Showing papers on "Graphene published in 2000"
TL;DR: The first all-electron ab initio study of Young's modulus and Poisson ratio for a number of closed single-walled nanotubes is presented in this paper.
502 citations
TL;DR: The data show direct evidence of one-dimensional quantized phonon subbands above 4 kelvin, in excellent agreement with model calculations of individual nanotubes and differ markedly from the specific heat of two-dimensional graphene or three-dimensional graphite.
Abstract: The electronic spectra of carbon nanotubes and other nanoscale systems are quantized because of their small radii. Similar quantization in the phonon spectra has been difficult to observe because of the far smaller energy scale. We probed this regime by measuring the temperature-dependent specific heat of purified single-wall nanotubes. The data show direct evidence of one-dimensional quantized phonon subbands. Above 4 kelvin, they are in excellent agreement with model calculations of individual nanotubes and differ markedly from the specific heat of two-dimensional graphene or three-dimensional graphite. Detailed modeling yields an energy of 4.3 millielectron volts for the lowest quantized phonon subband and a tube-tube (or “lattice”) Debye energy of 1.1 millielectron volts, implying a small intertube coupling in bundles.
465 citations
TL;DR: Density of states calculations of all structures revealed an intrinsic metallic behavior, independent of orientation, tube diameter, and chirality, and it is shown that their mechanical properties are similar to those of graphene.
Abstract: We propose a new family of layered sp(2)-like carbon crystals, incorporating five-, six-, and seven-membered rings in 2D Bravais lattices. These periodic sheets can be rolled so as to generate nanotubes of different diameter and chirality. We demonstrate that these sheets and tubes are metastable and more favorable than C-60, and it is also shown that their mechanical properties are similar to those of graphene. Density of states calculations of all structures revealed an intrinsic metallic behavior, independent of orientation, tube diameter, and chirality.
456 citations
TL;DR: In this paper, the authors measured the evolution of CO2 and CO(g) on heating to 1273 K and found that ∼5% of the carbon atoms in the c-SWNT samples were located at defective sites, capable of facile oxidation by O3.
370 citations
TL;DR: In this paper, the synthesis of chains of C60 molecules inside single-wall carbon nanotubes (SWNTs) is described, and the resulting Van der Waals interacting chains, called ''bucky-peapods'' are then formed into pairs of nested graphene cylinders.
349 citations
TL;DR: In this paper, electrochemical doping has been used to study a new carbon guest-host system: Li/carbon nanotubes, which can be distinguished according to their structural properties: multiwall (MWNT) and single wall (SWNT).
Abstract: Electrochemistry has proven to be very useful for the study of guest-host systems, particularly, carbon intercalation compounds. Not only does electrochemistry provide essential information about the thermodynamics and kinetics of these systems, but it also offers accurate control of guest stoichiometry which is difficult to achieve by other doping methods. Therefore, electrochemical doping has been used extensively to study the properties of carbon guest-host systems. In situ X-ray diffraction and electrochemical doping were used to study the phase diagram of Li xC6 graphite, 1 phase transitions in Li-doped polyacetylene 2 and the structure of Li-doped solid C 60. 3 In situ resistivity measurements were used to study the electronic transport properties of K- and Na-doped polyacetylene. 4,5 In this work, electrochemistry was used to study a new carbon guest-host system: Li/carbon nanotubes. Two types of carbon nanotubes can be distinguished according to their structural properties: multiwall (MWNT) and single wall (SWNT). 6 MWNT consist of graphitic sheets rolled into closed concentric cylinders, with a structure similar to that of Russian dolls. The concentric tubes are separated by Van der Waals gaps of ,3.4 A, a typical interlayer spacing in turbostratically disordered graphite. External diameters can be as large as 50 nm, and lengths are of micrometer scale. SWNT can be envisioned as a single graphene sheet rolled into a cylinder, with diameters in the range 1-2 nm and lengths of several micrometer. SWNT of nearly uniform diameters self-organize into long crystalline “ropes” in which parallel nanotubes are bound by Van der Waals forces. 7 The diameter of a rope is typically 10-50 nm corresponding to 30-600 tubes per rope. Ropes containing as few as 2-3 tubes or as many as several thousand are occasionally found. Figure 1 presents a high resolution transmission electron microscope (HRTEM) image of purified and annealed SWNT, in which several entangled ropes with different diameters can be observed. The parallel fringes within each rope are due to the constructive scattering from the parallel planes of SWNT. The fact that the fringe spacings differ among ropes does not arise from a wide distribution in nanotube diameters, but rather from the different orientation of each rope zone axis with respect to the electron beam. Figure 2 shows an X-ray profile from purified and annealed SWNT. The well
335 citations
TL;DR: In this paper, the authors show indisputable evidence that the filling of the nano-pores accounts for all the sodium and lithium inserted into these carbons at a chemical potential near that of metallic sodium (or lithium).
Abstract: An electrochemical cell with beryllium X‐ray windows has been designed and used for in situ small‐angle X‐ray‐scattering studies of operating electrodes for the first time. This cell is ideally suited to the study of the filling of nanoscopic pores in solids by electrochemically transported atoms. The mechanism of electrochemical lithium and sodium insertion in nanoporous carbonaceous materials has been the subject of some recent controversy, which is resolved by the studies reported here. We show indisputable evidence that the filling of the pores accounts for all the sodium (and lithium) inserted into these carbons at a chemical potential near that of metallic sodium (or lithium). At lower chemical potential (higher cell voltage), sodium (or lithium) is inserted between graphene layers in an intercalation mechanism. © 2000 The Electrochemical Society. All rights reserved.
265 citations
TL;DR: In this paper, the density functional theory has been used to study the adsorption of molecular H2 on a graphene layer and the most stable configuration of H2 is physisorbed above the center of a hexagon.
Abstract: Density functional theory has been used to study the adsorption of molecular H2 on a graphene layer. Different adsorption sites on top of atoms, bonds and the center of carbon hexagons have been considered and compared. We conclude that the most stable configuration of H2 is physisorbed above the center of a hexagon. Barriers for classical diffusion are, however, very small.
253 citations
TL;DR: In this paper, a growth mechanism for carbon nanotubes is suggested based on Raman studies, and the growth mechanism is based on a possible growth mechanism that can be used for the synthesis of carbon nano-tubes.
Abstract: Arrays of aligned nanotubes of large diameter (100–250 nm) are synthesized by pyrolyzing a jet (spray) solution of Fe(C5H5)2 and C6H6 in an Ar atmosphere at relatively low temperatures (850 °C). The tubular structures consist of highly crystalline nested graphene cylinders (<200 concentric tubes) with tips that are usually open. Raman studies confirm the high degree of perfection of these “thick” structures. Tube diameter, degree of alignment, and crystallinity can be controlled by varying the Ar flow rate and the Fe:C ratio within the precursor solution. Based on these observations a possible growth mechanism is suggested. This low cost route for the synthesis of carbon nanotubes is advantageous due to the absence of H2 as a carrier gas and the low pyrolytic temperature.
181 citations
TL;DR: The results agree with the classical theory of elasticity in the case of straight nanotubes and the Young modulus of coiled multiwalled nanotube remains comparable to the very high Youngmodulus of hexagonal graphene sheets.
Abstract: Coiled carbon nanotubes were produced catalytically by thermal decomposition of hydrocarbon gas. After deposition on a silicon substrate, the three-dimensional structure of the helix-shaped multiwalled nanotubes can be visualized with atomic force microscopy. Helical structures of both chiralities are present in the nanotube deposits. For larger coil diameters ( .170 nm), force modulation microscopy allows one to probe the local elasticity along the length of the coil. Our results agree with the classical theory of elasticity. Similar to the case of straight nanotubes, the Young modulus of coiled multiwalled nanotubes remains comparable to the very high Young modulus of hexagonal graphene sheets. ations in the elastic response of the coils along their length. Our results nicely agree with the classical theory of elas- ticity. From our FMM measurements we infer a Young modulus around 0.7 TPa for the coiled MWNTs. This re- sult is consistent with the reported high values of Young's modulus for straight carbon nanotubes which has been measured via resonant motion (8,9) of free standing tubes as well as via AFM induced deformations of nanotubes de- posited on a flat surface (10) or on substrates containing micropores (11). The nanotube material containing the helical MWNTs is produced by catalytic decomposition of acetylene, carried out at 700 ± C in a flow reactor at atmospheric pressure (12). The purified carbon nanotube material is sonicated at low power in isopropanol and is deposited onto a piece of an oxidized silicon wafer with gold markers fabricated by combining electron beam lithography and lift-off techniques. The nanotube deposits are first imaged with a scanning electron microscope (SEM: Philips, XL-30 FEG), allowing one to record the position of the coiled structures. Next, the AFM imaging and the FMM measurements are performed in air with a commercial system ( Park Scientific Instruments, M5) using silicon cantilevers with a tip apex radius of curvature of about 10 nm. The elastic response of the coiled nanotubes can be probed locally with the FMM technique (7) which is illustrated in Fig. 1(a). The Si cantilever is gently tapping the sample surface at the cantilever resonance frequency fres 98 kHz with an amplitude ranging between 0.2 and 5 nm. Additionally, the vertical position of the sample is periodically modulated at a much smaller frequency fmod in the range 8 11 kHz with a modulation amplitude between 1 and 2 nm. Harmonic detection at the frequency fmod of the periodically varying interaction between tip and coiled nanotube enables one to locally probe its elasticity.
151 citations
TL;DR: In this paper, single-wall carbon nanohorns (SWNHs) are synthesized by a CO 2 laser vaporization of a pure carbon target in an Ar gas.
TL;DR: By changing the angular alignment of the atomic lattices, it is found that contact resistance varied by more than an order of magnitude in a controlled and reproducible fashion, indicating that momentum conservation, in addition to energy conservation, can dictate the junction resistance in graphene systems such as carbon nanotube junctions and devices.
Abstract: The transfer of electrons from one material to another is usually described in terms of energy conservation, with no attention being paid to momentum conservation. Here we present results on the junction resistance between a carbon nanotube and a graphite substrate and show that details of momentum conservation also can change the contact resistance. By changing the angular alignment of the atomic lattices, we found that contact resistance varied by more than an order of magnitude in a controlled and reproducible fashion, indicating that momentum conservation, in addition to energy conservation, can dictate the junction resistance in graphene systems such as carbon nanotube junctions and devices.
TL;DR: It is shown that, while the carbon tubes with diameters smaller than 0.4 nm are energetically less favorable than a graphene sheet, some of them are indeed mechanically stable at temperatures as high as 1100 degrees C.
Abstract: Experimental evidence has been found for the existence of small single wall carbon nanotubes with diameters of 0.5 and 0.33 nm by high resolution transmission electron microscopy, and their mechanical stability was investigated using tight-binding molecular dynamics simulations. It is shown that, while the carbon tubes with diameters smaller than 0.4 nm are energetically less favorable than a graphene sheet, some of them are indeed mechanically stable at temperatures as high as 1100 degrees C. The 0.33 nm carbon tube observed is likely a (4, 0) tube and is indeed part of a compound nanotube system that forms perhaps the smallest metal-semiconductor-metal tubular junction yet synthesized.
TL;DR: In this article, a graphite highly oriented pyrolytic graphite (HOPG) substrate was manipulated with atomic force microscopy (AFM) to find certain discrete orientations in which the lateral force of manipulation dramatically increases as we rotate the CNT in the plane of the HOPG surface with the AFM tip.
Abstract: We report on experiments in which multiwall carbon nanotubes (CNT's) are manipulated with atomic force microscopy (AFM) on a graphite highly oriented pyrolytic graphite (HOPG) substrate. We find certain discrete orientations in which the lateral force of manipulation dramatically increases as we rotate the CNT in the plane of the HOPG surface with the AFM tip. The threefold symmetry of these discrete orientations indicates commensurate contact of the hexagonal graphene surfaces of the HOPG and CNT. As the CNT moves into commensurate contact, we observe the motion change from sliding/rotating in-plane to stick-roll motion.
TL;DR: The dynamic behavior of nickel atoms in graphitic carbon onions, observed by in situ atomic-resolution electron microscopy, shows the formation of stable new C- Ni phases, suggesting a possible phase transformation in C-Ni from a graphitelike to a diamondlike structure.
Abstract: The dynamic behavior of nickel atoms in graphitic carbon onions, observed by in situ atomic-resolution electron microscopy, shows the formation of stable new C-Ni phases. Nickel is observed to take substitutional in-plane positions in graphene layers, forming a planar graphitelike C-Ni lattice. Evidence is furthermore seen for the formation of a cubic C-NI phase, suggesting a possible phase transformation in C-Ni from a graphitelike to a diamondlike structure. The stability of the planar phases is shown by first-principles calculations which also indicate that the C-NI planes are metallic.
TL;DR: In this article, the authors review recent experimental results relating to the interaction of two chemical species in the interlayer spacing of graphite and report the successful anionic polymerization of unsaturated hydrocarbons within the graphite interlayer.
TL;DR: In this article, the electron-phonon interaction in low-dimensional tight-binding systems is discussed, and a sheet of graphite, which is two-dimensional, and an armchair single-wall carbon nanotube (SWNT), which is quasi-one dimensional, are taken as examples.
Abstract: The electron-phonon interaction in low-dimensional tight-binding systems is discussed. A sheet of graphite, which is two-dimensional, and an armchair single-wall carbon nanotube (SWNT), which is quasi-one-dimensional, are taken as examples. For the modulated hopping the matrix elements for both systems are derived in the context of a two parameter model for the phonon vibrational spectrum. It is found that they (for both structures) display a deformation type of potential, and are reduced by a factor of $(1\ensuremath{-}R),$ where R depends on the phonon parameters. It is also shown that the ordinary electron-phonon coupling displays a deformation type of approximation for both systems. Next, a different type of interaction is considered---the phonon modulated electron-electron interaction. It gives two contributions---random phase approximation with one phonon line and exchange interaction with one phonon line. We find that for the two-dimensional (2D) graphene and for the quasi-1D (10,10) SWNT, the modulated hopping and exchange coupling govern the electron transport at room temperatures.
TL;DR: In this paper, a double-atomic-layer system of monolayer graphene/monolayer h-BN has been prepared in an epitaxial manner on Ni(111) surface.
TL;DR: In this paper, an electrochemical intercalation of lithium into carbon electrodes containing multiwall carbon nanotubes produced by electric arc technique was carried out in button cells in different electrolytes.
TL;DR: In this article, microencapsulating graphite with nanosized Ni-composite particles was proposed to suppress the solvated lithium intercalation in graphite.
Abstract: A novel approach for suppressing the solvated lithium intercalation in graphite was developed by microencapsulating graphite with nanosized Ni-composite particles. The Ni-composite graphite showed great improvement in charge-discharge performance, coulomb efficiency, and cycling behavior when used as the negative electrode in a Li-ion cell with propylene carbonate (PC)-based electrolyte. For example, a 10 wt % Ni-composite coating increased the initial charge-discharge coulomb efficiency of SFG75 graphite (75 μm, Timcal America) from 59 to 84% and the reversible capacity by 30-40 mAh/g. The Ni-composite coating consisted of nanosized particles distributed over the surface of the graphite particle, which effectively blocked some of the edge surfaces exposed to the electrolyte. This minimized solvated lithium intercalation at these edge sites, which subsequently minimized the PC reduction within the graphite and the exfoliation of the graphene layers, and also gas evolution. Corresponding improvements in both the charge-discharge performance and safety of the negative electrode in a rechargeable Li-ion cell resulted.
TL;DR: In this paper, the amount of nitrogen atoms bonded to three carbon atoms in graphene layers increased with increasing deposition temperature, while the surface areas of C x N-coated activated carbons decreased with increasing depth and duration.
TL;DR: In this article, a coherent superposition of one-and two-photon (2v) electronic excitations is studied for graphene sheets and for carbon nanotubes using a long-wavelength theory for the low-energy electronic states.
Abstract: Coherent one-photon (2v) and two-photon (v) electronic excitations are studied for graphene sheets and for carbon nanotubes using a long-wavelength theory for the low-energy electronic states. For graphene sheets we find that a coherent superposition of these excitations produces a polar asymmetry in the momentum space distribution of the excited carriers with an angular dependence that depends on the relative polarization and phases of the incident fields. For semiconducting nanotubes we find a similar effect which depends on the square of the semiconducting gap, and we calculate its frequency dependence. We find that the third-order nonlinearity, which controls the direction of the photocurrent is robust for semiconducting tubes and vanishes in the continuum theory for conducting tubes. We calculate corrections to these results arising from higherorder crystal-field effects on the band structure and briefly discuss some applications of the theory.
TL;DR: In this article, three main types of tubes were observed and are characterised as follows: (1) multilayered surface modulated micro-and nanotubes (SMMTs and SMNTs, respectively) with fluctuating diameters caused by periodically interrupted movement of catalytic particles during tube formation.
TL;DR: In this paper, the solid product of CO disproportionation over well-calibrated Co/Al2O3 catalysts was studied by HRTEM, Raman spectroscopy and X-ray diffraction.
TL;DR: In this article, Nitrogen-containing polymeric carbon as anode material for the lithium ion secondary battery is prepared from polyacrylonitrile (PAN) and melamine-formaldehyde resin (MF) at 600 and 800°C.
Abstract: Nitrogen-containing polymeric carbon as anode materials for the lithium ion secondary battery is prepared from polyacrylonitrile (PAN) and melamine–formaldehyde resin (MF) at 600 and 800°C. Its physicochemical properties were investigated through elemental analysis, X-ray powder diffraction, X-ray photoelectron spectroscopy, and measurement of specific surface area. Results show that this kind of carbon is amorphous. Nitrogen atoms exist in the prepared polymeric carbon mainly as two states, that is, graphene nitrogen and conjugated nitrogen, and favor the enhancement of reversible lithium capacity. All the prepared polymeric carbon has a reversible capacity higher than that of the theoretic value of graphite, 372 mAh/g, and the highest reversible capacity can be up to 536 mAh/g. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1735–1741, 2000
TL;DR: In this article, a mechanism for Li-ion storage based on its structural characteristics was proposed. But this mechanism is not applicable to the case of polycyclic aromatic hydrocarbons (PAHs), which have a small specific surface area and small micropores.
Abstract: Polycyclic aromatic hydrocarbons (PAHs) with a discharge capacity of 1017 mAh/g and efficiency of 81.5% were developed for rechargeable Li‐ion batteries using isotropic pitch as the raw material. The PAHs have a very small specific surface area and small micropores. X‐ray diffraction results show that PAHs consist of a few graphene sheets stacked in a parallel fashion and separated by a small distance . The results of solid‐state magnetic resonance suggest that the graphene sheets have a coronene‐like structure, namely, they show a disk‐like shape. Based on its structural characteristics, we proposed a mechanism for Li‐ion storage. © 2000 The Electrochemical Society. All rights reserved.
TL;DR: The structure of the carbon is rather disordered, consisting of curved and faceted graphene sheets with little large scale graphitization, and resembles that of a microporous carbon following high temperature heat treatment as mentioned in this paper.
TL;DR: In this article, the authors interpreted the data as tightly wound, single-wall, coiled carbon nanotubes with an interspire distance of 0.34 nm, which is the same distance as the distance between graphene layers in graphite or the distance of single-walled carbon-nanotubes in ropes.
Abstract: Scanning tunneling microscopy (STM) images of carbon nanotubes grown by the catalytic cracking of hydrocarbons, which exhibit a well-defined axial periodicity in the 1 nm range, are reported. The data are interpreted as tightly wound, single-wall, coiled carbon nanotubes with an interspire distance of 0.34 nm as the distance between graphene layers in graphite or the distance of single-wall carbon nanotubes in ropes.
TL;DR: In this paper, the authors showed that there is no definite stage formation in the fluorinated compounds, rather fluorine is trapped in the defects or diffused in to graphene layers and form covalent C-F bond at the surface of the fibers.
TL;DR: In this paper, the putative Peierls transition in a (5,5) metallic nanotube was examined and it was shown that conduction electrons at the Fermi level do not couple to the longitudinal acoustic phonon but rather to a folded-in graphene zone edge phonon having the proper K-ekul\'e modulation symmetry.
Abstract: We reexamine the putative Peierls transition in a (5,5) metallic nanotube. We show that the conduction electrons at the Fermi level do not couple to the longitudinal acoustic phonon but rather to a folded-in graphene zone edge phonon having the proper K\'ekul\'e modulation symmetry. The calculation for the mean-field transition temperature gives 15 K, a value comparable to previous estimates. We discuss the significance of this transition temperature.