne Chains Research Articles

Carbyne from First Principles: Chain of C Atoms, a Nanorod or a Nanorope

We report an extensive study of the properties of carbyne using first-principles calculations. We investigate carbyne's mechanical response to tension, bending, and torsion deformations. Under tension, carbyne is about twice as stiff as the stiffest known materials and has an unrivaled specific strength of up to 7.5 × 10(7) N·m/kg, requiring a force of ∼10 nN to break a single atomic chain. Carbyne has a fairly large room-temperature persistence length of about 14 nm. Surprisingly, the torsional stiffness of carbyne can be zero but can be "switched on" by appropriate functional groups at the ends. Further, under appropriate termination, carbyne can be switched into a magnetic semiconductor state by mechanical twisting. We reconstruct the equivalent continuum elasticity representation, providing the full set of elastic moduli for carbyne, showing its extreme mechanical performance (e.g., a nominal Young's modulus of 32.7 TPa with an effective mechanical thickness of 0.772 Å). We also find an interesting coupling between strain and band gap of carbyne, which is strongly increased under tension, from 2.6 to 4.7 eV under a 10% strain. Finally, we study the performance of carbyne as a nanoscale electrical cable and estimate its chemical stability against self-aggregation, finding an activation barrier of 0.6 eV for the carbyne-carbyne cross-linking reaction and an equilibrium cross-link density for two parallel carbyne chains of 1 cross-link per 17 C atoms (2.2 nm).

Isomers of C46 fullerene with carbyne chains

The dynamics of the processes of isomerization and decomposition of C46 fullerene has been studied by computer simulation in the real-time regime. At an intermediate stage of evolution of the cluster (before it loses the spheroidal shape), isomers in which groups of adjacent pentagons and hexagons of C-C bonds are connected to each other with two-, four-, and six-atomic carbyne chains have been revealed. An analysis of the potential energy hypersurface has demonstrated that the isomers are quite stable and some of them can be observed experimentally.

Calcium-Decorated Carbyne Networks as Hydrogen Storage Media

Among the carbon allotropes, carbyne chains appear outstandingly accessible for sorption and very light. Hydrogen adsorption on calcium-decorated carbyne chain was studied using ab initio density functional calculations. The estimation of surface area of carbyne gives the value four times larger than that of graphene, which makes carbyne attractive as a storage scaffold medium. Furthermore, calculations show that a Ca-decorated carbyne can adsorb up to 6 H(2) molecules per Ca atom with a binding energy of ∼0.2 eV, desirable for reversible storage, and the hydrogen storage capacity can exceed ∼8 wt %. Unlike recently reported transition metal-decorated carbon nanostructures, which suffer from the metal clustering diminishing the storage capacity, the clustering of Ca atoms on carbyne is energetically unfavorable. Thermodynamics of adsorption of H(2) molecules on the Ca atom was also investigated using equilibrium grand partition function.

Bending Effect of sp-Hybridized Carbon (Carbyne) Chains on Their Structures and Properties

Density functional theory (DFT) calculations were exploited to evaluate the bending of polyynic and polycumulenic atomic carbon chains. It was found that the chains can be easily bent with a small arc−chord ratio. Furthermore, the bending of the chains caused the variation of bond lengths, leading to the change in the chain lengths; namely, the chain was first shortened slightly and then elongated with increasing arc−chord ratio. Furthermore, the bending decreased all bond angles as an oscillation manner, in which the larger decrease of bond angles occurred on even-ordinal-number carbon atoms than on corresponding odd-ordinal-number carbons, and the largest decrease was at the middle of the chain. With increasing the bending, the HOMO−LUMO energy gap of the polyynic chain was decreased, whereas the gap of the polycumulenic chain remained almost unchanged. This indicates that bending can increase the electric conductance of the polyynic chain, whereas the conductance of the polycumulenic chain is not affec...

Simulations of Aberration-Corrected High-Resolution Transmission Electron Microscope Images for Carbyne Chains

Herein, the feasibility to observe isolated sp carbon chains by aberration-corrected high-resolution transmission electron microscope (HRTEM) was demonstrated by image simulations. Furthermore, the simulations showed that an sp carbon chain with polyynic structure exhibits an escalloped dark line image, whereas an sp chain with polycumulenic structure forms a smooth dark line image. This image difference constitutes an effective method to identify the bonding structure of an sp carbon chain. Furthermore, a linear relationship between the bond length and the bond diameter of an sp carbon chain can allow one to estimate the bond length from its HRTEM images.

Stability of sp carbon (carbyne) chains

An sp carbon chain, which contains only one carbon atom in its cross section, is generally considered unstable. In this Letter, however, the DFT calculations showed that an isolated sp carbon chain is more stable than the smallest armchair ( 3 , 0 ) and zigzag ( 2 , 2 ) single-walled carbon nanotubes (SWCNT). This is consistent with the fact that an isolated sp carbon chain was observed by high-resolution transmission electron microscopy, but isolated ( 3 , 0 ) and ( 2 , 2 ) SWCNTs were never produced. Nevertheless, the sp chain is less stable than lager SWCNTs.

In Situ Monitoring the Thermal Dependence of the Growth of Carbon Nanotubes by Chemical Vapor Deposition Investigated by Tapered Element Oscillating Microbalance

Recently, it has been shown that the catalytic chemical vapor deposition (CCVD) synthesis at atmospheric pressure of multiwalled carbon nanotubes (MWCNTs) and carbon nanofibers can be very well monitored with a tapered element oscillating microbalance (TEOM) (V. Svrcek et al., J. Chem. Phys. 2006, 124, 184705). In this paper, the temperature dependence of the MWCNTs growth by thermal CCVD is investigated. Iron nanoparticle catalysts are dispersed on porous alumina powders. It is shown by scanning electron microscopy that MWCNTs appear above 903 K. The mass increase obtained from decomposition of an ethane-hydrogen gas mixture, monitored by TEOM, occurs with a large initial transient rate v 1 generally followed by a constant steady-state rate v 2 . Activation energy of around 100 kJ/mol is derived for the constant steady-state mass increase throughout the temperature range. A kinetic three-dimensional model based on finite differences is developed to account for these kinetic results. With only two basic assumptions, the calculations well agree with the experimental results. The first assumption supposes a variable competitive adsorption/desorption kinetics on the catalytic surface, and the other one assumes a transition of the iron catalyst from a solid to a state at 973 K. It is thus inferred that the rate of the steady-state growth is controlled by the competitive adsorption of hydrocarbon with hydrogen on the catalytic surface, the first step of the process. By contrast, the transient step displays abrupt changes that are governed by a partial melting of the iron-based nanoparticles above 973 K. In the solid state below 973K, carbon diffusion is controlled by the surface diffusion. Above 973K, the carbon diffusion is enhanced by several orders of magnitude corresponding to liquidlike diffusion. At high temperature, the suppression of the transient state is accounted for by an enhanced hydrocarbon desorption. A nucleation step involving preliminary carbon saturation of the catalytic nanoparticle as well as carbon surface coverage by the nucleation precursor is observed at low temperatures. From the simulations, it is proposed that a carbyne chain circumventing the catalytic nanoparticle may provide the nucleation precursor. A partial or collective poisoning of the catalyst interferes at high temperatures with this general scheme.

First principles study of the structure and stability of carbynes

Possible structures for carbynes are investigated by a first principles study and their free energy as a function of temperature and pressure is examined. A possible model combining elements from previous models is proposed for carbyne structures. Simulations show that structures can be constructed which agree well with results previously proposed in characterization work. The free energy of carbynes is calculated within wide ranges of temperature and pressure (1000–4000 K and 0–18 GPa) for 12 different structures. Results indicate that it is higher than the free energy of graphite in the whole studied region. Therefore, it seems that carbon-only carbynes are meta-stable structures. Introducing additional elements to stabilize the carbyne structures is discussed. Our calculations confirm that a solid consisting of carbyne chains can be stabilized by 3 CH 3 end groups.

Electronic and optical properties of functionalized carbon chains with the localized Hartree–Fock and conventional Kohn–Sham methods

Abstract The electronic and optical properties of extended functionalized carbyne chains, polyynes and cumulenes, are investigated with the localized Hartree–Fock method, with conventional Kohn–Sham methods, and with the Hartree–Fock method. It is found that even for very long polyynes the carbon–carbon bond lengths within a polyyne alternate while for long cumulenes no carbon–carbon bond length alternation occurs. Polyynes exhibit a finite HOMO–LUMO gap even if they become very long while cumulenes are found to become metallic in the limit of long chain lengths. The geometry and the electro-optical properties of polyynes cannot be influenced significantly by simple sp-σ-bonded end groups. The optically active 1 Σ u + ←X 1 Σ g + electronic transition in polyynes is investigated by time-dependent density-functional theory (TDDFT). The known systematic underestimation of excitation energies in large chain-like systems by TDDFT methods is also found for the systems considered here. Deficiencies in the commonly used exchange-correlation kernels are identified as the main source of this shortcoming of TDDFT methods. Unphysical Coulomb self-interactions present in conventional Kohn–Sham potentials seem to not contribute significantly to the problem.

GENERATION OF HIGHER FULLERENES FROM LASER ABLATION OF CARBYNE AND C60 PHOTOPOLYMER ASTROCHEMICAL IMPLICATIONS

ABSTRACT Laser ablation of targets of carbonaceous matter containing carbyne nanodomains (the sp hybridised carbon chains) or targets of C60 photopolymer produced carbon clusters which have been detected by FT-ICR (Fourier-Transform Ion Cyclotron Resonance) mass spectrometer. When the carbonaceous matter containing carbyne has been employed as laser target, no C60 has been generated but only fullerene cages from C74 up to C124. Larger cages were also obtained but with odd number. Starting from C60 photopolymer, laser ablation regenerates free C60 and creates a sequence of C60 superior homologues all possessing even number and each member of the series is separated from the preceding and the following member by the loss or by the addition respectively of a C2 unit. Fullerenes up to C162 have been recorded. The implications about the presence of free C60 fullerene in the interstellar and circumstellar space, its formation from carbyne chains and its stability towards its photopolymerization tendency and its regeneration from the photopolymer together with its superior homologues have been discussed thoroughly in the present paper.

Preparation and characterization of carbonaceous matter rich in diamond-like carbon and carbyne moieties

The microstructure of carbonaceous matter prepared from copper acetylide, by a coupling reaction promoted by air, hydrogen peroxide or Cu(NH 3) n 2+ oxidation has been studied by solid state C 13-NMR (CP/MAS), FT-IR and Raman spectroscopy. All three spectral techniques give clear evidences that the solid carbon produced contains sp-hybridized carbon chain moieties known as `acetylenic carbyne' (polyene-type, IUPAC notation: polyethynylene). Solid state C 13-NMR (CP/MAS) provides additional evidence on the presence of small cumulenic moiety `allenic or cumulenic carbyne' (polycumulene-type, IUPAC notation polyethylenediylidene). Solid state C 13-NMR (CP/MAS) in conjunction with Raman spectroscopy show sp 3-hybridized carbon moieties known also as `diamond-like carbon', formed by a crosslinking reaction of acetylenic carbyne chains; additionally sp 2-hybridized carbon atoms were detected and assigned to amorphous and graphitic carbon.

An interaction of amorphous carbyne with sodium: the formation of carbyne intercalation compounds

The carbyne intercalation compound with sodium (CICNa) has been synthesized for the first time using the chemical-transport reaction of amorphous carbyne with sodium metal in vacuum. A structural model of the intercalation compound has been proposed on the basis of experimental electron diffraction data. The molecular structure of carbyne chains in the intercalation compound has been confirmed by chemical properties. The interaction of CICNa with nitric acid does not result in the complete removal of alkali metal, residual sodium atoms orient carbyne chains during the crosslinking process. The carbyne single crystals thus formed can be considered as residue intercalation compound.

The treatment of electron correlation in aperiodic systems. II. Applications to poly(Li 2H 2) and poly(acetylene, carbyne) chains

A new method for the calculation of the density of states of aperiodic polymers at the quasiparticle level (electronic structure with correlation) has been applied to poly (Li 2H 2) and to poly (acetylene, carbyne) chains. Both the periodic and the aperiodic copolymers have been studied.