2024/07/22 更新

写真a

カコ グングン
賈 軍軍
所属
理工学術院 国際理工学センター(理工学術院)
職名
准教授(任期付)
学位
博士(環境学) ( 東京大学 )
プロフィール

私の研究活動は機能性酸化物に代表される無機固体物質及び関連した光・電子デバイスの研究分野に集約されている。薄膜トランジスタ(TFT)、熱電素子、光触媒、圧電デバイスなどのエネルギーならびに環境技術の応用に向けて、スパッタ法やMBE法を用いた無機薄膜材料の合成・物性評価、及び光・電子デバイスの作製・性能評価に取り組んでいる。

経歴

  • 2019年04月
    -
    継続中

    早稲田大学   准教授

  • 2012年09月
    -
    2019年03月

    青山学院大学   理工学部   助教

  • 2011年04月
    -
    2012年08月

    青山学院大学   理工学部   博士研究員

  • 2007年04月
    -
    2011年03月

    東京大学   新領域創成科学研究科   博士課程

委員歴

  • 2024年06月
    -
    継続中

    日本材料学会  副国際委員

  • 2024年04月
    -
    継続中

    日本表面真空学会 SP部会  幹事

  • 2022年04月
    -
    継続中

    総合研究奨励会 透明酸化物光・電子材料研究会  学界委員

  • 2012年09月
    -
    2022年03月

    日本学術振興会 「透明酸化物光・電子材料第166委員会」  学界委員・運営委員

研究分野

  • 半導体、光物性、原子物理

研究キーワード

  • 非線形光学

  • 欠陥構造解析

  • プラズモン二クス

  • 半導体物理とデバイス

受賞

  • Poster Encouragement Award

    2023年12月   Symposium S2 of MRM2023, 日本材料学会(MRSJ)   Tuning Polaron-Induced Coloration in Tungsten Oxide Films  

    受賞者: 賈 軍軍

  • 第11回 WASEDA e-Teaching Award

    2022年06月   早稲田大学  

    受賞者: 賈軍軍

  • 第5回 薄膜・表面物理分科会 論文賞

    2021年03月   日本応用物理学会  

  • 論文賞

    2019年11月   日本熱物性学会  

  • 研究奨励賞

    2017年08月   International Union of Materials Research Societies(IUMRS)   Tailoring Crystal Structures of Sputtered TiO2 Film by Impurity Doping  

    受賞者: 賈 軍軍

  • Best Poster Award

    2016年05月   European Materials Research Society (EMRS)   In-situ Brouwer analysis on possible defects in homologous In2O3(ZnO)m films  

    受賞者: 賈 軍軍

  • Silver Poster Award

    2015年07月   The 9th International Symposium on Transparent Oxide and Related Materials for Electronics and Optics (TOEO-9)   Sn-doping Induced Structural Changes for Sputtered TiO2 Films  

    受賞者: 賈 軍軍

  • JMR雑誌論文賞

    2015年04月   アメリカ材料学会   Thermophysical properties of SnO2-based transparent conductive films: Effect of dopant species and structure compared with In2O3-, ZnO-, and TiO2-based films  

    受賞者: N. Oka, S. Yamada, T. Yagi, N. Taketoshi, J. Jia, Y. Shigesato

▼全件表示

メディア報道

  • 早大、周波数フィルター用の圧電薄膜の電気機械結合係数の向上とメカニズムを解明

    新聞・雑誌

    執筆者: 本人以外  

    日本経済新聞   日本経済新聞  

    https://www.nikkei.com/article/DGXLRSP619157_X01C21A0000000/  

    2021年10月

  • スマートフォンの未来を支える周波数フィルター用の圧電薄膜の電気機械結合係数の向上とメカニズムの解明

    会誌・広報誌

    執筆者: 本人以外  

    科学技術振興機構 広報課   科学技術振興機構 広報課  

    https://www.jst.go.jp/pr/announce/20211008/index.html  

    2021年10月

 

論文

  • Emerging solid-state thermal switching materials, Accepted

    Junjun Jia, Shuchen Li, Xi Chen, Yuzo Shigesato

    Advanced Functional Materials    2024年07月  [査読有り]  [招待有り]

    担当区分:筆頭著者, 責任著者

  • Thermal conduction in polycrystalline or amorphous transparent conductive oxide films

    Junjun Jia, Takashi Yagi, Yuzo Shigesato

    Solar Energy Materials and Solar Cells    2024年07月  [査読有り]  [招待有り]

    担当区分:筆頭著者, 責任著者

    DOI

    Scopus

    1
    被引用数
    (Scopus)
  • Enhanced electromechanical coupling from cation local structures in (Mg,Zn)O

    Junjun Jia, Daiki Kishi, Ningrui Bai, Toshihiko Okajima, Fabio Lesari, Takahiko Yanagitani

    Physical Review B    2024年04月  [査読有り]

    担当区分:筆頭著者, 責任著者

    DOI

    Scopus

    1
    被引用数
    (Scopus)
  • Control of the Emission and Excitation Energies in Pr3+-Activated Perovskite Oxide–Oxynitrides by Bandgap Engineering

    Yasushi Sato, Jin Odahara, Rie Yanamoto, Suzuka Noda, Takuya Hasegawa, Shu Yin, Junjun Jia, Masato Kakihana

    Chemistry of Materials    2023年12月  [査読有り]

    DOI

    Scopus

    1
    被引用数
    (Scopus)
  • Tunable Organic ENZ Materials with Large Optical Nonlinearity

    Qili Hu, Xinlan Yu, Hongqi Liu, Jiahuan Qiu, Wei Tang, Sen Liang, Linjun Li, Miao Du, Junjun Jia, Hui Ye

    ACS Photonics    2023年09月  [査読有り]

    担当区分:責任著者

    DOI

    Scopus

    2
    被引用数
    (Scopus)
  • Pressure-Induced Transition from Wurtzite and Epitaxial Stabilization for Thin Films of Rocksalt MgSnN2

    Kaede Makiuchi, Fumio Kawamura, Junjun Jia, Yelim Song, Shunichiro Yata, Hitoshi Tampo, Hidenobu Murata, Naoomi Yamada

    Chemistry of Materials    2023年03月  [査読有り]

    DOI

    Scopus

    5
    被引用数
    (Scopus)
  • Revealing the simultaneous increase in transient transmission and reflectivity in InN

    Junjun Jia, Takashi Yagi, Mari Mizutani, Naoomi Yamada, Toshiki Makimoto

    Journal of Applied Physics   132 ( 16 ) 165702 - 165702  2022年10月  [査読有り]

    担当区分:筆頭著者, 責任著者

     概要を見る

    The ultrafast transient behavior of InN under intensive laser irradiation remains unclear. The simultaneous measurements of pump–probe transient transmission and reflectivity are reported in this study. The irradiation-induced change in the dielectric constant of InN films due to the generation of thermalized carriers gives rise to complex transient behavior, and simultaneous increase in both transient transmission and reflectivity are observed at certain wavelengths. Herein, transient transmission is interpreted as the occupation probability of thermalized electrons at the probing level originating from a hot Fermi–Dirac distribution, and our calculation results are in good agreement with the experiments. Likewise, the Drude-like response due to the collective motion of thermalized carriers causes the increase in transient reflectivity, which depends on the change of dielectric constant caused by the collective motion of thermalized carriers. The ultrafast carrier dynamics is modeled by calculating the temporal evolution of the occupation probability of thermalized electrons in the conduction band. On the basis of the two-temperature model, the electron–phonon scattering time is extrapolated to be [Formula: see text] fs in InN, which dominates the cooling of excited electrons.

    DOI

    Scopus

    1
    被引用数
    (Scopus)
  • Origin of Enhanced Electromechanical Coupling in (Yb,Al)N Nitride Alloys

    JUNJUN JIA

    Physical Review Applied   16   044009  2021年10月  [査読有り]

    担当区分:筆頭著者, 責任著者

    DOI

  • Temporal Evolution of Microscopic Structure and Functionality during Crystallization of Amorphous Indium-Based Oxide Films

    JUNJUN JIA

    ACS Applied Materials & Interfaces    2021年06月  [査読有り]

    担当区分:筆頭著者, 責任著者

    DOI

  • Evolution of Defect Structures and Deep Subgap States during Annealing of Amorphous In-Ga-Zn Oxide for Thin-Film Transistors

    Junjun Jia, Ayaka Suko, Yuzo Shigesato, Toshihiro Okajima, Keiko Inoue, Hiroyuki Hosomi

    Physical Review Applied   9 ( 1 )  2018年01月  [査読有り]

    担当区分:筆頭著者

     概要を見る

    We investigate the evolution behavior of defect structures and the subgap states in In-Ga-Zn oxide (IGZO) films with increasing postannealing temperature by means of extended x-ray absorption fine-structure (EXAFS) measurements, positron annihilation lifetime spectroscopy (PALS), and cathodoluminescence (CL) spectroscopy, aiming to understand the relationship between defect structures and subgap states. EXAFS measurements reveal the varied oxygen coordination numbers around cations during postannealing and confirm two types of point defects, namely, excess oxygen around Ga atoms and oxygen deficiency around In and/or Zn atoms. PALS suggests the existence of cation-vacancy (VM)-related clusters with neutral or negative charge in both amorphous and polycrystalline IGZO films. CL spectra show a main emission band at approximately 1.85 eV for IGZO films, and a distinct shoulder located at about 2.15 eV for IGZO films postannealed above 600 °C. These two emission bands are assigned to a recombination between the electrons in the conduction band and/or in the shallow donor levels near the conduction band and the acceptors trapped above the valence-band maximum. The shallow donors are attributed to the oxygen deficiency, and the acceptors are thought to possibly arise from the excess oxygen or the VM-related clusters. These results open up an alternative route for understanding the device instability of amorphous IGZO-based thin-film transistors, especially the presence of the neutral or negatively charged VM-related clusters in amorphous IGZO films.

    DOI

    Scopus

    28
    被引用数
    (Scopus)
  • In situ analyses on negative ions in the indium-gallium-zinc oxide sputtering process

    Junjun Jia, Yoshifumi Torigoshi, Yuzo Shigesato

    Applied Physics Letters   103 ( 1 )  2013年07月  [査読有り]

    担当区分:筆頭著者

     概要を見る

    The origin of negative ions in the dc magnetron sputtering process using a ceramic indium-gallium-zinc oxide target has been investigated by in situ analyses. The observed negative ions are mainly O- with energies corresponding to the target voltage, which originates from the target and barely from the reactive gas (O2). Dissociation of ZnO-, GaO-, ZnO2 -, and GaO2 - radicals also contributes to the total negative ion flux. Furthermore, we find that some sputtering parameters, such as the type of sputtering gas (Ar or Kr), sputtering power, total gas pressure, and magnetic field strength at the target surface, can be used to control the energy distribution of the O- ion flux. © 2013 AIP Publishing LLC.

    DOI

    Scopus

    36
    被引用数
    (Scopus)
  • Experimental observation on the Fermi level shift in polycrystalline Al-doped ZnO films

    Junjun Jia, Aiko Takasaki, Nobuto Oka, Yuzo Shigesato

    JOURNAL OF APPLIED PHYSICS   112 ( 1 )  2012年07月  [査読有り]

    担当区分:筆頭著者

     概要を見る

    The shift of the Fermi level in polycrystalline aluminum doped zinc oxide (AZO) films was studied by investigating the carrier density dependence of the optical band gap and work function. The optical band gap showed a positive linear relationship with the two-thirds power of carrier density n(e)(2/3). The work function ranged from 4.56 to 4.73 eV and showed a negative linear relationship with n(e)(2/3). These two phenomena are well explained on the basis of Burstein-Moss effect by considering the nonparabolic nature of the conduction band, indicating that the shift of Fermi level exhibits a nonparabolic nature of the conduction band for the polycrystalline AZO film. The variation of work function with the carrier density reveals that the shift of the surface Fermi level can be tailored by the carrier density in the polycrystalline AZO films. The controllability between the work function and the carrier density in polycrystalline AZO films offers great potential advantages in the development of optoelectronic devices. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4733969]

    DOI

    Scopus

    93
    被引用数
    (Scopus)
  • Co-sputtering construction of Gd-doped WO3 nano-stalagmites film for bi-funcional electrochromic and energy storage applications

    Yi Yin, Yiwen Zhu, Pengkun Liao, Xiaoyi Yuan, Junjun Jia, Changyong Lan, Chun Li

    Chemical Engineering Journal    2024年05月  [査読有り]

    担当区分:責任著者

    DOI

    Scopus

    2
    被引用数
    (Scopus)
  • Thin-film synthesis of metastable rocksalt MgSnN2 without epitaxial stabilization

    Kaede Makiuchi, Fumio Kawamura, Junjun Jia, Hidenobu Murata, Naoomi Yamada

    Materials Letters     135830 - 135830  2023年12月  [査読有り]

    DOI

    Scopus

  • Cyclic thermal conductivity changes of Pd-catalyzed Ni-Mg alloy films by gasochromic hydro- and dehydrogenations

    Hiroki Yagi, Takashi YAGI, Yuichiro Yamashita, makoto kashiwagi, Junjun Jia, Yuki Oguchi, Naoyuki Taketoshi, Yuzo SHIGESATO

    Applied Physics Express    2023年09月

     概要を見る

    Abstract

    To investigate the thermal-switching properties of Pd-catalyzed Ni-Mg alloy films, we conducted in-situ analyses of the films’ electrical, optical, and thermal properties through hydrogen gasochromic reactions. These reactions allow the films to reversibly switch between metallic (dehydride) and semiconductor (hydride) phases. The thermal conductivities of the metallic and semiconductor states were found to be 14 and 1.0 Wm−1K−1, respectively. By applying the Wiedemann–Franz law (WFL), we attributed the significant decrease in thermal conductivity during hydrogenation to the reduction in free electrons.

    DOI

    Scopus

    3
    被引用数
    (Scopus)
  • Structural, optical and electrical properties of ZnO–InN quaternary compound films

    Junjun Jia, Tomohiko Hara, Shin-ichi Nakamura, Yuzo Shigesato

    Thin Solid Films     139961 - 139961  2023年06月  [査読有り]

    担当区分:筆頭著者, 責任著者

    DOI

    Scopus

    3
    被引用数
    (Scopus)
  • Enhanced Electromechanical Coupling in Yb-Substituted III–V Nitride Alloys

    Junjun Jia, Naoya Iwata, Masashi Suzuki, Takahiko Yanagitani

    ACS Applied Electronic Materials    2022年06月  [査読有り]

    担当区分:筆頭著者, 責任著者

    DOI

    Scopus

    5
    被引用数
    (Scopus)
  • Electron transport properties in degenerate magnesium tin oxynitride (Mg1−xSn1+xN2−2yO2y) with average wurtzite structure

    Shunichiro Yata, Mari Mizutani, Kaede Makiuchi, Fumio Kawamura, Masataka Imura, Hidenobu Murata, Junjun Jia, Naoomi Yamada

    Journal of Applied Physics   131 ( 7 ) 075302 - 075302  2022年02月  [査読有り]

     概要を見る

    MgSnN2 with an average wurtzite structure (wz-MgSnN2) has recently emerged as a pseudo-III-nitride semiconductor, studied for applications in tandem solar cells, green light-emitting diodes, and other optoelectronic devices. This compound has only been researched recently, and, therefore, its charge-carrier transport properties are poorly understood. Understanding these properties is essential for optoelectronic applications. In this study, we grew wz-Mg1-xSn1+xN2 biaxially oriented polycrystalline films with x = -0.08 to 0.29 by reactive sputtering and investigated the charge-carrier transport properties using both direct current and optical techniques. We regarded the wz-Mg1-xSn1+xN2 films as magnesium tin oxynitride films (wz-MTNO) because a certain amount of oxygen was unintentionally incorporated into the sputtered wz-Mg1-xSn1+xN2 films. The wz-MTNO layers were n-type degenerate semiconductors with an electron density (n(e)) of the order of 10(20) cm(-3). In films with n(e) > 8 x 10(20) cm(-3), optically extracted resistivities (rho(opt)) obtained via a Drude-fit analysis of the infrared transmittance and reflectance spectra were almost identical to the direct-current resistivities (rho(dc)), indicating that the contribution of grain boundary scattering to the electron transport was negligible. However, the contribution of grain boundary scattering became unignorable with decreasing n(e). The Drude-fit analysis also allowed the determination of the conduction-band effective mass (m(c)*) for the first time. A band edge mass of m(c)*/m(0) & AP; 0.2 (m(0) denotes the free-electron mass) was obtained in the wz-MTNO layers with |x| < 0.1. As x was increased from -0.18 to 0.29, m(c)*/m(0) substantially increased from 0.18 to 0.56, indicating that the conduction-band dispersion decreased. That is, the conduction-band dispersion may be affected by the cation composition x. The findings of this study will provide important information to establish this material as a practical nitride semiconductor.

    DOI

    Scopus

    2
    被引用数
    (Scopus)
  • Band Gap-Tunable (Mg, Zn)SnN2 Earth-Abundant Alloys with a Wurtzite Structure

    Naoomi Yamada, Mari Mizutani, Kenta Matsuura, Masataka Imura, Hidenobu Murata, Junjun Jia, Fumio Kawamura

    ACS Applied Electronic Materials   3 ( 11 ) 4934 - 4942  2021年11月  [査読有り]

     概要を見る

    Herein, wurtzite-type MgSnN2-ZnSnN2 alloys (MgxZn1-xSnN2) are proposed as earth-abundant and band gap-tunable semiconductors with fundamental band gaps in the range of 1.5-2.3 eV. The alloys do not exhibit immiscibility, unlike the InN-GaN system, because the lattice mismatch between the endmembers is smaller than 1% in both a- and c-axis directions. The MgxZn1-xSnN2 alloys can be epitaxially grown on GaN(001) in the whole x range, and their fundamental band gap can be tuned from 1.5 to 2.3 eV with the increase in x from 0 to 1. Moreover, the MgxZn1-xSnN2 epilayers with x > 0.53 exhibit a green-light photoluminescence emission near room temperature, which indicates that they are direct-gap semiconductors. Direct-gap semiconductors with band gaps of 1.8-2.5 eV are eagerly anticipated for the development of green light-emitting diodes (LEDs) and top cells in high-efficiency tandem solar cells, though such wurtzite- or zincblende-type compounds that can be epitaxially integrated with conventional semiconductors are quite rare. Therefore, MgxZn1-xSnN2 alloys are attractive nitride semiconductors toward the development of green-LEDs and tandem solar cells.

    DOI

    Scopus

    16
    被引用数
    (Scopus)
  • Thermal conductivity across the van der Waals layers of α-MoO3 thin films composed of mosaic domains with in-plane 90° rotations

    JUNJUN JIA

    Journal of Applied Physics   130 ( 8 ) 085103 - 085103  2021年08月  [査読有り]

    DOI

    Scopus

    3
    被引用数
    (Scopus)
  • Experimental and theoretical investigation of kt2and mechanical quality factor Qm in YbAlN films using DFT

    Naoya Iwata, Sarina Kinoshita, Junjun Jia, Masashi Suzuki, Takahiko Yanagitani

    2020 IEEE International Ultrasonics Symposium (IUS)    2020年09月

    DOI

  • p-type conduction mechanism in continuously varied non-stoichimetric SnOx thin films deposited by reactive sputtering with the impedance control

    Junjun Jia, Takumi Sugane, Shin-ichi Nakamura, Yuzo Shigesato

    Journal of Applied Physics   127   185703  2020年05月  [査読有り]

    担当区分:筆頭著者, 責任著者

    DOI

    Scopus

    13
    被引用数
    (Scopus)
  • Carrier densities of Sn-doped In2O3 nanoparticles and their effect on X-ray photoelectron emission

    Junjun Jia, Ai Takaya, Takehiro Yonezawa, Kazuhiko Yamasaki, Hiromi Nakazawa, Yuzo Shigesato

    Journal of Applied Physics   125 ( 24 ) 245303  2019年06月  [査読有り]

    担当区分:筆頭著者, 責任著者

    DOI

    Scopus

    6
    被引用数
    (Scopus)
  • Thermal conductivity of hetero-epitaxial ZnO thin films on c- and r-plane sapphire substrates: Thickness and grain size effect

    Yuichiro Yamashita, Kaho Honda, Takashi Yagi, Junjun Jia, Naoyuki Taketoshi, Yuzo Shigesato

    Journal of Applied Physics   125 ( 3 ) 035101  2019年01月  [査読有り]

    DOI

    Scopus

    33
    被引用数
    (Scopus)
  • ScAlN polarization inverted resonators and enhancement of k(t)(2) in new YbAlN materials for BAW devices.

    Takahiko Yanagitani, Junjun Jia

    2019 IEEE INTERNATIONAL ULTRASONICS SYMPOSIUM (IUS)     894 - 899  2019年  [査読有り]

     概要を見る

    AlN thin piezoelectric films are attractive for RF filter applications because of their low mechanical loss 1/Q(m). We here introduce new AlN based materials: polarization inverted ScAlN multilayer and YbAlN films. Enhancement of electromechanical coupling coefficient in YbAlN were theoretically and experimentally demonstrated. These materials are promising for application in BAW and SAW devices.

  • Deposition of TiO2 photocatalyst on polyethylene terephthalate or polyimide polymer films by reactive sputtering for flexible photocatalytic sheets

    JUNJUN JIA

    Japanese Journal of Applied Physics   58 ( 5 ) 055503  2019年01月  [査読有り]

    DOI

  • How the sputtering process influence structural, optical, and electrical properties of Zn3N2 films?

    Junjun Jia, Hironori Kamijo, Shin-ichi Nakamura, Yuzo Shigesato

    MRS Communications   8   1 - 8  2018年06月  [査読有り]

     概要を見る

    © Copyright Materials Research Society 2018. The use of zinc nitride (Zn3N2) films as a transparent electrode in various electronic devices has attracted much attention owing to its high-carrier mobility. In this study, we investigate the influence of the sputtering process on structural, optical, and electrical properties of a Zn3N2 film deposited by reactive magnetron sputtering. The reactivity of nitrogen species can be improved by changing the type of sputtering gas. Compared with Ar or Ne sputtering gas, polycrystalline Zn3N2 films deposited using He sputtering gas have a larger grain size. The optical band gap of the Zn3N2 films varied from ∼1.2 to 1.5 eV depending on the N2 flow ratio and type of sputtering gas. The maximum mobility was 91.1 cm2/Vs when the Zn3N2 film was deposited using Ar sputtering gas with an N2 flow ratio of 40%. The carrier density of Zn3N2 films deposited using Ar sputtering gas was notably higher than those deposited using Ne or He sputtering gas, and more oxygen atoms are considered to substitute into nitrogen sites, where oxygen is considered to be from the residual water vapor in the sputtering chamber.

    DOI

    Scopus

    3
    被引用数
    (Scopus)
  • Geometric structure of Sn dopants in sputtered TiO2 film revealed by X-ray absorption spectroscopy and first-principles DFT calculations

    JUNJUN JIA

    Materials Research Express   5   046412  2018年04月  [査読有り]

  • A visible-light active TiO2 photocatalyst multilayered with WO3

    Junjun Jia, Kenta Taniyama, Masaaki Imura, Toshimasa Kanai, Yuzo Shigesato

    Physical Chemistry Chemical Physics   19 ( 26 ) 17342 - 17348  2017年07月  [査読有り]

    担当区分:筆頭著者

     概要を見る

    Sputter-deposited TiO2 films with high visible-light photocatalytic activity were successfully realized by a hybrid TiO2/Pt/WO3 film structure with Pt nanoparticles uniformly distributed at the interface of the TiO2 and WO3 films. The TiO2/Pt/WO3 hybrid films enable the complete decomposition of CH3CHO under visible-light irradiation. The water contact angle of the TiO2/Pt/WO3 hybrid films reaches below 51 under visible-light irradiation. Pt nanoparticles are considered to act as a cocatalyst to improve the electron-hole separation efficiency. We demonstrate that the photogenerated holes in WO3 are transferred to the surface of the TiO2 film with less hole-trapping and induce high visible-light photocatalytic activity and hydrophilic behavior, and the photogenerated electrons are accumulated in the Pt nanoparticles. The highly hydrophilic thin films with high visible-light photocatalytic activity can be applied to various indoor products possessing self-cleaning and antifogging properties.

    DOI

    Scopus

    23
    被引用数
    (Scopus)
  • Structure and thermophysical properties of GaN films deposited by reactive sputtering using a metal Ga target

    Yuji Isosaki, Yuichiro Yamashita, Takashi Yagi, Junjun Jia, Naoyuki Taketoshi, Shinichi Nakamura, Yuzo Shigesato

    Journal of Vacuum Science and Technology A   35 ( 4 )  2017年07月  [査読有り]

    担当区分:筆頭著者

     概要を見る

    The influence of dislocation density and impurities on the thermal conductivity of epitaxial GaN thin films on c-plane sapphire substrates was studied. GaN thin films with nominal thicknesses of 100, 300, and 1500 nm were fabricated by reactive direct current magnetron sputtering using a Ga metal target and a mixture gas of Ar and N-2. A 300-nm-thick GaN film was also fabricated using a mixture gas of Ar-N-2-H-2. For all the 300- and 1500-nm-thick films, epitaxial growth was confirmed from the sixfold symmetry spots in the pole figure and selected area electron diffraction patterns. Rocking curves of GaN(0002) of these films showed highly oriented growth along the c-axis. The dislocation density deduced from the rocking curves of GaN(10 (1) over bar0) ranged from 10 11 to 10(12) cm(-2). In the cases where a mixture gas of Ar-N-2 was used, films included O and H impurities on the order of 10(22) atoms cm(-3) in a layer of approximately 50-100 nm thickness near the substrate, and a low-impurity region with impurities on the order of 10(21) atoms cm(-3) existed above the high-impurity region. The addition of H-2 to the sputtering gas led to a reduction in the impurity concentration to a level on the order of 10(21) atoms cm(-3); it also prevented the formation of the high-impurity region near the substrate. The thermal conductivity of GaN thin films on c-plane sapphire substrates was measured by the pulsed-light-heating thermoreflectance method. The thermal conductivity of the low-impurity region in the 300-and 1500-nm-thick films ranged from 14 to 18W m(-1) K-1. The dislocation density and the oxygen impurities in our films were attributed to inhibitory factors of the thermal conductivity. The breakdown of the bonding network caused by the formations of Ga-NH2 and Ga-OH was not a negligible inhibitory factor of heat conduction. (C) 2017 American Vacuum Society.

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  • Indium oxide-based transparent conductive films deposited by reactive sputtering using alloy targets

    Yusuke Miyazaki, Eri Maruyama, Junjun Jia, Hironobu Machinaga, Yuzo Shigesato

    JAPANESE JOURNAL OF APPLIED PHYSICS   56 ( 4 )  2017年04月  [査読有り]

     概要を見る

    High-quality transparent conductive oxide (TCO) films, Sn-doped In2O3 (ITO) and In2O3-ZnO (IZO), were successfully deposited on either synthetic silica or polyethylene terephthalate ( PET) substrates in the "transition region" by reactive dc magnetron sputtering using In-Zn and In-Sn alloy targets, respectively, with a specially designed plasma emission feedback system. The composition, crystallinity, surface morphology, and electrical and optical properties of the films were analyzed. All of the IZO films were amorphous, whereas the ITO films were polycrystalline over a wide range of deposition conditions. The minimum resistivities of the IZO and ITO films deposited on the heated PET substrates at 150 degrees C were 3.3 x 10%(-4) and 5.4 x 10%(-4) Omega.cm, respectively. By applying rf bias to unheated PET substrates, ITO films with a resistivity of 4.4 x 10%(-4) Omega.cm were deposited at a dc self-bias voltage of -60 (C) 2017 The Japan Society of Applied Physics

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    3
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  • Effect of nitrogen addition on the structural, electrical, and optical properties of In-Sn-Zn oxide thin films

    Junjun Jia, Yoshifumi Torigoshi, Ayaka Suko, Shin-ichi Nakamura, Emi Kawashima, Futoshi Utsuno, Yuzo Shigesato

    Applied Surface Science   396   897 - 901  2017年02月  [査読有り]

    担当区分:筆頭著者, 責任著者

     概要を見る

    Indium-tin-zinc oxide ( ITZO) films were deposited at various nitrogen flow ratios using magnetron sputtering. At a nitrogen flow ratio of 40%, the structure of ITZO film changed from amorphous, with a short-range-ordered In2O3 phase, to a c-axis oriented InN polycrystalline phase, where InN starts to nucleate from an amorphous In2O3 matrix. Whereas, nitrogen addition had no obvious effect on the structure of indium-gallium-zinc oxide ( IGZO) films even at a nitrogen flow ratio of 100%. Nitrogen addition also suppressed the formation of oxygen-related vacancies in ITZO films when the nitrogen flow ratio was less than 20%, and higher nitrogen addition led to an increase in carrier density. Moreover, a red-shift in the optical band edge was observed as the nitrogen flow ratio increased, which could be attributed to the generation of InN crystallites. We anticipate that the present findings demonstrating nitrogen-addition induced structural changes can help to understand the environment-dependent instability in amorphous IGZO or ITZO based thin-film transistors ( TFTs). (C) 2016 Elsevier B.V. All rights reserved.

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    12
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  • On the Crystal Structural Control of Sputtered TiO2 Thin Films

    Junjun Jia, Haruka Yamamoto, Toshihiro Okajima, Yuzo Shigesato

    Nanoscale Research Letters   11 ( 1 )  2016年12月  [査読有り]

    担当区分:筆頭著者

     概要を見る

    In this study, we focused on the origin on the selective deposition of rutile and anatase TiO2 thin films during the sputtering process. The observation on microstructural evolution of the TiO2 films by transmission electron microscopy revealed the coexistence of rutile and anatase TiO2 phases in the initial stage under the preferential growth conditions for the anatase TiO2
    the observations further revealed that the anatase phase gradually dominated the crystal structure with increasing film thickness. These results suggest that the bombardment during the sputtering deposition did not obviously affect the TiO2 crystal structure, and this was also confirmed by off-axis magnetron sputtering experiments. We also investigated the mechanism of the effect of Sn impurity doping on the crystal structure using first-principles calculations. It is found that the formation energy of Sn-doped rutile TiO2 is lower than that of Sn-doped anatase TiO2
    this suggests that the Sn-doped TiO2 favours the rutile phase. These results offer a guideline for the utilization of selective deposition of rutile and anatase TiO2 thin films in various industrial applications.

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    33
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  • Influence of dopant species and concentration on grain boundary scattering in degenerately doped In2O3 thin films

    Mareike V. Frischbier, Hans F. Wardenga, Mirko Weidner, Oliver Bierwagen, Junjun Jia, Yuzo Shigesato, Andreas Klein

    Thin Solid Films   614   62 - 68  2016年09月  [査読有り]

     概要を見る

    The influence of dopant species and concentration on the grain boundary scattering of differently doped In2O3 thin films is studied by means of room temperature and temperature dependent Hall effect measurements. Barrier heights at grain boundaries E-B are evaluated from temperature dependent carrier mobility taking the theoretically calculated temperature dependence of intragrain mobility into account. It is thereby shown that also samples with a negative temperature coefficient of mobility exhibit significant grain boundary barrier heights and that E-B is usually underestimated when evaluated based on Seto's model. It is also shown that the most commonly used Sn doping of In2O3 with a dopant concentration &gt;2 wt.% SnO2 leads to significantly enhanced grain boundary scattering compared to nominally undoped, Zr-doped and H-doped films. An effect of grain boundary scattering is even observed for carrier concentrations similar to 10(21) cm(-3) if the films exhibit a pronounced (100) texture. The poor grain boundary properties of highly Sn-doped In2O3 are attributed to segregation of the Sn dopants, which is also indicated by measurements of surface Sn concentration. (C) 2016 Elsevier B.V. All rights reserved.

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  • Crystallization behavior during transparent In2O3-ZnO film growth

    Junjun Jia, Shin-ichi Nakamura, Yuzo Shigesato

    Physica Status Solidi A: Applications and materials Science   213 ( 9 ) 2291 - 2295  2016年09月  [査読有り]

    担当区分:筆頭著者

     概要を見る

    Structural evolution of transparent conductive In2O3-ZnO (IZO) films with increasing substrate temperature during sputtering was studied using transmission electron microscopy (TEM) and spectroscopic ellipsometry. Increasing the substrate temperature can induce film crystallization in the initial growth stage, and enhance the crystallization of IZO films. Extensive simulations using ellipsometry data demonstrated a decrease in the crystallization rate for IZO films deposited between 200 and 300 degrees C, which is attributed to the influence of the interference between nearby growing grains. TEM observations also reveal that the growth competition between different crystallites leads to an increase in the lateral grain size with increasing substrate temperature. (C) 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

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    6
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  • Formation of homologous In2O3(ZnO)(m) thin films and its thermoelectric properties

    Junjun Jia, Cleva Ow-Yang, Guliz Inan Akmehmet, Shin-ichi Nakamura, Kunihisa Kato, Yuzo Shigesato

    Journal of Vacuum Science & Technology A   34 ( 4 )  2016年07月  [査読有り]

    担当区分:筆頭著者

     概要を見る

    Homologous In2O3(ZnO)(5) thin films were produced on a synthetic quartz glass substrate by thermal annealing of magnetron sputtered In2O3-ZnO compound films. When the annealing temperature was increased to 700 degrees C, the sputtered In2O3-ZnO film with In2O3 microcrystalline changed to a c-oriented homologous In2O3(ZnO)(5) structure, for which the crystallization is suggested to begin from the surface and proceed along with the film thickness. The annealing temperature of 700 degrees C to form the In2O3(ZnO)(5) structure was substantially lower than temperatures of conventional solid state synthesis from In2O3 and ZnO powders, which is attributed to the rapid diffusional transport of In and Zn due to the mixing of In2O3 and ZnO in the atomic level for sputtered In2O3-ZnO compound films. The homologous structure collapsed at temperatures above 900 degrees C, which is attributed to (1) zinc vaporization from the surface and (2) a gradual increase of zinc silicate phase at the interface. This c-oriented layer structure of homologous In2O3(ZnO)(5) thin films along the film thickness allowed the thin film to reach a power factor of 1.3 x 10(-4) W/mK(2) at 670 degrees C, which is comparable with the reported maximum value for the textured In2O3(ZnO)(5) powder (about 1.6 x 10(-4) W/mK(2) at 650 degrees C). (C) 2016 American Vacuum Society.

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    5
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  • On the Crystal Structural Control of Sputtered TiO2 Thin Films

    Junjun Jia, Haruka Yamamoto, Toshihiro Okajima, Yuzo Shigesato

    NANOSCALE RESEARCH LETTERS   11  2016年07月  [査読有り]

     概要を見る

    In this study, we focused on the origin on the selective deposition of rutile and anatase TiO2 thin films during the sputtering process. The observation on microstructural evolution of the TiO2 films by transmission electron microscopy revealed the coexistence of rutile and anatase TiO2 phases in the initial stage under the preferential growth conditions for the anatase TiO2; the observations further revealed that the anatase phase gradually dominated the crystal structure with increasing film thickness. These results suggest that the bombardment during the sputtering deposition did not obviously affect the TiO2 crystal structure, and this was also confirmed by off-axis magnetron sputtering experiments. We also investigated the mechanism of the effect of Sn impurity doping on the crystal structure using first-principles calculations. It is found that the formation energy of Sn-doped rutile TiO2 is lower than that of Sn-doped anatase TiO2; this suggests that the Sn-doped TiO2 favours the rutile phase. These results offer a guideline for the utilization of selective deposition of rutile and anatase TiO2 thin films in various industrial applications.

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    33
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  • Comparative study of sputter-deposited SnO2 films doped with antimony or tantalum

    Mirko Weidner, Junjun Jia, Yuzo Shigesato, Andreas Klein

    Physica Status Solidi A: Basic Solid State Physics   253 ( 5 ) 923 - 928  2016年05月  [査読有り]

     概要を見る

    SnO2 films doped with antimony or tantalum were sputter-deposited for comparison, using an identical set of parameters. The influence of dopant concentration and choice of deposition parameters such as substrate temperature on the optoelectronic properties, especially film resistivity, were determined. Comparative analysis shows that tantalum doping yields lower film resistivity, probably due to an increased inhibiting influence of grain boundary scattering in the case of antimony doping. Sputter-deposited tantalum-doped films with lower than previously achieved resistivity 5.4 x 10(-4) Omega cm, carrier density 4.5 x 10(20) cm(-3), and mobility 25.7 cm(2) Vs(-1) are reported, while maintaining optical transmittance above 85% at a film thickness 400 nm. Ta/Sb co-doped thin films were synthesized for the first time, achieving similar results. (C) 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

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    18
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  • Tuning hole charge collection efficiency in polymer photovoltaics by optimizing the work function of indium tin oxide electrodes with solution-processed LiF nanoparticles

    Hasan Kurt, Junjun Jia, Yuzo Shigesato, Cleva W. Ow-Yang

    JOURNAL OF MATERIALS SCIENCE-MATERIALS IN ELECTRONICS   26 ( 11 ) 9205 - 9212  2015年11月  [査読有り]

    担当区分:筆頭著者

     概要を見る

    By varying the density of solution-processed lithium fluoride (sol-LiF) nanoparticles at the interface between tin-doped indium oxide (ITO) and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), we have demonstrated that the electronic hole collection efficiency of an organic photovoltaic cell can be optimized through tuning the energy level alignment at the ITO/PEDOT:PSS interface. We synthesized the LiF nanoparticles in solution and deposited them onto ITO electrodes with increasing surface coverage up to 13.2 %. The surface work function of the nanostructured ITO increased linearly from 4.88 to 5.30 eV. When the sol-LiF-modified ITO electrodes were incorporated into polymer solar cells based on a bulk heterojunction of poly(3-hexylthiophene) polymer and methanofullerene, a maximum power conversion efficiency was recorded for a device with an ITO anode modified by 5.3 % of sol-LiF coverage, which corresponded to a measured work function of 5.07 eV. The improvement in short circuit current density by 87 % and power conversion efficiency by 74.3 % suggest that the sol-LiF interlayer density enabled work function tuning of the ITO anode to better match the highest occupied molecular orbital level of PEDOT:PSS, facilitating hole charge collection. The increase in electronic hole collection efficiency is attributed to both a lowered resistance at the ITO modified by sol-LiF and faster hole transport, although these gains are offset by an associated increase in contact polarization. Our findings suggest that the surface work function of ITO can be tuned to improve energy level alignment with other contact layers via the surface density of sol-LiF particles. More efficient hole transport, due to higher recombination resistance, offset by an increased charge extraction barrier presented by contact polarization; the two effects combined give rise to an optimum in sol-LiF nanostructuring of the ITO surface properties.

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    5
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  • Visible-light active thin-film WO3 photocatalyst with controlled high-rate deposition by low-damage reactive-gas-flow sputtering

    Nobuto Oka, Akiyo Murata, Shin-ichi Nakamura, Junjun Jia, Yoshinori Iwabuchi, Hidefumi Kotsubo, Yuzo Shigesato

    APL MATERIALS   3 ( 10 )  2015年10月  [査読有り]

     概要を見る

    A process based on reactive gas flow sputtering (GFS) for depositing visible-light active photocatalytic WO3 films at high deposition rates and with high film quality was successfully demonstrated. The deposition rate for this process was over 10 times higher than that achieved by the conventional sputtering process and the process was highly stable. Furthermore, Pt nanoparticle-loaded WO3 films deposited by the GFS process exhibited much higher photocatalytic activity than those deposited by conventional sputtering, where the photocatalytic activity was evaluated by the extent of decomposition of CH3CHO under visible light irradiation. The decomposition time for 60 ppm of CH3CHO was 7.5 times more rapid on the films deposited by the GFS process than on the films deposited by the conventional process. During GFS deposition, there are no high-energy particles bombarding the growing film surface, whereas the bombardment of the surface with high-energy particles is a key feature of conventional sputtering. Hence, the WO3 films deposited by GFS should be of higher quality, with fewer structural defects, which would lead to a decrease in the number of centers for electron-hole recombination and to the efficient use of photogenerated holes for the decomposition of CH3CHO. (C) 2015 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.

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    23
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  • Tailoring the crystal structure of TiO2 thin films from the anatase to rutile phase

    Haruka Kotake, Junjun Jia, Shin-ichi Nakamura, Toshihiro Okajima, Yuzo Shigesato

    JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A   33 ( 4 )  2015年07月  [査読有り]

     概要を見る

    TiO2 films with various Sn concentrations were deposited on quartz substrates using rf reactive magnetron sputtering. The crystal structure was investigated by using x-ray diffraction, Raman spectroscopy, and transmission electron microscopy, and the chemical states of Ti and Sn were analyzed by x-ray absorption near edge structure (XANES) spectroscopy. Without Sn doping, TiO2 films change the crystal structure from rutile to anatase as the total gas pressure increases in the sputtering deposition. On the other hand, Sn doping induces the transformation of TiO2 crystalline structure from anatase to rutile phase, where the XANES spectra implied that Sn substitutes into Ti site of rutile TiO2. Atomic force microscope analyses revealed that the Sn-doped TiO2 films exhibited a flat surface with the roughness of approximately 2 nm. (C) 2015 American Vacuum Society.

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  • Temperature dependence of thermal conductivity of VO2 thin films across metal-insulator transition

    Hinako Kizuka, Takashi Yagi, Junjun Jia, Yuichiro Yamashita, Shinichi Nakamura, Naoyuki Taketoshi, Yuzo Shigesato

    JAPANESE JOURNAL OF APPLIED PHYSICS   54 ( 5 )  2015年05月  [査読有り]

     概要を見る

    Thermal conductivity of a 300-nm-thick VO2 thin film and its temperature dependence across the metal-insulator phase transition (TMIT) were studied using a pulsed light heating thermoreflectance technique. The VO2 and Mo/VO2/Mo films with a VO2 thickness of 300nm were prepared on quartz glass substrates: the former was used for the characterization of electrical properties, and the latter was used for the thermal conductivity measurement. The VO2 films were deposited by reactive rf magnetron sputtering using a V2O3 target and an Ar-O-2 mixture gas at 645 K. The VO2 films consisted of single phase VO2 as confirmed by X-ray diffraction and electron beam diffraction. With increased temperature, the electrical resistivity of the VO2 film decreased abruptly from 6.3 x 10(-1) to 5.3 x 10(-4) Omega cm across the T-MIT of around 325-340 K. The thermal conductivity of the VO2 film increased from 3.6 to 5.4W m(-1) K-1 across the T-MIT. This discontinuity and temperature dependence of thermal conductivity can be explained by the phonon heat conduction and the Wiedemann-Franz law. (C) 2015 The Japan Society of Applied Physics

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  • Amorphous indium-tin-zinc oxide films deposited by magnetron sputtering with various reactive gases: Spatial distribution of thin film transistor performance

    Junjun Jia, Yoshifumi Torigoshi, Emi Kawashima, Futoshi Utsuno, Koki Yano, Yuzo Shigesato

    APPLIED PHYSICS LETTERS   106 ( 2 )  2015年01月  [査読有り]

    担当区分:筆頭著者

     概要を見る

    This work presents the spatial distribution of electrical characteristics of amorphous indium-tinzinc oxide film (a-ITZO), and how they depend on the magnetron sputtering conditions using O-2, H2O, and N2O as the reactive gases. Experimental results show that the electrical properties of the N2O incorporated a-ITZO film has a weak dependence on the deposition location, which cannot be explained by the bombardment effect of high energy particles, and may be attributed to the difference in the spatial distribution of both the amount and the activity of the reactive gas reaching the substrate surface. The measurement for the performance of a-ITZO thin film transistor (TFT) also suggests that the electrical performance and device uniformity of a-ITZO TFTs can be improved significantly by the N2O introduction into the deposition process, where the field mobility reach to 30.8 cm(2) V-1 s(-1), which is approximately two times higher than that of the amorphous indium-gallium-zinc oxide TFT. (C) 2015 AIP Publishing LLC.

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  • Origin of carrier scattering in polycrystalline Al-doped ZnO films

    Junjun Jia, Nobuto Oka, Minehide Kusayanagi, Satoshi Nakatomi, Yuzo Shigesato

    APPLIED PHYSICS EXPRESS   7 ( 10 )  2014年10月  [査読有り]

    担当区分:筆頭著者

     概要を見る

    We observed the carrier transport phenomena in polycrystalline Al-doped ZnO (AZO) films with carrier densities ranging from 2.0 x 10(19) to 1.1 x 10(21) cm(-3). A comparison of the optical carrier density and Hall carrier density indicates that the conduction band in AZO films is nonparabolic above 2.0 x 10(20) cm(-3). A transition from grain boundary scattering to ionized impurity scattering is observed at a doping level of x 10(20) cm(-3). The trap density at the grain boundary increases with increasing Al concentration in the films, implying that the doping level plays a decisive role in the trap density. The excellent fitting of the optical mobility and carrier density using the Brooks-Herring model shows that the acceptor concentration increases with increasing doping level. (C) 2014 The Japan Society of Applied Physics

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  • Thermophysical properties of SnO2-based transparent conductive films: Effect of dopant species and structure compared with In2O3-, ZnO-, and TiO2-based films

    Nobuto Oka, Saori Yamada, Takashi Yagi, Naoyuki Taketoshi, Junjun Jia, Yuzo Shigesato

    Journal of Materials Research   29 ( 15 ) 1579 - 1584  2014年08月  [査読有り]

     概要を見る

    We investigate the effect of dopant species and structure on the thermal conductivity of Sb-doped SnO2 (ATO) and Ta-doped SnO2 (TTO) films and compare the results with those of In2O3-, ZnO-, and TiO2-based transparent conductive films. The thermal conductivities (lambda) of polycrystalline ATO and TTO films are 4.4-4.9 and 4.7 W m(-1) K-1, respectively. The thermal conductivities via phonons (lambda(ph)) are almost identical for both dopant species (Sb and Ta): 4.3 and 4.5 W m(-1) K-1 for Sb and Ta, respectively, on average. These results for lambda(ph) are larger than that for Sn-doped In2O3 films (3.8 W m(-1) K-1) and considerably larger than that for amorphous ATO films (1.0 W m(-1) K-1). These facts lead us to conclude that the base-material species (SnO2 or In2O3) and structure (polycrystalline or amorphous) affect the thermophysical properties of ATO and TTO much more than the dopant species.

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  • Transparent conductive Nb-doped TiO2 films deposited by reactive dc sputtering using Ti-Nb alloy target, precisely controlled in the transition region using impedance feedback system.

    Nobuto Oka, Yuta Sanno, Junjun Jia, Shin-ichi Nakamura, Yuzo Shigesato

    APPLIED SURFACE SCIENCE   301   551 - 556  2014年05月  [査読有り]

     概要を見る

    In this study, a stable reactive sputtering process using a Ti-Nb alloy target was achieved by applying a plasma impedance feedback system. High-quality transparent conductive Nb-doped TiO2 (Nb:TiO2) films were fabricated with high reproducibility. The films were deposited on unheated substrate and subsequently annealed at 873 K under vacuum conditions (below 6.0 x 10(-4) Pa) for 1 h. During reactive sputtering, the feedback system precisely controlled the oxidation of the target surface in the so-called transition region. The post-annealing process yielded polycrystalline Nb:TiO2 films whose lattice defects decreased with increasing Nb concentration. An extremely low resistivity (7.2 x 10(-4) Omega cm) was achieved for Nb:TiO2 film with 60-70% transmittance in the visible region. The reactive sputtering using Ti-Nb alloys is considered to be a strong candidate for industrial-scale thin-film deposition. Furthermore, it can also control the metal-oxygen stoichiometry of Nb:TiO2 films precisely to achieve desirable properties for each industrial application. (C) 2014 Elsevier B.V. All rights reserved.

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  • Transparent conductive Al and Ga doped ZnO films deposited using off-axis sputtering

    Junjun Jia, Aya Yoshimura, Yukihiro Kagoya, Nobuto Oka, Yuzo Shigesato

    Thin Solid Films   559   69 - 77  2014年05月  [査読有り]

    担当区分:筆頭著者

     概要を見る

    Al and Ga doped ZnO (AZO and GZO) films were deposited using an off-axis dc magnetron sputtering method. At the off-axis positions, both the mobility and carrier density increased, resulting in enhanced conductivity of both the AZO and GZO films due to an increase in the crystallinity. The lowest resistivities of the AZO and GZO films deposited at room temperature were 1.1 x 10(-3) Omega cm and 6.5 x 10(-4) Omega cm, respectively. Increasing the substrate temperature up to 130 C led to a decrease in the lowest resistivity to 6.1 x 10(-4) Omega cm for the AZO films. The transmittance of all films was above 80% in the visible region. These results suggest that off-axis magnetron sputtering might be a potentially effective deposition method with the reduced bombardments from high-energy particles. (C) 2014 Elsevier B. V. All rights reserved.

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  • Study on reactive sputtering to deposit transparent conductive amorphous In2O3-ZnO films using an In-Zn alloy target

    Naoki Tsukamoto, Sakae Sensui, Junjun Jia, Nobuto Oka, Yuzo Shigesato

    THIN SOLID FILMS   559   49 - 52  2014年05月  [査読有り]

     概要を見る

    Amorphous indium-zinc-oxide films were deposited in the "transition region" by reactive sputtering using an In-Zn alloy target with a specially designed double feedback system. The cathode voltage showed a V-and circle-shaped curve as a function of O-2 gas flow in the transition region, which differs from the S-shaped curve in Berg's model for reactive sputtering depositions. In-situ analyses with a quadrupole mass spectrometer combined with an energy analyzer revealed that the negative ions O-, O-2(-), InO-, and InO2-, with high kinetic energies corresponding to the cathode voltage, were generated at the partially oxidized target surface. Furthermore the positive ions O+, Ar+, In+, and Zn+ with rather low kinetic energies (around 10 eV) were confirmed to be generated by the charge exchange of sputtered neutral O, Ar, In and Zn atoms, respectively. (C) 2013 Elsevier B.V. All rights reserved.

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  • Work function tuning of tin-doped indium oxide electrodes with solution-processed lithium fluoride

    C. W. Ow-Yang, J. Jia, T. Aytun, M. Zamboni, A. Turak, K. Saritas, Y. Shigesato

    THIN SOLID FILMS   559   58 - 63  2014年05月  [査読有り]

     概要を見る

    Solution-processed lithium fluoride (sol-LiF) nanoparticles synthesized in polymeric micelle nanoreactors enabled tuning of the surface work function of tin-doped indium oxide (ITO) films. The micelle reactors provided the means for controlling surface coverage by progressively building up the interlayer through alternating deposition and plasma etch removal of the polymer. In order to determine the surface coverage and average interparticle distance, spatial point pattern analysis was applied to scanning electron microscope images of the nanoparticle dispersions. The work function of the sol-LiF modified ITO, obtained from photoelectron emission yield spectroscopy analysis, was shown to increase with surface coverage of the sol-LiF particles, suggesting a lateral depolarization effect. Analysis of the photoelectron emission energy distribution in the near threshold region revealed the contribution of surface states for surface coverage in excess of 14.1%. Optimization of the interfacial barrier was achieved through contributions from both work function modification and surface states. (C) 2013 Elsevier B.V. All rights reserved.

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    22
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  • Al-doped ZnO films deposited on a slightly reduced buffer layer by reactive dc unbalanced magnetron sputtering

    Minehide Kusayanagi, Azusa Uchida, Nobuto Oka, Junjun Jia, Shin-Ichi Nakamura, Yuzo Shigesato

    THIN SOLID FILMS   555   93 - 99  2014年03月  [査読有り]

     概要を見る

    Al-doped ZnO (AZO) films were deposited on a fused silica glass substrate by reactive dc unbalanced magnetron sputtering using a Zn-Al (Al: 3.6 at.%) alloy target with an impedance control system. A very thin slightly reduced AZO buffer layer was inserted between the glass substrate and AZO films. For the AZO films deposited at 200 degrees C, the lowest resistivity in the absence of the buffer layer was 8.0 x 10(-4) Omega cm, whereas this was reduced to 5.9 x 10(-4) Omega cm after introducing a 5-nm-thick buffer layer. The transmittance for all the films was above 80% in the visible region. The effects of the buffer layer were analysed and discussed in detail. It is found that the insertion of the buffer layer can improve the crystallinity of the AZO film. (C) 2013 Elsevier B.V. All rights reserved.

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    22
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  • Thermal Boundary Resistance of W/Al2O3 Interface in W/Al2O3/W Three-Layered Thin Film and Its Dependence on Morphology

    Shizuka Kawasaki, Yuichiro Yamashita, Nobuto Oka, Takashi Yagi, Junjun Jia, Naoyuki Taketoshi, Tetsuya Baba, Yuzo Shigesato

    JAPANESE JOURNAL OF APPLIED PHYSICS   52 ( 6 )  2013年06月

     概要を見る

    We investigated the dependence of the thermal boundary resistance of the W/Al2O3 interface in W/Al2O3/W three-layered thin films on the interface morphology. The layered structures, Al2O3 thin layers with thicknesses from 1 to 50nm covered by top and bottom W layers with a thickness of 100 nm, were fabricated by magnetron sputtering using a W target (99.99%) and an Al2O3 target (99.99%). The fabrication of polycrystalline W and amorphous Al2O3 films was confirmed by structural analysis. The morphology of the bottom W layer/Al2O3 layer and Al2O3 layer/top W layer interfaces showed a wavelike structure with a roughness of about 1 nm. Thermophysical properties and thermal boundary resistance were measured by a pulsed light heating thermoreflectance technique. The thermal boundary resistance of the W/Al2O3 interface was 1.9 x 10(-9) m(2)K W-1, which corresponds to the thermal resistance of a 3.7-nm-thick Al2O3 film or a 120-nm-thick W film. (C) 2013 The Japan Society of Applied Physics

    DOI

    Scopus

    9
    被引用数
    (Scopus)
  • Direct observation of the band gap shrinkage in amorphous In2O3-ZnO thin films

    Junjun Jia, Nobuto Oka, Yuzo Shigesato

    JOURNAL OF APPLIED PHYSICS   113 ( 16 )  2013年04月  [査読有り]

    担当区分:筆頭著者

     概要を見る

    We investigated the dependence of valence-and core-level photoemission spectra of amorphous In2O3-ZnO (a-IZO) films on carrier density by using hard x-ray photoemission spectroscopy (h nu = 8000 eV). The valence band edge distinctly shifts toward high binding energy with the increase in carrier density from 0.80 to 3.96 x 10(20) cm(-3), and an abrupt jump for the shift of the valence band edge from high to low binding energy occurs at a carrier density of 4.76 x 10(20) cm(-3). After considering the effect of nonparabolic bandstructure, the shifts are still less than the width of the occupied conduction band, providing direct evidence for the band gap shrinkage. Our calculation results indicate that the contribution of the band gap shrinkage increases as the carrier density increases, which accords with the observations in doped conducting crystal materials, such as Sn doped In2O3. Moreover, it is found that the conduction electrons of a-IZO films are strongly perturbed by the ionization of core levels, which leads to obvious plasmon satellites in core photoemission spectra lines. (C) 2013 AIP Publishing LLC

    DOI

    Scopus

    22
    被引用数
    (Scopus)
  • Thermal Conductivity of Amorphous Indium-Gallium-Zinc Oxide Thin Films

    Toru Yoshikawa, Takashi Yagi, Nobuto Oka, Junjun Jia, Yuichiro Yamashita, Koichiro Hattori, Yutaka Seino, Naoyuki Taketoshi, Tetsuya Baba, Yuzo Shigesato

    APPLIED PHYSICS EXPRESS   6 ( 2 )  2013年02月

     概要を見る

    We investigated the thermal conductivity of 200-nm-thick amorphous indium-gallium-zinc-oxide (a-IGZO) films. Films with a chemical composition of In : Ga : Zn = 1 : 1 : 0.6 were prepared by dc magnetron sputtering using an IGZO ceramic target and an Ar-O-2 sputtering gas. The carrier density of the films was systematically controlled from 10(14) to &gt; 10(19) cm(-3) by varying the O-2 flow ratio. Their Hall mobility was slightly higher than 10 cm(2) .V-1 .s(-1). Those films were sandwiched between 100-nm-thick Mo layers; their thermal diffusivity, measured by a pulsed light heating thermoreflectance technique, was similar to 5.4 x 10(-7) m(2) .s(-1) and was almost independent of the carrier density. The average thermal conductivity was 1.4W.m(-1) .K-1. (C) 2013 The Japan Society of Applied Physics

    DOI

    Scopus

    64
    被引用数
    (Scopus)
  • Bimodal colloidal mixtures: From fast to slow aggregation regions

    Junjun Jia, Zehong Jia, Shuichi Iwata

    Journal of Colloid and Interface Science   362 ( 2 ) 633 - 637  2011年10月  [査読有り]

    担当区分:筆頭著者, 責任著者

     概要を見る

    A Brownian dynamics simulation has been used to investigate the aggregation kinetics of bimodal colloidal mixtures with similar surface chemistries but different sizes, driven by the DLVO interaction potential. The time evolution of structural formation is examined by the mean number of neighbors under fast and slow aggregation regions. It was found that the electrolyte ionic strength affects the kinetic pattern of colloidal aggregation. Under the high electrolyte ionic strength conditions (fast aggregation), the selective aggregation of the least stable single component can take place in the early stage, while the other component is enriched in this least stable component in the later stage. With the ionic strength decreasing (towards the slow aggregation), the hybrid aggregation (selective aggregation and heteroaggregation) gradually dominates the aggregation kinetics. Also in the early stage, this evolves to the heteroaggregation of different components under lower ionic strength conditions. The volume fraction has no obvious influence on this kinetic pattern in the early stage. (C) 2011 Elsevier Inc. All rights reserved.

    DOI

    Scopus

    4
    被引用数
    (Scopus)
  • Nonequilibrium structure of primary particles in colloidal bidispersion

    Junjun Jia, Shuichi Iwata

    COLLOID AND POLYMER SCIENCE   288 ( 14-15 ) 1485 - 1493  2010年10月  [査読有り]

    担当区分:筆頭著者, 責任著者

     概要を見る

    The nonequilibrium aggregation structure of primary particles in colloidal bidispersions is investigated at high volume fractions by Brownian dynamics simulations. It is found that introducing limited different sized particles in the monodispersion can obviously affect the short-range structures of primary particles. In a bidispersion, fractal dimension of aggregates, only consisting of primary particles, increases with increasing the size difference in the long-range scale. The structure factor S(q) of aggregates, obtained from the particle correlation function g(r), suggests that fractal structure disappears when the primary particles become not "primary" in volume fraction.

    DOI

    Scopus

    2
    被引用数
    (Scopus)

▼全件表示

講演・口頭発表等

  • 後焼成における薄膜結晶化の解明

    賈軍軍  [招待有り]

    11th International Conference on Materials for Advanced Technologies, Singapore  

    発表年月: 2023年06月

    開催年月:
    2023年06月
     
     
  • IGZO TFTs: from deposition process to device performance

     [招待有り]

    16th International Thin-Film Transistor Conference (ITC 2020/2021) (招待講演)  

    発表年月: 2021年10月

    開催年月:
    2021年10月
     
     
  • Achieving thermally or optically switchable material via Pump-Probe Detection

    賈軍軍  [招待有り]

    The 8th World Materials Summit Forum and 1st World Energy Materials Conference (基調講演)  

    発表年月: 2023年11月

    開催年月:
    2023年11月
     
     
  • ゲルマニウム薄膜における超高速キャリアダイナミックス

    賈 軍軍, 八木 貴志, 葉 輝, 山田 直臣

    日本応用物理学会(23p-B204-8)  

    発表年月: 2023年09月

    開催年月:
    2023年09月
     
     
  • 薄膜の結晶化に関する数理モデルの構築

    賈 軍軍  [招待有り]

    8th International Symposium on Transparent Conductive Materials (招待講演)  

    発表年月: 2022年10月

    開催年月:
    2022年10月
     
     
  • InNにおける光誘起ブリーチング現象の解明

    賈軍軍, 八木貴志, 水谷真梨, 山田直臣, 牧本俊樹

    日本応用物理学会 (20a-A202-4)  

    発表年月: 2022年09月

    開催年月:
    2022年09月
     
     
  • 反応性スパッタによる SnOx薄膜のキャリアの発生源と伝導機構

    賈軍軍  [招待有り]

    第68回応用物理学会春季学術講演会 (招待講演・受賞講演)  

    発表年月: 2021年03月

    開催年月:
    2021年03月
     
     
  • Toward understanding the defect-functionality relationship in bipolar SnO thin films

    賈軍軍, 重里有三  [招待有り]

    Materials research Meeting 2019 (MRM2019) (招待講演)  

    発表年月: 2012年12月

    開催年月:
    2019年12月
     
     
  • スパッタ法を用いた酸化物半導体薄膜の作製およびTFT特性

    賈軍軍, 重里有三  [招待有り]

    第2回酸化物半導体討論会 (東京工業大学)  

    発表年月: 2018年10月

    開催年月:
    2018年10月
     
     
  • Phonon engineering on transparent conductive thin films

    賈軍軍  [招待有り]

    復旦大学の学内講演  

    発表年月: 2018年08月

    開催年月:
    2018年08月
     
     
  • Towards the property tailoring of transparent conducting In2O3-ZnO films

    賈軍軍, 重里有三  [招待有り]

    The 5th international symposium on transparent conductive materials (TCMs 2014) (基調講演)  

    発表年月: 2014年10月

    開催年月:
    2014年10月
     
     
  • Effects of aluminum doping on Fermi level in polycrystalline ZnO films

     [招待有り]

    SPIE Photonics West 2014 (国際光工学会・招待講演)  

    発表年月: 2014年02月

    開催年月:
    2014年02月
     
     

▼全件表示

共同研究・競争的資金等の研究課題

  • アニオン付加・脱離反応を伴う複合酸化物の複合アニオン化と新規光・電材料の創製

    日本学術振興会  科学研究費助成事業

    研究期間:

    2024年04月
    -
    2028年03月
     

    佐藤 泰史, 鱒渕 友治, 賈 軍軍

  • 間接遷移型化合物半導体薄膜における光ブリーチング現象の探究

    日本学術振興会  科学研究費助成事業 基盤研究(C)

    研究期間:

    2020年04月
    -
    2023年03月
     

    賈 軍軍

     概要を見る

    令和3年度には、高密度光励起により半導体中に生成される励起電子の位相散逸およびホット電子の緩和に関して、Pump-Probe測定に基づいた実験観測および物性理論の構築を行った。高強度パルスレーザをPump光として用いて、直接遷移型InN薄膜を照射することで、本来ほぼ不透明な波長領域にProbe光を透過することを観測し、さらにピコ秒オーダーで光の透過を超高速で切り替えることも確認した。この光ブリーチング現象は、励起電子がキャリア―キャリア散乱による位相散逸後に形成したホット電子が、価電子帯内の空準位を一時的に占有することにより、プローブ光が透過するということが実験により明らかになった。さらに、フェルミ‐ディラック分布関数により空準位を占有するホット電子の分布を表し、Two Temperature Modelを用いてホット電子の緩和過程を予測することに試みた。
    <BR>
    上記の物性理論の妥当性を検討するため、スーパーコンティニウム光源(SC光源)を購入し、フェムト秒超短パルスレーザ光をSC光源に入射することで広帯域なレーザ光をProbe光として発生し、広い波長領域での光ブリーチング現象を計測した。上記の理論により算出した結果とほぼ同様の傾向が得られ、理論の妥当性を確認した。これにより、価電子帯内におけるホット電子の分布を測定する方法を確立した(論文投稿中)。また、Two Temperature Modelを用いて、電子-フォノン結合定数も求めた。
    <BR>
    さらに、高密度光励起により間接遷移型半導体であるSnOとGeの光ブリーチング現象を詳細に観測した。間接遷移型Ge薄膜において、過渡透過・反射の同時測定によりホット電子の谷間散乱を見つけ、直接遷移型InN薄膜より光ブリーチングの持続時間が長くなることがわかった。

  • 酸化物薄膜を用いた高感度な環境適応型ガスセンシングデバイスの開発

    高橋産業経済研究財団  研究助成金

    研究期間:

    2019年04月
    -
     
     

    賈 軍軍

  • ガラス基板上に配向を有するIGZO薄膜の形成メカニズムの解明

    日本学術振興会  科学研究費助成事業 基盤研究(C)

    研究期間:

    2016年10月
    -
    2019年03月
     

    重里 有三, 岡島 敏浩, 賈 軍軍

     概要を見る

    アモルファスIGZO, IGO, In2O3薄膜の結晶化機構をIn-situ XRDと高分解能TEMによって解明した。10%程度のSnやGaの添加ではIn2O3本来の結晶構造であるビックスバイトに結晶化するが、Zn添加やZn, Gaの供添加の場合はアモルファス構造から層状構造であるホモロガスIZO, IGZO構造になった。TEMによる詳細な構造解析と放射光を利用したin-situ XRDの測定により、アモルファス In2O3薄膜の結晶化過程とその配向、並びに不純物Sn, Ga、Znの添加の影響を調べ、結晶化の活性化エネルギーの変化を定量的に解析しAvramiの式を用いて解釈した。

  • ホモロガスIn2O3‐ZnO薄膜の超格子形成機構とその熱電特性の解明

    日本学術振興会  科研費 若手研究(B)

    研究期間:

    2016年04月
    -
    2019年03月
     

    賈 軍軍

Misc

  • Enhanced Electromechanical Coupling Near the Phase Boundary in Wurtzite (Mg,Zn)O and (Sc,Al)N

    Junjun Jia, Takahiko Yanagitani

    2024 IEEE MTT-S International Conference on Microwave Acoustics &amp;amp; Mechanics (IC-MAM)    2024年05月  [査読有り]

    担当区分:筆頭著者, 責任著者

    研究発表ペーパー・要旨(国際会議)  

    DOI

  • c-Axis parallel ZnO piezoelectric multilayer for BAW gyroscope applications

    Ayaka Hanai, Shinya Kudo, Kohei Ekida, Junjun Jia, Takahiko Yanagitani

    2023 IEEE International Symposium on Inertial Sensors and Systems (INERTIAL)    2023年03月

    DOI

  • IBAD c-axis parallel ZnO piezoelectric film stack for gyroscope applications

    Shinya Kudo, Kohei Ekida, Junjun Jia, Takahiko Yanagitani

    2022 IEEE International Ultrasonics Symposium (IUS)    2022年10月

    DOI

  • Improvement of Electromechanical Coupling Coefficient of Piezoelectric LiNbO3 by Doping Praseodymium

    Kae Nakamura, Shinya Kudo, Junjun Jia, Takahiko Yanagitani

    2022 IEEE International Ultrasonics Symposium (IUS)    2022年10月

    DOI

  • Experimental and theoretical investigations of enhanced electromechanical properties in YbAlN and YbGaN films

    Song Li, Junjun Jia, Naoya Iwata, Takahiko Yanagitani

    2022 IEEE International Ultrasonics Symposium (IUS)    2022年10月

    DOI

  • Experimental and theoretical investigation of kt 2 and velocity in YbGaN films by DFT

    Yuna Koike, Junjun Jia, Masashi Suzuki, Takahiko Yanagitani

    2021 IEEE International Ultrasonics Symposium (IUS)    2021年09月

    DOI

  • ヘテロエピタキシャルIn2O3薄膜における熱と電気の輸送特性

    中野綾香, 竹歳尚之, 山下雄一郎, 八木貴志, 賈軍軍, 重里有三

    第39回日本熱物性シンポジウム    2018年11月  [査読有り]

    研究発表ペーパー・要旨(全国大会,その他学術会議)  

  • 放射光を用いたアモルファスIn2O3系薄膜の結晶化に関する評価

    賈軍軍, 岡島敏浩, 重里有三

        10 - 12  2017年10月  [招待有り]

    担当区分:筆頭著者, 最終著者, 責任著者

    記事・総説・解説・論説等(大学・研究所紀要)  

  • Change in structure and TFT performances of IZO, IGO and IGZO films by crystallization

    Suko Ayaka, Junjun Jia, Nakamura Shinichi, Shigesato Yuzo

    Proceedings of the International Display Workshops   1   524 - 525  2015年

    記事・総説・解説・論説等(国際会議プロシーディングズ)  

     概要を見る

    © 2015 Society for Information Display. How the a-IGZO films crystallize and how the crystallinity affects the electrical properties, hence the TFT performances, have been investigated in detail. a-IGZO thin films were post-annealed in air at 300-1000 °C for 1h. HREM analyses revealed the crystallization behavior in detail. For the comparative purpose the crystallization behaviors of a-IGO and a-IZO films are also investigated.

  • In2O3系透明酸化物薄膜の熱拡散率とその温度依存性

    吉川透, 岡伸人, JIA Junjun, 八木貴志, 山下雄一郎, 竹歳尚之, 馬場哲也, 服部浩一郎, 清野豊, 重里有三

    Thermophys Prop   33rd   47 - 49  2012年10月  [査読有り]

    J-GLOBAL

  • Annealing effects on Ta doped SnO2 films

    Junjun Jia, Yu Muto, Nobuto Oka, Yuzo Shigesato

    Materials Research Society Symposium Proceedings   1454   245 - 251  2012年  [査読有り]

    速報,短報,研究ノート等(学術雑誌)  

     概要を見る

    Ta doped SnO2 (TTO) films prepared on quartz glass substrates at 200°C were annealed in the air to investigate the annealing effect on the structural, the optical, and the electrical properties. It is shown that the annealing for TTO films resulted in beneficial effect on the electrical resistivity by improving the carrier density and Hall mobility. The lowest resistivity was 1.4 × 10-3 Ω cm obtained at 400°C annealing temperature. The scattering mechanism in TTO films was discussed from the optical and electrical perspectives. The variation in Hall mobility with increasing the annealing temperature may be attributed to the scattering from the ionized and neutral impurities in TTO films. © 2012 Materials Research Society.

    DOI

  • シミュレーションによるコロイド凝集の温度依存性の解明

    賈 軍軍, 亀田 尭宙, 岩田 修一

    日本シミュレーション学会大会発表論文集 : シミュレーション・テクノロジー・コンファレンス・計算電気・電子工学シンポジウム   28   261 - 266  2009年06月

    CiNii

  • An Approach for Microstructural Pattern Design of Materials

    ZHANG Zhiming, IWATA Shuichi, JIA Junjun

    形の科学会誌 = Bulletin of the Society for Science on Form   24 ( 1 ) 51 - 52  2009年06月

    CiNii

  • Temperature dependence of colloidal aggregation: Cluster-moving Monte Carlo simulation

    Junjun Jia, Jin Zhu, Shuichi Iwata

    Asia Simulation Conference 2009, JSST 2009    2009年01月

     概要を見る

    Colloidal aggregation plays an important role in the field of industrial production and environmental pollution. The temperature influence on colloidal aggregation is scarcely studied at present. In this paper, we simulated the temperature influence on colloidal aggregation dynamics and cluster structures using cluster-moving Monte Carlo simulation. It is found that increasing the temperature leads to an acceleration of colloidal aggregation. The particle distribution function indicated that the temperature has a weak influence on the short-range structure and when the volume fraction is 0.3 the temperature slightly affects the long-range structure.

  • Fractal characteristics of colloid deposition

    Junjun Jia, Shuichi Iwata, Yoshimi Seida, Yasunori Kaneta, Nobuto Oka, Zhiming Zhang

    Data Science Journal   6   S206 - S210  2007年04月  [査読有り]

     概要を見る

    It is widely accepted that colloids play an important role in the contaminant migration process at present. However, the colloid deposition structure on rock surfaces has scarcely been studied. In this paper, preliminary results for a fractal characterization for colloid deposition in saturated fractures are presented, which consider the pH value, ionic strength, and flow rate of the solution. Under different chemical conditions, deposition behavior obviously changed, and fractal analysis appears to be an effective tool to capture the evolution and general behavior of depositions. Scanning Electron Microscopy (SEM) is used to observe the colloidal growth on granite surfaces and to acquire the visual image on a detailed level. The images are analyzed for their mass fractal dimensions. The influence on colloid fractal deposition is discussed.

    DOI

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現在担当している科目

▼全件表示

担当経験のある科目(授業)

  • Seminar on Nonequilibrium Electronic Devices

    早稲田大学  

    2024年04月
    -
    継続中
     

  • 電気・電子のための電磁気学

    早稲田大学  

    2019年04月
    -
    継続中
     

  • 半導体デバイスの物理

    早稲田大学  

    2019年04月
    -
    継続中
     

  • 光・波・熱力学

    早稲田大学  

    2019年04月
    -
    継続中
     

  • 電磁気学

    早稲田大学  

    2019年04月
    -
    継続中
     

  • 計算物理概論

    早稲田大学  

    2019年04月
    -
    継続中
     

  • 真空技術

    早稲田大学  

    2019年04月
    -
    2024年03月
     

  • 薄膜工学

    早稲田大学  

    2019年04月
    -
    2024年03月
     

▼全件表示

 

学内研究所・附属機関兼任歴

  • 2022年
    -
    2024年

    理工学術院総合研究所   兼任研究員

特定課題制度(学内資金)

  • Ge薄膜における光誘起プラズモンの制御

    2023年   八木貴志

     概要を見る

    本研究では、高強度パルスレーザ光をP型Ge半導体薄膜に集光照射することで、Geの価電子帯から多くの電子を励起し、伝導帯のバンド端に緩和してきた電子の集団振動(いわゆる光誘起プラズモン)を研究した。この光誘起プラズモンは非平衡電子系における物理現象であり、半導体材料自身の電子・フォノン構造と深く関係する。私は、超高速時間分解分光法を用いて、レーザ光で励起した電子がその励起準位からGeの伝導帯にあるGamma谷とL谷への緩和時間を精密計測した。さらに物理モデルを構築し、Gamma谷からL谷への谷間散乱時間も抽出した。以上の研究成果は、第84回日本応用物理学会・秋季学術講演会(23p-B204-8)にて発表し、現在論文投稿中である。&nbsp;

  • 超高速時間分解分光法による光誘起プラズモン現象の解明

    2023年  

     概要を見る

    金などの貴金属のプラズモン共鳴周波数は金属の自由電子濃度によって固定され、自由に選択することができない。本研究では、有機半導体であるPEDOT薄膜の正孔濃度を自在に調整する実験手法を開発し、中赤外から可視領域までのプラズモン共鳴波長のチューニングに成功した。また、PEDOT薄膜のプラズモン共鳴波長における異常透過現象が観測され、最大で210%の透過率変化が観測された。超高速時間分解分光法により、この非線形効果はポーラロンの影響によるものと判明した。キャリア濃度が調整可能なPEDOT材料は非常に優れた非線形光学材料となり、プラズモニクスおよびOn-Chipナノフォトニックデバイスにおける新たな応用可能性が期待される。以上の研究成果は、ACS Photonics 10, 3612 (2023)にて公開された。

  • 化合物半導体における光ブリーチング現象の物理解明と新規応用

    2022年  

     概要を見る

    本研究では、高強度パルスレーザの集光照射により直接および間接遷移型化合物半導体中の電子が高いエネルギー準位に一時的に励起・占有し、本来はほぼ不透明な波長領域に光の透過を制御できることが明らかにした。この光ブリーチング現象の物理起源を解明するために、フェムト秒時間分解測定装置を用いて、励起電子の緩和・再結合過程を定量的に評価した。また、直接と間接遷移型化合物半導体において、光ブリーチングの持続時間や強度の違いを詳細に調べた。得られた実験結果に基づき、自ら物理モデルを構築し、直接遷移型半導体中の光ブリーチング現象を定量的に説明することができた。その研究成果はJournal of Applied Physics (2022)にて公開された。

  • フェムト秒時間分解分光法による光ブリーチング現象の解明

    2021年   八木貴志, 牧本俊樹

     概要を見る

    本研究では、高強度パルスレーザの照射による直接遷移型InN半導体の光ブリーチングのメカニズムを検討した。2021年度、産業総合技術研究所と共同で、波長の異なるフェムト秒時間分解ポンププローブ装置を開発し、直接遷移型InN半導体のブリーチング現象(ほぼ不透明→透明)を測定した。得られた実験データに基づいて、直接遷移型InNにおける光ブリーチング現象をモデル化し、レーザ照射による励起した電子の緩和時間と再結合時間を定量的に評価した。これらの結果は時間分解PL測定などで測定された結果と良好に一致した。本研究成果により、直接遷移型InN半導体は光通信ネットワークにおける超高速光スイッチの新規材料としての応用が期待される。

  • 超高速光制御に向けた光ブリーチング現象の物理解明

    2020年   八木貴志, 牧本俊樹

     概要を見る

    光ネットワークに代表される高速情報通信では、現在光導波路を瞬時に切り替えるMEMSスイッチングデバイスが主流であるが、申請者は近未来の光回路に必要な機械動作部のない超高速光スイッチングデバイスの創出を目的としている。2020年度に、高強度パルスレーザを用いて直接遷移型窒化物(InN)を照射することで、本来不透明な波長領域に光を透過することが確認し、光の透過を超高速で切り替えることが成功した。このブリーチング現象(不透明↔透明)を解明するため、産業総合技術研究所と共同で開発したフェムト秒時間分解過渡透過・反射測定装置を用いて、ブリーチング現象の物理機構を解明した。結果として、励起電子が一時的に励起準位を占有することによって、より多くの入射光が透過することが明らかになった。更に、過渡反射測定結果に基づいて、電子の励起によるバンド構造への影響を詳細に考察した。

  • 量子井戸構造を用いた新規非線形光学材料の創出

    2019年   牧本俊樹

     概要を見る

    高度な情報化社会を実現するため、現在Siフォトニクスをベースとする大規模電子・光集積回路をCMOS技術で実現することを進めている。この集積回路中に重要な構成要素の一つである高速光スイッチ素子は、高い非線形光学応答を示す材料が必要とされる。本研究では、量子井戸構造を用いた非線形光学材料を探索し、高い非線形屈折率を持つ新規光学材料の創出を目的とした。2019年度に、量子井戸構造の候補材料であるGaN/InN/GaN中の構成材料InN薄膜の非線形光学特性を評価した。波長800 nmにおいて、レーザ光を集光照射することによって光電界強度を高めていくと、InN薄膜の透過率が非線形的に増加することを観測した。さらに、自作したフェムト秒時間分解装置を用いて、この非線形光学現象の物理機構を検討した。本研究成果は光集積回路内における超高速光スイッチングや光ダイオードへの応用が期待される。

  • 両極性半導体薄膜材料における欠陥構造解析

    2019年   重里有三, 満汐孝治

     概要を見る

    本研究課題では、半導体の機能のオリジンであるpn接合現象に着目し、n型伝導とp型伝導の両方を持つ両極性SnO薄膜における電気伝導特性と欠陥構造との関係性を解明することを目的とした。反応性スパッタを用いて非化学量論組成を持つSnO薄膜を作製し、ホール測定によるp型伝導であることを確認した。光電子分光法(XPS)およびX線構造解析(XRD)によるSnO薄膜中に少量なSnO2とSn3O4相が存在することが明らかになった。また、僅かな化学組成変化に対して、SnO薄膜の電気特性は大きく変化する。これはp型伝導に寄与する格子間酸素と化学組成変動のトレードオフ関係によるのものだと考えられる。以上の研究結果はJournal of Applied Physicsにアクセプトされた。

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