Y. Maniwa

Optical properties of single-wall carbon nanotubes

Four kinds of single-wall carbon nanotubes (SWNTs) with different diameter distribution have been synthesized and optical absorption spectra have been measured. Three large absorption bands due to the optical transitions between spike-like density of states, characteristics of SWNTs, were observed from infrared to visible region. Comparing with the calculated energy band, it has been concluded that the first and the second lowest absorption bands are due to the optical transitions between spikes in semiconductor phases and the third one is due to that in metallic phases. Absorption Peaks sensitively shifted to higher energy side with decreasing tube diameters as the band calculation predicted. Resonance Raman spectra were also measured using various laser lines. When the excitation is in an energy region corresponding to the absorption band of metallic phase, spectra have shown Breit-Wigner-Fano line shape, which is a sign of metallic phase. Using these results, we can easily characterize SWNTs from the optical absorption spectra without Raman measurements and transmission electron microscope observations.

Gas adsorption in the inside and outside of single-walled carbon nanotubes

Abstract Adsorption properties of nitrogen and oxygen gases in single-walled carbon nanotube (SWNT) bundles were investigated by the isotherm and X-ray diffraction (XRD) studies. In the as-grown (AG) nanotubes with close-ended caps, both the gases are adsorbed only in the interstitial channels between triangular packed nanotubes. In the heat-treated (HT) nanotubes with open ends, the gases are adsorbed first in the inside of tubes, and next in the interstitial channels. In each site, gases can be adsorbed with the stoichiometory of C 20 N 2 or C 20 O 2 as a monolayer. These results indicate that the inside of nanotube has strong affinity for gas adsorption than the interstitial channels of bundles.

High-yield fullerene encapsulation in single-wall carbon nanotubes

We have successfully synthesized single-wall carbon nanotubes encapsulating specified fullerenes (peapods) in high yield using a sublimation method. Side and section images by HRTEM indicate that almost all nanotubes are filled with high-density fullerene chains. We measured Raman spectra to estimate macroscopic yield. The observed Raman intensity of C 70 molecules in the C 70 -peapods is 1/10 of that in C 70 film, which indicates a filling rate of C 70 to be higher than 26 %. In the case of C 60 -peapods, Raman spectrum has changed rapidly by laser irradiation. Since the final spectrum at room temperature is similar to that of the orthorhombic polymer phase, a formation of one-dimensional photopolymers inside SWNTs is suggested.

Anomaly of X-ray Diffraction Profile in Single-Walled Carbon Nanotubes

X-ray diffraction (XRD) studies on single-walled carbon nanotube (SWNT) samples prepared by the arc-discharge method were reported. The XRD profile was basically explained to be a result of triangular packing of SWNTs with a lattice constant of 17.1 A and an average nanotube radius of 7.1 A. We found an anomalous change in XRD profiles before and after heat-treatment of the SWNT samples in air at ~350°C. Combined with gravimetric measurements and resistivity measurements, a detailed simulation of the XRD profiles showed that air (oxygen, and/or nitrogen and/or water) can be condensed inside the SWNTs.

C70 Molecular Stumbling inside Single-Walled Carbon Nanotubes

We report the structural study of C 70 -one-dimensional (1D) crystal formed inside single-walled carbon nanotubes (SWNTs). X-ray diffraction measurements were performed between 100 K and 999 K on C...

Gas Storage in Single-Walled Carbon Nanotubes

Abstract X-ray diffraction (XRD) and electrical resistance measurement on single-walled carbon nan-otube (SWNT) samples prepared by the arc-discharge method are reported. The XRD profile of heat-treated sample indicated that air (oxygen, and/or nitrogen and/or water) can be condensed inside the SWNTs. We also found that the electrical resistance of SWNT soot is significantly affected by exposing to the oxygen gas and humid air.

Resonance Raman Scattering of Br2 Doped Single-Walled Carbon Nanotube Bundles

Abstract We have measured Raman spectra of bromine doped single-walled carbon nanotubes (SWNTs) using various laser lines to clarify the electronic states of the doped SWNT. In the case of evacuated sample after full doping, two breathing mode peaks were observed simultaneously by visible laser excitations. We assigned the higher frequency peak to the doped SWNT bundles, and the other peak to the undoped portions in the sample. Intensity ratio between them decreased with decreasing excitation energy, and in the infrared region, the breathing mode band of the doped bundle was not observed. These results can be explained by a simple rigid band model.

Magnetic properties of K-absorbing zeolite LTA

Abstract We report 29 Si-NMR and magnetic susceptibility measurements in K-absorbing zeolite LTA, K x /Na 12 y K 12(1− y ) –Si 12 Ai 12 O 48 where x =4.5 and 6, and y =0–1. It was confirmed that the ferromagnetic transition occurs in the bulk of K 4.5 /K 12 -Si 12 Ai 12 O 48 sample, and that the magnetic transition is very sensitive to Na content, y . It was also shown that the localized magnetic moments are confined to the cavities in the (–Si–O–Al–O–) zeolite framework.

NMR studies on antiferromagnetism in alkali-electro-sodalite

Abstract We report 27 Al-NMR and DC-magnetic susceptibility measurements on recently discovered alkali-electro-sodalite (AES, A=Sodium, Potassium). AES is known to be a Mott insulator consisting of a body-centered-cubic lattice of F -centers. 27 Al-NMR measurements demonstrate that SES (S=Sodium) and PES (P=Potassium) undergo an antiferromagnetic transition around T N ∼48 and 70 K, respectively. Magnetic properties, especially on the temperature dependence of the susceptibility, seem to be quite sensitive to the size of the F -centers.

Bundle Effects of Single-Wall Carbon Nanotubes

To see the bundle effects on the electronic and the vibrational properties of single-wall carbon nanotubes (SWNTs), we have measured the resonance Raman scattering of isolated SWNTs and thick bundles. For the measurements of the isolated SWNTs, we used an evacuated sample after bromine doping. A broad and asymmetric tangential mode band, which is a sign of the resonance of the metallic SWNTs and can be fitted by a Fano line shape, is not observed in the isolated SWNTs. This suggests the inter-tube interactions play an important role to the Fano interference. On the other hand, the purified sample shows very thick acquired bundles. We observed 4% higher breathing mode frequencies than in the pristine sample. Further, in the case of multi-wall nanotubes, we observed 5% higher breathing mode frequencies than the SWNTs. These results can be explained by the interlayer interactions.