研究者データベース

研究者情報

マスター

アカウント(マスター)

  • 氏名

    島田 敏宏(シマダ トシヒロ), シマダ トシヒロ

所属(マスター)

  • 工学研究院 応用化学部門 無機材料化学分野

所属(マスター)

  • 工学研究院 応用化学部門 無機材料化学分野

独自項目

syllabus

  • 2020, 大学院共通授業科目(一般科目):自然科学・応用科学, Inter-Graduate School Classes(General Subject):Natural and Applied Sciences, 修士課程, 大学院共通科目, electronic materials and devices, thermoelectrics, solar cells, hard materials, solid state physics
  • 2020, 応用物質化学(機能固体材料化学), Applied Materials Chemistry (Functional Solid State Materials Chemistry), 修士課程, 総合化学院, electronic materials and devices, thermoelectrics, solar cells, hard materials, solid state physics
  • 2020, 実践的計算化学, Practical Computational Chemistry, 修士課程, 総合化学院, 計算化学、理論化学、分子軌道法、密度汎関数法
  • 2020, 大学院共通授業科目(一般科目):自然科学・応用科学, Inter-Graduate School Classes(General Subject):Natural and Applied Sciences, 修士課程, 大学院共通科目, X線結晶構造解析,電子顕微鏡,中性子回折,X線吸収分光,固体NMR
  • 2020, 物質構造解析学特論, Structural Analysis of Inorganic Materials, 修士課程, 工学院, X線結晶構造解析,電子顕微鏡,中性子回折,X線吸収分光,固体NMR
  • 2020, 物質構造解析学特論, Structural Analysis of Inorganic Materials, 修士課程, 総合化学院, X線結晶構造解析,電子顕微鏡,中性子回折,X線吸収分光,固体NMR
  • 2020, 先端総合化学特論Ⅱ, Modern Trends in Chemical Sciences and Engineering II, 博士後期課程, 総合化学院, electronic materials and devices, thermoelectrics, solar cells, hard materials, solid state physics
  • 2020, 物質構造解析学特論, Structural Analysis of Inorganic Materials, 博士後期課程, 工学院, X線結晶構造解析,電子顕微鏡,中性子回折,X線吸収分光,固体NMR
  • 2020, 化学Ⅰ, Chemistry I, 学士課程, 全学教育, 原子の構造、原子軌道、化学結合、混成軌道、物質の三態、電解質溶液
  • 2020, 物性化学, Materials Physical Chemistry, 学士課程, 工学部, 熱力学・統計力学 量子力学 電磁気学 機能材料 生体機能
  • 2020, 固体化学, Solid State Chemistry, 学士課程, 工学部, 無機固体、結晶、構造、配位化学、物性
  • 2020, 物質変換工学, Applied Chemistry and Biochemistry, 学士課程, 工学部, 有機合成,有機材料,化学プロセス,反応器設計,生体材料,高分子材料,分子機能,無機材料,複合材料,電子材料,光機能材料

timetable

  • 修士課程, 総合化学院, 2020, 応用物質化学A(機能固体化学)

PositionHistory

  • 評価室室員, 2014年7月1日, 2016年6月30日
  • 評価室室員, 2016年7月1日, 2018年6月30日
  • 大学院総合化学院副学院長, 2020年4月1日, 2022年3月31日

researchmap

プロフィール情報

学位

  • 博士(理学)(東京大学)

プロフィール情報

  • プロフィール

    2010年4月から北海道大学・大学院工学研究院・物質化学部門・固体反応化学研究室
  • 島田, シマダ
  • 敏宏, トシヒロ
  • ID各種

    201201076448891313

対象リソース

業績リスト

研究キーワード

  • エピタキシ-   有機半導体   炭素材料   結晶成長   エピタキシャル成長   酸化物   層状物質   光電子分光   

研究分野

  • ものづくり技術(機械・電気電子・化学工学) / 電子デバイス、電子機器
  • ナノテク・材料 / 結晶工学
  • ナノテク・材料 / 応用物性
  • ナノテク・材料 / ナノマイクロシステム
  • ナノテク・材料 / ナノ材料科学
  • ナノテク・材料 / ナノバイオサイエンス
  • ナノテク・材料 / ナノ材料科学
  • ナノテク・材料 / ナノ構造物理
  • ナノテク・材料 / ナノ構造化学

経歴

  • 2010年04月 - 現在 北海道大学 工学(系)研究科(研究院) 教授
  • 2000年04月 - 2010年03月 東京大学 准教授
  • 1998年10月 - 2000年03月 東京大学 講師
  • 1993年11月 - 1998年10月 東京大学 助手

委員歴

  • 2013年04月 - 現在   日本化学会   Chemistry Letters編集委員
  • 2013年04月 - 現在   日本セラミックス協会   部会地区幹事
  • 2009年04月 - 現在   電気学会   調査研究委員会委員長/幹事
  • 2018年11月 - 2019年10月   SSDM   Area Vice Chair
  • 2016年11月 - 2018年10月   SSDM   Area Chair
  • 2013年04月 - 2017年03月   応用物理学会   分科会幹事
  • 2007年04月 - 2009年03月   応用物理学会   分科代表プログラム委員・講演会企画運営委員

論文

  • Hiroki Takehana, Ichiro Yamane, Takashi Yanase, Taro Nagahama, Toshihiro Shimada
    Carbon 182 585 - 592 2021年09月
  • Ichiro Yamane, Kota Sato, Ryoichi Otomo, Takashi Yanase, Akira Miura, Taro Nagahama, Yuichi Kamiya, 島田 敏宏
    Nanomaterials 11 4 1040 - 1040 2021年04月
  • Meijun Yang, Sunan Bai, Qingfang Xu, Jun Li, Toshihiro Shimada, Qizhong Li, Takashi Goto, Rong Tu, Song Zhang
    DIAMOND AND RELATED MATERIALS 109 2020年11月 
    High-crystalline diamond films were prepared by laser (wavelength: 532 nm) microwave plasma chemical vapor deposition (Laser MPCVD). The effects of laser power density (E) on the microstructure and properties of diamond films were investigated. The laser enhanced the precursor reaction process which reduces the non-diamond components such as graphite and amorphous carbon. At E = 40 W/cm(2), more methyl radicals and atomic hydrogen were generated with coupling of laser and plasma, which promoted crystal growth until the grain size reaches the maximum value of 0.72 mu m. The phase purity of film reached the highest as the full width at half maximum (FWHM) of Raman peak reached the minimum of FWHMmin = 4.2 cm(-1). And hardness (H) and Young's modulus (M) values reached the maximum of H-max = 91 GPa and M-ma(x) = 721 GPa, respectively. The discovery of the advantages of laser in diamond growth is of great significance for improving the synthesis of many technically crucial materials.
  • Takashi Yanase, Fumiya Uehara, Itsuki Naito, Taro Nagahama, Toshihiro Shimada
    ACS APPLIED NANO MATERIALS 3 10 10462 - 10469 2020年10月 
    Developing a technology to terminate chalcogen vacancies for transition-metal dichalcogenides is a crucial task for applications, such as transistors, diodes, and sensors, because chalcogen vacancies degrade the electronic and optical properties. This article reports a healing method of S vacancies in MoS2 by high-pressure annealing under a S vapor pressure of 5 atm. The crystal quality after mechanical transfer, S annealing, and vacuum annealing was systematically studied by observing the photoluminescence (PL). The remarkable recovery of the A-exciton emission peak in the PL spectrum indicated repair of the crystal quality in MoS2 by the S annealing. We also demonstrated that the S vacancies could be terminated by Se atoms using a high-pressure annealing method. The crystal quality of MoS2(1-x)Se2x alloys was confirmed by transmission electron microscopy and electron diffraction.
  • Asaka Tsujie, Yoshinori Hara, Takashi Yanase, Toshihiro Shimada, Taro Nagahama
    Applied Physics Letters 116 23 232404 - 232404 2020年06月08日
  • Wei Liu, Takashi Yanase, Nobuhiro Iwasa, Shin Mukai, Shinichiro Iwamura, Taro Nagahama, Toshihiro Shimada
    Journal of Colloid and Interface Science 567 369 - 378 2020年05月 [査読有り][通常論文]
  • Wei Liu, Takashi Yanase, Nobuhiro Iwasa, Hitoshi Koizumi, Shin Mukai, Shinichiro Iwamura, Taro Nagahama, Toshihiro Shimada
    International Journal of Hydrogen Energy 45 15 8444 - 8455 2020年03月 [査読有り][通常論文]
  • Takashi Yanase, Uika Ogihara, Yoshihiro Awashima, Takeshi Yanagida, Kazuki Nagashima, Taro Nagahama, Toshihiro Shimada
    CRYSTAL GROWTH & DESIGN 19 12 7257 - 7263 2019年12月 [査読有り][通常論文]
     
    Single-crystal Fe nanowires (NWs) were synthesized on SiO2/Si substrates by chemical vapor deposition (CVD) using a two-flow system in the presence of FeO nanoparticles as catalysts. Transmission electron microscopy observations and an electron diffraction analysis revealed that the NW was defect-free alpha-Fe (bcc structure) oriented in the < 100 > direction. A plausible mechanism of the Fe NW growth is suggested based on the observations of the morphology and characteristic diameter of the Fe NW. We found that the NWs became polycrystalline when their diameter was approximately 100 nm. The excellent crystal quality of the single-crystal NW was confirmed by electron diffraction and the residual resistance ratio. Magnetic uniformity and a strong shape-anisotropic behavior of magnetization were observed by measuring the hysteresis loop and the angle dependence of the magneto-optical Kerr effect, respectively.
  • FeOナノ粒子触媒によるMoS2ナノチューブのCVD成長と評価
    柳瀬 隆, Weng Mengting, Zhang Meiqi, 後藤真菜美, 長浜太郎, 島田 敏宏
    表面と真空 2019年10月 [査読有り][通常論文]
  • Characterization of magnetic properties of ultrathin CoFe2O4 films by utilizing magnetic proximity effect
    S. Nodo, T. Yamamoto, T. Yanase, T. Shimada, T. Nagahama
    Solid State Communications in press 2019年09月 [査読有り][通常論文]
  • Wei Liu, Nobuhiro Iwasa, Shinichiro Fujita, Hitoshi Koizumi, Makoto Yamaguchi, Toshihiro Shimada
    Applied Surface Science 2019年09月 [査読有り][通常論文]
  • Takashi Yanase, Takuya Miura, Tatsuya Shiratori, Mengting Weng, Taro Nagahama, Toshihiro Shimada
    C 5 3 46 - 46 2019年08月08日 [査読有り][通常論文]
     
    The choice of a catalyst for carbon nanotube (CNT) growth is critical to controlling the morphology and chirality of the final product. Plasma-enhanced chemical vapor deposition (PECVD) can alleviate the requirements of the catalyst, i.e., they must be active for both the decomposition of the source gas and graphitization in the conventional thermal CVD. However, it is still not well understood how the catalytic activity of the graphitization affects the yield and quality of CNTs. In this paper, we systematically investigated the influence of the catalytic activity of graphitization by tuning the composition of Fe1-xMnxO (x = 0-1) nanoparticles as catalysts. As the Mn component increased, the number of CNTs decreased because Mn has no catalytic function of the graphitization. The quality of CNTs also affected by the inclusion of the Mn component. Our study may provide useful information to develop a new catalyst for CNT growth in PECVD.
  • Y. Goto, T. Yanase, T. Shimada, M. Shirai, T. Nagahama
    AIP Advances 9 085322  2019年08月 [査読有り][通常論文]
  • Study on the requirements of catalytic function for the growth of carbon nanotubes by plasma-enhanced chemical vapor deposition
    Takashi Yanase, Takuya Miura, Tatsuya Shiratori, Mengting Weng, Taro Nagahama, Toshihiro Shimada
    C: Journal of Carbon Research 5 3 46 - 46 2019年08月 [査読有り][通常論文]
  • Wei Liu, Takashi Yanase, Taro Nagahama, Toshihiro Shimada
    Journal of Alloys and Compounds 792 1206 - 1212 2019年07月 [査読有り][通常論文]
  • さまざまな面指数を持つcBN表面のナノインデンテーション
    田村貴大, Roman Nowak, 高倉洋礼, 島田敏宏
    New Diamond 35 3 20 - 21 2019年06月 [査読有り][通常論文]
  • Ichiro Yamane, Takashi Yanase, Taro Nagahama, Toshihiro Shimada
    JAPANESE JOURNAL OF APPLIED PHYSICS 58 2019年04月 [査読有り][通常論文]
     
    Synthesis under high pressure is a powerful technique to obtain novel materials. We here report ultrahigh pressure experiments to search for new nitrogen-doped carbon materials. Crystalline powders of organic molecules with nitrogen atoms are used as precursors. After high pressure treatment at room temperature, precursor molecules underwent oligomerization accompanied by transformation from sp(2)-hybridization carbon atoms to sp(3) ones. (C) 2019 The Japan Society of Applied Physics
  • Single crystal growth, structural analysis and electronic band structure of a nitrogen-containing polyacene BBQPP
    Nobuhiko Sakai, Takahiro Tamura, Takashi Yanase, Taro Nagahama, Toshihiro Shimada
    Japanese Journal of Applied Physics 58 in press  2019年04月 [査読有り][通常論文]
  • Synthesis of metastable B2-type Fe–Sn alloy epitaxial films and study of their magnetic properties
    Yuki Goto, Masato Araki, Nozomi Takahashi, Takashi Yanase, Toshihiro Shimada, Masahito Tsujikawa, Masafumi Shirai, Akira Kamimaki, Satoshi Iihama, Shigemi Mizukami, Taro Nagahama
    Japanese Journal of Applied Physics 57 120302 - 120302 2018年10月 [査読有り][通常論文]
  • Catalytic chemical vapor deposition and structural analysis of MoS2 nanowires
    Mengting Weng, Meiqi Zhang, Takashi Yanase, Fumiya Uehara, Taro Nagahama, Toshihiro Shimada
    Japanese Journal of Applied Physics 2018年04月 [査読有り][通常論文]
  • Wei Xie, Takahiro Tamura, Takashi Yanase, Taro Nagahama, Toshihiro Shimada
    Japanese Journal of Applied Physics 57 4 2018年04月01日 [査読有り][通常論文]
     
    The effect of C doping to hexagonal boron nitride (h-BN) to its electronic structure is examined by first principles calculations using the association from π-electron systems of organic molecules embedded in a two-dimensional insulator. In a monolayered carbon-doped structure, odd-number doping with carbon atoms confers metallic properties with different work functions. Various electronic interactions occur between two layers with odd-number carbon substitution. A direct sp3 covalent chemical bond is formed when C replaces adjacent B and N in different layers. A charge transfer complex between layers is found when C replaces B and N in the next-neighboring region, which results in narrower band gaps (e.g., 0.37 eV). Direct bonding between C and B atoms is found when two C atoms in different layers are at a certain distance.
  • Takashi Yanase, Hiroaki Uwabe, Koki Hasegawa, Taro Nagahama, Makoto Yamaguchi, Toshihiro Shimada
    JAPANESE JOURNAL OF APPLIED PHYSICS 57 3 2018年03月 [査読有り][通常論文]
     
    We synthesized semitransparent conducting thin films of amorphous carbon from sp(3)-rich network polymer. The films showed a reasonable optical transparency (58-73% transmission in the wavelength range of 380-2200 nm), a low electric resistivity (6.7 x 10(-3) Omega cm), and durability against corrosive chemical reagents. The sintering of the amorphous films results in the formation of a carbon honeycomb lattice in the films. (C) 2018 The Japan Society of Applied Physics
  • Takashi Yanase, Sho Watanabe, Fumiya Uehara, Mengting Weng, Taro Nagahama, Toshihiro Shimada
    THIN SOLID FILMS 649 171 - 176 2018年03月 [査読有り][通常論文]
     
    The doping of element (Nb, Ta, etc.) into MoS2, one of the layered transition metal dichalcogenides, is a key technology for electronic devices because the lack of the p-type MoS2 has limited the range of applications. We report that the Mo1-xNbxS2 thin films were synthesized on SiO2/Si substrates by chemical vapor deposition (CVD). It was critical to use chloride sources ( MoCl5 and NbCl5) for the synthesis of Mo1-xNbxS2. The Nb concentration can be increased to 10% by controlling the supplied amount of Nb using a separate-flow CVD apparatus. The Raman spectra changed as the Nb concentration increased, appearing E-2(Nb-S) vibrational mode. The photoluminescence (PL) at 655 nm, attributed to emission from excitons, disappeared, when Nb was incorporated into the MoS2. PL due to trions at 680 nm was observed for the Mo1-xNbxS2 thin films.
  • Rong Tu, Tiantian Xu, Dengfeng Li, Song Zhang, Meijun Yang, Qizhong Li, Lianmeng Zhang, Toshihiro Shimada, Takashi Goto, Ji Shi
    RSC Advances 2018年
  • Nozomi Takahashi, Teodor Huminiuc, Yuta Yamamoto, Takashi Yanase, Toshihiro Shimada, Atsufumi Hirohata, Taro Nagahama
    Scientific Reports 7 1 7009 - 7009 2017年12月 [査読有り][通常論文]
  • Hideo Kaiju, Taro Nagahama, Shun Sasaki, Toshihiro Shimada, Osamu Kitakami, Takahiro Misawa, Masaya Fujioka, Junji Nishii, Gang Xiao
    Scientific Reports 7 1 2682  2017年12月 [査読有り][通常論文]
     
    Magnetocapacitance (MC) effect, observed in a wide range of materials and devices, such as multiferroic materials and spintronic devices, has received considerable attention due to its interesting physical properties and practical applications. A normal MC effect exhibits a higher capacitance when spins in the electrodes are parallel to each other and a lower capacitance when spins are antiparallel. Here we report an inverse tunnel magnetocapacitance (TMC) effect for the first time in Fe/AlOx/Fe3O4 magnetic tunnel junctions (MTJs). The inverse TMC reaches up to 11.4% at room temperature and the robustness of spin polarization is revealed in the bias dependence of the inverse TMC. Excellent agreement between theory and experiment is achieved for the entire applied frequency range and the wide bipolar bias regions using Debye-Frohlich model (combined with the Zhang formula and parabolic barrier approximation) and spin-dependent drift-diffusion model. Furthermore, our theoretical calculations predict that the inverse TMC effect could potentially reach 150% in MTJs with a positive and negative spin polarization of 65% and -42%, respectively. These theoretical and experimental findings provide a new insight into both static and dynamic spin-dependent transports. They will open up broader opportunities for device applications, such as magnetic logic circuits and multi-valued memory devices.
  • Kohei Fuchibe, Kento Shigeno, Nan Zhao, Hiromichi Aihara, Rikuo Akisaka, Toshiyuki Morikawa, Takeshi Fujita, Kie Yamakawa, Toshihiro Shimada, Junji Ichikawa
    JOURNAL OF FLUORINE CHEMISTRY 203 173 - 184 2017年11月 [査読有り][通常論文]
     
    Difluorinated polycyclic aromatic hydrocarbons (PAHs) containing three to five benzene rings were systematically synthesized by the Pd(II)-catalyzed Friedel-Crafts-type cyclization of 1,1,2-trifluoro- and 1,1-difluoro-1-alkenes and the In(III)-catalyzed tandem cyclization of bis(1,1-difluoroallene)s. Using an array of the di-fluorinated PAHs that were obtained and previously reported monofluorinated PAHs, the physical properties of the pinpoint-fluorinated PAHs were investigated. (i) The F-19 NMR signals of the bay-region fluorine atoms were shifted downfield by ca. 8-14 ppm for vic-difluorinated PAHs and ca. 11-19 ppm for non-vic-difludrinated and monofluorinated PAHs. (ii) The introduction of fluorine into PAH molecules increased their solubilities in organic solvents, which was best exemplified by the high solubilities of 6,7-difluoropicene (5.4 wt%) and 6-fluoropicene (5.3 wt%) in THF. (iii) The HOMO-LUMO energy gaps of the pinpoint-fluorinated PAHs were smaller than that of the corresponding fluorine-free PAH (i.e., picene) by 0.02-0.26 eV, and the HOMO and LUMO energy levels were lowered by 0.10-0.22 eV and 0.12-0.41 eV, respectively.
  • Akira Miura, Tsukasa Hokimoto, Masanori Nagao, Takashi Yanase, Toshihiro Shimada, Kiyoharu Tadanaga
    ACS omega 2 8 5271 - 5282 2017年08月31日 [査読有り][通常論文]
     
    The relationship of liquidus temperatures among six binary and four ternary phases in a Ag-Al-Sn-Zn system was analyzed by means of statistical modeling. Four statistical models to predict changes in the liquidus temperatures in Ag-Al-Sn-Zn were proposed on the basis of different hypotheses derived from macroscopic and microscopic standpoints. The results of interpolation tests to evaluate the prediction accuracies of the ternary liquidus temperatures suggested that the multivariate regression model based on binary liquidus temperatures, interactive binary liquidus temperatures, and products of atomic ratios was found to be the most effective among the four models. It was numerically shown that the prediction accuracies of the liquidus temperatures in local ternary systems of Ag-Al-Sn-Zn can be improved further by using the models identified in their neighboring systems. Finally, the possibility to extract the general trend and the abnormal combination of elements for the prediction of liquidus temperatures was discussed on the basis of the statistical framework we considered.
  • Weng Mengting, Takashi Yanase, Fumiya Uehara, Sho Watanabe, Takuya Miura, Taro Nagahama, Toshihiro Shimada
    CRYSTENGCOMM 19 28 3915 - 3920 2017年07月 [査読有り][通常論文]
     
    Nanowires of layered materials are important because they exhibit the highest sensitivity as electricallydetecting chemical sensors. MoS2 nanowires have been synthesized by a catalytic chemical vapor deposition method on silicon substrates drop-coated with FeO nanoparticles of different shapes. Switching of the products (MoS2 nanowires to SiO2 nanowires) has been observed when the shapes and sizes of the FeO nanoparticles changed. MoS2 nanowires were grown in the presence of six-horned octahedral nanoparticles, whereas SiO2 nanowires were formed in the presence of spherical nanoparticles. Their morphology, crystal structure and elemental composition have been fully investigated to elucidate the growth mechanism of the nanowires. The kinetics of the grown SiO2 and MoS2 nanowires are competing, giving rise to the observed switching.
  • Takahiro Tamura, Takuya Takami, Takashi Yanase, Taro Nagahama, Toshihiro Shimada
    JAPANESE JOURNAL OF APPLIED PHYSICS 56 6 2017年06月 [査読有り][通常論文]
     
    We studied the N-2 plasma etching of cubic boron nitride (cBN). We have developed experimental techniques for handling 200-mu m-size single crystals for the preparation of surfaces with arbitrary crystal indexes, plasma processes, and surface analyses. We successfully prepared smooth surfaces of cBN with roughness smaller than 10 nm and found that the etching behavior was strongly influenced by the surface indexes. The morphology of the etched surfaces can be explained by the chemical stability of (111)B surfaces. (C) 2017 The Japan Society of Applied Physics
  • K. Omori, T. Kawai, N. Takahashi, T. Yanase, T. Shimada, T. Nagahama
    Applied Physics Letters 110 21 212402 - 212402 2017年05月22日 [査読有り][通常論文]
     
    Fe3O4 possesses unique properties such as high Curie temperature and half-metallic nature and therefore can function as a high-spin-polarized electrode in spintronic devices. In order to use this compound in such devices, the magnetic characteristics of multilayers used in these devices, which include Fe3O4, should be highly controllable. In this study, we fabricated Fe3O4/Pt or Cr (0-10 nm)/Fe systems through epitaxial growth on MgO(110) substrates in order to investigate the magnetic coupling in Fe3O4 and metallic hybrid systems. We found that these two systems show a marked difference in the dependence of the coercive field (H-c) of the Fe layer on the nonmagneticmetal- layer thickness. Hc for the system with Pt showed variation characteristics of interlayer exchange coupling in metal systems, while H-c increased monotonically with the thickness of the Cr layer. Published by AIP Publishing.
  • Toshihiro Shimada, Takuya Miura, Wei Xie, Takashi Yanase, Taro Nagahama
    MEASUREMENT 102 244 - 248 2017年05月 [査読有り][通常論文]
     
    We report an accurate and easy-to operate instrument for the temperature control of an electrically floated sample using a thermocouple in direct contact with it. The signal was transmitted via 2.45 GHz WiFi. We measured and analyzed the discrepancy between the thermocouple and a radiation thermometer for the plasma CVD of carbon nanomaterials under sample bias. A successful protection method from abnormal discharge in the plasma is also provided. (C) 2017 Elsevier Ltd. All rights reserved.
  • Inverse Tunnel Magnetocapacitance in Fe/Al-oxide/Fe3O4
    Hideo Kaiju, Taro Nagahama, Shun Sasaki, Toshihiro Shimada, Osamu Kitakami, Takahiro Misawa, Masaya Fujioka, Junji Nishii, Gang Xiao
    Scientific Reports 7 2682 - 2682 2017年03月 [査読有り][通常論文]
  • N2 plasma etching processes of microscopic single crystals of cubic boron nitride
    Takahiro Tamura, Takuya Takami, Takashi Yanase, Taro Nagahama, Toshihiro Shimada
    Jpn. J. Appl. Phys. 56 06HF01  2017年03月 [査読有り][通常論文]
  • 島田敏宏, 柳瀬隆, 田村貴大, 高見拓哉, 伊髙健治
    表面科学 38 2017年02月 [査読有り][招待有り]
  • Weng Mengting, Takashi Yanase, Fumiya Uehara, Sho Watanabe, Takuya Miura, Taro Nagahama, Toshihiro Shimada
    CrystEngComm 19 28 3915 - 3920 2017年 [査読有り][通常論文]
     
    Nanowires of layered materials are important because they exhibit the highest sensitivity as electricallydetecting chemical sensors. MoS2 nanowires have been synthesized by a catalytic chemical vapor deposition method on silicon substrates drop-coated with FeO nanoparticles of different shapes. Switching of the products (MoS2 nanowires to SiO2 nanowires) has been observed when the shapes and sizes of the FeO nanoparticles changed. MoS2 nanowires were grown in the presence of six-horned octahedral nanoparticles, whereas SiO2 nanowires were formed in the presence of spherical nanoparticles. Their morphology, crystal structure and elemental composition have been fully investigated to elucidate the growth mechanism of the nanowires. The kinetics of the grown SiO2 and MoS2 nanowires are competing, giving rise to the observed switching.
  • Y. Nakano, T. Yanase, T. Nagahama, H. Yoshida, T. Shimada
    Scientific Reports 6 35408  2016年10月 [査読有り][通常論文]
     
    The water vapor transmission rate (WVTR) of a gas barrier coating is a critically important parameter for flexible organic device packaging, but its accurate measurement without mechanical stress to ultrathin films has been a significant challenge in instrumental analysis. At the current stage, no reliable results have been reported in the range of 10(-6) g m(-2) day(-1) that is required for organic light emitting diodes (OLEDs). In this article, we describe a solution for this difficult, but important measurement, involving enhanced sensitivity by a cold trap, stabilized temperature system, pumped sealing and calibration by a standard conductance element.
  • Takahiro Tamura, Takuya Takami, Sachio Kobayashi, Taro Nagahama, Takashi Yanase, Toshihiro Shimada
    Diamond and Related Materials 69 127 - 132 2016年10月 [査読有り][通常論文]
     
    This paper describes an attempt to synthesize bismuth-doped diamond by plasma CVD. Solid bismuth was inserted into the reaction plasma of CH4 and H-2. Examination by TEM showed that most of the bismuth was included as Bi nanoparticles in the carbon nanospheres, which segregated at the grain boundary of the diamond polycrystals. Diffraction peaks corresponding to the carbon allotrope Chaoite were observed at the grain boundaries. The Raman spectra showed very complex features between 100-1600 cm(-1), suggesting the existance of molecule-like species. (C) 2016 Elsevier B.V. All rights reserved.
  • Takashi Yanase, Sho Watanabe, Mengting Weng, Makoto Wakeshima, Yukio Hinatsu, Taro Nagahama, Toshihiro Shimada
    CRYSTAL GROWTH & DESIGN 16 8 4467 - 4472 2016年08月 [査読有り][通常論文]
     
    This article reports the growth and characterization of z-axis-oriented NbS2 thin films on SiO2/Si substrate by ambient pressure chemical vapor deposition (CVD) using a generic metal chloride source. We found that NbS2 nanosheets can be grown directly on the SiO2/Si substrate with the aid of hydrogen gas mixed in the carrier gas. Detailed examination Of the growth parameters was made possible using a separate-flow CVD apparatus. It appears that the major cause of the misorientation is the off-stoichiometry with surplus Nb. The quality of the films was evaluated by X-ray diffraction and Raman spectroscopy as well as resistivity measurements at low temperatures. They showed a resistivity minimum at the same temperature of the charge density wave (CDW) transition for a bulk single crystal of 3R-NbS2.
  • Takashi Yanase, Sho Watanabe, Mengting Weng, Taro Nagahama, Toshihiro Shimada
    JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY 16 4 3223 - 3227 2016年04月 [査読有り][通常論文]
     
    We report detailed experiments on chemical vapor deposition of an atomic layer semiconductor MoS2. We developed a new type of CVD system in which MoO3 and S sources are separately supplied to the substrates. It has become possible to precisely control the supply of the materials separately in the order of seconds. Raman and XPS analysis of the films grown under various conditions revealed that the initially obtained films are S-deficient and complete stoichiometry is reached after several minutes under S vapor flow.
  • 島田敏宏
    C: Journal of Carbon Research 2, 2(2016); doi:10.3390/c2010002 2 1 2 - 2 2016年01月29日 [査読有り][通常論文]
  • Nozomi Takahashi, Tomohiro Kawai, Takashi Yanase, Toshihiro Shimada, Taro Nagahama
    JAPANESE JOURNAL OF APPLIED PHYSICS 54 11 118003  2015年11月 [査読有り][通常論文]
     
    The combination of magnetic tunnel junctions (MTJs) and magnetic insulating (MI) layers has attracted much attention because of its potential as novel spintronic devices. To realize such devices, the epitaxial growth and magnetoresistance of MTJs with spinel ferrite were investigated. Nonmagnetic (NM) layers were inserted between the MTJs and MI layers as magnetic decoupling layers, the epitaxial growth of which was important to obtain high-quality epitaxial multilayers. Multilayers of MTJ/NM/MI and MI/NM/MTJ were fabricated and tunnel magnetoresistance (TMR) values of 70 and 50% at room temperature, respectively, were observed. The shape of the magnetoresistance curve depended on the sample structure. (C) 2015 The Japan Society of Applied Physics
  • Wei Xie, Aiko Kawahito, Takuya Miura, Takashi Endo, Yongming Wang, Takashi Yanase, Taro Nagahama, Yukitoshi Otani, Toshihiro Shimada
    CHEMISTRY LETTERS 44 9 1205 - 1207 2015年09月 [査読有り][通常論文]
     
    We report the synthesis of a new carbon material diamondlike carbon film codeposited with 1% C-60 molecules by plasma-assisted chemical vapor deposition. The synthesized films exhibited strong iridescent colors after being exposed to an atmosphere containing water vapor. An electron microscopy examination revealed that the film expanded by a factor of more than two, while forming 10-100-nm-sized grain-like structures after its exposure to water vapor. This work demonstrates a new concept of incorporating reaction centers in carbon solids to make carbon-based nanostructures.
  • 島田敏宏, 柳瀬隆, 長浜太郎
    電気学会論文C部門誌 135 2 164 - 167 2015年02月01日 [査読無し][通常論文]
     
    Charge storage devices in the film-base flexible electronics are very important for the application of those devices in daily life. In order to examine the recently reported solid state capacitor with ionizable charge traps, we present an analysis of an electrostatic model. It shows a charge-voltage characteristic resembling a chemical battery. While the energy density per charge is great in these devices, the energy density of the capacitor with ionizable traps will be lower than that of an ordinary capacitor with metal electrodes, assuming the same withstanding voltage and the same geometry.
  • Jeon, Il, Kutsuzawa, Dai, Hashimoto, Yu, Yanase, Takashi, Nagahama, Taro, Shimada, Toshihiro, Matsuo, Yutaka
    Organic Electronics 17 275 - 280 2015年 [査読有り][通常論文]
     
    We demonstrate the deposition of multilayered MoS2 on a low-cost metallic-semiconducting carbon nanotube via chemical vapor deposition, and the use of this material as electron acceptor species forming a bulk heterojunction with P3HT in inverted-type organic photovoltaics (OPVs). This is an uplifting discovery, in which MoS2 has been used as an electron acceptor in spite of its innate immiscibility with organic compounds. This is possible because we utilize carbon nanotube's nature to intercalate with P3HT through pi-pi interaction. The successful binding of MoS2 onto carbon nanotube bundles and its optoelectronic effect as a photovoltaic device has been lucidly analyzed through various techniques in this paper. The effect has been ultimately evidenced by a power conversion efficiency of 0.46%, which proves MoS2 with many advantages can also be used as a photoactive layer. (C) 2014 Elsevier B.V. All rights reserved.
  • 島田敏宏, 柳瀬隆, 長浜太郎
    電気学会論文C部門誌 135 2 164 - 167 2015年 [査読有り][通常論文]
     
    Charge storage devices in the film-base flexible electronics are very important for the application of those devices in daily life. In order to examine the recently reported solid state capacitor with ionizable charge traps, we present an analysis of an electrostatic model. It shows a charge-voltage characteristic resembling a chemical battery. While the energy density per charge is great in these devices, the energy density of the capacitor with ionizable traps will be lower than that of an ordinary capacitor with metal electrodes, assuming the same withstanding voltage and the same geometry.
  • 島田敏宏, 柳瀬隆, 長浜太郎, 土田裕也, 村谷直紀
    電気学会論文C部門誌 135 2 160 - 163 2015年 [査読有り][通常論文]
     
    Frontier Chemistry Center, Hokkaido University Kita 13, Nishi 8, Kita-ku, Sapporo 060-8628, Japan Graduate School of Chemical Sciences and Engineering, Hokkaido University Kita 13, Nishi 8, Kita-ku, Sapporo 060-8628, Japan Flexible solar cells made of organic semiconductors are promising for the application to the photovoltaic energy sources for flexible devices and those can be attached to any curved surfaces. Mixing and phase separation of different molecules are important for the formation of bulk-hetero junctions. We found that DNTT (dinaphtotienothiophene) and C60 spontaneously mixes when they are sequentially deposited. The driving force does not seem to be the charge transfer between p-type and n-type molecules but the maximization of van der Waals attraction coming from the molecular shapes.
  • Kawahito, A, Yanase, T, Endo, T, Nagahama, T, Shimada, T
    Journal of Applied Physics 117 17 17D506/1 - 17D506/4 2015年 [査読有り][通常論文]
     
    Magnetic nanowires (NWs) are promising as material for use in spintronics and as the precursor of permanent magnets because they have unique properties due to their high aspect ratio. The growth of magnetic Fe whiskers was reported in the 1960s, but the diameter was not on a nanoscale level and the growth mechanism was not fully elucidated. In the present paper, we report the almost vertical growth of Fe NWs on a single crystal yttrium-stabilized zirconia (Y0.15Zr0.85O2) by a thermal CVD method. The NWs show a characteristic taper part on the bottom growing from a trigonal pyramidal nucleus. The taper angle and length can be controlled by changing the growth condition in two steps, which will lead to obtaining uniformly distributed thin Fe NWs for applications. (C) 2015 AIP Publishing LLC.
  • 島田敏宏, 柳瀬隆, 長浜太郎, 土田裕也, 村谷直紀
    電気学会論文C部門誌 135 2 160 - 163 2015年 [査読無し][通常論文]
     
    Frontier Chemistry Center, Hokkaido University Kita 13, Nishi 8, Kita-ku, Sapporo 060-8628, Japan Graduate School of Chemical Sciences and Engineering, Hokkaido University Kita 13, Nishi 8, Kita-ku, Sapporo 060-8628, Japan Flexible solar cells made of organic semiconductors are promising for the application to the photovoltaic energy sources for flexible devices and those can be attached to any curved surfaces. Mixing and phase separation of different molecules are important for the formation of bulk-hetero junctions. We found that DNTT (dinaphtotienothiophene) and C60 spontaneously mixes when they are sequentially deposited. The driving force does not seem to be the charge transfer between p-type and n-type molecules but the maximization of van der Waals attraction coming from the molecular shapes.
  • Takahiro Tamura, Takashi Yanase, Taro Nagahama, Makoto Wakeshima, Yukio Hinatsu, Toshihiro Shimada
    CHEMISTRY LETTERS 43 10 1569 - 1571 2014年10月 [査読無し][通常論文]
     
    We demonstrate a new doping technique for chemical vapor deposition (CVD) growth of diamond. The method involves immersing a solid-state dopant source into the plasma during microwave plasma-assisted CVD. We applied this simple and versatile technique to the growth of boron-doped diamond. The grown films were characterized by X-ray diffraction (XRD), Raman microscopy, glow discharge optical emission spectroscopy (GDOES), and electrical conductivity measurements. The average concentration of boron was 0.5 atom % and the conductivity was 1.5 x 10(-2) Omega cm, which showed irregular behavior at low temperature.
  • Taro Nagahama, Yuya Matsuda, Kazuya Tate, Tomohiro Kawai, Nozomi Takahashi, Shungo Hiratani, Yusuke Watanabe, Takashi Yanase, Toshihiro Shimada
    APPLIED PHYSICS LETTERS 105 10 102410  2014年09月 [査読無し][通常論文]
     
    Fe3O4 is a ferrimagnetic spinel ferrite that exhibits electric conductivity at room temperature (RT). Although the material has been predicted to be a half metal according to ab-initio calculations, magnetic tunnel junctions (MTJs) with Fe3O4 electrodes have demonstrated a small tunnel magnetoresistance (TMR) effect. Not even the sign of the tunnel magnetoresistance ratio has been experimentally established. Here, we report on the magnetic properties of epitaxial Fe3O4 films with various crystal orientations. The films exhibited apparent crystal orientation dependence on hysteresis curves. In particular, Fe3O4(110) films exhibited in-plane uniaxial magnetic anisotropy. With respect to the squareness of hysteresis, Fe3O4 (111) demonstrated the largest squareness. Furthermore, we fabricated MTJs with Fe3O4(110) electrodes and obtained a TMR effect of -12% at RT. The negative TMR ratio corresponded to the negative spin polarization of Fe3O4 predicted from band calculations. (C) 2014 AIP Publishing LLC.
  • Toshihiro Shimada, Taro Nagahama, Takashi Yanase
    JAPANESE JOURNAL OF APPLIED PHYSICS 53 8 88004  2014年08月 [査読無し][通常論文]
     
    We present the analysis of a simple electrostatic model of a solid-state capacitor with ionizable charge traps. It shows a charge voltage characteristic resembling a chemical battery. With a given withstanding voltage and the same geometry, the energy density of the capacitor with ionizable traps will be lower than that of an ordinary capacitor with metal electrodes. (C) 2014 The Japan Society of Applied Physics
  • Toshihiro Shimada, Shosei Kubota, Takashi Yanase, Taro Nagahama
    CARBON 67 300 - 303 2014年02月 [査読無し][通常論文]
     
    We examined the edge structure of graphite formed by a cathodic electrochemical reaction in acid solutions associated with water electrolysis. Pole figures of the X-ray diffraction show that the edge orientation is parallel to the zigzag edge direction on a macroscopic scale. The polarization dependence of the G-band and D-band of the Raman spectra is consistent with the zigzag edge formation on a microscopic scale. It was found that the etched carbon atoms are converted to CH4 in the evolving gas and molecular species in the solution. (C) 2013 Elsevier Ltd. All rights reserved.
  • Wei Xie, Naoki Muraya, Takashi Yanase, Taro Nagahama, Toshihiro Shimada
    Jpn. J. Appl. Phys. 53 1 10203  2014年01月 [査読有り][通常論文]
     
    We demonstrate the synthesis of diamond-like carbon (DLC) doped with highly pi-conjugated molecules by codepositing organic semiconductor molecules during the plasma-assisted chemical vapor deposition of DLC. From the results of optical absorption spectroscopy, it was revealed that organic semiconductor molecules reacted with plasma but were not completely decomposed. The results of Raman spectroscopy strongly suggested that a certain chemical moiety remained in the film. (C) 2014 The Japan Society of Applied Physics
  • T. Yanase, A. Kawahito, Y. Hashimoto, T. Endo, Y. Wang, T. Nagahama, T. Shimada
    RSC ADVANCES 4 52 27620 - 27624 2014年 [査読無し][通常論文]
     
    We re-examined the growth of single crystalline Fe whiskers by chemical vapour deposition with regard to modern nanowire (NW) growth techniques. Single Fe NWs (100-300 nm diameter) with a high aspect ratio and unique [021] orientation were grown by optimizing the flow of raw materials (FeCl2 and H-2) and using a Au nanoparticle catalyst and single crystalline substrate. The growth mechanism was investigated by transmission electron microscopy and electron diffraction analysis of the NW-catalyst interface.
  • Takashi Yanase, Taro Nagahama, Toshihiro Shimada
    APPLIED PHYSICS LETTERS 103 13 133305  2013年09月 [査読無し][通常論文]
     
    In order to combine the photovoltaic and piezoelectric activities in a single film, we fabricated tricolor superlattices consisting of an organic p-n junction and a piezoelectric polymer with sub-nm thickness control. The photovoltaic response of each repeating unit was saturated at 10 nm each as a function of the layer thicknesses. The capacitance across the 50 periods of superlattice changed by 0.009 pF upon photo-irradiation, which corresponds to a 2 nm thickness change of a 1-mu m thick film. The characteristic time dependent behaviors of the capacitance of the superlattice consist of photocarrier generation, electrostriction, and poling of the piezoelectric polymer. (C) 2013 AIP Publishing LLC.
  • Manabu Ohtomo, Yuya Tsuchida, Naoki Muraya, Takashi Yanase, Seiji Sakai, Tetsu Yonezawa, Taro Nagahama, Tetsuya Hasegawa, Toshihiro Shimada
    JOURNAL OF PHYSICAL CHEMISTRY C 117 22 11555 - 11561 2013年06月 [査読有り][通常論文]
     
    We report the in-plane orientation control of a high-mobility organic semiconductor: 2,7-diphenyl[1]benzothieno[3,2-b][1]benzothiophene (DPh-BTBT). As previously reported for the monolayer pentacene, it was revealed that bunched steps on the vicinal Si(111) with a bismuth termination break the surface 3-fold symmetry and reduce the multiple orientation of the DPh-BTBT grains into a quasi-single orientation. Interestingly, the critical step height necessary for the orientation control was higher than that of pentacene. We examined several mechanisms of orientation control and concluded that the facet nanostructure fabricated by step bunching works as an anisotropic template for the nucleation. We also show the wettability optimization of the bismuth-terminated silicon surface and show that the growth mode of DPh-BTBT is dependent on the surface nanostructure of Bi-Si.
  • Manabu Ohtomo, Yuya Tsuchida, Naoki Muraya, Takashi Yanase, Seiji Sakai, Tetsu Yonezawa, Taro Nagahama, Tetsuya Hasegawa, Toshihiro Shimada
    JOURNAL OF PHYSICAL CHEMISTRY C 117 22 11555 - 11561 2013年06月 [査読有り][通常論文]
     
    We report the in-plane orientation control of a high-mobility organic semiconductor: 2,7-diphenyl[1]benzothieno[3,2-b][1]benzothiophene (DPh-BTBT). As previously reported for the monolayer pentacene, it was revealed that bunched steps on the vicinal Si(111) with a bismuth termination break the surface 3-fold symmetry and reduce the multiple orientation of the DPh-BTBT grains into a quasi-single orientation. Interestingly, the critical step height necessary for the orientation control was higher than that of pentacene. We examined several mechanisms of orientation control and concluded that the facet nanostructure fabricated by step bunching works as an anisotropic template for the nucleation. We also show the wettability optimization of the bismuth-terminated silicon surface and show that the growth mode of DPh-BTBT is dependent on the surface nanostructure of Bi-Si.
  • Toshihiro Shimada, Takashi Yanase, Taro Nagahama, Toshiyuki Kanno
    JAPANESE JOURNAL OF APPLIED PHYSICS 52 5 2013年05月 [査読有り][通常論文]
     
    Materials and structures for water vapor barrier sealing are now actively studied, as the commercialization of organic electronic devices has become a reality. In this paper, we focus on the edge sealing barriers, in which diffusion plays an essential role. In the past, the diffusion-limited gas barrier properties were analyzed in the steady-state approximation, which is never reached within the device lifetime in the application for organic electronics. We analyze them using a simple analytical model. The diffusion before reaching the steady state is a strongly non-linear process, as is well known, and the length scale of approximately 1-10mm is very important when a practical polymer resin is used for the edge seal. (C) 2013 The Japan Society of Applied Physics
  • Sakai Enju, Amemiya Kenta, Chikamatsu Akira, Hirose Yasushi, Shimada Toshihiro, Hasegawa Tetsuya
    JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 333 130 - 133 2013年05月 [査読有り][通常論文]
  • Toshihiro Shimada, Takashi Yanase, Taro Nagahama, Toshiyuki Kanno
    JAPANESE JOURNAL OF APPLIED PHYSICS 52 5 05DA12  2013年05月 [査読無し][通常論文]
     
    Materials and structures for water vapor barrier sealing are now actively studied, as the commercialization of organic electronic devices has become a reality. In this paper, we focus on the edge sealing barriers, in which diffusion plays an essential role. In the past, the diffusion-limited gas barrier properties were analyzed in the steady-state approximation, which is never reached within the device lifetime in the application for organic electronics. We analyze them using a simple analytical model. The diffusion before reaching the steady state is a strongly non-linear process, as is well known, and the length scale of approximately 1-10mm is very important when a practical polymer resin is used for the edge seal. (C) 2013 The Japan Society of Applied Physics
  • N. S. Sokolov, S. M. Suturin, B. B. Krichevtsov, V. G. Dubrovskii, S. V. Gastev, N. V. Sibirev, D. A. Baranov, V. V. Fedorov, A. A. Sitnikova, A. V. Nashchekin, V. I. Sakharov, I. T. Serenkov, T. Shimada, T. Yanase, M. Tabuchi
    Physical Review B - Condensed Matter and Materials Physics 87 12 2013年03月07日 [査読有り][通常論文]
     
    We study molecular beam epitaxy growth, morphology, crystal structure, and magnetic properties of Co nanoislands on CaF2/Si(111) surface. In order to have a full appreciation of complex growth kinetics at different stages, a comprehensive study of Co growth on CaF2 is carried out by atomic force, scanning electron, and transmission electron microscopies in the direct space, as well as by x-ray and electron diffraction in the reciprocal space. These experimental data are complemented by theoretical modeling. Magnetic properties are characterized by magneto-optical Kerr effect and superconducting quantum interference device magnetometries. Key effects influencing the Co growth on fluorite are addressed, including the sticking probability, the preferential nucleation sites, the size and shape time evolution, the dependence of Co morphology on temperature and Co exposure, and the coalescence mechanism. The two-stage deposition technique is developed, whereby the low-temperature seeding stage is used to facilitate Co nucleation, and the follow-up high-temperature deposition yields Co particles with high crystalline quality. Our results enable precise control over the resulting morphology, spatial ordering, and crystal structure affecting the magnetic properties. In particular, it is demonstrated that the transformation from dense to isolated Co nanoparticles leads to the change of the in-plane and out-of-plane magnetic anisotropy and also the sign of polar and longitudinal magneto-optical Kerr effects. © 2013 American Physical Society.
  • N. S. Sokolov, S. M. Suturin, B. B. Krichevtsov, V. G. Dubrovskii, S. V. Gastev, N. V. Sibirev, D. A. Baranov, V. V. Fedorov, A. A. Sitnikova, V. Nashchekin, V. I. Sakharov, I. T. Serenkov, T. Shimada, T. Yanase, M. Tabuchi
    PHYSICAL REVIEW B 87 12 125407  2013年03月 [査読無し][通常論文]
     
    We study molecular beam epitaxy growth, morphology, crystal structure, and magnetic properties of Co nanoislands on CaF2/Si(111) surface. In order to have a full appreciation of complex growth kinetics at different stages, a comprehensive study of Co growth on CaF2 is carried out by atomic force, scanning electron, and transmission electron microscopies in the direct space, as well as by x-ray and electron diffraction in the reciprocal space. These experimental data are complemented by theoretical modeling. Magnetic properties are characterized by magneto-optical Kerr effect and superconducting quantum interference device magnetometries. Key effects influencing the Co growth on fluorite are addressed, including the sticking probability, the preferential nucleation sites, the size and shape time evolution, the dependence of Co morphology on temperature and Co exposure, and the coalescence mechanism. The two-stage deposition technique is developed, whereby the low-temperature seeding stage is used to facilitate Co nucleation, and the follow-up high-temperature deposition yields Co particles with high crystalline quality. Our results enable precise control over the resulting morphology, spatial ordering, and crystal structure affecting the magnetic properties. In particular, it is demonstrated that the transformation from dense to isolated Co nanoparticles leads to the change of the in-plane and out-of-plane magnetic anisotropy and also the sign of polar and longitudinal magneto-optical Kerr effects. DOI: 10.1103/PhysRevB.87.125407
  • Toshihiro Shimada, Naoki Muraya, Jun Tomita, Takashi Yanase, Taro Nagahama
    Journal of Physics: Conference Series 441 1 12041  2013年 [査読無し][通常論文]
     
    The plasma treatment of organic semiconductor molecules includes issues related with nanoscale plasma interfaces. The process was examined by optical emission spectroscopy. It was found that molecules are sublimed by the heat and decomposed by the interaction with the plasma. The product carbon solids were examined by Raman spectroscopy. The raman spectra are strongly dependent on the molecular structures. The carbon solids which does not show graphitic Raman spectra have nanostructures originating from initial molecules.
  • Sawako Miyamoto, Tetsuya Hasegawa, Hiroyuki Takahashi, Tetsu Yonezawa, Hajime Kiyono, Takashi Yanase, Taro Nagahama, Toshihiro Shimada
    BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN 85 12 1287 - 1292 2012年12月 [査読有り][通常論文]
     
    We report a method to produce vapor species from ZnO powder for the fabrication of ZnO nanorods. Mixing ethanol vapor with the inert carrier gas substantially lowered the gasification temperature of ZnO. c Axis-aligned ZnO nanorods were obtained by dispersing gold nanoparticles on Si substrates. The growth was identified as a vapor-solid (VS) mechanism. Choice of the substrate materials and their surface morphology were both critically important to control the shapes and orientation of grown ZnO.
  • Takashi Yanase, Tetsuya Hasegawa, Taro Nagahama, Toshihiro Shimada
    JAPANESE JOURNAL OF APPLIED PHYSICS 51 11 111803  2012年11月 [査読有り][通常論文]
     
    The transient characteristics of electric double layer (EDL) gated field-effect transistors with Si as an active semiconductor were studied using various electrolyte solutions of LiBF4 by applying a step-function voltage to determine the optimum electrolyte for semiconductor circuits using EDLs. The t(R), determined by EDL dynamics in the present experiment, was minimum as a function of the kind of solvent used owing to the competing effects of the EDL thickness and viscosity. The responses of the electrolyte solutions with various solvents at the same concentration were classified into three categories on the basis of t(R): slow response of a complex-forming solvent, intermediate response of protic solvents, and fast response of nonprotic solvents. The best response time was 55 mu s when a 1.0M acetonitrile solution was used as the liquid-gate insulator. (C) 2012 The Japan Society of Applied Physics
  • Hajime Kiyono, Yuuya Matsuda, Toshihiro Shimada, Mariko Ando, Itaru Oikawa, Hideki Maekawa, Susumu Nakayama, Shinobu Ohki, Masataka Tansho, Tadashi Shimizu, Pierre Florian, Dominuqie Massiot
    SOLID STATE IONICS 228 64 - 69 2012年11月 [査読有り][通常論文]
     
    We used magic angle spinning (MAS), multiquantum (MQ)-MAS, and high-temperature (HT) nuclear magnetic resonance (NMR) measurements to investigate the oxide-ion conduction path of oxygen-17 (O-17) in apatite-type lanthanum silicate La-9.33(SiO4)(6)O-2. A highly crystalline apatite-type lanthanum silicate was specifically synthesized for the measurements. MAS and MQ-MAS NMR confirmed that four kinds of oxide-ion sites are present in the structure and showed a small extra peak (<1%) possibly due to an interstitial site. The high-temperature measurements showed that the line shape changed and sharpened with increasing temperature from 200 degrees C, and the peak position shifted at 700 degrees C. The comparison of the results between MAS NMR (room-temperature) and HT static NMR showed the exchange of oxide ions bonded to Si (O1, O2, and O3) but the apparent exchange between the oxide ions (O1, O2, and O3) and the oxide ion at the isolated site (O4) is not observed. The exchange of the oxide ions that are bonded to Si (O1, O2, and O3) suggests that they are the main diffusion species in oxide-ion conductivity. (C) 2012 Elsevier B.V. All rights reserved.
  • Satoru Mohri, Yasushi Hirose, Shoichiro Nakao, Naoomi Yamada, Toshihiro Shimada, Tetsuya Hasegawa
    JOURNAL OF APPLIED PHYSICS 111 9 093528  2012年05月 [査読有り][通常論文]
     
    Transparent conductive anatase TiO2-xFx(F:TiO2) epitaxial thin films were fabricated by reactive pulsed laser deposition with a solid fluorine source. F-doping as high as 1.6 x 10(21) cm(-3) (TiO1.95F0.05) was achieved under optimal growth conditions, and the obtained anatase TiO1.95F0.05 film had a low resistivity of 1.6 x 10(-3) Omega cm and a high internal transmittance of >95%. Furthermore, the refractive index of a TiO1.95F0.05 film was >0.2 less than that of undoped TiO2. By comparing the refractive indices of F:TiO2 and Nb:TiO2, we concluded that the decreased refractive index in F:TiO2 can be attributed to a reduced electronic polarizability due to increased bond ionicity as well as doped electrons. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4712061]
  • Takashi Yanase, Tetsuya Hasegawa, Taro Nagahama, Toshihiro Shimada
    JAPANESE JOURNAL OF APPLIED PHYSICS 51 4 041604  2012年04月 [査読有り][通常論文]
     
    We demonstrate that polyurea films can be prepared by alternating deposition with automated deposition control involving quartz crystal microbalance monitoring and optical source heating. The thickness of the films was linearly controlled by changing the repetition time of deposition, and the stoichiometry obtained was much higher than +/- 5%. The surface roughness of a 600-nm-thick film was 0.5 nm, which ensures the nm thickness control of the deposited polymers. The piezoelectricity of the films was confirmed by directly measuring the current transient induced by mechanical stress and by measuring the capacitance change induced by electric field. (C) 2012 The Japan Society of Applied Physics
  • Shosei Kubota, Tetsu Yonezawa, Taro Nagahama, Toshihiro Shimada
    CHEMISTRY LETTERS 41 2 187 - 188 2012年02月 [査読有り][通常論文]
     
    We found that graphite surfaces can be etched by electrochemical reduction in sulfuric acid. Terraces with straight edges crossing with 60 degrees-multiple angles were found on surfaces by AFM observation. It suggests that crystallographic edges can be formed at room temperature in a controlled manner. Layer-by-layer etching of graphene sheets was possible by tuning the etching condition.
  • Toshihiro Shimada, Yu Ikuta, Yuya Tsuchida, Manabu Ohtomo, Tetsuya Hasegawa
    APPLIED PHYSICS EXPRESS 4 6 061601  2011年06月 [査読有り][通常論文]
     
    In organic semiconductors, the sudden appearance of deep traps (30-100 meV) below 100-200 K is frequently observed experimentally even in highly crystalline films and single crystals. We analyzed this phenomenon by molecular dynamics combined with semi-empirical quantum chemical calculation, and found that defect levels are concealed by thermal disorder at high temperatures but appear as hole traps at low temperatures. We propose that the thermal energetic disorder may lead to a considerably large thermoelectric effect in organic semiconductors. (C) 2011 The Japan Society of Applied Physics
  • Naoomi Yamada, Tatsuo Shibata, Kenji Taira, Yasushi Hirose, Shoichiro Nakao, Ngoc Lam Huong Hoang, Taro Hitosugi, Toshihiro Shimada, Takayoshi Sasaki, Tetsuya Hasegawa
    APPLIED PHYSICS EXPRESS 4 4 045801  2011年04月 [査読有り][通常論文]
     
    Uniaxially (001)-oriented anatase Ti0.94Nb0.06O2 films were sputtered on a seed layer of glass covered with Ca2Nb3O10 nanosheets (CNO-NS). The films had an effective electron mass of 0.7m(0) (m(0) denotes the free electron mass), which was smaller than that of randomly oriented films, i.e., 0.9m(0). The as-grown films exhibited a low resistivity of 7.6 x 10(-4) Omega cm. Postdeposition annealing under H-2 atmosphere further reduced the resistivity to 4.0 x 10(-4) Omega cm. This value is comparable with that of conventional transparent conducting oxides. Results indicate that sputtering using CNO-NS is promising for the fabrication of highly conductive Ti1-xNbxO2 electrodes on glass. (C) 2011 The Japan Society of Applied Physics
  • Naoomi Yamada, Tatsuo Shibata, Kenji Taira, Yasushi Hirose, Shoichiro Nakao, Ngoc Lam Huong Hoang, Taro Hitosugi, Toshihiro Shimada, Takayoshi Sasaki, Tetsuya Hasegawa
    APPLIED PHYSICS EXPRESS 4 4 045801  2011年04月 [査読有り][通常論文]
     
    Uniaxially (001)-oriented anatase Ti0.94Nb0.06O2 films were sputtered on a seed layer of glass covered with Ca2Nb3O10 nanosheets (CNO-NS). The films had an effective electron mass of 0.7m(0) (m(0) denotes the free electron mass), which was smaller than that of randomly oriented films, i.e., 0.9m(0). The as-grown films exhibited a low resistivity of 7.6 x 10(-4) Omega cm. Postdeposition annealing under H-2 atmosphere further reduced the resistivity to 4.0 x 10(-4) Omega cm. This value is comparable with that of conventional transparent conducting oxides. Results indicate that sputtering using CNO-NS is promising for the fabrication of highly conductive Ti1-xNbxO2 electrodes on glass. (C) 2011 The Japan Society of Applied Physics
  • Manabu Ohtomo, Kenji Itaka, Tetsuya Hasegawa, Toshihiro Shimada
    APPLIED PHYSICS EXPRESS 4 2 021601  2011年02月 [査読有り][通常論文]
     
    We studied the sublimation of tetracene single crystals under vacuum and 1 atm inert gas to develop the surface cleaning technique for organic semiconductors. It was found that the microscopic sublimation behavior is strongly dependent on the gas pressure. Nanometer-scale roughening was observed after heating in vacuum, and layer-by-layer sublimation was observed under 1 atm Ar gas. Reflection high energy electron diffraction analysis of the topmost surface showed streak patterns, indicating that surface contaminants were successfully removed. (C) 2011 The Japan Society of Applied Physics
  • Manabu Ohtomo, Kenji Itaka, Tetsuya Hasegawa, Toshihiro Shimada
    APPLIED PHYSICS EXPRESS 4 2 021601  2011年02月 [査読有り][通常論文]
     
    We studied the sublimation of tetracene single crystals under vacuum and 1 atm inert gas to develop the surface cleaning technique for organic semiconductors. It was found that the microscopic sublimation behavior is strongly dependent on the gas pressure. Nanometer-scale roughening was observed after heating in vacuum, and layer-by-layer sublimation was observed under 1 atm Ar gas. Reflection high energy electron diffraction analysis of the topmost surface showed streak patterns, indicating that surface contaminants were successfully removed. (C) 2011 The Japan Society of Applied Physics
  • Shoichiro Nakao, Naoomi Yamada, Taro Hitosugi, Yasushi Hirose, Toshihiro Shimada, Tetsuya Hasegawa
    PHYSICA STATUS SOLIDI C: CURRENT TOPICS IN SOLID STATE PHYSICS, VOL 8, NO 2 8 2 543  2011年 [査読有り][通常論文]
     
    Pulsed laser deposition was used to grow W-doped SnO2 (WTO) thin films on glass substrates. By using 10-nm-thick polycrystalline anatase TiO2 seed layers formed on the glass substrates, the lowest resistivity of 3.5 x 10(-4) Omega cm, with a mobility of 84 cm(2)V(-1)s(-1) and a carrier concentration of 2.1 x 10(20) cm(-3), was obtained at a W concentration of 1.5 at.%. An optimized WTO film with a sheet resistance of 9.1 Omega/square exhibited an optical transmittance of over 70% at wavelengths ranging from 400 to 1950 nm. These transport and optical properties are comparable to those of Ta-doped SnO2. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
  • Toshihiro Shimada, Yoichiro Nakano, Yoshikazu Takahashi, Toshiyuki Kanno
    IDW'11: PROCEEDINGS OF THE 18TH INTERNATIONAL DISPLAY WORKSHOPS, VOLS 1-3 1717 - 1720 2011年 [査読有り][通常論文]
     
    We have developed an instrument for ultrasensitive (<10(-6) g/m(2)/day) and rapid (<1 day) measurement of water vapor transmission rate in gas barrier materials. Water vapor that has permeated through the barrier in atmospheric carrier gas is condensed by a cold trap and transferred to mass spectrometer in ultrahigh vacuum.
  • Yuichiro Goto, Takuya Noguchi, Utahito Takeuchi, Kunitada Hatabayashi, Yasushi Hirose, Takayuki Uchida, Takehiko Sasaki, Tetsuya Hasegawa, Toshihiro Shimada
    ORGANIC ELECTRONICS 11 7 1212 - 1216 2010年07月 [査読有り][通常論文]
     
    Fluorescent and phosphorescent organic light emitting diodes (OLEDs) were measured in high magnetic field up to 9 T. The current efficiency steeply increased below 100 mT as reported but gradually decreased when the field was larger. In the range of 0.1-6.5 T, the decrease was proportional to the square of the magnetic field, whereas in the range between 6.5 and 9 T, it was proportional to the square root of the magnetic field. In contrast, phosphorescent OLED did not show magnetic field dependence. Unipolar devices of n-type Alq(3) (tris-(8-hydroxyquinolino) aluminum) and p-type alpha-NPD (N',N'-di(naphthalene-1-yl)-N,N'-dipheyl-benzidine) showed positive linear magnetoresistance only for minority carriers. The mechanism of the quadratic dependence of the electroluminescent intensity is discussed based on the experimental results. (c) 2010 Elsevier B.V. All rights reserved.
  • Yuichiro Goto, Takuya Noguchi, Utahito Takeuchi, Kunitada Hatabayashi, Yasushi Hirose, Takayuki Uchida, Takehiko Sasaki, Tetsuya Hasegawa, Toshihiro Shimada
    ORGANIC ELECTRONICS 11 7 1212 - 1216 2010年07月 [査読有り][通常論文]
     
    Fluorescent and phosphorescent organic light emitting diodes (OLEDs) were measured in high magnetic field up to 9 T. The current efficiency steeply increased below 100 mT as reported but gradually decreased when the field was larger. In the range of 0.1-6.5 T, the decrease was proportional to the square of the magnetic field, whereas in the range between 6.5 and 9 T, it was proportional to the square root of the magnetic field. In contrast, phosphorescent OLED did not show magnetic field dependence. Unipolar devices of n-type Alq(3) (tris-(8-hydroxyquinolino) aluminum) and p-type alpha-NPD (N',N'-di(naphthalene-1-yl)-N,N'-dipheyl-benzidine) showed positive linear magnetoresistance only for minority carriers. The mechanism of the quadratic dependence of the electroluminescent intensity is discussed based on the experimental results. (c) 2010 Elsevier B.V. All rights reserved.
  • Shoichiro Nakao, Naoomi Yamada, Taro Hitosugi, Yasushi Hirose, Toshihiro Shimada, Tetsuya Hasegawa
    THIN SOLID FILMS 518 11 3093 - 3096 2010年03月 [査読有り][通常論文]
     
    We discuss the fabrication of highly conductive Ta-doped SnO2 (Sn1-xTaxO2: ITO) thin films on glass by pulse laser deposition. On the basis of the comparison of X-ray diffraction patterns and resistivity (rho) values between epitaxial films and polycrystalline films deposited on bare glass, we proposed the use of seed-layers for improving the conductivity of the TTO polycrystalline films. We investigated the use of rutile TiO2 and NbO2 as seed-layers; these are isostructural materials of SnO2, which are expected to promote epitaxial-like growth of the TTO films. The films prepared on the 10-nm-thick seed-layers exhibited preferential growth of the TTO (110) plane. The TTO film with x=0.05 on rutile TiO2 exhibited p = 3.5 x 10(-4)Omega cm, which is similar to those of the epitaxial films grown on Al2O3 (0001). (C) 2009 Elsevier B.V. All rights reserved.
  • Naoomi Yamada, Taro Hitosugi, Junpei Kasai, Ngoc Lam Huong Hoang, Shoichiro Nakao, Yasushi Hirose, Toshihiro Shimada, Tetsuya Hasegawa
    THIN SOLID FILMS 518 11 3101 - 3104 2010年03月 [査読有り][通常論文]
     
    Transparent conducting Nb-doped anatase TiO2 (TNO) epitaxial films were sputtered from TiO2-, Ti2O3-, and Ti-based targets at various oxygen partial pressures (Po-2). Using the TiO2- and Ti2O3-based targets, highly conductive films showing a resistivity (rho) of similar to 3 x 10(-4) Omega cm could be formed without postdeposition treatment. In the case of the TNO films formed from the Ti-based target, reductive annealing had to be carried out at a temperature of 600 degrees C to achieve similar resistivity values. Thus, the use of oxide targets is preferable to obtain as-grown transparent conducting TNO films. In particular, the Ti2O3-based target is practically advantageous, because it offers a wide range of optimal Po-2 values at which p values of the order of 10(-4) Omega cm are achievable. (C) 2009 Elsevier B.V. All rights reserved.
  • Takuya Noguchi, Toshihiro Shimada, Takashi Chiba, Masao Terada, Tetsuya Hasegawa
    DIAMOND AND RELATED MATERIALS 19 2-3 107 - 109 2010年02月 [査読有り][通常論文]
     
    We have carried out very high temperature heat treatment at 1400-2700 degrees C of about 10 nm-thick amorphous carbon thin films deposited on refractory substrates MgO, Al2O3, and yttria-stabilized zirconia (YSZ) using pulsed laser deposition techniques. After the annealing, a few nanometer scale sp(2) crystallization of the films and a large corrugation with a height of more than 1 mu m were observed by Raman spectroscopy analysis and optical/atomic force microscopes, respectively. The corrugation is probably caused by tire formation of gases at the film/substrate interface during the heat treatment. (C) 2009 Elsevier B.V. All rights reserved.
  • Utahito Takeuchi, Akira Chikamatsu, Taro Hitosugi, Hiroshi Kumigashira, Masaharu Oshima, Yasushi Hirose, Toshihiro Shimada, Tetsuya Hasegawa
    JOURNAL OF APPLIED PHYSICS 107 2 023705  2010年01月 [査読有り][通常論文]
     
    We have investigated the transport properties and electronic states of W-doped anatase TiO2 (Ti1-xWxO2) fabricated by pulsed-laser deposition. Based on transport and photoemission spectroscopy (PES) measurements, we discuss the conduction mechanism of Ti1-xWxO2, focusing on the valence state of W. The Ti0.95W0.05O2 film deposited under optimized conditions showed a resistivity of 2x10(-3) cm at room temperature, which is approximately ten times higher than that of Ti0.94Nb0.06O2. This is mainly due to the lower carrier density in Ti1-xWxO2 films. From PES measurements of Ti0.91W0.09O2 films, we observed the finite density of states originating from O 2p hybridized with W near the top of the valence band. However, we could not find any states at the same position in the Ti0.94Nb0.06O2 films. In addition, the density of states near the Fermi level [N(E-F)] was found to be quite low in the Ti0.91W0.09O2 films. Indeed, this is in sharp contrast to Ti0.94Nb0.06O2, which indicates a remarkably high N(E-F) value assigned to the bottom of the Ti 3d conduction band. The difference in transport properties between Ti1-xWxO2 and Ti1-xNbxO2 can be attributed to the existence of impurity states that trap carriers associated with doped W atoms.
  • Toshihiro Shimada, Yoshikazu Takahashi, Toshiyuki Kanno
    APPLIED PHYSICS EXPRESS 3 2 021701  2010年 [査読有り][通常論文]
     
    We developed a novel apparatus for the measurement of the gas barrier properties of soft materials. The measurement principle is based on the use of a low temperature trap to transfer the permeated vapor from the sample space under atmospheric pressure to the mass spectrometer situated in an ultrahigh vacuum. We have demonstrated that the sensitivity, dynamic range and lead time for the measurement can be significantly improved from those previously reported. It was revealed that the diffusion time in a polymer film must be considered in the measurement of high barrier films. (C) 2010 The Japan Society of Applied Physics DOI: 10.1143/APEX.3.021701
  • Shoichiro Nakao, Naoomi Yamada, Taro Hitosugi, Yasushi Hirose, Toshihiro Shimada, Tetsuya Hasegawa
    APPLIED PHYSICS EXPRESS 3 3 031102  2010年 [査読有り][通常論文]
     
    High-mobility Ta-doped SnO2 (TTO) thin films were grown on glass substrates by pulsed laser deposition using a seed-layer technique. The use of 10-nm-thick polycrystalline anatase TiO2 seed layers was found to lead to the preferred growth of (200)-oriented TTO films, resulting in a 30% increase in the carrier density and a more than two times increase in mobility, compared to films grown directly on the glass substrates. The highest mobility obtained was 83 cm(2) V-1 s(-1) with a resistivity of 2.8 x 10(-4) Omega cm, whereas the film with the lowest resistivity of 1.8 x 10(-4) Omega cm had a mobility of 60 cm(2) V-1 s(-1). (C) 2010 The Japan Society of Applied Physics
  • Enju Sakai, Akira Chikamatsu, Yasushi Hirose, Toshihiro Shimada, Tetsuya Hasegawa
    APPLIED PHYSICS EXPRESS 3 4 043001  2010年 [査読有り][通常論文]
     
    We have measured the magnetic and transport properties of FexNbyTi1-x-yO2-delta (x = 0.06, y = 0, 0.1, 0.03) films deposited by pulsed laser deposition at various partial oxygen pressures (PO2). The Fe and Nb codoped films have a carrier concentration of > 3 x 10(20) cm(-3), which is independent of PO2 and far exceeds the critical carrier concentration for ferromagnetic ordering in Fe0.06Ti0.94O2-delta (1 x 10(19) cm(-3)). Room-temperature ferromagnetism was observed only when deposition was conducted in reducing atmospheres (i.e., PO2 <= 1 x 10(-6) Torr) for all the FexNbyTi1-x-yO2-delta films, indicating that there is a critical oxygen vacancy density for the ferromagnetic transition. (C) 2010 The Japan Society of Applied Physics
  • Hiroyuki Nogawa, Taro Hitosugi, Akira Chikamatsu, Shoichiro Nakao, Yasushi Hirose, Toshihiro Shimada, Hiroshi Kumigashira, Masaharu Oshima, Tetsuya Hasegawa
    Jpn. J. Appl. Phys. 49 4 041102  2010年 [査読有り][通常論文]
     
    We report the effect of post-deposition annealing on the electrical transport properties of anatase Ti0.94Nb0.06O2 (TNO) epitaxial thin films. Annealing TNO films in pure oxygen drastically suppressed the carrier density (n(e)). A high n(e) of the order of 10(21) cm(-3) was recovered by successive annealing in pure hydrogen. Core-level X-ray photoemission spectroscopy revealed that Ti and Nb respectively exist as tetravalent and pentavalent ions in fully oxidized samples. The concentration of Nb5+ relative to that of Nb4+ tends to increase with O-2 annealing, suggesting that carriers released by Nb donors are compensated by electron-killing impurity states created by O-2 annealing. Based on these findings, we propose that excess oxygen atoms incorporated by O-2 annealing occupy interstitial sites and behave as deep acceptor states, which compensate electron carriers generated by Nb doping. Resonant valence-band photoemission spectroscopy directly confirmed the formation of deep acceptor states associated with oxygen annealing. (C) 2010 The Japan Society of Applied Physics
  • Takashi Yanase, Toshihiro Shimada, Tetsuya Hasegawa
    JAPANESE JOURNAL OF APPLIED PHYSICS 49 4 04DK06  2010年 [査読有り][通常論文]
     
    Electric double layer field-effect transistors (EDL-FETs) were fabricated using single crystal Si wafer as the active semiconductor and various characteristics were studied including dynamic response against step-function gate bias. The static FET mobility was more than 100 cm(2) V-1 s(-1). The response time of the drain current was 20 mu s for ionic liquid and 3 ms for poly(ethylene glycol) (PEG) solution of LiBF4. Unexpected fast response was observed at a certain "speed up bias'' condition. This effect will be useful to switching circuits using EDL-FETs. (C) 2010 The Japan Society of Applied Physics
  • Takuya Noguchi, Toshihiro Shimada, Akinori Hanzawa, Tetsuya Hasegawa
    THIN SOLID FILMS 518 2 778 - 780 2009年11月 [査読有り][通常論文]
     
    We carried out the preparation and characterization of new carbon films deposited using an organic molecular beam deposition apparatus with very high substrate temperature (from room temperature to 2670 K), which we newly developed. When we irradiated molecular beam of organic semiconductor perylene tetracarboxylic acid dianhydride (PTCDA) on Y(0.07)Zr(0.93)O(2) (111) at 2170 K, a new carbon material was formed via decomposition and fusing of the molecules. The films were characterized with an atomic force microscope (AFM), Raman spectroscopy, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Zirconium carbide (ZrC) films were identified beneath the topmost carbon layer by XRD and XPS analyses, which results from chemical reactions of the substrate and the molecules. Partially graphitized aromatic rings of PTCDA were observed from Raman spectroscopy. The present technique - very high temperature chemical vapor deposition using organic semiconductor sources - will be useful to study a vast unexplored field of covalent carbon solids. (C) 2009 Elsevier B.V. All rights reserved.
  • Akinori Hanzawa, Toshihiro Shimada, Tetsuya Hasegawa, Takahiro Sato, Takeo Kamino, Tetsu Yonezawa
    JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY 9 11 6736 - 6740 2009年11月 [査読有り][通常論文]
     
    The crystallization of polymer-mixed amorphous molybdenum sulfide was observed in-situ by a TEM equipped with a heated specimen holder. High electron beam irradiation induced the formation of a crystal structure with a lattice spacing of 0.62 nm, which corresponds to the layer spacing of MoS2. With a lower electron dose, a possible new crystal structure of molybdenum sulfide with several fringe spacings was identified at room temperature. An ordered layered structure Of MoS2 appeared after annealing at 600 degrees C. The completely different crystal phase found here might be responsible for the high temperature required for the formation of the MoS2 layered structure.
  • Miyamoto S, Shimada T, Ohtomo M, Chikamatsu A, Hasegawa T
    Japanese Journal of Applied Physics 48 11 118003-1 - 118003-2 2009年11月 [査読有り][通常論文]
  • Kunitada Hatabayashi, Taro Hitosugi, Yasushi Hirose, Xianqiang Cheng, Toshihiro Shimada, Tetsuya Hasegawa
    JAPANESE JOURNAL OF APPLIED PHYSICS 48 10 2009年10月 [査読有り][通常論文]
     
    We have fabricated high-quality epitaxial EuTiO3(100) films on SrTiO3 substrates by pulsed laser deposition. In situ reflection high-energy electron diffraction (RHEED) monitoring revealed clear intensity oscillation, indicating layer-by-layer growth of EuTiO3. Furthermore, the obtained films had atomically flat surfaces with a step-terrace structure. From magnetization vs temperature measurements, we confirmed that the EuTiO3 films have antiferromagnetic ordering with a Neel temperature of 3.7 K, and that they could be transformed to a ferromagnetic state by applying a magnetic field. We also found that the magnetic properties of the EuTiO3 films are sensitive to cell volume, as predicted by recent first-principles band calculations. (C) 2009 The Japan Society of Applied Physics
  • Manabu Ohtomo, Tadamasa Suzuki, Toshihiro Shimada, Tetsuya Hasegawa
    APPLIED PHYSICS LETTERS 95 12 123308  2009年09月 [査読有り][通常論文]
     
    Intermolecular band dispersion of thin film phase pentacene grown epitaxially on step-bunched root 3 x root 3 Bi-Si(111) was investigated using angle resolved photoemission spectroscopy at 130 K. We evaluated the transfer integrals using two-dimensional tight-binding fit to the experimental dispersion and found that adjacent molecules in Gamma-M direction have the strongest coupling as predicted. The estimated effective mass at the top of the valence band was isotropic and ranged between 0.8 and 1.0 of the electron mass. (C) 2009 American Institute of Physics. [doi: 10.1063/1.3232205]
  • Naoomi Yamada, Taro Hitosugi, Junpei Kasai, Ngoc Lam Huong Hoang, Shoichiro Nakao, Yasushi Hirose, Toshihiro Shimada, Tetsuya Hasegawa
    JOURNAL OF APPLIED PHYSICS 105 12 123702  2009年06月 [査読有り][通常論文]
     
    This paper proposes a novel sputter-based method for the direct growth of transparent conducting Ti1-xNbxO2 (TNO) polycrystalline films on glass, without the need for any postdeposition treatments, by the use of an initial seed-layer. Anatase TNO epitaxial films grown on LaAlO3 (100) substrates under a reducing atmosphere exhibited a low resistivity (rho) of (3-6) x 10(-4) Omega cm. On glass, however, highly resistive rutile phase polycrystalline films (rho similar to 100 Omega cm) formed preferentially under the same conditions. These results suggest that epitaxial stabilization of the oxygen-deficient anatase phase occurs on lattice-matched substrates. To produce a similar effect on a glass surface, we deposited a seed-layer of anatase TNO with excellent crystallinity under an increased oxygen atmosphere. As a result, anatase phase TNO polycrystalline films could be grown even under heavily reducing atmospheres. An optimized film exhibited rho = 1.1 x 10(-3) Omega cm and optical absorption lower than 10% in the visible region. This rho value is more than one order of magnitude lower than values reported for directly deposited TNO polycrystalline films. This indicates that the seed-layer method has considerable potential for producing transparent conducting TNO polycrystalline films on glass. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3148267]
  • Yasushi Hirose, Naoomi Yamada, Shoichiro Nakao, Taro Hitosugi, Toshihiro Shimada, Tetsuya Hasegawa
    PHYSICAL REVIEW B 79 16 165108  2009年04月 [査読有り][通常論文]
     
    Electron mass anisotropy in the Nb-doped anatase TiO2 (TNO) was determined by polarized infrared spectroscopy measurements for (012)-oriented TNO epitaxial films. The electron mass along the c axis, m(< 001 >)(*), derived by Drude analyses, was found to be 0.5-3.3 m(0), which was 3-6 times larger than that along the a axis, m(< 100 >)(*), 0.2-0.6 m(0). This large anisotropy was attributed to not only the anisotropic crystal structure but also the d-orbital-dominated conduction band. These results indicate that control of crystallographic orientation is of crucial importance for realizing high conductivity in polycrystalline TNO films.
  • Yuk Kihira, Toshihiro Shimada, Yutaka Matsuo, Eiichi Nakamura, Tetsuya Hasegawa
    NANO LETTERS 9 4 1442 - 1446 2009年04月 [査読有り][通常論文]
     
    Random telegraphic noises with a preferential jump height around 0.018G(0) were observed in the conductance traces of the Au-pentacene-Au junctions. The distribution of the plateau lifetime obeyed an exponential distribution, but the decay constants were independent of the height of the adjacent conductance jumps or the measurement temperature. This result, along with the buckyferrocene (Fe(C-60(CH3)(5))C5H5) result, suggests that the conductance fluctuation originates from the current-induced geometrical fluctuation around a single molecule.
  • Yuk Kihira, Toshihiro Shimada, Yutaka Matsuo, Eiichi Nakamura, Tetsuya Hasegawa
    NANO LETTERS 9 4 1442 - 1446 2009年04月 [査読有り][通常論文]
     
    Random telegraphic noises with a preferential jump height around 0.018G(0) were observed in the conductance traces of the Au-pentacene-Au junctions. The distribution of the plateau lifetime obeyed an exponential distribution, but the decay constants were independent of the height of the adjacent conductance jumps or the measurement temperature. This result, along with the buckyferrocene (Fe(C-60(CH3)(5))C5H5) result, suggests that the conductance fluctuation originates from the current-induced geometrical fluctuation around a single molecule.
  • Matsumoto Yoshihiro, Sakai Seiji, Takagi Yasumasa, Nakagawa Takeshi, Yokoyama Toshihiko, Shimada Toshihiro, Mitani Seiji, Naramoto Hiroshi, Maeda Yoshihito
    CHEMICAL PHYSICS LETTERS 470 4-6 244 - 248 2009年03月05日 [査読有り][通常論文]
  • T. Hitosugi, N. Yamada, N. L. H. Hoang, J. Kasai, S. Nakao, T. Shimada, T. Hasegawa
    THIN SOLID FILMS 517 10 3106 - 3109 2009年03月 [査読有り][通常論文]
     
    We report on preparation and properties of anatase Nb-doped TiO2 transparent conducting oxide films on glass and polyimide substrates. Amorphous Ti0.96Nb0.04O2 films were deposited at room temperature by using sputtering, and were then crystallized through annealing under reducing atmosphere. Use of a seed layer substantially improved the crystallinity and resistivity (rho) of the films. We attained rho=9.2 X 10(-4) Omega cm and transmittance of similar to 70% in the visible region on glass by annealing at 300 degrees C in vacuum. The minimum rho of 7.0 x 10(-4) Omega cm was obtained by 400 degrees C annealing in pure H-2. (C) 2008 Elsevier B.V. All rights reserved.
  • Tetsu Yonezawa, Hideya Kawasaki, Akira Tarui, Takehiro Watanabe, Ryuichi Arakawa, Toshihiro Shimada, Fumitaka Mafune
    ANALYTICAL SCIENCES 25 3 339 - 346 2009年03月 [査読有り][通常論文]
     
    In this paper, we describe systematic detailed considerations of the feasibility of using various metal nanoparticles for organic-matrix-free surface-assisted laser desorption/ionization mass spectrometry (SALDI-MS). In order to avoid the influence of organic molecules on the nanoparticles, stabilizer-free bare nanoparticles of Ag, Au, Cu and Pt were prepared by laser ablation. Although all metal nanoparticles absorbed N-2 laser light (337 nm) energy, the performance of desorption/ionization of a representative peptide, angiotensin 1, strongly depended on the metal element. Citrate buffer was used as a proton source; it reduced the amount of alkali cation adducts present. Then, protonated molecules of analytes predominated in the mass spectra when Au and Pt nanoparticles were used. Pt nanoparticles showed the highest performance in SALDI-MS, owing to their smaller heat conductivity and higher melting temperature. The selective desorption of a cationic surfactant with longer alkyl chains and a peptide with methionine was also observed.
  • Hatabayashi, K Hitosugi, T Hirose, Y Cheng, XQ Shimada, T Hasegawa, T
    Fabrication of EuTi, Epitaxial Thin Films by Pulsed Laser Deposition
    Japanese Journal of Applied Physics 48 100208  2009年 [査読有り][通常論文]
  • Toshihiro Shimada
    ARTIFICIALLY INDUCED GRAIN ALIGNMENT IN THIN FILMS 1150 139 - 150 2009年 [査読有り][通常論文]
     
    It is important to obtain single crystalline organic thin films for electronics and optics applications. Due to the mismatching in the crystal symmetry, it is difficult to align the crystalline grains of organic molecular films even on single crystalline surfaces. We have developed several techniques for the artificial grain alignment in organic epitaxial growth. (1) Use of nanoscale-textured surfaces prepared by step bunching of vicinally-cut single crystalline surfaces, in which the height of the steps is critically important. (2) Application of external electric field. (3) Optical excitation of the molecules which can be applied to the polar semiconducting molecules. These techniques might be applicable to other materials including ionic materials and ferroelectrics.
  • Hoang N.L.H, Yamada N, Hitosugi T, Kasai J, Nakao S, Shimada T, Hasegawa T
    Materials Research Society Symposium Proceedings 1109 25 - 30 2009年 [査読有り][通常論文]
  • Hirose Y, Yamada N, Nakao S, Hitosugi T, Shimada T, Konuma S, Hasegawa T
    Materials Research Society Symposium Proceedings 1109 86 - 91 2009年 [査読有り][通常論文]
  • Yamada N, Hitosugi T, Nakao S, Kasai J, Hirose Y, Hoang N.L.H, Shimada T, Hasegawa T
    Materials Research Society Symposium Proceedings 1109 15 - 24 2009年 [査読有り][通常論文]
  • Toshihiro Shimada, Manabu Ohtomo, Tadamasa Suzuki, Tetsuya Hasegawa, Keiji Ueno, Susumu Ikeda, Koichiro Saiki, Miho Sasaki, Katsuhiko Inaba
    APPLIED PHYSICS LETTERS 93 22 223303  2008年12月 [査読有り][通常論文]
     
    We developed a nanoscale orientation template for quasisingle crystalline epitaxial growth of thin film phase pentacene. By using alpha-3x3 Bi termination of surface dangling bonds on step-bunched vicinal surface of Si(111), thin film phase epitaxial pentacene was grown with the crystal axes aligned to the surface steps. Alignment occurred when the step height was higher than the molecular height. The mechanism of the alignment was examined by calculating the energy of the crystal edge.
  • Toshihiro Shimada, Yui Ishii, Keiji Ueno, Tetsuya Hasegawa
    JOURNAL OF CRYSTAL GROWTH 311 1 163 - 166 2008年12月 [査読有り][通常論文]
     
    We studied the effect of the substrate materials on the solution-mediated vacuum deposition of organic semiconductor rubrene using liquid flux with a low vapor pressure. We found that bis-2-ethylhexyl phthalate was suitable as the liquid flux. It was revealed that the microscopic crystal shape completely changed when different substrates were used. This result clearly indicates the nucleation of the crystals occurs on the substrate surface submerged in the solution. Epitaxially oriented needle crystals as long as 5 mm were obtained by using Au(111) substrate. (C) 2008 Elsevier B.V. All rights reserved.
  • Ngoc Lam Huong Hoang, Naoomi Yamada, Taro Hitosugi, Junpei Kasai, Shoichiro Nakao, Toshihiro Shimada, Tetsuya Hasegawa
    APPLIED PHYSICS EXPRESS 1 11 115001  2008年11月 [査読有り][通常論文]
     
    We present a low-temperature (similar to 300 degrees C) process for preparing transparent conducting anatase Nb-doped TiO2 (TNO) polycrystalline films by sputtering. We first deposited amorphous films composed of an oxygen-rich bottom layer and oxygen-deficient top layer at room temperature. These films were then crystallized in a reducing atmosphere. The oxygen-rich bottom layer behaved as a seed layer during crystallization of the top layer, resulting in significant improvement of crystallinity and reduction of crystallization temperature. We obtained TNO polycrystalline films showing a resistivity of 6.4 x 10(-4) Omega cm and absorption below 10% in the visible region by post-deposition annealing at 400 degrees C. The developed low-temperature process was applied to fabricating TNO films on plastics and glass with low glass-transition temperature. (C) 2008 The Japan Society of Applied Physics
  • Taro Hitosugi, Hideyuki Kamisaka, Koichi Yamashita, Hiroyuki Nogawa, Yutaka Furubayashi, Shoichiro Nakao, Naoomi Yamada, Akira Chikamatsu, Hiroshi Kumigashira, Masaharu Oshima, Yasushi Hirose, Toshihiro Shimada, Tetsuya Hasegawa
    APPLIED PHYSICS EXPRESS 1 11 111203  2008年11月 [査読有り][通常論文]
     
    We have investigated electronic band structure of a transparent conducting oxide, Nb-doped anatase TiO2 (TNO), by means of first-principles band calculations and photoemission measurements. The band calculations revealed that Nb 4d orbitals are strongly hybridized with Ti 3d ones to form a d-nature conduction band, without impurity states in the in-gap region, resulting in high carrier density exceeding 10(21) cm(-3) and excellent optical transparency in the visible region. Furthermore, we confirmed that the results of valence band and core-level photoemission measurements are consistent with prediction by the present band calculations. (C) 2008 The Japan Society of Applied Physics
  • 島田 敏宏
    應用物理 77 11 1332 - 1336 応用物理学会 2008年11月 [査読無し][招待有り]
  • Naoomi Yamada, Taro Hitosugi, Ngoc Lam Huong Hoang, Yutaka Furubayashi, Yasushi Hirose, Seiji Konuma, Toshihiro Shimada, Tetsuya Hasegawa
    THIN SOLID FILMS 516 17 5754 - 5757 2008年07月 [査読有り][通常論文]
     
    Transparent conductive oxide (TCO) films of polycrystalline Nb-doped TiO2 (TNO) were fabricated by post-annealing reactively sputtered amorphous films under H-2 atmosphere. Carrier transport properties of the H-2-annealed films were found to be strongly dependent on substrate temperature T-s and oxygen content in sputtering atmosphere. A minimum resistivity (rho) of 9.5 x 10(-4) Omega cm and an average visible transmittance of similar to 75% were obtained at T-s = RT and oxygen content of 10%. This rho value is of the same order as those of epitaxial TNO films, indicating that polycrystalline TNO has sufficient potential as a practical TCO suitable for large-area applications. (C) 2007 Elsevier B.V. All rights reserved.
  • T. Haosugi, A. Ueda, S. Nakao, N. Yamada, Y. Furubayashi, Y. Hirose, S. Konuma, T. Shimada, T. Hasegawa
    THIN SOLID FILMS 516 17 5750 - 5753 2008年07月 [査読有り][通常論文]
     
    We report on transparent conducting properties of anatase Ti0.94Nb0.06O2 (TNO) polycrystalline films on glass substrate, and discuss the role of grain crystallinity and grain boundary on resistivity. Thin films of TNO were deposited using pulsed laser deposition at substrate temperature ranging from room temperature to 350 degrees C, with subsequent H-2-annealing at 500 degrees C. Polycrystalline TNO films showed resistivity of 4.5 x 10(-4) Omega cm and 1.5 x 10(-3) Omega cm for films prepared at substrate temperature of room temperature and 250 degrees C, respectively. X-ray diffraction measurements and transmission electron microscopy reveal that grain crystallinity and grain boundary play key roles in conductive films. (C) 2007 Elsevier B.V. All rights reserved.
  • T. Hitosugi, N. Yamada, S. Nakao, K. Hatabayashi, T. Shimada, T. Hasegawa
    JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A 26 4 1027 - 1029 2008年07月 [査読有り][通常論文]
     
    We have investigated microscopic structures of sputter and pulsed laser deposited (PLD) anatase Nb-doped TiO2 transparent conducting films, and discuss what causes the degradation of resistivity in sputter-deposited films. Cross-sectional transmission electron microscope and polarized optical microscope images show inhomogeneous intragrain structures and small grains of similar to 10 mu m in sputter-deposited films. From comparison with PLD films, these results suggest that homogeneous film growth is the important factor to obtain highly conducting sputter-deposited film. (C) 2008 American Vacuum Society.
  • Susumu Ikeda, Koichiro Saiki, Yasuo Wada, Katsuhiko Inaba, Yoshiyasu Ito, Hirokazu Kikuchi, Kazuo Terashima, Toshihiro Shimada
    JOURNAL OF APPLIED PHYSICS 103 8 084313  2008年04月 [査読有り][通常論文]
     
    The factors influencing the graphoepitaxy of organic semiconductor alpha-sexithiophene (6T) on thermally oxidized silicon substrates were studied and it was discovered that a wider pitch in the microgrooves decreased the degree of graphoepitaxy. A more significant finding was that in-plane orientation could be changed by simple surface treatment. On UV/ozone-treated substrates (hydrophilic condition), the b-axis of 6T was parallel to the grooves. Further surface treatment with hexamethyl-disiloxane (under hydrophobic conditions) changed this in-plane orientation by 90 degrees. This change is due to the interaction between the topmost chemical species (functional groups) of the groove walls and organic molecules, a behavior peculiar to organic graphoepitaxy and exploitable for optimal orientation control in device processing. The nucleation and growth processes that cause the graphoepitaxy are discussed, based on the experimental results. (C) 2008 American Institute of Physics.
  • Toshihiro Shimada, Iwao Sugiura, Koichiro Saiki
    JAPANESE JOURNAL OF APPLIED PHYSICS 47 2 1422 - 1425 2008年02月 [査読有り][通常論文]
     
    Dielectric phase transition of epitaxial films of antiferroelectric squaric acid (SQ) with nanometer-order thickness was detected from the sample current measurement during reflection high-energy electron diffraction (RHEED) observation. The current changed markedly when the sample temperature was increased continuously. This phenomenon can be explained by considering the energy required to accommodate a charge in a molecule embedded on the surface of a dielectric, which is related to the phase transition in thin films through dielectric relaxation. The onset temperature was dependent on the substrate materials and film thickness, which indicates that the dielectric transition temperature is affected by epitaxial strain effects.
  • Toshihiro Shimada, Hiroyuki Nogawa, Takuya Noguchi, Yutaka Furubayashi, Yukio Yamamoto, Yasushi Hirose, Taro Hitosugi, Tetsuya Hasegawa
    JAPANESE JOURNAL OF APPLIED PHYSICS 47 2 1184 - 1187 2008年02月 [査読有り][通常論文]
     
    We fabricated heterojunctions using organic semiconductor pentacene sandwiched between two different magnetic electrodes: Co-doped TiO2 (Co:TiO2) and Fe. The conductance of the junctions was measured as a function of magnetic field. We found that the characteristics of the junctions are strongly dependent on the method used to deposit the Fe top electrode on pentacene. The magnetotransport properties can be explained by the effect of the interface morphology and spin polarization of interface traps.
  • N. Ogawa, A. Miyata, H. Tamaru, T. Suzuki, T. Shimada, T. Hasegawa, K. Saiki, K. Miyano
    CHEMICAL PHYSICS LETTERS 450 4-6 335 - 339 2008年01月 [査読有り][通常論文]
     
    For vapor-deposited tris(8-hydroxyquinoline) aluminum thin films, steady-state and subpicosecond transient optical anisotropy are investigated. It is found that the transient absorption anisotropy decays within tens of picoseconds. With a simple model calculation, the excited state population and anisotropy decay dynamics are disentangled, and the latter signal, the depolarization of the excited state, is explained by the energy transfer between the non-orthogonally-coordinated quinolate ligands. It is also shown that there are two pathways for this fast interligand energy transfer. (c) 2007 Elsevier B.V. All rights reserved.
  • Yasushi Hirose, Taro Hitosugi, Junpei Kasai, Yutaka Furubayashi, Kiyomi Nakajima, Toyohiro Chikyow, Seiji Konuma, Toshihiro Shimada, Tetsuya Hasegawa
    APPLIED PHYSICS LETTERS 92 4 042503  2008年01月 [査読有り][通常論文]
     
    A rutile CoxTi1-xO2-delta (100) film was heteroepitaxially grown on GaN (0001) by pulsed laser deposition. Magneto-optical Kerr effect and cross-sectional transmission electron microscope (TEM) measurements revealed that Co0.03Ti0.97O2-delta films prepared at an oxygen partial pressure of 10(-6)-10(-5) Torr with a carrier density n(e)>= 3x10(18) cm(-3) exhibit room-temperature ferromagnetism without any precipitates or secondary phase. High-resolution TEM observations confirmed that the interface between CoxTi1-xO2-delta and GaN is atomically smooth without intermixing. These results lead us to conclude that CoxTi1-xO2-delta is promising as a spin injector in GaN-based spin-electronic devices. (c) 2008 American Institute of Physics.
  • Hirose Yasushi, Hitosugi Taro, Kasai Junpei, Furubayashi Yutaka, Nakajima Kiyomi, Chikyow Toyohiro, Konuma Seiji, Shimada Toshihiro, Hasegawa Tetsuya
    PHYSICA STATUS SOLIDI C - CURRENT TOPICS IN SOLID STATE PHYSICS, VOL 5, NO 9 5 9 3104 - + 2008年 [査読有り][通常論文]
  • S. Ikeda, Y. Wada, K. Inaba, K. Terashima, T. Shimada, K. Saiki
    Materials Research Society Symposium Proceedings 1059 KK11-11  2008年 [査読有り][通常論文]
  • Sohei Okazaki, Noriaki Okazaki, Yasushi Hirose, Yutaka Furubayashi, Taro Hitosugi, Toshihiro Shimada, Tetsuya Hasegawa
    APPLIED SURFACE SCIENCE 254 3 757 - 759 2007年11月 [査読有り][通常論文]
     
    We propose a novel method for high-throughput quantitative analysis of thin-film conductivity sigma by using a scanning microwave microscope (S mu M). We demonstrated that composition spread thin films of Ti(1-x)Nb(x)O(2) can be utilized as a standard reference in a wide s range. The shift in Q-value measured by SmM along the composition-spread axis showed a single peak, which moved to the lower x side with film thickness. This behavior was confirmed by electrical field simulation using the finite element method. (C) 2007 Published by Elsevier B.V.
  • T. L. Chen, Y. Furubayashi, Y. Hirose, T. Hitosugi, T. Shimada, T. Hasegawa
    JOURNAL OF PHYSICS D-APPLIED PHYSICS 40 19 5961 - 5964 2007年10月 [査読有り][通常論文]
     
    Nb0.06Sn x Ti0.94-x O-2 ( x <= 0.3) thin films were grown by a pulsed-laser deposition method with varying Sn concentration. Through a combinatorial technique, we find that Sn concentration can reach a maximum of about x = 0.3 while maintaining the stable anatase phase and epitaxy. A doping concentration dependence of the refractivity is revealed, in which refractivity reduction at a wavelength of. = 500 nm is estimated to be 12.4% for Nb0.06Sn0.3Ti0.64O2 thin film. Sn doping induced band-gap blue shift can be contributed to the mixing of extended Sn 5s orbitals with the conduction band of TiO2. Low resistivity on the order of 10(-4) Omega cm at room temperature and high internal transmittance of more than 95% in the visible light region are exhibited for Nb0.06Sn x Ti0.94-x O2 thin films ( x <= 0.2). Optical and transport analyses demonstrate that doping Sn into Nb0.06Ti0.94O2 can reduce the refractivity while maintaining low resistivity and high transparency.
  • Manabu Ohtomo, Toshihiro Shimada, Tetsuya Hasegawa
    JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS & EXPRESS LETTERS 46 33-35 L817 - L819 2007年09月 [査読有り][通常論文]
     
    We report the correlation between sub-band-gap photocurrent and various device parameters of polycrystalline pentacene field-effect transistors. It was revealed that we can estimate various device characteristics including the origin of photocarriers and the density of gap states by changing the gate bias and drain voltage during the photocurrent measurement. In our experiment, carrier mobility was not related to photocurrent in the sub-band-gap region, even though a large photocurrent implies a large number of trapping states. The off-current obviously correlates with the photocurrent, suggesting that the origin of the off-currents is the gap states widely distributed near the valence band edge.
  • Manabu Ohtomo, Toshihiro Shimada, Koichiro Saiki, Tetsuya Hasegawa
    JOURNAL OF APPLIED PHYSICS 102 6 064510  2007年09月 [査読有り][通常論文]
     
    We investigated the photocurrent-voltage characteristics of pentacene field effect transistors in order to study the gap state distribution and carrier generation mechanism. In top-contact devices, the photocurrent spectrum versus photon energy exhibited the typical Urbach tail, while such a tail was not observed in bottom-contact devices. The formation of this Urbach tail can be explained by assuming that diffused gold nanoparticles at the gold/pentacene interface cause microfields and stabilize the excitons. This mechanism also provides an explanation for the reduced barrier height and Ohmic contact formation at "dirty" interfaces fabricated by metal deposition.
  • Naoomi Yamada, Taro Hitosugi, Ngoc Lam Huong Hoang, Yutaka Furubayashi, Yasushi Hirose, Toshihiro Shimada, Tetsuya Hasegawa
    JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS 46 8A 5275 - 5277 2007年08月 [査読有り][通常論文]
     
    Nb-doped anatase TiO2 (TNO) polycrystalline films with excellent conductivity and transparency were successfully fabricated by reactive sputtering combined with post annealing in H-2 gas. The H-2 annealing of as-deposited amorphous films caused an abrupt decrease in resistivity (p), which was accompanied by crystallization into the anatase structure. A film deposited on an unheated glass substrate with subsequent H2 annealing at 600 degrees C exhibited a resistivity of 9.5 x 10(-4) Omega cm and an average optical transmittance of similar to 75% in the visible region. This p value is of the same order as that of epitaxial TNO films, which indicates that sputtering is a promising technique for obtaining large-area TNO films.
  • Dong Guo, Tetsuhiko Miyadera, Susumu Ikeda, Toshihiro Shimada, Koichiro Saiki
    JOURNAL OF APPLIED PHYSICS 102 2 023706  2007年07月 [査読有り][通常論文]
     
    The gate bias and temperature dependent field-effect mobility and conductance of a polycrystalline pentacene thin film transistor (TFT) were analyzed to study the charge transport in the material. Since both heating and cooling can obviously change the film morphology, a relatively narrow temperature range was adopted to rule out the possible influence of structure variation on the device characterization. Both mobility and conductance values increased with the gate bias and showed a thermally activated Arrhenius-like behavior, while the threshold voltage deceased with temperature. Several models were compared, and it was found that the observations could only be well interpreted by a multiple trapping model, which suggests that the temperature and gate bias dependences should be attributed to the increased free charge carrier density. The density of trap states in the band gap was evaluated by the field-effect mobility as well as the field-effect conductance data. The results disclose a possible field-effect mobility much higher than the present record in a polycrystalline pentacene TFT. (C) 2007 American Institute of Physics.
  • Yui Ishii, Toshihiro Shimada, Noriaki Okazaki, Tetsuya Hasegawa
    LANGMUIR 23 12 6864 - 6868 2007年06月 [査読有り][通常論文]
     
    We found a novel oscillating phenomenon associated with surface wetting during the vacuum deposition of an organic semiconductor (rubrene) on a liquid film (bis(2-ethylhexyl)sebacate, B2EHS). In-situ observations by an optical microscope revealed that the oscillation was associated with the growth of the rubrene crystals. The oscillation frequency was proportional to the evaporation rate of rubrene. On the basis of the contact angle measurements, it was concluded that the oscillation is probably due to the change in the contact angle of the liquid caused by the formation of ultrathin rubrene films on the liquid surface.
  • Yui Ishii, Toshihiro Shimada, Noriaki Okazaki, Tetsuya Hasegawa
    LANGMUIR 23 12 6864 - 6868 2007年06月 [査読有り][通常論文]
     
    We found a novel oscillating phenomenon associated with surface wetting during the vacuum deposition of an organic semiconductor (rubrene) on a liquid film (bis(2-ethylhexyl)sebacate, B2EHS). In-situ observations by an optical microscope revealed that the oscillation was associated with the growth of the rubrene crystals. The oscillation frequency was proportional to the evaporation rate of rubrene. On the basis of the contact angle measurements, it was concluded that the oscillation is probably due to the change in the contact angle of the liquid caused by the formation of ultrathin rubrene films on the liquid surface.
  • S Ikeda, T Shimada, T Kiguchi, M, Saiki, K
    J. Appl. Phys. 101 094509  2007年05月 [査読有り][通常論文]
  • Yutaka Furubayashi, Naoomi Yamada, Yasushi Hirose, Yukio Yamamoto, Makoto Otani, Taro Hitosugi, Toshihiro Shimada, Tetsuya Hasegawa
    JOURNAL OF APPLIED PHYSICS 101 9 093705  2007年05月 [査読有り][通常論文]
     
    The transport properties of a d-electron-based transparent conducting oxide, Nb-doped anatase Ti1-xNbxO2, were investigated as a function of the Nb content x. From optical resistivity spectra, the static effective mass was evaluated to be similar to 0.4m(0) in the low-carrier-concentration (n(e)) regime, which is approximately the same as those of conventional transparent conducting oxides (TCOs), and two orders of magnitude smaller than that reported for rutile TiO2. The Hall mobility at room temperature, which is maximized at around x=0.01 (n(e)similar to 10(21) cm(-3)), was found to be mainly dominated by optical phonon scattering unlike that of other TCOs. (c) 2007 American Institute of Physics.
  • T. Hitosugi, A. Ueda, S. Nakao, N. Yamada, Y. Furubayashi, Y. Hirose, T. Shimada, T. Hasegawa
    APPLIED PHYSICS LETTERS 90 21 212106  2007年05月 [査読有り][通常論文]
     
    Nb-doped anatase TiO2 [Ti0.94Nb0.06O2 (TNO)] films with high electrical conductivity and transparency were fabricated on nonalkali glass using pulsed laser deposition and subsequent annealing in a H-2 atmosphere. The amorphous films as deposited on unheated substrates were found to crystallize, forming polycrystalline films at around 350 degrees C. The films annealed at 500 degrees C showed resistivity down to 4.6x10(-4) Omega cm at room temperature and optical transmittance of 60%-80% in the visible region, which are comparable to those of epitaxial films. These results indicate that TNO films have the potential to be practical transparent conducting oxides that could replace indium tin oxide. (c) 2007 American Institute of Physics.
  • Toshihiro Shimada, Koichiro Saiki
    JOURNAL OF ELECTRON SPECTROSCOPY AND RELATED PHENOMENA 154 3 119 - 122 2007年02月 [査読有り][通常論文]
     
    Electron energy loss spectra of ultrathin pentacene field effect transistors were measured by applying gate bias voltages. Tailing and shouldering of the primary peak on the energy loss side was observed for 1.5 nm thick films when a negative gate bias was applied. The energy loss spectra obtained from the deconvolution of the primary electron profile showed peaks, and the peak energies increased as a function of the gate bias voltage. This is consistent with the behavior of two-dimensional plasmons of field-induced carriers. The thickness dependence is explained by the thickness of the accumulation layer and the probing depth of the spectroscopy. (c) 2007 Elsevier B.V. All rights reserved.
  • Taro Hitosugi, Atsuki Ueda, Yutaka Furubayashi, Yasushi Hirose, Seiji Konuma, Toshihiro Shimada, Tetsuya Hasegawa
    JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS & EXPRESS LETTERS 46 1-3 L86 - L88 2007年01月 [査読有り][通常論文]
     
    Nb-doped anatase TiO2 (Ti0.94Nb0.06O2) films with excellent conductivity and transparency were deposited on non-alkali glass by pulsed laser deposition. X-ray diffraction analysis and transmission electron microscopy confirmed that the obtained films were polycrystalline with anatase structure. The films deposited at a substrate temperature of 250 degrees C with subsequent H-2 annealing at 500 degrees C showed a resistivity of 1.5 x 10(-3) Omega(.)cm at room temperature and an optical transmittance of 60-80% in the visible region. These results indicate that anatase Ti0.94Nb0.06O2 has great potential as a transparent conducting oxide that could replace Sn-doped In2O3 (ITO).
  • T. Suzuki, T. Shimada, K. Ueno, S. Ikeda, K. Saiki, T. Hasegawa
    Materials Research Society Symposium Proceedings 965 0965-S06-19  2007年 [査読有り][通常論文]
  • Toshihiro Shimada
    THIN SOLID FILMS 515 4 1568 - 1572 2006年12月 [査読有り][通常論文]
     
    We have examined the effect of the post-processing of spin-coated tetracene and DAST (4'-dimethylamino-N-methyl-4-stilbazolium tosylate) films in their solvent vapor to examine the possibility of precisely controlling the vapor pressure and studying the effect of applying electric fields to their structural properties. It was demonstrated that the solvent concentration in the vapor phase can be monitored by infrared spectroscopy. The thickness uniformity of the tetracene films was improved by the formation of a mixture of the tetracene crystals with the saturated solution ("solution ultrathin film") on the surface. Crystals with an ordered orientation were obtained by additionally applying an electric field during the vapor exposure of the DAST. The present technique for monitoring the solvent vapor pressure is also applicable for controlling the drying speed during the inkjet printing of functional organic materials. (c) 2006 Elsevier B.V. All rights reserved.
  • Toshihiro Shimada, Hisashi Ichikawa, Koichiro Saiki
    APPLIED PHYSICS LETTERS 89 14 141902  2006年10月 [査読有り][通常論文]
     
    Strong dependence of surface residence time of a planar organic molecule (hydrogen phthalocyanine) on vicinal surfaces of hydrogen-terminated Si(111) was observed in pulsed molecular beam scattering experiments. These results can be explained by the difference in the microscopic contact area of the molecules on the surface, which determines the binding force between the migrating molecules and the surface. The relationship between the observed behavior and the organic thin film growth is discussed. (c) 2006 American Institute of Physics.
  • H. Ichikawa, A. Koma, K. Saiki, T. Shimada
    SURFACE SCIENCE 600 17 L236 - L239 2006年09月 [査読有り][通常論文]
     
    The interaction between pentacene molecules and organic self-assembling monolayers formed on silicon oxides (SiO2) was studied by measuring the surface scattering time profile of the pulsed molecular beam of pentacene. It was found that the surface residence time (SRT) of pentacene was significantly reduced on a surface treated with hexamethyl silazarane (HMDS) compared with that on a bare SiO2 surface. The activation energies derived from the temperature dependence of the SRT were 24 kJ/mol and 100 kJ/mol for HMDS-SiO2 and the bare SiO2, respectively. A surface treated with octadecyltrichlorosilane (OTS) showed SRT values almost the same as those on the bare SiO2 surface, which was due to exposed SiO2 regions on the thermally-degraded OTS-SiO2. The growth mechanism with improved quality is due to the shallower adsorption potential and enhanced migration of pentacene by the surface alkylation. (c) 2006 Elsevier B.V. All rights reserved.
  • Susumu Ikeda, Koichiro Saiki, Ken Tsutsui, Tomohiko Edura, Yasuo Wada, Hiroyuki Miyazoe, Kazuo Terashima, Katsuhiko Inaba, Toru Mitsunaga, Toshihiro Shimada
    APPLIED PHYSICS LETTERS 88 25 251905  2006年06月 [査読有り][通常論文]
     
    Graphoepitaxial growth of a sexithiophene (6T) thin film was achieved on a thermally oxidized silicon surface with artificial periodic grooves. The surface structure was fabricated by electron beam lithography and the thin film was grown by molecular beam deposition. A well-pronounced, in-plane oriented component ([010](6T)parallel to grooves) was identified by grazing incidence x-ray diffraction, though there also existed some randomly oriented 6T grains. Presence of the graphoepitaxial component was also confirmed by results of the orientational analysis of atomic force microscopy images. It was shown that the in-plane orientation control of organic semiconductors is possible using graphoepitaxy. (c) 2006 American Institute of Physics.
  • Yasushi Hirose, Taro Hitosugi, Yutaka Furubayashi, Go Kinoda, Kazuhisa Inaba, Toshihiro Shimada, Tetsuya Hasegawa
    APPLIED PHYSICS LETTERS 88 25 252508  2006年06月 [査読有り][通常論文]
     
    We have investigated the Faraday spectra of ferromagnetic rutile Ti1-xCoxO2-delta films grown on Al2O3 (0001). The Faraday spectra strongly depended on the film thickness, revealing the significant effect of the multiple reflections of light. The intrinsic Faraday spectra of rutile Ti1-xCoxO2-delta were corrected for this multiple reflection effect on the basis of an optical model and compared with the absorption spectra in detail. The quantitatively good correspondence between intrinsic Faraday ellipticity and optical band edge strongly suggests that rutile Ti1-xCoxO2-delta is an intrinsic ferromagnetic semiconductor. The exchange parameters, N-0 alpha and N-0 beta, were estimated as the order of similar to 0.1 eV. (c) 2006 American Institute of Physics.
  • G Kinoda, T Hitosugi, Y Yamamoto, Y Furubayashi, K Inaba, Y Hirose, T Shimada, T Hasegawa
    JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS & EXPRESS LETTERS 45 12-16 L387 - L389 2006年04月 [査読有り][通常論文]
     
    We have fabricated Ti0.95-xNbxCo0.05O2 thin films by the pulsed laser deposition technique. Carrier density was found to be almost identical to the Nb concentration up to x = 0.06, indicating that doped Nb atoms generate carriers with > 80% efficiency. In this doping range, magneto-optical properties were significantly enhanced by Nb-doping. The remanent Faraday rotation at a wavelength of 405 nm was as high as 5.6 x 10(3) deg/cm, which is approximately one order of magnitude higher than that of a film free of Nb-doping. The present results support the hypothesis that conduction electrons play an essential role in the ferromagnetism of Co-doped TiO2.
  • T Hitosugi, G Kinoda, Y Yamamoto, Y Furubayashi, K Inaba, Y Hirose, K Nakajima, T Chikyow, T Shimada, T Hasegawa
    JOURNAL OF APPLIED PHYSICS 99 8 08M121  2006年04月 [査読有り][通常論文]
     
    We have investigated the carrier induced magnetic properties of anatase Ti1-x-yNbxMyO2 (M=Co,Fe) epitaxial films grown by the pulsed laser deposition technique. For Ti0.95-xNbxCo0.05O2, the n-type carrier density could be controlled in a wide range (4.9x10(17) cm(-3) to 2.7x10(21) cm(-3)) by Nb doping (x=0-0.2). The temperature dependence of the resistivity showed metallic behavior, suggesting that Ti0.95-xNbxCo0.05O2 undergoes a semiconductor to metal transition along with a slight carrier doping less than x < 0.03. In both Co-doped and Fe-doped films, we have confirmed hysteresis in M-H curves, and the anomalous Hall effect at room temperature. This strongly suggests that the charge carriers are spin polarized and mediate ferromagnetic interaction between local spins on transition metal ions. In the case of Ti0.94-xNbxFe0.06O2, ferromagnetism is sensitive to carrier concentration. That is, the x=0.002 film is nonmagnetic even at 3 K, while room-temperature ferromagnetism appears at x=0.01. (C) 2006 American Institute of Physics.
  • Y Furubayashi, T Hitosugi, Y Yamamoto, Y Hirose, G Kinoda, K Inaba, T Shimada, T Hasegawa
    THIN SOLID FILMS 496 1 157 - 159 2006年02月 [査読有り][通常論文]
     
    Single-crystalline Ti1-xNbxO2 (x = 0.2) films of 40 nm thickness were deposited on SrTiO3 (100) substrates by the pulsed laser deposition (PLD) technique. X-ray diffraction measurement confirmed epitaxial growth of anatase (001) film. The resistivity of Ti1-xNbxO2 films with x >= 0.03 is 2-3 x 10(-4) Omega cm at room temperature. The carrier density of Ti1-xNbxO2, which is almost proportional to the Nb concentration, can be controlled in a range of 1 x 10(19) to 2 x 10(21) cm(-3). Optical measurements revealed that internal transmittance in the visible and near-infrared region for films with x <= 0.03 was more than 97%. These results demonstrate that the presently developed anatase Ti1-xNxO2 is one of the promising candidates for the practical TCOs. (c) 2005 Elsevier B.V. All rights reserved.
  • K Inaba, T Hitosugi, Y Hirose, Y Furubayashi, G Kinoda, Y Yamamoto, TW Kim, H Fujioka, T Shimada, T Hasegawa
    JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS & EXPRESS LETTERS 45 4-7 L114 - L116 2006年02月 [査読有り][通常論文]
     
    Growth conditions for pulsed laser deposition of ferromagnetic Ti1-xFexO2 films with the rutile structure have been optimized on the basis of magnetooptical Kerr effect (MOKE) measurements. Thus, it was found that Ti0.94Fe0.06O2 films prepared under very limited growth conditions, at a substrate temperature of 650-675 degrees C and an oxygen pressure of similar to 1 x 10(-6) Torr, show ferromagnetism at room temperature. The optimized films revealed a saturation magnetization of 1.3 mu(B) and a coercive field of 0.14 kOe. From XPS measurements, the valence state of Fe was determined to be 3+, ruling out the possibility that ferromagnetism may arise from Fe3O4 nanoparticles.
  • M. Ohtani, T. Hitosugi, Y. Hirose, J. Nishimura, A. Ohtomo, M. Kawasaki, R. Inoue, M. Tonouchi, T. Shimada, T. Hasegawa
    Applied Surface Science 252 7 2622 - 2627 2006年01月21日 [査読有り][通常論文]
     
    We have developed a high-throughput combinatorial terahertz (THz) time-domain spectrometer (CTTDS) and applied to a ternary composition-spread film. This technique has possibilities to reveal a variety of physical properties such as complex refractive index, complex dielectric constant, and complex electrical conductivity. Further, this method is a non-contact and non-destructive way to map those physical properties. The demonstration of THz transmittance mapping of ternary composition-spread film, with a spatial resolution of 1 mm, reveals metallic behavior in specific range of film compositions. This prospective technique may serve as a convenient tool for the high-throughput, non-contact, non-destructive, and spatially resolved characterization suited for combinatorial composition-spread films. © 2005 Elsevier B.V. All rights reserved.
  • Ikeda, S Yamakawa, H Kiguchi, M Nakayama, M Saiki, K Shimada, T Miyadera, T Tsutsui, K, Wada, Y
    MOLECULAR CRYSTALS AND LIQUID CRYSTALS 455 347 - 351 2006年 [査読有り][通常論文]
  • Shimada, T Kaji, T, Saiki, K
    MOLECULAR CRYSTALS AND LIQUID CRYSTALS 455 317 - 325 2006年 [査読有り][通常論文]
  • Hidetaka Sugaya, Taro Hitosugi, Toshihiro Shimada, Toshihiko Nagamura, Yuji Matsumoto, Tetsuya Hasegawa
    AIP Conference Proceedings 850 1667 - 1668 2006年 [査読有り][通常論文]
     
    We have developed an ultrahigh-vacuum low-temperature magnetic force microscope (UHV-LT MFM) which can operate in magnetic fields. The microscope is based on a non-contact atomic force microscope using a piezoelectric cantilever. Measurements of hard disc media confirmed spatial resolution of ∼50 nm even at low temperatures down to 10 K. The maximum scanning area is as wide as 2.5 μm × 2.5 μm at 10 K and 7.5 μm × 7.5 μm at room temperature. We have also equipped the microscope with an electromagnet in order to apply external magnetic fields up to 0.25 T in the horizontal direction. The MFM head is mounted on a piezo-driven rotation stage, so that the direction of magnetic field relative to the sample surface can be set arbitrarily. © 2006 American Institute of Physics.
  • 福尾 則学, 眞嶋 秀樹, 一杉 太郎, 島田 敏宏, 内田 智史, 下山 淳一, 岸尾 光二, 松本 祐司, 長谷川 哲也
    日本物理学会講演概要集 61 0 648 - 648 一般社団法人 日本物理学会 2006年 [査読有り][通常論文]
  • 福尾 則学, 一杉 太郎, 島田 敏宏, 内田 智史, 下山 淳一, 岸尾 光二, 松本 祐司, 長谷川 哲也
    日本物理学会講演概要集 61 0 459 - 459 一般社団法人 日本物理学会 2006年 [査読有り][通常論文]
  • Toshihiro Shimada, Toshihiko Kaji, Koichiro Saiki
    MOLECULAR CRYSTALS AND LIQUID CRYSTALS 455 317 - 325 2006年 [査読有り][通常論文]
     
    Dye-sensitized anatase TiO2 (001) surface was prepared in the solution directly connected with an ultrahigh vacuum analysis chamber. We measured the ultraviolet photoelectron spectroscopy (UPS) and low energy electron transmission (LEET) of the dye-sensitized surfaces with and without illumination. The highest occupied molecular orbital (HOMO) and other levels showed different peak shifts in UPS when illuminated. The observations were discussed in relation to the device characteristics of a half photocell.
  • Susumu Ikeda, Hidemitsu Yamakawa, Manabu Kiguchi, Manabu Nakayama, Koichiro Saiki, Toshihiro Shimada, Tetsuhiko Miyadera, Ken Tsutsui, Yasuo Wada
    MOLECULAR CRYSTALS AND LIQUID CRYSTALS 455 347 - 351 2006年 [査読有り][通常論文]
     
    The influence of active layer thickness on transport characteristics of a copper phthalocyanine thin-film transistor was investigated by using the in situ FET measurement system with the film deposition continued up to several hundred nm in thickness. The drain current and mobility showed maximum values in the early stage of film growth and then decreased with the increasing film thickness. This result suggests that the over-grown layer affects the transport characteristics of the conductive accumulation layer, for example, owing to change of the electric field in the device.
  • Fukuo Noritaka, Mashima Hideki, Kinoda Go, Hitosugi Taro, Shimada Toshihiro, Shimizu Keisuke, Shimoyama Jun-ichi, Kishio Kohji, Matsumoto Yuji, Hasegawa Tetsuya
    LOW TEMPERATURE PHYSICS, PTS A AND B 850 797 - + 2006年 [査読有り][通常論文]
  • Hideki Mashima, Noritaka Fukuo, Go Kinoda, Taro Hitosugi, Toshihiro Shimada, Takeshi Kondo, Yoshinori Okada, Hiroshi Ikuta, Yuji Matsumoto, Tetsuya Hasegawa
    LOW TEMPERATURE PHYSICS, PTS A AND B 850 509 - + 2006年 [査読有り][通常論文]
     
    We have carried out scanning tunneling microscopy/spectroscopy (STM/STS) of heavily overdoped Bi2Sr2CuOy single crystals with T-c < 2 K. STS spectra showed a pseudogap structure with dull coherence peaks. Furthermore, we found that the magnitude of pseudogap is spatially non-uniform in a nm scale and varies from 10 to 30 meV. This supports a scenario that the electronic inhomogeneity is a consequence of randomly distributed Coulomb potential in the CuO2 layers induced by disorder of excess oxygen in the BiO layers.
  • 島田 敏宏
    日本結晶成長学会誌 32 5 347 - 352 日本結晶成長学会 2005年12月31日 [査読無し][通常論文]
     
    低分子の結晶性有機半導体薄膜は,トランジスタ等への応用が期待されており,結晶性・配向性を高める方法が探索されている.そのひとつとして,蒸着中に分子・薄膜を光励起する実験を行っている.励起状態の寿命が長く,光重合することが知られているC_<60>をMoS_2(0001)上に成長した場合と,有機ELに用いられ大きな静的双極子モーメントを持つ極性分子であるAlq3をKCl(001)上に成長した場合についての結果を紹介する.C_<60>については,光強度に対して閾値をもって核形成頻度が上昇した.また,第1層目の縁にそって第2層目が成長するという,光照射がない場合と異なる成長形態が見られた.Alq3については,照射するレーザーの偏光方向と平行に配向した針状結晶が成長することが見出された.
  • T Shimada, H Nogawa, T Hasegawa, R Okada, H Ichikawa, K Ueno, K Saiki
    APPLIED PHYSICS LETTERS 87 6 061917  2005年08月 [査読有り][通常論文]
     
    The epitaxial growth of pentacene on hydrogen-terminated Si(111) is reported. Reflection high energy electron diffraction (RHEED) revealed that the crystal packing resembles that in the bulk crystal even at a monolayer thickness, which was maintained in multilayers. A ripening effect was clearly observed by atomic force microscopy (AFM). These results are important to obtain oriented crystalline films of pentacene combined with silicon microdevices with reduced defect densities. (c) 2005 American Institute of Physics.
  • Toshihiro Shimada
    Electrical Engineering in Japan (English translation of Denki Gakkai Ronbunshi) 152 1 31 - 36 2005年07月15日 [査読有り][通常論文]
     
    Organic thin-film FETs have been studied by using electron spectroscopic techniques. Ultraviolet photoelectron spectroscopy has revealed that photopolymerization is enhanced by fabricating FET structure. Energy levels and the effective mass of charge carriers are discussed based on the results of photoelectron spectroscopy and electron energy loss spectroscopy. © 2005 Wiley Periodicals, Inc.
  • 島田 敏宏
    表面科学 = Journal of The Surface Science Society of Japan 26 7 410 - 414 日本表面科学会 2005年07月10日 [査読無し][通常論文]
  • Y Furubayashi, T Hitosugi, Y Yamamoto, K Inaba, G Kinoda, Y Hirose, T Shimada, T Hasegawa
    APPLIED PHYSICS LETTERS 86 25 252101  2005年06月 [査読有り][通常論文]
     
    This Letter focuses on the discovery of a transparent conducting oxide (TCO), anatase Ti1-xNbxO2 films with x=0.002-0.2. The resistivity of films with x >= 0.03 is 2-3x10(-4) Omega cm at room temperature. The carrier density of Ti1-xNbxO2 can be controlled in a range of 1x10(19) to 2x10(21) cm(-3). The internal transmittance for films with x <= 0.03 (40 nm thickness) is about 97% in the visible light region. The transport and optical parameters are comparable to those of typical TCOs, such as In2-xSnxO3 and ZnO. (c) 2005 American Institute of Physics.
  • M Kiguchi, M Nakayama, T Shimada, K Saiki
    PHYSICAL REVIEW B 71 3 035332  2005年01月 [査読有り][通常論文]
     
    The conductivity of organic semiconductors is measured in situ and continuously with a bottom contact configuration, as a function of film thickness at various gate voltages. The depletion layer thickness can be directly determined as a shift of the threshold thickness at which electric current began to flow. The in situ and continuous measurement can also determine qualitatively the accumulation layer thickness together with the distribution function of injected carriers. The accumulation layer thickness is a few monolayers and it does not depend on gate voltages. Rather it depends on the chemical species.
  • H Ichikawa, K Saiki, T Suzuki, T Hasegawa, T Shimada
    JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS & EXPRESS LETTERS 44 46-49 L1469 - L1471 2005年 [査読有り][通常論文]
     
    The surface morphology of tris(8-hydroxyquinoline)aluminum (III) (Alq(3)) epitaxially grown on KCl(001) was drastically changed by a simultaneous blue laser irradiation during vacuum deposition. Needle-shaped microcrystals were aligned to the polarization direction of the laser, Parallel to the KCl[010] axis. The origin of alignment was discussed in comparison with the growth of non-polar organic molecular films, in which anisotropic heating played an important role.
  • T Hitosugi, Y Hirose, J Kasai, Y Furubayashi, M Ohtani, K Nakajima, T Chikyow, T Shimada, T Hasegawa
    JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS & EXPRESS LETTERS 44 50-52 L1503 - L1505 2005年 [査読有り][通常論文]
     
    Rutile TiO2(100) thin films have been grown on GaN(0001) surfaces by using the pulsed laser deposition method. Reflection high-energy electron diffraction (RHEED) measurements during the deposition clearly revealed the layer-by-layer growth of TiO2 at a substrate temperature of 400 C under an oxygen pressure of 1 x 10(-5) Torr. X-ray diffraction and atomic force microscopy confirmed that the obtained films have high crystallinity with atomically flat surfaces. Pole figure measurements revealed the epitaxial relationship between TiO2 and GaN, namely that the in-plane TiO2< 010 > axis aligns parallel to the GaN < 10 (1) over bar0 >.
  • T Hitosugi, Y Furubayashi, A Ueda, K Itabashi, K Inaba, Y Hirose, G Kinoda, Y Yamamoto, T Shimada, T Hasegawa
    JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS & EXPRESS LETTERS 44 33-36 L1063 - L1065 2005年 [査読有り][通常論文]
     
    We present electrical transport and optical properties of Ta-doped TiO2 epitaxial thin films with varying Ta concentration grown by the pulsed laser deposition method. The Ti0.95Ta0.05O2 film exhibited a resistivity of 2.5 x 10(-4) Omega cm at room temperature, and an internal transmittance of 95% in the visible light region. These values are comparable to those of a Widely used transparent conducting oxide (TCO), indium tin oxide. Furthermore, this new material falls into a new category of TCOs that utilizes d electrons.
  • 福尾 則学, 長谷川 哲也, 眞嶋 秀樹, 木野田 剛, 一杉 太郎, 島田 敏宏, 清水 圭輔, 下山 淳一, 岸尾 光二, 松本 祐司
    日本物理学会講演概要集 60 0 498 - 498 一般社団法人 日本物理学会 2005年 [査読有り][通常論文]
  • 福尾 則学, 眞嶋 秀樹, 一杉 太郎, 島田 敏宏, 内田 智史, 下山 淳一, 岸尾 光二, 松本 祐司, 長谷川 哲也
    日本物理学会講演概要集 60 0 365 - 365 一般社団法人 日本物理学会 2005年 [査読有り][通常論文]
  • T Shimada, Y Yamamoto, T Kaji, K Itaka, H Koinuma, Y Kuninobu, Y Matsuo, E Nakamura, K Saiki
    SOLID STATE COMMUNICATIONS 132 3-4 197 - 201 2004年10月 [査読有り][通常論文]
     
    The Raman spectrum of buckyferrocene (Fe(C-60(CH3)(5))C5H5) changes during laser irradiation at 532 nm. A peak at 1465 cm(-1) decreases and a new peak at 1452 cm(-1) emerges, which resembles the change in the 'pentagonal pinch mode' during the photopolymerization of C-60- Photoinduced polymerization is strongly suggested because fragments from the buckyferrocene dimers are observed during the mass spectroscopy of laser desorbed solid samples. The rate constants of the photoinduced change for the powder crystals were determined at various photon intensities, and linearity was observed. The photoinduced change seems to occur extremely fast in densely packed buckyferrocene films fabricated by vacuum deposition. (C) 2004 Elsevier Ltd. All rights reserved.
  • Y Yamamoto, H Ichikawa, K Ueno, A Koma, K Saiki, T Shimada
    PHYSICAL REVIEW B 70 15 155415  2004年10月 [査読有り][通常論文]
     
    Thin films of C-60 were grown under laser irradiation at various intensities 0-200 mW/mm(2) and their growth shapes were investigated by ex situ atomic force microscopy (AFM) observation. The nucleation density of the first layer decreases with increasing laser intensity, probably due to the temperature rise of the migrating clusters. In addition to this gradual laser intensity dependence, an anomalous enhancement of the nucleation density was observed on irradiation at 50 mW/mm(2), which was attributed to the influence of photopolymerization. As for the second layer, there was a threshold laser intensity (200 mW/mm(2)) at which the nucleation density increased and the shape of the domains became irregular. This is due to the combined effect of hindered migration caused by the polymerized first layer and photopolymerization of the migrating molecules themselves. Energy transfer from the excited substrate to the migrating C-60 molecules is strongly suggested.
  • Y. Yamamoto, H. Ichikawa, K. Ueno, A. Koma, K. Saiki, T. Shimada
    Physical Review B - Condensed Matter and Materials Physics 70 15 1 - 155415 2004年10月 [査読有り][通常論文]
     
    Thin films of C60 were grown under laser irradiation at various intensities 0-200 mW/mm2 and their growth shapes were investigated by ex situ atomic force microscopy (AFM) observation. The nucleation density of the first layer decreases with increasing laser intensity, probably due to the temperature rise of the migrating clusters. In addition to this gradual laser intensity dependence, an anomalous enhancement of the nucleation density was observed on irradiation at 50 mW/mm2, which was attributed to the influence of photopolymerization. As for the second layer, there Was a threshold laser intensity (200 mW/mm2) at which the nucleation density increased and the shape of the domains became irregular. This is due to the combined effect of hindered migration caused by the polymerized first layer and photopolymerization of the migrating molecules themselves. Energy transfer from the excited substrate to the migrating C60 molecules is strongly suggested.
  • T Shimada, M Nagahori, A Koma
    SURFACE SCIENCE 564 1-3 L263 - L269 2004年08月 [査読有り][通常論文]
     
    We studied the effect of a direct electric field with an intensity gradient during the thin film deposition of liquid crystal molecules under ultrahigh vacuum. Alignment of elongated islands was observed when the electric field was higher than the threshold value of 4x10(5) to 5x10(6) Vm(-1), which was dependent on the substrate temperature. Layer-by-layer molecular aggregation in the direction of the higher field was observed when the force due to the field gradient was greater than 10(-20)-10(-19) N. The acceleration of molecular hopping between adjacent sites is not enough to account for the aggregation and enhancement of the long range hopping by the unidirectional force must be involved. The present observation indicates that the motion of a single molecule or a nm-sized cluster on the surface can be controlled by electric fields if the molecule has a permanent dipole. (C) 2004 Elsevier B.V. All rights reserved.
  • T Kaji, T Shimada, H Inoue, Y Kuninobu, Y Matsuo, E Nakamura, K Saiki
    JOURNAL OF PHYSICAL CHEMISTRY B 108 28 9914 - 9918 2004年07月 [査読有り][通常論文]
     
    Single crystalline epitaxial films of bucky ferrocene (Fe(C-60(CH3)(5))C5H5), a hybrid molecule of C-60 and ferrocene, were grown on MoS2(0001) substrates. By using reflection high-energy electron diffraction (RHEED) amplified by a microchannel plate (MCP), it was found that the lattice constant of the film decreased from 11.3 +/- 0.2 Angstrom at 1-2 monolayer (ML) to 10.2 +/- 0.2 Angstrom at 3 ML or thicker. Both of the lattice constants were incommensurate with that of the substrate, which indicates a new type of epitaxial growth. Valence electronic structures of the films at each thickness were measured with ultraviolet photoelectron spectroscopy (UPS) and the energy levels of molecular orbitals were identified in relation to the molecular orientation in the epitaxial film.
  • Nakashima Y, Shimada T, Yamada Y, Choi I, Yufu Y, Uike N
    [Rinsho ketsueki] The Japanese journal of clinical hematology 45 568 - 570 7 2004年07月 [査読有り][通常論文]
  • T Shimada, H Taira, T Miyadera, A Koma, K Saiki
    JOURNAL OF PHYSICAL CHEMISTRY B 108 17 5329 - 5332 2004年04月 [査読有り][通常論文]
     
    Ultraviolet photoelectron spectroscopy of epitaxial films of squaric acid (H2C4O4), a two-dimensional antiferroelectric organic material, is reported. The band structure parallel to the two-dimensional molecular plane was derived, in which the dispersion of the HOMO-2 band was found to be as large as 0.7 eV. The molecular orientation was estimated by analyzing the angular distribution of the photoelectron intensities from various molecular orbitals using independent atomic center approximation.
  • R Okada, T Miyadera, T Shimada, A Koma, K Ueno, K Saiki
    SURFACE SCIENCE 552 1-3 46 - 52 2004年03月 [査読有り][通常論文]
     
    Methyl-terminated Si(111) (Me-Si(111)) and bilayer-GaSe terminated Si (BGS) surfaces were investigated to explore their usefulness as the protection layer in the fabrication process of nanometer-scale self-assembled monolayers (SAMs). BGS was not stable in the reagent involved in the alkyl SAM formation, whereas Me-Si(111) was suitable for the protection layer. Anodization using atomic force microscope (AFM) and following HF and hexadecene treatments were performed to form nano-scale alkyl SAM lines on the Me-Si(111) surface. It was found from AFM observation and frictional force measurement that only the patterned areas were selectively covered with hexadecyl SAMs. (C) 2004 Elsevier B.V. All rights reserved.
  • T Shimada, T Suetsugu, T Miyadera, Y Yamamoto, A Koma, K Saiki, K Kudo
    APPLIED PHYSICS LETTERS 84 13 2439 - 2441 2004年03月 [査読有り][通常論文]
     
    Ultraviolet photoelectron spectroscopy (UPS) of C-60 thin-film field-effect transistors was measured with biasing gate voltages. A time-dependent change in the electronic structure of the C-60 film was, observed during the UPS measurement, which has never been observed in a C-60 film grown on a conductive substrate. The change was attributed to the accelerated polymerization of C-60 by comparing the UPS with that of the photopolymerized C-60. The polymerization Was associated with the increase in the field-effect electron mobility. This result indicates that mobile carriers produce reactive radicals in organic semiconductors. (C) 2004 American Institute of Physics.
  • 島田 敏宏
    電気学会論文誌. C, 電子・情報・システム部門誌 = The transactions of the Institute of Electrical Engineers of Japan. C, A publication of Electronics, Information and System Society 124 6 1229 - 1233 社団法人 電気学会 2004年 [査読無し][通常論文]
     
    Organic thin film FETs have been studied by using electron spectroscopic techniques. Ultraviolet photoelectron spectroscopy has revealed that photo polymerization is enhanced by fabricating FET structure. Energy levels and the effective mass of charge carriers are discussed based on the results of photoelectron spectroscopy and electron energy loss spectroscopy.
  • 福尾 則学, 眞嶋 秀樹, 木野田 剛, 一杉 太郎, 島田 敏宏, 清水 圭輔, 下山 淳一, 岸尾 光二, 長谷川 哲也
    日本物理学会講演概要集 59 0 463 - 463 一般社団法人 日本物理学会 2004年 [査読有り][通常論文]
  • M Kiguchi, M Nakayama, K Fujiwara, K Ueno, T Shimada, K Saiki
    JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS 42 12A L1408 - L1410 2003年12月 [査読有り][通常論文]
     
    We present a simple but powerful method to determine the thicknesses of the accumulation and depletion layers and the distribution curve of injected carriers in organic field effect transistors. The conductivity of organic semiconductors in thin film transistors was measured in situ and continuously with a bottom contact configuration, as a function of film thickness at various gate voltages. Using this method, the thicknesses of the accumulation and depletion layers of pentacene were determined to be 0.9 nm (V-G = - 15 V) and 5 nm (V-G = 15 V), respectively.
  • T Shimada, Y Yamamoto, K Saiki, A Koma
    JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS 42 8A L964 - L966 2003年08月 [査読有り][通常論文]
     
    It was found that electrochemical deposition of copper from a [Cu(2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline)(2)](+) ([Cu(bcp)(2)](+)) complex can be induced by photoirradiation at a certain cathode potential. It can be used for photopatterning of copper and controlling electrodeposition of copper in microelectronics applications. The mechanism of the photoassisted electrochemical deposition is suggested to be due to the reduced stability of the photoexcited complex.
  • T Shimada, T Kaji, K Saiki, A Koma
    JOURNAL OF CRYSTAL GROWTH 253 1-4 351 - 356 2003年06月 [査読有り][通常論文]
     
    Interferometric microscopy was used to observe the initial stage of the crystal growth of an organic charge transfer salt (DMe-DCNQI)(2)Cu by electrochemical reaction. It was found that concentric patterns started to appear after applying the potential difference between the electrodes. Bright rings of the concentric pattern moved outward for about 15 s and slowed down the movement after the period. It shows the change in the solution concentration just after the nucleation. (C) 2003 Elsevier Science B.V. All rights reserved.
  • Y Kaminuta, A Koma, T Shimada
    SOLID STATE COMMUNICATIONS 125 11-12 581 - 585 2003年03月 [査読有り][通常論文]
     
    Thin films of ionic compounds of ZnS clusters were measured by electron energy loss spectroscopy (EELS) and ultraviolet photoelectron spectroscopy (UPS). A size effect was observed in the valence plasmon energy measured by EELS from which the coherence length of the plasmon excitation can be estimated. The difference between the lowest excitations observed in UPS and EELS can be explained by the final state charging effect of a single cluster ion in UPS, which strongly depends upon the nominal charges of the clusters. (C) 2003 Published by Elsevier Science Ltd.
  • T Miyadera, A Koma, T Shimada
    SURFACE SCIENCE 526 1-2 177 - 183 2003年02月 [査読有り][通常論文]
     
    Angle-resolved ultraviolet photoelectron spectroscopy (ARUPS) of a Si(I 11) surface regularly terminated by methyl groups is reported. The electrochemical methylation was performed in inert atmosphere. The cleanliness and I x 1 ordering of the surface were confirmed by Auger electron spectroscopy and reflection high-energy electron diffraction, respectively. The energy band diagram has been obtained from ARUPS and each energy level was assigned from the comparison with the results of hydrogen-terminated Si(I 11) and quantum chemical cluster calculation. (C) 2002 Elsevier Science B.V. All rights reserved.
  • T Shimada, A Koma
    IEICE TRANSACTIONS ON ELECTRONICS E85C 6 1330 - 1331 2002年06月 [査読有り][通常論文]
     
    The prospects of electron spectroscopy of working organic electronic device structures are discussed. The experimental consideration and the result of actual measurement are presented.
  • K Ueno, H Shirota, T Kawamura, T Shimada, K Saiki, A Koma
    APPLIED SURFACE SCIENCE 190 1-4 485 - 490 2002年05月 [査読有り][通常論文]
     
    As a stable and 'epitaxial' passivation of a Si surface, we propose the bilayer-GaSe termination of a Si(1 1 1) surface. This surface is fabricated by depositing one monolayer of Ga on a clean Si(1 1 1) surface and subsequent annealing in a Se flux at around 520 degreesC, which results in unreconstructed 1 x 1 termination of the Si(1 1 1) surface by bilayer-GaSe. We found by scanning tunneling microscopy observation that slow cooling of the clean Si(1 1 1) surface from 850 to 520 degreesC with simultaneous deposition of a Ga flux results in better termination of the Si(1 1 1) surface. It was also found that this surface is stable against heating around 400 degreesC in O-2 atmosphere of 3 x 10(-3) Pa. By utilizing these properties of the bilayer-GaSe terminated surface, we have succeeded in fabricating ZnO quantum dots on this substrate. (C) 2002 Elsevier Science B.V. All rights reserved.
  • T Shimada, A Koma
    JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS 41 4B 2724 - 2726 2002年04月 [査読有り][通常論文]
     
    Electron spectroscopy experiments were attempted to the measure the electronic structure of organic field effect transistors (FETs) under a gate bias. Sample structure, experimental condition and results of FETs made of C-60 are described. C-60 FET structures showed irreversible change of the valence spectra during the ultraviolet photoelectron spectroscope measurement under a gate bias voltage. Electron energy loss spectroscopy after the change revealed a substantial lowering of the plasmon energy which indicates that the discrete spherical boundary condition of the molecular plasmon was broken. This suggests polymerization of C-60 by a combined effect of the gate bias and vacuum ultraviolet irradiation.
  • 島田 敏宏
    化学工業 52 8 605 - 609 化学工業社 2001年08月 [査読無し][通常論文]
  • T Shimada, H Nakatani, K Ueno, A Koma, Y Kuninobu, M Sawamura, E Nakamura
    JOURNAL OF APPLIED PHYSICS 90 1 209 - 212 2001年07月 [査読有り][通常論文]
     
    We demonstrate and analyze the epitaxial film formation of a molecular material that cannot be evaporated in vacuum due to thermal decomposition. A solution of the material is sprayed onto single crystalline van der Waals surfaces using a pulse valve under controlled vapor pressure of the solvent. Monolayer epitaxial films are obtained and we propose that the growth is mediated by liquid ultrathin films formed on the surface. Molecular arrangement and electronic structure of C-60(CH3)(5)H films are studied by reflection high energy electron diffraction and ultraviolet photoelectron spectroscopy, respectively. The present technique will be useful to study the electronic structure of recently synthesized molecular materials. (C) 2001 American Institute of Physics.
  • T Shimada, KA Cho, A Koma
    PHYSICAL REVIEW B 63 15 153404  2001年04月 [査読有り][通常論文]
     
    Kinetics of epitaxial thin film growth was analyzed from the experiments using pulsed organic molecular beams. It was found that a minimum appears in the nucleation density as a function of on-off cycle time when the substrate temperature is near the threshold between growth and reevaporation. This feature can be explained by assuming desorption of molecules induced by mutual collision on the surface, for which orientation-sensitive intermolecular forces are responsible.
  • H Ichikawa, T Shimada, A Koma
    JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS 40 3A L225 - L227 2001年03月 [査読有り][通常論文]
     
    Ordered films of tris-8-hydroxyquionolate-aluminum (Alq(3)) were grown by molecular beam deposition on cleaved KCl and KBr surfaces. The local molecular arrangements in the films were characterized by two-dimensional analysis of multiazimuth reflection medium energy electron diffraction (RMEED). A new type of curved one-dimensional crystallographic ordering was observed on KBr while a continuous point-on-line-type ordering was observed on KCl. Growth of the crystals consisting of mer isomers is suggested from the observed triple period superstructure.
  • T. Shimada, K. A. Cho, A. Koma
    Physical Review B - Condensed Matter and Materials Physics 63 15 2001年 [査読有り][通常論文]
     
    Kinetics of epitaxial thin film growth was analyzed from the experiments using pulsed organic molecular beams. It was found that a minimum appears in the nucleation density as a function of on-off cycle time when the substrate temperature is near the threshold between growth and reevaporation. This feature can be explained by assuming desorption of molecules induced by mutual collision on the surface, for which orientation-sensitive intermolecular forces are responsible. © 2001 The American Physical Society.
  • T. Shimada, R. Hashimoto, J. Koide, Y. Kamimuta, A. Koma
    Surface Science 470 1-2 L52 - L56 2000年12月20日 [査読有り][通常論文]
     
    Pulsed molecular beam scattering technique was applied to analyze the dynamics of a large planar molecule migrating on various surfaces (Au(1 1 1), graphite(0 0 0 1), mica (0 0 1), amorphous silicon oxide). It was found that molecules can stay on the surface for seconds without condensation. Activation energies have a magnitude comparable to those of a single ionic or covalent bonding, which reflects the additivity of the van der Waals interaction. Possible contribution of the diffusion to the surface residence time is discussed.
  • 島田 敏宏
    電子情報通信学会技術研究報告. OME, 有機エレクトロニクス 100 245 1 - 4 一般社団法人電子情報通信学会 2000年07月21日 [査読無し][通常論文]
     
    パルス分子線を用いて有機分子の真空蒸着における膜形成素過程の研究を行っている。水素フタロシアニンを様々な基板表面に照射し、反射時間プロファイルを測定した結果、低い基板温度においては秒単位の滞在時間を持つことがわかった。アレニウスプロットは直線にのり、表面・分子相互作用を決める特徴的なエネルギーが求められた。また、パルス分子線により成長したキナクリドン薄膜を原子間力顕微鏡で観察した結果、パルス幅に対して核形成密度に極小があらわれることが分かった。理論的解析を行い、分子2個が衝突することによる脱離過程がこの原因であることを明らかにした。
  • KA Cho, T Shimada, A Koma
    PHYSICA E 7 3-4 887 - 890 2000年05月 [査読有り][通常論文]
     
    Enhancement of the selectivity in organic molecular beam epitaxy was achieved by using pulsed molecular beams. It utilizes the nucleation kinetics before reaching stationary state of the growth. The time scale needed for the stationary state is estimated by changing the cycle time of the pulses. (C) 2000 Elsevier Science B.V. All rights reserved.
  • T Shimada, J Koide, KA Cho, A Koma
    JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A-VACUUM SURFACES AND FILMS 17 2 615 - 618 1999年03月 [査読有り][通常論文]
     
    Velocity distribution of the molecules emitted from effusion cells commonly used in molecular beam epitaxy was measured by using time-of-flight technique. The result for organic molecular phthalocyanine can be fitted by a shifted Maxwellian distribution. The effects of the temperature and the aspect ratios of the sources are discussed. (C) 1999 American Vacuum Society. [S0734-2101(99)03502-2].
  • T Shimada, H Nagahori, A Koma
    SURFACE SCIENCE 423 2-3 L285 - L290 1999年03月 [査読有り][通常論文]
     
    Ultrathin films of liquid crystal 12CB with monolayer-order thickness were grown on cleaved (001) surfaces of NaCl, KC1 and KBr substrates by molecular beam deposition. The molecular arrangement and the morphology of the films were analyzed by high sensitivity reflection high energy electron diffraction and atomic force microscopy (AFM), respectively. Epitaxial films were formed on KCI and KBr, whereas only one-dimensional ordering was observed on NaCl. AFM images of 12CB monolayers grown on NaCl just below the bulk transition temperature showed a characteristic morphology resembling an arabesque in sub-micron scales. It is attributed to orientational fluctuation of local crystal axes at growth fronts. (C) 1999 Elsevier Science B.V. All rights reserved.
  • T Shimada, T Sakurada, A Koma
    APPLIED PHYSICS LETTERS 74 7 941 - 943 1999年02月 [査読有り][通常論文]
     
    Selective epitaxial growth of organic materials is found and analyzed. It is observed during the molecular beam epitaxy of organic molecules and charge transfer complexes on ionic surfaces. The selectivity comes from lattice matching condition on critical nuclei formation in contrast to compound semiconductors for which covalent chemical bonding plays essential roles. It can be utilized to fabricate micropatterns of crystalline organic materials accompanied by lithography processes of alkali halides using NH3 plasma. Feasibility of building three-dimensional microstructures has also been shown, which is readily applicable to make photonic crystals from optically functional organic materials. (C) 1999 American Institute of Physics. [S0003-6951(99)02507-3].
  • KA Cho, T Shimada, M Sakurai, A Koma
    JOURNAL OF APPLIED PHYSICS 84 1 268 - 274 1998年07月 [査読有り][通常論文]
     
    Epitaxial growth of coronene (C24H12) was studied on substrates having no dangling bonds, such as hydrogen-terminated Si(lll), MoS2, MoTe2, and muscovite by using reflection high-energy electron diffraction. It was found that the sticking coefficient and the maximum thickness of the epitaxial films are strongly dependent on the substrate materials as well as on the growth temperature. The effectiveness of molecular mechanics calculation was examined by comparing the calculated stabilization energies with the experimental results. Importance of the electronic structure of substrates has been revealed and its effect was estimated quantitatively using the Lifshitz theory. The tendency that the interfacial dispersion force is stronger for smaller band gap materials has been shown from theoretical consideration. (C) 1998 American Institute of Physics.
  • T Shimada, H Taira, A Koma
    CHEMICAL PHYSICS LETTERS 291 3-4 419 - 424 1998年07月 [査読有り][通常論文]
     
    Ultrathin film growth of squaric add (H2C4O4) has been attempted on (001) surfaces of various alkali halides. Epitaxial films were obtained on KCl, NaBr and KBr substrates. Ultraviolet optical absorption spectra of the films were strongly dependent on the substrates, suggesting a possibility of modifying correlated hydrogen bonding by 'epitaxial pressure'. (C) 1998 Elsevier Science B.V. All rights reserved.
  • H Yamada, T Shimada, A Koma
    JOURNAL OF CHEMICAL PHYSICS 108 24 10256 - 10261 1998年06月 [査読有り][通常論文]
     
    We report the molecular beam epitaxy (MBE) growth of the manganese(II) phthalocyanine thin films with unique crystal structure and the measurement of their magnetic properties. The epitaxial films were grown on hydrogen-terminated Si(111) substrates. Reflection high energy electron diffraction observations showed that the crystal structure of the films is different from that of the bulk crystal. A large magnetic anisotropy was observed in the measurements with the SQUID magnetometer. The films did not show canted ferromagnetism which is usually observed in the beta-type crystal of manganese phthalocyanine. The magnetic susceptibility measured with magnetic field normal to the substrate obeyed the Curie-Weiss law with a negative Curie-Weiss constant, indicating the existence of the antiferromagnetic interaction. The negative Curie-Weiss constant was also observed in disordered films of manganese phthalocyanine. The variation of magnetic properties between the bulk crystal and the films is explained in terms of the difference in superexchange interaction caused by microscopic modification of the crystal structure, i.e., the stacking arrangement of the molecules. (C) 1998 American Institute of Physics.
  • T Shimada, K Hamaguchi, A Koma, FS Ohuchi
    APPLIED PHYSICS LETTERS 72 15 1869 - 1871 1998年04月 [査読有り][通常論文]
     
    Copper phtalocyanine (CuPc) films with the thickness controlled in molecular scales have been grown epitaxially on (0001) surfaces of layered materials, and electronic interaction at the interfaces have been studied by photoelectron spectroscopy. Materials with different electronic properties having different work functions (E-vac) were chosen as the substrates; semiconducting MoTe2 (E-vac=4.0 eV), semi-metallic highly oriented pyrolytic graphite (E-vac=4.5 eV) and metallic TaSe2 (E-vac=5.5 eV). Formation of interface dipole layers was found at CuPc/TaSe2 interfaces and molecular orbitals involved were identified. (C) 1998 American Institute of Physics.
  • M Mochida, T Shimada, A Koma
    JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A-VACUUM SURFACES AND FILMS 15 4 2119 - 2121 1997年07月 [査読有り][通常論文]
     
    Electron energy-loss spectroscopy (EELS) has been applied to in situ prepared (DMe-DCNQI)(2)Cu (DMe-DCNQI=2,5-dimethyl-N,N'-dicyanoquinonediimine). The intensity of the loss peaks changed significantly with the primary electron energies. It is probably due to the matrix element effects of the EELS. In conjunction with photoelectron spectroscopy using synchrotron radiation, the nature of the unoccupied levels has been elucidated. (C) 1997 American Vacuum Society.
  • T Shimada, H Taira, A Koma
    SURFACE SCIENCE 384 1-3 302 - 307 1997年07月 [査読有り][通常論文]
     
    Thermal desorption of epitaxial films of vanadyl phthalocyanine (VOPc:C32N8H16VO) and squaric acid (SQ:C4O4H2) was measured by using temperature programmed optical absorption spectroscopy. The activation energies for the desorption and pre exponential factors were determined by measuring the amount of the molecules remaining in the film. Change in the molecular arrangement of VOPc during the desorption was detected from the spectra. The effects of hydrogen bonding and antiferroelectric transition of SQ are discussed. (C) 1997 Elsevier Science B.V.
  • T Shimada, M Mochida, A Koma
    APPLIED SURFACE SCIENCE 113 322 - 325 1997年04月 [査読有り][通常論文]
     
    Ultraviolet photoelectron spectroscopy with various photon energies using synchrotron radiation was used to characterize chemical reactions associated with thin film growth of organic charge transfer complex (DMe-DCNQI)(2)Cu. Other molecular systems H2Pc, CuPc and C-60 were also studied to clarify the origin of the systematic relation between the spectra and the incident photon energy. Characteristic photon energy dependence of the photo-ionization cross section of molecular orbitals is useful to analyze the intermolecular reactions.
  • T Shimada, T Sakurada, A Koma
    ELECTROCHEMICAL SYNTHESIS AND MODIFICATION OF MATERIALS 451 167 - 172 1997年 [査読有り][通常論文]
     
    Ultrathin film growth of vanadyl phthalocyanine was attempted on vicinal surfaces of hydrogen-terminated Si(111) in order to see the effect of regularly spaced steps to the growth feature. It has been observed that molecular arrangement was substantially affected when the terrace width was narrower than 2 similar to 4 times of the molecular lattice constants. This result is probably due to the weakness of molecular interaction in the material and it accounts for the reason why ordinary graphoepitaxy has not been successful for the organic thin films.
  • T Shimada, H Nishikawa, A Koma, Y Furukawa, E Arakawa, K Takeshita, T Matsushita
    SURFACE SCIENCE 369 1-3 379 - 384 1996年12月 [査読有り][通常論文]
     
    The structure of ultrathin epitaxial films of layered NbSe2 and TaSe2 grown on Se-terminated GaAs((111) over bar) substrates was determined by grazing incidence X-ray diffraction. It was found that the crystallographic polytypes of the films were dependent on the growth temperatures. The temperature range for the growth of octahedrally coordinated TaSe2 was different from that of the bulk. Disappearance of 3R-type portion in NbSe2 at a high growth temperature will be favorable to fabricate superconducting ultrathin epitaxial films.
  • H Nishikawa, T Shimada, A Koma
    JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A-VACUUM SURFACES AND FILMS 14 5 2893 - 2896 1996年09月 [査読有り][通常論文]
     
    Epitaxial growth of TiSe2 films on Se-terminated GaAs(111)B substrates were carried out at different growth temperature by molecular beam epitaxy. Grown films have been investigated by reflection high energy electron diffraction, Auger electron spectroscopy, and measurements of resistivity parallel to the surface. TiSe2 epitaxial films have been obtained at various temperatures, but the optimum growth temperature was determined to be 400 degrees C. A charge density wave transition has been observed in the resistivity of the film grown at 400 degrees C, indicating that it has a good quality comparable to a bulk single crystal. (C) 1996 American Vacuum Society.
  • T Shimada, A Suzuki, T Sakurada, A Koma
    APPLIED PHYSICS LETTERS 68 18 2502 - 2504 1996年04月 [査読有り][通常論文]
     
    Hydrogen-terminated vicinal Si(lll) surfaces provide quasi-van der Waals substrates with regularly spaced atomic height steps for the epitaxy of organic material films. Molecular beam epitaxy of vanadyl and copper phthalocyanines (VOPc and CuPc) was attempted on just-cut and 7 degrees-miscut surfaces in order to investigate the effect of the steps on the epitaxial growth feature. The molecular arrangement of the films was characterized by a new technique using multiple-azimuth reflection high energy electron diffraction. Growth on misoriented substrates producted VOPc monolayer films consisting of one-dimensional chains nearly aligned to the steps and multilayer CuPc films with controlled domain orientations. (C) 1996 American Institute of Physics.
  • A Suzuki, T Shimada, A Koma
    JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS 35 2B L254 - L257 1996年02月 [査読有り][通常論文]
     
    A new method of patterning crystalline organic molecular films is proposed and demonstrated. It utilizes a selective growth, or the difference in the sticking coefficient of an organic material on various inorganic substrates in a certain temperature range. The object structure is first patterned on a single-crystalline substrate with an epitaxial film of a different material grown by molecular beam epitaxy (MBE) through a mask, and then a beam of the organic molecule is irradiated uniformly after removing the mask.
  • T SHIMADA, FS OHUCHI, BA PARKINSON
    JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS 33 5A 2696 - 2698 1994年05月 [査読有り][通常論文]
     
    Work functions and photothreshold values of various layered metal dichalcogenides (ZrSe2, HfSe2, NbSe2, 1T-TaS2, 2H-TaS2, MoS2, MoSe2, alpha-MoTe2, SnS2, SnSe2) have been measured by a photoemission technique. The measured photothreshold values, except for Sn compounds, are compared with the calculated values based on various band models. The agreement between the observed and calculated values is satisfactory for most of the materials.
  • T SHIMADA, Y FURUKAWA, E ARAKAWA, K TAKESHITA, T MATSUSHITA, H YAMAMOTO, A KOMA
    SOLID STATE COMMUNICATIONS 89 7 583 - 586 1994年02月 [査読有り][通常論文]
     
    Grazing incidence x-ray diffraction (GID) technique was applied to determine the three dimensional structures of NbSe2 films grown by van der Waals epitaxy. Atomic arrangements along the surface normal in nm-order films were established from the analysis of Bragg rod profiles measured with GID. The obtained structural polytypes of the films grown on HOPG and Se terminated GaAs(111BAR) were 2Hb and a mixture of 2Hb and 3R, respectively. This result indicates that the polytypes are controlled by the substrate materials in van der Waals epitaxy.
  • T SHIMADA, FS OHUCHI, A KOMA
    SURFACE SCIENCE 291 1-2 57 - 66 1993年07月 [査読有り][通常論文]
     
    Ultrathin films of TaS2, a two-dimensional metal known for charge density waves (CDWs) and polytypes, have been grown epitaxially on various layered substrates by molecular beam epitaxy and characterized with surface science techniques. STM image of the films shows irregular modulation which has similarity with that of the CDW. Ta(4f) XPS spectra of monolayer films have a correlation with the work functions of the substrates, probably due to the modification of the polytypes and the CDWs. The importance of the formation energy of the electric dipole layer at the interface is discussed.
  • T SHIMADA, FS OHUCHI, A KOMA
    JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS 32 3A 1182 - 1185 1993年03月 [査読有り][通常論文]
     
    A layered material SnSe2 was grown epitaxially on various layered materials (MoS2, NbSe2, graphite), while reacting with Al2O3(0001) substrates. The films were characterized by means of X-ray photoemission spectroscopy, reflection high energy electron diffraction, and scanning tunneling microscopy. The observed band bending was consistent to the work function difference between the film and the substrate, indicating the Schottky limit property of the junctions. Applications of this system are discussed.
  • T SHIMADA, FS OHUCHI, BA PARKINSON
    JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A-VACUUM SURFACES AND FILMS 10 3 539 - 542 1992年05月 [査読有り][通常論文]
     
    New sources of selenium and sulfur for UHV preparation of thin films are described. These sources, utilizing the high temperature thermal decomposition of SnSe2 and SnS2, are bakeable to at least 300-degrees-C providing much more convenience than element Se and S sources. The thermal decomposition is studied with thermal gravitometry, mass spectrometry, and x-ray photoemission spectroscopy. The utility of the sources is demonstrated by the epitaxial growth of TiSe2 on MoS2.
  • T SHIMADA, FS OHUCHI, BA PARKINSON
    PHASE TRANSFORMATION KINETICS IN THIN FILMS 230 231 - 236 1992年 [査読有り][通常論文]
  • FS OHUCHI, T SHIMADA, BA PARKINSON, K UENO, A KOMA
    JOURNAL OF CRYSTAL GROWTH 111 1-4 1033 - 1037 1991年05月 [査読有り][通常論文]
     
    The concept of Van der Waals epitaxy that has been recently introduced removes severe lattice matching requirement by using materials which only have strong bonding in two dimensions. We demonstrate that an epilayer of MoSe2 deposited on various substrates can produce films of high crystalline quality despite of large mismatch. RHEED oscillation, observed in-situ for growing MoSe2 epilayers, shows a layer-by-layer growth with evidence for for bilayer type growth, from which the 2H(b) polytype is determined. STM provides real space images of the morphology of the epilayer, and shows novel structures resulting from the large lattice mismatch where the epilayer atoms are commensurated.
  • T SHIMADA, FS OHUCHI, A KOMA
    ADVANCES IN SURFACE AND THIN FILM DIFFRACTION 208 47 - 52 1991年 [査読有り][通常論文]
  • K UENO, K SAIKI, T SHIMADA, A KOMA
    JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A-VACUUM SURFACES AND FILMS 8 1 68 - 72 1990年01月 [査読有り][通常論文]
  • K UENO, T SHIMADA, K SAIKI, A KOMA
    APPLIED PHYSICS LETTERS 56 4 327 - 329 1990年01月 [査読有り][通常論文]
  • Toshihiro Shimada, Hideki Yamamoto, Koichiro Saiki, Atsushi Koma
    Japanese Journal of Applied Physics 29 11 L2096 - L2098 1990年 [査読有り][通常論文]
     
    Diffracted beam intensities in reflection high energy electron diffraction (RHEED) have been observed to oscillate during the epitaxial growth of NbSe2and MoSe2on GaAs(111) infstrates. This is the first observation of RHEED oscillation in layered materials, to the author's knowledge. Monolayer- and bilayer-mode oscillations have been observed at different diffraction points. The existence of the bilayer-mode oscillation leads to the determination of the polytype of the grown films. it has also been shown that the antiphase portion of the grown film is considerably small. © 1990 IOP Publishing Ltd.
  • K SAIKI, K UENO, T SHIMADA, A KOMA
    JOURNAL OF CRYSTAL GROWTH 95 1-4 603 - 606 1989年02月 [査読有り][通常論文]
  • A. Kawahito, T. Endo, T. Yanase, T. Nagahama, T. Shimada
    J. Appl. Phys. in press [査読無し][通常論文]

MISC

講演・口頭発表等

  • MoS2のCVD成長-触媒ナノ粒子を用いたナノチューブ成長と薄膜の不純物・欠陥の解析  [招待講演]
    島田敏宏
    2018年日本表面真空学会学術講演会 2018年11月 口頭発表(招待・特別)
  • フラックス蒸発法による有機半導体単結晶成長と応用  [招待講演]
    島田敏宏
    応用物理学会第79回秋季学術講演会 2018年09月 口頭発表(招待・特別)
  • 有機半導体はどこまでフレキシブルか? ― 計算と実験から考える(特別講演)  [招待講演]
    島田敏宏
    第25回有機EL討論会 2017年11月 口頭発表(招待・特別)
  • Synthesis of nanomaterials by chemical vapor deposition  [招待講演]
    島田敏宏
    The 53rd Summer Annual Conference of the Korean Vacuum Society International Symposium, Gangwon-do, Korea 2017年08月 口頭発表(招待・特別)

担当経験のある科目(授業)

  • 大学院分析化学東京大学
  • 化学熱力学北海道大学
  • 化学I北海道大学
  • 大学院 応用物質化学I(固体化学)北海道大学
  • 無機化学「北海道大学」「東京大学」
  • 物性化学北海道大学

産業財産権



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