記述言語：英語   掲載種別：研究論文（学術雑誌）   参加形態：共同（副担当）  

Vanadium (V) is an attractive hydrogen separation membrane material. However, its diffusion behavior under hydrogen permeation is not well understood mainly because of surface oxidation. Here, we have attempted to observe the permeation of hydrogen through V by subjecting V samples to different surface treatments e.g., electropolishing and plasma-induced cleaning using a glow-discharge technique. We have achieved a high flux of hydrogen controlled by long-range diffusion under a low hydrogen potential at 723–973 K. The diffusion coefficients of hydrogen in defect-free and high-purity samples analyzed from the permeation curves at 823–973 K are almost consistent with the literature data obtained by Gorsky effect and absorption measurements. However, the activation energy of diffusion (19 kJ mol−1) is 8–14 kJ mol−1 higher than the literature values. This difference in activation energy suggests that permeation through the active surface of V is highly sensitive to trapping by oxygen—a slight amount of oxygen dissolved from a very thin native oxide layer would segregate near the surface to trap hydrogen. Furthermore, we have found that residual strain, grain boundaries, and lattice defects, induced by mechanical deformation, reduce the flux and retard the diffusion considerably.

DOI： 10.1016/j.memsci.2020.118522

Scopus

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=85089396151&origin=inward

記述言語：英語   掲載種別：研究論文（学術雑誌）   参加形態：共同（主担当）  

The crystallization behavior of sputter-deposited films of amorphous Si (a-Si) and SiGe alloys (a-SiGe) induced by electron irradiation at room temperature and by thermal annealing was investigated by in situ transmission electron microscopy. On electron irradiation at room temperature, extremely rapid crystallization, so-called explosive crystallization, occurred at a higher electron flux but not at a lower electron flux. On in situ thermal annealing, explosive crystallization occurred preferentially and partially at low temperatures in Ge-rich a-SixGe100-x for x < 50 but not for x > 50. These results indicate that the increase of Si content in a-SiGe prevents the occurrence of explosive crystallization. We previously proposed that explosive crystallization can occur in pristine a-Ge films via the interface of a liquid-like, high-density amorphous state at the growth front. An increase in the instability of this high-density amorphous state caused by the increase of Si in a-SiGe apparently gives rise to the suppression of explosive crystallization.

DOI： 10.1063/5.0010202

Scopus

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=85087622915&origin=inward

記述言語：英語   掲載種別：研究論文（学術雑誌）   参加形態：共同（主担当）  

We examined by transmission electron microscopy the structure and crystallization behavior of hydrogenerated and non-hydrogenerated amorphous germanium films (a-Ge:H and a-Ge) prepared by sputtering to figure out the effects of hydrogen on them. In pair-distribution function, first and second peaks at the interatomic distance of 0.26 and 0.40 nm, respectively, were found to be higher and sharper in a-Ge:H than in a-Ge; therefore amorphous structure was organized in a more ordered state within a short range by hydrogeneration. On thermal annealing, fine nanograins (FGs) of about 10 nm in size appeared preferentially at 350 °C and above in a-Ge:H, which is in contrast with the formation of coarse particles of about 100 nm in size at 500 °C in a-Ge. Hydrogeneration would make a certain number of short-range ordered clusters distributed in the amorphous matrix, inducing the preferential formation of FGs at lower temperatures.

DOI： 10.35848/1347-4065/ab9cd9

Scopus

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=85088319551&origin=inward

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：日本鉄鋼協会   参加形態：共同（主担当）  

We report an attempt to determine the diffusion coefficient of B in α Iron by measuring the penetration profile by means of secondary-ion mass spectrometry (SIMS). Pure iron plates of grain-size of 1 to 3 mm were prepared, and thin films of Fe-B alloy (200 nm) and alumina (50 nm) were deposited on the surface as a B source and a capping layer, respectively. The samples were subjected to diffusion annealing at 700ºC, 800ºC, and 900ºC for certain periods of time, and the intensity of secondary ions of B was measured as a function of depth by SIMS. The mesa method was employed, in which a groove is prepared first around the target area by sputtering, and then the depth profile of B through the inner pillar was obtained. The concentration profiles thus obtained were analysed with the thin-film solution, the error-function solution, and also using Hall’s method, depending on the form of the profile. The diffusion coefficient was of the order of 10–18 m2 s–1 in all the cases, which is seven to eight orders of magnitude smaller than those evaluated from deboronising experiments in the 1950 s, but is close to recent theoretical prediction for substitutional diffusion.

DOI： 10.2355/tetsutohagane.TETSU-2019-104

Scopus

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=85086225469&origin=inward

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 Applied Physics   参加形態：共同（副担当）  

Crystallization processes of amorphous germanium–tin (GeSn) under low-energy electron-beam irradiation were examined using transmission electron microscopy (TEM). Freestanding amorphous GeSn thin films were irradiated with a 100 keV electron beam at room temperature. The amorphous GeSn was athermally crystallized by electron-beam irradiation, when the electron flux exceeded the critical value. Heterogeneous structures consisting of nano- and micro-crystallites were formed after crystallization of amorphous GeSn with ∼24 at. % Sn in the as-sputtered amorphous state. In situ TEM observations of structural changes under electron-beam irradiation revealed that random nucleation and growth of nanocrystallites occur at the early stage of crystallization, followed by rapid formation of micro-grains surrounding the nanocrystals. It has been suggested that the growth of micro-grains progresses via supercooled liquid Sn at the amorphous/crystalline interface. The resultant GeSn grains with a size of a few micrometers contained ∼15 at. % Sn, much larger than the solubility limit of Sn in Ge (∼1 at. % Sn).

DOI： 10.1063/5.0006416

Scopus

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=85095736701&origin=inward

記述言語：英語   掲載種別：研究論文（学術雑誌）   参加形態：共同（副担当）  

The solubility limit of tin (Sn) in germanium (Ge) is very small, and, therefore, it is difficult to synthesize high Sn concentration GeSn crystals by conventional methods. An amorphous phase can contain elements beyond the solubility limit of the crystal state, and, therefore, recrystallization of the amorphous alloy is one of the possible ways to realize materials far from the equilibrium state. To suppress Sn precipitation during thermal annealing, knowledge of crystallization processes is required. In the present study, amorphous GeSn thin films with different Sn concentrations were prepared by sputtering, and their crystallization processes were examined by in situ transmission electron microscopy. It was found that the crystallization temperature decreases with increasing Sn concentration, and it became lower than the eutectic temperature when the Sn concentration exceeded ∼25 at. %. Radial distribution function analyses revealed that phase decomposition occurs in the amorphous state of the specimens which crystallize below the eutectic temperature, and Sn crystallites were simultaneously precipitated with crystallization. On the other hand, no remarkable phase decomposition was detected in amorphous GeSn with <25 at. % Sn. Sn precipitation occurred at a higher temperature than the crystallization in these specimens, and the difference between the crystallization and Sn precipitation temperatures became large with decreasing Sn concentration. Because of the existence of this temperature difference, a temperature window for suppressing Sn segregation existed. We demonstrated that large GeSn grains with high Sn concentration could be realized by annealing the specimens within the temperature window.

DOI： 10.1063/1.5086480

Scopus

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=85065127379&origin=inward

記述言語：英語   掲載種別：研究論文（学術雑誌）   参加形態：共同（主担当）  

In amorphous germanium (a-Ge) and amorphous silicon films, extremely rapid crystallization, called explosive crystallization, is known to occur by instantaneous processes such as mechanical stimulation, laser irradiation, and electron irradiation. In the present study, using transmission electron microscopy, we have investigated crystallization of a-Ge induced by electron irradiation and flash-lamp annealing (FLA). We have found that the mode of crystallization depends on the amorphous state: explosive crystallization occurred by both electron irradiation and FLA in pristine films, while it did not occur in those aged at room temperature for over 6 months. In a previous paper [Okugawa et al., J. Appl. Phys. 119, 214309 (2016)], it was reported that liquid-like high-density amorphous (HDA) regions were formed in a-Ge films by the long-term aging. The explosive crystallization observed in pristine a-Ge films is suggested to occur via liquid-like HDA interfaces at the growth front.

DOI： 10.7567/1347-4065/ab0909

Scopus

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=85065161182&origin=inward

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）   参加形態：共同（副担当）  

Amorphous structures of germanium-tin (GeSn) thin films as well as their recrystallization processes during thermal annealing were examined by means of transmission electron microscopy. The specimens were prepared by radio-frequency magnetron sputtering. The as-sputtered GeSn thin films possessed an amorphous structure with 16.4 at.%Sn. The specimen crystallized at 325 °C, and Sn atoms were substitutionally incorporated in a diamond structure. The Sn atoms were ejected from Ge at 350 °C, and molten Sn were formed. In the cooling process, it was confirmed that the molten Sn remained at 150 o C which is much lower than the eutectic temperature of the Ge-Sn binary system. Finally, a remarkable Sn precipitates were formed at room temperature.

DOI： 10.7449/2018/MST_2018_284_287

Scopus

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=85060220932&origin=inward

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：日本鉄鋼協会   参加形態：共同（主担当）  

Amorphous Fe-B thin films of the concentration range between 12 and 25 at.% B were prepared by radio frequency sputtering techniques, and their local structures were examined by transmission electron microscopy. Pair-distribution-function analyses of Fe-12,-18 and-25 at.%B for a region of 300 nm in diameter revealed a systematic trend according to the concentration; with the increase in B concentration, the intensity of the weak shoulder peak at 0.205 nm for the Fe-B pair increases whereas those of main peaks for Fe-Fe pair decrease. In electron diffraction patterns of the samples taken by a probe size of 2 nm, the specific spots of iron-borides, such as Fe3B and Fe23B6, were detected, suggesting the atomic arrangement of the compounds in the amorphous matrices.

DOI： 10.2355/tetsutohagane.TETSU-2019-032

Scopus

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=85073599358&origin=inward

記述言語：英語   掲載種別：研究論文（学術雑誌）   参加形態：共同（主担当）  

Pristine thin films of amorphous Ge prepared by sputtering are unstable and form coarse crystalline particles of 100 nm in size upon crystallization by electron irradiation. These crystalline particles exhibit unusual diffraction patterns that cannot be understood from the diamond cubic structure. The structure has previously been assumed to be a metastable hexagonal form. In the present work, the structure of the coarse crystalline particles has been analysed in detail by transmission electron microscopy, considering the possibility that those diffraction patterns might occur with the diamond cubic structure if the particle consists of thin twin layers. By high-resolution lattice imaging the particles have been shown to be of the diamond cubic structure containing a high density of twins and stacking faults parallel to {111}. With such defects, diffraction patterns can be complex because of the following effects: superposition of two or more diffraction patterns of the same structure but of different orientations, double diffraction through twin crystals, and streaks parallel to the thin crystal which give rise to extra diffraction spots. It is found that diffraction patterns taken from various orientations can be explained in terms of these effects.

DOI： 10.1107/S1600576718012153

Scopus

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=85054074132&origin=inward

記述言語：英語   掲載種別：研究論文（学術雑誌）   参加形態：共同（副担当）  

The low-temperature synthesis of high-Sn-concentration GeSn is challenging in realizing flexible thin-film transistors and solar cells. Because of athermal processes, irradiation with energetic particles is anticipated to significantly reduce the processing temperature for device fabrication. Here, we demonstrated that polycrystalline Ge with 30 at.% Sn can be realized at room temperature by the electron-beam-induced recrystallization of amorphous GeSn. We found that inelastic electronic stopping, the so-called electron excitation effect, plays an important role in the recrystallization of amorphous GeSn.

DOI： 10.7567/JJAP.56.100307

Scopus

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=85030646735&origin=inward

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）   参加形態：共同（主担当）  

Crystallization of amorphous germanium films induced by electron irradiation was investigated by in-situ transmission electron microscopy under a low electron-eneigy of 125 keV with various pre-Aging treatments at room temperature. Different microstructures were observed depending on the aging time: coarse and spherical nanoparticles grew rapidly in samples aged for less than 3 months, while a homogeneous nanociystalline structure with a grain size of about 10 nm appealed in samples aged for over 7 months. Analyses by the pair distribution lunction revealed that the initial structure is inhomogeneous, consisting of a mixture of amorphous regions and some ordered arrangements, but turned spontaneously to homogeneous random amorphous structures during aging. Such inhomogeneity could be an origin of the rapid growth of nanoparticles in the samples not subjected to the long-Time aging.

Scopus

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=85034443261&origin=inward

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）   参加形態：共同（副担当）  

DOI： 10.1017/S1431927617010893

記述言語：英語   掲載種別：研究論文（学術雑誌）   参加形態：共同（主担当）  

Following our previous studies on crystallization induced by electron irradiation, we have investigated the crystallization of sputter-deposited amorphous germanium films by heat treatments. On continuous heating, samples aged for 3 days and 4 months at room temperature crystallized at 500°C to form coarse spherical particles of a hexagonal structure, of about 100 nm in diameter, whereas samples aged for 7 months turned to homogeneous nanograins of the diamond cubic structure at 600°C. When the films aged for 4 months at room temperature were annealed at 350°C for 2 h and then heated, they crystallized at 550°C to form a mixture of the two microstructures, and those annealed at 350°C and further at 500°C for 1 h crystallized at 600°C mostly to nanograins. Crystallization by electron irradiation at 350°C to 4-month-aged samples has also been studied. With increasing annealing time at 350°C, coarse particles of a hexagonal structure ceased to appear, and were replaced by fine nanograins of the diamond cubic structure. These observations can be understood in terms of structural instability of sputter-deposited amorphous films. Medium-range ordered clusters must initially be present in the films and serve as nuclei of the metastable hexagonal phase. They are unstable, however, and are eliminated by annealing, resulting in the reduction in size and number of coarse particles with a metastable structure.

DOI： 10.1063/1.4972282

Scopus

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=85006829879&origin=inward

記述言語：英語   掲載種別：研究論文（学術雑誌）   参加形態：共同（主担当）  

We investigated the effect of low-flux electron irradiation with 125 keV to sputter-deposited amorphous germanium on the amorphous structure and electron-induced crystallization microstructure by TEM following our previous study on the effect of aging at room temperature. In samples aged for 3 days, coarse, spherical particles about 100 nm in diameter appear dominantly. By low-flux pre-irradiation to the samples, a reduction in the size and number of coarse particles, embedded in the matrix with fine nanograins of the diamond cubic structure, was noted with the increase in fluence. The crystal structure of these coarse particles was found to be not cubic but hexagonal. In samples aged for 4 months, a similar tendency was observed. In samples aged for 7 months, on the other hand, the homogeneous diamond cubic structured nanograins were unchanged by pre-irradiation. These results indicate that pre-irradiation as well as aging modifies the amorphous structure, preventing the appearance of a hexagonal phase. The elimination of a certain amount of medium-range ordered clusters by pre-irradiation, included in as-deposited samples and the samples aged for 4 months, apparently gives rise to a reduction in the size and number of coarse particles with a metastable hexagonal structure.

DOI： 10.1063/1.4964332

Scopus

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=84990853649&origin=inward

記述言語：英語   掲載種別：研究論文（学術雑誌）   参加形態：共同（主担当）  

The structure of amorphous Ge (a-Ge) films prepared by sputter-deposition and the effects of aging at ambient temperature and pressure were studied by pair-distribution-function (PDF) analysis from electron scattering and molecular dynamics simulations. The PDFs of the as-deposited and aged samples for 3-13 months showed that the major peaks for Ge-Ge bonds decrease in intensity and broaden with aging for up to 7 months. In the PDFs of a-Ge of molecular dynamics simulation obtained by quenching liquid at different rates, the major peak intensities of a slowly cooled model are higher than those of a rapidly cooled model. Analyses on short- and medium-range configurations show that the slowly cooled model includes a certain amount of medium-range ordered (MRO) clusters, while the rapidly cooled model includes liquid-like configurations rather than MRO clusters. The similarity between experimental and computational PDFs implies that as-deposited films are similar in structure to the slowly cooled model, whereas the fully aged films are similar to the rapidly cooled model. It is assumed that as they undergo room-temperature aging, the MRO clusters disintegrate and transform into liquid-like regions in the same matrix. This transition in local configurations is discussed in terms of instability and the non-equilibrium of nanoclusters produced by a vapor-deposition process.

DOI： 10.1063/1.4953234

Scopus

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=84974623840&origin=inward

記述言語：英語   掲載種別：研究論文（学術雑誌）   参加形態：共同（副担当）  

The anomalous hardening and microstructural evolution accompanied by the reordering and restoring of cold-rolled Co3Ti alloy annealed at 573-773K were investigated by hardness testing, SEM and TEM observations, XRD analysis and DSC measurements. The hardening observed in the heavily cold-rolled samples was similar to that observed in precipitation reactions, with the hardness increasing with increasing annealing time to a point and then decreasing. The hardness peak occurred more rapidly at higher annealing temperatures, and the annealing time leading to this peak was insensitive to the degree of cold-rolling reduction. The stored lattice strain evaluated from the half-width of the X-ray reflection peak steadily decreased with increasing annealing time but remained relatively high regardless of the degree of cold-rolling reduction or annealing temperature. The TEM deformation microstructures showed that a high density of dislocations was attained, even in an over-aged state. DSC measurements showed two exothermic peaks at low and high temperatures, which were attributed to the annihilation of point defects and/or reordering and to the rearrangement of dislocations, respectively. The observed anomalous hardening was discussed in association with the reordering of the mechanically disordered structure and the restoring of the plastically deformed microstructure.

DOI： 10.1016/j.msea.2014.10.035

Scopus

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=84910101387&origin=inward

記述言語：英語   掲載種別：研究論文（学術雑誌）   参加形態：共同（副担当）  

Hollow nanostructures are ranked among the top materials for applications in various modern technological areas including energy storage devices, catalyst, optics and sensors. The last years have witnessed increasing interest in the Kirkendall effect as a versatile route to fabricate hollow nanostructures with different shapes, compositions and functionalities. Although the conversion chemistry of nanostructures from solid to hollow has reached a very advanced maturity, there is still much to be discovered and learned on this effect. Here, the recent progress on the use of the Kirkendall effect to synthesize hollow nanospheres and nanotubes is reviewed with a special emphasis on the fundamental mechanisms occurring during such a conversion process. The discussion includes the oxidation of metal nanostructures (i.e., nanospheres and nanowires), which is an important process involving the Kirkendall effect. For nanospheres, the symmetrical and the asymmetrical mechanisms are both reviewed and compared on the basis of recent reports in the literature. For nanotubes, in addition to a summary of the conversion processes, the unusual effects observed in some particular cases (e.g., formation of segmented or bamboo-like nanotubes) are summarized and discussed. Finally, we conclude with a summary, where the prospective future direction of this research field is discussed.

DOI： 10.3762/bjnano.6.139

Scopus

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=84933046853&origin=inward

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）   参加形態：共同（副担当）  

To verify the assumption that the anelastic relaxation effect observed in Ni3Al is due to stress-induced reorientation of antisite Al atoms [Numakura and Nishi, Mater. Sci. Eng. A 442 (2006) 59-62], the magnitudes of the anisotropic distortion produced by the intrinsic point defects have been evaluated by ab initio calculations. The anisotropy of the λ tensor (the strain per unit concentration of a particular defect) for the two candidate defect species, namely a Ni vacancy and an antisite Al atom, has been computed by full structure optimization of a supercell containing a single point defect: the difference in the principal values is +0.46 and-1.12, respectively. The relaxation strength estimated for antisite Al atoms agrees fairly well with experiment, while that for Ni vacancies is far too small because of their much lower concentration. The relaxation is, therefore, conclusively attributed to antisite Al atoms.

DOI： 10.4028/www.scientific.net/DDF.363.101

Scopus

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=84960891802&origin=inward

記述言語：英語   掲載種別：研究論文（学術雑誌）   参加形態：共同（主担当）  

The self-diffusivity of oxygen in amorphous Al2O3 (a-Al2O3), a-Ta2O5, and a-Nb 2O5 was investigated along with structural analysis in terms of pair distribution function (PDF). The low activation energy, ∼1.2 eV, for diffusion in the oxides suggests a single atomic jump of oxygen ions mediated via vacancy-like defects. However, the pre-exponential factor for a-Ta2O5 and a-Nb2O5 with lower bond energy was two orders of magnitude larger than that for a-Al2O 3 with higher bond energy. PDF analyses revealed that the short-range configuration in a-Ta2O5 and a-Nb2O 5 was more broadly distributed than that in a-Al2O 3. Due to the larger variety of atomic configurations of a-Ta 2O5 and a-Nb2O5, these oxides have a higher activation entropy for diffusion than a-Al2O3. The entropy term for diffusion associated with short-range structures was shown to be a dominant factor for diffusion in amorphous oxides. © 2014 AIP Publishing LLC.

DOI： 10.1063/1.4889800

Scopus

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=84904655076&origin=inward

記述言語：英語   掲載種別：研究論文（学術雑誌）   参加形態：共同（主担当）  

Amorphous Ta-O nanotubes (NTs) prepared by anodization in a sulfuric-Acid-based solution have been found to contain considerable amounts of extra oxygen and sulfur. Their structural and thermal stability has been studied by combining x-ray diffractometry, transmission electron microscopy, and thermal analysis. The amorphous Ta-O, whose composition was estimated to be Ta2O6.6S0.7, crystallizes into orthorhombic β-Ta2O5 at temperatures around 1073 K by an endothermic reaction, at which excess oxygen and impurity sulfur are released. The amorphous NTs were found to be thermally more stable than stoichiometric amorphous Ta2O5, whose crystallization temperature is around 973 K. Excess oxygen and impurity sulfur, which form chemical bonds with Ta atoms in the amorphous solid, must be the origin of the stability. The crystallization follows the out-diffusion of oxygen and sulfur from the solid at temperatures where the mobility of atoms is high enough, indicating that the crystallization is kinetically arrested. Copyright © 2014 Materials Research Society.

DOI： 10.1557/jmr.2014.44

Scopus

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=84897408829&origin=inward

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）   出版者・発行元：Current Nanoscience   参加形態：共同（副担当）  

The formation of hollow Cu oxide nanoparticles through the oxidation process has been studied with Cu nanoparticles produced by the plasma arc discharge method. The initial copper nanoparticles had a size range of 40-60 nm and a thin Cu2O layer on the surface. After oxidation at 100°C, there was no significant change in the particles. After oxidation at 200°C, however, the particles consisted of Cu2O and CuO instead of metallic Cu. By further increasing the temperature up to 300°C, only CuO particles remained. The obtained CuO particles had a hollow structure which resulted from the Kirkendall effect. © 2014 Bentham Science Publishers.

DOI： 10.2174/1573413709666131108232654

Scopus

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=84894042636&origin=inward

記述言語：英語   掲載種別：研究論文（学術雑誌）   参加形態：共同（主担当）  

Formation of self-oriented and -elongated nanopores in annealed amorphous Nb2O5 and Ta2O5 was analyzed by transmission electron microscopy. Along with their crystal growth, nanopores were spontaneously elongated in the a-axis direction perpendicular to the longitudinal b axis of the orthorhombic structures with strong anisotropy. In addition, the effect of tungsten on the nanovoid formation in annealed amorphous Nb2O5 and Ta2O5 was also studied. Additive tungsten atoms of a few atomic percent into Nb2O5 and Ta2O5 were found to make the aspect ratio of nanopores larger. Electron diffraction experiments revealed that the crystallized regions including elongated nanopores possess a variety of periodicity in the b-axis direction. This structural flexibility in the crystal growth of strong anisotropic structures seems to play an important role on the unidirectional growth of nanopores. © 2013 AIP Publishing LLC.

DOI： 10.1063/1.4822300

Scopus

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=84885405481&origin=inward

記述言語：英語   掲載種別：研究論文（学術雑誌）   参加形態：共同（主担当）  

The electron-irradiation-induced crystallization of amorphous Al 2O3 (a-Al2O3) was investigated by in-situ transmission electron microscopy under the wide electron-energy region of 25-300 keV. The formation of γ-Al2O3 nanocrystallites was induced by irradiating the a-Al2O3 thin film along with the formation of nanovoids in the crystalline grains regardless of the acceleration voltage. The crystallization became more pronounced with decreasing the electron energy, indicating that electronic excitation processes play a dominant role in the formation of γ-Al 2O3. Radial distribution analyses suggested that a-Al 2O3 transforms to γ-phase via the "excited" ("stimulated") amorphous state, in which the breaking and rearrangement of unstable short-range Al-O bonds, i.e., fivefold-coordinated Al-O (AlO5) basic units, occur. © 2013 American Institute of Physics.

DOI： 10.1063/1.4790705

Scopus

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=84874332096&origin=inward

記述言語：英語   掲載種別：研究論文（学術雑誌）   参加形態：共同（主担当）  

Nanoporous Ta2O5 films with oriented and elongated nanopores have been prepared by a technique which utilizes the accumulation of free volume during the crystallization of amorphous Ta2O5 annealed above 973 K. The transmission electron microscopy analyses revealed that voids were elongated in the [1 0 0] direction perpendicular to the longitudinal b axis of the orthorhombic structure. The self-assembly of a significant amount of oriented nanovoids can be contributed to the strong anisotropic crystal structure of orthorhombic Ta2O5. © 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.scriptamat.2011.10.033

Scopus

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=82255192060&origin=inward

記述言語：英語   掲載種別：研究論文（学術雑誌）   参加形態：共同（主担当）  

The effect of W on the nanovoid formation in annealed amorphous Al 2O3 was studied by transmission electron microscopy and molecular dynamics simulations. A comparison of the void formation behavior in electron-beam deposited Al2O3 (without W) and resistance-heating deposited Al2O3 (with 10 at. W) revealed that W enhances the formation and growth of nanovoids. An analysis of the pair distribution function (PDF) in both types of amorphous Al 2O3 showed that the introduction of W into amorphous Al2O3 brings about a significant change in the amorphous structure. Furthermore, it was found by high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) that sub-nm sized W clusters exist in as-deposited Al2O3 prepared by resistance-heating and then dissolve in the amorphous matrix with annealing. The combination of PDF analysis and HAADF-STEM observation provides evidence that the enhancement of void formation originates in the heterogeneous short-range atomic configurations induced by the addition of W. © 2011 American Institute of Physics.

DOI： 10.1063/1.3639290

Scopus

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=80053537674&origin=inward

記述言語：英語   掲載種別：研究論文（学術雑誌）   参加形態：共同（副担当）  

The formation mechanism of a high density of nanovoids by annealing amorphous Al2O3 thin films prepared by an electron beam deposition method was investigated. Transmission electron microscopy observations revealed that nanovoids ∼1-2 nm in size were formed by annealing amorphous Al2O3 thin films at 973 K for 1-12 h, where the amorphous state was retained. The elastic stiffness, measured by a picosecond laser ultrasound method, and the density, measured by X-ray reflectivity, increased drastically after the annealing process, despite nanovoid formation. These increases indicate a change in the amorphous structure during the annealing process. Molecular dynamics simulations indicated that an increase in stable AlO6 basic units and the change in the ring distribution lead to a drastic increase in both the elastic stiffness and the density. It is probable that a pre-annealed Al2O3 amorphous film consists of unstable low-density regions containing a low fraction of stable AlO6 units and stable high-density regions containing a high fraction of stable AlO6 units. Thus, local density growth in the unstable low-density regions during annealing leads to nanovoid formation (i.e., local volume shrinkage). © 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.actamat.2011.04.008

Scopus

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=79956006968&origin=inward

記述言語：英語   掲載種別：研究論文（学術雑誌）   参加形態：共同（主担当）  

A high density of nanovoids between 2 and 13 nm in size was produced during the crystallization process when amorphous Al2O3 and WO3, which are 20-30% lower in density than their crystalline phases, were annealed. By contrast, no formation or growth of nanovoids was observed during the crystallization of amorphous TiO2, which has a density 2% lower than its crystalline phase. These results suggest that large differences in density between amorphous and crystalline oxides can be utilized to produce nanoporous structures. © 2010 Acta Materialia Inc. Published by Elsevier Ltd.

DOI： 10.1016/j.scriptamat.2010.09.043

Scopus

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=79251641923&origin=inward

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）   出版者・発行元：Materials Science Forum   参加形態：共同（主担当）  

Formation behavior of nanovoids during the annealing of amorphous Al 2O3 and WO3 was studied by transmission electron microscopy. The density and size of the voids in Al2O 3 and WO3 increase with increasing annealing temperature from 973 to 1123 K and from 573 to 673 K, respectively. It is suggested that the formation of nanovoids during annealing is attributed to the large difference in density between as-deposited amorphous and crystalline oxides. © (2011) Trans Tech Publications.

DOI： 10.4028/www.scientific.net/MSF.695.541

Scopus

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=80053272902&origin=inward

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）   出版者・発行元：Materials Science Forum   参加形態：共同（主担当）  

The formation mechanisms of hollow metal oxide through the oxidation of several metal nanoparticles have been studied by transmission electron microscopy. For Zn, Al, Cu, Ni and Fe nanoparticles, hollow oxide nanoparticles were obtained as a result of vacancy aggregation in the oxidation processes. The formation of the hollow morphology is attributed to the faster outward diffusion of metal ions through the oxide layer in the oxidation processes. Further changes in morphology during the annealing of hollow Cu, Ni and Fe oxides at higher temperatures in air were examined. © (2010) Trans Tech Publications.

DOI： 10.4028/www.scientific.net/MSF.638-642.67

Scopus

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=75849156891&origin=inward

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）   出版者・発行元：Materials Science Forum   参加形態：共同（主担当）  

The formation process of oxide nanotube via metal oxidation reaction was studied by transmission electron microscopy for Cu, Fe, and Ni nanowires. Cu2O and Fe3O4 nanotubes were formed after the oxidation of Cu and Fe nanowires with a diameter of 55 nm in air at 423 and 573 K for 3.6 ks, respectively. Both Cu2O and Fe3O4 nanotubes had a cylindrical interior pore with uniform diameter. On the other hand, Ni nanowires became bamboo-like structures of NiO with separate interior pores after oxidation at 673 K for 7.2 ks. The formation of the interior pores in Cu2O and Fe3O4 nanotubes and NiO bamboo-like structures can be explained by the rapid outward diffusion of metal ions through the oxide layers and the clustering of excess vacancies. © (2010) Trans Tech Publications.

DOI： 10.4028/www.scientific.net/MSF.658.232

Scopus

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=78649941242&origin=inward

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）   出版者・発行元：Materials Science Forum   参加形態：共同（主担当）  

Changes in morphology during the oxidation of iron nanoparticles and nanowires at 473∼ 873 K have been studied by transmission electron microscopy. Iron nanoparticles and wires become hollow nanoparticles and nanotubes of Fe3O4 at temperatures below 673 K as a result of vacancy aggregation in the oxidation process. On the other hand, the hollow magnetite transforms into duplex porous structures with an interior nanopore and additional nanovoids at higher temperatures above 673 K, where the shrinkage of hollow nanoparticles and nanotubes starts and the phase transformation from Fe3O4 to γ-Fe2O3 occurs. Transition in porous structure seems to be related to the outward diffusion of vacancies from interior pore and the phase transformation in the shrinkage process. © (2010) Trans Tech Publications,.

DOI： 10.4028/www.scientific.net/MSF.658.197

Scopus

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=78649978323&origin=inward

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）   出版者・発行元：Defect and Diffusion Forum   参加形態：共同（副担当）  

Reaction diffusion in liquid Pb free solder- and solid Pb free solder- pure Cu systems has been investigated in the temperature range between 397 K and 563 K. The Pb free solder of which composition is 95.7 mass% Sn, 2.8 mass% Ag, 1.0 mass% Bi and 0.5 mass% Cu and 99.99 mass% oxygen free Cu has been used. In the liquid Pb free solder-pure Cu system, as soon as the solder melted down, an intermetallic compound η phase formed preferentially, and grew with increasing diffusion time. Only the η phase exists in the experimental time up to 120 seconds. The layer thickness of the η phase obeyed the parabolic law. On the other hand, in the solid Pb free solder-pure Cu system two intermetallic compounds ε phase and η' phase form and grew with increasing diffusion time, although the ε phase forms after an incubation time at low temperature. The layer thickness of these intermetallic compounds obeyed the parabolic law. The growth rate of η' phase is greater than that of the ε phase. The growth kinetics of the intermetallic compounds and the diffusion behavior in the η' phase have been investigated. © (2010) Trans Tech Publications.

DOI： 10.4028/www.scientific.net/DDF.297-301.796

Scopus

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=77952296520&origin=inward

記述言語：英語   掲載種別：研究論文（学術雑誌）   参加形態：共同（主担当）  

Changes in the morphology of Fe, Cu and Ni nanowires with a diameter of 55 nm during oxidation at 423-923 K were studied by transmission electron microscopy. Oxide nanotubes with a cylindrical interior pore of uniform diameter were formed after the oxidation of Fe and Cu nanowires in air at 573 and 423 K, respectively, while the Ni nanowires became bamboo-like nanowires of NiO with separate interior voids after oxidation at 673-773 K. Oxide nanotubes of Fe and Cu and the bamboo structures of NiO showed a tendency to shrink into solid oxide nanowires after annealing at higher temperatures in air. In the shrinking process of Fe3O4 nanotubes, however, an array of additional nanovoids was observed along the inner wall of the nanotubes, suggesting the formation of a duplex porous nanostructure. This can be explained by the recombination of vacancies diffusing outward from the inner cylindrical pore. © 2009 Acta Materialia Inc.

DOI： 10.1016/j.actamat.2009.07.006

Scopus

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=69949115574&origin=inward

記述言語：英語   掲載種別：研究論文（学術雑誌）   参加形態：共同（主担当）  

Changes in morphology during the oxidation of iron nanoparticles and nanowires in the temperature range 473-873 K have been studied by transmission electron microscopy. Iron nanoparticles and wires become hollow nanoparticles and nanotubes of magnetite at temperatures below 673 K as a result of vacancy aggregation during the oxidation process, resulting from the outward diffusion of iron ions through the magnetite layer. On the other hand, the hollow magnetite transforms into duplex porous structures with an interior nanopore and additional nanovoids at higher temperatures above 673 K, where the inner and outer diameters of magnetite nanotubes shrink and the phase transformation from magnetite to maghemite occurs. Transition in the porous structure seems to be related to the outward diffusion of vacancies from interior pore and the phase transformation from magnetite to maghemite. © 2009 Acta Materialia Inc.

DOI： 10.1016/j.actamat.2009.05.023

Scopus

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=67650168877&origin=inward

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）   出版者・発行元：Journal of Nano Research   参加形態：共同（主担当）  

In intermetallic compounds, random vacancy motion is not possible as it would disrupt the equilibrium ordered arrangement of atoms on lattice sites. In view of this limitation, various atomistic models have been proposed, which allow atom-vacancy exchanges to take place without concomitant long range disordering. For a L12 -type A3 B structure, the major element A diffuses faster than the minor element B. The trend is attributed to the different diffusing paths; A atoms can diffuse through site exchanges with a neighbouring vacancy on its own sublattice, while the jump of a B atom to a neighbouring site always creates wrong bonds. For L10-type structures such as γ-TiAl, significant diffusion anisotropy is observed; Ti atoms diffuse on the Ti sublattice, while Al atoms also diffuse on the Ti sublattice. The formation of hollow metal oxide nanoparticles through the oxidation process has been studied by transmission electron microscopy for Cu, Zn, Al, Pb and Ni. The hollow structure is obtained as a result of vacancy aggregation, resulting from the rapid outward diffusion of metal ions through the oxide layer during the oxidation process. This suggests the occurrence of two different diffusion processes in the formation of hollow oxides.

DOI： 10.4028/www.scientific.net/JNanoR.7.1

Scopus

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=74949144093&origin=inward

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）   出版者・発行元：Defect and Diffusion Forum   参加形態：共同（主担当）  

The formation of hollow metal oxide nanoparticles through oxidation process has been studied by transmission electron microscopy for Cu, Zn, Al, Pb and Ni in order to clarify the detailed formation mechanism of hollow oxide nanoparticles and their governing factors. For Cu, Zn, Al and Ni nanoparticles, hollow oxide nanoparticles are obtained as a result of vacancy aggregation in the oxidation processes. These results arise from faster outward diffusion of metal ions through the oxide layer in the oxidation processes. On the other hand, Pb nanoparticles turn to solid PbO, because the diffusivity difference DPb < DO in PbO leads to no formation of vacancy clusters. © (2009) Trans Tech Publications.

DOI： 10.4028/www.scientific.net/DDF.289-292.649

Scopus

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=75949119398&origin=inward

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）   参加形態：共同（主担当）  

The structural stability of hollow Cu2O and NiO nanoparticles, which were obtained via oxidation of Cu and Ni nanoparticles in air, was studied by transmission electron microscopy (TEM). Hollow Cu2O and NiO were observed to have shrunk at 473 and 623 K in annealing under 5.0×10 -5 Pa, respectively, where the reduction reactions from oxides to metals started. As a result of shrinking associated with reduction, hollow oxides turned into solid metal nanoparticles after annealing at higher temperatures for a long time. In addition, hollow oxides shrunk and collapsed through high-temperature oxidation. It was found that shrinking of hollow oxides during oxidation occurs at temperature where the diffusion coefficients of slower diffusing species reach around 10-22 m2s -1. It seems that the hollow oxide nanoparticles tend to shrink and collapse at high temperatures because the hollow structures are energetically unstable. © (2009) Trans Tech Publications.

DOI： 10.4028/www.scientific.net/DDF.289-292.673

Scopus

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=75949118945&origin=inward

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）   参加形態：共同（主担当）  

The structural stability of hollow Cu2O and NiO nanoparticles, which were obtained via oxidation of Cu and Ni nanoparticles in air, was studied by transmission electron microscopy (TEM). Hollow Cu2O and NiO were observed to have shrunk at 473 and 623 K in annealing under 5.0×10 -5 Pa, respectively, where the reduction reactions from oxides to metals started. As a result of shrinking associated with reduction, hollow oxides turned into solid metal nanoparticles after annealing at higher temperatures for a long time. On the other hand, hollow oxides shrunk and collapsed through annealing in air at high temperatures. It was found that shrinking of hollow oxides during annealing in air occurs at temperature where the diffusion coefficients of slower diffusing species reach around 10 -22 m2s-1. We can conclude that hollow oxide nanoparticles tend to shrink and collapse at high temperatures because hollow structures with extra surface energy are energetically unstable. © 2009 IOP Publishing Ltd.

DOI： 10.1088/1742-6596/165/1/012072

Scopus

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=67651006088&origin=inward

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）   参加形態：共同（主担当）  

Formation of hollow oxides via the oxidation of Cu and Ni nanoparticles has been investigated by transmission electron microscopy. Hollow Cu2O was formed after the oxidation of Cu nanoparticles with around 40 run in diameter at around 350 K in air, while hollow NiO was obtained by oxidizing Ni nanopartciles with around 50 run at 673 K. Since the diffusion coefficients of metal ions are much larger than those of oxygen ions in Cu2O and NiO, the Kirkendall effect at the metal/oxide interface, where metal diffuses much faster than oxygen, brings about the generation of supersaturated vacancies in the metal side. As a result of vacancy clustering during oxidation reaction, a nano-pore is introduced in the metal oxide particle. In this paper, formation behavior of voids and nano-pores in the oxidation of Cu and Ni nanoparticles will be discussed on the basis of the diffusion properties of metals and their oxides.

Scopus

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=56549106963&origin=inward

記述言語：英語   掲載種別：研究論文（学術雑誌）   参加形態：共同（主担当）  

The structural stability of hollow Cu2O and NiO nanoparticles associated with reduction and oxidation reactions at high temperatures was studied by transmission electron microscopy (TEM). Hollow Cu2O and NiO in annealing under 5.0 × 10-5 Pa was observed to have shrunk at 473 and 623 K, respectively, where the reduction reactions from oxides to metals started. As a result of shrinking associated with reduction, hollow oxides turned into solid metal nanoparticles after annealing at higher temperatures for a long time. In addition, hollow oxides shrunk and collapsed through high-temperature oxidation. It was found that shrinking of hollow oxides during oxidation occurs at temperature where the diffusion coefficients of slower diffusing species reach around 10-22 m2 s-1. Annealing at high temperatures both in a vacuum and in air leads to atomic movement that results in the annihilation of nano-holes inside hollow nanoparticles, and a consequent reduction in the extra inner-surface energy. © 2008 Acta Materialia Inc.

DOI： 10.1016/j.actamat.2008.07.004

Scopus

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=53049105765&origin=inward

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）   参加形態：共同（主担当）  

The formation of hollow zinc oxide has been studied by oxidation and subsequent thermal treatment of nanometer-sized zinc particles using in-situ TEM. The zinc particles produced under UHV condition were exposed to air at room temperature for 0.6 ks, which resulted in the formation of oxide layer with thickness of 3 nm. Subsequent heating inside UHV chamber of TEM induced the evaporation of the inner zinc, which resulted in the formation of hollow zinc oxide. The produced hollow zinc oxide had the wurtzite structure. Based upon the vapor pressure of the inner zinc, it seems reasonable to consider that the internal zinc vapor leaks away through the interface between the oxide layer and the amorphous carbon film used as a supporting substrate.

DOI： 10.4028/3-908451-48-5.11

Scopus

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=45749098239&origin=inward

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Philosophical Magazine   参加形態：共同（主担当）  

The oxidation behaviour of Ni nanoparticles at temperatures from 573 to 673 K and the formation process of hollow oxide particles were studied by transmission electron microscopy. In the course of oxidation, a single large void was observed at one site of the interface between inner Ni and outer NiO layer due to vacancy clustering, which occurs during the oxidation process resulting from the rapid outward diffusion of Ni ions through the NiO layer. This suggests that supersaturated vacancies generated at the interface migrate to the site over a long-range distance and aggregate at the site. Ni nanoparticles were fully oxidized to become hollow NiO, in which nano-holes in the form of vacancy clusters were located at the off-centred positions. The de-centring of the voids in hollow NiO is probably due to the large mobility of vacancies inside Ni during oxidation.

DOI： 10.1080/14786430701819203

Scopus

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=38349126040&origin=inward

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）   出版者・発行元：TMS Annual Meeting   参加形態：共同（主担当）  

The formation of hollow metal oxide nanoparticles through oxidation process at low temperatures from 295 to 423 K has been studied by transmission electron microscopy for Cu, Zn, Al, and Pb. For Cu, Zn, and Al nanoparticles, hollow oxide nanoparticles are obtained as a result of vacancy aggregation in the oxidation processes. These results arise from faster outward diffusion of metal ions through the oxide layer in the oxidation processes. On the other hand, Pb nanoparticles turn to solid PbO, because the diffusivity difference D pb < Do in PbO leads to no formation of vacancy clusters. The oxide growth behavior on Cu, Zn, and Al nanoparticles with a larger size are summarized as follow; (i) for Zn and Al, the growth of oxide layer stops after the oxide layer with the critical thickness of about 7 and 1.5 nm are rapidly formed on their surfaces, respectively, (ii) the growth of Cu2O continues until hollow Cu2O with a certain thickness is completed. It seems that in the case of Zn and Al, rapid outward diffusion of metal ions based on the Cabrera-Mott theory plays an important role on the formation of hollow oxides. On the other hand, the Kirkendall effect at the Cu/Cu2O interface, where Cu diffuses much faster than oxygen, brings about the formation of hollow Cu2O.

Scopus

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=40749127916&origin=inward

記述言語：英語   掲載種別：研究論文（学術雑誌）   参加形態：共同（主担当）  

The growth of a Cu2O layer on Cu nanoparticles at 323-373 K was investigated by tiansmission electron microscopy to elucidate the influence of voids formed at the Cu/Cu2O interface on the oxidation rate. The thickness of the Cu2O formed on Cu nanoparticles with an initial diameter of 10 to ∼35 nm was measured as a function of oxidation time. During the initial oxidation stage until the oxide film is about 2.5 nm thick, the oxide film on nanoparticles of 10 to ∼35 nm in diameter grows rapidly at an almost consistent rate. After that, however, the growth rate of smaller nanoparticles decreases drastically compared with that of larger ones, suggesting that the voids formed near the Cu/Cu2O interface prevent Cu atoms from diffusing outward, because the volume ratio of voids to inner Cu in the case of smaller nanoparticles is considerably higher than that for larger ones at the same oxidation time. © 2007 Materials Research Society.

DOI： 10.1557/jmr.2007.0362

Scopus

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=35448998483&origin=inward

記述言語：英語   掲載種別：研究論文（学術雑誌）   参加形態：共同（主担当）  

The formation of hollow metal oxide nanoparticles through the oxidation process at low temperatures from 295 to 423 K has been studied by transmission electron microscopy for Cu, Al, and Pb. For Cu and Al, hollow oxide nanoparticles are obtained as a result of vacancy aggregation in the oxidation processes, resulting from the rapid outward diffusion of metal ions through the oxide layer during the oxidation process. On the other hand, Pb nanoparticles turn to solid PbO because the diffusivity difference Dpb, < D o in PbO does not lend itself to the formation of vacancy clusters. The oxide growth behavior of Cu and Al nanoparticles of a larger size at 423 K are summarized as follows: (i) for Al, the rapidly forming oxide layer on its surface stops growing once it reaches a critical thickness of about 1.5 nm, (ii) the growth of Cu2O continues until hollow Cu2O of a certain thickness is formed. This suggests the occurrence of two different diffusion processes in the formation of hollow oxides: the rapid outward diffusion of metal ions based on the Cabrera-Mott theory plays an important role in the formation of hollow Al-oxides, whereas the Kirkendall effect at the Cu/Cu2O interface, where Cu diffuses much faster than oxygen, brings about the formation of hollow Cu2O. © 2007 American Institute of Physics.

DOI： 10.1063/1.2711383

Scopus

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=34247273583&origin=inward

記述言語：英語   掲載種別：研究論文（学術雑誌）   参加形態：共同（主担当）  

The formation of vacancy complexes through aging heat treatments between 800 and 1200 K was studied for rapidly solidified NiAl and CoAl ribbons using TEM. In the case of the NiAl ribbons, the density of dislocations decreased with increasing annealing temperature, while voids with tens to a hundred nanometers in size were formed in a low density. In the CoAl ribbons, noteworthy microstructures of dislocations and voids appeared after annealing. A zone consisting of dislocation loops, in which prismatic loops 20-50 nm in diameter had formed at high density, was found in the CoAl ribbons annealed at 800 K for 360 ks. On the other hand, voids with a size of several nanometers and a remarkably high density were formed by annealing not only at 800 K but also at 1200 K, suggesting that the growth rate of voids is extremely low because of low diffusivity in CoAl. © 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.msea.2006.07.030

Scopus

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=33847183814&origin=inward

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Materials Letters   参加形態：共同（主担当）  

The hollow phenomenon with the oxidation of Zn nanoparticles was studied by transmission electron microscopy. Hollow ZnO was formed by oxidizing Zn nanoparticles with the diameter less than 20 nm at 423 K for 3.6 ks. Nano-hole in the center of ZnO can be considered as a vacancy cluster, which is formed as the result of the generation and aggregation of vacancies due to faster outward diffusion of Zn across ZnO in air at the initial oxidation stage. © 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.matlet.2006.06.039

Scopus

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=33845979500&origin=inward

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）   出版者・発行元：Materials Science Forum   参加形態：共同（主担当）  

Formation of hollow structure through oxidation of Al nanoparticles was studied by applying transmission electron microscopy. Al nanoparticles 6-8 nm in diameter were observed to become hollow particles after having been exposed to air at 295 K for a few minutes. An analysis of the Debye-Sherrer rings in the selected area diffraction patterns before and after oxidation showed that hollow oxide nanoparticles are amorphous. The formation mechanisms of hollow oxide are discussed based on the low-temperature oxidation mechanism of Al and on the comparison with our previous results of hollow ZnO formation via oxidation of Zn nanoparticles.

DOI： 10.4028/0-87849-431-6.347

Scopus

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=38349095111&origin=inward

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）   出版者・発行元：Materials Science Forum   参加形態：共同（主担当）  

Oxidation behavior of Cu nanoparticles in the formation process of hollow Cu2O spheres was investigated by TEM. The thickness of Cu 2O layers on Cu nanoparticles oxidized at 323 K in air was measured as a function of oxidation time. At the initial stage of oxidation until the oxide film with 2.5 nm in thickness is formed, the thickness of oxide films on Cu nanoparticles with the diameter of 10, 20 and 35 nm shows a nearly equal value regardless of diameter of Cu. After the formation of 2.5 nm layer, however, the growth rate of the oxide films on smaller nanoparticles becomes slower than that on larger nanoparticles. This result suggests that the voids formed at the Cu/Cu2O interface prevent Cu atoms from diffusing outward across the interface because the volume ratio of voids to inner Cu in smaller nanoparticles is much larger than that in larger nanoparticles.

DOI： 10.4028/0-87849-462-6.1703

Scopus

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=38349178443&origin=inward

記述言語：英語   掲載種別：研究論文（学術雑誌）   参加形態：共同（副担当）  

The surface morphology of B2-structured FeAl single crystals is modified on a nanoscale by the absorption process of supersaturated thermal vacancies. A high density of nano to mesoscale surface pores is successfully produced by the vacancy absorption process through water quenching, surface treatments, and aging heat treatment. Their shape, size, and density can be controlled by varying the surface orientation of single crystals, quenching temperature, aging temperature, and aging time. These results suggest that surface self-patterning by the vacancy absorption process is a useful bottom-up technique for obtaining nanoscale surface patterns in metallic materials. © 2006 American Institute of Physics.

DOI： 10.1063/1.2245215

Scopus

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=33747468639&origin=inward

記述言語：英語   掲載種別：研究論文（学術雑誌）   参加形態：共同（主担当）  

Annihilation stages of lattice defects induced into LaNi5 during hydrogenation were analyzed by differential scanning calorimetry from 300 to 1200 K. Five irreversible exothermic peaks were observed. They correspond to the annihilation of vacancy clusters at lower temperatures and of dislocations at higher temperatures in LaNi5. © 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jallcom.2005.03.112

Scopus

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=32944465750&origin=inward

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）   参加形態：共同（副担当）  

The effect of heat treatments (aging or annealing) on microstructure was investigated for rapidly solidified ribbons of near-stoichiometric TiCo. In as-spun ribbons, it was observed by TEM that an equiaxed grain structure was developed and its crystal structure had been already B2-ordered, while a small amount of a second phase, Ti2Co, finely disperses in grains and along grain boundaries. Some grains were dislocation-free but others contained curved or helical dislocations and prismatic loops having a Burgers vector parallel to 〈100〉 directions. By annealing the as-spun ribbons at 700°C for 24h, the dislocation density was obviously increased compared with that of the as-spun ribbons, while grain growth appears to occur slightly. The increase of the dislocation density in the annealed ribbons is believed to result from the condensation and/or absorption of supersaturated vacancies. Therefore, the TEM observation results indicate that a large amount of supersaturated thermal vacancies were retained in the TiCo ribbons by the rapid solidification. © 2005 Materials Research Society.

Scopus

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=23844478244&origin=inward

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）   出版者・発行元：Materials Research Society Symposium Proceedings   参加形態：共同（主担当）  

Relaxation behavior of supersaturated vacancies in water-quenched and rapidly solidified B2 type CoAl and NiAl with the stoichiometric composition was studied by differential scanning calorimetry (DSC). In both CoAl and NiAl quenched from 1773 K, a single exothermic peak due mainly to the recovery of supersaturated vacancies appeared near 950 K. On the other hand, the exothermic peak was also observed in as-spun rapidly solidified CoAl and NiAl ribbons, and the temperature range of the peak was much broader than that of quenched-in bulks, suggesting that the peak in the rapidly solidified ribbons results from not only a single recovery process of vacancies but also those of some other lattice defects. TEM observation showed that a large amount of dislocations were introduced in the NiAl ribbon and that comparatively many voids as well as an amount of dislocations were introduced in the CoAl ribbon. © 2005 Materials Research Society.

Scopus

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=23844486754&origin=inward

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：日本金属学会   参加形態：共同（副担当）  

Experimental techniques for precise determination of low tracer diffusion coefficients in solid metals and alloys using radioisotopes are reviewed. Sputter-microsectioning method is most useful to measure submicron diffusion profiles at low temperatures. Measurements of tracer diffusivity along grain boundaries and dislocations in iron and stainless steels from the analysis of type C kinetics as well as type B kinetics are discussed. © 2005 The Japan Institute of Metals.

DOI： 10.2320/jinstmet.69.321

Scopus

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=20944441971&origin=inward

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Intermetallics   参加形態：共同（主担当）  

The self-diffusion coefficient of 57Co in B2 type intermetallic compound CoAl at the concentrations of 42, 46, 50 and 52 at.% Al has been determined in the temperature range between 1250 and 1630 K by use of the serial radio-frequency sputter-microsectioning technique. The diffusion coefficient of cobalt, D*Co, decreases with increase in Al concentration from the Co-rich composition to the stoichiometry, while D*Co in Al-rich Co-52 at.% Al alloy is almost equal to that at the stoichiometry. At higher temperature region above 0.8 Tm (T m: melting temperature of alloys), D*Co deviates upward largely from the Arrhenius line, suggesting that the diffusion mechanism changes with increasing temperature from the monovacancy to the divacancy mechanism. © 2004 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.intermet.2004.07.040

Scopus

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=10444228895&origin=inward

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）   参加形態：共同（主担当）  

Activation volume for interdiffusion, ΔṼ, in B2 type intermetallic compounds NiAl (40 ∼ 49 at%Al) and FeAl (40 ∼ 50 at%Al) has been obtained above 0.75 Tm (Tm: melting temperature of alloys) by measuring the interdiffusion coefficient under the pressure from 0.1 MPa to 5 GPa. ΔṼ in NiA1 shows almost constant value of 1.0 V0 (V0 : molar volume of alloys), suggesting that the divacancy mechanism is dominant at higher temperature region. On the other hand, ΔṼ in FeA1 increases from 0.6 to 0.8∼0.9 V0 with increasing temperature, showing that the contribution of divacancies to diffusion increases with increasing temperature. Diffusion mechanisms in NiAl and FeAl have been discussed with the help of our experimental data on intrinsic diffusion in them.

DOI： 10.4028/www.scientific.net/ddf.237-240.364

Scopus

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=30844458844&origin=inward

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）   参加形態：共同（副担当）  

Interdiffusion in Fe/Pt multi-phase diffusion couples has been investigated in the range from 1173 to 1473 K. Interdiffusion coefficients, D were determined by the Boltzmann-Matano analysis. At 1473 K. The values of interdiffusion coefficients in Pt3Fe and FePt phases coincide well with those determined from single-phase diffusion couples. The extrapolated value of the interdiffusion coefficients at NFe=0 coincides with the impurity diffusion coefficient of Fe in Pt at 1473 K. However, the extrapolated values of interdiffusion coefficients at NFe=l is much smaller than the impurity diffusion coefficient of Pt in Fe. On the other hand, the interdiffusion coefficients obtained in both Pt3Fe and FePt at lower temperatures are much larger than those determined by single-phase diffusion couples. It is supposed that the interface reaction or short circuit diffusion such grain boundary diffusion in multi-phase diffusion couple predominated.

DOI： 10.4028/www.scientific.net/ddf.237-240.426

Scopus

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=30744477995&origin=inward

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）   参加形態：共同（副担当）  

Substructure development through aging and annealing treatments was studied for rapidly solidified TiCo ribbons using TEM. In as-spun ribbons, equiaxed grain structure was developed and its crystal structure was B2-ordered immediately after melt-spinning, while a small amount of fine precipitates existed as second phase. Some grains were dislocation-free but others contained a certain amount of curved or helical dislocations and loops. The dislocation density in the ribbons annealed at 700°C for 24 h was obviously higher than those in the as-spun ribbons and the ribbons aged at 200°C for 100 h. The increase of the dislocation density in the annealed ribbons would result from the absorption of excess vacancies. Therefore, the obtained results indicated that a large amount of supersaturated thermal vacancies were retained in TiCo as-spun ribbons by the rapid solidification. © 2005 Trans Tech Publications, Switzerland.

DOI： 10.4028/0-87849-960-1.849

Scopus

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=17144416523&origin=inward

記述言語：英語   掲載種別：研究論文（学術雑誌）   参加形態：共同（主担当）  

The activation volume ΔṼ for interdiffusion in bcc ordered and disordered phases of the Fe-Al system has been determined in the temperature range from 1173 to 1473 K by measuring the pressure dependence of the interdiffusion coefficient. ΔṼ in the concentration range from 10 to 20 at.% Al of the bcc disordered phase is found to have an almost constant value of (0.40-0.45) V0 (V0 is the molar volume of the alloys) against temperature, which corresponds to the lower limit for the monovacancy mechanism in bcc pure metals or random alloys. On the other hand, the value of ΔṼ in the B2 FeAl phase increases with increasing temperature from 0.60V0, the upper limit for the monovacancy mechanism, to (0.80-0.90)V0, suggesting that divacancies contribute substantially to the diffusion at higher temperatures and in the off-stoichiometric region.

DOI： 10.1080/14786430410001664492

Scopus

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=3142724937&origin=inward

記述言語：英語   掲載種別：研究論文（学術雑誌）   参加形態：共同（主担当）  

The intrinsic diffusivities of both components and the activation volume for interdiffusion in the B2 type NiAl phase have been measured in the high temperature region from 1473-1773 K. The activation volume for interdiffusion in 40-49 at% Al is found to be almost constant value of 1.0 V0 (V0: molar volume of alloys) at 1473-1773 K, suggesting that divacancies contribute to the diffusion. Near 43 at% Al, the diffusion mechanism for Al atoms is most likely the triple defect mechanism with the activation energy of 320 kJmol-1, while that of Ni atoms is probably the anti-structure bridge mechanism with the smaller activation energy of 240 kJmol-1. However, at 50.5 at% Al, Al atoms diffuse by the nearest neighbor mechanism with the smaller activation energy (260 kJmol-1), whereas Ni atoms diffuse probably by the next nearest neighbor jump related to the triple defect with the larger activation energy (360 kJmol-1). © 2003 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.

DOI： 10.1016/S1359-6454(03)00210-6

Scopus

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=0037774718&origin=inward

記述言語：英語   掲載種別：研究論文（学術雑誌）   参加形態：共同（主担当）  

The self-diffusion coefficient of Aluminium in the B2-type intermetallic compound Fe-48 at.% Al was determined. The self-diffusion coefficient of Al in Fe-48 at.% Al was estimated to be a factor of about 0.6 smaller than that of Fe. The activation energy for the self-diffusion of Al was found to be 280 kJ mol-1, which is a little larger than the value of 262 kJ mol -1 for the self-diffusion of Fe.

DOI： 10.1080/0141861021000055655

Scopus

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=0242285523&origin=inward

記述言語：英語   掲載種別：研究論文（学術雑誌）   参加形態：共同（主担当）  

Interdiffusion coefficient in the B2 FeAl phase at 46-50 at%Al has been measured in the temperature range from 1173 to 1473 K under the pressure from 0.1 MPa to 5 GPa. The activation volume for interdiffusion, ΔV̄, derived from the pressure dependence of interdiffusion coefficient is found to be 0.58-0.90Vm (Vm: molar volume of alloys), which is comparable to or larger than 0.4-0.6Vm for the monovacancy mechanism in bcc pure metals or random alloys. The value of ΔV̄ increases with increasing temperature and also with deviating from stoichiometry, suggesting that divacancy contributes to the diffusion in higher temperatures and in the region of off-stoichiometry.

DOI： 10.2320/matertrans.44.78

Scopus

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=0037230852&origin=inward

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Intermetallics   参加形態：共同（主担当）  

Interdiffusion coefficients, D̃, in the B2 type NiAl, CoAl and FeAl phases have been determined by single phase diffusion couples over a wide temperature range from 1073 to 1773 K. The value of D̃ in the NiAl and CoAl phases shows a minimum at about 47 at.% Al deviating slightly from the stoichiometric composition, while the value of D̃ in the FeAl phase has a weak minimum at about 41 at.% Al. The value of the activation energy, Q̃, for interdiffusion in the NiAl and CoAl phases shows a maximum at about 47 at.% Al, where the value of Q̃ in the CoAl phase is much higher than that in the NiAl phase, while the value of Q̃ in the FeAl phase is nearly constant and much lower than those in the other two phases. It is observed that the larger the lattice constant of the compounds becomes, the lower the activation energy for diffusion in the compounds becomes. Thus, the magnitude of activation energy for diffusion in the B2 type NiAl, CoAl and FeAl is probably related to the lattice constant of the compounds. Using the interdiffusion coefficient and the tracer diffusion coefficients of Ni and Fe with the help of Darken's relation, the diffusion coefficient of Al in the NiAl and FeAl phases has been estimated. © 2002 Published by Elsevier Science Ltd. All rights reserved.

DOI： 10.1016/S0966-9795(01)00125-X

Scopus

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=0036466785&origin=inward

記述言語：日本語   掲載種別：記事・総説・解説・論説等（商業誌、新聞、ウェブメディア）   出版者・発行元：アグネ技術センター   参加形態：共同（主担当）  

記述言語：日本語   掲載種別：速報，短報，研究ノート等（学術雑誌）   出版者・発行元：日本金属学会   参加形態：共同（主担当）  

DOI： 10.2320/materia.47.368

記述言語：日本語   掲載種別：記事・総説・解説・論説等（商業誌、新聞、ウェブメディア）   出版者・発行元：アグネ技術センター   参加形態：共同（主担当）  

記述言語：日本語   掲載種別：速報，短報，研究ノート等（学術雑誌）   出版者・発行元：日本金属学会   参加形態：共同（副担当）  

DOI： 10.2320/materia.39.497

記述言語：日本語   会議種別：口頭発表（招待・特別）  

記述言語：日本語   会議種別：口頭発表（一般）  

記述言語：日本語   会議種別：口頭発表（招待・特別）