Faculty Profiles - TOKUNAGA, Tomoharu

Shell-like structure to limit further densification formed during flash sintering under alternative current electric field for 8 mol %Y2O3-doped ZrO2 Reviewed

Seko, M; Hattori, K; Ishino, Y; Kodaira, A; Tokunaga, T; Yamamoto, T

JOURNAL OF THE CERAMIC SOCIETY OF JAPAN Vol. 130 ( 11 ) page： 895 - 898 2022.11

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of the Ceramic Society of Japan

A phenomenon often appears that the final achieved density is limited during conventional flash sintering even under alternative current electric field. By observing the cross-sectional microstructure of the flash sintered 8 mol %Y2O3-doped ZrO2 at this state, we found that a thin surface portion with near full density surrounds a porous inside with lower density. The densified thin surface portion is shell-like structure covering a whole of the sintered compact. The formation of this characteristic shell-like structure in the early stage of flash sintering greatly restricts subsequent densification of porous inside. In order to suppress the formation of the shell that inhibit densification, a technique of controlling a steep power spike at a flash event must be necessary to be appropriately transitioned.

DOI： 10.2109/jcersj2.22109

A first attempt of automated shrinkage-rate control flash sintering using a current profile without feedback of shrinkage behavior for 8 mol % Y2O3 -doped ZrO2 Reviewed

Koike, M; Ishino, Y; Tokunaga, T; Yamamoto, T

JOURNAL OF THE CERAMIC SOCIETY OF JAPAN Vol. 130 ( 4 ) page： 327 - 330 2022.4

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of the Ceramic Society of Japan

Shrinkage-rate control flash (SCF) sintering is an attractive flash sintering that is modified to densify ceramic green compacts up to high density, which controls electric current to keep shrinkage-rate constant by feedback from shrinkage behavior during a flash state. To build up easier sintering protocol and to realize faster shrinkage-rate, we attempted automated SCF-sintering using the predicted current profile without feedback of the shrinkage behavior. As results, 8YSZ polycrystal with a density of 5.83 g/cm3 and a grain size of 1.84.5 μm could be produced within 10 min during SCF and soaking regimes at the furnace temperature of 870 °C, although the linearity of shrinkage-rate during automated SCF-sintering is degraded from the assumed shrinkage-rate. In order to improve automated SCF-sintering further, a more accurate method of approximating the current profile would be necessary to realize the higher linearity of shrinkage-rate.

DOI： 10.2109/jcersj2.22009

Shrinkage rate control during a flash state by current-ramping for 3 mol% Y2O3-doped ZrO2 polycrystals Reviewed

Crystalline boron monosulfide nanosheets with tunable bandgaps Reviewed

Kusaka Haruki, Ishibiki Ryota, Toyoda Masayuki, Fujita Takeshi, Tokunaga Tomoharu, Yamamoto Akiyasu, Miyakawa Masashi, Matsushita Kyosuke, Miyazaki Keisuke, Li Linghui, Shinde Satish Laxman, Lima Mariana S. L., Sakurai Takeaki, Nishibori Eiji, Masuda Takuya, Horiba Koji, Watanabe Kenji, Saito Susumu, Miyauchi Masahiro, Taniguchi Takashi, Hosono Hideo, Kondo Takahiro

JOURNAL OF MATERIALS CHEMISTRY A Vol. 9 ( 43 ) page： 24631 - 24640 2021.11

Ishino Yuki, Taguchi Kimihiro, Koike Masao, Tokunaga Tomoharu, Yamamoto Takahisa

JOURNAL OF THE AMERICAN CERAMIC SOCIETY Vol. 104 ( 10 ) page： 4960 - 4967 2021.10

Rapid sintering of 3 mol % Y2O3-doped ZrO2 by a combined rapid furnace heating and shrinkage-controlled flash sintering protocol Reviewed

Ishino Yuki, Taguchi Kimihiro, Kodaira Ayu, Tokunaga Tomoharu, Yamamoto Takahisa

JOURNAL OF THE CERAMIC SOCIETY OF JAPAN Vol. 129 ( 8 ) page： 551 - 554 2021.8

Near complete densification of flash sintered 8YSZ: controlled shrinkage rate effects Reviewed

Taguchi Kimihiro, Ishino Yuki, Tokunaga Tomoharu, Yamamoto Takahisa

JOURNAL OF THE EUROPEAN CERAMIC SOCIETY Vol. 41 ( 8 ) page： 4567 - 4571 2021.7

Constant shrinkage rate control during a flash event for 8 mol%Y2O3-doped ZrO2 polycrystals Reviewed

Taguchi Kimihiro, Ishino Yuki, Tokunaga Tomoharu, Yamamoto Takahisa

JOURNAL OF THE CERAMIC SOCIETY OF JAPAN Vol. 129 ( 3 ) page： 204 - 207 2021.3

Power Dissipation Behaviors during SCF-sintering for 8 mol% Y<inf>2</inf>O<inf>3</inf>-doped ZrO<inf>2</inf>

Ishino Y., Taguchi K., Kodaira A., Tokunaga T., Yamamoto T.

Funtai Oyobi Fummatsu Yakin/Journal of the Japan Society of Powder and Powder Metallurgy Vol. 68 ( 11 ) page： 482 - 486 2021

Publisher：Funtai Oyobi Fummatsu Yakin/Journal of the Japan Society of Powder and Powder Metallurgy

Shrinkage behaviors during shrinkage rate-controlled flash (SCF) sintering were investigated for 8 mol% Y2O3–ZrO2 (8YSZ) when shrinkage rates were varied between 60 and 300 μm/min under alternating current fields of 50 Vrms/cm, 1200 mArms, and 1000 Hz at a furnace temperature of approximately 870°C. Volumetric power dissipation and electrical conductivity were shown to exhibit similar dependencies against linear shrinkages even if the shrinkage rates were changed. The 8YSZ polycrystals, with similar microstructure and density, could be produced under all SCF conditions used in this study, which was confirmed as a characteristic feature of SCF sintering. Finally, the 8YSZ polycrystals with a density of 5.91–5.93 g/cm3 and a grain size of 2.2–2.6 μm could be produced with a shrinkage process period of 15–65 min at a furnace temperature of approximately 870°C.

DOI： 10.2497/jjspm.68.482

Cross-sectional Area Dependency of Shrinkages and Grain Sizes of Flash-sintered 3 mol%Y<inf>2</inf>O<inf>3</inf>–ZrO<inf>2</inf> Polycrystals with a Circular Truncated Cone-shape at High Frequency Alternating Electric Current Fields

Kurachi T., Kobayashi K., Tokunaga T., Yamamoto T.

Funtai Oyobi Fummatsu Yakin/Journal of the Japan Society of Powder and Powder Metallurgy Vol. 68 ( 11 ) page： 487 - 493 2021

Publisher：Funtai Oyobi Fummatsu Yakin/Journal of the Japan Society of Powder and Powder Metallurgy

The uniformity of shrinkages and the distribution of grain sizes were investigated for flash-sintered 3 mol%Y2O3-ZrO2 compacts in direct current and alternating current (AC) electric fields using rectangular-shaped and circular truncated cone-shaped green compacts. The use of a high-frequency AC electric field enough to suppress electrode overvoltage was confirmed to be advantageous for uniform shrinkages, regardless of the shapes of the green compacts. However, the grain size distribution became larger in cone-shaped green compacts, the cross-sectional areas of which varied along the compact. The grain sizes in flashed cone-shaped green compacts were found to exhibit a near linear relation to current density, which provides a means for determining the grain size distribution upon the flash sintering of green compacts with different cross-sectional areas along an electric field.

DOI： 10.2497/jjspm.68.487

EBV status has prognostic implication among young patients with angioimmunoblastic T-cell lymphoma

Eladl Ahmed E., Shimada Kazuyuki, Suzuki Yuka, Takahara Taishi, Kato Seiichi, Kohno Kei, Elsayed Ahmed Ali, Wu Chun-Chieh, Tokunaga Takashi, Kinoshita Tomohiro, Sakata-Yanagimoto Mamiko, Nakamura Shigeo, Satou Akira

CANCER MEDICINE Vol. 9 ( 2 ) page： 678 - 688 2020.1

Language：Japanese Publisher：Cancer Medicine

Epstein-Barr virus (EBV)-positive B cells have been detected in 66%-86% of patients with angioimmunoblastic T-cell lymphoma (AITL). However, it remains controversial whether EBV status has an impact on the survival of patients with AITL. In this study, we aimed to reevaluate the impact of EBV on the clinicopathological characteristics of AITL. In particular, we focused on the impact of EBV in younger patients with AITL. In total, 270 cases of AITL were studied. Epstein-Barr virus-positive B cells were detected in 191 (71%) cases (EBER+ group). Among the patients who received anthracycline-based therapy, the EBER status did not affect the overall survival (OS) or progression-free survival (PFS). In the younger group of AITL (≤60 years), PFS was significantly worse in the EBER− group compared to the EBER+ group (P =.0013). Furthermore, the multivariate analysis identified EBER-negative status, thrombocytopenia, and elevated serum IgA level as significant adverse prognostic factors for PFS (P <.001, P <.001, and P =.002). Based on these findings, we constructed new prognostic model for the younger group, based on three adverse factors. We classified the patients into two risk groups: low risk (no or 1 adverse factor) and high risk (2 or 3 adverse factors). This new model for younger patients with AITL showed that both OS and PFS were significantly related to the level of risk (P <.0001). In summary, this study showed that, among younger patients with AITL, an EBER+ status significantly improved prognosis compared to an EBER− status. Our new prognostic model should be applicable to younger patients with AITL.

DOI： 10.1002/cam4.2742

Characterisation of bovine embryos following prolonged culture in embryonic stem cell medium containing leukaemia inhibitory factor

Hosoe Misa, Furusawa Tadashi, Hayashi Ken-Go, Takahashi Toru, Hashiyada Yutaka, Kizaki Keiichiro, Hashizume Kazuyoshi, Tokunaga Tomoyuki, Matsuyama Shuichi, Sakumoto Ryosuke

REPRODUCTION FERTILITY AND DEVELOPMENT Vol. 31 ( 6 ) page： 1157 - 1165 2019.5

Language：Japanese Publisher：Reproduction, Fertility and Development

In order to help elucidate the process of epiblast and trophoblast cell differentiation in bovine embryos in vitro, we attempted to develop a suitable culture medium to allow extended embryo culture. Day 7 bovine blastocysts developed in conventional medium were cultured further in embryonic stem cell medium with or without leukaemia inhibitory factor (LIF) until Day 23. At Day 14, the expression of octamer-binding transcription factor 3/4 (OCT3/4) and VIMENTIN was significantly higher in embryos cultured with than without LIF, but embryonic disc formation was not observed. Although expression of SRY (sex determining region Y)-box 17 (SOX17) mRNA was significantly lower in Day 14 embryos cultured with and without LIF than in in vivo embryos, hypoblast cells formed just inside the trophoblast cells of the in vitro-cultured embryos. On Day 23, expression of placental lactogen (PL) and prolactin-related protein 1 (PRP1) was not affected by LIF in in vitro-cultured embryos, levels of both genes were significantly lower in the in vitro than in vivo embryos. Similar to in vivo embryos, binucleate cell clusters seen in Day 23 in vitro-cultured embryos were composed of PL-negative and -positive cells. These results suggest that our culture system partially reproduced the differentiation process of trophoblast cells in vivo.

DOI： 10.1071/RD18343

Removal of carbon contamination in ETEM by introducing Ar during electron beam irradiation

Tokunaga T., Saito K., Kuno K., Higuchi K., Yamamoto Y., Yamamoto T.

JOURNAL OF MICROSCOPY Vol. 273 ( 1 ) page： 46 - 52 2019.1

Intentionally encapsulated metal alloys within vertically aligned multi-walled carbon nanotube array via chemical vapor deposition technique

Inoue H., Nishikawa T., Hayashi Y., Hada M., Tokunaga T., Amaratunga G., Amaratunga G.

Conference Program Digest - 7th International Conference on Manipulation, Manufacturing and Measurement on the Nanoscale, IEEE 3M-NANO 2017 Vol. 2018-January page： 357 - 361 2018.2

Language：Japanese Publisher：Conference Program Digest - 7th International Conference on Manipulation, Manufacturing and Measurement on the Nanoscale, IEEE 3M-NANO 2017

This paper presents a growth and characterization of vertically aligned PdxCoi-x alloy encapsulated inside Multi-Walled Carbon Nanotube (MWCNT) arrays on Pd/Co thin layers coated on Si substrate by a dc bias-enhanced plasma chemical vapor deposition (CVD) method. The Metal Alloy Encapsulated within MWCNTs (MAE-MWCNTs) were characterized by a scanning electron microscope (SEM) and a transmission electron microscopy (TEM). The SEM images show the teardrop-shape particles encapsulated within the tube top of MWCNTs. A vibrating sample magnetometer was used to study the magnetism of a large number of MAE-MWCNTs on Si substrate at room temperature. The hysteresis loop of the ME-MWCNTs shows clear ferromagnetic behavior and the easy axis of magnetization is parallel to the MEA-MWCNT tube axis, as can be elucidated from the large coercive fields and remanence values. Moreover, TEM off-axis electron holograms were used to study the magnetism of the individual MAE-MWCNT or the two pair of MAE-MWCNTs. Based on electron holography, we have successfully obtained the saturation magnetization of 0.7 T and 1.12 T for the individual MAE-MWCNT with diameters of 41 nm and 83 nm, respectively.

DOI： 10.1109/3M-NANO.2017.8286262

Microstructure analysis for zirconium oxynitrides formed in 8 mol% yttria-doped zirconia by a flash event under a direct current electric field in an ambient atmosphere Reviewed

Vol. 45 ( 7 ) 2025.7

Ultrasonically Activated Liquid Metal Catalysts in Water for Enhanced Hydrogenation Efficiency

Nichayanan Manyuan, Naoya Tanimoto, Kousuke Ueda, Ken Yamamoto, Tomoharu Tokunaga, Masaki Nishio, Tetsu Yonezawa, Hideya Kawasaki

ACS Applied Materials & Interfaces Vol. 17 ( 4 ) page： 6414 - 6427 2025.1

Variation of (001) surface structures of strontium titanate single crystals caused by flash event under direct/alternative current electric fields

Yutaro Katsuyama, Shunske Kayukawa, Tomoharu Tokunaga, Shunsuke Kobayashi, Shigekazu Hidaka, Atsutomo Nakamura, Takahisa Yamamoto

Ceramics International Vol. 50 ( 19 ) page： 37366 - 37372 2024.10

Topographical and morphological changes of the single‐crystal (La0.3Sr0.7)(Al0.65Ta0.35)O3 (001) surface treated with high‐purity deionized water

Yoshinori Tokuda, Naoki Nishikawa, Takeshi Irimoto, Yutaro Katsuyama, Shunsuke Kobayashi, Tomoharu Tokunaga, Takahisa Yamamoto

Surface and Interface Analysis Vol. 56 ( 8 ) page： 564 - 572 2024.8

Publishing type：Research paper (scientific journal) Publisher：Wiley

The topological and morphological changes of the (001) surface of single‐crystal (La0.3Sr0.7)(Al0.65Ta0.35)O3 during treatment with high‐purity deionized water (DI) have been investigated by atomic force microscopy and scanning transmission electron microscopy (STEM). Etching by DI treatment at room temperature proceeded mainly in anisotropic etching mode, resulting in rectangular etch pits with {001} inner surfaces forming in the surface. The dominant etching mode changed from anisotropic to isotropic with increasing DI‐treatment temperature, and the lowest surface roughness occurred for DI treatment at 50°C for 60 min. Direct observation of the atomic structure of the surface by STEM showed that the etched surface was the B‐site‐terminated (001) surface after anisotropic etching at 50°C for 60 min, in which the B‐site‐terminated atomic layer was found to maintain the B‐site ordered structure existing in the crystal. This is because DI treatment, which does not require high‐temperature heat treatment of the substrate, suppresses element diffusion, sublimation, and formation of point defects on and in the vicinity of the surface.

DOI： 10.1002/sia.7313

Optical and mechanical properties of rutile TiO2 subjected to AC flash processing

Hiroshi Masuda, Tomoharu Tokunaga, Takahisa Yamamoto, Hidehiro Yoshida

Scripta Materialia Vol. 246 page： 116088 - 116088 2024.6

Photoinduced dynamics during electronic transfer from narrow to wide bandgap layers in one-dimensional heterostructured materials Reviewed Open Access

Yuri Saida, Thomas Gauthier, Hiroo Suzuki, Satoshi Ohmura, Ryo Shikata, Yui Iwasaki, Godai Noyama, Misaki Kishibuchi, Yuichiro Tanaka, Wataru Yajima, Nicolas Godin, Gaël Privaul, Tomoharu Tokunaga, Shota Ono, Shin-ya Koshihara, Kenji Tsuruta, Yasuhiko Hayashi, Roman Bertoni, Masaki Hada

Nature Communications Vol. 15 ( 1 ) page： 4600 2024.5

The use of He buffer gas for moderating the plume kinetic energy during Nd:YAG-PLD growth of EuxY2−xO3 phosphor films Open Access

Shizuka Suzuki, Takuro Dazai, Tomoharu Tokunaga, Takahisa Yamamoto, Ryuzi Katoh, Mikk Lippmaa, Ryota Takahashi

Journal of Applied Physics Vol. 135 ( 19 ) 2024.5

Publishing type：Research paper (scientific journal) Publisher：AIP Publishing

We have investigated the He buffer gas process of moderating the kinetic energy of the pulsed laser deposition (PLD) plume during EuxY2−xO3 phosphor film growth. When using a neodymium yttrium aluminum garnet laser for PLD thin film growth, the kinetic energy of the ablation plumes can be high enough to cause the formation of point defects in the film. The buffer gas pressure is an important process parameter in PLD film growth. We find that the presence of the He buffer gas reduces the kinetic energy of the laser deposition plume through many low-angle collisions in the gas phase by a factor of 7 without reducing the deposition rate. This is because He is much lighter than any of the elements in the plume and it does not affect the composition of the oxide films. Consequently, the resputtering of the Y2O3 film surface by the plume was significantly suppressed in the presence of the He gas moderator, leading to a decrease of the defect density in the Y2O3 films. The improvement of the film quality was verified by a systematic analysis of time-resolved photoluminescence (PL) data for EuxY2−xO3 composition–gradient films. The PL lifetime and intensity of Eu0.2Y1.8O3, which shows the highest PL intensity, increased by 13.3% and 36.4%, respectively, when the He gas moderation process was used. The He buffer gas process is applicable to the PLD growth of the other oxide materials as well, where the reduction of the kinetic energy of the plume would bring the PLD process closer to the molecular beam epitaxy growth condition.

DOI： 10.1063/5.0196987

Open Access

Applying an alternating current to strontium titanate minimizes the change in oxidation state caused by flash sintering

Mikito Seko, Shunta Inagaki, Tomoharu Tokunaga, Shunsuke Kobayashi, Atsutomo Nakamura, Takahisa Yamamoto

Journal of the European Ceramic Society Vol. 44 ( 5 ) page： 2965 - 2971 2024.5

Flash healing of Vickers microcracks formed on the (001) surface of cubic zirconia single crystals

Shunsuke Kayukawa, Yutaro Katsuyama, Ayu Kodaira, Tomoharu Tokunaga, Koji Morita, Atsutomo Nakamura, Takahisa Yamamoto

Journal of the European Ceramic Society Vol. 43 ( 14 ) page： 6272 - 6278 2023.11

Near-full compaction within only 30min of total sintering time by shrinkage-rate-controlled flash sintering in 3mol% Y<inf>2</inf>O<inf>3</inf>-doped ZrO<inf>2</inf> polycrystal

Yuki Ishino, Masao Koike, Ayu Kodaira, Tomoharu Tokunaga, Takahisa Yamamoto

Journal of the Ceramic Society of Japan Vol. 131 ( 10 ) page： 600 - 607 2023.10

Publishing type：Research paper (scientific journal)

The development of a high-speed sintering method that can shorten the entire sintering time while guaranteeing the mechanical properties is very attractive as a sintering process for structural ceramic polycrystals. For this purpose, a sintering protocol that combines shrinkage-rate-controlled flash sintering, which controls the shrinkage rate to be constant with the use of an alternative current electric field, and a rapid furnace ramp were applied to 3-mol % Y2O3-doped ZrO2 (3YSZ). As a result, a 3YSZ sintered polycrystal with about the relative density of 99.5 % (6.06 g/cm3) could be successfully fabricated within 30 min as the entire sintering time, which includes the furnace-heating regime. The sintered 3YSZ polycrystal is confirmed to exhibit a Vickers hardness of approximately 1290 HV and a fracture toughness (KIC) of approximately 5.2 MPa m1/2, which are similar values to those obtained from a typical thermally sintered 3YSZ polycrystal.

DOI： 10.2109/jcersj2.23041

Structural Defect Effect on the Concentration Quenching of TbxY2–xO3 Phosphor Thin Films

Shizuka Suzuki, Takuro Dazai, Tomoharu Tokunaga, Takahisa Yamamoto, Ryuzi Katoh, Ryota Takahashi

The Journal of Physical Chemistry C Vol. 127 ( 19 ) page： 9380 - 9387 2023.5

Mechanistic consideration of ZnTe microspheres formation in a PVP-contained polyol system via hot injection method

Yuen-ting Rachel Chau, Mai Thanh Nguyen, Tomoharu Tokunaga, Tetsu Yonezawa

Advanced Powder Technology Vol. 34 ( 4 ) page： 103970 - 103970 2023.4

Microcrack healing in single-crystal cubic zirconia by thermal annealing Reviewed

Shunsuke Kayukawa, Yutaro Katsuyama, Ayu Kodaira, Tomoharu Tokunaga, Koji Morita, Atsutomo Nakamura, Kimitaka Higuchi, Takahisa Yamamoto

Journal of the European Ceramic Society Vol. 43 ( 3 ) page： 1078 - 1086 2023.3

Flash self-joining of Y-TZP ceramics assisted with an AC electric field Reviewed

Kohta Nambu, Taisuke Kitaoka, Koji Morita, Kohei Soga, Tomoharu Tokunaga, Takahisa Yamamoto, Hiroshi Masuda, Hidehiro Yoshida

Journal of the American Ceramic Society Vol. 106 ( 3 ) page： 2073 - 2082 2023.3

Language：English Publishing type：Research paper (scientific journal) Publisher：Wiley

In this study, flash joining experiments were conducted using an AC field on 3 mol% Y2O3‐stabilized tetragonal ZrO2 polycrystal (Y‐TZP) bodies. Furthermore, the necessary conditions to obtain an almost complete self‐joining of Y‐TZP bodies were clarified. The specimens were successfully joined by applying an AC field at 60 mA·mm−2 for 80 s at a furnace temperature of 1000°C, thus resulting in a successfully joined specimen with 92% of the flexural strength of the as‐sintered Y‐TZP body. Almost complete self‐joining of Y‐TZP was achieved at current densities above 30 mA·mm−2, and input energy densities of >24 J·mm−3. Both the input energy density and electric current were critical factors for producing the reliable joining of ceramics.

DOI： 10.1111/jace.18889

A technique to modify the photoluminescence intensity of β-Ga2O3 polycrystals using an electric field during sintering Reviewed

Ryonosuke Ono, Ayu Kodaira, Tomoharu Tokunaga, Hidehiro Yoshida, Takahisa Yamamoto

Journal of Luminescence Vol. 254 page： 119508 - 119508 2023.2

Local Crystallization of Amorphous Aluminum Oxide Thin Film Using Electron Beam Irradiation by SEM

Shunsuke Tanahashi, Sae Okawara, Tomoharu Tokunaga, Takahisa Yamamoto

MATERIALS TRANSACTIONS Vol. 64 ( 1 ) page： 184 - 190 2023.1

Apparent Sintering Activation Energy Estimated by Master Sintering Curves for 8 mol% Y<inf>2</inf>O<inf>3</inf> Doped ZrO<inf>2</inf> Polycrystals during Shrinkage-Rate Controlled Flash Sintering

Masao Koike, Ayu Kodaira, Tomoharu Tokunaga, Takahisa Yamamoto

Materials Transactions Vol. 64 ( 10 ) page： 2315 - 2320 2023

Publishing type：Research paper (scientific journal)

The apparent activation energy of sintering for 8-mol%-Y2O3-doped ZrO2 during shrinkage-rate-controlled flash sintering was determined using a master sintering curve. The activation energy during SCF sintering was found to decrease from approximately 700 to 430 kJ/mol with density. The activation energy in a high-density region is approximately similar value of lattice diffusion, 460 kJ/mol. The relative density range over which the decrease in activation energy occurred during SCF sintering was smaller than during thermal sintering and further moved to a lower temperature range. The increase in shrinkage rate at lower temperatures that occurs during SCF sintering could be considered to be related to this decrease in activation energy.

DOI： 10.2320/matertrans.MT-T2023002

Apparent Sintering Activation Energy Estimated by Master Sintering Curves for 8 mol% Y2O3 Doped ZrO2 Polycrystals during Shrinkage-Rate Controlled Flash Sintering

Masao Koike, Ayu Kodaira, Tomoharu Tokunaga, Takahisa Yamamoto

MATERIALS TRANSACTIONS Vol. 64 ( 9 ) page： 2315 - 2320 2023

Variation of photoluminescence intensity depending on the timing of electric field application during isothermal flash sintering for 3mol%Y2O3–ZrO2 polycrystal Reviewed

Asa Itoh, Tomoharu Tokunaga, Ayu Kodaira, Hidehiro Yoshida, Takahisa Yamamoto

Ceramics International Vol. 48 ( 19 ) page： 28712 - 28717 2022.10

Effect of He Buffer Gas on Pulsed Nd:YAG Laser Deposition of EuxY2–xO3 Phosphor Thin Films Reviewed

Shizuka Suzuki, Takuro Dazai, Kazuhiro Kawashima, Tomoharu Tokunaga, Takahisa Yamamoto, Ryota Takahashi

ACS Applied Electronic Materials Vol. 4 ( 9 ) page： 4419 - 4426 2022.9

A liquid metal catalyst for the conversion of ethanol into graphitic carbon layers under an ultrasonic cavitation field

Hideya Kawasaki, Tomoko Otsuki, Fumiya Sugino, Ken Yamamoto, Tomoharu Tokunaga, Rintaro Tokura, Tetsu Yonezawa

Chemical Communications Vol. 58 ( 56 ) page： 7741 - 7744 2022.7

Effect of electron beam irradiation in gas atmosphere during ETEM Reviewed

Tomoharu Tokunaga, Takumi Kawakami, Kimitaka Higuchi, Yuta Yamamoto, Takahisa Yamamoto

Micron Vol. 158 page： 103289 - 103289 2022.7

The role of surface oxides and stabilising carboxylic acids of copper nanoparticles during low-temperature sintering

Rintaro Tokura, Hiroki Tsukamoto, Tomoharu Tokunaga, Mai Thanh Nguyen, Tetsu Yonezawa

Materials Advances Vol. 3 ( 12 ) page： 4802 - 4812 2022.6

Publishing type：Research paper (scientific journal) Publisher：Royal Society of Chemistry (RSC)

1-Hexanoic acid stabilised copper nanoparticles were obtained. Cu64O phase could be found on the particle surface. During sintering, the stabilising molecule, 1-hexanoic acid, reduced Cu64O to Cu and it introduced neckings between the particles.

DOI： 10.1039/d1ma01242h

Excess oxygen-vacancy formed by FAST regime of direct-current electric field during flash sintering for 3 mol%–10 mol% Y2O3-doped ZrO2 Reviewed

Nobuhiro Morisaki, Tomoharu Tokunaga, Kiyoshi Kobayashi, Ayu Kodaira, Takahisa Yamamoto

Ceramics International Vol. 48 ( 9 ) page： 12091 - 12097 2022.5

Anelasticity induced by AC flash processing of cubic zirconia Reviewed

Hiroshi Masuda, Koji Morita, Tomoharu Tokunaga, Takahisa Yamamoto, Hidehiro Yoshida

Acta Materialia Vol. 227 page： 117704 - 117704 2022.4

Anisotropic Growth of Copper Nanorods Mediated by Cl– Ions Reviewed International coauthorship

Min Jia Saw, Mai Thanh Nguyen, Yuji Kunisada, Tomoharu Tokunaga, Tetsu Yonezawa

ACS Omega Vol. 7 ( 8 ) page： 7414 - 7420 2022.3

Direct determination of a topmost atomic layer of (100) surfaces on (La0.3Sr0.7)(Al0.65Ta0.35)O3 single crystals annealed in air by high‐resolution scanning transmission electron microscopy Reviewed

Yoshinori Tokuda, Takeshi Irimoto, Naoki Nishikawa, Yutaro Katsuyama, Shunsuke Kobayashi, Tomoharu Tokunaga, Takahisa Yamamoto

Surface and Interface Analysis Vol. 54 ( 3 ) page： 212 - 217 2022.3

Language：English Publishing type：Research paper (scientific journal) Publisher：Wiley

Herein, we investigated the surface of an (La0.3Sr0.7)(Al0.65Ta0.35)O3 (LSAT) single crystal via scanning transmission electron microscopy (STEM) after annealing in air. We found amorphous mounds and atomically flat surfaces formed on the surface of the (100) LSAT single crystal subsequent to heat treatment. These surface mounds mainly constituted SrO, including ~50 at.% Al. The atomically flat surface showed a B‐site termination determined by the direct surface observation at the atomic scale through HAADF‐STEM. The atomic arrangements on the surface were accommodated by surface‐mound formation and La evaporation. Consequently, the ordered structure disappeared because of the increase in the Ta content at the terminated B‐site layer.

DOI： 10.1002/sia.7043

Alginate-Stabilized Gold Nanoparticles Prepared Using the Microwave-Induced Plasma-in-Liquid Process with Long-Term Storage Stability for Potential Biomedical Applications Reviewed

Other Link： https://onlinelibrary.wiley.com/doi/full-xml/10.1002/sia.7043

Haoran Liu, Kai Ikeda, Mai Thanh Nguyen, Susumu Sato, Naoki Matsuda, Hiroki Tsukamoto, Tomoharu Tokunaga, Tetsu Yonezawa

ACS Omega Vol. 7 ( 7 ) page： 6238 - 6247 2022.2

Nanoporous ultra-high-entropy alloys containing fourteen elements for water splitting electrocatalysis

Ze-Xing Cai, Hiromi Goou, Yoshikazu Ito, Tomoharu Tokunaga, Masahiro Miyauchi, Hideki Abe, Takeshi Fujita

Chemical Science Vol. 12 ( 34 ) page： 11306 - 11315 2021.9

Language：English Publishing type：Research paper (scientific journal) Publisher：Royal Society of Chemistry (RSC)

Nanoporous ultra-high-entropy alloys containing 14 elements (Al, Ag, Au, Co, Cu, Fe, Ir, Mo, Ni, Pd, Pt, Rh, Ru, and Ti) were obtained by dealloying. The products showed excellent electrocatalytic performance for water splitting in acidic media.

DOI： 10.1039/d1sc01981c

Flash sintering for BaTiO<inf>3</inf> with square alternating current field including zero-field duration Invited Reviewed

Ryosuke Umemura, Tomoharu Tokunaga, Takahisa Yamamoto

Journal of the Ceramic Society of Japan Vol. 128 ( 12 ) page： 1018 - 1023 2020.12

Language：Japanese Publishing type：Research paper (scientific journal)

The shrinkage behavior of barium titanate (BaTiO3) green compacts during flash sintering with a square alternating current (AC) field including a zero-field duration (AC-pulse wave) was investigated. It was found that an AC-pulse wave is effective for the densification of BaTiO3 green compacts without reduction and discharge, which is confirmed by transmission electron microscopy and electron energy loss spectroscopy. BaTiO3 sintered polycrystal was obtained at a furnace temperature of 1000 °C by the optimal AC-pulse conditions of 285 V/cm at 250 Hz and a duty ratio of 30 %. A waveform with alternating polarity and the inclusion of a zero-field duration is shown to be possibly useful for flash sintering of oxide materials including altervalent cations.

DOI： 10.2109/jcersj2.20181

H-2 production from methane decomposition by fullerene at low temperature Reviewed

Tomoharu Tokunaga, Kohei Kuno, Takumi Kawakami, Takahisa Yamamoto, Akitaka Yoshigoe

INTERNATIONAL JOURNAL OF HYDROGEN ENERGY Vol. 45 ( 28 ) page： 14347 - 14353 2020.5

Language：English Publishing type：Research paper (scientific journal) Publisher：PERGAMON-ELSEVIER SCIENCE LTD

Carbon materials have previously been reported to work as catalysts for hydrogen (H-2) production from hydrocarbons. Mechanisms of the catalytic behavior of graphite and carbon black (CB) have often been discussed in literature. Graphite and CB is constructed from mainly 6-membered rings with sp(2) bonds. To understand the catalytic behavior of carbon materials for H-2 production by methane (CH4) decomposition, the catalytic behavior of fullerenes with 6-membered rings and also those comprising 5- and 7-membered rings with sp(2) bonds and their associated mechanisms should be investigated. In this study, the fullerene catalyst activity has been investigated using gas chromatography and the electronic states and nanoscale structures have been analyzed.H-2 production started at 400 degrees C and the H-2 production rate gradually increased with time, and the activation energy of the fullerene for H-2 production by CH4 decomposition was found to be 166 kJ/mol. Moreover, in situ heating X-ray photon spectroscopy (XPS) measurements showed that the pi-pi* transition signal becomes stronger with increasing temperature above the threshold of 300 degrees C. The transition of the pi. electrons to pi* orbitals upon heating is expected to decompose CH 4 absorbed on fullerene. Moreover, transmission electron microscopy (TEM) analysis revealed that the generated carbon atoms from the CH4 decomposition were deposited onto the surfaces of the fullerenes, forming amorphous and layered concentric sphere carbon. Amorphous carbon is reported to not work as a catalyst for CH4 decomposition at around 400 degrees C. From XPS analysis and TEM observations of these two structures, it is anticipated that the ring structures without 6-membered rings in carbon materials with sp(2) bonding contribute to this catalytic behavior for CH4 decomposition at a low temperature of 400 degrees C. (C) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.ijhydene.2020.03.178

Blue photo luminescence from 3 mol%Y2O3-doped ZrO2 polycrystals sintered by flash sintering under an alternating current electric field Reviewed

Yudai Yamashita, Tsuyoshi Kurachi, Tomoharu Tokunaga, Hidehiro Yoshida, Takahisa Yamamoto

JOURNAL OF THE EUROPEAN CERAMIC SOCIETY Vol. 40 ( 5 ) page： 2072 - 2076 2020.5

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCI LTD

We investigated the photoluminescence (PL) properties of 3 mol%Y2O3-ZrO2 (3YSZ) polycrystals. The 3YSZ polycrystals were prepared by an isothermal flash sintering technique in which an alternating electric field was applied at a predetermined furnace temperature. After flash sintering, clear, visibly blue PL at 2.82 eV (440 nm) was confirmed under an ultraviolet light (3.4 eV (365 nm)); however, no visible PL was observed from 3YSZ polycrystals conventionally sintered using the same raw powders. Thus, the emission of blue PL was induced by the electric field applied during sintering. The obtained PL band was related to excitation at 3.87 eV (320 nm), which is possibly assigned to the singly ionized associated oxygen vacancy defects (AOD + centers). Furthermore, the blue emission was stable after high temperature annealing at 1400 degrees C for 1 h in air. We possibly attribute the emission of this PL to the stabilization of AOD + centers by the electric field loading during flash sintering.

DOI： 10.1016/j.jeurceramsoc.2019.12.060

Suppression of nitridation of yttria-doped zirconia during flash sintering Reviewed International coauthorship

Tsuyoshi Kurachi, Yudai Yamashita, Tomoharu Tokunaga, Hidehiro Yoshida, Takahisa Yamamoto

JOURNAL OF THE AMERICAN CERAMIC SOCIETY Vol. 103 ( 5 ) page： 3002 - 3007 2020.5

Language：English Publishing type：Research paper (scientific journal) Publisher：WILEY

The effect of direct current (DC) and alternating current (AC) on nitridation of 3 mol% Y2O3-doped ZrO2 (3YSZ) after keeping in a flash state for 1 hour was investigated. The inside of the DC-flashed compact was confirmed to exhibit blacking. Scanning transmission electron microscopy, electron energy loss spectroscopy, and X-ray diffraction analysis revealed that zirconium nitrides formed in the blackened area. In contrast, a uniformly densified compact without blackening was obtained by AC fields. No zirconium nitrides formed in the compacts exposed to AC fields even when the flash state was maintained for 1 hour. Therefore, AC fields are effective to suppress nitridation of 3YSZ during flash sintering.

DOI： 10.1111/jace.16990

In situ TEM observation of liquid-state Sn nanoparticles vanishing in a SiO2 structure: a potential synthetic tool for controllable morphology evolution from core-shell to yolk-shell and hollow structures Reviewed International coauthorship

Shilei Zhu, Mai Thanh Nguyen, Tomoharu Tokunaga, Cheng-Yen Wen, Tetsu Yonezawa

NANOSCALE ADVANCES Vol. 2 ( 4 ) page： 1456 - 1464 2020.4

Language：English Publishing type：Research paper (scientific journal) Publisher：ROYAL SOC CHEMISTRY

Precise design of hollow nanostructures can be realized via various approaches developed in the last two decades, endowing nanomaterials with unique structures and outstanding performances, showing their usefulness in a broad range of fields. Herein, we demonstrate the formation of SnO2@SiO2 hollow nanostructures, for the first time, by interaction between liquid state Sn cores and SiO2 shell structures inside Sn@SiO2 core-shell nanoparticles with real-time observation via in situ transmission electron microscopy (TEM). Based on the in situ results, designed transformation of the nanoparticle structure from core-shell Sn@SiO2 to yolk-shell Sn@SiO2 and hollow SnO2@SiO2 is demonstrated, showing the controllable structure of core-shell Sn@SiO2 nanoparticles via fixing liquid-state Sn inside a SiO2 shell which has a certain Sn containing capacity. The present approach expands the toolbox for the design and preparation of yolk-shell and hollow nanostructures, thus providing us with a new strategy for fabrication of more complicated nanostructures.

DOI： 10.1039/c9na00782b

Lianlian Deng, Mai Thanh Nguyen, Jingming Shi, Yuen-Ting Rachel Chau, Tomoharu Tokunaga, Masaki Kudo, Syo Matsumura, Naoyuki Hashimoto, Tetsu Yonezawa

Langmuir : the ACS journal of surfaces and colloids Vol. 36 ( 12 ) page： 3004 - 3015 2020.3

Language：English

Pt/Au alloy nanoparticles (NPs) in a wide composition range have been synthesized by room-temperature simultaneous sputter deposition from two independent magnetron sources onto liquid PEG (MW = 600). The prepared NPs were alloyed with the face-centered cubic (fcc) structure. In addition, the particle sizes, composition, and shape are strongly correlated but can be tailored by an appropriate variation of the sputtering parameters. No individual particle but large agglomerates with partial alloy structure formed at Pt content of less than 16 atom %. Highly dispersed NPs with no agglomeration were observed in PEG when the quantity of Pt is more than 26 atom %. On the other hand, a small amount of Pt could terminate the agglomeration of Au when sputtering on the grids for transmission electron microscope observation. Our experiment and computer simulation carried out by two different methods indicate that the composition-dependent particle size of Pt/Au can be explained by the atomic concentration, formation energy of the cluster, and interaction between different metal atoms and the PEG molecule.

DOI： 10.1021/acs.langmuir.0c00152

Synthesis of composition-tunable Pd–Cu alloy nanoparticles by double target sputtering

Yuen-ting Rachel Chau, Mai Thanh Nguyen, Mingbei Zhu, Arnaud Romier, Tomoharu Tokunaga, Tetsu Yonezawa

New Journal of Chemistry Vol. 44 ( 12 ) page： 4704 - 4712 2020.3

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Royal Society of Chemistry (RSC)

In this work, we introduce a green synthesis technique, double-target sputtering into a liquid polymer – polyethylene glycol (PEG, M. W. = 600), to synthesize palladium–copper (Pd–Cu) alloy nanoparticles (NPs) dispersed in PEG.

DOI： 10.1039/d0nj00288g

Blue photoluminescence at room temperature from Y<inf>2</inf>O<inf>3</inf>-doped ZrO<inf>2</inf> polycrystals sintered by flash sintering

Yudai Yamashita, Asa Itoh, Tomoharu Tokunaga, Hidehiro Yoshida, Takahisa Yamamoto

Applied Physics Express Vol. 13 ( 3 ) 2020.3

Language：Japanese Publishing type：Research paper (scientific journal)

© 2020 The Japan Society of Applied Physics. Photoluminescence band variation of Y2O3-doped ZrO2 (YSZ) polycrystals was investigated for flash-sintered YSZ polycrystals. Nearly full density could be obtained by flash sintering under an alternating current field of 100 V cm-1, 100 Hz, limiting current of 1000 mA and at 1200 °C for 5 min. The flash-sintered YSZ polycrystals emitted blue photoluminescence even at room temperature under excitation of a handheld ultraviolet light, which could be observed with the naked eye. By contrast, conventionally sintered YSZ polycrystals emitted no photoluminescence despite using the same raw powders. In addition, the photoluminescence bands were tunable by varying the Y2O3 content.

DOI： 10.35848/1882-0786/ab7710

Green Synthesis of Size-Tunable Iron Oxides and Iron Nanoparticles in a Salt Matrix Reviewed

Mai Thanh Nguyen, Kai Yu, Tomoharu Tokunaga, Kornkit Boonyaperm, Soorathep Kheawhom, Masashi Arita, Tetsu Yonezawa

ACS SUSTAINABLE CHEMISTRY & ENGINEERING Vol. 7 ( 21 ) page： 17697 - 17705 2019.11

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER CHEMICAL SOC

This research is devoted for the synthesis of Fe oxide and Fe nanoparticles (NPs) via, respectively, thermal decomposition of iron(III) oleate and H-2 reduction of either iron(III) oleate or iron oxide NPs in a NaCl matrix. Lowering the weight ratios of metal precursor to NaCl and synthesis temperature results in smaller particle sizes. A higher uniformity of Fe NPs can be achieved with a two-step synthesis, that is, thermal decomposition of iron oleate followed by H-2 reduction of iron oxides, with the milling of iron oxides and NaCl prior to the reduction step. Fe NPs obtained in this study are stable in the air for long-time storage. It is found that thin oxide and C layers on the particle surface are responsible for their stability.

DOI： 10.1021/acssuschemeng.9b03950

Technique to control specimen electric current during a flash state with alternating current electric fields Reviewed

Yudai Yamashita, Tsuyoshi Kurachi, Tomoharu Tokunaga, Hidehiro Yoshida, Takahisa Yamamoto

JOURNAL OF THE CERAMIC SOCIETY OF JAPAN Vol. 127 ( 11 ) page： 849 - 851 2019.11

Language：English Publishing type：Research paper (scientific journal) Publisher：CERAMIC SOC JAPAN-NIPPON SERAMIKKUSU KYOKAI

A simple technique to control the specimen electric current during flash sintering was developed using AC electric fields in 3 mol% Y2O3-doped ZrO2. Flash sintering is characterized by the occurrence of a flash event, i.e., a spike in the specimen electric current, which makes it difficult to control the specimen electric current at/after the flash event for AC electric fields. However, AC electric fields are very attractive from the viewpoint of a suppression of the severe reduction arising from the unidirectional ionic flow during the flash event, which is a fatal phenomenon with DC electric fields. In this study, we develop a simple technique to control the AC electric fields at/after the flash event by limiting the AC electric fields under certain values. As a result, the flash state after the flash event is successfully maintained. Further, it is found that 3 mot% Y2O3-doped ZrO2 compacts prepared by DC- and AC-flash sintering emit blue fluorescence (FL) under 254 nm ultraviolet tight. The blue FL is not obtained in the compacts prepared by conventionally-sintering. The application of electric fields is confirmed to result in the blue florescent properties of 3 mot% Y2O3-doped ZrO2 compacts. (C) 2019 The Ceramic Society of Japan. All rights reserved.

DOI： 10.2109/jcersj2.19144

One-minute Joule Annealing Enhances the Thermoelectric Properties of Carbon Nanotube Yarns via the Formation of Graphene at the Interface Reviewed

Masaki Hada, Taisuke Hasegawa, Hirotaka Inoue, Makito Takagi, Kazuki Omoto, Daiki Chujo, Shogo Iemoto, Taihei Kuroda, Taiga Morimoto, Takuma Hayashi, Toru Iijima, Tomoharu Tokunaga, Naoshi Ikeda, Kazuhiro Fujimori, Chihiro Itoh, Takeshi Nishikawa, Yoshifumi Yamashita, Toshihiko Kiwa, Shin-ya Koshihara, Satoshi Maeda, Yasuhiko Hayashi

ACS Appl. Energy Mater. Vol. 2 ( 10 ) page： 7700 - 7708 2019.10

Selective Reduction Mechanism of Graphene Oxide Driven by the Photon Mode versus the Thermal Mode. Reviewed International journal

Masaki Hada, Kiyoshi Miyata, Satoshi Ohmura, Yusuke Arashida, Kohei Ichiyanagi, Ikufumi Katayama, Takayuki Suzuki, Wang Chen, Shota Mizote, Takayoshi Sawa, Takayoshi Yokoya, Toshio Seki, Jiro Matsuo, Tomoharu Tokunaga, Chihiro Itoh, Kenji Tsuruta, Ryo Fukaya, Shunsuke Nozawa, Shin-Ichi Adachi, Jun Takeda, Ken Onda, Shin-Ya Koshihara, Yasuhiko Hayashi, Yuta Nishina

ACS nano Vol. 13 ( 9 ) page： 10103 - 10112 2019.9

Language：English Publishing type：Research paper (scientific journal)

A two-dimensional nanocarbon, graphene, has attracted substantial interest due to its excellent properties. The reduction of graphene oxide (GO) has been investigated for the mass production of graphene used in practical applications. Different reduction processes produce different properties in graphene, affecting the performance of the final materials or devices. Therefore, an understanding of the mechanisms of GO reduction is important for controlling the properties of functional two-dimensional systems. Here, we determined the average structure of reduced GO prepared via heating and photoexcitation and clearly distinguished their reduction mechanisms using ultrafast time-resolved electron diffraction, time-resolved infrared vibrational spectroscopy, and time-dependent density functional theory calculations. The oxygen atoms of epoxy groups are selectively removed from the basal plane of GO by photoexcitation (photon mode), in stark contrast to the behavior observed for the thermal reduction of hydroxyl and epoxy groups (thermal mode). The difference originates from the selective excitation of epoxy bonds via an electronic transition due to their antibonding character. This work will enable the preparation of the optimum GO for the intended applications and expands the application scope of two-dimensional systems.

DOI： 10.1021/acsnano.9b03060

Porous ZnV2O4 Nanowire for Stable and High-Rate Lithium-Ion Battery Anodes Reviewed

Lyn Marie, Z. De Juan-Corpuz, Mai Thanh Nguyen, Ryan D. Corpuz, Tetsu Yonezawa, Nataly Carolina Rosero-Navarro, Kiyoharu Tadanaga, Tomoharu Tokunaga, Soorathep Kheawhom

ACS Applied Nano Materials Vol. 2 ( 7 ) page： 4247 - 4256 2019.7

Preparation and Growth Mechanism of Pt/Cu Alloy Nanoparticles by Sputter Deposition onto a Liquid Polymer. Reviewed International journal

Lianlian Deng, Mai Thanh Nguyen, Shuang Mei, Tomoharu Tokunaga, Masaki Kudo, Syo Matsumura, Tetsu Yonezawa

Langmuir : the ACS journal of surfaces and colloids Vol. 35 ( 25 ) page： 8418 - 8427 2019.6

Language：English

We use a green sputtering technique to deposit a Pt/Cu alloy target on liquid polyethylene glycol (PEG) to obtain well-dispersed and stable Pt29Cu71 alloy nanoparticles (NPs). The effects of sputtering current, rotation speed of the stirrer, sputtering time, sputtering period, and temperature of PEG on the particle size are studied systematically. Our key results demonstrate that the aggregation and growth of Pt/Cu alloy NPs occurred at the surface as well as inside the liquid polymer after the particles landed on the liquid surface. According to particle size analysis, a low sputtering current, high rotation speed for the stirrer, short sputtering period, and short sputtering time are found to be favorable for producing small-sized single crystalline alloy NPs. On the other hand, varying the temperature of the liquid PEG does not have any significant impact on the particle size. Thus, our findings shed light on controlling NP growth using the newly developed green sputtering deposition technique.

DOI： 10.1021/acs.langmuir.9b01112

Size-Tunable Alumina-Encapsulated Sn-Based Phase Change Materials for Thermal Energy Storage Reviewed

Shilei Zhu, Mai Thanh Nguyen, Tomoharu Tokunaga, Tetsu Yonezawa

ACS APPLIED NANO MATERIALS Vol. 2 ( 6 ) page： 3752 - 3760 2019.6

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER CHEMICAL SOC

The most commonly used phase change materials (PCMs), like organic compounds and inorganic salts, were limited in application by their low thermal conductivity. Herein, for the first time, alumina-encapsulated metallic Sn-based PCMs, named Sn@Al2O3, were successfully fabricated with tunable size (60-2000 nm) by a facile process from low-cost chemicals. The robust fabrication process consists of a surfactant-free solvothermal synthesis of SnO2 spheres, boehmite treatment on SnO2 spheres, calcination in the air, and the final hydrogen reduction to transform SnO2 to metallic Sn, endowing the PCMs with high potential for mass production. The as-obtained Sn@Al2O3 showed a core-shell structure, in which a main metallic Sn core located in the center covered with an Al2O3 shell with small Sn nanoparticles distributed inside. The boehmite treatment, in which the penetration of aluminum species into SnO2 spheres played an important role, was found to be responsible for the unique structure formation of final Sn@Al2O3. The understanding of structure formation mechanism gives the possibilities of a new facile way for the synthesis of metal nanoparticles and particle-distributed nanostructures. The obtained Sn@Al2O3 particles not only have high PCM content (92.37 wt %) but also show a stable thermal behavior and morphology during 100 melt freeze cycles in the air atmosphere. Furthermore, the low melting temperature of the PCM core, combined with high thermal conductivity of both core material (Sn, 66.8 W m(-1) K-1) and shell material (Al2O3, 35 W m(-1) K-1), makes Sn@Al2O3 potentially suitable for rapid thermal energy storage in the range 100-300 degrees C.

DOI： 10.1021/acsanm.9b00649

Topologically immobilized catalysis centre for long-term stable carbon dioxide reforming of methane Reviewed International journal

Shusaku Shoji, Xiaobo Peng, Tsubasa Imai, Paskalis Sahaya Murphin Kumar, Kimitaka Higuchi, Yuta Yamamoto, Tomoharu Tokunaga, Shigeo Arai, Shigenori Ueda, Ayako Hashimoto, Noritatsu Tsubaki, Masahiro Miyauchi, Takeshi Fujita, Hideki Abe

CHEMICAL SCIENCE Vol. 10 ( 13 ) page： 3701 - 3705 2019.4

Language：English Publishing type：Research paper (scientific journal) Publisher：ROYAL SOC CHEMISTRY

Methane reforming at low temperatures is of growing importance to mitigate the environmental impact of the production of synthesis gas, but it suffers from short catalyst lifetimes due to the severe deposition of carbon byproducts. Herein, we introduce a new class of topology-tailored catalyst in which tens-of-nanometer-thick fibrous networks of Ni metal and oxygen-deficient Y2O3 are entangled with each other to form a rooted structure, i.e., Ni#Y2O3. We demonstrate that the rooted Ni#Y2O3 catalyst stably promotes the carbon-dioxide reforming of methane at 723 K for over 1000 h, where the performance of traditional supported catalysts such as Ni/Y2O3 diminishes within 100 h due to the precluded mass transport by accumulated carbon byproducts. In situ TEM demonstrates that the supported Ni nanoparticles are readily detached from the support surface in the reaction atmosphere, and migrate around to result in widespread accumulation of the carbon byproducts. The long-term stable methane reforming over the rooted catalyst is ultimately attributed to the topologically immobilized Ni catalysis centre and the synergistic function of the oxygen-deficient Y2O3 matrix, which successfully inhibits the accumulation of byproducts.

DOI： 10.1039/c8sc04965c

Nanoporous Nickel Composite Catalyst for the Dry Reforming of Methane. Reviewed International journal

Takeshi Fujita, Xiaobo Peng, Akira Yamaguchi, Yohei Cho, Yongzheng Zhang, Kimitaka Higuchi, Yuta Yamamoto, Tomoharu Tokunaga, Shigeo Arai, Masahiro Miyauchi, Hideki Abe

ACS omega Vol. 3 ( 12 ) page： 16651 - 16657 2018.12

Language：English

The development of efficient catalysts with high activities and durabilities for use in the dry reforming of methane (DRM) is desirable but challenging. We report the development of a nanoporous nickel composite (nanoporous Ni/Y2O3) via a facile one-step dealloying technique, for use in the DRM. Focusing on the low-temperature DRM, our composite possessed remarkable activity and durability against coking compared with conventional particle-based Ni catalysts. This was attributed to the aluminum oxides present on the Ni surface, which suppress pore coarsening. In addition, the inert bundled Y2O3 nanowires are suitable for use as substrates for nanoporous Ni.

DOI： 10.1021/acsomega.8b02023

Intergranular amorphous films formed by DC electric field in pure zirconia Reviewed

Nobuhiro Morisaki, Hidehiro Yoshida, Tetsuro Kobayashi, Tomoharu Tokunaga, Takahisa Yamamoto

JOURNAL OF THE AMERICAN CERAMIC SOCIETY Vol. 101 ( 8 ) page： 3282 - 3287 2018.8

Language：English Publishing type：Research paper (scientific journal) Publisher：WILEY

It is difficult to obtain pure ZrO2 sintered compacts with a bulk style at room temperature because a large volumetric expansion from tetragonal to monoclinic phase (t/m) transformation occurs at around 1000 degrees C, which is lower than the sintering temperature. In contrast, pure monoclinic ZrO2 can be consolidated without shattering using flash-sintering at 1350 degrees C for 5minutes under an applied DC electric field of 175V/cm. High-resolution transmission electron microscopy and electron energy loss spectroscopy have revealed that amorphous films are formed along grain boundaries after flash-sintering at 1350 degrees C for 5minutes. Monoclinic ZrO2 flash-sintered compact including the amorphous films are able to survive without shattering through the t/m transformation, as the amorphous films partially absorb the large volumetric expansion arising from the t/m transformation. The formation of the amorphous films results from the severe reducing condition due to the applied DC electric fields during flash-sintering.

DOI： 10.1111/jace.15485

Ligand free green plasma-in-liquid synthesis of Au/Ag alloy nanoparticles Reviewed

David Čempel, Mai Thanh Nguyen, Yohei Ishida, Tomoharu Tokunaga, Tetsu Yonezawa

New Journal of Chemistry Vol. 42 ( 8 ) page： 5681 - U9 2018.4

Language：English Publishing type：Research paper (scientific journal) Publisher：Royal Society of Chemistry

Au/Ag alloy nanoparticles (NPs) were successfully prepared by a one step synthesis using HAuCl4 and [Ag(NH3)2]+ as the corresponding precursors in a microwave-induced plasma in liquid process (MWPLP) without the addition of any organic protecting or reducing agents. The time dependent reduction and particle formation during the 140 min plasma discharge were studied with TEM, UV-vis extinction spectra, and ICP-OES. After 140 min, the HAADF-STEM and EDX results indicated that the obtained Au/Ag NPs were alloy NPs. Varying the input molar ratios of the metal precursors allowed for control of the composition of the Au/Ag alloy NPs.

DOI： 10.1039/c7nj05154a

Sputter Deposition toward Short Cationic Thiolated Fluorescent Gold Nanoclusters: Investigation of Their Unique Structural and Photophysical Characteristics Using High-Performance Liquid Chromatography Reviewed International journal

Yohei Ishida, Akihiro Morita, Tomoharu Tokunaga, Tetsu Yonezawa

LANGMUIR Vol. 34 ( 13 ) page： 4024 - 4030 2018.4

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER CHEMICAL SOC

We herein present the preparation of short, bulky cationic thiolate (thiocholine)-protected fluorescent Au nanoclusters via sputter deposition over a liquid polymer matrix. The obtained Au nanoclusters showed near-infrared fluorescence and had an average core diameter of 1.7 +/- 0.6 nm, which is too large compared to that of the reported fluorescent Au nanoclusters prepared via chemical means. We revealed the mechanism of formation of this unique material using single particle electron microscopy, optical measurements, X-ray photoelectron spectroscopy (XPS), and high-performance liquid chromatography fractionations. The noncrystallized image was observed via single-particle high-angle annular dark-field scanning transmission electron microscopy observations and compared with chemically synthesized crystalline Au nanoparticle with the same diameter, which demonstrated the unique structural characteristic speculated via XPS. The size fractionation and size-dependent fluorescence measurement, together with other observations, indicated that the nanoclusters most probably contained a mixture of very small fluorescent species in their aggregated form and were derived from the sputtering process itself and not from the interaction between thiol ligands.

DOI： 10.1021/acs.langmuir.8b00067

Au/Cu Bimetallic Nanoparticles via Double-Target Sputtering onto a Liquid Polymer Reviewed International journal

Mai Thanh Nguyen, Hong Zhang, Lianlian Deng, Tomoharu Tokunaga, Tetsu Yonezawa

LANGMUIR Vol. 33 ( 43 ) page： 12389 - 12397 2017.10

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER CHEMICAL SOC

Alloy nanoparticles (NPs) of a bimetal system, Au/Cu, that form intermetallic compounds in a bulk state have been successfully produced using a double-target sputtering technique onto a low-cost and biocompatible liquid polymer (polyethylene glycol, PEG). The formation of an Au/Cu solid solution alloy in individual NPs was revealed by scanning transmission electron microscopy-energy-dispersive X-ray elemental mapping analysis. Altering the sputter currents for Au and Cu targets resulted in a tailored NP composition, but the particle sizes did not significantly vary. We found similar structures, sizes, and optical properties of Au/Cu NPs obtained by double-head sputtering on carbon-coated transmission electron microscopy grids or PEG and by Au/Cu alloy target sputtering. Random alloy formation occurred in matrix sputtering using double-target heads. This method is advantageous for manipulating the alloy composition through highly independent control of sputter parameters for each metal target.

DOI： 10.1021/acs.langmuir.7b03194

In-Situ TEM Study of a Nanoporous Ni-Co Catalyst Used for the Dry Reforming of Methane Reviewed

Takeshi Fujita, Kimitaka Higuchi, Yuta Yamamoto, Tomoharu Tokunaga, Shigeo Arai, Hideki Abe

METALS Vol. 7 ( 10 ) page： 406 2017.10

Language：English Publishing type：Research paper (scientific journal) Publisher：MDPI AG

We performed in-situ transmission electron microscopy (TEM) on a dealloyed nanoporous NiCo catalyst used for the dry reforming of methane (DRM) to investigate the origin of the catalytic activity and structural durability. The in-situ observations and local chemical analysis indicated that the DRM induced chemical demixing of Ni and Co accompanied by grain refinement, implying possible synergic effects in a general bimetallic NiCo catalyst when used for the DRM.

DOI： 10.3390/met7100406

Consolidation of undoped, monoclinic zirconia polycrystals by flash sintering Reviewed

Nobuhiro Morisaki, Hidehiro Yoshida, Tomoharu Tokunaga, Katsuhiro Sasaki, Takahisa Yamamoto

JOURNAL OF THE AMERICAN CERAMIC SOCIETY Vol. 100 ( 9 ) page： 3851 - 3857 2017.9

Language：English Publishing type：Research paper (scientific journal) Publisher：WILEY

Consolidated, monoclinic ZrO2 polycrystal was produced from undoped ZrO2 powders in air by flash sintering at the sintering temperature of 1350 degrees C for 5minutes or 3hours under an applied DC electric field of 175V/cm. When the ZrO2 was heated under the applied DC field, the electric current of the specimen steeply increased at the furnace temperature of 1335 degrees C below the sintering temperature of 1350 degrees C. When the furnace temperature was decreased from the sintering temperature of 1350 degrees C to room temperature, volumetric expansion associated with tetragonal-to-monoclinic phase transformation gradually took place at the furnace temperature from 1000 degrees C to 750 degrees C, and monoclinic ZrO2 body was remained consolidated even at room temperature in both specimens. In contrast, conventionally sintered ZrO2 without applying DC field exhibited the abrupt volumetric expansion at about 1000 degrees C, and shattered. SEM observation revealed the presence of grain-boundary second phase in the flash-sintered specimen for 3hours, which is a possible origin of keeping a bulk body at room temperature. The thinner second phase is considered to be formed also in the flash-sintered specimen for 5minutes, although the formation of the phase could not be observed clearly by SEM observation. On the other hand, XRD measurements showed that <001> directions of the monoclinic ZrO2 grains were oriented along the applied DC field after the isothermal flash sintering for 3hours while the grain alignment could not be observed in flash-sintered specimen for 5minutes. The alignment of ZrO2 grains observed in the isothermal flash sintering is considered to be closely related to the preferential direction of oxygen ionic conduction and the second phase formed along grain boundaries.

DOI： 10.1111/jace.14954

Electric current-controlled synthesis of BaTiO3 Reviewed

Yu Nakagawa, Hidehiro Yoshida, Akinori Uehashi, Tomoharu Tokunaga, Katsuhiro Sasaki, Takahisa Yamamoto

JOURNAL OF THE AMERICAN CERAMIC SOCIETY Vol. 100 ( 9 ) page： 3843 - 3850 2017.9

Language：English Publishing type：Research paper (scientific journal) Publisher：WILEY

In BaTiO3, flash-sintering associated with a surge of the specimen electric current sometimes results in an inhomogeneous microstructure including Ti-excess secondary phases because of discharging. We applied field-assisted sintering technique (FAST) under precisely controlled specimen current that was set just below the threshold value for the occurrence of flash event for BaTiO3, to avoid the occurrence of the discharging. As a result, uniform and fine-grained compacts were obtained without any secondary phases. A relative density of approximately 92% was achieved under FAST condition of 100 V/cm with a limiting current of 72 mA and soaking time of 3 hours at 1070 degrees C. The voltages during sintering under a constant current of 72 mA were found to decrease during the soaking process. Electron energy loss spectroscopy revealed the generation of excess oxygen vacancies at/near grain boundaries. The excess oxygen vacancies induced by application of DC electric fields were confirmed to reduce the voltages and to retard the shrinkage rate in a final sintering stage.

DOI： 10.1111/jace.14938

Structural Control Parameters for Formation of Single-Crystalline ss-Sn Nanorods in Organic Phase Reviewed

Lyn Marie Z. De Juan, Mai Thanh Nguyen, Tetsu Yonezawa, Tomoharu Tokunaga, Hiroki Tsukamoto, Yohei Ishida

CRYSTAL GROWTH & DESIGN Vol. 17 ( 9 ) page： 4554 - 4562 2017.9

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER CHEMICAL SOC

For the first time, investigation on the effect of lowering the synthesis temperature below room temperature (10 to -10 degrees C) and increasing the viscosity of the reaction solution at certain temperatures has been used to trigger the formation of single-crystalline ss-Sn nanorods (NRs) in a chemical synthesis using an organic solvent. These two parameters govern the energy of the particles in the solution, thereby mediating the selective attachment to the nuclei and the preferential growth of Sn along the c-axis. The length and aspect ratio of the NRs were inversely proportional to the synthesis temperature and directly proportional to the viscosity of the reaction solution. In addition, we found that poly(vinylpyrrolidone) with a high molecular weight aided the formation of longer and higher aspect ratio NRs via the bridge flocculation effect.

DOI： 10.1021/acs.cgd.7b00227

Water transport phenomena through membranes consisting of vertically-aligned double-walled carbon nanotube array

Hidetoshi Matsumoto, Shuji Tsuruoka, Yasuhiko Hayashi, Koji Abe, Kenjiro Hata, Shaoling Zhang, Yoshitaka Saito, Motohiro Aiba, Tomoharu Tokunaga, Toru Iijima, Takuma Hayashi, Hirotaka Inoue, Gehan A. J. Amaratunga

CARBON Vol. 120 page： 358 - 365 2017.8

Language：English Publishing type：Research paper (scientific journal) Publisher：PERGAMON-ELSEVIER SCIENCE LTD

Nanofluidics in CNTs is argumentative though it is theoretically calculated by various reports. It is because only a few of experimental reports are available, and the measured permeability is not so large as that suggested from the theoretical calculations. Also, water motion suppression in the confined space has not been exhibited by flux measurement. The present work explores these yet-unsolved discrepancies using the measurable size membrane of vertically aligned double-walled carbon nanotube array, which is borne with durability and flexibility, and a conventional measurement method is applied to the membranes. Water motion suppression occurs in the CNT confined space significantly, depending on temperature. Additionally, it is confirmed that the obtained permeability correlates to the reported experimental results with regard to the relationship between CNT length and permeability, and the correlation does not agree with permeability calculated from the Hagen-Poiseuille law. These results pose an insight into the inherent water transport characteristics in the CNT confined space. (C) 2017 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.carbon.2017.05.034

Small Nanosized Oxygen-Deficient Tungsten Oxide Particles: Mechanistic Investigation with Controlled Plasma Generation in Water for Their Preparation Reviewed International journal

Yohei Ishida, Shingo Motono, Wataru Doshin, Tomoharu Tokunaga, Hiroki Tsukamoto, Tetsu Yonezawa

ACS OMEGA Vol. 2 ( 8 ) page： 5104 - 5110 2017.8

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER CHEMICAL SOC

Production of oxygen-deficient tungsten oxide nanoparticles with a diameter of around 10 nm have been successfully developed using a microwave-induced plasma in liquid technique. The prepared blue-green nanoparticles exhibit strong absorption in the visible region; thus, these could be efficient visible-light photocatalysts. The high-angle annular dark-field images revealed the dislocation of tungsten, which causes oxygen deficiencies.

DOI： 10.1021/acsomega.7b00986

Nanophase-separated Ni3Nb as an automobile exhaust catalyst International journal

Toyokazu Tanabe, Tsubasa Imai, Tomoharu Tokunaga, Shigeo Arai, Yuta Yamamoto, Shigenori Ueda, Gubbala V. Ramesh, Satoshi Nagao, Hirohito Hirata, Shin-ichi Matsumoto, Takeshi Fujita, Hideki Abe

CHEMICAL SCIENCE Vol. 8 ( 5 ) page： 3374 - 3378 2017.5

Language：English Publishing type：Research paper (scientific journal) Publisher：ROYAL SOC CHEMISTRY

Catalytic remediation of automobile exhaust has relied on precious metals (PMs) including platinum (Pt). Herein, we report that an intermetallic phase of Ni and niobium (Nb) (i.e., Ni3Nb) exhibits a significantly higher activity than that of Pt for the remediation of the most toxic gas in exhaust (i.e., nitrogen monoxide (NO)) in the presence of carbon monoxide (CO). When subjected to the exhaust-remediation atmosphere, Ni3Nb spontaneously evolves into a catalytically active nanophase-separated structure consisting of filamentous Ni networks (thickness < 10 nm) that are incorporated in a niobium oxide matrix (i.e., NbOx (x < 5/2)). The exposure of the filamentous Ni promotes NO dissociation, CO oxidation and N-2 generation, and the NbOx matrix absorbs excessive nitrogen adatoms to retain the active Ni-0 sites at the metal/oxide interface. Furthermore, the NbOx matrix immobilizes the filamentous Ni at elevated temperatures to produce long-term and stable catalytic performance over hundreds of hours.

DOI： 10.1039/c6sc05473k

Methane decomposition for hydrogen production by catalytic activity of carbon black under low flow rate conditions

Tomoharu Tokunaga, Naoyuki Kishi, Kenya Yamakawa, Katsuhiro Sasaki, Takahisa Yamamoto

JOURNAL OF THE CERAMIC SOCIETY OF JAPAN Vol. 125 ( 4 ) page： 185 - 189 2017.4

Language：English Publishing type：Research paper (scientific journal) Publisher：CERAMIC SOC JAPAN-NIPPON SERAMIKKUSU KYOKAI

Recently, carbon materials were reported to work as catalysts for the production of H-2 from hydrocarbons. However, the hydrogen production rate is extremely low. To broaden the scope of carbon materials as catalysts for the decomposition of hydrocarbons, a higher H-2 production rate is required. Thus, the hydrogen production rate under conditions employing a low flow rate of hydrocarbon per unit area and a large quantity of carbon materials as the catalyst should be evaluated, and the influence of these conditions on the rate of H-2 production by carbon materials should be discussed. Herein, the H-2 production rate was measured under conditions employing a low flow rate of CH4 and a large quantity of carbon black (CB) as a catalyst. H-2 production started at 600 degrees C and the production rate was less than 0.1%. The transmission electron microscope image of CB heated in CH4 atmosphere demonstrated that a low flow rate of CH4 does not affect the reaction site (i.e., graphite edges) of CB. However, the H-2 production rate was extremely low compared to that achieved with a high flow rate. It is proposed that there is an optimal flow rate for maintaining the catalytic activity at the graphite edge of CB for decomposition of CH4. (C) 2017 The Ceramic Society of Japan. All rights reserved.

DOI： 10.2109/jcersj2.16246

Preparation of Au/Pd Bimetallic Nanoparticles by a Microwave-Induced Plasma in Liquid Process

Hiroaki Shirai, Mai Thanh Nguyen, David Cempel, Hiroki Tsukamoto, Tomoharu Tokunaga, Ying-Chih Liao, Tetsu Yonezawa

BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN Vol. 90 ( 3 ) page： 279 - 285 2017.3

Language：English Publishing type：Research paper (scientific journal) Publisher：CHEMICAL SOC JAPAN

Au/Pd alloy nanoparticles (NPs) were successfully synthesized using HAuCl4, H2PdCl4, and alpha-thioglycerol as precursors and a stabilizer, respectively, by microwave-induced plasma in liquid process (MWPLP). After only several minutes of microwave irradiation, metallic NPs were obtained in aqueous environment without any reducing agent. The reduction mechanism of metal ions was confirmed by UV-vis spectral changes. The results from HAADF-STEM and EDS indicated that synthesized NPs were bimetallic Au/Pd. Moreover, XRD patterns of synthesized NPs implied that the composition of bimetallic NPs could be controlled by changing the initial ratio of metal precursors.

DOI： 10.1246/bcsj.20160333

Directly determining the polarity of WC grains in WC-12 wt%Co alloy by ABF-STEM Reviewed

Yoshimitsu Hayashi, Tomoharu Tokunaga, Katsuhiro Sasaki, Takahisa Yamamoto

INTERNATIONAL JOURNAL OF REFRACTORY METALS & HARD MATERIALS Vol. 62 page： 9 - 13 2017.1

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCI LTD

WC grains in WC-Co alloys are shaped as truncated triangular prisms, each with a basal plane of a (0001) truncated triangle and two {1 (1) over bar 00} prismatic planes, one narrower and one wider. This anisotropic shape is related to the polarity of the WC lattice, which comes from the difference in the spacing of the W and C layers in the <0001> projection. We directly determined the relationship between the two {1 (1) over bar 00} prismatic planes and the polarity of the WC lattice by using high-resolution scanning transmission electron microscopy (STEM). High-angle annular dark-field STEM and annular bright-field STEM revealed that the wider prismatic plane had W and C atomic layers with a shorter spacing, while the narrower plane had a longer spacing. The WC/Co interface on the wider prismatic side was atomically flat, while many steps formed on the surface of the narrower prismatic side. This difference in step formation at these interfaces could have come from the difference in how their W-C bonds formed. (C) 2016 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.ijrmhm.2016.10.013

Methane Decomposition for Hydrogen Production by Catalytic Activity of Carbon Black under Low Flow Rate Conditions

Tomoharu Tokunaga, Naoyuki Kishi, Kenya Yamakawa, Katsuhiro Sasaki, Takahisa Yamamoto

ACS-Japan Vol. 125 ( 4 ) page： 185-189 2017

Water transport phenomena through membranes consisting of vertically-aligned double-walled carbon nanotube array

Hidetoshi Matsumoto, Shuji Tsuruoka, Yasuhiko Hayashi, Koji Abe, Kenjiro Hata, Shaoling Zhang, Yoshitaka Saito, Motohiro Aiba, Tomoharu Tokunaga, Toru Iijima, Takuma Hayashi

Carbon Vol. 120 page： 358–365 2017

Nanophase-separated Ni3Nb as Automobile Exhaust Catalysts Reviewed

Toyokazu Tanabe, Tsubasa Imai, Tomoharu Tokunaga, Shigeo Arai, Yuta Yamamoto, Shigenori Ueda, Gubbala V. Ramesh, Satoshi Nagao, Hirohito Hirata, Shin-ichi, Matsumoto, Takeshi Fujita, Hideki Abe

Chemical Science Vol. 8 page： 3374-3378 2017

Preparation of Au/Pd bimetallic nanoparticles by a microwave-induced plasma in liquid process Reviewed

Hiroaki Shirai, Mai Thanh Nguyen, David Čempel, Hiroki Tsukamoto, Tomoharu Tokunaga, Ying-Chih Liao, and Tetsu Yonezawa

Bulletin of the Chemical Society of Japan Vol. 90 ( 3 ) page： 279-285 2017

Intentionally Encapsulated Metal Alloys within Vertically Aligned Multi-Walled Carbon Nanotube Array via Chemical Vapor Deposition Technique

Hayashi Yasuhiko, Inoue Hirotaka, Hayashi Takuma, Hada Masaki, Nishikawa Takeshi, Tokunaga Tomoharu, Amaratunga G. A. J.

2017 IEEE INTERNATIONAL CONFERENCE ON MANIPULATION, MANUFACTURING AND MEASUREMENT ON THE NANOSCALE (3M-NANO) page： 357-361 2017

Intentionally Encapsulated Metal Alloys within Vertically Aligned Multi-Walled Carbon Nanotube Array via Chemical Vapor Deposition Technique Reviewed

Yasuhiko Hayashi, Hirotaka Inoue, Takuma Hayashi, Masaki Hada, Takeshi Nishikawa, Tomoharu Tokunaga, G. A. J. Amaratunga

2017 IEEE INTERNATIONAL CONFERENCE ON MANIPULATION, MANUFACTURING AND MEASUREMENT ON THE NANOSCALE (3M-NANO) page： 357 - 361 2017

Language：English Publishing type：Research paper (international conference proceedings) Publisher：IEEE

This paper presents a growth and characterization of vertically aligned PdxCo1-x alloy encapsulated inside Multi-Walled Carbon Nanotube (MWCNT) arrays on Pd/Co thin layers coated on Si substrate by a dc bias-enhanced plasma chemical vapor deposition (CVD) method. The Metal Alloy Encapsulated within MWCNTs (MAE-MWCNTs) were characterized by a scanning electron microscope (SEM) and a transmission electron microscopy (TEM). The SEM images show the teardrop-shape particles encapsulated within the tube top of MWCNTs. A vibrating sample magnetometer was used to study the magnetism of a large number of MAE-MWCNTs on Si substrate at room temperature. The hysteresis loop of the ME-MWCNTs shows clear ferromagnetic behavior and the easy axis of magnetization is parallel to the MEA-MWCNT tube axis, as can be elucidated from the large coercive fields and remanence values. Moreover, TEM off-axis electron holograms were used to study the magnetism of the individual MAE-MWCNT or the two pair of MAE-MWCNTs. Based on electron holography, we have successfully obtained the saturation magnetization of 0.7 T and 1.12 T for the individual MAE-MWCNT with diameters of 41 nm and 83 nm, respectively.