2023/09/20 更新

写真a

サトウ ダイキ
佐藤 大樹
SATO Daiki
所属
未来材料・システム研究所 Photo electron Soul GaN産学協同研究部門 特任助教
職名
特任助教
 

論文 8

  1. Investigation on Applying an InGaN Photocathode with Negative Electron Affinity for Electric Propulsion

    Inoue Yusuke, Nishitani Tomohiro, Honda Anna, Sato Daiki, Shikano Haruka, Koizumi Atsushi, Honda Yoshio, Ichihara Daisuke, Sasoh Akihiro

    TRANSACTIONS OF THE JAPAN SOCIETY FOR AERONAUTICAL AND SPACE SCIENCES   66 巻 ( 1 ) 頁: 10 - 13   2023年

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    記述言語:英語   出版者・発行元:一般社団法人 日本航空宇宙学会  

    DOI: 10.2322/tjsass.66.10

    Web of Science

    Scopus

    CiNii Research

  2. Photoelectron beam technology for SEM imaging with pixel-specific control of irradiation beam current

    Nishitani T., Arakawa Y., Noda S., Koizumi A., Sato D., Shikano H., Iijima H., Honda Y., Amano H.

    METROLOGY, INSPECTION, AND PROCESS CONTROL XXXVII   12496 巻   2023年

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    出版者・発行元:Proceedings of SPIE - The International Society for Optical Engineering  

    The scanning electron microscope (SEM) with photocathode technology was launched by retrofitting the photocathode electron gun to a commercial-based SEM system. In this SEM system, the excitation laser for photoelectron generation from the photocathode is synchronized to the scanning signal. SEM images were obtained by high-speed modulation of the photoelectron beam current using the photocathode SEM, where the location in the field of view and its irradiation current were arbitrarily selected on a pixel-by-pixel basis (Selective e-Beaming technology). As a demonstration experiment contributing to non-contact electrical inspection, low-voltage SEM imaging of MOS-FET structures in 3D-NAND flash memory was performed using this selective e-beam technology. As a result, changes in the voltage contrast of the drain electrode were observed in response to on/off selective electron beam irradiation to the gate electrode in the MOS-FET structure. As an extension of the selective electron beaming technology, a Yield Controlled e-beaming (YCeB) technology was invented to control the secondary electron yield generated in the entire field of view of the SEM image by feedback control of the laser power irradiating the photocathode to the intensity of each pixel in the SEM image. The YCeB image, in which the laser power intensity corresponding to the probe intensity is modulated so that the secondary electron yield generated in the entire field of view of the SEM image is constant, is a clearer image with less noise than the original SEM image.

    DOI: 10.1117/12.2657853

    Web of Science

    Scopus

  3. Novel Electron Beam Technology using InGaN Photocathode for High-Throughput Scanning Electron Microscope Imaging

    Sato Daiki, Koizumi Atsushi, Shikano Haruka, Noda Shotaro, Otsuka Yohei, Yasufuku Daisuke, Mori Kazumasa, Iijima Hokuto, Nishitani Tomohiro, Honda Yoshio, Amano Hiroshi

    METROLOGY, INSPECTION, AND PROCESS CONTROL XXXVII   12496 巻   2023年

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    出版者・発行元:Proceedings of SPIE - The International Society for Optical Engineering  

    An InGaN photocathode with a negative electron affinity (NEA) surface is suitable for industrial use because of features such as a long quantum efficiency lifetime, availability with a visible laser as an excitation light source, and the presence of a transmission-type structure. The first objective is the development of an InGaN photocathode electron gun that can be mounted on a scanning electron microscope (SEM) and the evaluation of the electron beam size at the emission point, maximum emission current, and transverse energy of the electron beam, which are important factors for realizing a high probe current in the SEM. The second objective is the evaluation of emission current stability, while the third objective is the generation of a pulsed electron beam and multi-electron beam from the InGaN photocathode. The parameters of the electron beam from the photocathode electron gun were an emission beam radius of 1 µm, transverse energy of 44 meV, and an emission current of up to 110 µA. Using a high beam current with low transverse energy from the photocathode, a 13 nA probe current with 10 nm SEM resolution was observed with 15 µA emission. At 15 µA, the continuous electron beam emission for 1300 h was confirmed; at 30 µA, the cycle time between the NEA surface reactivations was confirmed to be 90 h with 0.043% stability. Moreover, a 4.4 ns pulsed e-beam with a 4.7 mA beam current was generated, and a 5 × 5 multielectron beam with 12% uniformity was then obtained. The advantages of the InGaN photocathode, such as high electron beam current, low transverse energy, long quantum efficiency lifetime, pulsed electron beam, and multi-electron beam, are useful in industries including semiconductor device inspection tools.

    DOI: 10.1117/12.2657032

    Web of Science

    Scopus

  4. Scanning electron microscope imaging by selective e-beaming using photoelectron beams from semiconductor photocathodes

    Nishitani Tomohiro, Arakawa Yuta, Noda Shotaro, Koizumi Atsushi, Sato Daiki, Shikano Haruka, Iijima Hokuto, Honda Yoshio, Amano Hiroshi

    JOURNAL OF VACUUM SCIENCE & TECHNOLOGY B   40 巻 ( 6 )   2022年12月

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    出版者・発行元:Journal of Vacuum Science and Technology B  

    Pulsed electron beams from a photocathode using an InGaN semiconductor have brought selectively scanning technology to scanning electron microscopes, where the electron beam irradiation intensity and area can be arbitrarily selected within the field of view in SEM images. The p-type InGaN semiconductor crystals grown in the metalorganic chemical vapor deposition equipment were used as the photocathode material for the electron beam source after the surface was activated to a negative electron affinity state in the electron gun under ultrahigh vacuum. The InGaN semiconductor photocathode produced a pulsed electron beam with a rise and fall time of 3 ns, consistent with the time structure of the irradiated pulsed laser used for the optical excitation of electrons. The InGaN photocathode-based electron gun achieved a total beam operation time of 1300 h at 15 μA beam current with a downtime rate of 4% and a current stability of 0.033% after 23 cycles of surface activation and continuous beam operation. The InGaN photocathode-based electron gun has been installed in the conventional scanning electron microscope by replacing the original field emission gun. SEM imaging was performed by selective electron beaming, in which the scanning signal of the SEM system was synchronized with the laser for photocathode excitation to irradiate arbitrary regions in the SEM image at arbitrary intensity. The accuracy of the selection of regions in the SEM image by the selective electron beam was pixel by pixel at the TV scan speed (80 ns/pix, 25 frame/s) of the SEM.

    DOI: 10.1116/6.0002111

    Web of Science

    Scopus

  5. Time response measurement of pulsed electron beam from InGaN photocathode 招待有り 査読有り 国際共著

    Sato, D., Shikano, H., Koizumi, A., Nishitani, T.

    JOURNAL OF VACUUM SCIENCE & TECHNOLOGY B   40 巻   頁: 064204   2022年11月

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    担当区分:筆頭著者   掲載種別:研究論文(学術雑誌)  

    DOI: 10.1116/6.0002122

  6. Adsorption structure deteriorating negative electron affinity under the H2O environment

    Kashima M., Ishiyama S., Sato D., Koizumi A., Iijima H., Nishitani T., Honda Y., Amano H., Meguro T.

    APPLIED PHYSICS LETTERS   121 巻 ( 18 )   2022年10月

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    出版者・発行元:Applied Physics Letters  

    Photocathodes with negative electron affinity (NEA) characteristics have various advantages, such as small energy spread, high spin polarization, and ultrashort pulsing. Nitride semiconductors, such as GaN and InGaN, are promising materials for NEA photocathodes because their lifetimes are longer than those of other materials. In order to further prolong the lifetime, it is important to better understand the deterioration of NEA characteristics. The adsorption of residual gases and back-bombardment by ionized residual gases shorten the lifetime. Among the adsorbed residual gases, H2O has a significant influence. However, the adsorption structures produced by the reaction with H2O are not comprehensively studied so far. In this study, we investigated adsorption structures that deteriorated the NEA characteristics by exposing InGaN and GaAs to an H2O environment and discussed the differences in their lifetimes. By comparing the temperature-programmed desorption curves with and without H2O exposure, the generation of CsOH was confirmed. The desorption of CsOH demonstrated different photoemission behaviors between InGaN and GaAs results. InGaN recovered its NEA characteristics, whereas GaAs did not. Considering the Cs desorption spectra, it is difficult for an NEA surface on InGaN to change chemically, whereas that for GaAs changes easily. The chemical reactivity of the NEA surface is different for InGaN and GaAs, which contributes to the duration of photoemission. We have attempted to prolong the lifetime of InGaN by recovering its NEA characteristics. We found that InGaN with NEA characteristics can be reused easily without thermal treatment at high temperatures.

    DOI: 10.1063/5.0125344

    Web of Science

    Scopus

  7. Dependence of electron emission current density on excitation power density from Cs/O-activated negative electron affinity InGaN photocathode 査読有り

    Koizumi, A., Sato, D., Shikano, H., Iijima, H., Nishitani, T.

    JOURNAL OF VACUUM SCIENCE & TECHNOLOGY B   40 巻   頁: 062202   2022年10月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    DOI: 10.1116/6.0002124

  8. The photoemission characteristics of a NEA InGaN photocathode by simultaneously supplying Cs and O2

    Kashima Masahiro, Itokawa Yuya, Kanai Toshiya, Sato Daiki, Koizumi Atsushi, Iijima Hokuto, Nishitani Tomohiro, Honda Yoshio, Amano Hiroshi, Meguro Takashi

    APPLIED SURFACE SCIENCE   599 巻   2022年10月

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    出版者・発行元:Applied Surface Science  

    A high quantum efficiency (QE) can be obtained on negative electron affinity (NEA) surfaces. It is well-known that NEA surfaces can be formed on semiconductor materials such as GaAs by the alternating supply of cesium (Cs) and oxygen (O2), which is called the yo-yo method. While GaN and related compounds such as InGaN are expected to realize an NEA photocathode with a long lifetime, the surface reactions between GaAs and nitride semiconductors are completely different with respect to the increasing rate of QE induced by the supply of O2. In addition, the surface processes of photoemission from NEA nitride semiconductors have not yet been elucidated. In the present study, a higher QE was achieved in InGaN by simultaneously supplying Cs and O2 instead of using the conventional yo-yo method. The possible Cs adsorption states in relation to the photoemission are also discussed based on the QE tendencies and the temperature programmed desorption (TPD) spectra of the NEA surfaces formed under elevated temperature conditions. This study suggests that the Cs oxide species, which is one of the key compounds for imparting the NEA nature, decomposes at approximately 350 °C and that the InGaN-Cs2O2 structure is a possible candidate for NEA photocathodes.

    DOI: 10.1016/j.apsusc.2022.153882

    Web of Science

    Scopus

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