Faculty Profiles - MORI Yusuke

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MORI Yusuke

Organization

Institute of Materials and Systems for Sustainability Toyota Advanced Power Electronics Funded Research Division Designated professor

Degree 1

博士（工学）（ 1996.3 大阪大学）

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Papers 35

Solution-mediated phase transition of pharmaceutical compounds: Case studies of acetaminophen and aspirin Reviewed

Mihoko Maruyama, Hiroshi Y. Yoshikawa, Kazufumi Takano, Masashi Yoshimura and Yusuke Mori

Journal of Crystal Growth Vol. 602 page： 126990-1 - 126990-9 2023.1

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Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：Elsevier {BV}

Polymorphism is crucial in organic solid-state chemistry because different polymorphs exhibit different physical
properties. Thus, the control of crystal polymorphism is a long-standing issue. We have been engaged in crystal
polymorph control research, mainly targeting pharmaceutical compounds. Three processes to control the polymorphism must be considered: nucleation, crystal growth, and phase transition. Finding a metastable phase by
nucleation control techniques is the first step. The next crucial step is controlling phase transition and keeping
the metastable phase as long as possible. Understanding the phase transition from metastable to stable phase is
essential, especially to realize the high stability metastable phase. Herein we will show the phase transition
processes of acetaminophen and aspirin as model materials.

DOI： 10.1016/j.jcrysgro.2022.126990
Effects of pulse duration on laser-induced crystallization of urea from 300 to 1200 fs: impact of cavitation bubbles on crystal nucleation Reviewed

Yuka Tsuri, Mihoko Maruyama, Katsuo Tsukamoto, Hiroaki Adachi, Kazufumi Takano, Shigeyoshi Usami, Masayuki Imanishi, Masashi Yoshimura, Hiroshi Y. Yoshikawa and Yusuke Mori

Applied Physics A Vol. 128 ( 9 ) page： 803-1 - 803-7 2022.9

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Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：Springer Science and Business Media LLC

The dependence of pulse duration on crystal nucleation of urea induced by laser ablation of liquid was studied. The focused irradiation with laser pulses with all the duration conditions in this study (from 300 to 1200 fs) could induce the crystallization from the laser focus, which allowed for the systematic evaluation of probability of the laser-induced crystallization.
We also carried out the microsecond-scale fast imaging of laser ablation of urea solutions to investigate the spatiotemporal dynamics of generation, expansion, collapse of cavitation bubbles induced by laser ablation, which can be one of the main triggers for crystal nucleation. As the result, we found that the laser-induced crystallization of urea is governed by the inter play of supersaturation increase by cavitation bubbles and supersaturation decrease by temperature rise. The fndings provide the fundamental insight into the underlying mechanism of the laser-induced crystal nucleation and will also be useful for exploring optimized laser irradiation conditions for more efcient crystallization of organic materials in solutions.

DOI： 10.1007/s00339-022-05909-y
Kyropoulos growth of a 300-g SrB4O7 single crystal using a twin-type stirring blade Reviewed

Yasunori Tanaka, Ryota Murai, Yoshinori Takahashi, Melvin John Fernandez Empizo, Shigeyoshi Usami, Mihoko Maruyama, Masayuki Imanishi, Yusuke Mori and Masashi Yoshimura

Japanese Journal of Applied Physics Vol. 61 ( 7 ) page： 075503-1 - 075503-6 2022.7

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

We report the successful Kyropoulos growth of a large strontium tetraborate (SrB4O7, SBO) single crystal that weighs more than 300 g. In order to
grow the large and transparent crystal, a new twin-type stirring blade was used along with a 150 mm diameter crucible. The use of the stirring blade
results in the production of the world’s largest SBO crystal with dimensions of 100 mm (a) ×30 mm (b) ×32 mm (c), a weight of 328.2 g, and wide
transparency down to 130 nm. These results will then lead to the development of large SBO crystals as optical window materials for high-power
DUV laser processing systems.

DOI： 10.35848/1347-4065/ac6f35

Other Link： https://iopscience.iop.org/article/10.35848/1347-4065/ac6f35/pdf
Suppression of newly generated threading dislocations at the regrowth interface of a GaN crystal by growth rate control in the Na-flux method Reviewed

Hyoga Yamauchi, Ricksen Tandryo, Takumi Yamada, Kosuke Murakami, Shigeyoshi Usami, Masayuki Imanishi, Mihoko Maruyama, Masashi Yoshimura, Yusuke Mori

Japanese Journal of Applied Physics Vol. 61 ( 5 ) page： 055505-1 - 055505-6 2022.5

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Language：English Publishing type：Research paper (scientific journal)

In a previous study, we successfully obtained a large-diameter, low-dislocation-density GaN wafer using the flux-film-coated and the multi-point-seed technique (FFC-MPST). As a production cost-cutting strategy, we are aiming to reuse a part of grown GaN crystals and produce thicker films by the Na-flux regrowth. Recently, however, it was found that threading dislocations (TDs) were generated at the growth interface in homoepitaxial growth of GaN crystals by the Na-flux method. In this study, we found that rapid growth in the regrowth contributes to the formation of inclusions causing the generation of TDs at the regrowth interface. Hence, we succeeded in suppressing the generation of TDs by a low growth rate, realized by a low-pressure condition at an initial growth stage. These findings are valuable for the productivity enhancement of high-quality GaN wafers and help the widespread of GaN-based devices.

DOI： https://doi.org/10.35848/1347-4065/ac5787
Bulk laser-induced damage resistance of SrB4O7 single crystals under 266 nm DUV laser irradiation Reviewed

Yutaka Maegaki, Yasunori Tanaka, Haruki Marui, Atsushi Koizumi, Kota Tanaka, Tomosumi Kamimura, Ryota Murai, Yoshinori Takahashi, Melvin John F. Empizo, Shigeyoshi Usami, Masayuki Imanishi, Mihoko Maruyama, Yusuke Mori, and Masashi Yoshimura

apanese Journal of Applied Physics Vol. 61 ( 5 ) page： 052005-1 - 052005-5 2022.5

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

The bulk laser-induced damage threshold (LIDT) of a strontium tetraborate (SrB4O7, SBO) single crystal has been measured for the first time.
Single-shot and multi-shot tests are carried out using a 266 nm deep ultraviolet (DUV) laser. Under single-shot irradiation, the bulk LIDT of SBO
crystal is 1.5 times higher than that of synthetic silica glass. On the other hand, under multi-shot irradiation, the bulk LIDT of SBO is also higher
than synthetic silica glass regardless of the number of shots. When the number of shots increased from 102 to 104
, SBO crystal’s bulk LIDT has
only decreased by less than 11% compared to 44% of synthetic silica glass. Although the damage mechanism of SBO crystal under multi-shot
irradiation is considered to be due to material modification fatigue, SBO single crystals are found to be excellent optical materials that exhibit bulk
laser-induced damage resistance in the DUV region.

DOI： 10.35848/1347-4065/ac61f5
Comprehensive analysis of current leakage at individual screw and mixed threading dislocations in freestanding GaN substrates Reviewed

Takeaki Hamachi, Tetsuya Tohei, Yusuke Hayashi, Masayuki Imanishi, Shigeyoshi Usami, Yusuke Mori and Akira Sakai

Scientific Reports Vol. 13 ( 1 ) page： 2434-1 - 2423-14 2023.2

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Language：English Publishing type：Research paper (scientific journal) Publisher：Springer Science and Business Media LLC

The electrical characteristics of Schottky contacts on individual threading dislocations (TDs) with a
screw-component in GaN substrates and the structures of these TDs were investigated to assess the
efects of such defects on reverse leakage currents. Micrometer-scale platinum/GaN Schottky contacts
were selectively fabricated on screw- and mixed-TD-related etch pits classifed based on the pit size.
Current–voltage (I–V) data acquired using conductive atomic force microscopy showed that very few of
the screw TDs generated anomalously large reverse leakage currents. An analysis of the temperature
dependence of the I–V characteristics established that the leakage current conduction mechanisms for
the leaky screw TDs difered from those for the other screw and mixed TDs. Specifcally, anomalous
current leakage was generated by Poole–Frenkel emission and trap-assisted tunneling via distinctive
trap states together with Fowler–Nordheim tunneling, with the mechanism changing according to
variations in temperature and applied voltage. The leaky TDs were identifed as Burgers vector b= 1c
closed-core screw TDs having a helical morphology similar to that of other screw TDs generating
small leakage currents. Based on the results, we proposed that the atomic-scale modifcation of the
dislocation core structure related to interactions with point defects via dislocation climbing caused
diferent leakage characteristics of the TDs.

DOI： 10.1038/s41598-023-29458-3
Metastable Crystallization by Drop Impact Reviewed

Akari Nishigaki, Mihoko Maruyama, Shun-ichi Tanaka, Hiroshi Y. Yoshikawa, Masayuki Imanishi, Masashi Yoshimura, Yusuke Mori, Kazufumi Takano

Crystals Vol. 12 ( 8 ) page： 1104-1 - 1104-7 2022.8

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Language：English Publishing type：Research paper (scientific journal) Publisher：MDPI AG

It has been reported that cavitation bubbles (air–liquid interface) by femtosecond laser and
ultrasonic irradiations are effective for metastable phase crystallization in polymorph control. It has
also been noted that cavitation bubbles are generated by mechanical shock when dropping a vial. Here
we describe the crystallization of acetaminophen by drop impact. In the condition where spontaneous
nucleation did not occur, the drop impact produced the metastable form (form II) and trihydrate.
This supports the potency of the air–liquid interface in metastable phase formation. Furthermore,
crystallization by drop impact is a completely new phenomenon, and new developments are expected
in the future.

DOI： 10.3390/cryst12081104
Determination of the electron trap level in Fe-doped GaN by phonon-assisted conduction phenomenon Reviewed

Hiroki Fukuda, Akira Nagakubo, Shigeyoshi Usami, Masashi Ikeda, Masayuki Imanishi, Masashi Yoshimura,Yusuke Mori, Kanta Adachi, and Hirotsugu Ogi

Applied Physics Express Vol. 15 ( 7 ) page： 071003-1 - 071003-5 2022.5

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

We acoustically measured the energy level for thermally activated conduction (TAC) in high-resistivity Fe-doped GaN using the non-contacting
antenna-transmission acoustic-resonance method. The acoustic attenuation takes a maximum at a specific temperature, where the TAC is
accelerated with the help of phonon energy. The Debye-type relaxation is thus observed for acoustic attenuation, and its activation energy (0.54 
0.04 eV) was determined with attenuation measurements at various frequencies and temperatures. This value agrees with the E3 level in GaN,
indicating that thermally associated conduction originates from the E3 trap level. We also measured the five independent elastic constants at high
temperatures.

DOI： 10.35848/1882-0786/ac749c
DUV coherent light emission from ultracompact microcavity wavelength conversion device Reviewed

Tomoaki Nanbu, Takeo Yano, Soshi Umeda, Naoki Yokoyama, Hiroto Honda, Yaunori Tanaka, Yutaka Maegaki, Yusuke Mori, Masashi Yoshimura, Shuhei Kobayashi, Shuhei Ichikawa, Yasufumi Fujiwara, Ryota Ishii, Yoichi Kawakami, Masahiro Uemukai, Tomoyuki Tanikawa, and Ryuji Katayama

Optics Express Vol. 30 ( 11 ) page： 18628 - 18637 2022.5

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Language：English Publishing type：Research paper (scientific journal) Publisher：Optica Publishing Group

A unique design of our ultracompact microcavity wavelength conversion device exploits the simple principle that the wavelength conversion efficiency is proportional to the square of the electric field amplitude of enhanced pump light in the microcavity, and expands the range of suitable device materials to include crystals that do not exhibit birefringence or ferroelectricity. Here, as a first step toward practical applications of all-solid-state ultracompact deep-ultraviolet coherent light sources, we adopted a low-birefringence paraelectric SrB4O7 crystal with great potential for wavelength conversion and high transparency down to 130 nm as our device material, and demonstrated 234 nm deep-ultraviolet coherent light generation, whose wavelength band is expected to be used for on-demand disinfection tools that can irradiate the human body.

DOI： 10.1364/oe.457538
Influence of oxygen-related defects on the electronic structure of GaN Reviewed

Satoshi Ohata, Takahiro Kawamura, Toru Akiyama, Shigeyoshi Usami, Masayuki Imanishi, Masashi Yoshimura, Yusuke Mori, Tomoaki Sumi and Junichi Takino

Japanese Journal of Applied Physics Vol. 61 ( 6 ) page： 061004-1 - 061004-5 2022.5

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Language：English Publishing type：Research paper (scientific journal) Publisher：IOP Publishing Ltd

Perfect GaN is a colorless, transparent crystal. However, because of intentional and unintentional impurities, GaN crystals have colors and lose
some transparency. O impurities are generally considered to be the origin of the coloration. In this paper, electronic structures of GaN, which
include O-related point and complex defects, were analyzed using first-principles calculations to investigate their influence on the optical properties
of GaN. It is found that the defect levels due to native point defects of Ga and N vacancies were compensated by O and H impurities, as well as
divalent (Mg and Zn) and tetravalent (Si, Ge, and Sn) metal impurities.

DOI： 10.35848/1347-4065/ac6645
Identification of Burgers vectors of threading dislocations in free-standing GaN substrates via multiphoton-excitation photoluminescence mapping

Mayuko Tsukakoshi, Tomoyuki Tanikawa, Takumi Yamada, Masayuki Imanishi, Yusuke Mori, Masahiro Uemukai and Ryuji Katayama

Applied Physics Express Vol. 14 ( 5 ) 2021
Activation free energies for formation and dissociation of N–N, C–C, and C–H bonds in a Na–Ga melt

Takahiro Kawamura, Masayuki Imanishi, Masashi Yoshimur, Yusuke Mori and Yoshitada Morikawa

Computational Materials Science Vol. 194 2021
Vacancy-type defects in bulk GaN grown by oxide vapor phase epitaxy probed using positron annihilation

Akira Uedono, Junichi Takino, Tomoaki Sumi, Yoshio Okayama, Masayuki Imanishi, Shoji Ishibashi, Yusuke Mori

Journal of Crystal Growth 2021
Propagation of threading dislocations and effects of Burgers vectors in HVPE-grown GaN bulk crystals on Na-flux-grown GaN substrates

Takeaki Hamachi, Tetsuya Tohei, Yasuaki Hayashi, Masayuki Imanishi, Shigeyoshi Usami, Yusuke Mori, Nobuyuki Ikarashi and Akira Sakai

Journal of Applied Physics Vol. 129 ( 22 ) 2021
Terahertz time‑domain ellipsometry with high precision for the evaluation of GaN crystals with carrier densities up to 1020 cm−3

Verdad C. Agulto, Toshiyuki Iwamoto, Hideaki Kitahara, Kazuhiro Toya, Valynn Katrine Mag‑usara, Masayuki Imanishi, Yusuke Mori, Masashi Yoshimura, Makoto Nakajima

Scientific reports Vol. 11 2021
Local piezoelectric properties in Na-flux GaN bulk single crystals

Akira Ueda, Takeaki Hamachi, Akinori Okazaki, Shotaro Takeuchi, Tetsuya Tohei, Masayuki Imanishi, Mamoru Imade, Yusuke Mori and Akira Sakai

Journal of Applied Physics Vol. 128 ( 12 ) 2020
Growth of GaN single crystals with high transparency by the Li-added Na-flux method

Tatsuhiko Nakajima, Masayuki Imanishi, Takumi Yamada, Kosuke Murakami, Masahi Yoshimura, and Yusuke Mori

Journal of Crystal Growth Vol. 535 2020
Growth of GaN layers using Ga2O vapor synthesized from Ga2O3 and carbon

Akira Kitamoto, Yohei Yamaguchi, Shintaro Tsuno, Keiji Ishibashi, Yoshikazu Gunji, Masayuki Imanish. Mamoru Imade, Masashi Yoshimura, Masahiko Hata, Masashi Isemura, and Yusuke Mori

Journal of Crystal Growth Vol. 535 2020
Fabrication of GaN crystals with low threading dislocation density and low resistivity grown by thin-flux-growth in the Na-flux point seed technique

Kiyoto Endo, Masayuki Imanishi, Hitoshi Kubo, Takumi Yamada, Kosuke Murakami, Masashi Yoshimura, and Yusuke Mori

Japanese Journal of Applied Physics Vol. 59 ( 3 ) 2020
Influence of GaN/sapphire contact area on bowing of GaN wafer grown by the Na-flux method with a sapphire dissolution process

Takumi Yamada, Masayuki Imanishi, Kosuke Murakami, Kosuke Nakamura, Masashi Yoshimura, and Yusuke Mori

Japanese Journal of Applied Physics Vol. 59 ( 2 ) 2020
Temperature dependence of nitrogen dissolution on Na flux growth

Ricksen Tandryo, Kosuke Murakami, Kanako Okumura, Takumi Yamada, Tomoko Kitamura, Masayuki Imanishi, Masashi Yoshimura, and Yusuke Mori

Journal of Crystal Growth Vol. 535 2020
Extreme reduction of on-resistance in vertical GaN p–n diodes by low dislocation density and high carrier concentration GaN wafers fabricated using oxide vapor phase epitaxy method

Junichi Takino, Tomoaki Sumi, Yoshio Okayama, Akira Kitamoto, Masayuki Imanishi, Masashi Yoshimura, Naomi Asai, Hiroshi Ohta, Tomoyoshi Mishima and Yusuke Mori

Applied Physics Express Vol. 13 ( 7 ) 2020
Anomalous dislocation annihilation behavior observed in a GaN crystal grown on point seeds by the Na-flux method

Masayuki Imanishi, Kanako Okumura, Kousuke Nakamura, Tomoko Kitamura, Keisuke Kakinouchi, Kosuke Murakami, Masashi Yoshimura, Yu Fujita, Yoshiyuki Tsusaka, Junji Matsui and Yusuke Mori

Applied Physics Express Vol. 13 ( 8 ) 2020
High-rate OVPE-GaN growth by the suppression of polycrystal formation with additional H2O vapor in a high-temperature condition

Ayumu Shimizu, Shintaro Tsuno, Masahiro Kamiyama, Keiju Ishibashi, Akira Kitamoto, Masayuki Imanishi, Masashi Yoshimura, Masahiko Hata, Masashi Isemura and Yusuke Mori

Applied Physics Express Vol. 13 ( 9 ) 2020
Absolute surface energies of oxygen-adsorbed GaN surfaces

Takahiro Kawamura, Toru Akiyama, Akira Kitamoto, Masayuki Imanishi, Masashi Yoshimura, Yusuke Mori, Yoshitada Morikawa, Yoshihiro Kangawa and Koichi Kakimoto

Journal of Crystal Growth Vol. 549 2020
Fabrication of a 1.5-inch freestanding GaN substrate by selective dissolution of sapphire using Li after the Na-flux growth

Takumi Yamada, Masayuki Imanishi, Kosuke Murakami, Kosuke Nakamura, Masashi Yoshimura, and Yusuke Mori

Journal of Crystal Growth Vol. 532 2019
Promotion of lateral growth of GaN crystals on point seeds by extraction of substrates from melt in the Na-flux method

Masayuki Imanishi, Kosuke Murakami, Takumi Yamada, Keisuke Kakinouchi, Kosuke Nakamura, Tomoko Kitamura, Kanako Okumura, Masashi Yoshimura, and Yusuke Mori

Applied Physics Express Vol. 12 ( 4 ) 2019
Effect of methane additive on GaN growth using the OVPE method

Aakira Kitamoto, Junichi Takino, Tomoaki Sumi, Masahiro Kamiyama, Shintaro Tsuno, Keiji Ishibashi, Yoshikazu Gunji, Masayuki Imanishi, Yoshio Okayama, Masaki Nobuoka, Masashi Isemura, Masashi Yoshimura and Yusuke Mori

Japan Journal of Applied Physics Vol. 58 ( SC ) 2019
Recent progress of Na-flux method for GaN crystal growth

Yusuke Mori, Masayuki Imanishi, Kosuke Murakami, and Masashi Yoshimura

Japanese Journal of Applied Physics Vol. 58 2019
Monitoring of Ga-Na melt electrical resistance and its correlation with crystal growth on the Na Flux method

Ricksen Tandryo, Kosuke Murakami, Tomoko Kitamura, Masayuki. Imanishi, and Yusuke Mori

Applied Physics Express Vol. 12 ( 6 ) 2019
Development of a 2-inch GaN wafer by using the oxide vapor phase epitaxy method

Junichi Takino, Tomoaki Sumi, Yoshio Okayama, Masaki Nobuoka, Akira Kitamoto, Masayuki Imanishi, Masashi Yoshimura, and Yusuke Mori

Japanese Journal of Applied Physics Vol. 58 ( SC ) 2019
Thermal conductivity of GaN single crystals: Influence of impurities incorporated in different growth processes

Robert Rounds, Biplab Sarkar, Tomasz Sochacki, Michal Bockowski, Masayuki Imanishi, Yusuke Mori, Ronny Kirste, Ramón Collazo, and Zlatko Sitar

Journal of Applied Physics Vol. 124 ( 10 ) 2018
Homoepitaxial HVPE growth on GaN wafers manufactured by the Na-flux method

Masayuki Imanishi, Takehiro Yoshida, Tomoko Kitamura, Kosuke Murakami, Mamoru Imade, Masashi Yoshimura, Masastomo Shibata, Yoshiyuki Tsusaka, Junji Matsui, and Yusuke Mori

Crystal Growth & Design 2017
Increase in the growth rate of GaN crystals by using gaseous methane in the Na flux method

Kosuke Murakami, Shogo Ogawa, Masayuki Imanishi, Mamoru Imade, Mihoko Maruyama, Masashi Yoshimura, and Yusuke Mori

Japanese Journal of Applied Physics Vol. 56 ( 5 ) 2017
Enhancement of lateral growth of the GaN crystal with extremely low dislocation density during the Na-flux growth on a point seed

Masatoshi Hayashi, Masayuki Imanishi, Takumi Yamada, Daisuke Matsuo, Kosuke Murakami, Mihoko Maruyama, Mamoru Imade, Masashi Yoshimura, and Yusuke Mori

Journal of Crystal Growth Vol. 468 page： 827 - 830 2017

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MISC 1

光が創造するマテリアルの新価値～先端レーザープロセッシング～レーザーアブレーションによる有機・バイオマテリアルの結晶成長制御

吉川洋史, 丸山美帆子, 中嶋誠, 吉村政志, 森勇介

Vol. 41 ( 484 ) page： 159 - 162 2022.4

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Authorship：Last author Language：Japanese Publishing type：Article, review, commentary, editorial, etc. (scientific journal)

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