Showing papers on "Carbon nanotube published in 1993"

Single-shell carbon nanotubes of 1-nm diameter

Abstract: CARBON nanotubes1 are expected to have a wide variety of interesting properties. Capillarity in open tubes has already been demonstrated2–5, while predictions regarding their electronic structure6–8 and mechanical strength9 remain to be tested. To examine the properties of these structures, one needs tubes with well defined morphologies, length, thickness and a number of concentric shells; but the normal carbon-arc synthesis10,11 yields a range of tube types. In particular, most calculations have been concerned with single-shell tubes, whereas the carbon-arc synthesis produces almost entirely multi-shell tubes. Here we report the synthesis of abundant single-shell tubes with diameters of about one nanometre. Whereas the multi-shell nanotubes are formed on the carbon cathode, these single-shell tubes grow in the gas phase. Electron diffraction from a single tube allows us to confirm the helical arrangement of carbon hexagons deduced previously for multi-shell tubes1.

Cobalt-catalysed growth of carbon nanotubes with single-atomic-layer walls

Abstract: CARBON exhibits a unique ability to form a wide range of structures. In an inert atmosphere it condenses to form hollow, spheroidal fullerenes. Carbon deposited on the hot tip of the cathode of the arc-discharge apparatus used for bulk fullerene synthesis will form nested graphitic tubes and polyhedral particles. Electron irradiation of these nanotubes and polyhedra transforms them into nearly spherical carbon 'onions'. We now report that covaporizing carbon and cobalt in an arc generator leads to the formation of carbon nanotubes which all have very small diameters (about 1.2 nm) and walls only a single atomic layer thick. The tubes form a web-like deposit woven through the fullerene-containing soot, giving it a rubbery texture. The uniformity and single-layer structure of these nanotubes should make it possible to test their properties against theoretical predictions.

Self-assembling organic nanotubes based on a cyclic peptide architecture

Abstract: Hollow tubular structures of molecular dimensions may offer a variety of applications in chemistry, biochemistry and materials science. Concentric carbon nanotubes have attracted a great deal of attention, while the three-dimensional tubular pore structures of molecular sieves have long been exploited industrially. Nanoscale tubes based on organic materials have also been reported previously. Here we report the design, synthesis and characterization of a new class of organic nanotubes based on rationally designed cyclic polypeptides. When protonated, these compounds crystallize into tubular structures hundreds of nanometres long, with internal diameters of 7-8 A. Support for the proposed tubular structures is provided by electron microscopy, electron diffraction, Fourier-transform infrared spectroscopy and molecular modelling. These tubes are open-ended, with uniform shape and internal diameter. We anticipate that they may have possible applications in inclusion chemistry, catalysis, molecular electronics and molecular separation technology.

Capillarity-induced filling of carbon nanotubes

Abstract: THE recent discovery1 and bulk synthesis2 of nanometre-scale carbon tubules has led to much speculation about possible uses of these graphitic structures3–5. Broughton and Pederson predicted on the basis of computer simulations that open nanotubes may be filled with liquid by capillary suction6. Here we describe experiments in which annealing of the tubules in the presence of liquid lead results in opening of the capped tube ends and subsequent filling of the tubes with molten material through capillary action. The nanotubes thus act as moulds for the fabrication of (possibly metallic) wires, some of which are less than two nanometres in diameter.

Opening carbon nanotubes with oxygen and implications for filling

Abstract: CAPPED hollow carbon nanotubes1,2 can be modified into nanocomposite fibres by simultaneous opening of the caps (by heating in the presence of air and lead metal) and filling of the interior with an inorganic phase3. To generalize this approach, greater understanding is needed of the reaction mechanism between the tube caps and oxygen. Here we report that the oxidation of carbon nanotubes in air for short durations above about 700 °C results in the etching away of the tube caps and the thinning of tubes through layer-by-layer peeling of the outer layers, starting from the cap region. The oxidation reaction follows an Arrhenius-type relation with an activation energy barrier of about 225 kJ mol−1 in air. Heating of closed nanotubes with an oxide (Pb3O4) in an inert atmosphere lowers the activation barrier for the reaction and opening of the tubes occurs at lower temperatures. Contrary to intuition, however, open tubes are much more difficult to fill with inorganic materials than in the one-step filling of tubes reported previously3. But various other experiments might be possible in the inner nano-cavities of the open tubes such as studies of catalysis and of low-dimensional chemistry and physics.

Thinning and opening of carbon nanotubes by oxidation using carbon dioxide

Abstract: THE discovery1 and bulk synthesis2 of carbon nanotubes has stimulated great interest. It has been suggested that these structures may have useful electronic3–5 and mechanical6 properties, and these might be modified by introducing foreign materials into the nanotubes. But the tubes are invariably capped at the ends. Ajayan and lijima7 have succeeded in drawing molten material (lead or one of its compounds) into the tubes by heating them in the presence of lead and oxygen; less than 1% of the tubes in the sample studied could be filled in this way. Here we report that heating in carbon dioxide gas can result in the partial or complete destruction of the tube caps and stripping of the outer layers to produce thinner tubes. In some cases, we have thinned the extremity of tubes to a single layer. The opened tubes can be regarded as nanoscale test-tubes for adsorption of other molecules, and this controlled method of thinning may allow studies of the properties of single tubes.

Electronic States of Carbon Nanotubes

Abstract: The π-electron states of carbon nanotubes (CN's) in magnetic fields are calculated in the effective-mass theory. A sensitive change of CN from metal to semiconductor depending on its structure is well reproduced. The band gap is inversely proportional to the tube diameter and exhibits a drastic change as a function of magnetic flux passing through the cylinder with period c h / e due to the Aharonov-Bohm effect. In a magnetic field perpendicular to the tube axis, the band-gap is reduced strongly and the energy spectra approach those of a graphite sheet.

Synthesis of a tubular polymer from threaded cyclodextrins

Abstract: MUCH attention has been focused recently on the design and fabrication of large-scale molecular structures1. Carbon nanotubes formed by an arc-discharge method2,3 have attracted particular attention. These tubes range from about 1 to 30 nanometres in diameter and a micrometre or so in length. To construct smaller tubes, direct chemical synthesis may be a more convenient approach. The cyclic oligomers of glucose known as cyclodextrins (CDs) would seem to be ideal candidates for the components of a molecular tube: they contain cylindrical cavities about 0.7 nm deep, with diameters of 0.45 nm, 0.7 nm and 0.85 nm for α-CD, β-CD and γ-CD respectively4. Lehn has recently reported the use of 'bouquet molecules' built from β-CD with long side chains as artificial ion channels5. We have previously prepared rotaxane super-molecules in which CDs are threaded on a polymer chain, and we6 and others7,8, have reported polyrotaxanes with many threaded CDs. Here we report the crosslinking of adjacent CD units in apolyrotaxane to create a molecular tube. By removing the bulky ends of the polymer thread, the tube can be unthreaded and can act as a host for reversible binding of small molecules.

Radial deformation of carbon nanotubes by van der Waals forces

Abstract: THE discovery of carbon nanotubes1,2 has stimulated many theoretical studies of their physical properties3–12, and their bulk synthesis13 should soon make possible experimental measurements of these properties14. All studies so far have assumed that the nanotubes have perfect cylindrical symmetry. Here we show that van der Waals forces between adjacent nanotubes can deform them substantially, destroying this cylindrical symmetry. We present transmission electron microscopy images of two adjacent aligned tubes, about 100 A in diameter, which show flattening of the tubes along the contact region. Calculations on two-layer nested nanotubes indicate that these deformations can be explained on the basis of van der Waals interactions. We predict that these effects should be observable at least for tubes as small as 20 A in diameter, and suggest that they may have a significant influence on the tubes' physical properties.

Interlayer spacings in carbon nanotubes.

Abstract: Electron and x-ray-diffraction studies of nanotubes have revealed that the distances between the graphitic sheets are larger by a few percent than those in bulk graphite. The mean value of the interlayer spacings is 0.344\ifmmode\pm\else\textpm\fi{}0.001 nm.

Thermogravimetric analysis of carbon nanotubes and nanoparticles

Abstract: The oxidation of carbon nanotubes and nanoparticles has been studied by thermogravimetric analysis (TGA) in air. The maximum rate of weight loss took place at 695[degrees]C at a heating rate of 1[degrees]C/min. This result shows that the nanotubes and nanoparticles are more resistant to oxidation than other forms of carbon diamond, soot, graphite, and C[sub 60] studied previously under identical conditions. The TGA of the nanotubes/nanoparticles in argon showed no weight change or detectable thermal transformation up to 1000[degrees]C. 18 refs., 1 fig.

Growth of carbon nanotubes

Abstract: The production, morphologies and atomic structures of carbon nanotubes are reviewed, and a mechanism for tube growth is discussed on the basis of transmission electron microscopy observations. Capping of carbon nanotubes is explained nicely in terms of pentagons; distributions of pentagons in a hexagon network cause various cap morphologies. Heptagons, resulting in negative curvature into a graphitic plane, also provide a variety of graphitic structures. Pentagons and heptagons seem to play a key role in tube growth. On the basis of the consistency of various tube morphologies, we propose a model for tubule growth, in which the tubules are open at their ends while growing in the carbon arc plasma. To support this open-end growth mechanism, other evidence such as layer-by-layer growth on the tube surfacces and “over-shooting growth” on tube tips is given.

Erratum: Single-shell carbon nanotubes of 1-nm diameter

Abstract: Nature 363, 603-605 (1993) FIGURE \b in this letter was reproduced with insufficient quality for some labelled features to be visible. The improved version on the right shows the features 4 and 5 (arrowed) that were indistinguishable previously. Also, in the sixth paragraph of the paper, "(arrow 4 in Fig.

Preparation of Carbon Nanotubes by Arc-Discharge Evaporation

Abstract: Extremely thin graphite filaments with a tubular structure were grown in carbon deposits formed on the negative electrode during generation of fullerenes by dc carbon-arc-discharge evaporation. The filaments and small graphite particles coexist in the central portion of the deposits. Three kinds of morphologies of carbon, namely nanotubes, polyhedra and sheets were observed in transmission electron micrographs. The filaments were formed in He, Ar or CH4 gas environment at a pressure between 20-200 Torr.

Uncapped and thinned carbon nanotubes and process

Abstract: Uncapped and thinned carbon nanotubes are produced by reaction with a flowing reactant gas capable of reaction selectively with carbon atoms in the capped region of nanotubes. The uncapped and thinned nanotubes provide open compartments for insertion of chemicals and exhibit enhanced surface area with modified physical and chemical properties.

Osmylation of C70: reactivity versus local curvature of the fullerene spheroid

Abstract: Unlike C[sub 60], the higher fullerenes and carbon nanotubes contain carbons with different degrees of pyramidalization corresponding to different degrees of local curvature of the fullerene spheroid. In the simplest case, C[sub 70] contains eight types of C-C bonds, each positioned differently on the oblong fullerene surface. Here, we report an analysis of the regiochemistry of the osmylation of C[sub 70] where the observed ratio of isomeric 1:1 adducts 1, 2, 3, and 4 (2.1:1.0:<0.1:<0.1) demonstrates greater kinetic reactivity at sites of greater local curvature, rather than at sites of greater bond order. These results complement the thermodynamically controlled regiochemistry observed by Balch and co-workers. 17 refs., 1 fig., 1 tab.

Nanotube structure and electronic properties probed by scanning tunneling microscopy

Abstract: Scanning tunneling microscopy (STM) has been used to investigate the structure and electronic properties of carbon nanotubes produced from a discharge between graphite electrodes. STM images of the nanotubes deposited onto polycrystalline gold substrates resolve the three‐dimensional structure of the nanotubes and show that these tubes often exist as tightly packed bundles. In addition, bias‐voltage dependent imaging studies indicate that the nanotubes studied are semiconductors. The implications of these new data to the application of nanotubes in structural composites and nanoelectronics is discussed.

Method for purifying carbon nanotube

Abstract: PURPOSE: To obtain good quality carbon nanotubes which are uniform in molecular weight, size and electric conductivity by utilizing techniques such as column chromatography, ultracentrifugal separation, ultrasonic disintegration and membrane separation, and also employing a surfactant. CONSTITUTION: In this method, a crude product contg. carbon nanotubes is dispersed into a solution by adding a surfactant to the solution and using an ultrasonic wave and the resultant solution is allowed to pass through a chromatographic column. Accordingly, the carbon nanotubes can be separated from nanoparticles by the difference in development rate in the column between the nanotubes and the nanoparlicles due to the differences in molecular weight and shape between them. Then, the separated carbon nanotubes are scattered on a rotary drum and charged by irradiating them with an electron beam or showering a corona discharge on them and, thereafter, the rotary drum is rotated to remove uncharged metal type nanotubes from the drum. Thus, the carbon nanotubes can be separated into the metal type nanotubes and insulator type nanotubes. COPYRIGHT: (C)1996,JPO

Carbon Nanotubes at As-Grown Top Surface of Columnar Carbon Deposit

Abstract: Carbon nanotubes are usually found inside the carbon deposit, which grows on the cathode of dc carbon-arc rod, as fibers or whiskers with co-existing carbon nanoparticles. Curled and intertwined carbon nanotubes having random orientation were also found on the top surface of the columnar carbon deposit, which has a sootlike color. The growth of carbon nanotubes at the top surface of the columnar deposit suggests that carbon nanotubes are formed on the top surface and restored as a columnar deposit.

Shape transformations in single-layer carbon nanotubes

Abstract: 2014 We show that strong electron irradiation of single-layer carbon nanotubes introduces distinct changes in the preferred morphology (shape) of tubes, from perfect cylindrical to a necklace of ridges which result from local deformations of the tube surfaces with the curvature on the order of the tube radii. The shape transformations in these free-standing closed two dimensional surfaces seems to resemble closely the deformations observed in systems such as lipid bilayers and biological membranes. Microsc. Microanal. Microstruct. 4 (1993) DECEMBER 1993, PAGE 501 Classification Physics Abstracts 07.80 61.46 61.80 It is now well established that when carbon samples (multi-shell carbon nanotubes [1,2], carbon soot etc.) are subjected to intense electron irradiation, almost spherical graphitic structures result having concentric multi-layers nested one inside the other as if they were onions [3,4]. The process results from the concerted migration of the carbon species in the irradiated area through long/short range diffusion inside a carbon matrix towards thermodynamically more stable shapes of graphite particles. Heating of carbon black near melting temperatures or carbonization of some natural polymers under pressure has also been reported [5] to result in spherical or hemi-spherical structures with concentric carbonaceous shells. However, the monitoring of the exact shape transformations and evolution of the individual layers of the nanotubes to the final onionite stage is an impossible task since inter-layer disordering takes place during irradiation as a precursor stage, forming metastable structures full of defects [6]. Also, the formation of the graphite onions in the final state does not reflect the actual thermodynamic minimum shape that a carbon tube would assume if irradiated or subjected to extemal stresses but only reflects the minimum shape during the graphitization process of an intermediary disordered structure created out of destroying the original tubular but graphitic lattice of the nanotube. Article available at http://mmm.edpsciences.org or http://dx.doi.org/10.1051/mmm:0199300406050100

Working method of carbon nanotube

Abstract: PURPOSE: To provide a working method to work a part of a carbon nanotube. CONSTITUTION: In the subject working method, a stage in which at least carbon nanotube 1 is irradiated with an ion 4 having suitable mass and energy and a part of a bond of a carbon atom constituting the carbon nanotube is cut to make an unbonded hand (dangling bond) 5 is included. When the unbonded hand formed at a part of the carbon nanotube is increased, a hole is made, and other substance (impurity) can be introduced and discharge or cutting of the nanotube may be enabled. Further growing of a new crystal structure from the unbonded hand is made possible, and various structures of the carbon nanotube are obtained. COPYRIGHT: (C)1995,JPO

Carbon nanotubes opened by oxidation

Abstract: Two independent research groups have shown that the tips of carbon tubules with dimensions on the scale of nanometers—so-called carbon nanotubes—can be opened by exposure to an oxidizing agent and relatively mild heating. This research opens the way to further characterization of these cousins of the fullerenes. Carbon nanotubes consist of concentric graphitic carbon tubes capped by fullerenelike hemispheres that curve through incorporation of five-membered rings. Scientists speculate open tubes might act as "nanoscale test tubes" for studying catalysis and one- or low-dimensional chemistry and physics. At Oxford University, England, Malcolm L. H. Green and coworkers heated nanotubes in carbon dioxide gas to 850 °C. Corrosion in the cap region occurred in 5 to 10% of the nanotubes subjected to this treatment [ Nature , 362 , 520 (1993)]. Meanwhile, at NEC Corp. in Tsukuba, Japan, P. M. Ajayan, Thomas W. Ebbessen, Sumio Iijima, and coworkers showed that nanotube caps are attacked when ...

Formation of carbon thin film, its modifying method, electronic device formed by using this modifying method as well as x-ray multilayer film mirror and its production

Abstract: PURPOSE:To provide the method for formation of the carbon thin film capable of forming a thin film of flat carbon molecules, its modifying method, the electronic device formed by using this method as well as the X-ray multilayer film mirror and its production. CONSTITUTION:The molecules consisting of plural carbon atoms of any shape of polyhedron, cylinder or spiral or the molecules exclusive of these molecules or atoms are ionized >=1 and the ions are accelerated and deposited by evaporation on a substrate 46. The modifying method consists subjecting the above- mentioned carbon thin film to ion implantation or to a heat treatment together with the ion implantation. The above-mentioned carbon thin film is fullerenes or carbon nanotube.

Production of single-layer carbon nanotube

Abstract: PURPOSE: To produce a single-layer carbon nanotube in high efficiency. CONSTITUTION: The production of nanotube by arc discharge is carried out by using a negative electrode 7 consisting of a carbon rod electrode and a positive electrode 10 produced by boring a hole through a carbon rod and inserting a metallic wire into the hole. The metallic wire inserted into the carbon rod enables the control of areal ratio of the carbon to metal exposed to the surface to enable the control of the amounts of carbon and metal evaporated by discharge and the mass-production of the nanotube. The yield of single- layer carbon nanotube can be improved by adding hydrogen to rare gas and hydrocarbon gas used as the carrier gas. COPYRIGHT: (C)1995,JPO