Bonded Carbon Atoms Research Articles

Dynamic response of a carbon nanotube-based rotary nano device with different carbon-hydrogen bonding layout

In a nano rotational transmission system (RTS) which consists of a single walled carbon nanotube (SWCNT) as the motor and a coaxially arranged double walled carbon nanotube (DWCNT) as a bearing, the interaction between the motor and the rotor in bearing, which has great effects on the response of the RTS, is determined by their adjacent edges. Using molecular dynamics (MD) simulation, the interaction is analyzed when the adjacent edges have different carbon-hydrogen (CH) bonding layouts. In the computational models, the rotor in bearing and the motor with a specific input rotational speed are made from the same armchair SWCNT. Simulation results demonstrate that a perfect rotational transmission could happen when the motor and rotor have the same CH bonding layout on their adjacent ends. If only half or less of the carbon atoms on the adjacent ends are bonded with hydrogen atoms, the strong attraction between the lower speed (100GHz) motor and rotor leads to a synchronous rotational transmission. If only the motor or the rotor has CH bonds on their adjacent ends, no rotational transmission happens due to weak interaction between the bonded hydrogen atoms on one end with the sp1 bonded carbon atoms on the other end.

Studying the electronic and phononic structure of penta-graphane

In this paper, we theoretically consider a two dimensional nanomaterial which is a form of hydrogenated penta-graphene; we call it penta-graphane. This structure is obtained by adding hydrogen atoms to the sp2 bonded carbon atoms of penta-graphene. We investigate the thermodynamic and mechanical stability of penta-graphane. We also study the electronic and phononic structure of penta-graphane. Firstly, we use density functional theory with the revised Perdew–Burke–Ernzerhof approximation to compute the band structure. Then one–shot GW (G0W0) approach for estimating accurate band gap is applied. The indirect band gap of penta-graphane is 5.78 eV, which is close to the band gap of diamond. Therefore, this new structure is a good electrical insulator. We also investigate the structural stability of penta-graphane by computing the phonon structure. Finally, we calculate its specific heat capacity from the phonon density of states. Penta-graphane has a high specific heat capacity, and can potentially be used for storing and transferring energy.

What can tell the quantum chemical topology on carbon–astatine bonds?

ABSTRACTThe nature of carbon–astatine bonds involved in some model species that mimic 211At-labelled biomolecules, was investigated by means of ELF and QTAIM analyses in a context of two-component relativistic computations. The nature of the bonded carbon atom proved to be decisive. When At is bonded to an ethynyl group, some charge delocalisation with the vicinal triple C–C bond strengthens the At–C bond and gives it a multiple bond character. However, At displays also a large positive charge which may alter the in vivo stability of such At–C bonds. In the case of an isopropyl group, the At–C bond is less polarised but also much weaker. In contrast, the bond remains strong whilst retaining a small At positive charge when At is bonded to an sp2 carbon atom. Hence, these latter results rationalise why aromatic or aryl groups appear reasonably suited for a priori stable radiolabelling of biomolecules with 211At in the context of alpha therapy.

Recent progress on the development of metal oxides/graphene composites for gas sensing

Semiconductor metal oxides, a type of important sensing materials used extensively in the field of gas sensing, have excellent electrochemical, catalytic and impedance alternating properties, which make them suitable for sensing all kinds of oxidation and reduction gases. Meanwhile, graphene, a kind of unique two-dimensional and single-atom thick carbon material with sp2 bonded carbon atoms, shows excellent physical-chemical properties and attracts increasing attention in recent years. Great attention has been focused on the application of metal oxide/graphene hybrids in the field of gas sensing by taking advantages of the excellent gas sensing properties of metal oxides and the unique electrical, mechanical and thermal properties of graphene. This review summarizes the applications of different morphologies of metal oxides hybrided with different structured graphene composites in gas sensing field. Here, gas sensing properties of different metal oxide/graphene hybrids for the same target gas and the latest research progress of metal oxide/graphene hybrid materials are also highlighted. Finally, a brief conclusion and an outlook on the application of metal oxide/graphene composites in the field of gas sensing are discussed.

Quenching of liquid carbon under intensive heat transfer to the cold diamond substrate: Molecular-dynamic simulation

Quenching of liquid carbon (T = 6600 K) on a cold diamond substrate at T = 300 K in conditions close to the experimental laser melting of dispersed graphite on the substrate of natural diamond is investigated using molecular dynamics (MD) simulations. Quenching was carried out for two types of boundary conditions on the side opposite to the diamond substrate. The simulations confirmed the experimental result of the formation of amorphous carbon under such conditions. The calculations showed that the destruction of the diamond substrate did not take place because of its very high thermal conductivity. The estimation of the cooling rate of liquid carbon was done, the result is 1015 K/s. Temperature profiles in different layers of liquid carbon were restored to reproduce the detailed picture of the quenching process. We evaluated the radial distribution functions (RDF), the distribution of carbon atom bond fractions sp1-sp2-sp3, the average bond length and the azimuthal angles distributions for amorphous carbon atoms. This analysis confirmed that the amorphous carbon obtained by quenching in MD-simulations had a graphite-like structure.

Graphene synthesis: a Review

Abstract Graphene has achieved a great amount of popularity and interest from the science world because of its extraordinary physical, mechanical and thermal properties. Graphene is an allotrope of carbon, having one-atom-thick planar sheets of sp2 bonded carbon atoms densely packed in a honeycomb crystal lattice. Many methods to synthesize graphene have been developed over a short period and we believe it is necessary to create a list of the most notable approaches. This article focuses on the methods to synthesize graphene in an attempt to summarize and document advancements in the synthesis of graphene research and future prospects.

Short Access to Belt Compounds with Spatially Close C=C Bonds and Their Transannular Reactions.

Two domino Diels-Alder adducts were obtained from 3,7-bis(cyclopenta-2,4-dien-1-ylidene)-cis-bicyclo[3.3.0]octane and dimethyl acetylenedicarboxylate or N-methylmaleimide under microwave irradiation. From the first adduct, a C20H24 diene with C2v symmetry was obtained by Zn/AcOH reduction, hydrolysis, oxidative decarboxylation, and selective hydrogenation. Photochemical [2+2] cycloaddition of this diene gave a thermally unstable cyclobutane derivative, which reverts to the diene. However, both the diene and the cyclobutane derivatives could be identified by X-ray diffraction analysis upon irradiation of the diene crystal. New six-membered rings are formed upon the transannular addition of bromine or iodine to the diene. The N-type selectivity of the addition was examined by theoretical calculations, which revealed the distinct susceptibility of the doubly bonded carbon atoms to the bromine attack.

Interfacial Charge States in Graphene on SiC Studied by Noncontact Scanning Nonlinear Dielectric Potentiometry.

We investigate pristine and hydrogen-intercalated graphene synthesized on a 4H-SiC(0001) substrate by using noncontact scanning nonlinear dielectric potentiometry (NC-SNDP). Permanent dipole moments are detected at the pristine graphene-SiC interface. These originate from the covalent bonds of carbon atoms of the so-called buffer layer to the substrate. Hydrogen intercalation at the interface eliminates these covalent bonds and the original quasi-(6×6) corrugation, which indicates the conversion of the buffer layer into a second graphene layer by the termination of Si bonds at the interface. NC-SNDP images suggest that a certain portion of the Si dangling bonds remains even after hydrogen intercalation. These bonds are thought to act as charged impurities reducing the carrier mobility in hydrogen-intercalated graphene on SiC.

Adsorption behavior of Co anchored on graphene sheets toward NO, SO2, NH3, CO and HCN molecules

Abstract Based on the first-principles of density-functional theory (DFT), the effects of gas adsorption on the change in geometric stability, electronic structure and magnetic properties of graphene with anchored Co (Co–graphene) systems were investigated. A single Co adatom interacts much weaker with pristine graphene (Co/pri–graphene) than with the graphene containing a single vacancy (Co/SV–graphene). The Co dopant provides more electrons to the dangling bonds of carbon atom at defective site and exhibits more positive charges, which makes Co/SV–graphene less prone to be adsorbed by gas molecules in comparison to Co/pri–graphene. It is found that the electronic structure and magnetic properties of Co–graphene systems can be modulated by adsorbing gas molecules. Except the NH 3 molecule, the adsorbed NO, SO 2 , CO or HCN as electron acceptors on the Co/pri–graphene can exhibit semiconducting properties. Among the gas molecules, the strong adsorption of NO molecule can effectively regulate the magnetic properties of Co–graphene systems. Moreover, the stable configuration of Co/SV–graphene is more likely to be the gas sensor for detecting NO and SO 2 . The results validate that the reactivity of atomic-scale catalyst is supported on graphene sheets, which is expected to be potentially efficient in the gas sensors and electronic device.

Design, synthesis, and characterization of graphene-nanoparticle hybrid materials for bioapplications.

Graphene is composed of single-atom thick sheets of sp2 bonded carbon atoms that are arranged in a perfect two-dimensional (2D) honeycomb lattice. Because of this structure, graphene is characterized by a number of unique and exceptional structural, optical, and electronic properties.1 Specifically, these extraordinary properties include, but are not limited to, a high planar surface area that is calculated to be 2630 m2 g−1,2 superior mechanical strength with a Young’s modulus of 1100 GPa,3 unparalleled thermal conductivity (5000 W m−1 K−1),4 remarkable electronic properties (e.g., high carrier mobility [10 000 cm2 V−1 s−1] and capacity),5 and alluring optical characteristics (e.g., high opacity [~97.7%] and the ability to quench fluorescence).6 As such, it should come as no surprise that graphene is currently, without any doubt, the most intensively studied material for a wide range of applications that include electronic, energy, and sensing outlets.1c Moreover, because of these unique chemical and physical properties, graphene and graphene-based nanomaterials have attracted increasing interest, and, arguably, hold the greatest promise for implementation into a wide array of bioapplications.7 In the last several years, numerous studies have utilized graphene in bioapplications ranging from the delivery of chemotherapeutics for the treatment of cancer8 to biosensing applications for a host of medical conditions9 and even for the differentiation and imaging of stem cells.10 While promising and exciting, recent reports have demonstrated that the combination of graphene with nanomaterials such as nanoparticles, thereby forming graphene–nanoparticle hybrid structures, offers a number of additional unique physicochemical properties and functions that are both highly desirable and markedly advantageous for bioapplications when compared to the use of either material alone (Figure 1).11 These graphene–nanoparticle hybrid structures are especially alluring because not only do they display the individual properties of the nanoparticles, which can already possess beneficial optical, electronic, magnetic, and structural properties that are unavailable in bulk materials, and of graphene, but they also exhibit additional advantageous and often synergistic properties that greatly augment their potential for bioapplications. Open in a separate window Figure 1 Graphene nanoparticle hybrids exist in two forms, as graphene–nanoparticle composites and graphene-encapsulated nanoparticles, and can be used for various bioapplications including biosensors, photothermal therapies, stem cell/tissue engineering, drug/gene delivery, and bioimaging. Panel (A) reprinted with permission from ref 110. Copyright 2012 Wiley. Panel (B) reprinted with permission from ref 211. Copyright 2013 Elsevier. Panel (C) reprinted with permission from ref 244. Copyright 2013 Wiley.

Ultrathin undoped tetrahedral amorphous carbon films: thickness dependence of the electronic structure and implications for their electrochemical behaviour.

In this paper we show that the electronic properties of ultrathin tetrahedral amorphous carbon (ta-C) films are heavily dependent on their thickness. By using scanning tunnelling spectroscopy, Raman spectroscopy, and conductive atomic force microscopy, it was found that a decrease of ta-C thickness from 30 to 7 nm leads to (i) the narrowing of the band gap; (ii) appearance of shallower monoenergetic traps as well as the increase of their concentration; (iii) the increase of the equilibrium concentration of free charge carriers and their mobility; which were caused by (iv) the increase in the sp(2) fraction. However, beyond a certain ta-C thickness (7 nm) the electronic properties of the studied samples start to deteriorate, which is highly likely related to titanium oxide formation at the Ti/ta-C interface. The same tendency is observed for the sample with beforehand air-formed native titanium oxide at the interface. With respect to the last point, it is suggested that the ta-C layer has no uniform coverage if its thickness is small enough (less than 7 nm). The experimental results were rationalized by detailed atomistic simulations. By using the so-called "Tauc plot" we introduce the possibility of the coexistence of bulk and surface band gaps originating from the large increase in sp(2) bonded carbon atoms in the surface region compared to that in the bulk ta-C. The results from the simulations were found to be consistent with the experimental measurements. The previously stated variation in the electronic properties of the layers as a function of their thickness was also exhibited in the electrochemical properties of the samples. It appears that the thinner ta-C layers had more facile electron transfer kinetics as determined with a ferrocenemethanol (FcMeOH) outer sphere redox system. However, if the ta-C layer thickness was reduced too much, the films were not stable anymore.

First-principles study of electron-phonon coupling and superconductivity in compound Li2C2

One-dimensional carbon chains are expected to show outstanding optical and mechanical properties. But synthesis of the compounds containing one-dimensional carbon chains is a challenging work, because of the difficulty in saturating the dangling bonds of carbon atoms. Recently, the transition from the Immm phase to the Cmcm one at a transition pressure 5 GPa has been predicted for Li2C2 by density-functional theory calculations. In Cmcm-Li2C2, there are one-dimensional zigzag carbon chains caged by lithium atoms. Under ambient pressure, the electronic structure of Cmcm-Li2C2 is as follows: The hybridization among 2s, 2py, and 2pz orbitals of carbon atoms results in three sp2-hybridized orbitals that are coplanar with the zigzag chains of these carbon atoms, denoted as the y-z plane. The sp2-hybridized orbitals along y-axis (perpendicular to the zigzag chain) overlap with each other and form one πup-bonding band and one πup ^*-antibonding band. Likewise, the 2p_x orbitals of carbon atoms will provide also one πup-bonding band and one π*-antibonding band. These two π*-antibonding bands cross the Fermi level and contribute to the metallicity of Cmcm-Li2C2. The other two sp2-hybridized orbitals will give two σ-bonding bands, whose band tops are about 5 eV below the Fermi energy level. These two fully occupied σ bands are the framework of the zigzag carbon chains. The changes in electronic structure of Cmcm-Li2C2 under 5 GPa are negligible, compared with that in case of ambient pressure. To our best knowledge, there is no report upon the superconductivity for compounds containing one dimensional carbon chains. We choose Cmcm-Li2C2 as a model system to investigate its electron-phonon coupling and phonon-mediated superconductivity. To determine the phonon-mediated superconductivity, the electron-phonon coupling constant λ and logarithmic average frequency ωlog are calculated based on density functional perturbation theory and Eliashberg equations. We find that λ and ωlog are equal to 0.63 and 53.8 meV respectively at ambient pressure for Cmcm-Li2C2. In comparison, both the phonon density of states and the Eliashberg spectral function α2F(ω) are slightly blue-shifted at a pressure of 5 GPa. Correspondingly, λ and ωlog are calculated to be 0.56 and 58.2 meV at 5 GPa. Utilizing McMillian-Allen-Dynes formula, we find that the superconducting transition temperatures (Tc) for Cmcm-Li2C2 are 13.2 K and 9.8 K, respectively, at ambient pressure and 5 GPa. We also find that two phonon modes B1g and Ag at Γ point have strong coupling with π* electrons. Among lithium carbide compounds, the superconductivity is only observed in LiC2 below 1.9 K. Besides LiC2, theoretical calculations also predicted superconductivity in mono-layer LiC6, with Tc being 8.1 K. So if the superconductivity of Cmcm-Li2C2 is confirmed by experiment, it will be the first superconducting compound containing one dimensional carbon chains and its Tc will be the highest one among lithium carbide compounds. Thus experimental research to explore the possible superconductivity in Cmcm-Li2C2 is called for.

PS0002-153 化学的にハイブリッドしたG-CNTナノ材料の創製と評価

Graphene and carbon nanotube (CNT) exhibit excellent mechanical, electrical, and thermal properties. In a previous study, these materials were derived from sp2 bonded carbon atoms closely packed in a honeycomb crystal lattice. However, there were several problems with the derived materials including suboptimal mechanical properties, slippage within the graphene surface, leakage CNT from the resin, and lack of bonding between nanomaterials. To address the aforementioned deficiencies, we proposed the fabrication of a graphene CNT hybrid material (G-CNT) consisting of an extensive network of chemically bonded layers. Chemically bonding was performed via dehydration synthesis of amino and carboxyl groups. To analyze the produced material, we employed Fourier transform infrared spectroscopy (FT-IR) and tensile tests. The FT-IR spectra confirmed, amino modification of graphene, oxidation of carboxyl modified CNT, and oxidation of the amide group of G-CNT. The tensile tests, demonstrated that PVA films containing G-CNT have high ductility in comparison to both pure PVA and PVA lacking chemically bonded CNT and graphene.

Enhancement in the performance of multi-walled carbon nanotube: Poly(methylmethacrylate) composite thin film ethanol sensors through appropriate nanotube functionalization

We report for the first time, development of an efficient ethanol sensor using mild functionalized multiwalled carbon nanotubes (MWCNTs). A unique technique to functionalize MWCNT is reported to enhance the performance of the ethanol sensor based on it. The conventional functionalization techniques tend to damage physical structure of carbon nanotubes (CNTs) to a large extent and convert most of their sp2 bonds into sp3 bonded carbon atoms. This results in reduction of the available adsorption sites for ethanol vapors on the CNT surface and hence deteriorates the sensitivity. In this work, the functionalization of nanotubes is achieved through direct cycloaddition to π electrons of the CNT that does not hamper the physical structure of the nanotube. High resolution transmission electron microscopy (HRTEM) and Raman spectroscopy studies were employed to confirm the appropriate functionalization for better performance of the sensor. Electrical transport properties of the composites were also studied to understand the quality of the established CNT network. Out of the other functionalization technique, Diels Alder cyclo addition reaction based composite sensor was found to exhibit excellent performance and has an edge over the other reported CNT based sensor.

Annealing induced electrical conduction and band gap variation in thermally reduced graphene oxide films with different sp2/sp3 fraction

Temperature dependent electrical conductivity of as prepared and thermally reduced graphene oxide (GO) thin films was measured in the range 300–520K. As prepared GO films show very low conductivity ∼6.8×10−6S/cm at 300K, which increases slowly till 370K. A sharp increase in conductivity is observed in the temperature range 370–440K, beyond which conductivity is thermally activated with activation energy 0.26eV. Reduced GO films show an increase in conductivity at 300K with increase in reduction temperature. GO films reduced at 400°C exhibit high conductivity ∼40S/cm at 300K, with very low activation energy 0.05eV in the measured temperature range 300–520K. The increase in conductivity after thermal reduction is due to an increase in the ratio sp2/sp3 bonded carbon atoms. The band gap of as prepared GO is 3.20eV and it is decreased by approximately 0.4eV in the case of thermally reduced GO at 400°C in comparison to as prepared GO.

Hybridization and tribomechanical properties of ultrathin amorphous carbon films synthesized by radio-frequency low-pressure plasma discharges

Ultrathin amorphous carbon (a-C) films were deposited on Si(100) substrates by low-pressure radio-frequency plasma discharges of varying substrate bias voltage in pure Ar atmosphere. The surface roughness and tribomechanical properties of the a-C films were measured with an atomic force microscope and a surface force microscope, respectively. Insight into tetrahedral (sp3) and trigonal (sp2) atomic carbon hybridization was obtained from the deconvoluted C1s core level peak of X-ray photoelectron spectroscopy spectra. Energetic particle collision theory was used to correlate hybridization and tribomechanical properties to low-pressure plasma discharge conditions. The results are interpreted in the context of Ar+ ion collisions with carbon atoms on the growing film surface, followed by collision cascades between excited carbon atoms and other surface carbon atoms, resulting in the removal of weakly bonded carbon atoms and dominance of sp3 hybridization or the development of thermal spikes that promote sp2 hybridization. Particle collision analysis shows that the sp3 fraction is a function of Ar+ ion flux, sputtering yield of target carbon atoms, and kinetic energy of surface carbon atoms, in good qualitative agreement with experimental results of the sp3 content of a-C films versus substrate bias voltage.

Multi- and few-layer graphene on insulating substrate via pulsed laser deposition technique

In this paper, multilayer and few layer graphene (FLG) fabricated on fused silica substrate by pulsed laser deposition (PLD) technique without using any catalyst is reported. The effect of deposition temperature onto the formation of graphene layers is investigated. Raman spectra showed the characteristic features of sp2 bonded carbon atoms; G band, D band and 2D band. The line shape of 2D band structure and the relative intensities of G and 2D bands were used to estimate the number of graphene layers. The graphene layers deposited via PLD at room temperature has I2D/IG ratio ∼0.33, confirming the formation of multilayer whereas that of deposited at substrate temperature 700°C is ∼0.47 confirming the formation of less than five layers of graphene; few layers graphene. The decrease in separation of subpeaks of 2D band with deposition temperature further confirms the reduction in the number of layers of graphene from ∼10 deposited at room temperature to less than 5 layers at that of 700°C. The surface morphology of the deposited samples was recorded by field emission scanning electron microscope and transmission electron microscope.

ChemInform Abstract: Two‐Dimensional Carbon Leading to New Photoconversion Processes

AbstractReview: 50 refs.

From N,N-diphenyl-N-naphtho[2,1-b]thieno[2,3-b:3′,2′-d]dithiophene-5-yl-amine to propeller-shaped N,N,N-tri(naphtho[2,1-b]thieno[2,3-b:3′,2′-d]dithiophene-5-yl)-amine: syntheses and structures

Three unique propeller-shaped helicenyl amines compounds: N,N-diphenyl-N-naphtho[2,1-b]thieno[2,3-b:3′,2′-d]dithiophene-5-yl-amine (1), N-phenyl-N,N-di(naphtho[2,1-b]thieno[2,3-b:3′,2′-d]dithiophene-5-yl)amine (2), and N,N,N-tri(naphtho[2,1-b]thieno[2,3-b:3′,2′-d]dithiophene-5-yl)amine (3) were efficiently synthesized by Wittig reaction and oxidative photocyclization. The crystal structures of 1, 2 and molecular configuration optimization (DFT-B3LYP/6-31+G(d)) of 3 reveal that the steric hindrance from the moiety of trithia[5]helicene effectively forces the nitrogen atom and the three bonded carbon atoms to coplanar and the interplanar angles of the facing terminal thiophene ring and benzene ring becoming larger when the helical arm increased from 1 to 3. Electrochemical properties and UV–vis absorption behaviors of 1, 2, 3 were primarily determined by the moiety of trithia[5]helicene.

Microwave measurements of the spectra and molecular structure for phthalic anhydride

The microwave rotational spectrum for phthalic anhydride (PhA) has been measured in the 4–14GHz microwave region using a pulsed-beam Fourier transform (PBFT) Flygare–Balle type microwave spectrometer. Initially, the molecular structure was calculated using Gaussian 09 suite with mp2/6-311++G** basis and the calculations were used in predicting spectra for the measured isotopologues. The experimental rotational transition frequencies were measured and used to calculate the rotational and centrifugal distortion constants. The rotational constants for the normal isotopologue, four unique 13C substituted isotopologues and two 18O isotologues, were used in a least squares fit to determine nearly all structural parameters for this molecule. Since no substitutions were made at hydrogen sites, the calculated positions of the hydrogen atoms relative to the bonded carbon atoms were used in the structure determination. The rotational constants for the parent isotopologue were determined to be A=1801.7622(9)MHz, B=1191.71816(26)MHz, C=717.44614(28)MHz. Small values for the centrifugal distortion constants were obtained; DJ=0.0127kHz, DJK=0.0652kHz, and DK=−0.099kHz, indicating a fairly rigid structure. The structure of PhA is planar with a negative inertial defect of Δ=−0.154amuÅ2. Structural parameters from the mp2 and DFT calculations are in quite good agreement with measured parameters.