平原 佳織

We investigated the high-strength, electrically conductive attachment of carbon nanotubes on Pt-coated Si substrates. In a layer of a few molecules deposited on the substrate, C molecules changed their cage structure to form a graphitic structure by the irradiation of a convergent electron beam with ca. 3 × 10 electrons·nm . This structural change at the contact region between the nanotube and the substrate functioned effectively to attach the nanotube to the substrate. The attachment force was greater than 100 nN, which is comparable to the tensile strength of a 1-nm-thick nanotube. © 2010 The Japan Society of Applied Physics. 60 8 -2

We developed a well-controlled method for sharpening an isolated carbon nanotube (CNT) by inducing an electrical current. Conical CNT tips were produced by increasing the electrical current abruptly in isolated suspended CNTs to achieve sublimation temperature. Because of the parabolic temperature distribution along the CNT axis from the one-dimensional equation of heat conduction, the amount of sublimation from the CNT center region is greater than that from the region near the electrodes. Consequently, two conical tips were formed at the cutting section. The sharpening process mechanism was examined quantitatively through comparison with different sharpening methods reported by Yuzvinsky et al. [Nano Lett. 6 (2006) 2718]. © 2010 The Japan Society of Applied Physics.

We have investigated the trap and escape process of a nanocargo(NC) inside a multiwall carbon nanotube(CNT) using molecular dynamics simulation. It was revealed that the trapping and escaping motions of NC at the end of CNT are governed by the competition between thermal energy and the van der Waals(vdW) interaction between the NC and the CNT cap. The trapping and escaping motions of NC at a temperature higher than 1000 K showed neither chirality nor size dependence, because the thermal energy at 1000 K is much higher than the energy corrugation induced by the vdW interaction between the NC and the CNT sidewall. © 2009 The Japan Society of Applied Physics.

The key technologies to achieve mass production of brushlike multiwalled carbon nanotubes (CNTs) are rapid processing for substrate heating and growing CNTs, and then cooling the substrate. We used chemical vapor deposition at 800°C with a carbon source gas of acetylene to investigate how substrate heating rate affects CNT growth. The results revealed an effective layered structure of an Fe catalyst for the rapid heating process: an oxidized Fe layer and a metal Fe layer formed on a silicon dioxide layer. The relationship among the given structure of Fe catalysts, the catalyst shape after rapid heating, and the resultant CNTs were investigated. ©2009 The Japan Society of Applied Physics.

For a large-scale process of synthesizing vertically aligned (brushlike) multiwalled carbon nanotubes using a thermal catalyst chemical vapor deposition process, a wet process for coating Fe catalyst onto a substrate has been investigated. Dimethylformamide was used for dissolving Fe(NO ) to form uniform films of Fe catalyst, and hence to synthesize uniform brushlike nanotubes on 6-in. Si substrates. The advantages of amine series solvent are discussed in terms of solubility in water and formation of Fe complexes. © 2009 The Japan Society of Applied Physics. 3 3

We investigated the effect of oxygen incorporated in substrates for forming Fe-based catalytic particles and growing carbon nanotubes (CNTs) by water-assisted catalytic chemical vapor deposition. We examined two types of SiO -covered Si (SiO /Si) and oxygen-free Si N -covered Si (Si N /Si) as substrates for supporting Fe films. Well-aligned CNTs were synthesized at a higher growth rate on Si N /Si compared with those on SiO /Si. The compositions of Fe-based catalytic particles that were formed by heating the substrates were examined using X-ray photoelectron spectroscopy (XPS) to determine the differences. Results show that the concentration ratio of Fe to Fe oxide in the catalytic particles strongly affects the alignment and height of synthesized brushlike CNTs and is well optimized in oxygen-free substrates. © 2009 The Japan Society of Applied Physics. 2 2 3 4 3 4 3 4 2

We experimentally investigated a "molecular-linear-motor" system consisting of a capsule-like carbon nanotube (CNT) in the interior space of a host CNT. Transmission electron microscopy revealed the capsule traveled back and forth between both ends of the hollow space along the axial direction and rotated simultaneously. The mechanism was well explained with molecular dynamics simulation by considering the driving force supplied from thermal energy. The present system operates around room temperature and this opens up the possibility of designing novel nanodevices such as oscillators and switching memory devices. © 2009 American Chemical Society.

Multiwalled carbon nanocoils (CNCs) have been synthesized by a method of thermal chemical vapor deposition (CVD) using a codeposited thin film consisting of Fe and Sn as catalysts. It has been found that the multiwalled CNCs are thinner and have a higher crystallinity than conventional CNCs. The catalyst particles are observed at the roots of CNCs, with diameters much larger than the line diameters of the coils. These large particles are formed by the aggregation of Sn and Fe reduced by the C H gas in CVD. These results indicate that Sn plays a crucial role in the growth of the multiwalled CNCs, and a base growth mechanism that differs from conventional growth mechanisms has been experimentally observed and analyzed. © 2008 The Japan Society of Applied Physics. 2 2

The simultaneous sputter deposition of gold and silver onto ionic liquids formed bimetallic alloy nanoparticles, which exhibited composition-sensitive surface plasmon resonance, the peak wavelength being red-shifted with an increase in the surface area of the gold foil targets sputtered. © The Royal Society of Chemistry.

We have investigated the current-induced transformation from elastically buckled carbon nanotubes into plastically bent nanotubes with a large bending angle. For this study, C -encapsulated single wall nanotubes were used, enabling the estimation of energy barriers in the process from the well known coalescence reactions. Increasing the current caused a sequential change: (a) coalescence of C molecules to form tube structures; (b) merging of the newly formed tubes with the original nanotube; (c) disappearance of buckling to form a plastic bend; and finally (d) sublimation of the nanotube. The order of the energy barriers for (a), (b), and (d) is consistent with the experimental results, which suggests that the observed structural change is caused by thermally activated reactions. The barrier for the disappearance of buckling to form the plastic bend is between 6.0 and 6.9 eV. © 2007 The Japan Society of Applied Physics. 60 60

Determination of the structural features is a fundamental subject in nanotube research. A simple method is proposed to evaluate the structure of multiwalled carbon nanotubes (MWNTs) having either the concentric or the scrolled structure. Although transmission electron microscopy and Raman scattering did not indicate a distinct difference in the structural features of the MWNTs, the temperature dependence of the diamagnetic susceptibility showed a clear difference; one was temperature-independent constant diamagnetism and the others indicated temperature-dependent diamagnetic susceptibilities with different magnitudes. The former phenomenon can be explained by applying the nested concentric nature to the MWNTs, and the latter by the scrolled nature. The difference in the magnitude of the temperature dependence is evidence for the mixed nature of the concentric and scrolled structures. © Springer-Verlag 2007.

Atomic arrangements of the continuous network of six-membered rings in a single graphene sheet constituting a single-wall carbon nanotube was imaged successfully by employing a spherical aberration-corrected HRTEM operated at 120 kV acceleration voltage. Utilizing two advantages of the aberration-corrected HRTEM, the images separately resolved the rings in the upper and lower walls. Such images can be considered to be the first "tomographic" atomic images taken by HRTEM. This is a striking result that changes the conventional concept of HRTEM as a projection image. © 2006 American Chemical Society.

Structural correlation between two adjacent graphitic layers in double-wall carbon nanotubes (DWNTs) was systematically examined by using electron diffraction. Chiral angles and tube diameters were carefully measured, and the chiral indices of individual DWNTs were accurately determined. As a result, it was found that the interlayer distances of DWNTs were widely distributed in the range between 0.34 and 0.38 nm. Chiralities of the inner and outer tubes tended to be distributed at higher chiral angles, approaching 30°, for the tubes with diameter D<∼3 nm. On the other hand, for the tubes with D>∼3 nm, the chiral angles were widely distributed, covering the chiral map entirely. Therefore, we consider that tubes with small diameters have a tendency to form armchair type. Correlation of chiralities between the inner and outer tubes was found to be random. © 2006 The American Physical Society.

We describe spectroscopy measurements of double wall carbon nanotubes using a displacement photocurrent technique. Peaks in the photocurrent are observed at excitation energies corresponding to the spacing of van Hove singularities for both the inner and outer shells of the nanotube. The shell assignment for the peaks can be made by comparing the spectra before and after the formation of the inner shell. The level spacing observed for the inner shell suggests that the standard tight binding model is insufficient to describe the electron energy spectra for extremely small tubes. © 2005 Elsevier B.V. All rights reserved.

The effect of compression of polyhedral graphite up to 43 GPa on its crystal structure was investigated. The elasticity and stability of the graphite phase were also studied. X-ray power diffraction measurements were carried out for the study of the crystal structure. It was observed that the polyhedra maintained the graphite phase under pressure higher than 40 GPa. An unusual decrease in the interlayer distance of 25% was observed in a 29% compression in volume at 43 GPa.

The formation pathway to double-walled carbon nanotubes (DWNTs) from C encased within single-wailed carbon nanotubes (peapods) is introduced in this article. Onedimensionally arranged C molecules coalesce gradually within the nanotube and change the structure to C dimers, trimers, tetramers, and so on as intermediates. In addition to these interesting structural transformations visualized in the nanotube space, the nanotube itself is very stable, and this structural stability is very important when using the interior of the nanotube as the reaction field or the space for molecular storage. In terms of optical absorption, the lowest energy absorption band for DWNTs, ∼0.65 eV, shows broadened and downshifted features as compared with that of SWNTs We expect that this opticalabsorption feature will lead to the use of DWNTs in absorbing devices for optical-fiber communications. The Raman experiments give new information about the frequency of the C-C stretching-mode vibration for nanotubes with diameters of less than ∼1 nm, which shows a decrease in vibration frequency with decreasing tube diameter. This diameter dependence can be explained by an admixture of sp character in the C-C interaction.Therefore, the electronic and mechanical properties of nanotubes with diameters of <1 nm are expected to be different from nanotubes of the ∼1-nm-diameter class, and we anticipate that new phenomena will occur in small-diameter tubes. 60 60 60 3

The structures of the finite-length (5,5) and (9,0) carbon nanotubes capped with fullerene hemisphere are analyzed by quantum chemical calculations at the B3LYP DFT level of theory. DFT calculations demonstrate that the geometries of the armchair tubes depend on the number of cyclic cis-polyene chains lined up along the tube axis, whereas the zigzag tubes consist of Kekulé-type networks in the cylinder, the geometries being independent of the number of component cyclic trans-polyene chains. © 2004 Elsevier B.V. All rights reserved.

By heating of C peapods at 900°C in vacuum, eight or more Raman peaks associated with the inner tubes were observed in the frequency range of the radial breathing mode vibration. An analysis of time traces of the peak intensities led to the growing mechanism of double-wall nanotubes: inner tubes with ≈0.7 nm diameters are first formed and then increase their diameters. To explain these phenomena, we propose a model based on formation of short achiral zig-zag nanotubes in the beginning of C coalescence. © 2003 Elsevier B.V. All rights reserved. 60 60

Laser vaporization of graphite was carried out in the presence of high pressure Ar gas of 0.1 -0.8 MPa. We compared the growth processes of three synthesized graphitic carbon particles: single-wall carbon nanohorn, multi-layer graphene, and polyhedral graphite particles. We believe graphitization processes occurred from supersaturated hot carbon vapor, dependent on resident carbon densities and their temperature gradients, lead to the growth of the three graphitic particles.

CO laser vaporization of graphite was carried out in the presence of high pressure Ar gas up to 0.8 MPa. We compared transmission electron microscope images and Raman spectra of deposited particles and luminous laser plumes of vaporized and clustered carbon species. We discuss the growth mechanisms of three graphitic carbon particles, a single-wall carbon nanohorn aggregate, a platelet graphite particle, and a polyhedral graphite particle, grown depending on the confinement of the Ar atmosphere. The formation of graphitic sheet or shell structures, dependent on resident carbon densities and their temperature gradient, is thought to begin from supersaturated hot carbon vapor up to about 3000°C and leads to the growth of the three graphitic particles. © 2004 Elsevier Ltd. All rights reserved. 2

Electron microscopy with atomic sensitivity enables us to obtain a direct image of the intra-molecular structure of metallofullerenes encapsulated inside single-walled carbon nanotubes. By a comparison of high-resolution images with a simulation to extract the relative atom positions for encaged metal atoms in each molecule, the distribution of the molecular orientations and interactions between adjacent molecules in metallofullerene peapods have been statistically analyzed. The results are suggestive of strong interactions between fullerene-fullerene and fullerene-tube in peapods at room temperature.

We present a general and systematic method for determining the chiral indices of carbon nanotubes. This method relies on the semi-quantitative analysis of experimental selected area diffraction pattern intensities, together with extensive comparison with kinematic theory. We show how to retrieve the chiral indices of single walled or multiwalled carbon nanotubes, even when their radii are large (up to approximately 40 Å). All theoretical and experimental sources of errors are discussed. By discussing the experimental case of a double-walled carbon nanotube, we show how it is possible to determine the chiral indices of each of its constituant tubes independently, by analyzing parts of the diffraction pattern where the contributions of these tubes do not interfere. Using the parts where all the contributions do interfere, we successfully crosschecked independently the preceding determination. © EDP Sciences, Società Italiana, di Fisica, Springer-Verlag 2003.

A single nanotube was cut by electron beam heating in transmission electron microscope. The lifetimes of the tubes due to electron beam heating became the longest when the tubes were heated in dry air at 500 degreesC in advance. This behavior can be explained by considering the quantity of contaminated carbons on the tube and the number of defects on the tube-wall. The excitation energy dependence on the Raman spectra showed the decrease of the C-C stretching mode vibration frequency as decreasing the tube diameter. The softening of the frequency becomes conspicuous for the tube with diameter less than similar to1 nm. The chemical doping of Br-2 to double-wall carbon nanotubes (DWNTs) indicated that most of electron holes would be generated only for the outer tubes and the electron hole doping to the inner tubes was difficult to take place. This fact can be explained when we consider the electronic structures of outer and inner tubes and less interlayer interaction in DWNT.

Subnanoscale windows (nanowindows) were donated to the walls of single-wall carbon nanohorns (SWNHs) by oxidation in oxygen at different temperatures of 573-693 K. We determined the accessibility of internal nanospaces of the SWNHs through nanowindows to He, Ar, N , CH , SF , and C . An explicit molecular sieving effect of SWNHs due to the nanowindow was shown. 2 4 6 60

Measurements of the transport properties in combination with the determination of the structure of isolated carbon nanotubes via in situ transport measurements, and SAED in a TEM are presented. As such, the example of a double-walled nanotube (DWNT) with two NZG shells behaving Ohmically at room temperature is discussed. The choice of working with DWNT nanotubes relies on the fact that they are maybe the easiest multiwalled nanotube (MWNT) to deal with experimentally and theoretically.

Single-wall carbon nanotubes and nanohorns were fabricated by means of a torch arc method in open air. A graphite target containing Ni/Y catalyst was used as a counterelectrode of the welding arc torch. The target was blasted away by the DC arc, and soot was deposited on the substrate placed downstream of the arc plasma jet. The deposited soot was observed with a transmittance electron microscope, revealing that the soot contained single-wall carbon nanotubes and nanohorns. © 2002 Elsevier Science B.V. All rights reserved.

The electronic and geometric properties of the Samarium-metallofullerene peapods were investigated. The single-wall nanotubes (SWNT) samples were examined with high-resolution transmission electron microscopy (HRTEM) and electron energy-loss spectroscopy (EELS). The valence state of the encapsulated samarium atom was also investigated by EELS. The samarium atom was found to take a divalent Sm state irrespective of the physical properties of the SWNT. 2+

Multi-wall carbon nanotubes (MWNTs) have been grown from simple pyrolysis of camphor, a botanical hydrocarbon, at 900°C for 15 min in argon atmosphere at ambient pressure using ferrocene as a catalyst. The nanotube diameter is fairly uniform (20-40 nm) and the yield is extremely high (̃90%). Structural characterization is done by SEM, TEM, HRTEM, EDX and Roman analyses. Good crystallinity, high purity, and absence of amorphous carbon and metal particles are the special features of camphor-pyrolyzed nanotubes.

The weak scattering from smaller carbon nanotubes results in weak contrast in their electron microscope images, and observation and interpretation of such images require special attention in order to avoid erroneous conclusions. It is demonstrated that the 4 Å carbon nanotube, residing inside a multi-walled carbon nanotube, bears recognizable signature in its image contrast for identification. For an isolated single-walled carbon nanotube, observation should be made in areas where the nanotube is exposed. When the carbon nanotube is overlapped with a supporting glassy carbon film, it is practically impossible for the nanotube to produce usable contrast features for unambiguous identification. © 2001 Elsevier Science B.V.

The microporosity of the heat-treated single-wall carbon nanohorn (SWNH) particles is characterized by nitrogen adsorption at 77 K and the molecular potential calculation using the function, which is based on the Lennard-Jones pair potential. The depth difference of the molecular potential for N between the SWNH intraparticle pore and the interparticle space is close to 1000 K. Although the SWNH without the heat-treatment has no open intra-nanohorn space, the intraparticle pores open with the high-temperature treatment in O . The heat-treatment at 693 K opens almost perfectly the intraparticle pores, leading to 0.47 mL g of the micropore volume and 1010 m g of the specific surface area. The subtraction of the N adsorption isotherm of the SWNH from that of the SWNH treated at 693 K gave the N adsorption isotherm only in the intraparticle pore spaces. The adsorption sites derived from the difference adsorption isotherm are assigned to the pores having different interaction potentials. 2 2 2 2 -1 2 -1

Short-time arc discharges with a short gap were generated between heteroelectrodes in stationary and running arc mode, under 25 kP of He. The electrodes used were pure graphite (C), nickel and yttrium mixed graphite (C-Ni/Y), and molybdenum (Mo). After the arc discharge, the surfaces of the anode and cathode were microscopically observed. On Mo electrode surface, no nanotubes were observed. With regard to C electrode, the multiwall nanotubes were observed only at the cathode spot where the arc was forcibly extinguished, and no nanotubes were observed at the anode spot. On the other hand, when the C-Ni/Y was used for the electrode, the nanotubes were observed both at the cathode spot where the arc was forcibly extinguished, and at the anode spot. These nanotubes on C-Ni/Y electrode were of multiwall, not of single wall. © 2001 Elsevier Science B.V. All rights reserved.

A new, simple method of carbon nanotube fabrication was developed. The method employed a tungsten-electrode-inert-gas (TIG) welding arc torch, with a graphite electrode used instead of a conventional tungsten electrode in order to prevent contamination of the tungsten vapor and droplets. The substrates used as counterelectrodes for the torch arc were pure graphite and catalyst (Ni, Y)-mixed graphite. The torch arc was operated in open air with both DC and AC modes. Nanotubed surfaces were obtained on catalyst-mixed graphite with DC and AC modes, and on pure graphite with the AC mode.

High-quality single-walled carbon nanotubes (SWNTs) have been produced by DC arc discharge in hydrogen ambience. By using Fe 1% catalyst a large amount of SWNTs are produced in pure H gas. Other transition metals of iron group and its combination are also used as catalyst for preparing SWNTs by adding 1% H S gas in H . Tri-metal catalyst, Fe(0.25%)-Ni(0.9%)-Co(0.9%), is found to be most effective for high yield of SWNTs. The SWNTs diameters are fairly thick ∼1.4-4 nm, and some double-walled carbon nanotubes also exist with them. 2 2 2

Single-wall carbon nanotubes (SWNTs) encapsulating fullerenes, so-called fullerene-peapods, were synthesized in high yield. High-resolution transmission electron microscopy revealed that almost all nanotubes are filled with high-density fullerene chains. We measured Raman spectra of C - and C -peapods. In the case of C -peapods, C Raman active mode intensity decreased rapidly by laser irradiation at room temperature. The final spectrum is similar to that of orthorhombic polymer phase, which indicates one-dimensional photopolymerization. At liquid helium temperature, no photopolymerization was observed, and the Raman spectra obtained indicates a feature of C -dimer phase. Furthermore, C -C distance estimated from electron diffraction pattern measured at room temperature is consistent with C -dimer phase. The spontaneous dimerization should be explained in part by internal high-pressure effect. 60 70 60 60 60 60 60 60

A variety of fullerene molecules are found to be fully packed in the interior space of a single-wall carbon nanotube (SWNT) and form a novel one-dimensional crystal with a regular intermolecular distance. Using electron diffraction, we have successfully measured the "lattice constants" for these crystals of various fullerenes and found that the intermolecular spacing of adjacent fullerenes in SWNTs is smaller than that of the three-dimensional bulk crystal but larger than that of polymerized crystal. It is also revealed that elongated fullerenes with a certain aspect ratio [such as C-70 and C-80(D-5d)] exhibit polymorphic packing structures with different intermolecular distances due to their constrained orientations with respect to the tube axis. The packing orientations of elongated fullerenes strongly depend on the diameter of the host nanotube.

Double-wall carbon nanotubes (DWNTs) were prepared in quantitative amount from the chains of C molecules generated inside single-wall carbon nanotubes (SWNTs). The C molecules inside the SWNT unchange up to ~800°C without dedoping. Further heating at ~1200°C induces the coalescence between C and eventually the C molecules transform into a tubular structure. The DWNTs thus prepared show radial breathing mode (RBM) Raman scattering associated with inner tubes as well as those from parent outer tubes, which are all explained by a model of diameter pairing in DWNT with an inner tube diameter smaller by 0.71±0.05 nm than an outer one. © 2001 Elsevier Science B.V. 60 60 60 60

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 molecules in the C -peapods is 1/10 of that in C film, which indicates a filling rate of C to be higher than 26%. In the case of C -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. 70 70 70 70 60

The DC arc plasma jet method was newly developed for the mass-production of single-wall carbon nanotubes (SWNTs). The quantity of cathode deposit was efficiently reduced by this method, and the production rate of cotton-like soot including SWNTs was significantly higher than that by conventional DC arc discharge evaporation. Investigation by using scanning electron microscopy, high-resolution transmission electron microscopy and Raman spectroscopy indicated that more than 50% of the cotton-like soot was the fibrous bundles of SWNTs with diameters of 1.34-1.53 nm. © 2001 Elsevier Science B.V. All rights reserved.