Carbon Atom Wires Research Articles

Carbyne: from the elusive allotrope to stable carbon atom wires

Abstract

Semiconductor-to-Metal Transition in Carbon-Atom Wires Driven by sp2 Conjugated End Groups

Novel bis(biphenyl)-capped polyynes have been synthesized to investigate the modulation of the electronic and optical properties of sp-hybridized carbon-atom wires (CAWs) capped with {\pi}-conjugated $sp^{2}$ endgroups. Raman and Surface Enhanced Raman spectroscopy (SERS) investigation of these systems and Density Functional Theory (DFT) calculations reveal structural changes from polyyne-like with alternating single-triple bonds towards cumulene-like with more equalized bonds as a consequence of the charge transfer occurring when wires interact with metallic nanoparticles. While polyynes have semiconducting electronic properties, a more equalized system tends to a cumulene-like structure characterized by a nearly metallic behavior. The possibility to drive a semiconductor-to-metal transition has been investigated by systematic DFT calculations on a series of CAWs capped with different conjugated endgroups revealing that the modulation of the structural, electronic and vibrational properties of the sp-carbon chain towards the metallic wire cannot be simply obtained by using extended {\pi}-conjugated $sp^{2}$ carbon endgroups, but require a suitable chemical design of the endgroup and control of charge transfer. These results provide useful guidelines for the design of novel $sp-sp^2$ hybrid carbon nanosystems with tunable properties, where graphene-like and polyyne-like domains are closely interconnected. The capability to tune the final electronic or optical response of the material makes these hybrid $sp-sp^2$ systems appealing for a future all-carbon-based science and technology.

Carbon-atom wires produced by nanosecond pulsed laser deposition in a background gas

Wires of sp-hybridized carbon atoms are attracting interest for both fundamental aspects of carbon science and for their appealing functional properties. The synthesis by physical vapor deposition has been reported to provide sp-rich carbon films but still needs to be further developed and understood in detail. Here the synthesis of carbon-atom wires (CAWs) has been achieved by nanosecond pulsed laser deposition (PLD) expoliting the strong out-of-equilibrium conditions occurring when the ablation plasma is confined in a background gas. Surface Enhanced Raman Spectroscopy (SERS) spectra of deposited films indicate that CAWs are mixed with a mainly sp2 amorphous carbon in a sp-sp2 hybrid material. Optimal conditions for the deposition of sp-carbon phase have been investigated by changing deposition parameters thus suggesting basic mechanisms of carbon wires formation. Our proof-of-concept may open new perspectives for the targeted fabrication of CAWs and sp-sp2 structures.

Carbon-atom wires: 1-D systems with tunable properties.

This review provides a discussion of the current state of research on linear carbon structures and related materials based on sp-hybridization of carbon atoms (polyynes and cumulenes). We show that such systems have widely tunable properties and thus represent an intriguing and mostly unexplored field for both fundamental and applied sciences. We discuss the rich interplay between the structural, vibrational, and electronic properties focusing on recent advances and the future perspectives of carbon-atom wires and novel hybrid sp-sp(2)-carbon architectures.

Raman spectroscopy as a tool to investigate the structure and electronic properties of carbon-atom wires.

Graphene, nanotubes and other carbon nanostructures have shown potential as candidates for advanced technological applications due to the different coordination of carbon atoms and to the possibility of π-conjugation. In this context, atomic-scale wires comprised of sp-hybridized carbon atoms represent ideal 1D systems to potentially downscale devices to the atomic level. Carbon-atom wires (CAWs) can be arranged in two possible structures: a sequence of double bonds (cumulenes), resulting in a 1D metal, or an alternating sequence of single–triple bonds (polyynes), expected to show semiconducting properties. The electronic and optical properties of CAWs can be finely tuned by controlling the wire length (i.e., the number of carbon atoms) and the type of termination (e.g., atom, molecular group or nanostructure). Although linear, sp-hybridized carbon systems are still considered elusive and unstable materials, a number of nanostructures consisting of sp-carbon wires have been produced and characterized to date. In this short review, we present the main CAW synthesis techniques and stabilization strategies and we discuss the current status of the understanding of their structural, electronic and vibrational properties with particular attention to how these properties are related to one another. We focus on the use of vibrational spectroscopy to provide information on the structural and electronic properties of the system (e.g., determination of wire length). Moreover, by employing Raman spectroscopy and surface enhanced Raman scattering in combination with the support of first principles calculations, we show that a detailed understanding of the charge transfer between CAWs and metal nanoparticles may open the possibility to tune the electronic structure from alternating to equalized bonds.

Anti TNF-α drug inhibits initial process of vasculitis in animal model of Kawasaki disease

Wires of sp-hybridized carbon atoms are attracting interest for both fundamental aspects of carbon science and for their appealing functional properties. The synthesis by physical vapor deposition has been reported to provide sp-rich carbon films but still needs to be further developed and understood in detail. Here the synthesis of carbon-atom wires (CAWs) has been achieved by nanosecond pulsed laser deposition (PLD) expoliting the strong out-of-equilibrium conditions occurring when the ablation plasma is confined in a background gas. Surface Enhanced Raman Spectroscopy (SERS) spectra of deposited films indicate that CAWs are mixed with a mainly sp2 amorphous carbon in a sp-sp2 hybrid material. Optimal conditions for the deposition of sp-carbon phase have been investigated by changing deposition parameters thus suggesting basic mechanisms of carbon wires formation. Our proof-of-concept may open new perspectives for the targeted fabrication of CAWs and sp-sp2 structures.

Fabrication and characterization of oriented carbon atom wires assembled on gold

Carbon atom wires (CAWs) are of the sp-hybridized allotrope of carbon. To augment the extraordinary features based on sp-hybridization, we developed an approach to make CAWs be self-assembled and orderly organized on Au substrate. The self-assembling process was investigated in situ by using scanning tunneling microscopy (STM) and electrochemical quartz crystal microbalance (EQCM). The properties of the assembled film were characterized by voltammetry, Raman spectroscopy, electron energy loss spectroscopy (EELS), and the contact angle measurements. Experimental results indicated that the assembled CAW film was of the good structural integrity and well organized, with the sp-hybridized features enhanced.

Electrochemical Determination of Dihydroxybenzene Isomers at the Carbon-Atom-Wire-Modified Electrode

The electrochemical behavior of dihydroxybenzenes was investigated with stationary and rotating electrodes modified by a new material, carbon atom wires (CAWs), using cyclic and differential pulse voltammetry and a hydrodynamic technique. The CAW-modified electrode showed high electrocatalytic activity to the redox of dihydroxybenzenes and capability of determining three dihydroxybenzene isomers simultaneously. The anodic peak potential on the cyclic voltammogram shifted by , , and in an individual hydroquinone, catechol, and resorcinol solution, respectively, at the CAW-modified glassy carbon electrode compared to a bare electrode. In a solution containing coexistent dihydroxybenzenes, for each, the anodic peak potentials of hydroquinone and catechol were apart as far as on the differential pulse voltammogram, and the oxidative limiting currents of both hydroquinone and catechol were linear with respect to their concentrations in the range of in a pH 5.0 phosphate buffer solution at the CAW-modified electrode.

Electrochemical behavior of adrenaline at the carbon atom wire modified electrode

Electrochemical behavior of adrenaline at an electrode modified by carbon atom wires (CAWs), a new material, was investigated by cyclic voltammetry combined with UV–vis spectrometry, and forced convection method. As to the electrochemical response of redox of adrenaline/adrenalinequinone couple in 0.50 M H 2SO 4, at a nitric acid treated CAW modified electrode, the anodic and cathodic peak potentials E pa and E pc shifted by 87 mV negatively and 139 mV in the positive direction, respectively, and standard heterogeneous rate constant k 0 increased by 16 times compared to the corresponding bare electrode, indicating the extraordinary activity of CAWs in electrocatalysis for the process.

Selective determination of dopamine in the presence of ascorbic acid at the carbon atom wire modified electrode

To determine dopamine (DA) in the presence of high concentration of ascorbic acid (AA), a glassy carbon electrode modified by carbon atom wires (CAWs), a kind of new homemade material, was investigated by cyclic voltammetry. It was found that the electrochemical responses of DA were affected by the presence of AA, the pH value of the electrolytic solution and an acid treated process on CAWs. The HNO 3 treated CAW modified electrode exhibited excellent ability to discriminate DA from AA by means of cyclic voltammetry and the separation of their anodic peak potentials was apart as wide as 0.298 V in pH 6.00 phosphate buffer solution containing 0.50 mM DA and 5.00 mM AA at the scan rate of 50 mV/s at the modified electrode.

Investigation of the electrochemical behaviors of dopamine on the carbon atom wire modified electrode

A glassy carbon electrode was modified by a new homemade material, carbon atom wires (CAW). Electrochemical behaviors of the modified electrode were investigated by cyclic voltammetry and the electrode showed remarkable catalytic activity, stability and repetition to the redox reactions of dopamine (DA) in pH 6.80 phosphate buffer solution. It was found that the electrochemical responses of the CAW modified electrode in the case was affected by an acid treated process and the pH value of the electrolytic solution used. The anodic and cathodic peak currents had an excellent linear relation with the concentration of DA between 1.01 × 10 −5 and 6.15 × 10 −3 M with the detection limit of 1.5 × 10 −6 M.

Linear carbon allotrope – carbon atom wires prepared by pyrolysis of starch

A new method is reported to produce linear carbon allotrope from the pyrolysis of starch catalyzed by Fe. The pyrolytic product termed as carbon atom wires (CAW) is composed of winding lines with the diameter around 2.0 Å, indicated by magnified HRTEM images. The experimental results of UV and Raman spectra revealed a conjugated sequence of cumulated double bonds (CC) n presented in the hexane extract of CAW. Arguments about the sp hybridization bonding structure of CAW can also be supported by EELS and FT-IR measurements.

Oscillatory spin-polarized conductance in carbon atom wires

Zero temperature spin-polarized transport in atomic wires consisting of magnetic (Co) and nonmagnetic (C) atoms sandwiched between gold electrodes is investigated using gradient-corrected density functional theory and Landauer's formalism. Our calculation shows a spin valve behavior with the parallel magnetization state between the two Co atoms giving higher conductance than the respective antiparallel magnetization state and a nonmonotonic variation of magnetoconductance with wire length. We term the more conductive parallel magnetization state the on state and the antiparallel magnetization state the off state. The ground state of wires containing up to five carbon atoms has antiparallel (off) spin configurations between the Co. The additional stability of the antiferromagnetic state in wires containing an even number of carbon atoms is ascribed to an enhanced superexchange mechanism facilitated by \ensuremath{\sigma}-\ensuremath{\pi}-conjugation present in the systems.

Electrical conductance of parallel atomic wires

The effects of lateral interactions on the conductance of two atomic wires connected in parallel are investigated using density-functional theory. Carbon-atom wires with a cumulene structure end bonded to two metal electrodes are used as the model system. Large variations of the low-bias conductance of the system as a function of the separation of the two wires on the atomic scale are predicted. This variation results from two types of interactions: (a) a direct bonding interaction between the atomic wires, and (b) an indirect interaction associated with the presence of the metal electrodes. The electrodes transfer an amount of charge to the carbon wires that varies with the separation d between the wires by as much as a factor of 2. The conductance changes, as a function of d, follow closely the variation of the density-of-states of the system at the Fermi level.

Carbon-atom wires: charge-transfer doping, voltage drop, and the effect of distortions

We present first-principles calculations on electrical conduction through carbon atomic wires. The changes in charge distribution induced by a large bias exhibit the primary involvement of the wire's pi states. A significant fraction ( approximately 40%) of the voltage drops across the atomic wire itself. At zero bias, there is a large transfer of charge from the electrodes to the wire, effectively providing doping without introducing scattering centers. This transfer leads, however, to potential barriers at the wire-electrode junctions. Bending the wire reduces its conductance.