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論文

Repeatable photoinduced insulator-to-metal transition in yttrium oxyhydride epitaxial thin films

小松 遊矢*; 清水 亮太*; 佐藤 龍平*; Wilde, M.*; 西尾 和記*; 片瀬 貴義*; 松村 大樹; 齋藤 寛之*; 宮内 雅浩*; Adelman, J. R.*; et al.

Chemistry of Materials, 34(8), p.3616 - 3623, 2022/04

https://doi.org/10.1021/acs.chemmater.1c03450
 被引用回数：9 パーセンタイル：75.5(Chemistry, Physical)

Here, we demonstrate such a highly repeatable photoinduced insulator-to-metal transition in yttrium oxyhydride (YO$$_{x}$$H$$_{y}$$) epitaxial thin films. The temperature ($$T$$) dependence of the electrical resistivity ($$rho$$) of the films transforms from insulating to metallic ($$drho/dT > 0$$) under ultraviolet laser illumination. The sample is heated (125 $$^{circ}$$C) under an Ar atmosphere to recover its original insulating state. The films recover their original metallic conductivity when subsequently subjected to ultraviolet laser illumination, showing repeatable photoinduced insulator-to-metal transition. First principles calculations show that the itinerant carriers originate from the variations in the charge states of the hydrogen atoms that occupy octahedral interstitial sites. This study indicates that tuning the site occupancy (octahedral/tetrahedral) of the hydrogen atoms exerts a significant effect on the photoresponse of metal hydrides.

論文

Epitaxial thin film growth of europium dihydride

小松 遊矢*; 清水 亮太*; Wilde, M.*; 小林 成*; 笹原 悠輝*; 西尾 和記*; 重松 圭*; 大友 明*; 福谷 克之; 一杉 太郎*

Crystal Growth & Design, 20(9), p.5903 - 5907, 2020/09

https://doi.org/10.1021/acs.cgd.0c00602
 被引用回数：5 パーセンタイル：46.4(Chemistry, Multidisciplinary)

This paper reports the epitaxial growth of EuH$$_{2}$$ thin films with an $$omega$$-scan full width at half-maximum of 0.07$$^{circ}$$, the smallest value for metal hydride thin films reported so far. The thin films were deposited on yttria-stabilized ZrO$$_{2}$$ (111) substrates using reactive magnetron sputtering. The magnetization measurement showed that the saturation magnetization is $$sim$$7 $$mu_{B}$$/Eu atom, indicating that the EuH$$_{x}$$ films are nearly stoichiometric (x $$approx$$ 2.0) and that the Curie temperature is $$sim$$20 K. The optical measurements showed a bandgap of $$sim$$1.81 eV. These values are similar to those previously reported for bulk EuH$$_{2}$$. This study paves the way for the application of metal hydrides in the field of electronics through the fabrication of high-quality metal hydride epitaxial thin films.

論文

Hydrogenation and hydrogen diffusion at the anatase TiO$$_{2}$$(101) surface

長塚 直樹*; Wilde, M.*; 福谷 克之

Journal of Chemical Physics, 152(7), p.074708_1 - 074708_6, 2020/02

https://doi.org/10.1063/1.5142776
 被引用回数：10 パーセンタイル：59.98(Chemistry, Physical)

Hydrogenation of TiO$$_{2}$$ enhances its visible photoabsorption, leading to efficient photocatalytic activity. However, the role of hydrogen has not been fully understood. The anatase TiO$$_{2}$$(101) surface treated by hydrogen ion irradiation at 500 eV was investigated by photoemission spectroscopy and nuclear reaction analysis. Hydrogen irradiation induces an in-gap state 1-1.6 eV below the Fermi level and a downward band bending of 0.27 eV. The H depth profile at 300 K shows a surface peak with an H amount of (2.9$$pm$$0.3)$$times$$10$$^{15}$$ cm$$^{-2}$$ with little concentration in a deeper region. At 200 K, on the other hand, the H depth profile shows a maximum at about 1 nm below the surface corresponding to an H amount of (6.1$$pm$$0.3)$$times$$10$$^{15}$$ cm$$^{-2}$$ along with a broad distribution extending to 50 nm at an average concentration of 0.8 at. %. These results show that H diffusion in anatase TiO$$_{2}$$ is much faster than in rutile TiO$$_{2}$$ [Y. Ohashi, J. Phys. Chem. C 123, 10319-10324 (2019)]. The H diffusion coefficient at 200 K is determined to be 2.7$$pm$$0.1$$times$$10$$^{-13}$$ m$$^{2}$$ s$$^{-1}$$.

論文

Bias temperature instability characterization of advanced gate stacks

藤枝 信次*; 寺井 真之*; 西藤 哲史*; 戸田 昭夫*; 三浦 喜直*; Liu, Z.*; 寺岡 有殿; 吉越 章隆; Wilde, M.*; 福谷 克之*

ECS Transactions, 6(3), p.185 - 202, 2007/00

https://doi.org/10.1149/1.2728797

先端CMOSのバイアス温度不安定性に関する著者らの研究成果を招待講演で紹介する。25-nm SiO$$_{2}$$から1.8-nmプラズマ窒化SiON, 1.6-nm HfSiON high-k, 1.5-nm Ni-full-silicide/HfSiONまでというようにゲートスタックがスケーリングされるにつれ、負/正バイアス温度不安定性の原因として不純物,界面ストイキオメトリ,応力等の新しい化学的・物理的要因が現れてきたことを指摘する。

口頭

Growth mechanism of the ultra-thin oxide films on metal substrates

Wilde, M.*; 福谷 克之*; 盛谷 浩右; 吉越 章隆; 寺岡 有殿

no journal, , 

NiAl(100)表面酸化過程に見られる水素の影響をリアルタイムXPSを用いて調べた。酸素分子線及び水分子線を用いて表面を酸化し、膜厚が飽和した試料について酸化膜由来のAl$$^{3+}$$信号強度と基板由来のAl$$^{0}$$信号強度の取り出し角依存性を測定した。その結果、水分子線を用いて酸化した試料の方がAl$$^{3+}$$信号強度が強く、飽和酸化膜厚が厚いことがわかった。このことは、表面にOH基が形成されそれに基づく強い電場のために酸化が促進されるというモデルを支持すると考えられる。

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