H. Muramatsu

Nanotechnology: ‘Buckypaper’ from coaxial nanotubes

Double-walled carbon nanotubes are needed in a pure, highly crystalline form before features such as their electronic properties, thermal transport and mechanical behaviour can be investigated. Here we fabricate a paper-like material that consists of hexagonally packed bundles of clean, coaxial carbon nanotubes whose double walls vary little in diameter; it is prepared in high yields using chemical-vapour deposition with a conditioning catalyst and two-step purification. Our results will enable investigation of the physical properties of double-walled carbon nanotubes, which are predicted to be superior to those of both their single- and multiwalled relatives.

'Buckypaper' from coaxial nanotubes

Double-walled carbon nanotubes are needed in a pure, highly crystalline form before features such as their electronic properties, thermal transport and mechanical behaviour can be investigated. Here we fabricate a paper-like material that consists of hexagonally packed bundles of clean, coaxial carbon nanotubes whose double walls vary little in diameter; it is prepared in high yields using chemical-vapour deposition with a conditioning catalyst and two-step purification. Our results will enable investigation of the physical properties of double-walled carbon nanotubes, which are predicted to be superior to those of both their single- and multiwalled relatives.

Raman Spectroscopy Study of Isolated Double-Walled Carbon Nanotubes with Different Metallic and Semiconducting Configurations

A double-walled carbon nanotube (DWNT) provides the simplest system to study the interaction between concentric layers in carbon nanotubes. The inner and outer walls of a DWNT can be metallic (M) or semiconducting (S), and each of the four possible configurations (M@M, M@S, S@S, S@M) has different electronic properties. Here we report, for the first time, detailed Raman spectroscopy experiments carried out on individual DWNTs, where both concentric tubes are measured under resonance conditions, in order to understand the dependence of their electronic and optical properties according to their configuration. Interestingly, for the three DWNTs that were studied, the inner-outer tube distance (e.g., 0.31-0.33 nm) was less than the interlayer spacing in graphite. We believe these results have important implications in the fabrication of electronic devices using different types of S and M tubular interconnects.

Seasonal variations of 222Rn concentrations in the air of a tunnel located in Nagano city

The seasonal variation of 222Rn concentrations in the air of tunnels constructed during World War II at Nagano City has been investigated. The determination of 222Rn concentrations in tunnel air was performed using a solid-state nuclear track detector technique. The monthly radon concentrations changed smoothly, decreasing towards winter and increasing towards summer, and it was found that the concentrations strongly correlate with the temperature difference between the inside and the outside of the tunnel. In the innermost areas of the tunnel, the maximum concentration was observed in July, its value being about 6500 Bq m (-3). The concentrations of radon in the tunnel air decrease exponentially towards the openings of the tunnel, which indicates that the radon concentration in the tunnel is basically governed by diffusion and mixing of radon gas with air. These observations lead to the conclusion that the seasonal variation of the radon concentration in the tunnel air is mainly caused by a convection current due to a stack effect induced by the temperature difference between the tunnel air and the outside air.

An anticorrosive magnesium/carbon nanotube composite

Here, we report a drastically improved anticorrosive characteristic of magnesium alloy composites with the introduction of multiwalled carbon nanotubes. Highly depressed corrosion of nanotube-filled magnesium composite in salt water is due to the formation of stable oxide films along the grain boundaries of magnesium. Our results indicate that carbon nanotube acted as effective multifunctional filler to improve both mechanical and anticorrosive performances of magnesium alloy.

Double walled carbon nanotubes as ultrafast optical switches

Pristine and molybdenum filled double walled carbon nanotubes (DWNTs) suspended in D2O show excellent ultrafast optical switching properties investigated through femtosecond Z-scan and degenerate pump-probe method using 50 fs pulses with central photon energy of 1.57 eV. For pristine-DWNT, the two photon absorption coefficient, beta and nonlinear refraction coefficient, n2 are 4.9×10−8 cm/W, and 9.5×10−11 cm2/W, respectively, which yield one photon figure of merit, W=133 and two photon figure of merit, T=0.4. The degenerate pump-probe measurements show strong photoinduced bleaching with biexponential decay with time constants ~150 and 600 fs. ©2009 American Institute of Physics

Synthesis and Characterization of Selenium-Carbon Nanocables

In this letter, we report the synthesis and characterization of a novel Se-C hybrid nanostructure. X-ray diffraction data indicates a high degree of crystallinity for the nanostructured Se shell. High resolution transmission electron microscopy images show that the Se-C nanostructures consist of coaxial nanocables made of single wall carbon nanotubes, as the core, surrounded by a trigonal Selenium shell. Resonance Raman spectroscopy was used to access the properties of both the carbon nanotubes and selenium. The behavior of the radial breathing mode and the G-band indicates that the Se shell primarily covers semiconducting nanotubes. X-ray photoelectron spectroscopy show that the nanocables have a thin coverage of selenium oxide. We envisage that this system could be used in the fabrication of photonic devices as an interface between electronic and photonic materials.

Resonant Raman Study on Bulk and Isolated Graphitic Nanoribbons

Carbonaceous materials have been shown to graphitize up to different levels upon heat treatment, depending on the characteristics of their defects and the temperature reached during the heat treatment. In the literature there are reports on the annealing of materials, such as thin carbon films, graphite fibers, polyparaphenylene (PPP)-basedcarbons, cup-stacked carbon nanotubes, diamond-like carbon films, and more recently graphitic nanoribbons and flakes of highly oriented pyrolytic graphite (HOPG). The general behavior upon heat treatment is an increase of sp hybridization of the carbon atoms, an enlargement of the in-plane crystallite size (2D order of the

Production of endohedral 133Xe-fullerene by ion implantation

Ion implantation was applied to the production of endohedral 133Xe-fullerene. Using an isotope separator, 133Xe ions were implanted into a fullerene target of C60 and C70 produced by vacuum evaporation on a Ni backing. An HPLC analysis following dissolution of the fullerene targets in o-dichlorobenzene corroborated the formation of 133Xe@C60 and 133Xe@C70, showing a strong correlation between C60/C70 and 133Xe. The observed tailing following 133Xe peaks in the elution curves suggests a possibility of the isolation of endohedral 133Xe-fullerene from empty fullerene.

Induced transparency for gamma radiation via nuclear level mixing

A significant reduction of absorption of single gamma photons has been observed using the Mössbauer spectra of 57Fe in a FeCO3 crystal. The absorption deficit can be ascribed to partially destructive interference for absorption because of two indistinguishable absorption paths. The necessary coherence is created by means of level mixing produced by a suitable combination of a magnetic dipole and electric quadrupole interaction.