Y. Nishina

Resonance Raman scattering and diameter-dependent electronic states in single-wall carbon nanotubes

Abstract Resonance Raman scattering has been measured with laser wavelengths of 450–800 nm on single-wall carbon nanotubes with diameters of 1.1–1.4 nm. The observed intensity enhancements of the Raman peaks reveal resonance electronic transitions at 700, 750 and 780 nm for nanotubes with energies of the breathing mode at 184, 171 and 162 cm −1 , respectively. Calculations show that these nanotubes have diameters of 1.21, 1.29 and 1.37 nm, respectively, and exhibit metallic electronic structures produced by the zone-folding effect. It is shown that metallic and semiconducting nanotubes can be distinguished by Raman scattering.

Fullerene (C60) adsorption on Si surfaces

Abstract Field ion-scanning tunneling microscopy (FI-STM) was employed to characterize the adsorption behavior of fullerenes on the Si(111)7 × 7 and Si(100)2 × 1 surfaces. On the Si(111)7 × 7 surface, C 60 adsorbs preferentially on the faulted half of the 7 × 7 unit and stays still without rotation at room temperature, implying a reasonably strong interaction with the Si substrate. The C 60 molecules reside stably also at room temperature without rotation on the Si(100) surface. For the first and second layers on the Si(100) surface, only local ordering of square and quasi-hexagonal patterns was observed. The orderly Stranski-Krastanov mode island formation with hexagonal packing was observed above the third layer on the Si(100)2 × 1 surface.

Resonant Raman scattering from single-walled nanotubes of small diameters

Abstract In this report, we present a novel purification method of single-walled nanotubes (SWNTs) including their hydrothermal treatment by hydrothermally initiated dynamic extraction (HIDE) process. The purity of the SWNTs increases at each step of the integrated purification process (HIDE–extraction of fullerenes–oxidation–dissolution of metal particles) and the purity of the final product is over 95 wt.%. Furthermore, in order to study the detailed characterization of SWNTs, Resonant Raman scattering measurements were performed for the purified SWNTs.

Geometry of metallofullerenes adsorbed on the Si (100) 2×1 surface studied by scanning tunneling microscopy

Abstract Sc n C 74 ( n =1, 2) and Sc 2 C 84 metallofullerenes (MF), adsorbed on the Si (100) 2×1 surface were studied by scanning tunneling microscopy. The MF molecule images were spherical and randomly distributed, similar to those of C 60 , C 70 and C 84 , but were slightly larger than those of the pristine fullerenes. These results suggest that the Sc atoms were trapped inside fullerenes cages, with a significant charge transfer from the metal atom.

FI-STM study of the structure of Sc-encapsulated fullerenes

Abstract We report our recent study of the electronic and geometric structure of Sc-encapsulated fullerenes (metallofullerenes) ScC 74 , Sc 2 C 74 , and Sc 2 C 84 adsorption on the Si(100)2×1 surface with field ion scanning tunneling microscopy. A comparison with the pristine C 60 and C 84 confirmed the assumption that the Sc atoms are encapsulated inside the carbon cage. The charge transfer from the Sc atoms to the carbon cage is evidenced. The presented results also show that these metallofullerenes do not prefer to form dimers or trimers.

Thermal stability of fullerene (C70) on the Si(100)2×1 surface studied with FI-STM

Abstract We have studied the thermal stability of fullerene C 70 adsorbed on the Si(100)2×1 surface with the field ion-scanning tunneling microscope. The results show that the first layer of C 70 adsorbed considerably strongly due to the existence of Si dangling bonds on the surface. The first layer passivated the surface efficiently so that the multilayer crystalline film could be grown as close-packing array. The C 70 above the first layer can be easily desorbed at temperatures above approximately 250°C, which is similar to that of bulk C 70 . In contrast to that, the first layer remains stable without any evidence of cage breaking or reordering until at temperatures above 1000°C, resulting in well-ordered islands: β-SiC(100)3×2 surface, according to our STM observations. The present work reveals a novel fullerene property on the Si(100)2×1 surface.

Stability of SxSey ring clusters studied by Raman scattering

Abstract The compound clusters of S x Se y have been crystallized by vacuum distillation. The raman scattering was measured from samples deposited along the region of the temperature gradient. The results show a systematic shift of the spectral peaks along the gradient, indicating that the S x Se x − x with the larger values of x crystallized at lower temperatures. The crystal is in a rhombic structure which is not reported in the literature. Our experiments with liquid chromatography show that they are not stable in solution and are difficult to separate into single phases in solid form.

Resonant Raman scattering from single-wall nanotubes of diameters between 1.1 nm and 1.4 nm

Resonant Raman scattering has been measured on single-wall nanotubes of diameters from 1.1 nm to 1.4 nm. The spectra show groups of peaks near 180 cm−1, 360 cm−1, 440 cm−1, 600 cm−1, 720 cm−1, 880 cm−1, 1070 cm−1, 1320 cm−1 and 1580 cm−1. Observed resonant intensity enhancements show that peaks in each group belong to the same vibrational mode of different diameters, and hence different dependencies on the incident photon energy. These measurements, therefore, determine the diameter dependent vibrational modes and zone-folded electronic structures, yielding mode assignments that groups of peaks near 600 cm−1, 859 cm−1, 1070 cm−1 and 1580 cm−1 belong to optical modes and the rest to acoustic ones in graphite in the zone-folding scheme. Peaks near 360 cm−1, 720 cm−1 and 880 cm−1 are harmonics of 180 cm−1 or 440 cm−1.

Resonant Raman scattering and the zone-folding effects in single-wall nanotubes

Raman scatterings from optical phonons in single-wall nanotubes of mean radius between 0.55 nm and 1.0 have been measured in the wavelength of incident laser beam between 450 nm and 800 nm. The observed multiple splittings of optical phonon peaks and their resonant enhancement at the wavelength in the vicinity of 690 nm show the definite presence of zone-folding effect in both phonon and electronic systems. The results are well accounted for by the two-dimensional graphite dispersion relations. These measurements, therefore, provide direct experimental evidences on the diameter-dependent properties induced by the cylindrical symmetry of nanotubes.

Estimation of the mechanical strength of nanotube bundle

Mechanical strength of a nanotube bundle has been measured by using quartz glass enclosed-purified SWNTs as the specimen. These specimens were prepared by fast stretching quartz glass tube that contained purified nanotube bundles, at temperatures ranging from 900 to 1490 °C. The maximum average critical load was 42.3 kg/mm2 for the specimen prepared at 900 °C. However, at temperatures higher than 900 °C, the critical load value decreased and became almost equal to that of quartz glass at 1490 °C. It was believed that the decrease in the critical load value at temperatures higher than 900 °C was due to the partial conversion of nanotubes into amorphous carbon. Since the cross-sectional area used in arriving at the critical load value was that of nanotube and the quartz glass, the cross-sectional area ratio of the quartz to that of the nanotube suggested that the mechanical strength of nanotube would be two orders of magnitude higher than the value reported here.