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• Carrier and heat transport properties of poly-crystalline GeSn films for thin-film transistor applications

  Uchida N., Hattori J., Lieten R., Ohishi Y., Takase R., Ishimaru M., Fukuda K., Maeda T., Locquet J.

  Journal of Applied Physics    126 ( 14 )   2019年10月  [査読有り]

   概要を見る

  © 2019 Author(s). Thin-film transistors (TFTs) on insulator substrates are widely used in applications from liquid crystal displays to sensor devices. However, insulator substrates with low heat conductivity lead to unfavorable self-heating effects in the channel regions. Herein, the carrier and heat transport properties of polycrystalline GeSn films on SiO2/Si substrates were improved by suppressing Sn segregation in the films to fabricate GeSn channel TFTs. Alloying with 5.5% Sn enabled the formation of larger grains than those in poly-Ge films after low-temperature annealing (below 520 °C) without Sn segregation. In addition, the films had a hole mobility of 40 cm2 V-1 s-1 at a hole density of 1.1 × 1018 cm-3 and a thermal conductivity of 12.1 Wm-1 K-1 at room temperature. The temperature dependences of the carrier and heat transport properties of the poly-GeSn films were investigated to accurately simulate a device with a poly-GeSn channel TFT. This was achieved by using the carrier transport measurements and numerical simulations of the heat transport in the Debye model. The simulated device allowed an accurate assessment of the self-heating effects of the TFT and thus provides a design guide for TFTs.

  DOI Scopus

• Thermoelectric Property in Orthorhombic-Domained SnSe Film

  Horide T., Murakami Y., Hirayama Y., Ishimaru M., Matsumoto K.

  ACS Applied Materials and Interfaces    11 ( 30 ) 27057 - 27063   2019年07月  [査読有り]

   概要を見る

  © 2019 American Chemical Society. Single-crystal SnSe exhibits extremely high thermoelectric properties, and fabrication of SnSe films is promising for practical application and basic research on properties. However, the high thermoelectric properties have not yet been reported in SnSe films and their thermoelectric properties and nanostructure have not yet been analyzed in detail. In the present study, a-axis-oriented epitaxial SnSe films were prepared to discuss the thermoelectric properties of the SnSe films. While the electrical conductivity of the films was orders of magnitude smaller than that in the single crystals at room temperature, surprisingly, the thermoelectric property (power factor) of the films was slightly higher than that in the single crystals at high temperatures (∼300 °C). The SnSe films contained orthorhombic domain boundaries with a spacing of several hundred nanometers. The orthorhombic domain boundaries caused carrier scattering and degraded the mobility of the films at room temperature, but their effect decreased with increasing temperature. Thus, the carrier scattering at domain boundaries results in characteristic temperature dependence of thermoelectric properties in the SnSe films. High thermoelectric properties at high temperatures were successfully achieved in the SnSe films in spite of the existence of domain boundaries, demonstrating the possibility of high-performance of SnSe thermoelectric films.

  DOI Scopus

• Observation of inhomogeneous depinning in YBa<inf>2</inf>Cu<inf>3</inf>O<inf>7</inf> composite multilayers

  Horide T., Ishimaru M., Matsumoto K.

  Superconductor Science and Technology    32 ( 8 )   2019年06月  [査読有り]

   概要を見る

  © 2019 IOP Publishing Ltd. Composite multilayer films (CMLs) comprising YBa2Cu3O7 + BaHfO3 (4.7 vol%)/YBa2Cu3O7 + BaHfO3 (3.1 vol%) were fabricated, and vortex behavior in the CMLs was evaluated to discuss inhomogeneous depinning of vortices. Magnetic field and angular dependences of critical current density (J c) in the CMLs were similar to those in the YBa2Cu3O7 + BaHfO3 (4.7 vol%) single layer film (SL). Variation of the CML structure shifted the matching field effect in global pinning force and irreversibility temperature. The J c in the YBa2Cu3O7 + BaHfO3 (4.7 vol%) SL was smaller than that in the YBa2Cu3O7 + BaHfO3 (3.1 vol%) SL, suggesting that vortices preferentially moved along the low-J c layers in the CMLs. The high-J c layers pinned the vortices in the low-J c layers, resulting in a shift of the matching field effect. These observations are characteristic of inhomogeneous depinning of vortices in the CMLs. The inhomogeneous depinning as well as pinned configuration should be considered for understanding J c and for structural design of pinning centers in YBa2Cu3O7 films.

  DOI Scopus

• Direct observations of crystallization processes of amorphous GeSn during thermal annealing: A temperature window for suppressing Sn segregation

  Higashiyama M., Ishimaru M., Okugawa M., Nakamura R.

  Journal of Applied Physics    125 ( 17 )   2019年05月  [査読有り]

   概要を見る

  © 2019 Author(s). The solubility limit of tin (Sn) in germanium (Ge) is very small, and, therefore, it is difficult to synthesize high Sn concentration GeSn crystals by conventional methods. An amorphous phase can contain elements beyond the solubility limit of the crystal state, and, therefore, recrystallization of the amorphous alloy is one of the possible ways to realize materials far from the equilibrium state. To suppress Sn precipitation during thermal annealing, knowledge of crystallization processes is required. In the present study, amorphous GeSn thin films with different Sn concentrations were prepared by sputtering, and their crystallization processes were examined by in situ transmission electron microscopy. It was found that the crystallization temperature decreases with increasing Sn concentration, and it became lower than the eutectic temperature when the Sn concentration exceeded ∼25 at. %. Radial distribution function analyses revealed that phase decomposition occurs in the amorphous state of the specimens which crystallize below the eutectic temperature, and Sn crystallites were simultaneously precipitated with crystallization. On the other hand, no remarkable phase decomposition was detected in amorphous GeSn with <25 at. % Sn. Sn precipitation occurred at a higher temperature than the crystallization in these specimens, and the difference between the crystallization and Sn precipitation temperatures became large with decreasing Sn concentration. Because of the existence of this temperature difference, a temperature window for suppressing Sn segregation existed. We demonstrated that large GeSn grains with high Sn concentration could be realized by annealing the specimens within the temperature window.

  DOI Scopus

• Compositional effects on radiation tolerance of amorphous silicon oxycarbide

  Mizuguchi S., Inoue S., Ishimaru M., Su Q., Nastasi M.

  Journal of Nuclear Materials    518   241 - 246   2019年05月  [査読有り]

   概要を見る

  © 2019 Elsevier B.V. Relationships between amorphous structures and radiation tolerance of silicon oxycarbide (SiOC) glasses with different composition, SiO 2 :SiC = 2:1 (SiO 2 -rich), 1:1 (equiatomic), and 1:2 (SiC-rich), were examined by transmission electron microscopy and atomic pair-distribution function (PDF). These specimens were irradiated with 120 keV helium (He) ions at room temperature. The PDF results indicated that the structure of SiOC alloys are almost the same in irradiation and implantation regions. It was found that SiO 2 -rich specimens show a greater radiation resistance than SiC-rich ones: the formation of He bubbles was highly suppressed in the SiO 2 -rich and equiatomic compositions after even 90 at.% He implantation, whereas pronounced swelling occurred in the SiC-rich composition. The first sharp diffraction peak revealed that the size of network voids formed by connecting the SiO x C 4-x tetrahedra in SiO 2 -rich and equiatomic specimens is much larger than the diameter of He atom, suggesting that He atoms can easily migrate in the amorphous SiOC networks.

  DOI Scopus

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• Crystallization processes of amorphous GeSn on thermal annealing

  M. Ishimaru, R. Takase

  11th Polish-Japanese Joint Seminar on Micro and Nano Analysis  2016年09月  -  2016年09月   

• Radial distribution function analysis of ion-beam-irradiated covalent materials

  M. Ishimaru

  47th Annual Meeting of Korean Society of Microscopy “Session: Special International Symposium on Microscopy and Microanalysis of Materials”  2015年11月  -  2015年11月   

• Structural changes of nanostructured SiC under radiation environments

  M. Ishimaru, K. Imada, Y. Zhang, W. J. Weber, S. Shannon

  Materials Research Society 2014 Fall Meeting  2014年11月  -  2014年12月   

• Radiation-induced amorphization resistance of nanostructured SiC

  M. Ishimaru. K. Imada

  10th Japanese-Polish Joint Seminar on Micro and Nano Analysis  (Sapporo, Japan)  2014年10月  -  2014年10月   

• Electron diffraction study on radiation-induced chemical disorder in covalent materials

  M. Ishimaru

  9th Polish-Japanese Joint Seminar on Micro and Nano Analysis  (Sieniawa, Poland)  2012年09月  -  2012年09月   

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• 公益社団法人日本顕微鏡学会第６１回学会賞（瀬藤賞）（応用研究（非生物）部門）

  2016年06月   公益社団法人日本顕微鏡学会   日本国

  受賞者：  石丸　学

• 社団法人応用物理学会第６回JJAP（応用物理学会英文誌）編集貢献賞

  2008年04月11日   社団法人応用物理学会   日本国

  受賞者：  石丸　学

• 社団法人日本金属学会第６６回功績賞（物性部門）

  2008年03月26日   社団法人日本金属学会   日本国

  受賞者：  石丸　学

• 2007 MRS Fall Meeting Best Poster Award

  2007年11月26日   Materials Research Society   日本国

  受賞者：  J. H. Won, A. Kovács, M. Ishimaru, Y. Hirotsu

• 財団法人本多記念会第２７回本多記念研究奨励賞

  2006年05月12日   財団法人本多記念会   日本国

  受賞者：  石丸　学

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• 高レベル放射性廃棄物の処理用コンテナ材料の開発研究

  基盤研究(B)

  研究期間:  2013年04月  -  2016年03月

  研究課題番号:  25289249

• 自発的ナノスケール相分離とそれを利用した低次元ナノ構造体の創製

  基盤研究(C)

  研究期間:  2010年04月  -  2013年03月

  研究課題番号:  22560696

• 照射環境下における炭化ケイ素の非晶質化過程と化学的短範囲規則性

  基盤研究(C)

  研究期間:  2007年04月  -  2009年03月

  研究課題番号:  19560664

• 相変化型光メモリー材料における記録層の非晶質局所構造と結晶化速度の関係

  基盤研究(C)

  研究期間:  2004年04月  -  2006年03月

  研究課題番号:  16560008

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社会貢献活動（講演会・出前講義等） 【 表示 ／ 非表示 】

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• 電子で見る原子の世界－電子顕微鏡による材料の診断－

  2014年11月

  　

  　

   概要を見る

  福岡県立北筑高等学校