Updated on 2022/06/30

写真a

 
JIA, Junjun
 
Affiliation
Faculty of Science and Engineering, Global Center for Science and Engineering
Job title
Associate Professor(without tenure)
Profile
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、光触媒などのエネルギーならびに環境技術の応用に向けて、スプレーパイロリシス法やスパッタ法を用いた無機薄膜材料・ナノ粒子の合成と物性評価及びデバイスの作製に取り組んでいる。さらに上記の研究で得た実験結果に対して、様々な測定手法を開発・利用し、材料中の欠陥が物性に与える影響を検証し、欠陥構造と電子・光物性の関係を明らかにしている。

Research Institute

  • 2020
    -
    2022

    理工学術院総合研究所   兼任研究員

Degree

  • 東京大学   博士(環境学)

Research Experience

  • 2019.04
    -
    Now

    Waseda University   GCSE, Faculty of Science and Engineering   Associate Professor

  • 2012.09
    -
    2019.03

    Aoyama Gakuin University   Graduate School of Science and Engineering   Assistant Professor

  • 2011.04
    -
    2012.08

    Aoyama Gakuin University   Graduate School of Science and Engineering   Posdoctor Fellowship

  • 2007.04
    -
    2011.03

    The University of Tokyo

 

Research Areas

  • Semiconductors, optical properties of condensed matter and atomic physics

Research Interests

  • Nonlinear Optics

  • 欠陥構造解析

  • Plasmonics

  • Semiconductor Physics and Devices

Papers

  • Origin of Enhanced Electromechanical Coupling in (Yb,Al)N Nitride Alloys

    Junjun Jia, Takahiko Yanagitani

    Physical Review Applied   16   044009  2021.10  [Refereed]

    Authorship:Lead author, Corresponding author

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

    Junjun Jia, Shimpei Iwasaki, Shingo Yamamoto, Shin-ichi Nakamura, Eisuke Magome, Toshihiro Okajima, Yuzo Shigesato

    ACS Applied Materials & Interfaces    2021.06  [Refereed]

    Authorship:Lead author, Corresponding author

    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 )  2018.01  [Refereed]

    Authorship:Lead author

     View Summary

    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

  • 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 )  2013.07  [Refereed]

    Authorship:Lead author

     View Summary

    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

  • 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 )  2012.07  [Refereed]

    Authorship:Lead author

     View Summary

    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

  • Enhanced Electromechanical Coupling in Yb-Substituted III–V Nitride Alloys

    Junjun Jia, Naoya Iwata, Masashi Suzuki, Takahiko Yanagitani

    ACS Applied Electronic Materials    2022.06  [Refereed]

    Authorship:Lead author, Corresponding author

    DOI

  • 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  2022.02  [Refereed]

    DOI

  • 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  2021.11  [Refereed]

    DOI

  • Thermal conductivity across the van der Waals layers of α-MoO3 thin films composed of mosaic domains with in-plane 90° rotations

    Yuichiro Yamashita, Yuzuki Aoki, Takashi Yagi, Junjun Jia, Makoto Kashiwagi, Yuki Oguchi, Naoyuki Taketoshi, Yuzo Shigesato

    Journal of Applied Physics   130 ( 8 ) 085103 - 085103  2021.08  [Refereed]

    DOI

  • 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)    2020.09

    DOI

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

    Junjun Jia, Takumi Sugana, Shin-ichi Nakamura, and Yuzo Shigesato

    Journal of Applied Physics   127   185703  2020.05  [Refereed]

    Authorship:Lead author, Corresponding author

  • Carrier densities of Sn-doped In2O3 nanoparticles and their effect on X-ray photoelectron emission

    J. Jia, A. Takaya, T. Yonezawa, K. Yamasaki, H. Nakazawa, Y. Shigesato

    Journal of Applied Physics   125 ( 24 ) 245303  2019.06  [Refereed]

    Authorship:Lead author, Corresponding author

    DOI

  • 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  [Refereed]

     View Summary

    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

    Y. Kitazawa, J. Jia, S. Nakamura, Y. Shigesato

    Japanese Journal of Applied Physics   58 ( 5 ) 055503  2019.01  [Refereed]

    DOI

  • Thermal conductivity of hetero-epitaxial ZnO thin films on c - And r -plane sapphire substrates: Thickness and grain size effect

    Y. Yamashita, K. Honda, T. Yagi, J. Jia, N. Taketoshi, Y. Shigesato

    Journal of Applied Physics   125 ( 3 ) 035101  2019.01  [Refereed]

  • 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   314 - 321  2018.06  [Refereed]

     View Summary

    © 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

  • Geometric structure of Sn dopants in sputtered TiO2 film revealed by x-ray absorption spectroscopy and first-principles DFT calculations

    Toshihiro Okajima, Junjun Jia, Yuzo Shigesato

    Materials Research Express   5   046412  2018.04  [Refereed]

  • 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  2017.07  [Refereed]

    Authorship:Lead author

     View Summary

    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

  • 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 )  2017.07  [Refereed]

    Authorship:Lead author

     View Summary

    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.

    DOI

  • 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 )  2017.04  [Refereed]

     View Summary

    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

    DOI

  • 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  2017.02  [Refereed]

    Authorship:Lead author, Corresponding author

     View Summary

    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.

    DOI

  • On the Crystal Structural Control of Sputtered TiO2 Thin Films

    Junjun Jia, Haruka Yamamoto, Toshihiro Okajima, Yuzo Shigesato

    Nanoscale Research Letters   11 ( 1 )  2016.12  [Refereed]

    Authorship:Lead author

     View Summary

    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.

    DOI

  • 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  2016.09  [Refereed]

     View Summary

    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 >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.

    DOI

  • 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  2016.09  [Refereed]

    Authorship:Lead author

     View Summary

    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

    DOI

  • 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 )  2016.07  [Refereed]

    Authorship:Lead author

     View Summary

    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.

    DOI

  • On the Crystal Structural Control of Sputtered TiO2 Thin Films

    Junjun Jia, Haruka Yamamoto, Toshihiro Okajima, Yuzo Shigesato

    NANOSCALE RESEARCH LETTERS   11  2016.07  [Refereed]

     View Summary

    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.

    DOI

  • 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  2016.05  [Refereed]

     View Summary

    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

    DOI

  • 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  2015.11  [Refereed]

    Authorship:Lead author

     View Summary

    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.

    DOI

  • 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 )  2015.10  [Refereed]

     View Summary

    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.

    DOI

  • 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 )  2015.07  [Refereed]

     View Summary

    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.

    DOI

  • 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 )  2015.05  [Refereed]

     View Summary

    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

    DOI

  • 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 )  2015.01  [Refereed]

    Authorship:Lead author

     View Summary

    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.

    DOI

  • 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 )  2014.10  [Refereed]

    Authorship:Lead author

     View Summary

    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

    DOI

  • 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  2014.08  [Refereed]

     View Summary

    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.

    DOI

  • 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  2014.05  [Refereed]

     View Summary

    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.

    DOI

  • 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  2014.05  [Refereed]

    Authorship:Lead author

     View Summary

    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.

    DOI

  • 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  2014.05  [Refereed]

     View Summary

    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.

    DOI

  • 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  2014.05  [Refereed]

     View Summary

    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.

    DOI

  • 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  2014.03  [Refereed]

     View Summary

    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.

    DOI

  • 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 )  2013.06

     View Summary

    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

  • 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 )  2013.04  [Refereed]

    Authorship:Lead author

     View Summary

    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

  • 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 )  2013.02

     View Summary

    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 > 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

  • 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  2011.10  [Refereed]

    Authorship:Lead author, Corresponding author

     View Summary

    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

  • Nonequilibrium structure of primary particles in colloidal bidispersion

    Junjun Jia, Shuichi Iwata

    COLLOID AND POLYMER SCIENCE   288 ( 14-15 ) 1485 - 1493  2010.10  [Refereed]

    Authorship:Lead author, Corresponding author

     View Summary

    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

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Misc

  • 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

    Article, review, commentary, editorial, etc. (international conference proceedings)  

     View Summary

    © 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  2012.10  [Refereed]

    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  [Refereed]

    Rapid communication, short report, research note, etc. (scientific journal)  

     View Summary

    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  2009.06

    CiNii

  • An Approach for Microstructural Pattern Design of Materials

    ZHANG Zhiming, IWATA Shuichi, JIA Junjun

      24 ( 1 ) 51 - 52  2009.06

    CiNii

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

    Junjun Jia, Jin Zhu, Shuichi Iwata

    Asia Simulation Conference 2009, JSST 2009    2009.01

     View Summary

    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  2007.04  [Refereed]

     View Summary

    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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Awards

  • 第5回 薄膜・表面物理分科会 論文賞

    2021.03   日本応用物理学会  

  • 論文賞

    2019.11   日本熱物性学会  

  • Award for encouragement of research

    2017.08   International Union of Materials Research Societies(IUMRS)   Tailoring Crystal Structures of Sputtered TiO2 Film by Impurity Doping

    Winner: Junjun Jia

  • Best Poster Award

    2016.05   European Materials Research Society (EMRS)   In-situ Brouwer analysis on possible defects in homologous In2O3(ZnO)m films

    Winner: Junjun Jia

  • Silver Poster Award

    2015.07   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

    Winner: Junjun Jia

  • The 1st annual JMR Paper of the Year Award

    2015.04   Materials Research Society (MRS)   Thermophysical properties of SnO2-based transparent conductive films: Effect of dopant species and structure compared with In2O3-, ZnO-, and TiO2-based films

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

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Research Projects

  • 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)

    Project Year :

    2020.04
    -
    2023.03
     

    賈 軍軍

  • 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

    Project Year :

    2019.04
    -
     
     

    賈 軍軍

  • Experimental investigation on crystallization of In2O3 based amorphous transparent conductive oxide films

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (C)

    Project Year :

    2016.10
    -
    2019.03
     

     View Summary

    The amorphous structure and the generation of nano- to micro-sized crystallites with preferred crystallographic orientations have been discussed to improve the stability and performance of In-based amorphous oxide semiconductors. The in-situ X-ray diffraction measurements were performed at Kyushu Synchrotron Light Research Center for the rapid and precise estimation of the crystallization fraction. Crystal growth behaviors were also analyzed by TEM. The in-situ observation for the XRD of In2O3, IGO, IGZO films during annealing in air were carried out, where the annealing temperatures for the films were 150, 670 and 300-900 degree C, respectively. The amorphous films started to crystallize after the each annealing. The activation energies of the crystallization were estimated from the change of the integrated intensity of the In2O3 (222) peak with the increase in the annealing time. The crystallization kinetics of the films were successfully examined based on the Avrami analysis.

  • 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)

    Project Year :

    2016.04
    -
    2019.03
     

    賈 軍軍

Specific Research

  • 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   八木貴志, 牧本俊樹

     View Summary

    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   八木貴志, 牧本俊樹

     View Summary

    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。

  • 両極性半導体薄膜材料における欠陥構造解析

    2019   重里有三, 満汐孝治

     View Summary

    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。

  • 量子井戸構造を用いた新規非線形光学材料の創出

    2019   牧本俊樹

     View Summary

    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。

 

Syllabus

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Teaching Experience

  • Electromagnetism for Electrical and Electronic Engineering

    Waseda University  

    2019.04
    -
    Now
     

  • Thin Film Engineering

    Waseda University  

    2019.04
    -
    Now
     

  • Physics of Semiconductor Devices

    Waseda University  

    2019.04
    -
    Now
     

  • Light, Wave, and Thermodynamics

    Waseda University  

    2019.04
    -
    Now
     

  • Electromagnetism

    Waseda University  

    2019.04
    -
    Now
     

  • Introduction to Computational Physics

    Waseda University  

    2019.04
    -
    Now
     

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Committee Memberships

  • 2012.09
    -
    Now

    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