Showing papers on "Carbon nanotube published in 1999"
TL;DR: The synthesis of massive arrays of monodispersed carbon nanotubes that are self-oriented on patterned porous silicon and plain silicon substrates is reported and the mechanisms of nanotube growth and self-orientation are elucidated.
Abstract: The synthesis of massive arrays of monodispersed carbon nanotubes that are self-oriented on patterned porous silicon and plain silicon substrates is reported. The approach involves chemical vapor deposition, catalytic particle size control by substrate design, nanotube positioning by patterning, and nanotube self-assembly for orientation. The mechanisms of nanotube growth and self-orientation are elucidated. The well-ordered nanotubes can be used as electron field emission arrays. Scaling up of the synthesis process should be entirely compatible with the existing semiconductor processes, and should allow the development of nanotube devices integrated into silicon technology.
3,093 citations
TL;DR: In this article, four kinds of single-wall carbon nanotubes (SWNTs) with different diameter distribution have been synthesized and optical absorption spectra have been measured.
2,299 citations
TL;DR: The methods developed here have been applied to a nanobalance for nanoscopic particles and also to a Kelvin probe based on nanotubes, which indicates a crossover from a uniform elastic mode to an elastic mode that involves wavelike distortions in the nanotube.
Abstract: Static and dynamic mechanical deflections were electrically induced in cantilevered, multiwalled carbon nanotubes in a transmission electron microscope. The nanotubes were resonantly excited at the fundamental frequency and higher harmonics as revealed by their deflected contours, which correspond closely to those determined for cantilevered elastic beams. The elastic bending modulus as a function of diameter was found to decrease sharply (from about 1 to 0.1 terapascals) with increasing diameter (from 8 to 40 nanometers), which indicates a crossover from a uniform elastic mode to an elastic mode that involves wavelike distortions in the nanotube. The quality factors of the resonances are on the order of 500. The methods developed here have been applied to a nanobalance for nanoscopic particles and also to a Kelvin probe based on nanotubes.
1,834 citations
TL;DR: In this paper, single-walled carbon nanotubes (SWNTs) have been produced in a gas-phase catalytic process, where catalysts for SWNT growth form in situ by thermal decomposition of iron pentacarbonyl in a heated flow of carbon monoxide at pressures of 1-10 atm and temperatures of 800-1200°C.
1,812 citations
TL;DR: Masses of single-walled carbon nanotubes, synthesized by a semicontinuous hydrogen arc discharge method, were employed for hydrogen adsorption experiments in their as-prepared and pretreated states and show promise as an effective hydrogen storage material.
Abstract: Masses of single-walled carbon nanotubes (SWNTs) with a large mean diameter of about 1.85 nanometers, synthesized by a semicontinuous hydrogen arc discharge method, were employed for hydrogen adsorption experiments in their as-prepared and pretreated states. A hydrogen storage capacity of 4.2 weight percent, or a hydrogen to carbon atom ratio of 0.52, was achieved reproducibly at room temperature under a modestly high pressure (about 10 megapascal) for a SWNT sample of about 500 milligram weight that was soaked in hydrochloric acid and then heat-treated in vacuum. Moreover, 78.3 percent of the adsorbed hydrogen (3.3 weight percent) could be released under ambient pressure at room temperature, while the release of the residual stored hydrogen (0.9 weight percent) required some heating of the sample. Because the SWNTs can be easily produced and show reproducible and modestly high hydrogen uptake at room temperature, they show promise as an effective hydrogen storage material.
1,745 citations
TL;DR: In this paper, electrical transport measurements on single-wall carbon nanotubes (SWNTs) with intramolecular junctions are reported, showing that a metal-semiconductor junction behaves like a rectifying diode with nonlinear transport characteristics that are strongly asymmetric with respect to bias polarity.
Abstract: The ultimate device miniaturization would be to use individual molecules as functional devices. Single-wall carbon nanotubes (SWNTs) are promising candidates for achieving this: depending on their diameter and chirality, they are either one-dimensional metals or semiconductors1,2. Single-electron transistors employing metallic nanotubes3,4 and field-effect transistors employing semiconducting nanotubes5 have been demonstrated. Intramolecular devices have also been proposed which should display a range of other device functions6,7,8,9,10,11. For example, by introducing a pentagon and a heptagon into the hexagonal carbon lattice, two tube segments with different atomic and electronic structures can be seamlessly fused together to create intramolecular metal–metal, metal–semiconductor, or semiconductor–semiconductor junctions. Here we report electrical transport measurements on SWNTs with intramolecular junctions. We find that a metal–semiconductor junction behaves like a rectifying diode with nonlinear transport characteristics that are strongly asymmetric with respect to bias polarity. In the case of a metal–metal junction, the conductance appears to be strongly suppressed and it displays a power-law dependence on temperatures and applied voltage, consistent with tunnelling between the ends of two Luttinger liquids. Our results emphasize the need to consider screening and electron interactions when designing and modelling molecular devices. Realization of carbon-based molecular electronics will require future efforts in the controlled production of these intramolecular nanotube junctions.
1,485 citations
TL;DR: In this article, the authors presented a method to construct an LNNME-ARTICLE-1999-004, which is used in PhysRevLett.82.944.
Abstract: Reference LNNME-ARTICLE-1999-004doi:10.1103/PhysRevLett.82.944View record in Web of Science Record created on 2007-04-23, modified on 2016-08-08
1,447 citations
TL;DR: In this paper, untreated catalytically-grown carbon nanotubes were dispersed in an epoxy matrix and the electrical properties of the composite were measured in order to relate the filler volume fraction to the electrical conductivity.
1,429 citations
TL;DR: In this article, a fully sealed field-emission display 4.5 in. in size has been fabricated using single-wall carbon nanotube (CNT)-organic binders.
Abstract: A fully sealed field-emission display 4.5 in. in size has been fabricated using single-wall carbon nanotube (CNT)-organic binders. The fabricated displays were fully scalable at low temperature, below 415 °C, and CNTs were vertically aligned using paste squeeze and surface rubbing techniques. The turn-on fields of 1 V/μm and field emission current of 1.5 mA at 3 V/μm (J=90 μA/cm2) were observed. Brightness of 1800 cd/m2 at 3.7 V/μm was observed on the entire area of a 4.5 in. panel from the green phosphor-indium–tin–oxide glass. The fluctuation of the current was found to be about 7% over a 4.5 in. cathode area.
1,398 citations
TL;DR: A variety of outstanding experimental results on the elucidation of the elastic properties of carbon nanotubes are fast appearing as discussed by the authors, which are based mainly on the techniques of high-resolution transmission electron microscopy and atomic force microscopy (AFM) to determine the Young's moduli of single-wall nanotube bundles and multi-walled nanotubels.
Abstract: A variety of outstanding experimental results on the elucidation of the elastic properties of carbon nanotubes are fast appearing. These are based mainly on the techniques of high-resolution transmission electron microscopy (HRTEM) and atomic force microscopy (AFM) to determine the Young’s moduli of single-wall nanotube bundles and multi-walled nanotubes, prepared by a number of methods. These results are confirming the theoretical predictions that carbon nanotubes have high strength plus extraordinary flexibility and resilience. As well as summarising the most notable achievements of theory and experiment in the last few years, this paper explains the properties of nanotubes in the wider context of materials science and highlights the contribution of our research group in this rapidly expanding field. A deeper understanding of the relationship between the structural order of the nanotubes and their mechanical properties will be necessary for the development of carbon-nanotube-based composites. Our research to date illustrates a qualitative relationship between the Young’s modulus of a nanotube and the amount of disorder in the atomic structure of the walls. Other exciting results indicate that composites will benefit from the exceptional mechanical properties of carbon nanotubes, but that the major outstanding problem of load transfer efficiency must be overcome before suitable engineering materials can be produced.
1,362 citations
Abstract: Carbon nanotubes are cylindrical molecules with a diameter of as little as 1 nanometer and a length up to many micrometers They consist of only carbon atoms, and can essentially be thought of as a single layer of graphite that has been wrapped into a cylinder, (See figure 1 and the article by Thomas Ebbesen in PHYSICS TODAY, June 1996, page 26)
TL;DR: In this article, the authors measured the temperature-dependent thermal conductivity of single-walled carbon nanotubes from 350 K to 8 K and showed that the thermal conductivities are dominated by phonons at all temperatures.
Abstract: We have measured the temperature-dependent thermal conductivity $\ensuremath{\kappa}(T)$ of crystalline ropes of single-walled carbon nanotubes from 350 K to 8 K. $\ensuremath{\kappa}(T)$ decreases smoothly with decreasing temperature, and displays linear temperature dependence below 30 K. Comparison with electrical conductivity experiments indicates that the room-temperature thermal conductivity of a single nanotube may be comparable to that of diamond or in-plane graphite, while the ratio of thermal to electrical conductance for a given sample indicates that the thermal conductivity is dominated by phonons at all temperatures. Below 30 K, the linear temperature dependence and estimated magnitude of $\ensuremath{\kappa}(T)$ imply an energy-independent phonon mean free path of \ensuremath{\sim}0.5--1.5 \ensuremath{\mu}m.
TL;DR: The high hydrogen-uptake capacity of these systems may be derived from the special open-edged, layered structure of the carbon nanotubes made from methane, as well as the catalytic effect of alkali metals.
Abstract: Lithium- or potassium-doped carbon nanotubes can absorb approximately 20 or approximately 14 weight percent of hydrogen at moderate (200 degrees to 400 degrees C) or room temperatures, respectively, under ambient pressure. These values are greater than those of metal hydride and cryoadsorption systems. The hydrogen stored in the lithium- or potassium-doped carbon nanotubes can be released at higher temperatures, and the sorption-desorption cycle can be repeated with little decrease in the sorption capacity. The high hydrogen-uptake capacity of these systems may be derived from the special open-edged, layered structure of the carbon nanotubes made from methane, as well as the catalytic effect of alkali metals.
TL;DR: In this article, the synthesis of high quality single-walled carbon nanotubes (SWNTs) is accomplished by optimizing the chemical compositions and textural properties of the catalyst material used in the chemical vapor deposition (CVD) of methane.
Abstract: The synthesis of bulk amounts of high quality single-walled carbon nanotubes (SWNTs) is accomplished by optimizing the chemical compositions and textural properties of the catalyst material used in the chemical vapor deposition (CVD) of methane A series of catalysts are derived by systematically varying the catalytic metal compounds and support materials The optimized catalysts consist of Fe/Mo bimetallic species supported on a novel silica−alumina multicomponent material The high SWNT yielding catalyst exhibits high surface-area and large mesopore volume at elevated temperatures Gram quantities of SWNT materials have been synthesized in ∼05 h using the optimized catalyst material The nanotube material consists of individual and bundled SWNTs that are free of defects and amorphous carbon coating This work represents a step forward toward obtaining kilogram scale perfect SWNT materials via simple CVD routes
TL;DR: In this paper, high-purity aligned multi-walled carbon nanotubes were synthesized through the catalytic decomposition of a ferrocene-xylene mixture at ; 6758C in a quartz tube reactor and over quartz substrates, with a conversion of ; 25% of the total hydrocarbon feedstock.
TL;DR: In this paper, the work function and density of states (DOS) of multiwall carbon nanotubes (MWNTs) using ultraviolet photoelectron spectroscopy (UPS) were studied.
Abstract: We have studied the work function and density of states (DOS) of multiwall carbon nanotubes (MWNTs) using ultraviolet photoelectron spectroscopy (UPS) Raw MWNTs were purified by successive sonication, centrifugation, sedimentation, and filtration processes with the aid of a nonionic surfactant The purified MWNTs showed a slightly lower work function (43 eV) than that of highly oriented pyrolytic graphite (44 eV) Effects of three different oxidative treatments, air-, oxygen plasma-, and acid-oxidation, have also been studied It was found that oxidative treatments affect the DOS of valence bands and increase the work function X-ray photoelectron spectroscopy (XPS) measurements have suggested that gas-phase treatment preferentially forms hydroxyl and carbonyl groups, while liquid-phase treatment forms carboxylic acid groups on the surface of MWNTs These surface chemical groups disrupt the π-conjugation and introduce surface dipole moments, leading to higher work functions up to 51 eV We expect the
TL;DR: In this article, the authors proposed a supported catalyst-substrate system to promote the growth of single-wall carbon nanotubes in a specific size range, rather than the large irregular-sized multi-walled carbon fibrils that are known to grow from supported catalysts.
TL;DR: In this article, the structural, elastic, and vibrational properties of single-wall carbon nanotubes with different radii and chiralities were investigated using pseudopotential-density-functional theory, which allows calculations on systems with a large number of atoms per cell.
Abstract: A study based on ab initio calculations is presented on the structural, elastic, and vibrational properties of single-wall carbon nanotubes with different radii and chiralities. These properties are obtained using an implementation of pseudopotential-density-functional theory, which allows calculations on systems with a large number of atoms per cell. Different quantities are monitored versus tube radius. The validity of expectations based on graphite is explored down to small radii, where some deviations appear related to the curvature-induced rehybridization of the carbon orbitals. Young moduli are found to be very similar to graphite and do not exhibit a systematic variation with either the radius or the chirality. The Poisson ratio also retains graphitic values except for a possible slight reduction for small radii. It shows, however, chirality dependence. The behavior of characteristic phonon branches as the breathing mode, twistons, and high-frequency optic modes, is also studied, the latter displaying a small chirality dependence at the top of the band. The results are compared with the predictions of the simple zone-folding approximation. Except for the known deficiencies of the zone-folding procedure in the low-frequency vibrational regions, it offers quite accurate results, even for relatively small radii.
TL;DR: In this article, hydrogen adsorption on crystalline ropes of carbon single-walled nanotubes (SWNTs) was found to exceed 8 wt.%, which is the highest capacity of any carbon material.
Abstract: Hydrogen adsorption on crystalline ropes of carbon single-walled nanotubes (SWNT) was found to exceed 8 wt.%, which is the highest capacity of any carbon material. Hydrogen is first adsorbed on the outer surfaces of the crystalline ropes. At pressures higher than about 40 bar at 80 K, however, a phase transition occurs where there is a separation of the individual SWNTs, and hydrogen is physisorbed on their exposed surfaces. The pressure of this phase transition provides a tube-tube cohesive energy for much of the material of 5 meV/C atom. This small cohesive energy is affected strongly by the quality of crystalline order in the ropes.
TL;DR: In this article, the pyrolysis of acetylene with cobalt catalysis was used to grow carbon-nanotubes by using nano-structured template channels to grow individual Y-junction carbon nanotube heterostructures.
Abstract: The synthesis of connections between two or more different carbon nanotubes is an important step in the development of carbon nanotube-based electronic devices and circuits1,2,3,4. But this is difficult to achieve using conventional methods to grow carbon nanotubes5 because the straight tube structure cannot be controllably altered along its length. Various ideas for post-growth modifications have been suggested6, but these have been hard to implement and are prone to defects. Here we use nano-structured template channels to grow individual Y-junction carbon-nanotube heterostructures by the pyrolysis of acetylene with cobalt catalysis.
TL;DR: In this article, the authors report controlled, catalytic growth of metal-semiconductor junctions between carbon nanotubes and silicon nanowires, and show that these junctions exhibit reproducible rectifying behavior.
Abstract: Nanometre-scale electronic structures are of both fundamental and technological interest: they provide a link between molecular and solid state physics, and have the potential to reach far higher device densities than is possible with conventional semiconductor technology1,2. Examples of such structures include quantum dots,which can function as single-electron transistors3,4 (although theirsensitivity to individual stray charges might make them unsuitable for large-scale devices) and semiconducting carbon nanotubes several hundred nanometres in length, which have been used to create a field-effect transistor5. Much smaller devices could be made by joining two nanotubes or nanowires to create, for example, metal–semiconductor junctions, in which the junction area would be about 1 nm2 for single-walled carbon nanotubes. Electrical measurements of nanotube ‘mats’ have shown the behaviour expected for a metal–semiconductor junction6. However, proposed nanotube junction structures7 have not been explicitly observed, nor have methods been developed to prepare them. Here we report controlled, catalytic growth of metal–semiconductor junctions between carbon nanotubes and silicon nanowires, and show that these junctions exhibit reproducible rectifying behaviour.
TL;DR: In this article, the authors reported the injection of spin-polarized electrons from ferromagnetic contacts into multi-walled carbon nanotubes, finding direct evidence for coherent transport of electron spins.
Abstract: Conventional electronic devices generally utilize only the charge of conduction electrons; however, interest is growing in ‘spin-electronic’ devices1, whose operation depends additionally on the electronic spin. Spin-polarized electrons (which occur naturally in ferromagnetic materials) can be injected from a ferromagnet into non-ferromagnetic materials2,3,4, or through oxide tunnel barriers3,5,6,7,8,9,10. The electron-scattering rate at any subsequent ferromagnetic/non-ferromagnetic interface depends on the spin polarity, a property that is exploited in spin-electronic devices. The unusual conducting properties11,12,13,14,15,16,17,18 of carbon nanotubes offer intriguing possibilities for such devices; their elastic- and phase-scattering lengths are extremely long16,17, and carbon nanotubes can behave as one-dimensional conductors18. Here we report the injection of spin-polarized electrons from ferromagnetic contacts into multi-walled carbon nanotubes, finding direct evidence for coherent transport of electron spins. We observe a hysteretic magnetoresistance in several nanotubes with a maximum resistance change of 9%, from which we estimate the spin-flip scattering length to be at least 130 nm—an encouraging result for the development of practical nanotube spin-electronic devices.
TL;DR: In this article, high-ordered arrays of parallel carbon nanotubes were grown by pyrolysis of acetylene on cobalt within a hexagonal close-packed nanochannel alumina template at 650°C.
Abstract: Highly-ordered arrays of parallel carbon nanotubes were grown by pyrolysis of acetylene on cobalt within a hexagonal close-packed nanochannel alumina template at 650 °C. The nanotubes are characterized by a narrow size distribution, large scale periodicity, and high densities. Using this method ordered nanotubes with diameters from 10 nm to several hundred nm and lengths up to 100 μm can be produced. The high level of ordering and uniformity in these arrays is useful for applications in data storage, field emission displays and sensors, and offers the prospect of deriving computational functions from the collective behavior of symmetrically coupled nanotubes. The fabrication method used is compatible with standard lithographic processes and thus enables future integration of such periodic carbon nanotube arrays with silicon microelectronics.
TL;DR: In this paper, the authors reported magnetoresistance measurements on individual multi-walled carbon nanotubes and found that the oscillations are in good agreement with theoretical predictions for the Aharonov-Bohm effect in a hollow conductor with a diameter equal to that of the outermost shell of the nanotube.
Abstract: When electrons pass through a cylindrical electrical conductor aligned in a magnetic field, their wave-like nature manifests itself as a periodic oscillation in the electrical resistance as a function of the enclosed magnetic flux1. This phenomenon reflects the dependence of the phase of the electron wave on the magnetic field, known as the Aharonov–Bohm effect2, which causes a phase difference, and hence interference, between partial waves encircling the conductor in opposite directions. Such oscillations have been observed in micrometre-sized thin-walled metallic cylinders3,4,5 and lithographically fabricated rings6,7,8. Carbon nanotubes9,10 are composed of individual graphene sheets rolled into seamless hollow cylinders with diameters ranging from 1 nm to about 20 nm. They are able to act as conducting molecular wires11,12,13,14,15,16,17,18, making them ideally suited for the investigation of quantum interference at the single-molecule level caused by the Aharonov–Bohm effect. Here we report magnetoresistance measurements on individual multi-walled nanotubes, which display pronounced resistance oscillations as a function of magnetic flux.We find that the oscillations are in good agreement with theoretical predictions for the Aharonov–Bohm effect in a hollow conductor with a diameter equal to that of the outermost shell of the nanotubes. In some nanotubes we also observe shorter-period oscillations, which might result from anisotropic electron currents caused by defects in the nanotube lattice.
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28 Nov 1999TL;DR: The physics of nanotubes and their properties are discussed in this paper, where the ultimate carbon fibre is described as "curved crystals, inorganic fullerenes and nanorods".
Abstract: 1 Introduction 2 Synthesis 3 Structure 4 The physics of nanotubes 5 Nano-capsules and nano-test-tubes 6 The ultimate carbon fibre? 7 Curved crystals, inorganic fullerenes and nanorods 8 Carbon onions and spheroidal carbon 9 Future directions Index
01 Nov 1999-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, the experimental results show that carbon nanotubes (CNTs) can be initiated by AIBN to open their π-bonds, which imply that CNTs may participate in PMMA polymerization and form a strong combining interface between the CNT and the PMMA matrix.
Abstract: Carbon nanotubes (CNTs) can be used to compound poly (methyl methacrylate)/carbon nanotube (PMMA/CNT) composites by an in situ process. The experimental results show that CNTs can be initiated by AIBN to open their π-bonds, which imply that CNTs may participate in PMMA polymerization and form a strong combining interface between the CNTs and the PMMA matrix. Through the use of an improved in situ process, the mechanical properties and the heat deflection temperatures of composites rise with the increase of CNTs. The dispersion ratio of CNTs in the PMMA matrix is proportional to the reaction time of polymerizing MMA before CNTs are added into the PMMA mixture.
TL;DR: In this paper, a high degree of coupling between mesogenic side groups and the ethylene oxide backbone is invoked to suppress the formation of helical conformations favored by a free-o poly(ethylene oxide) chains.
Abstract: 834 Ó WILEY-VCH Verlag GmbH, D-69469 Weinheim, 1999 0935-9648/99/1007-0834 $ 17.50+.50/0 Adv. Mater. 1999, 11, No. 10 be detected. Furthermore, the mechanical properties of the complex are solid-like at temperatures below the observable glass transition, which would not be the case for a phase separated material containing rubbery microdomains. Instead, we advance an explanation for the extraordinary properties of this liquid crystal complex by invoking a high degree of coupling between mesogenic side groups and the ethylene oxide backbone which thereby inhibits the formation of helical conformations favored by afreeo poly(ethylene oxide) chains. Within such helical arrangements the lithium ions would be tightly coordinated below Tg and effectively trapped. By suppressing the formation of such helical structures, an open ethylene oxide structure is obtained within which lithium ions are free to move and where empty sites exist for the ions to occupy. It is remarkable that a similar (but weaker) effect is observed in the amorphous material. It seems that insertion of rigid isophthalate units also inhibits helical formation, sufficient to provide a measure of ionic decoupling, but for the liquid crystal complex the open structure is further stabilized via the interactions between the liquid crystal side groups. It is worth noting that this view is supported by the continuity of behavior from the melt into the glassy state in both the heat capacity and electrical conductivity, indicating that the structure of the melt is not strongly influenced by temperature. In addition, the dissolution of the ions in the backbone does not swell the smectic layer and thus, the open network must be relatively unchanged at least in the direction normal to the smectic layers. This suggests that by careful engineering of the types of liquid crystal phase present, it should be possible to tailor the conductivity mechanism to particular applications. It is also remarkable that the conductivity in the MeOC6G6 complex increases strongly (by several orders of magnitude) as the AO:Li ratio is decreased from 10:1 to 3:1. We should now be able to employ more concentrated polymer electrolytes than is presently possible with conventional materials. Transport number data for these electrolytes are not yet available, but it is tempting to speculate that the elimination of acation trappingo within the ethylene oxide helix will lead to substantial increases in cation mobility. For many years this has been one of the principal goals of polymer electrolyte research.