研究者データベース

米澤 徹(ヨネザワ テツ)
工学研究院 材料科学部門 マテリアル設計分野
教授

基本情報

所属

  • 工学研究院 材料科学部門 マテリアル設計分野

職名

  • 教授

学位

  • 博士(工学)(東京大学)

ホームページURL

科研費研究者番号

  • 90284538

J-Global ID

研究キーワード

  • フェロセン   プラズマ   複合材料   クラスター錯体   液中プラズマ   二酸化チタン   遷移金属錯体   連続調製   多重安定性   配列   ハイドロキシアパタイト   組織化   薄膜   半導体   水素結合   多重機能   キラリティー   超微粒子   表面ゾルゲル法   マイクロパターニング   自己組織化   ハイドロゲル   レドックス   銀   二分子膜   錯体   自己組織膜   光電変換   金   ナノ粒子   

研究分野

  • ナノテク・材料 / 機能物性化学
  • ナノテク・材料 / ナノバイオサイエンス
  • ナノテク・材料 / ナノ材料科学
  • ナノテク・材料 / 無機・錯体化学
  • ナノテク・材料 / 無機材料、物性

職歴

  • 2017年04月 - 2017年05月 チュラロンコン大学 工学部 訪問教授
  • 2009年04月 北海道大学 大学院工学研究科 教授
  • 2008年 - 2009年 東京大学 理学(系)研究科(研究院) 准教授
  • 2006年 東京大学 理学(系)研究科(研究院)・大学院理学系研究科 助教授
  • 2005年 東京大学 理学(系)研究科(研究院)・大学院・理学系研究科 助教授
  • 2003年 - 2004年 東京大学 大学院・理学系研究科 助教授
  • 2002年 名古屋大学 大学院・工学研究科 文部科学教官助教授
  • 2001年 九州大学 名古屋大学・工学(系)研究科(研究院)・大学院・工学研究科 助手・助教授
  • 2000年 九州大学 工学(系)研究科・大学院・工学研究院 助手
  • 1999年 九州大学 大学院・工学研究科 助手
  • 1998年 九州大学 工学部・工学研究科 助手
  • 1997年 九州大学 工学部 助手

学歴

  •         -   東京大学   大学院工学系研究科   工業化学専攻

所属学協会

  • 日本金属学会   日本質量分析学会   高分子学会   アメリカ化学会   イギリス王立化学会   日本顕微鏡学会   ナノ学会   日本化学会   

研究活動情報

論文

  • Haoran Liu, Naoki Miyamoto, Mai Thanh Nguyen, Hiroki Shirato, Tetsu Yonezawa
    Materials Advances 3 13 5430 - 5441 2022年05月 [査読有り]
  • Kai Ikeda, Haoran Liu, Naoki Miyamoto, Mai Thanh Nguyen, Hiroki Shirato, Tetsu Yonezawa
    ACS Applied Bio Materials 5 3 1259 - 1266 2022年03月21日 [査読有り]
     
    Image-guided radiation therapy (IGRT) has emerged as a promising technique for cancer treatment to improve radiation precision and accuracy, thereby reducing the treatment toxicity and optimizing therapeutic efficacy. In IGRT, fiducial markers are required to be inserted near the tumor to get the spatial information of the tumor. Currently used metal fiducial markers with large sizes would be highly invasive; therefore, it is critical to develop minimally invasive alternatives to these markers. In this work, an injectable marker based on Biopex-supported Au NPs with adequate radio-opacity for X-ray visualization was developed. Biopex can function as a substrate for the growth of Au NPs and avoid excessive reaction-induced aggregation and precipitation. The self-curing property of Biopex prevents the leakage and elimination of isolated Au NPs, enabling long-term X-ray observation and radiotherapy. The effect of Biopex amount, gold precursor concentration, and reaction time were evaluated. The visibility of samples prepared by the optimized formula was also examined. The developed Biopex-Au NPs could be injected through a 21 G needle and exhibit great visibility in the X-ray visualization test, showing great potential as a fiducial marker for image-guided radiation therapy.
  • Min Jia Saw, Mai Thanh Nguyen, Yuji Kunisada, Tomoharu Tokunaga, Tetsu Yonezawa
    ACS Omega 7 8 7414 - 7420 2022年03月01日 [査読有り]
  • M. Gopalakrishnan, A.A. Mohamad, M.T. Nguyen, T. Yonezawa, J. Qin, P. Thamyongkit, A. Somwangthanaroj, S. Kheawhom
    Materials Today Chemistry 23 100632 - 100632 2022年03月 [査読有り]
  • Haoran Liu, Kai Ikeda, Mai Thanh Nguyen, Susumu Sato, Naoki Matsuda, Hiroki Tsukamoto, Tomoharu Tokunaga, Tetsu Yonezawa
    ACS Omega 2022年02月22日 [査読有り]
  • Wei Jian Sim, Mai Thanh Nguyen, Zixuan Huang, Soorathep Kheawhom, Chularat Wattanakit, Tetsu Yonezawa
    Nanoscale 2022年 [査読有り][通常論文]
  • Rintaro Tokura, Hiroki Tsukamoto, Tomoharu Tokunaga, Mai Thanh Nguyen, Tetsu Yonezawa
    Materials Advances 2022年 [査読有り][通常論文]
     
    1-Hexanoic acid stabilised copper nanoparticles were obtained. Cu64O phase could be found on the particle surface. During sintering, the stabilising molecule, 1-hexanoic acid, reduced Cu64O to Cu and it introduced neckings between the particles.
  • Mohammad Etesami, Ahmad Azmin Mohamad, Mai Thanh Nguyen, Tetsu Yonezawa, Rojana Pornprasertsuk, Anongnat Somwangthanaroj, Soorathep Kheawhom
    Journal of Alloys and Compounds 889 161738 - 161738 2022年01月 [査読有り]
  • Kunihiro Narita, Yohei Ishida, Shuichi Nukui, Zhong Huang, Tetsu Yonezawa
    The Journal of Physical Chemistry Letters 12 49 11761 - 11765 2021年12月02日 [査読有り][通常論文]
  • Mai Thanh Nguyen, Lianlian Deng, Tetsu Yonezawa
    Soft Matter 2021年11月23日 [査読有り][招待有り]
     
    Sputter deposition onto a low volatile liquid matrix is a recently developed green synthesis method of metal/metal oxide nanoparticles (NPs). In this review, we introduce the synthesis method and highlight...
  • Nikdalila Radenahmad, Ramin Khezri, Ahmad Azmin Mohamad, Mai Thanh Nguyen, Tetsu Yonezawa, Anongnat Somwangthanaroj, Soorathep Kheawhom
    Journal of Alloys and Compounds 883 160935 - 160935 2021年11月 [査読有り][通常論文]
  • W. Kao-ian, M.T. Nguyen, T. Yonezawa, R. Pornprasertsuk, J. Qin, S. Siwamogsatham, S. Kheawhom
    Materials Today Energy 21 100738 - 100738 2021年09月 [査読有り]
  • Natta Jaikrajang, Wathanyu Kao-Ian, Tatsuki Muramatsu, Rungroj Chanajaree, Tetsu Yonezawa, Zakaria Y. Al Balushi, Soorathep Kheawhom, Rongrong Cheacharoen
    ACS Applied Energy Materials 4 7 7138 - 7147 2021年06月30日 [査読有り]
  • Mingbei Zhu, Mai Thanh Nguyen, Yuen-ting Rachel Chau, Lianlian Deng, Tetsu Yonezawa
    Langmuir 37 19 6096 - 6105 2021年05月18日 [査読有り]
     
    Pt/Ag solid solution alloy nanoparticles (NPs) with mean size below 3 nm were obtained with composition in miscibility gaps by cosputtering onto liquid polyethylene glycol (PEG, MW = 600). Adjusting the sputtering currents from 10 to 50 mA did not influence the particle sizes obviously but caused a substantial difference in the composition and distributions of Pt/Ag NPs. This is different from sputtered Pt/Au NPs where particle size is correlated with composition. For a pair of sputtering currents, the formed Pt/Ag alloy NPs have a range of compositions. The normal distribution with Pt of 60.2 +/- 16.2 at % is observed for the Pt/Ag sample with a nominal Pt content of 55.9 at %, whereas Pt-rich (85.1 +/- 14.0 at % Pt) and Ag-rich (19.8 +/- 12.2 at % Pt) Pt/Ag samples with nominal Pt contents of 90.9 and 11.9 at % contain more pure Pt and pure Ag NPs, respectively. Different from NPs obtained in PEG, the sputtered NPs on TEM grids had more uniform composition for a longer sputtering time along with a significant increase of particle sizes. This reveals that PEG hindered the combination of NPs and clusters, resulting in small particle sizes even for long time sputtering and broader composition distributions. Thus, the samples obtained in PEG have the compositions mainly determined by the random atom combination in the vacuum chamber and possibly in initial landing of atom/clusters on the PEG surface.
  • Ikumi Akita, Yohei Ishida, Tetsu Yonezawa
    The Journal of Physical Chemistry C 125 8 4917 - 4923 2021年03月04日 [査読有り]
  • Shilei Zhu, Mai Thanh Nguyen, Tetsu Yonezawa
    Nanoscale Advances 3 16 4626 - 4645 2021年 [査読有り]
     
    An overview of recent literature on the micro- and nano-encapsulation of metallic phase-change materials (PCMs) is presented in this review to facilitate an understanding of the basic knowledge, selection criteria, and classification of commonly used PCMs for thermal energy storage (TES). Metals and alloys with high thermal conductivity can be used as PCMs for rapid heat storage in compact systems owing to their high volumetric TES density. The emerging application of metal PCMs in different fields such as solar thermal energy management, smart wearable devices with thermal comfort control, and cooling of electronic devices call for the need of micro- and nano-TES particles, which can be synthesised in different forms to satisfy specific requirements. As metals are easily oxidised, especially at the micro- and nano-level, encapsulation of metal-based PCM particles is important for sustainable use at high operating temperature in ambient conditions. Recent studies focusing on the encapsulation of metallic PCMs at the micro- and nano-level have been reviewed and classified in terms of the melting point of metal/alloy PCMs used and types of encapsulation materials, such as oxides, polymers, carbon, and metals. The current review is expected to provide an outlook on novel metal and alloy PCMs with function-directed structures and superior TES properties for a broad range of applications.
  • Yuen-Ting Rachel Chau, Hsin-hui Huang, Mai Thanh Nguyen, Koji Hatanaka, Tetsu Yonezawa
    Applied Physics Express 14 1 012006 - 012006 2021年01月01日 [査読有り]
     
    Abstract Cu or Cu/Au (80 nm thick Cu, 50 nm thick Au) sputtered on Si were kept at 25 °C for a week or annealed at a temperature from 80 to 300 °C, then tested for THz emission under femtosecond laser irradiation (35 fs-800 nm). THz radiation was detected from samples annealed from 80 to 170 °C, which had a Cu2O/Cu interface as the THz source. Cu/Au/Si annealed at 80 °C emitted the highest THz radiation because of high laser absorption by the porous Cu2O layer formed at low temperature and the Au film reflected THz radiation and/or increased the laser absorption by the Fabry–Pérot effect.
  • Mai Thanh Nguyen, Krittaporn Wongrujipairoj, Hiroki Tsukamoto, Soorathep Kheawhom, Shuang Mei, Vipada Aupama, Tetsu Yonezawa
    ACS Sustainable Chemistry & Engineering 8 49 18167 - 18176 2020年12月14日 [査読有り]
  • Shuai Liu, Rintaro Tokura, Mai Thanh Nguyen, Hiroki Tsukamoto, Tetsu Yonezawa
    Advanced Powder Technology 31 11 4570 - 4575 2020年11月 [査読有り]
  • Ramin Khezri, Soraya Hosseini, Abhishek Lahiri, Shiva Rezaei Motlagh, Mai Thanh Nguyen, Tetsu Yonezawa, Soorathep Kheawhom
    International Journal of Molecular Sciences 21 19 7303 - 7303 2020年10月 [査読有り]
     
    Zinc–air batteries (ZABs) offer high specific energy and low-cost production. However, rechargeable ZABs suffer from a limited cycle life. This paper reports that potassium persulfate (KPS) additive in an alkaline electrolyte can effectively enhance the performance and electrochemical characteristics of rechargeable zinc–air flow batteries (ZAFBs). Introducing redox additives into electrolytes is an effective approach to promote battery performance. With the addition of 450 ppm KPS, remarkable improvement in anodic currents corresponding to zinc (Zn) dissolution and limited passivation of the Zn surface is observed, thus indicating its strong effect on the redox reaction of Zn. Besides, the addition of 450 ppm KPS reduces the corrosion rate of Zn, enhances surface reactions and decreases the solution resistance. However, excess KPS (900 and 1350 ppm) has a negative effect on rechargeable ZAFBs, which leads to a shorter cycle life and poor cyclability. The rechargeable ZAFB, using 450 ppm KPS, exhibits a highly stable charge/discharge voltage for 800 cycles. Overall, KPS demonstrates great promise for the enhancement of the charge/discharge performance of rechargeable ZABs.
  • Hsin-Hui Huang, Saulius Juodkazis, Eugene Gamaly, Takeshi Nagashima, Tetsu Yonezawa, Koji Hatanaka
    2020年09月23日 [査読有り]
  • Tanawat Phusittananan, Wathanyu Kao-Ian, Mai Thanh Nguyen, Tetsu Yonezawa, Rojana Pornprasertsuk, Ahmad Azmin Mohamad, Soorathep Kheawhom
    Frontiers in Energy Research 8 2020年07月31日 [査読有り][通常論文]
  • Hsin-hui Huang, Yuen-ting Rachel Chau, Tetsu Yonezawa, Mai Thanh Nguyen, Shilei Zhu, Dan Deng, Takeshi Nagashima, Koji Hatanaka
    Chemistry Letters 49 6 597 - 600 2020年06月05日 [査読有り]
  • Sonti Khamsanga, Mai Thanh Nguyen, Tetsu Yonezawa, Patchanita Thamyongkit, Rojana Pornprasertsuk, Prasit Pattananuwat, Adisorn Tuantranont, Siwaruk Siwamogsatham, Soorathep Kheawhom
    International Journal of Molecular Sciences 21 13 4689 - 4689 2020年06月 [査読有り]
  • Ikumi Akita, Yohei Ishida, Tetsu Yonezawa
    The Journal of Physical Chemistry Letters 11 9 3357 - 3361 2020年05月07日 [査読有り]
  • Pemika Teabnamang, Wathanyu Kao-ian, Mai Thanh Nguyen, Tetsu Yonezawa, Rongrong Cheacharoen, Soorathep Kheawhom
    Energies 2020年05月 [査読有り][通常論文]
  • Ryan Dula Corpuz, Lyn Marie De Juan-Corpuz, Mai Thanh Nguyen, Tetsu Yonezawa, Heng-Liang Wu, Anongnat Somwangthanaroj, Soorathep Kheawhom
    International Journal of Molecular Sciences 21 9 3113 - 3113 2020年04月28日 [査読有り][通常論文]
  • Shilei Zhu, Dan Deng, Mai Thanh Nguyen, Yuen-ting Rachel Chau, Cheng-Yen Wen, Tetsu Yonezawa
    Langmuir 36 13 3386 - 3392 2020年04月07日 [査読有り][通常論文]
     
    Metal@semiconductor core-shell nanoparticles (NPs) are widely used in photocatalysts, sensors, and optical applications owing to their unique metal-semiconductor interface and the integration of the properties from both core and shell materials. Although many efforts have been made toward the precise synthesis of Au@Cu2O core-shell structures, the chemical stability of Au@Cu2O aqueous suspensions, which is of great significance in many related applications, is not mentioned in any published research. Herein we report the synthesis of Au@Cu2O core-shell NPs with small shell thickness from 2 to 40 nm through a wet-chemistry method. The UV-vis absorption properties are found to be tunable with Cu2O thickness in the range of 2-40 nm. Furthermore, the chemical stability of Au@Cu2O core-shell nanoparticle suspensions in water/ethanol mixed solvents is investigated. It is found that water/ethanol mixed solvents with a larger amount of water are more likely to deteriorate the stability of Au@Cu2O NPs by oxidizing Cu2O to CuO. The results from this work may provide useful information for the preparation of metal@Cu2O water-based suspensions that are expected to be used for SERS, photocatalyst, or photothermal applications.
  • Shilei Zhu, Mai Thanh Nguyen, Tomoharu Tokunaga, Cheng-Yen Wen, Tetsu Yonezawa
    NANOSCALE ADVANCES 2 4 1456 - 1464 2020年04月 
    Precise design of hollow nanostructures can be realized via various approaches developed in the last two decades, endowing nanomaterials with unique structures and outstanding performances, showing their usefulness in a broad range of fields. Herein, we demonstrate the formation of SnO2@SiO2 hollow nanostructures, for the first time, by interaction between liquid state Sn cores and SiO2 shell structures inside Sn@SiO2 core-shell nanoparticles with real-time observation via in situ transmission electron microscopy (TEM). Based on the in situ results, designed transformation of the nanoparticle structure from core-shell Sn@SiO2 to yolk-shell Sn@SiO2 and hollow SnO2@SiO2 is demonstrated, showing the controllable structure of core-shell Sn@SiO2 nanoparticles via fixing liquid-state Sn inside a SiO2 shell which has a certain Sn containing capacity. The present approach expands the toolbox for the design and preparation of yolk-shell and hollow nanostructures, thus providing us with a new strategy for fabrication of more complicated nanostructures.
  • Lianlian Deng, Mai Thanh Nguyen, Jingming Shi, Yuen-ting Rachel Chau, Tomoharu Tokunaga, Masaki Kudo, Syo Matsumura, Naoyuki Hashimoto, Tetsu Yonezawa
    Langmuir 36 12 3004 - 3015 2020年03月31日 [査読有り][通常論文]
     
    Pt/Au alloy nanoparticles (NPs) in a wide composition range have been synthesized by room-temperature simultaneous sputter deposition from two independent magnetron sources onto liquid PEG (MW = 600). The prepared NPs were alloyed with the face-centered cubic (fcc) structure. In addition, the particle sizes, composition, and shape are strongly correlated but can be tailored by an appropriate variation of the sputtering parameters. No individual particle but large agglomerates with partial alloy structure formed at Pt content of less than 16 atom %. Highly dispersed NPs with no agglomeration were observed in PEG when the quantity of Pt is more than 26 atom %. On the other hand, a small amount of Pt could terminate the agglomeration of Au when sputtering on the grids for transmission electron microscope observation. Our experiment and computer simulation carried out by two different methods indicate that the composition-dependent particle size of Pt/Au can be explained by the atomic concentration, formation energy of the cluster, and interaction between different metal atoms and the PEG molecule.
  • Hsin-hui Huang, Takeshi Nagashima, Tetsu Yonezawa, Yasutaka Matsuo, Soon Hock Ng, Saulius Juodkazis, Koji Hatanaka
    Applied Sciences 10 6 2031 - 2031 2020年03月 [査読有り]
     
    Simultaneous measurements of THz wave and hard X-ray emission from thin and flat water flow when irradiated by double femtosecond laser pulses (800 nm, 35 fs/transform-limited, 0.5 kHz, delay times up to 15 ns) were carried out. THz wave measurements by time-domain spectroscopy and X-ray detection by Geiger counters were performed at the transmission and the reflection sides of the flow. THz wave emission spectra show their dynamic peak shifts toward the low frequency with the highest intensity enhancements more than 1.5 × 10 3 times in |E| 2 accumulated over the whole spectrum range of 0–3 THz at the delay time of 4.7 ns between the two pulses. On the other hand, X-ray intensity enhancements are limited to about 20 times at 0 ns under the same experimental conditions. The mechanisms for the spectral changes and the intensity enhancements in THz wave emission are discussed from the viewpoint of laser ablation on the water flow induced by the pre-pulse irradiation.
  • Yuen-ting Rachel Chau, Mai Thanh Nguyen, Mingbei Zhu, Arnaud Romier, Tomoharu Tokunaga, Tetsu Yonezawa
    New Journal of Chemistry 44 12 4704 - 4712 2020年 

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

  • Mai Thanh Nguyen, Kai Yu, Tomoharu Tokunaga, Kornkit Boonyaperm, Soorathep Kheawhom, Masashi Arita, Tetsu Yonezawa
    ACS SUSTAINABLE CHEMISTRY & ENGINEERING 7 21 17697 - 17705 2019年11月 [査読有り][通常論文]
     
    This research is devoted for the synthesis of Fe oxide and Fe nanoparticles (NPs) via, respectively, thermal decomposition of iron(III) oleate and H-2 reduction of either iron(III) oleate or iron oxide NPs in a NaCl matrix. Lowering the weight ratios of metal precursor to NaCl and synthesis temperature results in smaller particle sizes. A higher uniformity of Fe NPs can be achieved with a two-step synthesis, that is, thermal decomposition of iron oleate followed by H-2 reduction of iron oxides, with the milling of iron oxides and NaCl prior to the reduction step. Fe NPs obtained in this study are stable in the air for long-time storage. It is found that thin oxide and C layers on the particle surface are responsible for their stability.
  • Min JIa Saw, Batu Ghosh, Mai Thanh Nguyen, Kridsada Jirasattayaporn, Soorathep Kheawhom, Naoto Shirahata, Tetsu Yonezawa
    ACS Omega 4 8 13303 - 13308 2019年08月 [査読有り][通常論文]
     
    Silver nanowires (Ag NWs) as transparent conducting electrodes are widely used in many applications such as organic light-emitting diodes (OLEDs), polymer light-emitting diodes, touch screens, solar cells, and transparent heaters. In this work, using a large-scale synthesis, the synthesized Ag NWs had a high aspect ratio of 2820. The Ag NWs could be applied as a top transparent electrode in a device by simple drop-casting without any post-processing steps. The fabricated device comprised 4,4′-bis(carbazol-9-yl)biphenyl/MoO3 organic/inorganic layers which are parts of the inverted structure OLEDs or solar cells. The photodiode characteristics at the UV range were observed in the device. The ability of Ag NWs to replace opaque metals as top electrodes in a device has been demonstrated.
  • Kunihiro Narita, Yohei Ishida, Tetsu Yonezawa, Zhong Huang
    The Journal of Physical Chemistry C in press 35 21768 - 21773 2019年08月 [査読有り][通常論文]
     
    We have recently pioneered per-cationized molecular gold (Au) cluster compounds. Herein, we present a new series of per-cationized Au cluster compounds, Au144(SR+)60, which is the largest reported compound with the most stable and studied Au clusters. Although it is typically difficult to obtain a single composition of an Au144 cluster due to the existence of similar-sized quasi-stable compounds, optimized thermal etching and selective precipitation made strict size focusing into a single Au144 composition possible and produced Au144(SR+)60 with high atomic precision. In positive-mode high-resolution ESI-MS, per-cationized Au144(SR+)60 clusters with different numbers of PF6− counter anions for the +12 to +21-charged states were observed. The Au144(SR+)60, 60(+) termini distributed over a spherical surface of radius ~ 2.5 nm, presented here is, to the best of our knowledge, the most polycationic molecular compound reported thus far.
  • Tetsu YONEZAWA, Masaki MATSUBARA
    色材協会 92 7 205 - 209 2019年07月20日 [査読有り][招待有り]
  • Zhong Huang, Yohei Ishida, Tetsu Yonezawa
    Angewante Chemie International Edition in press 2019年07月 [査読有り][通常論文]
     
    The synthesis of high‐purity and high‐yield Au25 clusters protected by the basic pyridyl ethanethiol (HSCH2CH2Py, 4‐PyET and 2‐PyET) is presented. Single‐crystal X‐ray diffraction of the [Au25(4‐PyET)18]−⋅Na+ clusters has revealed a structure similar to that known for the phenyl ethanethiolate analogue, but with pyridyl‐N coordination to Na+, a more relaxed ligand shell, and a profoundly layered arrangement in the solid state. Because of the pendant Py moiety, the [Au25(PyET)18]− clusters are endowed with unique (de)protonation equilibria, which has been characterized in detail by UV/Vis absorption and 1H NMR spectroscopy. [Au25(PyET)18]− clusters showed an unexpectedly H+‐dependent solubility that is tunable in aqueous and organic solvents. The successful synthesis of the basic Py‐terminated thiolate‐protected Au25 clusters paves the way to realize a new family of metalloid clusters possessing basic properties.
  • Wan-Yu Chung, Yi-Chin Lai, Tetsu Yonezawa, Ying-Chih Liao
    Nanomaterials 9 8 1071  2019年07月 [査読有り][通常論文]
     
    In this study, an ink formulation was developed to prepare conductive copper thin films with compact structure by using intense pulsed light (IPL) sintering. To improve inter-particle connections in the sintering process, a cuprous oxide shell was synthesized over copper nanoparticles (CuNP). This cuprous oxide shell can be reduced by IPL with the presence of a reductant and fused to form connection between large copper particles. However, the thermal yield stress after strong IPL sintering resulted in cracks of conductive copper film. Thus, a multiple pulse sintering with an off time of 2 s was needed to reach a low resistivity of 10−5 Ω·cm. To increase the light absorption efficiency and to further decrease voids between CuNPs in the copper film, cupric oxide nanoparticles (CuONP) of 50 nm, were also added into ink. The results showed that these CuONPs can be reduced to copper with a single pulse IPL and fused with the surrounding CuNPs. With an optimal CuNP/CuONP weight ratio of 1/80, the copper film showed a lowest resistivity of 7 × 10−5 Ω·cm, ~25% conductivity of bulk copper, with a single sintering energy at 3.08 J/cm2. The ink can be printed on flexible substrates as conductive tracks and the resistance remained nearly the same after 10,000 bending cycles.
  • Lianlian Deng, Mai Thanh Nguyen, Shuang Mei, Tomoharu Tokunaga, Masaki Kudo, Syo Matsumura, Tetsu Yonezawa
    Langmuir : the ACS journal of surfaces and colloids 35 25 8418 - 8427 2019年06月25日 [査読有り][通常論文]
     
    We use a green sputtering technique to deposit a Pt/Cu alloy target on liquid polyethylene glycol (PEG) to obtain well-dispersed and stable Pt29Cu71 alloy nanoparticles (NPs). The effects of sputtering current, rotation speed of the stirrer, sputtering time, sputtering period, and temperature of PEG on the particle size are studied systematically. Our key results demonstrate that the aggregation and growth of Pt/Cu alloy NPs occurred at the surface as well as inside the liquid polymer after the particles landed on the liquid surface. According to particle size analysis, a low sputtering current, high rotation speed for the stirrer, short sputtering period, and short sputtering time are found to be favorable for producing small-sized single crystalline alloy NPs. On the other hand, varying the temperature of the liquid PEG does not have any significant impact on the particle size. Thus, our findings shed light on controlling NP growth using the newly developed green sputtering deposition technique.
  • Shilei Zhu, Mai Thanh Nguyen, Tomoharu Tokunaga, Tetsu Yonezawa
    ACS APPLIED NANO MATERIALS 2 6 3752 - 3760 2019年06月 [査読有り][通常論文]
     
    The most commonly used phase change materials (PCMs), like organic compounds and inorganic salts, were limited in application by their low thermal conductivity. Herein, for the first time, alumina-encapsulated metallic Sn-based PCMs, named Sn@Al2O3, were successfully fabricated with tunable size (60-2000 nm) by a facile process from low-cost chemicals. The robust fabrication process consists of a surfactant-free solvothermal synthesis of SnO2 spheres, boehmite treatment on SnO2 spheres, calcination in the air, and the final hydrogen reduction to transform SnO2 to metallic Sn, endowing the PCMs with high potential for mass production. The as-obtained Sn@Al2O3 showed a core-shell structure, in which a main metallic Sn core located in the center covered with an Al2O3 shell with small Sn nanoparticles distributed inside. The boehmite treatment, in which the penetration of aluminum species into SnO2 spheres played an important role, was found to be responsible for the unique structure formation of final Sn@Al2O3. The understanding of structure formation mechanism gives the possibilities of a new facile way for the synthesis of metal nanoparticles and particle-distributed nanostructures. The obtained Sn@Al2O3 particles not only have high PCM content (92.37 wt %) but also show a stable thermal behavior and morphology during 100 melt freeze cycles in the air atmosphere. Furthermore, the low melting temperature of the PCM core, combined with high thermal conductivity of both core material (Sn, 66.8 W m(-1) K-1) and shell material (Al2O3, 35 W m(-1) K-1), makes Sn@Al2O3 potentially suitable for rapid thermal energy storage in the range 100-300 degrees C.
  • Sonti Khamsanga, Rojana Pornprasertsuk, Tetsu Yonezawa, Ahmad Azmin Mohamad, Soorathep Kheawhom
    Scientific Reports 9 8441  2019年06月 [査読有り][通常論文]
     
    Manganese oxide (MnO2) is one of the most promising intercalation cathode materials for zinc ion batteries (ZIBs). Specifically, a layered type delta manganese dioxide (δ-MnO2) allows reversible insertion/extraction of Zn2+ ions and exhibits high storage capacity of Zn2+ ions. However, a poor conductivity of δ-MnO2, as well as other crystallographic forms, limits its potential applications. This study focuses on δ-MnO2 with nanoflower structure supported on graphite flake, namely MNG, for use as an intercalation host material of rechargeable aqueous ZIBs. Pristine δ-MnO2 nanoflowers and MNG were synthesized and examined using X-ray diffraction, electron spectroscopy, and electrochemical techniques. Also, performances of the batteries with the pristine δ-MnO2 nanoflowers and MNG cathodes were studied in CR2032 coin cells. MNG exhibits a fast insertion/extraction of Zn2+ ions with diffusion scheme and pseudocapacitive behavior. The battery using MNG cathode exhibited a high initial discharge capacity of 235 mAh/g at 200 mA/g specific current density compared to 130 mAh/g which is displayed by the pristine δ-MnO2 cathode at the same specific current density. MNG demonstrated superior electrical conductivity compared to the pristine δ-MnO2. The results obtained pave the way for improving the electrical conductivity of MnO2 by using graphite flake support. The graphite flake support significantly improved performances of ZIBs and made them attractive for use in a wide variety of energy applications.
  • Rasu Muruganantham, Irish Valerie Maggay, Lyn-Marie Z. De Juan, Tetsu Yonezawa, Mai Thanh Nguyen, Yan-Gu Lin, Chia-Her Lin, Wei-Ren Liu
    Inorganic Chemistry Frontiers in press 2019年06月 [査読有り][通常論文]
     
    Nowadays, transition metal oxides are being rapidly developed for application as Na-ion storage anode materials, which provide a relatively high theoretical capacity compared to the graphitic anode; however, the evaluation of enhanced electrochemical performance of SIBs via various approaches, such as coating or doping, is an ongoing process. Hence, in this study, a mesoporus ZnV2O4 anode material with a spinel structure was successfully synthesized via a solvothermal technique followed by calcination at different temperatures; moreover, the impact of the calcination temperature on the Na-ion storage performance of this anode material was thoroughly investigated for the first time. The initial discharge capacities of 178, 251, and 296 mA h g−1 were obtained for the cacination temperatures of 500, 600, and 700 °C, respectively; after 250 cycles, the ZVO-700 electrode retained the discharge capacity of 166 mA h g−1 at 200 mA g−1 with the high coulombic efficiency of 99%. Furthermore, ZVO-500 and ZVO-600 retained 55 mA h g−1 and 99 mA h g−1 with a ∼27% and ∼42% retention rate, respectively. The electrochemical Na-ion storage performance is predicted by the conversion reaction of ZnV2O4. Moreover, the ZVO-700 sample showed higher surface area and pore volume, which led to remarkable electrochemical performance, than the ZVO-500 and ZVO-600 samples.
  • Lyn Marie, Z. De Juan-Corpuz, Mai Thanh Nguyen, Ryan D. Corpuz, Tetsu Yonezawa, Nataly Carolina Rosero-Navarro, Kiyoharu Tadanaga, Tomoharu Tokunaga, Soorathep Kheawhom
    ACS Applied Nano Materials 2 7 4247 - 4256 2019年06月 [査読有り][通常論文]
     
    Porous ZnV2O4 nanowires (NWs) were successfully prepared by hydrothermal reaction followed by calcination. Despite the porous structure, these porous ZnV2O4 NWs are single crystal with {220} facets and a wire direction along the c-axis. On the basis of an electrochemical test, these porous ZnV2O4 NWs have better cycling stability and higher specific capacity (i.e., 460 mA h g–1 after 100 cycles and 149 mA h g–1 after 1000 cycles using 1 and 5 A g–1 current densities, respectively) compared to other morphologies (i.e., spherical and coral-like morphologies). As a ternary transition metal oxide, the produced porous ZnV2O4 NWs undergo phase transformation without compromising the resulting capacity. On the other hand, the CV curves at different scan rates indicate a pseudocapacitive electrochemical behavior of the porous ZnV2O4.
  • Min Jia Saw, Mai Thanh Nguyen, Shilei Zhu, Yongming Wang, Tetsu Yonezawa
    RSC Advances 9 38 21786 - 21792 2019年04月 [査読有り][通常論文]
     
    Tin (Sn) has a low melting temperature, i.e., 231.9 °C for the bulk, and the capability to form compounds with many metals. The galvanic reaction between Sn nanoparticles (NPs) as the core and silver nitrate at room temperature under argon gas in an organic solvent without any reducing power, was employed for the first time to coat an Ag–Sn intermetallic shell, i.e., Ag3Sn and/or Ag4Sn, on Sn NPs. For spherical Sn NPs, the NPs retained a spherical shape after coating. Uniform and Janus structures consisting of a β-Sn core with Ag–Sn shell were observed in the resulting NPs and their population related to the input molar ratios of the metal precursors. The observation of the intermetallic shell is general for both spherical and rod-shape Sn NPs. The formation of the intermetallic shell indicated that two reactions occurred sequentially, first reduction of Ag ions to Ag atoms by the Sn core, followed by interdiffusion of Ag and Sn to form the Ag–Sn intermetallic shell.
  • Tetsu Yonezawa, Jiajia Shi, Hiroki Tsukamoto, Mai Thanh Nguyen
    MRS Advances 4 7 413 - 418 2019年02月 [査読有り][通常論文]
  • Yuen-ting Rachel Chau, Lianlian Deng, Mai Thanh Nguyen, Tetsu Yonezawa
    MRS Advances 4 5-6 305 - 309 2019年01月
  • Irish Valerie B. Maggay, Lyn Marie Z. De Juan, Jeng-Shin Lu, Mai Thanh Nguyen, Tetsu Yonezawa, Ting-Shan Chan, Wei-Ren Liu
    Scientific Reports 8 1 2018年12月01日 [査読有り][通常論文]
     
    Spinel based transition metal oxide - FeV2O4 is applied as a novel anode for sodium-ion battery. The electrochemical tests indicate that FeV2O4 is generally controlled by pseudo-capacitive process. Using cost-effective and eco-friendly aqueous based binders, Sodium-Carboxymethylcellulose/Styrene butadiene rubber, a highly stable capacity of ~97 mAhg-1 is obtained after 200 cycles. This is attributed to the strong hydrogen bonding of carboxyl and hydroxyl groups indicating superior binding with the active material and current collector which is confirmed by the ex-situ cross-section images of the electrode. Meanwhile, only ~27 mAhg-1 is provided by the electrode using poly(vinylidene difluoride) due to severe detachment of the electrode material from the Cu foil after 200 cycles. The obtained results provide an insight into the possible applications of FeV2O4 as an anode material and the use of water-based binders to obtain highly stable electrochemical tests for sodium-ion battery.
  • Teerapon Pirom, Amornchai Arponwichanop, Ura Pancharoen, Tetsu Yonezawa, Soorathep Kheawhom
    Scientific Reports 8 1 2018年12月01日 [査読有り][通常論文]
     
    Yttrium (Y) is an essential lanthanide rare earth element and can be effectively extracted and purified using a hollow fiber supported liquid membrane (HFSLM) system. However, the stability of HFSLM system is a significant challenge. Pseudoemulsion-hollow fiber strip dispersion (PEHFSD) system, providing excellent stability, is attracting research attention. In this work, the recovery of Y(III) by PEHFSD system using di(2-ethylhexyl)phosphoric acid (D2EHPA) as a carrier was investigated. The effects of several operating parameters, including the initial concentration of Y(III) in the feed phase, the flow rate of feed, the stirring speed and the volumetric ratio of feed to strip on Y(III) separation were studied. The Y(III) transport was analyzed on the concentration ratio of Y(III) ions, percent extraction, percent stripping and overall mass transfer coefficient (K p ). The PEHFSD system outperformed HFSLM system regarding separation performance and stability. K p of HFSLM system decreased after the second run, but K p of PEHFSD system remained constant even at the fifth run. The dispersed droplets in the strip dispersion phase in the PEHFSD system enhanced separation performance and stability of the membrane module.
  • Tetsu Yonezawa, David Čempel, Mai Thanh Nguyen
    Bulletin of the Chemical Society of Japan 91 12 1781 - 1798 2018年12月 [査読有り][招待有り]
     
    In the past decades, various nanomaterials have been intensively developed because of their unique electrical, optical, magnetic as well as catalytic properties. In this review, we discuss the plasma-in-liquid process, especially the microwave-induced plasma-in-liquid process (MWPLP), for metal and metal oxide nanoparticle production. Various types of plasma systems have been employed to produce metal, alloy, and metal oxide nanoparticles. Nanoparticle production by plasma processes usually requires fewer chemical additives compared to other chemical processes. After discussing the bottom-up approach and the plasma-in-liquid process for nanoparticle synthesis, we have focused on MWPLP. Various apparatus systems and detailed mechanisms of MWPLP will be discussed and preparation of metal and metal oxide nanoparticles by MWPLP will be introduced in detail. The surface-coated-electrode system, which is a unique system for MWPLP, is also discussed in this review. This system prevents sample contamination due to the metal components, which are usually ejected into the surrounding liquid after plasma ignition during the production of nanoparticles.
  • Mai Thanh Nguyen, Tetsu Yonezawa
    Science and Technology of Advanced Materials 19 1 883 - 898 2018年10月 [査読有り][通常論文]
     
    The young history of sputtering onto a liquid features great achievements in the green production of various metal and metal oxide nanoparticles (NPs) and nanoclusters (NCs). Studies on how the sputtering parameters affect the properties of NPs and NCs have elucidated their formation mechanism and marked a crucial role of liquid matrix in the nucleation and growth of particles, controlling their various properties. Current research has been devoted to making alloy bi- and trimetallic NPs with a high level of control over the NP structure, composition, and size via well-designed target systems, sputtering steps, and liquid matrix materials. In this minireview, we discuss the recent advances in the use of various types of targets to prepare different bi- and trimetallic NPs. In single target sputtering, systems with alternative configurations of metals, alloy targets, monometallic targets in sequence, and a combination of sputtering and chemical reactions have been developed. On the other hand, a double head system was introduced to widen the range of controllable sputtering parameters yielding more versatility in particle composition and fine structure. The synergistic and tuneable properties exhibited by the multi-metallic components in small NPs and NCs for their use in catalysis and optical applications are discussed.
  • Wei-Hung Hsu, Frances Camille, P. Masim, Armandas Balcytis, Hsin-Hui Huang, Tetsu Yonezawa, Aleksandr A. Kuchmizhak, Saulius Juodkazis, Koji Hatanaka
    Beilstein Journal of Nanotechnology 9 2609 - 2617 2018年10月 [査読有り][通常論文]
     
    Enhancement of X-ray emission was observed from a micro-jet of a nano-colloidal gold suspension in air under double-pulse excitation of ultrashort (40 fs) near-IR laser pulses. Temporal and spatial overlaps between the pre-pulse and the main pulse were optimized for the highest X-ray emission. The maximum X-ray intensity was obtained at a 1–7 ns delay of the main pulse irradiation after the pre-pulse irradiation with the micro-jet position shifted along the laser beam propagation. It was revealed that the volume around gold nanoparticles where the permittivity is near zero, ε ≈ 0, accounts for the strongest absorption, which leads to the effective enhancements of X-ray emission.
  • Soraya Hosseini, Woranunt Lao-atiman, Siow Jing Han, Amornchai Arpornwichanop, Tetsu Yonezawa, Soorathep Kheawhom
    Scientific Reports 8 14909  2018年10月 [査読有り][通常論文]
     
    Zinc-air batteries are a promising technology for large-scale electricity storage. However, their practical deployment has been hindered by some issues related to corrosion and passivation of the zinc anode in an alkaline electrolyte. In this work, anionic surfactant sodium dodecyl sulfate (SDS) and nonionic surfactant Pluronic F-127 (P127) are examined their applicability to enhance the battery performances. Pristine zinc granules in 7 M KOH, pristine zinc granules in 0–8 mM SDS/7 M KOH, pristine zinc granules in 0–1000 ppm P127/7 M KOH, and SDS coated zinc granules in 7 M KOH were examined. Cyclic voltammograms, potentiodynamic polarization, and electrochemical impedance spectroscopy confirmed that using 0.2 mM SDS or 100 ppm P127 effectively suppressed the anode corrosion and passivation. Nevertheless, direct coating SDS on the zinc anode showed adverse effects because the thick layer of SDS coating acted as a passivating film and blocked the removal of the anode oxidation product from the zinc surface. Furthermore, the performances of the zinc-air flow batteries were studied. Galvanostatic discharge results indicated that the improvement of discharge capacity and energy density could be sought by the introduction of the surfactants to the KOH electrolyte. The enhancement of specific discharge capacity for 30% and 24% was observed in the electrolyte containing 100 ppm P127 and 0.2 mM SDS, respectively.
  • Megumi Sakurai, Mengrui Yang, Jiawei Xu, Mai Thanh Nguyen, Tetsu Yonezawa, Kenro Hashimoto, Tatsuya Fujino
    International Journal of Mass Spectroscopy 434 179 - 184 2018年09月 [査読有り][通常論文]
     
    CuO nanoparticles (CuO) loaded on zeolite (CuO/HM20) and zeolite whose active sites are substituted by copper (CuM20) have been developed as matrices for laser desorption ionization. CuO/HM20 showed efficient Cu+ production upon laser irradiation. By several spectroscopic results, it was found that CuO interacts with hydroxyl groups in zeolite and the lifetime of electron hole pair becomes long owing to the presence of the zeolite support. In addition, it was also found that water molecules surrounding the CuO play an important role in the Cu2++e → Cu+ reaction on the CuO surface. For CuM20, on the other hand, Cu+ production was not effective, probable because strong binding of Cu2+ with water molecules hindered the desorption of copper ions. These two matrices were applied to the desorption ionization of small molecules (arginine, tyrosine, heptacosan, melamine and creatinine). It was found that CuO/HM20 ionized analyte efficiently and CuM20 had selectivity for Cu+ adduction ionization.
  • Huang Zhong, Ishida Yohei, Narita Kunihiro, Yonezawa Tetsu
    JOURNAL OF PHYSICAL CHEMISTRY C 122 31 18142 - 18150 2018年08月09日 [査読有り][通常論文]
  • Zhu Shilei, Mai Thanh Nguyen, Fumoto Koji, Kanie Kiyoshi, Muramatsu Atsushi, Yonezawa Tetsu
    ACS APPLIED NANO MATERIALS 1 8 4073 - 4082 2018年08月 [査読有り][通常論文]
     
    We report a facile method for preparing a silica (SiO2)-based material containing Sn nanoparticles (NPs) distributed inside for enhancing the thermal cyclic stability of the inserted Sn NPs. Absorption of a Sn precursor (i.e., an aqueous SnCl2 solution) into a mesoporous SiO2 matrix resulted in confinement of the Sn precursor in a mesoporous SiO2 matrix. Hydrogen thermal reduction of the above composite yielded Sn nanoparticles with a diameter of ca. 30 nm uniformly distributed inside porous SiO2 (p-SiO2) spheres: Sn NPs@p-SiO2. Our investigation of the transformation ofthe porous SiO2 structure to hold Sn NPs revealed that the process was closely related to the transformation of the amorphous hydrolyzed Sn precursor into Sn oxides followed by, probably, the rearrangement of the SiO2 matrix via its interaction with the melting Sn. This led to the formation of stable Sn NPs@p-SiO2. The SiO2 matrix effectively prevented the coalescence of the Sn NPs, and the obtained product exhibited negligible changes in melting behavior during the second to 100th cycle of a freeze melt cycle test.
  • Yohei Ishida, Jun Suzuki, Ikumi Akita, Tetsu Yonezawa
    Langmuir 34 36 10668 - 10672 2018年08月 [査読有り][通常論文]
     
    We propose a novel method for the ultra-rapid cationization of gold nanoparticles with diameters ranging from several to a hundred nanometers via a single-step ligand exchange reaction of citrate-protected anionic gold nanoparticles with cationic thiol ligand. This reaction was performed only in an aqueous medium via a single step from citrate to cationic thiol, therefore enables a rapid preparation of cationic Au NPs without a contamination of organic solvent or lipid-soluble molecules. The cationization was successfully completed within 20 min without changes in the core diameter and optical characteristic.
  • Irish Valerie Buiser Maggay, Lyn Marie Z. De Juan, Mai Thanh Nguyen, Tetsu Yonezawa, B. K. Chang, T. S. Chan, Wei-Ren Liu
    Journal of the Taiwan Institute of Chemical Engineers 88 161 - 168 2018年07月01日 [査読有り][通常論文]
     
    A template-free solvothermal method was employed to successfully obtain ZnV2O4 spinel oxide and its electrochemical properties as anode materials for sodium ion battery system were investigated for the first time. The structural, morphological, elemental composition, electrochemical properties and theoretical calculations of the as-prepared ZnV2O4 were carried out. XRD revealed the presence of ZnO and VO2 impurities when synthesized for 1 day, while complete formation of ZnV2O4 was attained when the synthesis procedure was increased to 3 days. When cycled at 50 mA/g, it delivered an initial capacity of as high as 537 mAh/g at a potential window of 0.01–3.0 V. Meanwhile, a reversible capacity of ∼ 113 mAh/g was obtained when cycled at 100 mA/g for 30 cycles. These results indicate the potential applications of ZnV2O4 as anode materials for sodium ion battery systems.
  • Tetsu Yonezawa, Masaki Matsubara
    Journal of the Society of Powder Technology, Japan 55 6 325 - 333 2018年06月10日
  • Yohei Ishida, Akihiro Morita, Tomoharu Tokunaga, Tetsu Yonezawa
    Langmuir : the ACS journal of surfaces and colloids 34 13 4024 - 4030 2018年04月03日 [査読有り][通常論文]
     
    We herein present the preparation of short, bulky cationic thiolate (thiocholine)-protected fluorescent Au nanoclusters via sputter deposition over a liquid polymer matrix. The obtained Au nanoclusters showed near-infrared fluorescence and had an average core diameter of 1.7 ± 0.6 nm, which is too large compared to that of the reported fluorescent Au nanoclusters prepared via chemical means. We revealed the mechanism of formation of this unique material using single-particle electron microscopy, optical measurements, X-ray photoelectron spectroscopy (XPS), and high-performance liquid chromatography fractionations. The noncrystallized image was observed via single-particle high-angle annular dark-field scanning transmission electron microscopy observations and compared with chemically synthesized crystalline Au nanoparticle with the same diameter, which demonstrated the unique structural characteristic speculated via XPS. The size fractionation and size-dependent fluorescence measurement, together with other observations, indicated that the nanoclusters most probably contained a mixture of very small fluorescent species in their aggregated form and were derived from the sputtering process itself and not from the interaction between thiol ligands.
  • Lianlian Deng, Mai Thanh Nguyen, Tetsu Yonezawa
    Langmuir 34 8 2876 - 2881 2018年02月27日 [査読有り][通常論文]
     
    Matrix sputtering with the use of a low vapor pressure liquid as its matrix becomes a green technique to prepare nanoparticles dispersed in liquid. In the present study, we proposed using this method with polyethylene glycol (PEG, molecular weight = 600) as the liquid matrix to produce highly uniform Pt nanoparticles with a small size (below 2.0 nm) and a narrow size distribution. The results indicated that particle sizes were tailorable from 0.9 ± 0.3 to 1.4 ± 0.3 nm by varying the sputtering current (5-50 mA) with negligible particle aggregation that occurred in PEG during sputtering. The slight growth of the particle size observed after sputtering was attributed to the addition of free Pt atoms to the existing Pt nanoparticles. All samples formed stable dispersion in PEG for 5 month storage. This result suggested an advantage of using a liquid matrix to produce and stabilize nanoparticles.
  • David Čempel, Mai Thanh Nguyen, Yohei Ishida, Tomoharu Tokunaga, Tetsu Yonezawa
    New Journal of Chemistry 42 8 5680 - 5687 2018年 [査読有り][通常論文]
     
    Au/Ag alloy nanoparticles (NPs) were successfully prepared by a one step synthesis using HAuCl4 and [Ag(NH3)2]+ as the corresponding precursors in a microwave-induced plasma in liquid process (MWPLP) without the addition of any organic protecting or reducing agents. The time dependent reduction and particle formation during the 140 min plasma discharge were studied with TEM, UV-vis extinction spectra, and ICP-OES. After 140 min, the HAADF-STEM and EDX results indicated that the obtained Au/Ag NPs were alloy NPs. Varying the input molar ratios of the metal precursors allowed for control of the composition of the Au/Ag alloy NPs.
  • Preparation of Ag nanoparticles using hydrogen peroxide as a reducing agent
    M. Nishimoto, S. Abe, T. Yonezawa
    New J. Chemistry 42 14493 - 14501 2018年 [査読有り][通常論文]
  • David Čempel, Mai Thanh Nguyen, Yohei Ishida, Tetsu Yonezawa
    Bulletin of the Chemical Society of Japan 91 3 362 - 367 2018年 [査読有り][通常論文]
     
    Microwave induced plasma in liquid has become a green and effective method for preparation of metallic nanoparticles (NPs). In our research, we have introduced yttrium oxide (Y2O3) coated stainless steel electrodes to address impurity problems of resulting NPs due to the loss of electrode materials. We have proposed using [Ag(NH3)2]+ complex as an alternative precursor and L-arginine as the stabilizing agent to synthesize highly uniform Ag NPs with an average diameter of around 5nm. [Ag(NH3)2]+ complex was chosen as it can allow the reaction proceed at high pH for higher reaction yield compared with using AgNO3 whereas L-arginine can stabilize Ag NPs to attain highly uniform and small sizes. The influence of the selection of initial precursor on the reduction of metal precursor during the plasma irradiation, the particle size and size distribution of Ag NPs, and influence of the amount of L-arginine, were investigated.
  • Yohei Ishida, Ikumi Akita, Thomas Pons, Tetsu Yonezawa, Niko Hildebrandt
    Journal of Physical Chemistry C 121 51 28395 - 28402 2017年12月28日 [査読有り][通常論文]
     
    We herein report the first real-space investigation of Förster resonance energy transfer (FRET) in two different types of quantum dot (QD) supramolecular assemblies by observing their three-dimensional (3D) configurations through high-resolution electron tomography. Owing to its critical role in photosynthesis, artificial light-harvesting antennas, and investigation of protein-protein interactions, the mechanism of FRET has been intensively studied by monitoring its excited-state dynamics via various spectroscopic techniques. The utilized electron tomography technique allowed the direct localization of 3D coordinates of individual QDs in self-assembled nanostructures and theoretical estimation of the FRET efficiency of a single fluorophore, domain, or supramolecular assembly. Moreover, the experimental value of the FRET efficiency determined by fluorescence spectroscopy was in good agreement with the magnitude obtained via electron tomography. We believe that the described strategy can be used in single-molecule FRET studies and will help to create a new bridge between material science and molecular/supramolecular photochemistry.
  • Yohei Ishida, Ryan D. Corpuz, Tetsu Yonezawa
    ACCOUNTS OF CHEMICAL RESEARCH 50 12 2986 - 2995 2017年12月 [査読有り][招待有り]
     
    Noble metal nanoclusters are believed to be the transition between single metal atoms, which show distinct optical properties, and metal nanoparticles, which show characteristic plasmon absorbance. The interesting properties of these materials emerge when the particle size is well below 2 nm, such as photoluminescence, which has potential application particularly in biomedical fields. These photoluminescent ultrasmall nanoclusters are typically produced by chemical reduction, which limits their practical application because of the inherent toxicity of the reagents used in this method. Thus, alternative strategies are sought, particularly in terms of physical approaches, which are known as "greener alternatives," to produce high purity materials at high yields. Thus, a new approach using the sputtering technique was developed. This method was initially used to produce thin films using solid substrates; now it can be applied even with liquid substrates such as ionic liquids or polyethylene glycol as long as these liquids have a low vapor pressure. This revolutionary development has opened up new areas of research, particularly for the synthesis of colloidal nanoparticles with dimensions below 10 nm. We are among the first to apply the sputtering technique to the physical synthesis of photoluminescent noble metal nanoclusters. Although typical sputtering systems have relied on the effect of surface composition and viscosity of the liquid matrix on controlling particle diameters, which only resulted in diameters ca. 3-10 nm, that were all plasmonic, our new approach introduced thiol molecules as stabilizers inspired from chemical methods. In the chemical syntheses of metal nanoparticles, controlling the concentration ratio between metal ions and stabilizing reagents is a possible means of systematic size, control. However, it was not clear whether this would be applicable in a sputtering system. Our latest results showed that we were able to generically produce a variety of photoluminescent monometallic nanoclusters of Au, Ag, and Cu, all of which showed stable emission in both solution and solid form via our matrix sputtering method with the induction of cationic-, neutral-, and anionic-charged thiol ligands. We also succeeded in synthesizing photoluminescent bimetallic Au-Ag nanoclusters that showed tunable emission within the UV-NIR region by controlling the composition of the atomic ratio by a double-target sputtering technique. Most importantly, we have revealed the formation mechanism of these unique photoluminescent nanoclusters by sputtering, which had relatively larger diameters (ca. 1-3 nm) as determined using TEM and stronger emission quantum yield (max. 16.1%) as compared to typical photoluminescent nanoclusters prepared by chemical means. We believe the high tunability of sputtering systems presented here has significant advantages for creating novel photoluminescent nanoclusters as a complementary strategy to common chemical methods. This Account highlights our journey toward understanding the photophysical properties and formation mechanism of photoluminescent noble metal nanoclusters via the sputtering method, a novel strategy that will contribute widely to the body of scientific knowledge of metal nanoparticles and nanoclusters.
  • Mai Thanh Nguyen, Hong Zhang, Lianlian Deng, Tomoharu Tokunaga, Tetsu Yonezawa
    LANGMUIR 33 43 12389 - 12397 2017年10月 [査読有り][通常論文]
     
    Alloy nanoparticles (NPs) of a bimetal system, Au/Cu, that form intermetallic compounds in a bulk state have been successfully produced using a double-target sputtering technique onto a low-cost and biocompatible liquid polymer (polyethylene glycol, PEG). The formation of an Au/Cu solid solution alloy in individual NPs was revealed by scanning transmission electron microscopy-energy-dispersive X-ray elemental mapping analysis. Altering the sputter currents for Au and Cu targets resulted in a tailored NP composition, but the particle sizes did not significantly vary. We found similar structures, sizes, and optical properties of Au/Cu NPs obtained by double-head sputtering on carbon-coated transmission electron microscopy grids or PEG and by Au/Cu alloy target sputtering. Random alloy formation occurred in matrix sputtering using double-target heads. This method is advantageous for manipulating the alloy composition through highly independent control of sputter parameters for each metal target.
  • Lyn Marie Z. De Juan, Mai Thanh Nguyen, Tetsu Yonezawa, Tomoharu Tokunaga, Hiroki Tsukamoto, Yohei Ishida
    CRYSTAL GROWTH & DESIGN 17 9 4554 - 4562 2017年09月 [査読有り][通常論文]
     
    For the first time, investigation on the effect of lowering the synthesis temperature below room temperature (10 to -10 degrees C) and increasing the viscosity of the reaction solution at certain temperatures has been used to trigger the formation of single-crystalline ss-Sn nanorods (NRs) in a chemical synthesis using an organic solvent. These two parameters govern the energy of the particles in the solution, thereby mediating the selective attachment to the nuclei and the preferential growth of Sn along the c-axis. The length and aspect ratio of the NRs were inversely proportional to the synthesis temperature and directly proportional to the viscosity of the reaction solution. In addition, we found that poly(vinylpyrrolidone) with a high molecular weight aided the formation of longer and higher aspect ratio NRs via the bridge flocculation effect.
  • Masamu Nishimoto, Hiroki Tsukamoto, Mai Thanh Nguyen, Tetsu Yonezawa
    CHEMISTRYSELECT 2 26 7873 - 7879 2017年09月 [査読有り][通常論文]
     
    The effect of additives, i.e., H2O2 and pH adjustors, on the preparation of Ag nanoparticles (NPs) fabricated using the microwave-induced plasma in liquid process (MWPLP) has been investigated. When both aqueous ammonia and NaOH were used as pH adjustors, the rate of the reduction of silver ions decreased with lower concentrations of H2O2 or at higher pH values. Under these conditions, the aggregation of generated nuclei during the early stages of the reduction was suppressed, and the sizes of the obtained Ag NPs decreased. The amount of H2O2 and the pH of the reduction solutions are therefore highly important parameters for the preparation of well-dispersed Ag NPs using the MWPLP.
  • Ryan D. Corpuz, Yohei Ishida, Mai Thanh Nguyen, Tetsu Yonezawa
    LANGMUIR 33 36 9144 - 9150 2017年09月 [査読有り][通常論文]
     
    Herein, we report a novel positively charged photoluminescent Au-Ag bimetallic nanocluster synthesized using 11-mercaptoundecyl-N,N,N-trimethylammonium bromide as the capping ligand by means of green double-target sputtering method on a biocompatible polymer matrix. The photoluminescent Au-Ag bimetallic cluster showed emission tunability from blue to near infrared (NIR) regions with respect to change in the composition.
  • Yohei Ishida, Shingo Motono, Wataru Doshin, Tomoharu Tokunaga, Hiroki Tsukamoto, Tetsu Yonezawa
    ACS omega 2 8 5104 - 5110 2017年08月31日 [査読有り][通常論文]
     
    Production of oxygen-deficient tungsten oxide nanoparticles with a diameter of around 10 nm have been successfully developed using a microwave-induced plasma in liquid technique. The prepared blue-green nanoparticles exhibit strong absorption in the visible region; thus, these could be efficient visible-light photocatalysts. The high-angle annular dark-field images revealed the dislocation of tungsten, which causes oxygen deficiencies.
  • Frances Camille P. Masim, Wei-Hung Hsu, Hao-Li Liu, Tetsu Yonezawa, Armandas Balcytis, Saulius Juodkazis, Koji Hatanaka
    OPTICS EXPRESS 25 16 19497 - 19507 2017年08月 [査読有り][通常論文]
     
    Photoacoustic signal enhancements were observed with a pair of time-delayed femtosecond pulses upon excitation of gold nanosphere colloidal suspension. A systematic experimental investigation of photoacoustic intensity within the delay time, Delta t = 0 to 15 ns, was carried out. The results revealed a significant enhancement factor of similar to 2 when the pre-pulse energy is 20-30% of the total energy. Pre-pulse and main pulse energy ratios, E-p((1)) :E-s((2)) were varied to determine the optimal ratio that yields to maximum photoacoustic signal enhancement. This enhancement was ascribed to the initial stage of thermalization and bubble generation in the nanosecond time scale. Pre-pulse scattering intensity measurements and numerical finite-difference time-domain calculations were performed to reveal dynamics and light field enchancement, respectively. (C) 2017 Optical Society of America
  • Tetsu Yonezawa, Hiroki Tsukamoto, Mai Thanh Nguyen
    ADVANCED POWDER TECHNOLOGY 28 8 1966 - 1971 2017年08月 [査読有り][通常論文]
     
    Size tuning of metallic copper fine particles is highly important for their application to conductive pastes. Uniformly sized metallic copper fine particles could be successfully obtained by a chemical reduction of CuO micro powders using hydrazine in the presence of polypeptides as the stabilizing regent. Easy tuning of their particle sizes was successfully achieved via controlling the molecular weight of polypeptides. The obtained particles were covered by polypeptide capsules which were approximately 2 wt% of total mass. They are highly stable even under ambient conditions. (C) 2017 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.
  • Ryan D. Corpuz, Yohei Ishida, Tetsu Yonezawa
    NEW JOURNAL OF CHEMISTRY 41 14 6828 - 6833 2017年07月 [査読有り][通常論文]
     
    This study demonstrates a novel synthesis of cationically charged photoluminescent noble metal nanoclusters of Au, Ag, and Cu; these are known plasmonic elements utilizing 11-mercaptoundecyl-N,N,N-trimethyl ammonium bromide as a stabilizing and capping ligand via sputtering deposition over a liquid polymer matrix.
  • Chaorui Xue, Shengliang Hu, Wei Liu, Qing Chang, Tetsu Yonezawa, Jinlong Yang
    FUNCTIONAL MATERIALS LETTERS 10 3 2017年06月 [査読有り][通常論文]
     
    "Multi-layer" walled TiO2 nanotube array has been prepared by anodization with post-treatment of ethanol. Two post-treatment methods, which were ethanol and water treatment respectively, exerted a marked and different effect on the structure of nanotube. With ethanol immersion, the " multi-layer" walled nanotube can be obtained, while water treatment cannot produce the "multi-layer" walled structure. The main reason could be the uptake of carbon and fluoride during anodization process. Compared with "single-layer" walled TiO2 nanotube, "multi-layer" walled TiO2 nanotube demonstrated higher photocatalytic activity.
  • Masamu Nishimoto, Tetsu Yonezawa, David Cempel, Mai Thanh Nguyen, Yohei Ishida, Hiroki Tsukamoto
    MATERIALS CHEMISTRY AND PHYSICS 193 7 - 12 2017年06月 [査読有り][通常論文]
     
    The microwave-induced plasma in liquid process (MWPLP) has been attractive as a unique preparation method of metal nanoparticles. In this study, we investigated the effect of H2O2 on gold nanoparticles prepared using the MWPLP. Au nanoparticles were obtained without aggregation when the Au and H2O2 concentrations in the reaction solution were 0.3 mM and 0.03 mM, respectively. When the H2O2 concentration was lower or higher than the optimum range, aggregated particles were obtained. The results show that the addition of H2O2 had a great influence on the reduction rate and the dispersibility, and that Au nanoparticles prepared under optimum conditions were not aggregated and exhibited a high dispersibility. (C) 2017 Elsevier B.V. All rights reserved.
  • Yohei Ishida, Yu-Ling Huang, Tetsu Yonezawa, Kunihiro Narita
    CHEMNANOMAT 3 5 298 - 302 2017年05月 [査読有り][通常論文]
     
    Many thiolate-protected molecular Au clusters, of different cluster sizes and with varying neutral or anionic thiolate ligands, have been reported over the past two decades. Despite this abundance of information, to date there has been no report of atomically pure cationized molecular Au clusters that are protected with cationic thiolates. We herein present a novel, facile and high-yield synthetic approach towards producing a new series of thiolate- protected molecular Au clusters: a fully cationized Au-25(SR+)(18) cluster with atomic precision. The simple "charge neutralization strategy" presented enables treatment of the cationic thiols as neutral thiols, thus the well-established method for preparing Au-25 clusters with neutral thiolates can be adopted for cationic Au-25 clusters at a very high synthetic yield. We believe that this report will widen the spectrum of gold cluster chemistry and also help in the further development of cationized molecular clusters with various metals, core sizes, and ligand structures.
  • Yohei Ishida, Ryota Nakabayashi, Ryan D. Corpuz, Tetsu Yonezawa
    COLLOIDS AND SURFACES A-PHYSICOCHEMICAL AND ENGINEERING ASPECTS 518 25 - 29 2017年04月 [査読有り][通常論文]
     
    We have developed a novel physical approach for size-controlled synthesis of metal nanoparticles via sputtering deposition over liquid matrix. Here we report a novel water-dispersible, negatively charged fluorescent silver nanoparticles through this method with a very short anionic thiolate ligand. Our previous result showed that multiple hydrogen bonds between carboxylic groups in surface ligands resulted in a very poor dispersilibity of formed nanoparticles, however neutralized sodium 3-mercaptopropionate used in this work could overcome this limitation. We successfully obtained NIR fluorescent, water-dispersible silver nanoparticles for the first time among physical-based approach. Results presented here therefore will widen the spectrum of novel and environmental-friendly strategy for functionalized metal nanoparticles or fluorescent clusters. (C) 2017 Elsevier B.V. All rights reserved.
  • Hiroaki Shirai, Mai Thanh Nguyen, David Cempel, Hiroki Tsukamoto, Tomoharu Tokunaga, Ying-Chih Liao, Tetsu Yonezawa
    BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN 90 3 279 - 285 2017年03月 [査読有り][通常論文]
     
    Au/Pd alloy nanoparticles (NPs) were successfully synthesized using HAuCl4, H2PdCl4, and alpha-thioglycerol as precursors and a stabilizer, respectively, by microwave-induced plasma in liquid process (MWPLP). After only several minutes of microwave irradiation, metallic NPs were obtained in aqueous environment without any reducing agent. The reduction mechanism of metal ions was confirmed by UV-vis spectral changes. The results from HAADF-STEM and EDS indicated that synthesized NPs were bimetallic Au/Pd. Moreover, XRD patterns of synthesized NPs implied that the composition of bimetallic NPs could be controlled by changing the initial ratio of metal precursors.
  • Yingqiong Yong, Mai Thanh Nguyen, Hiroki Tsukamoto, Masaki Matsubara, Ying-Chih Liao, Tetsu Yonezawa
    SCIENTIFIC REPORTS 7 45150  2017年03月 [査読有り][通常論文]
     
    Mixtures of a copper complex and copper fine particles as copper-based metal-organic decomposition (MOD) dispersions have been demonstrated to be effective for low-temperature sintering of conductive copper film. However, the copper particle size effect on decomposition process of the dispersion during heating and the effect of organic residues on the resistivity have not been studied. In this study, the decomposition process of dispersions containing mixtures of a copper complex and copper particles with various sizes was studied. The effect of organic residues on the resistivity was also studied using thermogravimetric analysis. In addition, the choice of copper salts in the copper complex was also discussed. In this work, a low-resistivity sintered copper film (7 x 10(-6) Omega center dot m) at a temperature as low as 100 degrees C was achieved without using any reductive gas.
  • Kuan-Ming Huang, Hiroki Tsukamoto, Yingqiong Yong, Hsien-Lung Chiu, Mai Thanh Nguyen, Tetsu Yonezawa, Ying-Chih Liao
    RSC ADVANCES 7 40 25095 - 25100 2017年 [査読有り][通常論文]
     
    In this study, a thermally triggered self-reducible copper ink is developed to print conductive patterns on flexible substrates. Inks containing only copper formate (CuF) and monoisopropanol amine (MIPA) generated large bubbles in the CuF decomposing process, and thus the surface morphologies of prepared thin films were largely disturbed. With the addition of octylamine (OA), the bubbling disturbance was relieved due to the lower surface tension and the film uniformity was greatly improved. A low resistivity of 2 x 10(-7) Omega m (8.5% of bulk copper) can be reached by heating the ink at 140 degrees C for 5 minutes under a nitrogen environment. XRD results showed the synthesized copper films were comprised of pure metallic copper crystalline. The copper films were composed of closely packed spherical grains of 50 to 500 nm in diameter. After the addition of 1 wt% polyvinylpyrrolidone (PVP) in the ink, the synthesized copper thin films showed great adhesion on glass substrates, and sustained the same conductivity after repeated tape tests. The ink can also be printed on flexible substrates, such as polyethylene terephthalate (PET) or polyimide (PI) thin films, to create highly-conductive tracks with a strong mechanical stability. Finally, various conductive patterns were printed on flexible substrates to show the great potential of this ink for various printed electronic applications.
  • Y. Yong, M. T. Nguyen, T. Yonezawa, T. Asano, M. Matsubara, H. Tsukamoto, Y. Liao, T. Zhang, S. Isobe, Y. Nakagawa
    Journal of Materials Chemistry C 5 5 1033 - 1041 Royal Society of Chemistry 2017年 [査読有り][通常論文]
     
    A method for producing Cu films with low resistivity, based on low temperature sintering, is demonstrated. The Cu inks for preparing conductive Cu films consisted of Cu particles that were coated with a decomposable polymer (poly(propylenecarbonate), PPC) as well as a self-reducible copper formate/1-amino-2- propanol (CuF-IPA) complex as an additive. The sintering temperature used in this study was as low as 100 degrees C. Following sintering at a temperature of 100 degrees C, the lowest reported resistivity (8.8 x 10(-7) Omega m) was achieved through the use of Cu-based metal-organic decomposition (MOD) inks. This was due to the dual promotional effects of the aminolysis of PPC with IPA and the pyrolysis of the CuF-IPA complex.
  • Frances Camille P. Masim, Matteo Porta, Wei-Hung Hsu, Mai Thanh Nguyen, Tetsu Yonezawa, Armandas Balcytis, Saulius Juodkazis, Koji Hatanaka
    ACS PHOTONICS 3 11 2184 - 2190 2016年11月 [査読有り][通常論文]
     
    Hard X-ray generation up to 15 keV (similar to 1 angstrom) from Au nanoparticle suspensions was systematically investigated for different particle diameters ranging from 10 to 100 nm with a narrow size distribution of +/- 2%. Scaling law of X-ray generation is close to a 6-photon process before the onset of saturation for excitation by 40 fs laser pulses with central wavelength of 800 nm. This is consistent with bulk plasmon excitation at lambda(bulk)(p) similar or equal to 138 nm. The longitudinal E-field component due to nanoparticle focusing is responsible for the excitation of the longitudinal bulk plasmon. The proposed analysis also explains X-ray emission from water breakdown via an electron solvation mechanism at similar to 6.2 eV. The most efficient emission of X-rays was observed for 40 +/- 1 nm diameter nanoparticles which also had the strongest UV extinction. X-ray emission was the most efficient when induced by prechirped 370 +/- 20 fs laser pulses and exhibited the highest intensity at a negative chirp.
  • Matteo Porta, Mai Thanh Nguyen, Tomoharu Tokunaga, Yohei Ishida, Wei-Ren Liu, Tetsu Yonezawa
    LANGMUIR 32 46 12159 - 12165 2016年11月 [査読有り][通常論文]
     
    A modified magnetron sputtering technique using pentaerythritol tetrakis(3-mercaptopropionate) (PEMP) as a stabilizing agent and liquid dispersion medium was developed to generate photoluminescent copper nanoclusters. The results reveal that, over time, the as-prepared blue emitting copper nanoclusters were converted to red-emitting copper sulfide nanoclusters. The formation of copper oxide as an intermediate during the conversion of copper to copper sulfide nanoclusters was demonstrated. Furthermore, based on the mechanism of formation of copper sulfide, the kinetics of the conversion process could be controlled via ultraviolet (UV) irradiation of the as-synthesized dispersion. These findings shed light on the formation and conversion of nanoclusters obtained via sputtering into liquid, demonstrating that the method is highly versatile for producing metal nanoclusters and compounds with tailorable composition and optical properties.
  • Tetsu Yonezawa, Koji Kawai, Hayato Kawakami, Takashi Narushima
    BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN 89 10 1230 - 1232 2016年10月 [査読有り][通常論文]
     
    Water-dispersible palladium nanoparticle catalysts have been prepared using palladium-carbon covalent bonds. They worked as an excellent catalyst for Suzuki-Miyaura coupling reaction in water. Even though the particle size of Pd nano particles was much larger than the previously reported ones, they showed a very good catalytic activity for the coupling reaction.
  • Yohei Ishida, Kunihiro Narita, Tetsu Yonezawa, Robert L. Whetten
    JOURNAL OF PHYSICAL CHEMISTRY LETTERS 7 19 3718 - 3722 2016年10月 [査読有り][通常論文]
     
    Although many thiolate-protected Au clusters with different numbers of Au atoms and a variety of thiolate ligands have been synthesized, to date there has been no report of a fully cationized Au cluster protected with cationic thiolates. Herein, we report the synthesis of the first member of a new series of thiolate-protected Au cluster molecules: a fully cationized Au-25(SR+)(18) cluster.
  • Wei-Hung Hsu, Frances Camille P. Masim, Matteo Porta, Mai Thanh Nguyen, Tetsu Yonezawa, Armandas Balocytis, Xuewen Wang, Lorenzo Rosa, Saulius Juodkazis, Koji Hatanakai
    OPTICS EXPRESS 24 18 19994 - 20001 2016年09月 [査読有り][通常論文]
     
    Femtosecond laser-induced hard X-ray generation in air from a 100-mu m-thick solution film of distilled water or Au nano-sphere suspension was carried out by using a newly-developed automatic positioning system with 1-mu m precision. By positioning the solution film for the highest X-ray intensity, the optimum position shifted upstream as the laser power increased due to breakdown. Optimized positioning allowed us to control X-ray intensity with high fidelity. X-ray generation from Au nano-sphere suspension and distilled water showed different power scaling. Linear and nonlinear absorption mechanism are analyzed together with numerical modeling of light delivery. (C) 2016 Optical Society of America
  • Yohei Ishida, Satoshi Udagawa, Tetsu Yonezawa
    COLLOIDS AND SURFACES A-PHYSICOCHEMICAL AND ENGINEERING ASPECTS 504 437 - 441 2016年09月 [査読有り][通常論文]
     
    We report detailed aggregation mechanisms of sputtered silver nanoparticles in a viscous thiolate liquid matrix. Fluorescent silver nanoparticles were prepared by the sputtering deposition over pentaerythritol tetrakis(3-mercaptopropionate) (PEMP). The dependences of extinction, fluorescence and particle size on time were discussed in terms of two possible aggregation mechanisms. The main aggregation process was secondary aggregation, with primary aggregation (core coalescence) making a small contribution. The four thiol groups in the PEMP structure are the driving force determining the predominance of secondary aggregation. Finally, we successfully prepared a thiourethane resin by the polymerization of a thiolate matrix, and complete immobilization of nanoparticles in the resin resulted in no observable degradation of the photophysical properties. The demonstrations presented here will be beneficial in understanding the detailed aggregation mechanism and optical properties of nanoparticles. (C) 2016 Elsevier B.V. All rights reserved.
  • Ikumi Akita, Yohei Ishida, Tetsu Yonezawa
    BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN 89 9 1054 - 1056 2016年09月 [査読有り][通常論文]
     
    Sputtering deposition of gold over a liquid matrix containing different ligands with thiolate, amine, or carboxy groups resulted in the formation of spherical gold nanoparticles (Au NPs) in the range of 2.1 to 6.7 nm, and the diameters gradually decreased as the affinity of the ligands for Au increases.
  • David Cempel, Mai Thanh Nguyen, Yohei Ishida, Hiroki Tsukamoto, Hiroaki Shirai, Yongming Wang, Kevin C. -W. Wu, Tetsu Yonezwa
    JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY 16 9 9257 - 9262 2016年09月 [査読有り][通常論文]
     
    Plasma-in-liquid process (PLP) has become a hot topic in green synthesis of metal nanoparticles (NPs). In order to overcome one of the current challenges associated with the impurity produced from metal electrodes, this study utilized a ceramic-coated electrode to prepare pure Au NPs stabilized by L-arginine. Using this electrode, the reduction of Au ions during the plasma irradiation, the formation of Au NPs, their size and size distribution as a function of the pH were investigated. Our results show that a bimodal NP size distribution was obtained at pH 3.5-12.0. The fraction of small sized Au NPs becomes significant at pH 6.0 and 12.0 while that of big sized Au NPs is dominant at pH 3.5. The results in the present study suggested that this change in the size distribution of Au NPs was governed by the reduction rate of gold ion at different pH under plasma generated in water.
  • Frances Camille P. Masim, Wei-Hung Hsu, Chih-Hung Tsai, Hao-Li Liu, Matteo Porta, Mai Thanh Nguyen, Tetsu Yonezawa, Armandas Balcytis, Xuewen Wang, Saulius Juodkazis, Koji Hatanaka
    OPTICS EXPRESS 24 15 17050 - 17059 2016年07月 [査読有り][通常論文]
     
    Strong absorption of femtosecond laser pulses in Au nano-colloidal suspensions was used to generate coherent ultrasound signals at 1-20 MHz frequency range. The most efficient ultrasound generation was observed at negative chirp values and was proportional to the pulse duration. Maximization of a dimensionless factor A equivalent to alpha c(0)t(p) defined as the ratio of pulse duration t(p) and the time required for sound at speed c(0) to cross the optical energy deposition length (an inverse of the absorption coefficient alpha) given by 1/(alpha c(0)). Chirp controlled pulse duration allows effective enhancement of ultrasound generation at higher frequencies (shorter wavelengths) and is promising for a high spatial resolution acoustic imaging. (C) 2016 Optical Society of America
  • Ishida Y, Akita I, Sumi T, Matsubara M, Yonezawa T
    Scientific reports 6 29928 - 29928 Nature Publishing Group 2016年07月 [査読有り][通常論文]
     
    Here we report a novel physical approach for thiolate-protected fluorescent gold nanoparticles with a controlled size of the order of a few nanometers. This approach is based on a sputtering of gold into a liquid matrix containing thiolate ligand as a stabilizer at various concentrations, thus no reductant was used. The size of the gold nanoparticles was successfully controlled to range from 1.6 to 7.4 nm by adjusting the thiol concentrations. Surface plasmon absorption was observed in larger nanoparticles, but it was not observed in smaller ones. Such smaller nanoparticles fluoresced at around 670 nm with a small spectral shift according to their size, however, the diameter (1.6-2.7 nm) was very strange to show such red emission compared with photophysical characteristics of reported gold cluster or nanoparticles synthesized by chemical method. By detailed investigations using TEM, HAADF-STEM, XPS, and TGA, and size fractionation by size exclusion chromatography, we finally arrived at the plausible mechanism for the origin of unusual fluorescence property; the obtained gold nanoparticles are not single-crystal and are composed of aggregates of very small components such as multinuclear gold clusters or complexes.
  • Frances Camille P. Masim, Hao-Li Liu, Matteo Porta, Tetsu Yonezawa, Armandas Balcytis, Saulius Juodkazis, Wei-Hung Hsu, Koji Hatanaka
    OPTICS EXPRESS 24 13 14781 - 14792 2016年06月 [査読有り][通常論文]
     
    Enhanced photoacoustic (PA) intensity from gold nanosphere and nanorod colloidal suspensions in water under tightly-focused femtosecond pulsed laser irradiation was systematically investigated. PA signal amplitudes were measured by ultrasound transducers at frequencies of 5, 10, and 25 MHz. The experimental results revealed a linear-dependence of the relative photoacoustic amplitude on the laser power and the mechanism was attributed to non-radiative relaxation dynamics of surface plasmon oscillations. When gold nanorod with longitudinal absorption/extinction peak at 800 nm coincides with the wavelength of femtosecond laser pulses, the most efficient PA signal is generated. Laser excitation was kept within a thermal stability region of gold nanoparticles, i.e., colloidal suspension can be continuously reused for PA generation. (C) 2016 Optical Society of America
  • Yohei Ishida, Satoshi Udagawa, Tetsu Yonezawa
    COLLOIDS AND SURFACES A-PHYSICOCHEMICAL AND ENGINEERING ASPECTS 498 106 - 111 2016年06月 [査読有り][通常論文]
     
    A sputtering deposition of metals over liquid matrixes has been investigated as a novel and environmentally friendly method to generate stable colloidal metal nanoparticles. We have expanded this method by using the liquid monomers with mercapto groups in order to prepare more stable, uniform and size controllable nanoparticles. Here we report the systematic investigation on the growth mechanism of silver nanoparticles on pentaerythritol tetrakis(3-mercaptopropionate) (PEMP) matrix under the varied viscosities controlled by temperature. The diameter of obtained nanoparticles increased from 1.8 to 2.3 nm as the viscosity of the liquid matrix increased, and at higher viscosity region we obtained a thin deposited film on the liquid surface but no nanoparticles formed. The effect of viscosity on the particle diameter was much smaller than previous works using ionic liquids or polyethylene glycol, and then the phenomenon was understood by the structure of these matrixes where PEMP has four mercapto groups however ionic liquids or polyethylene glycol does not have any functional groups that introduce strong interaction with metals. These demonstrations suggest that the sputtering over mercaptan liquid matrix is a more favorable method for the stable preparation of uniform very small nanoparticles. (C) 2016 Elsevier B.V. All rights reserved.
  • Mai Thanh Nguyen, Tetsu Yonezawa, Yuan Wang, Tomoharu Tokunaga
    MATERIALS LETTERS 171 75 - 78 2016年05月 [査読有り][通常論文]
     
    A new approach using double target sputtering into liquid is proposed to synthesize Ag-Au alloy nanoparticles (NPs). The results reveal the formation of Ag-Au solid solution alloy as individual NPs. Variation of the applied target current allows fine tuning of the NP composition, and, therefore, variation of optical properties of the alloy NPs. The method offers highly independent control of sputter parameters for each metal target, thereby allowing manipulation of the NP composition, size and optical properties. (C) 2016 Elsevier B.V. All rights reserved.
  • Satoshi Tsuchiya, Shigeaki Abe, Yuko Era, Yukari Nakagawa, Shuichi Yamagata, Mariko Nakamura, Teruo Kusaka, Yasuhiro Yoshida, Tetsu Yonezawa, Junichiro Iida
    Nanoscience and Nanotechnology Letters 8 4 329 - 334 2016年04月 [査読有り][通常論文]
     
    In this study, we investigated the effects of the topological properties of ceramics nanoparticles (NPs) (i.e., TiO2, Fe2O3, and CuO) on their biocompatibility. In the case of particle size, cell viability was not affected by the size of TiO2 particles even when the size was varied from 30 to 250 nm. Although the cytocompatibilities of TiO2 NPs with different morphologies were compared, no substantial difference was observed. In the case of Fe2O3, the viability decreased slightly with increasing particle concentration without a particle-size effect. In contrast, the viability upon exposure to CuO NPs decreased drastically with increasing NP concentration. Furthermore, the viability improved when CuO NPs size was increased from the nano-regime to micro-regime. Interestingly, greater viability was exhibited by gelatin-coated Cu NPs than by CuO NPs. These results suggest that the cytocompatibility of ceramics NPs is more strongly affected by chemical species than by particle size and, morphology.
  • Ryan D. Corpuz, Yohei Ishida, Tetsu Yonezawa
    PHYSICAL CHEMISTRY CHEMICAL PHYSICS 18 13 8773 - 8776 2016年04月 [査読有り][通常論文]
     
    A novel positively charged fluorescent gold nanocluster was successfully synthesized using the shortest cationic thiol, thiocholine. Effective control of electrostatic repulsion by the introduction of an anionic surfactant afforded a nanocluster that showed blue fluorescence emission.
  • Tetsu Yonezawa, Takashi Asano, Masaki Matsubara
    BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN 89 3 346 - 353 2016年03月 [査読有り][通常論文]
     
    The ability of surface-assisted laser desorption/ionization mass spectroscopy (SALDI-MS) of low-molecular-weight compounds using six types of commercially available TiO2 nanoparticles (NPs) was examined. In all cases, TiO2 NPs gave strong Na+-adduct sample ion peaks. Some chemicals, which rarely show proton-adduct sample ion peaks by MALDI-MS, such as aspirin and barbital, could be easily detected by using TiO2 NPs. The key factors determining the SALDI ability of TiO2 NPs are their purity, ratio of rutile, and particle size.
  • Shigeaki Abe, Eri Seitoku, Nobuki Lwadera, Yusuke Hamba, Shuichi Yamagata, Tsukasa Akasaka, Teruo Kusaka, Satoshi Lnoue, Yasutaka Yawaka, Junichiro Lida, Hidehiko Sano, Tetsu Yonezawa, Yasuhiro Yoshida
    JOURNAL OF BIOMEDICAL NANOTECHNOLOGY 12 3 472 - 480 2016年03月 [査読有り][通常論文]
     
    We assessed the biocompatibility of nano-sized ceramic particles with several cells types. Though these particles have less than 100 nm in diameter, they act as submicron-sized particles in saline by aggregation that was estimated using laser diffraction particle size analysis (LDS). they act as submicro-sized particles in saline by aggregation based on laser diffraction particle size analysis (LDS). Several types of cells (osteoblasts, osteosarcoma and hepatocyte cells) were exposed to these particles and their cytocompatibility was estimated. Not only the cytotoxic assay but also their static and dynamic morphology under nanoparticles exposure were investigated. The intercellular uptake of particles was determined using a confocal fluorescence microscope. The particles used in this study did not inhibit cellular activity or growth even when their concentrations were high. Only copper oxide particles caused acute cytotoxicity depending on the particle size. The cytotoxicity assay, dynamic behavior of the nanoparticle-exposed cells and their examination under a confocal fluorescence microscope suggests that the irritative reaction was induced by contact between the cells and particles, whereas eluted copper ions are not dominant factor. These results indicate that nano-sized particles used in this study have excellent biocompatibility except copper oxide ones.
  • Hiroaki Shirai, Yu-Yuan Huang, Tetsu Yonezawa, Tomoharu Tokunaga, Wei-Chen Chang, Saad M. Alshehri, Bo Jiang, Yusuke Yamauchi, Kevin C. -W. Wu
    MATERIALS LETTERS 164 488 - 492 2016年02月 [査読有り][通常論文]
     
    Platinum (Pt) is widely applied for electrochemical catalysis, thus creating porosity in Pt-based materials would enhance their catalytic efficacy. This study demonstrates a new route to synthesize a Pt material with macropores and spherical morphology by the combination of evaporation induced self-assembly of a hard template (i.e., silica nanoparticles) and infiltration/reduction of Pt species in micro-emulsion systems. The synthesized macroporous Pt microballs (denoted as MPtM) are characterized with scanning electron microscopy (SEM), transmission electron microscopy (TEM), and it is found that MPtM exhibits uniform macropores (diameter of 300 nm) and Pt crystalline framework, which would be potential for enhanced catalytic reactions. (C) 2015 Elsevier B.V. All rights reserved.
  • Yu-Te Liao, Jeffrey E. Chen, Yohei Isida, Tetsu Yonezawa, Wei-Chen Chang, Saad M. Alshehri, Yusuke Yamauchi, Kevin C. -W. Wu
    CHEMCATCHEM 8 3 502 - 509 2016年02月 [査読有り][通常論文]
     
    A denovo synthesis of gold-nanoparticle-embedded, nitrogen-doped nanoporous carbon nanoparticles (Au@NC) was investigated in this work. Chloroauroic acid was encapsulated inside zeolitic imidazolate framework-8 (ZIF-8) nanoparticles during the synthesis and later reduced into gold nanoparticles. The as-synthesized gold-nanoparticle-embedded ZIF-8 (Au@ZIF-8) was then carbonized into Au@NC to enhance the stability of the nanoporous support. The results show that Au@NC exhibits a porous structure containing 3wt% of gold. 2-Methylimidazole provided an abundant amount of nitrogen (19wt%) on the carbon matrix, which resulted in a hydrophilic and positively charged surface that is useful for the reduction of 4-nitrophenol. The results of the catalytic reaction indicate that synthesized Au@NC could act as an effective catalyst with a turnover frequency (TOF) of 1185g(-1)s(-1), which is higher than that of conventional naked Au nanoparticles (TOF: 339g(-1)s(-1)) and that of Au nanoparticles on activated carbon (TOF: 89g(-1)s(-1)). We propose that the enhanced performance of Au@NC resulted from homogeneous distribution of Au nanoparticles along with the hydrophilic and positively charged nitrogen-doped carbon surface.
  • Matteo Porta, Mai Thanh Nguyen, Yohei Ishida, Tetsu Yonezawa
    RSC ADVANCES 6 107 105030 - 105034 2016年 [査読有り][通常論文]
     
    For the first time, magnetron sputtering of copper onto liquid was investigated for the preparation of stable blue-fluorescent copper nanoclusters. The fluorescent intensity increased linearly with an increase of mercaptan. Our finding casts light on the formation mechanism of metal photoluminescent nanoclusters via sputtering onto liquid.
  • Yohei Ishida, Tetsu Yonezawa
    KOBUNSHI RONBUNSHU 73 1 12 - 18 2016年 [査読有り][通常論文]
     
    In recent years, it has been revealed that light-harvesting systems (LHSs) are composed of beautifully aligned chlorophyll molecules; the regulated alignment of chlorophylls is responsible for the efficient and selective light-harvesting energy transfer processes in purple bacteria. This finding led to the construction of regularly arranged assemblies of functional dyes as a step toward fabricating artificial LHSs. While most researchers use molecular interactions such as covalent, coordination, and hydrogen bonds to produce dye assemblies, our approach involves guest-host interactions using an inorganic nanosheet as a host material. This short review presents the construction of a 2D dye assembly and its effective utilization in artificial light-harvesting applications. Owing to the highly stable and uniform 2D alignment of functional dyes on inorganic nanosheets, nearly 100% singlet-singlet energy transfer and efficient light-harvesting were achieved.
  • Matteo Porta, Mai Thanh Nguyen, Tetsu Yonezawa, Tomoharu Tokunaga, Yohei Ishida, Hiroki Tsukamoto, Yuichi Shishino, Yoshikiyo Hatakeyama
    NEW JOURNAL OF CHEMISTRY 40 11 9337 - 9343 2016年 [査読無し][通常論文]
     
    A transparent resin containing titanium oxide nanoparticles ( NPs) was prepared using a molten matrix sputtering ( MMS) technique. The low vapour pressure of the liquid, pentaerythritol ethoxylate ( PEEL) substrate permits the use of this vacuum technique directly with liquid PEEL under stirring conditions in order to obtain uniform dispersions of NPs. We found that it is possible to synthesize titanium oxide, TiOx, NPs with diameters of less than 5 nm with a controlled composition by simply adjusting the sputtering atmosphere. Furthermore, as the electronic structure of the TiOx NPs changes depending on the particle size, crystallinity and degree of oxidation, we were able to modify the optical properties of PEEL and the resin by embedding TiOx NPs in the matrix. The enhancement of the refractive index of a resin containing TiO2 NPs was also demonstrated. This synthetic method is promising for the advanced preparation of high purity TiOx NPs without using a reducing agent and leaving by-products for various applications in optical devices, energy conversion, and light harvesting in the UV visible region.
  • Mai Thanh Nguyen, Hiroaki Shirai, Chondanai Tiankanon, Hiroki Tsukamoto, Yohei Ishida, Tetsu Yonezawa
    RSC ADVANCES 6 32 26725 - 26733 2016年 [査読有り][通常論文]
     
    A straightforward method for synthesizing single-crystalline SnO micro particles in an organic medium using tin acetylacetonate as the precursor and oleylamine as the capping ligand is proposed. For the first time, well-defined four-petal starfish-like SnO sheets were obtained in the organic medium. In addition, the shape of the particles could be reproducibly tuned such that their structures varied from cubes to squares and then to starfish-like sheets by simply changing the concentration of oleylamine. The underlying mechanism of this process was found to be closely related to the interaction of the stabilizing agent with the SnO crystal planes. Changing the concentration of the stabilizing agent could modify this interaction, leading to the preferential growth of certain crystal planes of SnO particles which determined the particle shape. This synthesis approach is advantageous in terms of allowing control over the particle shape as well as for its simplicity and short reaction time. Our results yield crucial insights regarding the shape evolution of SnO particles.
  • Tetsu Yonezawa, Hiroki Tsukamoto, Yingqiong Yong, Mai Thanh Nguyen, Masaki Matsubara
    RSC ADVANCES 6 15 12048 - 12052 2016年 [査読有り][通常論文]
     
    A novel low cost sintering process of copper fine particles to a copper conductive layer was demonstrated at as low as 100 degrees C without reductive gas flow. Sintering of a mixture of copper particles and copper-based metal-organic-decomposition (MOD) ink gave a copper film with high packing density and low resistivity (9 x 10(-6) Omega m). This novel process may open a new strategy in the field of printed electronics.
  • Hiroaki Shirai, Mai Thanh Nguyen, Yohei Ishida, Tetsu Yonezawa
    JOURNAL OF MATERIALS CHEMISTRY C 4 11 2228 - 2234 2016年 [査読有り][通常論文]
     
    Tin nanoparticles (Sn NPs) are of considerable interest for conductive printing because of their low melting temperature and low cost. In the present study, polyvinylpyrrolidone (PVP) stabilized metallic Sn NPs were synthesized by a polyol process and the size of Sn NPs was controlled from 15 to 89 nm by adjusting the amount of PVP. For the first time, we demonstrated that conductive patterns fabricated from the inks of metallic Sn NPs were achieved readily at room temperature under N-2 without reducing gases or additives. The lowest obtained resistivity was 1.1 x 10 (3) Omega cm, which was 100 times higher than that of bulk Sn. The size of Sn NPs, the amount of the stabilizing agent, and the low melting temperature of Sn NPs were found to be the main factors controlling the conductivity of the obtained Sn pattern in room temperature sintering. This study offers a new approach for the room temperature fabrication of conductive electronics using the printing technique.
  • Kuan-Chou Chen, Saikat Dutta, Yusuke Yamauchi, Saad M. Alshehri, Mai Thanh Nguyen, Tetsu Yonezawa, Kun-Hung Shen, Kevin C. -W. Wu
    JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY 15 12 9802 - 9806 2015年12月 [査読有り][通常論文]
     
    Monodisperse and mesoporous europium (Eu)-doped titania nanoparticles (denoted as Eu-MTNs) were prepared by a co-synthesis method with the presence of a cationic surfactant (i.e., CTAB). A maximum loading amount of 8 mol% of Eu could be successfully incorporated into the framework of MTNs. The synthesized Eu-MTNs samples were characterized with X-ray diffraction (XRD) and scanning electron microscopy (SEM), with their luminescent property examined by photoluminescence (PL). Under ultraviolet irradiation, the Eu-MTNs samples exhibit several characteristic luminescence corresponding to D-5(0)-F-7(j) for Eu+3 ions, which can be attributed to the energy transfer from titania nanocrystallite to Eu3+ ions dispersed in amorphous mesoporous titania region. The potential intracellular bio-imaging application of the synthesized Eu-MTN nanoparticles was demonstrated with a breast cancer cell line (i.e., BT-20). High biocompatibility and strong luminescence of the Eu-MTNs show great potential in biomedical applications.
  • Masaki Matsubara, Tetsu Yonezawa, Hiroki Tsukamoto
    BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN 88 12 1755 - 1759 2015年12月 [査読有り][通常論文]
     
    It has been found in this study that the glass transition temperatures can be considered as the lowest temperature for sintering metal fine particles to obtain electro-conductive metallic layers from the differential scanning calorimetry measurement of the fine particles. Gelatin-stabilized copper fine particles could be sintered to form an electrically conductive copper layer with a resistivity of 1.9 x 10(-5) Omega cm at as low as 150 degrees C using oxidation-reduction two-step sintering.
  • Atsushi Hyono, Shigeaki Abe, Koji Kawai, Tetsu Yonezawa
    JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY 15 11 9272 - 9274 2015年11月 [査読有り][通常論文]
     
    In this study, we succeeded in acquiring scanning electron microscope (SEM) images of carbon nanotube (CNT) derivatives with different surface properties based on an electro-conductive pretreatment using a room temperature ionic liquid (IL). The quality of the obtained SEM images depended on their surface properties and the hydrophilicities of IL used. When the hydrophilicities of both the sample surface and the IL were close, the obtained SEM images had a high resolution. In contrast, SEM imges of samples pretreated with an IL, which had different hydrophilicities from the sample, was observed with low resolution and low quality. This result suggests that the relationship between both hydrophilicities is the dominant factor for this visualization method.
  • Yohei Ishida, Wataru Doshin, Hiroki Tsukamoto, Tetsu Yonezawa
    CHEMISTRY LETTERS 44 10 1327 - 1329 2015年10月 [査読有り][通常論文]
     
    We herein report a novel synthesis of black TiO2 nanoparticles by using a microwave-induced plasma over Ti complex aqueous solution. The resultant TiO2 nanoparticles showed very strong reflectance over the whole visible light region. Detailed HAADF-STEM analysis of the obtained particles revealed that this plasma method enables doping of W ions inside the TiO2 crystal structure.
  • Xu Lu, Yohei Ishida, Tomobumi Mishina, Mai Thanh Nguyen, Tetsu Yonezawa
    BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN 88 10 1385 - 1387 2015年10月 [査読有り][通常論文]
     
    We propose a novel method to enhance the THz emission from CuOx/metal nano thin film by using columnar-structured microsized porous silicon (MS-PSi) as the substrate. THz emission was improved several times higher than that from the planar substrate due to the decreased optical reflectance and enlarged surface area.
  • Yohei Ishida, Chaiyathat Lee, Tetsu Yonezawa
    SCIENTIFIC REPORTS 5 15382  2015年10月 [査読有り][通常論文]
     
    Knowledge on the synthesis of cationically charged fluorescent gold nanoparticles (Au NPs) is limited because the electrostatic repulsion between cationic ligands on the surface of NP hinders the formation of small Au NPs (usually less than ca. 2 nm) during nucleation in solvents. We herein propose a novel methodology for a synthesis of water-dispersible, cationic-thiolate protected fluorescent Au NPs by the sputtering of Au into liquid matrix containing thiolate ligands. By controlling mercaptan concentration the size and photophysical characteristics of Au NPs were directly controlled, resulting in near IR fluorescence with a 0.9% of absolute quantum yield. Cationically charged fluorescent metal NPs are promising, especially in biological fields, and this work provides a novel methodology towards the synthesis of a new series of functional metal NPs.
  • Reduction of carbon dioxide using a visible-light-induced electron transfer system with colloidal metal nanoparticle catalysts: evidence for production of methane
    責任著者, 平川 和貴, 共著者]Kazutaka Hirakawa, Yumi Yamaji, Tetsu Yonezawa, Naoki Toshima
    Current Topics in Catalysis 11 (num) 55 - 63 2015年05月 [査読有り][通常論文]
  • Taiki Sumi, Shingo Motono, Yohei Ishida, Naoto Shirahata, Tetsu Yonezawa
    LANGMUIR 31 14 4323 - 4329 2015年04月 [査読有り][通常論文]
     
    This paper proposes a novel methodology to synthesize highly fluorescent gold nanoparticles (NPs) with a maximum quantum yield of 16%, in the near-infrared (IR) region. This work discusses the results of using our (previously developed) matrix sputtering method to introduce mercaptan molecules, alpha-thioglycerol, inside the vacuum sputtering chamber, during the synthesis of metal NPs. The evaporation of alpha-thioglycerol inside the chamber enables to coordinate to the nucleation stage very small gold nanoclusters in the gas phase, thus retaining their photophysical characteristics. As observed through transmission electron microscopy, the size of the Au NPs obtained with the addition of alpha-thioglycerol varied from approximately 23 nm to approximately 5 nm. Plasmon absorption varied with the size of the resultant nanoparticles. Thus, plasmon absorption was observed at 2.4 eV in the larger NPs. However, it was not observed, and instead a new peak was found at approximately 3.4 eV, in the smaller NPs that resulted from the introduction of alpha-thioglycerol. The Au NPs stabilized by the alpha-thioglycerol fluoresced at approximately 1.8 eV, and the maximum wavelength shifted toward the red, in accordance with the size of the NPs. A maximum fluorescent quantum yield of 16% was realized under the optimum conditions, and this value is extremely high compared to values previously reported on gold NPs and clusters (generally similar to 1%). To our knowledge, however, Au NPs of size >2 nm usually do not show strong fluorescence. By comparison with results reported in previous literature, it was concluded that these highly fluorescent Au NPs consist of goldmercaptan complexes. The novel method presented in this paper therefore opens a new door for the effective control of size, photophysical characteristics, and structure of metal NPs. It is hoped that this research contributes significantly to the science in this field.
  • Chaorui Xue, Tetsu Yonezawa, Mai Thanh Nguyen, Xu Lu
    LANGMUIR 31 4 1575 - 1580 2015年02月 [査読有り][通常論文]
     
    Highly ordered double-wall TiO2 nanotube arrays were obtained by a two-step anodization method in a fluoride-containing glycerol based electrolyte. The low water and fluoride content and high viscosity of the electrolyte support a partly undissolved fluoride-rich layer, and its hydrolyzed products remain on the tube walls. The double-wall structure and a cladding layer originating from the fluoride-rich layer were clearly observed after annealing. The morphology and crystal structure of the cladding layer were investigated. The study of the cladding layer gives a fundamental insight into the wall structure design of the anodic TiO2 nanotubes in the glycerol-based electrolyte.
  • Masashi Chiba, Mai Nguyen Thanh, Yasuchika Hasegawa, Yasushi Obora, Hideya Kawasaki, Tetsu Yonezawa
    JOURNAL OF MATERIALS CHEMISTRY C 3 3 514 - 520 2015年 [査読無し][通常論文]
     
    We report the use of a DMF reduction method for straightforward synthesis of binary solid solution Cu-Pd nanoparticles (NPs) over the entire range of composition. The resulting NPs were uniform in size (less than 2.5 nm), tunable in composition, and exhibited photoluminescence properties that were nonlinear in composition. These binary solid solution NPs showed enhanced photoluminescence intensity and quantum yield compared to those of the single-metal NPs and their mixtures. The highest quantum yield of 3.10% for Cu-Pd alloy NPs synthesized using equimolar feeding ratio versus 2.75% for Cu and 0.71% for Pd NPs was obtained. These enhancements make the alloy NPs promising materials for optical applications.
  • Koji Kawai, Hayato Kawakami, Takashi Narushima, Tetsu Yonezawa
    JOURNAL OF NANOPARTICLE RESEARCH 17 2 1 - 9 2015年01月 [査読有り][通常論文]
     
    Water-dispersible silver nanoparticles stabilized by silver-carbon covalent bonds were prepared. They exhibited high catalytic activities for the selective hydration of nitriles to amides in water. The activation of a nitrile group by the functional groups of the substrates and the hydrophobic layer on the nanoparticles influenced the catalyzed reaction were confirmed. Alkyl nitriles could also be selectively hydrated.
  • Mami Mutoh, Shigeaki Abe, Atsushi Hyono, Hiroshi Matsuura, Ko Nakanishi, Koji Kawai, Mariko Nakamura, Satoshi Inoue, Yasuhiro Yoshida, Junichiro Iida, Tetsu Yonezawa
    Nano Biomedicine 7 2 80  2015年 [査読有り][通常論文]
  • Masaki Matsubara, Tetsu Yonezawa, Takato Minoshima, Hiroki Tsukamoto, Yingqiong Yong, Yohei Ishida, Mai Thanh Nguyen, Hiroki Tanaka, Kazuki Okamoto, Takuya Osaka
    RSC ADVANCES 5 124 102904 - 102910 2015年 [査読有り][通常論文]
     
    Metallic copper fine particles were prepared by chemical reduction of CuO in the presence of thermally degradable poly-1,4-butanediol-divinylether (BDVE). Because a BDVE thin layer formed on the particle surfaces, the obtained copper particles were stable and did not undergo obvious oxidation under ambient conditions. The ether groups of BDVE were hydrolyzed with protons, and this generated small fragment molecules. The BDVE-stabilized copper fine particles and their pastes can be therefore sintered at 150 degrees C in the presence of protons. Electro-conductive films with a relatively low resistivity of 8.5 x 10(-5) Omega cm were obtained on a alumina substrate in the presence of formic acid, and hot pressed conductive pellets with a resistivity of 2.9 x 10(-5) Omega cm were also obtained without any pre-oxidative annealing in the presence of proton generator molecules at very low temperatures. The hot pressed pellets show a high anti-oxidative ability and their corrosion tests revealed their good anti-corrosion property.
  • Tetsu Yonezawa, Yoshiki Uchida, Hiroki Tsukamoto
    PHYSICAL CHEMISTRY CHEMICAL PHYSICS 17 48 32511 - 32516 2015年 [査読有り][通常論文]
     
    Metallic copper fine particles used for electro conductive pastes were prepared by the chemical reduction of cupric oxide microparticles in the presence of gelatin. After reduction, the fine particles were collected by decantation with pH control and washing, followed by drying at a moderate temperature. The surface oxidation state of the obtained copper fine particles could be considerably varied by altering the pH of the particle dispersion, as shown by X-ray diffraction and high-resolution transmission electron microscopy. Our results strongly indicate that decantation under a nitrogen atmosphere can prevent the oxidation of copper fine particles but a slight oxidation was found.
  • Yohei Ishida, Thatchanont Jirasupangkul, Tetsu Yonezawa
    NEW JOURNAL OF CHEMISTRY 39 6 4214 - 4217 2015年 [査読有り][通常論文]
     
    We propose a novel synthetic approach for cationic charged platinum nanoparticles via the autocatalytic hydrolysis of acetylthiocholine. This method can be extended to the platinum group of metals.
  • Yohei Ishida, Taiki Sumi, Tetsu Yonezawa
    New Journal of Chemistry 39 8 5895 - 5897 2015年 [査読有り][通常論文]
     
    Herein we report for the first time the synthesis of octadecanethiol-capped gold nanoparticles (Au NPs) by sputtering of Au over a liquid matrix (silicone oil). Au NPs prepared in silicone oil showed plasmon absorption; however, those prepared in the presence of 1-octadecanethiol did not show plasmon absorption but fluoresced in the near IR region.
  • Xu Lu, Yohei Ishida, Mai Thanh Nguyen, Tetsu Yonezawa
    JOURNAL OF MATERIALS CHEMISTRY C 3 32 8358 - 8363 2015年 [査読有り][通常論文]
     
    A nanoisland-structured SiOx (x <= 2)/CuxO (x <= 2) composite was prepared from a Cu-deposited Si wafer by electrochemical anodization in a hydrofluoric acid (HF) and ferric nitrate (Fe(NO3)3) electrolyte. The surface of the nanoisland comprised Cu, Cu oxides, Si nanoparticles and Si oxides. The distribution of elemental Cu on the surface was uniform. Cracks and native Cu-oxides in the deposited Cu layer are the two main factors for the formation of the nanoisland-structured surface. Different from the single red photoluminescence (PL) band emitted from the electrochemical anodized bare Si wafer, a dualvisible PL band with comparable intensities at red and blue ranges was observed. The red PL quenching did not occur in this Cu-ion-doped nanostructured Si due to the different distribution areas of Cu+ and the red PL centre. The red PL originates due to oxygen defects in the band gap of Si nanoparticles/Si oxides; the blue PL is the consequence of the band-to-band transitions between 3d(10) and 3d(9)4s(1) of Cu+ ions and the intra d -> d band transition of Cu2+ ions in the interstitial vacancies of Si oxides. Compared with the electrochemical anodized bare Si sample with a single PL band, the nanoisland-structured SiOx/CuxO composite emitting a dual-PL-band is more promising for fabricating white light emitters.
  • Tetsu Yonezawa, Hiroki Tsukamoto, Masaki Matsubara
    RSC ADVANCES 5 75 61290 - 61297 2015年 [査読有り][通常論文]
     
    A conductive paste was prepared with submicrometer-sized copper fine particles that were coated by a gelatin nanoskin. The average particle size was ca. 130 nm. After drying, an oxidation-reduction two-step sintering process was proposed for these submicrometer-sized copper fine particles to obtain low-resistivity layers at a very low temperature. The optimized conditions gave a low resistivity of 8.2 x 10(-6) Omega cm, even when the particles were covered by a common polymer. Our results suggest that the formation of the small copper oxide prominences on the surface of the copper fine particles could be reduced at low temperatures, forming connected submicrometer-sized metallic copper particles.
  • Yohei Ishida, Yasutomo Motokane, Tomoharu Tokunaga, Tetsu Yonezawa
    PHYSICAL CHEMISTRY CHEMICAL PHYSICS 17 38 24556 - 24559 2015年 [査読有り][通常論文]
     
    Here we report a novel method for modifying commercially available TiO2 nanoparticles by a microwave-induced plasma technique. After the plasma treatment TiO2 nanoparticles showed enhanced visible absorption due to the doped W atoms, and the photocatalytic methylene blue degradation above 440 nm was successfully improved.
  • Jeffrey E. Chen, Hong-Yuan Lian, Saikat Dutta, Saad M. Alshehri, Yusuke Yamauchi, Mai Thanh Nguyen, Tetsu Yonezawa, Kevin C. -W. Wu
    PHYSICAL CHEMISTRY CHEMICAL PHYSICS 17 41 27653 - 27657 2015年 [査読有り][通常論文]
     
    This study illustrates the directed self-assembly of mesoporous TiO2 with magnetic properties due to its colloidal crystal structure with Fe3O4. The Fe3O4 nanoparticles were synthesized using co-precipitation techniques to a size of 28.2 nm and a magnetic saturation of 66.9 emu g(-1). Meanwhile, mesoporous titania nanoparticles (MTNs) with a particle diameter of 373 nm, a specific surface area of 236.3 m(2) g(-1), and a pore size of 2.8 nm were prepared by controlling the rate of hydrolysis. Magnetic colloidal crystals (a diameter of 10.2 mm) were formed by the aggregation of Fe3O4 and MTNs caused by the interface phenomena during solvent evaporation in emulsion. Even the anatase octahedrite produced from the colloidal crystal after a hydrothermal reaction retained a magnetic saturation of 2.8 emu g(-1). This study also investigates the photodegradation activity of our synthesized material as a photocatalyst, while utilizing its capability for magnetic separation to prove its usefulness in catalyst recycling.
  • Yingqiong Yong, Tetsu Yonezawa, Masaki Matsubara, Hiroki Tsukamoto
    JOURNAL OF MATERIALS CHEMISTRY C 3 23 5890 - 5895 2015年 [査読有り][通常論文]
     
    To facilitate sintering of copper particles at low temperatures and achieve excellent electrical conductivity of copper films, reducing particle size is a common method. However, strong reducing agents which are usually used for reducing the size of particles limit their application. Here we report a novel approach to obtain highly conductive copper films. Firstly, copper fine particles were prepared by a one-pot reduction reaction utilizing D-isoascorbic acid as a mild reductant. Secondly, tight connection facilitating the sintering of particles was formed by generating convex surfaces, nanorods or nanoparticles during the oxidation procedure. The mechanism of the oxidative preheating process and its effects on the conductivity were clarified. High conductivity of copper films at low temperatures can be achieved due to the critical role of the oxidative preheating process.
  • Yohei Ishida, Ryota Nakabayashi, Masaki Matsubara, Tetsu Yonezawa
    NEW JOURNAL OF CHEMISTRY 39 6 4227 - 4230 2015年 [査読有り][通常論文]
     
    We herein propose a novel methodology to synthesize silver nano-particles with precisely controlled diameters in single nano-meter orders by sputtering into a liquid matrix (polyethylene glycol) containing mercaptans (11-mercaptoundecanoic acid) as an environmental friendly preparation without reductants.
  • Chaorui Xue, Takashi Narushima, Yohei Ishida, Tomoharu Tokunaga, Tetsu Yonezawa
    ACS applied materials & interfaces 6 22 19924 - 32 2014年11月26日 [査読有り][通常論文]
     
    By decreasing the water content in an NH4F and glycerol-water electrolyte, the transition from single-wall to double-wall TiO2 nanotube arrays was successfully achieved using an anodization method. The double-wall TiO2 nanotube structures exhibited better photocatalytic activity than the typical single-wall structures. After modification with platinum nanoparticles, the photocatalytic activity of both the single- and double-wall TiO2 nanotubes was improved further. In situ observations at the annealing temperature of the TiO2 nanotubes were performed using a transmission electron microscopy (TEM) system. A slower structural failure of the nanotubes was obtained with the introduction of oxygen gas into the TEM column compared with the structural changes observed under high-vacuum conditions without the introduction of oxygen gas. These behaviors suggest that oxygen injection is an important factor in stabilizing the TiO2 nanotubes during the in situ TEM annealing process. The high-magnification TEM images of the double-wall TiO2 nanotubes revealed that the sintering of the inner wall can draw a clear distinction between the inner and outer walls.
  • Shigeaki Abe, Atsushi Hyono, Tetsu Yonezawa
    JOURNAL OF SOLUTION CHEMISTRY 43 9-10 1645 - 1654 2014年10月 [査読有り][通常論文]
     
    In this study, we observed hydrophobic or hydrophilic carbon nanotubes (CNTs) by scanning electron microscopy (SEM); the samples were pretreated with room temperature ionic liquids (RTILs) to impart electrical conductivity to their surfaces. When the amount of RTIL on the sample surface and the affinity between the RTIL and sample surface were tuned, suitable electroconductive thin layers were formed on the sample surfaces. The presence of these layers allowed high-quality SEM images to be observed at the nano level. Suitable pretreatments for CNT were achieved using dilute RTIL/ethanol solutions. By optimizing these conditions, we acquired SEM images that were similar in quality to those of samples subjected to the conventional pretreatment of metal sputtering. The highest resolution of the SEM images was less than 30 nm.
  • Gang Qin, Akira Watanabe, Hiroki Tsukamoto, Tetsu Yonezawa
    JAPANESE JOURNAL OF APPLIED PHYSICS 53 9 印刷中  2014年09月 [査読有り][通常論文]
     
    Laser sintering method was applied for copper fine particle paste to generate electrically conductive copper film. The one-step sintering of the copper fine particle coating films at room temperature was carried out by scanning irradiation of a line-shaped laser beam under various atmospheric conditions. The laser sintering of the copper fine particle coating film under a hydrogen/argon (4/96) gas mixture flow gave a copper film with a low resistivity of 1.05 x 10(-5) Omega cm. The scanning electron microscope (SEM) image of the laser sintered film showed the necking among copper fine particles. The film laser-sintered in air was insulator which showed the Raman band assigned to Cu2O. The laser sintering of the copper fine particle coating film under argon gas flow gave also copper films with resistivities of the order of 10(-5) Omega cm, which depended on the flow rate of argon gas. On the other hand, the film sintered by conventional heat treatment at 300 degrees C under argon gas flow showed a high resistivity. The formation of a copper wiring with several micrometers resolution was achieved by laser direct writing using copper fine particle with the size larger than 100 nm. The advantages of the laser sintering in the preparation of a conductive film from copper fine particle paste were demonstrated. (C) 2014 The Japan Society of Applied Physics
  • Chaorui Xue, Takashi Narushima, Yohei Ishida, Tomoharu Tokunaga, Tetsu Yonezawa
    CHEMISTRY LETTERS 43 9 1514 - 1516 2014年09月 [査読有り][通常論文]
     
    Double-wall TiO2 nanotube arrays were prepared using an anodization method in a glycerol-containing electrolyte. In situ TEM observation of these samples at high temperature was carried out with and without oxygen injections. With oxygen injection, an improved thermal stability of the nanotubes at high temperature was observed. It may provide more detailed information about the calcination process of TiO2 nanotubes and assist its morphology and structure modulation.
  • Takashi Narushima, Ren Lu, Tetsu Yonezawa
    MATERIALS TRANSACTIONS 55 9 1474 - 1478 2014年09月 [査読有り][通常論文]
     
    Urchin structured nickel fine particles were successfully obtained by the hydrazine reduction of NiCl2 center dot 6H(2)O in ethanol. The particle structures, particularly the aspect ratios of the nickel nanoneedles on the surface, were controlled by changing the sequence of the addition of hydrazine and sodium hydroxide. These particles were not stabilized by organic compounds. In situ TEM observations at high temperatures revealed that the obtained fine particles began to deform at 350 degrees C.
  • Tetsu Yonezawa, Yoshiki Uchida, Yuki Abe
    JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY 14 7 5402 - 5407 2014年07月 [査読有り][通常論文]
     
    Copper (Cu) fine particles were prepared by room-temperature hydrazine reduction of Cu oxide microparticles. In this study, to reveal the formation process of metallic Cu homogeneous fine particles from cupric oxide (CuO) microparticles, hydrazine was added to a CuO slurry at room temperature. The morphological changes in the product during the reduction with and without ammonia were observed by using scanning electron microscopy (SEM). The SEM images indicated that not only did the Cu2+ dissolve in water by complex formation with ammonia or hydrazine, but also that Cu2+ ions on the surface of CuO microparticles were reduced by hydrazine to form metallic Cu fine particles. Tuning the sizes of Cu particles by the stabilizing reagent is also discussed.
  • ABE Shigeaki, HYONO Atsushi, KAWAI Koji, NAKAMURA Koichi, YAWAKA Yasutaka, YOSHIDA Yasuhiro, YONEZAWA Tetsu
    Nano Biomed 6 1 41 - 46 2014年06月30日 [査読無し][通常論文]
  • 兵野 篤, 米澤 徹, 阿部 薫明, 赤坂 司, 亘理 文夫
    北海道外科雑誌 59 1 91 - 92 北海道外科学会 2014年06月
  • A. Hyono, T. Yonezawa, K. Kawai, S. Abe, M. Fujihara, H. Azuma, S. Wakamoto
    Surface and Interface Analysis 46 6 425 - 428 2014年06月 [査読有り][通常論文]
     
    In this study, we succeed in visualizing a living' morphology of red blood cells (RBCs) by a rapid and simple scanning electron microscope (SEM) pretreatment using a hydrophilic room temperature ionic liquid (RTIL) with asymmetrical structure. The conventional pretreatment induces size shrinkage of the cells, and the diameter observed in an SEM (less than 6 mu m) was smaller than that in an optical microscope (8 mu m). Though RBCs are well-known to be easily deformed with the environmental conditions, the cells did not show the deformation when they were pretreated with our RTILs. Since the chemical structure of our RTIL resembles a choline', which is a typical bioactive material, and has biocompatibilities, they may make it avoid from the deformation of RBCs. In fact, only immersing RBCs, our novel RTIL can provide a clear SEM image without size shrinkage and deformation. Interestingly, the obtained SEM image shows 8 mu m in the diameter, almost same size as that in optical microscope. Therefore, this method is expected for novel SEM pretreatment for various biological samples observation as living' matter. Copyright (c) 2014 John Wiley & Sons, Ltd.
  • Hashimoto M, Toshima H, Yonezawa T, Kawai K, Narushima T, Kaga M, Endo K
    Journal of biomedical materials research. Part A 102 6 1838 - 1849 2014年06月 [査読有り][通常論文]
     
    Nanometals are currently receiving considerable attention for industrial and biomedical applications, but their potentially hazardous and toxic effects have not been extensively studied. This study evaluated the biological responses of novel water-dispersible gold (Au-NPs) and silver nanoparticles (Ag-NPs) stabilized by Au-C or Ag-C sigma-bonds in cultured macrophages (RAW264.7), via analysis of the cell viability, the integrity of the plasma membrane, and the inflammatory and morphological properties. The cultured RAW264.7 was exposed to metal-NPs at various concentrations. The Ag-NPs showed cytotoxicity at high NP concentrations, but the cytotoxic effects of the Au-NPs were smaller than those of the Ag-NPs. For the microscopic analysis, both types of particles were internalized into cells, the morphological changes in the cells which manifested as an expansion of the vesicles' volume, were smaller for the Au-NPs compared with the Ag-NPs. For the Ag-NPs, the endocytosis abilities of the macrophages might have induced harmful effects, because of the expansion of the cell vesicles. Although an inflammatory response was observed for both the Au- and Ag-NPs, the harmful effects of the Au-NPs were smaller than those of the Ag-NPs, with minor morphological changes observed even after internalization of the NPs into the cells. (c) 2013 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 102A: 1838-1849, 2014.
  • Shigeaki Abe, Atsushi Hyono, Koji Kawai, Tetsu Yonezawa
    JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY 14 3 2620 - 2623 2014年03月 [査読有り][通常論文]
     
    In this study, we investigated conductivity preparation for scanning electron microscope (SEM) observation that used novel asymmetrical choline-type room temperature ionic liquids (RTIL). By immersion in only an RTIL solution, clear SEM images of several types of biological samples were successfully observed. In addition, we could visualize protozoans using RTILs without any dilution. These results suggested that the asymmetrical choline-type RTILs used in this study are suitable for visualizing of biological samples by SEM. Treatment without the need for dilution can obviate the need for adjusting the RTIL concentration and provide for a rapid and easy conductivity treatment for insulating samples.
  • 成島隆, Ren Lu, 米澤徹
    日本金属学会誌 78 2 98 - 102 2014年02月 [査読有り][通常論文]
     
    Urchin structured nickel fine particles have been successfully obtained by the hydrazine reduction of NiC12.6H20 in ethanol. Changing the time of the addition of hydrazine and sodium hydroxide can control the particle structures, especially the aspect ratio of the Ni nanoneedles. These particles were not stabilized by organic compounds. In-situ TEM observation at high temperature revealed the deformation of the obtained fine particles began at 350 degrees C.
  • Masanori Hashimoto, Hirokazu Toshima, Tetsu Yonezawa, Koji Kawai, Masahiro Iijima, Kazuhiko Endo
    JOURNAL OF BIOMATERIALS AND TISSUE ENGINEERING 4 1 51 - 58 2014年01月 [査読有り][通常論文]
     
    Clinically relevant in vitro models are required to rapidly evaluate the cytotoxicity of nanoparticles. Recently, numerous three-dimensional cell culture systems (3D) have been manufactured to mimic the properties of tissue in vivo. Spheroid culture models play an invaluable role in understanding tumor biology and in performing the screening of drugs and biomaterials. Nanoparticles (NPs) are currently receiving considerable attention for industrial and biomedical applications, yet their hazardous and potential toxic effects have not been studied extensively. The purpose of this study was to evaluate the biological effects of polyvinylpyrrolidone-coated silver nanoparticles (AgNPs) in murine macrophages (RAW264.7 cells) cultured in traditional two-dimensional (2D) and novel 3D systems. Biological assays and a micromorphological analysis was performed. Microscopic imaging revealed that the particles were internalized into cells and receptor-mediated endocytosis occurred. However, cells exposed to AgNPs exhibited minor morphological changes compared with cells no exposed. AgNPs displayed greater cytotoxicity in the 2D culture versus in the 3D. Moreover, in the 3D culture the AgNP cytotoxicity decreased over time, which did not occur in the 2D culture.
  • Tomomi Takeshima, Ling Sun, Yanqing Wang, Yoshihisa Yamada, Norio Nishi, Tetsu Yonezawa, Bunshi Fugetsu
    POLYMER JOURNAL 46 1 36 - 41 2014年01月 [査読有り][通常論文]
     
    A wet-chemical approach using DNA extracted from salmon milt as a template to mass produce Ag nanoparticles was developed. Spherical Ag nanoparticles with a main diameter of less than 10 nm were obtained. The concentration of Ag nanoparticles in the as-produced colloidal suspension was as high as 5.3 x 10(-2) mol I-1. This simple and effective procedure should offer an alternative route to the mass production of Ag nanoparticles for practical applications.
  • 米澤 徹
    オレオサイエンス 14 1 11 - 15 公益社団法人 日本油化学会 2014年 

    金ナノ粒子は,その興味深い赤色から古くから着色顔料として用いられてきている。古い教会のステンドグラスはガラスの中で金がナノ粒子として存在しているもので,透明性が高く鮮やかな赤色を示している。金ナノ粒子の化学的研究の歴史も古く1857年に文献にあるFaradayの金コロイドの合成から始まる1,2)。金それ自体は古くから価値のあるものとして用いられてきており,バルクでは鮮やかな黄金色であるが,その色とコロイドにした時の色は全く異なっていた。そうした直接目に見える興味深い現象から始まって,金ナノ粒子は常に人々の興味の中心となってきた。特に,化学還元法で容易に得られることも研究がこれだけ進んだことの理由でもあろう。さらに,Brustらによるシングルナノレベルの金ナノ粒子の合成がNaBH4による還元によって可能となってきてから爆発的な量の研究が報告されるとともに,一段と金ナノ粒子研究のステージは上がった3)。最近の制御された金クラスターや新しい触媒など,金は人々の興味を掻き立てるのをやめない。この総説ではそうした金をベースとしたナノ粒子研究を俯瞰し,人々がひきつけられていく原因を探ってみたい。

  • Xu Lu, Tetsu Yonezawa
    2014 INTERNATIONAL TOPICAL MEETING ON MICROWAVE PHOTONICS (MWP) AND THE 2014 9TH ASIA-PACIFIC MICROWAVE PHOTONICS CONFERENCE (APMP) 164 - 165 2014年 [査読有り][通常論文]
     
    Terahertz (THz) emission from copper oxides/gold interface was detected on silicon substrates. The unexpected THz emission was attributed to Schokkty barrier at the interface. Degree of oxidation of the copper layer significantly affected the THz emission amplitude by the difference of electronic structures between cuprous oxide and cupric oxide.
  • Tetsu Yonezawa, Takashi Asano, Tatsuya Fujino, Hiroshi Nishihara
    CHEMICAL PHYSICS 419 17 - 22 2013年06月 [査読有り][通常論文]
     
    A mass measurement technique for detecting low-molecular-weight drugs with a cyclodextrin-supported organic matrix was investigated. By using cyclodextrin-supported 2,4,6-trihydroxyacetophenone (THAP), the matrix-related peaks of drugs were suppressed. The peaks of protonated molecules of the sample and THAP were mainly observed, and small fragments were detected in a few cases. Despite the Na+ and K+ peaks were observed in the spectrum, Na+ or K+ adduct sample molecules were undetected, owing to the sugar units of cyclodextrin. The advantages of MALDI-MS with cyclodextrin-supported matrices as an analytical tool for forensic samples are discussed. The suppression of alkali adducted molecules and desorption process are also discussed. (C) 2012 Elsevier B.V. All rights reserved.
  • Manabu Ohtomo, Yuya Tsuchida, Naoki Muraya, Takashi Yanase, Seiji Sakai, Tetsu Yonezawa, Taro Nagahama, Tetsuya Hasegawa, Toshihiro Shimada
    JOURNAL OF PHYSICAL CHEMISTRY C 117 22 11555 - 11561 2013年06月 [査読有り][通常論文]
     
    We report the in-plane orientation control of a high-mobility organic semiconductor: 2,7-diphenyl[1]benzothieno[3,2-b][1]benzothiophene (DPh-BTBT). As previously reported for the monolayer pentacene, it was revealed that bunched steps on the vicinal Si(111) with a bismuth termination break the surface 3-fold symmetry and reduce the multiple orientation of the DPh-BTBT grains into a quasi-single orientation. Interestingly, the critical step height necessary for the orientation control was higher than that of pentacene. We examined several mechanisms of orientation control and concluded that the facet nanostructure fabricated by step bunching works as an anisotropic template for the nucleation. We also show the wettability optimization of the bismuth-terminated silicon surface and show that the growth mode of DPh-BTBT is dependent on the surface nanostructure of Bi-Si.
  • T. Yonezawa, H. Tsukamoto, S, Hayashi Y, Myojin H. Kawasaki, R.Arakawa
    Analyst 138, 995-999 2013年05月 [査読無し][通常論文]
     
    2013/5/
  • Kazuki Maruya, Ryoji Yamauchi, Takashi Narushima, Seiji Miura, Tetsu Yonezawa
    JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY 13 4 2999 - 3003 2013年04月 [査読有り][通常論文]
     
    Many nanoporous metals have been applied for catalysis and show active properties. In this study, nanoporous platinum was successfully prepared from a Cu-Pt (50/50 w/w) alloy plate by electrochemical dealloying. In order to reveal their detailed structures in nanometer order, TEM observation of the surface area of the alloy plate was performed by using focused ion beam (FIB) for sample preparation. Peeling off the surface platinum nanoparticles could be also successfully preformed by using ultra sonification and their TEM observation revealed the units of the platinum nanoporous. structures.
  • Koji Kawai, Kotaro Kaneko, Hayato Kawakami, Takashi Narushima, Tetsu Yonezawa
    COLLOIDS AND SURFACES B-BIOINTERFACES 102 9 - 12 2013年02月 [査読有り][通常論文]
     
    Choline-type ionic liquids (CILs), which have a molecular structure resembling that of the vitamin-like active substance choline, have high water solubility, high osmotic pressure, and high cell membrane permeability. Their physical properties make them a very useful pretreatment agent for scanning electron microscopy (SEM) observation of hydrous samples because they can replace water in the samples, causing them to retain their shapes. SEM images of pollen without dissolution of cell membranes, damage, or deformation were obtained by a simple visualization process using CILs. We also identified an easy pretreatment protocol for SEM observation of hydrous microsamples that uses a membrane filter as a sample stage to ensure correct sample placement. Bacteria were successfully observed by using this protocol. (c) 2012 Elsevier B.V. All rights reserved.
  • Tetsu Yonezawa
    Kobunshi Ronbunshu 70 12 684 - 692 2013年 [査読有り][通常論文]
     
    The application of a bio-polymer, gelatin, as a material for copper fine particles, used for electronics parts, is described. Gelatin is well-known as a good stabilizer of metal nano- and fine particles. However, gelatin has not been frequently applied to such materials. According to the properties of surface coatings by gelatin, these copper fine particles are not easily oxidized. They could also be applied as the material for the inner electrodes of ceramic condensers. Such applications of bio-polymers can be one good example for reaching a sustainable society. ©2013, The Society of Polymer Science,.
  • Masanori Hashimoto, Hirokazu Toshima, Tetsu Yonezawa, Koji Kawai, Takashi Narushima, Masayuki Kaga, Kazuhiko Endo
    Dental Materials Journal 32 5 725 - 733 2013年 [査読有り][通常論文]
     
    With the continuous progress in nanomaterial development for biomedicine, the potential cytotoxicity of nanoparticles is drawing more attention and concern for clinical applications. The purpose of this study was to evaluate biological responses of new water-dispersible silver nanoparticles (Ag-NPs) stabilized by Ag-C σ-bonds in cultured murine macrophages (RAW264.7) and osteoblast-like cells (MC3T3-E1) using cell viability and morphological analyses. For RAW264.7, Ag-NPs seemed to induce cytotoxicity that was dependent on the Ag-NP concentration. However, no cytotoxic effects were observed in the MC3T3-E1 cell line. In microscopic analysis, Ag-NPs were taken up by MC3T3-E1 cells with only minor cell morphological changes, in contrast to RAW264.7 cells, in which particles aggregated in the cytoplasm and vesicles. The ability of endocytosis of macrophages may induce harmful effects due to expansion of cell vesicles compared to osteoblast-like cells with their lower uptake of Ag-NPs.
  • Shigeaki Abe, Atsushi Hyono, Katsutoshi Nakayama, Tomoya Takada, Tetsu Yonezawa
    JAPANESE JOURNAL OF APPLIED PHYSICS 52 1 2013年01月 [査読有り][通常論文]
     
    A novel pre-treatment method for scanning electron microscopy (SEM) observation using room temperature ionic liquids (ILs) was used for several carbon nano materials. After the ILs pre-treatment, the quality of the SEM images obtained was almost the same as that obtained with conventional platinum/palladium (Pt/Pd) spattering pre-treatment. The highest resolution in this study was under 30 nm. This result means that the pre-treatment with IL can form ultrathin layer on the sample surface at several molecules level. Therefore, the ILs pre-treatment is a simple and easy tool for SEM observation of nano materials on insulating substrates. (C) 2013 The Japan Society of Applied Physics
  • Ko Nakagawa, Takashi Narushima, Satoshi Udagawa, Tetsu Yonezawa
    15TH INTERNATIONAL CONFERENCE ON THIN FILMS (ICTF-15) 417 2013年 [査読有り][通常論文]
     
    As a new method for nanoparticles preparation, magnetron sputtering of metal atoms and clusters into organic liquids has been intensively used recently. In this study, metallic copper nanoparticles dispersed in pentaerythritol ethoxylate were prepared by this process. Their size control was achieved by controlling the sputtering current. Specific absorption at ca. 580 nm was detected by UV-Vis measurement which is attributed to the specific plasmon absorption of metallic copper. TEM observation also revealed the formation of metallic nanoparticles.
  • Chaorui Xue, Takashi Narushima, Tetsu Yonezawa
    JOURNAL OF INORGANIC AND ORGANOMETALLIC POLYMERS AND MATERIALS 23 1 239 - 242 2013年01月 [査読有り][通常論文]
     
    Arrays of TiOF2 nanotubes of the diameters ca. 100 nm were successfully prepared by the anodization of a titanium foil in an aqueous electrolyte containing fluoride anion. Scanning electron microscope observation of the surface of TiOF2 arrays was performed, but the surface was charged, so no clear image was obtained. Meanwhile, when the specimen was pretreated with an ionic liquid, a clear surface image could be observed, and the degree of clarity corresponded to its ion conductivity. This result indicates that the advantage of using an ionic liquid for visualizing nanomaterials.
  • Shigeaki Abe, Yusaku Hamba, Nobuki Iwadera, Tsukasa Akasaka, Shuichi Yamagata, Yasutaka Yawaka, Junichiro Iida, Motohiro Uo, Tetsu Yonezawa, Fumio Watari
    BIOCERAMICS 24 529-530 625 - + 2013年 [査読有り][通常論文]
     
    We succeeded in determination the biodistribution of several nano-sized particles administered to mice through the tail vein. After administration, these particles were observed in the lung, liver and spleen. The distribution behaviors depend upon not only chemical species but also the particles size. To estimate their cytocompatibility, these particles were exposed to osteoblastic cell at several concentrations. When the concentration reached at 10 ppm, their viability remained at 80% or more even nano-sized particle contained rare earth element. Only CuO particles indicated the viability decrease. The effect depended on the particle size. These results suggested that the chemical species played a dominant key in the biodistribution and biocompatibility of nanoparticles compared with the size-effect.
  • Hong-Tao Sun, Yoshio Sakka, Naoto Shirahata, Minoru Fujii, Tetsu Yonezawa
    Journal of Materials Chemistry 22 47 24792 - 24797 2012年12月21日 [査読有り][通常論文]
     
    We report the observation of near-infrared photoluminescence from Te 4(Ga2Cl7)2 and Te 4(Al2Cl7)2 molecular crystals containing Te42+ polycations. The experimental and theoretical results clearly revealed that the Te42+ polycation is a smart near-infrared emitter with characteristic emission peaks at 1252 and 1258 nm for Te4(Ga2Cl7)2 and Te4(Al2Cl7)2 crystals, respectively, resulting from the intrinsic electronic transitions of Te 42+. Furthermore, it was also found that the emissions strongly depend on the excitation wavelengths for both Te4(Ga 2Cl7)2 and Te4(Al2Cl 7)2 samples, most possibly due to the co-existence of other Te-related optically active centers. This research not only enriches the species of luminescent charged p-block element polyhedra and deepens the understanding of Te-related photophysical behaviors, but also may stimulate efforts for designing novel material systems using such active centers. It is also greatly expected that these sub-nanometer optically active species could exist in other systems such as glasses, polymers, and bulk optical crystals, and the stabilization of these centers in widely used hosts will pave the way for their practical applications. © The Royal Society of Chemistry 2012.
  • T. Tokunaga, T. Narushima, T. Yonezawa, T. Sudo, S. Okubo, S. Komatsubara, K. Sasaki, Takahisa Yamamoto
    JOURNAL OF MICROSCOPY 248 3 228 - 233 2012年12月 [査読有り][通常論文]
     
    An electron beam (EB) generated by a scanning electron microscope (SEM) was used to irradiate two samples having different thermal conductivities, and the resulting temperatures of the EB-irradiated areas as well as the temperature distributions within the samples were then measured using a thermal camera. These measurements showed overall increases in sample temperatures, as well as revealed temperature rises at the EB-irradiated areas that had little difference with one of the theoretical predictions. Differences between the actual and the predicted temperature measurements were analysed in terms of the accuracy with which parameters could be estimated. The temperature distributions of the samples were measured and, On the basis of the results, it was hypothesized that the temperature differential over an irradiated sample will be inversely correlated with its thermal conductivity.
  • K. Kawai, T. Narushima, K. Kaneko, H. Kawakami, M. Matsumoto, A. Hyono, H. Nishihara, T. Yonezawa
    Appl. Surf. Sci. 262 76 - 80 2012年12月 [査読有り][通常論文]
     
    The synthesis of 4-diazoniumcarboxylbenzene fluoroborate, a new water-soluble stabilizer for metal nanoparticles (NPs), is described. A stable dispersion of Ag NPs in water was successfully produced by a simultaneous aqueous reduction of this diazonium salt and silver nitrate by NaBH4. UV-vis spectra, TEM images, XRD patterns, and XPS spectra of the obtained Ag NPs revealed that they were stabilized by Ag-C sigma-bonds. These NPs showed excellent antimicrobial properties against Staphylococcus aureus. (c) 2012 Elsevier B.V. All rights reserved.
  • Sawako Miyamoto, Tetsuya Hasegawa, Hiroyuki Takahashi, Tetsu Yonezawa, Hajime Kiyono, Takashi Yanase, Taro Nagahama, Toshihiro Shimada
    BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN 85 12 1287 - 1292 2012年12月 [査読有り][通常論文]
     
    We report a method to produce vapor species from ZnO powder for the fabrication of ZnO nanorods. Mixing ethanol vapor with the inert carrier gas substantially lowered the gasification temperature of ZnO. c Axis-aligned ZnO nanorods were obtained by dispersing gold nanoparticles on Si substrates. The growth was identified as a vapor-solid (VS) mechanism. Choice of the substrate materials and their surface morphology were both critically important to control the shapes and orientation of grown ZnO.
  • Takashi Narushima, Hiroki Tsukamoto, Tetsu Yonezawa
    AIP ADVANCES 2 4 2012年12月 [査読有り][通常論文]
     
    Metallic copper fine particles were prepared using CuO slurry by hydrazine reduction in the presence of gelatin. To observe a behavior of these particles at high temperature, in situ heating TEM observations were carried out. Oxygen gas was introduced and the pressure of the TEM column was kept at 10(-3) Pa, corresponding the pressure around the sample at 10(-1) Pa. The gelatin, which acts as a protective nanoskin on the particle surface was gradually decomposed. Around approximately 140 degrees C, it was observed that Cu2O dots formed on the surface of the copper particle. This result is well consistent with the behavior of the TG-DTA curve of the copper fine particles under ambient conditions, and provides key information of oxidative behavior of copper fine particles. Copyright 2012 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported license.[http://dx.doi.org/10.1063/1.4759498]
  • Hiroyuki Takahashi, Naoto Shirahata, Takashi Narushima, Tetsu Yonezawa
    APPLIED SURFACE SCIENCE 262 129 - 133 2012年12月 [査読有り][通常論文]
     
    Single crystalline sapphire is an atomically flat substrate with a high transparency in a wide wavelength region. However, its surface is chemically stable so that the modification by a self-assembled monolayer is somewhat difficult. We have used a H2O2 treatment at 70 degrees C to activate the surface and modified with a silan coupling reagent. The modification of the surface is discussed with the water contact angle. Immobilization of citrate-stabilized anionic gold nanoparticles on a cationically modified sapphire surface was carried out. (c) 2012 Elsevier B.V. All rights reserved.
  • Hong-Tao Sun, Tetsu Yonezawa, Miriam M. Gillett-Kunnath, Yoshio Sakka, Naoto Shirahata, Sa Chu Rong Gui, Minoru Fujii, Slavi C. Sevov
    Journal of Materials Chemistry 22 38 20175 - 20178 2012年10月14日 [査読有り][通常論文]
     
    For the first time, we report that a single crystal of (K-crypt) 2Bi2 containing [Bi2]2- displays ultra-broad near-infrared photoluminescence (PL) peaking at around 1190 nm and having a full width at the half maximum of 212 nm, stemming from the inherent electronic transitions of [Bi2]2-. The results not only add to the number of charged Bi species with luminescence, but also deepen the understanding of Bi-related near-infrared emission behavior and lead to the reconsideration of the fundamentally important issue of Bi-related PL mechanisms in some material systems such as bulk glasses, fibers, and conventional optical crystals. © 2012 The Royal Society of Chemistry.
  • Takashi Narushima, Atsushi Hyono, Naoki Nishida, Tetsu Yonezawa
    JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY 12 10 7764 - 7776 2012年10月 [査読有り][通常論文]
     
    Copper/gelatin composite particles with controlled sizes were prepared at room temperature from cupric sulfate pentahydrate in the presence of gelatin as a protective reagent by using hydrazine monohydrate as a reducing agent. The formed particles with the size between 190-940 nm were secondary aggregated particles which were composed of smaller nanosized particles ("particle-in-particle"), the presence of which was established by XRD patterns and a cross-sectional TEM image. The sintering behavior of these copper/gelatin composite particles was demonstrated by in-situ heating TEM under a high vacuum (similar to 10(-5) Pa) and separately with the oxygen partial pressure controlled at the 10(-4) Pa level. It was established that the particles began to sinter at about 330 degrees C with the oxygen and that they sublimate above 450 degrees C both in the vacuum and oxygen conditions. This result shows that the introduction of an adequate amount of oxygen was effective to remove the gelatin surrounding the particles. It can also be concluded that the sintering of the copper/gelatin composite particles occurred even in the absence of a reducing agent such as hydrogen gas.
  • Hong Tao Sun, Beibei Xu, Tetsu Yonezawa, Yoshio Sakka, Naoto Shirahata, Minoru Fujii, Jianrong Qiu, Hong Gao
    Dalton Transactions 41 36 11055 - 11061 2012年09月28日 [査読有り][通常論文]
     
    Bi 5(GaCl 4) 3 sample has been synthesized through the oxidation of Bi metal by gallium chloride (GaCl 3) salt. Powder X-ray diffraction as well as micro-Raman scattering results revealed that, in addition to crystalline Bi 5(GaCl 4) 3 in the product, an amorphous phase containing [GaCl 4] - and [Ga 2Cl 7] - units also exists. The thorough comparison of steady-state and time-resolved photoluminescent behaviors between the Bi 5(GaCl 4) 3 product and Bi 5(AlCl 4) 3 crystal leads us to conclude that Bi 53+ is the dominant emitter in the product, which gives rise to the ultrabroad emission ranging from 1 to 2.7 μm. Detailed quantum chemistry calculation helps us assign the observed excitations to some electronic transitions of the Bi 53+ polycation, especially at shorter wavelengths. It is believed that our work shown here is not only helpful to solve the confusions on the luminescent origin of bismuth in other material systems, but also serves to develop novel broadband tunable laser materials. © 2012 The Royal Society of Chemistry.
  • 米澤徹
    化学 67 8 64-65  2012年08月 [査読無し][招待有り]
  • Tomoharu Tokunaga, Takashi Narushima, Tetsu Yonezawa, Takayuki Sudo, Shuichi Okubo, Shigeyuki Komatsubara, Katsuhiro Sasaki, Takahisa Yamamoto
    JOURNAL OF ELECTRON MICROSCOPY 61 4 223 - 227 2012年08月 [査読有り][通常論文]
     
    The temperature distribution on a centre-holed thin foil of molybdenum, used as a sample and heated using a sample-heating holder for electron microscopy, was measured using an infrared thermal camera. The temperature on the heated foil area located near the heating stage of the heating holder is almost equal to the temperature on the heating stage. However, during the measurement of the temperature at the edge of the hole of the foil located farthest from the heating stage, a drop in temperature should be taken into consideration; however, so far, no method has been developed to locally measure the temperature distribution on the heated sample. In this study, a method for the accurate measurement of temperature distribution on heated samples for electron microscopy is discussed.
  • 川崎英也, 米澤徹, 荒川隆一
    ケミカルエンジニヤリング 57 7 538-542 - 542 化学工業社 2012年07月 [査読無し][招待有り]
  • Tetsu Yonezawa, Shigeo Arai, Hironori Takeuchi, Takeo Kamino, Kotaro Kuroda
    CHEMICAL PHYSICS LETTERS 537 65 - 68 2012年06月 [査読有り][通常論文]
     
    Naked silver nanoparticles supported on SiO2 were prepared in a TEM chamber in order to be directly observed in situ their structural changes at high temperature. Without exposing the samples in air, this method give a possibility to understand the behavior of metal itself without any contamination or oxidation. Melting temperature depression according to the particle size could be observed. (C) 2012 Elsevier B.V. All rights reserved.
  • 成島 隆, 吉岡 隆幸, 宮崎 英機, 菅 育正, 佐藤 進, 米澤 徹
    日本金属学会誌 76 4 229 - 233 日本金属学会 2012年04月 [査読有り][通常論文]
     
    Non-oxidized metallic copper particles were prepared by plasma irradiation into aqueous solution of cupric sulfate in the presence of gelatin as a protective agent using home-made microwave induced plasma equipment. Then, two different steric structures of ascorbic acid, L-ascorbic acid and isoascorbic acid, were added as reducing auxiliaries. In the case of isoascorbic acid addition, metallic copper particles were obtained by plasma irradiation within about 5 minute. This result suggests that the reduction of copper ion from Cu2+ to metallic Cu can be succeeded by hydrogen radical generated by plasma in water combination with isoascorbic acid, and without toxic chemical agent such as hydrazine. Additionally, the diameter of copper particles can be controlled by the mount of CuSO4 center dot 5H(2)O and gelatin. These results were indicated that the plasma in liquid process has possibilities for high-speed and low environmental load process to prepare metallic copper particles.
  • Shigeaki Abe, Nobuki Iwadera, Takashi Narushima, Yoshiki Uchida, Motohiro Uo, Tsukasa Akasaka, Yasutaka Yawaka, Fumio Watari, Tetsu Yonezawa
    e-Journal of Surface Science and Nanotechnology 10 33 - 37 2012年03月17日 [査読有り][通常論文]
     
    In this study, we investigated the biocompatibility of gelatin-coated copper nanoparticles. To estimate their cytotoxicity, the coated copper nanoparticles were exposed to osteoblastic cells. The cell proliferation remained above 80% even when the particles concentration increased. When uncoated copper oxide nanoparticles were exposed to the cells, the proliferation ratio rapidly decreased with the concentration reaching 20% under the same conditions. To determine their biodistribution, the nanoparticles were administered to mice through their tail veins. The particles were subsequently found in some organs using an energy-dispersed X-ray spectrometer and inductively coupled plasma-atomic emission spectroscopy. The polymer-coated nanoparticles were observed in the lung, liver and spleen. They were also detected in the urine at higher concentrations than the copper oxide nanoparticles. Thus, the polymer coating is expected to improve biocompatibility by virtue of the excellent cytocompatibility and acceleration of the excretion process. © 2012 The Surface Science Society of Japan.
  • Takashi Narushima, Takuya Makino, Tomoharu Tokunaga, Tetsu Yonezawa
    JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY 12 3 2612 - 2616 2012年03月 [査読有り][通常論文]
     
    We have successfully prepared Kompeito-like platinum particles by hydrogen reduction of Pt4+ in the presence of sodium polyacrylate. We performed in situ TEM observation of these platinum particles at high temperatures. At 300 degrees C, a thin carbon layer due to polyacrylate formed on the particle surface. The detailed structure of the particles did not change with temperatures up to 700 degrees C. Continuous heating up to 800 degrees C blunted the particles' edges and also sintering of the particles was observed. This result strongly indicates that the shape change and sintering of platinum particles are exclusively controlled by the carbon layer, which is generated from a surface stabilizer polymer.
  • Shosei Kubota, Tetsu Yonezawa, Taro Nagahama, Toshihiro Shimada
    CHEMISTRY LETTERS 41 2 187 - 188 2012年02月 [査読有り][通常論文]
     
    We found that graphite surfaces can be etched by electrochemical reduction in sulfuric acid. Terraces with straight edges crossing with 60 degrees-multiple angles were found on surfaces by AFM observation. It suggests that crystallographic edges can be formed at room temperature in a controlled manner. Layer-by-layer etching of graphene sheets was possible by tuning the etching condition.
  • Yuto Isomura, Takashi Narushima, Hideya Kawasaki, Tetsu Yonezawa, Yasushi Obora
    CHEMICAL COMMUNICATIONS 48 31 3784 - 3786 2012年 [査読有り][通常論文]
     
    Surfactant-free, single-nano-sized copper nanoparticles (Cu NPs) (size: about 2 nm) were prepared by the DMF reduction method. The Cu NPs showed high catalytic activity (with a turnover number (TON) of up to 2.2 X 10(4)) in Ullmann-type cross-coupling of aryl halides with phenols under ligand-free conditions.
  • Kiyonobu Ida, Masanori Tomonari, Yasuyuki Sugiyama, Yuki Chujyo, Tomoharu Tokunaga, Tetsu Yonezawa, Kotaro Kuroda, Katsuhiro Sasaki
    THIN SOLID FILMS 520 7 2789 - 2793 2012年01月 [査読有り][通常論文]
     
    Cu nanoparticle ink was prepared from Cu nanoparticles that were coated with a gelatin layer at an average diameter of 46 nm. The Cu nanoparticle ink was applied on the polyimide substrate. Conductive films were fabricated using the Cu nanoparticle ink with a two-step annealing process consisting of oxidative pre-heating at 200 degrees C under 10 ppm O-2-N-2 mixed gas flow and reductive calcination at 250 degrees C under 3 vol.% H-2-N-2 mixed gas flow showed a low resistivity of 5 mu Omega cm. The hydrolysis of the remaining gelatin layer by H2O vapor, which was formed during the reduction of the Cu oxide by 3 vol.% H-2-N-2 mixed gas, was suggested. The results suggest the possibility of the removal of the gelatin layer without oxidative pre-heating and simultaneous sintering of Cu nanoparticles in reductive calcination. (C) 2011 Elsevier B.V. All rights reserved.
  • Shigeaki Abe, Akiko Sakaki, Takashi Narushima, Yoshiki Uchida, Tsukasa Akasaka, Motohiro Uo, Tetsu Yonezawa, Fumio Watari
    Key Engineering Materials 493-494 752 - 756 2012年 [査読無し][通常論文]
     
    In this study, we succeeded in preparation and characterization of two types of biocompatible polymer-coated inorganic nanoparticles (cupper and silicone oxide). As a biocompatible polymer, gelatin and poly(lactic acid) were used. For determination of their biodistribution, the obtained particles were administered to mice through the tail vein. After administration, the particles in some organs were determined with energy-dispersed X-ray spectrometer. The cupper nanoparticles were observed in the lung and kidney, while the silica particles were in the lung, liver and spleen. The distribution behaviors were quite different from non-polymer coated nanoparticles. © (2012) Trans Tech Publications.
  • Hong-Tao Sun, Yoshio Sakka, Naoto Shirahata, Hong Gao, Tetsu Yonezawa
    JOURNAL OF MATERIALS CHEMISTRY 22 25 12837 - 12841 2012年 [査読有り][通常論文]
     
    The photophysical properties of Bi-8(2+) and Bi-5(3+) polycations stabilized by [AlCl4](-) have been studied experimentally and theoretically. The obtained product was thoroughly evaluated by powder X-ray diffraction and photoluminescence spectroscopy, making it clear that both Bi-8(2+) and Bi-5(3+) contribute to the observed broad near-infrared emission. Furthermore, it was revealed that the Bi-8(2+) polycation shows emission peaking at ca. 1180 nm, while Bi-5(3+) shows the longer-wavelength emission. The following quantum chemistry calculation on the Bi-8(2+) polycation helps us attribute some of the observed excitation bands in the visible spectral range to specific electronic transitions of bismuth polycations. It is believed that systematic investigation of structural and luminescent properties as well as detailed quantum chemistry calculation of molecular crystals containing such kinds of bismuth units allows us to obtain a clearer picture of bismuth-related photophysical behaviors, which not only serve to solve the confusions on the luminescence origin of bismuth in other material systems such as bulk glasses, glass fibers and conventional crystals, but also is helpful to develop novel applicable broadband tunable laser mediums.
  • Susumu Sato, Kunihiko Mori, Osamu Ariyada, Hyono Atsushi, Tetsu Yonezawa
    SURFACE & COATINGS TECHNOLOGY 206 5 955 - 958 2011年11月 [査読有り][通常論文]
     
    We have conducted a basic study of microwave plasma in liquid at atmospheric pressure. Plasma could be successfully induced by radiated microwave from pointed and ring tungsten electrodes. The tungsten electrode showed a long lifetime of 70 h. Melting and chemical etching of the electrode's top limited the lifetime. Silver cations from silver nitrates could be rapidly and completely reduced to generate metallic silver nanoparticles using this plasma source without any addition of reducing chemical reagents. Optimization of electric conductivity of the reaction solution was not needed. When the material of the electrode was changed to platinum from tungsten, platinum nanoparticles were produced by vaporization into pure water. Both these preparation processes can be expected to produce lower contamination than chemical synthesis. (C) 2011 Elsevier B.V. All rights reserved.
  • Masafumi Takesue, Takuya Tomura, Mitsuru Yamada, Katsuhiko Hata, Shigeo Kuwamoto, Tetsu Yonezawa
    JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 133 36 14164 - 14167 2011年09月 [査読有り][通常論文]
     
    The time dependence of small-angle X-ray scattering (SAXS) curves for silver nanoparticle formation was followed in situ at a time resolution of 0.18 ms, which is 3 orders of magnitude higher than that used in previous reports (ca. 100 ms). The starting materials were silver nitrate solutions that were reacted with reducing solutions containing trisodium citrate. The SAXS analyses showed that silver nanoparticles were formed in three distinct periods from a peak diameter of ca. 0.7 nm (corresponding to the size of a Ago cluster) during the nucleation and the early growth period. The Ago clusters are most likely elementary clusters that agglomerate to form silver nanoparticles.
  • Koji Kawai, Kotaro Kaneko, Hayato Kawakami, Tetsu Yonezawa
    LANGMUIR 27 16 9671 - 9675 2011年08月 [査読有り][通常論文]
     
    This letter proposes the use of choline-like hydrophilic ionic liquids (ILs) to visualize hydrous samples (e.g., seaweed and other biological or food samples) for scanning electron microscopy (SEM) observation. Some of the water in the samples was successfully replaced with these ILs, which penetrated the cell membranes. The treated samples did not contract much even after drying. The ILs' ionic conductivity decreased the charging of sample surfaces, and good SEM images were obtained.
  • Koji Kawai, Kotaro Kaneko, Tetsu Yonezawa
    LANGMUIR 27 12 7353 - 7356 2011年06月 [査読有り][通常論文]
     
    This Letter examines the relationship between the structures of ionic liquids and their water-solubility or osmotic pressure with a number of synthesized quaternary ammonium type ionic liquids and organic salts containing a hydroxyl group as hydrophilic substituted groups on ammonium group cations, and bromide or methylsulfonate as anions. The study found a linear relation between the amount and osmotic pressure of the water-soluble ionic liquids synthesized here, strongly indicating that these water-soluble ionic liquids are perfectly ionized in water like inorganic salts with small diameter ions.
  • Kazuki Uchida, Yoshinori Yamanoi, Tetsu Yonezawa, Hiroshi Nishihara
    JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 133 24 9239 - 9241 2011年06月 [査読有り][通常論文]
     
    The chemical functionalization of hydrogen-terminated silicon(111) surfaces with photochromic diarylethene using an ethylene anchoring group was achieved. Conductive atomic force microscopy measurements showed the current changes on modified silicon electrodes caused by light-induced isomerization of the diarylethene between an open form and a closed form.
  • Shigeaki Abe, Kosuke Ishikawa, Atsushi Hyono, Hirohisa Kobayashi, Takayuki Kiba, Tsukasa Akasaka, Motohiro Uo, Yasutaka Yawaka, Shin-Ichiro Sato, Tetsu Yonezawa, Fumio Watari
    e-Journal of Surface Science and Nanotechnology 9 80 - 84 2011年03月05日 [査読有り][通常論文]
     
    Development of scaffolds consisting of micro-/nano-sized materials have attracted a great deal of attention for their potential use in tissue engineering tools. We prepared a cell culture scaffold of carbon nanotubes, which is a typical bio-inert nanomaterial, and then investigated the surface morphology and properties. A three-dimensional nano-level network structure was observed using a scanning electron microscope and an atomic force microscope. The scaffold also exhibited excellent protein absorption. In order to apply the obtained scaffold to the cultivation of osteoblast cells, the cytocompatibility was comparable to that of a conventional cell culture dish. © 2011 The Surface Science Society of Japan.
  • 米澤 徹, 兵野 篤
    日本結晶成長学会誌 37 4 291 - 296 日本結晶成長学会 2011年01月 [査読無し][招待有り]
     
    金属ナノ粒子は,そのサイズに依存する融点の低下や局在表面プラズモン共鳴といった性質を有する.さらに,その加工しやすさから,微細配線や金属薄膜の材料など電子部材としての応用が進められている.ナノ粒子内の結晶構造の変化を観察するために,環境制御型のTEMその場観察が有用であり,いくつかの研究が行われている.これらの観察により,ナノ粒子の融点低下やアモルファスからの結晶形成過程,さらに焼結挙動などのその場観察が報告されている.
  • Yuichi Shishino, Tetsu Yonezawa, Satoshi Udagawa, Kaname Hase, Hiroshi Nishihara
    ANGEWANDTE CHEMIE-INTERNATIONAL EDITION 50 3 703 - 705 2011年 [査読有り][通常論文]
  • Hideya Kawasaki, Yuka Kosaka, Yuki Myoujin, Takashi Narushima, Tetsu Yonezawa, Ryuichi Arakawa
    CHEMICAL COMMUNICATIONS 47 27 7740 - 7742 2011年 [査読有り][通常論文]
     
    We report the synthesis of 2 nm copper nanocrystals (Cu NCs) via a microwave-assisted polyol method without using additional protective and reducing agents. The Cu NCs are oxidation resistant and exhibit photoluminescence and highly stable properties in a colloidal dispersion.
  • Tetsu Yonezawa, Hiroki Tsukamoto, Takashi Narushima
    Proceedings of the IEEE Conference on Nanotechnology 1588 - 1591 2011年 [査読有り][通常論文]
     
    Metallic copper nano and fine particles have been successfully prepared by a wet process using a biopolymer as an anti-oxidation reagent. Copper oxide (CuO) and copper sulfate (CuSO 4) were the metal sauces used in this study. Hydrazine was used as the reducing reagent in order to obtain copper metal atoms. Uniform sized metallic copper particles were obtained by this process. Detailed TEM observation revealed that the obtained copper nanoparticles were covered by a continuous thin gelatin layer with the thickness of a couple of nanometers, which prevented oxidation of the obtained metallic copper particles for months. On submicron-sized fine particles, the gelatin layers were very condensed and showed a smooth surface. These organic layers show a sharp gray amorphous contrast in the TEM image. On the other hand, room temperature reduction of Cu 2+ surprisingly gave very small copper nanoparticles with the size in a single digit nm level, but they form uniform-sized submicron sized secondary aggregations. The obtained particles can be kept non-oxidized for months in an ambient condition (under air). These particles could be successfully dispersed into an organic media to form stable electroconductive pastes, by using several physical dispersing steps and an organic coating polymer. Monodispersed particle pastes were obtained to form a continuous particle thin layer. These particles and pastes can be applied to printable electronics in the near future. © 2011 IEEE.
  • Tsuji, Takeshi, Mizuki, Takeshi, Yasutomo, Masato, Tsuji, Masaharu, Kawasaki, Hideya, Yonezawa, Tetsu, Mafuné, Fumitaka
    Applied Surface Science 257 2046 - 2050 2011年 [査読有り][通常論文]
  • Shigeaki Abe, Nobuki Iwadera, Mami Mutoh, Chika Koyama, Mitsue Esaki, Tsukasa Akasaka, Motohiro Uo, Manabu Morita, Yoshinori Kuboki, Koichi Haneda, Yasutaka Yawaka, Fumio Uchida, Tetsu Yonezawa, Fumio Watari
    Bioceramics Development and Applications 1 D110134  2011年01月 [査読有り][通常論文]
  • 宇田川 智史, 米澤 徹
    電気学会誌 = The journal of the Institute of Electrical Engineers of Japan 130 12 808 - 811 The Institute of Electrical Engineers of Japan 2010年12月01日 
    本記事に「抄録」はありません。
  • Tetsu Yonezawa, Atsushi Hyono, Naoki Nishida
    JOURNAL OF MATERIALS SCIENCE 45 23 6433 - 6439 2010年12月 [査読有り][通常論文]
     
    Copper fine particles were successfully prepared by hydrazine reduction of cupric oxide (CuO). Changes in the temperature and pH values during the redox reaction of cupric oxide and hydrazine monohydrate were observed in detail. These changes reflected the reaction steps leading to the formation of metallic copper particles. The reduction of cupric oxide proceeded mainly during the part of the process where the pH value changes little or only very slowly. This phenomenon strongly indicates that the reaction and the particle structures can be established by control of the pH during the formation.
  • マイクロ・ナノ粒子の体内循環挙動の追跡と生体への影響
    岩寺 信喜, 石川 紘佑, 伊藤 佐智子, 阿部 薫明, 赤坂 司, 宇尾 基弘, 八若 保孝, 亘理 文夫, 高田 知哉, 米澤 徹
    日本バイオマテリアル学会大会予稿集 32回 323 - 323 日本バイオマテリアル学会 2010年11月
  • 菊地 竜也, 島口 寛子, 上田 幹人, 坂入 正敏, 米澤 徹, 高橋 英明
    表面技術 = The journal of the Surface Finishing Society of Japan 61 9 652 - 657 表面技術協会 2010年09月 [査読有り][通常論文]
     
    A printing plate for gravure printing consisting of five layers of aluminum alloy / anodic oxide film / nickel / polypyrrole / copper was fabricated by anodizing, electro-less plating, electroplating, and electro-polymerization. Nickel layers were first deposited on anodic oxide film-covered aluminum alloy by electro-less plating and electroplating. The polypyrrole layer was then deposited on the nickel layer by anodic polarization in a pyrrole monomer solution. Many copper fine particles were deposited on the polypyrrole-deposited specimen at the initial stage of electroplating in the CuSO...
  • 米澤 徹
    化学と工業 = Chemistry and chemical industry 63 9 752 - 752 2010年09月01日 [査読無し][通常論文]
  • 成島 隆, 米澤 徹
    高圧ガス 47 8 632 - 635 高圧ガス保安協会 2010年08月 [査読無し][招待有り]
  • 兵野 篤, 米澤 徹
    セラミックス 45 8 609 - 612 日本セラミックス協会 2010年08月 [査読無し][招待有り]
  • Tatsuya Kikuchi, Yasuhito Hara, Masatoshi Sakairi, Tetsu Yonezawa, Akira Yamauchi, Hideaki Takahashi
    CORROSION SCIENCE 52 8 2525 - 2534 2010年08月 [査読有り][通常論文]
     
    Nine kinds of Al alloys were anodized to form porous anodic oxide films, and then anodized specimens were immersed in 2-(2-(2-methoxyethoxy)ethoxy)ethanol (MEEE) and 2-(2-(2-butoxyethoxy)ethoxy)ethanol (BEEE) at 415 K. Al-1.0%Sn-1.0%Bi alloy was corroded severely in both BEEE and MEEE, whereas other eight alloys showed no corrosion. The corrosion proceeded under the anodic oxide films through cracks formed in the film. Cathodic polarization in Cu electroplating solution after corrosion suggested that the crack formation during immersion in hot MEEE is due to thermal expansion of the substrate and Sn and Bi containing particles included in the anodic oxide film. (C) 2010 Elsevier Ltd. All rights reserved.
  • Tetsu Yonezawa, Atsushi Hyono, Susumu Sato, Osamu Ariyada
    CHEMISTRY LETTERS 39 7 783 - 785 2010年07月 [査読有り][通常論文]
     
    As a rapid and easy liquid process for preparation of ZnO nanoparticles, we propose here a microwave-induced plasma in water. Generation of plasma in liquid has been achieved at atmospheric pressure without external gas bubbling. After only several minutes of microwave irradiation, about 0.3 g of ZnO nanoparticles was obtained from an aqueous solution of zinc(II) acetate under alkaline conditions.
  • マウスに投与したマイクロ・ナノ無機粒子の生体内分布の追跡と細胞への影響
    岩寺 信喜, 阿部 薫明, 石川 紘佑, 赤坂 司, 宇尾 基弘, 大口 郁子, 八若 保孝, 亘理 文夫, 米澤 徹
    北海道外科雑誌 55 1 84 - 85 北海道外科学会 2010年06月
  • Shigeaki Abe, Ikuhiro Kida, Mitsue Esaki, Nobuki Iwadera, Mami Mutoh, Chika Koyama, Tsukasa Akasaka, Motohiro Uo, Yoshinori Kuboki, Manabu Morita, Yoshinori Sato, Koichi Haneda, Tetsu Yonezawa, Balachandran Jeyadevan, Kazuyuki Tohji, Fumio Watari
    JOURNAL OF THE CERAMIC SOCIETY OF JAPAN 118 1378 525 - 529 2010年06月 [査読有り][通常論文]
     
    Internal distribution of several nanoparticles in mice has been investigated using scanning X-ray analytical microscopy, magnetic resonance imaging and inductively coupled plasma atomic emission spectroscopy. According dynamic laser scattering analysis, the actual particle size of obtained metal oxide was similar to that of metal particles. The estimated diameters were ca. one micrometer. After administration through the tail vein of the mice, metal particles quickly reached some organs. The distribution ratio reached a constant value and was then maintained. On the other hand, the metal oxide particles were first localized in the spleen and lung. The concentration in the lung was decreased with post-injection time. This result suggested that the particles were temporally trapped in the lung then removed to other organs. The behaviors between metal and metal oxide were quite different even when those particles had a similar actual particle size. Therefore, the distribution behavior of particles depended on the chemical species. (C) 2010 The Ceramic Society of Japan All rights reserved.
  • Tetsu Yonezawa, Naoki Nishida, Atsushi Hyono
    CHEMISTRY LETTERS 39 6 548 - 549 2010年06月 [査読有り][通常論文]
     
    A one-pot and single-step reduction process for producing antioxidized copper fine particles will be described. This process can be carried out at room temperature, and size range is quite wide, from 190 nm to 1 mu m by varying the amount of gelatin, the stabilizing reagent. From SEM images it is revealed that higher loading of gelatin gave larger but relatively uniform particles. However, XRD patterns indicated that the large particles were composed of smaller particles; that is, they had a "particle-in-particle" structure. Cross-sectional TEM image strongly supports this structure and indicates that gelatin is a good antioxidizing coating material which kept 5-nm copper metallic.
  • Tatsuya Kikuchi, Yasuhito Hara, Masatoshi Sakairi, Tetsu Yonezawa, Akira Yamauchi, Hideaki Takahashi
    CORROSION SCIENCE 52 4 1482 - 1491 2010年04月 [査読有り][通常論文]
     
    Corrosion of free machining Al alloys that contain Sn and Bi was investigated at 391-415 K in 2-(2-(2-methoxyethoxy)ethoxy)ethanol (MEEE) and 2-(2-(2-butoxyethoxy)ethoxy)ethanol (BEEE) with/without SnCl(2), Sn(OC(2)H(5))(4), FeCl(3), and CuCl(2). The Al-Sn-Bi alloy displayed severe pitting corrosion in MEEE similar to the Al-Sn alloy in BEEE at 415 K, and Sn and Sn/Bi were enriched on the surface of pits. Immersion tests of pure Al in MEEE containing Sn/Cu-salts at 415 K also showed severe corrosion and the deposition of metallic Sn and Cu on the surface. The corrosion mechanisms are discussed in terms of the electro-catalytic activity of the Sn enriched on the surface. (C) 2009 Elsevier Ltd. All rights reserved.
  • 兵野 篤, DUVAL Jerome F. L, 大島 広行, 松田 利夫, 米澤 徹
    高分子論文集 67 12 654 - 665 高分子学会 2010年 [査読有り][招待有り]
     
    Analysis of human red blood cells surface properties and evaluation of the interactions among red blood cells were done to establish the mechanism of the enzyme method. Electrophoretic mobilities of intact and enzyme-treated red blood cells were analyzed with soft particle theories; one based on the diffuse models could provide further information about the properties of red blood cell surfaces. Therefore, the interaction energies between two red blood cells were evaluated and the closest distances between them were evaluated to decide the agglutinability of cells with a IgG molecule. It was concluded that thinning of the surface layer thickness plays more important role in the enzyme method than reducing the surface layer charge densities.
  • Hideya Kawasaki, Teruyuki Yao, Takashi Suganuma, Kouji Okumura, Yuichi Iwaki, Tetsu Yonezawa, Tatsuya Kikuchi, Ryuichi Arakawa
    CHEMISTRY-A EUROPEAN JOURNAL 16 35 10832 - 10843 2010年 [査読有り][通常論文]
     
    We report a new and facile method for synthesizing 3D platinum nanoflowers (Pt Nfs) on a scratched silicon substrate by electroless galvanic displacement and discuss the applications of the Pt Nfs in surface-assisted laser desorption/ionization-mass spectrometry (SALDI-MS). Surface scratching of n-type silicon is essential to induce Pt Nf growth on a silicon substrate (to obtain a Pt Nf silicon hybrid plate) by the galvanic displacement reaction. The Pt Nf silicon hybrid plate showed excellent SALDI activity in terms of the efficient generation of protonated molecular ions in the absence of a citrate buffer. We propose that the acidity of the Si-OH moieties on silicon increases because of the electron-withdrawing nature of the Pt Nfs; hence, proton transfer from the Si OH groups to the analyte molecules is enhanced, and finally, thermal desorption of the analyte ions from the surface occurs. Signal enhancement was observed for protonated molecular ions produced from a titania nanotube array (TNA) substrate on which Pt nanoparticles had been photochemically deposited. Moreover, surface modification of the Pt Nf silicon hybrid plate by perfluorodecyltrichlorosilane (FDTS) (to obtain an FDTS-Pt Nf silicon hybrid plate) was found to facilitate soft SALDI of labile compounds. More interestingly, the FDTS-Pt Nf silicon hybrid plate acts 1) as a high-affinity substrate for phosphopeptides and 2) as a SALDI substrate. The feasibility of using the FDTS-Pt Nf silicon hybrid plate for SALDI-MS has been demonstrated by using a beta-casein digest and various analytes, including small molecules, peptides, phosphopeptides, phospholipids, carbohydrates, and synthetic polymers. The hybridization of Pt Nfs with a scratched silicon substrate has been found to be important for achieving excellent SALDI activity.
  • Yuichi Shishino, Tetsu Yonezawa, Koji Kawai, Hiroshi Nishihara
    CHEMICAL COMMUNICATIONS 46 38 7211 - 7213 2010年 [査読有り][通常論文]
     
    Water-soluble luminescent AuNPs of 1.3 +/- 0.3 nm in diameter with a large Stokes shift were facilely synthesized by a new molten matrix sputtering (MMS) method.
  • Hideya Kawasaki, Tarui Akira, Takehiro Watanabe, Kazuyoshi Nozaki, Tetsu Yonezawa, Ryuichi Arakawa
    ANALYTICAL AND BIOANALYTICAL CHEMISTRY 395 5 1423 - 1431 2009年11月 [査読有り][通常論文]
     
    Bare FePtCu nanoparticles (NPs) are first prepared for laser desorption/ionization mass spectroscopy (LDI-MS) analysis as affinity probes to selectively trap oppositely charged analytes from a sample solution. Our present results demonstrate bare FePtCu NPs to be a potentially useful matrix for surface-assisted laser desorption/ionization mass spectroscopy (SALDI-MS), for the analysis of small proteins and peptides. The upper detectable mass range of peptides was approximately 5 kDa, and the detection limit for peptides approximately 5 fmol. Sulfonate group-modified FePtCu nanoparticles (FePtCu-SO(3)(-) NPs), with ionization being independent of the solution pH, can interact with a positively charged analyte, and the analyte-bound NPs can be separated from the reaction supernatant by centrifugation or an external magnetic field. An oligopeptide, Gly-Gly-Tyr-Arg (GGYR) from an oligopeptide mixture containing Asp-Asp-Asp-Asp (DDDD), Gly-Gly-Gly-Gly (GGGG) and GGYR, was detected using SALDI-MS with FePtCu-SO(3)(-) NPs employing electrostatic interaction. Furthermore, FePtCuSO(3)(-) NPs can detect lysozyme (Lyz) in human serum through the electrostatic attraction between positively charged Lyz and FePtCu-SO(3)(-) NPs at pH 8, while detection of negatively charged albumin in human serum is not possible.
  • Akinori Hanzawa, Toshihiro Shimada, Tetsuya Hasegawa, Takahiro Sato, Takeo Kamino, Tetsu Yonezawa
    JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY 9 11 6736 - 6740 2009年11月 [査読有り][通常論文]
     
    The crystallization of polymer-mixed amorphous molybdenum sulfide was observed in-situ by a TEM equipped with a heated specimen holder. High electron beam irradiation induced the formation of a crystal structure with a lattice spacing of 0.62 nm, which corresponds to the layer spacing of MoS2. With a lower electron dose, a possible new crystal structure of molybdenum sulfide with several fringe spacings was identified at room temperature. An ordered layered structure Of MoS2 appeared after annealing at 600 degrees C. The completely different crystal phase found here might be responsible for the high temperature required for the formation of the MoS2 layered structure.
  • 各種マイクロ・ナノ粒子の生体内での分布状態の追跡とその可視化
    阿部 薫明, 岩寺 信喜, 武藤 麻未, 林 大輔, 大口 郁子, 赤坂 司, 宇尾 基弘, 亘理 文夫, 高田 知哉, 米澤 徹
    日本バイオマテリアル学会大会予稿集 31回 414 - 414 日本バイオマテリアル学会 2009年11月
  • 兵野 篤, 米澤 徹
    色材協會誌 82 10 468 - 474 一般社団法人 色材協会 2009年10月20日 
    金属ナノ粒子は,そのサイズに依存して発現する局在表面プラズモン共鳴や触媒特性などの特徴によって,近年新規な工業材料として注目されている。そして単分散性に優れ,分散安定な粒子を生成するさまざまな方法が開発されている。とくに湿式法ではサイズ・形状の制御が可能である。金・銀・銅粒子は局在表面プラズモン共鳴によって可視光での発色性を有し,色材へ応用されている。サイズによる色調の変化や表面増強ラマン散乱などの特性は迅速・高感度なセンシングへ応用されている。また,特異な触媒活性はグリーンケミストリーへの応用展開が期待されている。
  • Shigeaki ABE, Tetsu YONEZAWA, Tsukasa AKASAKA, Motohiro UO, Fumio UCHIDA, Fumio WATARI
    Nano Biomedicine 1 1 70 - 74 2009年06月 [査読有り][通常論文]
  • Tetsu Yonezawa, Hideya Kawasaki, Akira Tarui, Takehiro Watanabe, Ryuichi Arakawa, Toshihiro Shimada, Fumitaka Mafune
    ANALYTICAL SCIENCES 25 3 339 - 346 2009年03月 [査読有り][通常論文]
     
    In this paper, we describe systematic detailed considerations of the feasibility of using various metal nanoparticles for organic-matrix-free surface-assisted laser desorption/ionization mass spectrometry (SALDI-MS). In order to avoid the influence of organic molecules on the nanoparticles, stabilizer-free bare nanoparticles of Ag, Au, Cu and Pt were prepared by laser ablation. Although all metal nanoparticles absorbed N-2 laser light (337 nm) energy, the performance of desorption/ionization of a representative peptide, angiotensin 1, strongly depended on the metal element. Citrate buffer was used as a proton source; it reduced the amount of alkali cation adducts present. Then, protonated molecules of analytes predominated in the mass spectra when Au and Pt nanoparticles were used. Pt nanoparticles showed the highest performance in SALDI-MS, owing to their smaller heat conductivity and higher melting temperature. The selective desorption of a cationic surfactant with longer alkyl chains and a peptide with methionine was also observed.
  • Mariko Miyachi, Yoshinori Yamanoi, Tetsu Yonezawa, Hiroshi Nishihara, Michinao Iwai, Masae Konno, Masako Iwai, Yasunori Inoue
    JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY 9 3 1722 - 1726 2009年03月 [査読有り][通常論文]
     
    We present a bio-photoelectrode made of photosystem I complex (PSI) of cyanobacteria, Thermosynechococcus elongatus, and molecular wires. The newly designed and synthesized molecular wire similar to vitamin K, (VK,) has a naphthoquinone moiety that can connect to PSI, and a terpyridine moiety for connection to a Co(II) ion. Surface immobilization of PSI and molecular wires was performed by a self-assembled monolayer (SAM) formation process at indium tin oxide (ITO) followed by stepwise coordination reactions. The PSI-immobilized ITO showed a photocurrent action spectrum, whose profile was consistent with that of PSI. We have demonstrated a new method for the immobilization of PSI on the electrode surface, useful in the construction of phovoltaic cells or photon-sensing devices.
  • Nao Terasaki, Noritaka Yamamoto, Takashi Hiraga, Yoshinori Yamanoi, Tetsu Yonezawa, Hiroshi Nishihara, Tsutomu Ohmori, Makoto Sakai, Masaaki Fujii, Akihiko Tohri, Masako Iwai, Yasunori Inoue, Satoshi Yoneyama, Makoto Minakata, Isao Enami
    ANGEWANDTE CHEMIE-INTERNATIONAL EDITION 48 9 1585 - 1587 2009年 [査読有り][通常論文]
  • Akira Tarui, Hideya Kawasaki, Takuma Taiko, Takehiro Watanabe, Tetsu Yonezawa, Ryuichi Arakawa
    JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY 9 1 159 - 164 2009年01月 [査読有り][通常論文]
     
    We developed surface-assisted laser desorption/ionization mass spectrometry (SALDI-MS) using nanocomposite films of cationic diblock copolymer micelles [poly(styrene-b-N-methyl-4-vinyl pyridinium iodide)] and ammonium citrated Au nanoparticles (AuNPs) on silicon. The nanocomposite film on silicon was suitable for use as a material for matrix-free LDI-MS of peptides due to its low matrix background from Au clusters and high ionization efficiency; this plate successfully ionized angiotensin I, and also insulin in the proton adduct forms, in contrast to methods using only AuNPs and those using nanocomposite films of cationic polymer in conjunction with Au NPs. The high ionization efficiency is discussed from the viewpoint of nanoparticle distribution controlled by polymers on the plate (aggregates vs. nonaggregates).
  • Tetsu Yonezawa
    BIO-MEDICAL MATERIALS AND ENGINEERING 19 1 29 - 34 2009年 [査読有り][通常論文]
     
    In-situ TEM (transmission electron microscopy) of silver nanoparticle ink at high temperature was carried out. Into a carbon film tube coating the spiral tungsten filament which was attached to the TEM specimen holder, a silver nanoparticle ink was injected. After evaporation, silver nanoparticles with an aggregated structure could be observed. The temperature of the tungsten wire can be controlled by DC current supplied by dry batteries. Fusion of smaller nanoparticles was observed at a higher temperature and some particles were incorporated to larger particles. This technique can be generally used to consider the sintering temperature of such metal nanoparticles.
  • 米澤 徹
    表面技術 = The journal of the Surface Finishing Society of Japan 59 11 712 - 717 The Surface Finishing Society of Japan 2008年11月01日
  • Hideya Kawasaki, Tsuyoshi Sugitani, Takehiro Watanabe, Tetsu Yonezawa, Hiroshi Moriwaki, Ryuichi Arakawa
    ANALYTICAL CHEMISTRY 80 19 7524 - 7533 2008年10月 [査読有り][通常論文]
     
    Layer-by-layer (LBL) self-assembled multilayer films of gold nanoparticles (AuNPs) on a silicon wafer were demonstrated to be promising substrates for surface-assisted laser desorption/ionization (SALDI) mass spectrometry (MS) of peptides and environmental pollutants for the first time. LBL multilayer films, (AuNPs/PAHC)(n), consisting of alternating layers of ammonium citrate capped AuNPs and poly(allylamine hydrochloride) (PAHC) were prepared on a silicon surface. Silicon plates with aggregated AuNPs were more suitable than those with dispersed AuNPs for the SALDI-MS of peptides. The number of particle layers had a significant effect on the laser desorption/ionization of angiotensin I; the peak intensity of the peptide (molecular ion amount) increased with an increase in the number of layers of AuNPs. As a result, the (AuNPs/PAHC)(5) multilayer films increased the sensitivity of the angiotensin I to subfemtomoles and raised the useful analyte mass range, thus making it possible to detect small proteins (a 12 kDa cytochrome c). The signal enhancement when using (AuNPs/PAHC)(5) may be due to (i) the high absorption of the UV laser fight at 337 nm by the AuNP layers, (ii) the low thermal conductivity due to the AuNPs being covered with a thin monolayer of PAHC, and (iii) the increase in the surface roughness (similar to 100 nm) with the number of AuNP layers. Thus, laser-induced rapid high heating of AuNPs for effective desorption/ionization of peptides is possible. In addition, it was found that (AuNPs/PAHC)(5) could be used to extract environmental pollutants (pyrene and dimethyldistearylammonium chloride) from very dilute aqueous solutions with concentrations less than 10(-10) mg/mL, and the analytes trapped in the LBL film could be identified by introducing the film directly into the SALDI mass spectrometer without needing to elute the analytes out of the film.
  • Takehiro Watanabe, Hideya Kawasaki, Tetsu Yonezawa, Ryuichi Arakawa
    JOURNAL OF MASS SPECTROMETRY 43 8 1063 - 1071 2008年08月 [査読有り][通常論文]
     
    We have developed surface-assisted laser desorption/ionization mass spectrometry using zinc oxide (ZnO) nanoparticles with anisotropic shapes (ZnO-SALDI-MS). The mass spectra showed low background noises in the low m/z, i.e. less than 500 u region. Thus, we succeeded in SALDI ionization on low molecular weight organic compounds, such as verapamil hydrochloride, testosterone, and polypropylene glycol (PPG) (average molecular weight 400) without using a liquid matrix or buffers such as citric acids. In addition, we found that ZnO-SALDI has advantages in post-source decay (PSD) analysis and produced a simple mass spectrum for phospholipids. The ZnO-SALDI spectra for synthetic polymers of polyethylene glycol (PEG), polystyrene (PS) and polymethylmethacrylate (PMMA) showed the sensitivity and molecular weight distribution to be comparable to matrix-assisted laser desorption/ionization (MALDI) spectra with a 2,5-dihydroxybenzoic acid (DHB) matrix. ZnO-SALDI shows good performance for synthetic polymers as well as low molecular weight organic compounds. Copyright (C) 2008 John Wiley & Sons, Ltd.
  • Masanori Tomonari, Kiyonobu Ida, Hiromi Yamashita, Tetsu Yonezawa
    JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY 8 5 2468 - 2471 2008年05月 [査読有り][通常論文]
     
    Size-controlled oxidation-resistant copper fine particles were prepared from insoluble CuO micronsized particles. The particle sizes were quite uniform and could be varied only by the concentration of the complex reagent from 45 to 175 nm. No template material was needed for size control. Gelatin was selected as the protective polymer. Addition of protease after formation of copper fine particles decomposed preferentially loop and tail parts of gelatin. The remaining nanoskin gelatin layer, covered on the particle surface, prevents oxidation of copper.
  • Tetsu Yonezawa, Shinsuke Takeoka, Hiroshi Kishi, Kiyonobu Ida, Masanori Tomonari
    NANOTECHNOLOGY 19 14 2008年04月 [査読有り][通常論文]
     
    Well size-controlled copper fine particles (diameter: 100-300 nm) were used as the inner electrode material of multilayered ceramic capacitors (MLCCs). The particles were dispersed in terpineol to form a printing paste with 50 wt% copper particles. The MLCC precursor modules prepared by the layer-by-layer printing of copper and BaTiO3 particles were cosintered. Detailed observation of the particles, paste, and MLCCs before and after sintering was carried out by electron microscopy. The sintering temperature of Cu-MLCC was as low as 960 degrees C. The permittivity of these MLCCs was successfully measured with the copper inner layers.
  • Mariko Miyachi, Makiko Ohta, Misaki Nakai, Yoshihiro Kubota, Yoshinori Yamanoi, Tetsu Yonezawa, Hiroshi Nishihara
    CHEMISTRY LETTERS 37 4 404 - 405 2008年04月 [査読有り][通常論文]
     
    We fabricated photoelectron conversion system with porphyrin-terminated "molecular wires" on an ITO surface synthesized using stepwise metal-terpyridine complexation reactions. The efficiency and the electrode potential singnificantly depended on the metal center of the bis(terpyridine) complex unit in the molecular wire.
  • Tetsu Yonezawa, Yoshinori Yamanoi, Hiroshi Nishihara
    JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY 8 3 1518 - 1522 2008年03月 [査読有り][通常論文]
     
    A thermal hydrosilylation process could successfully immobilize 5-heptene-1-thiol-stabilized gold nanoparticles onto hydrogen-terminated silicon surfaces. In order to understand the immobilization structures, it is very important to observe the linkage between the nanoparticles and the substrate surface. For this purpose, a cross-sectional observation of gold nanoparticle-attached silicon substrate was carried out by using a high resolution scanning transmission electron microscopy (HR-STEM). The specimens were prepared by using a focused ion-beam (FIB) machine. According to the Ga ion-beam irradiation, many single-nano-sized nanoparticles were fused to grow up to larger particles and amorphous Si layers were generated.
  • Tetsu Yonezawa, Keigo Kamoshita, Masayoshi Tanaka, Takatoshi Kinoshita
    JAPANESE JOURNAL OF APPLIED PHYSICS 47 2 1389 - 1392 2008年02月 [査読有り][通常論文]
     
    Iron oxide nanoparticles were prepared by adding NaBH(4) to aqueous solution of an Fe(3+) salt in the presence of gelatin as the stabilizing reagent. The obtained nanoparticles are relatively unique and can be separated by centrifugation. They can be collected in the dried powder form by centrifugation and freeze-drying. Their structural properties analyzed by transmission electron microscopy, atomic force microscopy and X-ray diffraction, as well as their magnetic properties measured by a superconducting quantum interface device are discussed in this paper.
  • Tetsu Yonezawa, Yoshinori Yamanoi, Hiroshi Nishihara
    Metal Nanoclusters in Catalysis and Materials Science: The Issue of Size Control 453 - 458 2008年 [査読有り][通常論文]
  • Tetsu Yonezawa, Kazuki Uchida, Yoshinori Yamanoi, Shintaro Horinouchi, Nao Terasaki, Hiroshi Nishihara
    PHYSICAL CHEMISTRY CHEMICAL PHYSICS 10 46 6925 - 6927 2008年 [査読有り][通常論文]
     
    Successful covalent soft immobilization of gold nanoparticles on Si(111) surface by simple immersion of hydrogen-terminated silicon wafer into a toluene dispersion of gold nanoparticles was achieved by use of a phenylalkyne-type stabilizing ligand, and the electron behaviour was investigated using a conducting AFM.
  • Fumio Watari, Shigeaki Abe, Chika Koyama, Atsuro Yokoyama, Tukasa Akasaka, Motohiro Uo, Makoto Matsuoka, Yasunori Totsuka, Mitsue Esaki, Manabu Morita, Tetsu Yonezawa
    JOURNAL OF THE CERAMIC SOCIETY OF JAPAN 116 1349 1 - 5 2008年01月 [査読有り][通常論文]
     
    To clarify the effect of micro/nanosizing of materials onto biological organism, the particle size dependence of reaction of cells and tissue as investigated by both biochemical cell functional test and animal implantation test. Especially for nanoparticles the behavior of invasion and internal diffusion inside body was visualized using an XSAM (X-ray Scanning Analytical Microscope). The increase of specific surface area is usually counted as nanosizing effect which causes the enhancement of chemical reactivity and therefore toxicity of materials such as carcinogenicity found in 500 nm Ni particles for the long term implantation in the soft tissue of rat. Even biocompatible materials such as Ti and TiO2 shows stimulus with the decrease of particle size. They cause phagocytosis to cells and inflammation to tissue when the size of particles is below 3 mu m. For the size below 50 nm, they may invade into the internal body through the respiratory or digestive system and diffuse inside body. After compulsory exposure test of 30 nm TiO2 particles through the respiratory system, the Ti mapping by XSAM showed the internal diffusion inside the whole body. Nanoparticles injected from caudal vein diffused with time course to lung, liver and spleen. The uptake of 30 nm TiO2 particles through the digestive system and diffusion into these organs was also confirmed. These phenomena observed in biocompatible or bioinert materials are the nonspecific, physical particle and shape effects which occur independent of materials. Nanoparticles might be the objects whose existence has not been assumed by the living body defense system.
  • Masanori Tomonari, Kiyonobu Ida, Hironori Imanishi, Tetsu Yonezawa, Kohsuke Mori, Hiromi Yamashita
    RESEARCH ON CHEMICAL INTERMEDIATES 34 5-7 641 - 647 2008年 [査読有り][通常論文]
     
    By the addition of sodium borohydride as a reducing agent into an aqueous solution of AgNO3 mixed with 3-mercapto-propionic acid as a protective agent, nano-sized Ag metal particles could be synthesized. Using this advanced wet-process the synthesis of an aqueous Ag colloid system with a high density became possible, because the surfaces of the synthesized nano-sized Ag metal particles were covered and protected by the adsorbed 3-mercapto-propionic acid. By changing the mix ratio of AgNO3 to 3-mercapto-propionic acid, the particle size of synthesized nano-sized Ag metal particles could be controlled; a higher 3-mercapto-propionic acid/AgNO3 ratio was preferable in the synthesis of smaller Ag metal particles. From the relationship between the Ag metal particle size and the residual S content adsorbed on the metal particles, the mechanism of dispersion of Ag particles can be proposed as that the 3-mercapto-propionic acid having a thiol group adsorbs on Ag particles by forming Ag-S bonds as a protective agent.
  • Misaki Nakai, Yoshinori Yamanoi, Yoshihiko Nishimori, Tetsu Yonezawa, Hiroshi Nishihara
    ANGEWANDTE CHEMIE-INTERNATIONAL EDITION 47 35 6699 - 6702 2008年 [査読有り][通常論文]
  • Naoto Shirahata, Tetsu Yonezawa, Yoshihiro Matsushita, Yoshitake Masuda, Kunihito Koumoto
    MACROMOLECULAR SYMPOSIA 270 82 - 87 2008年 [査読有り][通常論文]
     
    Fusion and growth behavior of gold nanoparticles in a relatively low temperature range were studied using a transmission electron microscopy (TEM). Using allylmercaptane (AM: 2-propene-1-thiol, HS-CH2-CH=CH2) as a particle stabilizer, a colloidal suspension of AM-terminated gold nanoparticles was prepared with a two-phase system. TEM observation revealed that the adjacent nanoparticles formed a particulate neck to give fused nanoproducts even at lower than 65 degrees C. Such fusion behavior allowed a non-spherical growth of the adjacent nanoparticles. Interestingly, the nanoparticle fused to form a nanowire-type structure when the thermal radical reaction occurred between the terminal double carbon bond of the stabilizer and the hydrogen terminated surface of silicon wafer.
  • Ikuse Nakamula, Yoshinori Yamanoi, Tetsu Yonezawa, Takane Imaoka, Kimihisa Yamamoto, Hiroshi Nishihara
    CHEMICAL COMMUNICATIONS 44 5716 - 5718 2008年 [査読有り][通常論文]
     
    The phenylazomethine dendrimer generation 4 (TPP-DPA G4) and polyamidoamine dendrimer (PAMAM G4-OH) encapsulating rhodium nanocluster were found to be highly effective for olefin and nitroarene hydrogenations, affording high TOF (up to 17520 h(-1)); the important feature of the nanocage catalyst is that substrates can pass through the branches of the protecting groups of nanoclusters without releasing nanoclusters from the dendrimer.
  • Hideya Kawasaki, Tetsu Yonezawa, Takehiro Watanabe, Ryuichi Arakawa
    JOURNAL OF PHYSICAL CHEMISTRY C 111 44 16278 - 16283 2007年11月 [査読有り][通常論文]
     
    No-template synthesis of surface clean platinum nanomaterials with thin projections (petals) on the Pt nanoparticle surface, termed Pt nanoflowers, has been developed, and Pt nanoflowers have achieved superior performance on surface-assisted laser desorption/ionization mass spectrometry (SALDI-MS) of biomolecules. With this new material, one can obtain high-resolution mass spectra with lower laser energy and smaller sample amounts, and no organic matrix is needed for laser desorption/ionization. The mass spectra also have fewer obstacle peaks at the lower m/z region. Furthermore, this novel substrate is quite stable against aging and showed no sweet-spot problems, that is, equal sensitivity on the whole substrate surface. Various biomolecules, including peptides and phospholipids, were examined, and Pt nanoflowers showed good performance for matrix-free laser desorption/ionization MS of these materials.
  • Tetsu Yonezawa, Tetsuya Itoh, Naoto Shirahata, Yoshitake Masuda, Kunihito Kournoto
    APPLIED SURFACE SCIENCE 254 2 621 - 626 2007年09月 [査読有り][通常論文]
     
    One-dimensional metal lines of silver nanoparticles with a nano-sized width were generated onto silicon surface by using a nano-level lithography technique, field induced oxidation (FIO) by AFM, on self-assembled monolayer-modified Si wafers. This FIO technique provided SiO2 lines a width of less than 100 nm. Short-time immersion of partially anodized silicon surface which is covered by a cationic silanol surfactant ((CH3O)(3)SiCH2CH2CH2N(CH3)(3)Cl-+(-))-monolayer into quaternary ammonium (HSCH2CH2N(CH3)(3)Br-+(-))-covered silver nanoparticles readily and reproducibly gave nano-metal lines of silver onto silicon wafers. Hydrophilicity of the whole wafer surface was indispensable for homogeneously wetting the anodized SiO2 area with a nanodimensional width. (c) 2007 Elsevier B.V. All rights reserved.
  • Hideya Kawasaki, Tetsu Yonezawa, Kouhei Nishimura, Ryuichi Arakawa
    CHEMISTRY LETTERS 36 8 1038 - 1039 2007年08月 [査読有り][通常論文]
     
    We first report the fabrication of submillimeter-sized Au plates (up to about I mm in size) through the simple thermal decomposition of HAUCl(4) in two-component ionic liquids of 1-butyl-3-methylimidazolium hexafluorophosphate (C4ImPF6) and 1-octyl-3-methylimidazolium hexafluorophosphate (C8ImPF6), which were about ten times larger sizes than those from the single-component ionic liquid of the either.
  • Nao Terasaki, Noritaka Yamamoto, Kaoru Tamada, Mineyuki Hattori, Takashi Hiraga, Akihiko Tohri, Ikutaro Sato, Masako Iwai, Michinao Iwai, Shunpei Taguchi, Isao Enami, Yasunori Inoue, Yoshinori Yamanoi, Tetsu Yonezawa, Katsuya Mizuno, Masaki Murata, Hiroshi Nishihara, Satoshi Yoneyama, Makoto Minakata, Tsutomu Ohmori, Makoto Sakai, Masaaki Fujii
    Biochimica et biophysica acta 1767 6 653 - 9 2007年06月 
    We report on the first successful output of electrons directly from photosystem I (PSI) of thermophilic cyanobacteria to the gate of a field-effect transistor (FET) by bypassing electron flow via a newly designed molecular wire, i.e., artificial vitamin K(1), and a gold nanoparticle; in short, this newly manufactured photosensor employs a bio-functional unit as the core of the device. Photo-electrons generated by the irradiation of molecular complexes composed of reconstituted PSI on the gate were found to control the FET. This PSI-bio-photosensor can be used to interpret gradation in images. This PSI-FET system is moreover sufficiently stable for use exceeding a period of 1 year.
  • Nao Terasaki, Noritaka Yamamoto, Kaoru Tamada, Mineyuki Hattori, Takashi Hiraga, Akihiko Tohri, Ikutaro Sato, Masako Iwai, Michinao Iwai, Shunpel Taguchi, Isao Enami, Yasunori Inoue, Yoshinori Yamanoi, Tetsu Yonezawa, Katsuya Mizuno, Masaki Murata, Hiroshi Nishihara, Satoshi Yoneyama, Makoto Minakata, Tsutomu Ohmori, Makoto Sakai, Masaaki Fujii
    BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 1767 6 653 - 659 2007年06月 [査読有り][通常論文]
     
    We report on the first successful output of electrons directly from photosystem I (PSI) of thermophilic cyanobacteria to the gate of a field-effect transistor (FET) by bypassing electron flow via a newly designed molecular wire, i.e., artificial vitamin K-1, and a gold nanoparticle; in short, this newly manufactured photosensor employs a bio-functional unit as the core of the device. Photo-electrons generated by the irradiation of molecular complexes composed of reconstituted PSI on the gate were found to control the FET. This PSI-bio-photosensor can be used to interpret gradation in images. This PSI-FET system is moreover sufficiently stable for use exceeding a period of I year. (c) 2006 Elsevier B.V. All rights reserved.
  • 米澤 徹
    日本写真学会誌 = Journal of The Society of Photographic Science and Technology of Japan 70 1 26 - 29 日本写真学会 2007年 [査読無し][招待有り]
  • Masanori Tomonari, Hilo Sadohara, Tetsu Yonezawa, Kohsuke Mori, Hiromi Yamashita
    JOURNAL OF CERAMIC PROCESSING RESEARCH 8 3 195 - 198 2007年 [査読有り][通常論文]
     
    Nano-sized Ag metal particles can be synthesized by the addition of sodium borohydride as a reducing agent into an aqueous solution of AgNO3 mixed with 3-mercapto-propionic acid as a protective agent. Using this method the synthesis of an aqueous Ag colloid system with a high density became possible, because the surfaces of synthesized nano-sized Ag metal particles were covered and protected by the adsorbed 3-mercapto-propionic acid. The strong electrostatic repulsion of the negative charge of the carboxylate anion of the adsorbed 3-mercapto-propionic acid disturbed the aggregation of metal particles in the solution with a high pH value (pH > 5), but the aggregation occurred in a solution of low pH value (pH < 2) because of the neutral surface of particles. Using simple coating and baking processes with this aqueous Ag colloid system, an Ag membrane can be formed on glass plate by the partial welding between the nano-size Ag particles. This Ag membrane exhibited a very low electrical resistivity even after baking at a low temperature such as 423 K.
  • Tetsu Yonezawa, Naoto Shirahata, Yoshiko Miura
    TRANSACTIONS OF THE MATERIALS RESEARCH SOCIETY OF JAPAN, VOL 32, NO 3 32 3 767 - 768 2007年 [査読有り][通常論文]
     
    Functionalization of silicon tip was carried out by photochemical/thermal hydrosilylation with an alkene-terminated sugar derivative. Si-C bond formation was suitable for preparation of monolayer on silicon surface. The tip was heated in a toluene solution of a sugar derivative with a special flask for hydrosilylation of small materials. With the functionalized tip, patterned surface of a silicon substrate was scanned.
  • Tetsu Yonezawa, Takashi Nomura, Takatoshi Kinoshita, Kunihito Koumoto
    JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY 6 6 1649 - 1654 2006年06月 [査読有り][通常論文]
     
    Helical polypeptides have a highly rigid conformation. In order to control self-assembling structure in nanoscale, the rigidity of the stabilizing molecules, which is working as scaffolds, is highly important. Furthermore, the molecular lengths of polypeptides can be readily controlled by using their unique polymerization methods. In this study, we have used helical polypeptides as the stabilizing reagent of metal nanoparticles. As for rigid helical polypeptides, poly(gamma-benzyl-L-glutamate) (PBLG) was selected, and was synthesized by N-carboxylic acid anhydride (NCA) polymerization. Preparation of helical polypeptide-stabilized gold nanoparticles using a two-phase reduction process from the corresponding metal salts with NaBH4 is therefore introduced. PBLG itself did not have good stabilizing ability for metal nanoparticles and a terminal attaching ligand was indispensable for nanoparticle stabilization and, for this purpose, lipoic acid was selected. It is estimated that lipoic acid functionalized polypeptide molecules were attached perpendicularly to the particle surface by lipoic acid group. The size and structure, as well as assembling will be discussed in this manuscript.
  • N Shirahata, A Hozumi, Y Miura, K Kobayashi, Y Sakka, T Yonezawa
    THIN SOLID FILMS 499 1-2 213 - 218 2006年03月 [査読有り][通常論文]
     
    Efficient matrix that resists the nonspecific adsorption of proteins from the contacting phosphate buffer silane (PBS) solution has been explored to fabricate carbohydrate arrays on silicon wafer. p-Vinylbenzyllactonoamide (VLA) was immobilized onto silicon through Si-C bond. The VLA-covered substrate was then photo lithographically micropatterned through a photomask by ultraviolet (UV) irradiation. The VLA-covered regions recognized specifically the lactose-binding lectin in PBS solution. On the other hand, the U-V-irradiated regions, i.e., SiOx surface, prevented the nonspecific adsorption of the lectin from the contacting PBS solution. Several control experiments have demonstrated that the resistant-ability of SiOx surface as the matrix was comparable to the best of known system for resisting the nonspecific adsorption. (c) 2005 Elsevier B.V All rights reserved.
  • Shintaro Horinouchi, Yoshinori Yamanoi, Tetsu Yonezawa, Toshihiro Mouri, Hiroshi Nishihara
    Langmuir 22 4 1880 - 1884 2006年02月14日 [査読有り][通常論文]
     
    Monodispersed palladium nanoparticles protected with n-octyl isocyanide were prepared, and their hydrogen absorption behavior was evaluated. The formation of the nanoparticles has been confirmed by means of 1H NMR and elemental analysis. Fourier transform infrared (FT-IR) showed that three distinct bands (2156, 1964, and 1611 cm-1) assigned to mono-, double-, and triple-bridged isocyanide ligands on the palladium surface. The average diameter of the particles was estimated to be 2.1±0.7 nm from observation by transmission electron microscopy (TEM). X-ray photoelectron spectroscopy (XPS) analysis revealed that the particles contained Pd(0) with little amounts of Pd(II) or Pd(IV), in sharp contrast to the thiol- or phosphine-stabilized palladium nanoparticles. The absorption and desorption of hydrogen were reversible, and the reactions were much faster for the nanoparticles than for the bulk palladium metal, whereas the storage capacity was almost the same, 0.6 wt %. © 2006 American Chemical Society.
  • K Nunokawa, S Onaka, M Ito, M Horibe, T Yonezawa, H Nishihara, T Ozeki, H Chiba, S Watase, M Nakamoto
    JOURNAL OF ORGANOMETALLIC CHEMISTRY 691 4 638 - 642 2006年02月 [査読有り][通常論文]
     
    An SR-modified Au cluster with a sub-nanometer size, Au-11(S-4-NC5H4)(3)(PPh3)(7) (1), has been synthesized by NaBH4 reduction of Au(S-py)(PPh3)or by reacting [Au-9(PPh3)(8)](NO3)(3) with HS-4-py in good yield. Its molecular structure has been elucidated by single crystal X-ray diffraction, and TEM observation has been achieved for the first time for this size of SR-modified An clusters. The core structure is best described in terms of an incomplete icosahedron. CV measurements in CH2Cl2 have suggested that the cluster does not coagulate in solution with significant concentration. (c) 2005 Elsevier B.V. All rights reserved.
  • Tetsu Yonezawa, Naoto Shirahata, Nao Terasaki, Yoshinori Yamanoi, Hiroshi Nishihara
    Polymer Preprints, Japan 55 1 1309  2006年 
    Alkene thiol-stabilized gold nanoparticles were immobilized onto hydrogen-terminated silicon surface by using hydrosilylation. 1-Hexenethiol-stabilized gold nanoparticles were obtained by NaBH4 reduction of HAuCl4. About half of C=C bonds are saturated during the preparation of nanoparticles. The obtained gold nanoparticles were tried to be immobilized onto silicon surface by thermal- and photo-assisted (Lamp: Sanei UVF-203S) hydrosilylation. Comparing the SEM images of the obtained silicon surfaces, both systems work very well but photo-assisted process gave a more dispersed structure.
  • Kazuki Uchida, Shintaro Horinouchi, Yoshinori Yamanoi, Tetsu Yonezawa, Hiroshi Nishihara, Nao Terasaki
    Polymer Preprints, Japan 55 2 3490  2006年 
    4-Ethynylbenzenethiolato-protected gold nanoparticles were prepared. Themal hydrosilylation was performed in order to immobilize nanoparticles onto a hydrogen-terminated silicon(111) surface through conjugated chains. The structure of the modified surface was mainly observed by SEM, AFM and IR.
  • Ikuse Nakamula, Yoshinori Yamanoi, Tetsu Yonezawa, Hiroshi Nishihara, Kimihisa Yamamoto
    Polymer Preprints, Japan 55 2 4082  2006年 
    Rh nanoparticles stabilized in phenylazomethine dendrimers were prepared by the chemical reduction of Rh(III)-dendrimer complexes. TEM and MALDI-TOF-MS studies provided the information on the encapsulation of the Rh nanoparticles by the dendrimers. These Rh nanoparticles showed higher catalytic ability for the hydrogenation of alkenes than Wilkinson complex.
  • Y Yamanoi, N Shirahata, T Yonezawa, N Terasaki, N Yamamoto, Y Matsui, K Nishio, H Masuda, Y Ikuhara, H Nishihara
    CHEMISTRY-A EUROPEAN JOURNAL 12 1 314 - 323 2006年 [査読有り][通常論文]
     
    The modification of flat semi-conductor surfaces with nanoscale materials has been the subject of considerable interest. This paper provides detailed structural examinations of gold nanoparticals covalently immobilized onto hydrogen-terminated silicon surfaces by a convenient thermal hydrosilylation to form Si-C bonds. Gold nanoparticles stabilized by omega-alkene-1-thiols with different alkyl chain lengths (C-3,C- C-6, and C-11), with average diameters of 2-3 nm and a narrow size distribution were used. The thermal hydrosilylation reactions of these nanoparticles with hydrogen-terminated Si(111) surfaces were carried out in toluene at various conditions under N-2. The obtained modified surfaces were observed by high-resolution scanning electron microscopy (HR-SEM). The obtained images indicate considerable changes in morphology with reaction time, reaction temperature, as well as the length of the stabilizing omega-alkene-1-thiol molecules. These surfaces are stable and can be stored under ambient conditions for several weeks without measurable decompostion. It was also found that the aggregation of immobilized particles on a silicon surface occurred at high temperature (> 100 degrees C). Precise XPS measurements of modified surfaces were carried out by using a Au-S ligand-exchange technique. The spectrum clearly showed the existence of Si-C bonds. Cross-sectional HR-TEM images also directly indicate that the particles were covalently attached to the silicon surface through Si-C bonds.
  • Tetsu Yonezawa
    TRANSACTIONS OF THE MATERIALS RESEARCH SOCIETY OF JAPAN, VOL 31, NO 2 31 2 553 - 555 2006年 [査読有り][通常論文]
     
    This review article describes about wet preparation of metal nanoparticles, especially, preparation is relatively easy and useful for high volume preparation. After the breakthrough of Brust's thiol stabilizing system, small and monodispersed nanoparticles have been demonstrated frequently. By using such thiol-stabilizing nanoparticles, their ordered two-dimensional arrangement has been prepared with tuned stabilizing molecules. In this manuscript, such techniques of 2-D arrangement preparation will be also discussed in detail.
  • Keiko Nunokawa, Mitsuhiro Ito, Tetsuya Sunahara, Satoru Onaka, Tomoji Ozeki, Hirokazu Chiba, Yasuhiro Funahashi, Hideki Masuda, Tetsu Yonezawa, Hiroshi Nishihara, Masami Nakamoto, Mari Yamamoto
    Dalton Transactions 16 2726 - 2730 2005年08月21日 [査読有り][通常論文]
     
    New mixed metal clusters with M19 metal frameworks have been synthesized by NaBH4 reduction of Au(NO3)(PMe 2Ph) together with AgNO3 in ethanol. Single crystal X-ray diffraction has revealed Au12Ag7 and Au 17Ag2 metal skeletons for these clusters, which are best described in terms of bicapped pentagonal antiprismatic cages with a staggered-staggered M5 ring configuration. These clusters connect the missing link between M13 icosahedral and M25 biicosahedral clusters providing a view of the cluster growth process. A TEM image of this cluster has been observed, which has clearly demonstrated single-sized nano-particles of less than 1.0 nm. © The Royal Society of Chemistry 2005.
  • 米澤 徹
    表面技術 = The Journal of the Surface Finishing Society of Japan 56 12 743 - 747 表面技術協会 2005年 [査読無し][招待有り]
  • Yoshinori Yamanoi, Shintaro Horinouchi, Kazuki Uchida, Tetsu Yonezawa, Hirishi Nishihara, Naoto Shirahata, Nao Terasaki, Noritaka Yamamoto, Yoshitaka Matusi, Kazuyuki Nishio, Hideki Masuda, Yuichi Ikuhara
    Polymer Preprints, Japan 54 2 3541  2005年 
    Gold nanoparticles, which have unsaturated C-C bonds in stabilizers, were prepared and then covalently linked to a hydrogen-terminated silicon(111) surface with Si-C bonds via a thermal hydrosilylation reaction. The modified silicon surfaces were observed mainly by high-resolution scanning electron microscopy (HR-SEM) and the fixation of nanoparticles through Si-C bonds was finally investigated by XPS and cross sectional TEM.
  • Tetsu Yonezawa, Yoshinori Yamanoi, Hiroshi Nishihara, Nao Terasaki, Noritaka Yamamoto, Naoto Shirahata
    Polymer Preprints, Japan 54 1 965  2005年 
    Hydrogen-terminated silicon surface is now becoming one of promising substrates to provide good SAM layers with Si-C covalent bonds. Many kinds of SAM layers have been proposed, such as simple alkyl SAMs for preventing oxidation of the surface or SAMs of functional molecules, e. g., bio molecules for bio-sensing. We applied this technique to immobilize gold nanoparticles. By simple sintering of H-terminated Si wafers into toluene dispersions of ω-alkene-1-thiol-stabilized gold nanoparticles gives Au-nanoparticle immobilized Si surface. Detailed structural analyses of these wafers will be reported.
  • N Shirahata, A Hozumi, T Yonezawa
    CHEMICAL RECORD 5 3 145 - 159 2005年 [査読有り][通常論文]
     
    This article describes a variety of monolayers anchored directly onto silicon surfaces without an oxide interlayer, their formation mechanisms, their technological applications, and our personal views on the future prospects for this field. The chemical modification of non-oxidized silicon surfaces utilizing monolayers was first reported in 1993. The basic finding that a non-oxidized silicon surface could be neutralized with alkyl chains through direct covalent linkage, i.e., silicon-carbon, has offered chemical scientists ease of handling even in an ambient environment and, thus, research has been predictably focused on forming anti-stiction coating films for nano- and micro-electromechanical systems (NEMS/MEMS). Such surface reforming has also been achieved by using other monolayers, which form interfacial bonds, e.g., silicon-nitrogen and silicon-oxygen. The resultant monolayer surfaces are useful for silicon-based applications including molecular electron transfer films, monolayer templates, molecular insulators, capsulators, and bioderivatives. Such monolayers are applicable not only for surface modification, but also for manipulating individual nanomaterials. By modifying the terminal groups of monolayers with nanomaterials including nanocrystals and biomolecules, the nanomaterials can remarkably be immobilized directly onto non-oxidized silicon surfaces based on the formation mechanisms of the monolayer. Such immobilizations will revolutionize the analysis of the specific features and capabilities of individual nanomaterials. Furthermore, the path will be opened for the development of more advanced monolayer-derived chip technology. To achieve this goal, it is extremely important to thoroughly understand the functionalization processes on silicon, since the resultant internal structures and properties of monolayer-derivative silicon may strongly depend on their course of formation. (c) 2005 The Japan Chemical Journal Forum and Wiley Periodicals, Inc.
  • Tetsu Yonezawa, Akihiro Miyata, Masayoshi Tanaka, Takatoshi Kinoshita
    Transactions of the Materials Research Society of Japan, Vol 30, No 4 30 4 1259 - 1261 2005年 [査読有り][通常論文]
     
    A hydrophobic polypeptide, poly(gamma-benzyl-L-glutamate) (PBLG), has a solid and rod-like a-helix structure. According to this rigid molecular conformation, this type of peptide molecules forms good Langmuir-Brodgett (LB) thin films. In this study, non-equilibrium self-assembled structures, called dissipated structures, of PBLG were observed by putting and drying a 1,2-dichloroethane drop of PBLG on a hydrophilic mica surface. AFM images of the dried sample on mica clearly show the multi-layered structure of PBLG molecules with honeycomb structures under high humidity conditions. On the contrary, under low humidity conditions, densely packed cholesteric liquid crystal-like structures were observed without holes.
  • Tetsu Yonezawa, Kazuhiko Shibuya, Hiroshi Nishihara
    Transactions of the Materials Research Society of Japan, Vol 30, No 4 30 4 1255 - 1257 2005年 [査読有り][通常論文]
     
    Well-defined surfactant-stabilized "Co-shell Au-core" bimetallic nanoparticles were successfully prepared in the presence of the mixture of two surfactant molecules. The formation of these core-shell structures is driven by the thermal deposition of Co(CO)(g) by refluxing p-xylene solution in the presence of the pre-formed gold nanoparticles which were prepared by NaBH4-reduction of RAuCl4. Continuous layer of cobalt without vacancies wrapping the gold core was revealed by TEM observation and the obtained bimetallic nanoparticles could be dispersed stably.
  • N Shirahata, WS Seo, T Kinoshita, T Yonezawa, A Hozumi, Y Yokogawa, T Kameyama, Y Masuda, K Koumoto
    LANGMUIR 20 20 8942 - 8946 2004年09月 [査読有り][通常論文]
     
    We have successfully observed that an octadecyltrichlorosilane self-assembled monolayer (OTS-SAM) can be anchored onto hydrated silicon surface utilizing several kinds of analytical methods as follows. HR-TEM observation found that no SiO2 interlayer formed between OTS-SAM and a hydrogen-terminated Si(001) surface. The static water-contact angle on the Si:H substrate increased with immersion time in anhydrous toluene containing 1.0 vol% of OTS molecules and reached 110°, resulting in formation of a pure methyl-terminated Si surface. The surface hydrophobicity was maintained even after the treatments of the scotch tape test and stringent sonication test in dilute alkaline aqueous base at pH 10. Octadecyltrimethoxysilane could not anchor onto the Si:H surface. It was thus clarified that only trichlorosilane molecule could anchor onto a Si surface without an intervening SiO2 interlayer.
  • Brian S. Zelakiewicz, Tetsu Yonezawa, YuYe Tong
    Journal of the American Chemical Society 126 26 8112 - 8113 2004年07月07日 [査読有り][通常論文]
     
    We report the first observation of 77Se nuclear magnetic resonance (NMR) in octaneselenol-protected Au nanoparticles of an average particle size of 2.5 nm. The 77Se NMR characteristics observed, i.e., broad line shape, fast nuclear spin-lattice, and spin-spin relaxation rates, which are reminiscent of 13C NMR of CO on transition metal surfaces, strongly suggest that Se becomes metallic upon binding to the Au nanoparticle surfaces. Copyright © 2004 American Chemical Society.
  • N Shirahata, T Yonezawa, WS Seo, K Koumoto
    LANGMUIR 20 4 1517 - 1520 2004年02月 [査読有り][通常論文]
     
    This is the first report for the photolithography of the Si-C linked monolayers directly bonded onto Si substrate surface. We experimentally found that the Si-C bonds formed between the terminated carbons of the monolayers and Si atoms at Si substrate surface are cleaved by ultra-violet (UV) irradiation in ambient air. In addition, HR-TEM observation clarified no SiO2 interlayer intervenes between alkyl monolayer and Si. This basic finding can extensively contribute to both the fields of (1) the academic photochemical study and (2) the monolayer technology including materials science, as follows.
  • Yoshinori Yamanoi, Tetsu Yonezawa, Naoto Shirahata, Hiroshi Nishihara
    LANGMUIR 20 4 1054 - 1056 2004年02月 [査読有り][通常論文]
     
    A novel immobilization method of gold nanowire onto silicon substrate without intervening silica interlayer is developed. The gold nanowire can be formed utilizing shape transformation of the adjacent gold nanoparticles on the substrate at low temperatures. Gold nanoparticle stabilized by 1-mercaptpropene (HSCH2CH=CH2), with particle size of 4.32 nm, was synthesized as a starting material. The nanoparticles were immobilized onto silicon surface by radical reaction between silicon-hydrogen bond of a hydrogen-terminated silicon (Si:H) substrate surface and terminal double bond on the nanoparticle surfaces in an anhydrous toluene solution. Above 110°C, the spherical particles with the size of several tens nanometer was observed on silicon surface because of an aggregation of the nanoparticles in the solution. In contrast, the gold nanowire structures were observed on silicon surfaces at the temperature ranging from 40°C to 65°C. The width and height of the nanowires increased with increasing reaction temperat
  • N Shirahata, Y Masuda, T Yonezawa, K Koumoto
    JOURNAL OF THE EUROPEAN CERAMIC SOCIETY 24 2 427 - 434 2004年 [査読有り][通常論文]
     
    We have succeeded in fabricating an atomic flattening surface of organosilane self-assembled monolayers (SAMs) on a Si substrate. In the present process, the octadecyltrichlorosilane (OTS) compound was selected as the starting material for the SAM. The OTS-SAM was formed by the reaction between the OTS molecules and the substrates, which were hydrogen terminated Si(001) (H:Si) and silica covered on Si(001) (SiO2/Si), at room temperature in a N-2 atmosphere. The formation rate of the OTS-SAM onto H:Si was smaller than that on SiO2/Si. Interestingly, the hydrophobicity of the OTS-SAM was observed to increase the amount formed on H:Si in comparison with that on SiO2/Si. The photo reactivity of the SAMs formed on each substrate was also investigated by using ultraviolet (UV) irradiation in ambient air. Tin hydroxide thin films were site-selectively deposited on the patterned OTS-SAM/Si substrate in order to clarify the cleavage of the OTS-SAM by the UV irradiation. (C) 2003 Elsevier Ltd. All rights reserved.
  • N Shirahata, T Yonezawa, Y Miura, K Kobayashi, K Koumoto
    LANGMUIR 19 22 9107 - 9109 2003年10月 [査読有り][通常論文]
     
    We propose a technique for fabricating a carbohydrate-terminated monolayer (CM) surface, which is extremely flat at the angstrom level. The CM was immobilized onto a Si surface by Si-C covalent bond. Specific adsorption of the protein molecule from a contacting solution was observed on the CM area of a patterned CM substrate surface, while its nonspecific adsorption was observed on the Si-O area.
  • Yanfeng Gao, Yoshitake Masuda, Tetsu Yonezawa, Kunihito Koumoto
    Materials Science and Engineering B: Solid-State Materials for Advanced Technology 99 1-3 290 - 293 2003年05月25日 [査読有り][通常論文]
     
    Successful preparation of strontium titanate (SrTiO3 STO) thin films has been realized by the liquid phase deposition method. The STO precursor solid thin films with close-packed grains smaller than 200 nm were fabricated from an aqueous solution of Sr(NO3)2/(NH4)2TiF6/H 3BO3 = 1/1/3 (molar ratio) at 50 °C on a Si substrate. X-ray photoelectron spectroscopy analysis showed that the as-deposited film contained fluorine as an impurity, which could be completely eliminated by annealing at 500 °C in air, accompanying the crystallization of the as-deposited amorphous thin film into perovskite-type STO. © 2002 Elsevier Science B.V. All rights reserved.
  • Yanfeng Gao, Yoshitake Masuda, Zifei Peng, Tetsu Yonezawa, Kunihito Koumoto
    Journal of Materials Chemistry 13 3 608 - 613 2003年03月01日 [査読有り][通常論文]
     
    A transparent, high purity, amorphous titanium dioxide thin film composed of densely packed nanometer-sized grains has been successfully deposited on a glass substrate at room temperature from an aqueous peroxotitanate solution using a simple, inexpensive, reproducible, and environmentally friendly method. The as-deposited thin film was 117 nm thick and composed of closely packed particles of 10-15 nm in diameter, but they aggregated into large grains of 50-100 nm in diameter. The aqueous peroxotitanate solution was obtained by dissolving metatitanic acid (H2TiO3) in a mixture of concentrated H2O2 and NH3·H2O. An anatase TiO2 thin film was obtained by heating the as-deposited thin film at 500°C for 1 h in air. A chemical composition of TiO1.4(O2)0.5(OH)0.2 ·1.34H2O is proposed for the as-deposited thin film, based on XPS, T-IR and TG-DTA data. Band gap energies of 3.20 eV for indirect transition and 3.63 eV for direct transition were obtained for the anatase TiO2 film.
  • Tetsu Yonezawa, Hideo Genda, Kunihito Koumoto
    Chemistry Letters 32 2 194 - 195 2003年02月05日 [査読有り][通常論文]
     
    Homogeneous and uniform-sized silver nanoparticles were obtained by reduction of insoluble silver halides. As the stabilizing reagent, a small cationic thiol, thiocholine bromide, was used. Even from large crystals of silver halides, nanosized particles were obtained. Under the optimum conditions, highly monodispersed nanoparticles with relative standard deviation of less than 7% were obtained.
  • Peixin Zhu, Yoshitake Masuda, Tetsu Yonezawa, Kunihito Koumoto
    Journal of the American Ceramic Society 86 5 782 - 790 2003年 [査読有り][通常論文]
     
    Hydroxyapatite (HAp) deposition onto positively charged surfaces (i.e., self-assembled monolayers (SAMs) terminated with NH2 head groups) and negatively charged surfaces (i.e., OH-SAMs (weak) and COOH-SAMs (strong)) soaked at 50°C in aqueous supersaturated solutions (1.5 SBF, pH 7.0-7.6 SBF = simulated body fluid) was investigated using a quartz-crystal microbalance. The results revealed that the solution conditions greatly influenced the formation of HAp on the charged surfaces. In a stable supersaturated solution of simulated body fluid (1.5 SBF, pH > 7.4), more strongly negative surfaces had a more powerful induction capability for the heterogeneous nucleation of HAp (COOH < OH), whereas nucleation was obviously prohibited on a positive surface (NH2-SAM). On the other hand, after the calcium phosphate particles had nucleated homogeneously in an unstable soaking solution (1.5 SBF, pH ≧7.4), adhesion of the HAp microparticles to the NH2-SAM was observed. A two-step interaction is conceivable to describe the formation of HAp on the positive NH2-SAM: At the first stage, electrostatic interaction dominates the adhesion of HAp microparticles at the second stage, hydrogen bonds possibly form between the HAp microparticles and the amino head groups of the NH2-SAM, for a firm bonding with the substrate, and the microparticles grow progressively into a thin film. The electrophoretic behaviors of the HAp microparticles confirmed this hypothesis.
  • Yanfeng Gao, Yoshitake Masuda, Tetsu Yonezawa, Kunihito Koumoto
    Chemistry of Materials 14 12 5006 - 5014 2002年12月01日 [査読有り][通常論文]
     
    We have succeeded in site-selective deposition of SrTiO3 (STO) thin films on patterned self-assembled monolayers (SAMs) by the liquid phase deposition (LPD) method. SAMs of heptadecafluoro-1,1,2,2,-tetrahydrodecyltrichlorosilanes [HFDTS, CF3(CF2)7(CH2)2SiCl3] were prepared on Si wafers and modified by UV irradiation through a photomask. This SAM template was composed of HFDTS surfaces (Si-CF3) and silanol surfaces. The patterned SAM-covered substrate was then immersed into a (NH4)TiF6/Sr(NO3)/H3 BO3 aqueous solution at 50°C to deposit a solid phase. (NH4)2TiF6, which could form [Ti(OH)nF6-n]2- slowly in an aqueous solution, was selected as a source of TiO32-. H3BO3 was a scavenger of fluorine and was used to control the reaction rate. The STO films were selectively deposited in the silanol regions. The as-deposited film was amorphous containing fluorine as a main impurity. With annealing at 500°C for 2 h in air, the as-deposited film was crystallized into SrTiO3 and the fluorine was eliminated. Film morphology was characterized by both SEM and AFM. Metal-oxide-semiconductor (MOS) devices were prepared by using an as-deposited film or a crystallized film as a gate oxide. The dielectric constant of SrTiO3 thin films and the leakage current of the MOS device were evaluated. These results indicate that the SrTiO3 film fabricated by a combination of the SAM technique with LPD method through a one-step process is promising for application to dielectric films.
  • N Shirahata, Y Masuda, T Yonezawa, K Koumoto
    LANGMUIR 18 26 10379 - 10385 2002年12月 [査読有り][通常論文]
     
    This paper presents a novel process for the fabrication of site-selectively deposited tin oxide ultrathin films (<10 nm) by using molecular recognition between the precursors and the surface of the Si substrate. Using this simple technique, the film thickness of micropatterned tin oxide films was easily controlled. Patterned self-assembled monolayers, in which both hydrophilic and hydrophobic areas formed, were used as templates for the site-selective deposition of the films. Two precursors of SnCl4 and C4H9SnCl3 were selected. The films were selectively deposited on the hydrophilic regions through the liquid phase. The growth rate of the film deposited in SnCl4 solution was approximately 6 times faster than that in C4H9SnCl3 solution. A quartz crystal microbalance measurement implied that film growth could be suppressed by the formation of hydrophobic surfaces on the growing films with increasing immersion time in C4H9SnCl3 solution.
  • Nagahama, D., Masuda, Y., Yonezawa, T., Koumoto, K.
    Key Engineering Materials 228-229 2002年 [査読有り][通常論文]
  • Nagahama, D, Tani, T, Masuda, Y, Itahara, H, Yonezawa, T, Koumoto, K, IEEE
    Xxi International Conference on Thermoelectrics, Proceedings Ict '02 2002- 211 - 214 2002年 [査読有り][通常論文]
     
    We fabricated highly textured Ca3Co4O9-based ceramics by using plate-like particles as a template in order to extract highly anisotropic thermoelectric properties. Plate-like powder and fine powder of (Ca2.7Na0.15Bi0.15)Co4O9 were synthesized and wet-mixed at the ratio of 1:4. The slurry was tape-cast into a form with the platelets aligned parallel to the tape surface. The tapes were stacked, and sintered or hot-pressed at 1193 K. The resultant ceramics showed highly preferred orientation with the (001) plane parallel to the tape surface. The electrical conductivity in the direction of the ab-plane was improved to 1.8 x 104S/m at 1073 K by the texture given. The maximum power factor reached 5.9 x 10-4W/mK2 at the same temperature.
  • Masuda, Y., Wang, D., Yonezawa, T., Koumoto, K.
    Key Engineering Materials 228-229 2002年 [査読有り][通常論文]
  • Masuda, Y., Jinbo, Y., Yonezawa, T., Koumoto, K.
    Chemistry of Materials 14 3 1236 - 1241 2002年 [査読有り][通常論文]
     
    TiO2 thin films were grown on several kinds of SAMs (self-assembled monolayers) using TC (titanium tetrachloride), TDD (titanium dichloride diethoxide), or TE (titanium tetraethoxide) as a starting material. We discussed the thin film formation mechanism and improvement of feature edge acuity through controlling the reactivity by changing functional groups of starting material and the surface functional groups of SAMs. The deposition of TiO2 from TC or TDD solution was promoted in the silanol group, and the deposition was suppressed on OTS (octadecyltrichloro-silane) SAM. On the other hand, TE was deposited regardless of the type of surface functional group in the whole area of patterned SAMs. The silanol group, which has high hydrophilicity, accelerated the growth of TiO2, and the OTS SAM, which has hydrophobicity, suppressed the growth of TiO2. It is also clarified that the chlorine atom in the starting material has high reactivity with silanol groups of SAMs.
  • Masuda, Y., Itoh, M., Yonezawa, T., Koumoto, K.
    Langmuir 18 10 4155 - 4159 2002年 [査読有り][通常論文]
     
    Novel processes to realize low-dimensional arrangement of SiOq2 particles were proposed. Particle wires and a pattern of the close-packed particle monolayer were fabricated in the solution at room temperature. SAMs (self-assembled monolayers) were formed on Si substrates and modified to be suitable for templates of precise arrangement. Particles were arranged precisely in the desired positions in the solution using well-controlled electrostatic interactions and chemical bond formation between particles and substrates.
  • Yanfeng Gao, Yoshitake Masuda, Tetsu Yonezawa, Kunihito Koumoto
    Journal of the Ceramic Society of Japan 110 1281 379 - 385 2002年 [査読有り][通常論文]
     
    Zirconia thin films were successfully micropatterned on octadecyltrichlorosilane (OTS)-self-assembled monolayers (SAM) in ZrOCl2 · 8H2O-ethanol solution at room temperature. OTS-SAM was modified by UV-irradiation through a photomask to change into a SAM template patterned with silanol and octadecyl groups. The films were selectively deposited in the silanol regions through hydration-alcoholysis and condensation reactions. The as-deposited film was amorphous with a complex composition, decomposed into tetragonal-zirconia at 500°C, and further transformed into monoclinic-zirconia at 600°C. The as-deposited film demonstrated a dielectric permittivity of 14 at 100 kHz, but a resistivity of 3.1 × 1011 Ω cm and a leakage current density of 9.0 × 10-7 Acm-2 obtained for a MOS device indicated that the film quality needed to be improved.
  • 米澤 徹
    高分子 50 4 262 - 262 The Society of Polymer Science, Japan 2001年04月01日
  • T. Sawadaishi, K. Ijiro, M. Shimomura, Y. Shiraishi, N. Toshima, T. Yonezawa, T. Kunitake
    MOLECULAR CRYSTALS AND LIQUID CRYSTALS 371 123 - 126 2001年 [査読有り][通常論文]
  • Tetsu Yonezawa, Toyoki Kunitake
    Colloids and Surfaces A: Physicochemical and Engineering Aspects 149 1-3 193 - 199 1999年04月15日 [査読有り][通常論文]
     
    Gold nanoparticles stabilized by a water-soluble mercapto ligand (sodium 3-mercaptopropionate) were produced by a modified citrate reduction of HAuCl4. No rigorous cleanliness is needed and the reductant is decomposed to CO2. Stable aqueous dispersions of gold nanoparticles without any precipitation for several months could be obtained. The particle size can be controlled by the stabilizer/gold ratios. These gold nanoparticles were incorporated successfully into the interlayers of cast films of cationic bilayers by immersion of the film in gold nanoparticle dispersions. Copyright (C) 1999 Elsevier Science B.V.
  • 米澤 徹, 尾上 慎弥, 國武 豊喜
    高分子論文集 56 12 855 - 859 The Society of Polymer Science, Japan 1999年 
    直鎖状アニオン性高分子としてDNAを用いて, 新規に調製したカチオン性金ナノ粒子をそれに沿って密に一次元配列させることに成功した. このカチオン性金ナノ粒子は, その表面に高密度なカチオン電荷を有しているため, DNA分子に強く吸着し, 吸着粒子間隙も非常に小さく, 一定であった. この粒子の吸着機構についても考察した.
  • Tetsu Yonezawa, Shin-Ya Onoue, Toyoki Kunitake
    Chemistry Letters 10 1061 - 1062 1999年 [査読有り][通常論文]
     
    Reduction of AuCl4 by sodium borohydride in the presence of quatemary ammonium disulfide gave an aqueous dispersion of cationic gold particles in nano-dimension. These cationic nanoparticles could be assembled effectively on an anionic amphiphile layer with a close-packed structure.
  • Tetsu Yonezawa, Shin-Ya Onoue, Toyoki Kunitake
    Chemistry Letters 7 689 - 690 1998年 [査読有り][通常論文]
     
    Quartz crystal microbalance (QCM) measurements and scanning electron microscopy revealed the formation of defect-free monolayer of anionic silica nanoparticles on a solid substrate coated with a cationic organized molecular layer.
  • Tetsu Yonezawa, Mizuki Sutoh, Toyoki Kunitake
    Chemistry Letters 7 619 - 620 1997年 [査読有り][通常論文]
     
    Facile, safe and efficient preparation of stable dispersions of gold nanoparticle from tetrachloroaureic(III) ion is achieved by simultaneous addition of citrate as reductant and sodium 3-mercaptopropionate as stabilizer. No rigorous cleanliness is needed and the reductant is decomposed to CO2. The particle size can be controlled in the range between 2.3 nm and 10 nm.
  • 米澤 徹, 戸嶋 直樹
    高分子論文集 52 12 809 - 820 高分子学会 1995年 [査読有り][通常論文]
  • T Yonezawa, N Toshima
    KOBUNSHI RONBUNSHU 52 12 809 - 820 1995年 [査読有り][通常論文]
     
    Irradiation of visible light and introduction of hydrogen into aqueous solutions of noble metal salts in the presence of surfactants gave stable colloidal dispersions of nanoscopic noble metal clusters protected by surfactant micelles with relatively narrow size distributions. The concentration of the surfactant had to be higher than the corresponding critical micelle concentration (CMC). These clusters can be used as active catalysts for hydrogenation of olefins or visible-light-induced hydrogen-evolution from water. In the case of hydrogenation of unsaturated fatty acids and their salts, some regio-selectivity is observed, probably because the substrates are aligned in the organized media surrounding the metal clusters. The protective structures of noble metal cluster particles protected by surfactants are analyzed by the chemical shifts of surfactant molecules in C-13 and H-1 NMR. The Stokes' radii of the surfactant-protected particles measured by a Taylor dispersion method were also helpful.
  • Tetsu Yonezawa, Yaeko Gotoh, Naoki Toshima
    Reactive Polymers 23 2-3 43 - 51 1994年 [査読有り][通常論文]
     
    Visible light irradiation of an aqueous solution of a platinum ion and a non-ionic surfactant, poly(ethylene glycol) monolaurate, gives a colloidal dispersion of nanoscopic platinum clusters protected by the surfactants. The structure of the surfactants protecting the platinum clusters is investigated by a nuclear magnetic resonance (NMR) technique. In the 13C NMR spectra, all carbon signals of the hydrophobic alkyl chain of the surfactant decrease in height with increasing concentration of the platinum cluster. This indicates that the platinum cluster particle is not incorporated into the central hydrophobic hole of the surfactant micelle, but is protected by the adsorption of surfactant molecules on the surface of the cluster particle at the hydrophobic part. © 1994.
  • N TOSHIMA, T YONEZAWA, M HARADA, K ASAKURA, Y IWASAWA
    CHEMISTRY LETTERS 5 815 - 818 1990年05月 [査読有り][通常論文]
  • N TOSHIMA, K KUSHIHASHI, T YONEZAWA, H HIRAI
    CHEMISTRY LETTERS 10 1769 - 1772 1989年10月 [査読有り][通常論文]
  • 川崎 英也, 大洞 康嗣, 米澤 徹, 荒川 隆一
    日本接着学会誌 = Journal of the Adhesion Society of Japan 49 5 171 - 176 一般社団法人 日本接着学会 2013年05月01日

書籍

  • 産業応用を目指した無機・有機新材料創製のための構造解析技術
    米澤 徹, 陣内浩司 (担当:監修)
    シーエムシー出版 2015年08月

講演・口頭発表等

  • カルボン酸被覆銅ナノ粒子による接合  [通常講演]
    田村 一樹, 高橋 悠太, 塚本 宏樹, 米澤 徹
    第12回CSJ化学フェスタ 2022年10月 ポスター発表
  • 金属ナノ粒子濃厚分散系の安定構築  [招待講演]
    米澤 徹
    第12回CSJ化学フェスタ 材料化学の最先端を歩み続ける濃厚分散系 2022年10月 シンポジウム・ワークショップパネル(指名)
  • Structure of Bimetallic Nanoparticles Synthesized by Sputtered Deposition onto Liquid and Their Catalytic Properties  [招待講演]
    Mai Thanh Nguyen, Tetsu Yonezawa
    第73回コロイドおよび界面化学討論会 2022年09月 口頭発表(招待・特別)
  • アルキルカルボン酸被覆銅微粒子の低温焼結とメカニズム解明  [通常講演]
    米澤 徹, 戸倉凛太郎
    第73回コロイドおよび界面化学討論会 2022年09月 口頭発表(一般)
  • 超音波照射下で誘起されるEGaIn液体金属ナノ粒子触媒によるエタノールからのグラファイトカーボン生成  [通常講演]
    川﨑 英也, 大槻 朋子, 杉野 史弥, 山本 健, 徳永智春, 戸倉凜太郎, 米澤 徹
    第73回コロイドおよび界面化学討論会 2022年09月 口頭発表(一般)
  • アルギン酸ナトリウム保護金ナノ粒子の合成と低侵襲X線マーカーとしての利用  [招待講演]
    米澤 徹, Haoran Liu
    第73回コロイドおよび界面化学討論会 2022年09月 口頭発表(招待・特別)
  • Pt/Ag Solid Solution Alloy Nanoparticles Co-sputtered onto Liquid Polyethylene Glycol Substrate  [通常講演]
    Mingbei Zhu, Mai Thanh Nguyen, Tetsu Yonezawa
    IVC-22 (The 22nd International Vacuum Congress) 2022年09月 口頭発表(一般)
  • エチレングリコールを用いて合成されたZnTe微粒子の生成機構  [通常講演]
    チャウユエンティンレイチェル, 米澤 徹
    日本化学会北海道支部2022年夏季研究発表会 2022年07月
  • 銅ニッケル錯体混合インクの調製と低温焼結  [通常講演]
    木村朋貴, 戸倉凜太郎, 米澤 徹
    日本化学会北海道支部2022年夏季研究発表会 2022年07月 口頭発表(一般)
  • 金属ナノ粒子・微粒子ペースト作製の実際  [招待講演]
    米澤 徹
    日本ディスパージョンセンター技術研究会 2022年06月 シンポジウム・ワークショップパネル(指名)
  • 金属ナノ粒子・微粒子の合成と回収の決め手  [招待講演]
    米澤 徹
    日本ディスパージョンセンター技術研究会 2022年05月 シンポジウム・ワークショップパネル(指名)
  • Cobalt Nickel Oxides Embedded on reduced graphene oxide as Catalysts for Rechargeable Zinc-air Battery  [通常講演]
    Zixuan Huang, Wei Jian, Sim・Tetsu Yonezawa・Thanh Mai Nguyen, Masayuki Takahashi
    化学系学協会北海道支部2022年冬季研究発表会 2022年01月
  • Graphene Oxide Induced Iron Cobalt Spinel Oxide Nanoparticles as Bifunctional Catalyst in Zinc-Air Battery  [通常講演]
    Wei Jian Sim, Zixuan Huang, Masayuki Takahashi, Mai Thanh Nguyen・Tetsu Yonezawa
    化学系学協会北海道支部2022年冬季研究発表会 2022年01月
  • Cu2O形成を抑制することでネッキング促進されるカルボン酸被覆銅微粒子  [通常講演]
    戸倉凜太郎, 米澤 徹
    化学系学協会北海道支部2022年冬季研究発表会 2022年01月 口頭発表(一般)
  • 画像誘導放射線治療に用いるフィデューシャルマーカーのためのRFプラズマを用いた金ナノ粒子の合成  [通常講演]
    古岡昂真, LIU Haoran, 宮本直樹, 米澤 徹
    2021年度日本金属学会・日本鉄鋼協会両北海道支部合同冬季講演大会 2022年01月
  • 酸化グラフェン(GO)上におけるFe-Co-Ni合金ナノ粒子の化学合成  [通常講演]
    新開裕二, 米澤 徹
    2021年度日本金属学会・日本鉄鋼協会両北海道支部合同冬季講演大会 2022年01月
  • プリンテッドエレクトロニクスにおけるカルボン酸被覆銅微粒子を利用した低温焼結の実現  [通常講演]
    戸倉凜太郎, 米澤 徹
    超異分野学会 北海道フォーラム 2021年12月 シンポジウム・ワークショップパネル(公募)
  • 結晶構造を制御して実現する銅微粒子低温迅速焼成  [招待講演]
    米澤 徹
    長崎大学第3期中期目標・中期計画重点研究課題「次世代エネルギー関連技術に向けた革新的物質科学研究拠点」第20回講演会 2021年11月 シンポジウム・ワークショップパネル(指名)
  • Body temperature-activated in situ-formation gel for the delivery and fixation of alginate-stabilized gold nanoparticles for proton beam therapy  [招待講演]
    Haoran Liu, Tetsu Yonezawa
    The 5th A3 Foresight Symposium on Organic/Inorganic Nanohybrid Platforms for Precision Tumor Imaging and Therapy 2021年10月 口頭発表(招待・特別)
  • Iron cobalt oxide nanoparticles supported on reduced graphene oxide bifunctional catalyst in high current density zinc-air battery  [招待講演]
    Wei Jen Sim, Mai Thanh Nguyen, Tetsu Yonezawa
    The 5th A3 Foresight Symposium on Organic/Inorganic Nanohybrid Platforms for Precision Tumor Imaging and Therapy 2021年10月 口頭発表(招待・特別)
  • Bimetal solid-solution alloy nanoparticles synthesized by sputter deposition onto liquid  [招待講演]
    Mai Thanh Nguyen, Tetsu Yonezawa
    The 5th A3 Foresight Symposium on Organic/Inorganic Nanohybrid Platforms for Precision Tumor Imaging and Therapy 2021年10月 口頭発表(招待・特別)
  • Synthesis of Pt/Ag solid solution alloy nanoparticles on liquid polymer by co-sputtering  [通常講演]
    Mingbei Zhu, Mai Thanh Nguyen, Tetsu Yonezawa
    第72回コロイドおよび界面化学討論会 国際シンポジウム 2021年09月 口頭発表(一般)
  • Alginate-stabilized gold nanoparticles preapred in microwave-induced plasma in liquid process with long-term strage stability for potential biomedical applications  [通常講演]
    Haoran Liu, Kai Ikeda, Mai Thanh Nguyen, Tetsu Yonezawa
    第72回コロイドおよび界面化学討論会 国際シンポジウム 2021年09月 口頭発表(招待・特別)
  • Effect of surface oxide on the sitnering of copper fine particels stablized surfacetant molecules in printed electronics  [通常講演]
    Rinatro Tokura, Tetsu Yonezawa
    第72回コロイドおよび界面化学討論会 国際シンポジウム 2021年09月
  • 画像誘導放射線治療で用いる低侵襲マーカーに対する高周波プラズマで合成した金ナノ粒子の適用可能性  [通常講演]
    古岡昂真, Liu Haoran, 米澤 徹
    第73回コロイドおよび界面化学討論会 2020年09月 ポスター発表
  • 低融点Bi-Sn-In合金を用いた潜熱蓄熱粒子の開発  [通常講演]
    樋口翔大, 米澤 徹
    第73回コロイドおよび界面化学討論会 2020年09月 ポスター発表
  • ホットインジェクション法によるZnTe微粒子の形成スキーム  [通常講演]
    チャウ ユエンティン, レイチェル・グエン タンマイ, 米澤 徹
    第73回コロイドおよび界面化学討論会 2020年09月
  • Gold Nanoparticles Sputtered onto Oleic Acid and Oleylamine Liquids  [通常講演]
    Mai Thanh Nguyen, Tetsu Yonezawa
    IVC-22 (The 22nd International Vacuum Congress) 2020年09月 口頭発表(一般)

その他活動・業績

受賞

  • 2022年08月 国立台北科技大学 Horonary International Chair Professor
  • 2022年01月 化学系学協会北海道支部2022年冬季研究発表会 優秀講演賞(口頭発表部門)
     Cu2O形成を抑制することでネッキング促進されるカルボン酸被覆銅微粒子 
    受賞者: 戸倉凜太郎;米澤 徹
  • 2016年 イギリス王立化学会 フェロー
     
    受賞者: 米澤徹
  • 2015年04月 北京大学 Xinda Lectureship
     
    受賞者: 米澤徹
  • 2012年10月 日本分析化学会 2011 Analytical Sciences 最多引用論文賞
     
    受賞者: 米澤徹
  • 2009年03月 日本分析化学会 ホットアーティクルアワード
     
    受賞者: 米澤徹

共同研究・競争的資金等の研究課題

  • フラッシュランプアニール法による高エントロピー合金ナノ粒子合成法の確立
    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 : 2021年04月 -2023年03月 
    代表者 : 米澤 徹
  • 超広帯域光源開発のためのナノ粒子の最適化
    日本学術振興会:科学研究費助成事業 国際共同研究加速基金(国際共同研究強化(B))
    研究期間 : 2018年10月 -2022年03月 
    代表者 : 米澤 徹, グエン タンマイ, 徳永 智春
  • 量子生命科学的アプローチによる金ナノ粒子の放射線増感効果の解明と最適化への挑戦
    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 : 2018年04月 -2022年03月 
    代表者 : 橋本 孝之, 米澤 徹, 柴山 環樹
     
    難治性がんの放射線治療成績向上を目的とする、体内の金属に対する放射線の影響に関する研究を行った。金粒子に関するナノテクノロジーで個々の細胞の遺伝子情報等の差異による放射線感受性の差を凌駕して、放射線治療の増感作用として活用する研究において、研究分担者である北海道大学工学研究院の柴山らと進める予定であった、細胞微細構造の電子顕微鏡による観察は、2018年9月の胆振東部地震の影響により、超高圧電子顕微鏡の除振台が損傷していたが、2019年度内に復旧済みである。またもう一名の研究分担者である北海道大学工学研究院の米澤らとは、体内投与可能な金ナノ粒子の化学的製造に関して、必要な物品の購入を行い、研究に着手済である。新型コロナウイルス感染の拡大を受け、全国もしくは一部地域に緊急事態宣言やまん延防止等重点措置が出ており、照射実験実施の日程調整に難航した状況が継続していて確定のめどが立っていないが、状況が改善しだいなるべく早期に実験を行うべく、研究実施期間について1年間の延長申請を行い承認された。放射線関連の国内外の学会・研究会は新型コロナウイルス感染防止の観点から現地参加は困難であるが、オンラインで参加し、最新の金ナノ粒子の放射線増感効果に関する研究発表について引き続き情報収集を行っている。また将来的に金ナノ粒子の放射線増感効果の臨床応用の期待が大きい、小児の髄芽腫や胚細胞腫瘍等の中枢神経腫瘍に対する全脳照射において、X線と陽子線との治療計画シミュレーション比較検討した内容についPTCOG2020(オンライン開催)で発表を行った。
  • 日本学術振興会:科学研究費助成事業 挑戦的研究(萌芽)
    研究期間 : 2019年06月 -2021年03月 
    代表者 : 米澤 徹, グエン タンマイ, 徳永 智春, 塚本 宏樹
     
    本研究では、低温焼成用銅微粒子として、微酸化銅ナノ粒子や微酸化相を表層にもつ銅微粒子を合成した。この数十g/バッチ以上得られる工業的合成法を確立することに成功した。得られた微粒子をジプロピレングリコールにビーズミルを用いて分散した。ビーズミル条件を決定して、安定なペーストを合成することができた。現時点では銅微粒子の含有量を80 wt%以上にもできることが分かった。これを基板に塗布し、200℃以下で焼結させたところ、バルクの数倍以内の低い抵抗率を示す導電被膜の形成に成功した。さらにその被膜形成機構が、原子の拡散強化である「ナノ銅吹き出し」によることを示した。
  • 液中プラズマプロセッシングを用いたバルクから合成するハイエントロピー合金ナノ粒子
    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 : 米澤 徹
     
    液中でのプラズマ法を用いたハイエントロピー合金(HEA)ナノ粒子の直接合成に引き続き従事した。ハイエントロピー合金とは多元素を等モル程度含んだ合金のことである。液中プラズマ、さらには、レーザーアブレーション法の適用、酸化した多元素合金の還元、その際における合金ナノ粒子のカプセル化に挑戦し結果をえた。レーザーアブレーション法と同様液中プラズマ法においても、前周期遷移金属の場合には酸化したナノ粒子が生成した。溶媒を有機溶媒に代えても、還元体を得ることが難しかった。 本研究では前周期遷移金属に集中し、得られたナノ粒子は還元操作によってハイエントロピーナノ粒子化できると考え、水素環境場における還元によって微細な合金ナノ粒子の合成に挑戦した。 筆者らは酸化スズをベーマイトでコーティングし還元操作によってコアシェル構造を持つナノ粒子の合成に成功している。そこで、ハイエントロピー合金ナノ粒子においても、還元操作においては金属酸化物コーティングを行い、還元操作時の融合・凝集を防ぐ操作を行った。本研究においてもべーマイト処理法を用いて、それによって粒子1つをアルミナコートすることに成功した。つまり、べーマイトコーティング手法は汎用的で、比較的幅広い合金系に適応できる可能性を見出した。 得られたナノ粒子についてさらにXRD、TEM、SEMなどによって構造解析を行った。まだ十分なデータの蓄積が得られていないので引き続き検討する。
  • 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 : 2018年04月 -2021年03月 
    代表者 : 米澤 徹, グエン タンマイ, 徳永 智春
     
    本研究では、多元マグネトロンスパッタ装置を用い、マトリクススパッタリング法によってナノ粒子合成、特に合金ナノ粒子の合成を行った。得られた粒子は安定で、よく分散していた。また、TEMグリッドへの直接スパッタリングなども行った。得られたの微細構造についてXRD、収差補正(原子分解)STEMなどを用いて詳細に行い、物性については、光学物性について検討をした。 XRDによる結晶構造解析と、STEMによる原子の配置の解析により、得られたナノ粒子は各々が合金であり、固溶体構造をとることが明確となった。これはマトリクススパッタリング法の特徴であった。光学特性についても検討し発光を示した。
  • マトリクススパッタリング法による無機元素ブロック包埋機能性ハイブリッド樹脂の構築
    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 : 2013年04月 -2015年03月 
    代表者 : 米澤 徹
     
    設計したマグネトロンスパッタリング装置を用い、そのチャンバー内に直接液状高分子や樹脂モノマー液を導入し、また場合によっては、添加剤となる金属錯形成物質を導入して無機ヘテロ元素ブロックとしての金属ナノ粒子・金属酸化物ナノ粒子の直接合成を試みた。これをマトリックススパッタリング法と名付けた。 ナノ粒子の粒子径制御には、金属配位化合物の利用が効果的である。液体マトリックス中にチオールなどの金属配位化合物を導入することによりナノ粒子の粒子径制御が可能であることを見出している。一方で、液体マトリックスとは別に、やや揮発性の高いチオール分子をチャンバー内に入れ、チャンバーのガス雰囲気にチオール分子を導入することによっても、ナノ粒子の小粒径化に成功した。このとき、得られたナノ粒子の量子収率は極めて高かった。一般に金ナノ粒子の発光量子収率は1-2%程度であるが、この手法で得られた金ナノ粒子は、10%を越える量子収率を示すものも多く、最大で16%にも達した。これは、チャンバー雰囲気にチオール分子を導入することにより、クラスター状態でナノ粒子がチオールに覆われ、スパッタリング液表面でそれらが凝集したものをナノ粒子として回収しているからと考えられる。そのため、金錯体のような高い量子収率を示しながら、安定にその発光特性を維持できる金ナノ粒子を合成できたことになる。極めて興味深い実用的な材料である。 金属酸化物ナノ粒子の合成では、チタニアの樹脂内への導入について議論を行ってきたが、酸素欠損型のチタニアが多く得られる場合があった。 また、共同研究の大きな成果としては、銅-パラジウム合金ナノクラスターをDMFを還元剤として用いて可能とした。このとき、この合金クラスターは固溶体構造を取っていることがXPSより示唆された。また、発光量子収率も金属組成によって変化することが示され、興味ある合金素材となった。
  • 文部科学省:科学研究費補助金(挑戦的萌芽研究)
    研究期間 : 2012年 -2012年 
    代表者 : 米澤 徹
     
    本研究では、常温で溶融した有機塩であり、真空中で蒸発をしないイオン液体を用い、それを導電体として試料表面の塗布することで、試料のチャージアップならびに乾燥を防ぎ、生体関連試料を湿潤状態で観察することを実現する。さらに、そうした手法の応用展開を図ることを目的とする。 研究期間の2年間で、非導電性物質、特にナノ物質のイオン液体による観察法について確立することができたとともに、生体関連物質の観察を、水溶性の高いコリンと呼ばれる生体関連化合物と同様の構造を持ったイオン液体を用い、さらに、試料をイオン液体に分散させたのちに、柔らかく吸引することで変形なく観察することを可能とした。
  • 文部科学省:科学研究費補助金(基盤研究(A))
    研究期間 : 2012年 -2012年 
    代表者 : 米澤 徹
     
    本研究では、SALDIに適したナノ粒子を合成し、それをイオン化支援材として基板上に塗布して用い、薬物・毒物分析が容易なレーザー脱離イオン化法の確立とそのメカニズムの解明を目的とした。同じ粒子では大きな粒子のほうがソフトイオン化能が高いことが分かり、ナノ粒子のレーザーによる昇温が穏やかな場合が適していると考えられた。また、Naをドープした酸化チタンが優れたSALDI能を示すことから、LDIではレーザーによって基板表面から脱離される中性分子は十分にあり、表面支援材であるナノ粒子のイオン附加能を引き上げることによって、検出イオンの量を増やすことができることを明らかとした。
  • 文部科学省:科学研究費補助金(特定領域研究)
    研究期間 : 2010年 -2011年 
    代表者 : 米澤 徹, 菊地 竜也
     
    本研究では、表面支援レーザー脱離イオン化質量分析法(SALDI-MS法)に用いられる金属ナノ粒子の合成とその挙動、さらには脱離・イオン化のメカニズム解明に挑戦した。まずは、サンプル用基板を作成するために、さまざまな金属・酸化物・半導体のナノ粒子および異方性粒子を作成した。結果として、その物質、構造、大きさ、形状がいずれも有機物の脱離に大きく影響することが分かった。そこで得られた粒子を用いて塗布した基板上に、波長を変えてパルスレーザーを照射したところ、可視光では、金ナノ粒子がそのプラズモン吸収で効率のいい脱離・イオン化性能を示したのに対し、紫外レーザーでは高い脱離・イオン化性能を示す酸化チタンナノ粒子は可視光では負の効果を示した、つまり脱離・イオン化する分子の量を平板基板よりも少なくしてしまった。この結果は、表面支援におけるレーザー脱離・イオン化においては、単純にパルスレーザー照射によって発生する局所的な熱による分子の基板表面からの脱離ではなく、光反応が脱離・イオン化に関与していることを明確に示している。さらに、紫外レーザーによる脱離では、金ではなく、白金は金属酸化物が効率のよい脱離とイオン化を見せていることから、単純に熱のみによるものではないことが分かる。メカニズムの明快な説明はまだできてはいないが、光による電子移動が関与している可能性がより高まったことで、SALDI-MSに...
  • 文部科学省:科学研究費補助金(基盤研究(B))
    研究期間 : 2009年 -2011年 
    代表者 : 米澤 徹
     
    表面支援レーザー脱離イオン化法に対する新しい基板の構築とその脱離・イオン化メカニズムの解明を行っている。本年度は、金属腐食の機構を有効に用いて、合金基板から特定の金属元素のみを選択的に溶解させるDealloy法(脱成分腐食法)や電気化学的手法によってナノ~オングストロームレベルでの凹凸をもつ金属ならびに半導体基板の作製ならびにその処理・表面構造解析とレーザー脱離イオン化について検証するとともに、そのメカニズム解明のための装置設計を行った。具体的には銅/白金合金基板から銅のみを溶解させエッチングし、表面でナノからオングストロームレベルの凹凸をもつ基板を作成することに成功した。その凹凸のサイズについては、処理法によって制御可能であった。その基板の表面SEM写真および断面TEM写真の撮影を行い、その凹凸について評価した。また、電気化学的操作によるナノレベルの凹凸をもち、かつ、先端を先鋭にした基板の開発にも成功している。こうした基板を用いたLDI実証試験を行っているところであり、いくつかの低分子化合物とペプチド・タンパクの高効率なソフトイオン化が可能となったことが示された。しかしながらいくつかの有機化合物は脱離されないことが見出され、その理由はまだ不明である。こうした脱離イオン化の詳細な機構を検証するために、レーザーによる有機物質脱離量を検量するためのシステム構築について設計を開始し...
  • 文部科学省:科学研究費補助金(特定領域研究)
    研究期間 : 2009年 -2010年 
    代表者 : 米澤 徹
     
    本研究では、光-分子強結合場を利用した、レーザー照射による有機分子の脱離とそのソフトイオン化について検討している。ソフトイオン化とは、有機物質を分解しないでイオン化することである。そこで、本年度は、光-分子強結合場を発現させる手段として金粒子の基板上への集積による表面支援レーザー脱離イオン化法について検証を行った。シリコン基板上にアミノシラン単分子膜を用いて作製した金粒子の集積した部分において、特に有機化合物の脱離・イオン化がレーザー照射によって起こりやすいことが見いだされた。一方で、単層の金粒子吸着層だと脱離・イオン化は生じにくい。このことは、レーザー脱離イオン化のメカニズムを考えるときに重要であり、金の場合においては、ナノ粒子の作る基板表面の凹凸ではなく、微粒子の凝集が有機物質の脱離およびイオン化に極めて有効に効いていることが明らかとなっている。つまり、ナノ粒子凝集エリアがつくる光-分子強結合場が脱離・イオン化を加速する方向に働いていることを示していると考えられる。一方で、レーザー照射による有機化合物の脱離量を相対的に比較したところ、金ナノ粒子の示すプラズモン吸収領域の波長のレーザーを用いた場合には脱離量が増大すると考えられた。この結果も、光-分子強結合場が光による基板表面からの有機物質の脱離・イオン化を促進していることを強く支持ずる。これは、本研究で目標とした、光-分子...
  • 文部科学省:科学研究費補助金(特定領域研究)
    研究期間 : 2008年 -2009年 
    代表者 : 米澤 徹
     
    本研究では、有機物のレーザーによる非分解イオン化(ソフトイオン化)のための無機ナノ構造体の設計を行っている。特に、これまでの研究から、先鋭化された部分をもつナノ構造を持たせた表面が電界集中に有効と考えられるため、そうしたナノ構造体の合成、基板構築を行ってきている。特に、白金などはそうした構造を作りやすい。また、レーザー照射による有機物の脱離量についても検証を行ってきた。これまでの検証から、白金を用いた場合のレーザーによる脱離量が非常に大きいことが見いだされた。また、半導体基板を用いたソフトイオン化についても検証した。その一方で、SALDI-MSではどうしても脱離・イオン化しない物質がいくつか見いだされた。低分子量の物質でもそのようなものがあるため、脱離とイオン化を分けて考えるシステムを構築する必要があることが明確となった。というのも、低分子量の物質が基板表面から脱離していないとは考えにくく、脱離したもののイオン化されていないと考察される。こうした物質をあつめ、構造を検証し、どのような構造が脱離・イオン化を抑制してしまうのか考える必要があると思われる。一方で、白金ナノ構造体を用いた基板上からは、長波長レーザーによっても有機物質をイオン化できることが明らかとなった。長波長のレーザーは、エネルギーが小さく、有機物質のソフトイオン化にはさらに好適であることは自明である。こうした可能性...
  • 文部科学省:科学研究費補助金(特定領域研究)
    研究期間 : 2008年 -2008年 
    代表者 : 米澤 徹
     
    従来、生体機能物質の非分解イオン化のためによく用いられてきたMALDI-MS法に代え、金属ナノ粒子を塗布した、ナノレベルの凹凸を有する基板を作製し、有機マトリクスフリーで、UVレーザーを用いて、合成高分子をソフト脱離・イオン化を起こすことを試みている。本研究では、特に、光-分子強結合場を利用したレーザーソフト脱離・イオン化を試みている。そこで、表面の清浄な金属ナノ粒子を合成するために、レーザーアビュレーション法を用いた。レーザーアビュレーション法は、インゴットから容易にナノ粒子を合成することができる手法である。その手法で、金、銀、白金、銅ナノ粒子を合成し、分子量10000程度までの分子のソフトイオン化を試みた。結果として、金および白金に顕著なソフト脱離・イオン化能があることが示された。白金は特に熱伝導率が小さいためにイオン化が促進されたと理解され、金の場合には、光-分子強結合場の可能性が見られた。しかし、銀および銅には脱離・イオン化能が見当たらず、現在、金ナノ粒子で試験を行っている。また、単層金ナノ粒子吸着では脱離イオン化能は見受けられないことから、高分子との交互積層を行った、ナノ粒子多積層体や、高濃度に基板上に塗布した金ナノ粒子凝集体が脱離・イオン化に重要なことも示されている。今後はさらに構造体制御を行って、効率のよいレーザー脱離・イオン化システムの構築を行う。
  • 文部科学省:科学研究費補助金(萌芽研究)
    研究期間 : 2007年 -2008年 
    代表者 : 島田 敏宏, 米澤 徹
     
    有機物は柔らかいため曲げに強い印刷可能な電子素子を作成できる利点はあるが、分子間振動のエネルギーが数十meVと低いことから、室温では振動によるキャリヤ散乱の影響が大きく、無機物に比べて移動度が桁違いに小さくなってしまう。おそらくこの理由により有機半導体の室温移動度は低い。これに対し、無機物のクラスターは溶液中で安定化するためのキャッピング層が通常絶縁物であり問題である。層状物質はもともと層に垂直方向の化学結合が閉じているためこの方向にキャッピング層は必要なく、層が積み重なる形で凝集するために空間充填率も高くなることが期待される。本研究では、層状物質をナノクラスター化することにより新たなフレキシブル電子材料を開発することを目標に、合成法と物性評価を行った。溶液から合成した層状物質クラスターはX線回折が非常に弱く、大部分がアモルファスであることが判明した。層状構造への結晶化は600℃以上の高温が必要であった。その理由を探るため、その場加熱のできる電子顕微鏡を用いて結晶化の過程を観察した結果、400℃程度で未知の結晶構造を持つ別の準安定相ができ、それが層状物質への変化を妨げていることがわかった(論文発表済)。加熱後の物性は、今のところ半導体特性を測定できない絶縁物である。欠陥を少なくする方法が必要であり、気相を経由する方法に切り替えて研究を進めている。本研究に関連した報文は2件、図...
  • 文部科学省:科学研究費補助金(基盤研究(A))
    研究期間 : 2005年 -2007年 
    代表者 : 西原 寛, 山野井 慶徳, 久米 晶子, 米澤 徹
     
    遷移金属錯体の化学・物理構造および多様な光学、磁気,電子物性が外部刺激に応答して可逆的に変化するインテリジェント分子系を創出し、それらを電極等と組合せることによって“分子レベルで機能する素子"をつくることを目的とした。II共役レドックス高分子錯体については、基板上への逐次的な錯形成法による一次元および三次元のII共役レドックス錯体オリゴマー、ポリマー鎖の合成を行い、レドックス伝導機構を電気化学的に解析し、その結果が、新しい分子鎖内電子輸送の概念で説明できることを提案した。さらにポルフィリンなどの色素を連結して、光電子移動分子ワイヤを構築した。フォトクロミック錯体については、記憶の深さを調節できる分子としてフェロセニルスピロピラン、電子コミュニケーションを光制御する分子としてビス(フェロセニルエチニル)エテンおよびそのトリエチルアミン置換体を開発し、緑色光とレドックスの組み合わせで可逆な異性化スイッチングを起こすフェロセニルアゾベンゼン単分子膜を作製した。ドナーアクセプター共役分子については、フェロセン-キノン共役分子系を対象とし、1,4-ビス(フェロセニルエチニル)アントラキノンが非常に速い結晶成長をし、さらにゲスト刺激による可逆的単結晶構造変換をすることを見出した。ドナーアクセプター共役分子については、1-フェロセニルアントラキノンがプロトン付加により温度により、原子価互変...
  • 文部科学省:科学研究費補助金(特定領域研究)
    研究期間 : 2004年 -2007年 
    代表者 : 西原 寛, 村田 昌樹, 山野井 慶徳, 久米 晶子, 米澤 徹
     
    金属錯体分子を界面に次元制御配列することによって、内部ポテンシャル分布が外場制御できる電子機能空間をつくり、その中で特異な現象を発現させ、その機構解明を行うことを目的とした。成果として、金電極にテルピリジンジスルフィド誘導体(tpy-AB-S)2 (1)を固定化し、適切な条件下で金属イオンの水溶液および二方向および三方向架橋ポリ(テルピリジン)配位子(tpy-L-tpy (2, 3)およびL(tpy)3 (4))の溶液に交互に浸漬させることにより、金属錯体の一次元鎖状および分岐形樹状錯体オリゴマーが定量的に作製できることを、サイクリックボルタンメトリー、UV-VIS吸収スペクトル、STMおよびSEMなどの結果より明らかにした。上記のようにして作製した一次元および樹状錯体分子鎖からなる電極薄膜内の電子移動をクロノアンペロメトリーで解析した。従来の拡散型の電子移動ではなく、一次元分子鎖内のレドックス伝導として、電極と一層目の電子移動速度定数をk1 (s-1)、錯体間の自己交換反応速度定数をk2 (mol cm-2 s-1)として順次電子が鎖内をホッピングする子移動メカニズムで考えると、実験値をシミュレーションできることを示し、その電解質濃度依存性や電場効果についても明らかにした。これは、レドックスポリマー被覆電極のレドックス伝導を、分子鎖内電子移動で解析した初めての例である。その...
  • 文部科学省:科学研究費補助金(萌芽研究)
    研究期間 : 2005年 -2006年 
    代表者 : 米澤 徹, 齋藤 永宏
     
    溶液中のプラズマを利用してナノ粒子を大量製造することを試みた。タングステン線を電極とし、高圧パルス電源を使用して、電極間に放電させ、プラズマを発生させた。電極間隔、印加電圧、電流、パルス間隔は、電極間にアーク放電が生じないようにするために適切に制御する必要があった。また、溶液の導電率をアルカリ金属塩の添加によって制御したが、それにはあまり大きく影響されなかった。このとき発生するラジカル、水素、電子によって金属イオンが還元されることが見出された。プラズマ計測を行ってみたところ、このような還元種が生成していることが見出された。また、金、白金、銀、パラジウム、ロジウムなどの貴金属イオンは還元されやすく、ナノ粒子を得ることができた。遷移金属塩からもナノ粒子が得られたように見受けられるが、十分な検証ができていない。多くの金属塩からナノ粒子を作ることに成功したが、ナノ粒子の安定性をさらに向上させるためには原料液の導電性制御のためのアルカリ金属塩の排除を行う必要があることが分かる。一方、原料塩のみでは還元によって導電性が変化していく問題があり、原料のさらなる検討が今後求められる。粒子径は、金属種にも依存するが、単一粒子径にほぼ近い形のものができ、全て球形のものが得られた。異方形状のものは残念ながら得られず、今後、更なる条件検討が必要である。さらに、連続調製装置を作製し、検討を行った。連続調...
  • 文部科学省:科学研究費補助金(基盤研究(S))
    研究期間 : 2002年 -2006年 
    代表者 : 河本 邦仁, 米澤 徹, 増田 佳丈
     
    フラックス法によりN型ZnO・In_2O_3系ホモロガス相単結晶を世界ではじめて育成し、熱電物性を精密に測定した結果,(ZnO)_5In_2O_3のin-plane導電率はout-of-plane導電率に比べて約100倍高く、大きな異方性を持つことを見出した。さらに、イットリウム(Y)をInに部分置換した系の単結晶を育成し、単結晶および配向セラミックスのin-plane物性に大きな差がないことが判明した。極限性能としてZ〜0.5程度まで達成可能との見通しを得た。Na_<0.8>CoO_2エピタキシャル薄膜から耐湿性に優れたSr_xCoO_2エピタキシャル薄膜や4Kで超伝導転移を示すNa_<0.3>CoO_2-1.3H_2Oエピタキシャル薄膜を作製することに初めて成功した。さらに、バルク単結晶と同等の熱電特性を示す高品質Ca_3Co_4_O9エピタキシャル薄膜の作製に成功した。NbヘビードープしたSTOが最大ZT=0.37@1000Kを発現することを見出した。さらに高効率化するためSrTiO_3のSr^<2+>サイトをイオン半径のほぼ等しいEu^<2+>で置換した(Eu_xSr_<1-x>)(Ti_<0.8>Nb_<0.2>)O_3緻密焼結体において、電子輸送に影響を及ぼすことなく、格子熱伝導を抑制することに成功し、最大ZT=0.39@1000Kまで向上することを示した。TiO...
  • 文部科学省:科学研究費補助金(基盤研究(A))
    研究期間 : 2002年 -2004年 
    代表者 : 西原 寛, 栗原 正人, 村田 昌樹, 米澤 徹
     
    本研究では、フォトクロミック分子ユニットと遷移金属錯体とを共役結合したフォトクロミック錯体を創製し、そこで発現する新しい多重機能を探索,解明し、さらにそれらを界面に配列固定することによって、非従来型の分子スイッチ,分子メモリシステムを構築する研究を行った。その結果、単一波長光とレドックスで可逆な異性化を達成できる系として、アゾベンゼン共役トリスピリジンコバルト錯体系およびm-フェロセニルアゾベンゼン系を開発した。発光特性が異性体間で異なるフォトクロミック分子として、アゾベンゼン共役テルピリジン白金錯体系を開発した。また2,2'-ビピリジンの4位にアゾベンゼンを結合し、6,6'位をメチル基で置換した新規配位子、dmpABとビピリジン、Cuイオンを混合した系で、Cu(II)/Cu(I)のレドックス変化と単一紫外光源を用いた可逆的異性化が実現した。可逆なレドックスとそれに伴う構造変化と配位子交換を光異性化特性と連動した系として、アゾベンゼン共役ビス(ビピリジン)銅錯体系を開発した。プロトネーションと異性化が共役する系として、アゾ共役ジチオレン錯体系、アゾ共役カテコラト錯体系を開発した。界面配列体の研究として、アゾ共役フェロセン系とアゾベンゼン架橋ビステルピリジン錯体系の自己集合単分子膜の作製に成功した。また、フェロセニルアゾベンゼン誘導体の自己集合単分子膜の作製も行った。視覚の化学...
  • ポリジアセチレン酸を用いたナノ結晶の2次元配列形成
    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 : 2003年 -2003年 
    代表者 : 米澤 徹, MA Zhangfang
     
    金属ならびに半導体のナノ粒子は「量子サイズ効果」を示す可能性が高く、バルクとも原子・分子とも異なる物性を示すことが期待される。現在はこうしたナノ粒子を湿式法で分散液として調製されることが多く、安価でナノサイズの粒子を単一粒径で得る技術が確立されつつある。こうした、ナノ粒子を材料として利用するとき、ある基板上に秩序を持たせて固定化することが望まれるが、本研究では、手法としてLB法を用いて、スタックさせる界面活性剤としてジアセチレン系カルボン酸に注目した。このカルボン酸は、紫外光によって均一に高分子化されたポリジアセチレン薄膜を形成する。 3種のジアセチレン系カルボン酸を用いて、等温線がpHによってどのような影響を受けるか検討した。その結果、比較的長鎖のカルボン酸が単分子膜を安定に作ることがわかった。さらに、半導体ナノ粒子であるCdSをジアセチレンカルボン酸単分子膜表面に形成させる試みを行った。調査カルボン酸では、1mM以上のカドミウムイオンを入れても安定に単分子膜ができた。しかし、現時点ではこれらを複写した膜はドメイン構造を作っていた。
  • 文部科学省:科学研究費補助金(萌芽的研究)
    研究期間 : 2001年 -2001年 
    代表者 : 河本 邦仁, 増田 佳丈, 米澤 徹
     
    N_2雰囲気下でSi基板をPTCS(フェニルトリクロロシラン)溶液中に浸漬してPTCS自己組織膜を作製し、ここにフォトマスクを通してUV照射を行う事により、フェニル基とOH基のマイクロパターンを作製した。SiO_2粒子(500nmφ及び15nmφ)の表面にTCES(トリクロロシアノエチルシラン)を結合させて最表面をCN基とし、さらにt-BuOK(カリウムブトキシド)によりCOOH基へと変性した。このSiO_2粒子最表面のCOOH基と自己組織膜上のOH基をDCC(ジシクロヘキシルカルボジイミド)により縮合させてエステル結合を形成させることにより、自己組織膜上のOH基上に選択的にSiO_2粒子を配置させることを試みた。UV照射によりシラノール基へと変性した領域からは、SEM観察によりSiO_2粒子が確認され、フェニル基上からは粒子は観測されなかった。この手法により、マイクロメーターオーダーの2次元粒子配列パターンが形成された。また、ダイヤモンドチップで自己組織膜表面を走査する事により、機械的にフェニル基を取り去り、任意の箇所をシラノール基へと変性した自己組織膜上からも粒子の選択的配列が確認され、1次元の粒子細線が形成できた。また、AFMリソグラフにより変性した自己組織膜上からも選択的粒子配列が確認された。上記のエステル結合の形成に代えて、酸あるいは塩基により粒子表面のシラノール基...
  • 文部科学省:科学研究費補助金(奨励研究(A))
    研究期間 : 2000年 -2001年 
    代表者 : 米澤 徹
     
    ナノ粒子の調製において、本研究では、これまでにあまり研究例のない、水に良く分散するナノ粒子とフッ素系溶媒に分散するナノ粒子を調製した。これらのナノ粒子は安定で、酸化されたり、沈澱を生じたりしない。特に、フッ素系配位子を用いた場合には遷移金属の微細で単分散なナノ粒子を安定に調製することが可能であることを見出している(特許出願済)。水に分散するナノ粒子は、末端に4級アンモニウム基をもった保護剤で保護したもので、どのようなpHでも正のゼータ電位を有している。そのため、アニオン性の高分子や二分子膜、無機物質表面に容易に吸着し、パターニングによる特殊配列の付与が可能であることがわかった。このような吸着力をもつナノ粒子は、これから期待される塗布用ナノ粒子材料の基材として非常に重要であることが考えられる。また、フッ素系保護剤により保護されたナノ粒子の構造および物性を詳細に検討したところ、これらのナノ粒子が(1)空気下で安定に調製できる、(2)空気中に安定に保存できる、(3)沈殿させて粉末状に保存ができる。(4)フッ素系溶剤を用いて簡単に薄く塗布できる。という特徴を有することが分かった。この塗布技術により、ナノ粒子の2次元パターニングが容易にできることが見出され、特殊配列の付与ができたといえる。このように本研究により、研究者らは新しい性質をもつナノ粒子の創成に成功した。また、それらに特殊配列...
  • 文部科学省:科学研究費補助金(基盤研究(B))
    研究期間 : 2000年 -2001年 
    代表者 : 河本 邦仁, 徐 元善, 増田 佳丈, 米澤 徹
     
    メチル基/シラノール基にパターン化した自己組織膜(OTS-SAM)をN2雰囲気下でTDD溶液に浸漬することにより、シラノール基上にのみ選択的にアモルファスTiO2薄膜を析出させることに成功した。このパターン解像度はおよそ2.1%であり、液相析出法における値(約28.0%)およびデバイス作製の基準値(5%)を下回るものであった。また、大気中での加熱により400℃でアナターゼ相に、1000℃でルチル相に相転移し、この際パターン精度に大きな変化はなく、高い解像度を持ったアナターゼ型TiO2のマイクロパターンが作製できた。析出したアモルファス膜の誘電特性を評価したところ、誘電体薄膜に典型なC-V特性を示した。また、I-V特性から見積もられたリーク電流は1.3×10-7A/cm2(at 1V)と低い値であった。これらの特性は、この薄膜のMOS-FETゲート酸化膜への適用の可能性を示している。一方、TDD溶液とパターン化OTS-SAMを窒素雰囲気下、90℃で2時間保持することにより、TDD分子を気相を介して基板上へと運び、シラノール基上へのアモルファスTiO2薄膜の選択析出を実現した。この薄膜もまた、加熱処理により400℃でアナターゼ相に、1000℃でルチル相に、相転移し、その際の解像度の劣化は見られなかった。さらに、フェニル基/シラノール基にパターン化したSAM上のフェニル基上に酸化亜...
  • 文部科学省:科学研究費補助金(特定領域研究(A))
    研究期間 : 2000年 -2000年 
    代表者 : 君塚 信夫, 米澤 徹
     
    ハロゲン架橋一次元白金混合原子価錯体[Pt(en)_2][PtCl_2(en)_2]と種々のアニオン性合成脂質とのポリイオンコンプレックス形成により、脂溶性の有機-無機超分子組織体を作成した。キラルなアニオン性脂質の合成について合成ルートを検討した結果、L-グルタミン酸ジドデシルエステルとスルホ酢酸を、ピリジン存在下BOP試薬で縮合させる方法が有効であることを明らかにした。この脂質と[Pt(en)_2]、[PtCl_2(en)_2]を含む水溶液を混合したところ、紫色の沈殿がえられた。この紫色はPt(II)→Pt(IV)の電荷移動吸収に基づくものであり、複合体中において一次元白金錯体が形成されていることが判った。この複合体はクロロホルムに分散すると淡黄色となり、これは分子錯体[PtCl_2(en)_2]の色であることから、クロロホルム中においてハロゲン架橋構造は解離していることがわかった。一方、ジクロルメタン中においては紫色の溶液として分散し、溶媒に依存して一次元白金錯体構造が保たれることが判った。この溶液について円偏光二色性スペクトルの測定を行ったところ、電荷移動吸収帯に励起子分裂型のコットン効果が観測された。これは、脂質の不斉によって一次元白金錯体にCDスペクトルが誘起された、はじめての例であり、脂質と一次元錯体の構造秩序性が極めて高いことが明らかとなった。さらに、AFM観...
  • 文部科学省:科学研究費補助金(特定領域研究(A))
    研究期間 : 1999年 -2000年 
    代表者 : 君塚 信夫, 一ノ瀬 泉, 米澤 徹
     
    我々は"分子組織性ハイドロゲル"を開発し、その基本特性を解明することを目的として、複数のアミド基を含み、かつグルタミン酸骨格を有するカチオン型脂質を合成した。その結果、従来の二分子膜形成化合物に比べて短いアルキル鎖(C_8:短鎖型脂質)ならびにイソプロピル基を疎水部側に導入した分岐型脂質に過塩素酸アニオン、ナフタレンスルホン酸などの疎水性アニオンを添加すると、ハイドロゲルが得られることが判った。これらの分散水溶液(1^〜2mM)について電子顕微鏡観察を行ったところ、幅8-10nm、長さ3μm以上のファイバー状会合体を基本とする網目状構造が観測された。これらの会合形態は二分子膜に特徴的なものであり、疎水性アニオンの添加によって、これらの短鎖型脂質や分岐型脂質が発達したファイバー状架橋構造を与えたことが判る。従来型の二分子膜形成化合物においては、このようなハイドロゲル形成が認められないことから、(i)結晶性を低めた疎水部構造、(ii)疎水性のイオンペアから成る親水部、かつ(iii)発達した水素結合ネットワークの形成が分子組織性ハイドロゲルを得るための条件であることが判った。ゲルを加熱すると、60-75℃の領域で溶解してゾルとなり、その後さらに加熱すると急激に白濁した。この変化は可逆的であり、冷却すると白濁が消失して元の均一なハイドロゲルが得られた。このように、分子組織性ハイドロゲ...
  • 文部科学省:科学研究費補助金(基盤研究(C))
    研究期間 : 1999年 -2000年 
    代表者 : 君塚 信夫, 一ノ瀬 泉, 米澤 徹
     
    本研究は、新しい分子組織化のための界面として高分子(あるいは分子集合体から成る)ゲルの表面に注目し、ゲル界面(表面)における分子組織化学の方法論を開拓した。【1】基質として水溶性ナノ粒子(シリカコロイドや蛋白質)を選び、これらをアガロースゲルの表面に展開した。チトクロムcを展開したところ、大部分がゲル表面に留まることが、蛋白質の色から確認された。このゲル表面に、雲母やグラファイトなどの基板を接触・剥離させて、転写基板上の組織状態を、蛍光顕微鏡、分子間力顕微鏡(AFM)、走査型電子顕微鏡ならびに水晶発振子により評価した。その結果、基板表面にゲル上に展開したシリカ粒子やヘム蛋白質が転写されることが判明した。【2】アガロースゲル表面に、フェリチンを展開し、電子顕微鏡グリッドに転写して電子顕微鏡観察を行ったところ、フェリチンが転写されていることが判った。【3】シリカナノ粒子を転写したグラファイト基板を水に浸漬し、超音波照射により洗浄した。洗浄後のグラファイト基板をAFM観察したところ、表面にアガロースの二次元状ネットワーク構造(高さ2-5nm)が観察された。このことから、アガロースゲルの表層はこの二次元ナノネットワークより覆われており、これがゲル表面上に展開された親水性ナノ粒子を固体基板上へ転写する際に、分子糊(molecular glue)として働くものと考えられる。以上より、ゲル...
  • 文部科学省:科学研究費補助金(特定領域研究(A))
    研究期間 : 1998年 -1998年 
    代表者 : 一ノ瀬 泉, 米澤 徹
     
    我々は、分子レベルで組成制御された傾斜機能材料を構築するために、新しい逐次吸着法によるナノ傾斜薄膜の作成を検討してきた。本研究では、互いに反対電荷を有する高分子電解質を用いた交互吸着法、金属アルコシキドの逐次吸着より酸化物ゲル薄膜を作成する表面ゾルゲル法、さらに重合溶媒から直に高分子超薄膜を作成する重合吸着法を確立し、様々な化学的機能の発現を謀った。表面ゾルゲル法では、分子的厚みの酸化物薄膜(チタン、インジウム、ニオブ等)や水酸基を有する有機分子を任意のシーケンスで積層化できる。我々は、酸化物ナノ薄膜とポルフィリン系色素分子との積層型薄膜を作成し、湿式系での光電変換特性を検討した。ITO基板に作成した約20ナノメートルの厚みのIn_2O_3/ポルフィリン多層薄膜にレーザーを照射すると、数μA/cm^2の光電流が観察された。光電流は、積層回数に比例して増大し、酸化物層の種類にも大きく依存した。一方我々は、末端に水酸基とチオール基を有する長鎖アルキル化合物を保護剤とし、粒径制御された金ナノ微粒子を合成する手法を確立させた。これらのナノ粒子は、表面に多くの水酸基を有し、チタンアルコキシドとの交互吸着により、ナノ粒子の構造を保持したまま、固体基板上への積層化が可能であった。表面ゾルゲル法を用いて水晶発振子上にアミノ酸誘導体を含んだ酸化チタンゲル薄膜を作成し、水酸化ナトリウム水溶液で処...
  • 文部科学省:科学研究費補助金(奨励研究(A))
    研究期間 : 1997年 -1998年 
    代表者 : 米澤 徹
     
    金属ナノ粒子として,本研究では金ナノ粒子を選択した.保護剤を添加せずにクエン酸還元法によって調製した金ナノ粒子はその濃縮が困難だが,限外ろ過膜を使用することで,常温で濃縮でき,さらに,分散液中に混在するクエン酸イオンなどを除去した.その分散液に,入れ子型構造単分子膜を形成している両親媒性分子基板を浸積すると,1度の浸積で,ほぼ最密充填の金ナノ粒子モノレイヤーが作成できた.このモノレイヤーも導電性を有し,透明である.静電相互作用でほぼ完璧なナノ粒子モノレイヤーの生成を報告したのはこれが世界で初めてである.こうした吸着挙動を高分子電解質を用いた場合や,様々な濃度の金ナノ粒子を用いる事によって比較検討した.また,粒径の揃った粒子ということで,同様にアニオン性のシリカナノ粒子の吸着挙動をモデルとして検討した.粒径によって,吸着挙動が異なる事が見出され,静電相互作用による粒子の有機層への吸着は,有機層自体の安定性や,相互作用の強さに大きく依存する事が示された.また,二分子膜の親水部層間に金イオンを取り込み,その後に還元する手法によっても金ナノ粒子を得ることができるが,この手法では,金ナノ粒子の形状が二分子膜の水中での膨潤状態によって異なり,分散液中による還元では得られにくい,プレート状や,珊瑚状の金ナノ粒子を得ることができた,さらには,金属と配位相互作用を持つ二分子膜物質を設計し,特異...

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    開講学部 : 大学院共通科目
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    開講年度 : 2021年
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    キーワード : Nanomaterials, Electron microscopy, Battery materials, Surface, Interface
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    開講年度 : 2021年
    課程区分 : 修士課程
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    開講年度 : 2021年
    課程区分 : 博士後期課程
    開講学部 : 工学院
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    開講年度 : 2021年
    課程区分 : 博士後期課程
    開講学部 : 工学院
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    開講年度 : 2021年
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    キーワード : 金属材料、電子、原子、結晶構造、機能性、構造材、表面、反応プロセス
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    課程区分 : 学士課程
    開講学部 : 工学部
    キーワード : 化学ポテンシャル、活量、化学平衡、X線結晶解析、X線回折、結晶構造、ミラー指数、逆格子   
  • マテリアルプロセス工学
    開講年度 : 2021年
    課程区分 : 学士課程
    開講学部 : 工学部
    キーワード : 材料熱力学、高温反応プロセス、非鉄金属の製造、座標系、反応操作、分離操作、分子運動論と真空科学技術
  • 材料工学演習Ⅲ
    開講年度 : 2021年
    課程区分 : 学士課程
    開講学部 : 工学部
    キーワード : 二元系・三元系平衡状態図、自由エネルギー・組成図、材料熱力学、混合と相平衡、気体の関与する状態図、真空技術、活量、座標系、反応操作、分離操作、精錬反応
  • 一般教育演習(フレッシュマンセミナー)
    開講年度 : 2021年
    課程区分 : 学士課程
    開講学部 : 全学教育
    キーワード : マテリアル工学、ナノマテリアル、省エネルギー、地球環境、持続的発展
  • 結晶解析学
    開講年度 : 2021年
    課程区分 : 学士課程
    開講学部 : 工学部
    キーワード : 結晶、結晶構造、結晶構造解析、X線回折、面指数、金属、金属酸化物

大学運営

委員歴

  • 2022年 - 現在   ナノ学会   第21回大会 現地実行委員長
  • 2021年 - 現在   ナノ学会   監事
  • 2022年10月 - 2022年10月   日本化学会   化学フェスタ2022 材料化学の最先端を歩み続ける濃厚分散系 担当委員
  • 2022年 - 2022年   日本化学会 コロイドおよび界面化学部会   第73回コロイドおよび界面化学討論会 一般シンポジウム 最先端電子部品にかかわるコロイド・界面化学 担当委員
  • 2006年 - 2021年   ナノ学会   理事
  • 2018年 - 2019年   日本化学会 コロイドおよび界面化学部会   第70回コロイドおよび界面化学討論会・国際会議(那覇、2019)企画/賞関連委員会委員長
  • 2016年 - 2019年   ナノ学会   編集委員長
  • 2018年 - 2018年   日本XAFS研究会   第21回XAFS討論会実行委員
  • 2016年 - 2017年   ナノ学会   第15回大会 現地実行副委員長
  • 2015年 - 2016年   日本学術振興会   科学研究費補助金 第一段審査 審査委員
  • 2014年 - 2015年   International Conference of Colloids and Interface Science (日台コロイド会議)   Chair person (organizing committee)
  • 2010年 - 2011年   日本学術振興会   科学研究費補助金 第一段審査 審査委員
  • 1998年 - 1999年   高分子学会   九州地区高分子若手研究会 幹事
  • 1990年 - 1991年   高分子学会   高分子錯体若手研究会 幹事

社会貢献活動

  • アカデミックファンタジスタ
    期間 : 2020年 - 2021年
    役割 : 出演
    主催者・発行元 : 北海道大学
    イベント・番組・新聞雑誌名 : 北海道新聞

学術貢献活動

  • 國立清華大学(台湾) 教授 外部書面審査委員
    期間 : 2020年
    役割 : 審査・評価
    主催者・責任者 : 國立清華大学
  • 國立清華大学(台湾) 准教授 外部書面審査委員
    期間 : 2017年 - 2017年
    役割 : 審査・評価
    主催者・責任者 : 國立清華大学


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