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4. Structure of Bi2Rh3Se2 above and below charge density wave transition determined by Bi Lα and Lγ X-ray fluorescence holography.

Author

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

Abstract

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. [ABSTRACT FROM AUTHOR]

Published
2024
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7. Nanophase Separation in K1–xCaxC8 Revealed by X-ray Fluorescence Holography and Extended X-ray Absorption Fine Structure

Author

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

Published
2024
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10. Pressure Dependence of the Structural and Superconducting Properties of the Bi-Based Superconductor Bi2Pd3Se2

Author

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

Published
2024
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11. Investigation on synthesis and physical properties of metal doped picene solids

Author

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

Subjects
Condensed Matter - Superconductivity
Abstract

We report electronic structure and physical properties of metal doped picene as well as selective synthesis of the phase exhibiting 18 K superconducting transition. First, Raman scattering is used to characterize the number of electrons transferred from the dopants to picene molecules. The charge transfer leads to a softening of Raman scattering peaks, which 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 the pressure dependence of Tc in 7 and 18 K phases of K3picene. The 7 K phase shows a negative pressure-dependence, while the 18 K phase exhibits a positive pressure-dependence which cannot be understood with a simple phonon mechanism of BCS superconductivity. Third, we report a new synthesis method for superconducting K3picene by a solution process with monomethylamine, CH3NH2. This method enables one to prepare selectively the K3picene sample exhibiting 18 K superconducting transition. The discovery of suitable way for preparing K3picene with Tc = 18 K may facilitate clarification of the mechanism of superconductivity., Comment: 18 pages, 2 tables, 8 figures

Published
2012
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12. Introducing Nonuniform Strain to Graphene Using Dielectric Nanopillars

Author

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

Subjects
Condensed Matter - Mesoscale and Nanoscale Physics
Abstract

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., Comment: Appl. Phys. Express, in press

Published
2011
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15. Inter-Layer Screening Length to Electric Field in Thin Graphite Film

Author

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

Subjects
Condensed Matter - Mesoscale and Nanoscale Physics, Condensed Matter - Materials Science
Abstract

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., Comment: 5 pages, 4 figures. To be published in Applied Physics Express

Published
2008
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18. Nanophase Separation in K1–xCaxC8Revealed by X-ray Fluorescence Holography and Extended X-ray Absorption Fine Structure

Author

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

Abstract

Even at low Ca concentrations, the binary-element intercalated graphite K1–xCaxC8exhibits high superconducting transition temperatures Tc, closer to that of CaC6(11.5 K) than KC8(0.169 K). To investigate the behaviors of K and Ca within the graphite matrix, their local structures have been investigated by using X-ray fluorescence holography and extended X-ray absorption fine structure (EXAFS) spectroscopy. The atomic images reconstructed from the K–Kα and Ca–Kβ holograms showed that K0.7Ca0.3C8did not take the solid-solution type random distribution of Ca and K atoms; instead, a nanoscale phase separation of CaC6and KC8was observed, which was also supported by the EXAFS results. While the lattice constant of K0.7Ca0.3C8was close to that of KC8, we found a nanoscale Ca layer dispersed within the sample. The Ca nanolayer was offset from the center between the C sublayers. The superconducting behavior found in K1–xCaxC8was discussed with two scenarios of percolation of CaC6and deformation of graphene based on such a specific inhomogeneous binary element monatomic layers. This study represents an important step for understanding the superconducting properties in a nanoscale phase-separated system.

Published
2024
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23. Pressure Dependence of Superconductivity in Alkaline Earth Metal-Doped FeSe: toward Completion of the Phase Diagram of Superconducting Transition Temperature Versus FeSe Layer Distance

Author

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

Published
2023
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25. Multiple-site Ag doping in Bi2Se3: Compositional crossover from substitution to intercalation as revealed by photoelectron diffraction and X-ray fluorescence holography

Author

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

Published
2023
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26. Photoelectron Holographic Atomic Arrangement Imaging of Cleaved Bimetal-intercalated Graphite Superconductor Surface

Author

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

Abstract

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)C8, 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 Å and 5.7 Å 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 × 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)C8 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.

Published
2023

27. Observation of the Superstructure in Fe5–xGeTe2by X-ray Fluorescence Holography

Author

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

Abstract

Fe5–xGeTe2is a two-dimensional van der Waals material that exhibits ferromagnetic order with a high Curie temperature (TC) of around room temperature. In addition to TC, two magnetic transitions occur with decreasing temperature, and a charge-ordered state is observed at low temperatures. We employed Ge Kα X-ray fluorescence holography (XFH) for Fe5–xGeTe2to directly investigate the local structure in the charge-ordered state, i.e., the 3×3superstructure. The Ge Kα XFH results revealed local atomic structures around the Ge atom, thus clarifying the simultaneous locations and arrangements of the Te, Fe, and Ge atoms. The atomic positions relative to the Ge atom are useful for understanding the coexistence of the ideal 1 × 1 structure and 3×3superstructure found in the charge-ordered state.

Published
2024
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33. Superconductivity in aromatic hydrocarbons

Author

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

Published
2015
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35. Relationship between Kita-Kyushu Lung Cancer antigen-1 expression and prognosis of cases with lung squamous cell carcinoma

Author

Ichiki, Yoshinobu, Fukuyama, Takashi, Ohmiya, Haruki, Ueno, Mari, Yanagi, Shinya, Kanasaki, Yoshiro, Goto, Hidenori, Mikami, Shuji, Yamazaki, Hitoshi, Nakanishi, Kozo, and Ishida, Tsuyoshi

Subjects
Kita-Kyushu Lung Cancer antigen-1 (KK-LC-1), Cancer Research, Oncology, programmed cell death protein ligand-1 (PD-L1), Original Article, Radiology, Nuclear Medicine and imaging, tumor immunology, Lung cancer, cytotoxic T lymphocyte (CTL)
Abstract

Background Previously, we identified the highly immunogenic cancer testicular antigen named Kita-Kyushu Lung Cancer antigen-1 (KK-LC-1). In this study, we analyzed the effect of KK-LC-1 expression on the prognosis of patients with resected squamous cell lung cancer. Methods Fifty squamous cell lung cancer patients, who received complete resection, were enrolled in this study. The expressions of KK-LC-1, CD8, human leukocyte antigen (HLA) class I, and programmed cell death protein ligand-1 (PD-L1) were assessed via immunohistochemistry staining using the specimens obtained from the participants. The association between the expression of the abovementioned molecules and patient prognosis was investigated. Results KK-LC-1 expression was observed in 21 of 50 recruited cases (42%). However, no significant correlation was found between KK-LC-1 expression and patient prognosis. The prognosis was significantly better in lung cancer cases with KK-LC-1 expression in which CD8+ T cells infiltrated the tumor. Regardless of the HLA class I expression or the PD-L1 expression, the KK-LC-1 expression in squamous cell lung cancer could not be detected as a significant prognostic factor. Furthermore, considering the polarity of the cancer tissue as epithelium, staining of KK-LC-1 tended to be strong in the area corresponding to the basal side of the tumor tissue. The Ki-67 expression was frequently observed in cancer cells on the basal side, which was consistent with the KK-LC-1 expression in representative four cases with KK-LC-1-positive squamous cell lung cancer. Conclusions Our results indicated that lung squamous cell cancer patients with KK-LC-1 expression and the tumor infiltrating CD8+ T cells might exhibit better prognosis. KK-LC-1 might be highly expressed in cancer cells with high proliferative capacity. Larger cohort analysis is still required for further elucidation and validation of the results of this study.

Published
2021
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37. Elucidation of the Local Structure of the Topological Insulator β-PdBi2 by X-ray Fluorescence Holography

Author

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

Published
2022
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41. Structural Characterization of Graphite Analogue BCxSynthesized Under Various Conditions and Its Application to Ti Intercalation

Author

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

Abstract

A graphite-like material boron carbide (BCx) was synthesized under various heat treatment conditions and extensively characterized. First, we synthesized the BCxprecursor phase by a single-step reaction using a mixed solution of BBr3and C6H6. We confirmed that the precursor phase had a graphite-like structure with B–C chemical bonds, but its crystallinity was poor. To improve their crystallinity, we annealed the precursor sample at high temperature using a high-frequency furnace and determined the annealing condition. We also investigated the magnetic properties of BCx. The high-temperature annealing for the precursor phase yields the highest Pauli paramagnetic susceptibility χPauli, indicating the highest density of states at the Fermi level. Accordingly, the high-temperature treatment for the precursor phase is significant to improve its crystallinity and physical properties. In addition, we synthesized a Ti-intercalated material TiBC by using the same procedure as that for making the BCxprecursor phase. The crystal structure can be indexed by the AlB2structure, indicating that Ti atoms are intercalated between the BC layers. The χPaulivalue of TiBC is obtained to be 1 order of magnitude smaller than that of BCx, suggesting the compensation of hole carriers by electron doping through Ti intercalation into the BCxsystem.

Published
2023
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44. Evaluation of Effective Field-Effect Mobility in Thin-Film and Single-Crystal Transistors for Revisiting Various Phenacene-Type Molecules

Author

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

Abstract

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.

Published
2022

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