Riichiro Saito

Electronic structure of chiral graphene tubules

The electronic structure for graphenemonolayer tubules is predicted as a function of the diameter and helicity of the constituent graphene tubules. The calculated results show that approximately 1/3 of these tubules are a one‐dimensional metal which is stable against a Peierls distortion, and the other 2/3 are one‐dimensional semiconductors. The implications of these results are discussed.

Perspectives on Carbon Nanotubes and Graphene Raman Spectroscopy

Raman spectroscopy is here shown to provide a powerful tool to differentiate between two different sp(2) carbon nanostructures (carbon nanotubes and graphene) which have many properties in common and others that differ. Emphasis is given to the richness of both carbon nanostructures as prototype examples of nanostructured materials. A glimpse toward future developments in this field is presented.

RAMAN SPECTROSCOPY ON ISOLATED SINGLE WALL CARBON NANOTUBES

A review is presented on the resonance Raman spectra from one isolated single wall carbon nanotube. The reasons why it is possible to observe the spectrum from only one nanotube are given and the important structural information that is provided by single nanotube spectroscopy is discussed. Emphasis is given to the new physics revealed by the various phonon features found in the single nanotube spectra and their connection to spectra observed for single wall nanotube bundles. The implications of this work on single wall carbon nanotube research generally are also indicated.

Physics of carbon nanotubes

The fundamental relations governing the geometry of carbon nanotubes are reviewed, and explicit examples are presented. A framework is given for the symmetry properties of carbon nanotubes for both symmorphic and non-symmorphic tubules which have screw-axis symmetry. The implications of symmetry on the vibrational and electronic structure of 1D carbon nanotube systems are considered. The corresponding properties of double-wall nanotubes and arrays of nanotubes are also discussed.

Characterizing carbon nanotube samples with resonance Raman scattering

The basic concepts and characteristics of Raman spectra from carbon nanotubes (both isolated and bundled) are presented. The general characteristics of the radial breathing mode, tangential mode (G band), disorder-induced mode (D-band) and other Raman features are presented, with the focus directed toward their use for carbon nanotube characterization. Polarization analysis, surface enhanced Raman spectroscopy and complementary optical techniques are also discussed in terms of their advantages and limitations.

Raman spectroscopy of graphene and carbon nanotubes

This paper reviews progress that has been made in the use of Raman spectroscopy to study graphene and carbon nanotubes. These are two nanostructured forms of sp2 carbon materials that are of major current interest. These nanostructured materials have attracted particular attention because of their simplicity, small physical size and the exciting new science they have introduced. This review focuses on each of these materials systems individually and comparatively as prototype examples of nanostructured materials. In particular, this paper discusses the power of Raman spectroscopy as a probe and a characterization tool for sp2 carbon materials, with particular emphasis given to the field of photophysics. Some coverage is also given to the close relatives of these sp2 carbon materials, namely graphite, a three-dimensional (3D) material based on the AB stacking of individual graphene layers, and carbon nanoribbons, which are one-dimensional (1D) planar structures, where the width of the ribbon is on the nanometer length scale. Carbon nanoribbons differ from carbon nanotubes is that nanoribbons have edges, whereas nanotubes have terminations only at their two ends.

Berry's Phase and Absence of Back Scattering in Carbon Nanotubes

The absence of back scattering in carbon nanotubes is shown to be ascribed to Berrys phase which corresponds to a sign change of the wave function under a spin rotation of a neutrino-like particle in a two-dimensional graphite. Effects of trigonal warping of the bands appearing in a higher order k · p approximation are shown to give rise to a small probability of back scattering.

Anomalous potential barrier of double-wall carbon nanotube

Abstract The stable structure of a double-wall carbon nanotube (DWNT) is calculated for various chirality pairs, (n,m) – (n ′ ,m ′ ) , of inner and outer constituent layers. The stability of a double-wall nanotube is found not to depend on chirality, but rather on the diameter difference between inner and outer layers. However, the potential barrier for the relative displacement of the inner and outer nanotube layers is found to depend significantly on the chirality difference of the pair. Mechanical motions like a bolt–nut pair or discrete rotations can be expected for special pairs of chiralities in double-wall nanotubes, and these special motions will be important for nano-technology.

Defect characterization in graphene and carbon nanotubes using Raman spectroscopy

This review discusses advances that have been made in the study of defect-induced double-resonance processes in nanographite, graphene and carbon nanotubes, mostly coming from combining Raman spectroscopic experiments with microscopy studies and from the development of new theoretical models. The disorder-induced peak frequencies and intensities are discussed, with particular emphasis given to how the disorder-induced features evolve with increasing amounts of disorder. We address here two systems, ion-bombarded graphene and nanographite, where disorder is represented by point defects and boundaries, respectively. Raman spectroscopy is used to study the ‘atomic structure’ of the defect, making it possible, for example, to distinguish between zigzag and armchair edges, based on selection rules of phonon scattering. Finally, a different concept is discussed, involving the effect that defects have on the lineshape of Raman-allowed peaks, owing to local electron and phonon energy renormalization. Such effects can be observed by near-field optical measurements on the G′ feature for doped single-walled carbon nanotubes.

Electronic structure of double‐layer graphene tubules

The electronic structure of coaxial, graphene double‐layer tubules is predicted for various combinations of metallic and insulating constituent inner and outer monolayers, depending on the diameter and chirality of the tubule. For the examples chosen, some of the energy bands of the inner and outer tubules are coupled to each other by commensurate interlayer interactions. Nevertheless, because of symmetry, the energy bands of metallic monolayer tubules remain metallic even after interlayer interactions are considered. The possible implications of these results on molecular metal‐insulator devices are discussed.