One-dimensional sp carbon: Synthesis,properties, and modifications

Carbyne, as the truly one-dimensional carbon allotrope with sp-hybridization, has attracted significant interest in recent years, showing potential applications in next-generation molecular devices due to its ultimate one-atom thinness. Various excellent properties of carbyne have been predicted, however, free-standing carbyne sample is extremely unstable and the corresponding experimental researches and modifications are under-developed compared to other known carbon allotropes. The synthesis of carbyne has been slowly developed for the past decades. Recently, there have been several breakthroughs in in-situ synthesis and measurement of carbyne related materials, as well as the preparation of ultra-long carbon chains toward infinite carbyne. These progresses have aroused widespread discussion in the academic community. In this review, the latest approaches in the synthesis of sp carbon are summarized. We then discuss its extraordinary properties, including mechanical, electronic, magnetic, and optical properties, especially focusing on the regulations of these properties. Finally, we provide a perspective on the development of carbyne.     

The influence of hydrogen impurities on the atomic and electronic structures of carbyne crystals

An ab initio DFT study of atomic and electronic structure of carbyne crystals was carried out. The influence of hydrogen impurities on carbyne structure was investigated. Calculations with atomic relaxations showed that carbon chains in the carbyne crystal structure are bow-like curved; free-energy calculations showed that the most probable lengths of those chains are four and six atoms, which is in a good agreement with experiments. Carbyne-crystal electronic-structure analysis showed that there is a small gap of 0.09 eV near the Fermi level in four-atomic carbyne, while there is no such gap in six-atomic carbyne. In studying of the hydrogen impurity influence on the atomic and electronic structure of carbyne crystals, hydrogen atoms were embedded in two directions: across and along carbon chains in the crystal. As a result we found that the crystal structure is not distorted in the case of hydrogen embedded across the chains, while the type of bonding between carbon atoms in carbon chains in the carbyne crystal structure depended on the impurity concentration. The crystal structure was distorted when hydrogen was embedded along the chains. The concentration of impurities influences the conductivity of a carbyne crystal.     

A review of arc-discharge method towards large-scale preparation of long linear carbon chains

Linear carbon chains as new one-dimensional (1D) nanomaterials attract attention for the predicted outstanding properties. However, the high reactivity of linear carbon chains hampers further experimental research. To date, different methods have been developed to synthesize new materials containing linear carbon chains. Among them, the arc-discharge method is a practical way to prepare both finite and infinite linear carbon chains. This review provides a brief discussion of the recent progress in the techniques to prepare carbon chain-based materials and then focuses on the arc-discharge method. The configuration of apparatus, optimal conditions, and the corresponding mechanism of arc-discharge method to prepare long linear carbon chain inside multi-walled carbon nanotubes are summarized in detail. The characterization techniques are introduced to evaluate the quality of products. Moreover, remaining challenges and perspectives are presented for further investigation of long linear carbon chains.     

First-principles study on the mechanics,optical, and phonon properties of carbon chains

Besides graphite, diamond, graphene, carbon nanotubes, and fullerenes, there is another allotrope of carbon, carbyne,existing in the form of a one-dimensional chain of carbon atoms. It has been theoretically predicted that carbyne would be stronger, stiffer, and more exotic than other materials that have been synthesized before. In this article, two kinds of carbyne, i.e., cumulene and polyyne are investigated by the first principles, where the mechanical properties, electronic structure, optical and phonon properties of the carbynes are calculated. The results on the crystal binding energy and the formation energy show that though both are difficult to be synthesized from diamond or graphite, polyyne is more stable and harder than cummulene. The tensile stiffness, bond stiffness, and Young's modulus of cumulene are 94.669 eV/?A,90.334 GPa, and 60.62 GPa, respectively, while the corresponding values of polyyne are 94.939 eV/?A, 101.42 GPa, and60.06 GPa. The supercell calculation shows that carbyne is most stable at N = 5, where N is the supercell number, which indicates that the carbon chain with 10 atoms is most stable. The calculation on the electronic band structure shows that cumulene is a conductor and polyyne is a semiconductor with a band gap of 0.37 eV. The dielectric function of carbynes varies along different directions, consistent with the one-dimensional nature of the carbon chains. In the phonon dispersion of cumulene, there are imaginary frequencies with the lowest value down to-3.817 THz, which indicates that cumulene could be unstable at room temperature and normal pressure.     

A new nanocluster carbyne-based material synthesized under high pressure

The DC and AC conductivities and the magnetoresistance and thermopower of carbyne samples were studied over the temperature range 1.8–300 K at frequencies 10 MHz–1 GHz. It was established that a variation in the fraction of sp ² bonds in carbynes induces a transition from one-to two-and then to three-dimensional conduction. The physical properties of the new carbyne-based solids may be understood within the model treating carbyne as a nanocluster material based on linear carbon chains and having a characteristic cluster size of 1 to 10 nm.     

On-surface synthesis of one-dimensional carbyne-like nanostructures with sp-carbon

Carbyne is an infinite one-dimensional carbon chain comprising of sp-hybridized carbons. Due to its high chemical reactivity and extreme instability, the synthesis and structural diversity of carbyne have been much less investigated in the past decades compared to carbon allotropes built with sp² hybridized carbons, such as fullerenes, carbon nanotubes, and graphene. The emerging on-surface synthesis strategy provides an extremely promising approach for the fabrication of novel carbyne-like nanostructures with atomic precision. Herein, we summarize recent exciting progress in the synthesis of carbyne-like nanostructures with one-dimensional sp-carbon on surfaces, including polyynes, cumulenes, and organometallic polyynes. We also point out the scientific challenges and prospects, encouraging scientists to explore the fabrication and characterization of single strands of carbyne in this young and promising research field.     

Structural transformations of the cumulene form of amorphous carbyne at high pressure

Structural transformations of the cumulene form of amorphous carbyne which are induced by heating at high pressure (7.7 GPa) are investigated. These can be described by the sequence amorphous phase — crystal — amorphous phase — disordered graphite. Raman scattering shows that predominately the chain structure of carbyne remains at the first three stages. It was found that the intermediate crystalline phase is an unknown modification of carbon whose structure is identified as cubic (a=3.145 Å). A mechanism of structural transformations in carbyne that involves the formation of new covalent bonds between chains is discussed. Pis’ma Zh. éksp. Teor. Fiz. 66, No. 4, 237–242 (25 August 1997)     

水分子链受限于单壁碳纳米管结构的密度泛函理论研究

本文采用第一性原理的密度泛函理论,主要以(6,6)Armchair型,(11,0)Zigzag型单壁碳纳米管为研究对象,研究了水分子链在碳纳米管内部吸附的稳定结构,以及结合能随其结构的变化.结果表明:当水分子链受限于碳纳米管内部时,引起碳纳米管直径收缩,这主要是由于水分子链与碳纳米管之间的氢键作用以及范德华弱相互作用所引起的.随着碳纳米管半径的增加,两种单体之间的结合能逐渐减小,但当碳纳米管半径增加至6.78时,其结合能又有所增加,这是由于在优化过程中,水分子链单体之间的氢键作用大于水分子链与碳纳米管之 关键词： 水分子链/单壁碳纳米管 密度泛函理论 结构稳定性     

Extraordinary mechanical performance in charged carbyne

Carbyne, the linear chain of carbon, promises the strongest and toughest material but possesses a Peierls instability (alternating single-bonds and triple-bonds) that reduces its strength and toughness. Herein, we computationally found that the gravimetric strength, strain-to-failure, and gravimetric toughness can be improved from 74 GPa·g^-1·cm³, 18%, and 9.4 kJ·g^-1 for pristine carbyne to the highest values of 106 GPa·g^-1·cm³, 26%, and 19.0 kJ·g^-1 for carbyne upon hole injection of +0.07 e/atom, indicating the charged carbyne with record-breaking mechanical performance. Based on the analyses of the atomic and electronic structures, the underlying mechanism behind the record-breaking mechanical performance was revealed as the suppressed and even eliminated bond alternation of carbyne upon charge injection.     

Equilibrium distribution of the wave energy in a carbyne chain

The steady-state energy distribution of thermal vibrations at a given ambient temperature has been investigated based on a simple mathematical model that takes into account central and noncentral interactions between carbon atoms in a one-dimensional carbyne chain. The investigation has been performed using standard asymptotic methods of nonlinear dynamics in terms of the classical mechanics. In the first-order nonlinear approximation, there have been revealed resonant wave triads that are formed at a typical nonlinearity of the system under phase matching conditions. Each resonant triad consists of one longitudinal and two transverse vibration modes. In the general case, the chain is characterized by a superposition of similar resonant triplets of different spectral scales. It has been found that the energy equipartition of nonlinear stationary waves in the carbyne chain at a given temperature completely obeys the standard Rayleigh–Jeans law due to the proportional amplitude dispersion. The possibility of spontaneous formation of three-frequency envelope solitons in carbyne has been demonstrated. Heat in the form of such solitons can propagate in a chain of carbon atoms without diffusion, like localized waves.     

Stable single helical C-and I-chains inside single-walled carbon nanotubes

The helicity of stable single helical carbon chains and iodine chains inside single-walled carbon nanotubes(SWCNTs)is studied by calculating the systematic van der Waals interaction energy.The results show that the optimal helical radius increases linearly with increasing tube radius,which produces a constant separation between the chain structure and the tube wall.The helical angle exhibits a ladder-like decrease with increasing tube radius,indicating that a large tube can produce a small helicity in the helical structures.     

Effect of hydrogen on the formation of the atomic structure of linear carbon chains: An ab initio approach

An ab initio study of the features of the formation of the atomic structure of carbon chains, which are structural parts of films of linear carbon chains, has been performed using the electron density functional theory. It has been shown that the formation and stabilization of experimentally observed kinks of carbon chains require the presence of hydrogen impurities in the chamber during the synthesis of linear carbon chains. The kinks of a carbon chain are formed in the process of the adsorption of hydrogen atoms on a chain. The optimal kink angle of carbon chains has been determined. The stability of kinks of carbon chains has been estimated as a function of the length of linear fragments. An additional mechanism has been proposed for the formation of kinks in carbon chains owing to the joining of short carbon chains with hydrogen ends.     

Carbon linear chains inside multiwalled nanotubes

Multiwalled carbon nanotubes have been deposited on graphite cathodes by using an arc discharge technique in He atmosphere, with the insertion of a catalytic Ni-Cr mixture as well as without catalysers. The topography of such deposition has been investigated by SEM, while a parallel micro-Raman study has revealed, in particular regions of the deposited cathodes, strong bands in the range 1780-1860 cm⁻¹, assignable to linear carbon chains inside the nanotubes. The variation of intensity, frequency and bandwidth of such bands has been investigated, in relation with the spectral characters of the host multiwalled carbon nanotube. In the cathode deposited without catalyst a quite ordered configuration of multiwalled carbon nanotubes is obtained in the central zone, while the maximum concentration of linear carbon chains is found in a ring shaped zone just inside the border. In sample obtained with catalyst the deposited multiwalled carbon nanotubes appear always more disordered, and a remarkable concentration of carbon chains appears in some zones, with a more casual distribution.     

Large-scale synthesis of polyynes with commercial laser marking technology

The space-confined synthesis method has been an efficient way for the preparation of linear carbon chains. However, the large-scale preparation of linear carbon chains still faces many challenges due to the lack of methods for the large-scale synthesis of precursors, such as short carbon chains (polyynes), and regulation technology for the transport of reactants in one-dimensional space. Here, we report a facile method for the rapid preparation of polyynes in large quantities using a commercial laser marking machine. Spectroscopic characterizations show that a large number of polyynes, such as C₈H₂, C₁₀H₂, C₁₂H₂, and C₁₄H₂, can be produced by ablating the graphite plate immersed in the organic liquid using a laser marking machine. The results of in situ Raman spectroscopy investigation of C_2nH₂-filled single-walled carbon nanotubes further confirm that a variety of polyyne molecules are synthesized. Meanwhile, in situ Raman spectroscopy also shows that the local heating treatment can accelerate the filling process of C_2nH₂ into one-dimensional channels. This work provides new insights into the study of linear carbon chains and space-confined synthesis methods.     

Length and temperature dependence of the mechanical properties of finite-size carbyne

Carbyne is an ideal one-dimensional conductor and the thinnest interconnection in an ultimate nano-device and it requires an understanding of the mechanical properties that affect device performance and reliability. Here, we report the mechanical properties of finite-size carbyne, obtained by a molecular dynamics simulation study based on the adaptive intermolecular reactive empirical bond order potential. To avoid confusion in assigning the effective cross-sectional area of carbyne, the value of the effective cross-sectional area of carbyne (4.148 Å²) was deduced via experiment and adopted in our study. Ends-constraints effects on the ultimate stress (maximum force) of the carbyne chains are investigated, revealing that the molecular dynamics simulation results agree very well with the experimental results. The ultimate strength, Young's Modulus and maximum strain of carbyne are rather sensitive to the temperature and all decrease with the temperature. Opposite tendencies of the length dependence of the overall ultimate strength and maximum strain of carbyne at room temperature and very low temperature have been found, and analyses show that this originates in the ends effect of carbyne.     

Effects of Carbon Black on Chain Mobility and Dynamic Mechanical Properties of Solution Polymerized Styrene-Butadiene Rubber

The structure of the bound rubber, the ¹H NMR (nuclear magnetic resonance) relaxation time, and the crosslink density of the physical network and the glass transition, were studied for solution polymerized styrene-butadiene rubber (SSBR) filled by carbon black, to investigate the effects of carbon black on the chain mobility and dynamic mechanical properties. It was found by ¹H NMR analysis that the rubber chains were adsorbed on the surface of carbon black to form physical crosslinks and restrict the mobility of the chains, especially for some high-mobility units such as chain ends. It was calculated, according to the molecular weight between adjacent crosslinks, that the main motion units of the tightly adsorbed chains appeared to be similar in size to the chain segments. The glass transition temperature (T _g) obtained by differential scanning calorimetry (DSC) could not be used to judge the effect of carbon black on chain mobility, while the appearance and change of the loss-tangent (tan δ) peak at high temperature in dynamic mechanical thermal spectrometry (DMTS) test showed that there were three chain states: free chains, loosely adsorbed chains, and tightly adsorbed chains. The dynamic rheology test showed that the unfilled SSBR compound had the rheological characteristics of entangled chain networks; however the nonlinear viscoelasticities of the filled SSBR were related to the gradual disentanglement of adsorbed chains and free chains. The peaks in tan δ vs. temperature curves implied that the motion unit size decreased with the increase of bound rubber content, and the modulus vs. temperature curve showed an apparently lower mobility of adsorbed chains than that of free chains through the very low dependence of modulus on temperature for the highly filled compounds. The extremely high tensile modulus of the vulcanizate with 63.6% carbon black at room temperature also implied that the adsorbed chains were in the glass state due to their restriction by the carbon black.     

Energetic barrier reduction at the carbyne film interface

An abnormal injection current density through SiO₂ has been observed recently for both signs of charge carriers in experiments with an oriented carbyne film grown on a SiO₂ layer. The absence of a surface leakage current and the insulating property of SiO₂ were experimentally proved. The temperature dependence of the current through SiO₂ showed low activation energy and confirmed the model of thermally activated injection. A strong influence of the electric field applied transverse to the carbon chains on the current through SiO₂ was observed. A model of energetic barrier reduction at the carbyne interface based on the hypothesis of transverse inter-chain hopping in the electric field was proposed. It was shown that a transverse electric field can be induced in a carbyne film as in one-dimensional media. The first organic light emitting device with a carbyne-based effective injector was fabricated.     

Conductance Spectra of Carbyne Transverse to Carbon Chains. Is It Related to the Soliton Lattice?

The influence of the thickness of an oriented carbyne film on the conductance of a special sample was investigated with an electric field of up to 1.8 ⋅ 10⁶ V/cm applied transverse to the carbon chains. A steplike dependence of the conductance on the thickness was observed. The general shape of the current-voltage characteristics, I ∝ U ^2.3, changes to I ∝ U ² when the thickness corresponding to a rapid change of conductance is attained. The characteristics presumably correspond to the space-charge limited current in the presence or absence of the trap band within the carbyne band gap. We propose the formation of a charge-topological soliton lattice at “magic” thicknesses which results in a layered structure of the film and in a bandlike conduction transverse to the chains.     

碳纳米管受限空间对共轭高分子聚(9,9-二辛基芴-2,7-二基)链段运动行为的影响

在纳米受限空间中,高分子往往会表现出与本体状态不同的性质,如异常的链段运动特性及晶相间转变行为等,这些性质对于研究和开发新型高分子材料具有重要的意义,因此针对受限环境下高分子的物理化学特性研究也一直是高分子界关注的焦点.本文通过化学气相沉积法制备垂直取向排列的多壁碳纳米管阵列,借助溶剂润湿–收缩法获得规整的高密度阵列结构,其取向排列的碳纳米管间隙形成了准一维的纳米受限空间,尺寸在5—50 nm尺度下可调.进一步将共轭高分子聚(9,9-二辛基芴-2,7-二基)(PFO)填充到碳管间隙的纳米空间中,制备PFO与取向多壁碳纳米管阵列复合膜.结果发现在碳纳米管形成的纳米受限空间中,PFO的链段热运动行为与本征态PFO薄膜相比受到了明显的抑制,不同晶型间转变速度大大减缓,提高了构象的热稳定性,同时取向排列的碳纳米管对PFO分子链取向排列分布具有明显的诱导作用,有利于获得高性能的PFO晶体.这种高密度取向排列的碳纳米管阵列结构未来可以用于制备优良发光性能及高稳定性的PFO光电器件.     

γ石墨炔衍生物结构稳定性和电子结构的第一性原理研究

通过基于密度泛函理论的第一原理计算,系统研究了γ石墨炔衍生物的结构稳定性、原子构型和电子性质.γ石墨炔衍生物的结构是由碳六元环以及连接六元环间的碳链组成,碳链上的碳原子数为N=1—6.研究结果表明,碳链上碳原子数的奇偶性对γ石墨炔衍生物的结构稳定和相应的原子构型、电子结构性质具有很大的影响.其奇偶性规律为:当六元环间的碳原子数为奇数时,体系中的碳链均为双键排布,系统呈现金属性;当六元环间的碳原子数为偶数时,系统中的碳链形式为单、三键交替排列,体系为直接带隙的半导体.直接带隙的存在能够促进光电能的高效转换,预示着石墨炔在光电子器件中的应用优势.N=2,4,6的带隙分布在0.94—0.84 eV之间,带隙的大小与碳链上三键的数量和长度有关.研究表明,将碳原子链引入到石墨烯碳六元环之间,通过控制引入的碳原子个数可以调控其金属和半导体电子特性,为设计和制备基于碳原子的可调控s-p杂化的二维材料和纳米电子器件提供了理论依据.