研究者詳細 - 徳永　智春

論文 - 徳永　智春

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Local Crystallization of Amorphous Aluminum Oxide Thin Film Using Electron Beam Irradiation by SEM

Tanahashi S., Okawara S., Tokunaga T., Yamamoto T.

Materials Transactions 64 巻 ( 1 ) 頁： 184 - 190 2023年1月

掲載種別：研究論文（学術雑誌）出版者・発行元：Materials Transactions

Amorphous thin film thinned for transmission electron microscopy observation is reported to crystallize by electron beam (EB) irradiation of TEM. If thin film deposited on substrates can be crystallized by EB irradiation of scanning electron microscopy (SEM), new nanoscale devices can be fabricated such as electronic nanoscale circuits in amorphous thin films. Therefore, an amorphous AlOx (am-AlOx) thin film is deposited onto a Si substrate by atomic layer deposition (ALD) and point and area scan irradiation of EBs were performed by SEM. Then, structure and elemental analyses are carried out by TEM. Only the point EB irradiated area crystallized from the surface to the interface between am-AlOx and the Si substrate, and £-Al2O3 appeared. Moreover, the oxygen content of the not irradiated area close to the irradiated area was lower than that of the not irradiated area far from the irradiated area. These results show that the EB irradiated area was positively charged by the emission of secondary and Auger electrons under point irradiation conditions, and that oxygen was supplied by attracting its negative charge to the EB irradiated area. Also, the electrostatic repulsion between positively charged atoms and the structure relaxation due to electron excitation were additional driving forces for the crystallization.

DOI： 10.2320/matertrans.mt-n2022004

Apparent Sintering Activation Energy Estimated by Master Sintering Curves for 8 mol% Y<inf>2</inf>O<inf>3</inf> Doped ZrO<inf>2</inf> Polycrystals during Shrinkage-Rate Controlled Flash Sintering

Koike M., Kodaira A., Tokunaga T., Yamamoto T.

Materials Transactions 64 巻 ( 10 ) 頁： 2315 - 2320 2023年

掲載種別：研究論文（学術雑誌）出版者・発行元：Materials Transactions

The apparent activation energy of sintering for 8-mol%-Y2O3-doped ZrO2 during shrinkage-rate-controlled flash sintering was determined using a master sintering curve. The activation energy during SCF sintering was found to decrease from approximately 700 to 430 kJ/mol with density. The activation energy in a high-density region is approximately similar value of lattice diffusion, 460 kJ/mol. The relative density range over which the decrease in activation energy occurred during SCF sintering was smaller than during thermal sintering and further moved to a lower temperature range. The increase in shrinkage rate at lower temperatures that occurs during SCF sintering could be considered to be related to this decrease in activation energy.

DOI： 10.2320/matertrans.MT-T2023002

Apparent Sintering Activation Energy Estimated by Master Sintering Curves for 8mol% Y2O3 Doped ZrO2 Polycrystals during Shrinkage-Rate Controlled Flash Sintering

Koike, M; Kodaira, A; Tokunaga, T; Yamamoto, T

MATERIALS TRANSACTIONS 64 巻 ( 9 ) 頁： 2315 - 2320 2023年

Variation of photoluminescence intensity depending on the timing of electric field application during isothermal flash sintering for 3mol% Y<sub>2</sub>O<sub>3</sub>-ZrO<sub>2</sub> polycrystal 査読有り

Itoh, A; Tokunaga, T; Kodaira, A; Yoshida, H; Yamamoto, T

CERAMICS INTERNATIONAL 48 巻 ( 19 ) 頁： 28712 - 28717 2022年10月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Ceramics International

The shrinkage process and the change in photoluminescence (PL) intensity during isothermal flash sintering were investigated for 3 mol% Y2O3–ZrO2 (3YSZ) polycrystals doped with 300 ppm Bi2O3 as a PL impurity centre. The PL intensity of 3YSZ is enhanced by isothermal flash sintering. However, the enhancement of the PL intensity was revealed to become smaller when flash-treatment was applied for thermally pre-sintered 3YSZ polycrystal. To maximize the efficiency of electric field on the enhancement of the PL intensity, the electric field needs to be applied throughout the sintering from the initial stage to the final densification. The necessity for continuing to apply the electric field until the densification is completed is due to the fact that the recovery of oxygen vacancies, the origin of the F+ band, must be suppressed.

DOI： 10.1016/j.ceramint.2022.06.185

Effect of He Buffer Gas on Pulsed Nd:YAG Laser Deposition of Eu<i><sub>x</sub></i>Y<sub>2-<i>x</i></sub>O<sub>3</sub> Phosphor Thin Films 査読有り

Suzuki, S; Dazai, T; Kawashima, K; Tokunaga, T; Yamamoto, T; Takahashi, R

ACS APPLIED ELECTRONIC MATERIALS 4 巻 ( 9 ) 頁： 4419 - 4426 2022年9月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ACS Applied Electronic Materials

We investigated the feasibility of using He buffer gas to moderate the kinetic energy of pulsed laser deposition (PLD) plumes during the growth of EuxY2-xO3phosphor films. The PLD growth of Y2O3films using a Nd yttrium aluminum garnet (Nd:YAG) laser results in expanded lattice parameters compared to those of the bulk crystals, indicating the presence of crystal defects in the Y2O3films. Ablation plumes with a high kinetic energy are generated by the Nd:YAG laser that operates at high energy densities, leading to defect formation. To moderate the kinetic energy without reducing the film growth rate, He buffer gas was used for the Nd:YAG-PLD growth of Y2O3films, resulting in the suppression of crystal defect generation. This process was demonstrated to improve the phosphor properties of EuxY2-xO3thin films grown via combinatorial PLD as the He buffer gas-induced reduction in crystal defect density enhances the phosphor properties of the EuxY2-xO3films. Using He buffer gas to moderate the kinetic energy of PLD plumes is expected to be useful in reducing the crystal defect density and improving the film characteristics.

DOI： 10.1021/acsaelm.2c00691

A liquid metal catalyst for the conversion of ethanol into graphitic carbon layers under an ultrasonic cavitation field

Kawasaki, H; Otsuki, T; Sugino, F; Yamamoto, K; Tokunaga, T; Tokura, R; Yonezawa, T

CHEMICAL COMMUNICATIONS 58 巻 ( 56 ) 頁： 7741 - 7744 2022年7月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Chemical Communications

Eutectic gallium indium (EGaIn) has drawn considerable research interest in potential liquid catalysis. Herein, we report that EGaIn liquid metal acts as a catalyst for the growth of a graphitic carbon layer from ethanol under ultrasonication. High-speed imaging demonstrated the formation of ultrasonic cavitation bubbles at the liquid metal/ethanol interface, which facilitated the pyrolysis of ethanol into graphitic carbon on the liquid metal surface.

DOI： 10.1039/d2cc02510h

Effect of electron beam irradiation in gas atmosphere during ETEM 査読有り

Tokunaga, T; Kawakami, T; Higuchi, K; Yamamoto, Y; Yamamoto, T

MICRON 158 巻頁： 103289 - 103289 2022年7月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Micron

Transmission electron microscopy (TEM) is used to observe the atomic structures of materials. Environmental TEM (ETEM) is a method wherein a gas can be evaluated and it has been used to observe the dynamic reaction between materials and gases at the atomic level. An electron beam (EB), which has a sufficiently high energy (exceeding a few tens of kilovolts), can be used to ionize gas molecules. Subsequently, the ionized molecules might react with the materials during ETEM. Therefore, the current generated by the ions and electrons were measured to verify the presence of ions generated due to the ionization of the N2 gas atmosphere during EB irradiation in ETEM. The electron energy loss spectra (EELS) were acquired from the N2 gas atmosphere to estimate the types of ions generated. The results demonstrated that ions and electrons were generated in the N2 atmosphere during ETEM and EB irradiation. Moreover, the EELS analysis indicated that the generated ion was N2+. The material observation conducted using gas ETEM can detect the reaction between gases, ions, and materials.

DOI： 10.1016/j.micron.2022.103289

The role of surface oxides and stabilising carboxylic acids of copper nanoparticles during low-temperature sintering

Tokura, R; Tsukamoto, H; Tokunaga, T; Nguyen, MT; Yonezawa, T

MATERIALS ADVANCES 3 巻 ( 12 ) 頁： 4802 - 4812 2022年6月

掲載種別：研究論文（学術雑誌）出版者・発行元：Materials Advances

This article provides a detailed discussion of 1-hexanoic-acid-stabilised copper nanoparticles with an average diameter of ∼80 nm prepared from cupric oxide micro-powders for low-temperature sintering applications. The obtained fine particles were dispersed in dipropylene glycol using a bead mill to obtain a stable paste containing 50 wt% copper. Sintering experiments at temperatures in the range of 120-250 °C were performed under a nitrogen or 3%H2-N2 gas flow. The lowest resistivity, approximately three times that of bulk copper, was obtained at 250 °C. These particles exhibited good conductivity upon sintering under nitrogen only. 1-Hexanoic acid contributed to the acceleration of sintering by removing the Cu64O oxide layer of the particles and activating the surface. The dispersed copper paste and the copper layer after sintering were observed using SEM.

DOI： 10.1039/d1ma01242h

Excess oxygen-vacancy formed by FAST regime of direct-current electric field during flash sintering for 3 mol%-10 mol% Y<sub>2</sub>O<sub>3</sub>-doped ZrO<sub>2</sub> 査読有り

Morisaki, N; Tokunaga, T; Kobayashi, K; Kodaira, A; Yamamoto, T

CERAMICS INTERNATIONAL 48 巻 ( 9 ) 頁： 12091 - 12097 2022年5月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Ceramics International

The amount of excess oxygen vacancies that are generated during FAST regime of direct-current flash sintering was estimated semi-quantitatively for 3 mol%–10 mol% Y2O3-doped ZrO2 (3–10YSZ) using the temperature dependence of the electrical conductivity. For the estimation, the electrical conductivity in the temperature range, where shrinkages are below a few percent, was used to avoid the effect of large microstructural changes on the electric conductivity. For all Y2O3 contents except 3YSZ, the amount of excess oxygen vacancies increased above a compact temperature of approximately 840 °C, which depended on Y2O3 content, and was highest in 8YSZ. Approximately 0.13% excess oxygen vacancy was generated by direct-current flashing in 8YSZ in the present electric field condition. In contrast, the increase in the excess oxygen vacancies is negligible in 3YSZ. The dependence of the amount of excess oxygen vacancies on the Y2O3 content was related possibly to the dependence of the electrode overvoltage on the Y2O3 content.

DOI： 10.1016/j.ceramint.2022.01.069

Anelasticityinduced by AC flash processing of cubic zirconia 査読有り

Masuda, H; Morita, K; Tokunaga, T; Yamamoto, T; Yoshida, H

ACTA MATERIALIA 227 巻頁： 117704 - 117704 2022年4月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Acta Materialia

The defect physics is important for understanding the athermal effect of electric fields and/or currents on the enhanced ionic diffusion during flash sintering of ceramics. In this study, conventionally sintered 8 mol% yttria-stabilized zirconia with a fluorite cubic structure was processed by AC flash and subsequently quenched to partially freeze the flash-induced defect structures. The dynamic and quasi-static mechanical properties of flashed and non-flashed samples were evaluated by a sound velocity measurement and a nanoindentation technique to characterize the mechanical responses attributed to the flash-induced defects. A negligible change was confirmed in the dynamic elastic constants even after flash, while the quasi-static elastic properties of the flashed sample exhibited a considerable rate dependence (i.e., the slower the loading rate, the lower the measured contact modulus). The contact modulus of the flashed sample tested at the slowest loading rate in this study was reduced to approximately 72% of the non-flashed one, where the contact modulus was rate-independent. The time-dependent mechanical behavior was also confirmed during nanoindentation creep. Such rate- and time-dependent mechanical properties are characterized as anelasticity (i.e., viscoelasticity or pseudoelasticity in other terms), which can be attributed to stress-induced and thermally activated recoverable motions of point defects. The flash process of cubic zirconia possibly induced point defects associated with short-range structural change, which could be the origin of anelasticity.

DOI： 10.1016/j.actamat.2022.117704

Anisotropic Growth of Copper Nanorods Mediated by Cl<SUP>-</SUP> Ions 査読有り国際共著

Saw, MJ; Nguyen, MT; Kunisada, Y; Tokunaga, T; Yonezawa, T

ACS OMEGA 7 巻 ( 8 ) 頁： 7414 - 7420 2022年3月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ACS Omega

Anisotropic growth to form Cu particles of rod and wire shapes has been obtained typically in a complex system that involves both organic capping agents and Cl- ions. However, the sole effect of Cl- ions on the formation of Cu wires has yet to be fully understood, especially in an organic system. This present work determines the effect of Cl- ions on the morphologies of Cu particles in an organic phase without any capping agents. The results revealed that anisotropic Cu rods could be grown with the sole presence of Cl- ions. The rods have the (011) facets as the long axis, the (111) facets as the tip, and the (100) facets as the side surface. By increasing the Cl- ion concentration, more Cu atoms contributed to the formation of Cu rods and the kinetic growth of the length and the diameter of the rods varied. This suggests that Cl- ions have preferential adsorption on the (100) Cu surfaces to promote the anisotropic growth of Cu. Meanwhile, the adsorption of Cl- to the (111) and (100) surfaces at high Cl- concentrations regulates the relative growth of the particle length and diameter.

DOI： 10.1021/acsomega.2c00359

Direct determination of a topmost atomic layer of (100) surfaces on (La<sub>0.3</sub>Sr<sub>0.7</sub>)(Al<sub>0.65</sub>Ta<sub>0.35</sub>)O<sub>3</sub> single crystals annealed in air by high-resolution scanning transmission electron microscopy 査読有り

Tokuda, Y; Irimoto, T; Nishikawa, N; Katsuyama, Y; Kobayashi, S; Tokunaga, T; Yamamoto, T

SURFACE AND INTERFACE ANALYSIS 54 巻 ( 3 ) 頁： 212 - 217 2022年3月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Surface and Interface Analysis

Herein, we investigated the surface of an (La0.3Sr0.7)(Al0.65Ta0.35)O3 (LSAT) single crystal via scanning transmission electron microscopy (STEM) after annealing in air. We found amorphous mounds and atomically flat surfaces formed on the surface of the (100) LSAT single crystal subsequent to heat treatment. These surface mounds mainly constituted SrO, including ~50 at.% Al. The atomically flat surface showed a B-site termination determined by the direct surface observation at the atomic scale through HAADF-STEM. The atomic arrangements on the surface were accommodated by surface-mound formation and La evaporation. Consequently, the ordered structure disappeared because of the increase in the Ta content at the terminated B-site layer.

DOI： 10.1002/sia.7043

その他リンク： https://onlinelibrary.wiley.com/doi/full-xml/10.1002/sia.7043

Alginate-Stabilized Gold Nanoparticles Prepared Using the Microwave-Induced Plasma-in-Liquid Process with Long-Term Storage Stability for Potential Biomedical Applications 査読有り

Liu, HR; Ikeda, K; Nguyen, MT; Sato, S; Matsuda, N; Tsukamoto, H; Tokunaga, T; Yonezawa, T

ACS OMEGA 7 巻 ( 7 ) 頁： 6238 - 6247 2022年2月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ACS Omega

A one-step preparation of alginate-stabilized gold nanoparticles (Au NPs) using the microwave-induced plasma-in-liquid process (MWPLP) was reported. Effects of alginate with various concentrations on the preparation and properties of the synthesized Au NPs, including reaction rate, morphology, size, and optical absorption property, were studied. The introduction of alginate (1) accelerated the reaction rate, (2) prevented aggregation and precipitation due to long time discharge in MWPLP, and (3) provided long-term colloidal stability. An abnormal size change (from large to small) of Au NPs during particle growth, which was opposite to the typical change in bottom-up chemical reduction, was observed and a possible mechanism was proposed based on the dynamical and thermodynamical instability of particles during growth. The strategy of drying and redispersion of Au NPs in alginate solution was also studied. The drying and redispersion process had an imperceptible effect on the Au NPs. As a consequence, this strategy might be an effective technique for the long-term storage of Au NPs and other metal NPs. The alginate-stabilized Au NPs without the addition of toxic reducing or stabilizing agents can be appropriate to biomedical applications.

DOI： 10.1021/acsomega.1c06769

Nanoporous ultra-high-entropy alloys containing fourteen elements for water splitting electrocatalysis

Cai, ZX; Goou, H; Ito, Y; Tokunaga, T; Miyauchi, M; Abe, H; Fujita, T

CHEMICAL SCIENCE 12 巻 ( 34 ) 頁： 11306 - 11315 2021年9月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Chemical Science

High-entropy alloys (HEAs) are near-equimolar alloys comprising five or more elements. In recent years, catalysis using HEAs has attracted considerable attention across various fields. Herein, we demonstrate the facile synthesis of nanoporous ultra-high-entropy alloys (np-UHEAs) with hierarchical porosityviadealloying. These np-UHEAs contain up to 14 elements, namely, Al, Ag, Au, Co, Cu, Fe, Ir, Mo, Ni, Pd, Pt, Rh, Ru, and Ti. Furthermore, they exhibit high catalytic activities and electrochemical stabilities in the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in acidic media, superior to that of commercial Pt/graphene and IrO2catalysts. Our results offer valuable insights for the selection of elements as catalysts for various applications.

DOI： 10.1039/d1sc01981c

Flash sintering for BaTiO<sub>3</sub> with square alternating current field including zero-field duration 招待有り査読有り

Umemura, R; Tokunaga, T; Yamamoto, T

JOURNAL OF THE CERAMIC SOCIETY OF JAPAN 128 巻 ( 12 ) 頁： 1018 - 1023 2020年12月

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of the Ceramic Society of Japan

The shrinkage behavior of barium titanate (BaTiO3) green compacts during flash sintering with a square alternating current (AC) field including a zero-field duration (AC-pulse wave) was investigated. It was found that an AC-pulse wave is effective for the densification of BaTiO3 green compacts without reduction and discharge, which is confirmed by transmission electron microscopy and electron energy loss spectroscopy. BaTiO3 sintered polycrystal was obtained at a furnace temperature of 1000 °C by the optimal AC-pulse conditions of 285 V/cm at 250 Hz and a duty ratio of 30 %. A waveform with alternating polarity and the inclusion of a zero-field duration is shown to be possibly useful for flash sintering of oxide materials including altervalent cations.

DOI： 10.2109/jcersj2.20181

H<sub>2</sub> production from methane decomposition by fullerene at low temperature 査読有り

Tokunaga, T; Kuno, K; Kawakami, T; Yamamoto, T; Yoshigoe, A

INTERNATIONAL JOURNAL OF HYDROGEN ENERGY 45 巻 ( 28 ) 頁： 14347 - 14353 2020年5月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：International Journal of Hydrogen Energy

Carbon materials have previously been reported to work as catalysts for hydrogen (H2) production from hydrocarbons. Mechanisms of the catalytic behavior of graphite and carbon black (CB) have often been discussed in literature. Graphite and CB is constructed from mainly 6-membered rings with sp2 bonds. To understand the catalytic behavior of carbon materials for H2 production by methane (CH4) decomposition, the catalytic behavior of fullerenes with 6-membered rings and also those comprising 5- and 7-membered rings with sp2 bonds and their associated mechanisms should be investigated. In this study, the fullerene catalyst activity has been investigated using gas chromatography and the electronic states and nanoscale structures have been analyzed. H2 production started at 400 °C and the H2 production rate gradually increased with time, and the activation energy of the fullerene for H2 production by CH4 decomposition was found to be 166 kJ/mol. Moreover, in situ heating X-ray photon spectroscopy (XPS) measurements showed that the π-π∗ transition signal becomes stronger with increasing temperature above the threshold of 300 °C. The transition of the π electrons to π∗ orbitals upon heating is expected to decompose CH4 absorbed on fullerene. Moreover, transmission electron microscopy (TEM) analysis revealed that the generated carbon atoms from the CH4 decomposition were deposited onto the surfaces of the fullerenes, forming amorphous and layered concentric sphere carbon. Amorphous carbon is reported to not work as a catalyst for CH4 decomposition at around 400 °C. From XPS analysis and TEM observations of these two structures, it is anticipated that the ring structures without 6-membered rings in carbon materials with sp2 bonding contribute to this catalytic behavior for CH4 decomposition at a low temperature of 400 °C.

DOI： 10.1016/j.ijhydene.2020.03.178

Blue photo luminescence from 3 mol%Y<sub>2</sub>O<sub>3</sub>-doped ZrO<sub>2</sub> polycrystals sintered by flash sintering under an alternating current electric field 査読有り

Yamashita, Y; Kurachi, T; Tokunaga, T; Yoshida, H; Yamamoto, T

JOURNAL OF THE EUROPEAN CERAMIC SOCIETY 40 巻 ( 5 ) 頁： 2072 - 2076 2020年5月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of the European Ceramic Society

We investigated the photoluminescence (PL) properties of 3 mol%Y2O3-ZrO2 (3YSZ) polycrystals. The 3YSZ polycrystals were prepared by an isothermal flash sintering technique in which an alternating electric field was applied at a predetermined furnace temperature. After flash sintering, clear, visibly blue PL at 2.82 eV (440 nm) was confirmed under an ultraviolet light (3.4 eV (365 nm)); however, no visible PL was observed from 3YSZ polycrystals conventionally sintered using the same raw powders. Thus, the emission of blue PL was induced by the electric field applied during sintering. The obtained PL band was related to excitation at 3.87 eV (320 nm), which is possibly assigned to the singly ionized associated oxygen vacancy defects (AOD + centers). Furthermore, the blue emission was stable after high temperature annealing at 1400 °C for 1 h in air. We possibly attribute the emission of this PL to the stabilization of AOD + centers by the electric field loading during flash sintering.

DOI： 10.1016/j.jeurceramsoc.2019.12.060

Suppression of nitridation of yttria-doped zirconia during flash sintering 査読有り国際共著

Kurachi, T; Yamashita, Y; Tokunaga, T; Yoshida, H; Yamamoto, T

JOURNAL OF THE AMERICAN CERAMIC SOCIETY 103 巻 ( 5 ) 頁： 3002 - 3007 2020年5月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of the American Ceramic Society

The effect of direct current (DC) and alternating current (AC) on nitridation of 3 mol% Y2O3-doped ZrO2 (3YSZ) after keeping in a flash state for 1 hour was investigated. The inside of the DC-flashed compact was confirmed to exhibit blacking. Scanning transmission electron microscopy, electron energy loss spectroscopy, and X-ray diffraction analysis revealed that zirconium nitrides formed in the blackened area. In contrast, a uniformly densified compact without blackening was obtained by AC fields. No zirconium nitrides formed in the compacts exposed to AC fields even when the flash state was maintained for 1 hour. Therefore, AC fields are effective to suppress nitridation of 3YSZ during flash sintering.

DOI： 10.1111/jace.16990

<i>In situ</i> TEM observation of liquid-state Sn nanoparticles vanishing in a SiO<sub>2</sub> structure: a potential synthetic tool for controllable morphology evolution from core-shell to yolk-shell and hollow structures 査読有り国際共著

Zhu, S; Nguyen, MT; Tokunaga, T; Wen, CY; Yonezawa, T

NANOSCALE ADVANCES 2 巻 ( 4 ) 頁： 1456 - 1464 2020年4月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Nanoscale Advances

Precise design of hollow nanostructures can be realized via various approaches developed in the last two decades, endowing nanomaterials with unique structures and outstanding performances, showing their usefulness in a broad range of fields. Herein, we demonstrate the formation of SnO2@SiO2 hollow nanostructures, for the first time, by interaction between liquid state Sn cores and SiO2 shell structures inside Sn@SiO2 core-shell nanoparticles with real-time observation via in situ transmission electron microscopy (TEM). Based on the in situ results, designed transformation of the nanoparticle structure from core-shell Sn@SiO2 to yolk-shell Sn@SiO2 and hollow SnO2@SiO2 is demonstrated, showing the controllable structure of core-shell Sn@SiO2 nanoparticles via fixing liquid-state Sn inside a SiO2 shell which has a certain Sn containing capacity. The present approach expands the toolbox for the design and preparation of yolk-shell and hollow nanostructures, thus providing us with a new strategy for fabrication of more complicated nanostructures.

DOI： 10.1039/c9na00782b

Highly Correlated Size and Composition of Pt/Au Alloy Nanoparticles via Magnetron Sputtering onto Liquid 査読有り国際誌

Deng, LL; Nguyen, MT; Shi, JM; Chau, YTR; Tokunaga, T; Kudo, M; Matsumura, S; Hashimoto, N; Yonezawa, T

LANGMUIR 36 巻 ( 12 ) 頁： 3004 - 3015 2020年3月

記述言語：英語出版者・発行元：Langmuir

Pt/Au alloy nanoparticles (NPs) in a wide composition range have been synthesized by room-temperature simultaneous sputter deposition from two independent magnetron sources onto liquid PEG (MW = 600). The prepared NPs were alloyed with the face-centered cubic (fcc) structure. In addition, the particle sizes, composition, and shape are strongly correlated but can be tailored by an appropriate variation of the sputtering parameters. No individual particle but large agglomerates with partial alloy structure formed at Pt content of less than 16 atom %. Highly dispersed NPs with no agglomeration were observed in PEG when the quantity of Pt is more than 26 atom %. On the other hand, a small amount of Pt could terminate the agglomeration of Au when sputtering on the grids for transmission electron microscope observation. Our experiment and computer simulation carried out by two different methods indicate that the composition-dependent particle size of Pt/Au can be explained by the atomic concentration, formation energy of the cluster, and interaction between different metal atoms and the PEG molecule.

DOI： 10.1021/acs.langmuir.0c00152

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