Dongsheng Tang

Double wall carbon nanotubes promoted by sulfur in a floating iron catalyst CVD system

Double wall carbon nanotubes (DWCNTs) were mass-produced by pyrolizing C2H2 at the temperature range of 900–1100 °C on a floating iron catalyst with sulfur promoted. Our experiments indicated that the growth of DWCNTs was strongly dependent on the sulfur addition, and without sulfur only single wall carbon nanotubes (SWCNTs) were produced. The outer tube diameters of DWCNTs observed by high resolution electron microscopy (HRTEM) vary from 1.05 to 2.89 nm, and the inner tube diameters vary from 0.40 to 2.19 nm. The effect mechanism of sulfur to the growth of DWCNTs was discussed.

Crystallization behavior of the amorphous carbon nanotubes prepared by the CVD method

We report the crystallization behavior of the amorphous carbon nanotubes at high temperature in this paper. Transmission electron microscopy and X-ray diffraction were performed to characterize the structures of the carbon nanotubes. The results reveal that the microstructure of the as-grown carbon nanotubes, prepared by the floating catalyst method, is roughly amorphous. The as-grown carbon nanotubes were annealed at high temperatures, and the crystallization behavior of the amorphous carbon nanotubes was investigated systematically. Because the carbon nanotubes have finite dimensions and tube-like shape, their crystallization behavior is completely different from the bulk amorphous carbons. The results reveal that the graphene layers in the annealed carbon nanotubes will form into a uniform two-dimensional turbostratic stack, a configuration of carbon nanotubes with the lower Gibbs free energy. A thermodynamic model is presented to explain the crystallization behavior of the amorphous carbon nanotube.

Materials - Creating the narrowest carbon nanotubes

The properties of carbon nanotubes depend on their diameter and on the two integers (m,n) that describe their roll-up vector. The smallest nanotube reported previously had a diameter of 0.7 nm, the same as that of a C60 structure, although nanotubes with a diameter of 0.4 nm have been predicted. Here we report that simple improvements in the electric-arc technique can create a carbon nanotube with a diameter of 0.5 nm — the same as a C36 molecule.

Controllable growth of single wall carbon nanotubes by pyrolizing acetylene on the floating iron catalysts

Single wall carbon nanotubes (SWNTs) without amorphous carbon coating were prepared by thermally decomposing acetylene (C2H2) at the temperature range 750–1200 °C in a floating iron catalyst system. The C2H2 partial pressure was controlled to make a carbon supply limiting growth of SWNTs. The higher reaction temperature above 1100 °C seemed not to favor the SWNT production due to the quick thermal decomposition of C2H2.

Large-scale synthesis of β-SiC nanorods in the arc-discharge

Single crystals of Tb2Fe17 have been grown by Czochralski method cold crucible system. Good-quality crystals can be obtained by using the relative low growth rate and stoichiometrical composition. The single crystalline sample shows a pure hexagonal Th2Ni17 structure with lattice parameters of n=0.8368 +/- 0.0005nm, c=0.8331 +/- 0.0003nm. No detectable traces of Th2Zn17 phase can be found. A new phase diagram has been given based on the DTA results. Tb2Fe17 compound shows a congruent melting point of 1316 degreesC with 89.5 at % Fe and an eutectic point at 1301 degreesC With 92.5 at % Fe, which is different From the peritectic reacting published in some previous reports (see Dariel et al., J. Lesscommon Met. 35 (1976) 91). The magnetic measurements revealed a small difference in the magneto-crystalline anisotropy which could be measured in good crystal samples. Some growth conditions, such as high rate and non-stoichiometrical starting material, caused second-phase defects. Those defects are difficult to be observed by metallography. but can be indirectly found by measuring the magnetization behavior, type II first-order magnetization process (FOMP). Our results indicate that some defects might affect the rotation path of the magnetic victors in the FOMP

Growth of amorphous silicon nanowires

We have grown vertically aligned amorphous silicon nanowires on Au-Pd co-deposition silicon oxide substrate by thermal chemical vapor deposition using SiH4 gas at 800 degreesC. The diameter of silicon nanowires is in the range 10-50 nm and the length is about 1 mum. Transmission electron microscopy (TEM) observations show that the grown silicon nanowires are of an amorphous state and some of nanowires appear to bifurcate in the vertically growth process. The effect of Hz gas etchings on the catalytic size and the effect of catalytic size on the formation of the vertical growth nanowires are discussed

Conductivity and magnetic susceptibility of nanotube/polypyrrole nanocomposites

A method has been developed to produce a carbon nanotube/conducting polymer nano-composite through in-situ polymerization of pyrrole in the carbon nanotube template. The nano-composites of carbon nanotube and polypyrrole have been characterized by SEM, TEM, XRD, Raman Scattering. The thermal stability was studied by TGA (Thermal Gravity Analysis). The measurements of conductivity and magnetic susceptibility of the composites have been studied.

Nanographite ribbons grown from a SiC arc-discharge in a hydrogen atmosphere

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Catalytic synthesis of straight silicon nanowires over Fe containing silica gel substrates by chemical vapor deposition

We report a new method to synthesize very straight silicon nanowires using a porous iron/SiO2 gel as a template by thermal chemical vapor deposition at a temperature of about 500 degreesC. Scanning electron microscopy, transmission electron microscopy and Raman scattering spectroscopy were used to characterize the samples. The results show that a large amount of straight Si nanowires with diameters of about 30 nm and lengths of about 1 mum was obtained. High-resolution transmission electron microscopy observation shows that microtwin defects lie in the straight silicon nanowires. Raman scattering from the nanowires shows a larger line width (about 15 cm(-1)) and a down-shifted (about 9 cm(-1)) peak as compared to that of bulk crystalline silicon

Raman scattering and thermogravimetric analysis of iodine-doped multiwall carbon nanotubes

Iodine-doped multiwall carbon nanotubes ~I-MWNTs! were characterized by means of Raman scattering and thermogravimetric analysis. The results show that multiwall carbon nanotubes ~MWNTs! can be effectively doped by iodine and exchange electrons with iodine. Iodine atoms form charged polyiodide chains inside tubes of different inner diameter, which is similar to the iodine-doped single-wall carbon nanotubes ~I-SWNTs!, but can not intercalate into the graphene walls of MWNTs. The Raman scattering behavior of I-MWNTs exhibits some differences from that of I-SWNTs and the low-dimensional conductive hydrocarbon-iodine complex ‘‘peryleneiI 2.92 .’’