研究者詳細 - 後藤　秀徳

論文 - 後藤　秀徳

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Band Engineering of Bilayer Graphene through Combination of Direct Electron Transfer and Electrostatic Gating 査読

Lei Zhi, Hidenori Goto, Akihisa Takai, Akari Miura, Shino Hamao, Ritsuko Eguchi, Takao Nishikawa, Shizuo Tokito, Yoshihiro Kubozono

The Journal of Physical Chemistry C 124 ( 43 ) 24001 - 24008 2020年10月

Difference in gating and doping effects on the band gap in bilayer graphene 査読

Takaki Uchiyama, Hidenori Goto, Hidehiko Akiyoshi, Ritsuko Eguchi, Takao Nishikawa, Hiroshi Osada, Yoshihiro Kubozono

SCIENTIFIC REPORTS 7 2017年9月

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

A band gap is opened in bilayer graphene (BLG) by applying an electric field perpendicular to the layer, which offers versatility and controllability in graphene-based electronics. The presence of the band gap has been confirmed using double-gated BLG devices in which positive and negative gate voltages are applied to each side of BLG. An alternative method to induce the electric field is electron and hole doping of each side of BLG using electron-transfer adsorbates. However, the generation of the band gap by carrier doping is still under investigation. Here, we determined whether the electron/hole doping can produce the electric field required to open the band gap by measuring the temperature dependence of conductivity for BLG placed between electron-donor self-assembled monolayers (SAMs) and electron-acceptor molecules. We found that some devices exhibited a band gap and others did not. The potentially irregular and variable structure of SAMs may affect the configuration of the electric field, yielding variable electronic properties. This study demonstrates the essential differences between gating and doping.

DOI： 10.1038/s41598-017-11822-9

Carrier Accumulation in Graphene with Electron Donor/Acceptor Molecules 査読

Hidehiko Akiyoshi, Hidenori Goto, Eri Uesugi, Ritsuko Eguchi, Yukihiro Yoshida, Gunzi Saito, Yoshihiro Kubozono

Advanced Electronic Materials 1 ( 7 ) 1500073 - 1500073 2015年7月

Electric double-layer capacitance between an ionic liquid and few-layer graphene 査読

Uesugi Eri, Goto Hidenori, Eguchi Ritsuko, Fujiwara Akihiko, Kubozono Yoshihiro

Scientific Reports 3 ( 1 ) 2013年12月

担当区分：責任著者記述言語：英語掲載種別：研究論文（学術雑誌）

Ionic-liquid gates have a high carrier density due to their atomically thin electric double layer (EDL) and extremely large geometrical capacitance C-g. However, a high carrier density in graphene has not been achieved even with ionic-liquid gates because the EDL capacitance C-EDL between the ionic liquid and graphene involves the series connection of C-g and the quantum capacitance C-q, which is proportional to the density of states. We investigated the variables that determine C-EDL at the molecular level by varying the number of graphene layers n and thereby optimising C-q. The C-EDL value is governed by C-q at n, 4, and by C-g at n > 4. This transition with n indicates a composite nature for C-EDL. Our finding clarifies a universal principle that determines capacitance on a microscopic scale, and provides nanotechnological perspectives on charge accumulation and energy storage using an ultimately thin capacitor.

DOI： 10.1038/srep01595

その他リンク： http://www.nature.com/articles/srep01595.pdf

Parity effects in few-layer graphene 査読

Hidenori Goto, Eri Uesugi, Ritsuko Eguchi, Yoshihiro Kubozono

Nano Letters 13 ( 11 ) 5153 - 5158 2013年11月

担当区分：筆頭著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）

We study the electronic properties in few-layer graphenes (FLGs) classified by even/odd layer number n. FLGs with even n have only parabolic energy dispersions, whereas FLGs with odd n have a linear dispersion besides parabolic ones. This difference leads to a distinct density of states in FLGs, experimentally confirmed by the gate-voltage dependence of the electric double-layer capacitance. Thus, FLGs with odd n are unique materials that have relativistic carriers originating in linear energy dispersion. © 2013 American Chemical Society.

DOI： 10.1021/nl402404z

Edge-Dependent Transport Properties in Graphene 査読

Hidenori Goto, Eri Uesugi, Ritsuko Eguchi, Akihiko Fujiwara, Yoshihiro Kubozono

NANO LETTERS 13 ( 3 ) 1126 - 1130 2013年3月

担当区分：筆頭著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER CHEMICAL SOC

Graphene has two kinds of edges which have different electronic properties. A singular electronic state emerges at zigzag edges, while it disappears at armchair edges. We study the edge-dependent transport properties in few-layer graphene by applying a side gate voltage to the edge with an ionic liquid. The devices indicating a conductance peak at the charge neutrality point have zigzag edges, confirmed by micro-Raman spectroscopy mapping. The hopping transport between zigzag edges increases the conductance.

DOI： 10.1021/nl3044844

Gate control of spin transport in multilayer graphene 査読

Goto H, Kanda A, Sato T, Tanaka S, Ootuka Y, Odaka S, Miyazaki H, Tsukagoshi K, Aoyagi Y

Applied Physics Letters 92 ( 21 ) 212110 2008年

Biosensor Application of CMOS Inverter and Ring Oscillator with Organic Field-Effect Transistors

Masaki Utsumi, Akihiko Fujiwara, Hidenori Goto, Hideki Okamoto, Nobuyuki Takeyasu, Yasunori Saitoh, Michihiro Suga, Yuichiro Takahashi, Hiroyuki Imanaka, Hiroki Taniguchi, Shintaro Yasui, Ritsuko Eguchi, Yoshihiro Kubozono

ACS Applied Electronic Materials 2025年2月

Structural and Superconducting Properties of Bi₂Rh₃(Se_1–xS_x)₂ (x = 0–1.0) 査読

Zhiyan Zhang, Wanli Pan, Masaki Utsumi, Yuki Yamamoto, Hidenori Goto, Ryusuke Kondo, Takayoshi Yokoya, Ryota Goban, Tomoki Higashikawa, Ritsuko Eguchi, Yasuhiro Takabayashi, Koichi Hayashi, Hirofumi Ishii, Tatsuo C. Kobayashi, Yoshihiro Kubozono

Inorganic Chemistry 63 ( 45 ) 21531 - 21540 2024年10月

Superstructure of Fe_5–xGeTe₂ Determined by Te K-Edge Extended X-ray Absorption Fine Structure and Te Kα X-ray Fluorescence Holography 査読

Ritsuko Eguchi, Halubai Sekhar, Koji Kimura, Hirokazu Masai, Naohisa Happo, Mitsuki Ikeda, Yuki Yamamoto, Masaki Utsumi, Hidenori Goto, Yasuhiro Takabayashi, Hiroo Tajiri, Koichi Hayashi, Yoshihiro Kubozono

ACS Omega 9 ( 19 ) 21287 - 21297 2024年5月

Nanophase Separation in K_1–xCa_xC₈ Revealed by X-ray Fluorescence Holography and Extended X-ray Absorption Fine Structure 査読

Naohisa Happo, Atsushi Kubota, Xiaofan Yang, Ritsuko Eguchi, Hidenori Goto, Mitsuki Ikeda, Koji Kimura, Yasuhiro Takabayashi, Jens R. Stellhorn, Shinjiro Hayakawa, Koichi Hayashi, Yoshihiro Kubozono

Chemistry of Materials 36 ( 9 ) 4135 - 4143 2024年4月

Pressure Dependence of the Structural and Superconducting Properties of the Bi-Based Superconductor Bi₂Pd₃Se₂ 査読

Zhiyan Zhang, Mitsuki Ikeda, Masaki Utsumi, Yuki Yamamoto, Hidenori Goto, Ritsuko Eguchi, Yen-Fa Liao, Hirofumi Ishii, Yasuhiro Takabayashi, Koichi Hayashi, Ryusuke Kondo, Tatsuo C. Kobayashi, Yoshihiro Kubozono

Inorganic Chemistry 63 ( 5 ) 2553 - 2561 2024年1月

Structure of Bi<inf>2</inf>Rh<inf>3</inf>Se<inf>2</inf> above and below charge density wave transition determined by Bi Lα and Lγ X-ray fluorescence holography 査読

Zhiyan Zhang, Ritsuko Eguchi, Halubai Sekhar, Koji Kimura, Naohisa Happo, Yuki Yamamoto, Masaki Utsumi, Hidenori Goto, Koichi Hayashi, Yoshihiro Kubozono

Physical Chemistry Chemical Physics 2024年

掲載種別：研究論文（学術雑誌）

The local structure of a two-dimensional layered material, Bi2Rh3Se2, in which superconducting (SC) and charge-density wave (CDW) states coexist, was investigated using Bi Lα and Lγ X-ray fluorescence holography (XFH). The crystal of Bi2Rh3Se2 adopts a monoclinic lattice with a space group of C2/m (No. 12) at room temperature; however, the structure below the CDW transition (∼240 K) is still unclear because of the difficulty in analyzing single-crystal X-ray diffraction. Therefore, information on the crystal structure below 240 K is significant to fully investigate the relationship between the SC and CDW states. Precisely, the value of β has not been definitely determined, i.e., β ∼ 90° or ∼134° is still unclear. Therefore, the crystal structure above 240 K is still under discussion. In this study, we attempted to determine the crystal structure at 300 and 200 K by comparing the atomic images reconstructed from Bi Lγ holograms with images simulated based on crystal structure models. A Bi Lα hologram was also exploited to determine suitable atomic locations by comparison with the simulated ones. The atomic image simulated with the crystal structure of Bi2Rh3S2 below the structural phase transition temperature reproduced well the experimental atomic image at 200 K. Specifically, the line profiles of the reconstructed images at 300 and 200 K, which exactly reflect the intensity of the atomic spots, clearly indicate the structural variation above and below the CDW transition temperature, i.e., the supercell structure is suggested as the atomic location for Bi2Rh3Se2 below the CDW transition temperature.

DOI： 10.1039/d4cp02694b

Observation of the Superstructure in Fe_5–xGeTe₂ by X-ray Fluorescence Holography 査読

Ritsuko Eguchi, Mitsuki Ikeda, Yuki Yamamoto, Hidenori Goto, Naohisa Happo, Koji Kimura, Koichi Hayashi, Yoshihiro Kubozono

Inorganic Chemistry 2023年12月

Coulomb Scattering Controlled by Ionized Molecules Adsorbed on Graphene 査読

Akihisa Takai, Hidenori Goto, Hidehiko Akiyoshi, Lei Zhi, Misuzu Kitahara, Hideki Okamoto, Ritsuko Eguchi, Yukihiro Yoshida, Gunzi Saito, Yoshihiro Kubozono

The Journal of Physical Chemistry C 128 ( 1 ) 467 - 473 2023年12月

Structural Characterization of Graphite Analogue BC_x Synthesized Under Various Conditions and Its Application to Ti Intercalation 査読

Kazumasa Horigane, Masayuki Tadokoro, Ritsuko Eguchi, Hirofumi Ishii, Shinichi Nakamura, Takashi Kambe, Naoshi Ikeda, Hidenori Goto, Yoshihiro Kubozono, Jun Akimitsu

Inorganic Chemistry 62 ( 48 ) 19466 - 19473 2023年11月

Correlation between electronic structure and emergence of superconductivity in Bi2−xSbxTe3−ySey ( y∼1.2 ) studied by x-ray emission spectroscopy and density functional theory 査読

Hitoshi Yamaoka, Harald O. Jeschke, Huan Li, Tong He, Naohito Tsujii, Nozomu Hiraoka, Hirofumi Ishii, Hidenori Goto, Yoshihiro Kubozono

Physical Review B 2023年7月

Pressure Dependence of Superconductivity in Alkaline Earth Metal-Doped FeSe: toward Completion of the Phase Diagram of Superconducting Transition Temperature Versus FeSe Layer Distance 査読

Mitsuki Ikeda, Huan Li, Zhiyan Zhang, Yuki Yamamoto, Hidenori Goto, Ritsuko Eguchi, Hirofumi Ishii, Yen-Fa Liao, Yasuhiro Takabayashi, Koichi Hayashi, Yoshihiro Kubozono

Chemistry of Materials 35 ( 11 ) 4338 - 4346 2023年6月

Pressure Dependence of Superconductivity in a Charge-Density-Wave Superconductor Bi2Rh3Se2 査読

Mitsuki Ikeda, Zhiyan Zhang, Hidenori Goto, Ritsuko Eguchi, Yen-Fa Liao, Hirofumi Ishii, Yoshihiro Kubozono

Inorganic Chemistry 62 ( 19 ) 7453 - 7460 2023年5月

Multiple-site Ag doping in Bi2Se3: Compositional crossover from substitution to intercalation as revealed by photoelectron diffraction and X-ray fluorescence holography 査読

Fumihiko Matsui, Hiroshi Ota, Ritsuko Eguchi, Hidenori Goto, Kaya Kobayashi, Jun Akimitsu, Hikaru Ozaki, Takumi Nishioka, Koji Kimura, Kouichi Hayashi, Takuya Shimano, Naohisa Happo, Yoshihiro Kubozono

Journal of Electron Spectroscopy and Related Phenomena 264 147295 - 147295 2023年4月

Semiconductor–metal transition in Bi2Se3 caused by impurity doping 査読

Takaki Uchiyama, Hidenori Goto, Eri Uesugi, Akihisa Takai, Lei Zhi, Akari Miura, Shino Hamao, Ritsuko Eguchi, Hiromi Ota, Kunihisa Sugimoto, Akihiko Fujiwara, Fumihiko Matsui, Koji Kimura, Kouichi Hayashi, Teppei Ueno, Kaya Kobayashi, Jun Akimitsu, Yoshihiro Kubozono

Scientific Reports 13 ( 1 ) 2023年1月

担当区分：責任著者掲載種別：研究論文（学術雑誌）出版者・発行元：Springer Science and Business Media LLC

Abstract

Doping a typical topological insulator, Bi₂Se₃, with Ag impurity causes a semiconductor–metal (S-M) transition at 35 K. To deepen the understanding of this phenomenon, structural and transport properties of Ag-doped Bi₂Se₃ were studied. Single-crystal X-ray diffraction (SC-XRD) showed no structural transitions but slight shrinkage of the lattice, indicating no structural origin of the transition. To better understand electronic properties of Ag-doped Bi₂Se₃, extended analyses of Hall effect and electric-field effect were carried out. Hall effect measurements revealed that the reduction of resistance was accompanied by increases in not only carrier density but carrier mobility. The field-effect mobility is different for positive and negative gate voltages, indicating that the E_F is located at around the bottom of the bulk conduction band (BCB) and that the carrier mobility in the bulk is larger than that at the bottom surface at all temperatures. The pinning of the E_F at the BCB is found to be a key issue to induce the S-M transition, because the transition can be caused by depinning of the E_F or the crossover between the bulk and the top surface transport.

DOI： 10.1038/s41598-023-27701-5

その他リンク： https://www.nature.com/articles/s41598-023-27701-5

Superconducting Behavior of BaTi₂(Sb_1–yBi_y)₂O under Pressure 査読国際共著

Mitsuki Ikeda, Ai Suzuki, Yanting Zhang, Hidenori Goto, Ritsuko Eguchi, Yen-Fa Liao, Hirofumi Ishii, Yoshihiro Kubozono

Inorganic Chemistry 61 ( 50 ) 20538 - 20546 2022年12月

Elucidation of the Local Structure of the Topological Insulator β-PdBi₂ by X-ray Fluorescence Holography 査読

Ai Suzuki, Yanting Zhang, Mitsuki Ikeda, Yuki Yamamoto, Ritsuko Eguchi, Hidenori Goto, Kaisei Yamamoto, Naohisa Happo, Koji Kimura, Kouichi Hayashi, Hirofumi Ishii, Yoshihiro Kubozono

The Journal of Physical Chemistry C 2022年12月

Charge Transport Capabilities of Dibenzo[n]phenacenes (n = 5–7): Influence of Trap States and Molecular Packing 査読

Yanting Zhang, Shino Hamao, Hidenori Goto, Yoshihiro Kubozono, Hideki Okamoto, Kunihisa Sugimoto, Nobuhiro Yasuda, Akihiko Fujiwara, Ritsuko Eguchi

The Journal of Physical Chemistry C 2022年10月

Superconducting Properties of Pd_1–xPt_xBi₂ over a Wide Pressure Range 査読

Ai Suzuki, Mitsuki Ikeda, Hirofumi Ishii, Yen-Fa Liao, Yasuhiro Takabayashi, Kouichi Hayashi, Hidenori Goto, Ritsuko Eguchi, Yoshihiro Kubozono

The Journal of Physical Chemistry C 126 ( 23 ) 9948 - 9955 2022年6月

Pressure dependence of superconductivity in alkali-Bi compounds KBi2 and RbBi2 査読

Huan Li, Mitsuki Ikeda, Ai Suzuki, Tomoya Taguchi, Yanting Zhang, Hidenori Goto, Ritsuko Eguchi, Yen-Fa Liao, Hirofumi Ishii, Yoshihiro Kubozono

PHYSICAL CHEMISTRY CHEMICAL PHYSICS 24 ( 12 ) 7185 - 7194 2022年3月

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

The structural and superconducting properties of alkali-Bi-based compounds, KBi2 and RbBi2, were investigated over a wide pressure range for the first time. The samples of KBi2 and RbBi2 were prepared using a liquid ammonia (NH3) technique, and demonstrated superconductivity with superconducting transition temperatures, T-c, of 3.50 and 4.21 K at ambient pressure, respectively. The onset superconducting transition temperature, T-c(onset), of KBi2 decreased slightly; however, it suddenly jumped at 2 GPa and increased gradually with pressure, indicating the presence of two superconducting phases in the low-pressure range. The pressure-dependent X-ray diffraction patterns indicate that the KBi2 sample decomposed into KBi and Bi at pressures higher than 2.5 GPa. Moreover, a discontinuous change in T-c(onset) was observed for KBi2 at 9 GPa, which reflects the decomposition of KBi2 into KBi and Bi. By contrast, the value of T-c(onset) of RbBi2 was almost constant over a pressure range of 0-8 GPa. Thus, the superconducting properties and stability of alkali-Bi-based compounds against pressure were comprehensively explored in this study. In addition, the superconducting Cooper pair symmetry was investigated from the magnetic field dependence of T-c of KBi2 at 0.790 and 2.32 GPa, and of RbBi2 at 1.17 GPa, indicating the exact deviation from the simple s-wave paring model, which may be due to the complex electronic structure of Bi. The results elucidated the exotic superconducting properties of KBi2 and RbBi2 based on the pressure and magnetic field dependence of T-c and verified the chemical stability of KBi2 under pressure.

DOI： 10.1039/d2cp00679k

Evaluation of Effective Field-Effect Mobility in Thin-Film and Single-Crystal Transistors for Revisiting Various Phenacene-Type Molecules 査読

Yanting Zhang, Ritsuko Eguchi, Shino Hamao, Hideki Okamoto, Hidenori Goto, Yoshihiro Kubozono

ACS OMEGA 7 ( 6 ) 2022年2月

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

The magnitude of the field-effect mobility mu of organic thin-film and single-crystal field-effect transistors (FETs) has been over-estimated in certain recent studies. These reports set alarm bells ringing in the research field of organic electronics. Herein, we report a precise evaluation of the mu values using the effective field-effect mobility, mu(eff), a new indicator that is recently designed to prevent the FET performance of thin-film and single-crystal FETs based on various phenacene molecules from being overestimated. The transfer curves of a range of FETs based on phenacene are carefully categorized on the basis of a previous report. The exact evaluation of the value of mu(eff) depends on the exact classification of each transfer curve. The transfer curves of all our phenacene FETs could be successfully classified based on the method indicated in the aforementioned report, which made it possible to evaluate the exact value of mu(eff) for each FET. The FET performance based on the values of mu(eff) obtained in this study is discussed in detail. In particular, the mu(eff) values of single-crystal FETs are almost consistent with the mu values that were reported previously, but the mu(eff) values of thin-film FETs were much lower than those previously reported for mu, owing to a high absolute threshold voltage, vertical bar V-th vertical bar. The increase in the field-effect mobility as a function of the number of benzene rings, which was previously demonstrated based on the mu values of single-crystal FETs with phenacene molecules, is well reproduced from the mu(eff) values. The FET performance is discussed based on the newly evaluated mu(eff) values, and the future prospects of using phenacene molecules in FET devices are demonstrated.

DOI： 10.1021/acsomega.1c06932

Fabrication and characterization of thin-film field-effect transistors with alkyl-phenyl[n]phenacenes (n = 4–6) 査読

Yanting Zhang, Ritsuko Eguchi, Hideki Okamoto, Kenta Goto, Fumito Tani, Minoru Yamaji, Hidenori Goto, Yoshihiro Kubozono

Journal of Materials Chemistry C 10 ( 43 ) 16309 - 16320 2022年

Superconductivity of topological insulator Sb2Te3−ySey under pressure 査読

Tomoya Taguchi, Mitsuki Ikeda, Huan Li, Ai Suzuki, Xiaofan Yang, Hirofumi Ishii, Yen-Fa Liao, Hiromi Ota, Hidenori Goto, Ritsuko Eguchi, Yoshihiro Kubozono

Journal of Physics: Condensed Matter 33 ( 48 ) 485704 - 485704 2021年9月

Superconducting properties of BaBi3 at ambient and high pressures 査読

Yanan Wang, Tomoya Taguchi, Huan Li, Ai Suzuki, Yanting Zhang, Akari Miura, Mitsuki Ikeda, Hidenori Goto, Ritsuko Eguchi, Takafumi Miyazaki, Yen-Fa Liao, Hirofumi Ishii, Yoshihiro Kubozono

Physical Chemistry Chemical Physics 23 ( 40 ) 23014 - 23023 2021年9月

Pressure Dependence of Superconducting Behavior of 4d and 5d Transition Metal Compounds CaRh2 and CaIr2 査読

Huan Li, Tomoya Taguchi, Yanan Wang, Hidenori Goto, Ritsuko Eguchi, Hirofumi Ishii, Yen-Fa Liao, Yoshihiro Kubozono

The Journal of Physical Chemistry C 125 ( 37 ) 20617 - 20625 2021年9月

Emergence of a Pressure-Driven Superconducting Phase in Ba0.77Na0.23Ti2Sb2O 査読

Tomoya Taguchi, Yanan Wang, Xiaofan Yang, Huan Li, Yasuhiro Takabayashi, Kouichi Hayashi, Takafumi Miyazaki, Yen-Fa Liao, Hirofumi Ishii, Hidenori Goto, Ritsuko Eguchi, Yoshihiro Kubozono

Inorganic Chemistry 60 ( 6 ) 3585 - 3592 2021年2月

Fabrication of ring oscillators using organic molecules of phenacene and perylenedicarboximide 査読

Niko Fioravanti, Luca Pierantoni, Davide Mencarelli, Claudio Turchetti, Shino Hamao, Hideki Okamoto, Hidenori Goto, Ritsuko Eguchi, Akihiko Fujiwara, Yoshihiro Kubozono

RSC Advances 11 ( 13 ) 7538 - 7551 2021年2月

Superconductivity in topological insulator β-PdBi2 under pressure 査読

Ai Suzuki, Tomoya Taguchi, Huan Li, Yanan Wang, Hirofumi Ishii, Yen-Fa Liao, Hidenori Goto, Ritsuko Eguchi, Yoshihiro Kubozono

Journal of Physics: Condensed Matter 33 ( 13 ) 135702 - 135702 2021年1月

Electronic structures of Bi2Se3 and AgxBi2Se3 under pressure studied by high-resolution x-ray absorption spectroscopy and density functional theory calculations 査読

Hitoshi Yamaoka, Harald O. Jeschke, Xiaofan Yang, Tong He, Hidenori Goto, Nozomu Hiraoka, Hirofumi Ishii, Jun'ichiro Mizuki, Yoshihiro Kubozono

Physical Review B 102 ( 15 ) 2020年10月

Superconducting behavior of BaTi2Bi2O and its pressure dependence 査読

Yanan Wang, Huan Li, Tomoya Taguchi, Ai Suzuki, Akari Miura, Hidenori Goto, Ritsuko Eguchi, Takafumi Miyazaki, Yen-Fa Liao, Hirofumi Ishii, Yoshihiro Kubozono

Physical Chemistry Chemical Physics 22 ( 40 ) 23315 - 23322 2020年10月

Superconductivity in Bi2−xSbxTe3−ySey (x = 1.0 and y = 2.0) under pressure 査読

Tong He, Xiaofan Yang, Tomoya Taguchi, Lei Zhi, Takafumi Miyazaki, Kaya Kobayashi, Jun Akimitsu, Hirofumi Ishii, Yen-Fa Liao, Hidenori Goto, Ritsuko Eguchi, Yoshihiro Kubozono

Journal of Physics: Condensed Matter 32 ( 46 ) 465702 - 465702 2020年8月

A new protocol for the preparation of superconducting KBi2 査読

Huan Li, Yanan Wang, Yutaro Aoki, Saki Nishiyama, Xiaofan Yang, Tomoya Taguchi, Akari Miura, Ai Suzuki, Lei Zhi, Hidenori Goto, Ritsuko Eguchi, Takashi Kambe, Yen-Fa Liao, Hirofumi Ishii, Yoshihiro Kubozono

RSC Advances 10 ( 45 ) 26686 - 26692 2020年7月

Structure and superconducting properties of multiple phases of (NH3)yAExFeSe (AE: Ca, Sr and Ba) 査読

Huan Li, Yanan Wang, Xiaofan Yang, Tomoya Taguchi, Lei Zhi, Hidenori Goto, Ritsuko Eguchi, Hirofumi Ishii, Yen-Fa Liao, Yoshihiro Kubozono

Journal of Physics: Condensed Matter 32 ( 39 ) 395704 - 395704 2020年6月

Inhomogeneous superconductivity in thin crystals of FeSe1−xTex (x=1.0, 0.95, and 0.9) 査読

Ritsuko Eguchi, Megumi Senda, Eri Uesugi, Hidenori Goto, Akihiko Fujiwara, Yasuhiko Imai, Shigeru Kimura, Takashi Noji, Yoji Koike, Yoshihiro Kubozono

Materials Research Express 7 ( 3 ) 036001 - 036001 2020年3月

Superconducting properties of (NH3)yLixFeSe0.5Te0.5 under pressure 査読

Xiaofan Yang, Tong He, Tomoya Taguchi, Huan Li, Yanan Wang, Hidenori Goto, Ritsuko Eguchi, Takafumi Miyazaki, Hitoshi Yamaoka, Hirofumi Ishii, Yen Fa Liao, Yoshihiro Kubozono

New Journal of Physics 21 ( 11 ) 113010 2019年11月

Preparation and characterization of superconducting Ba1-xCsxTi2Sb2O, and its pressure dependence of superconductivity 査読

Wang Yanan, Yang Xiaofan, Taguchi Tomoya, Li Huan, He Tong, Goto Hidenori, Eguchi Ritsuko, Miyazaki Takafumi, Liao Yen-Fa, Ishii Hirofumi, Kubozono Yoshihiro

JAPANESE JOURNAL OF APPLIED PHYSICS 58 ( 11 ) 110603-1 - 110603-7 2019年10月

Superconducting behavior of a new metal iridate compound, SrIr2, under pressure 査読

Xiaofan Yang, Huan Li, Tong He, Tomoya Taguchi, Yanan Wang, Hidenori Goto, Ritsuko Eguchi, Rie Horie, Kazumasa Horigane, Kaya Kobayashi, Jun Akimitsu, Hirofumi Ishii, Yen Fa Liao, Hitoshi Yamaoka, Yoshihiro Kubozono

Journal of Physics Condensed Matter 32 ( 2 ) 2019年10月

Pressure-induced superconductivity in Bi2-xSbxTe3-ySey 査読

Tong He, Xiaofan Yang, Tomoya Taguchi, Teppei Ueno, Kaya Kobayashi, Jun Akimitsu, Hitoshi Yamaoka, Hirofumi Ishii, Yen Fa Liao, Hiromi Ota, Hidenori Goto, Ritsuko Eguchi, Kensei Terashima, Takayoshi Yokoya, Harald O. Jeschke, Xianxin Wu, Yoshihiro Kubozono

Physical Review B 100 ( 9 ) 094525-1 - 094525-11 2019年9月

Fabrication of flexible high-performance organic field-effect transistors using phenacene molecules and their application toward flexible CMOS inverters 査読

Emanuela Pompei, Claudio Turchetti, Shino Hamao, Akari Miura, Hidenori Goto, Hideki Okamoto, Akihiko Fujiwara, Ritsuko Eguchi, Yoshihiro Kubozono

Journal of Materials Chemistry C 7 ( 20 ) 6022 - 6033 2019年4月

Fermi level tuning of Ag-doped Bi2Se3 topological insulator 査読

Eri Uesugi, Takaki Uchiyama, Hidenori Goto, Hiromi Ota, Teppei Ueno, Hirokazu Fujiwara, Kensei Terashima, Takayoshi Yokoya, Fumihiko Matsui, Jun Akimitsu, Kaya Kobayashi, Yoshihiro Kubozono

Scientific Reports 9 ( 1 ) 5376 2019年3月

Synthesis of the extended phenacene molecules, [10]phenacene and [11]phenacene, and their performance in a field-effect transistor 査読

Hideki Okamoto, Shino Hamao, Ritsuko Eguchi, Hidenori Goto, Yasuhiro Takabayashi, Paul Yu, Hsiang Yen, Luo Uei Liang, Chia Wei Chou, Germar Hoffmann, Shin Gohda, Hisako Sugino, Yen Fa Liao, Hirofumi Ishii, Yoshihiro Kubozono

Scientific Reports 9 ( 1 ) 4009 2019年3月

Materials for organic electronics and bioelectronics

Yoshihiro Kubozono, Hidenori Goto, Hiroko Yamada

3d Local Structure And Functionality Design Of Materials 173 - 195 2018年12月

記述言語：英語掲載種別：論文集(書籍)内論文出版者・発行元：World Scientific Publishing Co.

In this chapter, the principles behind the mechanism of operation of organic transistors are described, as they are both important in their own right and also a representative example of organic electronics. Accordingly, the recent progress in organic transistors will be explored in depth. The term “organic transistor” generally refers to the field-effect transistor (FET), which uses thin films of organic materials. The study of these “organic FETs” began in the 1980s.1 Initially, the available fieldeffect mobility (µ), which is one determinant of the performance of an FET, was ca. 10-5 cm2 V-1 s-1, a value that is insufficient for practical applications. In the late 1990s, it was found that pentacene, in which five benzene rings are connected in a linear structure (Fig. 8.1.1), and C60, in which 60 carbon atoms form a spherical structure, were good candidates for the active layer of an FET device. The µ value became ~1 cm2 V-1 s-1 in FETs using these molecules.2, 3 This µ value raised the expectation that organic FETs might in the future become practical devices. On the other hand, since the year 2000, some work on FETs has demonstrated that the physical properties of materials can be controlled by carrier accumulation, such as the field-induced carrier doping of C60 for inducing superconductivity. These studies were not the case, but the interest in field-induced carrier doping to control the physical properties of materials has attracted much attention from researchers in solid-state physics. Consequently, some control of the physical properties of inorganic materials has been achieved by field-induced carrier accumulation using a device with the structure of an FET.4, 5 Research on organic FETs has been brought to a new stage by the participation of many researchers from other fields, where FET performance was pursued not only to find practical applications, but also to investigate fundamental physics. In 2003, a device with excellent FET properties that used a single crystal was fabricated using rubrene (Fig. 8.1.1).6 This showed that transistor operation in an organic FET could be achieved using not only thin films but also single crystals. An FET using a single crystal is superior to a thin-film FET for studying the intrinsic nature of organic materials because many interfering factors such as structural defects, grain boundaries, and impurities can be removed from the active layer. Generally, FET performance is also higher in a single-crystal FET than in a thin-film FET. Clearly, these studies have led to remarkable advances in the research on organic FETs. Furthermore, Hall-effect measurements were achieved in single crystals of organic molecules, 7, 8 and angle-resolved photoemission spectroscopy (ARPES) was performed on some organic single crystals.9, 10 Based on these results, it was suggested that electron transport in organic singlecrystal FETs occurs by band transport rather than hopping transport. Since then, the idea that electron transport in an organic thin-film FET is explained by simple hopping transport has been modified due to analyses based on the multiple shallow trap-and-release (MTR) model for the temperature-dependence of transport properties in organic thinfilm FETs exhibiting a high µ value.11-13 The MTR model assumes that the carriers in a band are captured by trap states and thermally excited up to the conduction (or valence) band, i.e. this concept is substantially based on band transport. Furthermore, the reduction of µ value caused by thermal scattering of phonons was determined from the temperature-dependence of µ in organic single-crystal FETs.14, 15 This constituted the direct observation of band transport in organic single-crystal FETs. These studies have enabled the full discussion of the mechanism of organic FET operation. An FET using pentacene (Fig. 8.1.1) as the active layer shows typical pchannel operation with Au source/drain electrodes, but shows n-channel operation with Ca source/drain electrodes.16 So an organic FET can operate both as p-channel and n-channel depending on the electrode metal, a flexibility termed “ambipolar”. Thus, an organic FET can operate in an ambipolar way by changing the metal of the source/drain electrodes (or changing the work function of the electrodes), unlike the operation of Si MOSFETs, which can operate in either p-channel or n-channel through the formation of an inversion layer in which minority carriers in the bulk become the majority in the channel region. Also, neither organic thin films nor crystals are doped with any impurities, unlike the Si crystal used in Si MOSFETs, which can be doped with an acceptor (p-type Si) or with a donor (n-type Si) material. In Section 8.1.1, we will fully examine organic FETs based on the background described above.

DOI： 10.1142/9789813273672_0010

Preparation and characterization of a new metal-intercalated graphite superconductor 査読

Yang Xiaofan, Taguchi Tomoya, Wang Yanan, He Tong, Uchiyama Takaki, Takai Akihisa, Zhi Lei, Miyazaki Takafumi, Goto Hidenori, Eguchi Ritsuko, Ishii Hirofumi, Liao Yen-Fa, Yamaoka Hitoshi, Kubozono Yoshihiro

MATERIALS RESEARCH EXPRESS 6 ( 1 ) 016003 2018年10月

Pressure dependence of superconductivity in low- and high- T c phases of (NH3)yNaxFeSe 査読

Takahiro Terao, Xiaofan Yang, Xiao Miao, Lu Zheng, Hidenori Goto, Takafumi Miyazaki, Hitoshi Yamaoka, Hirofumi Ishii, Yen-Fa Liao, Yoshihiro Kubozono

Physical Review B 97 ( 9 ) 2018年3月

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

We prepared two superconducting phases, which are called "low-Tc phase" and "high-Tc phase" of (NH3)yNaxFeSe showing Tc's of 35 and 44 K, respectively, at ambient pressure, and studied the superconducting behavior and structure of each phase under pressure. The Tc of the 35 K at ambient pressure rapidly decreases with increasing pressure up to 10 GPa, and it remains unchanged up to 22 GPa. Finally, superconductivity was not observed down to 1.4 K at 29 GPa, i.e., Tc&lt
1.4K. The Tc of the 44 K phase also shows a monotonic decrease up to 15 GPa and it weakly decreases up to 25 GPa. These behaviors suggest no pressure-driven high-Tc phase (called "SC-II") between 0 and 25 GPa for the low-Tc and high-Tc phases of (NH3)yNaxFeSe, differing from the behavior of (NH3)yCsxFeSe, which has a pressure-driven high-Tc phase (SC-II) in addition to the superconducting phase (SC-I) observed at ambient and low pressures. The Tc-c phase diagram for both low-Tc and high-Tc phases shows that the Tc can be linearly scaled with c (or FeSe plane spacing), where c is a lattice constant. The reason why a pressure-driven high-Tc phase (SC-II) was found for neither low-Tc nor high-Tc phases of (NH3)yNaxFeSe is fully discussed, suggesting a critical c value as the key to forming the pressure-driven high-Tc phase (SC-II). Finally, the precise Tc-c phase diagram is depicted using the data obtained thus far from FeSe codoped with a metal and NH3 or amine, indicating two distinct Tc-c lines below c=17.5Å.

DOI： 10.1103/PhysRevB.97.094505

Pressure-induced superconductivity in AgxBi2-xSe3 査読

Tong He, Xiaofan Yang, Takahiro Terao, Takaki Uchiyama, Teppei Ueno, Kaya Kobayashi, Jun Akimitsu, Takafumi Miyazaki, Takumi Nishioka, Koji Kimura, Kouichi Hayashi, Naohisa Happo, Hitoshi Yamaoka, Hirofumi Ishii, Yen-Fa Liao, Hiromi Ota, Hidenori Goto, Yoshihiro Kubozono

Physical Review B 97 ( 10 ) 2018年3月

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

We investigated the pressure dependence of electric transport and crystal structure of Ag-doped Bi2Se3. In the sample prepared by Ag doping of Bi2Se3, the Bi atom was partially replaced by Ag, i.e., Ag0.05Bi1.95Se3. X-ray diffraction patterns of Ag0.05Bi1.95Se3 measured at 0-30 GPa showed three different structural phases, with rhombohedral, monoclinic, and tetragonal structures forming in turn as pressure increased, and structural phase transitions at 8.8 and 24 GPa. Ag0.05Bi1.95Se3 showed no superconductivity down to 2.0 K at 0 GPa, but under pressure, superconductivity suddenly appeared at 11 GPa. The magnetic field (H) dependence of the superconducting transition temperature Tc was measured at 11 and 20.5 GPa, in order to investigate whether the pressure-induced superconducting phase is explained by either p-wave polar model or s-wave model.

DOI： 10.1103/PhysRevB.97.104503

Preparation and characterization of a new graphite superconductor: Ca0.5Sr0.5C6 査読

Saki Nishiyama, Hidenori Fujita, Masatoshi Hoshi, Xiao Miao, Takahiro Terao, Xiaofan Yang, Takafumi Miyazaki, Hidenori Goto, Tomoko Kagayama, Katsuya Shimizu, Hitoshi Yamaoka, Hirofumi Ishii, Yen-Fa Liao, Yoshihiro Kubozono

SCIENTIFIC REPORTS 7 2017年8月

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

We have produced a superconducting binary-elements intercalated graphite, CaxSr1-xCy, with the intercalation of Sr and Ca in highly-oriented pyrolytic graphite; the superconducting transition temperature, T(c1)was similar to 3 K. The superconducting CaxSr1-xCy sample was fabricated with the nominal x value of 0.8, i.e., Ca0.8Sr0.2Cy. Energy dispersive X-ray (EDX) spectroscopy provided the stoichiometry of Ca0.5(2)Sr0.5(2)C-y for this sample, and the X-ray powder diffraction (XRD) pattern showed that Ca0.5(2)Sr0.5(2)Cy took the SrC6-type hexagonal-structure rather than CaC6-type rhombohedral-structure. Consequently, the chemical formula of CaxSr1-xCy sample could be expressed as 'Ca0.5(2)Sr0.5(2)C6'. The XRD pattern of Ca0.5(2)Sr0.5(2)C6 was measured at 0-31 GPa, showing that the lattice shrank monotonically with increasing pressure up to 8.6 GPa, with the structural phase transition occurring above 8.6 GPa. The pressure dependence of Tc was determined from the DC magnetic susceptibility and resistance up to 15 GPa, which exhibited a positive pressure dependence of T-c up to 8.3 GPa, as in YbC6, SrC6, KC8, CaC6 and Ca0.6K0.4C8. The further application of pressure caused the rapid decrease of Tc. In this study, the fabrication and superconducting properties of new binary-elements intercalated graphite, CaxSr1-xCy, are fully investigated, and suitable combinations of elements are suggested for binaryelements intercalated graphite.

DOI： 10.1038/s41598-017-07763-y

Preparation of new superconductors by metal doping of two-dimensional layered materials using ethylenediamine 査読

Xiao Miao, Takahiro Terao, Xiaofan Yang, Saki Nishiyama, Takafumi Miyazaki, Hidenori Goto, Yoshihiro Iwasa, Yoshihiro Kubozono

PHYSICAL REVIEW B 96 ( 1 ) 2017年7月

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

We have studied new superconductors prepared by metal doping of two-dimensional (2D) layered materials, FeSe and FeSe0.5Te0.5, using ethylenediamine (EDA). The superconducting transition temperatures (T(c)s) of metal-doped FeSe and metal-doped FeSe0.5Te0.5, i.e., (EDA)(y)MxFeSe and (EDA)(y)MxFeSe0.5Te0.5 (M: Li, Na, and K), were 31-45 K and 19-25 K, respectively. The stoichiometry of each sample was clarified by energy dispersive x-ray (EDX) spectroscopy, and the x-ray powder diffraction pattern indicated a large expansion of lattice constant c, indicating the cointercalation of metal atoms and EDA. The pressure dependence of superconductivity in (EDA)(y)NaxFeSe0.5Te0.5 has been investigated at a pressure of 0-0.8GPa, showing negative pressure dependence in the same manner as (NH3)(y)NaxFeSe0.5Te0.5. The T-c-c phase diagrams of MxFeSe and MxFeSe0.5Te0.5 were drawn afresh from the T-c and c of (EDA)(y)MxFeSe and (EDA)(y)MxFeSe0.5Te0.5, showing that the T-c increases with increasing c but that extreme expansion of c reverses the T-c trend.

DOI： 10.1103/PhysRevB.96.014502

Transistor properties of exfoliated single crystals of 2H-Mo(Se1-x Te-x) 2 ( 0 <= x <= 1) 査読

Eri Uesugi, Xiao Miao, Hiromi Ota, Hidenori Goto, Yoshihiro Kubozono

PHYSICAL REVIEW B 95 ( 24 ) 2017年6月

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

Field-effect transistors (FETs) were fabricated using exfoliated single crystals of Mo(Se1-x Te-x)(2) with an x range of 0 to 1, and the transistor properties fully investigated at 295 K in four-terminal measurement mode. The chemical composition and crystal structure of exfoliated single crystals were identified by energy-dispersive x-ray spectroscopy (EDX), single-crystal x-ray diffraction, and Raman scattering, suggesting the 2H - structure in all Mo(Se1-x Te-x)(2). The lattice constants of a and c increase monotonically with increasing x, indicating the substitution of Se by Te. When x < 0.4 in a FET with a thin single crystal of Mo(Se1-x Te-x)(2), n-channel FET properties were observed, changing to p-channelor ambipolar operation for x > 0.4. In contrast, the polarity of a thick single-crystal Mo(Se1-x Te-x)(2) FET did not change despite an increase in x. The change of polarity in a thin single-crystal FET was well explained by the variation of electronic structure. The absence of such change in the thick single-crystal FET can be reasonably interpreted based on the large bulk conduction due to naturally accumulated electrons. The mu value in the thin single-crystal FET showed a parabolic variation, with a minimum mu at around x = 0.4, which probably originates from the disorder of the single crystal caused by the partial replacement of Se by Te, i.e., a disorder that may be due to ionic size difference of Se and Te.

DOI： 10.1103/PhysRevB.95.245310

Electrostatic electron-doping yields superconductivity in LaOBiS2 査読

Eri Uesugi, Saki Nishiyama, Hidenori Goto, Hiromi Ota, Yoshihiro Kubozono

APPLIED PHYSICS LETTERS 109 ( 25 ) 2016年12月

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

Electrostatic carrier-doping is attracting serious attention as a meaningful technique for producing interesting electronic states in two-dimensional (2D) layered materials. Ionic-liquid gating can provide the critical carrier density required to induce the metal-insulator transition and superconductivity. However, the physical properties of only a few materials have been controlled by the electrostatic carrier-doping during the past decade. Here, we report an observation of superconductivity in a 2D layered material, LaOBiS2, achieved by the electrostatic electron-doping. The electron doping of LaOBiS2 induced metallic conductivity in the normally insulating LaOBiS2, ultimately led to superconductivity. The superconducting transition temperature, T-c, was 3.6 K, higher than the 2.7K seen in LaO1-xFxBiS2 with an electron-doped BiS2 layer. A rapid drop in resistance (R) was observed at low temperature, which disappeared with the application of high magnetic fields, implying a superconducting state. This study reveals that electron-doping is an important technique for inducing superconductivity in 2D layered BiS2 materials. Published by AIP Publishing.

DOI： 10.1063/1.4972400

Photoelectron Holographic Atomic Arrangement Imaging of Cleaved Bimetal-intercalated Graphite Superconductor Surface 査読

Fumihiko Matsui, Ritsuko Eguchi, Saki Nishiyama, Masanari Izumi, Eri Uesugi, Hidenori Goto, Tomohiro Matsushita, Kenji Sugita, Hiroshi Daimon, Yuji Hamamoto, Ikutaro Hamada, Yoshitada Morikawa, Yoshihiro Kubozono

SCIENTIFIC REPORTS 6 2016年11月

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

From the C 1s and K 2p photoelectron holograms, we directly reconstructed atomic images of the cleaved surface of a bimetal-intercalated graphite superconductor, (Ca, K) C-8, which differed substantially from the expected bulk crystal structure based on x-ray diffraction (XRD) measurements. Graphene atomic images were collected in the in-plane cross sections of the layers 3.3 angstrom and 5.7 angstrom above the photoelectron emitter C atom and the stacking structures were determined as AB-and AA-type, respectively. The intercalant metal atom layer was found between two AA-stacked graphenes. The K atomic image revealing 2 x 2 periodicity, occupying every second centre site of C hexagonal columns, was reconstructed, and the Ca 2p peak intensity in the photoelectron spectra of (Ca, K) C-8 from the cleaved surface was less than a few hundredths of the K 2p peak intensity. These observations indicated that cleavage preferentially occurs at the KC8 layers containing no Ca atoms.

DOI： 10.1038/srep36258

Superconductivity in (NH3)(y)NaxFeSe0.5Te0.5 査読

Lu Zheng, Yusuke Sakai, Xiao Miao, Saki Nishiyama, Takahiro Terao, Ritsuko Eguchi, Hidenori Goto, Yoshihiro Kubozono

PHYSICAL REVIEW B 94 ( 17 ) 2016年11月

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

Na-intercalated FeSe0.5Te0.5 was prepared using the liquid NH3 technique, and a superconducting phase exhibiting a superconducting transition temperature (T-c) as high as 27 K was discovered. This can be called the high-T-c phase since a 21 K superconducting phase was previously obtained in (NH3)(y)NaxFeSe0.5Te0.5. The chemical composition of the high-T-c phase was determined to be (NH3)(0.61(4))Na-0.63(5) Fe0.85Se0.55(3) Te-0.44(2). The x-ray diffraction patterns of both phases show that a larger lattice constant c (i.e., FeSe0.5Te0.5 plane spacing) produces a higher T-c. This behavior is the same as that of metal-doped FeSe, suggesting that improved Fermi-surface nesting produces the higher T-c. The high-T-c phase converted to the low-T-c phase within several days, indicating that it is a metastable phase. The temperature dependence of resistance for both phases was recorded at different magnetic fields, and the critical fields were determined for both phases. Finally, the T-c versus c phase diagram was prepared for the metal-doped FeSe0.5Te0.5, which is similar to that of metal-doped FeSe, although the T-c is lower.

DOI： 10.1103/PhysRevB.94.174505

Chemical analysis of superconducting phase in K-doped picene 査読

Takashi Kambe, Saki Nishiyama, Huyen L. T. Nguyen, Takahiro Terao, Masanari Izumi, Yusuke Sakai, Lu Zheng, Hidenori Goto, Yugo Itoh, Taiki Onji, Tatsuo C. Kobayashi, Hisako Sugino, Shin Gohda, Hideki Okamoto, Yoshihiro Kubozono

JOURNAL OF PHYSICS-CONDENSED MATTER 28 ( 44 ) 2016年11月

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

Potassium-doped picene (K(3.0)picene) with a superconducting transition temperature (TC) as high as 14 K at ambient pressure has been prepared using an annealing technique. The shielding fraction of this sample was 5.4% at 0 GPa. The TC showed a positive pressure-dependence and reached 19 K at 1.13 GPa. The shielding fraction also reached 18.5%. To investigate the chemical composition and the state of the picene skeleton in the superconducting sample, we used energy-dispersive x-ray (EDX) spectroscopy, MALDI-time-of-flight (MALDI-TOF) mass spectroscopy and x-ray diffraction (XRD). Both EDX and MALDI-TOF indicated no contamination with materials other than K-doped picene or K-doped picene fragments, and supported the preservation of the picene skeleton. However, it was also found that a magnetic K-doped picene sample consisted mainly of picene fragments or K-doped picene fragments. Thus, removal of the component contributing the magnetic quality to a superconducting sample should enhance the volume fraction.

DOI： 10.1088/0953-8984/28/44/444001

Recent progress on carbon-based superconductors 査読

Yoshihiro Kubozono, Ritsuko Eguchi, Hidenori Goto, Shino Hamao, Takashi Kambe, Takahiro Terao, Saki Nishiyama, Lu Zheng, Xiao Miao, Hideki Okamoto

JOURNAL OF PHYSICS-CONDENSED MATTER 28 ( 33 ) 2016年8月

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

This article reviews new superconducting phases of carbon-based materials. During the past decade, new carbon-based superconductors have been extensively developed through the use of intercalation chemistry, electrostatic carrier doping, and surface-proving techniques. The superconducting transition temperature T-c of these materials has been rapidly elevated, and the variety of superconductors has been increased. This review fully introduces graphite, graphene, and hydrocarbon superconductors and future perspectives of high-T-c superconductors based on these materials, including present problems. Carbon-based superconductors show various types of interesting behavior, such as a positive pressure dependence of T-c. At present, experimental information on superconductors is still insufficient, and theoretical treatment is also incomplete. In particular, experimental results are still lacking for graphene and hydrocarbon superconductors. Therefore, it is very important to review experimental results in detail and introduce theoretical approaches, for the sake of advances in condensed matter physics. Furthermore, the recent experimental results on hydrocarbon superconductors obtained by our group are also included in this article. Consequently, this review article may provide a hint to designing new carbon-based superconductors exhibiting higher T-c and interesting physical features.

DOI： 10.1088/0953-8984/28/33/334001

Emergence of superconductivity in (NH3)(y)MxMoSe2 (M: Li, Na and K) 査読

Xiao Miao, Saki Nishiyama, Lu Zheng, Hidenori Goto, Ritsuko Eguchi, Hiromi Ota, Takashi Kambe, Kensei Terashima, Takayoshi Yokoya, Huyen T. L. Nguyen, Tomoko Kagayama, Naohisa Hirao, Yasuo Ohishi, Hirofumi Ishii, Yen-Fa Liao, Yoshihiro Kubozono

SCIENTIFIC REPORTS 6 2016年7月

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

We report syntheses of new superconducting metal-doped MoSe2 materials (MxMoSe2). The superconducting MxMoSe2 samples were prepared using a liquid NH3 technique, and can be represented as '(NH3)(y)MxMoSe2'. The T(c)s of these materials were approximately 5.0 K, independent of x and the specific metal atom. X-ray diffraction patterns of (NH3)(y)NaxMoSe2 were recorded using polycrystalline powders. An increase in lattice constant c showed that the Na atom was intercalated between MoSe2 layers. The x-independence of c was observed in (NH3)(y)NaxMoSe2, indicating the formation of a stoichiometric compound in the entire x range, which is consistent with the x-independence of T-c. A metallic edge of the Fermi level was observed in the photoemission spectrum at 30 K, demonstrating its metallic character in the normal state. Doping of MoSe2 with Li and K also yielded superconductivity. Thus, MoSe2 is a promising material for designing new superconductors, as are other transition metal dichalcogenides.

DOI： 10.1038/srep29292

Fabrication of new superconducting materials, CaxK1-xCy (0 < x < 1) 査読

Huyen T. L. Nguyen, Saki Nishiyama, Masanari Izumi, Lu Zheng, Xiao Miao, Yusuke Sakai, Hidenori Goto, Naohisa Hirao, Yasuo Ohishi, Tomoko Kagayama, Katsuya Shimizu, Yoshihiro Kubozono

CARBON 100 641 - 646 2016年4月

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

Metal intercalation to graphite produces various types of superconductors. The highest superconducting transition temperature T-c (onset temperature, T-c(onset), of 11.5 K) was found in Ca intercalated graphite, denoted CaC6.T-c(onset) increased up to 15.1 K at 7.5 GPa, implying a positive pressure dependence. However, no new metal-intercalated graphite superconductors with T-c(onset) higher than 11.5 K at ambient pressure have so far been reported. To search for new graphite superconductors, we successfully synthesized binary-element-intercalated graphite, CaxK1-xCy. Their structure resembles that of KC8. T-c increased continuously with increasing x. Furthermore, the pressure dependence of T-c in Ca0.6K0.4C8 was investigated over a wide pressure range from 0-43 GPa. T-c (= 9.6 K at 0 GPa) increased to 11.6 K at 3.3 GPa, and decreased to 2.0 K at 41 GPa. This behavior is similar to that of CaC6, albeit with a lower maximum T-c. Xray diffraction patterns were measured under high pressures of 0-24 GPa, and suggest a structural transition at 15 GPa. Evidence is given for superconducting graphite involving binary metal intercalation. (C) 2016 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.carbon.2016.01.071

Correlation of superconductivity with crystal structure in (NH3)(y)CsxFeSe 査読

Lu Zheng, Xiao Miao, Yusuke Sakai, Hidenori Goto, Eri Uesugi, Ritsuko Eguchi, Saki Nishiyama, Kunihisa Sugimoto, Akihiko Fujiwara, Yoshihiro Kubozono

PHYSICAL REVIEW B 93 ( 10 ) 2016年3月

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

The superconducting transition temperature T-c of ammoniated metal-doped FeSe (NH3)(y)MxFeSe (M: metal atom) has been scaled with the FeSe plane spacing, and it has been suggested that the FeSe plane spacing depends on the location of metal atoms in (NH3)(y)MxFeSe crystals. Although the crystal structure of (NH3)(y)LixFeSe exhibiting a high T-c (similar to 44 K) was determined from neutron diffraction, the structure of (NH3)(y)MxFeSe exhibiting a low T-c (similar to 32 K) has not been determined thus far. Here, we determined the crystal structure of (NH3)(y)Cs0.4FeSe (T-c = 33 K) through the Rietveld refinement of the x-ray diffraction (XRD) pattern measured with synchrotron radiation at 30 K. The XRD pattern was analyzed based on two different models, on-center and off-center, under a space group of 14/mmm. In the on-center structure, the Cs occupies the 2a site and the N of NH3 may occupy either the 4c or 2b site, or both. In the off-center structure, the Cs may occupy either the 4c or 2b site, or both, while the N occupies the 2a site. Only an on-center structure model in which the Cs occupies the 2a and the N of NH3 occupies the 4c site provided reasonable results in the Rietveld analysis. Consequently, we concluded that (NH3)(y)Cs0.4FeSe can be assigned to the on-center structure, which produces a smaller FeSe plane spacing leading to the lower T-c.

DOI： 10.1103/PhysRevB.93.104508

Synthesis and transistor application of the extremely extended phenacene molecule, [9] phenacene 査読

Yuma Shimo, Takahiro Mikami, Shino Hamao, Hidenori Goto, Hideki Okamoto, Ritsuko Eguchi, Shin Gohda, Yasuhiko Hayashi, Yoshihiro Kubozono

SCIENTIFIC REPORTS 6 2016年2月

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

the widespread interest in the chemistry, physics and materials science of such molecules and their potential applications. In particular, extended phenacene molecules, consisting of coplanar fused benzene rings in a repeating W-shaped pattern have attracted much attention because field-effect transistors (FETs) using phenacene molecules show promisingly high performance. Until now, the most extended phenacene molecule available for transistors was [8] phenacene, with eight benzene rings, which showed very high FET performance. Here, we report the synthesis of a more extended phenacene molecule, [9] phenacene, with nine benzene rings. Our synthesis produced enough [9] phenacene to allow the characterization of its crystal and electronic structures, as well as the fabrication of FETs using thin-film and single-crystal [9] phenacene. The latter showed a field-effect mobility as high as 18 cm(2) V-1 s(-1), which is the highest mobility realized so far in organic single-crystal FETs.

DOI： 10.1038/srep21008

Application of organic semiconductors toward transistors 査読

Yoshihiro Kubozono, Xuexia He, Shino Hamao, Eri Uesugi, Yuma Shimo, Takahiro Mikami, Hidenori Goto, Takashi Kambe

Nanodevices for Photonics and Electronics: Advances and Applications 351 - 383 2016年1月

Emergence of Multiple Superconducting Phases in (NH3)(y)MxFeSe (M: Na and Li) 査読

Lu Zheng, Xiao Miao, Yusuke Sakai, Masanari Izumi, Hidenori Goto, Saki Nishiyama, Eri Uesugi, Yuichi Kasahara, Yoshihiro Iwasa, Yoshihiro Kubozono

SCIENTIFIC REPORTS 5 2015年8月

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

We previously discovered multiple superconducting phases in the ammoniated Na-doped FeSe material, (NH3)(y)NaxFeSe. To clarify the origin of the multiple superconducting phases, the variation of T-c was fully investigated as a function of x in (NH3)(y)NaxFeSe. The 32 K superconducting phase is mainly produced in the low-x region below 0.4, while only a single phase is observed at x = 1.1, with T-c = 45 K, showing that the T-c depends significantly on x, but it changes discontinuously with x. The crystal structure of (NH3)(y)NaxFeSe does not change as x increases up to 1.1, i.e., the space group of I4/mmm. The lattice constants, a and c, of the low-T-c phase (T-c = 32.5 K) are 3.9120(9) and 14.145(8) angstrom, respectively, while a = 3.8266(7) angstrom and c = 17.565(9) angstrom for the high-T-c phase (similar to 46 K). The c increases in the high T-c phase, implying that the T-c is directly related to c. In (NH3)(y)LixFeSe material, the T-c varies continuously within the range of 39 to 44 K with changing x. Thus, the behavior of T-c is different from that of (NH3)(y)NaxFeSe. The difference may be due to the difference in the sites that the Na and Li occupy.

DOI： 10.1038/srep12774

1D and 2D Bi Compounds in Field-Effect Transistors 査読

Eri Uesugi, Saki Nishiyama, Hidehiko Akiyoshi, Hidenori Goto, Yoji Koike, Kazuyoshi Yamada, Yoshihiro Kubozono

ADVANCED ELECTRONIC MATERIALS 1 ( 8 ) 2015年8月

Superconductivity in aromatic hydrocarbons 査読

Yoshihiro Kubozono, Hidenori Goto, Taihei Jabuchi, Takayoshi Yokoya, Takashi Kambe, Yusuke Sakai, Masanari Izumi, Lu Zheng, Shino Hamao, Huyen L. T. Nguyen, Masafumi Sakata, Tomoko Kagayama, Katsuya Shimizu

PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS 514 199 - 205 2015年7月

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

'Aromatic hydrocarbon' implies an organic molecule that satisfies the (4n + 2) pi-electron rule and consists of benzene rings. Doping solid aromatic hydrocarbons with metals provides the superconductivity. The first discovery of such superconductivity was made for K-doped picene (K(x)picene, five benzene rings). Its superconducting transition temperatures (T-c's) were 7 and 18 K. Recently, we found a new superconducting K(x)picene phase with a T-c as high as 14 K, so we now know that K(x)picene possesses multiple superconducting phases. Besides K(x)picene, we discovered new superconductors such as Rb(x)picene and Caxpicene. A most serious problem is that the shielding fraction is <= 615% for K(x)picene and Rb(x)picene, and it is often similar to 1% for other superconductors. Such low shielding fractions have made it difficult to determine the crystal structures of superconducting phases. Nevertheless, many research groups have expended a great deal of effort to make high quality hydrocarbon superconductors in the five years since the discovery of hydrocarbon superconductivity. At the present stage, superconductivity is observed in certain metaldoped aromatic hydrocarbons (picene, phenanthrene and dibenzopentacene), but the shielding fraction remains stubbornly low. The highest priority research area is to prepare aromatic superconductors with a high superconducting volume-fraction. Despite these difficulties, aromatic superconductivity is still a core research target and presents interesting and potentially breakthrough challenges, such as the positive pressure dependence of T-c that is clearly observed in some phases of aromatic hydrocarbon superconductors, suggesting behavior not explained by the standard BCS picture of superconductivity. In this article, we describe the present status of this research field, and discuss its future prospects. (C) 2015 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physc.2015.02.015

Emergence of double-dome superconductivity in ammoniated metal-doped FeSe 査読

Masanari Izumi, Lu Zheng, Yusuke Sakai, Hidenori Goto, Masafumi Sakata, Yuki Nakamoto, Huyen L. T. Nguyen, Tomoko Kagayama, Katsuya Shimizu, Shingo Araki, Tatsuo C. Kobayashi, Takashi Kambe, Dachun Gu, Jing Guo, Jing Liu, Yanchun Li, Liling Sun, Kosmas Prassides, Yoshihiro Kubozono

SCIENTIFIC REPORTS 5 2015年4月

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

The pressure dependence of the superconducting transition temperature (T-c) and unit cell metrics of tetragonal (NH3)(y)Cs0.4FeSe were investigated in high pressures up to 41 GPa. The T-c decreases with increasing pressure up to 13 GPa, which can be clearly correlated with the pressure dependence of c (or FeSe layer spacing). The T-c vs. c plot is compared with those of various (NH3)(y)MxFeSe (M: metal atoms) materials exhibiting different T-c and c, showing that the T-c is universally related to c. This behaviour means that a decrease in two-dimensionality lowers the T-c. No superconductivity was observed down to 4.3 K in (NH3)(y)Cs0.4FeSe at 11 and 13 GPa. Surprisingly, superconductivity re-appeared rapidly above 13 GPa, with the T-c reaching 49 K at 21 GPa. The appearance of a new superconducting phase is not accompanied by a structural transition, as evidenced by pressure-dependent XRD. Furthermore, T-c slowly decreased with increasing pressure above 21 GPa, and at 41 GPa superconductivity disappeared entirely at temperatures above 4.9 K. The observation of a double-dome superconducting phase may provide a hint for pursuing the superconducting coupling-mechanism of ammoniated/non-ammoniated metal-doped FeSe.

DOI： 10.1038/srep09477

Erratum: Transistor application of new picene-type molecules, 2,9-dialkylated phenanthro[1,2-b:8,7-b′]dithiophenes (Journal of Materials Chemistry C (2015) 3 DOI: 10.1039/c4tc02413c) 査読

Yoshihiro Kubozono, Keita Hyodo, Hiroki Mori, Shino Hamao, Hidenori Goto, Yasushi Nishihara

Journal of Materials Chemistry C 3 ( 12 ) 2960 2015年3月

Transistor application of new picene-type molecules, 2,9-dialkylated phenanthro[1,2-b:8,7-b ']dithiophenes 査読

Yoshihiro Kubozono, Keita Hyodo, Hiroki Mori, Shino Hamao, Hidenori Goto, Yasushi Nishihara

JOURNAL OF MATERIALS CHEMISTRY C 3 ( 10 ) 2413 - 2421 2015年

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

Field-effect transistors (FETs) have been fabricated with thin films of a series of 2,9-dialkylated phenanthro [1,2-b:8,7-b'] dithiophene derivatives (C-n-PDTs). The FET characteristics of C-n-PDT thin-film FETs with an SiO2 gate dielectric as well as high-k gate dielectrics were recorded, and the dependence of the field-effect mobility, mu, on the number (n) of carbon atoms in the alkyl chains was investigated, showing that the 2,9-didodecylphenanthro[1,2-b:8,7-b'] dithiophene (C-12-PDT) thin-film FET displays superior properties, with mu s as high as 1.8 cm(2) V-1 s(-1) for the SiO2 gate dielectric and 2.2 cm(2) V-1 s(-1) for the HfO2 gate dielectric. The average mu values, <mu >, reach 1.1(5) and 1.8(6) cm(2) V-1 s(-1), respectively, for the SiO2 and ZrO2 gate dielectrics. Low-voltage operation, showing an absolute average threshold voltage <|V-th|> of similar to 11 V, was implemented, together with the above high <mu > of similar to 2 cm(2) V-1 s(-1). Also, a flexible FET was fabricated with a parylene gate dielectric. The results of this study show the potential of the C-12-PDT molecule for application in a high-performance transistor.

DOI： 10.1039/c4tc02413c

Transistors fabricated using the single crystals of [8]phenacene 査読

Yuma Shimo, Takahiro Mikami, Hiroto T. Murakami, Shino Hamao, Hidenori Goto, Hideki Okamoto, Shin Gohda, Kaori Sato, Antonio Cassinese, Yasuhiko Hayashi, Yoshihiro Kubozono

JOURNAL OF MATERIALS CHEMISTRY C 3 ( 28 ) 7370 - 7378 2015年

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

Field-effect transistors (FETs) with single crystals of a new phenacene-type molecule, [8]phenacene, were fabricated and characterized. This new molecule consists of a phenacene core of eight benzene rings, with an extended p-conjugated system, which was recently synthesized for use in an FET by our group. The FET characteristics of an [8]phenacene single-crystal FET with SiO2 gate dielectrics show typical p-channel properties with an average field-effect mobility, <mu >, as high as 3(2) cm(2) V-1 s(-1) in two-terminal measurement mode, which is a relatively high value for a p-channel single-crystal FET. The hmi was determined to be 6(2) cm(2) V-1 s(-1) in four-terminal measurement mode. Low-voltage operation was achieved with PbZr0.52Ti0.48O3 (PZT) as the gate dielectric, and an electric-double-layer (EDL) capacitor. The <mu > and average values of absolute threshold voltage, <vertical bar V-th vertical bar >, were 1.6(4) cm(2) V-1 s(-1) and 5(1) V, respectively, for PZT, and 4(2) x 10(-1) cm(2) V-1 s(-1) and 2.38(4) V, respectively, for the EDL capacitor; these values were evaluated in two-terminal measurement mode. The inverter circuit was fabricated using [8]phenacene and N, N'-1H, 1H-perfluorobutyldicyanoperylene-carboxydi-imide single-crystal FETs. This is the first logic gate circuit using phenacene molecules. Furthermore, the relationship between mu and the number of benzene rings was clarified based on this study and the previous studies on phenacene single-crystal FETs.

DOI： 10.1039/c5tc00960j

Transistor application of new picene-type molecules, 2,9-dialkylated phenanthro[1,2-b:8,7-b '] dithiophenes (vol 3, pg 2413, 2015) 査読

Yoshihiro Kubozono, Keita Hyodo, Hiroki Mori, Shino Hamao, Hidenori Goto, Yasushi Nishihara

JOURNAL OF MATERIALS CHEMISTRY C 3 ( 12 ) 2960 - 2960 2015年

Transistor Application of Phenacene Molecules and Their Characteristics 査読

Yoshihiro Kubozono, Xuexia He, Shino Hamao, Kazuya Teranishi, Hidenori Goto, Ritsuko Eguchi, Takashi Kambe, Shin Gohda, Yasushi Nishihara

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY ( 24 ) 3806 - 3819 2014年8月

記述言語：英語出版者・発行元：WILEY-V C H VERLAG GMBH

The characteristics of field-effect transistors (FETs) fabricated from thin films and single crystals of phenacene molecules are fully reported in this review together with the electronic and crystal structures of phenacenes. Phenacene molecules possess a low HOMO level and a wide band gap. The highest mobility observed in the phenacene thin-film FETs is 7.4 cm(2)V(-1)s(-1) for [6]phenacene, and in single-crystal FETs the highest value is 6.3 cm(2)V(-1)s(-1) for [7]phenacene. The phenacene thin-film FETs show O-2-sensing properties unlike their single-crystal FETs. The bias-stress effect is fully investigated for phenacene single-crystal FETs. Furthermore, the low-voltage operation of phenacene single-crystal FETs with electric-double-layer (EDL) capacitors is reported. The temperature dependence of phenacene single-crystal FETs is reported to clarify the transport mechanism, which is suggestive of band-like transport.

DOI： 10.1002/ejic.201402168

An Extended Phenacene-type Molecule, [8] Phenacene: Synthesis and Transistor Application 査読

Hideki Okamoto, Ritsuko Eguchi, Shino Hamao, Hidenori Goto, Kazuma Gotoh, Yusuke Sakai, Masanari Izumi, Yutaka Takaguchi, Shin Gohda, Yoshihiro Kubozono

SCIENTIFIC REPORTS 4 2014年6月

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

A new phenacene-type molecule, [8] phenacene, which is an extended zigzag chain of coplanar fused benzene rings, has been synthesised for use in an organic field-effect transistor (FET). The molecule consists of a phenacene core of eight benzene rings, which has a lengthy pi-conjugated system. The structure was verified by elemental analysis, solid-state NMR, X-ray diffraction (XRD) pattern, absorption spectrum and photoelectron yield spectroscopy (PYS). This type of molecule is quite interesting, not only as pure chemistry but also for its potential electronics applications. Here we report the physical properties of [8] phenacene and its FET application. An [8] phenacene thin-film FET fabricated with an SiO2 gate dielectric showed clear p-channel characteristics. The highest m achieved in an [8] phenacene thin-film FET with an SiO2 gate dielectric is 1.74 cm(2) V-1 s(-1), demonstrating excellent FET characteristics; the average mu was evaluated as 1.2(3) cm(2) V-1 s(-1). The mu value in the [8] phenacene electric-double-layer FET reached 16.4 cm(2) V-1 s(-1), which is the highest reported in EDL FETs based on phenacene-type molecules; the average m was evaluated as 8(5) cm(2) V-1 s(-1). The mu values recorded in this study show that [8] phenacene is a promising molecule for transistor applications.

DOI： 10.1038/srep05330

Transistor application of alkyl-substituted picene 査読

Hideki Okamoto, Shino Hamao, Hidenori Goto, Yusuke Sakai, Masanari Izumi, Shin Gohda, Yoshihiro Kubozono, Ritsuko Eguchi

SCIENTIFIC REPORTS 4 2014年5月

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

Field-effect transistors (FETs) were fabricated with a thin film of 3,10-ditetradecylpicene, picene-(C14H29)(2), formed using either a thermal deposition or a deposition from solution (solution process). All FETs showed p-channel normally-off characteristics. The field-effect mobility, m, in a picene-(C14H29)(2) thin-film FET with PbZr0.52Ti0.48O3 (PZT) gate dielectric reached similar to 21 cm(2) V-1 s(-1), which is the highest mu value recorded for organic thin-film FETs; the averagem mu value (<mu >) evaluated from twelve FET devices was 14(4) cm(2)V(-1) s(-1). The, m. values for picene-(C14H29)(2) thin- film FETs with other gate dielectrics such as SiO2, Ta2O5, ZrO2 and HfO2 were greater than 5 cm(2) V-1 s(-1), and the lowest absolute threshold voltage, vertical bar V-th vertical bar, (5.2 V) was recorded with a PZT gate dielectric; the average jVthj for PZT gate dielectric is 7(1) V. The solution-processed picene-(C14H29)(2) FET was also fabricated with an SiO2 gate dielectric, yielding mu = 3.4 x 10(-2) cm(2) V-1 s(-1). These results verify the effectiveness of picene-(C14H29)(2) for electronics applications.

DOI： 10.1038/srep05048

Superconducting phases in (NH3)(y)MxFeSe1-zTez (M = Li, Na, and Ca) 査読

Yusuke Sakai, Lu Zheng, Masanari Izumi, Kazuya Teranishi, Ritsuko Eguchi, Hidenori Goto, Taiki Onji, Shingo Araki, Tatsuo C. Kobayashi, Yoshihiro Kubozono

PHYSICAL REVIEW B 89 ( 14 ) 2014年4月

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

Superconducting phases of (NH3)(y)MxFeSe1-z Te-z have been synthesized by the intercalation of metal atoms (M: Li, Na, Ca) into FeSe and FeSe0.5Te0.5 using a low-temperature liquid NH3 technique. The superconducting transition temperature (T-c) is 31.5 K for Na-doped FeSe, and for Li-, Na-, and Ca-doped FeSe0.5Te0.5 it is 26, 22, and 17 K, respectively. The 31.5 K superconducting is the superconducting phase in ammoniated Na-doped FeSe. The T-c is lower than that (onset T-c = 46 K) of the superconducting phase reported previously. The reason why the T-c of this phase is lower is discussed based on the structure. The pressure dependences of T-c in the (NH3)(y)Na0.5FeSe and (NH3)(y)Na0.4FeSe0.5Te0.5 samples have been measured and a negative pressure dependence is observed; i.e., a decrease in lattice constant c leads to a decrease in Tc, consistent with the behavior of (NH3)(y)Cs0.4FeSe reported previously by our group. Furthermore, the magnetic behavior of (NH3)(y)Na0.4FeSe0.5Te0.5 has been fully investigated at different applied magnetic fields (H) to determine the critical magnetic This is a successful metal intercalation into FeSe1-z Te-z (z not equal 0) and an observation of superconductivity.

DOI： 10.1103/PhysRevB.89.144509

Superconducting phases in (NH3)(y)MxFeSe1-zTez (M = Li, Na, and Ca) 査読

Sakai Yusuke, Zheng Lu, Izumi Masanari, Teranishi Kazuya, Eguchi Ritsuko, Goto Hidenori, Onji Taiki, Araki Shingo, Kobayashi Tatsuo C, Kubozono Yoshihiro

PHYSICAL REVIEW B 89 ( 14 ) 144509 2014年4月

Systematic Control of Hole-Injection Barrier Height with Electron Acceptors in [7]phenacene Single-Crystal Field-Effect Transistors 査読

Xuexia He, Shino Hamao, Ritsuko Eguchi, Hidenori Goto, Yukihiro Yoshida, Gunzi Saito, Yoshihiro Kubozono

JOURNAL OF PHYSICAL CHEMISTRY C 118 ( 10 ) 5284 - 5293 2014年3月

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

The interface between the single crystal and the Au source/drain electrodes in [7]phenacene single-crystal field-effect transistors (FETs) was modified using 14 electron acceptors with different redox potentials. The effective hole-injection barrier heights (phi(eff)(h)s) for [7]phenacene single-crystal FETs have been plotted as a function of the redox potential (E-redox) of the inserted electron acceptors, showing that the phi(eff)(h) decreases with increasing E-redox. The highest phi(eff)(h) occurs without inserted material (electron acceptors), and this deviates from the otherwise linear relationship between phi(eff)(h) and E-redox. We have investigated the temperature dependence of phi(eff)(h) in an attempt to determine why the phi(eff)(h) value without inserted material is so high, which suggests that no additional barrier, such as a tunneling barrier, is formed in the device. We conclude that the pure Schottky barrier in this FET is lowered very significantly by the insertion of an electron acceptor. The gate-voltage dependence of phi(eff)(h) suggests a slight reduction of Schottky barrier height owing to hole accumulation. Furthermore, the clear correlation between threshold voltage and redox potential suggests a relationship between threshold voltage and phi(eff)(h). Controlling the interface between the single crystal and the source/drain electrodes in this FET produced a very high mu (similar to 6.9 cm(2) V-1 s(-1)) and low absolute threshold voltage, i.e., excellent FET characteristics. The topological characterization of inserted materials on [7]phenacene single crystals are achieved using atomic force microscope (AFM) and X-ray diffraction (XRD). The results show that the single crystals are not completely covered with the inserted materials and the inhomogeneous modification of inserted materials for single crystals effectively leads to the drastic change of hole-injection barrier between source/drain electrodes and single-crystal active layer.

DOI： 10.1021/jp4107469

Superconductivity in (NH3)yCs0.4FeSe 査読

Lu Zheng, Masanari Izumi, Yusuke Sakai, Ritsuko Eguchi, Hidenori Goto, Yasuhiro Takabayashi, Takashi Kambe, Taiki Onji, Shingo Araki, Tatsuo C. Kobayashi, Jungeun Kim, Akihiko Fujiwara, Yoshihiro Kubozono

Physical Review B - Condensed Matter and Materials Physics 88 ( 9 ) 2013年9月

記述言語：英語掲載種別：研究論文（学術雑誌）

Alkali-metal-intercalated FeSe materials, (NH3) yM0.4FeSe (M: K, Rb, and Cs), have been synthesized using the liquid NH3 technique. (NH3)yCs 0.4FeSe shows a superconducting transition temperature (T c) as high as 31.2 K, which is higher by 3.8 K than the Tc of nonammoniated Cs0.4FeSe. The Tcs of (NH 3)yK0.4FeSe and (NH3) yRb0.4FeSe are almost the same as those of nonammoniated K0.4FeSe and Rb0.4FeSe. The Tc of (NH 3)yCs0.4FeSe shows a negative pressure dependence. A clear correlation between Tc and lattice constant c is found for ammoniated metal-intercalated FeSe materials, suggesting a correlation between Fermi-surface nesting and superconductivity. © 2013 American Physical Society.

DOI： 10.1103/PhysRevB.88.094521

Fabrication of single crystal field-effect transistors with phenacene-type molecules and their excellent transistor characteristics 査読

Xuexia He, Ritsuko Eguchi, Hidenori Goto, Eri Uesugi, Shino Hamao, Yasuhiro Takabayashi, Yoshihiro Kubozono

ORGANIC ELECTRONICS 14 ( 6 ) 1673 - 1682 2013年6月

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

Single crystal field-effect transistors (FETs) using [6] phenacene and [7] phenacene show p-channel FET characteristics. Field-effect mobilities, mu s, as high as 5.6 x 10 (1) cm(2) V (1) s (1) in a [6] phenacene single crystal FET with an SiO2 gate dielectric and 2.3 cm(2) V (1) s (1) in a [7] phenacene single crystal FET were recorded. In these FETs, 7,7,8,8-tetracyanoquinodimethane (TCNQ) was inserted between the Au source/drain electrodes and the single crystal to reduce hole-injection barrier heights. The mu reached 3.2 cm(2) V (1) s (1) in the [7] phenacene single crystal FET with a Ta2O5 gate dielectric, and a low absolute threshold voltage vertical bar V-TH vertical bar (6.3 V) was observed. Insertion of 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F(4)TCNQ) in the interface produced very a high mu value (4.7-6.7 cm(2) V (1) s (1)) in the [7] phenacene single crystal FET, indicating that F(4)TCNQ was better for interface modification than TCNQ. A single crystal electric double-layer FET provided mu as high as 3.8 x 10 (1) cm(2) V (1) s (1) and vertical bar V-TH vertical bar as low as 2.3 V. These results indicate that [6] phenacene and [7] phenacene are promising materials for future practical FET devices, and in addition we suggest that such devices might also provide a research tool to investigate a material's potential as a superconductor and a possible new way to produce the superconducting state. (C) 2013 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.orgel.2013.03.035

Observation of zero resistivity in K-doped picene 査読

Teranishi Kazuya, He Xuexia, Sakai Yusuke, Izumi Masanari, Goto Hidenori, Eguchi Ritsuko, Takabayashi Yasuhiro, Kambe Takashi, Kubozono Yoshihiro

PHYSICAL REVIEW B 87 ( 6 ) 06505 2013年2月

Observation of zero resistivity in K-doped picene 査読

Kazuya Teranishi, Xuexia He, Yusuke Sakai, Masanari Izumi, Hidenori Goto, Ritsuko Eguchi, Yasuhiro Takabayashi, Takashi Kambe, Yoshihiro Kubozono

PHYSICAL REVIEW B 87 ( 6 ) 2013年2月

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

We report the observation of zero resistivity (rho) in a hydrocarbon superconductor, and describe the temperature dependence of rho in metal-doped hydrocarbons. The resistivity of K-doped picene (K(x)picene) has been recorded from pellet samples in a four-terminal measurement mode. A drop in rho is observed below 7 K for K(3.1)picene and below 11 K for K(3.5)picene, which clearly displays zero resistivity. The resistivity drop at 7 K is consistent with the superconducting critical temperature (T-c) obtained from the magnetic susceptibility of the 7 K phase of K(3)picene, while the drop at 11 K is inconsistent with the T-c's of both the 7 and 18 K phases of K(3)picene reported previously. The temperature dependence of rho for both samples exhibits granular-metal-like behavior in the normal state. DOI: 10.1103/PhysRevB.87.060505

DOI： 10.1103/PhysRevB.87.060505

Phenanthro[1,2-b: 8,7-b '] dithiophene: a new picene-type molecule for transistor applications 査読

Yasushi Nishihara, Megumi Kinoshita, Keita Hyodo, Yasuhiro Okuda, Ritsuko Eguchi, Hidenori Goto, Shino Hamao, Yasuhiro Takabayashi, Yoshihiro Kubozono

RSC ADVANCES 3 ( 42 ) 19341 - 19347 2013年

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

A new picene-type molecule, phenanthro[1,2-b : 8,7-b'] dithiophene, has been synthesized for use in organic field-effect transistors (OFETs). The molecule consists of a phenanthrene core with two thiophene rings fused on the ends. This molecule can be recognized as a picene analogue. The electronic structure of the molecule was determined by its optical absorption spectrum together with a theoretical calculation based on density functional theory (DFT). The topological and electronic structures of thin films produced by direct thermal evaporation of the compounds and by deposition from a solution were characterized by optical imaging, X-ray diffraction, and atomic force microscopy. FET devices were fabricated with these thin films, and showed field-effect mobility as high as 10(-1) cm(2) V-1 s(-1).

DOI： 10.1039/c3ra44050h

Fabrication of high performance/highly functional field-effect transistor devices based on [6]phenacene thin films 査読

Ritsuko Eguchi, Xuexia He, Shino Hamao, Hidenori Goto, Hideki Okamoto, Shin Gohda, Kaori Sato, Yoshihiro Kubozono

PHYSICAL CHEMISTRY CHEMICAL PHYSICS 15 ( 47 ) 20611 - 20617 2013年

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

Field-effect transistors (FETs) based on [6]phenacene thin films were fabricated with SiO2 and parylene gate dielectrics. These FET devices exhibit field-effect mobility in the saturation regime as high as 7.4 cm(2) V-1 s(-1), which is one of the highest reported values for organic thin-film FETs. The two- and four-probe mobilities in the linear regime display nearly similar values, suggesting negligible contact resistance at 300 K. FET characteristics were investigated using two-probe and four-probe measurement modes at 50-300 K. The two-probe mobility of the saturation regime can be explained by the multiple shallow trap and release model, while the intrinsic mobility obtained by the four-probe measurement in the linear regime is better explained by the phenomenon of transport with charge carrier scattering at low temperatures. The FET device fabricated with a parylene gate dielectric on polyethylene terephthalate possesses both transparency and flexibility, implying feasibility of practical application of [6] phenacene FETs in flexible/transparent electronics. N-channel FET characteristics were also achieved in the [6] phenacene thin-film FETs using metals that possess a small work function for use as source/drain electrodes.

DOI： 10.1039/c3cp53598c

Electric-double-layer transistors with thin crystals of FeSe_1-xTe_x (x = 0.9 and 1.0) 査読

R. Eguchi, M. Senda, E. Uesugi, H. Goto, T. Kambe, T. Noji, Y. Koike, A. Fujiwara, Y. Kubozono

Appl. Phys. Lett. 102 103506-1 - 103506-4 2013年

Synthesis and physical properties of metal-doped picene solids 査読

Takashi Kambe, Xuexia He, Yosuke Takahashi, Yusuke Yamanari, Kazuya Teranishi, Hiroki Mitamura, Seiji Shibasaki, Keitaro Tomita, Ritsuko Eguchi, Hidenori Goto, Yasuhiro Takabayashi, Takashi Kato, Akihiko Fujiwara, Toshikaze Kariyado, Hideo Aoki, Yoshihiro Kubozono

PHYSICAL REVIEW B 86 ( 21 ) 2012年12月

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

We report electronic-structure and physical properties of metal-doped picene as well as selective synthesis of the phase that exhibits 18-K superconducting transition. First, Raman scattering is used to characterize the number of electrons transferred from the dopants to picene molecules, where a softening of Raman scattering peaks enables us to determine the number of transferred electrons. From this, we have identified that three electrons are transferred to each picene molecule in the superconducting doped picene solids. Second, we report pressure dependence of T-c in 7- and 18-K phases of K(3)picene. The 7-K phase shows a negative pressure dependence, while the 18-K phase exhibits a positive pressure dependence which can not be understood with a simple phonon mechanism of BCS superconductivity. Third, we report a synthesis method for superconducting K(3)picene by a solution process with monomethylamine CH3NH2. This method enables us to prepare selectively the K(3)picene sample exhibiting 18-K superconducting transition. The method for preparing K(3)picene with T-c = 18 K found here may facilitate clarification of the mechanism of superconductivity.

DOI： 10.1103/PhysRevB.86.214507

O-2-exposure and light-irradiation properties of picene thin film field-effect transistor: A new way toward O-2 gas sensor 査読

Yasuyuki Sugawara, Keiko Ogawa, Hidenori Goto, Shuhei Oikawa, Kouki Akaike, Noriko Komura, Ritsuko Eguchi, Yumiko Kaji, Shin Gohda, Yoshihiro Kubozono

SENSORS AND ACTUATORS B-CHEMICAL 171 544 - 549 2012年8月

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

Transistor characteristics and O-2 gas sensing properties are investigated for picene thin film field-effect transistors (FETs) with ZrO2, Ta2O5, HfO2 and BaxSr1-xTiO3 (x = 0.4). The low-voltage operation is achieved using the above oxides with high gate dielectric constant, contrary to SiO2 gate dielectric. The O-2 gas sensing is achieved at 11 s intervals without any bias stress by an application of pulse drain and gate voltages (V-D and V-G), in contrast to previous result in which the O-2 gas sensing was performed at least at 1 h step because of bias stress effect. The actual O-2 sensing-speed in the picene thin film FET was similar to 10 s for 3.8 Torr O-2, and the O-2 sensing limit was concluded to be 0.15-0.38 Torr. Furthermore, it has been found that the O-2 sensing properties are observed only under irradiation of light with wavelength below 400 nm. From the result, we have presented two scenarios for O-2 sensing mechanism in picene thin film FET. (C) 2012 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.snb.2012.05.030

Characteristics of [6]phenacene thin film field-effect transistor 査読

Noriko Komura, Hidenori Goto, Xuexia He, Hiroki Mitamura, Ritsuko Eguchi, Yumiko Kaji, Hideki Okamoto, Yasuyuki Sugawara, Shin Gohda, Kaori Sato, Yoshihiro Kubozono

APPLIED PHYSICS LETTERS 101 ( 8 ) 2012年8月

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

Transistor characteristics are studied for field-effect transistors (FETs) with thin films of [6]phenacene, which has six benzene rings and W-shape structure. The molecular alignment preferable for FET transport is found to be formed in [6]phenacene thin films. The transistor shows clear p-channel FET characteristics with field-effect mobility mu as high as 3.7 cm(2) V-1 s(-1). The similar O-2 sensing properties to picene FET are observed in [6]phenacene thin film FET. The bias stress properties are observed in [6]phenacene thin film FET. The pulse-voltage application suppresses the bias-stress effect and it enables a continuous O-2 sensing in [6]phenacene FET. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4747201]

DOI： 10.1063/1.4747201

Characteristics of Single Crystal Field-Effect Transistors with a New Type of Aromatic Hydrocarbon, Picene 査読

Nobuyuki Kawai, Ritsuko Eguchi, Hidenori Goto, Kouki Akaike, Yumiko Kaji, Takashi Kambe, Akihiko Fujiwara, Yoshihiro Kubozono

JOURNAL OF PHYSICAL CHEMISTRY C 116 ( 14 ) 7983 - 7988 2012年4月

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

Picene is a phenacene-type aromatic hydrocarbon molecule with five benzene rings. We have fabricated picene single crystal (SC) field-effect transistors (FETs) with solid gate and ionic liquid gate dielectrics. Although the picene SC FET showed a large hole-injection barrier without any modification of interface between source/drain electrodes and picene SC, such a large hole-injection barrier could be effectively reduced by modifying the interface with tetracyanoquinodimethane (TCNQ). Picene SC FET with an HfO2 gate dielectric and TCNQ:coated electrodes shows p-channel characteristics with a smooth hole injection and a field-effect mobility more than 1 cm(2) V-1 s(-1) in two-terminal measurement. Picene SC FET could be operated even in bottom-contact structure by modifying the interface with octanethiol. Furthermore, picene SC FET operated with ionic liquid gate dielectric, [1-butyl-3-methylimidazolium][hexafluorophosphate], showing the field-effect mobility of 1.8 X 10(-1) cm(2) V-1 s(-1) and low absolute value, 1.9 V, of threshold voltage.

DOI： 10.1021/jp300052p

Characteristics of conjugated hydrocarbon based thin film transistor with ionic liquid gate dielectric 査読

Yumiko Kaji, Keiko Ogawa, Ritsuko Eguchi, Hidenori Goto, Yasuyuki Sugawara, Takashi Kambe, Koki Akaike, Shin Gohda, Akihiko Fujiwara, Yoshihiro Kubozono

ORGANIC ELECTRONICS 12 ( 12 ) 2076 - 2083 2011年12月

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

Thin film transistors (TFTs) with ionic liquid gate dielectrics, [1-ethyl-3-methylimidazolium][bis(trifluoromethanesulfonyl) imide] (emim[TFSI]) and [1-butyl-3-methylimidazolium][hexafluorophosphate] (bmim[PF6]), are fabricated with thin films of one dimensional (1D) hydrocarbon, [7]phenacene. P-channel characteristics are observed for [7] phenacene TFTs with both ionic liquids by use of platinum electrode. The field-effect mobility mu for [7]phenacene TFT with bmim[PF6] was recorded to be 0.28 cm(2) V-1 s(-1). The value of absolute threshold voltage, vertical bar V-TH vertical bar, was less than 2.5 V, showing low-voltage operation. The accumulation of hole in the [7]phenacene TFTs with ionic liquids was confirmed from the voltage or time dependence of capacitance in metal-insulator-semiconductor structure, which shows that these TFTs operate electrochemically and the carriers are accumulated in the whole of [7]phenacene thin films. (C) 2011 Elsevier B. V. All rights reserved.

DOI： 10.1016/j.orgel.2011.08.016

Introducing Nonuniform Strain to Graphene Using Dielectric Nanopillars 査読

Hikari Tomori, Akinobu Kanda, Hidenori Goto, Youiti Ootuka, Kazuhito Tsukagoshi, Satoshi Moriyama, Eiichiro Watanabe, Daiju Tsuya

APPLIED PHYSICS EXPRESS 4 ( 7 ) 2011年7月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：JAPAN SOC APPLIED PHYSICS

A method for inducing nonuniform strain in graphene films is developed. Pillars made of a dielectric material (electron beam resist) are placed between graphene and the substrate, and graphene sections between pillars are attached to the substrate. The strength and spatial pattern of the strain can be controlled by the size and separation of the pillars. Application of strain is confirmed by Raman spectroscopy as well as from scanning electron microscopy (SEM) images. From SEM images, the maximum stretch of the graphene film reaches about 20%. This technique can be applied to the formation of band gaps in graphene. (C) 2011 The Japan Society of Applied Physics

DOI： 10.1143/APEX.4.075102

Fabrication of ultrashort graphene Josephson junctions 査読

Tomori H, Kanda A, Goto H, Takana S, Ootuka Y, Tsukagoshi K

Physica C: Superconductivity 470 ( 20 ) 1492 - 1495 2010年

Effect of current annealing on electronic properties of multilayer graphene 査読

Tanaka S, Goto H, Tomori H, Ootuka Y, Tsukagoshi K, Kanda A

Journal of Physics: Conference Series 232 ( 1 ) 012015 2010年

Dependence of proximity-induced supercurrent on junction length in multilayer-graphene Josephson junctions 査読

Kanda A, Sato T, Goto H, Tomori H, Takana S, Ootuka Y, Tsukagoshi K

Physica C: Superconductivity 470 ( 20 ) 1477 - 1480 2010年

Inverse spin valve effect in multilayer graphene device 査読

Goto H, Tanaka S, Tomori H, Ootuka Y, Tsukagoshi K, Kanda A

Journal of Physics: Conference Series 232 ( 1 ) 012002 2010年

Inter-layer screening length to electric field in thin graphite film 査読

Hisao Miyazaki, Shunsuke Odaka, Takashi Sato, Sho Tanaka, Hidenori Goto, Akinobu Kanda, Kazuhito Tsukagoshi, Youiti Ootuka, Yoshinobu Aoyagi

APPLIED PHYSICS EXPRESS 1 ( 3 ) 2008年3月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：JAPAN SOC APPLIED PHYSICS

Electric conduction in thin graphite film was tuned by two gate electrodes to clarify how the gate electric field induces electric carriers in thin graphite. The graphite was sandwiched between two gate electrodes arranged in a top and bottom gate configuration. A scan of the top gate voltage generates a resistance peak in ambiploar response. The ambipolar peak is shifted by the bottom gate voltage, where the shift rate depends on the graphite thickness. The thickness-dependent peak shift was clarified in terms of the inter-layer screening length to the electric field in the double-gated graphite film. The screening length of 1.2 nm was experimentally obtained. (C) 2008 The Japan Society of Applied Physics.

DOI： 10.1143/APEX.1.034007

Coulomb blockade oscillations in narrow corrugated graphite ribbons 査読

Hisao Miyazaki, Shunsuke Odaka, Takashi Sato, Sho Tanaka, Hidenori Goto, Akinobu Kanda, Kazuhito Tsukagoshi, Youiti Ootuka, Yoshinobu Aoyagi

APPLIED PHYSICS EXPRESS 1 ( 2 ) 2008年2月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：JAPAN SOC APPLIED PHYSICS

We report Coulomb blockade oscillations in an atomically thin graphite ribbon fabricated by the micromechanical cleavage technique. Aperiodic current oscillations as a function of the gate voltage indicate the formation of multiple Coulomb islands inside the thin graphite ribbon. We conclude that the Coulomb islands originate from puddles of electrons and holes caused by the inhomogeneous interface between the ribbon and the substrate. (C) 2008 The Japan Society of Applied Physics.

DOI： 10.1143/APEX.1.024001

A different type of reentrant behavior in superconductor/thin graphite film/superconductor Josephson junctions 査読

Sato T, Kanda A, Moriki T, Goto H, Tanaka S, Ootuka Y, Miyazaki H, Odaka S, Tsukagoshi K, Aoyagi Y

Physica C: Superconductivity and its applications 468 ( 7 ) 797 2008年

Gate-controlled superconducting proximity effect in ultrathin graphite films 査読

Sato T, Moriki T, Tanaka S, Kanda A, Goto H, Miyazaki H, Odaka S, Ootuka Y, Tsukagoshi K, Aoyagi Y

Physica E: Low-dimensional Systems and Nanostructures 40 ( 5 ) 1495 2008年

Observation of gate-controlled superconducting proximity effect in microfabricated thin graphite films 査読

Sato T, Kanda A, Tanaka S, Goto H, Ootuka Y, Miyazaki H, Odaka S, Tsukagoshi K, Aoyagi Y

Journal of Physics: Conference Series 109 ( 1 ) 012031 2008年

Observation of vortex expulsion in mesoscopic superconducting disks 査読

H. Goto, K. Kono

Physica E: Low-Dimensional Systems and Nanostructures 40 ( 2 ) 339 - 342 2007年12月

記述言語：英語掲載種別：研究論文（学術雑誌）

We have studied vortex expulsion processes in a superconducting disk with a multi-terminal Hall sensor. Various combinations of these terminals enabled us to obtain an angular dependence of magnetization in the disk. The resolution of π/4 allowed us to identify three vortices. With a decrease in magnetic fields, vortices were expelled one by one from the different edges. After each expulsion the residual vortices were reconfigured in a complicated way. Their equilibrium positions changed with lowering temperatures. These results are interpreted in terms of repulsively interacting particles in the confinement and the pinning potential. The latter potential is found to be important at low temperatures. © 2007 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physe.2007.06.021

Magnetic response of a mesoscopic superconducting disk surrounded by a normal metal 査読

Hidenori Goto, Kazuhito Tsukagoshi, Kimitoshi Kono

LOW TEMPERATURE PHYSICS, PTS A AND B 850 753 - + 2006年

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）出版者・発行元：AMER INST PHYSICS

Magnetic response of a superconductor/normal-metal (S/N) concentric disk is studied by use of a ballistic Hall magnetometer, which enables us to investigate the mutual proximity effects in a single and a micrometer-sized sample. The core of the sample is a type-I superconductor whose diameter is comparable to the coherence length and the magnetic penetration depth. The core and the surround are prepared by an improved double-angle evaporation method to realize their metallic contacts. At T = 1.3 K, the pair breaking effect on the S has been predominant. We have observed the smaller diamagnetic susceptibility, the larger critical field, and the less stable vortex states in the S/N sample than in only S sample. These results are attributed to the suppression of the surface superconductivity, which effectively decreases the diameter of the superconductor.

DOI： 10.1063/1.2354923

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