W. Y. Zhou

Very long carbon nanotubes

Carbon nanotubes can now be produced in large quantities by either arc methods, or thermal decomposition of hydrocarbons,. Here we report that pyrolysis of acetylene over iron/silica substrates is an effective method with which to produce very long, multiwalled carbon nanotubes that reach about 2 mm in length, which is an order of magnitude longer than that described in most previous reports,.

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.

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.

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.

Fabrication and characteristics of porous germanium films

Abstract Porous germanium films with good adhesion to the substrate were produced by annealing GeO2 ceramic films in H2 atmosphere. The reduction of GeO2 started at the top of a film and resulted in a Ge layer with a highly porous surface. TEM and Raman measurements reveal small Ge crystallites at the top layer and a higher degree of crystallinity at the bottom part of the Ge film; visible photoluminescence was detected from the small crystallites. Porous Ge films exhibit high density of holes (1020 cm−3) and a maximum of Hall mobility at ∼225 K. Their p-type conductivity is dominated by the defect scattering mechanism.

Strong Spin-Orbit Interactions in an InAlAs/InGaAs/InAlAs Two-Dimensional Electron Gas by Weak Antilocalization Analysis

Spin-orbit interactions in a two-dimensional electron gas were studied in an InAlAs/InGaAs/InAlAs quantum well. Since weak anti localization effects take place far beyond the diffusive regime, (i.e., the ratio of the characteristic magnetic field, at which the magnetoresistance correction maximum occurs, to the transport magnetic field is more than ten) the experimental data are examined by the Golub theory, which is applicable to both diffusive regime and ballistic regime. Satisfactory fitting lines to the experimental data have been achieved using the Golub theory. In the strong spin-orbit interaction two-dimensional electron gas system, the large spin splitting energy of 6.08 meV is observed mainly due to the high electron concentration in the quantum well. The temperature dependence of the phase-breaking rate is qualitatively in agreement with the theoretical predictions

Fabrication, characterization and property of aligned multi-walled carbon nanotubes

In this paper, we described the recent progress about fabrication and characterization of aligned and very long multi-walled carbon nanotubes (MWNTs) done in our group. Typically, MWNTs arrays were prepared by chemical vapor deposition (CVD) of hydrocarbon gas, for example acetylene, on porous substrates. Aligned MWNTs array with high density and purity were achieved by CVD on both bulk silica substrate and the film-like substrates. Basically, the carbon nanotubes have the uniform diameter of 10-20nm and the spacing among the tubes is about lOOnm. There are no catalysis metal particles detected by EDX and TEM in the arrays. Furthermore, very long carbon nanotubes of length ~ 2 mm were produced, which is an order of magnitude longer (1 mm vs. 100 μηι) than that described in most previous reports. Based on the aligned, discrete and long tubes rope, various physical properties have been investigated. At first, efforts have been made to characterize the mechanical properties of aligned MWNTs arrays such as tensile strength, Youngs modulus. We have directly measured the Youngs modulus and tensile strength of MWNTs arrays by pulling very long (~2mm) aligned carbon nanotubes ropes with a specially designed stress-strain puller. The average Youngs modulus and tensile strength obtained were 0.45Tpa and 1.72Gpa respectively, which were lower than those measured by AFM previously. Besides, we have also used a scanning probe microscope with an indentation/scratch function to investigate the radial compression of an individual multi-walled carbon nanotube under an asymmetric stress and to determine the radial compression elastic modulus at different compression levels. Using this kind of samples, we were able to measure the specific heat and the thermal conductivity of MWNTs arrays in the range from room temperature up to 20mk. We found that the specific heat of MWNTs follows a strikingly linear temperature dependence over the entire temperature range measured (10-300K), and the thermal conductivity takes a quadratic T-dependence below -120 Κ and turns to be linear above that temperature. The results indicate that the inter-wall coupling in MWNTs is extremely weak.

Creating the narrowest carbon nanotubes: Materials

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.