Fumio Kokai

Nano-aggregates of single-walled graphitic carbon nano-horns

Abstract We have found a new type of carbon particle produced by the CO 2 laser ablation of carbon at room temperature without a metal catalyst. The product has a powder form of graphitic particles with a uniform size of about 80 nm. An individual particle is composed of an aggregate of many horn-shaped sheaths of single-walled graphene sheets, which we named carbon nano-horns. The nano-horns can be produced at about 10 g/h.

Interlayer spacing anomaly of single-wall carbon nanohorn aggregate

Abstract Newly found single-wall carbon nanohorns (SWNH) are synthesized by a CO 2 laser vaporization of a pure carbon target in an Ar gas. Purification method using centrifugal separation and structural features of aggregated form of SWNHs (SWNH aggregate) are studied in this Letter. Although the X-ray diffraction profile taken for highly purified SWNH aggregates does not show any sharp 002 diffraction corresponding to that of the ordinary graphite, a huge broad diffraction comes to be observed. This huge broad diffraction is well explained by the double layer diffraction model associated with two graphene sheets apart from 0.40 nm.

Adsorption and catalytic properties of single-wall carbon nanohorns

Abstract The recently discovered single-wall carbon nanohorns (SWNH) are found to adsorb liquid ethanol effectively. The amount of liquid ethanol adsorbed by SWNHs is about 3.5 times larger than that of a super high surface area carbon. It is also found that SWNHs act as a catalyst for the oxidation of ethanol into acetaldehyde. Their thermal stability in oxygen is also discussed.

Field emission properties of carbon nanohorn films

Self-supporting carbon films were prepared from a carbonaceous material, nanohorns. Nanohorns are spherical particles built of sharp cones of a single graphene sheet. The films show good field emission characteristics due to the sharp horn-like structures, in particular a low turn-on field and good long-term stability.

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.

Laser ablation of boron carbide : thin-film deposition and plume analysis

Abstract Thin films of boron carbide were formed by pulsed laser deposition at room temperature using a sintered B 4 C target. The nature of the particulates embedded in the films and the composition and bonding states of the films varied depending on the laser fluence. The formation of non-stoichiometric amorphous films appeared to be dominated by the arrival of energetic B and C atomic species with expansion velocities of 1–30 km/s and the stability of chemical bonds.

Adsorbate binding energy and adsorption capacity of xenon on carbon nanohorns

Xenon adsorption studies were performed on aggregates of single-walled carbon nanohorns (SWNHs). The SWNHs were prepared in two different batches; the adsorption results from the two batches were essentially identical. Isotherms were performed in two groups of experiments: low-coverage data were used to measure the binding energy of Xe on the SWNHs; and full isotherms were measured to determine specific surface areas. The binding energy value for Xe on the SWNHs was intermediate between those for Xe on single-walled carbon nanotubes, and that for Xe on graphite. The specific surface area of the SWNHs was of the order of 250 m2 g-1.

The Fraction of Sp3 Bonding in Carbon Thin Film Prepared Using Pulsed Laser Deposition

The fraction of sp3 bonding in carbon thin film prepared using pulsed laser deposition with a KrF excimer laser is investigated. The carbon film deposited at the laser fluence of 0.2 J/cm2 has a graphitic structure. It is suggested that the neutral species of C3 is effective in the formation of this structure. The C+ ion increases with a laser fluence higher than 0.9 J/cm2 and the sp3 bonding fraction in carbon film increases. The sp3 fraction in the film also increases with a negative bias to the substrate. The impact of energetic C+ species to the substrate is attributed to the formation of sp3 bonding.

Magnetic field enhanced growth of carbon cluster ions in the laser ablation plume of graphite

Time-of-flight mass spectrometric studies were carried out on neutral and positive ion clusters, composed of up to twenty carbon atoms, produced by Nd:YAG laser ablation of graphite in the presence of magnetic fields in the range of 0.03–0.10 T. The growth of larger carbon cluster ions with C11+ dominance in the laser-ionized ablation plume of graphite was found to be enhanced by the magnetic fieds. We believe that an enhancement of ion-neutral reactions due to an increase of ionic species, resulting from collisional ionization of neutral species through a confinement of electrons, leads to the growth of larger carbon cluster ions.

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.