Katsumi Tanigaki

Raman studies of carbon nanotubes

First- and second-order Raman spectra of closed-carbon nanostructures (nanotubes and nanoparticles) have been measured and compared to those of glassy carbon and highly oriented pyrolitic graphite. It is shown that this novel material has unique Raman spectral features which should be useful in its identification. Furthermore, the results indicate that nanotubes possess a high degree of crystalline order.

EXCITED-STATE PROPERTIES OF C60

Abstract The excited singlet-state and triplet-state properties of C 60 in toluene have been measured by picosecond and nanosecond laser-flash photolysis. S 1 has absorption maxima at 513, 759 and 885 nm with differential molar extinction coefficients (Δϵ S ) of 4500, 3700 and 6300 M −1 cm −1 , respectively. T 1 has absorption maxima at 457, 509 and 747 nm with Φ T Δϵ T =3400, 3000 and 15000 M −1 cm −1 , respectively. The lifetime of S 1 is 1.2 × 10 −9 s and that of T 1 is ⩾ 2.8 × 10 −4 s. T 1 also undergoes triplet—triplet annihilation with a rate constant ⩾ 4.8 × 10 9 M −1 s −1 .

Patterns in the bulk growth of carbon nanotubes

Abstract The growth of nanotubes in carbon arc plasma is described in detail. The structure and organization of the nanotube deposits observed by SEM and AFM reveal a fractal-like pattern of growth. One of the key units of growth appears to be the micro-bundle composed of neatly packed and aligned nanotubes. The micro-bundle together with the field and current might explain the high formation yield of nanotubes.

ANNEALING EFFECT ON CARBON NANOTUBES AN ESR STUDY

The effect of annealing on the electronic properties of nanotubes has been studied. The conduction ESR intensity is temperature-independent for both annealed and non-annealed nanotubes. However, the g-value of the nanotubes and its temperature dependence change significantly after annealing. These results suggest that some types of defects are present in the nanotubes which are then removed by the annealing process. The ESR studies of the annealed nanotubes indicate that the intrinsic electronic properties of nanotubes are quite different from those of graphite.

Crystal structure, bonding, and phase transition of the superconducting Na2CsC60 fulleride

The crystal structure of superconducting Na2CsC60 was studied by high-resolution powder neutron diffraction between 1.6 and 425 K. Contrary to the literature, the structure at low temperatures is primitive cubic [See equation in the PDF file], isostructural with pristine C60. Anticlockwise rotation of the C60 units by 98� about [111] allows simultaneous optimization of C60-C60 and alkali-fulleride interactions. Optimal Na+-C603- coordination is achieved with each sodium ion located above one hexagon face and three hexagon-hexagon fusions of neighboring fulleride ions (coordination number 12). Reduction of the C60 molecule lengthens the hexagon-hexagon fusions and shortens the pentagon-hexagon fusions (to ∼1.43 angstroms). On heating, Na2CsC60 undergoes a phase transition to a face-centered-cubic [See equation in the PDF file] phase, best modeled as containing quasi-spherical C603- ions. The modified structure and intermolecular potential provide an additional dimension to the behavior of superconducting fullerides and should sensitively affect their electronic and conducting properties.

The mechanistics of fullerene formation

Abstract Through 12 C/ 13 C isotope scrambling measurements, the mechanistics of the initial stages of fullerene formation are unambiguously clarified. The distribution of 13 C among the C 60 molecules follows exactly Poisson statistics for every ratio of unmixed 12 C and 13 C in the feed of these arc plasma experiments. Furthermore no magic mass numbers are observed. This totally random scrambling shows not only that C 60 is grown in the plasma but also that the starting point is atomic carbon vapour.

Crystal growth of C60 thin films on layered substrates

The process of the C60 thin film crystal growth on layered materials such as MoS2 and mica is studied in detail with a combination of atomic force microscopy (AFM) and reflection high‐energy electron diffractometry, and is compared to that on alkali‐halide (NaCl) substrates. AFM shows that a single crystal containing triangle‐shaped grains of 1–2 μm size with a (111) surface terrace is grown on the MoS2 substrate over a large area through a layer‐by‐layer process, while the grains on mica are 200–400 nm in size and distribute with some disorder in the orientation. The epitaxial characteristics of the C60 crystal growth on these layered substrates are discussed in comparison with that on alkali‐halides.

Picosecond and nanosecond studies of the excited state properties of C70

Abstract The excited singlet and triplet state properties of C 70 in toluene have been measured by picosecond and nanosecond laser flash photolysis. Between 450 and 950 nm, S 1 has a maximum at 675 nm with a differential molar absorption coefficient of 3800 M −1 cm −1 while T 1 has a maximum at 579 nm where the product of the triplet quantum yield and the differential molar absorption coefficient is 1800 M −1 cm −1 . S 1 decays with a lifetime of 670 ps while the T 1 lifetime (> 200 μs) is shortened by diffusion limited triplet—triplet annihilation (≈ 8 × 10 9 M −1 cm −1 ).

Electron spin resonance of carbon nanotubes

Abstract The electron spin resonance (ESR) of carbon nanotubes at various stages of purification have been measured between 4 and 296 K. The conduction electron spin resonance is identified and the results imply that metallic and/or narrow gap semiconducting nanotubes are actually present as predicted by theory. From the temperature dependences of the ESR intensity, linewidth and g -value, the electronic properties of the observed nanotubes are found to be similar to those of graphite.

Crystal growth and structure of fullerene thin films

Abstract The growth and structure of C60 and C70 thin film crystals on alkali halide and layered material substrates are described. It is demonstrated that fairly large grains can be grown with the specific orientation to the substrate lattice, especially on layered substrates. The defects in the films fabricated on alkali halides are studied by transmission electron microscopy in detail. The growth mechanism of C60 and C70 thin films on these substrates is discussed on a basis of reflection high-energy electron diffraction and atomic force microscopy observation and compared with that on other substrates. The unusual growth characteristics of C60 and C70 are discussed and compared with those encountered in thin films of conventional van der Waals crystals.