Masaru Tachibana

Raman spectra of carbon nanowalls grown by plasma-enhanced chemical vapor deposition

Raman spectra of carbon nanowalls (CNWs) grown using dc plasma-enhanced chemical vapor deposition were analyzed. The Raman spectra of CNWs exhibited G and D bands at ∼1580 and ∼1350cm−1, respectively. It is found that the bandwidth of the G band is relatively narrow, even when the peak intensity ratio of D band to G band is significantly high. This spectral feature of CNWs is distinguished from those of typical graphitelike carbons reported so far. From the comparison of these spectral features, it is shown that CNWs are composed of small crystallites with a high degree of graphitization.

Nanographite domains in carbon nanowalls

The nanostructure of carbon nanowalls (CNWs), composed of a stack of several graphite sheets, was investigated by transmission electron microscopy. Our detailed analysis revealed that numerous graphite regions with an average size of about 20 nm were formed in the CNWs. The formation of these regions originates from the introduction of lattice defects such as dislocations and the slight rotation of the graphite sheets. On this basis, it is concluded that the graphite regions, so-called “nanographite domains,” are the constitutional units of the CNWs.

Photo-assisted growth and polymerization of C60 ‘nano’whiskers

Abstract C60 nanowhiskers are grown by a liquid–liquid interfacial precipitation method at 21 °C. It is found that the growth of the nanowhiskers is promoted under illumination even with weak room light (fluorescent light). The maximum of their lengths exceeds 1 mm where the diameter is about 250 nm. From Raman scattering measurements, it is shown that C60 molecules in the pristine nanowhiskers are bonded by weak van der Waals forces. The nanowhiskers is easily polymerized under irradiation with laser light. The cross section for this photo-polymerization is much large compared with that for intrinsic C60 bulk crystals.

Carbon nanowalls as platinum support for fuel cells

Platinum catalysts supported on carbon nanowalls (Pt/CNW) were prepared by a solution-reduction method. It is shown that Pt nanoparticles with a mean diameter of 3.5 nm are well dispersed along domain boundaries in each CNW. In addition, it is shown that the Pt/CNW has high electrochemical active surface area and utilization, comparable to those for commercially available T–Pt/CB with good performance. Such high electrocatalytic activity could be attributed to the high electric conductivity of CNW and the improvement of electronic properties of Pt nanoparticles on the domain boundaries, in addition to the high dispersion of Pt particles.

Identification of dislocations in large tetragonal hen egg-white lysozyme crystals by synchrotron white-beam topography.

Large tetragonal hen egg-white (HEW) lysozyme crystals have been grown by a salt concentration-gradient method. The grown crystals, of thicknesses greater than 1.5 mm, were observed by means of X-ray topography using white-beam synchrotron radiation. Line contrasts clearly appeared on the Laue topographs. Extinction of the line images was observed in specific reflections. These results mean that the observed lines correspond to dislocation images. From the extinction criterion it is shown that the predominant dislocations are of screw character with <110> Burgers vectors. In addition, dislocation loops with [001] Burgers vectors have been found in a tetragonal HEW lysozyme crystal including some cracks. These results are discussed in the light of dislocation elastic energy and slip systems in the crystals.

The feature of the Breit-Wigner-Fano Raman line in DNA-wrapped single-wall carbon nanotubes

Breit-Wigner-Fano (BWF) Raman line in DNA-wrapped single-wall carbon nanotubes (SWNTs) was investigated. For as-produced HiPco SWNT bundles, the asymmetric profile of BWF line is clearly observed with an excitation energy of 2.33eV. The asymmetric feature almost disappears in isolated HiPco SWNTs by DNA wrapping in aqueous solution. Such a significant change provides evidence that the asymmetric feature of BWF line is attributed to the bundling effect of SWNTs. In addition, the asymmetric feature of BWF line strongly appears even when the DNA-wrapped SWNTs are exposed to air. This means that the rebundling in the DNA-wrapped SWNTs can occur due to drying.

Characterization of Grown-in Dislocations in Benzophenone Single Crystals by X-Ray Topography

Benzophenone single crystals were grown by the Czochralski method. The dislocations introduced during the crystal growth were examined using X-ray topography. Double images of single dislocations were found on the topographs taken in some reflection planes. The Burgers vector of predominant grown-in dislocations was estimated from analysis of the dislocation images on the basis of kinematical theory.

Photo-illumination hardening of C60 crystals

The effect of light on the hardness of C60 crystals was investigated. The hardness increased after the crystals were illuminated with white light. Such a photo-illumination hardening was effective in a temperature range of 298–380 K. The photopolymerized C60 molecules near the crystal surface were responsible for the hardening. The anomalous temperature dependence of the hardness at temperatures higher than 300 K, which we previously have observed, is explained as due to the photo-illumination hardening.

Screw dislocation lines in lysozyme crystals observed by Laue topography using synchrotron radiation

Laue topography of the tetragonal crystals of hen egg-white lysozyme has been carried out using synchrotron radiation. Straight-line images extending from the core part to the growth fronts were observed and interpreted as dislocations. They had the displacement vectors parallel to the line; they are similar type of dislocations common to the crystals grown from solutions. The Laue spots showed uniform distortion. The water filter 10 mm thick was effective in avoiding radiation damages.

Thermal relaxation kinetics of defects in single-wall carbon nanotubes

The defects in single-wall carbon nanotubes irradiated with a 248 nm pulsed excimer laser were studied using Raman spectroscopy. The thermal relaxation kinetics of the laser-induced defects was examined at sample temperatures from 296 to 698 K. Two relaxation processes are revealed; one is the fast process with an activation energy of 0.4 eV and the other is the slow process with an activation energy of 0.7 eV. These two processes can correspond to vacancy-interstitial recombination and vacancy migration along the tube axis, respectively.