Long Sun

Tensile tests of ropes of very long aligned multiwall carbon nanotubes

We have directly measured the Young’s modulus and tensile strength of multiwall carbon nanotubes by pulling very long (∼2 mm) aligned nanotube ropes with a specially designed stress-strain puller. This puller can apply an axial force to the rope and simultaneously measure the corresponding rope elongation and the change in rope resistance. The average Young’s modulus and tensile strength obtained were 0.45±0.23u200aTPa and 1.72±0.64u200aGPa, respectively, which are lower than those calculated and measured previously. The factors that affect the mechanical strengths of nanotubes are discussed.

Direct growth of aligned open carbon nanotubes by chemical vapor deposition

Abstract Open carbon nanotubes were directly obtained at a very high yield by pyrolysis of acetylene over iron/silica substrates. Scanning electron microscope images show that the nanotubes grow outwards perpendicularly and separately from the surface of the substrate and form an aligned nanotube array. The bottom ends of the tubes can be easily stripped off from the substrate and are found to be opened while the top ends are closed, as verified by transmission electron microscope. The tip growth of tubes might be responsible for the formation of open carbon nanotubes.

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.

Growth of straight nanotubes with a cobalt-nickel catalyst by chemical vapor deposition

In this letter, we report the catalytic synthesis of a large amount of straight carbon nanotubes using a transition-metal cobalt–nickel/zeolite catalyst. High-resolution transmission electron microscopy images show that they are well graphitized. Raman spectrum shows its peak at 1349 cm−1 (D band) is much weaker than that at 1582 cm−1 (G band). We believe that straight carbon nanotubes contain much less defects than curved nanotubes and might have potential applications in the future.

Synthesis and Characterization of Aligned Carbon Nanotube Arrays

Highly ordered, isolated, long carbon nanotubes can be grown over large areas using the improved chemical vapor deposition (CVD) method reported here. The secret to the controlled growth lies in the substrate used-mesoporous silica embedded with iron nanoparticles. After synthesis, the substrate can be removed, retaining aligned tubes with neat roots. The production of pure, homogeneous, and uniform samples of highly graphitized nanotubes is important not only for potential applications but also for detailed characterization of the nanotubes properties.

Growth of carbon nanotubes on cobalt disilicide precipitates by chemical vapor deposition

We have successfully grown carbon nanotubes on cobalt-implanted silicon with various doses. The morphology of such tubes has been examined by scanning electron microscopy, transmission electron microscopy, and Raman scattering. On contrary to the commonly used transition-metal nanoparticle catalysts, nanometer-sized CoSi2 precipitates produced in the as-implanted substrates are believed to act as nucleation centers for the formation of carbon nanotubes.

The electrical behavior of carbon nanotubes under high pressure

Abstract The electrical resistance and capacitance of multiwalled carbon nanotubes produced by modified arc discharge were studied under pressure up to 20xa0GPa on a diamond anvil cell (DAC). The electrical resistance decreases gradually with pressure below 3.21xa0GPa and shows a bump around 5.0xa0GPa, and the capacitance exhibits a minimum value at 2.14xa0GPa, which corresponds to the changes of the electronic structure and lattice constants of carbon nanotubes under pressure. These results were conformed by the synchrotron X-ray diffraction and coincided with the prediction of the theoretical calculation.

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.

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