Ryoei Kato

Buckling of C60 whiskers

The authors demonstrated the mechanics of materials for crystalline whiskers composed of C60 molecules; compressive deformation of the whiskers was observed by in situ transmission electron microscopy with simultaneous force measurement by means of an optical cantilever method, as used in atomic force microscopy. In response to compression along the long axis, the whiskers bent first elastically, then buckled. A whisker with 160nm diameter fractured brittlely at a strain of 0.08. According to Euler’s formula, Young’s modulus of the whisker was estimated to be 32–54GPa, which is 160%–650% of that of C60 bulk crystals.

Light-emitting filaments composed of nanometer-sized carbon hollow capsules

Filaments composed of multilayered carbon hollow capsules less than 10nm in diameter have been synthesized from crystalline whiskers of fullerene C60 of submicrometer in diameter by preliminary heating at 1373K and successive impression of current. The structural, electrical and optical properties of the filaments were studied by in situ transmission electron microscopy combined with the functions of scanning probe microscopy. We found that the filaments easily emit visible light at a maximum wavelength of 700-730 nm by the application of a few volts.

Improved fullerene nanofiber electrodes used in direct methanol fuel cells

Platinum supported on fullerene nanofibers as possible electrodes for direct methanol fuel cells (DMFC) were studied. Fullerene nanofiber with 20 wt% Pt loading was mixed with 5 wt% Nafion solution. The mixture paste was coated on Nafion 117 membrane and sandwiched with silicon plates. To increase the surface reaction area of catalyst, nanoimprint was used to fabricate micro-patterns in the Nafion proton exchange membrane. Nanoimprint pattern consisted of dots of 500 nm-in-diameter, 140 nm-in-depth and 1 μm-in-spacing. The nanoimprint of the treated proton exchange membrane (PEM) was carried out in a desktop thermal nanoimprint system (NI273, Nano Craft Tech. Corp., Japan) at the optimized conditions of 130 °C and pressure of 3 MPa for 6 min. Then the Pt-coated PEM was sandwiched with micro-channelled silicon plates to form a micro-DMFC. With passively feeding of 1 M methanol solution and air at room temperature, the as-prepared cell had the open circuit voltage of 0.34 V and the maximum power density of 0.30 mW/cm2. Compared with a fresh cell, the results shows that nanofibers used in nanoimprinted PEM have an improvement on the performance of micro fuel cells.

Raman Laser Polymerization of C60 Nanowhiskers

Photopolymerization of C60 nanowhiskers (C60NWs) was investigated by using a Raman spectrometer in air at room temperature, since the polymerized C60NWs are expected to exhibit a high mechanical strength and a thermal stability. Short C60NWs with a mean length of 4.4 μm were synthesized by LLIP method (liquid-liquid interfacial precipitation method). The Ag(2) peak of C60NWs shifted to the lower wavenumbers with increasing the laser beam energy dose, and an energy dose more than about 1520 J/mm2 was found necessary to obtain the photopolymerized C60NWs. However, excessive energy doses at high-power densities increased the sample temperature and lead to the thermal decomposition of polymerized C60 molecules.

Surface breakdown dynamics of carbon nanocapsules

The structural variation in a single-molecule junction consisting of a hollow multi-walled carbon nanocapsule sandwiched between two gold electrodes during the breakdown of the outermost wall layer was observed in situ by high-resolution transmission electron microscopy. Simultaneously, the current-voltage curve of the junction was measured. The differential conductance of the junction decreased discontinuously from 1G(0) (where G(0) = 2e(2)/h is the conductance quantum, e is the electron charge and h is Plancks constant) to 0.5 G(0) and then to 0.2G(0) when the total number of wall layers decreased from four to three owing to the breakdown of the outermost layer. The maximum current decreased by 19 microA when the differential conductance decreased discontinuously. Our direct observation of the correlation between the atomistic structure and the conductance provides evidence for electron transport through several layers of the multi-walled nanocapsule, similar to that through carbon nanotubes with their surface in contact with electrodes.

In Situ High-Resolution Transmission Electron Microscopy of Elastic Deformation and Fracture of Nanometer-Sized Fullerene C60 Whiskers

We deformed crystalline whiskers composed of fullerene C60 molecules inside a high-resolution transmission electron microscope. The diameters of the whiskers ranged from 200 to 1000 nm and the length extended to the submillimeter scale. We selected one whisker with a body-centered tetragonal structure with a typical diameter, i.e., 540 nm, for analyses of deformation. It was found that the whisker arched elastically and the radius of curvature decreased to 20 µm until fracture, showing that the whiskers fracture strain was 0.013. Fracture occurred along {100} of the whisker, perpendicular to its longer growth axis.

Deformation of multiwalled nanometer-sized carbon capsules

The deformation of isolated multiwalled carbon capsules of a few nanometers in diameter was observed by in situ transmission electron microscopy with simultaneous force measurement by means of an optical cantilever method as used in atomic force microscopy. The mechanical properties of the carbon nanocapsules were investigated on an atomic scale. A carbon nanocapsule of 2.50±0.06nm in diameter was selected and compressed upto a strain of 0.06 at a force of up to 4.5±0.5nN using a nanometer-sized gold tip of a microcantilever. By subsequent retraction, we measured the force between the carbon nanocapsule and the gold tip, and assessed the adhesion.

High-resolution transmission electron microscopy of heat-treated C60 nanotubes

Fullerene nanowhiskers and nanotubes are single crystals consisting of C60 molecules with a high aspect ratio of length to diameter. In this study, C60 nanowhiskers and nanotubes were heat-treated at various temperatures up to 3000 °C. The structural characteristics of the heated samples were examined using transmission electron microscopy (TEM) and Raman spectroscopy. By the high-temperature heat treatment, the C60 nanotubes turned to glassy carbon composed of randomly oriented ribbons with graphitic layers with an interlayer spacing which is close to that of the (002) planes of graphite.

Fullerene nanowhiskers and related fullerene nanomaterials

Since the discovery of C60 nanowhiskers in a colloidal solution of PZT in 2001, various low-dimensional fullerene nanomaterials such as fullerene nanotubes and fullerene nanosheets have been synthesized by the liquid-liquid interfacial precipitation method (LLIP method) as well as the C60 and C70 nanowhiskers. The LLIP method is an excellent process to synthesize the quasi one-dimensional fullerene nanomaterials. This paper first reviews the typical fullerene nano and micro materials that have been prepared by the LLIP method and then show that the LLIP method is also applicable to the synthesis of composite C60 nano and micro whiskers containing wide compositions of C60 derivative molecules.

Growth Control and Properties of Fullerene Nanofibers

Fullerene nanofibers are the fine needle-like crystals composed of fullerene molecules and can be synthesized in a solution at ambient temperature and atmosphere. The growth control of the fullerene nanofibers are necessary in order to apply them for practical uses. We have developed a method to synthesize short fullerene nanowhiskers with a uniform length suitable for the electrodes in solar cells and fuel cells. This paper reports the synthesis of C60 nanofibers, including their properties and application.Copyright