The Infona portal uses cookies, i.e. strings of text saved by a browser on the user's device. The portal can access those files and use them to remember the user's data, such as their chosen settings (screen view, interface language, etc.), or their login data. By using the Infona portal the user accepts automatic saving and using this information for portal operation purposes. More information on the subject can be found in the Privacy Policy and Terms of Service. By closing this window the user confirms that they have read the information on cookie usage, and they accept the privacy policy and the way cookies are used by the portal. You can change the cookie settings in your browser.
Carbon nanotubes prepared by thermal decomposition of hydrocarbons on supported Co catalysts were investigated by STM in air. An interpretation of the STM images is proposed which accounts for specific distortions taking place while scanning three-dimensional objects whose dimensions are of the order of the curvature radius of the tip. These distortions have both geometric and electronic origins,...
Closed fullerenes and nanotubes exhibiting high topologies from genus 5 to genus 21 are proposed. These structures (holey-balls and holey-tubes) possess only hexagonal and heptagonal (negative Gaussian curvature) rings of carbon with no dangling bonds and no pentagonal rings (no positive Gaussian curvature). Holey-balls and holey-tubes can be seen as finite zeolites since they present interconnected...
The first results of a novel laser induced pyrolysis (LIP) method for high yield production of fullerene and single walled nanotubes are reported. The pyrolysis process of graphite targets is carried out by means of a continuous CO 2 laser under a flowing argon atmosphere. The vaporization of the targets and the deposition of the generated soot take place in a vertical experimental set-up.
Carbon is the most versatile element in the periodic table. Due to its ability to form both sp 3 , sp 2 , and sp hybrids and stable multiple p π &z.sbnd;p π bonds, carbon can build up 3-, 2-, 1-, and 0-dimensionally structured substances with a broad variety of physical and chemical properties. In the last decade diamond films, active carbons, carbon fibres, and...
Using the same experimental set-up as for the solar production of fullerenes, we can also produce carbon nanotubes by direct vaporization of a mixture of powdered carbon and catalyst (Co, Ni, Y). The structure of the nanotubes is strongly dependent on the experimental conditions (pressure and flow rate of Ar gas) and we can obtain either multi-walled nanotubes or ropes of single-walled nanotubes.
The spatial homogeneity of electronic properties, as evidenced by the local density of states (LDOS) of pure and B-doped multi-walled carbon nanotubes, is investigated using scanning tunneling microscopy and tunneling spectroscopy. For pure nanotubes, the LDOS is found to be uniform except for the tip of the tubes. B-doped tubes, in contrast, show characteristic spatial variations in the electronic...
Pyrolysis of benzene at ca 600–900 °C over Ni powder generated different types of carbon nanostructures possessing a wide range of morphologies. The effects of temperature and time on carbon nanotubes growth were evaluated. The deposited carbon yield was measured, and the quality of the nanotubes was analyzed by transmission electron microscopy (TEM).
Nanotubes filled with pure Cu and Ge have been formed by using an arc discharge with metal/graphite composite anodes in a hydrogen atmosphere. These nanotubes are found in the soot deposited on the chamber walls instead of on the redeposited rod on the cathode as is the case with experiments in He. Since Cu and Ge do not form stable carbide phases, catalyze carbon fiber growth or have significant...
Co-evaporation of carbon, in the presence of helium with some other element as catalyst, yields interesting new molecules of the fullerene family which have tubular morphologies with a cross-section at the nanoscale but lengths at the macroscale. In particular, using Ni or Co based mixtures as catalyst with the electric arc technique, one obtains single wall carbon nanotubes in large quantities, with...
Multi-wall carbon nanotubes (MWNTs) deposited on various substrates were analysed by scanning tunneling microscopy (STM) and atomic force microscopy (AFM). A dispersion of carbon nanotubes in ethanol was drawn through a 200 nm pore ceramic filter to produce a thin film of nanotubes. This film was brushed along one direction with a Teflon rod involving a change of optical properties. Scanning probe...
The electronic and optical properties of nitrogen doped tetrahedral amorphous carbon (ta-C:N) are compared with those of a new form of carbon ta-C film in which nanotube regions are included (ta-C:(NT)). It is found that nanotubes in ta-C inhibit the N doping effect in ta-C and leads to a reduction in conductivity. The results point to the nanotube regions acting as electronically isolated graphitic...
Carbon single walled nanotubes (SWNTs) have been produced in high yields using the electric arc technique. TEM studies show that the SWNTs have a narrow diameter distribution around an average value of 1.3 nm. In this paper, we focus on the characterization of these samples by high resolution Raman spectroscopy (HRRS). The presence of large amounts of SWNTs in the samples induces a very rich structure...
High resolution electron microscopy (HREM) reveals that carbon nanotubes obtained by heating a polyethylene precursor in the presence of catalytic Ni particles have a structure consisting of stacked conical carbon layers. Two main types of nanotube structures were identified. When the conical angle along the tubes is in the range 16-35°, bamboo -shaped nanotubes are observed, characterized by...
The transitional model from carbon nanotube to diamond has been established. The transition has been accomplished from carbon nanotube to carbon onion and then to diamond through laser irradiation. The transition from tube to onion under laser irradiation experiences the process of structure collapse of the tube and re-organization of carbon clusters. Carbon atoms in onions have some sp 3 ...
The electron spin resonance of multiwall carbon nanotubes has been measured in the temperature range 100–550K. The spin paramagnetic susceptibility and g-shift are connected with 2-D current carriers and low density of localized centers. The temperature dependence of the g-factor and spin paramagnetic susceptibility are well described in terms of the band model of quasi-two-dimensional graphite. The...
New quasi one-dimensional (1D) and dimensionless (0D) objects–nanotubes constructed of C and BN fragments–are considered and their electron spectra are computed by the method of crystal orbitals. Main and mini-zone gaps are shown to be considerably varied for (n,0) zigzag tube superlattices with C 2kn BN ln (l,k=1,…) unit cells when C (or BN) fragment length is changed. Dot and interface...
Multiwalled carbon nanotubes (MWNT) have been obtained by catalytic decomposition of acetylene at 900°C over silica supported cobalt. The thermal treatment at 1600, 2000 and 2800°C allowed improvement of their structural and microtextural organization as well as the elimination of any remaining nanoparticles of cobalt. Such a tubular carbon host with graded texture and chemical composition is a very...
Carbon nanotubes were treated by high-energy ball milling processing for different milling times, and the samples were observed by HRTEM. The broken nanotubes and lots of carbon onion-like particles were obtained in the sample milled for 15 min. When the milling time was up to 60 min, carbon nanotubes turned into amorphous carbon. On the basis of HRTEM observation of carbon nanotubes and carbon nanoparticles,...
Aluminum-carbon nanotube (CNT) composites were fabricated by hot-pressing the respective powders. The microstructural characteristics and the distribution of carbon nanotubes in the aluminum matrix were investigated. The electrical resistivities of the composites were measured from room temperature down to 4.2 K. The electrical resistivity at room temperature increases slightly with increasing volume...
We have carried out momentum-dependent measurements of the density response function of bulk samples of purified single wall nanotubes using electron energy-loss spectroscopy. Carbon nanotubes support both excitations between delocalized and localized electronic states. The π-plasmon exhibits significant q-dependence, with a dispersion relation similar to that of the graphite plane, demonstrating...
Set the date range to filter the displayed results. You can set a starting date, ending date or both. You can enter the dates manually or choose them from the calendar.