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研究者情報

マスター

アカウント（マスター）

  • 氏名

    上野　貢生(ウエノ　コウセイ), ウエノ　コウセイ

所属（マスター）

  • 理学研究院　化学部門　無機・分析化学分野

所属（マスター）

  • 理学研究院　化学部門　無機・分析化学分野

独自項目

syllabus

  • 2021, 分子化学（光化学）, Molecular Chemistry (Photochemistry), 修士課程, 総合化学院, 電?的励起状態　　蛍光・りん光　　無輻射過程　光物理化学過程　　光化学反応　　分光計測
  • 2021, 化学特別講義, Advanced Chemistry, 修士課程, 総合化学院, ナノカーボン, カーボンナノチューブ, ナノ物質, 物性科学, 太陽光, 熱, エネルギー科学
  • 2021, 大学院共通授業科目（一般科目）：自然科学・応用科学, Inter-Graduate School Classes(General Subject):Natural and Applied Sciences, 修士課程, 大学院共通科目, マイクロ化学，ナノ化学，微細加工，化学チップ，バイオチップ，マイクロリアクター，単一原子・分子操作
  • 2021, マイクロ・ナノ化学, Micro-Nanochemistry, 修士課程, 総合化学院, マイクロ化学，ナノ化学，微細加工，化学チップ，バイオチップ，マイクロリアクター，単一原子・分子操作
  • 2021, 分析化学Ⅰ, Analytical Chemistry Ⅰ, 学士課程, 理学部, 定量分析化学・溶液内化学平衡
  • 2021, 化学実験Ⅰ, Laboratory Work in Chemistry I, 学士課程, 理学部, 分析化学、錯体化学、溶液内平衡、電子状態
  • 2021, 化学実験Ａ, Laboratory Work in Chemistry A, 学士課程, 理学部
  • 2021, 分析化学Ⅱ, Analytical Chemistry II, 学士課程, 理学部, 機器分析，定性分析，定量分析

researchmap

プロフィール情報

学位

  • 博士（理学）（北海道大学）

プロフィール情報

  • 公開用メールアドレス

    uenosci.hokudai.ac.jp

  • 姓

    上野, Ueno

  • 名

    貢生, Kosei

  • ID各種

    D-6710-2012, 200901041520310190

対象リソース

業績リスト

研究キーワード

  • プラズモニクス   光化学   分析化学   Nano Fabrication   Near-Field Optics   

研究分野

  • ナノテク・材料 / 基礎物理化学
  • ナノテク・材料 / 分析化学

経歴

  • 2019年04月 - 現在 北海道大学 大学院理学研究院 化学部門 教授
  • 2009年04月 - 2019年03月 北海道大学 電子科学研究所 准教授
  • 2008年04月 - 2009年03月 北海道大学 電子科学研究所 特任准教授
  • 2007年04月 - 2008年03月 北海道大学 電子科学研究所 助教
  • 2006年04月 - 2007年03月 北海道大学 電子科学研究所 助手

学歴

  • 1999年04月 - 2004年03月   北海道大学   大学院理学研究科   化学専攻
  • 1995年04月 - 1999年03月   北海道大学   理学部   化学科

受賞

  • 2015年03月 北海道大学 北海道大学研究総長賞（奨励賞）
     
    受賞者: 上野 貢生
  • 2011年03月 日本化学会 日本化学会進歩賞
     
    受賞者: 上野 貢生
  • 2010年09月 光化学協会 光化学協会奨励賞
     
    受賞者: 上野 貢生
  • 2007年09月 日本分析化学会 日本分析化学会奨励賞
     
    受賞者: 上野 貢生
  • 2004年02月 日本分析化学会北海道支部 北海道分析化学奨励賞
     
    受賞者: 上野 貢生

論文

  • Kosei Ueno, Hong-Bo Sun, Paul Mulvaney, Stephan Link, Johan Hofkens
    The Journal of Physical Chemistry C 2024年09月26日
  • Keisuke Imaeda, Yuto Shikama, Shimba Ushikoshi, Satoshi Sakai, Sou Ryuzaki, Kosei Ueno
    The Journal of Chemical Physics 2024年04月14日
  • Keisuke Imaeda, Junfeng Yue, Hiroki Takeuchi, Kosei Ueno
    The Journal of Physical Chemistry C 2024年04月04日
  • Takuya Okamoto, Azusa Onishi, Xu Shi, Tomoya Oshikiri, Kosei Ueno, Hiroaki Misawa, Vasudevanpillai Biju
    The Journal of Physical Chemistry C 2024年03月14日
  • Hiroki Takeuchi, Keisuke Imaeda, Sou Ryuzaki, Kosei Ueno
    The Journal of Physical Chemistry C 2024年02月15日
  • Chih-Hao Huang, Ya-Chiao Lee, Tetsuhiro Kudo, Xu Shi, Kosei Ueno, Teruki Sugiyama, Hiroaki Misawa, Hiroshi Masuhara
    The Journal of Physical Chemistry C 2023年09月28日
  • Pedro Paulo Ferreira da Rosa, Yuichi Kitagawa, Sunao Shoji, Hironaga Oyama, Keisuke Imaeda, Naofumi Nakayama, Koji Fushimi, Hidehiro Uekusa, Kosei Ueno, Hitoshi Goto, Yasuchika Hasegawa
    Nature Communications 13 1 2022年12月 [査読有り]
     
    Abstract Soft-crystals are defined as flexible molecular solids with highly ordered structures and have attracted attention in molecular sensing materials based on external triggers and environments. Here, we show the soft-crystal copolymerization of green-luminescent Tb(III) and yellow-luminescent Dy(III) coordination centers. Soft-crystal polymerization is achieved via transformation of monomeric dinuclear complexes and polymeric structures with respect to coordination number and geometry. The structural transformation is characterized using single-crystal and powder X-ray diffraction. The connected Tb(III) crystal-Dy(III) crystal show photon energy transfer from the Dy(III) centre to the Tb(III) centre under blue light excitation (selective Dy(III) centre excitation: 460 ± 10 nm). The activation energy of the energy transfer is estimated using the temperature-dependent emission lifetimes and emission quantum yields, and time-dependent density functional theory (B3LYP) calculations. Luminescence-conductive polymers, photonic molecular trains, are successfully prepared via soft-crystal polymerization on crystal media with remarkable long-range energy migration.
  • Chiaki Kojima, Akemi Noguchi, Tatsuya Nagai, Ken-ichi Yuyama, Sho Fujii, Kosei Ueno, Nobuaki Oyamada, Kei Murakoshi, Tatsuya Shoji, Yasuyuki Tsuboi
    ACS Omega 7 15 13120 - 13127 2022年04月19日 [査読有り]
  • Hiroki Ago, Susumu Okada, Yasumitsu Miyata, Kazunari Matsuda, Mikito Koshino, Kosei Ueno, Kosuke Nagashio
    Science and Technology of Advanced Materials 2022年04月07日 [査読有り]
  • Yusuke Ueda, Yusuke Masuda, Tomohiro Iwai, Keisuke Imaeda, Hiroki Takeuchi, Kosei Ueno, Min Gao, Jun-ya Hasegawa, Masaya Sawamura
    Journal of the American Chemical Society 2022年02月09日 [査読有り]
  • Giles Allison, Amrita Kumar Sana, Yuta Ogawa, Hidemi Kato, Kosei Ueno, Hiroaki Misawa, Koki Hayashi, Hironori Suzuki
    Nature Communications 2021年11月10日 [査読有り]
  • Xiaoqian Zang, Xu Shi, Tomoya Oshikiri, Kosei Ueno, Yuji Sunaba, Keiji Sasaki, Hiroaki Misawa
    The Journal of Physical Chemistry C 125 36 19880 - 19886 2021年09月16日 [査読有り]
  • Kai Sun, Masato Ueno, Keisuke Imaeda, Kosei Ueno, Masaya Sawamura, Yohei Shimizu
    ACS Catalysis 11 15 9722 - 9728 2021年08月06日 [査読有り]
  • Keisuke Nakamura, Tomoya Oshikiri, Kosei Ueno, Hiromichi Ohta, Hiroaki Misawa
    Chemistry Letters 50 2 374 - 377 2021年02月05日 [査読有り]
  • Yongjoon Kim, Tomohiro Iwai, Sho Fujii, Kosei Ueno, Masaya Sawamura
    Chemistry – A European Journal 27 7 2289 - 2293 2021年02月 [査読有り]
     
    Dumbbell-shaped bipyridines, featuring distal steric effects of bipyridine C5- and C5'-triarylmethyl substituents, allowed controlled monochelation to transition metals. These newly synthesized ligands showed improved ligand performance compared to conventional bipyridine ligands in the Ni-catalyzed cross-electrophile coupling and the Ni/photoredox-synergistically catalyzed decarboxylative coupling. More information can be found in the Communication by T. Iwai, M. Sawamura, et al. (DOI: 10.1002/chem.202004053).
  • Yuto Kitajima, Hiyori Sakamoto, Kosei Ueno
    Nanoscale 13 10 5187 - 5201 2021年 [査読有り]
     

    A review on molecular detection using coupled plasmonic systems based on spectral modulations and further near-field enhancements.

  • Shota Naka, Tatsuya Shoji, Sho Fujii, Kosei Ueno, Yumi Wakisaka, Kei Murakoshi, Tadashi Mizoguchi, Hitoshi Tamiaki, Yasuyuki Tsuboi
    ACS Applied Nano Materials 2020年10月23日 [査読有り]
  • Xu Shi, Xiaowei Li, Takahiro Toda, Tomoya Oshikiri, Kosei Ueno, Kentaro Suzuki, Kei Murakoshi, Hiroaki Misawa
    ACS Applied Energy Materials 3 6 5675 - 5683 2020年06月22日 [査読有り][通常論文]
  • Xiao-Yan Zhang, Zhe-Yu Li, Kose Ueno, Hiroaki Misawa, Nan-Qi Ren, Kai Sun
    Micromachines 11 2 207 - 207 2020年02月17日 [査読有り][通常論文]
  • Yaguang Wang, Xu Shi, Tomoya Oshikiri, Shuai Zu, Kosei Ueno, Hiroaki Misawa
    Nanoscale 12 44 22674 - 22679 2020年 [査読有り]
     

    The plasmonic Ga2O3 photoanode with the interfacial TiO2 modification provide both a high reduction ability and an oxidation ability.

  • Mari Kimura, Masaki Yoshida, Sho Fujii, Atsushi Miura, Kosei Ueno, Yasuhiro Shigeta, Atsushi Kobayashi, Masako Kato
    Chemical Communications 56 85 12989 - 12992 2020年 [査読有り]
     

    A Pt(ii)-based luminescent porous molecular crystal was selectively crystallised at the liquid–liquid interface, allowing control of porosity and luminescence.

  • Li, Y., Sun, Q., Zu, S., Shi, X., Liu, Y., Hu, X., Ueno, K., Gong, Q., Misawa, H.
    Physical Review Letters 124 16 163901 - 163901 2020年 [査読有り][通常論文]
     
    Near-field enhancement and dephasing time play critical roles in several applications of localized surface plasmon resonance. Here, using an example gold dimer system, we reveal the correlation between the near-field enhancement and dephasing time via time-resolved photoemission electron microscopy. Compared with isolated particles, dimers with small gap sizes show stronger near-field enhancement and shorter dephasing times. These results are well reproduced by numerical simulations and further explained by a coupled dipole approximation model. The roles of near- and far-field coupling and plasmon localization in balancing near-field enhancement and dephasing time are also unveiled.
  • Oshikiri, T., Sawayanagi, H., Nakamura, K., Ueno, K., Katase, T., Ohta, H., Misawa, H.
    Journal of Chemical Physics 152 3 2020年 [査読有り][通常論文]
  • Shibata, K., Fujii, S., Sun, Q., Miura, A., Ueno, K.
    Journal of Chemical Physics 152 10 2020年 [査読有り][通常論文]
  • Yanfeng Cao, Tomoya Oshikiri, Xu Shi, Kosei Ueno, Jie Li, Hiroaki Misawa
    ChemNanoMat 5 8 972 - 972 Wiley 2019年08月29日 [査読有り][通常論文]
  • Wei‐Yi Tsai, Quan Sun, Guangwei Hu, Pin Chieh Wu, Ren Jie Lin, Cheng‐Wei Qiu, Kosei Ueno, Hiroaki Misawa, Din Ping Tsai
    Advanced Optical Materials 7 8 1801060 - 1801060 2019年04月21日 [査読有り][通常論文]
  • Xiao-Yan Zhang, Zhe-Yu Li, Yu Zhang, Xiao-Qian Zang, Kosei Ueno, Hiroaki Misawa, Kai Sun
    Micromachines 10 1 2019年01月14日 [査読有り][通常論文]
     
    Capacitively coupled contactless conductivity detection (C4D) is an improved approach to avoid the problems of labor-intensive, time-consuming and insufficient accuracy of plate count as well as the high-cost apparatus of flow cytometry (FCM) in bacterial counting. This article describes a novel electrode-integrated printed-circuit-board (PCB)-based C4D device, which supports the simple and safe exchange of capillaries and improves the sensitivity and repeatability of the contactless detection. Furthermore, no syringe pump is needed in the detection, it reduces the system size, and, more importantly, avoids the effect on the bacteria due to high pressure. The recovered bacteria after C4D detection at excitation of 25 Vpp and 60–120 kHz were analyzed by flow cytometry, and a survival rate higher than 96% was given. It was verified that C4D detection did not influence the bacterial viability. Moreover, bacteria concentrations from 106 cells/mL to 108 cells/mL were measured in a linear range, and relative standard deviation (RSD) is below 0.2%. In addition, the effects on bacteria and C4D from background solutions were discussed. In contrast to common methods used in most laboratories, this method may provide a simple solution to in situ detection of bacterial cultures.
  • Hiroaki Misawa, Xu Shi, Kosei Ueno, Tomoya Oshikiri, Quan Sun, Keiji Sasaki
    Plasmonics: Design, Materials, Fabrication, Characterization, and Applications XVII 2019年 [査読有り][通常論文]
  • Quan Sun, Han Yu, Kosei Ueno, Shuai Zu, Yasutaka Matsuo, Hiroaki Misawa
    Opto-Electronic Advances 2 4 18003001 - 18003007 2019年 [査読有り]
     
    We studied the near-field properties of localized surface plasmon resonances in finite linear gold nanochains using photoemission electron microscopy (PEEM). The localization of the electromagnetic field in the near-field region was mapped at high spatial resolution. By tuning the excitation laser wavelength, we can obtain the near-field spectra, from which the energy splitting between longitudinal (L) and transverse (T) plasmon modes can be revealed. In particular, the L-mode red shifts and the T-mode blue shifts with increasing chain length. The red shift of the L-mode is highly dependent on the gap distance. In contrast, the T-mode almost remains constant within the range of gap distance we investigated. This energy splitting between the L-mode and the T-mode of metallic chains is in agreement with previous far-field measurements, where it was explained by dipole-dipole near-field coupling. Here, we provide direct proof of this near-field plasmon coupling in nanochains via the above-described near-field measurements using PEEM. In addition, we explore the energy transport along the gold nanochains under excitation at oblique illumination via PEEM measurements together with numerical simulations.
  • Oshikiri, T., Ueno, K., Misawa, H.
    Green Chemistry 21 16 4443 - 4448 2019年 [査読有り]
     

    Ammonia photosynthesis under visible light irradiation via an associative pathway using a plasmonic photoanode and a zirconium cathode is proposed.

  • Lee, K.-L., You, M.-L., Shi, X., Li, Y.-R., Ueno, K., Misawa, H., Wei, P.-K.
    Applied Materials Today 16 2019年 [査読有り][通常論文]
  • Quan Sun, Han Yu, Kosei Ueno, Shuai Zu, Yasutaka Matsuo, Hiroaki Misawa
    Chinese Journal of Lasers 46 5 0508001 - 0508001 2019年 [査読有り]
  • Cao, Y., Oshikiri, T., Shi, X., Ueno, K., Li, J., Misawa, H.
    ChemNanoMat 5 8 1008 - 1014 2019年 [査読有り][通常論文]
  • Eguchi, Miharu, Li, Jie, Ueno, Kosei, Misawa, Hiroaki
    Chemistry Letters 48 3 211 - 214 2019年 [査読有り][通常論文]
  • Ueno, Kosei, Yang, Jinghuan, Sun, Quan, Aoyo, Daisuke, Yu, Han, Oshikiri, Tomoya, Kubo, Atsushi, Matsuo, Yasutaka, Gong, Qihuang, Misawa, Hiroaki
    Applied Materials Today 14 159 - 165 2019年 [査読有り][通常論文]
  • Song, Hanfa, Sun, Quan, Li, Jie, Yang, Fan, Yang, Jinghuan, Li, Yaolong, Ueno, Kosei, Gong, Qihuang, Misawa, Hiroaki
    Journal of Physical Chemistry C 123 2 1398 - 1405 2019年 [査読有り][通常論文]
  • Weiwei Liu, Zijie Dai, Jing Yang, Quan Sun, Cheng Gong, Nan Zhang, Kosei Ueno, Hiroaki Misawa
    IEEE Photonics Technology Letters 30 24 2103 - 2106 2018年12月15日 [査読有り][通常論文]
  • Jinghuan Yang, Quan Sun, Kosei Ueno, Xu Shi, Tomoya Oshikiri, Hiroaki Misawa, Qihuang Gong
    Nature Communications 9 1 2018年12月 [査読有り][通常論文]
  • Xu Shi, Kosei Ueno, Tomoya Oshikiri, Quan Sun, Keiji Sasaki, Hiroaki Misawa
    Nature Nanotechnology 13 10 953 - 958 2018年10月30日 [査読有り][通常論文]
  • Man-Nung Su, Quan Sun, Kosei Ueno, Wei-Shun Chang, Hiroaki Misawa, Stephan Link
    The Journal of Physical Chemistry C 2018年08月09日 [査読有り][通常論文]
  • Keisuke Nakamura, Tomoya Oshikiri, Kosei Ueno, Takayoshi Katase, Hiromichi Ohta, Hiroaki Misawa
    The Journal of Physical Chemistry C 2018年06月28日 [査読有り][通常論文]
  • Tomoya Oshikiri, Ryohei Takakura, Xu Shi, Kosei Ueno, Hiroaki Misawa
    ECS Meeting Abstracts 2018年04月13日
  • Kosei Ueno, Jingchun Guo, Xu Shi, Tomoya Oshikiri, Hiroaki Misawa
    ECS Meeting Abstracts 2018年04月13日
  • Kosei Ueno, Tomoya Oshikiri, Quan Sun, Xu Shi, Hiroaki Misawa
    Chemical Reviews 118 6 2955 - 2993 2018年03月28日 [査読有り][通常論文]
     
    Metallic nanoparticles such as silver and gold show localized surface plasmon resonances (LSPRs), which are associated with near-field enhancement effects in the vicinity of nanoparticles. Therefore, strong light-matter interaction is induced by the near-field enhancement effects of LSPRs. Because the resonant wavelength of LSPRs can be easily controlled by the size and shape of the metallic nanoparticles in the visible and near-infrared wavelength range, LSPRs have received considerable attention as optical antennae for light energy conversion systems such as solar cells. LSPRs decay very quickly as a result of light scattering and excitation of electron-hole pairs in the metal itself. However, in addition to the near-field enhancement effect, this light scattering and electron-hole pair excitation, which are known to cause loss of LSPRs, can be utilized as a solar cell enhancement mechanism. Here, we focus on plasmonic solid-state solar cells. The mechanisms of the light scattering by LSPRs, near-field enhancement, and plasmon-induced charge separation based on electron-hole pair excitations can be clarified. We review the related studies from the viewpoint of these mechanisms rather than material science.
  • Construction of visible responsive broadband absorber utilizing strong coupling between plasmon and nanocavity modes and its application to light energy conversions
    Kosei Ueno, Xu Shi, Quan Sun, Tomoya Oshikiri, Keiji Sasaki, Hiroaki Misawa
    Optics InfoBase Conference Papers 2018 2018年 
    Nanoparticles colloidal solutions of metals such as gold (Au) and silver (Ag) show very intense color due to localized surface plasmon resonances (LSPRs). LSPRs which are collective oscillations of conduction electrons give rise to the enhancement of electromagnetic field in the vicinity of nanoparticles and are expected as a light harvesting optical antenna for light energy conversion devices based on their spectrum tunability. We have successfully developed the plasmon-induced energy conversions such as water splitting and ammonia synthesis systems as well as solid-state plasmonic solar cells based on the principle of plasmon-induced hot electron transfer from gold nanoparticles (Au-NPs) to the semiconductor electrode.1-5 In these days, the plasmon-induced hot electron transfer has received considerable attention as a novel strategy for the solar energy conversion.6,7 However, the insufficient absorption limited its solar energy conversion efficiency for the monolayer of Au-NPs only dispersed on the semiconductor electrode. In the present study, we apply the principle of modal strong coupling to visible responsive broadband absorber for plasmonic water splitting using Au-NPs/titanium dioxide (TiO2)/Au-film electrode.
  • Quan Sun, Kosei Ueno, Hiroaki Misawa
    The 9th International Symposium on Ultrafast Phenomena and Terahertz Waves OSA 2018年 [査読有り][通常論文]
  • Jingchun Guo, Kosei Ueno, Jinghuan Yang, Xu Shi, Jie Li, Quan Sun, Tomoya Oshikiri, Hiroaki Misawa
    JOURNAL OF PHYSICAL CHEMISTRY C 121 39 21627 - 21633 2017年10月 [査読有り][通常論文]
     
    Near-field spectrum measurement techniques, including near-field scanning optical microscopy, electron energy loss spectroscopy, and multiphoton photoemission electron microscopy, are powerful means to investigate near-field interactions directly on closely spaced metallic nanoparticles or a metallic nanostructure coupled with optical modes, such as whispering gallery mode and waveguide mode, which are called coupled plasmonic systems. In the present study, we have successfully measured the near-field spectra of coupled plasmonic systems using a simple photoelectrochemical measurement based on plasmon-induced water oxidation. Coupling was explored between the localized surface plasmon resonance (LSPR.) mode and waveguide mode of periodic gold nanogratings patterned on a thin titanium dioxide waveguide film. It is known that the far-field reflection spectrum of this waveguide-LSPR coupling system shows a complicated shape with multiple peaks, and the coupling has been explored by numerical electromagnetic simulations so far. However, in this study, it was clearly elucidated that an internal quantum efficiency (IQE) spectrum observed in the plasmon-induced photocurrent generation has successfully reproduced the near-field spectrum predicted by electromagnetic simulations under the coupling conditions. The photocurrent generation based on the plasmon-induced charge separation is due to the near-field effect, and it can be considered that the IQE spectrum corresponds to the near-field spectrum. This study paves a new way to indirectly measure the near-field spectrum of plasmonic systems.
  • Chung V. Hoang, Koki Hayashi, Yasuo Ito, Naoki Gorai, Giles Allison, Xu Shi, Quan Sun, Zhenzhou Cheng, Kosei Ueno, Keisuke Goda, Hiroaki Misawa
    NATURE COMMUNICATIONS 8 1 2017年10月 [査読有り][通常論文]
     
    Plasmon-induced hot-electron generation has recently received considerable interest and has been studied to develop novel applications in optoelectronics, photovoltaics and green chemistry. Such hot electrons are typically generated from either localized plasmons in metal nanoparticles or propagating plasmons in patterned metal nanostructures. Here we simultaneously generate these heterogeneous plasmon-induced hot electrons and exploit their cooperative interplay in a single metal-semiconductor device to demonstrate, as an example, wavelength-controlled polarity-switchable photoconductivity. Specifically, the dual-plasmon device produces a net photocurrent whose polarity is determined by the balance in population and directionality between the hot electrons from localized and propagating plasmons. The current responsivity and polarity-switching wavelength of the device can be varied over the entire visible spectrum by tailoring the hot-electron interplay in various ways. This phenomenon may provide flexibility to manipulate the electrical output from light-matter interaction and offer opportunities for biosensors, long-distance communications, and photoconversion applications.
  • Jinghuan Yang, Quan Sun, Han Yu, Kosei Ueno, Hiroaki Misawa, Qihuang Gong
    PHOTONICS RESEARCH 5 3 187 - 193 2017年06月 [査読有り][通常論文]
     
    We investigate the superposition properties of the dipole and quadrupole plasmon modes in the near field both experimentally, by using photoemission electron microscopy (PEEM), and theoretically. In particular, the asymmetric near-field distributions on gold (Au) nanodisks and nanoblocks under oblique incidence with different polarizations are investigated in detail. The results of PEEM measurements show that the evolutions of the asymmetric near-field distributions are different between the excitation with s-polarized and p-polarized light. The experimental results can be reproduced very well by numerical simulations and interpreted as the superposition of the dipole and quadrupole modes with the help of analytic calculations. Moreover, we hypothesize that the electrons collected by PEEM are mainly from the plasmonic hot spots located at the plane in the interface between the Au particles and the substrate in the PEEM experiments. (C) 2017 Chinese Laser Press
  • Ryohei Takakura, Tomoya Oshikiri, Kosei Ueno, Xu Shi, Toshiaki Kondo, Hideki Masuda, Hiroaki Misawa
    GREEN CHEMISTRY 19 10 2398 - 2405 2017年05月 [査読有り][通常論文]
     
    In this study, we developed a three-dimensional plasmonic photoanode using titanium dioxide nanotunnels (TNTs) loaded with gold nanoparticles (Au-NPs) for water splitting, to enhance the reaction efficiency. We also optimized the procedure of loading Au-NPs on complex three-dimensional structures. We discuss the correlation between the plasmon-induced charge separation obtained from photoelectrochemical measurement and the morphology of Au-NPs observed by transmission electron microscopy. We have successfully deposited well-dispersed Au-NPs on the walls of TNTs using HAu(OH)(4) as a precursor. The amount of Au-NPs on the TNTs was estimated to be approximately 15-fold larger than that on the thin film titanium dioxide substrate, and the particle size remained small. Photoelectrochemical water splitting was achieved by using a two-electrode system rather than a three-electrode system. Furthermore, stoichiometric water splitting was confirmed by estimating the amounts of the evolved H-2 and O-2 gases under visible light irradiation.
  • Jingchun Guo, Tomoya Oshikiri, Kosei Ueno, Xu Shi, Hiroaki Misawa
    ANALYTICA CHIMICA ACTA 957 70 - 75 2017年03月 [査読有り][通常論文]
     
    We developed a localized surface plasmon-induced visible light-responsive photoelectrochemical (PEC) biosensor using a titanium dioxide (TiO2) photoelectrode loaded with gold nanoislands (AuNIs) for in situ real-time measurement of biotin-streptavidin association. As a proof of concept, self-assembled thiol-terminated biotin molecules bound on a AuNls/TiO2 photoelectrode were successfully utilized to explore the photocurrent response to streptavidin-modified gold nanoparticle (STA-AuNP) solutions. This plasmon-induced PEC biosensor is simple and easy to miniaturize. Additionally, the PEC biosensor achieves highly sensitive measurements under only visible light irradiation and prevents the UV-induced damage of samples. Furthermore, a novel approach has been proposed to realize the real-time monitoring of biotin-STA binding affinities and kinetics by analyzing the PEC sensing characteristics. This PEC biosensor and novel analysis method could provide a new approach for the specific electrical detection and real-time kinetic measurements for clinical diagnostics and drug development. (C) 2016 The Authors. Published by Elsevier B.V.
  • Hidetoshi Mizobata, Kosei Ueno, Hiroaki Misawa, Hiromi Okamoto, Kohei Imura
    OPTICS EXPRESS 25 5 5279 - 5289 2017年03月 [査読有り][通常論文]
     
    We examine the far-field and near-field properties of complementary screens made of nanostructured gold thin films, a rectangular nanowire and a nanovoid, using an aperture-type scanning near-field optical microscope and electromagnetic field calculations, and discuss the applicability of Babinet's principle in the optical region. The far-field transmission spectra of the complementary screens are considerably different from each other. On the other hand, genuine near-field extinction spectra exhibit nearly complementary characteristics. The spatial features of the observed near-field images for the complementary screens show little correlation. We have found from the Fourier analysis of the simulated images that high spatial-frequency components of the electromagnetic fields show mutual spatial correlation. These results suggest that Babinet's principle is applicable to the high spatial-frequency components of electromagnetic fields for the complementary screens. (C) 2017 Optical Society of America
  • Han Yu, Quan Sun, Jinghuan Yang, Kosei Ueno, Tomoya Oshikiri, Atsushi Kubo, Yasutaka Matsuo, Qihuang Gong, Hiroaki Misawa
    OPTICS EXPRESS 25 6 6883 - 6894 2017年03月 [査読有り][通常論文]
     
    We investigated the grating effect in complex gold dolmen structures, in which multiple plasmon modes are present due to plasmon hybridization, experimentally from both the far field and the near field. In particular, the near-field properties were investigated using photoemission electron microscopy, and it was demonstrated that two hybridized plasmon modes on the dolmen structures could be influenced by the grating effect. For comparison, we also investigated the grating effect in arrays of simple nanoblocks and heptamer structures, which were supposed to support a strong bright plasmon mode and a strong dark plasmon mode, respectively, in the near field. We found that the spectral responses of the two hybridized modes on the dolmen structures as the pitch size changed evolved in a manner similar to that of the bright dipole mode on the nanoblocks, whereas the dark mode on the heptamer structures is less sensitive to the pitch size. (C) 2017 Optical Society of America
  • Kuang-Li Lee, Hsuan-Yeh Hsu, Meng-Lin You, Chia-Chun Chang, Ming-Yang Pan, Xu Shi, Kosei Ueno, Hiroaki Misawa, Pei-Kuen Wei
    SCIENTIFIC REPORTS 7 2017年03月 [査読有り][通常論文]
     
    Metallic nanostructure-based surface plasmon sensors are capable of real-time, label-free, and multiplexed detections for chemical and biomedical applications. Recently, the studies of aluminum-based biosensors have attracted a large attention because aluminum is a more cost-effective metal and relatively stable. However, the intrinsic properties of aluminum, having a large imaginary part of the dielectric function and a longer evanescent length, limit its sensing capability. Here we show that capped aluminum nanoslits fabricated on plastic films using hot embossing lithography can provide tailorable Fano resonances. Changing height of nanostructures and deposited metal film thickness modulated the transmission spectrum, which varied from Wood's anomaly-dominant resonance, asymmetric Fano profile to surface plasmon-dominant resonance. For biolayer detections, the maximum surface sensitivity occurred at the dip of asymmetric Fano profile. The optimal Fano factor was close to -1.3. The wavelength and intensity sensitivities for surface thickness were up to 2.58 nm/nm and 90%/nm, respectively. The limit of detection (LOD) of thickness reached 0.018 nm. We attributed the enhanced surface sensitivity for capped aluminum nanoslits to a reduced evanescent length and sharp slope of the asymmetric Fano profile. The protein-protein interaction experiments verified the high sensitivity of capped nanostructures. The LOD was down to 236 fg/mL.
  • Ahmed Esmail Shalan, Tomoya Oshikiri, Hiroki Sawayanagi, Keisuke Nakamura, Kosei Ueno, Quan Sun, Hui-Ping Wu, Eric Wei-Guang Diau, Hiroaki Misawa
    NANOSCALE 9 3 1229 - 1236 2017年01月 [査読有り][通常論文]
     
    Plasmonics is a highly promising approach to enhancing the light-harvesting properties of hybrid organic/ inorganic perovskite solar cells. In the present work, our cells have a p-i-n inverted planar structure. An ultrathin NiO film with two different thicknesses of 5 and 10 nm prepared by a pulsed laser deposition process on an ITO substrate with a faceted and furrowed surface enabled the formation of a continuous and compact layer of well-crystallized CH3NH3PbI3 via an anti-solvent chlorobenzene process. The coverage mechanism of the NiO film on the ITO was clearly demonstrated through the J-V and external quantum efficiency (EQE) curves. Moreover, the results demonstrated that the gold nanoislands (Au NIs) increased the power conversion efficiency to 5.1%, almost double that of the samples without Au NIs. This result is due to the excitation of surface plasmons, which is characterized by strong scattering and enhancement of the electric field in the vicinity of the Au NIs loaded at the interface between the NiO and perovskite films. Additionally, we observed an enhancement of the EQE at wavelengths shorter than the plasmon resonance peak. In the current state, we speculate that the plasmoelectric potential effect is considered to be a good explanation of the photocurrent enhancement at the off-resonance region. Our work provides good guidance for the design and fabrication of solar-energy-related devices employing NiO electrodes and plasmonic Au NIs.
  • Shalan, A.E., Narra, S., Oshikiri, T., Ueno, K., Shi, X., Wu, H.-P., Elshanawany, M.M., Diau, E.W.G., Misawa, H.
    Sustainable Energy and Fuels 1 7 1533 - 1540 2017年 [査読有り][通常論文]
  • Kuang-Li Lee, Po-Cheng Tsai, Meng-Lin You, Ming-Yang Pan, Xu Shi, Kosei Ueno, Hiroaki Misawa, Pei-Kuen Wei
    ACS Omega 2 10 7461 - 7470 2017年 [査読有り][通常論文]
     
    The studies of nanostructure-based aluminum sensors have attracted huge attention because aluminum is a more cost-effective plasmonic material. However, the intrinsic properties of the aluminum metal, having a large imaginary part of the dielectric function and a longer electromagnetic field decay length and problems of poor long-term chemical stability, limit the surface-sensing capability and applicability of nanostructures. We propose the combination of capped aluminum nanoslits and a thin-capped dielectric layer to overcome these limitations. We show that the dielectric layer can positively enhance the wavelength sensitivities of the Wood's anomaly-dominant resonance and asymmetric Fano resonance in capped aluminum nanoslits. The maximum improvement can be reached by a factor of 3.5. Besides, there is an optimal layer thickness for the surface sensitivity because of the trade-off relationship between the refractive index sensitivity and decay length. We attribute the enhanced surface sensitivity to a reduced evanescent length, which is confirmed by the finite difference time-domain calculations. The protein-protein interaction experiments verify the high-surface sensitivity of the structures, and a limit of quantification (LOQ) of 1 pg/mL antibovine serum albumin is achieved. Such low-cost, highly sensitive aluminum-based nanostructures can benefit various sensing applications.
  • Ahmed Esmail Shalan, Tomoya Oshikiri, Sudhakar Narra, Mahmoud M. Elshanawany, Kosei Ueno, Hui-Ping Wu, Keisuke Nakamura, Xu Shi, Eric Wei-Guang Diau, Hiroaki Misawa
    ACS APPLIED MATERIALS & INTERFACES 8 49 33592 - 33600 2016年12月 [査読有り][通常論文]
     
    CoOx is a promising hole-extracting layer (HEL) for inverted planar perovskite solar cells with device configuration ITO/CoOx/CH3NH3PbI3/PCBM/Ag. The devices fabricated according to a simple solution procedure showed the best photovoltaic performance attaining power conversion efficiency (PCE) of 14.5% under AM 1.5 G 1 sun irradiation, which is significantly superior to those of materials fabricated with a traditional HEL such as PEDOT:PSS (12.2%), NiOx (10.2%), and CuOx (9.4%) under the same experimental conditions. We characterized the chemical compositions with XPS, crystal structures with XRD, and film morphology with SEM/AFM techniques. Photoluminescence (PL) spectra and the corresponding PL decays for perovskite deposited on varied HEL films were recorded to obtain the hole-extracting characteristics, for which the hole extracting times show the order CoOx (2.8 ns) < PEDOT:PSS (17.5 ns) < NiOx (22.8 ns) < CuOx (208.5 ns), consistent with the trend of their photovoltaic performances. The reproducibility and enduring stability of those devices were examined to show the outstanding long-term stability of the devices made of metal oxide HEL, for which the CoOx device retained PCE approximate to 12% for over 1000 h.
  • Han Yu, Quan Sun, Kosei Ueno, Tomoya Oshikiri, Atsushi Kubo, Yasutaka Matsuo, Hiroaki Misawa
    ACS NANO 10 11 10373 - 10381 2016年11月 [査読有り][通常論文]
     
    The extraordinary optical properties of coupled plasmonic nanostructures make these materials potentially useful in many applications; thus, they have received enormous attention in basic and applied research. Coupled plasmon modes have been characterized predominantly using far-field spectroscopy. In near-field spectroscopy, the spectral response of local field enhancement in coupled plasmonic nanostructures remains largely unexplored, especially experimentally. Here, we investigate the coupled gold dolmen nanostructures in the near field using photoemission electron microscopy, with wavelength tunable femtosecond laser pulses as an excitation source. The spatial evolution of near-field mapping of an individual dolmen structure with the excitation wavelength was successfully obtained. In the near field, we spatially resolved an anti-bonding mode and a bonding mode as the result of plasmon hybridization. Additionally, the quadrupole plasmon mode that could be involved in the formation of a Fano resonance was also revealed by spatially resolved near-field spectra, but it only contributed little to the total near-field enhancement. On the basis of these findings, we obtained a better understanding of the near-field nanostructures, where the plasmon hybridization and the plasmonic Fano resonance were mixed.
  • Kosei Ueno, Quan Sun, Masahiro Mino, Takumi Itoh, Tomoya Oshikiri, Hiroaki Misawa
    OPTICS EXPRESS 24 16 17728 - 17737 2016年08月 [査読有り][通常論文]
     
    Infrared light has received attention for sensor applications, including fingerprint spectroscopy, in the bioengineering and security fields. Surface plasmon physics enables the operation of a light harvesting optical antenna. Gold nanochains exhibit localized surface plasmon resonance (LSPR) in the infrared region with high frequency selectivity. However, a feasible design for optical antennae with a higher resonant efficiency and frequency selectivity as a function of structural design and periodicity is still unknown. In the present study, we investigated the relationship between the resonant efficiency and frequency selectivity as a function of the structural design of gold nanochains and explored structural periodicity for obtaining highly frequency-selective optical antennae. An optical antenna design with higher resonant efficiency is proposed on the basis of its efficient interaction with non-polarized light. (C) 2016 Optical Society of America
  • Jie Li, Kosei Ueno, Hiyori Uehara, Jingchun Guo, Tomoya Oshikiri, Hiroaki Misawa
    JOURNAL OF PHYSICAL CHEMISTRY LETTERS 7 14 2786 - 2791 2016年07月 [査読有り][通常論文]
     
    We report on the spectral properties of strong coupling between the localized surface plasmon resonances (LSPRs) of aluminum (Al) nanostructures and tetraphenylporphyrin tetrasulfonic acid hydrate (TPPS) J-aggregates. Because of their wide spectral range of LSPR bands from ultraviolet to near-infrared wavelengths by controlling structural size, Al nanodisks can realize strong coupling with different excitons of TPPS J-aggregates. The Rabi splitting energies of the excitons based on Soret and Qbands are 300 and 180 meV, respectively. In addition to extinction spectrum, we have also measured an excitation spectrum to determine the essential absorption of the hybrid states and successfully confirmed a shoulder peak corresponding to a lower branch of hybrid states. In Al nanorod systems, strong coupling with two excitons can also be selectively induced by merely rotating the polarization of the incident light, which constituted a simple platform for the dynamic control of exciton/plasmon coupling states.
  • Yukie Yokota, Kosei Ueno, Hiroaki Misawa, Takuo Tanaka
    Photonics 3 2 2016年06月01日 [査読有り][通常論文]
     
    We designed and fabricated gold curvilinear nanorod periodical arrays using microfabrication techniques. The gold curvilinear nanorods had two distinct resonant peaks in the near-infrared region between 1630 nm and 3000 nm. Similar peak was observed in gold straight nanorods at specific lengths. At lengths identical to the arc length of the curvilinear nanorod, the peak was in the relative range of 3000 nm, which corresponds to the longitudinal plasmon mode (L-mode). At lengths identical to half of the arc length of the curvilinear nanorod, the peak was close to 1630 nm. Plasmon resonant peaks were tunable in the infrared region by changing the arc length of the curve, the line width, and distance between the curvilinear nanorods. In particular, when two curvilinear nanorods were closely packed in a range of less than 100 nm, the peak wavelength of curvilinear nanorod was shifted due to the plasmonic coupling of each mode.
  • Spectral response and spatial evolution of plasmonic near field in coupled gold nanostructures
    Han,Yu, Quan,Sun, Oshikiri,T, Ueno,Kosei, Kubo,Atsushi, Matsuo,Yasutaka, Misawa,Hiroaki
    日本化学会第96春季年会 予稿集 4E3-12  2016年03月 [査読無し][通常論文]
  • Tomoya Oshikiri, Kosei Ueno, Hiroaki Misawa
    ANGEWANDTE CHEMIE-INTERNATIONAL EDITION 55 12 3942 - 3946 2016年03月 [査読有り][通常論文]
     
    The generation of ammonia from atmospheric nitrogen and water using sunlight is a preferable approach to obtaining ammonia as an energy carrier and potentially represents a new paradigm for achieving a low-carbon and sustainable-energy society. Herein, we report the selective conversion of dinitrogen into ammonia through plasmon-induced charge separation by using a strontium titanate (SrTiO3) photoelectrode loaded with gold nanoparticles (Au-NPs) and a zirconium/zirconium oxide (Zr/ZrOx) thin film. We observed the simultaneous stoichiometric production of ammonia and oxygen from nitrogen and water under visible-light irradiation.
  • Keisuke Nakamura, Tomoya Oshikiri, Kosei Ueno, Yongming Wang, Yoshiomi Kamata, Yuki Kotake, Hiroaki Misawa
    JOURNAL OF PHYSICAL CHEMISTRY LETTERS 7 6 1004 - 1009 2016年03月 [査読有り][通常論文]
     
    We have successfully fabricated all-solid-state plasmonic photoelectric conversion devices composed of titanium dioxide (TiO2)/nickel oxide (NiO) p-n junctions with gold nanoparticles (Au-NPs) as prototype devices for a plasmonic solar cell. The characteristics of the crystal structures and the photoelectric properties of the all-solid-state devices were demonstrated. We observed that the crystalline structure of the NiO thin film and the interfacial structure of TiO2/Au-NPs/NiO changed significantly during an annealing treatment. Furthermore, the photoelectric conversion devices exhibited plasmon-induced photocurrent generation in the visible-wavelength region. The photo current may result from plasmon-induced charge separation. The photoelectric conversion properties via plasmon-induced charge separation were strongly correlated with the morphology of the TiO2/Au-NPs/NiO interface. The long-term stability of the plasmonic photoelectric conversion device was found to be very high because a stable photocurrent was observed even after irradiation for 3 days.
  • Quan Sun, Han Yu, Kosei Ueno, Atsushi Kubo, Yasutaka Matsuo, Hiroaki Misawa
    ACS NANO 10 3 3835 - 3842 2016年03月 [査読有り][通常論文]
     
    Dipole and quadrupole modes are the two lowest orders of localized surface plasmon resonance (LSPR) eigenmodes in metallic nanoparticles. Of these two modes, the quadrupole mode is forbidden for symmetric metallic nanoparticles excited by linearly polarized light at normal incidence. Here, we demonstrate excitation of the quadrupole mode in symmetrical gold (Au) nanoblocks shined with s -polarized light at oblique incidence. In particular, we probe the near -field LSPR in Au nanoblocks using photoemission electron microscopy (PEEM) and find that at oblique incidence, the dipole and quadrupole modes can be selectively excited, in terms of near -field enhancement, by manipulating the light polarization state. More importantly, by time -resolved PEEM measurements, we experimentally demonstrate that the quadrupole mode in symmetrical Au nanoblocks has longer dephasing time than that of the dipole mode.
  • Kosei Ueno
    2016 PROGRESS IN ELECTROMAGNETICS RESEARCH SYMPOSIUM (PIERS) 1865 - 1865 2016年 [査読有り][通常論文]
  • Kosei Ueno, Tomoya Oshikiri, Hiroaki Misawa
    CHEMPHYSCHEM 17 2 199 - 215 2016年01月 [査読有り][通常論文]
     
    Visible- and near-infrared-light-driven water splitting, which splits water molecules to generate hydrogen and oxygen gases, is a significant subject in artificial photosynthesis with the goal of achieving a low-carbon society. In recent years, considerable attention has been paid to studies on the development of a plasmon-induced water-splitting system responding to visible light. In this review, we categorized water-splitting systems as gold-nanoparticle-loaded semiconductor photocatalytic particles system and metallic-nanoparticles-loaded semiconductor photoelectrode systems, and introduce the latest studies according to these categories. Especially, we describe the studies that optimize a material or a structural design of metallic-nanoparticle-loaded semiconductor photoelectrodes and consider a whole water-splitting system, including a cathode design. Furthermore, we discuss important points when studying plasmon-induced water splitting, and we describe a methodology that enhances plasmon-induced water-splitting efficiency.
  • Exploring plasmonic hot spots and their dynamics by photoemission electron microscopy
    Quan,Sun, Han,Yu, Ueno,Kosei, Kubo,Atsushi, Matsuo,Yasutaka, Misawa,Hiroaki
    Pacifichem 2015 2015年12月 [査読無し][通常論文]
  • Fano resonances on gold nano dolmen structures probed by photoemission electron microscopy
    Han,Yu, Quan,Sun, Ueno,Kosei, Kubo,Atsushi, Matsuo,Yasutaka, Misawa,Hiroaki
    Pacifichem 2015 2015年12月 [査読無し][通常論文]
  • Kosei Ueno, Sho Nozawa, Hiroaki Misawa
    OPTICS EXPRESS 23 22 28584 - 28592 2015年11月 [査読有り][通常論文]
     
    Terahertz (THz) spectroscopy is a promising method to measure the spectrum of low-frequency modes of molecules or ensembles, such as crystals and polymers, including proteins. However, the main drawback of THz spectroscopy is its extremely low sensitivity. In the present study, we report on signal enhancement in THz spectroscopy achieved by depositing amino acid molecules or their derivatives on a gold rod structured silicon substrate whose localized surface plasmon resonance is exhibited in the THz frequency region. The distinct peaks derived from the enhancement of the inherent spectrum based on a molecular crystal were clearly observed when a longitudinal plasmon resonance mode of the gold rod structure was excited and the plasmon resonance band overlapped the molecular/intermolecular vibrational mode. We discuss the mechanism by which surface-enhanced THz spectroscopy was induced from the viewpoint of the enhancement of light-matter coupling due to plasmon excitation and the modulation of the plasmon band by dipole coupling between the plasmon dipole and molecular/intermolecular vibrational modes. (C) 2015 Optical Society of America
  • Kosei Ueno, Tomoya Oshikiri, Xu Shi, Yuqing Zhong, Hiroaki Misawa
    INTERFACE FOCUS 5 3 2015年06月 [査読有り][通常論文]
     
    We have successfully developed a plasmon-induced artificial photosynthesis system that uses a gold nanoparticle-loaded oxide semiconductor electrode to produce useful chemical energy as hydrogen and ammonia. The most important feature of this system is that both sides of a strontium titanate single-crystal substrate are used without an electrochemical apparatus. Plasmon-induced water splitting occurred even with a minimum chemical bias of 0.23 V owing to the plasmonic effects based on the efficient oxidation of water and the use of platinum as a co-catalyst for reduction. Photocurrent measurements were performed to determine the electron transfer between the gold nanoparticles and the oxide semiconductor. The efficiency of water oxidation was determined through spectroelectrochemical experiments aimed at elucidating the electron density in the gold nanoparticles. A set-up similar to the water-splitting system was used to synthesize ammonia via nitrogen fixation using ruthenium instead of platinum as a co-catalyst.
  • Kosei Ueno, Tomoya Oshikiri, Kei Murakoshi, Haruo Inoue, Hiroaki Misawa
    PURE AND APPLIED CHEMISTRY 87 6 547 - 555 2015年06月 [査読有り][通常論文]
     
    We have successfully demonstrated plasmon-enhanced photocurrent generation using gold nan-oparticle- loaded titanium dioxide single-crystal (TiO2) photoelectrodes with visible-light irradiation. Water molecules serve as an electron source in photocurrent generation, and oxygen evolution occurs due to water oxidation from a gold nanostructured TiO2 photoelectrode as a half reaction of water splitting. On the basis of this property, the photocurrent generation system was applied to the plasmon-induced water-splitting system using both sides of the same strontium titanate (SrTiO3) single-crystal substrate without an electrochemical apparatus. The chamber on the side of the gold nanoparticles was the anode side, whereas the chamber on the side of the platinum plate was the cathode side. Platinum was used as a co-catalyst for hydrogen evolution. Hydrogen and oxygen were separately evolved from the anode and cathode chambers, respectively. Water splitting was induced with a relatively low chemical bias of 0.23 V due to plasmonic effects based on efficient water oxidation. Similar to the artificial photosynthesis system, we have also demonstrated ammonia formation via nitrogen fixation using ruthenium as a co-catalyst via an analogous setup of the water-splitting system.
  • Yuqing Zhong, Kosei Ueno, Yuko Mori, Tomoya Oshikiri, Hiroaki Misawa
    CHEMISTRY LETTERS 44 5 618 - 620 2015年05月 [査読有り][通常論文]
     
    A plasmon-enhanced water splitting system using a gold nanostructured strontium titanate (SrTiO3) single-crystal photoelectrode with a titanium dioxide (TiO2) thin film heterojunction was developed. Simultaneous evolution of hydrogen and oxygen was observed in separate reaction chambers under visible light irradiation. The substrate composed of single-crystal SrTiO3 with a rutile TiO2 thin film heterojunction exhibited enhanced water splitting activity compared with the electrode without the TiO2 thin film because the synergistic effect may prevent the back-electron-transfer reaction.
  • Yuqing Zhong, Kosei Ueno, Yuko Mori, Tomoya Oshikiri, Hiroaki Misawa
    JOURNAL OF PHYSICAL CHEMISTRY C 119 16 8889 - 8897 2015年04月 [査読有り][通常論文]
     
    We explored the performance of hydrogen (H-2) evolution using noble metals or their metal oxides as cocatalysts in the plasmon-induced water-splitting system. Although many studies have employed n-type semiconductor particle systems to investigate cocatalyst effects, evaluating only the catalytic activity of H-2 and oxygen (O-2) evolution has been limited by (1) the difficulty of transferring an electron injected into the conduction band of a semiconductor to a cocatalyst due to the formation of a Schottky barrier when a metallic cocatalyst for H2 evolution contacts the n-type semiconductor and (2) the potential for a reverse water-splitting reaction, which occurs due to the promotion of the reduction of the evolved O-2 by the cocatalyst. To overcome these limitations, in the present study, we eliminated the adverse effect of the Schottky barrier by obtaining ohmic contact between the semiconductor and the metal or metal oxide cocatalysts, and we used two separate reaction chambers for H-2 and O-2 evolution to avoid reverse water-splitting reactions such as H2O2 recombination or the photoreduction of O-2. A 23 nm thick rhodium layer deposited on a platinum board exhibited relatively high performance, a 3-fold increase compared with the absence of a metal or metal oxide cocatalyst thin layer.
  • Exploring quadrupole and higher order surface plasmon resonances in individual plasmonic nanoantennas by PEEM
    Q.,Sun, H.,Yu, K.,Ueno, Kubo,Atsushi, Y.,Matsuo, H.,Misawa
    LEEM/PEEM 9 Book of Abttracts 75 - 75 Forschungszentrum Jülich GmbH 2014年09月 [査読無し][通常論文]
  • Tomoya Oshikiri, Kosei Ueno, Hiroaki Misawa
    ANGEWANDTE CHEMIE-INTERNATIONAL EDITION 53 37 9802 - 9805 2014年09月 [査読有り][通常論文]
     
    We have successfully developed a plasmon-induced technique for ammonia synthesis that responds to visible light through a strontium titanate (SrTiO3) photoelectrode loaded with gold (Au) nanoparticles. The photoelectrochemical reaction cell was divided into two chambers to separate the oxidized (anodic side) and reduced (cathodic side) products. To promote NH3 formation, a chemical bias was applied by regulating the pHvalue of these compartments, and ethanol was added to the anodic chamber as a sacrificial donor. The quantity of NH3 formed at the ruthenium surface, which was used as a co-catalyst for SrTiO3, increases linearly as a function of time under irradiation with visible light at wavelengths longer than 550nm. The NH3 formation action spectrum approximately corresponds to the plasmon resonance spectrum. We deduced that plasmon-induced charge separation at the Au/SrTiO3 interface promotes oxidation at the anodic chamber and subsequent nitrogen reduction on the cathodic side.
  • Yuqing Zhong, Kosei Ueno, Yuko Mori, Xu Shi, Tomoya Oshikiri, Kei Murakoshi, Haruo Inoue, Hiroaki Misawa
    ANGEWANDTE CHEMIE-INTERNATIONAL EDITION 53 39 10350 - 10354 2014年09月 [査読有り][通常論文]
     
    A plasmon-induced water splitting system that operates under irradiation by visible light was successfully developed; the system is based on the use of both sides of the same strontium titanate (SrTiO3) single-crystal substrate. The water splitting system contains two solution chambers to separate hydrogen (H-2) and oxygen (O-2). To promote water splitting, a chemical bias was applied by regulating the pH values of the chambers. The quantity of H-2 evolved from the surface of platinum, which was used as a reduction co-catalyst, was twice the quantity of O-2 evolved from an Au-nanostructured surface. Thus, the stoichiometric evolution of H-2 and O-2 was clearly demonstrated. The hydrogen-evolution action spectrum closely corresponds to the plasmon resonance spectrum, indicating that the plasmon-induced charge separation at the Au/SrTiO3 interface promotes water oxidation and the subsequent reduction of a proton on the backside of the SrTiO3 substrate. The chemical bias is significantly reduced by plasmonic effects, which indicates the possibility of constructing an artificial photosynthesis system with low energy consumption.
  • Bin-Bin Xu, Lei Wang, Zhuo-Chen Ma, Ran Zhang, Qi-Dai Chen, Chao Lv, Bing Han, Xin-Ze Xiao, Xu-Lin Zhang, Yong-Lai Zhang, Kosei Ueno, Hiroaki Misawa, Hong-Bo Sun
    ACS NANO 8 7 6682 - 6692 2014年07月 [査読有り][通常論文]
     
    We report polarized femtosecond laser-light-mediated growth and programmable assembly of photoreduced silver nanoparticles into triply hierarchical micropatterns. Formation of erected arrays of nanoplates with a thickness as small as lambda/27 (lambda, the writing laser wavelength) level is demonstrated. The growth mechanism of nanoplates has been clarified: (i) the excited surface plasmons enhance the local electric field and lead to spatially selective growth of silver atoms at the opposite ends of dipoles induced on early created silver seeds; (ii) the optical attractive force overcomes electrostatic repulsion in the enhanced local electric field to assemble the silver nanoparticles directly. The triply hierarchical micropattern shape and location, the nanoplate orientation, and thickness are all attained in controlled fashion.
  • Olivier Lecarme, Quan Sun, Kosei Ueno, Hiroaki Misawa
    ACS PHOTONICS 1 6 538 - 546 2014年06月 [査読有り][通常論文]
     
    We investigate the far-field and near-field properties of aluminum nanorods fabricated by electron beam lithography and exhibiting plasmonic resonance in the near-infrared region. First, we show that plasmonic modes within nanorod arrays can be tuned by geometrical parameters, allowing one to control the system transparency. Next, the light absorption in this structure is closely examined, and we demonstrate that aluminum has great potential due to its unique interband transition at 800 nm. The roles of the dielectric confinement and the coupling between plasmonic resonance and the interband transition are particularly emphasized, as their adjustment can be used to switch from highly scattering particles to absorbing particles without a significant modification of the plasmonic resonance position. Finally, we image the plasmon-generated local field distribution in the aluminum nanostructures and observe, for the first time, the effect of the interband transition on the near-field behavior. The effect of the dielectric confinement is also numerically investigated, as it is shown to play a significant role in near-field enhancement.
  • K. Imura, K. Ueno, H. Misawa, H. Okamoto, D. McArthur, B. Hourahine, F. Papoff
    OPTICS EXPRESS 22 10 12189 - 12199 2014年05月 [査読有り][通常論文]
     
    Optical properties of single gold nanodiscs were studied by scanning near-field optical microscopy. Near-field transmission spectra of a single nanodisc exhibited multiple plasmon resonances in the visible to near-infrared region. Near-field transmission images observed at these resonance wavelengths show wavy spatial features depending on the wavelength of observation. To clarify physical pictures of the images, theoretical simulations based on spatial correlation between electromagnetic fundamental modes inside and outside of the disc were performed. Simulated images reproduced the observed spatial structures excited in the disc. Mode-analysis of the simulated images indicates that the spatial features observed in the transmission images originate mainly from a few fundamental plasmon modes of the disc. (C) 2014 Optical Society of America
  • Revealing higher order surface plasmon resonances and their dynamics by PEEM
    Quan,Sun, Han,Yu, Kosei,Ueno, Kubo,Atsushi, Yasutaka,Matsuo, Hiroaki,Misawa
    第61回応用物理学会春季学術講演会 講演予稿集 2014年03月 [査読無し][通常論文]
  • Gang Bi, Li Wang, Chunfeng Cai, Kosei Ueno, Hiroaki Misawa, Jianrong Qiu
    JOURNAL OF MODERN OPTICS 61 15 1231 - 1235 2014年 [査読有り][通常論文]
     
    The periodic arrays of gold nanocylinder with 121 nm in diameter, 6.3 nm in gap, and 34 nm in thickness are fabricated on glass by electron-beam lithography and lift-off techniques. Some crystal violet molecules are coated on the array by using the dipping and drawing method. In addition, the surface-enhanced Raman scattering (SERS) spectra of these samples with and without gold nanocylinder arrays are characterized specifically. The largest enhancement factor is obtained when the excitation wavelength corresponds to the peak wavelength of localized surface plasmon resonance (LSPR). The density functional theory and the finite-difference time-domain method are used for the calculations of the extinction spectrum of the arrays and Raman spectra of the crystal violet, respectively. These results unambiguously demonstrate that the periodic arrays of gold nanocylinder have good and effective surface-enhanced properties for Raman scattering of crystal violets, and they also show that the excitation wavelength corresponding to the peak one of the LSPR is one of the major reasons causing SERS.
  • Anri Watanabe, Yuki Kotake, Yoshiomi Kamata, Akira Chikamatsu, Kosei Ueno, Hiroaki Misawa, Tetsuya Hasegawa
    JOURNAL OF PHYSICAL CHEMISTRY LETTERS 5 1 25 - 29 2014年01月 [査読有り][通常論文]
     
    The use of localized surface plasmon resonance induced by Ag nanostructures is a promising way for high-efficiency photoelectric conversion. In plasmonic photoelectric conversion devices, however, the chemical instability of Ag in ambient atmosphere and its immediate deterioration have been a critical issue. Here, we propose a Ag-Co nanostructure array embedded in a TiO2 matrix as a plasmonic resonator that ensures long-term stability. We also developed an electrochemical process to remove surface Co nanoclusters protecting fresh Ag from exposure to air. This enabled us to "unseal" Ag at the desired time. Furthermore, we confirmed photoelectric conversion using Ag-Co-TiO2 nanocomposite films in contact with solution; the photoelectric conversion was substantially enhanced by the plasmon resonance of the Ag nanorods. The Ag nanostructures sealed in a TiO2 matrix are expected to be used in other application fields, such as catalytisis and sensing, in which a fresh Ag surface is needed.
  • Quan Sun, Kosei Ueno, Han Yu, Atsushi Kubo, Yasutaka Matsuo, Hiroaki Misawa
    LIGHT-SCIENCE & APPLICATIONS 2 2013年12月 [査読有り][通常論文]
     
    Localized surface plasmon resonance (LSPR) can be supported by metallic nanoparticles and engineered nanostructures. An understanding of the spatially resolved near-field properties and dynamics of LSPR is important, but remains experimentally challenging. We report experimental studies toward this aim using photoemission electron microscopy (PEEM) with high spatial resolution of sub-10 nm. Various engineered gold nanostructure arrays (such as rods, nanodisk-like particles and dimers) are investigated via PEEM using near-infrared (NIR) femtosecond laser pulses as the excitation source. When the LSPR wavelengths overlap the spectrum of the femtosecond pulses, the LSPR is efficiently excited and promotes multiphoton photoemission, which is correlated with the local intensity of the metallic nanoparticles in the near field. Thus, the local field distribution of the LSPR on different Au nanostructures can be directly explored and discussed using the PEEM images. In addition, the dynamics of the LSPR is studied by combining interferometric time-resolved pump-probe technique and PEEM. Detailed information on the oscillation and dephasing of the LSPR field can be obtained. The results identify PEEM as a powerful tool for accessing the near-field mapping and dynamic properties of plasmonic nanostructures.
  • Xu Shi, Kosei Ueno, Tomoya Oshikiri, Hiroaki Misawa
    JOURNAL OF PHYSICAL CHEMISTRY C 117 47 24733 - 24739 2013年11月 [査読有り][通常論文]
     
    In this study, we demonstrated an improvement in the plasmon-enhanced photocurrent generation due to Fabry-Perot interference of titanium dioxide (TiO2) thin-film electrodes loaded with Au nanoislands (Au-NIs). TiO2 thin films with thicknesses of 215-274 nm, which show obvious Fabry-Perot interference, were deposited via atomic layer deposition (ALD) onto silica glass and were modified by the deposition of Au-NIs onto their surface. Anodic plasmon-enhanced photocurrent generation was observed over the Au-NIs-loaded TiO2 thin-film photoelectrodes. The incident photon to current efficiency (IPCE) action spectra correlated strongly with the Au-NIs plasmon resonance and exhibited a strong dependence on the thickness of the TiO2 thin film. The photocurrent conversion efficiency increased when the transmission constructive interference wavelength overlapped with the Au-NIs plasmon resonance band. This work provides a simple and applicable approach for the further design of low-cost and lightweight plasmon-enhanced energy conversion devices.
  • Kosei Ueno, Hiroaki Misawa
    NPG ASIA MATERIALS 5 2013年09月 [査読有り][通常論文]
     
    This paper presents recent investigations of plasmon-enhanced photoelectric conversion and water oxidation by visible and near-infrared light irradiation. Since the discovery of the Honda-Fujishima effect in 1972, significant efforts have been devoted to lengthening the light-energy conversion wavelength. In this context, plasmonic photoelectric conversion has been recently demonstrated at visible-to-near-infrared wavelengths without deteriorating photoelectric conversion by employing titanium dioxide (TiO2) single-crystal photoelectrodes, in which gold nanorods are elaborately arrayed on the surface. A potassium perchlorate aqueous solution was employed as an electrolyte solution without additional electron donors; thus, water molecules provided the electrons. The stoichiometric evolution of oxygen and hydrogen peroxide as a result of the four-or two-electron oxidation of water molecules, respectively, was accomplished with near-infrared light irradiation using the plasmonic optical antenna effect. As there is very little overpotential for water oxidation, these results constitute a significant advancement in this field. In addition, this photoelectric conversion system could potentially be employed in artificial photosynthesis systems that exceed the photosynthetic capabilities of plants by allowing for photoconversion over a wide range of wavelengths.
  • Kosei Ueno, Hiroaki Misawa
    Journal of Photochemistry and Photobiology C: Photochemistry Reviews 15 1 31 - 52 2013年06月 [査読有り][通常論文]
     
    The electromagnetic field enhancement effect based on the excitation of localized surface plasmon resonance was developed for various photochemical reaction systems, such as nano-lithography, photovoltaic cells, photocatalysis, and water splitting systems. As with most points characteristic of these surface plasmon-enhanced photochemical reactions, spatially selective photochemical reactions can be induced and photons can be efficiently utilized, a concept that could contribute to the development of green nanotechnology. Electromagnetic field enhancement effects based on plasmon excitation have contributed not only to physical processes, such as excitation efficiency, but also to chemical processes, such as photo-induced electron transfer reactions. This review article describes advanced studies on a wide variety of surface plasmon-enhanced photochemical reactions. © 2013 Elsevier B.V.
  • Gang Bi, Li Wang, Li Ling, Yukie Yokota, Yoshiaki Nishijima, Kosei Ueno, Hiroaki Misawa, Jianrong Qiu
    Optics Communications 294 213 - 217 2013年05月01日 [査読有り][通常論文]
     
    Gold-bowtie nanostructures are fabricated by electron beam lithography and lift-off techniques. Their optical properties are investigated by both experimental studies and numerical simulations. The influence of sharpness and gap of nano-bowtie on optical properties such as extinction cross section, local electric field intensity, and surface resonance wavelength is explored. The experimental extinction spectra agree well with the simulation results. This investigation may help us to design plasmonic sub-wavelength gold-bowtie nanostructure with desired spectral properties. © 2013 Elsevier B.V.
  • Kosei Ueno, Hiroaki Misawa
    Physical Chemistry Chemical Physics 15 12 4093 - 4099 2013年03月28日 [査読有り][通常論文]
     
    Plasmonic chemistry, a new research field dedicated to understanding plasmon-enhanced photochemical reactions, has become a principal area of chemical research, especially in the field of physical chemistry. In this perspective review article, we describe our recent research regarding the development of a fabrication methodology for metallic nanostructures that exhibit localized surface plasmon resonance, the spectral properties of the fabricated metallic nanostructures and their electromagnetic field enhancement effects using two-photon-induced photoluminescence from gold nanoparticles. © 2013 the Owner Societies.
  • Near Infrared Fluorescence Enhancement by Local Surface Plasmon Resonance from Arrayed Gold Nanoblocks
    F. Ito, R. Ohta, Y. Yokota, K. Ueno, H. Misawa, T. Nagamura
    Optics and Photonics Journal 3 27 - 31 2013年03月 [査読有り][通常論文]
  • Xu Shi, Kosei Ueno, Naoki Takabayashi, Hiroaki Misawa
    Journal of Physical Chemistry C 117 6 2494 - 2499 2013年02月14日 [査読有り][通常論文]
     
    Metallic nanoparticles showing localized surface plasmon resonance (LSPR) are efficient elements in the localization of light to nanometer-scale regions and enhance the light-matter interaction. We show that gold nanoisland (Au-NI)-loaded titanium dioxide (TiO2) photoelectrodes exhibited plasmon-enhanced photocurrent generation in the visible wavelength region, and the photocurrent action spectrum was corresponding to the LSPR band. The photocurrent enhancement may result from the plasmon-assisted electron transfer reaction from Au-NI to TiO2. A hole with high oxidation ability was left at the TiO2 surface states near the Au-NIs/TiO2 interface, which has the potential for photocatalytic water oxidation. The photocurrent generation efficiency of Au-NIs/TiO2 photoelectrode is highly dependent on the annealing temperature for the preparation of Au-NIs. High-resolution transmission electron microscopy and electron energy-loss spectroscopy analyses show that the interfacial structure between Au-NI and TiO2 plays a crucial role in the photocurrent generation efficiency and photocatalytic ability. © 2012 American Chemical Society.
  • Kohei Imura, Kosei Ueno, Hiroaki Misawa, Hiromi Okamoto
    JOURNAL OF PHYSICAL CHEMISTRY C 117 6 2449 - 2454 2013年02月 [査読有り][通常論文]
     
    We studied optical properties of single elongated rectangular nanovoids opened on a thin gold film by scanning near-field optical microscopy. We found that the luminescence is induced via two-photon absorption of near-infrared pulses when the sample is locally photoexcited inside the void as well as on the film. The luminescence spectrum of the void shows spectral features very similar to those observed for gold nanorods and is attributable to that from gold. On the basis of the near-field two-photon excitation imaging by detecting the luminescence, we visualized the optical fields near the voids. The optical image shows a characteristic spatial feature depending on the dimension of the void. From the dose inspection of the topography and the optical images, we found that excitation probability becomes high at the metal void boundary as well as inside the void. We found an oscillating feature along the long axis of the void. The observed spatial features were qualitatively reproduced by photonic local density-of-states based on electromagnetic calculations, and we conduded that the oscillation observed inside the void is attributed to the electromagnetic modes in the void coupled with the plasmon excitations.
  • Tatsuya Konishi, Manabu Kiguchi, Mai Takase, Fumika Nagasawa, Hideki Nabika, Katsuyoshi Ikeda, Kohei Uosaki, Kosei Ueno, Hiroaki Misawa, Kei Murakoshi
    Journal of the American Chemical Society 135 3 1009 - 1014 2013年01月23日 [査読有り][通常論文]
     
    The in situ observation of geometrical and electronic structural dynamics of a single molecule junction is critically important in order to further progress in molecular electronics. Observations of single molecular junctions are difficult, however, because of sensitivity limits. Here, we report surface-enhanced Raman scattering (SERS) of a single 4,4′-bipyridine molecule under conditions of in situ current flow in a nanogap, by using nano-fabricated, mechanically controllable break junction (MCBJ) electrodes. When adsorbed at room temperature on metal nanoelectrodes in solution to form a single molecule junction, statistical analysis showed that nontotally symmetric b1 and b2 modes of 4,4′-bipyridine were strongly enhanced relative to observations of the same modes in solid or aqueous solutions. Significant changes in SERS intensity, energy (wavenumber), and selectivity of Raman vibrational bands that are coincident with current fluctuations provide information on distinct states of electronic and geometrical structure of the single molecule junction, even under large thermal fluctuations occurring at room temperature. We observed the dynamics of 4,4′-bipyridine motion between vertical and tilting configurations in the Au nanogap via b1 and b2 mode switching. A slight increase in the tilting angle of the molecule was also observed by noting the increase in the energies of Raman modes and the decrease in conductance of the molecular junction. © 2012 American Chemical Society.
  • K. Ueno, H. Misawa
    ADVANCED FABRICATION TECHNOLOGIES FOR MICRO/NANO OPTICS AND PHOTONICS VI 8613 2013年 [査読有り][通常論文]
     
    Nanoparticles of noble metals show localized surface plasmon resonance. Plasmon resonances which are collective oscillations of conduction electrons give rise to the enhancement of electromagnetic field to the local surface of metallic nanoparticles. Therefore, various plasmonic near-field lithography systems were proposed so far. Here, we report on a plasmon-assisted nanolithography used for the fabrication of nano-patterns with nanometric accuracy. The lithography system can form deep nano-patterns on positive photoresist film using scattering component of multipole plasmon resonances as an exposure light. Two-photon-induced reaction of a photoresist enabled the formation of fine patterns even using plasmonic scattering light.
  • Yu Teng, Kosei Ueno, Xu Shi, Daisuke Aoyo, Jianrong Qiu, Hiroaki Misawa
    ANNALEN DER PHYSIK 524 11 733 - 740 2012年11月 [査読有り][通常論文]
     
    The authors report on surface plasmon-enhanced fluorescence of Eosin Y molecules induced by gold nanostructures. Al2O3 films deposited by atomic layer deposition with sub-nanometer resolution were used as the spacer layer to control the distance between molecules and the gold surface. As the thickness of the Al2O3 film increased, the fluorescence intensity first increased and then decreased. The highest enhancement factor is achieved with a 1 nm Al2O3 film. However, the trend for the fluorescence lifetime is the opposite. It first decreased and then increased. The changes in the fluorescence quantum yield were also calculated. The yield shows a similar trend to the fluorescence intensity. The competition between the surface plasmon-induced increase in the radiative decay rate and the gold-induced fluorescence quenching is responsible for the observed phenomenon. In addition, this competition strongly depends on the thickness of the spacer layer between Eosin Y molecules and the gold surface.
  • Gang Bi, Li Wang, Wei Xiong, Kosi Ueno, Hiroaki Misawa, Jianrong Qiu
    CHINESE OPTICS LETTERS 10 9 2012年09月 [査読有り][通常論文]
     
    We experimentally verify that surface plasmon (SP) enhances the photoluminescence (PL) of visible light from Tb3+-doped 60SiO(2)-20Al(2)O(3)-20CaF(2):0.3Tb(3+), 20Yb(3+) glass ceramics by using electron beam lithography to fabricate silver nanoparticles on the surface of the glass ceramics. Numerical calculation for the SP enhancement spectroscopy is achieved by using the finite-difference time-domain algorithm. A PL enhancement of Tb3+ by as much as 1.6 times is observed. The PL enhancement is mainly due to the coupling of excitation from F-7(6) to D-5(4) transition dipole of Tb3+ ion with SP mode induced from the silver nanoparticles.
  • Kuang-Li Lee, Min-Jian Chih, Xu Shi, Kosei Ueno, Hiroaki Misawa, Pei-Kuen Wei
    ADVANCED MATERIALS 24 35 OP253 - OP259 2012年09月 [査読有り][通常論文]
  • Kosei Ueno, Hiroaki Misawa
    BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN 85 8 843 - 853 2012年08月 [査読有り][通常論文]
     
    We used metallic nanoparticles exhibiting localized surface plasmon resonance and electromagnetic (EM) field enhancement effects induced by plasmon excitation for the photochemical reaction field; this approach makes it possible to increase the probability of an interaction between photons and the materials. EM field enhancement effects induced by gold nanostructures were elucidated using two-photon-induced photoluminescence from nanogap-spaced gold nanoparticles. The photoluminescence was promoted mainly in the surface regions of the gold nanoblocks adjacent to the nanogaps due to the EM field enhancement effect. To elucidate the near-field intensity distribution of the nanogap gold structures, we investigated the photopolymerization of a commercially available negative photoresist assisted by EM field enhancement in the nanogaps separating the gold nanoblocks. Photopolymerization rates were enhanced by several orders of magnitude in the gold nanoblock structures that contained nanogaps narrower than 10 nm. We propose two surface plasmon-assisted nanolithography techniques based on spatially selective photochemical reactions promoted by the EM field enhancement effect. The first method uses ultimate near-field lithography with a local near-field distribution induced in the nanogaps, and the second technique uses the scattering component of multipole plasmon resonance as an exposure mechanism. These lithographic techniques represent a type of application based on plasmon-enhanced chemical reactions.
  • Li Wang, Yoshiaki Nishijima, Kosei Ueno, Hiroaki Misawa, Naoto Tamai
    JOURNAL OF PHYSICAL CHEMISTRY C 116 33 17838 - 17846 2012年08月 [査読有り][通常論文]
     
    We examined the vibrational dynamics of periodic gold pair nanocuboids with various nanogaps and various pair-to-pair separations under 400 nm excitation by near-IR transient absorption spectroscopy. Multi-oscillation behavior of the coherent acoustic phonon vibration was observed for all the gold pair nanocuboid arrays. Two symmetric breathing modes were assigned to the displacement of edge-to-edge and its second harmonic, and the displacement of tip-to-tip of gold nanocuboids. We assigned the driving mechanisms of the edge-to-edge and the tip-to-tip modes to thermal expansion and hot-electron pressure, respectively, due to the different amplitudes and the phase mismatch between both modes. Moreover, Young's modulus of gold nanocuboids was estimated to be 97 GPa by using the measured vibrational periods of the edge mode. A little deviation from the bulk value (78 GPa) was interpreted in terms of an interaction of a gold nanocuboid with a substrate. In addition, the oscillation periods and damping constants of the phonon vibration were similar for all of the arrays, even though localized surface plasmon resonance (LSPR) bands were shifted due to near- and far-field dipole couplings. This phenomenon suggested that the phonon vibration was only influenced by the intrinsic properties of the nanomaterials. Furthermore, the oscillation amplitudes of the bleaching peaks exponentially decayed with the increase of the nanogap. We calculated the LSPR bands of gold pair nanocuboids with structural deformation by finite-difference time-domain simulation, and the estimated spectral shift was in good agreement with the experimental results.
  • Tobias Geldhauser, Andreas Kolloch, Naoki Murazawa, Kosei Ueno, Johannes Boneberg, Paul Leiderer, Elke Scheer, Hiroaki Misawa
    LANGMUIR 28 24 9041 - 9046 2012年06月 [査読有り][通常論文]
     
    The quantitative determination of the strength of the near-field enhancement in and around nanostructures is essential for optimizing and using these structures for applications. We combine the Gaussian intensity distribution of a laser profile and two-photon-polymerization of SU-8 to a suitable tool for the quantitative experimental measurement of the near-field enhancement of a nanostructure. Our results give a feedback to the results obtained by finite-difference rime-domain (FDTD) simulations. The structures under investigation are gold nanotriangles on a glass substrate with 85 nm side length and a thickness of 40 nm. We compare the threshold fluence for polymerization for areas of the Gaussian intensity profile with and without the near-field enhancement of the nanostructures. The experimentally obtained value of the near-field intensity enhancement is 600 140, independent of the laser power, irradiation time, and spot size. The FDTD simulation shows a pointlike maximum of 2600 at the tip. In a more extended area with an approximate size close to the smallest polymerized structure of 25 nm in diameter, we find a value between 800 and 600. Using our novel approach, we determine the threshold fluence for polymerization of the commercially available photopolymerizable resin SU-8 by a femtosecond laser working at a wavelength of 795 nm and a repetition rate of 82 MHz to be 0.25 J/cm(2) almost independent of the irradiation time and the laser power used. This finding is important for future applications of the method because it enables one to use varying laser systems.
  • Botao Wu, Kosei Ueno, Yukie Yokota, Kai Sun, Heping Zeng, Hiroaki Misawa
    JOURNAL OF PHYSICAL CHEMISTRY LETTERS 3 11 1443 - 1447 2012年06月 [査読有り][通常論文]
     
    We performed a quantitative analysis of plasmon-assisted two-photon photochromic reactions on light-harvesting gold nanodimer structures. Our strategy for the quantitative analysis of two-photon-induced photochemical reactions on gold nanostructures is using not only a confined photochemical reaction chamber but also a solution system. The strong intensification of near-field light at the nanogap positions on gold nanodimer pairs promoted two-photon absorption by a closed-form diarylethene derivative, resulting in highly efficient photochromic conversion to the open-form structure.
  • Yoshiaki Nishijima, Kosei Ueno, Yuki Kotake, Kei Murakoshi, Haruo Inoue, Hiroaki Misawa
    JOURNAL OF PHYSICAL CHEMISTRY LETTERS 3 10 1248 - 1252 2012年05月 [査読有り][通常論文]
     
    We report the stoichiometric evolution of oxygen via water oxidation by irradiating a plasmon-enhanced photocurrent generation system with near-infrared light (lambda: 1000 am), in which gold nanostructures were arrayed on the surface of TiO2 electrode. It is considered that multiple electron holes generated by plasmon-induced charge excitation led to the effective recovery of water oxidation after the electron transfer from gold to TiO2. The proposed system containing a gold nanostructured TiO2 electrode may be a promising artificial photosynthetic system using near-infrared light.
  • Gang Bi, Wei Xiong, Li Wang, Kosei Ueno, Hiroaki Misawa, Jian-rong Qiu
    OPTICS COMMUNICATIONS 285 9 2472 - 2477 2012年05月 [査読有り][通常論文]
     
    This paper presents optical property of the periodical bowties structure of Au nanoparticles on glass substrate fabricated by high-resolution electron beam lithography. Numerical calculation is used to examine the shape-induced surface plasmon enhancement and extinction spectroscopy by using Finite-Difference Time Domain algorithm and Lorentz model of surface plasmon. The calculated extinction spectra of the periodical nanoparticles are consistent with the experimental results. The influence of the geometrical shape on the spectral properties of bowtie nanoparticles is discussed. This investigation may help one to design plasmonic sub-wavelength devices with desired spectral properties. (C) 2012 Elsevier B.V. All rights reserved.
  • Jun Sakai, Daniel Roldan, Kosei Ueno, Hiroaki Misawa, Yoichiroh Hosokawa, Takanori Iino, Shigeyuki Wakitani, Mutsumi Takagi
    CYTOTECHNOLOGY 64 3 323 - 329 2012年05月 [査読有り][通常論文]
     
    The effect of femtosecond laser irradiation on adherent mesenchymal stem cell was investigated with the aim to develop a novel noninvasive cell purification system. A single mesenchymal stem cell was irradiated with a femtosecond laser on the center of the cell using several energy values and the cell lost its replication capacity with one time irradiation with an energy of 2.0 mu J. Besides at a neighbor point in the major axis, when irradiated in the minor axis at a distance shorter than 10 mu m, the cell stopped its replication capacity. The accumulation effect of cell damage caused by multiple laser shots at a neighbor point in the minor axis was correlated with the critical distance at which the cell lost its replication capacity. Finally, a novel equation of laser cell damage as a function of laser pulse energy and laser shot number is proposed.
  • Quan Sun, Kosei Ueno, Hiroaki Misawa
    OPTICS LETTERS 37 4 710 - 712 2012年02月 [査読有り][通常論文]
     
    We report on experimental study of the shrinkage of photopolymerized micro/nanostructures fabricated by femto-second direct laser writing in organic-inorganic resists. Blueshift of the stop-band positions of fabricated photonic crystals during the drying process, which follows the development and rinsing stages, indicates that the drying process plays an important role in the formation of the shrinkage. It is further confirmed that the shrinkage almost completely occurs during the drying process by in situ optical monitoring the structures. These findings will help to better understand, control, and even positively utilize the shrinkage in the applications of the photopolymerization-based direct laser writing technique. (C) 2012 Optical Society of America
  • Microfluidic devices for fractionation of DNA fragments
    Kai Sun, Zheyu Li, Kosei Ueno, Nanqi Ren, Hiroaki Misawa
    Proceedings of the 16th International Conference on Miniaturized Systems for Chemistry and Life Sciences, MicroTAS 2012 1165 - 1167 2012年 
    The fraction collection of DNA fragments for studying gene expression, suffered from technical difficulties, including those related to the accurate capture of fast moving targets and pure collection under conditions of insufficient separation. We introduces a new concept of simultaneous space sampling for capturing targets in complicated situation, like overlapping fragments. Ten parallel extraction channels which covered 1.5 mm long sampling ranges were used to facilitate the capturing of fast moving fragments. Furthermore, the space-sampling extraction made it possible to acquire pure collection, even from partly overlapping fragments that had been insufficiently separated after a short electrophoretic run. Three fragments differed in size by one base bases, were simultaneously collected within 10 min.
  • Kosei Ueno, Hiroaki Misawa
    ICALEO 2012 - 31st International Congress on Applications of Lasers and Electro-Optics 1150 - 1159 2012年 
    State of the art lithography such as ArF immersion and EUV (Extreme Ultra-Violet) lithography systems have attained a 32 nm node and has been already employed in the development of electronic devices. However, the lithography systems are not appropriate for making nanopatterns on a positive photoresist film, such as rectangular cuboids, triangular prisms, chains, and nanogaps. These nanostructures are utilized for various applications such as plasmonic solar cells and photonic crystal lasers. Here, we describe a new plasmon-assisted nanolithography system that is used for fabricating nano-patterns with a nanometer precision. The most attractive merit of this system is to form deep nano-patterns on a positive photoresist film. The formed nano-patterns are completely reflected on the photomask's design. The key technology is using two-photon-induced reaction of a positive photoresist promoted not only by plasmonic near-field light but also by propagating light in a photoresist film. This propagating light is a radiation mode from a multipole localized surface plasmon resonances scattered by gold nanostructures. The system does not induce nano-pattern deformation in the case of mask release. This system presents a simple alternative for producing nano-patterns instead of nanoimprinting technology.
  • K. Ueno, H. Misawa
    LASER APPLICATIONS IN MICROELECTRONIC AND OPTOELECTRONIC MANUFACTURING (LAMOM) XVII 8243 2012年 [査読有り][通常論文]
     
    Advanced lithography systems, such as ArF immersion lithography, have achieved a 32 nm node(1,2) and are already used in electronic device development. However, the advanced lithography systems are not suitable for fabricating nanostructures, such as rectangular cuboids, triangular prisms, chains, and nanogaps. These nanostructures are being used for various applications that include plasmonic solar cells(3-5) and photonic crystal lasers. (6, 7) In this proceeding, we report an innovative lithography system appropriate for fabricating such nano-patterns with nanometric accuracy based on plasmon-assisted photolithography. The key technology is the two-photon photochemical reaction of a photoresist induced by plasmonic near-field light and propagating light in a photoresist film. This propagating light is a radiation mode from a higher order of localized surface plasmon resonances scattered by metallic nanostructures. The system does not induce nano-pattern deformation at the time of mask release. This system presents a simple alternative for producing nano-patterns instead of using nanoimprinting.
  • S. Danworaphong, T. A. Kelf, O. Matsuda, M. Tomoda, Y. Tanaka, N. Nishiguchi, O. B. Wright, Y. Nishijima, K. Ueno, S. Juodkazis, H. Misawa
    APPLIED PHYSICS LETTERS 99 20 2011年11月 [査読有り][通常論文]
     
    We image gigahertz surface acoustic waves normally incident on a microscopic linear array of triangular holes-a generic "acoustic diode" geometry-with a real-time ultrafast optical technique. Spatiotemporal Fourier transforms reveal wave diffraction orders in k-space. Squared amplitude reflection and transmission coefficients for incidence on both sides of the array are evaluated and compared with numerical simulations. We thereby directly demonstrate acoustic rectification with an asymmetric structure. (C) 2011 American Institute of Physics. [doi:10.1063/1.3662930]
  • Yosuke Harada, Kohei Imura, Hiromi Okamoto, Yoshiaki Nishijima, Kosei Ueno, Hiroaki Misawa
    JOURNAL OF APPLIED PHYSICS 110 10 2011年11月 [査読有り][通常論文]
     
    Modification of photovoltaic devices with metallic nanoparticles is expected to be one of the key methods for development of high performance devices as a future energy source. To clarify the mechanism of photocurrent changes induced by surface plasmon resonances of metal nanoparticles, we measured near-field photocurrent excitation images for a GaAs photodiode modified with gold nanospheres (diameter 100 nm) with a spatial resolution higher than 100 nm. The relationship between the photovoltaic efficiency and the plasmons of the gold nanospheres was investigated through the measurements of incident wavelength and polarization dependence of the near-field photocurrent images. Isolated nanospheres deposited on the GaAs active surface caused local photocurrent suppressions at the plasmon resonance wavelengths. In the case of assemblies (dimers and trimers) of the spheres, a remarkable decrease of photocurrent at the gap site between the spheres was observed. From the results, it turned out that the enhanced optical fields created via the plasmons on the metal nanostructures do not improve the photovoltaic efficiency and that forward scattering of photons by the gold nanoparticles is considered to be more important than the enhanced field effect at the particles for the GaAs photovoltaic device studied. (C) 2011 American Institute of Physics. [doi:10.1063/1.3662114]
  • Zheyu Li, Kai Sun, Misato Sunayama, Ryoko Araki, Kosei Ueno, Masumi Abe, Hiroaki Misawa
    ELECTROPHORESIS 32 23 3392 - 3398 2011年11月 [査読有り][通常論文]
     
    Fraction collection of selected components from a complex mixture plays a critical role in biomedical research, environmental analysis, and biotechnology. Here, we introduce a novel electrophoretic chip device based on a signal processing theorem that allows simultaneous space sampling for fractionation of ssDNA target fragments. Ten parallel extraction channels, which covered 1.5-mm-long sampling ranges, were used to facilitate the capturing of fast-moving fragments. Furthermore, the space sampling extraction made it possible to acquire pure collection, even from partly overlapping fragments that had been insufficiently separated after a short electrophoretic run. Fragments of 180, 181, and 182 bases were simultaneously collected, and then the recovered DNA was PCR amplified and assessed by CE analysis. The 181-base target was shown to be isolated in a 70-mm-long separation length within 10?min, in contrast to the >50?min required for the 300-mm-long separation channel in our previous study. This method provides effective combination of time and space, which is a breakthrough in the traditional concept of fraction collection on a chip.
  • Kosei Ueno, Hiroaki Misawa
    SPIE Newsroom 2011年10月03日
  • Li Wang, Wei Xiong, Yoshiaki Nishijima, Yukie Yokota, Kosei Ueno, Hiroaki Misawa, Jianrong Qiu, Gang Bi
    APPLIED OPTICS 50 28 5600 - 5605 2011年10月 [査読有り][通常論文]
     
    Ag/Au bimetallic nanoparticles possess the combinatory advantages of Au and Ag nanoparticles and can also be utilized to tune the properties of localized surface plasmon resonance. Ag/Au bilayer nanorods were prepared by electron beam lithography, and their spectral properties were investigated. Compared with Ag monolayer nanorods, Ag/Au bilayer nanorods show broader localized surface plasmon resonance bands, and the longitudinal mode and transverse mode localized surface plasmon bands show blueshift and redshift, respectively. The maximum near-field intensity of the longitudinal mode of the Ag/Au nanorod is less than half that of the Ag/Au nanorod without gold layer. Shape-induced modification of Ag/Au bilayer nanorods on their spectral properties was also discussed. (C) 2011 Optical Society of America
  • E. Wu, Yingzhi Chi, Botao Wu, Kangwei Xia, Yukie Yokota, Kosei Ueno, Hiroaki Misawa, Heping Zeng
    JOURNAL OF LUMINESCENCE 131 9 1971 - 1974 2011年09月 [査読有り][通常論文]
     
    Metallic bowtie nanostructures as plasmonic nanoantennas can create highly enhanced local fields when resonating with the incident light. With Au bowtie nanostructures fabricated by lithography method, we experimentally observed that the photoluminescence (PL) spatial profile from a single Au bowtie nanoantenna was strongly dependent on the excitation light polarization. While varying the incident light polarization, the spatial distribution of the PL intensity in the nanogap of an Au bowtie changed as predicted by the simulation results on the electromagnetic field enhancement distribution. The polarization feature of the PL intensity relative to the polarization direction of incident excitation light was also discussed. The study may find application in the design of polarization sensitive plasmonic sensors. (C) 2011 Elsevier B.V. All rights reserved.
  • Li Wang, Wei Xiong, Yoshiaki Nishijima, Yukie Yokota, Kosei Ueno, Hiroaki Misawa, Gang Bi, Jianrong Qiu
    IEEE PHOTONICS TECHNOLOGY LETTERS 23 17 1216 - 1218 2011年09月 [査読有り][通常論文]
     
    Plasmonic spectral properties of silver nanoblocks fabricated by electron beam lithography are investigated. The extinction spectra of silver nanoblocks showed a red shift, broadening, and damping with the passage of storage time. In contrast, silver nanoblocks with titanium coating on the top did not show apparent spectral change even after storage for two months. Morphological change of the silver nanoblocks was characterized by scanning electron microscope. The present work clearly demonstrates that coating titanium on the top of the silver nanostructures is an effective way to prevent them from chemical corrosion and stabilize their plasmonic spectral properties.
  • A. Kolloch, T. Geldhauser, K. Ueno, H. Misawa, J. Boneberg, A. Plech, P. Leiderer
    APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING 104 3 793 - 799 2011年09月 [査読有り][通常論文]
     
    We report on recent insights into the interaction between ultra-fast laser pulses and plasmonic nanoparticles. We discuss femtosecond near-field ablation as a simple but versatile tool for the nanoscale modification of surfaces and the high-resolution measurement of a nanostructure's near field. Two model systems are presented, illustrating the complexity of near-field distributions. Furthermore, finite difference time domain calculations in combination with absorption spectra provide a deeper insight into the factors influencing the near-field distribution. For the first time, an almost perfect agreement between the measured ablation pattern and experiment has been reached for gold triangles with a side length around 500 nm. Additionally, the results from picosecond laser irradiated plasmonic structures display a new regime of nanoscale laser material processing. We present first results showing nanometre confined melting induced by laser pulses.
  • Yutaka Yoshida, Seiichi Watanabe, Yoshiaki Nishijima, Kosei Ueno, Hiroaki Misawa, Takahiko Kato
    NANOTECHNOLOGY 22 37 2011年09月 [査読有り][通常論文]
     
    A gold/silicon nanocomposite structure (NCS) was formed on a Si(100) surface by nanosecond pulsed laser irradiation. The Au/Si NCS contained both Au nanoparticles (NPs) and Au-Si alloy layers. We report that the use of laser irradiation to form Au NPs comprises two competing processes: a top-down effect involving decomposition into smaller NPs and a bottom-up effect involving self-assembly or self-organization into larger NPs. The formation of the periodic structure involved self-organization, i.e., the bottom-up effect, and was observed in situ using a pulsed-laser-equipped high-voltage electron microscope. The NCS formed by laser irradiation can be controlled by adjusting the laser energy density and the number of laser pulses.
  • Kosei Ueno, Satoaki Takabatake, Ko Onishi, Hiroko Itoh, Yoshiaki Nishijima, Hiroaki Misawa
    APPLIED PHYSICS LETTERS 99 1 2011年07月 [査読有り][通常論文]
     
    We report an innovative lithography system appropriate for fabricating sharp-edged nanodot patterns with nanoscale accuracy using plasmon-assisted photolithography. The key technology is two-photon photochemical reactions of a photoresist induced by plasmonic near-field light and the scattering component of the light in a photoresist film. The scattering component of the light is a radiation mode from higher order localized surface plasmon resonances scattered by metallic nanostructures. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3606505]
  • Tobias Geldhauser, Shintarou Ikegaya, Andreas Kolloch, Naoki Murazawa, Kosei Ueno, Johannes Boneberg, Paul Leiderer, Elke Scheer, Hiroaki Misawa
    PLASMONICS 6 2 207 - 212 2011年06月 [査読有り][通常論文]
     
    We report in this paper the near-field distribution in the case of gold triangle arrays by means of two-photon polymerization for a dipole and a quadrupole plasmon mode. In order to link the finite difference in the time domain (FDTD) simulations of the triangle array and the experimental results, extinction spectra for both cases in air and SU-8 environments are shown. In case of the 40-nm thick gold triangles with 85-nm side-length, we show that the calculated and experimentally obtained near-field for the excited dipole mode has the same distribution along the polarization of the exciting laser beam. In case of bigger triangles of 540-nm side-length a quadrupole mode is excited, which leads to a rotation of the near-field distribution by 90A degrees referred to the polarization of the beam. This effect is also shown in the FDTD simulations.
  • Susumu Haruta, Hiroaki Misawa, Kosei Ueno, Yukie Yokota, Hiroki Uehara, Hiroshi Hiratsuka, Hiroaki Horiuchi, Tetsuo Okutsu
    JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY A-CHEMISTRY 221 2-3 268 - 272 2011年06月 [査読有り][通常論文]
     
    Photochemically induced protein crystallization byprotein's multiphoton excitation based on enhanced field of localized surface plasmon resonance (LSPR) of gold nanostructures was investigated. As strong photons-molecules coupling fields, gold nanostructures composed of nanoblocks and gold nanocolloid were used. With gold nanostructures, we could observe enzyme activity decrease by light irradiation that protein does not absorb. Surface observation of gold nanostructure by DFM (non-contact dynamic force microscope) shows that proteins were aggregated at around the nanoblock due to photochemical reaction by enhanced field. Crystallization probability depends on the excitation photon fluence, which indicates 3 photons absorption process occurred. (C) 2011 Elsevier B.V. All rights reserved.
  • Li Wang, Yoshiaki Nishijima, Kosei Ueno, Hiroaki Misawa, Naoto Tamai
    JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY A-CHEMISTRY 221 2-3 164 - 168 2011年06月 [査読有り][通常論文]
     
    Gold pair nanocuboids (size: 150 nm x 150 nm x 20 nm) with different nanogaps ranging from 0 to 10.6 nm were prepared by the electron-beam lithography. Effect of plasmon coupling on coherent acoustic phonon dynamics of gold pair nanocuboids was examined as a function of nanogaps by near-IR transient absorption spectroscopy at 400-nm excitation. The similar oscillation periods of coherent acoustic phonon vibration (88 +/- 1 ps) were observed for all the gold pair nanocubiods irrespective of the nanogaps, which was analyzed by the oscillation of bleaching peaks of SPR bands and the transient absorption dynamics. The coherent acoustic phonon vibration of gold nanocuboids was only influenced by the nanostructure itself, even though SPR band was much influenced due to the dipole coupling between the adjacent Au nanocuboids. In addition, it was revealed that the electron-phonon coupling (similar to 0.7 ps) was followed by the initial size change of gold nanocuboid with the time scale that was a little slower (similar to 1.7 ps) than the electron-phonon coupling. (C) 2011 Elsevier B.V. All rights reserved.
  • Kosei Ueno, Hiroaki Misawa
    JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY A-CHEMISTRY 221 2-3 130 - 137 2011年06月 [査読有り][通常論文]
     
    To achieve a future low-carbon society, the effective utilization of photons is essential for the development of technologies based on photochemistry, such as photocatalysis and dye-sensitized solar cells, which have the potential to produce clean energy as well as preserve the environment. Here, we propose that gold nanostructures exhibiting localized surface plasmon (LSP) resonance are promising sites for photochemical reaction fields that increase the interaction between a photon and molecule. These interactions are based on electromagnetic field enhancement effects that are induced by LSP excitations and their localization. In this review, recent studies on the strong coupling field between a photon and molecule for photochemical reactions are discussed. As an outstanding example, this concept was applied to the plasmonic, photoelectric conversion of visible to near-infrared wavelengths using electrodes in which gold nanoblocks were elaborately arrayed on the surface of a single TiO2 crystal. The most important characteristic of this photoelectric conversion is that the photocurrent was stable for more than 200 h without adding the donors, which suggests the possibility that water molecules can act as donors that provide electrons to the d-band holes assisted by the LSP excitation. Therefore, this system has the potential for use in artificial photosynthesis systems with irradiation from near-infrared light. (C) 2011 Elsevier B.V. All rights reserved.
  • Li Wang, Wei Xiong, Yoshiaki Nishijima, Yukie Yokota, Kosei Ueno, Hiroaki Misawa, Gang Bi, Jian-rong Qiu
    OPTICS EXPRESS 19 11 10640 - 10646 2011年05月 [査読有り][通常論文]
     
    The instability of silver nanoblocks under atmospheric conditions is investigated. The localized surface plasmon resonance band of the silver nanoblocks shows a red shift, broadening, and damping with increasing storage time under atmospheric conditions. The change in spectral properties of silver nanoblocks is considered to be due to sulfidation of silver and structural breakage of silver nanoblock based on scanning electron microscope observation and numerical simulation. The effect of aspect ratio of silver nanoblocks on the change in spectral properties of the nanoengineered silver blocks is also discussed. (C) 2011 Optical Society of America
  • Shuyan Gao, Kosei Ueno, Hiroaki Misawa
    ACCOUNTS OF CHEMICAL RESEARCH 44 4 251 - 260 2011年04月 [査読有り][通常論文]
     
    Efficient solar energy conversion has been vigorously pursued since the 1970s, but its large-scale implementation hinges on the availability of high-efficiency modules. For maximum efficiency, it is important to absorb most of the incoming radiation, which necessitates both efficient photoexcitation and minimal electron hole recombination. To date, researchers have primarily focused on the latter difficulty: finding a strategy to effectively separate photoinduced electrons and holes. Very few reports have been devoted to broadband sunlight absorption and photoexdtation. However, the currently available photovoltaic cells, such as amorphous silicon, and even single-crystal silicon and sensitized solar cells, cannot respond to the wide range of the solar spectrum. The photoelectric conversion characteristics of solar cells generally decrease in the infrared wavelength range. Thus, the fraction of the solar spectrum absorbed is relatively poor. In addition, the large mismatch between the diffraction limit of light and the absorption cross-section makes the probability of interactions between photons and cell materials quite low, which greatly limits photoexcitation efficiency. Therefore, there is a pressing need for research aimed at finding conditions that lead to highly efficient photoexdtation over a wide spectrum of sunlight, particularly in the visible to near-infrared wavelengths. As characterized in the emerging field of plasmonics, metallic nanostructures are endowed with optical antenna effects. These plasmonic antenna effects provide a promising platform for artificially sidestepping the diffraction limit of light and strongly enhancing absorption cross-sections. Moreover, they can efficiently excite photochemical reactions between photons and molecules dose to an optical antenna through the local field enhancement. This technology has the potential to induce highly efficient photoexcitation between photons and molecules over a wide spectrum of sunlight, from visible to near-infrared wavelengths. In this Account, we describe our recent work in using metallic nanostructures to assist photochemical reactions for augmenting photoexcitation efficiency. These studies investigate the optical antenna effects of coupled plasmonic gold nanoblocks, which were fabricated with electron-beam lithography and a lift-off technique to afford high resolution and nanometric accuracy. The two-photon photoluminescence of gold and the resulting nonlinear photopolymerization on gold nanoblocks substantiate the existence of enhanced optical field domains. Local two-photon photochemical reactions due to weak incoherent light sources were identified. The optical antenna effects support the unprecedented realization of (i) direct photocarrier injection from the gold nanorods into TiO(2) and ID) efficient and stable photocurrent generation in the absence of electron donors from visible (450 nm) to near-infrared (1300 nm) wavelengths.
  • Yoshito Tanaka, Hiroyasu Ishiguro, Hideki Fujiwara, Yukie Yokota, Kosei Ueno, Hiroaki Misawa, Keiji Sasaki
    OPTICS EXPRESS 19 8 7726 - 7733 2011年04月 [査読有り][通常論文]
     
    We perform direct local-field imaging of a plasmon-resonant gold nanoparticle pair separated by a gap of several nanometers using a scattering-type near-field optical microscope with a sharp silicon tip of atomic force microscope. The sharp tip allows the access for the nanogap and the high spatial resolution. Our results provide experimental evidence that the nanogap structure produces an optical spot with the size of a single nanometer (< 10 nm). This is not only of fundamental importance in the field of nanophotonics, but also provide significant information for the development of plasmonic devices with the nanogap structures. (C) 2011 Optical Society of America
  • Kohei Imura, Kosei Ueno, Hiroaki Misawa, Hiromi Okamoto
    Nano Letters 11 3 960 - 965 2011年03月09日 [査読有り][通常論文]
     
    We report an anomalous light transmission phenomenon for a nanoaperture on an opaque screen when the aperture is covered with an opaque cap. In conventional optics, light transmission must decrease when the aperture is capped. However, we found that light transmission is enhanced when the nanodisk is in close proximity to the aperture at a wavelength close to the plasmon resonance. This effect even occurs when the disk is larger than the aperture. © 2011 American Chemical Society.
  • Kohei Imura, Kosei Ueno, Hiroaki Misawa, Hiromi Okamoto
    NANO LETTERS 11 3 960 - 965 2011年03月 [査読有り][通常論文]
     
    We report an anomalous light transmission phenomenon for a nanoaperture on an opaque screen when the aperture is covered with an opaque cap. In conventional optics, light transmission must decrease when the aperture is capped. However, we found that light transmission is enhanced when the nanodisk is in close proximity to the aperture at a wavelength dose to the plasmon resonance. This effect even occurs when the disk is larger than the aperture.
  • Zheyu Li, Kai Sun, Misato Sunayama, Yasutaka Matsuo, Vygantas Mizeikis, Ryoko Araki, Kosei Ueno, Masumi Abe, Hiroaki Misawa
    JOURNAL OF CHROMATOGRAPHY A 1218 7 997 - 1003 2011年02月 [査読有り][通常論文]
     
    High efficiency and high-purity fraction collection is highly sought in analysis of fragments-of-interest from selective polymerase chain reaction (PCR) products generated by High Coverage Gene Expression Profiling (HiCEP) methods. Here we demonstrate a new electrophoretic chip device enabling automatic high-efficient fractionation of multiple ssDNA target fragments during a run of separation. We used thoroughly isolated extraction channels for each selected target to reduce the risk of cross-contamination between targets due to cross-talk of extraction channels. Fragments of 35, 108 and 138 b, were successfully isolated, then the recovery was PCR-amplified and assessed by capillary electrophoresis (CE) analysis. Total impurity level of the targets due to unwanted fragments of 0.7%, 2% and 6% respectively, was estimated. Difficulties in collecting multiple target factions are due to band diffusion and DNA adsorption to the walls for the fragments in the separation channel, which is generated by transferring the DNA target fraction from the extraction section to the target reservoir. Therefore, we have carefully measured band broadening and analyzed its influence on the separation resolution due to the delay. (C) 2010 Elsevier B.V. All rights reserved.
  • Plasmon-Enhanced Water Oxidation on Gold Nanostructured TiO2 Single Crystal Substrates
    Misawa Hiroaki, Nishijima Yoshiaki, Ueno Kosei, Murakoshi Kei, Inoue Haruo
    Meeting Abstracts 36 1295  2011年 [査読有り][通常論文]
  • Controlling plasmonic spectral properties of engineered silver nanorods by using titanium coating
    Wang Li, Xiong Wei, Nishijima Y, Yokota Y, Ueno K, Misawa H, Bi G, Qiu JR
    IEEE Photon. Technol. Lett. 2011年 [査読有り][通常論文]
  • Fuyuki Ito, Ryuichi Ohta, Yukie Yokota, Kosei Ueno, Hiroaki Misawa, Toshihiko Nagamura
    MOLECULAR CRYSTALS AND LIQUID CRYSTALS 538 265 - 271 2011年 [査読有り][通常論文]
     
    The polarization dependence of excitation light for fluorescence enhancement of near-infrared dyes immobilized in hydrophobic DNA thin film on glass substrates with regularly arranged Au nanoblocks was investigated. The enhancement factor for S-polarized excitation was about 1.2 to 1.5 times as large as that for P-polarized excitation. P-polarized light contributed to the excitation of plasmon band both of horizontal and vertical direction of Au nanoblocks. The vertical direction corresponds to the short axis for height direction which has the absorption in visible region did not contribute the excitation of IR780. When the absorption band of Au array and the fluorescence band of IR780 were overlapped, the fluorescence enhancement did not depend on the polarization of excitation light. It is suggested that the fluorescence quenching originates from the energy transfer from the excited state of IR780 to Au nanoblocks or the increased deactivation of excited dye molecules induced by resonance with Au nanoblocks.
  • Ya-Wei Hao, Hai-Yu Wang, Ying Jiang, Qi-Dai Chen, Kosei Ueno, Wen-Quan Wang, Hiroaki Misawa, Hong-Bo Sun
    ANGEWANDTE CHEMIE-INTERNATIONAL EDITION 50 34 7824 - 7828 2011年 [査読有り][通常論文]
  • Yukie Yokota, Kosei Ueno, Hiroaki Misawa
    SMALL 7 2 252 - 258 2011年01月 [査読有り][通常論文]
     
    Well defined gold nanostructures of various sizes are fabricated on glass substrates using high-resolution electron-beam lithography/lift-off techniques and detailed surface-enhanced Raman scattering (SERS) properties of crystal violet molecules are studied in order to elucidate electromagnetic (EM) field enhancement effects on the fabricated structures. SERS measurements are performed with high reproducibility using in situ Raman microspectroscopy in aqueous solution. An analysis based on EM theory is performed using field-enhancement factors obtained from finite-difference time-domain (FDTD) simulations and the analysis reproduces experimental results very well. It is noteworthy, furthermore, that the proposed analytic method of EM effects on SERS allows the estimate of the ideal local temperature of gold nanostructures by canceling out the difference in EM field factors at Stokes and anti-Stokes Raman scattering wavelengths. Thus, these experimental results demonstrate that quantitative analysis based on EM theory can be obtained using highly controlled gold nanostructures for SERS measurements with high reproducibility, a result that is promising for the construction of a SERS analysis chip. Although no SERS chip reported so far has been usable for quantitative analysis, this study opens the door for construction of a quantitative SERS chip.
  • Yukie Yokota, Kosei Ueno, Hiroaki Misawa
    CHEMICAL COMMUNICATIONS 47 12 3505 - 3507 2011年 [査読有り][通常論文]
     
    We have demonstrated the essential nanogap effects on surface-enhanced Raman scattering (SERS) signals obtained from two diagonally aligned gold nanoparticles with several nanometre separations, which were precisely fabricated on a glass substrate. This is the first proof of principle for extracting the light localization effects on SERS due to the formation of nanogaps from experimentally observed SERS signals.
  • Quan Sun, Hidenori Asahi, Yoshiaki Nishijima, Naoki Murazawa, Kosei Ueno, Hiroaki Misawa
    OPTICS EXPRESS 18 24 24495 - 24503 2010年11月 [査読有り][通常論文]
     
    The nonlinear propagation of a single focused femtosecond laser pulse in fused silica has been investigated both experimentally and by numerical simulations. In particular, the filamentation behavior was systematically studied by varying pulse duration. At low pulse energy, the peak plasma density inside the filament first increases to a maximum value with increasing pulse duration and then begins to decrease. At relatively high pulse energy, denser plasma can be induced around the geometrical focus with a certain longer pulse duration, where the peak power is already below the self-focusing critical power and no filament is formed. This pulse duration dependent behavior can be explained by different ionization mechanisms. (c) 2010 Optical Society of America
  • Fuyuki Ito, Ryuichi Ohta, Yukie Yokota, Kosei Ueno, Hiroaki Misawa, Toshihiko Nagamura
    CHEMISTRY LETTERS 39 11 1218 - 1219 2010年11月 [査読有り][通常論文]
     
    Fluorescence intensity of near Infrared dyes immobilized in hydrophobic DNA thin film spin-coated on glass substrates with regularly arranged gold (Au) nanoblocks was about 2 5 times larger than that without Au nanoblocks, strongly suggesting the fluorescence intensity was enhanced by increased electric field intensity of excitation light due to local plasmon resonance of Au nanoblocks
  • Yoshiaki Nishijima, Kosei Ueno, Yukie Yokota, Kei Murakoshi, Hiroaki Misawa
    JOURNAL OF PHYSICAL CHEMISTRY LETTERS 1 13 2031 - 2036 2010年07月 [査読有り][通常論文]
     
    Nanoparticles of noble metals exhibit localized surface plasmons (LSPs) associated with the enhancement of an electromagnetic field due to its localization in nanometric domains at the surface of nanoparticles. We demonstrate the plasmonic photoelectric conversion from visible to near-infrared wavelength without deteriorating photoelectric conversion by using electrodes in which gold nanorods are elaborately arrayed on the surface of a TiO2 single crystal.
  • Hiroyo Segawa, Kosei Ueno, Yukie Yokota, Hiroaki Misawa, Tetsuji Yano, Shuichi Shibata
    JOURNAL OF THE AMERICAN CERAMIC SOCIETY 93 6 1634 - 1638 2010年06月 [査読有り][通常論文]
     
    Nanopatterns of a TiO2-organic hybrid material have been fabricated with the use of a localized surface plasmon (LSP). The TiO2-organic hybrid material was prepared by the sol-gel method and was coated on a glass substrate with gold nanoblocks. After the hybrid films were irradiated with a femtosecond laser, the unreacted parts were removed, leaving the TiO2-organic hybrid materials around the nanoblocks. In the nanopatterns of the TiO2-organic hybrid materials, the pi - pi* transition absorption band of the chelate compound formed between Ti-alkoxide and beta-diketone was excited by the two-photon absorption induced by the LSP of gold nanoblocks, and the chelate compound was decomposed and dissolved in alcohol. It was confirmed that the hybrid material changed to anatase upon sintering above 450 degrees C.
  • T. Dehoux, T. A. Kelf, M. Tomoda, O. Matsuda, O. B. Wright, K. Ueno, Y. Nishijima, S. Juodkazis, H. Misawa, V. Tournat, V. E. Gusev
    Optics Letters 35 7 940  2010年04月01日 [査読有り][通常論文]
  • T. Dehoux, T. A. Kelf, M. Tomoda, O. Matsuda, O. B. Wright, K. Ueno, Y. Nishijima, S. Juodkazis, H. Misawa, V. Tournat, V. E. Gusev
    OPTICS LETTERS 35 7 940 - 940 2010年04月 [査読有り][通常論文]
  • Takeshi Tsuji, Kosei Ueno, Yukie Yokota, Masaharu Tsuji, Hiroaki Misawa
    JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY A-CHEMISTRY 212 1 20 - 26 2010年04月 [査読有り][通常論文]
     
    Photoinduced shape changes of metal nanostructures in halide solutions were investigated using gold and silver nanoblocks (NBs) patterned on a glass substrate, instead of nanoparticles dispersed in solution. It was found that size reduction of the NBs by halide etching was enhanced by photoirradiation. Furthermore, it was revealed that the halide etching efficiency corresponded to the intensity of the electric field induced by localized surface plasmon resonance (LSPR) of the NBs. The enhancement of halide etching by LSPR was explained on the basis of electron transfer reactions from metal NBs. Throughout this study, it was demonstrated that metal NBs fabricated on a substrate constitute a powerful system to investigate photoinduced shape changes of nanostructures, because of their defined shape, position, and configuration. (C) 2010 Elsevier B.V. All rights reserved.
  • Kosei Ueno, Satoaki Takabatake, Yoshiaki Nishijima, Vygantas Mizeikis, Yukie Yokota, Hiroaki Misawa
    JOURNAL OF PHYSICAL CHEMISTRY LETTERS 1 3 657 - 662 2010年02月 [査読有り][通常論文]
     
    Nanoparticles of noble metals exhibit localized surface plasmons (LSP) associated with enhancement of the electromagnetic field due to its localization in nanometric domains at the surface of nanoparticles. Especially, nanogapmetallic structures show strong enhancement of the electromagnetic field at the nanogap position. This can be achieved up to 10(5) times larger than the incident light field. We have explored the possibility to use the localized field for nanogap-assisted surface plasmon nanolithography. For the purpose, monidisperse arrays consisting of pairs of rectangular gold nanoblocks separated by nanogaps were fabricated on glass substrates using electron beam lithography and lift-off techniques. Nanoblock structures were used as photomasks for contact exposure of thinfilms of positive photoresist on glass substrates. Thus, ordered clusters of nanoparticles separated by nanogaps can provide a stable and versatile platform for further development of optical subwavelength nanolithography. To the best of our knowledge, this is the first proof-of-principle demonstration of such a technique.
  • Quan Sun, Hidenori Asahi, Naoki Murazawa, Kosei Ueno, Hiroaki Misawa
    2010 OSA-IEEE-COS Advances in Optoelectronics and Micro/Nano-Optics, AOM 2010 2010年 [査読無し][通常論文]
     
    We present the fabrication of photonic microstructures using femtosecond laser direct writing technique in resist. The effect of drying process on photo-polymerized microstructures is investigated. We find that shrinkage mostly arises during the drying process.
  • Md Monirul Islam, Kosei Ueno, Hiroaki Misawa
    ANALYTICAL SCIENCES 26 1 19 - 24 2010年01月 [査読有り][通常論文]
     
    Nanostructured interdigitated array (IDA) electrodes with different inter-electrode spacing were demonstrated to improve the detection sensitivity of short-lived electroactive species and to follow interfacial dynamics by their surface-enhanced Raman scattering (SERS) functionality. Nanostructured IDA electrodes fabricated using electron beam lithography were used for an electrochemical SERS study of irreversible electroactive species, crystal violet (CV), in an aqueous KCl solution in single and generation-collection (GC) mode experiments. The GC mode enabled us to amplify the SERS intensity. An inter-electrode spacing dependent study found the maximum number of redox cycling, collection efficiency and amplification of the SERS intensity. Its SERS function disclosed the potential-dependent dynamics of CV molecules at the electrode surface, which was not observed in the redox current. Miniaturized nanostructured IDA electrodes are of great importance for developing lab on chip devices, and are useful for analyzing dynamical features within small space/volume domains, which require small amounts and/or concentration of analytes.
  • Md Monirul Islam, Kosei Ueno, Saulius Juodkazis, Yukie Yokota, Hiroaki Misawa
    ANALYTICAL SCIENCES 26 1 13 - 18 2010年01月 [査読有り][通常論文]
     
    Interdigitated array electrodes with surface-enhanced Raman scattering (SERS) functionality for in situ qualitative and quantitative analysis of electroactive species are demonstrated. Gold nanostructured interdigitated array electrodes (NIDAEs) were fabricated by electron beam lithography, and used for an electrochemical SERS study of K(3)[Fe(CN(6))] in aqueous KClO(4) solution in single and generation-collection modes. The generation-collection mode experiment showed amplification of the SERS band intensity for adsorbed ferricyanide ions at the negative end of the applied potential, while in single mode it was reduced to near zero. This new finding reveals that NIDAEs offer a new opportunity for analytical science by improving analytical sensitivity and detection ability of electroactive species. The electric fields accumulating at nanogaps are promising for manipulating linear and nonlinear optical phenomena. In addition, miniaturized NIDAEs are of great importance for developing lab-on-a-chip devices, and are useful for measurements within small space/volume domains, requiring only small amounts and/or concentrations of analytes.
  • T. Dehoux, T. A. Kelf, M. Tomoda, O. Matsuda, O. B. Wright, K. Ueno, Y. Nishijima, S. Juodkazis, H. Misawa, V. Tournat, V. E. Gusev
    OPTICS LETTERS 34 23 3740 - 3742 2009年12月 [査読有り][通常論文]
     
    We use ultrashort optical pulses to excite and detect vibrations of single silica spheres with a diameter of 5 mu m placed at the surface of an acoustically mismatched substrate. In addition to the photoelastic detection of picosecond longitudinal acoustic pulses propagating inside the bulk, we detect gigahertz acoustic resonances of the sphere through probe beam defocusing. The mode frequencies are in close accord with those calculated from the elastic vibrations of a free sphere. We also record a resonant enhancement in the amplitude of specific modes of two touching spheres. (C) 2009 Optical Society of America
  • Kai Sun, Nobuko Suzuki, Zheyu Li, Ryoko Araki, Kosei Ueno, Saulius Juodkazis, Masumi Abe, Sumihare Noji, Hiroaki Misawa
    Electrophoresis 30 24 4277 - 84 2009年12月 [査読有り][通常論文]
     
    For the fractionation of fragments of interest from selective PCR products generated by high coverage gene expression profiling (HiCEP) analysis, high-resolution with the ability to discriminate and fractionate fragments differing by one base (base pair) in size is highly required. We report here on a new 4-inch diameter spiral-channel chip device for automatic high-fidelity fractionation. Overlapping DNA fragments of 180, 181 and 182 bases, with only one-base difference in size, were successfully fractionated. The collected fragments were PCR amplified, and then evaluated by size checking analysis, DNA sequencing, and homolog search. The high-resolution fractionation has been achieved because of the combined contributions of (i) the high-resolution separation using a 30 cm long spiral channel, (ii) a blocking technique to avoid contamination from unselected fragments during CE, and (iii) precise micro-scale target extraction. Contaminations due to unselected fractions have been greatly decreased to a negligible level by optimization of the extraction position and extraction time corresponding to the targeted segment only. This technique can be adapted to a wide range of applications, such as protein or cell collections where requirements for the high purity are more important than the amount of recovered fractionated material.
  • Yukie Yokota, Kosei Ueno, Saulius Juodkazis, Vygantas Mizeikis, Naoki Murazawa, Hiroaki Misawa, Haruya Kasa, Kenji Kintaka, Junji Nishii
    JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY A-CHEMISTRY 207 1 126 - 134 2009年09月 [査読有り][通常論文]
     
    This work describes fabrication of three-dimensionally nano-textured silicon surface structures metalized by thin gold films,and their application for optical sensing and detection of solute molecules utilizing surface-enhanced Raman scattering (SERS) effect. Two types of sensitive surfaces were prepared by different techniques. The first of them was a checkerboard pattern of 3D nanoblocks defined in compact areas on the surface of a silicon wafer using highly accurate electron-beam lithography (EBL) technique, and fabricated by dry reactive-ion etching (RIE) technique with subsequent metalization of the surface by gold sputtering. The second type of sensitive surface consisted of a square array of nano-apertures. defined on a large area of the silicon surface by a less accurate but simpler ultraviolet holographic lithography, and subsequently fabricated in a sequence of dry and wet etching as well as gold sputtering steps. The fabricated structures were found to exhibit significant near-field enhancement, as evidenced by strong SERS signal from the sensors immersed in aqueous pyridine solutions with concentrations as low as 10(-9) M due to the presence of well-defined 3D periodic texture of the structure. (C) 2008 Elsevier BY. All rights reserved.
  • Li Wang, Yoshiaki Nishijima, Kosei Ueno, Hiroaki Misawa, Naoto Tamai
    APPLIED PHYSICS LETTERS 95 5 2009年08月 [査読有り][通常論文]
     
    We examined vibrational dynamics of periodic gold single and pair nanocuboids with 9 nm separation at 400 nm excitation by near-IR transient absorption spectroscopy. The similar oscillation periods of coherent phonon vibration (77 +/- 1 ps) were observed for both nanocuboids while the damping of the pair was faster than that of the single. From the analysis of bleaching peak shift and finite-difference time-domain calculation, the lattice change in coherent phonon vibration was estimated to be +/- 1% for a quasiextensional and +/- 3% for an quasibreathing modes of a single nanocuboid.
  • Kosei Ueno, Saulius Juodkazis, Toshiyuki Shibuya, Vygantas Mizeikis, Yukie Yokota, Hiroaki Misawa
    Journal of Physical Chemistry C 113 27 11720 - 11724 2009年07月09日 [査読有り][通常論文]
     
    Photopolymerization of commercial photoresist SU-8 assisted by plasmonic near-field enhancement in nanogaps separating gold nanoblocks was investigated. Photopolymerization rates enhanced by orders of magnitude were found in gold nanoblock structures with nanogaps narrower than 10 nm. The mechanisms responsible for local and nonlocal nonlinear photopolymerization of SU-8 are discussed. ©2009 American Chemical Society.
  • Yoshiaki Nishijima, Kosei Ueno, Saulius Juodkazis, Vygantas Mizeikis, Hideki Fujiwara, Keiji Sasaki, Hiroaki Misawa
    OPTICS EXPRESS 17 4 2976 - 2983 2009年02月 [査読有り][通常論文]
     
    Lasing in dye solution-embedded inverse silica opal structures was investigated. The opal films were prepared by sedimentation of polystyrene microspheres on a cover glass. The polystyrene structures were inverted using sol-gel infiltration of silica and subsequent removal of polystyrene. Photoluminescence of rhodamine ( rhodamine B, 6G and sulfo-rhodamine 101) dye solutions embedded into the inverse silica opal structures exhibited clear signatures of the lasing via a distributed feedback (DFB) and gain modulation. The refractive index contrast between the dye and the inverse opal was small enough (similar to 0.03%) for the formation of refractive index coupling between the lasing modes. The lasing spectrum exhibited a highly regular periodic structure of modal peaks, rather than the chaotic superposition of peaks reported in previous studies. Lasing modes having a spectral width of about 0.25 nm and a free spectral range of about 0.75 nm appeared at the position of the maximum gain ( the maximum fluorescence of the dye). (c) 2009 Optical Society of America
  • 3P1-18
    Tomoda Motonobu, Matsueda Shinnosuke, Wright Oliver B, Matsuda Osamu, Nishijima Yoshiaki, Ueno Kosei, Saulius Juodkazis, Misawa Hiroaki
    Proceedings of Symposium on Ultrasonic Electronics 2009年 [査読無し][通常論文]
  • Naoki Murazawa, Kosei Ueno, Vygantas Mizeikis, Saulius Juodkazis, Hiroaki Misawa
    JOURNAL OF PHYSICAL CHEMISTRY C 113 4 1147 - 1149 2009年01月 [査読有り][通常論文]
     
    Qualitative resemblance between photopolymerization patterns induced in a commercial photoresist SU-8 by optical near-field of surface plasmons localized on rectangular gold nanorods was observed. This finding indicates the possibility of a fast qualitative near-field imaging by embedding metallic nanoparticle structures into photopolymerizeable media and examining the shapes of polymerized regions using high-resolution electron-scanning or atomic force microscopies following the optical exposure.
  • Hideki Nabika, Naozumi Iijima, Baku Takimoto, Kosei Ueno, Hiroaki Misawa, Kei Murakoshi
    ANALYTICAL CHEMISTRY 81 2 699 - 704 2009年01月 [査読有り][通常論文]
     
    A new methodology for nanoscopic molecular filtering was developed using a substrate with a periodic array of metallic nanogates with various widths between 75 and 500 nm. A self-spreading lipid bilayer was employed as the molecular transport and filtering medium. Dye-labeled molecules doped in the self-spreading lipid bilayer were filtered after the spreading less than a few tens of micrometers on the nanogate array. Quantitative analysis of the spreading dynamics suggests that the filtering effect originates from the formation of the chemical potential barrier at the nanogate region, which is believed to be due to structural change such as compression imposed on the spreading lipid bilayer at the gate. A highly localized chemical potential barrier affects the ability of the doped dye-labeled molecules to penetrate the gate. The use of the self-spreading lipid bilayer allows molecular transportation without the use of any external field such as an electric field as is used in electrophoresis. The present system could be applied micro- and nanoscopic device technologies as it provides a completely nonbiased filtering methodology.
  • Kai Sun, Nobuko Suzuki, Zheyu Li, Ryoko Araki, Kosei Ueno, Saulius Juodkazis, Masumi Abe, Sumihare Noji, Hiroaki Misawa
    Electrophoresis 29 19 3959 - 63 2008年10月 [査読有り][通常論文]
     
    A microchannel chip has been used to fractionate selected segments from an electrophoretic flow of separated fragments. A sample, which covers the size from 35 to 670 bp, was initially separated using an 8.8-cm-long channel at the electric field strength of 100 V/cm. The target fragment of 318 bp was selected and extracted from the separation channel. High-resolution fractionation was achieved by introducing new procedures for blocking, extraction, and segment transfer. Fractionation quality with and without blocking were compared using a 310 Genetic Analyzer (Applied Biosystems). The results show that no contamination was found in the sample, which was fractionated with blocking; however, a contamination by short segments was found in the sample, which was fractionated without blocking. Furthermore, fractionation by the chip was found to be of higher fidelity than that by the polyacrylamide slab gel, which displayed a small overlapped peak after the target peak. Compared with the traditional method, our chips enable faster and high-fidelity fractionation, thus providing a new tool for bioanalysis and other applications.
  • Yoshiaki Nishijima, Keisei Ueno, Saulius Juodkazis, Vygantas Mizeikis, Hiroaki Misawa, Mitsuru Maeda, Masashi Minaki
    OPTICS EXPRESS 16 18 13676 - 13684 2008年09月 [査読有り][通常論文]
     
    Lasing from zirconia inverse opal photonic crystal structures infiltrated by solutions of rhodamine dyes was found to exhibit single-mode lasing peaks with spectral width less than 1 nm and quality factor in excess of 4000. The lasing occurs within the approximate range of high-reflectance spectral region associated with photonic stop band along < 111 > crystallographic direction, but its wavelength is not fixed to the corresponding Bragg wavelength of the periodic structure, and depends on the spectral position of the gain band. This lasing regime can be useful for realizing tunable single-mode photonic crystal lasers. (c) 2008 Optical Society of America.
  • Kosei Ueno, Yukie Yokota, Saulius Juodkazis, Vygantas Mizeikis, Hiroaki Misawa
    CURRENT NANOSCIENCE 4 3 232 - 235 2008年08月 [査読有り][通常論文]
     
    We investigate functional capabilities of large arrays of gold and silver nanorods as elements of plasmonic devices. The samples were fabricated by electron beam lithography and lift-off techniques on glass substrates. The areas patterned by the nanorods or other nanoparticles can be large, with dimensions of up to about one centimeter. Structural and optical characterization has allowed confirmation of a high homogeneity of the fabricated ensembles of nanorods, and a high sensitivity of their longitudinal extinction bands to the variations of the nanorod length and the refractive index of the environment. Applications of nanorods as refractive-index sensors is discussed.
  • Mutsumi Takagi, Takayuki Kitabayashi, Satoru Koizumi, Haruka Hirose, Shin-ichi Kondo, Masashi Fujiwara, Kosei Ueno, Misawa Hiroaki, Yoichiroh Hosokawa, Hiroshi Masuhara, Shigeyuki Wakitani
    BIOTECHNOLOGY LETTERS 30 7 1189 - 1195 2008年07月 [査読有り][通常論文]
     
    A morphological parameter of polygonal index was defined as the ratio of cell adhesion area versus the square of the major cell axis, and cells that had an adhesion area larger than 4000 mu m(2) and a polygonal index larger than 0.3 were considered large polygonal cells. Cell morphology tended to change from fibroblast-like to polygonal and the percentage of the large polygonal cells increased almost in proportion to aggrecan mRNA expression level during the differentiation culture of mesenchymal stem cells (MSCs) to chondrocytes. Approximately 80% of the large polygonal cells were negative for MSC marker (CD90, CD166) expression and the aggrecan mRNA expression level of the large polygonal cells was markedly higher than that of cells with other morphologies.
  • Kosei Ueno, Saulius Juodkazis, Toshiyuki Shibuya, Yukie Yokota, Vygantas Mizeikis, Keiji Sasaki, Hiroaki Misawa
    JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 130 22 6928 - + 2008年06月 [査読有り][通常論文]
     
    We demonstrate the possibility to achieve optical triggering of photochemical reactions via two-photon absorption using incoherent light sources. This is accomplished by the use of arrays of gold nanoparticles, specially tailored with high precision to obtain high near-field intensity enhancement.
  • Noboru Kitamura, Kosei Ueno, Haeng-Boo Kim
    ANALYTICAL SCIENCES 24 6 701 - 710 2008年06月 [査読有り][通常論文]
     
    The paper describes the fabrication and chemical applications of polymer microchannel chips, with special reference to in situ observations of the chemical/physical processes occurring in polystyrene microchannel chips, including those in microchannel-microelectrode/microheater chips. On the basis of absorption/fluorescence microspectroscopy and microelectrochemistry techniques, we show some characteristic features of liquid/liquid extraction, electrochemical responses, and photochemical/electrochemical/thermal synthetic reactions in microchannel chips.
  • Kosei Ueno, Saulius Juodkazis, Vygantas Mizeikis, Keiji Sasaki, Hiroaki Misawa
    ADVANCED MATERIALS 20 1 26 - + 2008年01月 [査読有り][通常論文]
     
    Gold nanostructures consisting of nanoblocks separated by a few nanometer-wide gaps were fabricated, and found to exhibit strong photoluminescence due to enhancement of the optical near-field localized in the nanogaps. The fabricated structures demonstrate a nanostructured metallic material capable of efficient photoluminescence, whose efficiency can be adjusted by tailoring the nanogap width.
  • Kosei Ueno, Saulius Juodkazis, Vygantas Mizeikis, Dai Ohnishi, Keiji Sasaki, Hiroaki Misawa
    OPTICS EXPRESS 15 25 16527 - 16539 2007年12月 [査読有り][通常論文]
     
    Periodically corrugated chains of gold nanoblocks, fabricated with high precision by electron-beam lithography and lift-off techniques, were found to exhibit optical signatures of particle plasmon states in which relative contribution of longitudinal multipolar plasmons is significantly lower than that in equivalent rectangular gold nanorods. Plasmonic response of periodic chains is dominated by dipolar plasmon modes, which in the absence of multipolar exciations are seen as background-free and spectrally well-resolved extinction peaks at infrared (IR) wavelengths. This observation may help improve spectral parameters of IR plasmonic sub-wavelength antennae. Comparative studies of plasmon damping and dephasing in corrugated chains of nanoblocks and smooth rectangular nanorods are also presented. (C) 2007 Optical Society of America.
  • Y. Nishijima, K. Ueno, S. Juodkazis, V. Mizeikis, H. Misawa, T. Tanimura, K. Maeda
    OPTICS EXPRESS 15 20 12979 - 12988 2007年10月 [査読有り][通常論文]
     
    This work reports fabrication of inverse silica opal photonic crystal structures from direct polystyrene micro sphere opals using low-temperature sol-gel infiltration of silica, and examines performance of these photonic crystals as environmental refractive index sensors. Sensitivity of the spectral position and optical attenuation of photonic stop gaps is found to allow detection of the index changes by the amount of similar to 10(-3). The high value of sensitivity, which is comparable with those of other optical sensing techniques, along with simplicity of the optical detection setup required for sensing, and the low-temperature, energy-efficient fabrication process make inverse silica opals attractive systems for optical sensing applications. (c) 2007 Optical Society of America.
  • Kenji Kamada, Yoshihiko Tanamura, Kosei Ueno, Koji Ohta, Hiroaki Misawa
    Journal of Physical Chemistry C 111 30 11193 - 11198 2007年08月02日 [査読有り][通常論文]
     
    We report the enhancement of molecular two-photon absorption (2PA) of a dicationic 2PA chromophore (MPPBT) by confining it in a two-dimensional (2D) nanospace formed in nanolayered silicate clay by the cation exchange method in a water-dimethyl sulfoxide mixture. The 2PA property of the MPPBT/silicate nanocomposite prepared from the mixture by casting is characterized by the femtosecond open-aperture Z-scan method. We found that the 2PA cross-section of the chromophore in the nanocomposite is enhanced by a few times that of the dimethylsulfoxide solution at all wavelengths employed. This enhancement is accompanied by a bathochromic shift of the 2PA peak. The origin of this enhancement is discussed in terms of low dimensionality, suppressed internal twisting motion of the chromophore in the 2D confined space, and ionic interactions with the silicate surfaces. © 2007 American Chemical Society.
  • Kai Sun, Zheyu Li, Kosei Ueno, Saulius Juodkazis, Sumihare Noji, Hiroaki Misawa
    Electrophoresis 28 10 1572 - 1578 2007年05月 [査読有り][通常論文]
     
    We report the high fidelity, on-chip fractionation of selected segments front an electrophoretic flow of separated fragments. dsDNA fragments (10-330 base pairs (bp)) were initially separated using a 6.5 cm long channel with an electric field strength of 150 V/cm. As an example of the fractionation process, a target fragment of 20 bp was selected and extracted from the separation channel. The extraction was confirmed and evaluated by fluorescence imaging. High resolution and extraction fidelity were achieved by introducing new procedures for (i) extraction channel-blocking and (ii) segment transfer with cleaning. These procedures are necessary for the development of a practical, fully automated multitarget fractionation electrophoretic chip. A kind of CCD image processing method was introduced to monitor, control, and evaluate the procedure of fractionation. The resolution limits of the separation and extraction are discussed. © 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.
  • Kosei Ueno, Saulius Juodkazis, Masahiro Mino, Vygantas Mizeikis, Hiroaki Misawa
    JOURNAL OF PHYSICAL CHEMISTRY C 111 11 4180 - 4184 2007年03月 [査読有り][通常論文]
     
    Uniform, ordered arrays of gold nanorods on glass substrates were fabricated with high accuracy using electron beam lithography and lift-off techniques. These structures exhibit longitudinal mode of localized surface plasmon (LSP) resonance with spectral position highly sensitive to the refractive index of local dielectric environment of the nanorods. The LSP resonance was found to red-shift nearly linearly, both with refractive index and aspect ratio of the nanorods, to the extent that enables optical detection of the refractive index changes of the order of 10(-2). The entire spectral range of the detection can be defined by tailoring size and aspect ratio of the nanorods during the fabrication and typically falls into the optical communications region. These structures are therefore promising as optical sensors enabling simple and efficient monitoring of chemical and biological processes.
  • Yukie Yokota, Kosei Ueno, Vygantas Mizeikis, Saulius Juodkazis, Keiji Sasaki, Hiroaki Misawa
    JOURNAL OF NANOPHOTONICS 1 011594/1-15  2007年 [査読有り][通常論文]
     
    Highly homogeneous arrays of Ag, Au and Cu nanorods were fabricated on glass substrates using electron-beam lithography and lift-off techniques. Optical properties of the fabricated structures related to localized surface plasmons (LSP), and their dependencies on the nanorod size were studied experimentally by optical extinction spectroscopy. Spectral tuning of LSP resonant scattering bands in a wide spectral range, from visible to near-infrared wavelengths, can be accomplished by tailoring of the nanorod dimensions, aspect ratios, and heights. The observed results qualitatively agree with Gans theory and numerical modeling by finite-difference time-domain technique.
  • Noboru Kitamura, Konatsu Yamada, Kosei Ueno, Satoshi Iwata
    Journal of Photochemistry and Photobiology A: Chemistry 184 1-2 170 - 176 2006年11月15日 [査読有り][通常論文]
     
    Silica gel beads (diameter ∼10 μm) covalently modified with metal-free monopyridyltriphenylporphyrin (PyTPP) via a silane coupling reagent (PyTPP-SiO2) were introduced into a polymer microchannel and, the microchip was applied to photodecomposition of phenol under solution-flow conditions. The photodecomposition yield of phenol in the microchannel was dependent on the solution-flow rate (ν) and increased with decreasing ν. At ν = 0.5 μL/min, the decomposition yield was as high as 93% with the reaction time of 42 s, while that in a bulk aqueous PyTPP-SiO2 suspension was 73% with the reaction time of 2 h. In the microchannel chip experiments, furthermore, the yield increased with decreasing the thickness of the solution-flow layer above the PyTPP-SiO2 particles. On the basis of optical trapping-absorption microspectroscopy of single PyTPP-SiO2 particles before and after the photoreaction, we discuss characteristics of the photoreaction in the microchannel accommodated with PyTPP-SiO2 particles. © 2006 Elsevier B.V. All rights reserved.
  • Kosei Ueno, Saulius Juodkazis, Vygantas Mizeikis, Keiji Sasaki, Hiroaki Misawa
    JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 128 44 14226 - 14227 2006年11月 [査読有り][通常論文]
  • Takeshi Araki, Kousei Ueno, Hiroaki Misawa, Noboru Kitamura
    Analytical Sciences 22 10 1283 - 1289 2006年10月 [査読有り][通常論文]
     
    Temperature-dependent phase-vanishing processes between perfluorohexane (FC-72) and n-heptane (C7H16, volume ratio of 1:1 and phase-vanishing temperature > 41°C), were studied in a glass microchannel-microheater chip under solution-flow conditions. Without applying a voltage to the heater at 21°C, the two liquids in the microchannel were separated into two streams at a solution flow rate (v) of 0.975 cm/s, while the phase boundary between FC-72 and C7H16 vanished in the downstream side of the heater at V = 4.5 V. Then, we conducted Raman intensity imaging during the phase vanishing processes in the microchannel by monitoring the band at 756 (FC-72) or 1456 cm-1 (C7H16). At V = 4.5 V and v = 0.975 cm/s, although no phase boundary between the two liquids in the microchannel was observed, the relevant Raman intensity images indicated the inhomogeneous nature of the solution, and distribution of C7H16 to the FC-72 phase along with solution flow was observed. 2006 © The Japan Society for Analytical Chemistry.
  • Kosei Ueno, Vygantas Mizeikis, Saulius Juodkazis, Keiji Sasaki, Hiroaki Misawa
    Optics Letters 30 16 2158 - 2160 2005年08月15日 [査読有り][通常論文]
     
    We report on control over the extinction spectrum of tetragonal gold nanoblocks by changing their lateral aspect ratio. Nanoblocks were patterned on a glass substrate by electron-beam lithography and were 40-400 nm in lateral dimensions and spanned from 1 to 9 in aspect ratio. This allowed us to tune the localized surface plasmon bands from 700 nm to 1.5 nm (longitudinal mode) and from 700 to 550 nm (transverse mode). Unprecedented polarization selectivity of the transverse and longitudinal plasmon bands was achieved via alignment and 3D control of the dimensions of the nanoblocks. © 2005 Optical Society of America.
  • K Ueno, M Hayashida, JY Ye, H Misawa
    ELECTROCHEMISTRY COMMUNICATIONS 7 2 161 - 165 2005年02月 [査読有り][通常論文]
     
    Interdigitated nanoelectrode arrays with controlled electrode bandwidth and gap geometries ranging from 30 nm to 1 mum were fabricated on glass substrates by a planar process involving high resolution electron beam lithography and lift-off, and their characteristic electrochemical responses to an aqueous ferrocene derivative solution were examined using fundamental electrochemical techniques. Despite the comparatively large electrode area of electrode arrays containing 10 bands to a single band electrode, quasi-steady-state currents with high current density were obtained at a slow potential sweep rate in cyclic voltammograms of ferrocene derivative since the lateral dimension of the nanoelectrode arrays was considerably less than the scale of the diffusion layer of redox species. Additionally, it was demonstrated that the electrode thickness influenced limiting currents of voltammograms in the case of nanoelectrode arrays. In generation-collection mode experiments, furthermore, a collection efficiency as high as similar to99% was attained by 100 nm wide electrode arrays with a gap dimension of 30 nm. (C) 2004 Elsevier B.V. All rights reserved.
  • K Ueno, Mizeikis, V, S Juodkazis, K Sasaki, H Misawa
    2005 PACIFIC RIM CONFERENCE ON LASERS AND ELECTRO-OPTICS 857 - 858 2005年 [査読有り][通常論文]
     
    Two-photon excited fluorescence of organic dye by embedding them with gold nanostructures fabricated on a glass substrate was enhanced on the basis of increasing electromagnetic field induced by nanogap configuration.
  • Noboru Kitamura, Yukiko Hosoda, Kosei Ueno, Satoshi Iwata
    Analytical Sciences 20 5 783 - 786 2004年05月 [査読有り][通常論文]
     
    Polystyrol microchannel-microheater chips were fabricated on the basis of imprinting and photolithography techniques. The solution (i.e., methanol) temperature in the vicinity of the microheater (width = 100 or 200 μm and length = 100 μm) integrated in the channel (width = 100 μm and depth = 20 μm) was evaluated on the basis of the temperature-dependent fluorescence lifetime of Rhodamine B as a function of a flow rate and the voltage applied to the heater. The study demonstrated that the fabricated chip acted certainly as a microheater. The chip was then applied to the thermal reaction between benzaldehyde and malononitrile in methanol. Under optimum conditions, benzilidenemalononitrile as the product of the reaction was obtained in a 96% yield with the reaction time of 84 s.
  • Kosei Ueno, Fumihiko Kitagawa, Noboru Kitamura
    Bulletin of the Chemical Society of Japan 77 7 1331 - 1338 2004年 [査読有り][通常論文]
     
    Polymer microchannel chips (100 μm width × 20 μm depth) integrated with electrodes were fabricated and applied to a one-step electrochemical cyanation reaction of pyrene (PyH). An acetonitrile solution of PyH containing tetrabutylammonium perchlorate and an aqueous NaCN solution were brought into the chip by pressure-driven flow, PyH was then oxidized at the working band electrode in the channel (1.5 vs Ag). Under the optimum conditions, 1-cyanopyrene (PyCN) was produced very efficiently in the microchannel: 61% yield. It was also confirmed that, although 1,3-dicyanopyrene (Py(CN) 2) was produced by bulk electrolysis (14% yield), its yield decreased to 4% in the microchip, with the PyCN/Py(CN)2 yield ratio being 2.9 or 15.3 for the bulk or chip experiments, respectively. In the case of an oil/water interfacial reaction system, a propylene carbonate solution of PyH and an aqueous NaCN solution were introduced to the channel, where an electrochemical cyanation reaction of PyH analogous to that mentioned above was conducted. The interfacial reaction in the microchip was successful and the yield of PyCN as the sole product was shown to be controlled by both the flow rate and the electrode position in the chip. In-situ space-resolved absorption spectroscopy of the electrochemical intermediate in the channel chip was also conducted to allow discussion of the reaction mechanisms.
  • Noboru Kitamura, Yukiko Hosoda, Chiaki Iwasaki, Kosei Ueno, Haeng-Boo Kim
    Langmuir 19 20 8484 - 8489 2003年09月30日 [査読有り][通常論文]
     
    Plastic microchannel-microheater chips were fabricated on the basis of imprinting and photolithography/etching techniques. Knowing the temperature-dependent fluorescence lifetime of Rhodamine B in water, the temperature profile of the solution phase in the microchannel in the vicinity of the heater was evaluated by space- and time-resolved fluorescence microspectroscopies. The fabricated chip was then applied to control the thermal phase transition of an aqueous poly(N-isopropylacrylamide) (PNIPAM) solution. PNIPAM particle formation by the phase transition was controlled by both the applied voltage to the heater and the solution-flow rate. The temperature profile showing below or above the phase-transition temperature (i.e., 32°C) and solution-flow profile in the microchannel were visualized successfully on the basis of the PNIPAM particle formation. The continuous and automated concentration of a hydrophobic solute by the PNIPAM particles produced by the phase transition was also explored under solution-flow conditions by using the fabricated chip.
  • Kosei Ueno, Haeng-Boo Kim, Noboru Kitamura
    Analytical Chemistry 75 9 2086 - 2091 2003年05月01日 [査読有り][通常論文]
     
    Polymer microchannel chips (dimension of the channel, 20 μm (depth) × 100 μm (width)) integrated with dual microband electrodes were fabricated by an imprinting method, and their characteristic electrochemical responses were elucidated in detail. A silicon micromachined template fabricated by photolithography and dry etching techniques was used for imprinting. An aqueous solution of a ferrocene derivative was brought into the microchannel by pressure-driven flow, and the electrode responses were studied on the basis of voltammetry and chronoamperometry. A linear sweep voltammetry of 1-hydroxyethylferrocene (FeCp-OH) in water demonstrated that the electrode responses in the microchannel chip were best characterized by one-dimensional diffusion along the channel length, reflecting the structural dimension of the channel. In generation-collection mode experiments, furthermore, a collection efficiency as high as ∼90% was attained in the microchannel owing to both restricted space and characteristics of solution flow in the channel. It was confirmed that diffusion and solution flow made molecular transport very efficient in the microchannel. The experimental results were also compared with those predicted by computer simulations.
  • Kosei Ueno, Haeng-Boo Kim, Noboru Kitamura
    Analytical Sciences 19 3 391 - 394 2003年03月01日 [査読有り][通常論文]
     
    A polymer microchannel chip with a symmetrical or unsymmetrical zigzag-side-walled structure was fabricated by an imprinting method, and applied to study shape effects on solution flow characteristics as well as on the liquid/liquid extraction efficiency of an aluminium(III) chelate complex (Al-DHAB: DHAB = o,o′-dihydroxyazobenzene) in a microchannel chip. In an unsymmetrical zigzag-side-walled channel chip (us-channel), an oil/water interface was sinusoidal, while that in a symmetrical zigzag-side-walled channel chip (s-channel) was flat as long as the observation was made under an optical microscope. It was demonstrated that the efficiency of the water-to-oil (1-butanol) extraction of Al-DHAB in the microchannel was governed by the contact time between the two phases. As the most important results, furthermore, the extraction efficiency was higher in the us-channel, as compared with that in the s-channel, owing to the sinusoidal liquid/liquid interfacial structure and, therefore, to the high interfacial area between the two phases.
  • Ueno, K., Kitamura, N.
    Analyst 128 12 2003年
  • Ueno, K, Kitamura, N
    Analyst 128 12 2003年
  • Ueno, K., Kitagawa, F., Kitamura, N.
    Lab on a Chip 2 4 2002年
  • Ueno, K, Kitagawa, F, Kitamura, N
    Lab on a Chip 2 4 2002年
  • H. B. Kim, K. Ueno, M. Chiba, O. Kogi, N. Kitamura
    Analytical Sciences 16 8 871 - 876 2000年 [査読有り][通常論文]
     
    The liquid/liquid extraction of an Al3+-DHAB chelate (DHAB = 2,2'-dihydroxyazobenzen) from water to 1-buthanol (BuOH) in a polymer-based microchannel chip was studied by spatially-resolved fluorescence microspectroscopy. A microchannel (depth, 10 μm width, 200 μm) was fabricated on a styrol-plastic substrate by an imprinting method. A template for imprinting was prepared by photolithography, in which a spatial pattern printed on a transparency film by a standard drawing software package was used as a photomask. When two immiscible fluids were brought together into the channel chip by pressure-driven flow at the same velocity, a stable parallel stream was observed for each phase without mutual mixing. The extraction of Al-DHAB from water to BuOH was then studied as a fluorescence-intensity profile of the complex in the BuOH phase along the flow direction as well as along the channel-width direction. It was confirmed that extraction proceeded with solution flow and was governed by the contact time between the two phases. The results were explained by a one-dimensional mass-transfer model along the channel-width direction.
  • Kousei Ueno, Fumihiko Kitagawa, Haeng-Boo Kim, Tomonobu Tokunaga, Shigeki Matsuo, Hiroaki Misawa, Noboru Kitamura
    Chemistry Letters 8 858 - 859 2000年 [査読有り][通常論文]
     
    A polymer microchannel (width = 100 μm and depth = 20 μm) chip integrated with band Au electrodes (47 × 100 μm) was fabricated on the basis of photolithography/etching and imprinting techniques, and its characteristic electrochemical responses have been demonstrated.

MISC

書籍等出版物

担当経験のある科目（授業）

  • 分析化学II北海道大学
  • 分子化学（光化学）北海道大学
  • 分析化学I北海道大学
  • 生体工学概論北海道大学
  • ナノフォトニクス特論北海道大学
  • バイオフォトニクス特論北海道大学
  • ナノ工学基礎北海道大学
  • 電気回路北海道大学
  • 化学I北海道大学

所属学協会

  • 日本分析化学会   日本化学会   光化学協会   応用物理学会   

共同研究・競争的資金等の研究課題

  • 日本学術振興会：科学研究費助成事業
    研究期間 : 2021年09月 -2026年03月 
    代表者 : 上野 貢生, 長汐 晃輔, 大野 雄高, 松尾 吉晃
     
    研究代表者の上野は、長汐Gと共同で積層型グラフェンナノ構造を作製する技術を構築するとともに、A01班の吾郷Gと共同でグラフェンナノ構造を精緻に作製する方法論を見出し、中赤外波数域におけるプラズモンの分光特性を明らかにすることに成功した。また、光エネルギー変換デバイスを構築するため、A02班の宮田Gと共同で大面積に二硫化モリブデンの薄片を高密度にCVD合成する技術を構築した。 分担者の長汐は、A01班の渡邊Gと共同で2.5次元構造を利用したフラッシュメモリーを構築し50nsでの動作を実証した。また、超短パルス電圧下でのトンネルバリアh-BNの高い絶縁破壊耐性がその起源であることが分かってきた。統計的な実験を実施することで層状物質の絶縁破壊に対する理解が深まると期待できる。 大野は、A01班の櫻井Gと共同で高密度ニューロモルフィックチップの創製の研究を新たに開始し、その要素となるナノ積層メモリスタの構築を進めた。ナノ積層構造の骨格となるカーボンナノチューブとスマネンとの相互作用を電界効果トランジスタの特性から調べ、特に、一部の水素をフッ素に置換したモノフルオロスマネンによって、予想に反してカーボンナノチューブに電子がドーピングされることを見出し、カーボンナノチューブに対してスマネンの椀型構造の底面が特異的に吸着し、スマネンの分極によってドーピングが生じることが示唆された。 松尾は、A02班の松本と共同で、グラフェンライクグラファイト（GLG）へのイオンの貯蔵挙動を調べ、黒鉛には挿入されないナトリウム、マグネシウム等の挿入に成功した。また、GLGの電気化学的アニオン挿入脱離挙動を調べ、これが黒鉛よりも高容量を示すことを明らかにした。さらに、GLGをリチウムイオン電池負極として用いた場合の高入出力特性は、グラフェン内に存在するナノ孔によるものであることを見出した。
  • 日本学術振興会：科学研究費助成事業
    研究期間 : 2021年09月 -2026年03月 
    代表者 : 吾郷 浩樹, 岡田 晋, 宮田 耕充, 松田 一成, 越野 幹人, 上野 貢生, 長汐 晃輔, 町田 友樹, 高村 由起子, 櫻井 英博, 西堀 英治, 大野 雄高
     
    学術変革領域研究（A）「２.５次元物質科学：社会変革に向けた物質科学のパラダイムシフト」の領域研究を活性化するための活動を総括班で計画し実行した。 (1)第1回領域会議として、キックオフミーティングを2021年11月に九州大学筑紫キャンパスにて開催し、領域内研究者が一堂に会することにより領域内の連携を深め、共同研究の推進へと繋げた。また2022年3月には第2回領域会議を新型コロナウィルス感染防止のためオンラインにて開催した。研究者の他にも研究室メンバーも参加し、共同研究の進捗状況を発表、招聘した領域アドバイザーや学術調査官から指導を受けた。他にもオンラインで5回の総括班ミーティングや全体会議、各支援グループにおいても活発にミーティングを実施することで、領域の活動を支える組織のフレームワークの構築に尽力した。 (2)九州大学グローバルイノベーションセンターに領域事務局を設置、東京大学大学院工学系研究科にサイエンスコミュニケーターを1名雇用、WEBサイトの設置（https://25d-materials.jp/）、ニュースレター第1号・第2号の発行およびTwitterアカウントを開設、STAM誌へレビュー論文を投稿するなど、領域外への情報発信の基盤を整えた。 (3) 領域内共同研究拠点設備の購入計画を策定・実施することで、共用設備の充実とその積極的な運営を行った。 (4）公募班の受け入れ体制を構築し、12月に公募説明会を実施するとともに、視聴できなかった方のためホームページで動画を公開した。 (5)2021年10月にGraphene Flagship、2022年2月に日中韓フォーサイト事業との共催で国際ワークショップを開催するとともに、国際連携セミナーも企画して国際共同研究の促進を図った。
  • 日本学術振興会：科学研究費助成事業
    研究期間 : 2021年04月 -2025年03月 
    代表者 : 澤村 正也, 上野 貢生, 長谷川 淳也
  • 日本学術振興会：科学研究費助成事業 特別推進研究
    研究期間 : 2018年04月 -2023年03月 
    代表者 : 三澤 弘明, 笹木 敬司, 村越 敬, Biju V・Pillai, 上野 貢生
     
    高い量子収率を示すプラズモン誘起電子移動反応を実現するためには、１）強結合系積層ナノ電極の作製と２）局在プラズモン誘起電子移動反応機構の解明が鍵となる。平成30年度は、強結合系積層ナノ電極構造の作製とその分光特性の評価、および時間分解光電子顕微鏡による位相緩和時間の測定に注力した。 位相緩和時間の計測から強結合系積層ナノ電極は、非強結合電極に比べて位相緩和時間が短いとの結果が得られ、Nat. Nanotechnol., 13, 953 (2018)に報告した。さらに、ナノ共振器長をより短くした積層ナノ構造電極では、金ナノ微粒子の局在プラズモンと反射膜として用いた金フィルムの伝搬型プラズモンとが強結合を形成し、それによって位相緩和時間を能動的に制御できることを初めて見出し、Nat. Commun., 9, 4858 (2018)に報告した。これらは本モーダル型強結合を理解する上で極めて重要な知見を与える意義ある成果であった。また、研究分担者である北大電子研の笹木教授と共同で任意の数の金ナノディスク構造を酸化チタン／金フィルム基板上に作製し、構造密度が強結合に与える影響を検討した。その結果、本モーダル型強結合においては、構造密度によって結合強度を能動的に制御できるとともに、光電変換効率の増強も可能であることを見出し、変換効率向上の糸口を掴んだことは意義深い。また、強結合が蛍光やラマン散乱といった光の放射に与える影響についても検討したところ、非強結合と比較して数倍の増強効果が得られること明らかにし、より高い光電場増強が実現できることを示した。さらに、研究分担者である北大理学研究院の村越教授と共同で光アノードにおける水の酸化反応の中間体をラマン分光により捕捉する実験系を構築した。平成30年度は、非結合系電極を用いて水の酸化反応の中間体が計測できることを実証した。
  • 日本学術振興会：科学研究費助成事業 基盤研究(B)
    研究期間 : 2019年04月 -2022年03月 
    代表者 : 上野 貢生
     
    パルス幅17 fsのフェムト秒レーザーをビームスプリッターで2つのビームに分割し、光学遅延回路を含むマイケルソン干渉計により2つのレーザーパルスを同軸上に形成した。顕微鏡下で金ナノ構造の自己相関波形を計測するため、プリズムペア―を用いて分散補償を行い、対物レンズ下で最もパルス幅が短くなるように、BBO結晶からの第二高調波の自己相関波形を測定しながら最適化を行った。様々な構造間距離を有するナノギャップ金2量体構造や金ナノブロック構造の自己相関波形を金からの2光子発光を用いて計測したところ、構造周期によってプラズモンの位相緩和時間が変化することを明らかにした。これは、遠方場でのプラズモンのカップリングに起因しており、これまで位相緩和時間は数 fs以下と考えられてきたナノギャップ金2量体構造（ギャップ幅 5 nm）の位相緩和時間が5-6 fs程度と結合系プラズモニックナノ構造の構造設計次第では長寿命化できることを明らかにした。重要な点は、近接場増強が、プラズモンの位相緩和時間に大きく影響を及ぼしていることを明らかにした点である。一次元フォトニック結晶上に、上記と同じ設計のナノギャップ金2量体構造を作製して、分光特性を検討するとともに、近接場励起スペクトル計測や表面増強ラマン散乱計測を行ってみたところ、プラズモンとフォトニック結晶のストップバンドのバンド端が重なる波長で強い光電場増強を確認した。そこで、干渉型ポンプ&プローブ測定によりプラズモンの位相緩和ダイナミクスを計測してみたところ、自己相関波形のブロード化と顕著なビートシグナルが観測された。これは、フォトニック結晶や金ナノ構造だけでは観測されないことから、強いモード間のカップリングとプラズモン位相緩和の長寿命化を伴っている。このことから、プラズモンの長寿命化が近接場増強に密接に関連していることが明らかになった。
  • 日本学術振興会：科学研究費助成事業 新学術領域研究(研究領域提案型)
    研究期間 : 2019年04月 -2021年03月 
    代表者 : 上野 貢生
     
    ナノギャップ金2量体構造のナノギャップ領域に生じる勾配力によって誘起されるプラズモン誘起光圧を蛍光相関分光法により定量的に計測する方法論を確立した。粒径サイズが40 nmの蛍光性のポリスチレンビーズを用いて、蛍光相関分光計測を行ったところ、濃度から見積もられる共焦点光学顕微鏡のコンフォーカル体積内に存在するポリスチレンビーズの数と蛍光相関分光によって観測された蛍光ビーズの数が良い一致を示した。レーザー光強度依存性を測定したところ、0.1～0.6 KT程度の低いポテンシャル領域で高い直線性が得られることが明らかになった。さまざまなギャップ幅（0, 5, 10, 15, 20, 50 nm）を有するナノギャップ金2量体構造を作製し、ポテンシャルのギャップ幅依存性を検討したところ、ギャップ幅の減少とともにポテンシャルの増大が観測された。このことから、光電場の局在効果（光圧における空間の効果）を明らかにすることに成功した。一方、光圧における時間の効果を明らかにするため、プラズモンの寿命がポテンシャルに与える影響を検討した。ガラス基板上に構造周期が異なるナノギャップ金2量体構造アレイ（ギャップ幅は5 nmで統一）を作製し、プラズモンの寿命（位相緩和時間）をパルス幅17 fsのフェムト秒レーザーを用いた干渉型ポンプ＆プローブ測定により測定したところ、構造周期によって散乱光のコンストラクティブ、およびディストラクティブな干渉により大きく寿命が変化することが明らかになった。そこで、蛍光相関分光によりポテンシャル計測を行ったところ、プラズモンの寿命が長い構造においてポテンシャルの増大が観測された。このことから、プラズモンの寿命が光圧に大きく影響を及ぼすことが明らかになった。
  • 日本学術振興会：科学研究費助成事業 新学術領域研究(研究領域提案型)
    研究期間 : 2017年04月 -2019年03月 
    代表者 : 上野 貢生
     
    分子振動モードとプラズモンモードとの強結合が分子の振動状態だけではなく、電子状態にまで影響を及ぼすことを明らかにするために、平成30年度は赤外の幅広い波長域において高い光電場増強効果を示す金属ナノ構造体の構造設計を明らかにした。まず、可視波長域において光ナノ共振器と金ナノ微粒子のプラズモン共鳴がモード強結合を示して、幅広い波長において高い光吸収と光電場増強効果を示すことを明らかにした。特筆すべき点は、プラズモンの位相緩和時間が、モード強結合に基づくプラズモン状態の変調により変化することを明らかにした点である。この可視域におけるモード強結合の原理を利用して、赤外域に共鳴を示す構造設計に展開した。石英基板上に厚さ100 nmの金フィルムを成膜し、その上に厚さ450 nmの酸化チタン層を成膜することで、2400cm-1に共振を示すファブリ・ペロー共振器を構築した。その上に電子ビームリソグラフィー／リフトオフ法により赤外に波長選択的にプラズモン共鳴を示す金ナノチェイン構造を作製したところ、2000～4000cm-1においてモード強結合によりスペクトルが分裂する現象が観測された。また、金ナノチェイン構造の長さにより共鳴波長を変化させたところ、共鳴効率の増大により顕著に赤外光の吸収効率が増大することを吸収スペクトル測定から明らかにした。つまり、赤外の幅広い波長域で高い光吸収と光電場増強効果を示す構造が得られた。この構造に蛍光分子であるEosin Yを成膜したところ、Eosin YのOH伸縮振動と赤外モード強結合が強い相互作用を示し、蛍光寿命が赤外波長における光電場増強の大きさとともに顕著に且つ系統的に短くなること、そして解析の結果、赤外振動モードと光場の相互作用により無放射失活が大きくなることが示され、高次の電子状態に強く影響を及ぼすことが明らかとなった。
  • 日本学術振興会：科学研究費助成事業 新学術領域研究(研究領域提案型)
    研究期間 : 2017年04月 -2019年03月 
    代表者 : 上野 貢生
     
    ナノ物質を高効率にトラップするためには光を強く閉じ込めるナノ構造体の設計が重要である。本研究では、結合系プラズモニックナノ構造による高効率な光トラッピングと光反応場の構築を行った。金属／誘電体／金属の積層ナノ構造が、四重極子共鳴により高い光電場増強を示すことから、A03班の笹木グループと連携して蛍光ビーズを用いたプラズモンオプティカルトラッピング系を構築し、遠方場でのスペクトルでは観測されないダークな四重極共鳴モードによるオプティカルトラッピング特性を明らかにした。プラズモンオプティカルトラッピングの作用スペクトルを測定したところ、Fanoディップ波長より若干短波長域において直径100 nmの蛍光ビーズが強くトラップされることがわかり、当初の研究目標であるダークプラズモンによる高効率なオプティカルトラッピングの実証に成功した。また、金／誘電体／金ナノ構造の上下の構造のサイズ比により近接場結合の度合いを制御することでプラズモンの寿命を3倍長寿命化することに成功し、高効率な光反応場を構築した。また、金属ナノ構造／誘電体／金フィルム構造の構造設計により、種々の結合系プラズモニックナノ構造の創製に成功した。初めに、A03班の笹木グループと共同で、金ナノ微粒子／酸化チタン／金フィルム構造が、金ナノ微粒子の局在プラズモンと酸化チタン／金フィルム基板に誘起されるファブリ・ペローナノ共振器モードとのモード強結合を示すことや光化学反応を促進することを明らかにした。また、同様の金属ナノ構造／誘電体／金フィルム構造により金フィルム上の表面プラズモンと金ナノ構造の局在プラズモンがモード強結合を示すことを明らかにした。さらに、モード強結合系においてもプラズモンと結合する光学モードの寿命により、プラズモンの寿命を自在に制御することが可能であることを明らかにした。
  • 日本学術振興会：科学研究費助成事業 基盤研究(C)
    研究期間 : 2015年04月 -2018年03月 
    代表者 : 上野 貢生
     
    本研究では、酸化チタン基板上に金ナノ粒子を担持することにより金ナノ微粒子から酸化チタン電子伝導帯へのホットエレクトロントランスファーを利用した光触媒反応系を構築した。各種分光法や透過電子顕微鏡を用いて光触媒反応過程を計測し、界面におけるホットエレクトロントランスファーのダイナミクスや正孔による反応機構について議論するとともに、高効率な光触媒の設計指針を明らかにした。
  • 制御された金属ナノ構造による励起子ポラリトン素過程の追跡と反応場への応用
    日本学術振興会：科学研究費助成事業 新学術領域研究(研究領域提案型)
    研究期間 : 2015年04月 -2017年03月 
    代表者 : 上野 貢生
     
    平成28年度は、ポルフィリンのＪ会合体分子をアルミニウムナノ構造体近傍に配置すると、ポルフィリンのSoret帯とQ帯の波長でそれぞれプラズモンと強結合を示し、分散カーブにおける半交差な振る舞いと結合振動子モデルによる解析に加えて、励起スペクトルの測定からSoret帯およびＱ帯のそれぞれの強結合系でハイブリッド準位の形成に基づくスペクトル変調が観測された。このことから、電子状態が変調していることを実験的に明らかにすることに成功した。特筆すべきは、Soret帯とQ帯の2つの波長域において電子状態の変調によるスペクトルの広帯域化がそれぞれ観測され、太陽光の幅広い波長をアンテナする光反応場として有用であることを示した。 同様の考え方を結合プラズモニック系にも適用した。複雑な形状の金dolmen構造（結合プラズモニック構造）はスペクトルが分裂することが知られており、これまで双極子モードと四重極子モード間の干渉（ファノ共鳴）に基づいてスペクトルに凹みが生じ、スペクトルが分裂すると考えられてきた。本研究では、波長可変レーザーと光電子顕微鏡を用いて金dolmen構造における光電子放出の作用スペクトルを測定したところ、強結合に基づいてハイブリッド準位が形成されたこと、そしてハイブリッド準位の形成に基づきスペクトルが分裂することを明らかにした。したがって、電子状態や振動状態の変調、そして禁制遷移モードのダイナミクスを明らかにするという観点、そして電子状態の変調による光吸収波長の広帯域化、禁制遷移モードが示す高い光閉じ込め効果によって創出される有用な光反応場の構築という観点から、強結合に基づいて電子状態を変調し高効率な光化学反応場を構築する当初の目的を達成した。
  • 日本学術振興会：科学研究費助成事業 基盤研究(S)
    研究期間 : 2011年04月 -2016年03月 
    代表者 : 三澤 弘明, 村越 敬, 上野 貢生, 村澤 尚樹, 押切 友也, 上原 日和, ルカルメ オリビエ
     
    局在プラズモンを示す金ナノ構造を光アンテナとした光電変換系において、水が酸化的に分解して酸素が発生することを明らかにした。また、光電気化学重合反応を用いて本水分解が金ナノ構造/半導体基板/水の接触するナノ空間で生起することを明らかにした。これらの成果を人工光合成へ展開し、可視光による水の完全分解、並びにアンモニア合成にも成功した。一方、独自に開発した超高速時間分解光電子顕微鏡を活用し、四重極子プラズモンや局在プラズモンと分子系との強結合状態を利用した光アンテナが高い光閉じ込め機能を有することも明らかにした。さらに、ホール移動層に酸化ニッケルを用いた全固体プラズモン太陽電池の創出にも成功した。
  • 日本学術振興会：科学研究費助成事業 若手研究(A)
    研究期間 : 2011年04月 -2014年03月 
    代表者 : 上野 貢生
     
    金や銀などの局在表面プラズモン共鳴を示す金属ナノ構造が光をシングルナノメートルの微小な空間に局在化させることが可能な特徴を利用して、ポジ型フォトレジスト膜上にナノパターンを高精細に転写露光するナノ光リソグラフィー技術を構築した。その結果、未踏の10 nm-nodeの非接触光リソグラフィー技術の原理検証を達成することに成功した。
  • 日本学術振興会：科学研究費助成事業 若手研究(B)
    研究期間 : 2008年 -2010年 
    代表者 : 上野 貢生
     
    構造間距離が数nmのナノギャップを有する金属ダイマー構造を精緻に作製し、プラズモンの共鳴エネルギー移動の本質を光学特性や種々の計測、および時間領域差分法により詳細に明らかにした。また、通常では起こらないエネルギーの低い近赤外光照射によって発光や光電流を観測することに成功し、当初の計画通り、研究を達成することに成功した。
  • 日本学術振興会：科学研究費助成事業 特定領域研究
    研究期間 : 2007年 -2010年 
    代表者 : 三澤 弘明, 上野 貢生, 村澤 尚樹
     
    我々は、照射された光を高効率に分子に吸収させる「光の有効利用」という新しい概念を光化学の研究に導入した。光と分子を強く結合させ、光の有効利用を可能にする光反応場として、局在プラズモン共鳴によって高い光電場増強効果を示す金属のナノ構造体に着目した。金属ナノ構造が示す光電場増強効果は、分子の光励起を高効率に誘起し、微弱な光によるフォトレジスト材料の空間選択的な2光子重合反応を実現した。また,金ナノ構造を配列した酸化チタン電極を用いた光電気化学測定により、可視・近赤外光を光電変換できることも明らかにした.
  • 日本学術振興会：科学研究費助成事業 若手研究(スタートアップ)
    研究期間 : 2006年 -2007年 
    代表者 : 上野 貢生
     
    ガラス基板上に電子線リソグラフィー/リフトオフ技術により、可視域から近赤外領域にプラズモン共鳴バンドを有する金ナノ構造の作製を行った。作製した金ナノ構造は、縦方向と横方向の長さが同じ(アスペクト比:1,厚みは40nmと一定とした)で、構造のサイズのみ10nm(一辺)ずつ変化させることにより、単一ピークのプラズモン共鳴スペクトルが約20nmずつ波長シフトする設計とした(構造サイズが大きくなると、共鳴スペクトルは長波長シフト)。作製した構造体に、センター波長800nmのフェムト秒レーザービーム(〜10μW)を集光照射し、得られた金構造からの2光子励起発光強度を計測した。金2光子励起発光強度は、構造のサイズが140nmの時に最大となり、金ナノ構造の厚みを30,20,10nmと薄く設定して作製すると、発光強度が最大となる構造体のサイズが、120nm,80nm,60nmと小さくなることが明らかになった。これは、金ナノ構造の厚みが薄くなると、プラズモン共鳴波長は長波長シフトすることから、構造サイズが小さい構造において光電場増強がより大きく誘起されたものと考えられる。以上の結果から、金2光子励起発光強度は、入射レーザー光の波長とプラズモン共鳴スペクトルのピーク波長が一致するときに最大となることが明らかになった。一方、表面増強ラマン散乱(SERS)強度は、入射レーザー光の波長では最大とならずに、散乱光波長と入射光波長の中間にプラズモン共鳴バンドを有する金ナノ構造体で最大となることが明らかになった。これまでのSERS分光法に関する理論的研究から、SERS強度は入射光電場強度だけではなく、散乱光輻射場における電磁的な増強効果においてもシグナルが増大することが示唆されているが、本研究では実験的に散乱光の輻射効率がSERS強度に及ぼすことを明らかにすることに成功した。
  • 日本学術振興会：科学研究費助成事業 基盤研究(B)
    研究期間 : 2005年 -2007年 
    代表者 : 三澤 弘明, 上野 貢生
     
    ガラスなどの固体基板上に電子線リソグラフィー/リフトオフ技術により、金属ナノ周期構造をシングルナノメートルの加工分解能で作製する技術を確立した。作製した金ナノ構造のプラズモン共鳴スペクトルが、構造体表面の誘電率変化に対して鋭敏に応答する光学特性を利用して、DNAのハイブリダイゼーションを共鳴スペクトルの波長シフトにより系統的にセンシングすることが可能であることを明らかにした。また、上記の方法だけでなく、金属ナノ構造がプラズモン増強により構造表面に光電場を著しく増大(入射光電場強度の〓10^5倍増強)させる効果を有する特徴を利用して、表面増強ラマン散乱(SERS)分光法を用いた化学/バイオセンサーチップの構築を行った。本研究では、金2光子励起発光計測、表面増強ラマン散乱計測、ならびに金属ナノ構造の光学特性とコンピューターシミュレーションによる金属構造の電場強度プロファイル解析を組み合わせることにより、金属ナノ構造の設計が光電場増強に及ぼす効果を詳細に明らかにし、高い電場増強を示す構造設計の最適化を導き出すことに成功した。また、半導体加工技術により金属ナノ構造を精密に作製することによってはじめて、ピリジンなどのSERS活性分子で、SERS強度がバルクに比べて10^<10>倍増強することを再現性高く観測することが可能であることを明らかにした。さらに、金属ナノ周期構造基板をレーザー干渉露光法により大面積に作製する方法論を示し、本成果により色素分子をラベルしなくてはならない従来型のDNAチップとは全く異なる検出原理に基づいた信頼性が高く、また低コストで迅速な遺伝子診断を可能にするDNAチップデバイスの開発が近い将来アウトプットされるものと期待される。
  • 日本学術振興会：科学研究費助成事業 特別研究員奨励費
    研究期間 : 2004年 -2006年 
    代表者 : 上野 貢生
     
    マイクロチャンネルチップ内に機能を集積するために、金属ナノ構造体による局在表面プラズモンを用いた分析システムの構築を行った。ガラス基板上に電子線リソグラフィー/リフトオフ技術を用いることにより数10nm〜数100nmサイズの金属のナノ構造体を作製した。局在表面プラズモンの光学特性は、構造体のサイズや形状、あるいは周囲の誘電率や構造間距離などによって鋭敏に変化する。そこで、本研究では、この原理を利用することによる分析システム構築の一例としてDNAチップの創製を試みた。構造体上にDNA分子を固定してハイブリダイゼーションを誘起することにより、反応に基づく誘電率変化から局在表面プラズモンのスペクトルがシフトし、高感度にDNAを検出可能な新しい発想のマイクロアレイチップを構築すること可能である。実験では、構造体へのDNA分子の固定化は3'末端にチオール基を有する合成ヌクレオチドを金構造体との共有結合により行い、一本鎖DNAを固定化した構造体上にターゲットDNAのバッファー溶液を滴下することによりハイブリダイゼーションを誘起したところ、ハイブリダイゼーション前後において金属ナノ構造体のスペクトルの顕著なシフトが観測された。また、作製した金属ナノ構造体を用いて、表面増強ラマン散乱分光法による計測システムの構築を行った。ラマン散乱測定は、振動分光法であり分子分析能力が高いため定性的な分析チップを構築することが可能である。特に、金属構造体の構造間距離がナノメートルオーダーで近接した場合、ギャップ内に存在する分子のラマン散乱強度が著しく増強されることが知られているが、その原理を再現性高く計測するのは従来の微粒子を集積する方法では困難であった。本研究では、微細加工による構造体制御によりラマン散乱増強の近接場効果やプラズモンバンドと励起レーザー光波長の関係について詳細に明らかにすることに成功した。
  • 日本学術振興会：科学研究費助成事業 特別研究員奨励費
    研究期間 : 2001年 -2003年 
    代表者 : 上野 貢生
     
    電極内蔵型ポリマー基板マイクロチャンネルチップ(流路幅100μm、深さ20μm)の作製を行った。作製した電極チップを用いてピレン分子を一段階でシアノ化する化学反応をマイクロチップ中で行い、その特徴について明らかにした。本研究では、ラージスケールの反応をアセトニトリル-水の混合溶媒系で行う場合とマイクロチップ中で反応を同様の混合溶媒系で行う場合およびマイクロチップ中で油水界面を反応場として用いた場合の3種類の実験により比較検討を行った。反応スキームは、電極上で電解生成されたピレンカチオンラジカルがシアン化物イオンと求核置換反応して、1-シアノピレンが生成するものと考えられる。ラージスケールの反応では、一時間反応後GC-MSの測定から原料であるピレンはほぼ消費され、新たに生成物であるシアノピレンが41%、副生成物としてジシアノピレンが14%生成することが確認された。一方、同様の条件でマイクロチャンネルチップ中において電解反応を行った場合、最適流速条件でチャンネルチップ中の溶液の滞留時間1分ほどで生成物が60%副生成物が4%生成することがわかった。生成物の収率の向上はマイクロチップ中で効率良く電解反応が行われたためであるが、生成物の選択率がチップ中のほうが向上したところがマイクロチップ反応の特徴的な点である。一方、油水界面反応では生成物の相(有機相)をチャンネル出口において分離することが可能であるため、油水界面反応-溶媒抽出系により反応の自動化が行うことが可能であることを明らかにした。また、油水界面反応では物質移動の数値シミュレーションや顕微分光測定による反応中間体の追跡により、反応の律速段階の理解や反応速度論的な研究に応用が可能であることを示し、マイクロチップを用いた化学システムの構築と幅広い化学研究に展開が可能であることを実験的に明ちかにした。
  • 金属ナノ構造の物理・物理化学とその化学的応用
  • Physics and Physical Chemistry of Metal Nanostructures, and Its Chemical Application

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