2024/05/27 更新

写真a

オオト タツヒコ
大戸 達彦
OHTO Tatsuhiko
所属
大学院工学研究科 材料デザイン工学専攻 計算材料設計 准教授
大学院担当
大学院工学研究科
学部担当
工学部 マテリアル工学科
職名
准教授
外部リンク

学位 1

  1. 博士(工学) ( 2013年3月   東京大学 ) 

研究分野 1

  1. ナノテク・材料 / 基礎物理化学

経歴 2

  1. 名古屋大学   工学研究科   准教授

    2023年3月 - 現在

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    国名:日本国

  2. 大阪大学   基礎工学研究科   助教

    2013年6月 - 2023年2月

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    国名:日本国

 

論文 77

  1. Heterodyne-Detected Sum-Frequency Generation Vibrational Spectroscopy Reveals Aqueous Molecular Structure at the Suspended Graphene/Water Interface 査読有り

    Wang, YK; Tang, FJ; Yu, XQ; Ohto, T; Nagata, Y; Bonn, M

    ANGEWANDTE CHEMIE-INTERNATIONAL EDITION   63 巻 ( 20 )   2024年3月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Angewandte Chemie - International Edition  

    Graphene, a transparent two-dimensional conductive material, has brought extensive new perspectives and prospects to various aqueous technological systems, such as desalination membranes, chemical sensors, energy storage, and energy conversion devices. Yet, the molecular-level details of graphene in contact with aqueous electrolytes, such as water orientation and hydrogen bond structure, remain elusive or controversial. Here, we employ surface-specific heterodyne-detected sum-frequency generation (HD-SFG) vibrational spectroscopy to re-examine the water molecular structure at a freely suspended graphene/water interface. We compare the response from the air/graphene/water system to that from the air/water interface. Our results indicate that the (Formula presented.) spectrum recorded from the air/graphene/water system arises from the topmost 1–2 water layers in contact with the graphene, with the graphene itself not generating a significant SFG response. Compared to the air/water interface response, the presence of monolayer graphene weakly affects the interfacial water. Graphene weakly affects the dangling O−H group, lowering its frequency through its interaction with the graphene sheet, and has a very small effect on the hydrogen-bonded O−H group. Molecular dynamics simulations confirm our experimental observation. Our work provides molecular insight into the interfacial structure at a suspended graphene/water interface, relevant to various technological applications of graphene.

    DOI: 10.1002/anie.202319503

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  2. Seebeck Effect in Molecular Wires Facilitating Long-Range Transport 査読有り

    Jang, J; Jo, JW; Ohto, T; Yoon, HJ

    JOURNAL OF THE AMERICAN CHEMICAL SOCIETY   146 巻 ( 7 ) 頁: 4922 - 4929   2024年2月

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    担当区分:責任著者   記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Journal of the American Chemical Society  

    The study of molecular wires facilitating long-range charge transport is of fundamental interest for the development of various technologies in (bio)organic and molecular electronics. Defining the nature of long-range charge transport is challenging as electrical characterization does not offer the ability to distinguish a tunneling mechanism from the other. Here, we show that investigation of the Seebeck effect provides the ability. We examine the length dependence of the Seebeck coefficient in electrografted bis-terpyridine Ru(II) complex films. The Seebeck coefficient ranges from 307 to 1027 μV/K, with an increasing rate of 95.7 μV/(K nm) as the film thickness increases to 10 nm. Quantum-chemical calculations unveil that the nearly overlapped molecular-orbital energy level of the Ru complex with the Fermi level accounts for the giant thermopower. Landauer-Büttiker probe simulations indicate that the significant length dependence evinces the Seebeck effect dominated by coherent near-resonant tunneling rather than thermal hopping. This study enhances our comprehension of long-range charge transport, paving the way for efficient electronic and thermoelectric materials.

    DOI: 10.1021/jacs.3c14012

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  3. Dynamic Variation of Rectification Observed in Supramolecular Mixed Mercaptoalkanoic Acid 査読有り

    Kong, GD; Jang, J; Choi, S; Lim, G; Kim, IS; Ohto, T; Maeda, S; Tada, H; Yoon, HJ

    SMALL   20 巻 ( 5 ) 頁: 2305997   2024年2月

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    担当区分:責任著者   記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Small  

    Functionality in molecular electronics relies on inclusion of molecular orbital energy level within a transmission window. This can be achieved by designing the active molecule with accessible energy levels or by widening the window. While many studies have adopted the first approach, the latter is challenging because defects in the active molecular component cause low breakdown voltages. Here, it is shown that control over the packing structure of monolayer via supramolecular mixing transforms an inert molecule into a highly tunable rectifier. Binary mixed monolayer composed of alkanethiolates with and without carboxylic acid head group as a proof of concept is formed via a surface-exchange reaction. The monolayer withstands high voltages up to |4.5 V| and shows a dynamic rectification–external bias relationship in magnitude and polarity. Sub-highest occupied molecular orbital (HOMO) levels activated by the widened transmission window account for these observations. This work demonstrates that simple supramolecular mixing can imbue new electrical properties in electro-inactive organic molecules.

    DOI: 10.1002/smll.202305997

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  4. Interfacial negative magnetization in Ni encapsulated layer-tunable nested MoS2 nanostructure with robust memory applications 査読有り

    Shatabda Bhattacharya, Tatsuhiko Ohto, Hirokazu Tada, Shyamal K. Saha

    Nanoscale Advances   6 巻   頁: 1091 - 1105   2024年1月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    DOI: 10.1039/D3NA00343D

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  5. Durable high-entropy non-noble metal anodes for neutral seawater electrolysis 査読有り

    Shiokawa, F; Tajuddin, AAH; Ohto, T; Yu, Y; Fujita, T; Tanimoto, H; Xi, ZY; Jeong, S; Ito, Y

    CHEMICAL ENGINEERING JOURNAL   479 巻   頁: 147862 - 147862   2024年1月

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    担当区分:責任著者   記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Chemical Engineering Journal  

    Enhancing hydrogen production is key to achieving a carbon–neutral world. Among the various technologies available, using renewable energy for water electrolysis stands out as a leading method for creating green hydrogen. However, standard water electrolysis requires substantial quantities of ultra-clean fresh water for optimal energy efficiency and operations. This poses a problem as fresh water only represents a minuscule 0.01 % of our planet's water reserves. Seawater electrolysis is a potential solution to resolve this limitation and attain sustainable hydrogen production. Nevertheless, electrolysis of seawater in its neutral state demands stringent reaction conditions, making it imperative to thoughtfully design the electrodes, particularly the anodes. This study presents the development of highly durable, noble-metal-free, high-entropy alloy anodes suitable for neutral seawater under highly fluctuating power operation. The anode demonstrates impressive stability (up to 6,000 cycles), lasting over 100 h at 100 mA cm−2 in a 0.5 M aqueous NaCl electrolyte. Its Faradaic efficiency for O2 production is 42 %. Density functional theory calculations reveal that the oxidized surface (passivation layer) of the anode prevents Cl− adsorption, helping to protect the catalytically active sites and prevent catalyst degradation. This finding suggests that noble-metal-free anodes can serve as practical alternatives to those made from noble metals for neutral seawater electrolysis. Moreover, the utilization of seawater without acid or alkali treatment paves the way for safer and more sustainable hydrogen production. This is a significant stride toward realizing our goal of carbon neutrality.

    DOI: 10.1016/j.cej.2023.147862

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  6. Suppression of Methanol and Formate Crossover through Sulfanilic-Functionalized Holey Graphene as Proton Exchange Membranes 査読有り

    Jeong, S; Ohto, T; Nishiuchi, T; Nagata, Y; Fujita, J; Ito, Y

    ADVANCED SCIENCE   10 巻 ( 31 ) 頁: 2304082   2023年9月

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    担当区分:責任著者   記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Advanced Science  

    Proton exchange membranes with high proton conductivity and low crossover of fuel molecules are required to realize advanced fuel-cell technology. The selective transportation of protons, which occurs by blocking the transportation of fuel molecules across a proton exchange membrane, is crucial to suppress crossover while maintaining a high proton conductivity. In this study, a simple yet powerful method is proposed for optimizing the crossover-conductivity relationship by pasting sulfanilic-functionalized holey graphenes onto a Nafion membrane. The results show that the sulfanilic-functionalized holey graphenes supported by the membrane suppresses the crossover by 89% in methanol and 80% in formate compared with that in the self-assembled Nafion membrane; an ≈60% reduction is observed in the proton conductivity. This method exhibits the potential for application in advanced fuel cells that use methanol and formic acid as chemical fuels to achieve high energy efficiency.

    DOI: 10.1002/advs.202304082

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  7. Deposition condition impacts charge tunneling and thermoelectric properties of N-heterocyclic carbene monolayers 査読有り

    Kang, H; Jang, J; Kong, GD; Jung, S; Ohto, T; Yoon, HJ

    JOURNAL OF MATERIALS CHEMISTRY A   11 巻 ( 30 ) 頁: 16233 - 16242   2023年7月

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    担当区分:責任著者   記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Journal of Materials Chemistry A  

    N-heterocyclic carbene (NHC) is an emerging anchor moiety for surface engineering and various applications. While various deposition conditions have been reported, how these affect the charge transport properties of NHC adsorbates remains uncertain. A NHC salt precursor based on benzo[d]imidazole with a PF6− counterion was deposited onto an ultrasmooth gold substrate using three different conditions for creating NHC monolayers: ambient incubation (AI), base (tert-butoxide)-induced deprotonation (BD), and electrochemical deprotonation (ED). Junction measurements using the EGaIn technique revealed that current density increased by ∼101.7 in the order of AI < BD < ED, while the Seebeck coefficient showed the opposite trend, ranging from 9.3 to 13.5 μV K−1. First-principles calculation reproduced the experimentally observed positive sign of the Seebeck coefficient. Further surface characterizations and computational calculations indicated that the different deposition conditions cause variation in surface coverage in the order of AI < BD < ED. This variation has a significant influence on the broadening of HOMO level and marginal impact on the energy offset between HOMO and Fermi levels, accounting for the opposite trends of electrical conductance and thermopower as a function of the deposition conditions. Finally, we found that the power factor of the NHC monolayer can increase by ∼102 depending on the deposition condition.

    DOI: 10.1039/D3TA02443A

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  8. 6,6 '-Biindeno[1,2-b]anthracene: An Open-Shell Biaryl with High Diradical Character 査読有り

    Xiushang Xu, Satoshi Takebayashi, Hiroki Hanayama, Serhii Vasylevskyi, Takatsugu Onishi, Hirokazu Tada, Tatsuhiko Ohto, Akimitsu Narita

    JOURNAL OF THE AMERICAN CHEMICAL SOCIETY     2023年2月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:AMER CHEMICAL SOC  

    We report in situ generation of a 6,6 '-biindeno[1,2-b]anthracene (BIA) derivative as an open-shell biaryl with high diradical character, which could be identified by mass spectrometry, NMR spectroscopy, single-crystal X-ray analysis, UV-vis-NIR absorption spectroscopy, and electron paramagnetic resonance (EPR) spectroscopy. Theoretical calculations by various methods and variable-temperature EPR analyses were performed to tackle the elusive ground state of BIA diradical, suggesting a singlet ground state with a nearly degenerate triplet state. These results provide insight into the design of unique open-shell biaryls.

    DOI: 10.1021/jacs.2c13890

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  9. Corrosion‐Resistant and High‐Entropic Non‐Noble‐Metal Electrodes for Oxygen Evolution in Acidic Media 査読有り

    Aimi A. H. Tajuddin, Mitsuru Wakisaka, Tatsuhiko Ohto, Yue Yu, Haruki Fukushima, Hisanori Tanimoto, Xiaoguang Li, Yoshitatsu Misu, Samuel Jeong, Jun‐ichi Fujita, Hirokazu Tada, Takeshi Fujita, Masaki Takeguchi, Kaori Takano, Koji Matsuoka, Yasushi Sato, Yoshikazu Ito

    Advanced Materials   35 巻 ( 3 ) 頁: 2207466 - 2207466   2023年1月

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    担当区分:責任著者   掲載種別:研究論文(学術雑誌)   出版者・発行元:Wiley  

    DOI: 10.1002/adma.202207466

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    その他リンク: https://onlinelibrary.wiley.com/doi/full-xml/10.1002/adma.202207466

  10. Coexistence of Urbach‐Tail‐Like Localized States and Metallic Conduction Channels in Nitrogen‐Doped 3D Curved Graphene 査読有り

    By Yoichi Tanabe, Yoshikazu Ito, Katsuaki Sugawara, Samuel Jeong, Tatsuhiko Ohto, Tomohiko Nishiuchi, Naoaki Kawada, Shojiro Kimura, Christopher Florencio Aleman, Takashi Takahashi, Motoko Kotani, Mingwei Chen

    Advanced Materials     頁: 2205986 - 2205986   2022年10月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:Wiley  

    DOI: 10.1002/adma.202205986

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  11. Controlling the Emissive, Chiroptical, and Electrochemical Properties of Double [7] Helicenes through Embedded Aromatic Rings 査読有り

    Juan Hong, Xuxian Xiao, Haoliang Liu, Evgenia Dmitrieva, Alexey A. Popov, Zidong Yu, Ming-De Li, Tatsuhiko Ohto, Jun Liu, Akimitsu Narita, Pengcai Liu, Hirokazu Tada, Xiao-Yu Cao, Xiao-Ye Wang, Yingping Zou, Klaus Muellen, Yunbin Hu

    CHEMISTRY-A EUROPEAN JOURNAL   28 巻 ( 58 )   2022年10月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:WILEY-V C H VERLAG GMBH  

    We present here the synthesis and in-depth physicochemical characterization of a double hetero[7]helicene fused with four triazole rings at both helical ends. The comparison of this triazole-fused double helicene with the previously reported all-carbon and thiadiazole-fused analogs revealed the huge impact of the embedded aromatic rings on the photophysical features. The small structural variation of the terminal rings from thiadiazole to triazole caused a dramatic change of the photoluminescence quantum yields (PLQYs) from <1 % to 96 %, while the replacement of the terminal benzene rings with triazole rings induced a tenfold enhancement of the circularly polarized luminescence dissymmetry factor. These observations were well corroborated with transient absorption analysis and/or theoretic calculations. In addition, the triazole-fused double helicene exhibited ambipolar redox behavior, enabling the generation of radical cation and anion species by electrochemical and chemical methods and showing its potential for spin-related applications.

    DOI: 10.1002/chem.202202243

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  12. Thermopower in Transition from Tunneling to Hopping 査読有り

    Sohyun Park, Jeong Woo Jo, Jiung Jang, Tatsuhiko Ohto, Hirokazu Tada, Hyo Jae Yoon

    Nano Letters   22 巻 ( 18 ) 頁: 7682 - 7689   2022年9月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:AMER CHEMICAL SOC  

    The Seebeck effect of a molecular junction in a hopping regime or tunneling-to-hopping transition remains uncertain. This paper describes the Seebeck effect in molecular epitaxy films (OPIn where n = 1-9) based on imine condensation between an aryl amine and aldehyde and investigates how the Seebeck coefficient (S, mu V/K) varies at the crossover region. The S value of OPIn linearly increased with increasing the molecular length (d, nm), ranging from 7.2 to 38.0 mu V/K. The increasing rate changed from 0.99 to 0.38 mu V.K-1 & Aring;(-1) at d = 3.4 nm (OPI4). Combined experimental and theoretical studies indicated that such a change stems from a tunneling-to-hopping transition, and the small but detectable length-dependence of thermopower in the long molecules originates from the gradual reduction of the tunneling contribution to the broadening of molecular orbital energy level, rather than its relative position to the Fermi level. Our work helps to bridge the gap between bulk and nanoscale thermoelectric systems.

    DOI: 10.1021/acs.nanolett.2c03083

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  13. Modular Redox Switching of Dinuclear Organometallic Molecular Junctions 査読有り

    Yuya Tanaka, Naoki Morozumi, Tatsuhiko Ohto, Satoshi Kaneko, Yasuhisa Naitoh, Hirokazu Tada, Shintaro Fujii, Tomoaki Nishino, Munetaka Akita

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  14. Catalytic activity of graphene-covered non-noble metals governed by proton penetration in electrochemical hydrogen evolution reaction 査読有り

    Kailong Hu, Tatsuhiko Ohto, Yuki Nagata, Mitsuru Wakisaka, Yoshitaka Aoki, Jun ichi Fujita, Yoshikazu Ito

    Nature Communications   12 巻 ( 1 )   2021年12月

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    掲載種別:研究論文(学術雑誌)  

    Graphene-covering is a promising approach for achieving an acid-stable, non-noble-metal-catalysed hydrogen evolution reaction (HER). Optimization of the number of graphene-covering layers and the density of defects generated by chemical doping is crucial for achieving a balance between corrosion resistance and catalytic activity. Here, we investigate the influence of charge transfer and proton penetration through the graphene layers on the HER mechanisms of the non-noble metals Ni and Cu in an acidic electrolyte. We find that increasing the number of graphene-covering layers significantly alters the HER performances of Ni and Cu. The proton penetration explored through electrochemical experiments and simulations reveals that the HER activity of the graphene-covered catalysts is governed by the degree of proton penetration, as determined by the number of graphene-covering layers.

    DOI: 10.1038/s41467-020-20503-7

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  15. Geometric model of 3D curved graphene with chemical dopants 査読有り

    Dechant, A; Ohto, T; Ito, Y; Makarova, MV; Kawabe, Y; Agari, T; Kumai, H; Takahashi, Y; Naito, H; Kotani, M

    CARBON   182 巻   頁: 223 - 232   2021年9月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:Carbon  

    Geometric structures of carbon networks are key in designing their material properties. In particular, optimization of curved structures through the introduction of topological defects and doping of heteroatoms in the lattice is crucial to the design of carbon-based, non-noble-metal-free catalysts. A simple and practical mathematical model based on discrete geometric analysis is proposed to describe the geometric features of carbon networks and their relationships to their material properties. This model can pre-screen candidates for novel material design, and these candidates can be further examined by the density functional theory (DFT). Inspired by observations regarding the preferential doping of heteroatoms at local curved sites, the important characteristics of the candidate material were experimentally realized, and its enhanced catalytic activity facilitated by chemical dopants was confirmed in the designed carbon network.

    DOI: 10.1016/j.carbon.2021.06.004

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  16. Polyethylene Glycol Covered Sn Catalysts Accelerate the Formation Rate of Formate by Carbon Dioxide Reduction 査読有り

    Samuel Jeong, Tatsuhiko Ohto, Tomohiko Nishiuchi, Yuki Nagata, Jun-ichi Fujita, Yoshikazu Ito

    ACS Catalysis     頁: 9962 - 9969   2021年8月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:American Chemical Society ({ACS})  

    DOI: 10.1021/acscatal.1c02646

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  17. Phase-Dependent Electrochemical CO2 Reduction Ability of NiSn Alloys for Formate Generation 査読有り

    Yoshikazu Ito, Suresh Kukunuri, Samuel Jeong, Ganesan Elumalai, Aimi Asilah Haji Tajuddin, Zeyu Xi, Kailong Hu, Tatsuhiko Ohto

    ACS Applied Energy Materials   4 巻 ( 7 ) 頁: 7122 - 7128   2021年7月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:American Chemical Society ({ACS})  

    DOI: 10.1021/acsaem.1c01207

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  18. Acceleration of Electrochemical CO2 Reduction to Formate at the Sn/Reduced Graphene Oxide Interface 査読有り

    Takuya Tsujiguchi, Yusuke Kawabe, Samuel Jeong, Tatsuhiko Ohto, Suresh Kukunuri, Hirotaka Kuramochi, Yasufumi Takahashi, Tomohiko Nishiuchi, Hideki Masuda, Mitsuru Wakisaka, Kailong Hu, Ganesan Elumalai, Jun-ichi Fujita, Yoshikazu Ito

    ACS Catalysis   11 巻 ( 6 ) 頁: 3310 - 3318   2021年3月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:American Chemical Society ({ACS})  

    Electrochemical CO2 reduction is a key technology to recycle CO2 as a renewable resource, but adsorbing CO2 on the catalyst surface is challenging. We explored the effects of reduced graphene oxide (rGO) in Sn/rGO composites and found that the CO2 adsorption ability of Sn/rGO was almost 4-times higher than that of bare Sn catalysts. Density functional theory calculations revealed that the oxidized functional groups of rGO offered adsorption sites for CO2 toward the adjacent Sn surface and that CO2-rich conditions near the surface facilitated the production of formate via COOH∗ formation while suppressing CO∗ formation. Scanning electrochemical cell microscopy directly indicated that CO2 reduction was accelerated at the interface, together with the kinetic suppression of undesirable and competitive hydrogen evolution at the interface. Thus, the synergism of Sn/rGO ensures a substantial/rapid supply of CO2 from the functional groups to the Sn surface, thereby enhancing the Faradaic efficiency 1.8-times compared with that obtained with bare Sn catalysts.

    DOI: 10.1021/acscatal.0c04887

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  19. Improving Intramolecular Hopping Charge Transport via Periodical Segmentation of π-Conjugation in a Molecule 査読有り

    Yutaka Ie, Yuji Okamoto, Takuya Inoue, Takuji Seo, Tatsuhiko Ohto, Ryo Yamada, Hirokazu Tada, Yoshio Aso

    Journal of the American Chemical Society   143 巻 ( 2 ) 頁: 599 - 603   2021年1月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:American Chemical Society ({ACS})  

    DOI: 10.1021/jacs.0c10560

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  20. Single‐Molecule Conductance of a π‐Hybridized Tripodal Anchor while Maintaining Electronic Communication 査読有り

    Tatsuhiko Ohto, Aya Tashiro, Takuji Seo, Nana Kawaguchi, Yuichi Numai, Junpei Tokumoto, Soichiro Yamaguchi, Ryo Yamada, Hirokazu Tada, Yoshio Aso, Yutaka Ie

    Small   17 巻 ( 3 ) 頁: 2006709 - 2006709   2021年1月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:Wiley  

    DOI: 10.1002/smll.202006709

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    その他リンク: https://onlinelibrary.wiley.com/doi/full-xml/10.1002/smll.202006709

  21. Control of dominant conduction orbitals by peripheral substituents in paddle-wheel diruthenium alkynyl molecular junctions 査読有り

    Shiori Ogawa, Swarup Chattopadhyay, Yuya Tanaka, Tatsuhiko Ohto, Tomofumi Tada, Hirokazu Tada, Shintaro Fujii, Tomoaki Nishino, Munetaka Akita

    Chemical Science   12 巻 ( 32 ) 頁: 10871 - 10877   2021年

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:Royal Society of Chemistry ({RSC})  

    Control of charge carriers that transport through the molecular junctions is essential for thermoelectric materials. In general, the charge carrier depends on the dominant conduction orbitals and is dominantly determined by the terminal anchor groups. The present study discloses the synthesis, physical properties in solution, and single-molecule conductance of paddle-wheel diruthenium complexes 1R having diarylformamidinato supporting ligands (DArF: p-R-C6H4-NCHN-C6H4-R-p) and two axial thioanisylethynyl conducting anchor groups, revealing unique substituent effects with respect to the conduction orbitals. The complexes 1R with a few different aryl substituents (R = OMe, H, Cl, and CF3) were fully characterized by spectroscopic and crystallographic analyses. The single-molecule conductance determined by the scanning tunneling microscope break junction (STM-BJ) technique was in the 10-5 to 10-4G0 region, and the order of conductance was 1OMe > 1CF3 ≫ 1H ∼ 1Cl, which was not consistent with the Hammett substituent constants σ of R. Cyclic voltammetry revealed the narrow HOMO-LUMO gaps of 1R originating from the diruthenium motif, as further supported by the DFT study. The DFT-NEGF analysis of this unique result revealed that the dominant conductance routes changed from HOMO conductance (for 1OMe) to LUMO conductance (for 1CF3). The drastic change in the conductance properties originates from the intrinsic narrow HOMO-LUMO gaps. This journal is

    DOI: 10.1039/D1SC02407H

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  22. Correlation between the Dipole Moment of Nonfullerene Acceptors and the Active Layer Morphology of Green-Solvent-Processed P3HT-Based Organic Solar Cells 査読有り

    Shreyam Chatterjee, Tatsuhiko Ohto, Hirokazu Tada, Seihou Jinnai, Yutaka Ie

    ACS Sustainable Chemistry & Engineering   8 巻 ( 51 ) 頁: 19013 - 19022   2020年12月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:American Chemical Society ({ACS})  

    DOI: 10.1021/acssuschemeng.0c07114

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  23. Vibrational couplings and energy transfer pathways of water's bending mode 査読有り

    Chun-Chieh Yu, Kuo-Yang Chiang, Masanari Okuno, Takakazu Seki, Tatsuhiko Ohto, Xiaoqing Yu, Vitaly Korepanov, Hiro-o Hamaguchi, Mischa Bonn, Johannes Hunger, Yuki Nagata

    NATURE COMMUNICATIONS   11 巻 ( 1 )   2020年12月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:NATURE RESEARCH  

    Coupling between vibrational modes is essential for energy transfer and dissipation in condensed matter. For water, different O-H stretch modes are known to be very strongly coupled both within and between water molecules, leading to ultrafast dissipation and delocalization of vibrational energy. In contrast, the information on the vibrational coupling of the H-O-H bending mode of water is lacking, even though the bending mode is an essential intermediate for the energy relaxation pathway from the stretch mode to the heat bath. By combining static and femtosecond infrared, Raman, and hyper-Raman spectroscopies for isotopically diluted water with ab initio molecular dynamics simulations, we find the vibrational coupling of the bending mode differs significantly from the stretch mode: the intramode intermolecular coupling of the bending mode is very weak, in stark contrast to the stretch mode. Our results elucidate the vibrational energy transfer pathways of water. Specifically, the librational motion is essential for the vibrational energy relaxation and orientational dynamics of H-O-H bending mode. Vibrational energy transfer in water involves intermolecular coupling of O-H stretching modes, but much less is known about the role of the bending modes. Here the authors, combining static and femtosecond infrared, Raman, and hyper-Raman spectroscopy and ab initio molecular dynamics simulations, provide insight into the energy dynamics of the bend vibrations.

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  24. Vibrational mode frequency correction of liquid water in density functional theory molecular dynamics simulations with van der Waals correction 査読有り

    Kai Zhong, Chun-Chieh Yu, Mayank Dodia, Mischa Bonn, Yuki Nagata, Tatsuhiko Ohto

    Physical Chemistry Chemical Physics   22 巻 ( 22 ) 頁: 12785 - 12793   2020年5月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:Royal Society of Chemistry ({RSC})  

    DOI: 10.1039/c9cp06335h

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  25. Molecular Structure and Modeling of Water–Air and Ice–Air Interfaces Monitored by Sum-Frequency Generation 査読有り

    Fujie Tang, Tatsuhiko Ohto, Shumei Sun, Jérémy R. Rouxel, Sho Imoto, Ellen H. G. Backus, Shaul Mukamel, Mischa Bonn, Yuki Nagata

    Chemical Reviews   120 巻 ( 8 ) 頁: 3633 - 3667   2020年4月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:American Chemical Society ({ACS})  

    DOI: 10.1021/acs.chemrev.9b00512

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  26. Hydrogen Bonds and Molecular Orientations of Supramolecular Structure between Barbituric Acid and Melamine Derivative at the Air/Water Interface Revealed by Heterodyne-Detected Vibrational Sum Frequency Generation Spectroscopy 査読有り

    Masanari Okuno, Shuhei Yamada, Tatsuhiko Ohto, Hirokazu Tada, Waka Nakanishi, Katsuhiko Ariga, Taka-aki Ishibashi

    The Journal of Physical Chemistry Letters   11 巻 ( 7 ) 頁: 2422 - 2429   2020年4月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:American Chemical Society ({ACS})  

    DOI: 10.1021/acs.jpclett.0c00329

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  27. Decoding the molecular water structure at complex interfaces through surface-specific spectroscopy of the water bending mode 査読有り

    Takakazu Seki, Chun-Chieh Yu, Xiaoqing Yu, Tatsuhiko Ohto, Shumei Sun, Konrad Meister, Ellen H. G. Backus, Mischa Bonn, Yuki Nagata

    Physical Chemistry Chemical Physics   22 巻 ( 19 ) 頁: 10934 - 10940   2020年4月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:Royal Society of Chemistry ({RSC})  

    <p>The water bending mode vibrational spectroscopy provides a new avenue for unveiling the hydrogen bonding structure of interfacial water at complex aqueous interfaces such as solid–water and bio–water interfaces.</p>

    DOI: 10.1039/d0cp01269f

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  28. Mechanical switching of current-voltage characteristics in spiropyran single-molecule junctions 査読有り

    Takashi Tamaki, Keigo Minode, Yuichi Numai, Tatsuhiko Ohto, Ryo Yamada, Hiroshi Masai, Hirokazu Tada, Jun Terao

    NANOSCALE   12 巻 ( 14 ) 頁: 7527 - 7531   2020年4月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:ROYAL SOC CHEMISTRY  

    The electrical properties of a single-molecule junction of spiropyran are investigated through the break junction (BJ) method, and the current-voltage (I-V) characteristics are switched from rectified to symmetric through mechanical stimulus. This phenomenon indicates isomerization from spiropyran to merocyanine. In addition, an increase in the conductance associated with isomerization is observed.

    DOI: 10.1039/d0nr00277a

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  29. Effect of Graphene Encapsulation of NiMo Alloys on Oxygen Evolution Reaction 査読有り

    Samuel Jeong, Kailong Hu, Tatsuhiko Ohto, Yuki Nagata, Hideki Masuda, Jun-ichi Fujita, Yoshikazu Ito

    ACS Catalysis   10 巻 ( 1 ) 頁: 792 - 799   2020年1月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:American Chemical Society ({ACS})  

    DOI: 10.1021/acscatal.9b04134

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  30. Accessing the Accuracy of Density Functional Theory through Structure and Dynamics of the Water–Air Interface 査読有り

    Tatsuhiko Ohto, Mayank Dodia, Jianhang Xu, Sho Imoto, Fujie Tang, Frederik Zysk, Thomas D. K, ne, Yasuteru Shigeta, Mischa Bonn, Xifan Wu, Yuki Nagata

    The Journal of Physical Chemistry Letters   10 巻 ( 17 ) 頁: 4914 - 4919   2019年9月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:American Chemical Society ({ACS})  

    DOI: 10.1021/acs.jpclett.9b01983

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  31. Effects of cis–trans Conformation between Thiophene Rings on Conductance of Oligothiophenes 査読有り

    Tatsuhiko Ohto, Takuya Inoue, Helen Stewart, Yuichi Numai, Yoshio Aso, Yutaka Ie, Ryo Yamada, Hirokazu Tada

    The Journal of Physical Chemistry Letters   10 巻 ( 18 ) 頁: 5292 - 5296   2019年9月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:American Chemical Society ({ACS})  

    DOI: 10.1021/acs.jpclett.9b02059

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  32. Chemical Dopants on Edge of Holey Graphene Accelerate Electrochemical Hydrogen Evolution Reaction 査読有り

    Akichika Kumatani, Chiho Miura, Hirotaka Kuramochi, Tatsuhiko Ohto, Mitsuru Wakisaka, Yuki Nagata, Hiroki Ida, Yasufumi Takahashi, Kailong Hu, Samuel Jeong, Jun‐ichi Fujita, Tomokazu Matsue, Yoshikazu Ito

    Advanced Science   6 巻 ( 10 ) 頁: 1900119   2019年5月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    DOI: 10.1002/advs.201900119

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  33. Impact of intermolecular vibrational coupling effects on the sum-frequency generation spectra of the water/air interface 査読有り

    Naveen Kumar Kaliannan, Andres Henao Aristizabal, Hendrik Wiebeler, Frederik Zysk, Tatsuhiko Ohto, Yuki Nagata, Thomas D. Kühne

    Molecular Physics     2019年5月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    DOI: 10.1080/00268976.2019.1620358

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  34. Highly Planar and Completely Insulated Oligothiophenes: Effects of π-Conjugation on Hopping Charge Transport 査読有り

    Yutaka Ie, Yuji Okamoto, Takuya Inoue, Saori Tone, Takuji Seo, Yasushi Honda, Shoji Tanaka, See Kei Lee, Tatsuhiko Ohto, Ryo Yamada, Hirokazu Tada, Yoshio Aso

    The Journal of Physical Chemistry Letters   10 巻 ( 12 ) 頁: 3197 - 3204   2019年5月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:American Chemical Society ({ACS})  

    DOI: 10.1021/acs.jpclett.9b00747

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  35. Structure and Dynamics of Water at the Water–Air Interface Using First-Principles Molecular Dynamics Simulations. II. NonLocal vs Empirical van der Waals Corrections 査読有り

    Mayank Dodia, Tatsuhiko Ohto, Sho Imoto, Yuki Nagata

    Journal of Chemical Theory and Computation   15 巻 ( 6 ) 頁: 3836 - 3843   2019年5月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:American Chemical Society ({ACS})  

    DOI: 10.1021/acs.jctc.9b00253

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  36. Boosting electrochemical water splitting via ternary NiMoCo hybrid nanowire arrays 査読有り

    Kailong Hu, Mingxing Wu, Satoshi Hinokuma, Tatsuhiko Ohto, Mitsuru Wakisaka, Jun-ichi Fujita, Yoshikazu Ito

    Journal of Materials Chemistry A   7 巻 ( 5 ) 頁: 2156 - 2164   2019年1月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:Royal Society of Chemistry ({RSC})  

    DOI: 10.1039/C8TA11250A

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  37. Three site molecular orbital controlled single-molecule rectifiers based on perpendicularly linked porphyrin–imide dyads 査読有り

    Murni Handayani, Hirofumi Tanaka, Shinichi Katayose, Tatsuhiko Ohto, Zhijin Chen, Ryo Yamada, Hirokazu Tada, Takuji Ogawa

    Nanoscale   11 巻 ( 47 ) 頁: 22724 - 22729   2019年

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:Royal Society of Chemistry ({RSC})  

    <p>Single-molecule rectifiers with perpendicularly connected metal porphyrin–imide dyads showed high rectification ratio, which could be tuned by the central metal inside the porphyrin. The features can be explained with a three sight model.</p>

    DOI: 10.1039/C9NR07105A

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  38. Large Hydrogen-Bond Mismatch between TMAO and Urea Promotes Their Hydrophobic Association 査読有り

    Wen Jun Xie, Seoncheol Cha, Tatsuhiko Ohto, Wataru Mizukami, Yuezhi Mao, Manfred Wagner, Mischa Bonn, Johannes Hunger, Yuki Nagata

    Chem   4 巻 ( 11 ) 頁: 2615   2018年11月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:Elsevier {BV}  

    DOI: 10.1016/j.chempr.2018.08.020

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  39. Graphene Layer Encapsulation of Non-Noble Metal Nanoparticles as Acid-Stable Hydrogen Evolution Catalysts 査読有り

    Hu Kailong, Ohto Tatsuhiko, Chen Linghan, Han Jiuhui, Wakisaka Mitsuru, Nagata Yuki, Fujita Jun-ichi, Ito Yoshikazu

    ACS ENERGY LETTERS   3 巻 ( 7 ) 頁: 1539 - 1544   2018年7月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:American Chemical Society ({ACS})  

    DOI: 10.1021/acsenergylett.8b00739

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  40. Definition of Free O-H Groups of Water at the Air-Water Interface 査読有り

    Fujie Tang, Tatsuhiko Ohto, Taisuke Hasegawa, Wen Jun Xie, Limei Xu, Mischa Bonn, Yuki Nagata

    Journal of Chemical Theory and Computation   14 巻 ( 1 ) 頁: 357 - 364   2018年6月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:American Chemical Society  

    Free O-H groups of water are often found at the water-hydrophobic medium interface, e.g. for water contact with hydrophobic protein residues, or at the water-air interface. In surface-specific vibrational spectroscopic studies using sum-frequency generation (SFG) spectroscopy, free O-H groups are experimentally well characterized in the O-H stretch region by a sharp 3700 cm-1 peak. Although these free O-H groups are often defined as the O-H groups which are not hydrogen-bonded to other water molecules, a direct correlation between such non-hydrogen-bonded O-H groups and the 3700 cm-1 SFG response has been lacking. Our data show that commonly used hydrogen bond definitions do not adequately capture the free O-H groups contributing to the 3700 cm-1 peak. We thus formulate a new definition for capturing the subensemble of the surface free O-H groups using the intermolecular distance and the angle formed by the water dimer, through the comparison of the ∼3700 cm-1 SFG response and the responses from the selected free O-H groups at the HOD-air interface. Using these optimized free O-H group definitions, we infer the fraction of interfacial water molecules with free O-H groups of 28%, a vibrational lifetime of the free O-H groups of 1.3 ps, and the angle formed by the free O-H groups and the surface normal of 67° at the water-air interface. We expect that this improved free O-H group definition can be helpful in exploring the structure and dynamics of the interfacial water.

    DOI: 10.1021/acs.jctc.7b00566

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  41. Aggregation-Induced Emission Enhancement from Disilane-Bridged Donor-Acceptor-Donor Luminogens Based on the Triarylamine Functionality 査読有り

    Tsukasa Usuki, Masaki Shimada, Yoshinori Yamanoi, Tatsuhiko Ohto, Hirokazu Tada, Hidetaka Kasai, Eiji Nishibori, Hiroshi Nishihara

    ACS Applied Materials and Interfaces   10 巻 ( 15 ) 頁: 12164 - 12172   2018年4月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:American Chemical Society  

    Six novel donor-acceptor-donor organic dyes containing a Si-Si moiety based on triarylamine functionalities as donor units were prepared by Pd-catalyzed arylation of hydrosilanes. Their photophysical, electrochemical, and structural properties were studied in detail. Most of the compounds showed attractive photoluminescence (PL) and electrochemical properties both in solution and in the solid state because of intramolecular charge transfer (ICT), suggesting these compounds could be useful for electroluminescence (EL) applications. The aggregation-induced emission enhancement (AIEE) characteristics of 1 and 3 were examined in mixed water/THF solutions. The fluorescence intensity in THF/water was stronger in the solution with the highest ratio of water because of the suppression of molecular vibration and rotation in the aggregated state. Single-crystal X-ray diffraction of 4 showed that the reduction of intermolecular π-π interaction led to intense emission in the solid state and restricted intramolecular rotation of the donor and acceptor moieties, thereby indicating that the intense emission in the solid state is due to AIEE. An electroluminescence device employing 1 as an emitter exhibited an external quantum efficiency of up to 0.65% with green light emission. The emission comes solely from 1 because the EL spectrum is identical to that of the PL of 1. The observed luminescence was sufficiently bright for application in practical devices. Theoretical calculations and electrochemical measurements were carried out to aid in understanding the optical and electrochemical properties of these molecules.

    DOI: 10.1021/acsami.7b14802

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  42. Cooperation between holey graphene and NiMo alloy for hydrogen evolution in an acidic electrolyte 査読有り

    Yoshikazu Ito, Tatsuhiko Ohto, Daisuke Hojo, Mitsuru Wakisaka, Yuki Nagata, Linghan Chen, Kailong Hu, Masahiko Izumi, Jun-Ichi Fujita, Tadafumi Adschiri

    ACS Catalysis   8 巻 ( 4 ) 頁: 3579 - 3586   2018年4月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:American Chemical Society  

    The development of noble-metal-free hydrogen evolution reaction (HER) materials for electrochemical water splitting is the key to achieving low-cost and efficient electrocatalysis that drives electrochemical hydrogen evolution. However, the electrocatalytic activities of most non-noble metals decrease in acidic electrolytes. Here, we have fabricated non-noble-metal electrodes using a bicontinuous and open porous NiMo alloy covered by nitrogen-doped (N-doped) graphene with nanometer-sized holes. This noble-metal-free HER catalyst exhibits performance almost identical with that of a Pt/C electrode, while its original catalytic activity is preserved even in acidic electrolytes. Density functional theory calculations indicate that the interfacial fringes between the nanoholes and NiMo surface induce charge transfer and promote hydrogen adsorption and desorption. The nanometer-sized holes simultaneously provide minimal surface area for chemical reactions, while delaying NiMo dissolution in excessive amounts of acidic electrolyte. Our method for the fabrication of the NiMo alloy provides a route to a promising class of electrochemical hydrogen-producing electrodes.

    DOI: 10.1021/acscatal.7b04091

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  43. Orientational Distribution of Free O-H Groups of Interfacial Water is Exponential 査読有り

    Shumei Sun, Fujie Tang, Sho Imoto, Daniel R. Moberg, Tatsuhiko Ohto, Francesco Paesani, Mischa Bonn, Ellen H.{\hspace, m } }G. Backus, Yuki Nagata

    Physical Review Letters   121 巻 ( 24 )   2018年

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:American Physical Society ({APS})  

    DOI: 10.1103/physrevlett.121.246101

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  44. Structure and dynamics of water at water-graphene and water-hexagonal boron-nitride sheet interfaces revealed by: Ab initio sum-frequency generation spectroscopy 査読有り

    Tatsuhiko Ohto, Hirokazu Tada, Yuki Nagata

    Physical Chemistry Chemical Physics   20 巻 ( 18 ) 頁: 12979 - 12985   2018年

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Royal Society of Chemistry  

    We simulate sum-frequency generation (SFG) spectra of isotopically diluted water at the water-graphene and water-hexagonal boron-nitride (hBN) sheet interfaces, using ab initio molecular dynamics simulations. A sharp 'dangling' O-D peak around ∼2640 cm-1 appearing in both simulated SFG spectra evidences that both graphene and hBN are hydrophobic. The dangling O-D peak is 10 cm-1 red-shifted at the water-hBN interface relative to the peak at the water-graphene interface. This frequency difference gives a stronger O-D⋯N intermolecular interaction between water and hBN than the O-D⋯C interaction between water and graphene. Accordingly, the anisotropy decay of such a dangling O-D group slows down near hBN compared with near graphene, illustrating that the dynamics of the dangling O-D group are also affected by the stronger O-D⋯N interaction than the O-D⋯C interaction. We discuss molecular-level insights into the structure and dynamics of interfacial water in the context of the friction of hBN and graphene.

    DOI: 10.1039/c8cp01351a

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  45. Structure and Dynamics of Water at the Water–Air Interface Using First-Principles Molecular Dynamics Simulations within Generalized Gradient Approximation 査読有り

    Tatsuhiko Ohto, Mayank Dodia, Sho Imoto, Yuki Nagata

    Journal of Chemical Theory and Computation     2018年

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:American Chemical Society ({ACS})  

    DOI: 10.1021/acs.jctc.8b00567

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  46. Single-molecule rectifiers based on voltage-dependent deformation of molecular orbitals in carbazole oligomers 査読有り

    Ryo Yamada, Ken Albrecht, Tatsuhiko Ohto, Keigo Minode, Kimihisa Yamamoto, Hirokazu Tada

    Nanoscale   10 巻 ( 42 ) 頁: 19818 - 19824   2018年

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Royal Society of Chemistry ({RSC})  

    DOI: 10.1039/c8nr06049e

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  47. Magnetic field effect on pentacene-doped sexithiophene diodes 査読有り

    Song-Toan Pham, Marine Fayolle, Tatsuhiko Ohto, Hirokazu Tada

    APPLIED PHYSICS LETTERS   111 巻 ( 20 ) 頁: 203303   2017年11月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:AMER INST PHYSICS  

    We studied the effect of impurities on the magnetoresistance of sexithiophene-based diodes using impedance spectroscopy. The impurities were introduced by doping pentacene molecules into a sexithiophene film through a co-evaporation process. The pentacene molecules act as charge-scattering centers, which trigger the negative magnetoresistance of the device. This makes it possible to tune the value of magnetoresistance from positive to negative by increasing the applied voltage. The beneficial properties induced by impurities suggest a potential route to integrate additional functions into organic devices. Published by AIP Publishing.

    DOI: 10.1063/1.5006547

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  48. Highly Luminescent 2D-Type Slab Crystals Based on a Molecular Charge-Transfer Complex as Promising Organic Light-Emitting Transistor Materials 査読有り

    Sang Kyu Park, Jin Hong Kim, Tatsuhiko Ohto, Ryo Yamada, Andrew O. F. Jones, Dong Ryeol Whang, Illhun Cho, Sangyoon Oh, Seung Hwa Hong, Ji Eon Kwon, Jong H. Kim, Yoann Olivier, Roland Fischer, Roland Resel, Johannes Gierschner, Hirokazu Tada, Soo Young Park

    ADVANCED MATERIALS   29 巻 ( 36 ) 頁: 1701346   2017年9月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:WILEY-V C H VERLAG GMBH  

    A new 2:1 donor (D):acceptor (A) mixed-stacked charge-transfer (CT) cocrystal comprising isometrically structured dicyanodistyrylbenzene-based D and A molecules is designed and synthesized. Uniform 2D-type morphology is manifested by the exquisite interplay of intermolecular interactions. In addition to its appealing structural features, unique optoelectronic properties are unveiled. Exceptionally high photoluminescence quantum yield (Phi(F) approximate to 60%) is realized by non-negligible oscillator strength of the S-1 transition, and rigidified 2D-type structure. Moreover, this luminescent 2D-type CT crystal exhibits balanced ambipolar transport (mu(h) and mu(e) of approximate to 10(-4) cm(2) V-1 s(-1)). As a consequence of such unique optoelectronic characteristics, the first CT electroluminescence is demonstrated in a single active-layered organic light-emitting transistor (OLET) device. The external quantum efficiency of this OLET is as high as 1.5% to suggest a promising potential of luminescent mixed-stacked CT cocrystals in OLET applications.

    DOI: 10.1002/adma.201701346

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  49. Analysis of Single Molecule Conductance of Heterogeneous Porphyrin Arrays by Partial Transmission Probabilities 査読有り

    Takashi Tamaki, Tatsuhiko Ohto, Ryo Yamada, Hirokazu Tada, Takuji Ogawa

    CHEMISTRYSELECT   2 巻 ( 25 ) 頁: 7484 - 7488   2017年8月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:WILEY-V C H VERLAG GMBH  

    Single molecule conductance (SMC) of a series of porphyrin derivatives, whose porphyrin units are connected through a phenylene bridge that have one or two thiolate end groups, was measured by a scanning tunneling microscopic break junction (STM-BJ) technique. The observed conductance values were analyzed by partial transmission probabilities (T-i) for the molecular parts using the equation G=G(0)Pi T-N(i)i. Unique combination of Ti was obtained, which indicates the validity of this analysis. By the analysis, the free-base porphyrin ring interacting with the gold electrode was found to show a greater transmission probability Tpor-Au than that of the bridge between thiolate and the gold electrode (TS-Au).

    DOI: 10.1002/slct.201701015

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  50. Electrochemical TERS Elucidates Potential-Induced Molecular Reorientation of Adenine/Au(111) 査読有り

    Natalia Martin Sabanes, Tatsuhiko Ohto, Denis Andrienko, Yuki Nagata, Katrin F. Domke

    ANGEWANDTE CHEMIE-INTERNATIONAL EDITION   56 巻 ( 33 ) 頁: 9796 - 9801   2017年8月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:WILEY-V C H VERLAG GMBH  

    Electrochemical surface activity arises from the interaction and geometric arrangement of molecules at electrified interfaces. We present a novel electrochemical tip-enhanced Raman spectroscope that can access the vibrational fingerprint of less than 100 small, non-resonant molecules adsorbed at atomically flat Au electrodes to study their adsorption geometry and chemical reactivity as a function of the applied potential. Combining experimental and simulation data for adenine/Au(111), we conclude that protonated physisorbed adenine adopts a tilted orientation at low potentials, whereas it is vertically adsorbed around the potential of zero charge. Further potential increase induces adenine deprotonation and reorientation to a planar configuration. The extension of EC-TERS to the study of adsorbate reorientation significantly broadens the applicability of this advanced spectroelectrochemical tool for the nanoscale characterization of a full range of electrochemical interfaces.

    DOI: 10.1002/anie.201704460

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  51. Multifunctional Octamethyltetrasila[2.2]cyclophanes: Conformational Variations, Circularly Polarized Luminescence, and Organic Electroluminescence 査読有り

    Masaki Shimada, Yoshinori Yamanoi, Tatsuhiko Ohto, Song-Toan Pham, Ryo Yamada, Hirokazu Tada, Kenichiro Omoto, Shohei Tashiro, Mitsuhiko Shionoya, Mineyuki Hattori, Keiko Jimura, Shigenobu Hayashi, Hikaru Koike, Munetaka Iwamura, Koichi Nozaki, Hiroshi Nishihara

    JOURNAL OF THE AMERICAN CHEMICAL SOCIETY   139 巻 ( 32 ) 頁: 11214 - 11221   2017年8月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:AMER CHEMICAL SOC  

    Both symmetrical and unsymmetrical cyclophanes containing disilane units, tetrasila[2.2]cyclophanes 1-9, were synthesized. The syn and anti conformations and the kinetics of inversion between two anti-isomers were investigated by X-ray diffraction and variable-temperature NMR analysis, respectively. The flipping motion of two aromatic rings was affected by the bulkiness of the aromatic moiety (1 vs 6), the phase (solid vs solution), and the inclusion by host molecules (1 vs 1 subset of[Ag2L](2+)). The photophysical, electrochemical, and structural properties of the compounds were thoroughly investigated. Unsymmetrical tetrasila[2.2]cyclophanes 5-8 displayed blue-green emission arising from intramolecular charge transfer. Compound 6 emitted a brilliant green light in the solid state under 365 nm irradiation and showed a higher fluorescence quantum yield in the solid state (Phi = 0.49) than in solution (Phi = 0.05). We also obtained planar chiral tetrasila[2.2]cyclophane 9, which showed interesting chiroptical properties, such as a circularly polarized luminescence (CPL) with a dissymmetry factor of vertical bar g(lum)vertical bar = ca. 2 X 10(-3) at 500 nm. Moreover, an organic green light-emitting diode that showed a maximum external quantum efficiency (eta(ext)) of ca. 0.4% was fabricated by doping 4,4'-bis(2,2'-diphenylvinyl)-1,1'-biphenyl with 6.

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  52. Electrochemical TERS Elucidates Potential-Induced Molecular Reorientation of Adenine/Au(111) 査読有り

    Natalia Mart{\'{\i, n{\hspace, m } }Saban{\'{e } }s, Tatsuhiko Ohto, Denis Andrienko, Yuki Nagata, Katrin F. Domke

    Angewandte Chemie   129 巻 ( 33 ) 頁: 9928   2017年7月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:Wiley  

    DOI: 10.1002/ange.201704460

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  53. Encapsulated Oligothiophenes: Synthesis and Single-Molecule Conductance 査読有り

    Yoshio Aso, Yutaka Ie, Takuya Inoue, Yuji Okamoto, See K. Lee, Tatsuhiko Ohto, Ryo Yamada, Hirokazu Tada

        2017年7月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    DOI: 10.1002/anie.201104700

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  54. Chemisorbed and Physisorbed Water at the TiO2/Water Interface 査読有り

    Saman Hosseinpour, Fujie Tang, Fenglong Wang, Ruth A. Livingstone, Simon J. Schlegel, Tatsuhiko Ohto, Mischa Bonn, Yuki Nagata, Ellen H. G. Backus

    JOURNAL OF PHYSICAL CHEMISTRY LETTERS   8 巻 ( 10 ) 頁: 2195 - 2199   2017年5月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:AMER CHEMICAL SOC  

    The interfacial structure of water in contact with TiO2 is the key to understand the mechanism of photocatalytic water dissociation as well as photoinduced superhydrophilicity. We investigate the interfacial molecular structure of water at the surface of anatase TiO2 using phase-sensitive sum frequency generation spectroscopy together with spectra simulation using ab initio molecular dynamic trajectories. We identify two oppositely oriented, weakly and strongly hydrogen-bonded subensembles of O-H groups at the superhydrophilic UV irradiated TiO2 surface. The water molecules with weakly hydrogen-bonded O H groups are chemisorbed, i.e. form hydroxyl groups, at the TiO2 surface with their hydrogen atoms pointing toward bulk water. The strongly hydrogen-bonded O H groups interact with the oxygen atom of the chemisorbed water. Their hydrogen atoms point toward the TiO2. This strong interaction between physisorbed and chemisorbed water molecules causes superhydrophilicity.

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  55. Trimethylamine-N-oxide: its hydration structure, surface activity, and biological function, viewed by vibrational spectroscopy and molecular dynamics simulations 査読有り

    Tatsuhiko Ohto, Johannes Hunger, Ellen H. G. Backus, Wataru Mizukami, Mischa Bonn, Yuki Nagata

    PHYSICAL CHEMISTRY CHEMICAL PHYSICS   19 巻 ( 10 ) 頁: 6909 - 6920   2017年3月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:ROYAL SOC CHEMISTRY  

    The osmolyte molecule trimethylamine-N-oxide (TMAO) stabilizes the structure of proteins. As functional proteins are generally found in aqueous solutions, an important aspect of this stabilization is the interaction of TMAO with water. Here, we review, using vibrational spectroscopy and molecular dynamics simulations, recent studies on the structure and dynamics of TMAO with its surrounding water molecules. This article ends with an outlook on the open questions on TMAO-protein and TMAO-urea interactions in aqueous environments.

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  56. pi(+)-pi(+) stacking of imidazolium cations enhances molecular layering of room temperature ionic liquids at their interfaces6 査読有り

    Fujie Tang, Tatsuhiko Ohto, Taisuke Hasegawa, Mischa Bonn, Yuki Nagata

    PHYSICAL CHEMISTRY CHEMICAL PHYSICS   19 巻 ( 4 ) 頁: 2850 - 2856   2017年1月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:ROYAL SOC CHEMISTRY  

    The interfacial structure of room temperature ionic liquids (RTILs) controls many of the unique properties of RTILs, such as the high capacitance of RTILs and the efficiency of charge transport between RTILs and electrodes. RTILs have been experimentally shown to exhibit interfacial molecular layering structures over a 10 angstrom length scale. However, the driving force behind the formation of these layered structures has not been resolved. Here, we report ab initio molecular dynamics simulations of imidazolium RTIL/air and RTIL/graphene interfaces along with force field molecular dynamics simulations. We find that the pi(+)-pi(+) interaction of imidazolium cations enhances the layering structure of RTILs, despite the electrostatic repulsion. The length scales of the molecular layering at the RTIL/air and RTIL/graphene interfaces are very similar, manifesting the limited effect of the substrate on the interfacial organization of RTILs.

    DOI: 10.1039/c6cp07034e

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  57. Enhancement of Carrier Mobility through Deformation Potential in Metal-Containing Insulated Molecular Wires 査読有り

    Tatsuhiko Ohto, Hiroshi Masai, Jun Terao, Wakana Matsuda, Shu Seki, Yasushi Tsuji, Hirokazu Tada

    Journal of Physical Chemistry C   120 巻 ( 47 ) 頁: 26637 - 26644   2016年12月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:AMER CHEMICAL SOC  

    We used first-principles calculations to investigate the hole mobility of metal-containing poly(phenylene ethynylene) insulated molecular wires. The metal-organic bond effects were considered using ruthenium(II) porphyrin-pyridyl and platinum(II) acetylide as the organometallic moieties. We found that high hole mobility can be achieved even when the metal-organic d pi-p pi interaction is weak. The weak metal-organic interaction reduces the structural deformation that accompanies hole hopping and compensates the reduced conjugation inside the molecular wire. Our results suggest a new principle for the design of functionalized metallopolymers with high carrier mobilities.

    DOI: 10.1021/acs.jpcc.6b08557

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  58. Unveiling the Amphiphilic Nature of TMAO by Vibrational Sum Frequency Generation Spectroscopy 査読有り

    Tatsuhiko Ohto, Ellen H. G. Backus, Wataru Mizukami, Johannes Hunger, Mischa Bonn, Yuki Nagata

    JOURNAL OF PHYSICAL CHEMISTRY C   120 巻 ( 31 ) 頁: 17435 - 17443   2016年8月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:AMER CHEMICAL SOC  

    By combining heterodyne-detected sum-frequency generation (SFG) spectroscopy, ab initio molecular dynamics (AIMD) simulation, and a post-vibrational self-consistent field (VSCF) approach, we reveal the orientation and surface activity of the amphiphile trimethylamine-N-oxide (TMAO) at the water/air interface. Both measured and simulated C-H stretch SFG spectra show a strong negative and a weak positive peak. We attribute these peaks to the symmetric stretch mode/Fermi resonance and antisymmetric in-plane mode of the methyl group, respectively, based on the post-VSCF calculation. These positive and negative features evidence that the methyl groups of TMAO are oriented preferentially toward the air phase. Furthermore, we explore the effects of TMAO on the interfacial water structure. The O-H stretch SFG spectra manifest that the hydrogen bond network of the aqueous TMAO-solution/air interface is similar to that of the amine-N-oxide (AO) surfactant/water interface. This demonstrates that, irrespective of the alkyl chain length, the AO groups have a similar impact on the hydrogen bond network of the interfacial water. In contrast, we find that adding TMAO to water makes the orientation of the free O-H groups of the interfacial water molecules more parallel to the surface normal. Invariance of the free O-H peak amplitude despite the enhanced orientation of the topmost water layer illustrates that TMAO is embedded in the topmost water layer, manifesting the clear contrast of the hydrophobic methyl group and the hydrophilic AO group of TMAO.

    DOI: 10.1021/acs.jpcc.6b04852

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  59. Surface tension of ab initio liquid water at the water-air interface 査読有り

    Yuki Nagata, Tatsuhiko Ohto, Mischa Bonn, Thomas D. Kuehne

    JOURNAL OF CHEMICAL PHYSICS   144 巻 ( 20 ) 頁: 204705   2016年5月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:AMER INST PHYSICS  

    We report calculations on the surface tension of the water-air interface using ab initio molecular dynamics (AIMD) simulations. We investigate the influence of the cell size on surface tension of water from force field molecular dynamics simulations. We find that the calculated surface tension increases with increasing simulation cell size, thereby illustrating that a correction for finite size effects is essential for small systems that are customary in AIMD simulations. Moreover, AIMD simulations reveal that the use of a double-zeta basis set overestimates the experimentally measured surface tension due to the Pulay stress while more accurate triple and quadruple-zeta basis sets give converged results. We further demonstrate that van der Waals corrections critically affect the surface tension. AIMD simulations without the van der Waals correction substantially underestimate the surface tension while the van derWaals correction with the Grimme's D2 technique results in a value for the surface tension that is too high. The Grimme's D3 van derWaals correction provides a surface tension close to the experimental value. Whereas the specific choices for the van derWaals correction and basis sets critically affect the calculated surface tension, the surface tension is remarkably insensitive to the details of the exchange and correlation functionals, which highlights the impact of long-range interactions on the surface tension. Our simulated values provide important benchmarks, both for improving van derWaals corrections and AIMD simulations of aqueous interfaces. Published by AIP Publishing.

    DOI: 10.1063/1.4951710

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  60. Molecular Modeling of Water Interfaces: From Molecular Spectroscopy to Thermodynamics 査読有り

    Yuki Nagata, Tatsuhiko Ohto, Ellen H. G. Backus, Mischa Bonn

    JOURNAL OF PHYSICAL CHEMISTRY B   120 巻 ( 16 ) 頁: 3785 - 3796   2016年4月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:AMER CHEMICAL SOC  

    Understanding aqueous interfaces at the molecular level is not only fundamentally important, but also highly relevant for a variety of disciplines. For instance, electrode water interfaces are relevant for electrochemistry, as are mineral water interfaces for geochemistry and air water interfaces for environmental chemistry; water lipid interfaces constitute the boundaries of the cell membrane, and are thus relevant for biochemistry. One of the major challenges in these fields is to link macroscopic properties such as interfacial reactivity, solubility, and permeability as well as macroscopic thermodynamic and spectroscopic observables to the structure, structural changes, and dynamics of molecules at these interfaces. Simulations, by themselves, or in conjunction with appropriate experiments, can provide such molecular-level insights into aqueous interfaces. In this contribution, we review the current state-of-the-art of three levels of molecular dynamics (MD) simulation: ab initio, force field, and coarse-grained. We discuss the advantages, the potential, and the limitations of each approach for studying aqueous interfaces, by assessing computations of the sum-frequency generation spectra and surface tension. The comparison of experimental and simulation data provides information on the challenges of future MD simulations, such as improving the force field models and the van der Waals corrections in ab initio MD simulations. Once good agreement between experimental observables and simulation can be established, the simulation can be used to provide insights into the processes at a level of detail that is generally inaccessible to experiments. As an example we discuss the mechanism of the evaporation of water. We finish by presenting an outlook outlining four future challenges for molecular dynamics simulations of aqueous interfacial systems.

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  61. Lipid Carbonyl Groups Terminate the Hydrogen Bond Network of Membrane-Bound Water 査読有り

    Tatsuhiko Ohto, Ellen H. G. Backus, Cho-Shuen Hsieh, Marialore Sulpizi, Mischa Bonn, Yuki Nagata

    JOURNAL OF PHYSICAL CHEMISTRY LETTERS   6 巻 ( 22 ) 頁: 4499 - 4503   2015年11月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:AMER CHEMICAL SOC  

    We present a combined experimental sum-frequency generation (SFG) spectroscopy and ab initio molecular dynamics simulations study to clarify the structure and orientation of water at zwitterionic phosphatidylcholine (PC) lipid and amine N-oxide (AO) surfactant monolayers. Simulated O-H stretch SFG spectra of water show good agreement with the experimental data. The SFG response at the PC interface exhibits positive peaks, whereas both negative and positive bands are present for the similar zwitterionic AO interface. The positive peaks at the water/ PC interface are attributed to water interacting with the lipid carbonyl groups, which act as efficient hydrogen bond acceptors. This allows the water hydrogen bond network to reach, with its (up-oriented) O-H groups, into the headgroup of the lipid, a mechanism not available for water underneath the AO surfactant. This highlights the role of the lipid carbonyl group in the interfacial water structure at the membrane interface, namely, stabilizing the water hydrogen bond network.

    DOI: 10.1021/acs.jpclett.5b02141

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  62. Toward ab initio molecular dynamics modeling for sum-frequency generation spectra; an efficient algorithm based on surface-specific velocity-velocity correlation function 査読有り

    Tatsuhiko Ohto, Kota Usui, Taisuke Hasegawa, Mischa Bonn, Yuki Nagata

    JOURNAL OF CHEMICAL PHYSICS   143 巻 ( 12 ) 頁: 124702   2015年9月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:AMER INST PHYSICS  

    Interfacial water structures have been studied intensively by probing the O-H stretch mode of water molecules using sum-frequency generation (SFG) spectroscopy. This surface-specific technique is finding increasingly widespread use, and accordingly, computational approaches to calculate SFG spectra using molecular dynamics (MD) trajectories of interfacial water molecules have been developed and employed to correlate specific spectral signatures with distinct interfacial water structures. Such simulations typically require relatively long (several nanoseconds) MD trajectories to allow reliable calculation of the SFG response functions through the dipole moment-polarizability time correlation function. These long trajectories limit the use of computationally expensive MD techniques such as ab initio MD and centroid MD simulations. Here, we present an efficient algorithm determining the SFG response from the surface-specific velocity-velocity correlation function (ssVVCF). This ssVVCF formalism allows us to calculate SFG spectra using a MD trajectory of only similar to 100 ps, resulting in the substantial reduction of the computational costs, by almost an order of magnitude. We demonstrate that the O-H stretch SFG spectra at the water-air interface calculated by using the ssVVCF formalism well reproduce those calculated by using the dipole moment-polarizability time correlation function. Furthermore, we applied this ssVVCF technique for computing the SFG spectra from the ab initio MD trajectories with various density functionals. We report that the SFG responses computed from both ab initio MD simulations and MD simulations with an ab initio based force field model do not show a positive feature in its imaginary component at 3100 cm(-1). (C) 2015 AIP Publishing LLC.

    DOI: 10.1063/1.4931106

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  63. Ab Initio Liquid Water Dynamics in Aqueous TMAO Solution 査読有り

    Kota Usui, Johannes Hunger, Marialore Sulpizi, Tatsuhiko Ohto, Mischa Bonn, Yuki Nagata

    JOURNAL OF PHYSICAL CHEMISTRY B   119 巻 ( 33 ) 頁: 10597 - 10606   2015年8月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:AMER CHEMICAL SOC  

    Ab initio molecular dynamics (AIMD) simulations in trimethylamine N-oxide (TMAO)-D2O solution are employed to elucidate the effects of TMAO on the reorientational dynamics of D2O molecules. By decomposing the O-D groups of the D2O molecules into specific subensembles, we reveal that water reorientational dynamics are retarded considerably in the vicinity of the hydrophilic TMAO oxygen (O-TMAO) atom, due to the O-D center dot center dot center dot O-TMAO hydrogen-bond. We find that this reorientational motion is governed by two distinct mechanisms: The O-D group rotates (1) after breaking the O-D center dot center dot center dot O-TMAO hydrogen-bond, or (2) together with the TMAO molecule while keeping this hydrogen-bond intact. While the orientational slow-down is prominent in the AIMD simulation, simulations based on force field models exhibit much faster dynamics. The simulated angle-resolved radial distribution functions illustrate that the O-D center dot center dot center dot O-TMAO hydrogen-bond has a strong directionality through the sp(3) orbital configuration in the AIMD simulation, and this directionality is not properly accounted for in the force field simulation. These results imply that care must be taken when modeling negatively charged oxygen atoms as single point charges; force field models may not adequately describe the hydration configuration and dynamics.

    DOI: 10.1021/acs.jpcb.5b02579

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  64. Impedance spectroscopy of organic magnetoresistance devices - Effect of interface disorder 査読有り

    M. Fayolle, M. Yamaguchi, T. Ohto, H. Tada

    Journal of Applied Physics   117 巻 ( 7 )   2015年2月

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    掲載種別:研究論文(学術雑誌)  

    Organic magnetoresistance (OMAR) can be caused by either single carrier (bipolaron) or double carriers (electron-hole)-based mechanisms. In order to consider applications for OMAR, it is important to control the mechanism present in the device. In this paper, we report the effect of traps on OMAR resulting of disorder at the interface between the organic active layer with the hole injection layer [poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate): PEDOT:PSS]. It has been found that while the single carriers OMAR is enhanced by the presence of traps, the double carriers OMAR is totally removed in a sample with a high interface trap density. The reasons for these results are discussed based on the impedance spectroscopy measurements. First, the mechanism (single or double carriers) responsible of the OMAR was determined with the support of the capacitance measurement. Then, the influence of traps was discussed with the Nyquist diagrams and phase angle-frequency plots of the samples. The results suggested that with a rough interface and thus high disorder, the presence of traps enhanced the bipolaron formation. Traps also acted as recombination centers for electron-hole pairs, which prevented the double carriers OMAR in devices with a rough interface. On the other hand, with a low trap density, i.e., with a smooth surface, the single carrier OMAR decreased, and double carriers OMAR appeared. The sign of the OMAR could then be controlled by simply sweeping the bias voltage. This work demonstrated that the roughness at the interface is important for controlling OMAR and its reproducibility, and that the combination of OMAR measurement and impedance spectroscopy is helpful for clarifying the processes at the interface.

    DOI: 10.1063/1.4913272

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  65. Determination of the mechanism behind the organic magnetoresistance (OMAR) effect by using impedance spectroscopy 査読有り

    Marine Fayolle, Mariko Yamaguchi, Song Toan Pham, Tatsuhiko Ohto, Hirokazu Tada

    INTERNATIONAL JOURNAL OF NANOTECHNOLOGY   12 巻 ( 3-4 ) 頁: 238 - 247   2015年

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:INDERSCIENCE ENTERPRISES LTD  

    We investigated the organic magnetoresistance (OMAR) mechanism in poly(3-hexylthiophene-2,5-diyl) (P3HT)-based diodes, by using impedance spectroscopy. We have prepared layered structures consisting of indium tin oxide, poly(3,4-ethylenedioxythiophene): poly(styrenesulphonate) (PEDOT:PSS), P3HT and aluminium and measured the bias voltage dependence of the OMAR and of the impedance spectra. The capacitance deduced from the impedance data indicated that the OMAR was explained by the single-carrier (bipolaron) model at lower bias voltages as well as double-carrier models at higher bias voltages. The impedance response also suggested that the OMAR from the single-carrier model was governed by the PEDOT: PSS/P3HT interface whereas the double-carrier OMAR was mainly related to the P3HT layer.

    DOI: 10.1504/IJNT.2015.067209

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  66. The surface roughness, but not the water molecular orientation varies with temperature at the water-air interface 査読有り

    Yuki Nagata, Taisuke Hasegawa, Ellen H. G. Backus, Kota Usui, Seiji Yoshimune, Tatsuhiko Ohto, Mischa Bonn

    PHYSICAL CHEMISTRY CHEMICAL PHYSICS   17 巻 ( 36 ) 頁: 23559 - 23564   2015年

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:ROYAL SOC CHEMISTRY  

    We examine the temperature dependence of the interfacial molecular structure at the water-air interface by combining experimental and simulated sum-frequency generation (SFG) spectroscopy. The experimental SFG spectra of the OH-stretching mode show a decrease in the amplitude at similar to 3300 cm(-1) with increasing temperature, while the 3700 cm(-1) 'free OH' SFG feature is insensitive to temperature changes. The simulated spectra are in excellent agreement with experiment. A comparison between interfacial SFG spectra and bulk infrared/Raman spectra reveals that the variation of the SFG signal due to the temperature change is not caused by a temperature-dependent OH bond orientation of the interfacial water molecules, but can be fully accounted for by the temperature dependence of the optical response of water. These results indicate that while the thickness of the interfacial region varies with temperature, the molecular organization of interfacial water at the water-air interface is surprisingly insensitive to temperature changes.

    DOI: 10.1039/c5cp04022a

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  67. Thermopower of Benzenedithiol and C-60 Molecular Junctions with Ni and Au Electrodes 査読有り

    See Kei Lee, Tatsuhiko Ohto, Ryo Yamada, Hirokazu Tada

    NANO LETTERS   14 巻 ( 9 ) 頁: 5276 - 5280   2014年9月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:AMER CHEMICAL SOC  

    We have performed thermoelectric measurements of benzenedithiol (BDT) and C-60 molecules with Ni and Au electrodes using a home-built scanning tunneling microscope. The thermopower of C60 was negative for both Ni and Au electrodes, indicating the transport of carriers through the lowest unoccupied molecular orbital in both cases, as was expected from the work functions. On the other hand, the NiBDTNi junctions exhibited a negative thermopower, whereas the AuBDTAu junctions exhibited a positive thermopower. First-principle calculations revealed that the negative thermopower of NiBDTNi junctions is due to the spin-split hybridized states generated by the highest occupied molecular orbital of BDT coupled with s- and d-states of the Ni electrode.

    DOI: 10.1021/nl502305e

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  68. Influence of surface polarity on water dynamics at the water/rutile TiO2(110) interface 査読有り

    Tatsuhiko Ohto, Ankur Mishra, Seiji Yoshimune, Hisao Nakamura, Mischa Bonn, Yuki Nagata

    JOURNAL OF PHYSICS-CONDENSED MATTER   26 巻 ( 24 ) 頁: 244102   2014年6月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:IOP PUBLISHING LTD  

    We report molecular dynamics (MD) simulations of the water/clean rutile TiO2 (110) interface using polarizable and non-surface polarity force field models. The effect of surface polarity on the water dynamics near the TiO2(110) surface is addressed, specifically by calculating the water hydrogen bond and reorientational dynamics. The hydrogen bond lifetime of interfacial water molecules is several times longer than that of bulk water due to the strong water-TiO2 interactions. A comparison of the dynamics simulated with the polarizable and non-surface polarity models shows that, while the hydrogen bond lifetime between the interfacial water and TiO2 surface is insensitive to the surface polarity, the reorientational dynamics around this hydrogen bond axis is significantly influenced by the surface polarity; the surface polarity of the TiO2 increases the water-TiO2 interactions, stabilizing the local structure of the interfacial water molecules and restricting their rotational motion. This reorientation occurs predominantly by rotation around the O-H group hydrogen bonded to the TiO2 surface. Furthermore, we correlate the dynamics of the induced charge on the TiO2 surface with the interfacial water dynamics. Our results show that the timescale of correlations of the atom charges induced by the local electric field in bulk water is influenced by the rotational motion, hydrogen bond rearrangement and translational motion, while the induced charge dynamics of the TiO2 surface is governed primarily by the rotational dynamics of the interfacial water molecules. This study demonstrates that the solid surface polarity has a significant impact on the dynamics of water molecules near TiO2 surfaces.

    DOI: 10.1088/0953-8984/26/24/244102

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  69. Single Molecular Resistive Switch Obtained via Sliding Multiple Anchoring Points and Varying Effective Wire Length 査読有り

    Manabu Kiguchi, Tatsuhiko Ohto, Shintaro Fujii, Kazunori Sugiyasu, Shigeto Nakajima, Masayuki Takeuchi, Hisao Nakamura

    JOURNAL OF THE AMERICAN CHEMICAL SOCIETY   136 巻 ( 20 ) 頁: 7327 - 7332   2014年5月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:AMER CHEMICAL SOC  

    A single molecular resistive (conductance) switch via control of anchoring positions was examined by using a molecule consisting of more than two same anchors. For this purpose, we adopted the covered quaterthiophene (QT)-based molecular wire junction. The QT-based wire consisted of two thiophene ring anchors on each side; thus, shift of anchors was potentially possible without a change in the binding modes and distortion of the intramolecular structure. We observed three distinct conductance states by using scanning tunneling microscope-based break junction technique. A detailed analysis of the experimental data and first-principles calculations revealed that the mechanism of the resistive switch could be explained by standard length dependence (exponential decay) of conductance. Here, the length is the distance between the anchoring points, i.e., length of the bridged pi-conjugated backbone. Most importantly, this effective tunneling length was variable via only controlling the anchoring positions in the same molecule. Furthermore, we experimentally showed the possibility of a dynamic switch of anchoring positions by mechanical control. The results suggested a distinct strategy to design functional devices via contact engineering.

    DOI: 10.1021/ja413104g

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  70. Thermoelectric Efficiency of Organometallic Complex Wires via Quantum Resonance Effect and Long-Range Electric Transport Property 査読有り

    Hisao Nakamura, Tatsuhiko Ohto, Takao Ishida, Yoshihiro Asai

    JOURNAL OF THE AMERICAN CHEMICAL SOCIETY   135 巻 ( 44 ) 頁: 16545 - 16552   2013年11月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:AMER CHEMICAL SOC  

    Superior long-range electric transport has been observed in several organometallic wires. Here, we discuss the role of the metal center in the electric transport and examine the possibility of high thermoelectric figure of merit (ZT) by controlling the quantum resonance effects. We examined a few metal center (and metal-free) terpyridine-based complexes by first-principles calculations and clarified the role of the metals in determining the transport properties. Quasi-resonant tunneling is mediated by organic compounds, and narrow overlapping resonance states are formed when d-electron metal centers are incorporated. Distinct length (L) and temperature (T) dependencies of thermopower from semiconductor materials or organic molecular junctions are presented in terms of atomistic calculations of ZT with and without considering the phonon thermal conductance. We present an alternative approach to obtain high ZT for molecular junctions by quantum effect.

    DOI: 10.1021/ja407662m

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  71. Optical and redox properties of phenyl-capped cyclohexa[c]-oligothiophenes 査読有り

    Yijun Zheng, Tatsuhiko Ohto, Dian Liu, Hans-Juergen Butt, Taichi Ikeda

    SYNTHETIC METALS   181 巻   頁: 1 - 9   2013年10月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:ELSEVIER SCIENCE SA  

    A series of phenyl-capped cyclohexa[c]thiophene derivatives (nCHT-TEG, n = 2, 4, or 6) have been synthesized. nCHT-TEG are well-soluble in common organic solvents. The absorption spectra of neutral nCHT-TEG oligomers indicated a shorter effective conjugation length than conventional oligothiophenes based on the non-coplanarity of the thiophene rings. nCHT-TEG can be oxidized/reduced reversibly. The results of cyclic voltammetry and UV-Vis-NIR spectroscopy of the oxidized nCHT-TEG revealed that the effective conjugation length increases at the higher oxidation state. Density functional theory (DFT) calculations indicate that the quinoidal structure of the oxidized nCHT contributes to the improved effective conjugation length. nCHT-TEG radical cations and dications were characterized by electron spin resonance (ESR) and nuclear magnetic resonance (NMR) spectroscopies, respectively. NMR results of nCHT-TEG dication revealed that 2CHT-TEG(2+) have closed-shell bipolaron structure, while 4CHT-TEG(2+) and 6CHT-TEG(2+) are the mixture of closed-shell bipolaron and open-shell two-polaron structures. (C) 2013 Elsevier B.V. All rights reserved.

    DOI: 10.1016/j.synthmet.2013.08.005

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  72. Chirality dependence of quantum thermal transport in carbon nanotubes at low temperatures: A first-principles study 査読有り

    Tomoyuki Hata, Hiroki Kawai, Tatsuhiko Ohto, Koichi Yamashita

    JOURNAL OF CHEMICAL PHYSICS   139 巻 ( 4 ) 頁: 044711   2013年7月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:AMER INST PHYSICS  

    We study the transport properties of single-walled carbon nanotubes (SWCNTs) using the nonequilibrium Green's function method based on first-principles calculations. We compared three SWCNTs with different chiralities (3, 3), (5, 0), and (4, 2), and found that the thermal conductance varies significantly with the chirality, especially at low temperatures. Such differences are attributed to the dependence on the chirality of the frequency of the lowest optical mode and phonon-phonon interaction with the semi-infinite leads. To obtain accurate low-vibrational frequencies, a force constant correction based on the Lagrange undetermined multiplier method was employed. The phonon-phonon interaction was analyzed in terms of the projection of the phonon coupling with the semi-infinite leads onto the normal modes of the center region. Our result indicates that high optical mode frequency and weak phonon coupling on the armchair (3, 3) SWCNT are the origin of the long quantized plateau found in the experimental thermal conductance. (C) 2013 AIP Publishing LLC.

    DOI: 10.1063/1.4816476

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  73. Ab initio theory for current-induced molecular switching: Melamine on Cu(001) 査読有り

    Tatsuhiko Ohto, Ivan Rungger, Koichi Yamashita, Hisao Nakamura, Stefano Sanvito

    Physical Review B - Condensed Matter and Materials Physics   87 巻 ( 20 )   2013年5月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:American Physical Society ({APS})  

    Melamine on Cu(001) is mechanically unstable under the current of a scanning tunneling microscope tip and can switch among configurations. However, these are not equally accessible, and the switching critical current depends on the bias polarity. In order to explain such rich phenomenology, we have developed a scheme to evaluate the evolution of the reaction paths and activation barriers as a function of bias, which is rooted in the nonequilibrium Green's function method implemented within density functional theory. This, combined with the calculation of the inelastic electron tunneling spectroscopy signal, allows us to identify the vibrational modes promoting the observed molecular conformational changes. Finally, once our ab initio results are used within a resonance model, we are able to explain the details of the switching behavior, such as its dependence on the bias polarity, and the noninteger power relation between the reaction rate constants and both the bias voltage and the electric current. © 2013 American Physical Society.

    DOI: 10.1103/PhysRevB.87.205439

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  74. Polarizable Site Charge Model at Liquid/Solid Interfaces for Describing Surface Polarity: Application to Structure and Molecular Dynamics of Water/Rutile TiO2(110) Interface 査読有り

    Hisao Nakamura, Tatsuhiko Ohto, Yuki Nagata

    JOURNAL OF CHEMICAL THEORY AND COMPUTATION   9 巻 ( 2 ) 頁: 1193 - 1201   2013年2月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:AMER CHEMICAL SOC  

    We present a novel scheme to construct a polarizable force field for liquid/solid interfaces, which takes into account the effect of the surface polarity induced by liquid-solid interactions explicitly. We extend the charge response kernel (CRK) method for molecules to solid surfaces by introducing the surface CRK The CRK parameters are systematically determined by the first-principles calculations in the slab model with the dipole-correction method. Our methodology is applied to the water/clean rutile TiO2(110) interface. Structures and induced charges of a single water molecule attached to the TiO2 surface optimized by our polarizable force field show good agreement with those predicted by the first-principles calculations. Further, we carried out MD simulations for the liquid water/TiO2 interface and found three stable structures of water attached to the TiO2 surface. Two of them are predicted by both the polarizable and the nonpolarizable force fields, while the polarizable force field model predicts a structure of water with the hydrogen and oxygen atoms interacting with the oxygen atom of the surface TiO2 and the hydrogen atom of the other water molecule, respectively, which was reported by the previous first-principles MD simulation. This indicates that the dipole moments of water and TiO2 induced by the water-TiO2 interactions have significant impact on molecular conformations of the water/TiO2 interface.

    DOI: 10.1021/ct300998z

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  75. First-principles study of electronic structure and charge transport at PTCDA molecular layers on Ag(111) and Al(111) electrodes 査読有り

    Tatsuhiko Ohto, Koichi Yamashita, Hisao Nakamura

    PHYSICAL REVIEW B   84 巻 ( 4 )   2011年7月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:AMER PHYSICAL SOC  

    We performed first-principles transport calculations of the contact consisting of 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) molecular layers and metal electrodes using the nonequilibrium Green's function method combined with the density functional theory. To analyze roles of organic/metal interfacial states for transport, we examined two kinds of electrodes: Ag(111) and Al(111). By quantitative evaluation of the coupling strength between PTCDA molecular orbitals and electrodes, we found the creation of the Shockley-type state at the interface of PTCDA and Ag(111). In contrast, the Al(111) surface formed a strong chemical bond with PTCDA. A clear Shockley-type state was not created, and an ohmic bias voltage (V) and electric current (I) behavior was found for contacts consisting of thin PTCDA layers and Al(111) electrodes. We also predicted that further stacking of PTCDA layers will make I-V characteristics more Schottky-like for both Ag and Al electrodes, regardless the different microscopic mechanism.

    DOI: 10.1103/PhysRevB.84.045417

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  76. Effect of Anchoring Group Position on Formation and Conductance of a Single Disubstituted Benzene Molecule Bridging Au Electrodes: Change of Conductive Molecular Orbital and Electron Pathway 査読有り

    Manabu Kiguchi, Hisao Nakamura, Yuuta Takahashi, Takuya Takahashi, Tatsuhiko Ohto

    JOURNAL OF PHYSICAL CHEMISTRY C   114 巻 ( 50 ) 頁: 22254 - 22261   2010年12月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:AMER CHEMICAL SOC  

    We investigated the effect of anchoring group position on the formation and electric conductance of single molecule junctions for benzenedithiol and benzenediamine by the scanning tunneling microscope break junction technique. The conductances of the single 1,4-benzenedithiol, 1,3-benzenedithiol, 1,4-benzenediamine, and 1,3-benzenediamine molecules were 0.005 (+/- 0.001) G(0) (G(0)=2e(2)/h), 0.004 (+/- 0.001) G(0), 0.01 (+/- 0.003) G(0), and 0.005 (+/- 0.002) G(0), respectively. No 1,2-disubstituted benzene molecules formed junctions. While the 1,4-position provided larger conductance than the 1,3-position for both anchoring groups, the effect of the anchoring position on conductance was clearer for benzenediamine than benzenedithiol. The resulting anchoring position and its stability are discussed in consideration of the formation of the single molecular junction. The relationship between conductance and anchoring group (position) was analyzed based on ab initio transport calculations. The deformation and change of the energy alignment of the "conductive" molecular orbital give clearer insight to the anchoring position effect than to quantum interference.

    DOI: 10.1021/jp1095079

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  77. First-principles study of charge-density waves on Cu surfaces covered by In, Pb, and Bi atoms: Analysis of electronic structure and surface phonons 査読有り

    Tatsuhiko Ohto, Akihiro Nojima, Koichi Yamashita, Hisao Nakamura

    PHYSICAL REVIEW B   82 巻 ( 15 )   2010年10月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:AMER PHYSICAL SOC  

    We performed a first-principles density-functional calculation to investigate the difference in the mechanisms of phase transitions for In/Cu(001) and W(001). We also explain the origins of surface states of In, Pb, and Bi/Cu(001)-0.5 ML having c(2x2) structure that cause a phase transition via the generation of a charge-density wave (CDW). The perfect theoretical/experimental agreement for the wave numbers of nesting vectors corresponding to the well-nested surface states of In and Pb/Cu(001)-0.5 ML is reported. Band-structure analysis suggests a common mechanism of CDW transition for In and Pb/Cu(001)-0.5 ML. The absorption of In and Pb on Cu(001) leads to a reduction in the energy of the band composing the edge of bulk band gap. As a result, the band enters the bulk band gap and has the character of the surface state. Since these surface states compose a well-nested Fermi surface, CDW transition would be induced. In addition, we studied the relationship between the lattice distortions and the band dispersions of the surface states of In/Cu(001)-0.5 ML and W(001) in terms of the Jahn-Teller effect (JTE). While we find promoting modes that resolve the degeneracy of surface states of W(001), any surface-localized mode of In/Cu(001) does not split the band of surface state. Therefore, the static electron-phonon interaction of In/Cu(001) is weak. We propose that the dynamic JTE contributes to the CDW transition of In/Cu(001) and the dynamic nature is related to the spatial coherence length of the CDW.

    DOI: 10.1103/PhysRevB.82.155415

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書籍等出版物 1

  1. スピントロニクスのための計算機ナノマテリアルデザイン

    吉田 博 , 白井 正文, 赤井 久純 , 浜田 典昭, 小田 竜樹, 中村 浩次, 神吉 輝夫, 佐藤 和則, 真砂 啓, 福島 鉄也, 新屋 ひかり, 三浦 良雄, 大戸 達彦, 阿部 英介

    内田老鶴圃  2022年  ( ISBN:9784753622016

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    記述言語:日本語

    CiNii Books

MISC 1

  1. 物性物理学に関する学生実験のオンライン化の試み

    蓑輪 陽介, 藤原 秀紀, 大戸 達彦, 山田 亮, 後藤 穣, 細井 優, 生田 力三, 鶴田 篤史, 横山 知大, 夛田 博一  

    大学の物理教育28 巻 ( 2 ) 頁: 83 - 87   2022年7月

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    記述言語:日本語   掲載種別:記事・総説・解説・論説等(学術雑誌)   出版者・発行元:一般社団法人 日本物理学会  

    1.はじめに

    2020年1月に国内で最初の感染者が報告された新型コロナウィルス感染症は瞬く間に広がり,4月には緊急事態宣言が発出されるに至り,生活様式に大きな変革をもたらした.大学の授業も例

    DOI: 10.11316/peu.28.2_83

    CiNii Books

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講演・口頭発表等 6

  1. メルカプトアルカン酸超分子混合膜における整流効果の第一原理計算

    大戸 達彦、前田 青也、Gyu Don Kong、Jiung Jang、Suin Choi、In Soo Kim、Hyo Jae Yoon、夛田 博一

    2024年第71回応用物理学会春季学術講演会  2024年3月22日 

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    開催年月日: 2024年3月

    会議種別:ポスター発表  

  2. 長距離伝導分子ワイヤーのゼーベック効果

    大戸 達彦、Jiung Jang、Jeong Woo Jo、Hyo Jae Yoon

    2024年第71回応用物理学会春季学術講演会  2024年3月23日 

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    開催年月日: 2024年3月

    会議種別:口頭発表(一般)  

  3. 卑金属を用いた水電解用電極の開発:第一原理計算と機械学習の観点から 招待有り

    大戸達彦

    CMCリサーチウェビナー  2024年2月28日 

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    開催年月日: 2024年2月

    会議種別:公開講演,セミナー,チュートリアル,講習,講義等  

  4. 卑金属のみを用いた固体高分子型水電解用酸素発生電極の開発:第一原理計算と機械学習の観点から 招待有り

    大戸達彦

    CMCリサーチウェビナー  2023年12月8日 

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    開催年月日: 2023年12月

    会議種別:公開講演,セミナー,チュートリアル,講習,講義等  

  5. 表面科学と機械学習 招待有り

    大戸達彦

    レア・イベントの計算科学 第6回ワークショップ  2023年12月3日 

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    開催年月日: 2023年12月

    会議種別:口頭発表(招待・特別)  

  6. Theoretical study of molecular thermoelectric devices 招待有り 国際会議

    Tatsuhiko Ohto

    International Congress on Pure & Applied Chemistry (ICPAC) Bali 2023  2023年9月15日 

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    開催年月日: 2023年9月

    会議種別:口頭発表(招待・特別)  

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科研費 10

  1. 単一分子接合における電荷と熱の輸送機構の解明とその制御に関する研究

    研究課題/研究課題番号:22H00315  2022年4月 - 2026年3月

    日本学術振興会  科学研究費助成事業  基盤研究(A)

    夛田 博一, 山田 亮, 大戸 達彦

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    担当区分:研究分担者 

    金属電極間に分子を架橋した単一分子接合の電気伝導度(σ)と熱伝導度(κ)を広い温度範囲で計測し,キャリアと熱の輸送機構に関する学理を構築するとともに,それらの制御を行うための指針を導出し,熱電変換素子への応用の可能性を提示する。微細加工技術を駆使して,周辺から熱的に遮断されたサスペンション型のデバイスを作製し,構造の規定された分子を架橋して,分子長や分子骨格,アンカー部の違いが σ と κ に与える影響を考察する。

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  2. 先端分光計測と精密合成を活用したグラフェンナノリボンの微細構造と機能の制御

    研究課題/研究課題番号:21KK0091  2021年10月 - 2025年3月

    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))

    奥野 将成, 成田 明光, 大戸 達彦

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    担当区分:研究分担者 

    初年度はほぼ計画通りの研究を行うことができた。実施した内容は以下のとおりである。
    (1) 多波長での測定が可能な顕微ラマン分光装置を構築した。671 nmおよび785 nmのレーザーを新規に導入することで、従来保有していた532 nmに加えて、さらにこれら二波長での顕微ラマン分光測定を可能にした。これによって、電子二重共鳴効果による、グラフェンのラマンバンドのピーク位置のシフトなどの詳細な検証を行うことが可能になった。また、蛍光性の分子試料についてもさまざまな波長によるラマン測定の試行が可能になった。
    (2) グラフェンナノリボンおよびその構成分子のラマン測定を行った。新奇グラフェンナノリボンを合成するための原料分子について、ラマン測定を行い、良好なラマンスペクトルを得ることに成功した。10種類を超える分子について、極少量(< 1 mg)あればラマン測定が可能であることを示した。特に、532 nmでは蛍光が強くラマン信号が埋没してしまった試料についても、より長波長の671 nm励起によってラマン信号を得ることができた。これは、(1)で多波長顕微ラマン分光装置を構築したことにより、信号取得が可能になったといえる。分子構造のわずかな違いにより、蛍光の大きさおよびラマンシフトが誘発されることを見出し、今後の構造解析についての情報を得ることができた。また、金属基板上のグラフェンナノリボンについても、十分な信号ノイズ比でラマン測定が行えることを示した。詳細については現在解析中であるが、試料の状態を反映して異なったスペクトルを得ることに成功した。

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  3. 第一原理計算と離散曲面論を用いたグラフェンナノ構造体の触媒活性制御 公募研究

    研究課題/研究課題番号:20H04639  2020年4月 - 2022年3月

    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)  新学術領域研究(研究領域提案型)

    大戸 達彦

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    担当区分:研究代表者 

    配分額:7410000円 ( 直接経費:5700000円 、 間接経費:1710000円 )

    グラフェンに化学修飾を施して触媒として用いようとする研究が盛んに行われているが、化学修飾の自由度の大きさから、触媒としての設計指針を確立することは容易ではない。第一原理計算による触媒表面と反応物の吸着構造の決定は有用な手法であるが、実験との突き合わせが大きな課題となる。本研究では、欠陥・ドーパント(N、P)・官能基を導入したグラフェンに対して水分解反応の第一原理計算を行い、数学的モデルと実験にフィードバックすることで高活性の触媒開発に結びつける。
    普遍的かつ貴金属を使用しない触媒材料設計を達成するため、数学的に炭素ネットワーク構造を予測する標準実現に対して、窒素原子などの化学元素を導入する枠組みを提唱した。より正確に構造を再現するために、近接原子間の反発力を考慮することで、必要最小限の物理現象を組み入れた改善型標準実現モデルを開発し、既存のシミュレーション法を用いて材料設計可能なレベルで構造を再現できていることを確認した。また、数学モデルから導き出された最適な材料設計を用いて、実際に 3 次元グラフェンを作製し、意図した触媒設計が有用であることを実験的に実証した(Carbon 182, 2021, 223-232)。
    3 次元グラフェン触媒の設計を行う上で、曲面を形成するために導入された欠陥構造を持つカーボンネットワークの単純化を行った。カーボンネットワークをバネの連結体とみなした標準実現に対して、第二近接原子間の反発力を加えた改善型標準実現を構築した。この改善型標準実現が正しく構造を構築できるかどうかを最も精度の信頼性が高いとされる第一原理計算手法と比較して調べた。六員環から構成されるグラフェンの格子に五員環と七員環のペア欠陥(以下、5-7 欠陥)を二つ導入した構造を再現したところ、両者の構造特徴は定性的にほぼ一致し、曲面の指標であるガウス曲率の変化を再現できることが明らかとなった。CPU1 コアでの計算時間を簡単に比較すると、改善型標準実現の計算時間が 39 マイクロ秒に対して、第一原理計算手法の計算時間は 4 万 6 千秒であったので、改善型標準実現は第一原理計算より 10 億倍速く計算できることがわかった。
    令和3年度が最終年度であるため、記入しない。
    令和3年度が最終年度であるため、記入しない。

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  4. 単一分子接合中における化学反応の統計的シミュレーション

    研究課題/研究課題番号:19K15505  2019年4月 - 2022年3月

    科学研究費助成事業  若手研究

    大戸 達彦

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    担当区分:研究代表者 

    配分額:4290000円 ( 直接経費:3300000円 、 間接経費:990000円 )

    これまでの単一分子接合の研究では、実験では破断過程に沿って大量の電流-電圧曲線が得られるのに対し、理論計算では最安定構造の電流-電圧曲線のみを計算して比較することが一般的であった。本研究では反応力場と第一原理計算を用いて大量の電流-電圧曲線を取得し、機械学習の手法を活用して架橋構造を特定する手法を開発する。破断過程に沿って分子構造が変化するような分子に対してこの手法を適用することで、分子構造変化を引き起こすトリガーとなる構造変化を見出し、オン・オフ比と操作性の高い分子スイッチの開拓を目指す。
    単一分子接合の構造とトンネル伝導の機構を原子レベルで明らかにすることが研究期間全体を通じた本研究課題の一つの目標であるが、三脚型分子の架橋構造の推定と伝導特性(Small 17, 2006709 (2021).)の解明が代表的な成果となった。通常の単一分子接合ではチオールアンカーなどを用いて電極と接合させるが、より安定な接合を維持するため、アンカー部位と分子骨格の間でπ共役が維持された新たな三脚型分子の架橋構造と伝導特性を明らかにした。特に架橋構造の解析には、測定で得られた電流―電圧曲線に対して教師なしクラスタリングを導入し、データ科学の観点からも新たな解析方法を提案することができた。
    人間が作ることのできる最小単位の部品である分子1つを電極間に架橋した単一分子接合は、電子デバイスの小型化や有機物ならではの電気応答の利用に向けて研究が進められている。単一分子の架橋構造を直接視認することはできず、電気伝導度の計測を通じて分子架橋を確認することになるため、単一分子デバイスの電気伝導特性の計測と評価の手法を確立することは重要な課題である。我々は、ブレークジャンクション法と教師なしクラスタリング、第一原理計算を組み合わせることで、架橋構造の特徴に従って電気伝導度を分類する手法を開発し、3脚型アンカー部位を用いた分子の架橋構造解析に応用した。

  5. 単一分子接合の熱電特性の計測と素子設計指針の導出

    研究課題/研究課題番号:18H03899  2018年4月 - 2022年3月

    日本学術振興会  科学研究費助成事業  基盤研究(A)

    夛田 博一, 山田 亮, 大戸 達彦, 山田 亮, 大戸 達彦

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    担当区分:研究分担者 

    ナノ接合は、バルク材料とは異なる特性を示すため新しい電子素子への応用を意図した研究が進められている。熱の輸送についても興味が持たれているが、熱は電子の流れと違ってさまざまな物質中に容易に散逸してしまうためその制御が難しく挑戦的な課題である。本研究では、金属ー分子ー金属(単一分子接合)の熱伝導度およびゼーベック係数を測定する手法を確立することを目的とした。Si 上のSiN 膜を基板とし、電子ビームリソグラフィー技術とエッチング技術を駆使して、ナノ狭窄部を挟んで、ヒーター部と温度検出部を宙吊り構造として作製し、狭窄部をエレクトロマイグレーション法で原子レベルまで細くする。今年度は、金属狭窄部の電気伝導度、熱伝導度、ゼーベック係数を極低温から室温までの広い温度範囲で計測し、理論で予測されていた量子化現象を確認した。細線の直径は、4端子法による電気伝導度の計測から算出した。電気伝導度に対して熱伝導度は線形に応答するのに対し、ゼーベック係数は、狭窄部が細くなるにつれて、急激に増大することを見出し、理論予測を再現した。さらに、狭窄部分を破断することでナノギャップ電極を作製し、その部分に梁を取り付ける加工を行なった。梁に通電すると熱膨張を引き起こし、電極を平面方向に移動させることが可能となる。印加する電圧を制御することで、ギャップ間の電流値が可逆的に変化し、ブレークジャンクション法が可能であることを示した。

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  6. 分子スピンバルブと非弾性トンネル電子分光の第一原理計算

    研究課題/研究課題番号:16K17855  2016年4月 - 2019年3月

    科学研究費助成事業  若手研究(B)

    大戸 達彦

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    担当区分:研究代表者 

    配分額:4290000円 ( 直接経費:3300000円 、 間接経費:990000円 )

    Ni-C60-Ni接合において、C60が両電極に等しく結合している場合と片側のC60-Ni電極間距離を十分離した時の磁気抵抗比を第一原理伝導計算手法を用いて評価した。一般に、分子軌道と左右電極へのカップリングが等しければ正の磁気抵抗が得られると言われている(共鳴反転モデル)。-0.7eVのピークは共鳴反転モデルの通り正負反転するが、0eV付近のピークは負に転じることはない。この違いは、共鳴反転モデルに含まれていない要素、すなわち当該エネルギーに位置する分子軌道のスピン分極の様子の相違に起因するものであることを明らかにした。
    ハードディスクのデータ読み取りなどに用いられる磁気抵抗素子は無機物で作製されているが、分子軌道のスピン分裂に伴うスピンフィルター効果を用いれば、有機物でより性能の高い磁気抵抗素子を作製できる可能性がある。しかしこれまで有機物では、電極の磁化が反平行の時により伝導度が高まる、負の磁気抵抗が見られることがあった。本研究では、分子軌道の観点からその原因を明らかにすることができたため、、理論計算からの分子磁気抵抗素子の設計につながることが期待できる。

  7. 第一原理分子動力学法による界面のシミュレーション

    研究課題/研究課題番号:16H00835  2016年4月 - 2018年3月

    科学研究費助成事業  新学術領域研究(研究領域提案型)

    大戸 達彦

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    担当区分:研究代表者 

    配分額:6760000円 ( 直接経費:5200000円 、 間接経費:1560000円 )

    第一原理計算の計算コストは高いが、モデルの任意性が少なく、従来の古典力場による取り扱いが難しい系に対しても計算を行うことが可能である。第一原理トラジェクトリから和周波発生(SFG)分光シグナルを計算するための速度・速度相関関数を本公募研究期間中に開発した[1]が、本年度はそれを溶液界面・固液界面に適用して微視的な界面の構造の探索を行った。はじめに、浸透圧調整物質として知られるトリメチルアミンオキサイド(TMAO)の水溶液と空気の界面について第一原理計算分子動力学シミュレーションを行った。得られたSFGスペクトルは実験とよく一致し、メチル基の対称伸縮振動に由来する強い負のピークが見られた。TMAOのメチル基は空気側に、酸素は水側に存在し、このような小さい分子でも疎水部・親水部の違いが現れることが明らかになった[2]。また、光触媒として知られる酸化チタン表面に紫外線照射したとき、OH基が界面に存在するかどうかが議論されている。我々はOH基がある場合とない場合での酸化チタン・水界面の和周波発生分光スペクトルを第一原理分子動力学シミュレーションから計算し、水素結合の強度が大きく変化することを示唆した。[3]。
    [1] T. Ohto et al., J. Chem. Phys. 143 124702 (2015).[2] T. Ohto et al., Phys. Chem. Chem. Phys. 19 6909 (2017). [3] S. Hosseinpour et al., J. Phys. Chem. Lett. 8 2195 (2017).
    29年度が最終年度であるため、記入しない。
    29年度が最終年度であるため、記入しない。

  8. 単一分子の熱電性能の計測と熱電変換素子の開発

    研究課題/研究課題番号:15K13673  2015年4月 - 2017年3月

    日本学術振興会  科学研究費助成事業  挑戦的萌芽研究

    夛田 博一, 大戸 達彦, 田中 彰治, 後北 寛明, 信末 俊平, 山田 亮, 大戸 達彦, 田中 彰治, 後北 寛明, 信末 俊平, 山田 亮

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    担当区分:連携研究者 

    オリゴチオフェン分子ワイヤーを金電極間に架橋し,電極間に温度差を与えて発生する起電力を計測した。温度差を大きくすると,熱起電圧が大きくなる.温度変化に対して観測された電圧の最頻値をプロットすると,温度差にほぼ比例して大きくなり,ゼーベック係数が正であることから,電荷キャリアが正孔であることが示された。また,AC カロリメトリー法を用いて,高分子薄膜の面内方向の熱伝導度を計測し,3ω法で計測した面直方向の値と比べ, 2倍以上大きいことがわかり,熱電変換性能の過大評価を防ぐためにも,電気伝導度,ゼーベック係数,熱伝導度は試料に対して同方向で計測することの重要性を示した。

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  9. 第一原理計算を用いた分子動力学法の開発と界面への応用

    研究課題/研究課題番号:26104522  2014年4月 - 2016年3月

    科学研究費助成事業  新学術領域研究(研究領域提案型)

    大戸 達彦

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    担当区分:研究代表者 

    配分額:4810000円 ( 直接経費:3700000円 、 間接経費:1110000円 )

    界面付近に存在する少数の分子の構造とダイナミクスを分子レベルで理解することで、より自在な浸透性や濡れ性の設計が可能になると期待される。全原子分子動力学(MD)シミュレーションは、物質の挙動を分子レベルで理解するための強力な手法である。原子間相互作用を古典力場で表現した古典MDシミュレーションが広く行われており、分子からなる系に対しては特に有効であるが、古典力場は質点としての原子同士の相互作用に基づいて構築されており、非局在化した電荷分布や方向性のある化学結合を表現しにくいという弱点がある。そこで、最小限のパラメータから様々な物質を計算することのできる第一原理計算MDシミュレーションが強く望まれる。本研究では浸透圧調節物質として重要なトリメチルアミンオキサイド(TMAO)と水の混合物の第一原理MDシミュレーションを行い、これまでの古典MDシミュレーションでは再現できていなかった、TMAOの酸素まわりに水素結合するOH伸縮振動ピークの赤方偏移を再現した。これは第一原理計算によって水素結合の方向性を記述することができるためであり、今後の古典力場構築の指針としても重要になる結果である。さらに、界面近傍の分子の振動を検出することのできる和周波発生(SFG)分光スペクトルをシミュレーションすることで、実験結果と照らし合わせながら界面での水の挙動を明らかにしてきた。限定されたトラジェクトリからもSFGスペクトルを計算できるよう、SFG応答関数に対応した表面選択的速度・速度相関関数とそれに基づいたSFGスペクトルの表式を導出した。この表式の有効性を実証した上で、水/空気界面の第一原理MDトラジェクトリからSFGスペクトルを計算し、最新の実験結果と一致する結果を得ることができた。
    27年度が最終年度であるため、記入しない。
    27年度が最終年度であるため、記入しない。

  10. 単一分子および分子組織体のスイッチング機能の創出

    研究課題/研究課題番号:25110012  2013年6月 - 2018年3月

    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)

    夛田 博一, 田中 彰治, 山田 亮, 大戸 達彦, 田中 彰治, 山田 亮, 大戸 達彦

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    担当区分:研究分担者 

    メカニカルコントラーブルブレークジャンクション(MCBJ)法および走査トンネル顕微鏡ブレークジャンクション(STMBJ)法を用いて単一分子接合の電流ー電圧特性、熱起電力、磁気抵抗効果を計測した。カルバゾーオリゴマーの分子接合では、電界により分子軌道が変化し、左右電極との接続強度が非対称となり整流特性が発現した。ニッケルを電極した接合では、磁気抵抗効果特性が確認され、電圧印加方向による磁気抵抗比の変化を確認した。熱起電力測定では、電極として金を用いた場合とニッケルを用いた場合で、ゼーベック係数の負号が変わることを確認した。分子のアンカー部の官能基によっても負号が代わり、接合構造の重要性を示した。

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