氏名

カコ グングン

賈 軍軍

職名

准教授(任期付)

所属

(国際理工学センター)

本属以外の学内所属

学内研究所等

理工学術院総合研究所

兼任研究員 2019年-

学歴・学位

学位

博士(環境学) 課程 東京大学 ナノ構造物理

論文

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, and Yuzo Shigesato

Journal of Applied Physics査読有り125(24)p.245303-1 - 245303-62019年06月-

DOIlink

詳細

掲載種別:研究論文(学術雑誌)

概要:Sn-doped In2O3 (ITO) nanoparticles with various Sn doping concentrations were successfully fabricated using a liquid phase coprecipitation method. Similar to sputtered ITO thin films, Sn doping reaches a maximum carrier density (1.52 × 10^21 cm^−3) at 10 at% in ITO nanoparticles, which was estimated from the bulk plasmon energy based on a scanning ellipsometry (SE) simulation. Interestingly, the X-ray photoelectron emission spectra (XPS) of In 3d core levels show a clear asymmetric peak with a shoulder on the high-binding-energy side for degenerated ITO nanoparticles, which may be associated with the influence of the surface plasmon or plasmonic coupling. Our results suggest that combining the SE simulation and XPS measurements effectively provides a new way to understand the difference between bulk plasmons and surface plasmons for transparent conductive oxide nanoparticles

Deposition of TiO2 photocatalyst on PET or PI polymer films by reactive sputtering for flexible photocatalytic sheets

Yuka Kitazawa, Junjun Jia, Shin-ichi Nakamura, Yuzo Shigesato

Japanese Journal of Applied Physics査読有り58(3)p.055503-1 - 055503-92019年04月-

DOI

詳細

掲載種別:研究論文(学術雑誌)

概要:Polycrystalline anatase TiO2 films were deposited by rf reactive magnetron sputtering on polyethylene terephthalate (PET) or polyimide (PI) films with different buffer layers, such as SiO2 or Zn2SnOx (ZTO) between the TiO2 film and the substrate. Such TiO2/(SiO2 or ZTO)/(PET or PI) sheets with high transmittance in the visible region of light performed high photo-decomposition ability of CH3CHO under the UV irradiation of the black light centered at 352 nm. In the case of using SiO2 as the buffer layer, “nano-pore layer” was observed clearly in full area of the polymer substrates close to the buffer layers after the UV irradiation, whereas such degradation was suppressed drastically in the case of using ZTO as the buffer layer. Such photocatalytic sheets performed also photo-induced hydrophilicity by the UV irradiation, where the contact angle to pure water became around 5O under the UV irradiation. After additional deposition of SiO2 by the reactive sputtering under rather high total gas pressure of 3.0 Pa on the outermost surface of the TiO2 films, the photo-induced hydrophilicity was maintained for more than 98 days in the dark. Such 3-layerd SiO2/TiO2/ZTO on PET or PI substrates should be the promising flexible photocatalytic sheets with the retentional photo-induced hydrophilicity.

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, and Yuzo Shigesato

Journal of Applied Physics査読有り125(3)p.035101-1 - 035101-112019年01月-

DOI

詳細

掲載種別:研究論文(学術雑誌)

概要:The thermal conductivities of c- and a-axis-oriented zinc oxide (ZnO) thin films with nominal thicknesses of 100, 200, and 300 nm are investigated. The c- and a-axis-oriented ZnO thin films were synthesized by radio frequency magnetron sputtering on the c- and r-plane sapphire substrates, respectively. The epitaxial relationship between the ZnO thin film and the c-plane sapphire substrate is (0001)[11¯00] || (0001)[112¯0], and that between the ZnO thin film and the r-plane sapphire substrate is (112¯0)[11¯00] || (011¯2)[112¯0]. The c-axis-oriented ZnO thin film has a columnar structure, whereas the a-axis-oriented ZnO thin film has a single domain-like structure and a significantly flat surface. The thermal conductivity of the c-axis-oriented ZnO thin film is in the range of 18–24 W m−1 K−1, whereas for the a-axis-oriented ZnO thin film, it is in the range of 24–29 W m−1 K−1. For the c-axis-oriented ZnO thin films, the phonon scattering on both the out-of-plane and in-plane grain boundaries affects the thermal conductivity. In contrast, the thermal conductivity of the a-axis-oriented ZnO thin films decreases with the decrease of the film thickness. The distribution of the normalized cumulative thermal conductivity of the a-axis-oriented ZnO thin films suggests that the heat transport carrier mostly consists of phonons with the mean free paths between 100 nm and 1 μm

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査読有り5(4)p.046412-1 - 046412-92018年04月-

DOI

詳細

掲載種別:研究論文(学術雑誌)

概要:The crystal structure of tin (Sn)-doped titanium dioxide (TiO2) film was investigated by using x-ray absorption fine structure (XAFS) measurement and first principle calculations. XAFS measurements suggest that Sn doping can enhance the growth of rutile TiO2 phase, where Sn ions are considered to substitute into Ti sites with a valence of 4+. First principles calculation reveals that Sn doping can reduce obviously the formation energy of the rutile phase. By comparing the measured and calculated XAFS spectra, we found that the geometric structure of Sn dopant can be understood as the alignment of SnO6 tetrahedrons through a corner oxygen in the Sn-doped TiO2 film, that is, the Sn ions substituted in the Ti sites and made a one-dimensional zigzag '–Sn–O–Sn–' chain.

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, and Hiroyuki Hosomi

Physical Review Applied査読有り9(1)p.014018-1 - 014018-132018年01月-

DOIlink

詳細

掲載種別:研究論文(学術雑誌)

概要: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.

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

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

MRS Communications査読有り8(2)p.314 - 3212018年03月-

DOIlink

詳細

掲載種別:研究論文(学術雑誌)

概要: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 aZn3N2film 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 Zn3N2films varied from∼1.2 to 1.5 eV depending on the N2flow 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 N2flow ratio of 40%. The carrier density of Zn3N2films 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.

A visible-light active TiO2 photocatalyst multilayered with WO3

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

Physical Chemistry Chemical Physics査読有り19p.17342 - 173482017年06月-

DOIlink

詳細

掲載種別:研究論文(学術雑誌)

概要: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 5° 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.

外部研究資金

科学研究費採択状況

研究種別:若手研究(B)

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

2016年04月-2019年03月

研究分野:薄膜・表面界面物性

配分額:¥4160000

研究種別:基盤研究(C)

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

2016年10月-2019年

研究分野:薄膜・表面界面物性

配分額:¥4810000

研究資金の受入れ状況

提供機関:公益財団法人 高橋産業経済研究財団実施形態:研究助成金

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2019年04月-2020年03月

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