Weiqing Xu, Kunimitsu Takahashi, Y. Matsuo, Yoshiyuki Hattori, Mikio Kumagai, Shintaro Ishiyama, Katsumi Kaneko, Sumio Iijima,
Hydrogen storage capacity of various carbon materials, including activated carbon (AC), single-walled carbon nanohorn, single-walled carbon nanotubes, and graphitic carbon nanofibers, was investigated at 303 and 77 K, respectively. The results showed that hydrogen storage capacity of carbon materials was less than 1 wt% at 303 K, and a super activated carbon, Maxsorb, had the highest capacity (0.67 wt%). By lowering adsorption temperature to 77 K, hydrogen storage capacity of carbon materials increased ...
Tópico(s): Carbon Nanotubes in Composites
2007 - Elsevier BV | International Journal of Hydrogen Energy
Shigenori Utsumi, Hiroaki Honda, Yoshiyuki Hattori, Hirofumi Kanoh, Kunimitsu Takahashi, Hideki Sakai, Masahiko Abe, Masako Yudasaka, Sumio Iijima, Katsumi Kaneko,
The structure of single-wall carbon nanohorn (SWNH) was analyzed with X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. The considerably strong peak due to single bonding carbons was observed in C1s XPS spectrum of SWNH. This peak intensity increases with oxidation treatment, coinciding with the decrease in Raman G/D intensity ratio. It is concluded that the presence of a considerable amount of single bonding carbons is the reason for the unique assembly structure accompanying with a ...
Tópico(s): Diamond and Carbon-based Materials Research
2007 - American Chemical Society | The Journal of Physical Chemistry C
Suzana Gotovac Atlagić, Hiroaki Honda, Yoshiyuki Hattori, Kunimitsu Takahashi, Hirofumi Kanoh, Katsumi Kaneko,
Liquid-phase adsorption of tetracene and phenanthrene on a single-walled carbon nanotube (SWCNT) was examined. Tetracene adsorption was more than six times greater than that of phenanthrene. X-ray photoelectron spectroscopic examination clearly showed that tetracene and phenanthrene molecules efficiently coated the SWCNT external surfaces. The remarkable difference between the adsorption amounts of tetracene and phenanthrene was caused by the nanoscale curvature effect of the tube surface, resulting ...
Tópico(s): Graphene research and applications
2007 - American Chemical Society | Nano Letters
Dong Young Kim, Cheol‐Min Yang, Masahiro Yamamoto, Dae Ho Lee, Yoshiyuki Hattori, Kunimitsu Takahashi, Hirofumi Kanoh, Katsumi Kaneko,
Ultramicropore-enriched single-wall carbon nanotube (SWCNT) sheet was prepared by a filtration process after acid treatment using HNO3/H2SO4 solution. Field emission scanning electron microscopic observation showed that a highly dense entangled structure of SWCNT bundles was formed by acid treatment. The pore structure of the SWCNT sheet was evaluated from adsorption isotherms of N2 at 77 K and CO2 at 273 K. The SWCNT sheet gave remarkably developed uniform ultramicroporosity and reduced mesoporosity ...
Tópico(s): Supercapacitor Materials and Fabrication
2007 - American Chemical Society | The Journal of Physical Chemistry C
Suzana Gotovac Atlagić, Cheol‐Min Yang, Yoshiyuki Hattori, Kunimitsu Takahashi, Hirofumi Kanoh, Katsumi Kaneko,
Adsorption from toluene solution of phenanthrene and tetracene on single wall carbon nanotubes (SWCNT) is measured. Comparison of adsorbents such as laser ablation and HipCO samples reveals multiple factors influencing the adsorption mechanism. Acid functionalized carbon nanotubes have shown markedly increased adsorbability for the polyaromatic molecules. The linear tetracene molecule's adsorption is more promoted on nanotubes with increasing diameter, but also additionally with presence of the carboxylic ...
Tópico(s): Advanced Physical and Chemical Molecular Interactions
2007 - Elsevier BV | Journal of Colloid and Interface Science
F. Kokai, Akira Koshio, D. Kasuya, Kaori Hirahara, Kunimitsu Takahashi, Atsuko Nakayama, Masatou Ishihara, Yasutoshi Koga, Sumio Iijima,
Tópico(s): Graphene research and applications
2004 - Elsevier BV | Carbon
F. Kokai, Kunimitsu Takahashi, D. Kasuya, Atsuko Nakayama, Yasutoshi Koga, Masako Yudasaka, Sumio Iijima,
Tópico(s): Advanced Materials Characterization Techniques
2003 - Springer Science+Business Media | Applied Physics A
Kazuharu Suzuki, Kunimitsu Takahashi, Yoshimi Seida, Kouki Shimizu, Mikio Kumagai, Yoshio Taniguchi,
We describe a continuously tunable organic solid-state laser based on a flexible distributed-feedback (DFB) resonator. The tunable laser is made up of three organic layers. The active layer is a thin film of PVK (poly(9-vinylcarbazole)) doped with Bis-MSB (p-bis(o-methylstyryl)-benzene), the grating layer is a thin film of PVA (poly(vinylalcohol)), and the base substrate is a plate of PDMS (poly(dimethylsiloxane)). The active layer is pumped by the third harmonics of a Nd:YAG laser. The wavelength of ...
Tópico(s): Photonic and Optical Devices
2003 - Institute of Physics | Japanese Journal of Applied Physics
Elena Bekyarova, Katsumi Kaneko, D. Kasuya, Kunimitsu Takahashi, F. Kokai, Masako Yudasaka, Sumio Iijima,
Abstract Pore structure changes of single-walled carbon nanohorns (SWNHs) after oxidation with O 2 and CO 2 at different temperatures were studied. Low-temperature N 2 adsorption isotherms were analyzed to evaluate the parameters of both types of porosities present: interparticle pores and intraparticle cavities. Bud -SWNHs, produced by laser ablation of carbon in He atmosphere, have completely closed intraparticles. Oxidation in O 2 at 693 K opens 77% of the closed nanohorns.
Tópico(s): Fullerene Chemistry and Applications
2002 - Elsevier BV | Physica B Condensed Matter
J.-M. Bonard, Richard Gaál, Slaven Garaj, L. Thiên-Nga, Lászlø Forró, Kunimitsu Takahashi, F. Kokai, Masako Yudasaka, Sumio Iijima,
Self-supporting carbon films were prepared from a carbonaceous material, nanohorns. Nanohorns are spherical particles built of sharp cones of a single graphene sheet. The films show good field emission characteristics due to the sharp horn-like structures, in particular a low turn-on field and good long-term stability.
Tópico(s): Diamond and Carbon-based Materials Research
2002 - American Institute of Physics | Journal of Applied Physics
Katsuyuki Murata, Katsumi Kaneko, Hirofumi Kanoh, D. Kasuya, Kunimitsu Takahashi, F. Kokai, Masako Yudasaka, Sumio Iijima,
The exact physical adsorption amounts of supercritical hydrogen on the single-wall carbon nanohorn (SWNH) assemblies were determined at 77, 196, and 303 K. There are two physical adsorption sites of interstitial and internal spaces on SWNH assemblies. The interaction potential depths of interstitial and internal spaces are −1000 and −600 K, respectively. However, both hydrogen densities in interstitial and internal spaces were about 70 g L-1 at 77 K at 5 MPa, though the hydrogen densities in interstitial ...
Tópico(s): Hydrogen Storage and Materials
2002 - American Chemical Society | The Journal of Physical Chemistry B
D. Kasuya, Masako Yudasaka, Kunimitsu Takahashi, F. Kokai, Sumio Iijima,
Single-wall carbon nanohorn (SWNH) aggregates can be produced by CO2 laser vaporization of carbon, and a single aggregate can take either a "dahlia-like" or "bud-like" form. We found that "dahlia-like" SWNH aggregates were produced with a yield of 95% when Ar at 760 Torr was used as the buffer gas, while "bud-like" SWNH aggregates were formed with a yield of 70 or 80% when either He or N2 at 760 Torr was used. The internal structures of both aggregates were studied by partially burning them in an O2 ...
Tópico(s): Laser-Ablation Synthesis of Nanoparticles
2002 - American Chemical Society | The Journal of Physical Chemistry B
A. Zambano, S Talapatra, Khalid Lafdi, Majid Aziz, W. McMillin, Gerald Shaughnessy, Aldo Migone, Masako Yudasaka, Sumio Iijima, F. Kokai, Kunimitsu Takahashi,
Xenon adsorption studies were performed on aggregates of single-walled carbon nanohorns (SWNHs). The SWNHs were prepared in two different batches; the adsorption results from the two batches were essentially identical. Isotherms were performed in two groups of experiments: low-coverage data were used to measure the binding energy of Xe on the SWNHs; and full isotherms were measured to determine specific surface areas. The binding energy value for Xe on the SWNHs was intermediate between those for ...
Tópico(s): Nuclear Physics and Applications
2002 - IOP Publishing | Nanotechnology
F. Kokai, Kunimitsu Takahashi, D. Kasuya, Masako Yudasaka, Sumio Iijima,
We synthesized single-wall carbon nanotubes (SWNTs), 1.2–1.4 nm in diameter, and aggregates of single-wall carbon nanohorns (SWNHs) by CO2 laser vaporization in Ar gas under pressures of 150–760 Torr. At 150 Torr, SWNTs with smaller diameters were synthesized together with amorphous carbon. With an increase in the gas pressure, the yield of SWNTs decreased, the tube diameters increased, and SWNH aggregates were synthesized. At 760 Torr, most of the products were SWNH aggregates. We discuss the temperature- ...
Tópico(s): Transition Metal Oxide Nanomaterials
2002 - Elsevier BV | Applied Surface Science
Tsuyoshi Yoshitake, Yuichi Shimakawa, Sadanori Kuroshima, H. Kimura, T. Ichihashi, Yoshimi Kubo, D. Kasuya, Kunimitsu Takahashi, F. Kokai, Masako Yudasaka, Sumio Iijima,
Platinum catalyst was supported on single-wall carbon nanohorns (SWNHs) to demonstrate the suitability of SWNH's application to the electrodes of polymer–electrolyte fuel cells. The Pt particles were homogeneously dispersed on the SWNHs, and their particle size was about 2 nm. This size was less than half of that supported on conventional carbon black. A fuel cell using the SWNHs had a larger current density than one using the carbon black.
Tópico(s): Carbon Nanotubes in Composites
2002 - Elsevier BV | Physica B Condensed Matter
Katsuyuki Murata, Katsumi Kaneko, William A. Steele, F. Kokai, Kunimitsu Takahashi, D. Kasuya, Masako Yudasaka, Sumio Iijima,
The adsorption isotherm of N2 in internal nanopores of the single wall carbon nanohorn (SWNH) particles was compared with that of the external surfaces of the SWNH assembly. The presence of two strong adsorption sites of the internal nanopores and external nanopores of the assembly were evidenced by the analysis of the adsorption isotherm. The calculated interaction potential of the external nanopore was much deeper than that of the internal nanopore.
Tópico(s): Graphene research and applications
2001 - American Chemical Society | Nano Letters
Katsuyuki Murata, Katsumi Kaneko, William A. Steele, F. Kokai, Kunimitsu Takahashi, D. Kasuya, Kaori Hirahara, Masako Yudasaka, Sumio Iijima,
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 N2 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- ...
Tópico(s): Boron and Carbon Nanomaterials Research
2001 - American Chemical Society | The Journal of Physical Chemistry B
D. Kasuya, F. Kokai, Kunimitsu Takahashi, Masako Yudasaka, Sumio Iijima,
C60 was synthesized using 500 ms CO2 laser pulses to irradiate graphite in the presence of a buffer gas (He, Ar or N2) at room temperature. The yield of C60 produced at 150 Torr in He gas was a maximum of 4%, comparable to that produced by nanosecond-pulsed Nd:YAG laser ablation with the use of an electric furnace (1150°C). C60 formation is discussed in relation to the effect of the type and pressure of the buffer gas.
Tópico(s): Diamond and Carbon-based Materials Research
2001 - Elsevier BV | Chemical Physics Letters
F. Kokai, Manabu Taniwaki, Kunimitsu Takahashi, Akiko Goto, Masatou Ishihara, Kazuhiro Yamamoto, Yasutoshi Koga,
Tópico(s): Metal and Thin Film Mechanics
2001 - Elsevier BV | Diamond and Related Materials
Tomonori Ohba, Katsuyuki Murata, Katsumi Kaneko, William A. Steele, F. Kokai, Kunimitsu Takahashi, D. Kasuya, Masako Yudasaka, Sumio Iijima,
N2 adsorption in the internal nanospace and on the external suface of the single SWNH particle is studied by grand canonical Monte Carlo simulation and is compared with the experimental result. The detailed comparison of the simulated adsorption isotherm with the experimental isotherm in the internal nanospaces provides 2.9 nm of the average pore width of the internal nanospaces.
Tópico(s): Graphene research and applications
2001 - American Chemical Society | Nano Letters
Katsuyuki Murata, Katsumi Kaneko, F. Kokai, Kunimitsu Takahashi, Masako Yudasaka, Sumio Iijima,
Single-wall carbon nanohorn aggregates were characterized by N2 adsorption at 77 K and `particle density' measurement using the high pressure He buoyancy method. The single-wall carbon nanohorn aggregate had micropores and its pore volume was 0.11mlg−1. The particle density was 1.25gml−1. The particle density was not equal to the solid density of graphite (2.27gml−1), but it agreed within 15% with the density of the single-wall carbon nanohorn estimated using previous TEM data. Hence single-wall carbon ...
Tópico(s): Graphene research and applications
2000 - Elsevier BV | Chemical Physics Letters
Shunji Bandow, Apparao M. Rao, Gamini Sumanasekera, P. C. Eklund, F. Kokai, Kunimitsu Takahashi, Masako Yudasaka, Sumio Iijima,
Tópico(s): Advancements in Battery Materials
2000 - Springer Science+Business Media | Applied Physics A
J. Adelene Nisha, Masako Yudasaka, Shunji Bandow, F. Kokai, Kunimitsu Takahashi, Sumio Iijima,
Tópico(s): Fullerene Chemistry and Applications
2000 - Elsevier BV | Chemical Physics Letters
Shunji Bandow, F. Kokai, Kunimitsu Takahashi, Masako Yudasaka, Lu‐Chang Qin, Sumio Iijima,
Newly found single-wall carbon nanohorns (SWNH) are synthesized by a CO2 laser vaporization of a pure carbon target in an Ar gas. Purification method using centrifugal separation and structural features of aggregated form of SWNHs (SWNH aggregate) are studied in this Letter. Although the X-ray diffraction profile taken for highly purified SWNH aggregates does not show any sharp 002 diffraction corresponding to that of the ordinary graphite, a huge broad diffraction comes to be observed. This huge ...
Tópico(s): Graphene research and applications
2000 - Elsevier BV | Chemical Physics Letters
F. Kokai, Kunimitsu Takahashi, Masako Yudasaka, Sumio Iijima,
To study the Nd:YAG laser ablation of graphite−Co/Ni (1.2 at. %) and the growth of single-wall carbon nanotubes (SWNTs) in an Ar atmosphere at 1200 °C, we applied time-resolved imaging and spectroscopic techniques. These techniques are based on measuring the laser plume emission and light scattering of growing materials. Laser ablation was performed at a fluence of 1.7 J/cm2 at 1200 °C and at room temperature for comparison. At 1200 °C, we observed temporally and spatially dependent emissions of C, C2, ...
Tópico(s): Laser-Ablation Synthesis of Nanoparticles
2000 - American Chemical Society | The Journal of Physical Chemistry B
F. Kokai, Kunimitsu Takahashi, D. Kasuya, T. Ichihashi, Masako Yudasaka, Sumio Iijima,
Synthesis of single-wall carbon nanotubes (SWNTs) was carried out by irradiating a graphite–Co/Ni target at room temperature with CO2 laser pulses with durations of 1–20 ms. The length and bundle structure of SWNTs depended on the pulse duration. Most of the SWNTs formed by 1 ms laser pulses were individual tubes only 30–70 nm long. We discuss the growth dynamics of individual and bundled SWNTs based on the successive formation of metal nucleation sites in carbon–metal composite particles.
Tópico(s): Fullerene Chemistry and Applications
2000 - Elsevier BV | Chemical Physics Letters
Slaven Garaj, L. Thiên-Nga, Richard Gaál, Lászlø Forró, Kunimitsu Takahashi, F. Kokai, Masako Yudasaka, Sumio Iijima,
The magnetic properties of carbon nanohorns were investigated by electron spin resonance. Two decoupled electronic systems were found. The first one, which has a spin susceptibility linearly varying with temperature, was tentatively attributed to two-dimensional graphenelike sheets. The second contribution, showing a Curie-like behavior with a non-negligible Pauli part, was ascribed to the interior of the structures of coagulated nanohorns. Surprisingly, this second line shows a strong suppression ...
Tópico(s): Fullerene Chemistry and Applications
2000 - American Physical Society | Physical review. B, Condensed matter
Masako Yudasaka, F. Kokai, Kunimitsu Takahashi, R. Yamada, N. Sensui, T. Ichihashi, Sumio Iijima,
Investigating the formation of single-wall carbon nanotubes (SWNTs) from a target composed of graphite, Ni, and Co, we compared the use of a pulsed CO2 laser (pulse width of 20 ms, laser-power density of 0.1 MW/cm2) with the use of a pulsed Nd:YAG laser (pulse width of 5−7 ns, laser-power density of 4 GW/cm2). When the total irradiation energy was 2 kW/cm2 for the CO2 laser ablation and 2.4 kW/cm2 for the Nd:YAG laser ablation, SWNTs could be formed at 300 K by CO2 laser ablation, whereas the lowest ...
Tópico(s): Fullerene Chemistry and Applications
1999 - American Chemical Society | The Journal of Physical Chemistry B
Sumio Iijima, Masako Yudasaka, R. Yamada, Shunji Bandow, Kazu Suenaga, F. Kokai, Kunimitsu Takahashi,
We have found a new type of carbon particle produced by the CO2 laser ablation of carbon at room temperature without a metal catalyst. The product has a powder form of graphitic particles with a uniform size of about 80 nm. An individual particle is composed of an aggregate of many horn-shaped sheaths of single-walled graphene sheets, which we named carbon nano-horns. The nano-horns can be produced at about 10 g/h.
Tópico(s): Graphene research and applications
1999 - Elsevier BV | Chemical Physics Letters
F. Kokai, Kunimitsu Takahashi, Katsuya Shimizu, Masako Yudasaka, S. Iijima,
Tópico(s): Laser Design and Applications
1999 - Springer Science+Business Media | Applied Physics A