研究者詳細 - 石丸　学

論文 - 石丸　学

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Explosive crystallization of amorphous germanium-tin films by irradiation with a 3-keV electron beam 査読有り

Nakamura R., Miyamoto M., Ishimaru M.

Journal of Applied Physics 133 ( 18 ) 2023年05月

担当区分：最終著者記述言語：英語掲載種別：研究論文（学術雑誌）

Much effort has been expended to obtain thin films of metastable solid solutions of germanium (Ge) that contain as high tin (Sn) content as possible because of their excellent electronic and optoelectronic properties. On the basis of our previous study on amorphous Ge, we demonstrated in this study that irradiation of substrate-free films of amorphous Ge100−xSnx (x = 8, 11, and 19 at. %) with a low-energy electron beam of 3 keV at ambient temperature can induce instantaneous wide-area crystallization (explosive crystallization). Characteristic spiral crystal growth associated with explosive crystallization occurred with areas exceeding 50 μm in diameter around a scanned area of the electron beam of 8 × 8 μm2. As a result, solid solutions of GeSn with Sn concentration up to 19 at. % were obtained with the suppression of precipitation of β-Sn. The region of explosive crystallization reduced in size with increasing Sn content. In addition, thermal analyses revealed that the heat released during crystallization of amorphous GeSn films decreased with increasing Sn content. This relationship indicates that the heat release at the growth front plays a key role in the propagation of explosive crystallization of a-GeSn.

DOI： 10.1063/5.0147022

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Planar defects-induced low thermal conductivity in a superhard material SiB<inf>6</inf> 査読有り国際誌

Tanusilp S.a., Kumagai M., Ohishi Y., Ishimaru M., Sadayori N., Kurosaki K.

Journal of Alloys and Compounds 939 2023年04月

記述言語：英語掲載種別：研究論文（学術雑誌）

Generally materials with low thermal conductivity require weaker interatomic bonding, considered as soft materials. Here we demonstrate that SiB6 with planar structural defects shows low thermal conductivity, but uncommonly high strength. Planar defects-induced polycrystalline SiB6 (PD-SiB6) has a relatively large Vickers hardness, which is comparable to those of well-known superhard materials, despite of relatively low thermal conductivity (<10 W m-1 K-1 at 300 K). Transmission electron microscopy observations confirmed the presence of numerous planar defects, which were thought to contribute to the improvement of hardness. Thanks to the special characteristics of a trade-off relationship between low thermal conductivity and high strength, we believe that PD-SiB6 can be used in new strategies of controlling thermal and mechanical properties in various functional materials.

DOI： 10.1016/j.jallcom.2023.168744

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Microstructure and Phase Transformation in Fe<inf>20</inf>Co<inf>20</inf>Ni<inf>20</inf>Cr<inf>20</inf>B<inf>20</inf><sup>1</sup><inf>x</inf>Si<inf>x</inf> Alloys Prepared by Mechanical Alloying 査読有り

Zhang Y., Ishimaru M., Tokunaga T., Era H.

Materials Transactions ( 公益社団法人日本金属学会 ) 64 ( 11 ) 2568 - 2574 2023年01月

記述言語：英語掲載種別：研究論文（学術雑誌）

In this study, microstructure and phase transformation behavior in Fe20Co20Ni20Cr20B201xSix alloys prepared by the mechanical alloying (MA) method were investigated by X-ray diffraction (XRD) measurements, scanning electron microscopy, transmission electron microscopy, and differential scanning calorimetry (DSC). The Fe20Co20Ni20Cr20B201xSix alloys prepared by the melt-spinning method were composed of FCC and compounds, and the FCC and BCC phases predicted by the valance electron concentration parameter were not formed. However, alloy powders prepared by the MA method were revealed to be composed of the FCC and BCC phases. Small amounts of unreacted pure B and Si particles were observed in alloy powders with high and low B content, respectively. XRD and DSC measurements revealed that the BCC phase in MA powder disappeared, and compounds were formed by heating up to 700°C. Especially the compound formation temperature was higher than that of the same alloy prepared by the melt-spinning method, suggesting that the thermal stability of the alloy powders prepared by the MA method was higher than that of the alloy ribbons prepared by the melt-spinning method. [doi:10.2320/matertrans.MT-M2023040]

DOI： 10.2320/matertrans.MT-M2023040

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Impact of supercooled liquid structures on the crystallization processes of amorphous Ge 査読有り

Nagaoka S., Tahara C., Ishimaru M.

Applied Physics Express 16 ( 1 ) 2023年01月

担当区分：最終著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）

The crystallization processes of amorphous Ge as well as the atomistic structures of the growth front were examined by molecular-dynamics simulations. An amorphous Ge network was annealed in a thermal bath with a temperature gradient. Crystallization proceeded via the supercooled liquid, and changed from random nanocrystallization to large-oriented grain growth. The resultant structures qualitatively reproduced the explosive crystallization observed with pulsed-laser irradiation and flash lamp annealing. The supercooled liquid was found to transform from a tetrahedral liquid to a more highly-coordinated liquid with increasing temperature, which was attributed to the change in growth mode.

DOI： 10.35848/1882-0786/aca87a

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Thermoelectric Property of SnSe Films on Glass Substrate: Influence of Columnar Grain Boundary on Carrier Scattering 査読有り国際誌

Horide T., Murakami Y., Ishimaru M., Matsumoto K.

ACS Applied Electronic Materials 4 ( 12 ) 6364 - 6372 2022年12月

記述言語：英語掲載種別：研究論文（学術雑誌）

Thermoelectric SnSe exhibits a very high figure of merit, and the a-axis orientation is needed because a high thermoelectric property is obtained along the bc-plane. Here, in spite of the amorphous nature of glass, a-axis-oriented SnSe films were fabricated using pulsed laser deposition on a glass substrate, which is more practical than single-crystal oxide substrates. Transmission electron microscopy indicated that a-axis-oriented SnSe films with a columnar grain structure grew on amorphous SiO2. The electrical conductivity and the Seebeck coefficient at room temperature showed almost the same trend with respect to the hole concentration in both the SnSe/glass and SnSe/single-crystal-substrate films. The electrical conductivity increased with increasing temperature more slowly in SnSe/glass films than in SnSe/single-crystal-substrate films. This indicates that the grain boundary contribution to carrier scattering is significant at high temperatures, while the grain boundary contribution is as strong as the orthorhombic domain boundary contribution at room temperature. In spite of the grain boundary effect, the power factor in SnSe/glass was as high as that for single-crystal SnSe at high temperatures. Considering the grain boundary effect on electrical conductivity, the structure and process of SnSe films on amorphous substrates should be designed.

DOI： 10.1021/acsaelm.2c01486

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Investigation of Nanoscale Phase Formation in Rapidly Solidified Fe20Co20Ni20Cr20B201xSix Alloys 査読有り国際誌

Zhang Yicheng, Inoue Koji, Ishimaru Manabu, Tokunaga Tatsuya, Era Hidenori

MATERIALS TRANSACTIONS ( 公益社団法人日本金属学会 ) advpub ( 0 ) 1211 - 1216 2022年09月

記述言語：英語掲載種別：研究論文（学術雑誌）

<p>In this study, nanoscale phase formation in rapidly solidified Fe<sub>20</sub>Co<sub>20</sub>Ni<sub>20</sub>Cr<sub>20</sub>B<sub>20−</sub><i><sub>x</sub></i>Si<i><sub>x</sub></i> alloys was investigated using atom probe tomography (APT) and transmission electron microscopy (TEM). According to previous X-ray diffraction measurements and scanning electron microscopy with energy-dispersive X-ray spectroscopy results, it was thought that this alloy system was composed of almost a single face-centered cubic (FCC) solid solution phase when the Si content was 5 at.%. However, APT and TEM results at the nanoscale showed that both an FCC solid solution and compound phases formed for all alloy compositions. The rapidly solidified alloy ribbon with a Si content of 5 at.% showed the presence of nanoscale FCC and Cr<sub>2</sub>B phases. Furthermore, in addition to the nanoscale FCC and Cr<sub>2</sub>B phases, a nanoscale Cr<sub>3</sub>Ni<sub>5</sub>Si<sub>2</sub> phase was observed when the Si content exceeded 7.5 at.%.</p>

DOI： 10.2320/matertrans.mt-m2022058

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Anomalous structural phase transformation in swift heavy ion-irradiated δ-Sc<inf>4</inf>Hf<inf>3</inf>O<inf>12</inf> 招待有り査読有り国際誌

Iwasaki M., Kanazawa Y., Manago D., Patel M.K., Baldinozzi G., Sickafus K.E., Ishimaru M.

Journal of Applied Physics 132 ( 7 ) 2022年08月

担当区分：責任著者記述言語：英語掲載種別：研究論文（学術雑誌）

Swift heavy ion irradiation was carried out to examine the ionization effects on structural changes of δ-Sc4Hf3O12 in which oxygen vacancies are regularly arranged. The specimens were irradiated at room temperature with 92 MeV xenon ions to fluences ranging from 3 × 1012 to 1 × 1014/cm2 and characterized by grazing (glancing) incidence x-ray diffraction, transmission electron microscopy, and scanning transmission electron microscopy. It was found that the pristine long-range ordered rhombohedral δ-phase undergoes a reconstructive transformation toward a long-range disordered cubic oxygen-deficient fluorite phase promoted by ionization effects. In addition, an ordered phase with a short-range structure different from the δ-type was formed in a layer going from the surface to a depth of ∼4.5 μm in the specimen irradiated to a fluence of 1 × 1014/cm2. It was found that the ordered phase is formed from the disordered cubic fluorite phase. This structural change is anomalous, because it is the opposite process of the usual irradiation-induced structural change, the order-to-disorder phase transformation. Electron diffraction experiments revealed that short-range ordered regions in this layer possess an oxygen-excess bixbyite organization (C-type heavy rare-earth oxides) with randomly filled anion vacant sites to account for the different stoichiometry and a long-range average oxygen-deficient fluorite phase.

DOI： 10.1063/5.0098518

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Self-Organized Nanocomposite Structure Controlled by Elemental Site Occupancy to Improve Vortex Pinning in YBa<inf>2</inf>Cu<inf>3</inf>O<inf>7</inf>Superconducting Films 査読有り国際誌

Horide T., Yoshida Y., Kita R., Gondo M., Ishimaru M., Matsumoto K.

ACS Applied Electronic Materials 4 ( 6 ) 3018 - 3026 2022年06月

記述言語：英語掲載種別：研究論文（学術雑誌）

To fabricate high performance YBa2Cu3O7 superconducting films and tapes, the critical current density (Jc) should be enhanced and the nanocomposite structure should be very effective in controlling the vortex pinning and Jc. Although the nanoscale morphology has been a basic parameter from the early stages of nanorod control, compositional factors should be discussed to effectively control not only the superconducting order parameter distribution but also the thermodynamic parameter relating to crystal growth. In this study, a double perovskite oxide, Ba2RENbO6 (RE = Yb, Lu), was incorporated in YBa2Cu3O7 films, where the site occupancy of the RE element is focused to control the nanocomposite structure. The elongated nanorods were formed in both the YBa2Cu3O7+Ba2YbNbO6 and YBa2Cu3O7+Ba2LuNbO6 films. While Lu mainly existed in the nanorods, Yb was observed not only in the nanorods but also in the matrix. As a result, at the fixed nanorod content, while the matching field was larger for the YBa2Cu3O7+Ba2YbNbO6 film, the Jc in the high magnetic field was larger for the YBa2Cu3O7+Ba2LuNbO6 film. The angular dependence of Jc depended on the RE due to the pinning contribution from the Y-rich nanoparticles. These are unconventional phenomena that are not observed in the YBa2Cu3O7+BaMO3 (M = Zr, Sn, Hf) films. Thus, the site occupancy of the RE element affects the Jc characteristics. The self-organization and the nanocomposite structure can be designed by considering the site occupancy as a variable parameter.

DOI： 10.1021/acsaelm.2c00438

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Impact of annealing on electric and elastic properties of 10-nm Hf<inf>0.5</inf>Zr<inf>0.5</inf>O<inf>2</inf> films prepared on Si by sputtering 査読有り国際誌

Bolotov L., Migita S., Fujio R., Ishimaru M., Hatayama S., Uchida N.

Microelectronic Engineering 258 2022年04月

記述言語：英語掲載種別：研究論文（学術雑誌）

HfO2-based films are important materials used in broad range of electronic applications from high-performance transistors and memory cells, to thermoelectric and energy harvesting elements. By employing scanning probe methods, we made nanoscale comparison of chemical composition, surface morphology, the elastic modulus and the surface potential of bare 10-nm thick Hf0.5Zr0.5O2 films prepared on Si by a carbon-free sputtering process. The composition mapping confirmed uniform distribution of Hf and Zr in the film along wafer size. Suppression of the monoclinic phase in films annealed at 600 - 800 °C had strong impact on spatial variations of film properties. Small surface roughness, large electric domain sizes (50–200 nm at 700 °C) and small fluctuations of the surface potential (40–50 meV) in Si coated with the films are appealing for gate-stack applications. Films annealed at 600-700 °C showed the elastic modulus of about 169 GPa and the ferroelectric polarization reversal at a field of ~1 MV/cm as observed by nanoscale poling with a Pt-coated scanning probe. In contrast, properties of films annealing at 800 °C were affected by growth of thick interfacial oxide layer. The presented nanoscale approach is beneficial in optimizing of physical and mechanical properties of thin dielectric films.

DOI： 10.1016/j.mee.2022.111770

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Electron diffraction radial distribution function analysis of amorphous boron carbide synthesized by ion beam irradiation and chemical vapor deposition 査読有り国際誌

Ishimaru M., Nakamura R., Zhang Y., Weber W.J., Peterson G.G., Ianno N.J., Nastasi M.

Journal of the European Ceramic Society 42 ( 2 ) 376 - 382 2022年02月

担当区分：筆頭著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）

Amorphous boron carbide (a-BxC) networks consist of light elements, and their low atomic scattering factors makes structural analysis by x-ray diffraction difficult. Electron diffraction has an advantage of detecting the light elements, because of the strong interaction between the matter and electrons. We prepared a-BxC by ion beam technologies and plasma-enhanced chemical vapor deposition, and characterized their structures via atomic pair-distribution functions derived from electron diffraction intensity profiles. It was found that a pentagonal pyramid is the most favorable cluster in a-B4C generated by ion irradiation, while C[sbnd]C homonuclear bonds were formed in the deposited a-BxC thin film. X-ray photoemission spectroscopy revealed that the a-BxC thin film possesses more carbon than B4C, which is responsible for the formation of the homonuclear bonds.

DOI： 10.1016/j.jeurceramsoc.2021.10.020

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Aligned Self-Organization Induced by Epitaxial Stress and Shear Deformation in Jahn–Teller Spinel ZnMnGaO<inf>4</inf> 査読有り

Horide T., Morishita K., Horibe Y., Usuki M., Ishimaru M., Matsumoto K.

Journal of Physical Chemistry C 126 ( 1 ) 806 - 814 2022年01月

記述言語：英語掲載種別：研究論文（学術雑誌）

Spinel ZnMnGaO4 exhibits the characteristic self-organization dominated by phase separation and strain to realize an ordered nanostructure. To control the self-organization, ZnMnGaO4 films fabricated using pulsed laser deposition were postannealed. While the ordered nano-checkerboard and the slightly coarse nanolamellar structures were observed for the moderate annealing temperature and the long annealing time, the twin structure was formed in the films annealed at the low temperature for the short annealing time. The cross-sectional observation showed the vertically aligned nanostructure near the surface (twin, nano-checkerboard, or nanolamellar) and the nondefective epitaxial layer near the substrate. The ZnMnGaO4 films exhibited the same in-plane lattice parameter as that of MgO along the MgO[110]//ZMGO[101] regardless of annealing conditions, and the stress analysis indicates that the epitaxial stress at the epitaxial ZnMnGaO4/MgO and the shear stress at the epitaxial ZnMnGaO4/twinned ZnMnGaO4 determined the vertical structure and the twin width. The thermodynamic stability and the Mn and Ga diffusion basically bring about the self-organized nanostructure formation as in bulk, and the epitaxial stress and the interface shear stress align the self-organization in the films. Thus, the highly aligned self-organized nanostructures can be fabricated in the annealed ZnMnGaO4 films by tuning these factors.

DOI： 10.1021/acs.jpcc.1c09324

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Thermoelectric Property of n-Type Bismuth-Doped SnSe Film: Influence of Characteristic Film Defect 査読有り

Horide T., Nakamura K., Hirayama Y., Morishita K., Ishimaru M., Matsumoto K.

ACS Applied Energy Materials 4 ( 9 ) 9563 - 9571 2021年09月

記述言語：英語掲載種別：研究論文（学術雑誌）

Highly aligned SnSe exhibits very high thermoelectric properties, and orientation control in films is very promising for developing high-performance thermoelectric modules. While SnSe films with intrinsic p-type nature have been reported, fabrication of the highly aligned n-type SnSe films is difficult due to thermodynamic restriction on the solubility of the doping elements. Here, highly oriented SnSe films doped with Bi were successfully fabricated using pulsed laser deposition. Characteristic film structures were observed: doped Bi in the SnSe matrix; domain boundaries with a spacing of ∼200 nm; self-organized Bi precipitates with a bimodal size distribution; and stacking faults. The most important result is observation of the n-type Hall resistivity and the n-type Seebeck coefficient. The stacking faults and the doped Bi in the films degraded the room-temperature Seebeck coefficient. While the electron carrier mobility in room temperature was smaller than that in the single crystal due to the domain boundary scattering, the domain boundary scattering was suppressed in the high temperature of 300 °C. Thus, the characteristic film structures significantly affect the thermoelectric properties of SnSe. The doped Bi in the SnSe matrix, the stacking faults, and the domain boundaries should be controlled for further improvement of the thermoelectric properties in the Bi-SnSe films, and the self-organized Bi nanoprecipitates are very promising for achieving high-performance Bi-SnSe with decreased thermal conductivity.

DOI： 10.1021/acsaem.1c01722

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Review of “12th Japanese-Polish joint seminar on micro and nano analysis (August 29-September 1, 2018)” 査読有り

Ishimaru M.

Materials Transactions ( 公益社団法人日本金属学会 ) 62 ( 9 ) 1420 - 1423 2021年09月

担当区分：筆頭著者,　責任著者記述言語：英語掲載種別：記事・総説・解説・論説等（学術雑誌）

“The 12th Japanese-Polish Joint Seminar on Micro and Nano Analysis” was held in Fukuoka, Japan from August 29 to September 1, 2018, and the proceedings were published in May, 2019, as a special issue of Materials Transactions (Vol. 60, No. 5). The main purpose of this seminar is to discuss the structural analysis of materials by electron microscopy techniques. Among the papers presented at the seminar, this article briefly reviews the following topics: observations of dislocations in a thick specimen by ultra-high voltage electron microscopy, suppression of geometric phase shift due to antiphase boundaries in dark-field electron holography, and structural characterization of amorphous materials by electron diffraction techniques.

DOI： 10.2320/matertrans.MT-M2021094

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Explosive crystallization of sputter-deposited amorphous germanium films by irradiation with an electron beam of SEM-level energies 査読有り国際誌

Nakamura R., Matsumoto A., Ishimaru M.

Journal of Applied Physics 129 ( 21 ) 2021年06月

担当区分：最終著者記述言語：英語掲載種別：研究論文（学術雑誌）

The crystallization of sputter-deposited substrate-free films of amorphous germanium was induced by electron irradiation at SEM-level energies of less than 20 keV at ambient temperature using an electron probe microanalyzer. Instantaneous crystallization, referred to as explosive crystallization, occurred consistently at 2-20 keV; the threshold of electron fluxes is 1015-1016 m−2 s−1, which is five to six orders of magnitude lower than those at 100 keV reported previously. This process is expected to be advantageous in the production of polycrystalline Ge films since it is rapid, requires little energy, and results in negligible damage to the substrate.

DOI： 10.1063/5.0052142

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Nanostructures and flux pinning properties in YBa<inf>2</inf>Cu<inf>3</inf>O<inf>7- y </inf>thin films with double perovskite Ba<inf>2</inf>LuNbO<inf>6</inf>nanorods 査読有り国際誌

Gondo M., Yoshida M., Yoshida Y., Ishimaru M., Horide T., Matsumoto K., Kita R.

Journal of Applied Physics 129 ( 19 ) 2021年05月

担当区分：責任著者記述言語：英語掲載種別：研究論文（学術雑誌）

Double perovskite Ba2LuNbO6 (BLNO)-doped YBa2Cu3O7-y (YBCO) thin films are fabricated on a SrTiO3 (001) substrate by pulsed laser deposition, and their nanostructures are characterized by transmission electron microscopy and scanning transmission electron microscopy. Cross-sectional observations and elemental mapping reveal that BLNO self-assembles during thin film deposition, and consequently, nanorods extending straight from the substrate to the surface are formed in the YBCO thin films. It is confirmed that stacking faults perpendicular to the growth direction disturb the formation of BLNO nanorods. Strain maps extracted by geometric phase analysis reveal that the tensile strain occurs in the YBCO matrix around the BLNO nanorods. Misfit dislocations are periodically introduced at the interface between the nanorod and the matrix, which results in the inhomogeneous strain of YBCO around the BLNO nanorods. The superconducting properties of the YBCO + BLNO thin films are compared with those of other previously reported YBCO thin films with normal perovskite and double perovskite nanorods.

DOI： 10.1063/5.0048693

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Enhancement of Thermoelectric Properties of n-Type Bi<inf>2</inf>Te<inf>3- x</inf>Se<inf>x</inf>by Energy Filtering Effect 査読有り

Kawajiri Y., Tanusilp S.A., Kumagai M., Ishimaru M., Ohishi Y., Tanaka J., Kurosaki K.

ACS Applied Energy Materials 4 ( 10 ) 11819 - 11826 2021年01月

記述言語：英語掲載種別：研究論文（学術雑誌）

A pair of n-type Bi2Te3-xSex and p-type (Bi,Sb)2Te3 is known as a promising candidate for assembling a high thermoelectric efficiency module operating at near room temperature. While the dimensionless figure of merit (zT) of p-type (Bi,Sb)2Te3 is commonly larger than 1.0, n-type Bi2Te3-xSex has a lower zT value of μ0.8 at room temperature. Here, we aim to enhance the zT of n-type Bi2Te3-xSex through the energy filtering effect that can improve the Seebeck coefficient by adding Au. In the Bi2Te2.8Se0.2 + 5 at % Au composite, the Seebeck coefficient is significantly improved, and the electrical resistivity does not change significantly, leading to an approximately twice as high power factor as that of the non-Au-added one at near room temperature. Also, the addition of Au suppresses the thermal conductivity. These advantages result in a maximum zT of over 1.0 at room temperature and average zT value of 1.05 at T = 300-400 K, an μ75% improvement, which is comparable to those of the reported n-type Bi2Te3-based materials. Also, Au addition shows no negative effect on the mechanical properties as well as high-temperature stability of Bi2Te3-xSex. These results indicate that Au addition is a promising method to improve the thermoelectric properties of n-type Bi2Te3-xSex used for assembling a practical thermoelectric module operating at near room temperature.

DOI： 10.1021/acsaem.1c02560

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Structure analysis of Hf<inf>0.5</inf>Zr<inf>0.5</inf>O<inf>2</inf> thin films crystallized from amorphous phase by thermal annealing below 500°C 査読有り

Fujio R., Ishimaru M., Migita S., Uchida N.

2021 Silicon Nanoelectronics Workshop, SNW 2021 2021年01月

担当区分：責任著者記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）

Hf0.5Zr0.5O2, (HZO) films are anticipated as a noval insulating material for ferroelectric field-effect transistors. These materials are fabricated by crystallization of amorphous HZO, and therefore knowledge of crystallization processes is required. We examined thermally-induced crystallization processes of amorphous HZO prepared by sputtering using x-ray diffraction and transmission electron microscopy. It was found that a metastable orthorhombic phase is formed in 10 nm thick HZO films after thermal annealing at 500°C.

DOI： 10.1109/SNW51795.2021.00018

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アモルファスGeSnの結晶化におけるSnの振る舞い招待有り査読有り

石丸　学, 仲村龍介

まてりあ 59 ( 12 ) 662 - 668 2020年12月

Combined effect of nanorod and stacking fault for improving nanorod interface in YBa<inf>2</inf>Cu<inf>3</inf>O<inf>7-δ</inf>nanocomposite films 査読有り国際誌

Horide T., Ishimaru M., Sato K., Matsumoto K.

Superconductor Science and Technology 33 ( 11 ) 2020年11月

記述言語：英語掲載種別：研究論文（学術雑誌）

Self-organized nanorods in YBa2Cu3O7-δ films are important pinning centers from the technical and fundamental views. While influence of nanoscale factors (>4-5 nm) on the vortex pinning has already been discussed in detail, the interface control of nanorods (at the smaller scale) has not yet been performed. Here, it is demonstrated that the stacking faults can control the nanorod interface to improve the vortex pinning. The stacking faults were formed across the nanorods by post-annealing the YBa2Cu3O7-δ films containing BaMO3 (M = Zr, Sn, Hf) nanorods. The strong bonding between YBa2Cu3O7-δ and BaMO3 varies the atomic position of YBa2Cu3O7-δ, degrading an interface sharpness and an elementary pinning force of the nanorod. Scanning transmission electron microscopy and density functional theory calculation clarified that the stacking faults broke the strong bonding between YBa2Cu3O7-δ and BaMO3 at the nanorod interface, and reduced the local strain around the nanorods, improving the elementary pinning force. As a result, the critical current density was improved in low temperature and low magnetic field when magnetic field was aligned with the c-axis. Thus, the combined effect of nanoinclusions and crystalline defects, in the present case, nanorods and stacking faults, can control the interface of nanoinclusion pinning centers, opening the interface design to realize the ideal pinning situation.

DOI： 10.1088/1361-6668/abaebf

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=85092915022&origin=inward

Dual-Beam Irradiation Stability of Amorphous Silicon Oxycarbide at 300°C and 500°C 査読有り

Su Q., Greaves G., Donnelly S.E., Mizuguchi S., Ishimaru M., Nastasi M.

JOM 72 ( 11 ) 4002 - 4007 2020年11月

記述言語：英語掲載種別：研究論文（学術雑誌）

The irradiation stability of a material in the temperature range from 300°C to 500°C represents an important step for a variety of nuclear applications. Here we used dual-beam irradiation to investigate the response of an amorphous silicon oxycarbide (SiOC) to extreme environments (temperature and irradiation). The amorphous SiOC was prepared in thin film form by sputtering and then fabricated into cross-sectional transmission electron microscopy (TEM) specimens, and finally irradiated with helium (He) and krypton (Kr) ions inside a TEM. In-situ TEM observations revealed that He bubble and void formation are highly suppressed after irradiation up to 95 dpa with simultaneous He implantation up to 231 at.%. Atomic pair-distribution functions suggested that the amorphous structures are almost the same before and after irradiation, and no crystallization, nor phase separation was detected. This study demonstrates the stability of amorphous SiOC under dual-beam irradiation at nuclear reactor operation temperatures, suggesting that this material is applicable as a structural material for advanced nuclear reactors.

DOI： 10.1007/s11837-020-04332-z

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=85090212693&origin=inward

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