Kaori Hirahara

The smallest carbon nanotube

We report here the discovery of the smallest possible carbon nanotube. This has a diameter of 4 Å, which is the narrowest attainable that can still remain energetically stable, as predicted by theory. These nanotubes are confined inside multiwalled carbon nanotubes and their diameter corresponds to that of a C20 dodecahedron with a single carbon atom at each of its twenty apices. Unlike larger carbon nanotubes, which, depending on their diameter and helicity, can be either metallic or semiconducting, these smallest nanotubes are always metallic.

Effect of oxidation on single-wall carbon nanotubes

Abstract Two common methods of oxidation, gas-phase oxidation by heat treatment in oxygen gas and liquid-phase oxidation using nitric acid, were applied to single-wall carbon nanotubes (SWNT). The heat treatment in oxygen showed that thinner SWNTs burn more quickly. The nitric acid treatment showed that SWNTs are relatively inert to oxidation using acids. When the nitric acid treated samples were further oxidized by heat treatment in oxygen, selective oxidation of thinner SWNTs occurred.

Mass production of single-wall carbon nanotubes by the arc plasma jet method

Abstract Single-wall carbon nanotubes (SWNTs) were mass-produced by a newly developed DC arc plasma jet method for the evaporation of a metal-doped carbon anode. The production rate of the cottonlike soot was significantly higher than that by conventional DC arc discharge evaporation, and the highest yield was 1.24 g/min. Investigations by scanning electron microscopy, high-resolution transmission electron microscopy and Raman spectroscopy indicated that more than 50% of the cottonlike carbon soot was composed of fibrous bundles of SWNTs. Through analysis of the breathing modes in the Raman spectra of the cottonlike soot, the diameter of each SWNT was determined to range from 1.28 to 1.52 nm.

Fabrication of single-walled carbon nanotubes and nanohorns by means of a torch arc in open air

Single-wall carbon nanotubes and nanohorns were fabricated by means of a torch arc method in open air. A graphite target containing Ni/Y catalyst was used as a counterelectrode of the welding arc torch. The target was blasted away by the DC arc, and soot was deposited on the substrate placed downstream of the arc plasma jet. The deposited soot was observed with a transmittance electron microscope, revealing that the soot contained single-wall carbon nanotubes and nanohorns.

Compression of polyhedral graphite up to 43 GPa and x-ray diffraction study on elasticity and stability of the graphite phase

The crystal structure of polyhedral graphite particles (“G balls”) has been investigated under pressure up to 43 GPa and at room temperature by x-ray powder diffraction measurements. The polyhedra maintain the graphite phase under pressure higher than 40 GPa. A 29% compression in volume at 43 GPa involves an unusual decrease in the interlayer distance of 25%. The polyhedra recover their original crystal structure by releasing the pressure. A closed and solid structure of the polyhedra, suppressing a transition into another phase, causes them to become metallic under pressures higher than 20 GPa.

Electronic and geometric structures of metallofullerene peapods

Abstract The electronic and geometric structures of the Sm-metallofullerene peapods (Sm@C82)n@SWNTs, are investigated by in situ high-resolution transmission electron microscopy (HRTEM) and electron energy-loss spectroscopy (EELS). The obtained EELS spectra reveal that the encapsulated Sm ion takes +2 state in (Sm@C82)n@SWNTs irrespective of the physical and the electronic properties of single-wall nanotubes.

Arc plasma jet method producing single-wall carbon nanotubes

Abstract The DC arc plasma jet method was newly developed for the mass-production of single-wall carbon nanotubes (SWNTs). The quantity of cathode deposit was efficiently reduced by this method, and the production rate of cotton-like soot including SWNTs was significantly higher than that by conventional DC arc discharge evaporation. Investigation by using scanning electron microscopy, high-resolution transmission electron microscopy and Raman spectroscopy indicated that more than 50% of the cotton-like soot was the fibrous bundles of SWNTs with diameters of 1.34–1.53 nm.

Carbon nanotubes from camphor by catalytic cvd

Multi-wall carbon nanotubes (MWNTs) have been grown from simple pyrolysis of camphor, a botanical hydrocarbon, at 900°C for 15 min in argon atmosphere at ambient pressure using ferrocene as a catalyst. The nanotube diameter is fairly uniform (20-40 nm) and the yield is extremely high (∼90%). Structural characterization is done by SEM, TEM, HRTEM, EDX and Raman analyses. Good crystallinity, high purity, and absence of amorphous carbon and metal particles are the special features of camphor-pyrolyzed nanotubes.

Boron-catalyzed multi-walled carbon nanotube growth with the reduced number of layers by laser ablation

Abstract Multi-walled carbon nanotubes with the reduced number of layers (2 or 3 layers) are dominantly produced by the laser ablation method using a carbon target mixed with boron. Chemical analysis with sub-nanometer resolution has revealed that the obtained nanotubes are composed of pure carbon layers with no boron concentration, while the boron carbide particle is found to be encapsulated at the nanotube tip. It is considered that the boron (in the form of boron carbide) acts as a catalyst during the nanotube formation. A critical particle size of the boron carbide for the tubular growth is found to be ∼5 nm.

Electron microscopic imaging and contrast of smallest carbon nanotubes

The weak scattering from smaller carbon nanotubes results in weak contrast in their electron microscope images, and observation and interpretation of such images require special attention in order to avoid erroneous conclusions. It is demonstrated that the 4 A carbon nanotube, residing inside a multi-walled carbon nanotube, bears recognizable signature in its image contrast for identification. For an isolated single-walled carbon nanotube, observation should be made in areas where the nanotube is exposed. When the carbon nanotube is overlapped with a supporting glassy carbon film, it is practically impossible for the nanotube to produce usable contrast features for unambiguous identification.