Yositaka Yosida

Variable range hopping conduction in bulk samples composed of single-walled carbon nanotubes

An experimental study of the electrical transport phenomena in magnetic fields H up to 15 T in pressed samples of a porous system composed of single-walled carbon nanotubes in the temperature range 1.39 K <T<300 K is reported. Below 60 K, the exp[1/T1/4] temperature dependence of the direct current electrical resistance R(T,0) is found. Low-field transverse magnetoresistance (MR), [R(T,H)−R(T,0)]/R(T,0), below 60 K is negative and is discussed in terms of a quantum interference effect on a three-dimensional variable range hopping (3D–VRH) mechanism. Based on the results of R(T,0) and MR, we propose 3D–VRH conduction within the nanotube bundles (intrabundle hopping) or between the nanotube bundles (interbundle hopping) through their contacts.

High-temperature shrinkage of single-walled carbon nanotube bundles up to 1600 K

An experimental study of x-ray diffraction of single-walled carbon nanotube (SWNT) bundles in the temperature range from 290 to 1600 K is reported. The lattice constant (L0) of a close-packed trigonal arrangement of SWNTs in the bundles shrank over the entire temperature range. The hysteretic temperature dependence of L0 was observed and discussed in terms of desorption of molecules from the bundle surface and of a magnetic phase transition of ferromagnetic metal catalyst particles. The coefficient of volume thermal expansion for the bundles is suggested to be negative over the measured temperature range by assuming that the tube-axis expansion is similar to the in-plane expansion for graphite.

Synthesis, identification, and growth mechanism of Fe, Ni, and Co crystals encapsulated in multiwalled carbon nanocages

Nanometer size crystalline particles of α‐Fe, γ‐Fe, Ni, β‐Co, and Co3C encapsulated in multiwalled carbon cages are synthesized by a standard dc arc evaporation of composite anodes containing 10–15 wt. % each of the metals or their compounds. The typical particle size is ∼10 nm. Elemental analysis is made by x‐ray energy dispersive spectroscopy. The spectra show only the peaks associated with the respective metal and carbon. The stoichiometry and phase of the crystals are assigned from the characteristic lattice spacings obtained by high‐resolution transmission electron microscopy and x‐ray diffractometry. Particle size distribution is obtained from a statistical survey of electron micrographs. A statistical growth model is adequate for explaining the crystalline particle size distribution of the encapsulated crystals consisting of α‐Fe and γ‐Fe smaller than 15 nm. Significant deviation from the model is found for the encapsulated crystals consisting of α‐Fe and γ‐Fe larger than 15 nm, those of Ni larger ...

Superconducting single crystals of TaC encapsulated in carbon nanotubes

The synthesis and electron microscopic studies of TaC single crystals encapsulated in carbon nanotubes are reported. The crystal structure is the NaCl type with the lattice parameter a0=4.455±0.003 A. The typical crystalline size is ∼7 nm. The epitaxial growth of carbon nanotube on the {100} plane of the TaC single crystal is observed. The statistical growth model is adequate for explaining the crystalline‐particle size distribution of the encapsulated crystals. Magnetic susceptibility measurements show a superconducting transition at 10.0 K, which is the expected critical temperature for the bulk TaC having the highest carbon composition.

Synthesis of CeC2 crystals encapsulated within gigantic super fullerenes

A new synthesis of nanometer‐sized crystals encapsulated within gigantic super fullerenes by dc arc evaporation of composite carbon rods containing ∼3 wt % CeO2 is reported. Transmission electron microscopy showed the crystals CeC2 with the CaC2 type structure.

Variable range hopping conduction in multiwalled carbon nanotubes

An experimental study of electrical transport phenomena in magnetic-fields H up to 5 T in pressed samples of a porous system composed of multiwalled carbon nanotubes is reported. The exp[(T0/T)1/4] temperature dependence in the zero-field dc electrical resistance R(0) is found at low temperatures. Below 50 K, transverse magnetoresistance (MR), [R(H)−R(0)]/R(0), is negative. In the weak-field region (H<0.1 T), the negative MR is quadratic in H, and becomes linear in the field range 0.1–0.3 T. The linear and negative MR shows T−0.65±0.06 temperature dependence. The temperature dependence of R(0) is described in terms of Mott’s law for three-dimensional variable range hopping (3D VRH) conduction. The low-field magnetotransport features support a predicted quantum interference effect on 3D VRH conduction.

Growth of face‐centered‐cubic single crystals of C60 from boiling benzene

We report a new synthesis technique of face‐centered‐cubic single crystals of C60 with a macroscopic dimension of 0.3×0.3×0.5 mm3. The crystals are grown from a benzene heated above 80 °C. The mosaic spread of the crystal is about 0.5°.

A new type of ultrafine particles: Rare earth dicarbide crystals encapsulated in carbon nanocages

Abstract A synthesis of rare earth dicarbides crystals (RC2; R  La, Ce, Pr, Nd, Gd, Tb, Dy, Ho, Er, Tm, and Lu) encapsulated in carbon nanocages or nanotubes by a standard DC arc discharge experiment is reported. The stoichiometry and phase of the encapsulated crystals were assigned from the characteristic lattice spacings obtained by high-resolution transmission electron microscopy and X-ray diffractometry. Size distribution for the encapsulated crystals and carbon nanocages is obtained from a statistical survey of electron micrographs. The size distribution is successfully explained in terms of a statistical growth model. It has been pointed out that an eutectic reaction for the RC2C systems during DC arc discharge gives rise the encapsulation compounds.

Stage Stability and Stage Transformation of SbCl5-Graphite Intercalation Compounds

Stage stability and stage transition in SbCl 5 -graphite intercalation compounds have been investigated by use of the in situ X-ray diffraction technique. A precise isotherm of stage n has been determined for stages up to 6. The stage-stability range in chemical potential Δµ( n ) is evaluated from the isotherm. A comparison of Δµ( n ) with the theoretical results of the electrostatic interlayer interaction model gives the ionicity of 1/4< f <1/2 for SbCl 5 -graphite intercalation compounds. A very narrow two-phase region is observed in the stage transition region, in which two single-stage phases coexist in thermal equilibrium.

High-Resolution Electron Microscopic Study of the Growth Mechanism of Gigantic Tubular Super-Fullerenes

Abstract I report a new synthesis of gigantic tubular super-fullerenes : tubular carbon cages with shell structure showing maximum sizes of ∼ 10 μ m in length and ∼ 30 nm in the outermost diameter. For the innermost tubule a similar diameter to C60 is found occasionally. Direct evidence of coaxial tubules capped on the ends is presented by high-resolution electron microscopy. I propose a new growth model: growth of the tubular super-fullerenes initiates at the outermost cage and proceeds towards the core. I would like to thank Oosuna, T. for obtaining TEM images and Shida, S. for preparing photographs.