Publisher：Journal of Materials Chemistry A  

A new TlF phase with a cubic structure containing intrinsic F vacancies is synthesized with one-step chemical fluorination, not a conventional solid-state reaction. The crystal structure is the electronically inverted anti-α-CuBr structure of the Cu+ superionic conductor α-CuBr, with F occupying the Cu site and Tl occupying the Br site. The F− conductivity at room temperature is increased by more than four orders of magnitude compared with the conventional orthorhombic phase, and F− superionic conductivity (≥1 mS cm−1) is observed at around 60 °C. Neural-network potential molecular dynamics demonstrates the F− diffusion via intrinsic F vacancies. The calculated F− conductivity (6.8 mS cm−1 at 400 K) and activation energy (0.4 eV) are comparable to the experimental values (4.3 mS cm−1 at 398 K, 0.3 eV). We propose a new design guideline that uses intrinsic F vacancies for outstanding F− conductors instead of conventional material design based on the introduction of extrinsic F vacancies by aliovalent doping.

DOI： 10.1039/d4ta06334a

Web of Science

Scopus

Language：English   Publisher：Science Advances  

Stacked teacups inspired the idea that columnar assemblies of stacked bowl-shaped molecules may exhibit a unique dynamic behavior, unlike usual assemblies of planar disc- and rod-shaped molecules. On the basis of the molecular design concept for creating higher-order discotic liquid crystals, found in our group, we synthesized a sumanene derivative with octyloxycarbonyl side chains. This molecule forms an ordered hexagonal columnar mesophase, but unexpectedly, the columnar assembly is very soft, similar to sugar syrup. It displays, upon application of a shear force on solid substrates, a flexible bending motion with continuous angle variations of bowl-stacked columns while preserving the two-dimensional hexagonal order. In general, alignment control of higher-order liquid crystals is difficult to achieve due to their high viscosity. The present system that brings together higher structural order and mechanical softness will spark interest in bowl-shaped molecules as a component for developing higher-order liquid crystals with unique mechanical and stimuli-responsive properties.

DOI： 10.1126/sciadv.adg8202

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PubMed

Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Physical Society (APS)  

Using an incoherent quasielastic neutron scattering (QENS) technique, we investigate H- dynamics in a series of oxyhydrides LaH3-2xOx that exhibit characteristic high H- conductivity. In the end member LaH3 (x = 0), two kinds of H- dynamics are identified: the jump diffusion and the localized motion. The jump length in the jump diffusion mode increases with increasing T. The localized motion is identified as a jump between the two inequivalent sites. These dynamics are corroborated by our molecular dynamical simulations. Our QENS data suggest that similar H- dynamics occurs also in oxyhydrides LaH3-2xOx (x≠ 0), whose H- concentration dependence is consistent with the previous measurement of ionic conductivity. We also discuss the possibility that LaH3-2xOx is an example of H- ion conductors governed by the concerted migration mechanism. The identified H- dynamics is key to understanding the anomalous hydrogen concentration dependence of the diffusion coefficient in lanthanum hydrides, which has been a longstanding mystery in this compound.

DOI： 10.1103/physrevb.107.184114

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researchmap

Other Link： http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevB.107.184114/fulltext

Publisher：Journal of Physical Chemistry C  

It is believed that the anionic electrons localized in the crystallographic subnanometer space (void, channel, and interlayer) can stabilize electrides and affect their electronic and magnetic properties. However, the influence of anionic electrons on the stability and properties of electrides is not clear yet. In the present work, ab initio evolutionary structure searches, combined with the first-principles calculations, were employed to predict the stable structures of the Ba-P system under external pressures of 0-20 GPa. Among these predicted compounds, Ba5P3 and Ba8P5 were identified as 1D and 0D electrides, respectively. Our calculations proved that anionic electrons dominate the magnetic and electronic properties of Ba-P electrides. Moreover, it is revealed that anionic electrons have two effects on the stability of electrides: the stabilizing effect caused by the attraction of anionic electrons and the surrounding cations in both 0D and 1D electrides and the destabilizing effect caused by the repulsion between anionic electrons in 1D electrides. Upon the applied external pressure, both effects can be weakened in Ba5P3, while only the former effect was weakened in Ba8P5. Therefore, the 1D electride Ba5P3 becomes thermodynamically stable over the 0D electride Ba8P5 with increasing pressure, which is opposite with the previous concept that the low-dimensional electrides are usually more stable than the high-dimensional ones. The finding of this study may shed light on the design and synthesis of new electrides with different dimensions with the assistance of an external pressure.

DOI： 10.1021/acs.jpcc.2c04042

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Scopus

Authorship：Last author,　Corresponding author   Publisher：Materials and Design  

Fast proton conductors are important materials for catalysis and energy conversion applications. The glassy coordination polymers are an important class of proton conductors due to their good mechanical moldability; however, their conductivity has been limited to ca. 10 mS cm−1 at 100 °C. The systematic design of coordination polymers with fast proton conduction requires an atomistic simulation method that can describe long-range proton diffusion within an affordable computational time. The methodologies of atomistic simulations are separately limited and cannot fairly describe the long-range proton conduction in non-crystalline materials. In this work, we develop a hybrid approach that combines the molecular dynamics based on a conventional force-field and the kinetic Monte Carlo method, which allows for the large-scale (thousands of atoms) and long time (few nanoseconds) simulation of the long-range ionic diffusion in non-crystalline materials. Based on the developed approach, we propose and confirm a design concept for a fast proton-conducting coordination polymer based on Zn2+ ions and phosphoric acid.

DOI： 10.1016/j.matdes.2022.111094

Scopus

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

DOI： https://doi.org/10.1021/acs.jpcc.2c04042

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

DOI： https:// doi.org/10.1016/j.matdes.2022.111094

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Physical Review A  

Correlated electron materials, such as superconductors and magnetic materials, are regarded as fascinating targets in quantum computing. However, the quantitative resources, specifically the number of quantum gates and qubits, required to perform a quantum algorithm to simulate correlated electron materials remain unclear. In this study, we estimate the resources required for the Hamiltonian simulation algorithm for correlated electron materials, specifically for organic superconductors, iron-based superconductors, binary transition-metal oxides, and perovskite oxides, using the fermionic swap network. The effective Hamiltonian derived using the ab initio downfolding method is adopted for the Hamiltonian simulation, and a procedure for the resource estimation by using the fermionic swap network for the effective Hamiltonians including the exchange interactions is proposed. For example, in the system for the 102 unit cells, the estimated numbers of gates per Trotter step and qubits are approximately 107 and 103, respectively, on average for the correlated electron materials. Furthermore, our results show that the number of interaction terms in the effective Hamiltonian, especially for the Coulomb interaction terms, is dominant in the gate resources when the number of unit cells constituting the whole system is up to 102, whereas the number of fermionic swap operations is dominant when the number of unit cells is more than 103.

DOI： 10.1103/PhysRevA.106.012612

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Scopus

Publisher：Acta Materialia  

Solid hydrides are a new class of ionic conductors promising for future applications for hydrogen-carrier, catalysis, and energy conversion. The record-high H− conductivity reported for LaH2.5O0.25 is caused by extraordinarily large pre-exponential factor, which cannot be justified within any simple diffusion picture. To reveal H− dynamics in LaH2.5O0.25 on atomistic level, we developed DFT-based neural-network-potential for large-scale molecular dynamics (MD) simulation and discovered the H− diffusion mechanism: the stoichiometric vacancies are ordered and almost immobile, but they can be rarely kicked-out and become fast mobile vacancies that migrate in a coupled manner with 3H− ring-like rotations. The MD and DFT phonon analysis reveal that the mobile vacancy formation gives rise to an extremely large entropy leading to the anomalously large pre-exponential factor, and that the anharmonicity of H− vibrations causes the large pre-exponential factor. A design concept for faster H− conductor is proposed based on the present finding.

DOI： 10.1016/j.actamat.2022.117825

Web of Science

Scopus

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

DOI： doi.org/10.1016/j.actamat.2022.117825

Publisher：Journal of Physical Chemistry C  

Rayleigh scattering attributed to the density fluctuation of silica glass is considered as the intrinsic origin of optical loss in glass fiber. Therefore, minimizing the density fluctuation is key to improving the information and telecommunications networks. In this study, classical molecular dynamics (MD) simulations were employed to theoretically examine the effectiveness of codoping boron and fluorine for ameliorating the homogeneity of silica glass. For the MD simulations, the force-matching potential (FMP) with a Buckingham formula was developed by optimizing the parameters to reproduce the force and energy calculated by the density functional theory (DFT). The accuracy of the FMP was confirmed via comparisons with available experimental data as well as glass models constructed using the neural network potential, which was superior in reproducing the force and energy of the DFT data to the FMP. As a result, the small amount of boron and fluorine added to the silica glass was found not to deteriorate the density fluctuation of silica glass. The additives reduce the viscosity of silica glass, which leads to a lower fictive temperature and, thus, to a better homogeneity. Consequently, the codoping of boron and fluorine was suggested as a possible solution to suppress the Rayleigh scattering of optical glass fiber.

DOI： 10.1021/acs.jpcc.1c10300

Web of Science

Scopus

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

DOI： 10.1021/jacs.1c11353

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

DOI： 10.1021/jacs.1c11353

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

DOI： https://doi.org/10.1021/acs.jpcc.1c10300

CiNii Research

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

DOI： https://doi.org/10.1021/acs.jpclett.1c03637

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

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

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

DOI： doi.org/10.1080/27660400.2021.1930915

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

DOI： 10.1039/d1sc02407h

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

In this work, the design, synthesis, and single-molecule conductance of ethynyl- and butadiynyl-ruthenium molecular wires with thioether anchor groups [RS=n-C6H13S, p-tert-Bu−C6H4S), trans-{RS−(C≡C)n}2Ru(dppe)2 (n=1 (1R), 2 (2R); dppe: 1,2-bis(diphenylphosphino)ethane) and trans-(n-C6H13S−C≡C)2Ru{P(OMe)3}4 3hex] are reported. Scanning tunneling microscope break-junction study has revealed conductance of the organometallic molecular wires with the thioacetylene backbones higher than that of the related organometallic wires having arylethynylruthenium linkages with the sulfur anchor groups, trans-{p-MeS−C6H4-(C≡C)n}2Ru(phosphine)4 4n (n=1, 2) and trans-(Th−C≡C)2Ru(phosphine)4 5 (Th=3-thienyl). It should be noted that the molecular junctions constructed from the butadiynyl wire 2R, trans-{Au−RS−(C≡C)2}2Ru(dppe)2 (Au: gold metal electrode), show conductance comparable to that of the covalently linked polyynyl wire with the similar molecular length, trans-{Au−(C≡C)3}2Ru(dppe)2 63. The DFT non-equilibrium Green's function (NEGF) study supports the highly conducting nature of the thioacetylene molecular wires through HOMO orbitals.

DOI： 10.1002/chem.202100828

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

DOI： 10.21203/rs.3.rs-128647/v1

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

DOI： https://doi.org/10.1002/chem.202100828

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

DOI： 10.1021/acs.chemmater.1c00064

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

Here, we report multinuclear organometallic molecular wires having (2,5-diethynylthiophene)diyl-Ru(dppe)2repeating units. Despite the molecular dimensions of 2-4 nm the multinuclear wires show high conductance (up to 10−2to 10−3G0) at the single-molecule level with small attenuation factors (β) as revealed by STM-break junction measurements. The high performance can be attributed to the efficient energy alignment between the Fermi level of the metal electrodes and the HOMO levels of the multinuclear molecular wires as revealed by DFT-NEGF calculations. Electrochemical and DFT studies reveal that the strong Ru-Ru interaction through the bridging ligands raises the HOMO levels to access the Fermi level, leading to high conductance and smallβvalues.

DOI： 10.1039/d0sc06613c

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

DOI： https://doi.org/10.1111/jace.17774

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

DOI： https://doi.org/10.1039/D0SC06613C

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

DOI： https://doi.org/10.1021/acs.chemmater.1c00064

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

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

DOI： https://doi.org/10.1016/j.matdes.2020.109210

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

Single-molecule conductance studies on metal-containing inorganic and organometallic molecular wires are relatively less explored compared to those on organic molecular wires. Furthermore, conductance and transmission profiles of the metal-containing wires insensitive to the metal centers often hinder rational design for high performance wires. Here, synthesis and single-molecule conductance measurements of the bis(butadiynyl)rhodium wires with tetracarbene ligands 1H and 1Au are reported as rare examples for Rh(III) diacetylide molecular wires. The rhodium wires derived from the terminal acetylene and gold-functionalized precursors show comparable, high single-molecule conductance ((6-7) × 10-3 G0) as determined by the STM break-junction measurements, suggesting formation of virtually the same covalently linked metal electrode-molecule-metal electrode junctions. The values for the metallapolyynes are larger than those of the organic polyyne wires having the similar molecular lengths. The hybrid DFT-NEGF calculations of the model systems suggest that profiles of transmission spectra are highly sensitive to the presence and species of the metal fragments doped into the polyyne molecular wire because the conductance orbitals of the metallapolyynes molecular junctions carry significant metal fragment characters. Thus, the metallapolyyne junctions turn out to be suitable platforms for rationally designed molecular wires.

DOI： 10.1021/acs.inorgchem.0c01609

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

DOI： 10.1021/acs.inorgchem.0c01609

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

DOI： 10.1021/acs.chemmater.0c02139?ref=pdf

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

Ammonia (NH3) is pivotal to the fertilizer industry and one of the most commonly produced chemicals(1). The direct use of atmospheric nitrogen (N-2) had been challenging, owing to its large bond energy (945 kilojoules per mole)(2,3), until the development of the Haber-Bosch process. Subsequently, many strategies have been explored to reduce the activation barrier of the N equivalent to N bond and make the process more efficient. These include using alkali and alkaline earth metal oxides as promoters to boost the performance of traditional iron- and ruthenium-based catalysts(4-6)via electron transfer from the promoters to the antibonding bonds of N(2)through transition metals(7,8). An electride support further lowers the activation barrier because its low work function and high electron density enhance electron transfer to transition metals(9,10). This strategy has facilitated ammonia synthesis from N(2)dissociation(11)and enabled catalytic operation under mild conditions; however, it requires the use of ruthenium, which is expensive. Alternatively, it has been shown that nitrides containing surface nitrogen vacancies can activate N-2(refs.(12-15)). Here we report that nickel-loaded lanthanum nitride (LaN) enables stable and highly efficient ammonia synthesis, owing to a dual-site mechanism that avoids commonly encountered scaling relations. Kinetic and isotope-labelling experiments, as well as density functional theory calculations, confirm that nitrogen vacancies are generated on LaN with low formation energy, and efficiently bind and activate N-2. In addition, the nickel metal loaded onto the nitride dissociates H-2. The use of distinct sites for activating the two reactants, and the synergy between them, results in the nickel-loaded LaN catalyst exhibiting an activity that far exceeds that of more conventional cobalt- and nickel-based catalysts, and that is comparable to that of ruthenium-based catalysts. Our results illustrate the potential of using vacancy sites in reaction cycles, and introduce a design concept for catalysts for ammonia synthesis, using naturally abundant elements.Ammonia is synthesized using a dual-site approach, whereby nitrogen vacancies on LaN activate N-2, which then reacts with hydrogen atoms produced over the Ni metal to give ammonia.

DOI： 10.1038/s41586-020-2464-9

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

Electrically conductive molecular junctions are highly desirable components for applications in future molecular-scale electronic circuits. Here, we demonstrate an electrically conductive hybrid molecular junction that consists of Au-S and Au-πbindings using a sumanene derivative with three phosphine-sulfide anchoring groups at the periphery of the sumanene backbone. The molecular junction was prepared between the Au electrodes by the scanning tunneling microscopy-based break junction method. The three anchoring groups and the sumanene backbone in the junction form the Au-S chemical bonds and Au-πdirect bonds, respectively. The Au-S chemical binding immobilized the molecule on the Au electrode and provided the high mechanical stability of the junction, while the direct Au-πbinding led to the large metal-molecule electric coupling and high electronic conductance of the molecular junction. This study analyzes the molecular design of the electrically conductive molecular junctions based on the hybrid binding groups.

DOI： 10.1021/acs.jpcc.9b11725

Language：English  

Ru担持の水素化物は温和な環境下でのアンモニア合成の効率的触媒として知られている。特に、Ca2NH等の水素化物においては、表面水素欠陥により生成する表面のアニオン電子がアンモニア合成を促進し、同水素欠陥の存在がRu上の水素被毒をも回避する効果を有していると考えられている。しかしながら、これらの水素化物触媒におけるアンモニア合成反応の律速段階の微視的理解はまだ不十分である。本論文では、第一原理計算とマイクロキネティック手法を結合することで、同触媒の反応の全体像を微視的観点から把握し、律速段階を明確に決定することに成功した。

DOI： 10.1021/acs.jpcc.9b10850

Language：English  

本研究では、2次元MOFのプロトン伝導率とテラヘルツ領域振動との相関性について分光法と第一原理計算を用いて調査し、テラヘルツ領域振動がプロトン伝導性を指標付ける有益な物性量の一つであることを明らかにした。 分光法からは、二次元層のテラヘルツ領域における集団運動が効率的なH +伝導に重要な役割を果たすことを明らかにし、 第一原理計算からは、集団運動が金属イオンに依存する価電子構造によって支配される、という明確な相関関係を導いた。

DOI： 10.1039/c9sc05757a

Language：English  

Ruを担持した水素化物は低温でのアンモニア合成の効率的な触媒として機能することが知られており、
その高活性の起源は次の理由による（i）水素化物の表面水素空孔（VH）を介した水素化物からRuへの電子注入、（ii）Ruに吸着された水素の可逆的移動反応（H + e-↔H-）。これらの現象はRu /水素化物界面での表面VH形成が、アンモニア合成の重要な要素であることを意味している。
そこで本研究では、Ru /水素化物界面でのVH形成をさらに促進するために、Ruに遷移金属（TM）を混合させたナノクラスターを用い、
典型的な水素化物であるCa2NHにおけるVH形成と、水素移動反応について
第一原理計算で有効な遷移金属（TM）を調べた。その結果、
TMとしてFe、Co、Rh、Os、Ir、および8つの前期遷移金属、Sc、Ti、Y、Zr、Nb、La、Hf、およびTaは、VHを促進することが見出された。
また、Nb、Hf、Ta、Os、Irは、Ru-TMクラスターと水素化物界面でのH移動反応の反応障壁を減らすことが出来ることも判明した。
また、化学結合論等をもとにした、高活性の起源を化学的に明確化し、触媒設計における設計指針を明確に与えた。

DOI： 10.1021/acs.jpcc.9b10544

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

DOI： 10.1021/jacs.9b10726

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

Palladium-bearing intermetallic electride as an efficient and stable catalyst for Suzuki cross-coupling reactions
<title>Abstract</title>Suzuki cross-coupling reactions catalyzed by palladium are powerful tools for the synthesis of functional organic compounds. Excellent catalytic activity and stability require negatively charged Pd species and the avoidance of metal leaching or clustering in a heterogeneous system. Here we report a Pd-based electride material, Y₃Pd₂, in which active Pd atoms are incorporated in a lattice together with Y. As evidenced from detailed characterization and density functional theory (DFT) calculations, Y₃Pd₂ realizes negatively charged Pd species, a low work function and a high carrier density, which are expected to be beneficial for the efficient Suzuki coupling reaction of activated aryl halides with various coupling partners under mild conditions. The catalytic activity of Y₃Pd₂ is ten times higher than that of pure Pd and the activation energy is lower by nearly 35&#37;. The Y₃Pd₂ intermetallic electride catalyst also exhibited extremely good catalytic stability during long-term coupling reactions.

DOI： 10.1038/s41467-019-13679-0

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

Characteristic fast H- ion conduction in oxygen-substituted lanthanum hydride
Fast ionic conductors have considerable potential to enable technological development for energy storage and conversion. Hydride (H−) ions are a unique species because of their natural abundance, light mass, and large polarizability. Herein, we investigate characteristic H− conduction, i.e., fast ionic conduction controlled by a pre-exponential factor. Oxygen-doped LaH3 (LaH3−2xOx) has an optimum ionic conductivity of 2.6 × 10−2 S cm−1, which to the best of our knowledge is the highest H− conductivity reported to date at intermediate temperatures. With increasing oxygen content, the relatively high activation energy remains unchanged, whereas the pre-exponential factor decreases dramatically. This extraordinarily large pre-exponential factor is explained by introducing temperature-dependent enthalpy, derived from H− trapped by lanthanum ions bonded to oxygen ions. Consequently, light mass and large polarizability of H−, and the framework comprising densely packed H− in LaH3−2xOx are crucial factors that impose significant temperature dependence on the potential energy and implement characteristic fast H− conduction.

DOI： 10.1038/s41467-019-10492-7

Language：English  

DOI： 10.1038/s41467-019-10297-8

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

Triptycene Tripods for the Formation of Highly Uniform and Densely Packed Self-Assembled Monolayers with Controlled Molecular Orientation
When employing self-assembled monolayers (SAMs) for tuning surface and interface properties, organic molecules that enable strong binding to the substrate, large-area structural uniformity, precise alignment of functional groups, and control of their density are highly desirable. To achieve these goals, tripod systems bearing multiple bonding sites have been developed as an alternative to conventional monodentate systems. Bonding of all three sites has, however, hardly been achieved, with the consequence that structural uniformity and orientational order in tripodal SAMs are usually quite poor. To overcome that problem, we designed 1,8,13-trimercaptomethyltriptycene (T1) and 1,8,13-trimercaptotriptycene (T2) as potential tripodal SAM precursors and investigated their adsorption behavior on Au(111) combining several advanced experimental techniques and state-of-the-art theoretical simulations. Both SAMs adopt dense, nested hexagonal structures but differ in their adsorption configurations and structural uniformity. While the T2-based SAM exhibits a low degree of order and noticeable deviation from the desired tripodal anchoring, all three anchoring groups of T1 are equally bonded to the surface as thiolates, resulting in an almost upright orientation of the benzene rings and large-area structural uniformity. These superior properties are attributed to the effect of conformationally flexible methylene linkers at the anchoring groups, absent in the case of T2. Both SAMs display interesting electronic properties, and, bearing in mind that the triptycene framework can be functionalized by tail groups in various positions and with high degree of alignment, especially T1 appears as an ideal docking platform for complex and highly functional molecular films.

DOI： 10.1021/jacs.9b00950

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

DOI： 10.1021/acs.jpcc.9b00869

Language：English  

DOI： 10.1246/cl.180880

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

Enhanced Catalytic Ammonia Synthesis with Transformed BaO
© 2018 American Chemical Society. We report that a simple mixture of BaO and CaH2 powders with ruthenium nanoparticles acts as an effective heterogeneous catalyst for low-temperature ammonia synthesis with a very small activation energy (41 kJ mol-1). The high catalytic performance of this material is not due to either the original CaH2 or BaO particles but to BaO transformed by reaction with CaH2. The transformed BaO contains BaH2, a stable and strong electron-donating material that facilitates a reversible hydrogen storage-release reaction and significantly enhances electron donation to Ru, which results in high catalytic performance.

DOI： 10.1021/acscatal.8b02839

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

Self-sorting, in which multiple components selectively assemble themselves by recognising self from others, is an attractive approach to produce supramolecular assemblies with controlled structures. Lock-and-key type complementary physical interactions are required for self-sorting because selective affinity is necessary to distinguish self from others. Here we show self-sorting behaviour based on a principle of geometrical complementarity by shape during our investigation of assembly of pentagonal pillar[5]arenes and hexagonal pillar[6]arenes on a surface. In the homoassembly systems, anionic pillar[5]arenes and pillar[6]arenes are adsorbed onto positively charged layers of cationic pillar[5]arenes and pillar[6]arenes, respectively, through cationic-anionic electrostatic interactions. In contrast, ionic pillar[5]arenes are adsorbed onto layers constructed from oppositely charged pillar[5]arenes, but ionic pillar[6] arenes are not. Equally, for the reverse combination, ionic pillar[6]arenes are adsorbed onto layers constructed from oppositely charged pillar[6]arenes, but ionic pillar[5]arenes are not. The geometrical complementarity by shape realises effective self-sorting even in non-directional multivalent ionic interactions.

DOI： 10.1038/s42004-018-0094-z

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

Controlling stacking order and charge transport in -stacks of aromatic molecules based on surface assembly
Here, we report a facile procedure based on surface self-assembly for controlling the π-π stacking order and relevant rectified charge transport properties in stacks of aromatic molecules on a single-molecule scale. A high rectification ratio of 10 was achieved and the rectification direction was uniquely determined by the controlled stacking order of the aromatic molecules on the graphene layers of HOPG.

DOI： 10.1039/c8cc06430j

Language：English  

DOI： 10.1103/PhysRevB.98.125128

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

"Doping" of Polyyne with an Organometallic Fragment Leads to Highly Conductive Metallapolyyne Molecular Wire
Exploration of highly conductive molecules is essential to achieve single-molecule electronic devices. The present paper describes the results on single-molecule conductance study of polyyne wires doped with the organometallic Ru(dppe)2 fragment, X - (C≡C)n - Ru(dppe)2 - (C≡C)n - X. The metallapolyyne wires end-capped with the gold fragments (X = AuL) are subjected to single-molecule conductance measurements with the STM break junction technique, which reveal the high conductance (10-3-10-2 G0; n = 2-4) with the low attenuation factor (0.25 Å-1) and the low contact resistance (33 kω). A unique "'doping'" effect of Ru(dppe)2 fragment was found to lead to the high performance as suggested by the hybrid density functional theory-nonequilibrium green function calculation.

DOI： 10.1021/jacs.8b04484

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

DOI： 10.1039/C7QM00591A

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

DOI： 10.1021/acs.jpcc.8b02128

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

DOI： https://doi.org/10.1002/chem.201800467

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

DOI： 10.1039/c7cp08572a

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

Language：English  

DOI： 10.2477/jccj.2017-0067

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

Inspired by the successful synthesis of alkaline-earth-metals-based electrides [Ca24Al28O64](4+) (e(-))(4) (C12A7:e(-)) and [Ca2N](+):e(-) and high-throughput database screening results, we explore the potential for new electrides to emerge in the Sr-P system through a research approach combining ab initio evolutionary structure searches and experimental validation. Through employing an extensive evolutionary structure search and first principles calculations, we first predict the new structures of a series of strontium phosphides: Sr5P3, Sr8P5, Sr3P2 and Sr4P3. Of these structures, we identify Sr5P3 and Sr8P5 as being potential electrides with quasi-one-dimensional (1D) and zero-dimensional (0D) character, respectively. Following these theoretical results, we present the successful synthesis of the new compound Sr5P3 and the experimental confirmation of its structure. Although, density functional calculations with the generalized gradient approximation predict Sr5P3 to be a metal, electrical conductivity measurement reveal semiconducting properties characterized by a distinct band gap, which indicates that the newly synthesized Sr5P3 is an ideal one-dimensional electride with the half-filled band by unpaired electrons. In addition to presenting the novel electride Sr5P3, we discuss the implications of its semiconducting nature for 1D electrides in general and propose a mechanism for the formation of electrides with an orbital level diagram based on first-principles calculations.

DOI： 10.1021/jacs.7b06279

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

DOI： https://doi.org/10.1021/jacs.7b08252

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

DOI： 10.1021/acs.jpcc.7b07268

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

A one-dimensional microkinetic model combining, H and O migration mechanisms is used to simulate the surface diffusion, chemical and charge-transfer reactions near the triple phase boundary of the Ni/YSZ patterned anode. A number of parameter sets are exhaustively examined in the microkinetic schemes to obtain a proper set for the explanation of experimental observations. We find a set of parameters free from unphysical fitting parameters, and can explain a large activity gap of patterned anodes reported in literature. From our simulation, we found that the lower activity patterned anode is kinetically governed by both H and O migration across the triple phase boundary, while the higher activity patterned anodes are governed by the O migration.

DOI： 10.1021/acs.jpcc.7b05914

Language：English  

DOI： 10.1149/07801.1469ecst

Language：English  

DOI： 10.1149/07801.2815ecst

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

Recently, the successful synthesis of two-dimensional (2D) boron on metallic surfaces has motivated great interest in improving the stability of 2D boron to allow the realization of promising materials. Through the use of an ab initio evolutionary search algorithm, we have discovered a series of TiBx (2 <= x <= 16) structures that consist of earth-abundant titanium and boron atoms in 2D arrangements. These structures are greatly stabilized by electron transfer from Ti to B, therefore, leading to much better stability than the 2D boron sheets proposed so far. In particular, TiB12 has a low enough energy to make it competitive to a mixture of the well-known TiB, compound and a 2D alpha-boron sheet and exhibits a quasi-Dirac point with a 0.02 eV gap. Interestingly, the work function and conductivity of this 2D TiB12 material are calculated to be tunable through the application of biaxial strain. The possibility of synthesis and novel electronic properties expected for 2D TiB12 render it a promising new 2D material for nanoelectronic applications.

DOI： 10.1021/acs.chemmater.7b01433

Language：Others   Publishing type：Research paper (other academic)  

Multi-Scale, Multi-Physics Approach for Solid Oxide Fuel Cell Anode Reaction
© The Electrochemical Society. The electrode performance in solid oxide fuel cell depends both on electrode materials and microstructure. Therefore, it is important to breakdown the complexity of multi-physics in the porous electrode into processes in different scales. To clarify the multi-physics toward better electrode design, the use of both the advanced measurement and the simulation techniques is inevitable. For this purpose, we have taken the combined top-down and bottom-up approaches. In this manuscript, we discuss the practical issues in multi-scale, multi-physics simulation, focusing on the local activity of Ni-YSZ anode.

DOI： 10.1149/07801.2835ecst

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

A triphosphasumanene trisulfide was designed and synthesized as an out-of-plane anisotropic pi-conjugated molecule. Incorporating three anisotropic phosphine sulfide moieties into a sumanene skeleton induced a cumulative anisotropy with a large dipole moment (12.0 D), which is aligned in perpendicular direction with respect to the pi-framework and more than twice as large as those of conventional out of-plane anisotropic molecules. In the crystal, the molecules align to form columnar structures, in which electron-rich and electron-deficient sides of the pi-framework face each other. The interactions between the electron-rich surfaces, which contain three sulfur atoms, and Au(111) were examined by X-ray photoelectron spectroscopy.

DOI： 10.1021/jacs.6b12119

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

Compounds having excess electrons from the formal valence viewpoint (electrides) are a newclass of materials, which often take low-dimensional structures. We studied the (001) surface electronic structures of quasi-twodimensional electrides Ca2N and Y2C by density functional theory using a slab model. Both materials were found to have a clean surface state well separated in energy from the bulk states. Furthermore, this state virtually floats above the surface and may be considered to be a hallmark of two-dimensional electrides. For Ca2N, a tight-binding model in the Wannier representation was derived and analyzed, from which we concluded that the surface state, described by extra-surface s-like orbitals, is a Tamm state originating from an abrupt increase in potential energy at the surface.

DOI： 10.1103/PhysRevB.95.165430

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

A supramolecular complex was constructed by encapsulation of a O-3(2) molecule inside an open-cage C-60 derivative. Its single-crystal X-ray diffraction analysis revealed the presence of the O-3(2) at the center of the fullerene cage. The CV measurements suggested that unprecedented dehydrogenation was promoted by the encapsulated O-3(2) after two-electron reduction. The ESR measurements displayed the triplet character as well as the anisotropy of the O-3(2). Additionally, the SQUID measurements also demonstrated the paramagnetic behavior above 3K without an antiferromagnetic transition. Upon photoirradiation with visible light, three phosphorescent bands at the NIR region were observed, arising from the exited O-1(2) generated by self-sensitization with the outer cage, whose lifetimes were not affected by the environments. These studies confirmed that the complex is a crystalline triplet system with incompatible "high spin density" but "small interspin interaction" properties.

DOI： 10.1002/anie.201701212

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

We report that the interlayer states common to the compounds AeAlSi (Ae = Ca, Sr, Ba) arise from F-center like electrons arrayed in periodic cavities. The SrPtSb-type intermetallic phases exhibit electrons localized to columns of the trigonal bipyramidal Ae(3)Al(2) cages running perpendicular to the honeycomb layers. Ab initio calculations in combination with hard/soft x-ray photoemission spectroscopic measurements reveal that these features correspond to the anionic electrons that hybridize with apical Al 3p(z) orbitals from the honeycomb layers above and below. Extra bands with a significant dispersion along the k(z) direction therefore contribute to the Fermi level in contrast to the apparent two-dimensional connectivity of the bonding in the compounds, and completely account for the presence of interlayer states. Our study demonstrates how the cage centers may serve as electronically important crystallographic sites, and extend the anionic electron concept into honeycomb lattice compounds.

DOI： 10.1103/PhysRevB.95.125117

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

The size of metal particles is a key factor governing the catalytic performance of metal-supported catalysis, and revealing the essential factor controlling the size of metal particles on support materials is crucial for a new guideline in metal-supported catalysts. In this study, we found adsorption and migration energies of a single metal atom on supports are useful for the qualitative prediction of metal particle sizes on supports by means of the first-principles electronic structure calculations of Ru loaded Ca3N2, CaO, CaF2, and Ca2Si and transmission electron microscopy (TEM) measurements. The first-principles calculations revealed that the adsorption and migration energies of a Ru atom on Ca3N2 and Ca2Si are larger than those on CaO and CaF2 and that the energetic trend shows an excellent correspondence with the bond strengths of Ru anions. In accordance with the first-principles calculations, TEM measurements showed that Ru particles sizes on Ca3N2 and Ca2Si are much smaller than those on CaO and CaF2; the hemisphere-shaped particles on Ca3N2 and Ca2Si are smaller than 15 nm, whereas the needle like particles on CaO and CaF2 are in the range from 10 to 100 nm. The theoretical and experimental results clearly indicate the presence of a correlation between the strength of Ru anion chemical bonds and Ru particle sizes on supports, which will be a good indicator for metal particle size on supports.

DOI： 10.1021/acs.jpcc.6b03400

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

Electronic and structural detail at the electrode-molecule interface have a significant influence on charge transport across molecular junctions. Despite the decisive role of the metal-molecule interface, a complete electronic and structural characterization of the interface remains a challenge. This is in no small part due to current experimental limitations. Here, we present a comprehensive approach to obtain a detailed description of the metal-molecule interface in single-molecule junctions, based on current-voltage (I-V) measurements. Contrary to conventional conductance studies, this I-V approach provides a correlated statistical description of both, the degree of electronic coupling across the metal-molecule interface, and the energy alignment between the conduction orbital and the Fermi level of the electrode. This exhaustive statistical approach was employed to study single-molecule junctions of 1,4-benzenediamine (BDA), 1,4-butanediamine (C4DA), and 1,4-benzenedithiol (BDT). A single interfacial configuration was observed for both BDA and C4DA junctions, while three different interfacial arrangements were resolved for BDT. This multiplicity is due to different molecular adsorption sites on the Au surface namely on-top, hollow, and bridge. Furthermore, C4DA junctions present a fluctuating I-V curve arising from the greater conformational freedom of the saturated alkyl chain, in sharp contrast with the rigid aromatic backbone of both BDA and BDT.

DOI： 10.1038/srep26606

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

DOI： 10.1039/C6SC00767H

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

Polycrystalline beta-PbO films were grown by pulsed laser deposition in atmospheres ranging from oxygen-poor (the oxygen pressure of 0.01 Pa) to oxygen-rich (13 Pa) conditions, and the oxygen chemical potential was further enhanced by ozone annealing to examine hole doping. It was found that each of the as-grown beta-PbO films showed poor electrical conductivity, sigma > 1.4 x 10(-7) S cm(-1), regardless of the oxygen pressure. The density functional calculations revealed that native defects including Pb and O vacancies have deep transition levels and extremely high formation enthalpies, which indicates difficulty of carrier generation in beta-PbO and explains the experimentally observed poor electrical conductivity. The analysis of the electronic structures showed that the interaction between Pb 6s and O 2p orbitals is weak due to the deep energy level of Pb 6s and does not raise the valence band maximum (VBM) level unlike that observed in SnO, which is also supported by ultraviolet photoemission spectroscopy measurements. The deep acceptor transition levels of the native defects are attributed to the deep VBM of beta-PbO. On the other hand, annealing b-PbO films in reactive oxygen-containing atmospheres (i.e., O-3) led to a significantly enhanced electrical conductivity (i.e., sigma > 7.1 x 10(2) S cm(-1)) but it is the result of the formation of an n-type PbO2 phase because oxygen chemical potential exceeded the phase boundary limit. The striking difference in carrier generation between PbO and SnO is discussed based on the electronic structures calculated by density functional theory. Published by AIP Publishing.

DOI： 10.1063/1.4947456

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

DOI： 10.1039/C6CC01705C

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

We report an air and water stable electride Y5Si3 and its catalytic activity for direct ammonia synthesis. It crystallizes in the Mn5Si3-type structure and confines 0.79/f.u. anionic electrons in the quasi-one-dimensional holes. These anionic electrons strongly hybridize with yttrium 4d electrons, giving rise to improved chemical stability. The ammonia synthesis rate using Ru(7.8 wt &#37;)-loaded Y5Si3 was as high as 1.9 mmol/g/h under 0.1 MPa and at 400 degrees C with activation energy of similar to 50 kJ/mol. Its strong electron-donating ability to Ru metal of Y5Si3 is considered to enhance nitrogen dissociation and reduce the activation energy of ammonia synthesis reaction. Catalytic activity was not suppressed even after Y5Si3, once dipped into water, was used as the catalyst promoter. These findings provide novel insights into the design of simple catalysts for ammonia synthesis.

DOI： 10.1021/jacs.6b00124

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

We analyzed the X-ray absorption spectra (XAS) of Co 2p orbital in LaCoO3 by using density functional theory method to understand the temperature effect on the electronic structures, especially low-spin (LS), intermediate-spin (IS), and high-spin (HS) states of Co3+ ion. We considered the lattice change, thermal excitation of electrons, and displacement of atoms from equilibrium position in LaCoO3 as a temperature effect in this study. We observed negligible change in the shape of Co 2p XAS of LaCoO3 for each LS, IS, and HS state associated with the lattice expansion due to temperature increase, while different spectral features for LS, IS, and HS states were observed. The change of spectra observed by in situ XAS measurement of LaCoO3 at Co L-II- and L-III-edges would be due to the increase in HS and decrease in LS and IS at higher temperature. In addition, the geometry change by thermal displacement of atomic position was analyzed by using first-principles molecular dynamics calculation. Our results indicated that the electronic structure is sensitively changed by the change of Co-O bond distance due to the displacement of atoms from the equilibrium position at studied temperature when the spin state was IS. (C) 2015 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

DOI： 10.1016/j.ssi.2015.08.017

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

Metal-peroxo species on oxides are recognized as important intermediates for catalytic reactions on oxides. In this work, surface structures of stoichiometric and non-stoichiometric yttria stabilized zirconia (YSZ) were investigated for the low index surfaces (111), (110), and (100) by using first principles electronic structure calculations, and the energetic stabilities of non-stoichiometric surfaces with respect to the stoichiometric ones were calculated as a function of oxygen chemical potential. In the oxygen-rich condition, a unique form of zirconium-peroxo embedded in the lattice oxygen sites was found in YSZ(110); the embedded peroxo was recently confirmed in experimental observations for TiO2 anatase (101) (M. Setvin et al., Science 341 (2013) 988) and cubic In2O3 (001) (D. R. Hagleitner et al., Phys. Rev. B 85 (2012) 115441). The electronic structure of the embedded peroxo found in O-rich YSZ(110) was analyzed in details by means of orbital energy diagrams and density of states. (C) 2015 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.ssi.2015.05.011

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

DOI： 10.1039/C5CP05423K

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

Theoretical Study on Oxygen Dissociation Reaction on LaSrCoO₃

DOI： 10.1149/06801.0651ecst

Language：English  

DOI： 10.1149/06801.3203ecst

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

Aromatic stacks formed through self-assembly are promising building blocks for the construction Of molecular electronic devices with adjustable electronic functions, in which noncovalently bound pi-stacks act as replaceable modular components. Here we describe the electron-transport properties of single-molecule aromatic stacks aligned in a self-assembled cage, using scanning probe microscopic and break junction methods. Same and different modular aromatic pairs are noncovalently bound and stacked within the molecular cage holder, which leads to diverse electronic functions. The insertion of same pairs induces high electronic conductivity (10(-3)-10(-2) G(0), G(0) = 2e(2)/h), while different pairs develop additional electronic rectification properties. The rectification ratio was, respectively, estimated to be 1.4-2 and >10 in current voltage characteristics and molecular orientation-dependent conductance measurements at a fixed bias voltage. Theoretical calculations demonstrate that this rectification behavior originates from the distinct stacking order of the internal aromatic components against the electron-transport direction and the corresponding lowest unoccupied molecular orbital conduction channels localized on one side of the molecular junctions.

DOI： 10.1021/jacs.5b00086

Language：English  

DOI： 10.1149/06801.2875ecst

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

High-throughput ab initio screening of approximately 34000 materials in the Materials Project was conducted to identify two-dimensional (2D) electride materials, which are composed of cationic layers and anionic electrons confined in a 2D empty space. The screening was based on three indicators: (1) a positive total formal charge per formula unit; (2) layered structures for two-dimensionality; (3) empty spaces between the layer units. Three nitrides, Ca2N, Sr2N, and Ba2N, and the carbide Y2C were identified as 2D electrides, where Ca2N is the only experimentally confirmed 2D electride (Lee, K.; et al. Nature 2013, 494, 336-341). Electron density analysis using ionic radii revealed a smaller number of anionic electrons in Y2C than those in the three nitrides as a result of the partial occupation of the anionic electrons in the d orbitals of Y. In addition, no candidates were identified from the p-block elements, and thus the ab initio screening indicates that the s-block elements (i.e., alkali or alkaline-earth metals) are highly preferable as cation elements. To go beyond the database screening, a tailored modeling was conducted to determine unexplored compounds including the s-block elements that are suitable for 2D electrides. The tailored modeling found that (1) K2Cl, K2Br, Rb2Cl, and Rb2Br dialkali halides are highly plausible candidates, (2) Li2F and Na2Cl dialkali halides are highly challenging candidates, and (3) the Cs2O1-xFx halogen-doped dialkali oxide is a promising candidate.

DOI： 10.1021/ic501362b

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

DOI： 10.1039/C3CP53689K

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

We have examined the structure of Cu filaments in Cu/amorphous-Ta2O5 (a-Ta2O5)/Pt atomic switch from first principles. We have found that the Cu single atomic chains are unstable during the molecular dynamics (MD) simulation and thus cannot work as conduction paths. On the other hand, Cu nanowires with various diameters are stable and can form conductive paths. In this case, the Cu-Cu bonding mainly contributes to the conductive, delocalized defect state. These make a sharp contrast with the case of single Cu chains in crystalline Ta2O5, which can be conductive paths through the alternant Cu-Ta bonding structure. A series of MD simulations suggest that even Cu nanowires with a diameter of 0.24nm can work as conduction paths. The calculations of the transport properties of Cu/a-Ta2O5/Pt heterostructures with Cu nanowires between two electrodes further confirm the conductive nature of the Cu nanowires in the a-Ta2O5. (C) 2014 AIP Publishing LLC.

DOI： 10.1063/1.4861724

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

The feasibility of using p-conjugated polymers as next-generation electronic materials is extensively studied; however, their charge mobilities are lower than those of inorganic materials. Here we demonstrate a new design principle for increasing the intramolecular charge mobility of p-conjugated polymers by covering the p-conjugated chain with macrocycles and regularly localizing p-molecular orbitals to realize an ideal orbital alignment for charge hopping. Based on theoretical predictions, insulated wires containing meta-junctioned poly(phenylene-ethynylene) as the backbone units were designed and synthesized. The zigzag wires exhibited higher intramolecular charge mobility than the corresponding linear wires. When the length of the linear region of the zigzag wires was increased to 10 phenylene-ethynylene units, the intramolecular charge mobility increased to 8.5 cm(2)V(-1) s(-1). Theoretical analysis confirmed that this design principle is suitable for obtaining ideal charge mobilities in p-conjugated polymer chains and that it provides the most effective pathways for inter-site hopping processes.

DOI： 10.1038/ncomms2707

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

We present a theoretical study on inelastic transient electrical currents and the effects of phonon heating in a single-level quantum dot system weakly coupled to a localized vibration degree of freedom, using the nonequilibrium Green's function method under the wide-band-limit and the lowest-order-expansion approximations. The energy transfer between electron and phonon systems is evaluated using both approximations, which separately are exact in the limits of the equilibrium state (t<0) and steady state (t ->infinity). The time-dependent phonon number, which determines the system temperature and heating effects on the inelastic current, is calculated using a phenomenological method employing the time-dependent power transfer. The two approximations are shown to provide qualitatively similar dynamical behaviors for the system temperature, which can be grouped under two responses: if the energy corresponding to the applied bias voltage is smaller than or equal to the phonon energy, the temperature first increases because of phonon emission, and then decreases because of phonon absorption; alternatively, if the energy corresponding to the bias voltage is larger than the phonon energy, the temperature increases monotonically until a steady state is reached. The total electrical current is suppressed by phonon heating, while heat transferring between dot and environment mitigates the effects of such heating. Furthermore, the relaxation time of the current is extended by phonon scattering and heating. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4796137]

DOI： 10.1063/1.4796137

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

DOI： https://doi.org/10.1002/anie.201301665

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

DOI： 10.1149/05701.2437ecst

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

The space charge formation at metal/yttria-stabilized zirconia interface is investigated by combining defect formation energies from first principles with a parallel-sheets model. In this model, the crystal orientation and interlayer distances between crystal planes are taken into account explicitly. This is in contrast to previous space charge models, which utilized a continuum approximation. The crystal-plane-resolved picture of the space charge is discussed in detail. It is found that the results from the parallel-sheets model resemble closely those of the continuum model. We find this to be the case even for the polar (111) orientation of cubic zirconia, despite the fact that continuum approximations implicitly assume a homogeneous system. We also examine the effect of yttrium dopant segregation on the space charge utilizing the parallel-sheets model. It is found that dopant segregation tends to decrease the width of the oxygen vacancy depletion layer that occurs in oxidizing atmosphere, and that it tends to increase the accumulation of vacancies in reducing atmosphere. (c) 2012 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.ssi.2012.08.009

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

We derive a nonequilibrium Green's function formalism to study the transient energy currents carried by electrons in a single-level quantum dot system sandwiched between two electrodes. The energy current shows the same relaxation time and oscillation behavior as the electrical current. In contrast to the steady state case, the energy currents in deep insides of the two electrodes do not balance each other in the time domain. The sum of energy currents in the two electrodes corresponds to the time-dependent energy change in the sandwiched region, and the fact that the energy change in this region is not necessarily zero reflects the real-time electron redistribution in energy domain. Moreover, the amplitude of the energy change does not vary monotonically with the coupling strength between the dot and electrode, in contrast to the relaxation time, which is inversely proportional to the coupling strength. (C) 2012 The Japan Society of Applied Physics

DOI： 10.1143/JJAP.51.094303

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

An electronic conductance with small fluctuations, which is stipulated in single-molecule junctions, is necessary for the precise control of single-molecule devices. However, the suppression of conductance fluctuations in conventional molecular junctions is intrinsically difficult because the fluctuations are related to the contact fluctuations and molecular motion. In the present study involving experimental and theoretical investigations, it is found that covering a single p-conjugated wire with an a-cyclodextrin molecule is a promising technique for suppressing conductance fluctuations. The conductance histogram of the covered molecular junction measured with the scanning tunneling microscope break-junction technique shows that the conductance peak for the covered junction is sharper than that of the uncovered junction. The covering technique thus has two prominent effects: the suppression of intramolecular motion, and the elimination of intermolecular interactions. Theoretical calculations of electronic conductance clearly support these experimental observations.

DOI： 10.1002/smll.201102075

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

The spin-dependent electron transport correlated with spin-flip dynamics in a molecular junction was investigated in the wave-packet and Green's function approaches. The molecular junction adopted in this work is described by a simple one-dimensional tight-binding chain including a localized spin. The spin exchange coupling J between the localized and conduction electron spins was taken into account through the s-d Hamiltonian. The wave-packet simulations showed that the transmission probabilities in both the spin-flip and no-flip processes show large peaks at the eigenvalues of the spin singlet (-3J/4) and triplet (J/4) states, and that, different transmission properties appear at the mid-gap of the two eigenvalues: the spin-flip process shows a moderate decrease, whereas the no-flip process an abrupt drop. Dividing the s-d Hamiltonian into two submatrices and referring to the molecular orbital concept for the coherent electron transport, we found that the moderate decrease in the spin-flip process at the mid-gap is the result of a coherent-and-cooperative contribution from the singlet and triplet states of the conduction and localized electron spins, and that, the abrupt drop in the no-flip process at the mid-gap is mainly caused by the coherent cancellation from the singlet and triplet states. The molecular orbital concept available for the electron transport including spin-flip scattering processes is described in Green's function method, in analogy to the one derived for the spinless electron transport.

DOI： 10.1007/s00214-011-1028-3

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

We examine the space charge layer formation at metal/ionic conductor interfaces by solving Poisson's equation using defect energetics calculated from first principles. The scheme is applied to zirconia, and we find that oxidizing atmosphere and high valence band offset result in negative space charge accumulation at the interface, while reducing atmosphere and low valence band offset result in positive charge accumulation. This is explained in terms of the alignment of the Fermi levels in the metal and the ionic conductor. (C) 2010 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.ssi.2010.11.022

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

DOI： https://doi.org/10.1002/ange.201100431

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

The conductive path formed by the interstitial Cu or oxygen vacancies in the Ta2O5 atomic switch were investigated in detail by first principles methods The calculated results indicated that the defect state induced by the interstitial Cu is located just at the Fermi level of the Cu and Pt electrodes in the Cu/Ta2O5/Pt heterostructure that conduction channel is formed in the Ta2O5 film via the interstitial Cu On the other hand oxygen vacancies in Ta2O5 do not form such a conduction channel because of the lower energy positions of their defect states The above results suggest that the,conductive path could be formed by interstitial Cu in the Ta2O5 atomic switch, whereas oxygen vacancies do not contribute to the formation of the conductive path

DOI： 10.1021/nn101410s

Language：English   Publishing type：Research paper (other academic)  

The effect of the nickel/zirconia (111) interface on oxygen vacancy formation energies in zirconia is investigated utilizing first principles simulation. The relationship between vacancy formation energy and the Fermi level is found to be similar to that calculated in the bulk system when the vacancy is located at three oxygen layers away from the interface. Moreover, we find a modulation of about 1 eV in the formation energies when the vacancies are located closer to the interface and relate this to the interface electronic states. © 2010 The Surface Science Society of Japan.

DOI： 10.1380/ejssnt.2010.93

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

DOI： 10.1088/1367-2630/12/8/083017

Language：English   Publishing type：Research paper (other academic)  

The electronic transport in benzene-1, 4-dithiolate molecule in aqueous solution sandwiched between gold electrodes have been investigated by the ab initio nonequilibrium Green's function method combined with Car- Parrinello molecular dynamics. We have found that the C-S bond length shows clear negative correlation with the conductance both in aqueous solution and vacuum, whereas the Au-S and C-C bond lengths have little correlation. This originates from large local density of states around C-S bonds at the Fermi level. © 2010 The Surface Science Society of Japan.

DOI： 10.1380/ejssnt.2010.38

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

Electronic structures and transport properties of bulk Ta2O5 and Cu/Ta2O5/Pt heterojunction have been studied from first principles. Of the two room-temperature phases of bulk Ta2O5, beta-, and delta-Ta2O5, our calculated results showed that the beta phase has much narrower band gap than the delta-Ta2O5. For Cu/delta-Ta2O5/Pt heterojunction, the p-type Schottky barriers between the Cu (Pt) and Ta2O5 were estimated as 0.9-1.2 eV. Both the standard density-functional calculation and the nonequilibrium Green's function showed that no conducting channels were formed from Cu to Pt through delta-Ta2O5. (C) 2009 American Institute of Physics. [doi:10.1063/1.3260244]

DOI： 10.1063/1.3260244

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

As a first step to clarify the microscopic working mechanism of atomic switches using solid electrolytes, we have examined electronic states and electron transport properties of Ag-Ag2S-Ag and Cu-Ta2O5-Pt systems using standard density functional theory and novel non-equilibrium Green's function method. In both the systems, we found that the bridge structures consisting of excess Ag or Cu in the middle solid electrolyte layer work as electronic conduction paths. In Cu-Ta2O5-Pt, we also found that O vacancy is much less effective for the enhancement of electronic conduction than excess Cu.

DOI： 10.2320/jinstmet.73.577

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

DOI： 10.1103/PhysRevB.79.195436

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

DOI： -

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

DOI： 10.1103/PhysRevB.80.073409

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

DOI： https://doi.org/10.1021/jp905296q

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

First principles study on electronic structures of Ni/H/ZrO2 triple phase boundary
We have investigated the electronic structures of Ni/H/ZrO2 triple phase boundary (TPB) from first principles. For this purpose, we constructed a novel computational model for the TPB having a point contact of a Ni-tip and ZrO2(111) surface. We examined several locations of the tip with respect to the ZrO2(111) surface, and found that the fee location of the Ni-tip is the most stable point contact TPB. The projected density of states (PDOS) of the apex Ni atom of the point contact TPB shows a large and sharp peak at 0.5 eV above the Fermi level. Such a large peak, on the other hand, is not seen in Ni(111) surface without Ni protrusions. We also revealed that the adsorption of hydrogen atom at the Ni-tip leads to a wider peak of PDOS of the apex Ni atom. The change in the shape of the PDOS suggests that the adsorption of hydrogen atom at the Ni-tip will alter the reactivity of the TPB of Ni-tip/ZrO2(111). ©The Electrochemical Society.

DOI： 10.1149/1.3242241

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

DOI： https://doi.org/10.1016/j.physleta.2008.09.020

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

DOI： https://doi.org/10.1063/1.2814245

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

DOI： https://doi.org/10.1063/1.2963197

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

DOI： https://doi.org/10.1021/nl0711054

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

To analyze electronic conduction through surface states in micro-multipoint measurements using scanning tunneling microscopy, we calculated electron density and current distribution in a surface with Tamm states of a simple cubic lattice using a tight-binding method with the Huckel approximation. Both wave function and Green's function methods were employed in the calculations, and two peaks of the transmission spectrum were obtained at -1.10 and 2.91 eV using both methods. The analysis Of Current distribution revealed that the transmission at 2.91 eV mainly corresponds to surface state conduction, whereas that at -1.10eV includes bulk state conduction. These results suggest that whether or not a measured conductance corresponds to pure surface state conduction is dependent on the energy of injected electrons.

DOI： 10.1143/JJAP.45.2136

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

DOI： https://doi.org/10.1380/ejssnt.2006.484

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

DOI： https://doi.org/10.1016/j.cplett.2006.06.074

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

The stable atomic structures, formation energies, and conductance of single benzene-dithiolate between two facing gold electrodes are studied within the framework of density functional theory using a two-layered cluster model for the Au(111) surface of both electrodes. The computed conductance depends on both the adsorption site and the angle between the molecule and electrode surface. In the case where the molecule is perpendicular to the Au(111) surface. the expected value of conductance is strongly dominated by the configuration in which the molecule is adsorbed onto the electrodes at the fcc site because of large differences in formation energies between fcc and other configurations.

DOI： 10.1143/JJAP.44.7729

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

The electrical transmission of copper(II) phthalocyanine (CuPc) sandwiched between gold nanoelectrodes is studied on the basis of the Green function formalism coupled with the Gaussian-broadening technique. In the Au-CuPc-Au junction, broadened density of states (DOS) of the An chains is defined as continuous DOS of electrodes to calculate the Green function of the electrodes. Two peaks of the transmission function found in the vicinity of the Fermi level are analyzed in terms of molecular orbitals (MOs). A convenient procedure to analyze MO contribution to a transmission peak is proposed. It is found that (I) symmetry-matched interactions between CuPc and the gold nanoelectrodes are important to the enhancement of the transmission function and (II) the nanoelectrodes have almost no effect on the electronic states of CuPc.

DOI： 10.1021/jp0442596

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

DOI： 10.1016/j.cplett.2005.05.126

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

DOI： https://doi.org/10.1021/ja031736+

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

DOI： 10.1080/00268970410001728889

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

DOI： https://doi.org/10.1021/jp0310908

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

DOI： https://doi.org/10.1021/jp038018u

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

DOI： https://doi.org/10.1063/1.1799991

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

DOI： https://doi.org/10.1021/ja044787v

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

DOI： https://doi.org/10.1021/jp0309724

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

DOI： https://doi.org/10.1021/jp021739t

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

DOI： 10.1002/cphc.200300811

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

It was demonstrated from the molecular orbital theory that CH2-(C6H4)(n)- in which at least one H atom on the end of poly(para-phenylene) (PPP) is replaced by CH2 group of the chain, provides nearly zero band gaps in the long chains with n>6. This behavior was explained by the band overlap leading to metallic characteristics from the perspective of the intermolecular interaction between ethylene units in the oligomer.

DOI： 10.1103/PhysRevB.66.193104

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

It was demonstrated from the molecular orbital theory that CH2-(C6H4)n- in which at least one H atom on the end of poly (para-phenylene) (PPP) is replaced by CH2 group of the chain, provides nearly zero band gaps in the long chains with n>6. This behavior was explained by the band overlap leading to metallic characteristics from the perspective of the intermolecular-interaction between ethylene units in the oligomer.

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

In low-dimensional molecular crystals that exhibit Peierls instability, the intercolumnar interaction plays an important role in the determination of the conducting property. To predict the crystal structure that exhibits an electronic conduction, we proposed a simple formula based on the molecular orbital theory. In this approach, analytical molecular orbitals of polyene were extended to be applicable for molecular crystals of charge-transfer complexes, and the Peierls distortion was represented by using the first- and second-order perturbation theory. It was concluded that the energetic behaviors and structures calculated by the analytical method developed in the present work are identical to those obtained by the tight-binding ab initio molecular orbital calculation. (C) 2002 John Wiley Sons, Inc.

DOI： 10.1002/qua.10032

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

DOI： 10.1002/cphc.200290006

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

DOI： https://doi.org/10.1103/PhysRevB.65.113113

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

We have already proposed a convenient method to estimate the magnitude of the Peierls instability in molecular crystals. In the present paper to examine the reliability of our treatment, we apply it to the two types of model crystals composed of naphthalene cations and chalcogen substituted ones (planar-1,4,5,8-tetrathianaphthalene [TTN](+)). The results show that the chalcogen atoms in TTN molecules play an important role in the electronic conductivity. It was demonstrated that this treatment could reproduce ab initio results and become a useful tool to investigate the relationship between the crystal structure of charge-transfer complexes and their electronic conductivity. (C) 1998 Elsevier Science S.A. All rights reserved.

DOI： 10.1016/S0379-6779(98)00047-2

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

We have already proposed a convenient method to estimate the magnitude of the Peierls instability in finite one- and two-dimensional (1D and 2D) polyenes from the viewpoint of orbital symmetry [J. Chem. Phys., 103, 9726 (1995)]. This treatment is applied to a model system for charge-transfer complexes, in which the unpaired electron is occupied in a molecule, generating a half-filled energy band by intermolecular interaction. As the first step, a model molecular crystal composed of ethylene anion (or cation) molecules is treated to confirm the applicability of our formulas for 2D polyene. It is clearly shown that molecules in a crystal are structurally distorted to gain the energetic stabilization within the 1D structure, while they are rearranged in a regularly equidistant structure under strong interchain interaction. This treatment would provide insight into the relationship between the crystal structure of charge-transfer complexes and its electronic property. (C) 1997 John Wiley & Sons, Inc.

DOI： 10.1002/(SICI)1097-461X(1997)64:3<325::AID-QUA5>3.0.CO;2-Y

Language：English   Book type：Scholarly book

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Venue：熊本県   Country：Japan  

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Event date： 2009.9

Language：Japanese  

Venue：静岡県伊豆(修善寺)   Country：Japan  

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Event date： 2009.3

Language：English  

Venue：Pittsburgh   Country：Other  

Event date： 2009.3

Language：English  

Venue：Pittsburgh  

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Event date： 2009.3

Language：English  

Venue：Jeju Island   Country：Korea, Republic of  

Event date： 2009.3

Language：English  

Venue：Jeju Island   Country：Korea, Republic of  

Event date： 2009.3

Language：English  

Venue：Jeju Island   Country：Korea, Republic of  

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Event date： 2009.3

Language：English  

Venue：Jeju Island   Country：Korea, Republic of  

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Event date： 2009.3

Language：English  

Venue：Jeju   Country：Korea, Republic of  

Event date： 2009.3

Language：Japanese  

Venue：東京都   Country：Japan  

Event date： 2009.3

Language：Japanese  

Venue：東京都   Country：Japan  

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Event date： 2009.2

Language：English  

Venue：Tokyo(Univ. of Tokyo)   Country：Japan  

Event date： 2009.2

Language：English  

Venue：Tokyo(Univ. of Tokyo)   Country：Japan  

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Event date： 2008.12

Language：English  

Venue：Shizuoka(Atagawa)   Country：Japan  

Event date： 2008.12

Language：English  

Venue：Shizuoka(Atagawa)   Country：Japan  

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Event date： 2008.12

Language：Japanese  

Venue：東京都   Country：Japan  

Event date： 2008.12

Language：Japanese  

Venue：東京都   Country：Japan  

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Event date： 2008.11

Language：English  

Venue：Tokyo(Waseda Univ.)   Country：Japan  

Event date： 2008.11

Language：English  

Venue：Tokyo(Waseda Univ.)   Country：Japan  

Event date： 2008.11

Language：English  

Venue：Tokyo(Waseda Univ.)   Country：Japan  

Event date： 2008.11

Language：English  

Venue：Tokyo(Waseda Univ.)   Country：Japan  

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Event date： 2008.11

Language：English  

Venue：Tokyo(Waseda Univ.)   Country：Japan  

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Event date： 2008.11

Language：English  

Venue：Tokyo(Waseda Univ.)   Country：Japan  

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Event date： 2008.11

Language：English  

Venue：Kaohsiung(National Sun Yat-sen University)   Country：Taiwan, Province of China  

Event date： 2008.11

Language：English  

Venue：Kaohsiung(National Sun Yat-sen University)   Country：Taiwan, Province of China  

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Event date： 2008.10

Language：English  

Venue：Kanagawa(Hakone Prince Hotel)   Country：Japan  

Event date： 2008.10

Language：English  

Venue：Kanagawa(Hakone Prince Hotel)   Country：Japan  

Event date： 2008.10

Language：English  

Venue：Kanagawa(Hakone Prince Hotel)   Country：Japan  

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Event date： 2008.10

Language：English  

Venue：Kanagawa(Hakone Prince Hotel)   Country：Japan  

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Event date： 2008.10

Language：English  

Venue：Honolulu   Country：Other  

Event date： 2008.10

Language：English  

Venue：Honolulu  

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Event date： 2008.10

Language：English  

Venue：Honolulu(Hilton Hawaiian Village)   Country：Other  

Event date： 2008.9

Language：English  

Venue：Madrid   Country：Spain  

Event date： 2008.9

Language：English  

Venue：Madrid   Country：Spain  

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Event date： 2008.9

Language：English  

Venue：Miyagi(Hotel New Mitoya)   Country：Japan  

Event date： 2008.9

Language：English  

Venue：Miyagi(Hotel New Mitoya)   Country：Japan  

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Event date： 2008.9

Language：Japanese  

Venue：福岡県   Country：Japan  

Event date： 2008.9

Language：Japanese  

Venue：福岡県   Country：Japan  

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Event date： 2008.6

Language：English  

Venue：Chonqing(Chonqing International Convention & Exhibition Center)   Country：China  

Event date： 2008.6

Language：English  

Venue：Chonqing(Chonqing International Convention & Exhibition Center)   Country：China  

Event date： 2008.6

Language：English  

Venue：Chonqing(Chonqing International Convention & Exhibition Center)   Country：China  

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Event date： 2008.6

Language：English  

Venue：Chonqing(Chonqing International Convention & Exhibition Center)   Country：China  

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Event date： 2008.5

Language：English  

Venue：Tokyo(Univ. of Tokyo)   Country：Japan  

Event date： 2008.5

Language：English  

Venue：Tokyo(Univ. of Tokyo)   Country：Japan  

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Event date： 2008.5

Language：English  

Venue：Beijing   Country：China  

Event date： 2008.5

Language：English  

Venue：Beijing   Country：China  

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Event date： 2008.3

Language：English  

Venue：New Orleans(New Orleans Convention Center)   Country：Other  

Event date： 2008.3

Language：English  

Venue：New Orleans(New Orleans Convention Center)   Country：Other  

Event date： 2008.3

Language：English  

Venue：New Orleans(New Orleans Convention Center)  

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Event date： 2008.3

Language：English  

Venue：New Orleans(New Orleans Convention Center)  

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Event date： 2008.3

Language：English  

Venue：Denver(Colorado Convention Center)   Country：Other  

Event date： 2008.3

Language：Japanese  

Venue：大阪府東大阪市   Country：Japan  

Event date： 2008.3

Language：Japanese  

Venue：大阪府東大阪市   Country：Japan  

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Event date： 2007.12

Language：English  

Venue：Tokyo(Tokyo Institute of Technology)   Country：Japan  

Event date： 2007.12

Language：English  

Venue：Tokyo(Tokyo Institute of Technology)   Country：Japan  

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Event date： 2007.12

Language：Japanese  

Venue：愛知県名古屋市   Country：Japan