Showing papers on "Nanotube published in 1994"

Aligned Carbon Nanotube Arrays Formed by Cutting a Polymer Resin—Nanotube Composite

Abstract: A simple technique is described here that produces aligned arrays of carbon nanotubes. The alignment method is based on cutting thin slices (50 to 200 nanometers) of a nanotube-polymer composite. With this parallel and well-separated configuration of nanotubes it should be possible to measure individual tube properties and to demonstrate applications. The results demonstrate the nature of rheology, on nanometer scales, in composite media and flow-induced anisotropy produced by the cutting process. The fact that nanotubes do not break and are straightened after the cutting process also suggests that they have excellent mechanical properties.

Growth and sintering of fullerene nanotubes.

Abstract: Carbon nanotubes produced in arcs have been found to have the form of multiwalled fullerenes, at least over short lengths. Sintering of the tubes to each other is the predominant source of defects that limit the utility of these otherwise perfect fullerene structures. The use of a water-cooled copper cathode minimized such defects, permitting nanotubes longer than 40 micrometers to be attached to macroscopic electrodes and extracted from the bulk deposit. A detailed mechanism that features the high electric field at (and field-emission from) open nanotube tips exposed to the arc plasma, and consequent positive feedback effects from the neutral gas and plasma, is proposed for tube growth in such arcs.

Nanoscale Tubular Ensembles with Specified Internal Diameters. Design of a Self-Assembled Nanotube with a 13-.ANG. Pore

Abstract: Here we demonstrate, for the first time, that the internal diameter of the peptide nanotubes can be rigorously controlled simply by adjusting the ring size of the peptide subunit employed. In this study we present the design and synthesis of a 12-residue cyclic peptide structure and document its utility in the construction of nanotube ensembles having a uniform 13-[angstrom] van der Waals pore diameter. Formation to the tubular structures is supported by high-resolution imaging using cryo electron microscopy, electron diffraction, Fourier-transform infrared spectroscopy, and molecular modeling. 11 refs., 3 figs.

Molecular Nanotube Aggregates of β- and γ-Cyclodextrins Linked by Diphenylhexatrienes

Abstract: Linked by strings of diphenylhexatriene (DPH) molecules, beta- and gamma-cyclodextrins (CDs) can form nanotube aggregates that contain as many as approximately 20 betaCDs (20 nanometers long) or approximately 20 to 35 gammaCDs (20 to 35 nanometers long). Nanotube formation was indicated in solution, by fluorescence anisotropy and light scattering results, and on graphite surfaces, by scanning tunneling microscopy. Tubes were not observed for the smaller alphaCDs. Molecular modeling shows that CD cavity size and the rodlike DPH structure are key factors in nanotube formation. Spectra generated by proton nuclear magnetic resonance indicate the inclusion of DPH in the interior of the CDs and formation of nanotubes in betaCDs and gammaCDs only. The photophysical properties of DPH are affected by its arrangement into a one-dimensional array within the CD nanotube, possibly because of exciton formation.

High-resolution electron microscopy studies of a microporous carbon produced by arc-evaporation

Abstract: The soot produced as a byproduct of fullerene synthesis by arc-evaporation consists of a microporous carbon with a surface area, after activation with carbon dioxide, of ca. 700 m2 g–1. Here, we investigate the structure of this material, and its appearance after electron irradiation and high-temperature heat treatment, using high-resolution electron microscopy. We show that the heat treatment transforms the new carbon into a structure containing large, tube-like pores, rather than into polycrystalline graphite. This suggests that the arc-evaporated carbon may have a novel, fullerene-related microstructure, and that it may be the precursor for nanotube formation.

Scanning tunneling spectroscopy of carbon nanotubes

Abstract: Calculations predict that carbon nanotubes may exist as either semimetals or semiconductors, depending on diameter and degree of helicity. This communication presents experimental evidence supporting the calculations. Scanning tunneling microscopy and spectroscopy (STM-S) data taken in air on nanotubes with outer diameters from 17 to 90 A show evidence of one-dimensional behavior; the current-voltage (I-V) characteristics are consistent with a density of states containing Van Hove type singularities for which the energies vary linearly with inverse nanotube diameter.

Magnetic energy bands of carbon nanotubes.

Abstract: Landau quantization of the \ensuremath{\pi} energy bands of a carbon nanotube is calculated within the tight-binding approximation The energy bands do not show explicit Landau levels, but they do have energy dispersion for all values of magnetic field The energy bandwidth shows oscillations with a period that is scaled by a cross section of the unit cell of the tubule, which is specified by the symmetry of the nanotube

Light emitting device.

Abstract: PROBLEM TO BE SOLVED: To provide a light emitting device having a nanotube structure, especially realize a nanotube light emitting device having high light emission efficiency. SOLUTION: This light emitting device has the nanotube structure which is constituted of at least one kind of element out of carbon atoms, boron atoms and nitrogen atoms. Electrons are injected from one end or vicinity thereof, holes are injected from the other end or vicinity thereof, and light emission by recombination of the electrons and the holes is obtained. In an axial direction of the nanotube, the nanotube is constituted of at least three regions wherein at least one element out of three elements, i.e., diameter, composition and chirality of the nanotube is different. Band gap energy in regions of both ends is the largest, and band gap energy is reduced gradually as approaching to the inside regions. As a result, the nanotube light emitting device having high light emission efficiency can be realized. COPYRIGHT: (C)2003,JPO

Purifying-opening method of carbon-nanotube in liquid phase and introducing method of functional group

Abstract: PURPOSE: To efficiently and simply produce an opened nanotube and a high quality purified nanotube. CONSTITUTION: A reaction reagent selected from among an oxidizing agent, a nitration agent and a sulfonating agent and a carbon.nanotube is mixed in a liq. phase to produce a treated carbon.nanotube which is opened by various chemical reactions under moderate conditions, and the nanotubes introduced with various functional groups such as nitro (NO 2 ), sulfoneate (SO 3 H), carboxyl (COOH), carbonyl (C=O), ether (C-O-C) and phenolic hydroxide (OH) are produced. A carbon impurity other than the carbon.nanotube is decomposed at similar condition to purify the carbon.nanotube. COPYRIGHT: (C)1996,JPO

Purification of carbon-nanotube

Abstract: PURPOSE:To develop a method for readily and effectively purifying carbon- nanotube on a larger scale. CONSTITUTION:Synthesized crude nanotube 1 in a bulk state is ground by using a grinder, subsequently put in a suitable vessel and heated in an oven at 600 to 1000 deg.C. During the heat treatment, the oven is filled with an oxidizing agent (air, oxygen, water, carbon dioxide, etc.). After a suitable reaction period, impurities contained in the crude nanotube 1, i.e., nanoparticles 2 (particles covered with a carbon-polyhedron shell and having a particle size of nonometer order) and amorphous carbon having no structure are selectively oxidized by the oxidizing agent and removed therefrom. As the result, the objective pure nanotube 1 (>=99.9%) can be obtained.

Investigations of carbon nanotubes

Abstract: Experiments have been carried out to optimize the yields of carbon nanotubes obtained by the arc-evaporation of graphite. Other types of carbon particles such as nanocrystalline graphite usually present along with the nanotubes are readily removed by heating the material in oxygen around 763 K. Clean nanotubes so obtained have been characterized by X-ray diffraction. The clean tubes are thermally more stable than graphite or fullerenes. The tips of carbon nanotubes are opened by reaction with oxygen, but more interestingly, when the oxygen produced by the decomposition of a metal oxide is used to open the tube tips, the metal formed in the process enters the nanotube. Electrical resistance of pressed pellets of clean tubes is not unlike that of graphite. Tunnelling conductance measurements on isolated tubes characterized by means of scanning tunnelling microscopy however show that the conductance gap increases with decreasing tube diameter.

Nanotube Carbon Structure Tips - A Source of High Field Emission of Electrons

Abstract: We present the finding of experiments of considerable field emission from the films consisting of nanotube carbon structures-on various substrates (Si, quartz, glass): density of emission current was up to 1–3 A/cm2 while electric field was about 100 V/μ m. The “reconstruction” and “inversion” of field emission have also been observed after current breakdown.

Field Emission and Growth of Fullerene Nanotubes

Abstract: Efforts to control the growth of individual carbon nanotubes from nanotube seed crystals have led to a characterization of their field-induced electron emission behavior. The application of a bias voltage in the growth apparatus was motivated by the prolific formation of nanotubes in the carbon are growth method, in which the electric field appears to play a central role. The authors report here the ability to achieve various tube tip configurations by the controlled application of voltage, heat and chemicals to an individual nanotube, and that these states are well characterized by the emission currents they induce.

Measurements of the Conductivity of Individual 10 Nm Carbon Nanotubes

Abstract: Catalytically grown carbon fibers approximately 10 nm in diameter and several microns long were characterized by transmission electron microscopy and determined to be multiple- walled nanotubes, and a technique was developed to measure the conductivity of an individual nanotube. Nanotubes were dispersed in solvents and precipitated onto lithographically defined gold contacts to make a 'nano-wire' circuit. Non-contact AFM was used to image the nano- wires, and a resistance o_f LI.4 (+ 1.0 ) MC) was measured through a single nanotube at23o C. A resistivity of 9.5x10-) Q m was estimated for carbon conducting along the axis of a fiber. Local heating of nanotubes appeared to occur at high current densities. The nanotubes could sustain currents on the order of 10 pA per fiber, but application ofcurrents on the order of 100 pA per fiber resulted in rapid decomposition in air and breaking of the circuit.

Electronic properties of carbon nanotube

Abstract: The electronic properties of purified carbon nanotube (multicylinder structure with an outer diameter of ≈ 20 nm and a length of ≈ 10 μm) was first examined based on the electron spin resonance (ESR) spectroscopy. By the Raman scattering measurement, only one peak at 1581 cm −1 similar to that of graphite was found. The purified nanotube was almost ESR silent as well as the K- and the I 2 -doped samples. This indicates that the purified nanotube examined in the present study is a ‘clean’ semiconductor almost without magnetic impurity and is doping inactive.

Fine diameter conductive tube and manufacture thereof

Abstract: PURPOSE:To provide a fine, low-resistance conductive tube whose diameter is one nanometer to one micron CONSTITUTION:Radiations 1 are irradiated to a carbon nanotube 2 to nuclear- transform part of carbon atoms which are component atoms into vacancies or another atoms, and to supply electrons or positive holes to the nanotube 2 Or, the carbon nanotube 2 is kept in a metal vapor to intercalate metal atoms onto the tube surface and to supply electrons or positive holes to the nanotube 2

Effects of Catalyst Promoters on the Growth of Single-Layer Carbon Nanotubes

Abstract: The discovery of a catalytic route to the growth of single-layer carbon nanotubes suggests that it may be possible to produce these materials with better selectivity and in higher yield1,2. Increasing the production efficiency is essential for characterization and application of these materials. We have discovered several catalyst promoters, in particular S, Bi, and Pb, that greatly enhance the single-layer carbon nanotube yield, and extend the distribution of nanotube diameters to much larger sizes (> 3 nm). Co crystallites encapsulated in graphitic polyhedra also form abundantly when S, Bi, or W is present. Understanding these catalytic process is of substantial scientific and technological importance.

Magnetoresistance of carbon nanotube bundles

Abstract: Summary form only given. Since the discovery of carbon nanotubes a large number of theoretical studies predicted that their band gap changes significantly between zero and nonzero values depending on the diameter and degree of helicity of the nanotube. A magnetic field is expected either to reduce the band gap or to produce Aharonov-Bohm oscillations, when the tube axis is perpendicular or parallel to the magnetic field respectively. It was previously shown (1) that it was possible to realise a direct measurement of the electrical resistance of a single nanotube bundle. In the present work, we present more detailed results on the electrical resistance of single nanotube bundles. The results of an extensive study on the effect of magnetic field intensity and orientation with respect to sample axis as a function of temperature is reported. The electrical resistance measurements were performed from room temperature down to 10 mK in a magnetic field up to 14T.