Direct observation of Tomonaga-Luttinger-liquid state in carbon nanotubes at low temperatures.

The electronic transport properties of conventional three-dimensional metals are successfully described by Fermi-liquid theory. But when the dimensionality of such a system is reduced to one, the Fermi-liquid state becomes unstable to Coulomb interactions, and the conduction electrons should instead behave according to Tomonaga-Luttinger-liquid (TLL) theory. Such a state reveals itself through interaction-dependent anomalous exponents in the correlation functions, density of states and momentum distribution of the electrons. Metallic single-walled carbon nanotubes (SWNTs) are considered to be ideal one-dimensional systems for realizing TLL states. Indeed, the results of transport measurements on metal-SWNT and SWNT-SWNT junctions have been attributed to the effects of tunnelling into or between TLLs, although there remains some ambiguity in these interpretations. Direct observations of the electronic states in SWNTs are therefore needed to resolve these uncertainties. Here we report angle-integrated photoemission measurements of SWNTs. Our results reveal an oscillation in the pi-electron density of states owing to one-dimensional van Hove singularities, confirming the one-dimensional nature of the valence band. The spectral function and intensities at the Fermi level both exhibit power-law behaviour (with almost identical exponents) in good agreement with theoretical predictions for the TLL state in SWNTs.

Purification of single-walled carbon nanotubes generated in helium ambient gas atmosphere with arc-burning apparatus by utilizing mono-dispersion technique.

Raw soot containing single-walled carbon nanotubes (SWNTs), generated with arc-burning apparatus in helium gas atmosphere, was dispersed in 1 wt% sodium cholate (SC)/D2O solution. This solution was then used for successive ultracentrifugation procedure. After ultracentrifugation, UV-VIS and Raman spectra of the supernatant of the solution were investigated. The obtained spectra demonstrate that SWNTs generated with arc-burning method can be well mono-dispersed in surfactant solution, even though large amount of carbonaceous impurities were also included in the raw soot. This finding indicates that mono-dispersion technique can also be applied as the purification procedure for the raw soot including SWNTs of poor quality. Also, it was found that, although the yield of empty fullerenes (as byproduct) decreases as the helium gas pressure increases, that of SWNTs still increases, and shows a maximum at higher pressure. The diameter distribution of semi-conductive SWNTs included in the soot was compared with that generated in nitrogen atmosphere, based on the experimental results obtained by utilizing fluorescence mapping technique to mono-dispersed solutions.

Synthesis of superparamagnetic carbon nanotubes immobilized Pt and Pd pincer complexes: highly active and selective catalysts towards cyclohexane oxidation with dioxygen.

Single-walled carbon nanotubes (SWNTs) with Ni/Co have been prepared using an arc discharge technique and Ni/Co-carbon composite rods in an inert atmosphere and were surface modified using 3-aminophenyl trimethoxysilane. These NH2-functionalized magnetic carbon nanotubes have been used as a novel support for Pd((II)) and Pt((II)) pincer complexes immobilized as magnetic nano-catalysts. The morphology of the support and the catalysts have been characterized by IR, EPR, SEM, TGA, TEM, XRD, AAS and EDS analysis. These magnetic nano-catalysts have been tested on the industrially important cyclohexane (Cy-hx) oxidation with O2 and significantly high TONs of 1678 to 1946 were achieved under solvent free and relatively mild conditions. The SWNTs/Pd catalyst provided the best conversion, 22.7%, but the SWNTs/Pt system also provided a good conversion of 20.7%.

Water-filled single-wall carbon nanotubes as molecular nanovalves.

It is known that at low temperature, water inside single-wall carbon nanotubes (water-SWNTs) undergoes a structural transition to form tube-like solid structures. The resulting ice NTs are hollow cylinders with diameters comparable to those of typical gas molecules. Hence, the gas-adsorption properties of ice- and water-SWNTs are of interest. Here, we carry out the first systematic investigation into the stability of water-SWNTs in various gas atmospheres below 0.1 MPa by means of electrical resistance, X-ray diffraction, NMR measurements and molecular dynamics calculations. It is found that the resistivity of water-SWNTs exhibits a significant increase in gas atmospheres below a critical temperature Tc, at which a particular type of atmospheric gas molecule enters the SWNTs in an on-off fashion. On the basis of this phenomenon, it is proposed that water-SWNTs can be used to fabricate a new type of molecular nanovalve.