Tadanobu Yoshikawa

Growth and structure of graphitic tubules and polyhedral particles in arc-discharge

Abstract Graphite tubules and polyhedral particles grown on an electrode surface of arc-discharge have been studied by electron microscopy. The observations of their structures and morphologies lead to a growth model in which ion bombardment and high electric field at the tip of a tubule play crucial roles for the tube growth.

Carbon nanocapsules encaging metals and carbides

Abstract Experiments aimed at the encapsulation of foreign materials within hollow graphitic cage were carried out for a series of lanthanide elements and for iron group metals (Fe, Co, Ni). A carbon arc reactor was used for the synthesis, and the products formed on the cathode were investigated by transmission electron microscopy. The lanthanides were encapsulated in the form of dicarbides within multilayered polyhedral carbon cages. For iron group metals, particles of both a carbide phase (M 3 C, M = Fe, Co, Ni) and also a metallic phase (α-Fe, γ-Fe; hcp-Co, fcc-Co; fcc-Ni) were encapsulated in graphitic carbon. Based on their morphology and structure, growth mechanism is proposed. Especially for Ni, exotic carbon materials with hollow structures, bamboo-shaped tubes and nanochains as well as single-layered nanotubes, were discovered.

Bamboo-shaped carbon tube filled partially with nickel

Abstract An encapsulation experiment of nickel metal within hollow graphitic cages was carried out by using a carbon arc reactor. Among the carbonaceous materials formed on an electrode surface, carbon tubes with special features of bamboo-like structure, i.e., consisting of a series of long hollow compartments, were found by electron microscopy. The diameter of the tubes was about 30 nm and the length on the order of a few μm. The ends of the tubes were capped with needle-shaped nickel particles.

Iron particles nesting in carbon cages grown by arc discharge

Fine particles of iron and iron carbide wrapped in multilayered graphitic sheets, which were synthesized by arc discharge of carbon rods containing iron oxide (Fe2O3), were studied by transmission electron microscopy. The size of the wrapped particles was typically in the range 20–200 nm. Two kinds of nested materials were found; one was α-Fe and the other, Fe3C (cementite).

Single-Wall Carbon Nanotubes Growing Radially from Ni Fine Particles Formed by Arc Evaporation

DC arc evaporation of nickel-graphite composite in helium atmosphere produces single-wall (SW) nanotubes. Electron microscopy examination of carbonaceous soot synthesized by this method revealed that the SW tubes grew radially from ultrafine nickel particles, and that they were found exclusively in soot material formed on the surface of a sluglike deposit grown on the end of a cathode.

Cobalt particles wrapped in graphitic carbon prepared by an arc discharge method

Fine particles of cobalt and cobalt carbide nesting in multilayered graphitic sheets, which were synthesized by an electric arc discharge of carbon rods containing cobalt oxide (CoO), were studied by transmission electron microscopy, including microdiffraction and energy dispersive x‐ray analysis. The size of the wrapped particles was typically in a range from 50 to 200 nm. Three phases of nested materials, hcp(α)‐Co, fcc(β)‐Co, and Co3C, were identified.

Magnetic Properties of Iron in Nanocapsules

We have studied the magnetic properties of fine particles of iron and iron carbide nested in carbon cages (nanocapsules), which were synthesized by arc discharge of carbon rods. It is clarified by Mossbauer spectroscopy and thermomagnetic ( M-T ) curve that these particles consist of α-Fe, γ-Fe and Fe3C. Their coercive force is larger than that of bulk α-iron, being ascribed to the small particle size observed by high-resolution (HR) transmission electron microscopy (TEM).

Synthesis of Sc15C19 Crystallites Encapsulated in Carbon Nanocapsules by Arc Evaporation of Sc-C Composite

Crystallites of scandium carbides nesting in multilayered, polyhedral graphitic cages (nanocapsules) were produced by evaporating a scandium-graphite composite rod by electric arc discharge in helium gas. The composite particles were characterized by analytical electron microscopy and X-ray diffraction. The encapsulated scandium carbide was identified to be Sc15C19, instead of dicarbide RC2 (R represents rare-earth elements) which was the form of carbide commonly found for other rare-earth elements entrapped in nanocapsules. The size of the capsules ranged from about 10 to 100 nm. Morphological features of the outer graphitic carbon, multilayered and polyhedral, were quite similar to those previously discovered for the capsules protecting RC2 (R=Y, La, Ce,..., Lu).

Electron microscopy of fullerene thin films grown on solid surfaces

C 60 and C 70 fullerenes were vacuum deposited onto cleaved surfaces of NaCl and mica. Both C 60 and C 70 formed islands during a first stage of growth, indicative of the Volmer-Weber growth mode. The crystal structure of C 60 films on NaCl was f.c.c. with abundant lamella twinning and stacking faults. The structure of C 70 films on NaCl was also predominantly f.c.c. when the substrate was held above about 370 K. The films on NaCl were polycrystalline. On mica, single-crystal epitaxial films were formed for both C 60 and C 70 with the orientation relationship (111)[110] C60orC70 ∥(001)[100] mica