Faculty Profiles - OHNO, Noriyasu

Papers - OHNO, Noriyasu

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Nanoporous Helium–Silicon Co-Deposition Thin Film via Plasma-Assisted Process for Lithium-Ion-Battery Anodes Reviewed International journal Open Access

Kajita S., Uchida G., Tanaka H., Tabata K., Yamamoto Y., Ohno N.

Advanced Energy and Sustainability Research Vol. 6 ( 3 ) 2025.3

Language：English Publishing type：Research paper (scientific journal) Publisher：Advanced Energy and Sustainability Research

In this study, silicon (Si) deposition is performed in a high-density (1018 m−3) helium (He) plasma environment, and He–Si co-deposition layers, where He atoms are implanted into the Si thin film, are formed. The He-containing thin film, which has a porosity of ≈0.5, is composed of smaller clusters with the size of 100–200 nm including many pores with different sizes, which is advantageous for lithium-ion-battery (LIB) negative electrode. It is also shown that substrate copper (Cu) atoms are diffused into the deposition layer and Cu doping occurred naturally. The LIB performance of the He–Si co-deposited thin film (>1 μm in thickness) is evaluated. When the substrate temperature is at 523 K during the deposition, the Si layer has amorphous structure, and the LIB discharge capacity remains 1800 mAh g−1 after 100 cycles. In the results, it is shown that the Si–He co-deposition method can be a novel method to fabricate Cu-doped porous amorphous Si thin film for high-performance LIB application.

DOI： 10.1002/aesr.202400300

Open Access

Scopus

Tungsten fuzz growth at low temperatures (<900 K) on a surface with nanocones Reviewed International journal

Shi Q., Kajita S., Ohno N.

Nuclear Materials and Energy Vol. 39 page： 101668 2024.5

Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：Nuclear Materials and Energy

The tungsten (W) fuzzy structure was widely observed in linear plasma devices under the fusion-relevant condition. This type of structure can be used in many application fields benefiting from its larger surface area and high optical absorbance. However, W fuzz can be barely formed when the sample temperature is lower than 900 K. This study decreased the threshold to ∼800 K using W co-deposition on a Si nanocones substrate. It suggests that the conventional threshold temperature is only necessary for He bubble rupture to create a rough surface that induces the uneven trapping of the adatom diffusion.

DOI： 10.1016/j.nme.2024.101668

Scopus

Surface modification of ZrC dispersion-strengthened W under low energy He plasma irradiation Reviewed International coauthorship

Li L., Liu Z., Chen Z., Yin C., Mao S., Wu X., Ohno N., Ye M.

Nuclear Fusion Vol. 64 ( 5 ) page： 56008 2024.5

Language：English Publishing type：Research paper (scientific journal) Publisher：Nuclear Fusion

ZrC dispersion-strengthened W exhibits high strength/ductility, low ductile-to-brittle transition temperature, and excellent thermal shock resistance, making it a promising candidate plasma-facing material for future fusion devices. In this study, surface modification of 0.5 wt.% ZrC dispersion-strengthened W (WZrC) under low energy and high fluence He plasma irradiation at high temperature was presented. Under the energy of 90 eV and fluence ranging from 6 × 1024 He·m−2-2 × 1026 He·m−2 He irradiation at 920 °C, a typical fuzz nanostructure appeared on the W matrix of WZrC. The thickness of fuzz layer is proportional to the square root of He irradiation fluence. The fuzz showed comparable thickness and structural features to pure W, indicating limited effects of the particle’s addition on resistance to high fluence He irradiation at high temperatures. Under continuous He injection, the fuzz would grow extending onto the particle area, making the particle obscured. Besides, the erosion behavior of particles under He plasma irradiation has been investigated, which is thought to be dominated by a sputtering process. Under the He influence of 6 × 1024 He·m−2, only nanopores were observed in the surface region. With fluence increasing to 5 × 1025 He·m−2, the surface became relatively uneven with larger holes. W aggregated in spots and distributed on the surface of the particle, which might be the result of subthreshold sputtering and deposition. When fluence further increased to 2 × 1026 He·m−2, the particles were eroded completely and covered by the extended fuzz, forming cavities. In addition, distinctive layered nanotendrils were observed above the cavities, which were characterized to consist of inner W-riched skeletons and outer Zr-riched layers. It indicates that the layered nanotendrils should be the result of fuzz extension combined with particle sputtering/deposition.

DOI： 10.1088/1741-4326/ad2f4c

Scopus

Nanopatterning of Si surfaces by normal incident He plasma irradiation Reviewed

Liu Z., Li L., Gao Z., Chen Z., Yin C., Mao S., Kajita S., Ohno N., Ye M.

Applied Physics Letters Vol. 124 ( 10 ) 2024.3

Publisher：Applied Physics Letters

This study reports on the formation of self-organized silicon (Si) nanostructures by 75 eV helium (He) plasma irradiation at normal incidence without the presence of impurities. In contrast to the featureless surface after normal incidence argon (Ar) ion beam irradiation without the co-deposition of impurities, the Si surface exhibits the development of faceted nanostructures under 75 eV He plasma irradiation. The faceted structures are interspersed with valleys that extend in two orthogonal directions, imparting a mountain-like morphology to the surface. Our investigation verifies that the He bubbles align themselves along the direction perpendicular to the surface underneath these valleys. Furthermore, the presence of He bubbles induces distortion in the surface layer and leads to the formation of an amorphous Si layer. The underlying mechanism driving this surface evolution could be attributed to the instability induced by the presence of He bubbles.

DOI： 10.1063/5.0186756

Scopus

Cone array formation on Si surfaces by low-energy He plasma irradiation with magnetron sputtering pre-deposited Ta Reviewed International coauthorship

Liu Z., Li L., Gao Z., Chen Z., Yin C., Mao S., Kajita S., Ohno N., Ye M.

Journal of Applied Physics Vol. 135 ( 9 ) page： 93302 2024.3

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Applied Physics

Low-energy ion beam irradiation, combined with the introduction of impurities, presents a promising approach for nanopatterning silicon (Si) surfaces. In this research, we investigate the surface evolution of Si (100) surfaces irradiated by 75 eV helium (He) plasma, in the presence of tantalum (Ta), traditionally regarded as an impurity incapable of initiating pattern formation, as evidenced in prior studies. The Ta impurities are pre-deposited onto the Si surfaces using the magnetron sputtering method, which offers a more controlled and quantifiable approach compared with the conventional co-deposition route. After irradiation at 800 K, dense cone arrays are produced on the Si surface. The growth of the cones is explored for fluence spanning (1-10) × 1025 m−2. The cross-sectional scanning electron microscope images indicate that the cone lengths and base width are well characterized by t1/2 dependence. The kinetics of the cone growth follow Fick’s law, characterized by an effective diffusive mechanism with the coefficients of diffusion: D = 6.49 ± 0.83 × 10−16 m−2 s−1. Transmission electron microscope observations reveal that the cone has distinct inner and outer parts with different microstructures and a clear interface. The growth mechanism of these cones is elucidated as a composite process involving preferential sputtering, the destabilizing influence of He bubbles, and the migration of adatoms.

DOI： 10.1063/5.0187265

Scopus

Plasma-Driven Sciences: Exploring Complex Interactions at Plasma Boundaries Reviewed International journal

Ishikawa K., Koga K., Ohno N.

Plasma Vol. 7 ( 1 ) page： 160 - 177 2024.3

Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：Plasma

Plasma-driven science is defined as the artificial control of physical plasma-driven phenomena based on complex interactions between nonequilibrium open systems. Recently, peculiar phenomena related to physical plasma have been discovered in plasma boundary regions, either naturally or artificially. Because laboratory plasma can be produced under nominal conditions around atmospheric pressure and room temperature, phenomena related to the interaction of plasma with liquid solutions and living organisms at the plasma boundaries are emerging. Currently, the relationships between these complex interactions should be solved using science-based data-driven approaches; these approaches require a reliable and comprehensive database of dynamic changes in the chemical networks of elementary reactions. Consequently, the elucidation of the mechanisms governing plasma-driven phenomena and the discovery of the latent actions behind these plasma-driven phenomena will be realized through plasma-driven science.

DOI： 10.3390/plasma7010011

Scopus

Thermal Conductivity Measurement of Fuzzy W Using a Thermoreflectance Method Reviewed

Kajita S., Yagi T., Ohno N.

IEEE Transactions on Plasma Science Vol. Early Access page： 1 - 6 2024.1

Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：IEEE Transactions on Plasma Science

Fuzzy nanostructured tungsten (W) is formed by helium (He) plasma irradiation. In fusion devices, the thermophysical properties are important to consider the response to pulsed heat load from the plasma. In this work, the thermal conductivity of the W fuzz is measured using a pulsed light heating thermoreflectance method. A detailed model was developed to explain the entire temporal evolution of the thermoreflectance signal. It was found that the thermal conductivity of the nanostructured layer was deduced to be in the range of 0.18%–0.21% of the pure (ideal) W and lower than the previously reported highly porous metallic materials. In addition to the porosity, the specific nonuniform nanofiber structure is likely to contribute to the low effective thermal conductivity.

DOI： 10.1109/TPS.2023.3348465

Scopus

Thermal response of nano-tendril bundles to steady heat load Reviewed International coauthorship

Xue Qi, Tanaka Hirohiko, Zhang Rongshi, Kajita Shin, Hori Kenta, Shi Quan, Kuwabara Tatsuya, Ohno Noriyasu

JAPANESE JOURNAL OF APPLIED PHYSICS Vol. 62 ( SN ) 2023.11

Transition from MAR to EIR of deuterium plasma detachment in NAGDIS-II Reviewed International coauthorship

Shi J., Kaizawa H., Tanaka H., Kajita S., Ohno N., Ding H.

Physica Scripta Vol. 98 ( 11 ) page： 115605 2023.10

Language：English Publishing type：Research paper (scientific journal) Publisher：Physica Scripta

Volumetric plasma recombination in a detached deuterium (D) plasma was experimentally studied in the linear plasma device NAGDIS-II. The radial distributions of the electron temperature (Te) and the electron density (ne) were measured by upstream and downstream laser Thomson scattering (LTS) systems and D-atom excited states of the Balmer series (n = 3-7) were measured by optical emission spectroscopy (OES). The results indicated that the electron static pressure, particle flux and heat flux present a two-step reduction with an increasing neutral pressure, suggesting that molecule activated recombination (MAR) and electron-ion recombination (EIR) were activated, respectively. The difference in the distributions of the atomic state population densities was observed to be a feature of the transition from the MAR-dominant phase to the EIR-dominant phase. The transition between the two phases had a distinct boundary at Te ∼0.7 eV, which was considered a transition point between the phases. The ratios of the atomic state population densities showed different features in the two phases, and are expected to be useful in characterizing the phase and degree of plasma detachment.

DOI： 10.1088/1402-4896/acfeb4

Scopus

Application of machine learning for optical emission spectroscopy data in NAGDIS-II Reviewed

Kajita S., Sakakibara T., Kaizawa H., Natsume H., Tanaka H., Fujii K., Ohno N.

Fusion Engineering and Design Vol. 196 page： 114012 2023.9

Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：Fusion Engineering and Design

In this study, we applied machine learning to optical emission spectroscopy (OES) data and device parameters from the linear plasma device NAGDIS-II to explore the potential application of machine learning for predicting electron density, ne, and temperature, Te. The covered ranges of ne and Te, which were measured by an electrostatic probe, are 3.6 × 1017–2.4×1019 m−3 and 0.3–7.1eV, respectively. A three hidden layer neural network (NN) is introduced to model the relationship between ne/Te and the combination of line intensities, radial position, and device parameters. It is shown that the errors in ne and Te become 18.0 and 18.8%, respectively, which were almost the same level for the electrostatic probe, using all available data. Lasso regression and greedy algorithm are used to select the necessary line emissions. It is shown that four or five line intensities are sufficient to obtain almost the same quality as the one with all the other lines.

DOI： 10.1016/j.fusengdes.2023.114012

Scopus

Fabrication of tungsten-based optical diffuser using fiberform nanostructure via efficient plasma route Reviewed International coauthorship

Feng Shuangyuan, Natsume Hiroki, Kajita Shin, Li Enhao, Yasuhara Ryo, Tokitani Masayuki, Tanaka Hirohiko, Ohno Noriyasu

OPTICS EXPRESS Vol. 31 ( 16 ) page： 25438 - 25445 2023.7

Field emission properties of nano-tendril bundles formed via helium plasma exposure with various additional impurity gases Reviewed International coauthorship

Zhang Rongshi, Kajita Shin, Hwangbo Dogyun, Tanaka Hirohiko, Feng Shuangyuan, Ohno Noriyasu

MATERIALS RESEARCH EXPRESS Vol. 10 ( 5 ) page： 054002 2023.5

Growth origin of large-scale fiberform nanostructures in He-W co-deposition environment Reviewed

Hori K, Kajita S, Zhang R, Tanaka H, Ohno N

Scientific reports Vol. 13 ( 1 ) page： 5450 2023.4

Rapid growth of nanostructure on tungsten thin film by exposure to helium plasma Reviewed

Feng Shuangyuan, Kajita Shin, Tokitani Masayuki, Nagata Daisuke, Ohno Noriyasu

PLASMA SCIENCE & TECHNOLOGY Vol. 25 ( 4 ) page： 042001 2023.4

Erratum: Morphologies of co-depositing W layer formed during He plasma irradiation (International Atomic Energy Agency (2018) 58 (106002) DOI: 10.1088/1741-4326/aad24e) Reviewed

Kajita S., Kawaguchi S., Yoshida N., Ohno N., Tanaka H.

Nuclear Fusion Vol. 63 ( 4 ) 2023.4

Correlation of the Orthogonal Basis of the Core Plasma Distribution to the Divertor Footprint Distribution in LHD

TANAKA Hirohiko, MASUZAKI Suguru, KAWAMURA Gakushi, HAYASHI Yuki, KOBAYASHI Masahiro, SUZUKI Yasuhiro, MUKAI Kiyofumi, KAJITA Shin, OHNO Noriyasu

Plasma and Fusion Research Vol. 18 ( 0 ) page： 2402021 - 2402021 2023.3

Language：English Publishing type：Research paper (scientific journal) Publisher：The Japan Society of Plasma Science and Nuclear Fusion Research

<p>We have applied the multivariable analysis technique called the proper orthogonal decomposition (POD) to both the divertor particle flux distribution and the electron pressure distribution in the core region of LHD. The cross-correlation analysis indicates that 3rd, 4th, and 5th POD modes of the electron pressure distribution are highly correlated with the divertor footprint index which is a measure of where the peak position of the particle flux distribution is located on the inner divertor plate. Both the 3rd and 4th modes seem to correspond to the shift of the electron pressure peak position from the magnetic-axis radius. In contrast, 5th mode has a strong influence on the peripheral gradient of the electron pressure distribution. Their relationships with the divertor footprint could be explained by the finite βand the Pfirsch-Schlüter current effects.</p>

DOI： 10.1585/pfr.18.2402021

Web of Science

Scopus

CiNii Research

Study of the intermittent plasma structure around the divertor simulation experimental module in GAMMA 10/PDX Reviewed

Tanaka H., Ezumi N., Sugiyama T., Gamo H., Shigematsu N., Yoshikawa M., Kohagura J., Hirata M., Togo S., Ohno N., Sakamoto M.

PHYSICS OF PLASMAS Vol. 30 ( 3 ) page： 32501 2023.3

Structural Correlation of Random Lasing Performance in Plasma-Induced Surface-Modified Gallium Nitride Reviewed

Shi Q., Fujiwara H., Kajita S., Yasuhara R., Tanaka H., Ohno N., Uehara H.

ACS Applied Optical Materials Vol. 1 ( 1 ) page： 412 - 420 2023.1

Publisher：ACS Applied Optical Materials

The surface of GaN has been modified by a simple method that irradiates the substrate with Ar plasma and impurity codeposition, which is termed CoDE (Co-Deposition Etching). Unique structures were formed by the assistance of a small amount of Mo deposition without degradation of the crystal structure. The size of protrusions on the structure is influenced by the amount of deposited Mo particles. The mechanism for the structure formation is discussed based on transmission electron microscopy (TEM) observations and energy dispersive X-ray spectroscopy (EDS) measurements. Based on the GaN surface roughness, we have demonstrated random laser action in the UV region under photoexcitation. The lowest threshold (0.06 J/cm2) for random lasing was observed where the size of the structure is larger than 0.05 μm2, which was formed under conditions with the least amount of deposition. The correlation between the submicro/nanosize structures generated by plasma irradiation and lasing was evaluated in detail. The critical parameter to optimize the random lasing was determined to be the size of structures that can be modified by the Mo deposition rate. The results confirmed that the emission properties can be controlled by the processing conditions. This random laser fabrication technique is expected to be widely applicable to various direct-bandgap compound semiconductors.

DOI： 10.1021/acsaom.2c00085

Scopus

Motion analysis of arc spots on tungsten fuzz by means of self-avoiding random walk model Reviewed

Hwangbo Dogyun, Nishijima Daisuke, Kajita Shin, Ohno Noriyasu

JAPANESE JOURNAL OF APPLIED PHYSICS Vol. 62 ( SA ) page： SA1007 2023.1

Field emission current from protrusion structures formed by helium plasma with various impurity gases Reviewed

Zhang R., Kajita S., Tanaka H., Hwangbo D., Ohno N.

Proceedings - International Symposium on Discharges and Electrical Insulation in Vacuum, ISDEIV Vol. 2023-June page： 529 - 532 2023

Publisher：Proceedings - International Symposium on Discharges and Electrical Insulation in Vacuum, ISDEIV

Rod-like protrusion structures were formed on tungsten by helium plasma exposure with various impurity gases seeded as nitrogen (N2) and argon (Ar). Surface morphology observations and field emission current measurements were done for two samples. Cross-section observation shows that the inside of the protrusions was solid but not porous like conventional fuzz. Therefore, a new formation mechanism which is different from fuzz can be considered. The field emission current from N2-seeded case was slightly higher than that from fuzz, but much lower than that from NTBs, while the field emission current from Ar-seeded case was similar to that from NTBs. The difference in field emission current could be due to the different morphology of the tips between two samples.

DOI： 10.23919/ISDEIV55268.2023.10200357

Scopus

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Papers - OHNO, Noriyasu