Showing papers on "Carbon nanotube published in 1997"
TL;DR: In this paper, the Young's modulus, strength, and toughness of nanostructures are evaluated using an atomic force microscopy (AFM) approach. And the results showed that the strength of the SiC NRs were substantially greater than those found previously for larger SiC structures, and they approach theoretical values.
Abstract: The Young's modulus, strength, and toughness of nanostructures are important to proposed applications ranging from nanocomposites to probe microscopy, yet there is little direct knowledge of these key mechanical properties. Atomic force microscopy was used to determine the mechanical properties of individual, structurally isolated silicon carbide (SiC) nanorods (NRs) and multiwall carbon nanotubes (MWNTs) that were pinned at one end to molybdenum disulfide surfaces. The bending force was measured versus displacement along the unpinned lengths. The MWNTs were about two times as stiff as the SiC NRs. Continued bending of the SiC NRs ultimately led to fracture, whereas the MWNTs exhibited an interesting elastic buckling process. The strengths of the SiC NRs were substantially greater than those found previously for larger SiC structures, and they approach theoretical values. Because of buckling, the ultimate strengths of the stiffer MWNTs were less than those of the SiC NRs, although the MWNTs represent a uniquely tough, energy-absorbing material.
4,627 citations
TL;DR: In this article, a gas can condense to high density inside narrow, single-walled nanotubes (SWNTs) under conditions that do not induce adsorption within a standard mesoporous activated carbon.
Abstract: Pores of molecular dimensions can adsorb large quantities of gases owing to the enhanced density of the adsorbed material inside the pores1, a consequence of the attractive potential of the pore walls. Pederson and Broughton have suggested2 that carbon nanotubes, which have diameters of typically a few nanometres, should be able to draw up liquids by capillarity, and this effect has been seen for low-surface-tension liquids in large-diameter, multi-walled nanotubes3. Here we show that a gas can condense to high density inside narrow, single-walled nanotubes (SWNTs). Temperature-programmed desorption spectrosocopy shows that hydrogen will condense inside SWNTs under conditions that do not induce adsorption within a standard mesoporous activated carbon. The very high hydrogen uptake in these materials suggests that they might be effective as a hydrogen-storage material for fuel-cell electric vehicles.
3,558 citations
TL;DR: In this article, electrical transport measurements on individual single-wall nanotubes have been performed to confirm the theoretical predictions of single-walled nanotube quantum wires, and they have been shown to act as genuine quantum wires.
Abstract: Carbon nanotubes have been regarded since their discovery1 as potential molecular quantum wires. In the case of multi-wall nanotubes, where many tubes are arranged in a coaxial fashion, the electrical properties of individual tubes have been shown to vary strongly from tube to tube2,3, and to be characterized by disorder and localization4. Single-wall nanotubes5,6 (SWNTs) have recently been obtained with high yields and structural uniformity7. Particular varieties of these highly symmetric structures have been predicted to be metallic, with electrical conduction occurring through only two electronic modes8–10. Because of the structural symmetry and stiffness of SWNTs, their molecular wavefunctions may extend over the entire tube. Here we report electrical transport measurements on individual single-wall nanotubes that confirm these theoretical predictions. We find that SWNTs indeed act as genuine quantum wires. Electrical conduction seems to occur through well separated, discrete electron states that are quantum-mechanically coherent over long distance, that is at least from contact to contact (140nm). Data in a magnetic field indicate shifting of these states due to the Zeeman effect.
2,678 citations
TL;DR: In this article, it was shown that the growth mechanism for SWNTs must be independent of the details of the technique used to make them, and that the ready availability of large amounts of SWNT can make them much more accessible for further study.
Abstract: Single-walled carbon nanotubes (SWNTs) offer the prospect of both new fundamental science and useful (nano)technological applications1. High yields (70–90%) of SWNTs close-packed in bundles can be produced by laser ablation of carbon targets2. The electric-arc technique used to generate fullerenes and multi-walled nanotubes is cheaper and easier to implement, but previously has led to only low yields of SWNTs3,4. Here we show that this technique can generate large quantities of SWNTs with similar characteristics to those obtained by laser ablation. This suggests that the (still unknown) growth mechanism for SWNTs must be independent of the details of the technique used to make them. The ready availability of large amounts of SWNTs, meanwhile, should make them much more accessible for further study.
2,568 citations
TL;DR: In this paper, the Raman spectra of single wall carbon nanotubes (SWNTs) were studied using laser excitation wavelengths in the range from 514.5 to 1320 nanometers.
Abstract: Single wall carbon nanotubes (SWNTs) that are found as close-packed arrays in crystalline ropes have been studied by using Raman scattering techniques with laser excitation wavelengths in the range from 514.5 to 1320 nanometers. Numerous Raman peaks were observed and identified with vibrational modes of armchair symmetry (n, n) SWNTs. The Raman spectra are in good agreement with lattice dynamics calculations based on C-C force constants used to fit the two-dimensional, experimental phonon dispersion of a single graphene sheet. Calculated intensities from a nonresonant, bond polarizability model optimized for sp2 carbon are also in qualitative agreement with the Raman data, although a resonant Raman scattering process is also taking place. This resonance results from the one-dimensional quantum confinement of the electrons in the nanotube.
1,882 citations
TL;DR: In this article, the elastic properties of carbon nanotubes and nanoropes were investigated using an empirical force-constant model and it was shown that the tensile Young's modulus and the torsion shear modulus of tubes are comparable to that of the diamond, while the bulk modulus is smaller.
Abstract: Elastic properties of carbon nanotubes and nanoropes are investigated using an empirical force-constant model. For single and multiwall nanotubes the elastic moduli are shown to be insensitive to structural details such as the helicity, the radius, and the number of walls. The tensile Young's modulus and the torsion shear modulus of tubes are comparable to that of the diamond, while the bulk modulus is smaller. Nanoropes composed of single wall nanotubes have the ideal elastic properties of high tensile stiffness and light weight.
1,431 citations
TL;DR: It is shown that multiwalled carbon nanotubes can be bent repeatedly through large angles using the tip of an atomic force microscope, without undergoing catastrophic failure.
Abstract: The curling of a graphitic sheet to form carbon nanotubes produces a class of materials that seem to have extraordinary electrical and mechanical properties. In particular, the high elastic modulus of the graphite sheets means that the nanotubes might be stiffer and stronger than any other known material, with beneficial consequences for their application in composite bulk materials and as individual elements of nanometre-scale devices and sensors. The mechanical properties are predicted to be sensitive to details of their structure and to the presence of defects, which means that measurements on individual nanotubes are essential to establish these properties. Here we show that multiwalled carbon nanotubes can be bent repeatedly through large angles using the tip of an atomic force microscope, without undergoing catastrophic failure. We observe a range of responses to this high-strain deformation, which together suggest that nanotubes are remarkably flexible and resilient.
1,430 citations
TL;DR: In this paper, a carbon nanotube sheet electrode with high power and long cycle life was used for a single cell device with 38 wt% H2SO4 as the electrolyte.
Abstract: Carbon nanotube sheet electrodes have been prepared from catalytically grown carbon nanotubes of high purity and narrow diameter distribution, centered around 80 A. Our study shows that the electrodes are free-standing mats of entangled nanotubes with an open porous structure almost impossible to obtain with activated carbon or carbon fiber. These properties are highly desirable for high power and long cycle life electrochemical capacitors. Specific capacitances of 102 and 49 F/g were measured at 1 and 100 Hz, respectively, on a single cell device with 38 wt % H2SO4 as the electrolyte. The same cell had a power density of >8000 W/kg.
1,410 citations
TL;DR: In this paper, the carbon nanotube acts as a template to confine the reaction, which results in the gallium nitride nanorods having a diameter similar to that of the original nanotubes.
Abstract: Gallium nitride nanorods were prepared through a carbon nanotube–confined reaction. Ga2O vapor was reacted with NH3 gas in the presence of carbon nanotubes to form wurtzite gallium nitride nanorods. The nanorods have a diameter of 4 to 50 nanometers and a length of up to 25 micrometers. It is proposed that the carbon nanotube acts as a template to confine the reaction, which results in the gallium nitride nanorods having a diameter similar to that of the original nanotubes. The results suggest that it might be possible to synthesize other nitride nanorods through similar carbon nanotube–confined reactions.
1,212 citations
TL;DR: In this paper, the electrical properties of individual bundles of single-walled carbon nanotubes have been measured and the results are interpreted in terms of singleelectron charging and resonant tunneling through the quantized energy levels of the nanotube composing the rope.
Abstract: The electrical properties of individual bundles, or “ropes,” of single-walled carbon nanotubes have been measured. Below about 10 kelvin, the low-bias conductance was suppressed for voltages less than a few millivolts. In addition, dramatic peaks were observed in the conductance as a function of a gate voltage that modulated the number of electrons in the rope. These results are interpreted in terms of single-electron charging and resonant tunneling through the quantized energy levels of the nanotubes composing the rope.
1,173 citations
01 Mar 1997
TL;DR: The electrical properties of individual bundles, or “ropes,” of single-walled carbon nanotubes have been measured, and dramatic peaks were observed in the conductance as a function of a gate voltage that modulated the number of electrons in the rope.
Abstract: The electrical properties of individual bundles, or “ropes,” of single-walled carbon nanotubes have been measured. Below about 10 kelvin, the low-bias conductance was suppressed for voltages less than a few millivolts. In addition, dramatic peaks were observed in the conductance as a function of a gate voltage that modulated the number of electrons in the rope. These results are interpreted in terms of single-electron charging and resonant tunneling through the quantized energy levels of the nanotubes composing the rope.
TL;DR: In this paper, a method for generating aligned carbon nanotubes by pyrolysis of 2-amino-4,6-dichloro-s-triazine over thin films of a cobalt catalyst patterned on a silica substrate by laser etching is described.
Abstract: Carbon nanotubes1, 2 might be usefully employed in nanometre-scale engineering and electronics. Electrical conductivity measurements on the bulk material3, 4, on individual multi-walled5, 6 and single-walled7 nanotubes and on bundles of single-walled nanotubes8, 9 have revealed that they may behave as metallic, insulating or semiconducting nanowires, depending on the method of production—which controls the degree of graphitization, the helicity and the diameter. Measurements of Young's modulus show10 that single nanotubes are stiffer than commercial carbon fibres. Methods commonly used to generate nanotubes—carbon-arc discharge techniques1, 2, 4, catalytic pyrolysis of hydrocarbons11, 12 and condensed-phase electrolysis13, 14—generally suffer from the drawbacks that polyhedral particles are also formed and that the dimensions of the nanotubes are highly variable. Here we describe a method for generating aligned carbon nanotubes by pyrolysis of 2-amino-4,6-dichloro-s-triazine over thin films of a cobalt catalyst patterned on a silica substrate by laser etching. The use of a patterned catalyst apparently encourages the formation of aligned nanotubes. The method offers control over length (up to about 50 mum) and fairly uniform diameters (30–50 nm), as well as producing nanotubes in high yield, uncontaminated by polyhedral particles.
TL;DR: In this article, the authors report the doping of bulk samples of carbon nanotubes by vapour-phase reactions with bromine and potassium, a prototypical electron acceptor and donor respectively.
Abstract: Single-walled carbon nanotubes (SWNTs), prepared by metal-catalysed laser ablation of graphite, form close-packed bundles or ‘ropes;1. These rope crystallites exhibit metallic behaviour above 50K (ref. 2), and individual tubes behave as molecular wires, exhibiting quantum effects at low temperatures3,4. They offer an all-carbon host lattice that, by analogy with graphite5 and solid C60 (ref. 6), might form intercalation compounds with interesting electronic properties, such as enhanced electrical conductivity and superconductivity. Multi-walled nanotube materials have been doped with alkali metals7 and FeCl3 (ref. 8). Here we report the doping of bulk samples of SWNTs by vapour-phase reactions with bromine and potassium—a prototypical electron acceptor and donor respectively. Doping decreases the resistivity at 300K by up to a factor of 30, and enlarges the region where the temperature coefficient of resistance is positive (the signature of metallic behaviour). These results suggest that doped SWNTs represent a new family of synthetic metals.
TL;DR: In this paper, the authors studied the nanotube behavior at high rate tensile strain (~ 1 MHz) using a realistic many-body interatomic potential and showed that the strength of the influence of helicity is very weak.
TL;DR: In this paper, the authors review the present state of understanding of the structure, growth and properties of nanometre-size tubes of carbon and present promising areas of future applications, for example as tiny field-emitting devices, micro-electrodes, nanoprobes and hydrogen storage material.
Abstract: We review the present state of understanding of the structure, growth and properties of nanometre-size tubes of carbon. Two different types of carbon nanotubes, namely single-shell nanotubes made of single layers of graphene cylinders and multishell nanotubes made of concentric cylinders of graphene layers have now become available. The subtle structure parameters such as helicity in the carbon network and the nanometre diameters give the nanotubes a rich variety in physical properties. Recent experimental progress on the measurements of properties using electron-energy loss spectroscopy, Raman spectroscopy, electron-spin resonance, electrical conductance, mechanical stiffness and theoretical predictions on electronic and mechanical properties of nanotubes will be discussed. In addition to synthesis techniques, methods to purify and make aligned arrays of nanotubes will be described. Different approaches for fabricating composite structures using nanotubes as moulds and templates and their future implications in materials science will be evaluated. Finally, promising areas of future applications, for example as tiny field-emitting devices, micro-electrodes, nanoprobes and hydrogen storage material will be outlined.
TL;DR: In this article, a low-energy theory for single-wall carbon nanotubes including Coulomb interactions is derived and analyzed, which describes two fermion chains without interchain hopping but coupled in a specific way by the interaction.
Abstract: The low-energy theory for single-wall carbon nanotubes including Coulomb interactions is derived and analyzed. It describes two fermion chains without interchain hopping but coupled in a specific way by the interaction. The strong-coupling properties are studied by bosonization, and consequences for experiments on single armchair nanotubes are discussed.
TL;DR: In this article, a purification procedure for single-wall carbon nanotubes (SWNTs) prepared by pulsed laser ablation is discussed, which separates coexisting carbon nanospheres (CNS), metal nanoparticles, polyaromatic carbons, and fullerenes from the SWNT fraction.
Abstract: A purification procedure for single-wall carbon nanotubes (SWNTs) prepared by pulsed laser ablation is discussed, which separates coexisting carbon nanospheres (CNS), metal nanoparticles, polyaromatic carbons, and fullerenes from the SWNT fraction. The process involves the suspension of CNS, metal nanoparticles, and SWNTs in an aqueous solution using a cationic surfactant and the subsequent trapping of SWNTs on a membrane filter. No oxidative treatment is required. Scanning/transmission electron microscopy and Raman scattering were used to evaluate the purification process and the vibrational features of SWNTs. Purity of SWNTs at the final stage sample is in excess of 90% by weight, and no evidence of impurity carbon phases was revealed in the Raman spectrum of the SWNT fraction.
TL;DR: In this article, the elastic behavior of open-ended, free-standing, single wall, carbon nanotubes is investigated by a Tersoff-Brenner potential, and typical failure modes as well as stress-strain curves for a number of tube radii are shown.
TL;DR: The application of the carbon nanotube as an electrode material is demonstrated in this article, where the authors show that the carbon nano-tubes give reproducible, well-behaved voltammetric responses.
TL;DR: In this article, the resonance behavior and higher-order Raman bands up to fourth order have been observed and compared with those of carbon nanotubes produced by arc discharge and highly oriented pyrolytic graphite.
Abstract: Raman characterization of aligned carbon nanotubes of average diameter 10–15 nm, produced by chemical vapor deposition on a mesoporous substrate, has been carried out. The resonance behavior and higher-order Raman bands up to fourth order have been observed and compared with those of carbon nanotubes produced by arc discharge and highly oriented pyrolytic graphite, as well as pyrolytic graphite. The phonon properties have been analyzed with the help of high-resolution transmission electron microscope studies.
TL;DR: In this paper, the NiO and MgO components in this catalyst precursor formed, due to their highly mutual solubility, a NixMg1 − xO solid solution, and the high dispersion of Ni-species in this solid solution and the effect of valence-stabilization by the mgO crystal field would be in favor of inhibiting deep reduction of Ni2+ to Ni0 and aggregation of the Ni0 to form large metal particles at the surface of catalyst.
TL;DR: In this article, a field electron emitter from hollow, open-ended carbon nanotubes has been made, which can emit electrons by tunnelling effects in electric fields, with their small size, small energy spread, high current density and no requirement for heat.
Abstract: Electron guns are indispensable devices that are widely used in household and industrial appliances. Field electron-emitting sources (which emit electrons by tunnelling effects in electric fields), with their small size, small energy spread, high current density and no requirement for heat, have distinct advantages over thermionic emitters. We have made a field electron emitter from hollow, open-ended carbon nanotubes.
TL;DR: In this article, it was shown that pyrolysis of metallocenes such as ferrocene, cobaltocene and nickelocene yields carbon nanotubes and metal-filled onion-like structures.
TL;DR: In this paper, a non-destructive method for the separation and size selection of carbon nanotubes and nanoparticles produced by arc discharge is presented, which can achieve yields as high as 90 % in weight without any damage to tube tips or tube walls following the separation process.
Abstract: We report on a non-destructive method for the separation and size-selection of carbon nanotubes and nanoparticles produced by arc discharge. A liquid-phase separation of nanotubes and nanoparticles was performed by filtering a kinetically stable colloidal dispersion consisting of the carbon material in a water/surfactant solution, allowing thus to extract the nanotubes from the suspension while leaving the nanoparticles in the filtrate. Further purification was accomplished by size-selection through controlled floculation of the dispersion. Final separation yields as high as 90 % in weight were obtained without any damage to tube tips or tube walls following the separation process.
TL;DR: In this article, topology related changes in the local density of states near the ends of closed carbon nanotubes are investigated using spatially resolved scanning tunneling spectroscopy and tight binding calculations.
Abstract: Topology related changes in the local density of states near the ends of closed carbon nanotubes are investigated using spatially resolved scanning tunneling spectroscopy and tight binding calculations. Sharp resonant valence band states are observed in the experiment at the tube ends, dominating the valence band edge and filling the band gap. Calculations show that the strength and position of these states with respect to the Fermi level depend sensitively on the relative positions of pentagons and their degree of confinement at the tube ends.
TL;DR: In this article, the authors proposed a catalytic growth mechanism of single-wall carbon nanotubes based on density functional total energy calculations, and showed that the nanotube with an "armchair" edge was energetically favored over the zigzag edge.
Abstract: We propose a catalytic growth mechanism of single-wall carbon nanotubes based on density functional total energy calculations Our results indicate nanotubes with an “armchair” edge to be energetically favored over “zigzag” nanotubes We also suggest that highly mobile Ni catalyst atoms adsorb at the growing edge of the nanotube, where they catalyze the continuing assembly of hexagons from carbon feedstock diffusing along the nanotube wall In a concerted exchange mechanism, Ni atoms anneal carbon pentagons that would initiate a dome closure of the nanotube [S0031-9007(97)02791-9]
TL;DR: In this article, the T junctions of single-walled carbon nanotubes forming one of the smallest prototypes of microscopic metal-semiconductor-metal contacts are proposed, which are found to be local minima of the total energy on relaxation with a generalized tight-binding molecular dynamics scheme.
Abstract: Stable ``T junctions'' of single-walled carbon nanotubes forming one of the smallest prototypes of microscopic metal-semiconductor-metal contacts are proposed. The structures have been found to be local minima of the total energy on relaxation with a generalized tight-binding molecular dynamics scheme. These quasi-2D junctions could be the building blocks of nanoscale tunnel junctions in a 2D network of nanoelectronic devices.
TL;DR: In this paper, hollow nanotubes of SiO2, Al2O3, V2O5, and MoO3 have been prepared using carbon as templates using tetraethylorthosilicate, aluminum isopropoxide, or vanadium pentoxide gel.
Abstract: Hollow nanotubes of SiO2, Al2O3, V2O5, and MoO3 have been prepared using carbon nanotubes as templates. The procedure involves coating the carbon nanotubes with tetraethylorthosilicate, aluminum isopropoxide, or vanadium pentoxide gel, followed by calcination and heating at higher temperatures in air to oxidize the carbon. SiO2 nanotubes containing transition metal ions have been prepared by this procedure since such materials may be of use in catalysis.
TL;DR: De Heer et al. as mentioned in this paper presented an effective medium theory in order to analyze the reported optical properties of aligned carbon nanotube films, based on photonic band structure calculations and allowing treatment of complex media consisting of particles that interact strongly.
Abstract: We present an effective medium theory in order to analyze the reported optical properties of aligned carbon nanotube films [W. A. de Heer et al., Science 268, 845 (1995)]. This methodology is based on photonic band structure calculations and allows treatment of complex media consisting of particles that interact strongly. We also develop a simple Maxwell-Garnett type approach for studying this system. In comparing the results of both mean field theories, we demonstrate that the inclusion of the full electromagnetic coupling between the nanotubes, as our numerical scheme does, is necessary for a complete explanation of the experimental data.
TL;DR: Bond rotation defects close the gap in large-gap nanotubes, open the gap of small-gap Nanotubes and increase the density of states in metallic nanite as discussed by the authors.
Abstract: Bond rotation defects close the gap in large-gap nanotubes, open the gap in small-gap nanotubes, and increase the density of states in metallic nanotubes. Not only are these defects likely to be present in as-grown nanotubes, but they could be introduced locally into intact nanotubes, thereby opening a new road towards device applications. {copyright} {ital 1997} {ital The American Physical Society}