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Books and Other Publications Presentations Research Projects Educational Activities Contributions Other Kenta Yoshida Section Institute for Materials Research Job title Associate Professor Degree 博士（工学）（名古屋大学） 修士（工学）（名古屋大学） researchmap https://researchmap.jp/7000012652 J-GLOBAL ID 201501016368746304 Research History 4 2015/04 - 2018/03 Tohoku University Institute for Materials Research Assistant Professor 2012/04 - 2015/03 Nagoya University, Institute for Advanced Research Projected Assistant Professor 2007/04 - 2014/11 Japan Fine Ceramics Center 博士研究員 2008/08 - 2010/03 The University of York, York-Jeol Nanocentre Ph.D Researcher Education 2 Nagoya University Graduate School, Division of Engineering Department of Crystalline Materials Science 2004/04 - 2007/03 Nagoya University Faculty of Engineering Physical Engineering / Applied Physics 2002/04 - 2004/03 Professional Memberships 5 Institute of Physics The Atomic Energy Society of Japan 日本物理学会 日本金属学会 日本顕微鏡学会 Research Interests 5 Interface Surface Nanoparticles In-situ Electron Microscopy Research Areas 3 Nanotechnology/Materials / Thin-film surfaces and interfaces / Nanotechnology/Materials / Nanostructure physics / Nanotechnology/Materials / Nanostructure chemistry / Papers 80 Impact of trace silicon on irradiation hardening and embrittlement of RAFM steel subjected to neutron irradiation Lei Zhang, Yifan Zhang, Wentuo Han, Xiaoou Yi, Pingping Liu, Kenta Yoshida, Takeshi Toyama, Qian Zhan, Yasuyoshi Nagai, Somei Ohnuki, Akihiko Kimura, Farong Wan Fusion Engineering and Design 2024/04 DOI： 10.1016/j.fusengdes.2024.114309 ISSN：0920-3796 Microstructure and mechanical property of Y2O3-based ODS-Cu alloy fabricated by MA-HIP with novel elemental addition process Yusuke Shimada, Yuta Nakajima, Yoshimitsu Hishinuma, Ken-ichi Ikeda, Hiroyuki Noto, Takeo Muroga, Kenta Yoshida, Toyohiko J. Konno, Yasuyoshi Nagai Materials Chemistry and Physics 307 128223-128223 2023/10 Publisher: Elsevier BV DOI： 10.1016/j.matchemphys.2023.128223 ISSN：0254-0584 The neglected activation of tantalum in reduced activation materials Lei Zhang, Yufeng Du, Wentuo Han, Xiaoou Yi, Pingping Liu, Kenta Yoshida, Takeshi Toyama, Chi Xu, Qian Zhan, Yasuyoshi Nagai, Somei Ohnuki, Farong Wan Nuclear Materials and Energy 35 2023/06 DOI： 10.1016/j.nme.2023.101432 eISSN：2352-1791 More details Close Due to the expression of “reduced activation”, the severe radioactivity of tantalum (Ta) after neutron irradiation in early decay years is easily neglected. In the presented study, after an irradiation of only 0.3 dpa by fission neutron and followed by a cooling stage of 305 days, the RAFM steel specimen with a weight of 0.8 g possessed drastic radioactivity of 4 mSv/hour at a measuring distance of 20 cm. It was ascertained that the high radioactivity was generated by 182Ta. The severe radioactivity seriously increased the danger of material experiments, even though the original Ta addition of the steel was only 0.13 wt%. Similar deteriorative radioactivity of Ta can be generated in both fission and fusion neutron irradiations. We appeal to seriously deliberate the radioactivity of Ta and control the Ta content in the RAFM steel. Cavity evolution and void swelling in dual ion irradiated tempered martensitic steels Takuya Yamamoto, Yuan Wu, Kiyohiro Yabuuchi, Jack Haley, Kenta Yoshida, Akihiko Kimura, G. Robert Odette Journal of Nuclear Materials 576 2023/04 DOI： 10.1016/j.jnucmat.2022.154201 ISSN：0022-3115 More details Close Microstructural evolutions in two variants of the F82H 8 wt%Cr tempered martensitic steel under dual (He+ plus Fe3+) ion irradiations at 500 °C have been characterized by transmission electron microscopy. Emphasis is on understanding the combined effects of displacements per atom (dpa) and the helium/dpa ratio (He/dpa) on cavity evolution and void swelling (fv). The dual ion database includes 231 alloy-dpa-He/dpa conditions for irradiations up to ∼ 82 dpa and 3700 appm helium. We hypothesize that the large “scatter” observed in the fv data is primarily due to local microstructural variations, especially those that shield regions at shallower depths from the effects of injected interstitial atoms, which would otherwise reduce fv. More generally, our hypothesis is that the highest fv data, at a specified dpa and He/dpa, provides the most appropriate estimate of swelling for fusion neutron irradiation conditions. The dose dependence of fv can be described by an incubation dpai, marking the onset of significant void growth, and a post-incubation swelling rate, fv’ = Δfv/Δdpa. Both dpai and fv’ decrease with increasing He/dpa. The fv’ data are quantitatively consistent with a simple model for defect partitioning between evolving bubble, void, and dislocation sinks strengths and biases. Most notably, the model correctly predicts both the incubation dpai, and the subsequent fv’, in spite of the fact that they reflect somewhat different physics. Our analysis also suggests that defect recombination is modest at 500 °C. Along with other considerations, this supports the hypothesis that, even at high dpa rates, dual ion irradiations can be used to reasonably emulate void nucleation and growth for a range of fusion-relevant neutron irradiation service conditions. A companion paper incorporates the results of this study in a reduced-order, data-driven void swelling model. In situ thermal annealing transmission electron microscopy of irradiation induced Fe nanoparticle precipitation in Fe-Si alloy Y. Shimada, Y. Ikeda, K. Yoshida, M. Sato, J. Chen, Y. Du, K. Inoue, R. Maaß, Y. Nagai, T. J. Konno Journal of Applied Physics 131 (16) 2022/04 DOI： 10.1063/5.0070471 ISSN：0021-8979 eISSN：1089-7550 More details Close The typical experimental conditions inside a transmission electron microscope (TEM), such as ultra-high vacuum, high-energy electron irradiation, and surface effects of ultrathin TEM specimens, can be the origin of unexpected microstructural changes compared with that of bulk material during in situ thermal-annealing experiments. In this paper, we report on the microstructural changes of a Fe-15%Si alloy during in situ TEM annealing, where, in its bulk form, it exhibits an ordering transformation from D03 to B2 at 650 °C. Using a heating-pot type double tilt holder with a proportional-integral-differential control system, we observed the precipitation of α-Fe both at the sample surface and inside the sample. Surface precipitates formed via surface diffusion are markedly large, several tens of nm, whereas precipitates inside the specimen, which are surrounded by Fe-poor regions, reach a maximum size of 20 nm. This unexpected microstructural evolution could be attributed to vacancies on Si sites, which are induced due to high-energy electron irradiation before heating, as well as enhanced thermal diffusion of Fe atoms. Dissolution and precipitation behaviors of zircon under the atmospheric environment Toru Kitagaki, Kenta Yoshida, Pengfei Liu, Takahisa Shobu npj Materials Degradation 6 (1) 2022/02 DOI： 10.1038/s41529-021-00214-0 eISSN：2397-2106 More details Close The reactive behavior of zircon in three different solutions: 0.1 M HCl (aq), ultrapure water, and 0.1 M NaOH (aq) was examined under normal temperature and pressure conditions. Dissolved Si and Zr concentrations show that considerable Zr precipitated on the surface in all immersion cases. Bulk changes in the zircon were insignificant. However, the obvious surface change of the zircon immersed in 0.1 M NaOH (aq) was confirmed. Porous layer comprising an amorphous SiOx phase and needle crystals of ZrSiO4 around pores were detected on the near-surface area of the zircon immersed in 0.1 M NaOH (aq). Consequently, the reaction was limited when zircon was immersed in ultrapure water. Zr precipitated on the surface after the dissolution of ZrSiO4 in 0.1 M HCl (aq). Dissolved Zr and Si in 0.1 M NaOH (aq) precipitated on the surface, then the dissolution of ZrSiO4 formed a porous layer, and most dissolved Zr precipitated as zircon crystals. In Situ TEM Observation and MD Simulation of Frank Partial Dislocation Climbing in Al-Cu Alloy Jiao Chen, Kenta Yoshida, Tomoaki Suzudo, Yusuke Shimada, Koji Inoue, Toyohiko J. Konno, Yasuyoshi Nagai MATERIALS TRANSACTIONS 63 (4) 468-474 2022 Publisher: JAPAN INST METALS & MATERIALS DOI： 10.2320/matertrans.MT-M2021233 ISSN：1345-9678 eISSN：1347-5320 More details Close In situ electron irradiation using high-resolution transmission electron microscopy (HRTEM) was performed to visualize the Frank loop evolution in aluminum-copper (Al-Cu) alloy with an atomic-scale spatial resolution of 0.12 nm. The in situ HRTEM observation along the [110] direction of the FCC-Al lattice, Frank partial dislocation bounding an intrinsic stacking fault exhibited an asymmetrical climb along the (112) direction opposed to those in the reference pure Al under an electron irradiation, with a corresponding displacement-per-atom rate of 0.055- 0.120 dpa/s in a high vacuum (1.2 (c) 1015 Pa). We performed theoretical calculations to simulate the asymmetrical climb of the dislocation with Burgers vector b of 1/3(111). The Cu-Cu bonding in Guinier-Preston zones was described as a possible pinning site of the dislocation climb by molecular dynamics simulation. Microstructure, hardening and deuterium retention in CVD tungsten irradiated with neutrons at temperatures of defect recovery stages II and III Xiao Ou Yi, Tatsuya Kuwabara, Vladimir Kh Alimov, Yu Feng Du, Wen Tuo Han, Ping Ping Liu, Bin You Yan, Jiu Peng Song, Kenta Yoshida, Takeshi Toyama, Fa Rong Wan, Somei Ohnuki, Yuji Hatano, Yasuyoshi Nagai Tungsten 4 (3) 248-260 2022 DOI： 10.1007/s42864-022-00161-6 ISSN：2661-8028 eISSN：2661-8036 More details Close Samples of ultra-high-purity tungsten prepared using chemical vapour deposition (CVD) technique were irradiated with neutrons at temperatures Tirr = 373–483 K (stage II of defect recovery) and Tirr = 573–673 K (stage III) up to 0.15 displacements per atom (dpa) in the Belgian reactor (BR2). The study of the microstructure of neutron-damaged samples using transmission electron microscopy (TEM) revealed visible defects with a predominance of dislocation loops. With an increase in the neutron irradiation temperature, the spatial distribution of the loops acquired pronounced inhomogeneity, and their average size moderately increased. Cavities and voids were not observed. Irradiation-induced hardening was found and a linear correlation was obtained between Vickers microhardness and nanohardness for undamaged and neutron-irradiated CVD-W samples. Irradiation of tungsten with neutrons led to a significant increase in the retention of deuterium, which accumulated mainly in vacancy-type traps. Furthermore, the influence of the columnar grain structure in low-dose neutron-irradiated tungsten seemed to be non-trivial upon deuterium retention. Radiation-induced amorphization of M23C6 in F82H steel: An atomic-scale observation Sho Kano, Huilong Yang, John McGrady, Yoshiyuki Watanabe, Masami Ando, Dai Hamaguchi, Takashi Nozawa, Hiroyasu Tanigawa, Kenta Yoshida, Tamaki Shibayama, Hiroaki Abe Journal of Nuclear Materials 558 2022/01 DOI： 10.1016/j.jnucmat.2021.153345 ISSN：0022-3115 More details Close The purpose of the present study is to clarify the instability behavior of M23C6 under irradiation, specifically the occurrence of radiation-induced amorphization (RIA). Ion irradiation of 10.5 MeV-Fe3+ at elevated temperatures from 573 to 623 K was conducted into the reduced activation ferritic/martensitic steels (F82H) and its model alloy (Fe-8Cr-0.1C). A bilayer contrast of the particle consisting of an amorphous-rim phase and inner crystalline core of M23C6 was observed in the irradiated F82H specimen, but not in the model alloy. From the high-resolution electron microscope observation, the preferential occupation site of W into M23C6 lattice was identified as 8c-site prior to irradiation in F82H specimen, which shifted to other sites due to chemical disordering upon irradiation. Evaluation of the intensity ratio between 8c and another site of M23C6, 8c/4a, then revealed that the extent of chemical disordering of W was mitigated at the amorphous-crystal interface region in comparison with the central of the particle. The hypothesis for the formation mechanism of an amorphous-rim in M23C6 was presumed as the deviation from the stoichiometric composition at the local interface due to the irradiation-enhanced diffusion and/or ballistic mixing under the current circumstances, although the efforts from experimental and/or simulation studies are still necessary to achieve a further understanding of the RIA behavior in M23C6. Microstructural changes of oxide dispersion strengthened copper powders fabricated by mechanical alloying Yusuke Shimada, Masataka Mizumoto, Yoshimitsu Hishinuma, Ken-ichi Ikeda, Kenta Yoshida, Hiroyuki Noto, Bing Ma, Takeo Muroga, Yasuyoshi Nagai, Toyohiko J. Konno Fusion Engineering and Design 173 112804-112804 2021/12 Publisher: Elsevier BV DOI： 10.1016/j.fusengdes.2021.112804 ISSN：0920-3796 Lattice Softening in Metastable bcc CoxMn100−x (001) Ferromagnetic Layers for a Strain-Free Magnetic Tunnel Junction Kevin Elphick, Kenta Yoshida, Tufan Roy, Tomohiro Ichinose, Kazuma Kunimatsu, Tomoki Tsuchiya, Kazuya Z. Suzuki, Masahito Tsujikawa, Yasuyoshi Nagai, Shigemi Mizukami, Masafumi Shirai, Atsufumi Hirohata Physical Review Applied 16 (5) 2021/11/30 Publisher: American Physical Society (APS) DOI： 10.1103/physrevapplied.16.054052 eISSN：2331-7019 Strategy of Extra Zr Doping on the Enhancement of Thermoelectric Performance for TiZrxNiSn Synthesized by a Modified Solid-State Reaction. International-journal Jun-Liang Chen, Hengquan Yang, Chengyan Liu, Jisheng Liang, Lei Miao, Zhongwei Zhang, Pengfei Liu, Kenta Yoshida, Chen Chen, Qian Zhang, Qi Zhou, Yuntiao Liao, Ping Wang, Zhixia Li, Biaolin Peng ACS applied materials & interfaces 13 (41) 48801-48809 2021/10/20 DOI： 10.1021/acsami.1c14723 More details Close Half-Heusler alloys, which possess the advantages of high thermal stability, a large power factor, and good mechanical property, have been attracting increasing interest in mid-temperature thermoelectric applications. In this work, extra Zr-doped TiZrxNiSn samples were successfully prepared by a modified solid-state reaction followed by spark plasma sintering. It demonstrates that extra Zr doping could not only improve the power factor on account of an increase in the Seebeck coefficient but also suppress the lattice thermal conductivity originated from the strengthened phonon scattering by the superlattice nanodomains and the secondary nanoparticles. As a consequence, an increased power factor of 3.29 mW m-1 K-2 and a decreased lattice thermal conductivity of 1.74 W m-1 K-1 are achieved in TiZr0.015NiSn, leading to a peak ZT as high as 0.88 at 773 K and an average ZT value up to 0.62 in the temperature range of 373-773 K. This work gives guidance for optimizing the thermoelectric performance of TiNiSn-based alloys by modulating the microstructures on the secondary nanophases and superlattice nanodomains. Heavy-ion irradiation and post-irradiation annealing effects in explosion-welded CuCrZr/316LN joints for ITER application Xiaoou Yi, Yufeng Du, Diancheng Geng, Zihao Li, Wentuo Han, Pingping Liu, Jiming Chen, Kiyohiro Yabuuchi, Kenta Yoshida, Somei Ohnuki, Qian Zhan, Farong Wan, Yasuyoshi Nagai Materials Characterization 178 2021/08 DOI： 10.1016/j.matchar.2021.111252 ISSN：1044-5803 More details Close Bimetallic plates of CuCrZr/316LN are important heat sink components in the ITER first wall. Their in-reactor performance was investigated with 6.4 MeV Fe3+ ion irradiation (500 °C/10.5 dpa), as an analogue for neutron damage. Detailed characterizations showed that the CuCrZr/316LN joints have maintained good structural integrity after irradiation. The as-irradiated interface consisted of a nanocrystalline interlayer, typically of <1 μm in width, mixed of CuCrZr and 316LN grains measuring 20–250 nm in size. Black-spots and loop/loop rafts dominated the damage microstructure on 316LN and CuCrZr sides of the interface, respectively. A series of 30 min long post-irradiation annealing experiments saw the onset of interlayer evolution in CuCrZr/316LN joints at 400 °C by grain boundary motion and Ostwald ripening, and further acceleration at ≥600 °C. Structural collapse of the interlayer is expected at extended time scales. Finally, a brief comparison between heavy-ion and neutron irradiation damage (Yi et al. 2021) in CuCrZr/316LN joints is made, with regard to defect production and interfacial transport behaviour of chemical elements. Neutron irradiation response of explosion-welded CuCrZr/316LN joints for ITER application Xiaoou Yi, Yufeng Du, Yihang Li, Wentuo Han, Pingping Liu, Kenta Yoshida, Takeshi Toyama, Jiming Chen, Qian Zhan, Farong Wan, Somei Ohnuki, Yasuyoshi Nagai Fusion Engineering and Design 169 112620-112620 2021/08 Publisher: Elsevier BV DOI： 10.1016/j.fusengdes.2021.112620 ISSN：0920-3796 Radiation-enhanced diffusion of copper in iron studied by three-dimensional atom probe T. Toyama, C. Zhao, T. Yoshiie, S. Yamasaki, S. Uno, M. Shimodaira, H. Miyata, T. Suzudo, Y. Shimizu, K. Yoshida, K. Inoue, Y. Nagai Journal of Nuclear Materials 556 153176-153176 2021/07 Publisher: Elsevier BV DOI： 10.1016/j.jnucmat.2021.153176 ISSN：0022-3115 Correlative atom probe tomography and scanning transmission electron microscopy reveal growth sequence of LPSO phase in Mg alloy containing Al and Gd. International-journal Koji Inoue, Kenta Yoshida, Yasuyoshi Nagai, Kyosuke Kishida, Haruyuki Inui Scientific reports 11 (1) 3073-3073 2021/02/04 DOI： 10.1038/s41598-021-82705-3 More details Close Atom probe tomography (APT) and transmission electron microscopy (TEM)/scanning transmission electron microscopy (STEM) have been used correlatively to explore atomic-scale local structure and chemistry of the exactly same area in the vicinity of growth front of a long-period stacking ordered (LPSO) phase in a ternary Mg-Al-Gd alloy. It is proved for the first time that enrichment of Gd atoms in four consecutive (0001) atomic layers precedes enrichment of Al atoms so that the formation of Al6Gd8 clusters occurs only after sufficient Al atoms to form Al6Gd8 clusters diffuse into the relevant portions. Lateral growth of the LPSO phase is found to occur by &＃39;ledge&＃39; mechanism with the growth habit plane either {1[Formula: see text]00} or {11[Formula: see text]0} planes. The motion of ledges that give rise to lateral growth of the LPSO phase is considered to be controlled by diffusion of Al atoms. Iron nitride, α″-Fe16N2, around <100> interstitial type dislocation loops in neutron-irradiated iron T. Yoshiie, K. Inoue, K. Yoshida, T. Toyama, Y. Satoh, Y. Nagai Philosophical Magazine 101 (10) 1202-1213 2021 DOI： 10.1080/14786435.2021.1891317 ISSN：1478-6435 eISSN：1478-6443 More details Close Atom probe tomography (APT) and selected area electron diffraction (SAED) by transmission electron microscopy (TEM) were applied to nano-scale precipitates formed in a neutron-irradiated iron (99.99% pure) at high temperatures. In the conventional TEM, we discovered donut-type precipitates on the {100} planes that formed at the dilatational side of interstitial type dislocation loops with the Burgers vector of <100> on the habit planes of {100} in the bcc iron lattice. The precipitates were identified as nitride, bct α″-Fe N , by chemical composition and lattice structural analyses using APT and SAED. Image contrasts of the α″-Fe N in a weak beam dark-field electron microscopy study were carefully analysed with the diffraction vector and the sign of deviation parameter from the Bragg condition, and it was concluded to be a selective visualisation of α″-Fe N on one of the {100} planes. These results were in agreement with the crystallographic orientation between the α″-Fe N and matrix iron, thereby bridging a knowledge gap in α″-Fe N formation during neutron irradiation using a sodium-cooled experimental fast reactor, JOYO, or a 14 MeV D-T neutron source, RTNS-II. 16 2 16 2 16 2 16 2 16 2 In-situ WB-STEM observation of dislocation loop behavior in reactor pressure vessel steel during post-irradiation annealing Yufeng Du, Kenta Yoshida, Yusuke Shimada, Takeshi Toyama, Koji Inoue, Kazuto Arakawa, Tomoaki Suzudo, Konstantinovic J. Milan, Robert Gerard, Somei Ohnuki, Yasuyoshi Nagai Materialia 12 2020/08 DOI： 10.1016/j.mtla.2020.100778 eISSN：2589-1529 More details Close To better understand the thermal stability of dislocation loops formed by long-term neutron irradiation in reactor pressure vessel (RPV) steels, in-situ scanning transmission electron microscopy (STEM) observation was performed for a surveillance test specimen of a European pressurized water reactor (PWR). The surveillance test specimen was neutron irradiated to a fluence of 8.2 × 10 neutrons•m . A membrane sample from the surveillance test specimen was annealed at 673 K and 723 K for 30 min using a heating holder, and the same area was in-situ observed under STEM. After annealing, dislocation loops with Burgers vectors of ½ 〈111〉 and 〈100〉 were quantitatively examined. When annealing temperature increased from 673 K to 723 K, the number of dislocation loops decreases, whereas the size of them becomes larger. Correspondingly, the proportion of 〈100〉 dislocation loops changes from 27% to 45%. The ratio of 〈100〉 to ½ 〈111〉 loops increases with annealing temperature rising. The evolution process of dislocation loops during annealing at 723 K was in-situ observed and analyzed to shed light on the transformation mechanism of dislocation loops going from ½ 〈111〉 to 〈100〉. It is the first time to directly observe that two ½ 〈111〉 dislocation loops collide with each other and coalesce to form a 〈100〉 dislocation loop. Moreover, small ½ 〈111〉 dislocation loops could be absorbed by large 〈100〉 dislocation loops, whereas the Burgers vector of 〈100〉 loops remained unchanged. Dislocation decoration occurs during annealing due to the interaction between dislocations and loops. The dislocations decorated by loops are pretty stable during the continuous annealing process, which is well explained by molecular dynamics simulation. 23 −2 Experimental inspection of a computationally-designed NiCrMnSi Heusler alloy with high Curie temperature Peer-reviewed Yuta Onodera, Kelvin Elphick, Takuro Kanemura, Tufan Roy, Tomoki Tsuchiya, Masahito Tsujikawa, Kenta Yoshida, Yasuyoshi Nagai, Shigemi Mizukami, Atsufumi Hirohata, Masafumi Shirai Japanese Journal of Applied Physics (accepted) 59 (7) 073003-073003 2020/06 Publisher: IOP Publishing DOI： 10.35848/1347-4065/ab9c75 ISSN：0021-4922 eISSN：1347-4065 Boosting High Thermoelectric Performance of Ni-Doped Cu1.9S by Significantly Reducing Thermal Conductivity. International-journal Peer-reviewed Feihong Shen, Yanyan Zheng, Lei Miao, Chengyan Liu, Jie Gao, Xiaoyang Wang, Pengfei Liu, Kenta Yoshida, Huanfu Cai ACS applied materials & interfaces 12 (7) 8385-8391 2020/02/19 Publisher: AMER CHEMICAL SOC DOI： 10.1021/acsami.9b18078 ISSN：1944-8244 eISSN：1944-8252 More details Close At present, copper sulfide materials have been predicted as promising thermoelectric materials due to their inexpensiveness and nontoxicity property. Most researches on copper sulfide are focused on Cu2S and Cu1.8S because they are more easily synthesized into a single phase; however, the improper electrical conductivity greatly hindered their thermoelectric properties. In this work, a series of high-performance Cu1.9-xNi x S (x = 0, 0.01, 0.015, and 0.02) bulk samples were fabricated by accurately manipulating the ratio of Cu/S with appropriate Ni-doping. The thermoelectric properties of Ni-doped Cu1.9S were explored in detail for the first time. It can be found that carrier thermal conductivity and lattice thermal conductivity of Cu1.9-xNi x S were effectively reduced via Ni-doping, simultaneously, without the great influence on the power factor. Here, the carrier thermal conductivity (κe) was reduced due to the extreme reduction of Hall carrier concentration. In addition, amounts of nanopores introduced by Ni-doping and complex crystal structure from the phase transition of the second phase strengthen the phonon scattering and reduce lattice thermal conductivity (κl) remarkably. As a consequence, the lowest carrier thermal conductivity and lattice thermal conductivity reach 0.006 and 1.08 W m-1 K-1 for Cu1.88Ni0.02S at 773 K, and the average ZT is about 0.39 from 323 to 773 K (the ZTmax is about 0.9 at 773 K). This work demonstrates that low-cost and easily fabricated Ni-doped Cu1.9S is a pleasurable candidate for thermoelectric application despite it usually being treated as an ion conductor. Helium effects on recovery and recrystallization of powder metallurgically processed tungsten Akira Hasegawa, Takeshi Miyazawa, Daichi Itou, Takaya Hattori, Kenta Yohida, Shuhei Nogami Physica Scripta 2020 (T171) 2020/01/01 DOI： 10.1088/1402-4896/ab408d ISSN：0031-8949 eISSN：1402-4896 More details Close To study the effects of helium (He) produced by the nuclear transmutation of 14 MeV neutron irradiation on the stability of grain microstructure of tungsten (W)-fabricated through a powder metallurgically (PM) process-high energy He and post implantation experiments were conducted. The recovery of worked structure and recrystallization behavior were examined using hardness measurement and microstructural observation. He with a concentration of 20 appm was implanted homogeneously though the specimen thickness below 100 °C. Post-implantation annealing was then conducted from 1100 °C to 1500 °C in vacuum. The hardness of the PM-W specimen increased after the He implantation, and the decrease of the hardening through the annealing was suppressed in the He-implanted specimens. Metallographic observations demonstrated that the dislocation cell structure in the grain of He-implanted PM-W was retained even after the 10 h annealing at 1500 °C. In conclusion, the 20 appm He suppressed the recovery of cell structure and recrystallization of the PM-W up to 1500 °C. Defect characterization, mechanical and thermal property evaluation in CVD-W after low-dose neutron irradiation Peer-reviewed Xiaoou Yi, Lei Zhang, Wentuo Han, Jiao Chen, Pingping Liu, Yanwei Lv, Jiupeng Song, Luwei Xue, Diancheng Geng, Kenta Yoshida, Takeshi Toyama, Qian Zhan, Farong Wan, Somei Ohnuki, Yasuyoshi Nagai International Journal of Refractory Metals and Hard Materials 85 2019/12 DOI： 10.1016/j.ijrmhm.2019.105004 ISSN：0263-4368 eISSN：2213-3917 More details Close © 2019 Elsevier Ltd Ultra-high purity (> 99.9999 wt%) chemical vapour deposited tungsten (CVD–W) samples were neutron irradiated in the BR2 reactor (Belgium) at Tirr < 210 °C to ~ 0.15 dpa, followed by isochronal annealing at 500, 800 and 1100 °C. Defect characterization showed that dislocation loops dominated the as-irradiated damage microstructure and were mostly ≤5 nm. Void formation was observed after post-irradiation annealing at 1100 °C. The mechanical and thermal properties of CVD-W were evaluated based on tensile tests, Vickers hardness and temperature wave analysis. Fractography study suggested that a transition from intergranular fracture to cleavage fracture took place in the material after neutron irradiation. Hardening was found ~ 23% after irradiation. Subsequent annealing below 800 °C saw further increase in hardness, featuring a maximum value of about Hv = 487. Softening occurred at 1100 °C. Thermal diffusivity dropped by ~ 65% after irradiation and ~ 40% of this degradation recovered at 1100 °C. Evaluation of spatial and temporal resolution on in situ annealing aberration-corrected transmission electron microscopy with proportional-integral-differential controller. International-journal Peer-reviewed Yusuke Shimada, Kenta Yoshida, Koji Inoue, Takahisa Shiraishi, Takanori Kiguchi, Yasuyoshi Nagai, Toyohiko J Konno Microscopy (Oxford, England) 68 (3) 271-278 2019/06/01 DOI： 10.1093/jmicro/dfz010 More details Close The in situ annealing observation in transmission electron microscope (TEM) is one of the effective methods for imaging thermally induced microstructural changes. For applying this dynamical characterization to bulk samples fabricated by ion-milling, electro-polishing or focused ion beam (FIB) mill, it is generally needed to use a heating-pot type system. We here report an initial trial to improve the spatial and temporal resolution during the in-situ annealing observation of bulk samples using a spherical aberration corrected (AC) TEM with a new thermal control unit. The information limit of 1.5 Å and the point resolution of 2.0 Å are achieved under isothermal annealing at 350°C, which is the same resolution at room temperature, and it is affected strongly of sample drift by the temperature variation. The sample is heated at a heating rate of +1.0°C/s, the drift distance observed by a TV readout speed CCD camera is less than 2.0 Å/s. Influence of gas environment and heating on atomic structures of platinum nanoparticle catalysts for proton-exchange membrane fuel cells. International-journal Peer-reviewed Kenta Yoshida, Xudong Zhang, Yusuke Shimada, Yasuyoshi Nagai, Tomoki Hiroyama, Nobuo Tanaka, Leonardo Lari, Michael R Ward, Edward D Boyes, Pratibha L Gai Nanotechnology 30 (17) 175701-175701 2019/04/26 Publisher: IOP PUBLISHING LTD DOI： 10.1088/1361-6528/aafe1e ISSN：0957-4484 eISSN：1361-6528 More details Close Atomic-scale relaxations of platinum nanoparticles (Pt NPs) for fuel-cell catalysts are evaluated by spherical-aberration corrected environmental transmission electron microscopy (ETEM) under reference high-vacuum and N2 atmospheres, and then under reactive H2, CO and O2 atmospheres, combined with ex situ durability test using an electrochemical half-cell. In high-vacuum, increasing roughness due to continuous relaxation of surface-adsorbed Pt atoms is quantified in real-space. Under H2 and N2 atmospheres at a critical partial pressure of 1 × 10-2 Pa the stability of the surface facets is for the first time found to be improved. The adsorption behaviour of CO molecules is investigated using experimentally measured Pt-Pt bond lengths on the topmost surface layer of Pt NPs. The deactivation of Pt NPs in the anode environment of a proton-exchange-membrane fuel-cell is demonstrated at the atomic-scale in the ETEM, and the transformation of NPs into disordered nanoclusters is systematically quantified using the partial size distribution of Pt atomic clusters under controlled heating experiments at 423, 573 and 723 K. Radiation-hardening and nano-cluster formation in neutron-irradiated 9Cr–2W low activation steels with different Si contents Peer-reviewed Y. F. Zhang, Q. Zhan, S. Ohnuki, A. Kimura, F. R. Wan, K. Yoshida, Y. Nagai Journal of Nuclear Materials 517 1-8 2019/04 DOI： 10.1016/j.jnucmat.2019.01.053 ISSN：0022-3115 More details Close © 2019 Elsevier B.V. Two kinds of 9Cr–2W steels with and without the addition of 0.1 wt% Si were irradiated with neutrons up to a fluence of 4.8 × 10 23 n/m 2 at 563 K. Precipitates, dislocation loops, radiation-enhanced nano-clusters and radiation-hardening were studied using advanced electron microscopy and micro-hardness test. Si reduced the number density of dislocation loops, and therefore the extent of radiation-hardening decreased. It also favored the formation of silicide-like nano-clusters. In this study, the role of Si in neutron irradiated 9Cr–2W steels is discussed, and then extended to nano-clusters and irradiation-hardening. Contribution of irradiation-induced defects to hardening of a low-copper reactor pressure vessel steel Peer-reviewed Masaki Shimodaira, Takeshi Toyama, Kenta Yoshida, Koji Inoue, Naoki Ebisawa, Keiko Tomura, Toshimasa Yoshiie, Milan J. Konstantinovic, Robert Gerard, Yasuyoshi Nagai ACTA MATERIALIA 155 402-409 2018/08 Publisher: PERGAMON-ELSEVIER SCIENCE LTD DOI： 10.1016/j.actamat.2018.06.015 ISSN：1359-6454 eISSN：1873-2453 More details Close We investigated the fluence dependence of irradiation-induced solute cluster, dislocation loop, and very small defect to reveal the hardening mechanism in surveillance test specimens from a reactor pressure vessel steel with low-Cu content (0.04 wt%) using atom probe tomography (APT), weak-beam scanning transmission electron microscopy (WB-STEM), and positron annihilation spectroscopy. A high number density (>10(23) m(-3)) of solute clusters mainly composed of Ni, Mn, and Si atoms were found in highly neutron irradiated specimens (similar to 10(24) neutrons m(-2) (E>1 MeV)) by APT. These solute clusters were one of the main sources of hardening as reported previously. On the other hand, it was also revealed that dislocation loops were formed with a number density of similar to 10(22) m(-3) in the high-fluence specimens by WB-STEM. The estimated hardening due to dislocation loops was more than half of the actual hardening, showing that dislocation loops are also main source of irradiation hardening at high neutron fluence with the solid experimental evidences. Regarding specimens subjected to a low neutron fluence (similar to 10(23) neutrons m(-2)), very small defects, not detected by either WB-STEM or APT, were formed by positron annihilation spectroscopy. This result suggested that, at a low neutron fluence, the defects were the initial hardening source and they may grow the dislocation loops observed by WB-STEM at high fluence range. (C) 2018 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. Weak-beam scanning transmission electron microscopy for quantitative dislocation density measurement in steels. International-journal Peer-reviewed Kenta Yoshida, Masaki Shimodaira, Takeshi Toyama, Yasuo Shimizu, Koji Inoue, Toshimasa Yoshiie, Konstantinovic J Milan, Robert Gerard, Yasuyoshi Nagai Microscopy (Oxford, England) 66 (2) 120-130 2017/04/01 Publisher: OXFORD UNIV PRESS DOI： 10.1093/jmicro/dfw111 ISSN：2050-5698 eISSN：2050-5701 More details Close To evaluate dislocations induced by neutron irradiation, we developed a weak-beam scanning transmission electron microscopy (WB-STEM) system by installing a novel beam selector, an annular detector, a high-speed CCD camera and an imaging filter in the camera chamber of a spherical aberration-corrected transmission electron microscope. The capabilities of the WB-STEM with respect to wide-view imaging, real-time diffraction monitoring and multi-contrast imaging are demonstrated using typical reactor pressure vessel steel that had been used in an European nuclear reactor for 30 years as a surveillance test piece with a fluence of 1.09 × 1020 neutrons cm-2. The quantitatively measured size distribution (average loop size = 3.6 ± 2.1 nm), number density of the dislocation loops (3.6 × 1022 m-3) and dislocation density (7.8 × 1013 m m-3) were carefully compared with the values obtained via conventional weak-beam transmission electron microscopy studies. In addition, cluster analysis using atom probe tomography (APT) further demonstrated the potential of the WB-STEM for correlative electron tomography/APT experiments. Reassessment of oxidation-induced amorphization and dissolution of Nb precipitates in Zr-Nb nuclear fuel cladding tubes Peer-reviewed Matsukawa, Y., Kitayama, S., Murakami, K., Shinohara, Y., Yoshida, K., Maeno, H., Yang, H. L., Toyama, T., Yasuda, K., Watanabe, H., Kimura, A., Muta, H., Yamanaka, S., Li, Y. F., Satoh, Y., Kano, S., Abe, H. Acta Materialia 127 153-164 2017 DOI： 10.1016/j.actamat.2017.01.032 Atomic-Resolution HAADF-STEM Study of Ag/Al2O3 Catalysts for Borrowing-Hydrogen and Acceptorless Dehydrogenative Coupling Reactions of Alcohols Peer-reviewed Kenta Yoshida, Kenichi Kon, Ken-ichi Shimizu TOPICS IN CATALYSIS 59 (19-20) 1740-1747 2016/12 Publisher: SPRINGER/PLENUM PUBLISHERS DOI： 10.1007/s11244-016-0695-7 ISSN：1022-5528 eISSN：1572-9028 More details Close We study HAADF-STEM analysis of Ag/Al2O3 samples (as-calcined and reduced at 25, 300, 500 and 900 degrees C). Ag atoms are classified into subnanoclusters (0.3-1 nm), nanoclusters (1-3 nm), nanoparticles (3-10 nm) and polycrystals ([10 nm). The size of Ag increases with the reduction temperature, which is supported by EXAFS analysis. The effect of Ag size on the activity for borrowing-hydrogen and acceptorless dehydrogenative couplings of alcohols is discussed. Strain Field in Ultrasmall Gold Nanoparticles Supported on Cerium-Based Mixed Oxides. Key Influence of the Support Redox State Peer-reviewed Miguel Lopez-Haro, Kenta Yoshida, Eloy del Rio, Jose A. Perez-Omil, Edward D. Boyes, Susana Trasobares, Jian-Min Zuo, Pratibha L. Gai, Jose J. Calvino LANGMUIR 32 (17) 4313-4322 2016/05 Publisher: AMER CHEMICAL SOC DOI： 10.1021/acs.langmuir.6b00758 ISSN：0743-7463 More details Close Using a method that combines experimental and simulated Aberration-Corrected High Resolution Electron Microscopy images with digital image processing and structure modeling, strain distribution maps within gold nanoparticles relevant to real powder type catalysts, i.e., smaller than 3 nm, and supported on a ceria-based mixed oxide have been determined. The influence of the reduction state of the support and particle size has been examined. In this respect, it has been proven that reduction even at low temperatures induces a much larger Compressive strain on the first {111} planes at the; interface. This increase in compression fully explains, in accordance with previous DFT calculations, the loss of CO adsorption capacity of the interface area previously reported for Au supported on ceria-based oxides. Visualisation of single atom dynamics in water gas shift reaction for hydrogen generation Peer-reviewed Pratibha L. Gai, Kenta Yoshida, Michael R. Ward, Michael Walsh, Richard T. Baker, Leon van de Water, Mike J. Watson, Edward D. Boyes CATALYSIS SCIENCE & TECHNOLOGY 6 (7) 2214-2227 2016 Publisher: ROYAL SOC CHEMISTRY DOI： 10.1039/c5cy01154j ISSN：2044-4753 eISSN：2044-4761 More details Close The water gas shift (WGS) reaction, CO + H2O -> CO2 + H-2, is the basis of heterogeneous catalysis important in the generation of clean hydrogen energy for fuel cells, transportation fuels and in ammonia manufacture. Ceria supported gold and related nanoparticles are potentially viable catalysts for the low temperature WGS reaction. The WGS catalytic reaction is a dynamic process and takes place on the solid catalyst surface at the atomic level. The current understanding of the reaction is inferred from studies of static catalysts and from indirect chemical studies without single atom sensitivity. Therefore the nature of dynamic atomic processes in the WGS reaction has remained inaccessible. Since the catalyst reaction site and atomic processes by which it activates and deactivates, change both in magnitude and mechanism with the reaction environment it is of fundamental importance to visualise the dynamic catalyst at the atomic level in WGS (CO + water mixture) environments, in real time. Novel environmental (scanning) transmission electron microscope with singe atom resolution is used herein to directly visualise and characterise, in real time, evolving atomic structures and processes in practical gold/ceria catalysts in controlled WGS environments. The in situ observations in WGS have revealed the formation of clusters of only a few gold atoms resulting from single atom dynamics and the catalytic effect of low coordination surface sites. The new insights have important implications for applications of nanoparticles in chemical process technologies including for transportation fuels and emission control. Dynamic wet-ETEM observation of Pt/C electrode catalysts in a moisturized cathode atmosphere. International-journal Peer-reviewed Kenta Yoshida, Alexander N Bright, Michael R Ward, Leonardo Lari, Xudong Zhang, Tomoki Hiroyama, Edward D Boyes, Pratibha L Gai Nanotechnology 25 (42) 425702-425702 2014/10/24 Publisher: IOP PUBLISHING LTD DOI： 10.1088/0957-4484/25/42/425702 ISSN：0957-4484 eISSN：1361-6528 More details Close The gas injection line of the latest spherical aberration-corrected environmental transmission electron microscope has been modified for achieving real-time/atomic-scale observations in moisturised gas atmospheres for the first time. The newly developed Wet-TEM system is applied to platinum carbon electrode catalysts to investigate the effect of water molecules on the platinum/carbon interface during deactivation processes such as sintering and corrosion. Dynamic in situ movies obtained in dry and 24% moisturised nitrogen environments visualize the rapid rotation, migration and agglomeration of platinum nanoparticles due to the physical adsorption of water and the hydroxylation of the carbon surface. The origin of the long-interconnected aggregation of platinum nanoparticles was discovered to be a major deactivation process in addition to conventional carbon corrosion. In situ observation on hydrogenation of Mg-Ni films using environmental transmission electron microscope with aberration correction Peer-reviewed Junko Matsuda, Kenta Yoshida, Yukichi Sasaki, Naoki Uchiyama, Etsuo Akiba APPLIED PHYSICS LETTERS 105 (8) 083903 2014/08 Publisher: AMER INST PHYSICS DOI： 10.1063/1.4894101 ISSN：0003-6951 eISSN：1077-3118 More details Close In situ transmission electron microscopy (TEM) was performed to observe the hydrogenation of Mg-Ni films in a hydrogen atmosphere of 80-100 Pa. An aberration-corrected environmental TEM with a differential pumping system allows us to reveal the Angstrom-scale structure of the films in the initial stage of hydrogenation: first, nucleation and growth of Mg2NiH4 crystals with a lattice spacing of 0.22 nm in an Mg-rich amorphous matrix of the film occurs within 20 s after the start of the high-resolution observation, then crystallization of MgH2 with a smaller spacing of 0.15 nm happens after approximately 1 min. Our in situ TEM method is also applicable to the analysis of other hydrogen-related materials. (C) 2014 AIP Publishing LLC. Correlations between atomic structure and giant magnetoresistance ratio in Co-2(Fe, Mn) Si spin valves Peer-reviewed L. Lari, K. Yoshida, P. L. Galindo, J. Sato, J. Sizeland, D. Gilks, G. M. Uddin, Z. Nedelkoski, P. J. Hasnip, A. Hirohata, M. Oogane, Y. Ando, V. K. Lazarov JOURNAL OF PHYSICS D-APPLIED PHYSICS 47 (32) 322003 2014/08 Publisher: IOP PUBLISHING LTD DOI： 10.1088/0022-3727/47/32/322003 ISSN：0022-3727 eISSN：1361-6463 More details Close We show that the magnetoresistance of Co2FexMn1-x Si-based spin valves, over 70% at low temperature, is directly related to the structural ordering in the electrodes and at the electrodes/spacer (Co2FexMn1-x Si/Ag) interfaces. Aberration-corrected atomic resolution Z-contrast scanning transmission electron microscopy of device structures reveals that annealing at 350 degrees C and 500 degrees C creates partial B-2/L(2)1 and fully L2(1) ordering of electrodes, respectively. Interface structural studies show that the Ag/Co2FexMn1-x Si interface is more ordered compared to the Co2FexMn1-x Si/Ag interface. The release of interface strain is mediated by misfit dislocations that localize the strain around the dislocation cores, and the effect of this strain is assessed by first principles electronic structure calculations. This study suggests that by improving the atomic ordering and strain at the interfaces, further enhancement of the magnetoresistance of CFMS-based current-perpendicular-to-plane spin valves is possible. B2 Atomic Disorder in Co2FexMn1-xSi Heusler Alloys Peer-reviewed P.J. Hasnip, C. H. Loach, J. H. Smith, M. I. J. Probert, D. Gilks, J. Sizeland, K. Yoshida, M. Oogane, A. Hirohata, V. K. Lazarov Journal of the Magnetics Society of Japan 38 50-55 2014/03/20 DOI： 10.3379/msjmag.1402R010 The Effect of Cobalt-Sublattice Disorder on Spin Polarisation in Co2FexMn1-xSi Heusler Alloys Peer-reviewed Philip J. Hasnip, Christian H. Loach, Joseph H. Smith, Matthew I. J. Probert, Daniel Gilks, James Sizeland, Leonardo Lari, James Sagar, Kenta Yoshida, Mikihiko Oogane, Atsufumi Hirohata, Vlado K. Lazarov MATERIALS 7 (3) 1473-1482 2014/03 Publisher: MDPI AG DOI： 10.3390/ma7031473 ISSN：1996-1944 eISSN：1996-1944 More details Close In this work we present a theoretical study of the effect of disorder on spin polarisation at the Fermi level, and the disorder formation energies for Co2FexMn1-xSi (CFMS) alloys. The electronic calculations are based on density functional theory with a Hubbard U term. Chemical disorders studied consist of swapping Co with Fe/Mn and Co with Si; in all cases we found these are detrimental for spin polarisation, i.e., the spin polarisation not only decreases in magnitude, but also can change sign depending on the particular disorder. Formation energy calculation shows that Co-Si disorder has higher energies of formation in CFMS compared to Co2MnSi and Co2FeSi, with maximum values occurring for x in the range 0.5-0.75. Cross-sectional structural studies of reference Co2MnSi, Co2Fe0.5Mn0.5Si, and Co2FeSi by Z-contrast scanning transmission electron microscopy are in qualitative agreement with total energy calculations of the disordered structures. Spin-Polarised Electron Transport across an Abrupt or Partially Intermixed Fe/GaAs(001) Interface Peer-reviewed A. Hirohata, L. R. Fleet, K. Yoshida, H. Kobayashi, Y. Kaneko, Y. Ohno, S Honda, J. Inoue, H. Ohno Journal of the Magnetics Society of Japan 38 66-70 2014/02/19 DOI： 10.3379/msjmag.1402R006 Key factors for the dynamic ETEM observation of single atoms Peer-reviewed K. Yoshida, T. Tominaga, T. Hanatani, A. Tagami, Y. Sasaki, J. Yamasaki, K. Saitoh, N. Tanaka Journal of Electron Microscopy 62 (6) 571-582 2013/12 DOI： 10.1093/jmicro/dft033 ISSN：0022-0744 1477-9986 More details Close We present further modifications to aberration-corrected environmental transmission electron microscopy (AC-ETEM) for the dynamic HRTEM observation of single atoms. Additional pumping levels that include three additional turbomolecular pumps (TMPs) enable a base pressure of 3.5 × 10 -5 Pa in the sample chamber. The effect of these additional TMPs on image resolution was measured in reciprocal space using information limit (Young&＃39;s fringes) on a standard cross grating sample and also with platinum (Pt) single atoms on an amorphous carbon film (Pt/a-carbon). The Pt/a-carbon was used for measuring the effect of gas pressure on single-atom imaging in addition to the evaluation of vibrations of TMPs, samples, magnetic lenses and a microscope column of the AC-ETEM. TMPs did not affect the ETEM imaging performance when an anti-vibration table was used, and 0.10-nm resolution was achieved. Dynamic ETEM observation of Pt single atoms was achieved in 4.0 × 10-2 Pa of air, using a modified AC-ETEM system and a high-speed CCD camera with a time resolution of 0.05 s. © 2013 The Author. Key factors for the dynamic ETEM observation of single atoms Peer-reviewed K. Yoshida, T. Tominaga, T. Hanatani, A. Tagami, Y. Sasaki, J. Yamasaki, K. Saitoh, N. Tanaka MICROSCOPY 62 (6) 571-582 2013/12 Publisher: OXFORD UNIV PRESS DOI： 10.1093/jmicro/dft033 ISSN：2050-5698 eISSN：2050-5701 More details Close We present further modifications to aberration-corrected environmental transmission electron microscopy (AC-ETEM) for the dynamic HRTEM observation of single atoms. Additional pumping levels that include three additional turbomolecular pumps (TMPs) enable a base pressure of 3.5 x 10(-5) Pa in the sample chamber. The effect of these additional TMPs on image resolution was measured in reciprocal space using information limit (Young&＃39;s fringes) on a standard cross grating sample and also with platinum (Pt) single atoms on an amorphous carbon film (Pt/a-carbon). The Pt/a-carbon was used for measuring the effect of gas pressure on single-atom imaging in addition to the evaluation of vibrations of TMPs, samples, magnetic lenses and a microscope column of the AC-ETEM. TMPs did not affect the ETEM imaging performance when an anti-vibration table was used, and 0.10-nm resolution was achieved. Dynamic ETEM observation of Pt single atoms was achieved in 4.0 x 10(-2) Pa of air, using a modified AC-ETEM system and a high-speed CCD camera with a time resolution of 0.05 s. Dynamic environmental transmission electron microscopy observation of platinum electrode catalyst deactivation in a proton-exchange-membrane fuel cell Peer-reviewed Kenta Yoshida, Zhang Xudong, Alexander N. Bright, Koh Saitoh, Nobuo Tanaka Nanotechnology 24 (6) 065705 2013/02/15 DOI： 10.1088/0957-4484/24/6/065705 ISSN：0957-4484 1361-6528 More details Close Spherical-aberration-corrected environmental transmission electron microscopy (AC-ETEM) was applied to study the catalytic activity of platinum/amorphous carbon electrode catalysts in proton-exchange-membrane fuel cells (PEMFCs). These electrode catalysts were characterized in different atmospheres, such as hydrogen and air, and a conventional high vacuum of 10 -5 Pa. A high-speed charge coupled device camera was used to capture real-time movies to dynamically study the diffusion and reconstruction of nanoparticles with an information transfer down to 0.1 nm, a time resolution below 0.2 s and an acceleration voltage of 300 kV. With such high spatial and time resolution, AC-ETEM permits the visualization of surface-atom behaviour that dominates the coalescence and surface-reconstruction processes of the nanoparticles. To contribute to the development of robust PEMFC platinum/amorphous carbon electrode catalysts, the change in the specific surface area of platinum particles was evaluated in hydrogen and air atmospheres. The deactivation of such catalysts during cycle operation is a serious problem that must be resolved for the practical use of PEMFCs in real vehicles. In this paper, the mechanism for the deactivation of platinum/amorphous carbon electrode catalysts is discussed using the decay rate of the specific surface area of platinum particles, measured first in a vacuum and then in hydrogen and air atmospheres for comparison. © 2013 IOP Publishing Ltd. Correlating the interface structure to spin injection in abrupt Fe/GaAs(001) films Peer-reviewed L. R. Fleet, K. Yoshida, H. Kobayashi, Y. Kaneko, S. Matsuzaka, Y. Ohno, H. Ohno, S. Honda, J. Inoue, A. Hirohata Physical Review B - Condensed Matter and Materials Physics 87 (2) 2013/01/02 DOI： 10.1103/PhysRevB.87.024401 ISSN：1098-0121 1550-235X More details Close Understanding the effect of the interface on electrical spin injection is of great importance for the development of semiconductor spintronics. Fe/GaAs(001) is one of the leading systems for exploring these effects due to the small lattice mismatch. We report on the correlation between the experimentally observed Fe/GaAs(001) interface with the spin-transport properties. Using high-angle annular dark-field scanning transmission electron microscopy, we observe a predominantly abrupt interface with some regions of partial mixing also observed in the same film. We report that reproducible behavior with no bias-dependent polarization inversion was achieved for three-terminal devices. Using ab initio calculations of the experimentally observed interfaces, we show that the contribution to the transport from minority carriers is strongly dependent on the interface structure. © 2013 American Physical Society. Influence of total beam current on HRTEM image resolution in differentially pumped ETEM with nitrogen gas Peer-reviewed A. N. Bright, K. Yoshida, N. Tanaka ULTRAMICROSCOPY 124 46-51 2013/01 Publisher: ELSEVIER SCIENCE BV DOI： 10.1016/j.ultramic.2012.08.007 ISSN：0304-3991 More details Close Environmental transmission electron microscopy (ETEM) enables the study of catalytic and other reaction processes as they occur with Angstrom-level resolution. The microscope used is a dedicated ETEM (Titan ETEM, FEI Company) with a differential pumping vacuum system and apertures, allowing aberration corrected high-resolution transmission electron microscopy (HRTEM) imaging to be performed with gas pressures up to 20 mbar in the sample area and with significant advantages over membrane-type E-cell holders. The effect on image resolution of varying the nitrogen gas pressure, electron beam current density and total beam current were measured using information limit (Young&＃39;s fringes) on a standard cross grating sample and from silicon crystal lattice imaging. As expected, increasing gas pressure causes a decrease in HRTEM image resolution. However, the total electron beam current also causes big changes in the image resolution (lower beam current giving better resolution), whereas varying the beam current density has almost no effect on resolution, a result that has not been reported previously. This behavior is seen even with zero-loss filtered imaging, which we believe shows that the drop in resolution is caused by elastic scattering at gas ions created by the incident electron beam. Suitable conditions for acquiring high resolution images in a gas environment are discussed. Lattice images at nitrogen pressures up to 16 mbar are shown, with 0.12 nm information transfer at 4 mbar. (C) 2012 Elsevier B.V. All rights reserved. Correlating the interface structure to spin injection in abrupt Fe/GaAs(001) films Peer-reviewed L. R. Fleet, K. Yoshida, H. Kobayashi, Y. Kaneko, S. Matsuzaka, Y. Ohno, H. Ohno, S. Honda, J. Inoue, A. Hirohata PHYSICAL REVIEW B 87 (2) 024401 2013/01 Publisher: AMER PHYSICAL SOC DOI： 10.1103/PhysRevB.87.024401 ISSN：2469-9950 eISSN：2469-9969 More details Close Understanding the effect of the interface on electrical spin injection is of great importance for the development of semiconductor spintronics. Fe/GaAs(001) is one of the leading systems for exploring these effects due to the small lattice mismatch. We report on the correlation between the experimentally observed Fe/GaAs(001) interface with the spin-transport properties. Using high-angle annular dark-field scanning transmission electron microscopy, we observe a predominantly abrupt interface with some regions of partial mixing also observed in the same film. We report that reproducible behavior with no bias-dependent polarization inversion was achieved for three-terminal devices. Using ab initio calculations of the experimentally observed interfaces, we show that the contribution to the transport from minority carriers is strongly dependent on the interface structure. DOI: 10.1103/PhysRevB.87.024401 On the Effect of Atomic Structure on the Activity and Deactivation of Catalytic Gold Nanoparticles Peer-reviewed Michael J. Walsh, Kenta Yoshida, Mungo L. Pay, Pratibha L. Gai, Edward D. Boyes CHEMCATCHEM 4 (10) 1638-1644 2012/10 Publisher: WILEY-V C H VERLAG GMBH DOI： 10.1002/cctc.201200261 ISSN：1867-3880 More details Close We present studies of the structure and stability of catalytic gold nanoparticles through in situ aberration-corrected electron microscopy to investigate the effect of heating on the nature of the identified atomic active sites. Low coordination surface atoms are replaced by atomically clean surface facets through local rearrangements to minimise surface energy. The associated movement of surface atoms is proposed to directly precede Ostwald ripening. Expansive surface strain resulting from inherently strained structures, such as the decahedra, is shown to diminish with increasing particle size and the associated elastic energy is reduced through a shifting of the disclination axis towards the particle surface. At elevated temperatures a reduction in surface energy anisotropy may lead to energetically favourable morphologies with minimal intrinsic strain. Such processes will act as structural deactivation mechanisms, resulting in a loss of active sites without any necessary associated loss of surface area or change in particle size through traditional sintering mechanisms. Considerations of the active site stability and the particle size according to the reaction conditions are described. Transport Properties of Closely-Packed Carbon Nanotubes Film on SiC Tuned by Si-Doping Peer-reviewed Wataru Norimatsu, Takehiro Maruyama, Kenta Yoshida, Koichi Takase, Michiko Kusunoki APPLIED PHYSICS EXPRESS 5 (10) 105102 2012/10 Publisher: IOP PUBLISHING LTD DOI： 10.1143/APEX.5.105102 ISSN：1882-0778 eISSN：1882-0786 More details Close Here, we reveal origins of the planar electrical transport of closely-packed carbon nanotubes (CNTs) and silicon-doped CNTs (Si-CNTs) films. Their electrical resistivities increased with decreasing temperature, but exhibit a plateau below 60 K. This phenomenon can be well described using the simple-two-band model, which is often used to understand the electronic properties of graphite. Cryogenic energy-filtered transmission electron microscopy visualizes Si atoms dispersed finely in CNTs, preserving the structural features of CNTs. These Si atoms induced effective carriers above 150 K, while three-dimensional variable range hopping and weak localization are dominant in their transport below 50 and 10 K, respectively. (C) 2012 The Japan Society of Applied Physics Imaging Nanostructural Modifications Induced by Electronic Metal-Support Interaction Effects at Au parallel to Cerium-Based Oxide Nanointerfaces Peer-reviewed Miguel Lopez-Haro, Jose M. Cies, Susana Trasobares, Jose A. Perez-Omil, Juan J. Delgado, Serafin Bernal, Pascale Bayle-Guillemaud, Odile Stephan, Kenta Yoshida, Edward D. Boyes, Pratibha L. Gai, Jose J. Calvino ACS NANO 6 (8) 6812-6820 2012/08 Publisher: AMER CHEMICAL SOC DOI： 10.1021/nn301557u ISSN：1936-0851 More details Close A variety of advanced (scanning) transmission electron microscopy experiments, carried out in aberration-corrected equipment, provide direct evidence about subtle structural changes taking place at nanometer-sized Aullceria oxide interfaces, which agrees with the occurrence of charge transfer effects between the reduced support and supported gold nanoparticles suggested by macroscopic techniques. Tighter binding of the gold nanoparticles onto the ceria oxide support when this is reduced is revealed by the structural analysis. This structural modification is accompanied by parallel deactivation of the CO chemisorption capacity of the gold nanoparticles, which is interpreted in exact quantitative terms as due to deactivation of the gold atoms at the perimeter of the Aullcerium oxide interface. On the Structural Origin of the Catalytic Properties of Inherently Strained Ultrasmall Decahedral Gold Nanoparticles Peer-reviewed Michael J. Walsh, Kenta Yoshida, Akihide Kuwabara, Mungo L. Pay, Pratibha L. Gai, Edward D. Boyes NANO LETTERS 12 (4) 2027-2031 2012/04 Publisher: AMER CHEMICAL SOC DOI： 10.1021/nl300067q ISSN：1530-6984 More details Close A new mechanism for reactivity of multiply twinned gold nanoparticles resulting from their inherently strained structure provides a further explanation of the surprising catalytic activity of small gold nanoparticles. Atomic defect structural studies of surface strains and quantitative analysis of atomic column displacements in the decahedral structure observed by aberration corrected transmission electron microscopy reveal an average expansion of surface nearest neighbor distances of 5.6%, with many strained by more than 10%. Density functional theory calculations of the resulting modified gold d-band states predict significantly enhanced activity for carbon monoxide oxidation. The new insights have important implications for the applications of nanoparticles in chemical process technology, including for heterogeneous catalysis. Direct observation of the initial process of Ostwald ripening using spherical aberration-corrected transmission electron microscopy Peer-reviewed Kenta Yoshida, Alexander Bright, Nobuo Tanaka JOURNAL OF ELECTRON MICROSCOPY 61 (2) 99-103 2012/04 Publisher: OXFORD UNIV PRESS DOI： 10.1093/jmicro/dfr100 ISSN：0022-0744 More details Close We study in situ behavior of platinum single atoms on amorphous carbon (a-carbon) using a spherical aberration-corrected transmission electron microscope (AC-TEM). Diffusion of single atoms, bi-atoms, clusters (< 1 nm) and nanoparticles (< 3 nm) was recorded in the same image with a time resolution of 1 s, and such diffusion matches the expected mechanism of Ostwald ripening, which was seen on these samples. In situ AC-TEM shows promise for dynamical observation of single atom diffusion, which is important for understanding nanosized catalysts and ceramic sintering processes. We apply in situ AC-TEM to image platinum (Pt) nanoparticles on a-carbon, which is a model catalyst system for the real Pt electrode catalysts using alloys and core-shell structures supported on carbon/oxide composite materials in the proton exchange membrane fuel cell. The effect of MgO(111) interlayer on the interface phase stability and structure of BaFe12O19/SiC(0001) Peer-reviewed V. K. Lazarov, P. J. Hasnip, Z. Cai, K. Yoshida, K. S. Ziemer JOURNAL OF APPLIED PHYSICS 111 (7) 07A515 2012/04 Publisher: AMER INST PHYSICS DOI： 10.1063/1.3676614 ISSN：0021-8979 eISSN：1089-7550 More details Close We present a study on the effect of an interlayer of thin MgO(111) film on SiC(0001) on the interface phase stability and structure of the BaFe12O19 (BaM). The 10 nm MgO(111) interlayer followed by the BaM film were grown by molecular beam epitaxy on 6H-SiC. Cross-sectional transmission electron microscopy shows the formation of a magnesium ferrite spinel phase at the interface, and after 25 nm, a well structured BaM film was observed. In addition to the two main phases (Mg-ferrite and BaM), a thin layer of SiOx (2-3 nm) is formed at the SiC interface. In spite of the formation of this amorphous layer, the diffraction studies show that the BaM film is epitaxially grown and it has a single crystal structure. The energy dispersive x-ray analysis from the interface region shows that the MgO layer prevents significant outdiffusion of the Si into the film. Total energy calculations by density functional theory were used to investigate the stability of the various phases and to explain the observed interfacial phases in the studied system. (C) 2012 American Institute of Physics. [doi:10.1063/1.3676614] In situ TEM study of platinum electrode catalysts with 80kV-1MV accelerating voltage Peer-reviewed K. Yoshida, A. Carlsson, J. R. Jinschek, D. J. Stokes, P. L. Gai, S. Arai, K. Saitoh, N. Tanaka Journal of Physics: Conference Series 371 2012 Publisher: Institute of Physics Publishing DOI： 10.1088/1742-6596/371/1/012044 ISSN：1742-6596 1742-6588 More details Close We perform transmission electron microscopy (TEM) at different accelerating voltages for analysis of complex nano-structures of platinum (Pt) nanoparticle catalysts synthesized on titanium dioxide. TEM images obtained at 80, 200, 300, and 1000kV are carefully compared. The particle size, density and volume of the Pt nanoparticles deposited under different conditions are evaluated using electron tomography. The atomic structures of Pt nanoparticles on the TiO 2 and amorphous carbon a surfaces are also investigated using spherical aberration corrected TEM in order to study the diffusion of these Pt nanoparticles and atoms. In-situ gas study and 3D quantitation of titania photocatalysts by advanced electron microscopy Peer-reviewed N. Tanaka, K. Yoshida, S. Arai Journal of Physics: Conference Series 371 2012 Publisher: Institute of Physics Publishing DOI： 10.1088/1742-6596/371/1/012043 ISSN：1742-6596 1742-6588 More details Close Titanium dioxide (TiO2) with metal nanoparticles exhibits a high photocatalytic activity by a charge separation. Recently the size of the nanoparticles has been reduced to less than 1 nm. In contrast, the size of TiO2 support particles has been kept at sub-micron sizes to ensure stability for practical use at high temperatures. For visualizing and analyzing the metal nanoparticles which are supported on different positions of those complex substrates, a high voltage transmission electron microscope(HVEM) shows a strong performance because of its high transmission capability to view whole areas of the catalysts. Electron tomography is also important to quantify the three-dimensional morphology such as size, density, surface area and nearest particle distance. Here we report the data obtained by using He-cooled 3D TEM/STEM, a newly developed 1MV high voltage environmental TEM/STEM and a 200kV aberration corrected TEM/STEM. Nanostructures of catalytic samples are characterized using these EMs as well as measurement of their chemical activity. Insights into the microwave-assisted preparation of supported iron oxide nanoparticles on silica-type mesoporous materials Peer-reviewed Alina M. Balu, Doris Dallinger, David Obermayer, Juan M. Campelo, Antonio A. Romero, Daniel Carmona, Francisco Balas, Kenta Yohida, Pratibha L. Gai, Carolina Vargas, C. Oliver Kappe, Rafael Luque GREEN CHEMISTRY 14 (2) 393-402 2012 Publisher: ROYAL SOC CHEMISTRY DOI： 10.1039/c1gc16119a ISSN：1463-9262 eISSN：1463-9270 More details Close A detailed investigation on the microwave-assisted preparation of iron oxide nanoparticles on mesoporous Si-SBA-15 support is described, employing a dedicated single-mode microwave reactor with internal reaction temperature control. Using iron(II) chloride as iron precursor and ethanol as solvent, extensive optimization studies demonstrate that after 3-5 min at 150-200 degrees C well-defined 3-5 nm iron oxide nanoparticles (Fe2O3, hematite phase) are obtained. In contrast to the chosen reaction temperature, reaction time and stirring efficiency are of critical importance in the preparation of these supported nanoparticles. Extended reaction times (>10 min) lead to a significant proportion of larger aggregates while inefficient stirring also produces low quality nanoparticles as a result of poor dispersion and delivery of the iron precursor to the mesoporous support. Carefully executed control studies between microwave and conventionally heated experiments applying otherwise identical reaction conditions demonstrate that the quality of the obtained supported iron oxide nanoparticles is largely independent on the heating mode, as long as a the exact same temperature profile can be maintained. Layer-by-layer crystallization of Co2FeSi Heusler alloy thin films Peer-reviewed L. R. Fleet, G. Cheglakov, K. Yoshida, V. K. Lazarov, T. Nakayama, A. Hirohata JOURNAL OF PHYSICS D-APPLIED PHYSICS 45 (3) 032001 2012/01 Publisher: IOP PUBLISHING LTD DOI： 10.1088/0022-3727/45/3/032001 ISSN：0022-3727 More details Close Grain-size evolution with increasing annealing time has been investigated in polycrystalline Co2FeSi films. The samples were prepared by sputtering giving differing grain sizes. Large grains were formed after annealing at 500 degrees C, with grains over 200 nm forming in the L2(1) phase in a layer-by-layer mode. Further annealing causes a decrease in the average grain size, agreeing well with previously reported results for Co2MnSi. Magnetic measurements showed moments with values of up to 75% of those predicted from the Slater-Pauling curve providing further evidence for the formation of the L2(1) phase. Broadband Near Ultraviolet Random Lasing in ZnO 3-D Nanowalls Peer-reviewed Lei Miao, Sakae Tanemura, Hui Ying Yang, Kenta Yoshida JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY 11 (10) 9326-9332 2011/10 Publisher: AMER SCIENTIFIC PUBLISHERS DOI： 10.1166/jnn.2011.4317 ISSN：1533-4880 More details Close Broadband near ultraviolet (NUV) random laser was achieved by Au nanoparticle loaded ZnO 3-D nanowalls. Au nanoparticle was loaded on ZnO 3-D nanowalls by photo-chemical deposition method using ionic liquid. The optical confinement by the 3-D nanowalls and enhancement of incident light scattering by Au nanoparticle increase the number of resonant modes, and thus leading to a broadband multiple spectrum random lasing. The results demonstrate an important step towards to expand the application scope of NUV laser on medical imaging of cells, solid-state lighting and optical sensor. Dynamically Stabilized Growth of Polar Oxides: The Case of MgO(111) Peer-reviewed Vlado K. Lazarov, Zhuhua Cai, Kenta Yoshida, K. Honglian L. Zhang, M. Weinert, Katherine S. Ziemer, Philip J. Hasnip PHYSICAL REVIEW LETTERS 107 (5) 056101 2011/07 Publisher: AMER PHYSICAL SOC DOI： 10.1103/PhysRevLett.107.056101 ISSN：0031-9007 eISSN：1079-7114 More details Close By using MgO(111) as a model system for polar oxide film growth, we show by first-principles calculations that H acts as a surfactant, i.e., the H changes its position and bonding during the growth process, remaining in the surface region. Continuous presence of H during the growth of MgO(111) film efficiently removes the microscopic dipole moment, thus enabling the growth of perfect fcc-ordered MgO(111) films. These theoretical predictions are confirmed experimentally by molecular beam epitaxy single crystal growth of MgO(111) on SiC(0001). Probing Structures of Nanomaterials Using Advanced Electron Microscopy Methods, Including Aberration-Corrected Electron Microscopy at the Angstrom Scale Peer-reviewed Pratibha L. Gai, Kenta Yoshida, Carla Shute, Xiaoting Jia, Michael Walsh, Michael Ward, Mildred S. Dresselhaus, Julia R. Weertman, Edward D. Boyes MICROSCOPY RESEARCH AND TECHNIQUE 74 (7) 664-670 2011/07 Publisher: WILEY-BLACKWELL DOI： 10.1002/jemt.20933 ISSN：1059-910X More details Close Structural and compositional studies of nanomaterials of technological importance have been carried out using advanced electron microscopy methods, including aberration-corrected transmission electron microscopy (AC-TEM), AC-high angle annular dark field scanning TEM (AC-HAADF-STEM), AC-energy filtered TEM, electron-stimulated energy dispersive spectroscopy in the AC-(S) TEM and high-resolution TEM (HRTEM) with scanning tunneling microscopy (STM) holder. The AC-EM data reveal improvements in resolution and minimization in image delocalization. A JEOL 2200FS double-AC field emission gun TEM/STEM operating at 200 kV in the Nano-centre at the University of York has been used to image single metal atoms on crystalline supports in catalysts, grain boundaries in nanotwinned metals, and nanostructures of tetrapods. Joule heating studies using HRTEM integrated with an STM holder reveal in situ crystallization and edge reconstruction in graphene. Real-time in situ AC-HAADF-STEM studies at elevated temperatures are described. Dynamic in-column energy filtering in an AC environment provides an integral new approach to perform dynamic in situ studies with aberration correction. The new results presented here open up striking new opportunities for atomic scale studies of nanomaterials and indicate future development directions. Microsc. Res. Tech. 74: 664-670, 2011. (C) 2010 Wiley-Liss, Inc. The effect of film and interface structure on the transport properties of Heusler based current-perpendicular-to-plane spin valves Peer-reviewed V. K. Lazarov, K. Yoshida, J. Sato, P. J. Hasnip, M. Oogane, A. Hirohata, Y. Ando APPLIED PHYSICS LETTERS 98 (24) 242508 2011/06 Publisher: AMER INST PHYSICS DOI： 10.1063/1.3600792 ISSN：0003-6951 eISSN：1077-3118 More details Close We present direct link between the transport properties of Co2MnSi and Co2FeMnSi Heusler based current-perpendicular-to-plane spin valves (CPP-SVs) and interface atomic structures resolved by aberration-corrected electron microscopy. The structure of the Co2FeMnSi electrodes is L2(1) but their interface with the CoSi spacer is disordered. In contrast to the Co2FeMnSi-electrodes, the Co2MnSi-electrodes have abrupt interfaces with the Ag spacer though their ordering is not fully L2(1). The magnetoresistance of the Co2MnSi-SV is over two orders of magnitude better than those of Co2FeMnSi-SV, demonstrating that the atomic interface ordering is crucial for the enhancement of the magnetoresistance in the Heusler CPP-SVs. (C) 2011 American Institute of Physics. [doi:10.1063/1.3600792] Growth and interface phase stability of barium hexaferrite films on SiC(0001) Peer-reviewed V. K. Lazarov, P. J. Hasnip, Z. Cai, K. Yoshida, K. S. Ziemer JOURNAL OF APPLIED PHYSICS 109 (7) 07E520 2011/04 Publisher: AMER INST PHYSICS DOI： 10.1063/1.3559496 ISSN：0021-8979 More details Close We have studied interface phase stability of the BaFe(12)O(19) (BaM) thin films grown by molecular beam epitaxy on SiC(0001). The films were epitaxially grown with the following crystallographic relation: BaM(0001)parallel to SiC(0001) and BaM(11-20)parallel to SiC(11-20). High resolution TEM reveals the existence of two interfacial bands with different structure than BaM. The first band close to SiC is SiO(x) while the second has spinel structure and chemically corresponds to Fe(3)O(4). These findings suggest that at initial growth stages Fe(3)O(4) is more favorable than BaM. Density functional theory modeling of the phase stability of BaM compared to Fe(3)O(4) shows that BaM is only stable at high oxygen partial pressures. (C) 2011 American Institute of Physics. [doi:10.1063/1.3559496] Specific Surface Area and Three-Dimensional Nanostructure Measurements of Porous Titania Photocatalysts by Electron Tomography and Their Relation to Photocatalytic Activity Peer-reviewed Kenta Yoshida, Masaki Makihara, Nobuo Tanaka, Shinobu Aoyagi, Eiji Nishibori, Makoto Sakata, Edward D. Boyes, Pratibha L. Gai MICROSCOPY AND MICROANALYSIS 17 (2) 264-273 2011/04 Publisher: CAMBRIDGE UNIV PRESS DOI： 10.1017/S1431927610094419 ISSN：1431-9276 eISSN：1435-8115 More details Close Various porous titania photocatalysts are analyzed three-dimensionally in real space by electron tomography. Shapes and three-dimensional (3D) distributions of fine pores and silver (Ag) particles (2 nm in diameter) within the pores are successfully reconstructed from the 3D data. Electron tomography is applied for measuring the specific surface area of the porous structures including open and closed porosity. Calculated specific surface areas of 22.8 m(2)/g for a conventional sol-gel TiO2 sample and 366 m(2)/g for a highly porous TiO2 sample prepared using the Pluronic P-123 self-assembly process are compared with those measured by the general BET method. The real-space surface measurement indicates that the highly porous TiO2 produced by the present method using block copolymers has a greater number of effective reaction sites for the degradation of methylene blue. Electron tomography shows a great potential to contribute considerably to the nanostructural analysis and design of such catalyst materials for photocatalysis. The location of gold nanoparticles on titania: A study by high resolution aberration-corrected electron microscopy and 3D electron tomography Peer-reviewed Juan C. Hernandez-Garrido, Kenta Yoshida, Pratibha L. Gai, Edward D. Boyes, Claus H. Christensen, Paul A. Midgley CATALYSIS TODAY 160 (1) 165-169 2011/02 Publisher: ELSEVIER SCIENCE BV DOI： 10.1016/j.cattod.2010.06.010 ISSN：0920-5861 More details Close Using HAADF-STEM electron tomography and aberration-corrected TEM/STEM electron microscopy, 3D reconstructions and high resolution images have been recorded of heterogeneous catalysts consisting of gold nanoparticles supported on titanium dioxide (anatase); these catalysts have gained attention recently because of their potential for use in many reactions with both industrial and environmental importance. We will illustrate how through the combination of high resolution images and segmented 3D tomographic data, structural features of the supported phase can be revealed which are normally not accessible through conventional imaging. The location of the nanoparticles preferentially at the grain boundaries, confirmed by these studies, is likely to influence the stability of the nanoparticles and is a key step in understanding and facilitating the development of better catalysts. (C) 2010 Elsevier B.V. All rights reserved. Dynamic atomic scale in situ electron microscopy in the development of an efficient heterogeneous catalytic process for pharmaceutical NSAIDS Peer-reviewed N. R. Shiju, Kenta Yoshida, Edward D. Boyes, Robert Brown, Pratibha L. Gai CATALYSIS SCIENCE & TECHNOLOGY 1 (3) 413-425 2011 Publisher: ROYAL SOC CHEMISTRY DOI： 10.1039/c0cy00063a ISSN：2044-4753 More details Close In heterogeneous catalysis the identification of the active site and crucially its location to prevent unwanted sintering and deactivation during the transformation of the precursor to active catalyst require the integration of dynamic in situ imaging at the atomic level and reactivity studies. We report nanostructural and physico-chemical studies towards an efficient low temperature heterogeneous catalytic process for nonsteroidal anti-inflammatory drugs (NSAIDS) such as N-acetyl-p-aminophenol (paracetamol or acetaminophen) on tungstated zirconia nanocatalysts of only a few nanometres in size. We directly visualised, in real-time, the dynamic precursor transformation to the active catalyst, which is of great significance in heterogeneous catalysis, using double aberration-corrected in situ electron microscopy at the atomic level under controlled conditions. We quantified the observations with catalytic activity studies for the NSAIDS. The observations using negative defocus imaging in AC-TEM combined with HAADF-STEM have provided the direct evidence for the presence of surface WO(x) species with dimensions of <= 0.35 nm, nanoclusters and nanoparticles of WO(x) from up to 0.6 to 1 nm, located at grain boundaries on the surface of the zirconia nanoparticles. The observations illustrate that the nanoparticles (NPs) are disordered (distorted) tungsten trioxide. The correlation between the nanostructure and activity of catalysts with different W loadings indicate that surface WO(x) species, nanoclusters and distorted WO(3) nanoparticles create Bronsted acid sites highly active for the low temperature N-acetyl-p-aminophenol reaction, with distorted WO(3) NPs contributing to the activity. The results further elucidate that the anchoring of active sites at grain boundaries of the zirconia nanoparticles prevents undesirable coalescence of the active species and improves the catalyst stability and performance to make more product. Quantification of metallic nanoparticle morphology on TiO2 using HAADF-STEM tomography Peer-reviewed S. Sueda, K. Yoshida, N. Tanaka ULTRAMICROSCOPY 110 (9) 1120-1127 2010/08 Publisher: ELSEVIER SCIENCE BV DOI： 10.1016/j.ultramic.2010.04.003 ISSN：0304-3991 More details Close Electron tomography is applied to photocatalytic gold/titanium oxide and gold/silver/titanium oxide samples. In order to obtain a tilt series for the electron tomography measurement, high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) is used under cryogenic conditions. Dedicated programs have been developed for measuring volume, surface area, thickness distribution and nearest-neighbour distance of metallic nanoparticles on samples. Using these quantification programs, the 3D morphology of gold and silver nanoparticles is accurately characterized. We paid particular attention to the quantitative measurement of surface area. The measurement error of the method and appropriate magnification are defined using spherical nanoparticle models. We measured the 3D morphology of gold nanoparticles supported on titanium oxide (total volume=6.5 x 10(5) [nm(3)j, surface area=1.4 x 10(5) [nm(2)], and average nearest-neighbour distance=40 [nm]). (C) 2010 Elsevier B.V. All rights reserved. Schottky Barrier Height in Fe/GaAs Films Peer-reviewed L. R. Fleet, K. Yoshida, H. Kobayashi, Y. Ohno, H. Kurebayashi, J. -Y. Kim, C. H. W. Barnes, A. Hirohata IEEE TRANSACTIONS ON MAGNETICS 46 (6) 1737-1740 2010/06 Publisher: IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC DOI： 10.1109/TMAG.2010.2045483 ISSN：0018-9464 More details Close We discuss the effect of annealing on the interfacial structure of Fe/GaAs films, with 2 x 4 surface reconstructions, and the subsequent effect on the Schottky barrier height. Images of the interfaces indicate that the annealing process can greatly reduce the level of atomic mixing. A study of the I-V characteristics of Fe/GaAs Schottky barrier diodes, in a wide temperature range of 10-300 K, reveals a strong temperature dependence for the unannealed case, arising from the presence of mixed surface states. The annealing process reduces the existence of the interfacial states, leading to more ideal behavior, with a reduced temperature dependence of the Schottky behavior. Efficient hydrogenation of carbonyl compounds using low-loaded supported copper nanoparticles under microwave irradiation Peer-reviewed Kenta Yoshida, Camino Gonzalez-Arellano, Rafael Luque, Pratibha L. Gai APPLIED CATALYSIS A-GENERAL 379 (1-2) 38-44 2010/05 Publisher: ELSEVIER SCIENCE BV DOI： 10.1016/j.apcata.2010.02.028 ISSN：0926-860X More details Close Highly active and dispersed copper (Cu) nanoparticles on mesoporous silicas have been prepared via microwave irradiation of a solution of copper precursors with a previously synthesized mesoporous hexagonal silica (HMS) support. The protocol allowed differently low-loaded (typically 0.5 wt%) Cu materials containing Cu metal and small quantities of metal oxides. Materials were then tested as catalysts in the hydrogenation of carbonyl compounds under microwave irradiation. Cu materials were found to be highly active, selective and reusable in the reduction of substituted aromatic ketones and aldehydes, providing quantitative conversion of starting material within 5-10 min reaction at mild reaction conditions with complete selectivity to the alcohols. (C) 2010 Elsevier B.V. All rights reserved. Quantitative high-resolution microscopy of size-controlled metallic nanodots on titania photocatalysts Peer-reviewed K. Yoshida, S. Tanemura, T. Torimoto, N. Tanaka, E. D. Boyes, P. L. Gai ELECTRON MICROSCOPY AND ANALYSIS GROUP CONFERENCE 2009 (EMAG 2009) 241 2010 Publisher: IOP PUBLISHING LTD DOI： 10.1088/1742-6596/241/1/012047 ISSN：1742-6588 More details Close We applied the cryo-HAADF-STEM tomography (cryogenic Tecnai G2 Plara) for analysing three-dimensional nano-structures of platinum (Pt) and gold (Au) nanodots synthesised on titanium dioxide. The structural parameters such as particle size, density and volume were successfully evaluated and compared between macroscopic properties (inethylene blue dissolution and CO oxidation). The atomic structures of metallic clusters on the TiO2 surface were also carefully investigated by using double aberration corrected TEM/STEM (double AC JEOL JEM-2200FS) in order to study the quantum size effect of these noble metals. Fe/Al synergy in Fe2O3 nanoparticles supported on porous aluminosilicate materials: excelling activities in oxidation reactions Peer-reviewed Alina Mariana Balu, Antonio Pineda, Kenta Yoshida, Juan Manuel Campelo, Pratibha L. Gai, Rafael Luque, Antonio Angel Romero CHEMICAL COMMUNICATIONS 46 (41) 7825-7827 2010 Publisher: ROYAL SOC CHEMISTRY DOI： 10.1039/c0cc02015j ISSN：1359-7345 More details Close A synergetic Fe-Al effect in Fe2O3 nanoparticles supported on mesoporous aluminosilicates compared to pure siliceous silicates has been demonstrated, for the first time, by a remarkably superior catalytic activity of the former in the microwave-assisted selective oxidation of benzyl alcohol to benzaldehyde. This significant finding, that also deeply influences the acidity of the materials (increasing total and particularly Lewis acidity), can have important consequences in the improved efficiency of these systems in related oxidations as well as in acid catalysed processes. Highly active and selective supported iron oxide nanoparticles in microwave-assisted N-alkylations of amines with alcohols Peer-reviewed Camino Gonzalez-Arellano, Kenta Yoshida, Rafael Luque, Pratibha L. Gai GREEN CHEMISTRY 12 (7) 1281-1287 2010 Publisher: ROYAL SOC CHEMISTRY DOI： 10.1039/c003410j ISSN：1463-9262 More details Close Highly active and stable supported iron oxide nanoparticles show excellent activities and switchable selectivities to target products in the microwave-assisted N-alkylation of amines with alcohols. Direct observation of TiO6 octahedron forming titanate nanotube by advanced transmission electron microscopy Peer-reviewed K. Yoshida, L. Miao, N. Tanaka, S. Tanemura NANOTECHNOLOGY 20 (40) 405709 2009/10 Publisher: IOP PUBLISHING LTD DOI： 10.1088/0957-4484/20/40/405709 ISSN：0957-4484 More details Close The nanostructure of titanate nanotubes known as a one-dimensional catalytic/electric subject is combinatorially characterized using x-ray diffraction (XRD), micro-Raman, photoluminescence (PL) and advanced electron microscopy. The micro-Raman and PL spectra prove the successful synthesis of TiO6 octahedron units in macroscopic scale. Cryo-high-angle annular dark-field (HAADF)-STEM and aberration-corrected (AC) TEM visualize in real-space the TiO6 octahedron unit formed as a TiO2-based tubular structure prepared by the alkaline hydrothermal methods. The chirality and scrolling-up mechanism of the TiO6 octahedron nanosheets in relation to an asymmetrical chemical environment and mechanical tensions are discussed. The three-dimensional morphology of nickel nanodots in amorphous silica and their role in high-temperature permselectivity for hydrogen separation Peer-reviewed Kenta Yoshida, Yumi H. Ikuhara, Seiji Takahashi, Tsukasa Hirayama, Tomohiro Saito, Shogo Sueda, Nobuo Tanaka, Pratibha L. Gai NANOTECHNOLOGY 20 (31) 315703 2009/08 Publisher: IOP PUBLISHING LTD DOI： 10.1088/0957-4484/20/31/315703 ISSN：0957-4484 More details Close We report the development of technologically important nickel (Ni) nanodots (nanoparticles) dispersed in amorphous silica (SiO(2)) for high-temperature permselectivity for hydrogen separation membranes, crucial in hydrocarbon reactions and H(2) production, and present the systematic reconstruction of the three-dimensional (3D) structures of the nanodots using electron nano-tomography. 3D structures using cryogenic high-angle annular dark field scanning transmission electron microscopy (Cryo-HAADF-STEM), which is a more accurate method for nanoparticle morphology than conventional chemisorption, are correlated with experimental reversible hydrogen adsorption properties. The correlations provide the first direct evidence of very high activity on the nanoparticle surface and the nature of adsorption sites. The results have important implications in general for the use of electron nano-tomography in the design of supported metallic nanoparticles for hydrogen separation membranes. The first observation of titanate nanotubes by spherical aberration corrected high-resolution transmission electron microscopy Peer-reviewed L. Miao, S. Tanemura, T. Jiang, M. Tanemura, K. Yoshida, N. Tanaka, G. Xu SUPERLATTICES AND MICROSTRUCTURES 46 (1-2) 357-364 2009/07 Publisher: ACADEMIC PRESS LTD- ELSEVIER SCIENCE LTD DOI： 10.1016/j.spmi.2008.12.017 ISSN：0749-6036 More details Close Multi-wall titanate nanotubes (MW-TNNTs) with high aspect ratio, large surface area and good uniformity were produced by alkaline hydrothermal treatment of grounded TiO(2) aerogels and further by applying freeze-drying. Not only the crystal phase and diameter, but also morphology of the starting materials impact on the aspect ratio and transformation efficiency of the obtained nanotubes. Other parameters, such as pH value during neutralization process and drying method for the final products, are important to control length and dispersion of MW-TNNTs. By spherical aberration corrected high-resolution transmission-electron-microscopy (Cs-corrected HRTEM) with lateral space resolution of 0.14 nm at 200 W accelerating voltage and electron energy loss spectrum (EELS), the detailed structural analysis of MW-TNNTs reveals that (1) diameters of inner and outer tubes are about 4-7 nm and 10 nm, respectively, (2) numbers of layers are different from part to part along the longitudinal tube axis, (3) the walls of the tubes have interlayer spacing of 0.70-0.80 nm and the lateral fringes which are vertical to the walls have spacing of 0.32 nm, (4) each layer of MW-TNNT is the nanosheet composed by the arrayed TiO(6) octahedrons, and respective octahedron being slightly strained, and (5) no chirality of MW-TNNT tubular structure is observed. (C) 2009 Published by Elsevier Ltd Efficient aqueous hydrogenation of biomass platform molecules using supported metal nanoparticles on Starbons (R) Peer-reviewed Rafael Luque, James H. Clark, Kenta Yoshida, Pratibha L. Gai CHEMICAL COMMUNICATIONS (35) 5305-5307 2009 Publisher: ROYAL SOC CHEMISTRY DOI： 10.1039/b911877b ISSN：1359-7345 More details Close An efficient protocol for the hydrogenation of platform molecules (e.g. succinic acid) in aqueous environments using supported metal nanoparticles on polysaccharide derived mesoporous carbonaceous materials is reported for the first time. Quantitative STEM tomography for size-controlled metallic nanodots on sintered titania photocatalysts Peer-reviewed K. Yoshida, L. Miao, T. Hirayama, S. Tanemura, T. Torimoto, N. Tanaka Microscopy and Microanalysis 14 (2) 1418-1419 2008/08 DOI： 10.1017/S1431927608084146 ISSN：1431-9276 1435-8115 In situ high-resolution transmission electron microscopy of photocatalytic reactions by excited electrons in ionic liquid Peer-reviewed Kenta Yoshida, Tsutomu Nozaki, Tsukasa Hirayama, Nobuo Tanaka JOURNAL OF ELECTRON MICROSCOPY 56 (5) 177-180 2007/10 Publisher: OXFORD UNIV PRESS DOI： 10.1093/jmicro/dfm021 ISSN：0022-0744 eISSN：1477-9986 More details Close A transmission electron microscope (TEM) sample for observing photocatalysis in a liquid was prepared by using N,N,N-trimetyl-N-propylammonium-bis(trifluoromethanesulfonyl)imide. The ionic liquid (IL) was used as a reaction solvent. Tetrachloroauric acid was dissolved in the IL as gold ion species. Rutile particles were added in the solution as a photocatalyst. The low vapor pressure of the IL enables a diffusing system in high vacuum of TEM. Rutile particles were UV irradiated in that liquid phase. After 3 h UV irradiation, a gold particle of 8 nm diameter was grown on the TiO2 surface. Photonucleation of Au/TiO2 system was discussed from the high-resolution TEM images. Preparation of strain-included rutile titanium oxide thin films and influence of the strain upon optical properties Peer-reviewed T. Nambara, K. Yoshida, L. Miao, S. Tanemura, N. Tanaka THIN SOLID FILMS 515 (5) 3096-3101 2007/01 Publisher: ELSEVIER SCIENCE SA DOI： 10.1016/j.tsf.2006.09.004 ISSN：0040-6090 More details Close Rutile type titanium dioxide (TiO2) thin films are prepared by pulse laser deposition (PLD) with controlled oxygen pressure. Transmission electron microscopy (TEM) analysis clarified that crystalline structures, surface structures and electric states of the TiO2 films almost correspond to those of the bulk rutile. We observed crystalline domain including strain in the PLD film. The strain of the TiO2 film was measured by nano-beam diffraction. The strain-included domains affected properties of the film as optical absorption. The obtained optical band gap energy value was 3.30 eV, which was larger than that of bulk. TEM results such as crystalline grain sizes and distribution were used to consider quantum size effect in order to explain the larger band gap value. Moreover the influence of strain in rutile crystalline grains upon optical properties was suggested in the present study. The difference of band gap energy between experimental and theoretically calculated ones was considered to come from the strain effects. (c) 2006 Elsevier B.V. All rights reserved. Present status of Cs-corrected HRTEM and future prospects Peer-reviewed N. Tanaka, J. Yamasaki, K. Hirahara, K. Yoshida, K. Saitoh Microscopy and Microanalysis 12 (2) 158-159 2006/08 DOI： 10.1017/S1431927606064233 ISSN：1431-9276 1435-8115 eISSN：1435-8115 Direct observation of oxygen atoms in rutile titanium dioxide by spherical aberration corrected high-resolution transmission electron microscopy Peer-reviewed Kenta Yoshida, Tomoyuki Kawai, Takahiro Nambara, Sakae Tanemura, Koh Saitoh, Nobuo Tanaka NANOTECHNOLOGY 17 (15) 3944-3950 2006/08 Publisher: IOP PUBLISHING LTD DOI： 10.1088/0957-4484/17/15/056 ISSN：0957-4484 eISSN：1361-6528 More details Close We have developed a spherical aberration corrected transmission electron microscopy (C-s-corrected TEM) technique that allows us to obtain clearer images in real space than ever before. We applied this technique to titanium oxide, in which light elements such as oxygen are difficult to observe using TEM because of its small cross section and electronic damage. In the present study, we successfully observed oxygen atoms in rutile TiO2. In addition, this direct observation of oxygen atoms enabled us to study the Magneli structure (TinO2n-1), which is caused by oxygen vacancies. These vacancies caused an atomic relaxation of the titanium and oxygen atoms. The relaxed atoms formed a characteristic shear structure of rutile titanium dioxide phase. This shear structure of the Magneli structure (TinO2n-1) was visualized with a spatial resolution of 0.119 nm. At the same time, the selected area diffraction ( SAD) pattern of the defect structure was obtained. Additional spots were shown inside the rutile [110] spot. We made structural models of the shear structure and simulated the diffraction pattern and images using a multi-slice simulation. Additional spots in the simulated diffraction patterns accurately reconstructed the experimental data. We also considered the possibility of the real-space analysis of local structures using spherical aberration corrected transmission electron microscopy. Oxygen release and structural changes in TiO2 films during photocatalytic oxidation Peer-reviewed Kenta Yoshida, Takahiro Nanbara, Jun Yamasaki, Nobuo Tanaka JOURNAL OF APPLIED PHYSICS 99 (8) 084908 2006/04 Publisher: AMER INST PHYSICS DOI： 10.1063/1.2190721 ISSN：0021-8979 eISSN：1089-7550 More details Close Changes in the crystal structure and grain modifications in titanium oxide (TiO2) thin films were observed during the photocatalytic oxidation of hydrocarbons. When the hydrocarbon and collodion films were irradiated, single crystalline titanium oxide transformed into polycrystals. The titanium oxide films gradually became network aggregates. These changes were analyzed with a dedicated in situ transmission electron microscope and observed three dimensionally by electron tomography. A detailed analysis of electron energy loss spectra of the samples also revealed that the changes were associated with the loss of oxygen atoms in the TiO2 crystal lattice. Correlations between the polycrystalline grain size of TiO2 and its catalyst activity were discussed based on the measured data. (C) 2006 American Institute of Physics. Observation of photo-decomposition process of poly-hydrocarbons on catalytic TiO2 films detected in dedicated in-situ TEM Peer-reviewed K. Yoshida, T. Nanbara, J. Yamasaki, N. Tanaka Microscopy and Microanalysis 11 (2) 214-215 2005 DOI： 10.1017/S1431927605503003 ISSN：1431-9276 A trial for in situ quantitative TEM-EELS measurement related to the photoreaction process of TiO2 films Peer-reviewed K Yoshida, J Yamasaki, N Tanaka NANOTECHNOLOGY 15 (6) S349-S354 2004/06 Publisher: IOP PUBLISHING LTD DOI： 10.1088/0957-4484/15/6/006 ISSN：0957-4484 More details Close Ultraviolet light was used to irradiate hydrocarbons on TiO2 thin film in high-resolution transmission electron microscopy (TEM). The hydrocarbon was decomposed by photocatalysis of titanium oxide. Reaction processes were studied by using an in situ TEM observation system which was newly constructed for the present study. For measuring photocatalytic activities, electron energy loss spectroscopy (EELS) was used. We developed a new TEM method for observing crystal structures of TiO2 and quantifying photocatalytic activities concurrently. We succeeded in measuring the photodecomposition activity of hydrocarbons on TiO2 films in a submicron area. The spatial resolutions of the present method were compared with those of other methods for measuring photocatalytic activity. In situ high-resolution transmission electron microscopy observation of photodecomposition process of poly-hydrocarbons on catalytic TiO2 films Peer-reviewed K Yoshida, J Yamasaki, N Tanaka APPLIED PHYSICS LETTERS 84 (14) 2542-2544 2004/04 Publisher: AMER INST PHYSICS DOI： 10.1063/1.1689747 ISSN：0003-6951 More details Close Photocatalytic TiO2 materials have been one of the strong subjects of investigation for these ten years among various kinds of advanced functional materials. For studying the catalytic reaction by physical science techniques, a kind of transmission electron microscope technique is presented and applied to the study of photocatalysis on TiO2 films by UV light. Using the technique, we visualized in situ the decomposition process of hydrocarbons deposited on the TiO2 films in atomic level and elucidated a mechanism of the decomposition process. (C) 2004 American Institute of Physics. Show all ︎Show first 5 Misc. 30 Defect Analysis of Matrix Damage in Reactor Pressure Vessel Steel Using WB-STEM Invited Peer-reviewed Kenta Yoshida, Takeshi Toyama, Koji Inoue, Yasuyoshi Nagai, Masaki Shimodaira Materia Japan 62 (3) 154-158 2023/03/01 Publisher: Japan Institute of Metals DOI： 10.2320/materia.62.154 ISSN：1340-2625 eISSN：1884-5843 Development of ultramicro analysis technology for fuel debris analysis (8) Nanostructure analysis of fuel debris by TEM 吉田健太, 嶋田雄介, DU Y., 宮田穂高, 北垣徹, 池田篤史, 渡邉英雄, 小無健司, 永井康介 日本原子力学会秋の大会予稿集(CD-ROM) 2021 2021 球面収差補正透過電子顕微鏡による空孔クラスター由来のAl格子ひずみの定量解析 CHEN Jiao, 吉田健太, ZHAO Can, 嶋田雄介, 井上耕治, 今野豊彦, 鈴土知明, 永井康介 日本物理学会講演概要集(CD-ROM) 76 (2) 2021 ISSN：2189-079X Influence on Fe atom diffusion of electron irradiation dose in the FeSi ordered alloy 嶋田雄介, CHEN J., 池田裕樹, 吉田健太, 井上耕治, MAASS Robert, 今野豊彦, 永井康介 日本物理学会講演概要集(CD-ROM) 76 (2) 2021 ISSN：2189-079X Heavy-ion irradiation and post-irradiation annealing effects in explosion-welded CuCrZr/316LN joints for ITER application Yi Xiaoou, Du Yufeng, Geng Diancheng, Geng Diancheng, Li Zihao, Han Wentuo, Liu Pingping, Chen Jiming, Yabuuchi Kiyohiro, Yoshida Kenta, Ohnuki Somei, Zhan Qian, Wan Farong, Nagai Yasuyoshi Materials Characterization 178 2021 ISSN：1044-5803 In-situ WB-STEM Study of Annealing Process of Neutron Irradiation Induced Dislocation Loops 吉田健太, DU Yufeng, 嶋田雄介, 鈴土知明, 荒河一渡, 外山健, 井上耕治, 大貫聡明, 永井康介 日本原子力学会春の年会予稿集(CD-ROM) 2020 2020 照射誘起転位ループの熱的安定性のその場WB-STEM計測 吉田健太, YUFENG D., 嶋田雄介, 鈴土知明, 荒河一渡, 外山健, 井上耕治, 大貫聡明, 永井康介 日本物理学会講演概要集(CD-ROM) 75 (1) 2020 ISSN：2189-079X In-situ WB-STEM evaluation of thermal stability of the neutron induced dislocation loops during post-irradiation-annealing 吉田健太, DU Yufeng, 嶋田雄介, 鈴土知明, 荒河一渡, 外山健, 井上耕治, 大貫聡明, 永井康介 日本原子力学会秋の大会予稿集(CD-ROM) 2020 2020 その場WB-STEM計測による中性子照射誘起転位ループの熱的安定性の評価 吉田健太, YUFENG D., 嶋田雄介, 鈴土知明, 荒河一渡, 外山健, 井上耕治, 大貫聡明, 永井康介 日本物理学会講演概要集(CD-ROM) 75 (2) 2020 ISSN：2189-079X その場WB-STEM法による照射誘起転位ループ焼鈍過程の定量解析 吉田健太, YUFENG D., 嶋田雄介, 荒河一渡, 外山健, 井上耕治, KONSTANTINOVICH Milan, GERARD Robert, 永井康介 日本物理学会講演概要集(CD-ROM) 74 (2) 2019 ISSN：2189-079X 球面収差補正透過電子顕微鏡による金属/Si界面反応の原子分解能その場加熱観察 原田寛大, 嶋田雄介, 吉田健太, 井上耕治, 永井康介, 今野豊彦 日本金属学会東北支部研究発表大会予稿集 18th 2019 3D-AP/ weaak-beam STEM for nanostructural analysis TOYAMA Takeshi, YOSHIDA Kenta ΑΤΟΜΟΣ 60 231-235 2018/04 透過電子顕微鏡内加熱ホルダーを用いたその場観察における試料中温度分布の影響 池田裕樹, 嶋田雄介, 吉田健太, 井上耕治, 永井康介, 今野豊彦 日本金属学会講演概要(CD-ROM) 163rd 2018 ISSN：2433-3093 ヒーター式その場加熱観察手法のSTEMへの適用 嶋田雄介, 吉田健太, 井上耕治, 白石貴久, 木口賢紀, 永井康介, 今野豊彦 日本金属学会講演概要(CD-ROM) 163rd 2018 ISSN：2433-3093 原子炉圧力容器材料の焼鈍過程を解明にするためのIn situ WB-STEM法の開発 吉田健太, 下平昌樹, 外山健, 嶋田雄介, 井上耕治, 張磊, 鈴木克弥, 海老澤直樹, 永井康介 東北大学金属材料研究所附属量子エネルギー材料科学国際研究センター共同利用研究経過報告書(CD-ROM) 34 2017 ヒーター式加熱による原子分解能その場加熱観察 嶋田雄介, 吉田健太, 井上耕治, 白石貴久, 木口賢紀, 永井康介, 今野豊彦 日本金属学会講演概要(CD-ROM) 161st 2017 ISSN：2433-3093 Zr‐Nb合金腐食材中析出物の酸化過程のTEM/STEM‐EDS分析 喜多山周平, 松川義孝, 吉田健太, 楊会龍, 佐藤裕樹, 篠原靖周, 村上健太, 叶野翔, 阿部弘亨 日本金属学会講演概要(CD-ROM) 158th ROMBUNNO.469 2016/03/09 ISSN：2433-3093 燃料電池電極触媒の劣化機構の液中電圧印加その場TEM観察 Peer-reviewed 加藤 久雄, 長島 真也, 木下 圭介, 吉田 健太 自動車技術会論文集 47 (2) 595-601 2016/01 DOI： 10.11351/jsaeronbun.47.595 J‐Alloy腐食材の表面酸化被膜のTEM‐EDS分析:FeとNbの偏析について 松川義孝, 喜多山周平, YANG Huilong, 外山健, 吉田健太, 叶野翔, 佐藤裕樹, 阿部弘亨, 吉田健太, 外山健, 村上健太, 篠原靖周, 牟田浩明, 山中伸介 日本原子力学会秋の大会予稿集(CD-ROM) 2015 ROMBUNNO.J53 2015/08/21 Electron Microscopic Study of Heterogeneous Catalysts with 80 kV-1 MV Accelerating Voltage Kenta Yoshida, Shigeo Arai, Koh Saito, Nobuo Tanaka Microscopy 46 (1) 11-15 2011/03/30 Publisher: Japanese Society of Microscopy ISSN：1349-0958 透過電子顕微鏡その場観察法を用いた光触媒材料の研究 田中信夫, 吉田健太 名古屋大学電子光学研究のあゆみ 22 43-48 2010 In-situ TEM Observation of Photo-cataritic Interface Kenta Yoshida, Nobuo Tanaka セラミックス 44 (9) 688-691 2009/09/01 Publisher: 日本セラミックス協会 ISSN：0009-031X 電子線トモグラフィーによるナノ結晶性セラミックスの３次元定量解析 吉田健太, 末田昇吾, 田中信夫 工業製品技術協会 36 119-123 2008/11/28 イオン液体を用いた酸化チタン上のAu光電析過程の研究 吉田健太, 野崎勉, 田中信夫 まてりあ 47 (12) 650-650 2008 Publisher: 日本金属学会 DOI： 10.2320/materia.47.650 ISSN：1340-2625 In-situ high-resolution transmission electron microscopy of photocatalytic reactions by excited electrons in ionic liquid 吉田健太, 田中信夫 触媒 49 642-647 2007/12 Publisher: 触媒学会 電子線トモグラフィーによる酸化チタン光触媒材料の反応界面の研究 吉田健太, 牧原正樹, 南原孝弘, 山崎順, 田中信夫 まてりあ 46 (12) 791-791 2007 Publisher: 日本金属学会 DOI： 10.2320/materia.46.791 ISSN：1340-2625 高分解能化学反応その場観察装置による酸化チタンの光伝導計測 吉田健太, 田中信夫 名古屋大学電子光学研究のあゆみ 21 41-42 2007 ピエゾ駆動 STM ホルダーを用いたチタニアナノロッドの光伝導特性その場計測 吉田健太, 南原孝啓, 田中信夫 まてりあ 45 (12) 12-903 2006 Publisher: 日本金属学会 DOI： 10.2320/materia.45.903 ISSN：1340-2625 In-situ TEM observations of photocatalysis on TiO_2 Yamasaki J., Yoshida K., Kimura K., Tanaka N. Meeting abstracts of the Physical Society of Japan 58 (2) 780-780 2003/08/15 Publisher: The Physical Society of Japan (JPS) ISSN：1342-8349 In-situ TEM observation system for photoreactions and its application Tanaka N., Yoshida K., Yamasaki J., Kimura K. Meeting abstracts of the Physical Society of Japan 58 (2) 873-873 2003/08/15 Publisher: The Physical Society of Japan (JPS) ISSN：1342-8349 Show all ︎Show first 5 Books and Other Publications 3 触媒技術の動向と展望 吉田健太 一般財団法人 触媒学会 2016/04/10 Controlled Atmosphere Transmission Electron Microscopy Gai, Pratibha L. Boyes, Edward D. Yoshida, Kenta Hansen, Thomas Springer International Publishing 2016/01 ISBN: 9783319229874 環境調和型社会のためのナノ材料科学 余語利信, 田中信夫, 吉田健太, 齋藤晃, 丹司敬義, 田中成泰, 森竜雄, 坂本渉, 梅村知也 コロナ社 2015/07/03 ISBN: 9784339068825 More details Close ナノ材料科学の観点から，触媒反応の観察，省電力デバイスである半導体の解析，燃料電池，太陽電池，電子セラミックス，これらの基礎となる元素について，それぞれの専門家がこれまでの実績を踏まえて解説した。 Presentations 6 WB-STEMと3D-APを組み合わせた格子欠陥への溶質原子析出挙動の三次元定量解析 吉田健太, 下平昌樹, 外山健, 海老澤直樹, 戸村恵子, 井上耕治, Milan Konstantinovic, Robert Gerard, 永井 康介 日本物理学会2017年春季大会 2017/03/20 欠陥および格子歪みの三次元定量解析法の確立とRPV鋼への応用 吉田健太, 下平昌樹, 山﨑順, 佐藤和久, Milan Konstantinovich, Robert Gerard, 外山健, 井上耕治, 永井康介 日本金属学会2017年春期大会 2017/03/15 高分解能透過電子顕微鏡法によるRPV鋼内の中性子照射欠陥の観察 吉田健太, 下平昌樹, 外山健, 海老澤直樹, 戸村恵子, 井上耕治, Milan Konstantinovic, Robert Gerard, 永井 康介 日本金属学会2016年秋期大会 2016/09/22 WB-STEMを用いた転位組織可視化:原子炉圧力容器鋼への応用 吉田健太, 下平昌樹, 外山健, 海老澤直樹, 戸村恵子, 井上耕治, 永井 康介 日本顕微鏡学会第72回学術講演会 2016/06/14 STEM を用いた微小照射損傷組織解析法：原子炉圧力容器鋼への応用 下平昌樹, 外山健, 海老澤直樹, 戸村恵子, 井上耕治, 永井康介 日本金属学会春期講演大会（2016） 2016/03/23 透過電子顕微鏡で視るナノ粒子触媒の構造と機能 第２５回キャラクタリゼーション講習会 2015/11/13 Show all Show first 5 Research Projects 13 高温重イオン照射と新組織追跡法の融合によるダイバータ接合面の実環境下原子挙動解析 嶋田 雄介, 菱沼 良光, 渡辺 英雄, 池田 賢一, 吉田 健太 Offer Organization: 日本学術振興会 System: 科学研究費助成事業 Category: 基盤研究(B) Institution: 東北大学 2023/04/01 - 2027/03/31 In-situ annealing observation of inhomogeneous dislocation network by auto-tuned weak-beam transmission electron microscopy Offer Organization: Japan Society for the Promotion of Science System: Grants-in-Aid for Scientific Research Category: Grant-in-Aid for Scientific Research (C) Institution: Tohoku University 2022/04/01 - 2025/03/31 サブナノ分解能応力下その場観察法の開拓による新たな照射硬化機構の解明 永井 康介, 吉田 健太, 外山 健, 井上 耕治, 嶋田 雄介, 清水 康雄, 鈴土 知明 Offer Organization: 日本学術振興会 System: 科学研究費助成事業 基盤研究(A) Category: 基盤研究(A) Institution: 東北大学 2020/04/01 - 2023/03/31 More details Close 応力印加下その場観察のためのデバイス作製のため、ビッカース試験機による圧痕導入、FIBマイクロサンプリング、その場焼鈍などの実験工程を確立した。外部応力によって導入された残留ひずみの微視的構造およびその熱緩和過程が明らかになってきた。低合金鋼で得られた初期データは学会発表を行い、論文投稿準備を進めた。
その場等温焼鈍は、F82H鋼およびLAF 9Cr-W鋼、ODS鋼の中性子照射材に適用した。F82H鋼では、中性子照射材とイオン照射材に硬さ試験、3D-AP計測を実施し、室温から525℃まで、その場WB-STEM焼鈍実験により転位ループなど照射欠陥集合体の熱的安定性を評価した。それにより、従来の静的な照射欠陥分析では分からなかった照射欠陥集合体－転位複合体の形成など照射脆化機構における新しい素過程が見つかった。ODS鋼 中性子照射材は、600℃まで焼鈍試験を行い高い耐照射損傷特性の原因である酸化物粒子の構造安定性を評価した。 核融合炉ダイバータ材ブレージング接合界面での照射欠陥を伴う熱的三次元組織変化解析 嶋田 雄介, 吉田 健太, 菱沼 良光 Offer Organization: 日本学術振興会 System: 科学研究費助成事業 基盤研究(C) Category: 基盤研究(C) Institution: 東北大学 2020/04/01 - 2023/03/31 More details Close 2021年度は、2020年度に作製した酸化物分散銅合金と純タングステン接合体について、界面構造の詳細について解析を行った。その結果得られた知見を以下に示す。 1．銅-タングステン界面においては透過電子顕微鏡を用いた解析から金属ろう材（ニッケル－リン化合物）とタングステンが反応した金属間化合物（NiW2）が形成していたことがわかった。収束イオンビームを装備した走査電子顕微鏡を用いたシリアルセクショニング法による三次元観察から、その厚みは750ナノメートル程度で界面を被覆するように分布していることが明らかとなった。さらに金属間化合物層と銅合金相の間にマイクロメートルスケールのボイドが形成しており、これはNiがCuへ固溶したことによるものと考えらえる。このボイドは界面割れの要因となることから、その抑制のため、今後は作製にホットプレス法よりも高い圧力付加が可能な熱間等方加圧焼結法を用いた界面の高密度化を検討している。 2．銅金内部については、界面から20のマイクロメートルの領域において結晶粒のわずかな粗大化ならびに粒内ひずみの低下、さらには粒の形状のアスペクト比減少がみられた。これは粒成長に伴うものと示唆されるが、ただ一方で、粒内に分散したアルミナ粒子により転位の移動を阻害しているような組織もみられ、その結果として大規模な粒成長が抑制されたものと考えられた。また粒内には8at%程度のニッケルが固溶していることに加え、粒界には粒界拡散によるものと示唆される先述のNiW2が形成していた。 Developments of the three dimensional nanoscale analysis for acceleration effects on the interface corrosion of neutron irradiated steels Yoshida Kenta Offer Organization: Japan Society for the Promotion of Science System: Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (C) Category: Grant-in-Aid for Scientific Research (C) Institution: Tohoku University 2019/04/01 - 2022/03/31 More details Close In this study, we developed a &＃34;3D nanoanalysis for corrosion interface&＃34;, which consists of a reaction tank that can introduce electrochemically controlled corrosion to activated nuclear materials and analytical instruments that can visualize and quantify the strain and chemical composition of interface corrosion in nanometer scale. The 3D nanoanalysis method was applied to neutron-irradiated materials such as F82H, ODS, low-activated steels, then the sizes of dislocation loops before and after corrosion tests were quantitatively analyzed in three dimensions with a resolution of 1 nm. The behavior of solute atomic clusters and nanovoids during corrosion was quantitatively analyzed in a three-dimensional space. Study of Radiation Damage Mechanisms of Structural Materials in Nuclear Reactors by Defect structure - Elemental distribution Tomography Nagai Yasuyoshi, SUZUDO tomoaki Offer Organization: Japan Society for the Promotion of Science System: Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (A) Category: Grant-in-Aid for Scientific Research (A) Institution: Tohoku University 2016/04/01 - 2019/03/31 More details Close “Defect structure - Elemental distribution Tomography”, method to map irradiation-induced fine defects structures obtained by transmission electron microscopy (TEM) and inhomogeneous elemental distribution obtained by 3D atom probe (3D-AP) in the same 3D real space with sub-nm special resolution, has been successfully developed. Using this new method, we have found unsolved degradation mechanisms of the structural materials of nuclear reactors, which is very important for the safety operation. For example, the fine dislocation loops formed in reactor pressure vessel steels are one of the main origins of the embrittlement by the long term neutron irradiation, similar revel to the well-known contribution of the solute clusters. Synthesis of Pt nanocluster catalysts on strained multiple twin particles Yoshida Kenta, Nagai Yasuyoshi Offer Organization: Japan Society for the Promotion of Science System: Grants-in-Aid for Scientific Research Grant-in-Aid for Young Scientists (A) Category: Grant-in-Aid for Young Scientists (A) Institution: Tohoku University 2016/04/01 - 2019/03/31 More details Close We explored stable surface structures on multiple twin gold nanoparticles for achieving downsizing of platinum sub-nano-cluster catalysts. In order to distinguish gold and platinum in real space, a novel three-dimensional strain analysis was also developed based on atom-probe tomography and transmission electron microscopy. Investigation of microstructure evolution during hydrogenation/dehydrogenation MATSUDA Junko, YOSHIDA Kenta, SHAO Huaiyu, LI Haiwen, SASAKI Yukichi, AKIBA Etsuo Offer Organization: Japan Society for the Promotion of Science System: Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (C) Category: Grant-in-Aid for Scientific Research (C) Institution: Kyushu University 2012/04/01 - 2015/03/31 More details Close In situ transmission electron microscopy (TEM) was performed to observe the hydrogenation of Mg-Ni films in a hydrogen atmosphere of 80-100 Pa. An aberration-corrected environmental TEM with a differential pumping system allows us to reveal the Angstrom-scale structure of the films in the initial stage of hydrogenation: first, nucleation and growth of Mg2NiH4 crystals with a lattice spacing of 0.22 nm in an Mg-rich amorphous matrix of the film occurs within 20 seconds after the start of the high-resolution observation, then crystallization of MgH2 with a smaller spacing of 0.15 nm happens after approximately 1 min. Our in situ TEM method is also applicable to the analysis of other hydrogen-related materials. Dynamic and 3D TEM study of diffusion process of photoexcited electron YOSHIDA Kenta Offer Organization: Japan Society for the Promotion of Science System: Grants-in-Aid for Scientific Research Grant-in-Aid for Young Scientists (B) Category: Grant-in-Aid for Young Scientists (B) Institution: Nagoya University 2012/04/01 - 2014/03/31 More details Close During the academic year 2012-2013, Professor Kenta Yoshida explored catalytic potential of gold multiple twin particles. Relation between local strain of {111} surfaces of decahedral multiple twin particles and its CO adsorption properties were published. He has successfully applied high-resolution transmission electron microscopy to real-time visualisation of coalescence of the gold nanoparticle and thermal diffusion of platinum single atom. His publication during the academic year 2012-2013 were &＃34;On the Structural Origin of the Catalytic Properties of Inherently Strained Ultrasmall Decahedral Gold Nanoparticles&＃34;, Nano Lett., Vol. 12, pp.2027(2012),&＃34;Direct observation of the initial process of Ostwald ripening using spherical aberration-corrected transmission electron microscopy&＃34;, J. Electron Microsc., Vol.61, pp.99(2012) and &＃34;On the effect of atomic structure on the activity and deactivation of catalytic gold nanoparticles&＃34;, Chem. Cat. Chem., Vol.4, pp.1638(2012). Studies of the production of electron vortex beams and their interaction with chiral materials KOH Saitoh, TANAKA Nobuo, YOSHIDA Kenta, UCHIDA Masaya Offer Organization: Japan Society for the Promotion of Science System: Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (A) Category: Grant-in-Aid for Scientific Research (A) Institution: Nagoya University 2011/04/01 - 2014/03/31 More details Close 1) Forked gratings and spiral zone plates for electron beams were nano-fabricated and introduced into electron microscopes. We confirmed that a spiral zone plate introduced into the condenser lens system of an electron microscope produced an electron vortex beam carrying an orbital angular momentum of 90h. 2) Young&＃39;s double slit experiment was conducted using two electron vortex beams with different orbital angular momenta. It was confirmed that the two electron vortex beams are interfered with each other irrespective of their orbital angular momenta. 3) We confirmed that a forked grating transfers not only linear (transverse) momentum but also orbital angular momentum. 4) Electron vortex beams were illuminated to nano particles deposited on graphene and Si3N4 thin files to study the manipulation of the nano particles using the electron vortex beams. 環境セルを用いた気相中の酸化チタン光触媒反応の原子レベル3次元その場観察 吉田 健太 Offer Organization: 日本学術振興会 System: 科学研究費助成事業 特別研究員奨励費 Category: 特別研究員奨励費 Institution: (財)ファインセラミックスセンター 2007 - 2009 More details Close ヨーク大学内のYork-JEOL Nanocentreで世界初の国産品(日本製)となる200-300kV型ガス環境制御球面収差補正透過電子顕微鏡の開発・導入に携わった。 「環境セル電子顕微鏡を用いた酸化チタンの酸化・還元その場観察」の研究を行った。 ガス導入セルに分圧・温度の制御機構に加えて、気体分子の検出機構を利用して、導入ガスに一酸化炭素や窒素酸化物を用いて光酸化・還元をその場観察した。 光触媒反応が進んでいるまさにその状況を、原子分解能で3次元その場観察(および記録)した。それにより、粒界や転位といった反応活性サイトを特定することができた。電子線回折(TED、CBED)・蛍光X線分析(STEM-EDX)によって得た、試料中のひずみ組成揺らぎの情報と紫外-可視光吸収スペクトルから酸化チタンの二次構造が光触媒活性に与える影響についての新たな知見を得た。 光触媒反応が進んでいるまさにその状況を、原子分解能で3次元その場観察(および記録)した。それにより、粒界や転位といった反応活性サイトを特定することができた。 (収束)電子線回折(TED、CBED)・蛍光X線分析(STEM-EDX)によって得た、試料中のひずみ組成揺らぎの情報と紫外-可視光吸収スペクトルから酸化チタンの二次構造が光触媒活性に与える影響を考察した。 The direct analysis of 3-Dnanostructure in TiO2 nanotubes by using all angle rotation electron tomography MIAO Lei, YOSHIDA Kenta Offer Organization: Japan Society for the Promotion of Science System: Grants-in-Aid for Scientific Research Grant-in-Aid for Young Scientists (Start-up) Category: Grant-in-Aid for Young Scientists (Start-up) Institution: Japan Fine Ceramics Center 2007 - 2008 透過電子顕微鏡内光化学反応のその場観察用装置の作製と光触媒反応のメカニズム解明 吉田 健太 Offer Organization: 日本学術振興会 System: 科学研究費助成事業 特別研究員奨励費 Category: 特別研究員奨励費 Institution: 名古屋大学 2004 - 2006 More details Close 1、酸化チタン実用触媒の局所構造解析 通常、酸化チタンの構造を原子レベルの空間分解能で画像化しようとする場合、STMやTEMなど「固体物理」のキャラクタリゼーション手法の適用が容易な単結晶二酸化チタンを試料に用いられる。しかし、本研究では単結晶に限定されない酸化チタン(酸素欠損してn型半導体となっている酸化チタン)を使用したモデル触媒を作製することで、より実用触媒に近い系(より複雑な系)における原子スケール実空間解析の実現を目指した。そのために、実用触媒であるP25とウェットプロセスで大量合成したアナターゼ酸化チタンの精密構造解析を行った。高分解能透過電子顕微鏡法はP25の表面近傍に存在する、非晶質酸化チタンと酸素欠損した酸化チタンを視覚化した。放射光回折は酸化チタンの粉体試料の中に、1%程度の酸素欠陥した酸化チタンや窒化チタンなどの不純物が含有していることを明らかにした。 2、非化学量論組成酸化チタンの構造解析 世界最高の空間分解能を有する球面収差補正透過電子顕微鏡を用いて、酸化チタン結晶中の酸素原子を捕捉した。従来の透過電子顕微鏡の空間分解能0.19nmを凌駕する0.119nmの空間分解を達成し、rutile型二酸化チタン中の酸素原子を直視観察することに成功した。二酸化チタン中の酸素原子コラムを視覚的に補足したのは本研究が初めてである。さらに試料中に酸素とチタン原子がなす特異なジグザグ構造を観察した。シミュレーションとEELSを用いた組成分析の結果、その局所的な結晶構造は酸素欠損による非化学量論組成酸化チタンであることが示された。 Show all Show first 5
