Faculty Profiles - HARADA Shunta

Encapsulated Platinum-Tin Nanoparticles in Silicalite-1 Zeolite for Methylcyclohexane Dehydrogenation

Shi, W; Oda, A; Yamamoto, Y; Harada, S; Ohtsu, T; Sawabe, K; Satsuma, A

ACS SUSTAINABLE CHEMISTRY & ENGINEERING Vol. 13 ( 9 ) page： 3608 - 3621 2025.2

Language：English Publishing type：Research paper (scientific journal) Publisher：ACS Sustainable Chemistry and Engineering

Catalytic dehydrogenation of methylcyclohexane (MCH) is of great importance for hydrogen storage and transportation, but currently used Pt-based nanoparticle catalysts still suffer from insufficient activity, low selectivity, and short-term stability. In this study, we encapsulated Pt-Sn nanoparticles into the silicalite-1 (S-1) matrix and incorporated Sn into the zeolite framework through one-pot hydrothermal synthesis to overcome the above problems. These Pt-Sn bimetallic catalysts were designed for the first time with a high Sn content (2.8-3.9 wt %, Sn/Pt ratio = 6-8) in zeolite mother gel for MCH dehydrogenation. The introduction of Sn significantly improved the activity and durability of Pt@S-1. Especially, the PtSn@S-1 (Sn/Pt ratio = 6) catalyst showed high MCH conversion (>80% for 2 h) and toluene (TOL) selectivity (∼100%) without cofeeding H2. Even after a long-term stability test for 33 h under a weight hourly space velocity (WHSV) of 120,000 mL/g/h, no obvious deactivation was observed, and this catalyst retained a superior H2 evolution rate normalized with a surface Pt content of 1343 mmolH2/gPt/min. The structure-catalytic property relationship of PtSn@S-1 catalysts was systematically studied. Upon Sn introduction, PtOx species on Pt@S-1 were transformed into the PtSn alloy. With the further increase of the Sn/Pt ratio from 1 to 6, Sn was gradually incorporated into the zeolite framework, and this PtSn alloy evolved into a core-shell structure with a Pt core and a Sn shell. Despite the reduced proportion of surface Pt, these unique structures enabled the modification of the Pt local structure, promoted TOL desorption, and enhanced the stability of Pt-Sn nanoparticles, therefore achieving high activity, selectivity, and durability for MCH dehydrogenation.

DOI： 10.1021/acssuschemeng.4c09762

Nondestructive analysis of threading mixed dislocations in SiC using x-ray topography and birefringence Reviewed Open Access

Harada, S; Matsubara, Y; Hayashi, S; Kawase, M; Seo, K; Mizutani, S; Mizutani, Y; Mizutani, S; Murayama, K

AIP ADVANCES Vol. 15 ( 2 ) 2025.2

Authorship：Lead author,　Corresponding author Language：English Publishing type：Research paper (scientific journal) Publisher：AIP Advances

In this study, we combined x-ray topography (XRT) and birefringence imaging to identify the Burgers vectors in threading mixed dislocations (TMDs) in SiC. XRT was utilized to determine the screw components of the Burgers vectors, while the edge components were ascertained using birefringence images obtained by polarized light microscopy. Our analysis, validated against transmission electron microscopy and large-angle convergent beam electron diffraction, provides a novel, nondestructive approach for examining defects in SiC power devices. The results demonstrate a significant advancement in the characterization of TMDs, contributing insights into enhancing the quality and reliability of semiconductor devices. This research paves the way for future developments in SiC technology, highlighting the importance of a detailed dislocation analysis in the field of semiconductor materials.

DOI： 10.1063/5.0238854

Advances in defect characterization techniques using polarized light observation in SiC wafers for power devices Invited Reviewed Open Access

Harada, S; Murayama, K

JOURNAL OF CRYSTAL GROWTH Vol. 650 2025.1

Authorship：Lead author,　Corresponding author Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Crystal Growth

This short review provides an overview of advancements in the characterization of defects in silicon carbide (SiC) wafers using polarized light observation. SiC, which has a wide bandgap and excellent thermal and electrical properties, is widely used in power devices. However, various defects such as threading screw dislocations (TSD), threading edge dislocations (TED), and basal plane dislocations (BPD) can significantly affect device performance and reliability. Polarized light observation offers a nondestructive method for visualizing these defects and analyzing the stress fields induced within the SiC crystal structure. This paper summarizes recent developments in this technique, including the application of analyzer rotation to enhance the contrast in defect visualization. Furthermore, the development of automated systems for rapid wafer evaluation is discussed, highlighting the role of polarized light observation in improving quality control and production efficiency in SiC power device manufacturing.

DOI： 10.1016/j.jcrysgro.2024.127982

Observation of point defect and carrier lifetime distributions in hydrogen or helium ion implanted SiC PiN diodes for suppression of bipolar degradation Reviewed

Kato, M; Li, T; Sakane, H; Harada, S

JAPANESE JOURNAL OF APPLIED PHYSICS Vol. 64 ( 1 ) 2025.1

Polarized Light Observation for Visualization of Crystalline Defects in SiC Wafers for Power Device Applications Invited Reviewed

Harada Shunta, Murayama Kenta

Materia Japan Vol. 63 ( 10 ) page： 687 - 694 2024.10

The effects of polyethylene glycol on the nucleation and growth of DNA-functionalized gold nanoparticles crystals Invited Reviewed

Shoko Kojima, Lidong Zhang, Chandan Kumar, Hayato Sumi, Norobu Ohta, Hiroshi Sekiguchi, Kentaro Tsuzuki, Shunta Harada, Toru Ujihara, Katsuo Tsukamoto, Miho Tagawa

Journal of Crystal Growth Vol. 640 page： 127740 2024.8

Suppression of stacking-fault expansion in 4H-SiC diodes by helium implantation Reviewed Open Access

Li, T; Sakane, H; Harada, S; Kato, M

APPLIED PHYSICS EXPRESS Vol. 17 ( 8 ) 2024.8

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

Bipolar degradation is a critical problem in Silicon carbide devices, caused by the expansion of single Shockley stacking faults (1SSFs) from basal plane dislocations. This paper presents the effects of helium implantation on the suppression of 1SSFs expansion. The fabricated PiN diodes were analyzed using current-voltage characteristics and electroluminescence imaging. The results show that helium implantation can effectively suppress 1SSFs expansion without significantly degrading diode performance. We consider that this suppression is due to the pinning of dislocations by point defects introduced during helium implantation, and the reduction of carrier lifetime may also play a role in suppressing 1SSFs expansion.

DOI： 10.35848/1882-0786/ad6be5

Modulated crystallographic shear structure in titanium-chromium oxides: their structure and phonon-transport properties

スペクトル超解像解析によるX線光電子分光測定時間の短縮 Invited Reviewed

原田俊太

Isotope News Vol. 794 page： 7 - 10 2024.8

Harada, S; Hattori, T; Inden, M; Sugimoto, S; Ito, M; Tagawa, M; Ujihara, T

JOURNAL OF APPLIED CRYSTALLOGRAPHY Vol. 57 ( Pt 4 ) page： 1212 - 1216 2024.8

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

Advancements in phonon engineering have propelled the study of heat conduction within nanostructures, focusing on the wave nature of phonons for thermal conductivity manipulation. This work investigates the annealing-induced structural transformation of titanium-chromium oxide crystals, highlighting a role in modulating thermal conductivity through the regularization of crystallographic shear (CS) plane spacing. Utilizing high-angle annular dark-field scanning transmission electron microscopy and selected-area electron diffraction, a transformation from disordered to ordered arrangements of CS planes was observed through annealing at high temperatures. The thermal conductivity increased following annealing. The variability observed in the spacing of CS planes before annealing implies that phonon Anderson localization might play a role in the changes in thermal conductivity.

DOI： 10.1107/S1600576724006381

Analysis of Macrostep Interaction via Carbon Diffusion Field in SiC Solution Growth Reviewed

Atomic Structure and Thermal Conduction and in Titanium Oxide Natural Superlattices Invited Reviewed

Shunta Harada

Journal of the Heat Transfer Society of Japan Vol. 63 page： 40 - 45 2024.7

Effects of proton implantation into 4H-SiC substrate: Stacking faults in epilayer on the substrate Reviewed Open Access

Masashi Kato, Ohga Watanabe, Shunta Harada, Hitoshi Sakane

Materials Science in Semiconductor Processing Vol. 175 page： 108264 - 108264 2024.6

Automated control algorithm for FZ crystal growth by using Gaussian mixture model and reinforcement learning Invited Reviewed

Harada Shunta, Tosa Yusuke, Omae Ryo, Matsumoto Ryohei, Sumitani Shogo

Journal of the Japanese Association for Crystal Growth Vol. 51 ( 1 ) page： 4 2024.4

Authorship：Lead author,　Corresponding author Language：Japanese Publishing type：Research paper (scientific journal) Publisher：The Japanese Association for Crystal Growth

<p> The automation of manufacturing processes and improvement of productivity are key challenges in the manufacturing industry. In the Floating Zone (FZ) method, a process used for the growth of crystals in the manufacturing of semiconductor wafers, operators adaptively control input parameters based on the state of the crystal growth process. The operational dynamics of crystal growth using the FZ method are complex, making automation a challenging task. This study aims to automate the control of FZ crystal growth using reinforcement learning, employing dynamics predicted by a Gaussian Mixture Model (GMM) based on a limited amount of operational data. The results from studies using an emulator program for FZ crystal growth demonstrated that the constructed control model can achieve ideal crystal shapes more effectively than human operation.</p>

DOI： 10.19009/jjacg.51-1-04

CiNii Research

Yuki Nakanishi, Kentaro Kutsukake, Yifan Dang, Shunta Harada, Miho Tagawa, Toru Ujihara

Journal of Crystal Growth Vol. 631 page： 127609 - 127609 2024.4

Accelerating X-ray photoemission spectroscopy measurements using Bayesian super-resolution Reviewed Open Access

Shunta Harada, Kota Tsujimori, Toyokazu Nomoto, Takahiro Ito

Japanese Journal of Applied Physics Vol. 63 ( 4 ) 2024.4

Authorship：Lead author,　Corresponding author Language：English Publishing type：Research paper (scientific journal)

This study applies Bayesian super-resolution to X-ray photoelectron spectroscopy (XPS), achieving up to a 20-fold reduction in measurement time while preserving data quality. Traditional XPS, crucial for surface analysis, typically requires extensive measurement durations. Our methodology significantly accelerates the process, as demonstrated with glass and Polytetrafluoroethylene samples, where we reduced measurement times by up to 1/20th without compromising spectral accuracy. This approach decreases noise levels and retains spectral integrity, offering a highly efficient solution for XPS. This innovation is particularly valuable in material science, enabling rapid, reliable surface analysis.

DOI： 10.35848/1347-4065/ad3140

Effects of proton implantation for expansion of basal plane dislocations in SiC toward suppression of bipolar degradation: review and perspective Reviewed

Masashi Kato, Shunta Harada, Hitoshi Sakane

Japanese Journal of Applied Physics Vol. 63 ( 2 ) page： 020804 - 020804 2024.2

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

Abstract

Silicon carbide (SiC) is widely used in power semiconductor devices; however, basal plane dislocations (BPDs) degrade device performance, through a mechanism called bipolar degradation. Recently, we proposed that proton implantation could suppress BPD expansion by reducing BPD mobility. We considered three potential mechanisms: the hydrogen presence around BPDs, point defects induced by implantation, and carrier lifetime reduction. In this study, we discuss the mechanisms of proton implantation and its applicability to SiC power device production.

DOI： 10.35848/1347-4065/ad1779

Other Link： https://iopscience.iop.org/article/10.35848/1347-4065/ad1779/pdf

Effect of Solution Components on Solvent Inclusion in SiC Solution Growth Reviewed

Huiqin Zhou, Hitoshi Miura, Yuma Fukami, Yifan Dang, Kentaro Kutsukake, Shunta Harada, Miho Tagawa, Toru Ujihara

Crystal Growth & Design Vol. 24 ( 4 ) page： 1806 - 1817 2024.2

Improved Protein Model in SPICA Force Field Open Access

Yamada, T; Miyazaki, Y; Harada, S; Kumar, A; Vanni, S; Shinoda, W

JOURNAL OF CHEMICAL THEORY AND COMPUTATION Vol. 19 ( 23 ) page： 8967 - 8977 2023.11

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Chemical Theory and Computation

The previous version of the SPICA coarse-grained (CG) force field (FF) protein model focused primarily on membrane proteins and successfully reproduced the dimerization free energies of several transmembrane helices and the stable structures of various membrane protein assemblies. However, that model had limited accuracy when applied to other proteins, such as intrinsically disordered proteins (IDPs) and peripheral proteins, because the dimensions of the IDPs in an aqueous solution were too compact, and protein binding on the lipid membrane surface was overstabilized. To improve the accuracy of the SPICA FF model for the simulation of such systems, in this study, we introduce protein secondary structure-dependent nonbonded interaction parameters to the backbone segments and reoptimize almost all nonbonded parameters for amino acids. The improved FF proposed here successfully reproduces the radii of gyration of various IDPs, the binding sensitivity of several peripheral membrane proteins, and the dimerization free energies of several transmembrane helices. The new model also shows improved agreement with experiments on the free energy of peptide association in water. In addition, an extensive library of nonbonded interactions between proteins and lipids, including various glycerophospholipids, sphingolipids, and cholesterol, allows the study of specific interactions between lipids and peripheral and transmembrane proteins. Hence, the new SPICA FF (version 2) proposed herein is applicable with high accuracy for simulating a wide range of protein systems.

DOI： 10.1021/acs.jctc.3c01016

DNA修飾ナノ粒子の結晶化とX線小角散乱による構造解析

PubMed

田川美穂, 張力東, 小島憧子, 鷲見隼人, 横森真麻, 太田昇, 関口博史, 原田俊太, 宇治原徹

日本結晶学会誌 Vol. 65 ( Supplement ) page： s19 - s19 2023.10

Non-destructive identification of edge-component burgers vector of threading dislocations in SiC wafers by birefringence imaging Reviewed

Shunta Harada, Yasutaka Matsubara, Kenta Murayama

Diamond and Related Materials Vol. 138 2023.10

Authorship：Lead author,　Corresponding author Language：English Publishing type：Research paper (scientific journal)

Non-destructive characterization of crystalline defects in SiC wafers is important for manufacturing high-performance SiC power devices with high productivity. The present study shows that the edge component of the Burgers vector can be identified by birefringence imaging under conditions deviating slightly from the crossed-Nicols condition and by calculation of the in-plane shear stress distribution. It is also found that the combination of birefringence observation and X-ray topography allows the discrimination of the family of threading screw dislocations. The present results will further the understanding of the relationship between defect structure and the properties of SiC power devices.

DOI： 10.1016/j.diamond.2023.110192