Akira Koshio

Bulk production of quasi-aligned carbon nanotube bundles by the / catalytic chemical vapour deposition CCVD method

Abstract The large-scale production of quasi-aligned carbon nanotube bundles is reported. The method includes catalytic decomposition of acetylene over well-dispersed metal particles embedded in commercially available zeolite at a lower temperature (700°C). In-depth studies of this nanotube through scanning electron microscopy and transmission electron microscopy reveal their homogeneity as well as perfect graphitization, along with inner (2.5–4 nm) and outer diameters (10–12 nm) of the tubes. Details of the optimum conditions for producing these nanotubes are also described.

A Simple and Novel Way to Synthesize Aligned Nanotube Bundles at Low Temperature

Large scale quantities of quasi-aligned carbon nanotube bundles have been synthesized by catalytic decomposition of acetylene over well dispersed metal particles (cobalt and vanadium) embedded in commercially available zeolite at 700°C. Scanning electron microscopy analysis revealed the homogenous nature of the sample while transmission electron microscopy studies revealed the perfect graphitization as well as the inner and outer diameters of the tubes.

Metal-free production of high-quality multi-wall carbon nanotubes, in which the innermost nanotubes have a diameter of 0.4 nm

The production of high-purity multi-wall carbon nanotubes (MWNTs) without metal catalysts was produced using radio-frequency plasma. The MWNTs had diameters of about 5 nm, with the innermost tubes having a diameter of 0.4 nm, the smallest value possible for a single-wall carbon nanotube. Two types of aggregates were obtained, depending on the conditions of formation: moss-like aggregates (diameter: about 1 lm) and long bundles (length: 10 lm, diameter: 100 nm). The MWNTs in the moss-like aggregate, referred to as acute MWNTs, had tips with a cone angle of 19.2. 2002 Published by Elsevier Science B.V.

Thermogravimetric analysis of single-wall carbon nanotubes ultrasonicated in monochlorobenzene

The single-wall carbon nanotubes (SWNTs) purified by nitric acid were ultrasonicated in monochlorobenzene solution. Thermogravimetric analysis complemented by transmission electron microscopy and Raman spectroscopy was used to analyze the thus ultrasonicated SWNTs. The results show that two kinds of modified SWNTs and one modification-free SWNT coexist in ultrasonicated SWNTs and burned in three different temperature ranges. The different chemical modifications of SWNTs are likely to arise from their different structures. This provides a possible way to analyze and separate different structures of SWNTs.

Effect of polymer and solvent on purification and cutting of single-wall carbon nanotubes

Following our recent report that it is possible to purify and cut SWNTs by using a saw-edged homogenizer in a monochlorobenzene (MCB) solution of polymethylmethacrylate (PMMA) [Appl. Phys. A 71 (2000) 451], we report here our investigation of the effect of PMMA and MCB on the purification and cutting of SWNTs by thermogravimetric analyses. Our results show that MCB helps the a-C aggregation states to homogenize during the ultrasonic treatment. The PMMA helps to make bundles of SWNTs thinner and accelerates both the cutting and damaging of them.

Field emission patterns from multiwall carbon nanotubes with a cone-shaped tip

Electron emission from multiwall carbon nanotubes (CNTs) with a cone-shaped tip, on the apex of which five pentagons are present, has been studied by field emission microscopy (FEM). Two types of FEM patterns were observed: one is a well-defined “pentagon” pattern that is typically observed for ordinal multiwall CNTs though the number of pentagons is five in the case of cone-shaped CNTs, and the other is a “dim” pattern that is usually observed for single-wall CNTs. Appearance voltages of the respective patterns and transmission electron microscopy study of the cone-shaped CNTs suggest that the pentagon patterns originate from CNTs with apex radii larger than approximately 2nm while the dim patterns originate from those with the smaller apex radii.

High-yield synthesis of single-walled carbon nanotubes by gravity-free arc discharge

Single-walled carbon nanotubes (SWNTs) have been produced in high yield by the dc arc discharge technique under gravity-free conditions. Gravity-free conditions can reduce the convection flow of the buffer gas during the arc discharge, which results in the increase of high thermostatic volume around the arc flame. The yields of both the total soot and SWNTs in soot are significantly increased. Raman spectroscopy and transmission electron microscopy analyses reveal that the diameter distribution of SWNTs has shifted to a larger diameter region under the gravity-free condition. The annealing process in high-thermostatic atmosphere is a crucial experimental factor to selectively synthesize a certain diameter SWNT in high yield.

Bending of multiwalled carbon nanotubes over gold lines

We have investigated an experimentally moderate bending of multiwalled carbon nanotubes (MWNTs) in the perpendicular direction from flat substrates. The tubes were in the diameter range of 3–13nm and deposited over lithographically fabricated gold lines whose height determined the total bending. In our model for the bending profile we take into account the van der Waals attraction between the substrate and the MWNT and the opposing elastic bending force. With reasonable parameters for the competing forces we obtain an agreement between the model and the experimental data for the critical distance between two adjacent lines when the van der Waals attraction can no longer prevent elastic forces from straightening the tube to a suspended position between the lines. However, for the smallest nanotubes a simple classical model is clearly insufficient.

Effect of Fe Loading Condition and Reductants on CO2 Reduction Performance with Fe/TiO2 Photocatalyst

Fe-doped TiO2 (Fe/TiO2) film photocatalyst was prepared by sol-gel and dip-coating process and pulse arc plasma method. The effect of pulse number on the CO2 reduction performance with the Fe/TiO2 was investigated in this study. In addition, the effect of reductants such as H2O, H2, and NH3/H2O on the CO2 reduction performance with the Fe/TiO2 photocatalyst was also investigated. The characteristics of the prepared Fe/TiO2 film coated on a netlike glass fiber which is a base material were analyzed by SEM, EPMA, EDX, and EPMA. Furthermore, the CO2 reduction performance of the Fe/TiO2 film was tested under a Xe lamp with or without ultraviolet (UV) light. The results show that the CO2 reduction performance with the pulse number of 100 is the best with H2O and/or H2 as reductant under UV light illumination, while that with the pulse number of 500 is the best when NH3/H2O is used as reductant. On the other hand, the CO2 reduction performance with the pulse number of 500 is the best under every reductant condition without UV light illumination. The highest CO2 reduction performance with the Fe/TiO2 is obtained under H2

Formation of nanocarbon and composite materials by laser vaporization of graphite and eleven metals

Eleven metals were laser-vaporized with carbon into Ar gas, and the growth of various nanocabon and composite materials were investigated. Controlling the Ar gas pressure and the metal content for Fe, Co, Ni, Cu, and Ag enabled the high yield (~70%) fabrication of single-wall carbon nanohorn particles including metal- or carbide-containing carbon nanocapsules. With the use of B, multi-wall carbon nanotubes were grown with a high yield of ~50%. For Al, Si, La, Y, and Gd, products such as carbide particles, polyhedra, and sea-urchin-type single-wall carbon nanotubes were formed. We will discuss the growth of these structures based on metal-catalyzed graphitization together with thermal graphitization.