論文 - 角屋 智史
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Accumulated charge measurement using a substrate with a restricted-bottom-electrode structure 査読あり
Toshiaki Tanimura, Hiroyuki Tajima, Akinari Ogino, Yuta Miyamoto, Tomofumi Kadoya, Takeshi Komino, Tokuji Yokomatsu, Kazusuke Maenaka, Yuka Ikemoto
Organic Electronics 74 251 - 257 2019年11月
© 2019 Elsevier B.V. Accumulated charge measurement (ACM) is a new experimental technique for organic semiconductors to evaluate the charge injection barrier at the semiconductor–metal interface directly using a metal–insulator–semiconductor–metal (MISM) capacitor. In this technique, the precise estimation of the electrostatic capacity of the insulator layer (CI) is required for the analysis. The information of this parameter is, in principle, included in the ACM data; however, it is not directly evaluated because of the error resulting from the charge-spreading effect in an organic MISM capacitor with an unrestricted electrode structure. Therefore, the CI in previous ACM experiments has been independently estimated from the area of the electrode. In this study, a novel design of a substrate with a restricted-bottom-electrode structure is reported. Using the newly designed substrate, it was possible to suppress the charge-spreading effect and successfully estimate precise values of CI directly from the ACM data. Subsequently, it was possible to evaluate the injection barriers at the metal-free phthalocyanine (H2Pc)–Ag and pentacene–Au interfaces, which were 0.4 and 0.15 eV, respectively. The built-in potentials in the semiconductor layer were also determined for the samples used in the measurement.
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K. Tahara, Y. Ashihara, T. Higashino, Y. Ozawa, T. Kadoya, K. Sugimoto, A. Ueda, H. Mori, M. Abe
Dalton Trans. 48 ( 21 ) 7367 - 7377 2019年
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T. Kadoya(corresponding author, R. Oki, Y. Kiyota, Y. Koyama, T. Higashino, K. Kubo, T. Mori, J. Yamada
J. Phys. Chem. C 123 ( 9 ) 5216 - 5222 2019年
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Mott Transition Coupled to Molecular Motion in a Quasi-Two-Dimensional Organic Material 査読あり
Ryosuke Takehara, Kohei Nakada, Kazuya Miyagawa, Tomofumi Kadoya, Jun-ichi Yamada, Kazushi Kanoda
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 87 ( 9 ) 094707 2018年9月
出版者・発行元：PHYSICAL SOC JAPAN
We performed resistivity and H-1-NMR measurements of a quasi-two-dimensional organic material, beta-(BDA-TTP)(2)I-3, to investigate its electronic and magnetic properties across the Mott transition. The NMR spectra and spin-lattice relaxation rate, T-1(-1), show a commensurate antiferromagnetic order in a Mott insulating phase at low pressures and a strongly discontinuous Mott transition around 8 kbar. In the metallic state, the resistivity shows Fermi liquid behavior at low temperatures, whereas (T1T)(-1) is weakly temperature-dependent in the same temperature range. The temperature profile of T-1(-1) indicates that the Mott transition is associated with a marked change in molecular dynamics, suggesting the strong coupling of the Mott transition to the intramolecular degrees of freedom, which is very probably associated with a structural transition.
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H. Akutsu, S. Ito, T. Kadoya, J. Yamada, S. Nakatsuji, S. S. Turner, Y. Nakazawa
Inorg. Chim. Acta 482 654 - 658 2018年
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Hiroyuki Tajima, Naoto Yasukawa, Hisaki Nakatani, Seiichi Sato, Tomofumi Kadoya, Jun-ichi Yamada
ORGANIC ELECTRONICS 51 162 - 167 2017年12月
出版者・発行元：ELSEVIER SCIENCE BV
Hole injection barriers at the regioregular-poly-3(hexylthiophene) (RR-P3HT)/metal (Cu or Ag) interface were investigated using the accumulated charge measurement (ACM). Thermal annealing of RR-P3HT at 55 degrees C decreased the injection barrier. RR-P3HT thermally annealed in N-2 forms an ohmic contact with Ag and a Schottky contact with Cu. The obtained values of the injection barriers, phi(B) were well expressed by the Mott-Schottky rule, i. e., phi(B) = IE - W-m', where IE is the ionization energy of RR-P3HT and W-m' is the work function of the metal electrode in air. The effect of the large vacuum level shift, reported in UPS studies conducted under ultrahigh vacuum, was not observed. (C) 2017 Elsevier B.V. All rights reserved.
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Hiroyuki Tajima, Kesuke Yoshida, Seiichi Sato, Tomofumi Kadoya, Jun-ichi Yamada
JOURNAL OF PHYSICAL CHEMISTRY C 121 ( 27 ) 14725 - 14730 2017年7月
出版者・発行元：AMER CHEMICAL SOC
The effect of the offset bias voltage on the threshold voltage of the hole injection into the organic-semiconductor (OS) layer was examined in detail in the accumulated charge measurement (ACM) for the n-type Si/SiO2/OS/Ag (OS = zinc phthalocyanine [ZnPc] or metal-free phthalocyanine [H2Pc]) capacitor. The threshold highly depends on the offset bias voltages, when the OS layer is in the hole depletion regime. On the contrary, the threshold was nearly constant when the OS layer operated in the hole-accumulation regime. The hole injection barrier of the Ag/OS interface was obtained by the threshold in the accumulation regime. The obtained values were 0.41 and 0.05 eV for H2Pc/Ag and ZnPc/Ag interfaces, respectively. The study revealed that accurate estimation of the injection barrier is possible by examining the offset voltage dependence in the ACM.
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Ryonosuke Sato, Masaki Dogishi, Toshiki Higashino, Tomofumi Kadoya, Tadashi Kawamoto, Takehiko Mori
JOURNAL OF PHYSICAL CHEMISTRY C 121 ( 12 ) 6561 - 6568 2017年3月
出版者・発行元：AMER CHEMICAL SOC
n-Channel organic transistors with excellent air stability are realized on the basis of charge-transfer complexes, (BTBT)(TCNQ), (BTBT)(F(2)TCNQ), (BSBS)(F(2)TCNQ), and (BTBT)(F(4)TCNQ), where BTBT is benzothieno[3,2-b]benzothiophene, BSBS is benzoseleno[3,2-b]benzoselenophene, and F(n)TCNQ (n = 0, 2, and 4) are fluorinated 7,7,8,8-tetracyanoquinodimethanes. These complexes consist of mixed stacks of essentially neutral molecules, and the transistors are air stable even after several-month storage in ambient conditions.
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Tomofumi Kadoya, Masato Otsuka, Akinari Ogino, Seiichi Sato, Tokuji Yokomatsu, Kazusuke Maenaka, Jun-ichi Yamada, Hiroyuki Tajima
JOURNAL OF PHYSICAL CHEMISTRY C 121 ( 5 ) 2882 - 2888 2017年2月
出版者・発行元：AMER CHEMICAL SOC
The charge-injection barrier from metal electrodes to thin-film pentacene is investigated using accumulated charge measurements. When a gold electrode is deposited on a pentacene film, the interface forms a Schottky contact with a hole-injection barrier of 0.2 eV. However, interfacial carrier motion is reversible between charge injection and discharge. The result suggests that the reported electrical hysteresis in typical pentacene transistors is caused by carrier traps that are localized primarily in the SiO2/pentacene interface. The Ag/pentacene junction has a large barrier height of 0.5 eV. The barrier height is significantly reduced, and an Ohmic contact is realized by using molybdenum oxide (MoO3) as a buffer layer.
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Ambipolar organic transistors based on isoindigo derivatives 査読あり
Minoru Ashizawa, Naoaki Masuda, Toshiki Higashino, Tomofumi Kadoya, Tadashi Kawamoto, Hidetoshi Matsumoto, Takehiko Mori
ORGANIC ELECTRONICS 35 95 - 100 2016年8月
出版者・発行元：ELSEVIER SCIENCE BV
Structural and transistor properties of isoindigo derivatives are investigated. The unsubstituted isoindigo affords two polymorphs in addition to the reported brickwork structure; one has a stacking structure analogous to indigo, and another consists of nonplanar molecules. The unsubstituted isoindigo exhibits ambipolar transistor properties with the hole and electron mobilities more than 0.01 cm(2)/Vs, and 6.6 '-diphenylisoindigo shows ambipolar transistor properties with the hole/electron mobilities of 0.037/0.027 cm(2)/Vs. Isoindigo derivatives with electron withdrawing groups show only electron transport, indicating that the lower limit of the HOMO level showing the hole transport is -5.7 eV. (C) 2016 Published by Elsevier B.V.
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Yasuhiro Kiyota, Tomofumi Kadoya, Kaoru Yamamoto, Kodai Iijima, Toshiki Higashino, Tadashi Kawamoto, Kazuo Takimiya, Takehiko Mori
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 138 ( 11 ) 3920 - 3925 2016年3月
出版者・発行元：AMER CHEMICAL SOC
On the basis of an excellent transistor material, [1]benzothieno[3,2-b][1]benzothiophene (BTBT), a series of highly conductive organic metals with the composition of (BTBT)(2)XF6 (X = P, As, Sb, and Ta) are prepared and the structural and physical properties are investigated. The room temperature conductivity amounts to 4100 S cm(-1) in the AsF6 salt, corresponding to the drift mobility of 16 cm(2) V-1 s(-1). Owing to the high conductivity, this salt shows a thermoelectric power factor of 55-88 mu W K-2 m(-1), which is a large value when this compound is regarded as an organic thermoelectric material. The thermoelectric power and the reflectance spectrum indicate a large bandwidth of 1.4 eV. These salts exhibit an abrupt resistivity jump under 200 K, which turns to an insulating state below 60 K. The paramagnetic spin susceptibility, and the Raman and the IR spectra suggest 4k(F) charge-density waves as an origin of the low-temperature insulating state.
DOI： 10.1021/jacs.6b01213
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Chika Fujisue, Tomofumi Kadoya, Toshiki Higashino, Ryonosuke Sato, Tadashi Kawamoto, Takehiko Mori
RSC ADVANCES 6 ( 58 ) 53345 - 53350 2016年
出版者・発行元：ROYAL SOC CHEMISTRY
It has been known that organic charge-transfer complexes with a mix-stacked structure show transistor properties, and particularly complexes containing 7,7,8,8-tetracyano-p-quinodimethane (TCNQ) show air-stable n-channel transistor properties in thin-film transistors, though ambipolar properties have been reported in a few single-crystal transistors. Here we report, when TCNQ is replaced by 2,5-dimethyl-N, N'-dicyano-p-quinonediimine (DMDCNQI), the dibenzopyrrolo[3,2-b]pyrrole (DBPP) complex exhibits ambipolar properties even in the thin-film transistor. The ambipolar operation is stable in air after several weeks. In addition, the transistor shows a very small difference in the electron and hole threshold voltages.
DOI： 10.1039/c6ra10606d
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有機導体β-(BDA-TTP)<sub>2</sub>I<sub>3</sub>における圧力下<sup>1</sup>H-NMR研究
中田 耕平, 宮川 和也, 角屋 智史, 山田 順一, 鹿野田 一司
日本物理学会講演概要集 71 1713 - 1713 2016年
出版者・発行元：一般社団法人 日本物理学会
<p>!LaTeX 有機導体$\beta$-(BDA-TTP)$_{2}$I$_{3}$は常圧でモット絶縁体として振る舞い、加圧によって超伝導を生じる有機導体である。BDA-TTP分子は一次元的なカラム構造をなして積み重なり、加えてカラム間の相互作用のために擬二次元的な電子系を形成しており、その磁気構造が興味の対象となる。本研究では加圧下での$^{1}$H-NMR測定を行い、試料の電子状態の振る舞いを微視的な視点から明らかにすることを目論む。</p>
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Thermoelectric power of oriented thin-film organic conductors 査読あり
Ryonosuke Sato, Yasuhiro Kiyota, Tomofumi Kadoya, Tadashi Kawamoto, Takehiko Mori
RSC ADVANCES 6 ( 47 ) 41040 - 41044 2016年
出版者・発行元：ROYAL SOC CHEMISTRY
The temperature dependence of thermoelectric power is investigated down to low temperatures for oriented thin films of organic conductors. In addition to the evaporated films, highly oriented films consisting of nanoparticles are fabricated by the solution method for tetrathiafulvalene: tetracyanoquinodimethane (TTF)(TCNQ) and (TTF)[Ni(dmit)(2)](2) (dmit: 1,3-dithiole-2-thione-4,5-dithiolato). The resulting films show n-type thermoelectric power, whose temperature dependence is similar to the single-crystal result along the most conducting axis. Owing to the ordered orientation and nanostructures, the thermoelectric power factor is considerably improved in comparison with the ordinary organic films.
DOI： 10.1039/c6ra04455g
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Enantiopure and Racemic Radical-Cation Salts of B(malate)2 anions with BEDT-TTF 査読あり
J. R. Lopez, L. Martin, J. D. Wallis, H. Akutsu, Y. Nakazawa, J. Yamada, T. Kadoya, S. J. Coles, C. Wilson
Dalton Trans 45 ( 22 ) 9285 - 9293 2016年
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Toshiki Higashino, Masaki Dogishi, Tomofumi Kadoya, Ryonosuke Sato, Tadashi Kawamoto, Takehiko Mori
JOURNAL OF MATERIALS CHEMISTRY C 4 ( 25 ) 5981 - 5987 2016年
出版者・発行元：ROYAL SOC CHEMISTRY
A new donor molecule 3,8-dimethoxy-[1] benzothieno[3,2-b][1] benzothiophene ( DMeO-BTBT) is synthesized and the charge-transfer complexes with fluorinated 7,7,8,8-tetracyanoquinodimethane (F-n-TCNQ; n = 0, 2, and 4) are prepared. All complexes (DMeO-BTBT)(F-n-TCNQ) have mixed stack structures, and the thin-film and single-crystal organic transistors show n-channel transistor performance both in vacuum and in air even after one-year storage. Although the performance and stability of the thin-film transistors are improved according to the acceptor ability of F-n-TCNQ, all single-crystal transistors exhibit similar performance and excellent air stability, among which the (DMeO-BTBT)(F-2-TCNQ) transistor exhibits the highest mobility of 0.097 cm(2) V-1 s(-1).
DOI： 10.1039/c6tc01532h
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Suppression of access resistance using carbon electrodes in organic transistors based on alkyl-substituted thienoacene 査読あり
Tomofumi Kadoya, Oratai Pitayatanakul, Takehiko Mori
ORGANIC ELECTRONICS 21 106 - 110 2015年6月
出版者・発行元：ELSEVIER SCIENCE BV
Contact resistance of bottom-contact organic transistors based on dihexyl-substituted dibenzo[d,d'] thieno[3,2-b; 4,5-b'] dithiophene is reduced substantially using carbon electrodes. In the Au top-contact transistors, the contact resistance increases proportionally to the semiconductor thickness owing to the access resistance, whereas the performance of the carbon-electrode transistors does not depend strongly on the active-layer thickness. This is attributed to the lateral charge injection from the side of the thick carbon electrode. (C) 2015 Elsevier B.V. All rights reserved.
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Benzobisthiadiazole-Based Conjugated Donor-Acceptor Polymers for Organic Thin Film Transistors: Effects of -conjugated Bridges on Ambipolar Transport 査読あり
Y. Wang, T. Kadoya, L. Wang, T. Hayakawa, T. Mori, T. Michinobu
J. Mater. Chem. C 3 ( 6 ) 1196 - 1207 2015年
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Ambipolar Organic Field-Effect Transistors Based on Indigo Derivatives 査読あり
Oratai Pitayatanakul, Kodai Iijima, Tomofumi Kadoya, Minoru Ashizawa, Tadashi Kawamoto, Hidetoshi Matsumoto, Takehiko Mori
ENGINEERING JOURNAL-THAILAND 19 ( 3 ) 61 - 73 2015年
出版者・発行元：CHULALONGKORN UNIV, FAC ENGINEERING
In order to improve the ambipolar performance of indigo-based semiconductors, we have investigated halogen-substituted (1 - 4) and phenyl-substituted (5) indigo derivatives at the 5-position. We show that introduction of iodine atoms, namely 5,5'-diiodoindigo (4), leads to the strong halogen-halogen interaction (iodine-iodine interaction) that gives a significant effect on the molecular packing. Thanks to the supramolecular network coming from the extra iodine-iodine interaction, the molecules are arranged approximately perpendicular to the substrate in the thin film. This results in remarkable transistor performance of the maximum hole and electron mobilities (mu(h)/mu(e)) = 0.42/0.85 cm(2)V(-1)s(-1), which are one of the highest among small-molecule ambipolar organic transistors. Furthermore, introducing phenyl groups, 5 improves the transistor performances up to the maximum mobilities mu(h)/mu(e) = 0.56/0.95 cm(2)V(-1)s(-1). We have found that the phenyl groups destroy the standard molecular packing of indigo to achieve a unique structure that is a hybrid of the herringbone and brickwork structures.
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21aAS-6 有機伝導体(BTBT)_2X (X: PF_6,AsF_6,SbF_6,TaF_6)の伝導性と熱起電力
清田 泰裕, 角屋 智史, 飯嶋 広大, 東野 寿樹, 川本 正, 瀧宮 和男, 森 健彦
日本物理学会講演概要集 70 1789 - 1789 2015年