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Journal Articles

Thermally altered subsurface material of asteroid (162173) Ryugu

Kitazato, Kohei*; Milliken, R. E.*; Iwata, Takahiro*; Abe, Masanao*; Otake, Makiko*; Matsuura, Shuji*; Takagi, Yasuhiko*; Nakamura, Tomoki*; Hiroi, Takahiro*; Matsuoka, Moe*; et al.

Nature Astronomy (Internet), 5(3), p.246 - 250, 2021/03

https://doi.org/10.1038/s41550-020-01271-2
 Times Cited Count：44 Percentile：97.1(Astronomy & Astrophysics)

Here we report observations of Ryugu's subsurface material by the Near-Infrared Spectrometer (NIRS3) on the Hayabusa2 spacecraft. Reflectance spectra of excavated material exhibit a hydroxyl (OH) absorption feature that is slightly stronger and peak-shifted compared with that observed for the surface, indicating that space weathering and/or radiative heating have caused subtle spectral changes in the uppermost surface. However, the strength and shape of the OH feature still suggests that the subsurface material experienced heating above 300 $$^{circ}$$C, similar to the surface. In contrast, thermophysical modeling indicates that radiative heating does not increase the temperature above 200 $$^{circ}$$C at the estimated excavation depth of 1 m, even if the semimajor axis is reduced to 0.344 au. This supports the hypothesis that primary thermal alteration occurred due to radiogenic and/or impact heating on Ryugu's parent body.

Journal Articles

Measurements of electron-induced neutrons as a tool for determination of electron temperature of fast electrons in the task of optimization laser-produced plasma ions acceleration

Sakaki, Hironao; Nishiuchi, Mamiko; Maeda, Shota; Sagisaka, Akito; Pirozhkov, A. S.; Pikuz, T.; Faenov, A.*; Ogura, Koichi; Fukami, Tomoyo; Matsukawa, Kenya*; et al.

Review of Scientific Instruments, 85(2), p.02A705_1 - 02A705_4, 2014/02

https://doi.org/10.1063/1.4825154
 Times Cited Count：2 Percentile：11.15(Instruments & Instrumentation)

High intensity laser-plasma interaction has attracted considerable interest for a number of years. The laser-plasma interaction is accompanied by generation of various charged particle beams. Results of simultaneous novel measurements of electron-induced photonuclear neutrons (photoneutron), which are a diagnostic of the laser-plasma interaction, are proposed to use for optimization of the laser-plasma ion generation. The proposed method is demonstrated by the laser irradiation with the intensity os 1$$times$$10$$^{21}$$ W/cm$$^{2}$$ on the metal foil target. The photoneutrons are measured by using NE213 liquid scintillation detectors. Heavy-ion signal is registered with the CR39 track detector simultaneously. The measured signals of the electron-induced photoneutrons are well reproduced by using the Particle and Heavy Ion Transport code System (PHITS). The results obtained provide useful approach for analyzing the various laser based ion beams.

Journal Articles

Synchrotron radiation photoemission study of Ge$$_{3}$$N$$_{4}$$/Ge structures formed by plasma nitridation

Hosoi, Takuji*; Kutsuki, Katsuhiro*; Okamoto, Gaku*; Yoshigoe, Akitaka; Teraoka, Yuden; Shimura, Takayoshi*; Watanabe, Heiji*

Japanese Journal of Applied Physics, 50(10), p.10PE03_1 - 10PE03_5, 2011/10

https://doi.org/10.1143/JJAP.50.10PE03
 Times Cited Count：11 Percentile：43.84(Physics, Applied)

Journal Articles

Interface engineering of Ge MOS devices with ZrO$$_{2}$$ gate dielectrics

Hosoi, Takuji*; Okamoto, Gaku*; Kutsuki, Katsuhiro*; Kagei, Yusuke*; Harries, J.; Yoshigoe, Akitaka; Teraoka, Yuden; Shimura, Takayoshi*; Watanabe, Heiji*

Oyo Butsuri Gakkai Hakumaku, Hyomen Butsuri Bunkakai, Shirikon Tekunoroji Bunkakai Kyosai Tokubetsu Kenkyukai Kenkyu Hokoku, p.145 - 148, 2010/01

We developed high quality high-$$k$$/Ge gate stacks with reduced leakage current and superior interface quality, which was fabricated by direct deposition of ZrO$$_{2}$$ on Ge substrate and thermal oxidation. Synchrotron radiation photoelectron spectroscopy revealed that thermal oxidation at 823 K caused not only an intermixing between ZrO$$_{2}$$ and Ge but also the formation of GeO$$_{2}$$ at the interlayer. We obtained an equivalent oxide thickness (EOT) of 1.9 nm, and an interface state density of 10$$^{11}$$ cm$$^{-2}$$eV$$^{-1}$$ for Au/ZrO$$_{2}$$/Ge capacitors. Furthermore, we found that the A1$$_{2}$$0$$_{3}$$ capping on the Zr0$$_{2}$$ 1ayer is effective for decreasing EOT. The interface state density as low as 5.3$$times$$10$$^{10}$$ cm$$^{-2}$$eV$$^{-1}$$ was obtained for the Al$$_{2}$$O$$_{3}$$/ZrO$$_{2}$$/Ge stack with 30 min oxidation. The EOT could be reduced to l.6 nm by 10 min oxidation. The leakage current was two orders of magnitude lower than the conventional poly-Si/SiO$$_{2}$$/Si stack.

Oral presentation

In-situ characterization of chemical bonding states and thermal decomposition of Ge$$_{3}$$N$$_{4}$$ film by SR-XPS

Hosoi, Takuji*; Kutsuki, Katsuhiro*; Okamoto, Gaku*; Harada, Makoto*; Yoshigoe, Akitaka; Teraoka, Yuden; Shimura, Takayoshi*; Watanabe, Heiji*

no journal, , 

After wet cleaning of p-Ge(001) by HF solution, the surface was anealed in an ultra-high vacuum and was nitrided using a large area nitrogen plasma apparatus in the conditions of surface temperature: 623 K, RF power: 50 W, nitrogen pressure:10.5 Torr, and reaction period: 30 min. The chemical bonding states and thermal decomposition processes of the nitide film was in-situ analyzed by synchrotron radiation photoemission spectroscopy. XPS spectra of clean Ge surface showed binding energies of Ge3d5/2 and 3/2 levels were 29.2 eV and 29.8 eV, respectively. The Ge surface nitrided by the high density plasma was oxidized by exposure to the air so that both components of nitride and oxide were observed by the SR-XPS before thermal anealing. GeO$$_{2}$$ component was selectively removed by thermal anealing up to 773 K in the UHV condition. After that XPS spectra of pure Ge$$_{3}$$N$$_{4}$$ film could be observed. We concluded chemical shift of the nitrided Ge was 2.2 eV.

Oral presentation

Fabrication and characterization of high quality Al$$_{2}$$O$$_{3}$$/ZrO$$_{2}$$/GeO$$_{2}$$ layered gate dielectrics

Okamoto, Gaku*; Kutsuki, Katsuhiro*; Kagei, Yusuke*; Harries, J.; Yoshigoe, Akitaka; Teraoka, Yuden; Hosoi, Takuji*; Shimura, Takayoshi*; Watanabe, Heiji*

no journal, , 

Structure analyses and electrical characteristic tests have been conducted for a high-k/Ge stuck of Al$$_{2}$$O$$_{3}$$/ZrO$$_{2}$$/GeO$$_{2}$$/Ge structure. A ZrGeO layer and intermediate oxidation number states for Ge have been confirmed in photoemission spectra in addition to a chemically-shifted Ge$$^{4+}$$ component suggesting the growth of GeO$$_{2}$$ interface layer. An Au electrode was capped on this dielectic substrate to make an Au/Al$$_{2}$$O$$_{3}$$/ZrO$$_{2}$$/GeO$$_{2}$$/Ge capacitor. C-V measurements were conducted for the capacitor. Hysteresis was so small of 21 mV and frequency dispersion was also small. Interface state density near a mid gap, estimated by a low temperature conductance method, was 5.3$$times$$10$$^{10}$$ cm$$^{-2}$$eV$$^{-1}$$. As a conclusion, we succeeded to make a high-k/Ge stuck which has excellent interface characteristics.

Oral presentation

SR-XPS analysis of SiO$$_{2}$$/SiC interfaces formed by thermal oxidation of 4H-SiC(000$$bar{1}$$) surfaces

Kirino, Takashi*; Kagei, Yusuke*; Okamoto, Gaku*; Harries, J.; Yoshigoe, Akitaka; Teraoka, Yuden; Mitani, Shuhei*; Nakano, Yuki*; Nakamura, Takashi*; Hosoi, Takuji*; et al.

no journal, , 

In order to study the origin of degradation for interface chracteristics and reliability of SiC(0001)C surfaces, chemical bonding states at SiO$$_{2}$$/SiC interfaces made on (000$$bar{1}$$)$$_{Si}$$ and (000$$bar{1}$$)$$_{C}$$ surfaces have been analyzed by using a synchrotron radiation XPS method. Si2p$$_{3/2}$$ components were extracted from Si2p photoemission peaks. Sub-oxidea components were observed in addition to the SiC substrate and the oxide layer. In the interface of the oxide layer formed on the (000$$bar{1}$$)$$_{C}$$ surface, Si$$^{1+}$$ component was small, higher oxidation number components were larger, and total amount od sub-oxides was larger comparing to that of the (000$$bar{1}$$)$$_{Si}$$ surface. A binding energy for oxide formed on the (000$$bar{1}$$)$$_{C}$$ surface was shifted to 0.22 eV higher side comparing to that of the (000$$bar{1}$$)$$_{Si}$$ surface. It indicates that band off-set of conduction band is small in the SiO$$_{2}$$/SiC interface.

Oral presentation

SR-XPS study on energy band structure of thermally grown SiO$$_{2}$$/4H-SiC interface

Kirino, Takashi*; Kagei, Yusuke*; Okamoto, Gaku*; Harries, J.; Yoshigoe, Akitaka; Teraoka, Yuden; Mitani, Shuhei*; Nakano, Yuki*; Nakamura, Takashi*; Hosoi, Takuji*; et al.

no journal, , 

Device ability of SiC-MOSFET's expected from physical data has not been achieved because channel resistance increases by mobility degradation due to Si0$$_{2}$$/SiC interface defects. Although high channel mobility is obtained in the MOSFET's made on a 4H-SiC(000-1)c face compared to them on a 4H-SiC(0001)Si face, reliability of an oxide film is preferential in the MOSFET's on a 4H-SiC(000-1)c face. Conduction band off-set of SiO$$_{2}$$/SiC interface and energy distribution of the interface level density are known to be different between MOSFET's on a 4H-SiC(000-1)c face and a 4H-SiC(0001)Si face. Physical origins for them are not known yet. In order to make clear the reasons for degradation of interface characteristics and reliability in the MOSFET's made on an SiC(000-1)c face, we evaluated chemical bonding states and energy band structures of SiO$$_{2}$$/SiC interfaces formed on an SiC(0001)Si face and an SiC(000-1)c face using synchrotron radiation photoemission spectroscopy.

Oral presentation

Impact of Ge$$_{3}$$N$$_{4}$$ interface layer on EOT scaling in high-k/Ge gate stacks

Kutsuki, Katsuhiro*; Okamoto, Gaku*; Hideshima, Iori*; Uenishi, Yusuke*; Kirino, Takashi*; Harries, J.; Yoshigoe, Akitaka; Teraoka, Yuden; Hosoi, Takuji*; Shimura, Takayoshi*; et al.

no journal, , 

Direct deposition of ZrO$$_{2}$$ films on Ge substrates and subsequent thermal oxidation results in an equivalent oxide thickness (EOT) of above 2 nm while obtaining good interface quality due to interfacial GeO$$_{2}$$ formation. In this work, we proposed the use of Ge$$_{3}$$N$$_{4}$$ interlayer formed by high-density plasma nitridation for further EOT scaling because of its high resistance to oxidation and superior thermal stability. The structural modification of ZrO$$_{2}$$/Ge$$_{3}$$N$$_{4}$$/Ge after oxidation was characterized by synchrotron-radiation X-ray photoelectron spectroscopy at BL23SU in SPring-8. Ge 3d core-level spectra revealed that the Ge$$_{3}$$N$$_{4}$$ interlayer was slightly oxidized after thermal oxidation at 823 K, but N 1s spectra remained almost unchanged. This indicates that the Ge$$_{3}$$N$$_{4}$$ interlayer is effective in suppressing interfacial oxidation, thus obtaining an EOT of 1.8 nm.

Oral presentation

Determination of SiO$$_{2}$$/4H-SiC conduction band offset by SR-XPS

Kirino, Takashi*; Kagei, Yusuke*; Okamoto, Gaku*; Harries, J.; Yoshigoe, Akitaka; Teraoka, Yuden; Mitani, Shuhei*; Nakano, Yuki*; Nakamura, Takashi*; Hosoi, Takuji*; et al.

no journal, , 

It has been reported that hydrogen incorporation into thermally grown SiO$$_{2}$$/4H-SiC structures not only improves the interface quality, but also degrades the gate oxide reliability depending on SiC surface orientation. In this study, energy band diagrams of thermally grown SiO$$_{2}$$/4H-SiC(0001) and SiO$$_{2}$$/4H-SiC(000-1) structures with and without high-temperature hydrogen annealing were evaluated by synchrotron radiation X-ray photoelectron spectroscopy. The SiO$$_{2}$$ band gap and valence band offset at SiO$$_{2}$$/SiC interface were extracted from O 1s energy loss spectra and valence band spectra, respectively. The obtained energy band diagrams revealed that conduction band offsets at SiO$$_{2}$$/SiC interfaces were decreased after the hydrogen annealing especially for 4H-SiC(000-1) substrates. This is one possible reason for the reliability degradation of 4H-SiC metal-oxide-semiconductor devices by hydrogen incorporation.

Oral presentation

Interface engineering of ZrO$$_{2}$$/Ge gate stacks by post-deposition annealing and Al$$_{2}$$O$$_{3}$$ capping layers

Watanabe, Heiji*; Okamoto, Gaku*; Kutsuki, Katsuhiro*; Harries, J.; Yoshigoe, Akitaka; Teraoka, Yuden; Hosoi, Takuji*; Shimura, Takayoshi*

no journal, , 

We fabricated high-quality high-k/Ge gate stacks by direct deposition of ZrO$$_{2}$$ layers on Ge substrates and subsequent post-deposition annealing. Synchrotron-radiation X-ray photoelectron spectroscopy revealed that thermally oxidizing a ZrO$$_{2}$$/Ge structure at 823 K caused not only ZrO$$_{2}$$ and Ge to intermix but also a pure GeO$$_{2}$$ interlayer to form. By optimizing subsequent oxidation conditions, we obtained a minimum EOT of 1.9 nm, negligible C-V hysteresis, and an interface state density (Dit) of a few 10$$^{11}$$ cm$$^{-2}$$eV$$^{-1}$$ for Au/ZrO$$_{2}$$/Ge capacitors. We also developed Al$$_{2}$$O$$_{3}$$/ZrO$$_{2}$$ stacked gate dielectrics to control interface reaction during the post treatment. The Al$$_{2}$$O$$_{3}$$ capping on the ZrO$$_{2}$$ layer was found to be beneficial for further EOT scaling because it suppressed excess interface reaction. Scaled EOT value down to 1.6 nm and leakage current reduction were achieved.

Oral presentation

In situ synchrotron radiation photoemission study of Ge$$_{3}$$N$$_{4}$$/Ge structures formed by plasma nitridation

Hosoi, Takuji*; Kutsuki, Katsuhiro*; Okamoto, Gaku*; Yoshigoe, Akitaka; Teraoka, Yuden; Shimura, Takayoshi*; Watanabe, Heiji*

no journal, , 

Oral presentation

Off-axis XUV harmonics from relativistic laser - gas jet interaction

Pirozhkov, A. S.; Kando, Masaki; Esirkepov, T. Z.; Pikuz, T.; Faenov, A. Ya.*; Ogura, Koichi; Hayashi, Yukio; Kotaki, Hideyuki; Ragozin, E. N.*; Neely, D.*; et al.

no journal, , 

Oral presentation

Off-axis high-order harmonics from relativistic laser - gas jet interaction

Pirozhkov, A. S.; Kando, Masaki; Esirkepov, T. Z.; Pikuz, T.; Faenov, A. Ya.*; Ogura, Koichi; Hayashi, Yukio; Kotaki, Hideyuki; Ragozin, E. N.*; Neely, D.*; et al.

no journal, , 

Oral presentation

High-order harmonic comb from relativistic electron spikes

Pirozhkov, A. S.; Kando, Masaki; Esirkepov, T. Z.; Pikuz, T.; Faenov, A. Ya.*; Ogura, Koichi; Hayashi, Yukio; Kotaki, Hideyuki; Ragozin, E. N.*; Neely, D.*; et al.

no journal, , 

Oral presentation

On-axis and off-axis high order harmonics generation by relativistic laser in gas jet target

Pirozhkov, A. S.; Kando, Masaki; Esirkepov, T. Z.; Pikuz, T.; Faenov, A. Ya.*; Ogura, Koichi; Hayashi, Yukio; Kotaki, Hideyuki; Ragozin, E. N.*; Neely, D.*; et al.

no journal, , 

Oral presentation

Laser driven ion acceleration experiment by high contrast high intensity laser J-KAREN system

Nishiuchi, Mamiko; Sakaki, Hironao; Sagisaka, Akito; Maeda, Shota; Pirozhkov, A. S.; Pikuz, T.; Faenov, A. Ya.*; Ogura, Koichi; Fukuda, Yuji; Matsukawa, Kenya*; et al.

no journal, , 

no abstracts in English

Oral presentation

Measurement of electron spectrum generated by irradiating thin-Foil target with Ultra-intense Ultra-short pulse laser

Maeda, Shota; Nishiuchi, Mamiko; Sakaki, Hironao; Sagisaka, Akito; Pirozhkov, A. S.; Pikuz, T.; Faenov, A. Ya.*; Ogura, Koichi; Fukuda, Yuji; Matsukawa, Kenya*; et al.

no journal, , 

In JAEA, the high energy ions generated by the interaction between Ultra-intense Ultra-Short pulse laser and thin-foil target is being studied. Irradiating condition must be optimized to generate higher energy ions while suppress the becoming gigantic of laser. It is necessary to know the physical phenomenon in plasma to determine the parameter to optimize from the information on the electron and neutron, X-rays, which are generated simultaneously with ion. In this study, in order to measure electron temperature accurately, an electron spectrometer was developed which have broad range (1-200 MeV). The detector is comprised of permanent magnets and a fluorescent plate, CCD camera. In the presentation, the result of the calibration experiment carried out using 4, 9, 12, 15 MeV quasi-monoenergetic electron beam in HIBMC will be reported. Moreover, response analysis method was inspected using PHITS which is particle transporting Monte Carlo simulation code, and will also report the result.

Oral presentation

High-order harmonics from relativistic electron spikes

Pirozhkov, A. S.; Kando, Masaki; Esirkepov, T. Z.; Pikuz, T.; Faenov, A. Ya.*; Ogura, Koichi; Hayashi, Yukio; Kotaki, Hideyuki; Ragozin, E. N.*; Neely, D.*; et al.

no journal, , 

Oral presentation

Source structure of high-order harmonics from relativistic electron spikes

Pirozhkov, A. S.; Kando, Masaki; Esirkepov, T. Z.; Pikuz, T.; Faenov, A. Ya.*; Ogura, Koichi; Hayashi, Yukio; Kotaki, Hideyuki; Ragozin, E. N.*; Neely, D.*; et al.

no journal, , 

21 (Records 1-20 displayed on this page)