研究者詳細 - 仲村　龍介

論文 - 仲村　龍介

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Crystallization of sputter-deposited amorphous Ge films by electron irradiation: Effect of low-flux pre-irradiation 査読国際誌

Okugawa M., Nakamura R., Ishimaru M., Yasuda H., Numakura H.

Journal of Applied Physics 120 ( 13 ) 134308.1 - 134308.7 2016年10月

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

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Structural transition in sputter-deposited amorphous germanium films by aging at ambient temperature 査読国際誌

Okugawa M., Nakamura R., Ishimaru M., Watanabe K., Yasuda H., Numakura H.

Journal of Applied Physics 119 ( 21 ) 214309.1 - 214309.7 2016年6月

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

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Anomalous hardening and microstructural evolution accompanied by reordering and restoring of plastically deformed Co<inf>3</inf>Ti 査読国際誌

Oka T., Kaneno Y., Semboshi S., Nakamura R., Takasugi T.

Materials Science and Engineering A 620 411 - 419 2015年1月

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

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The Kirkendall effect and nanoscience: Hollow nanospheres and nanotubes 招待査読国際誌

El Mel A.A., Nakamura R., Bittencourt C.

Beilstein Journal of Nanotechnology 6 ( 1 ) 1348 - 1361 2015年1月

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

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Theoretical evaluation of anisotropic distortion associated with point defects in ordered compounds 査読国際誌

Maaouia S., Ryusuke N., Hiroshi N.

Defect and Diffusion Forum 363 101 - 105 2015年1月

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

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Diffusion of oxygen in amorphous Al2O3, Ta2O5, and Nb2O5 査読国際誌

Nakamura R., Toda T., Tsukui S., Tane M., Ishimaru M., Suzuki T., Nakajima H.

Journal of Applied Physics 116 ( 3 ) 033504.1 - 033504.8 2014年7月

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

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Stability of amorphous Ta-O nanotubes prepared by anodization: Thermal and structural analyses 査読国際誌

Nakamura R., Asano K., Ishimaru M., Sato K., Takahashi M., Numakura H.

Journal of Materials Research 29 ( 6 ) 753 - 760 2014年3月

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

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Formation of hollow Copper Oxide by oxidation of Cu nanoparticles 査読国際誌

Lee J.G., Nakamura R., Choi Y.S., Yu J.H., Choi C.J.

Current Nanoscience 10 ( 1 ) 101 - 103 2014年1月

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

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Formation of highly oriented nanopores via crystallization of amorphous Nb2O5 and Ta2O5 査読国際誌

Nakamura R., Ishimaru M., Sato K., Tanaka K., Nakajima H., Konno T.J.

Journal of Applied Physics 114 ( 12 ) 124308.1 - 124308.8 2013年9月

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

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Atomic rearrangements in amorphous Al2O3 under electron-beam irradiation 査読国際誌

Nakamura R., Ishimaru M., Yasuda H., Nakajima H.

Journal of Applied Physics 113 ( 6 ) 064312.1 - 064312.7 2013年2月

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

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Self-elongated growth of nanopores in annealed amorphous Ta2O5 films 査読国際誌

Nakamura R., Tanaka K., Ishimaru M., Sato K., Konno T.J., Nakajima H.

Scripta Materialia 66 ( 3-4 ) 182 - 185 2012年2月

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

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Enhancement of nanovoid formation in annealed amorphous Al2O3 including W 査読国際誌

Nakamura R., Ishimaru M., Hirata A., Sato K., Tane M., Kimizuka H., Shudo T., Konno T.J., Nakajima H.

Journal of Applied Physics 110 ( 6 ) 064324.1 - 064324.7 2011年9月

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

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Nanovoid formation by change in amorphous structure through the annealing of amorphous Al2O3 thin films 査読国際誌

Tane M., Nakano S., Nakamura R., Ogi H., Ishimaru M., Kimizuka H., Nakajima H.

Acta Materialia 59 ( 11 ) 4631 - 4640 2011年6月

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

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Nanovoid formation through the annealing of amorphous Al2O3 and WO3 films 査読国際誌

Nakamura R., Shudo T., Hirata A., Ishimaru M., Nakajima H.

Scripta Materialia 64 ( 2 ) 197 - 200 2011年1月

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

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TEM analysis on nanovoid formation in annealed amorphous oxides 査読国際誌

Nakamura R., Shudo T., Hirata A., Ishimaru M., Nakajima H.

Materials Science Forum 695 541 - 544 2011年1月

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

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Fabrication of hollow nano particles of metallic oxides through oxidation process 招待査読国際誌

Nakajima H., Nakamura R.

Materials Science Forum 638-642 67 - 72 2010年1月

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

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Reaction diffusion in Pb free solder-Cu system 査読国際誌

Taguchi O., Lee C.G., Park D.Y., Shin G.S., Suzuki S., Nakamura R.

Defect and Diffusion Forum 297-301 796 - 801 2010年1月

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

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Formation of oxide nanotubes and bamboo-like structures via oxidation of Cu, Fe and Ni nanowires 査読国際誌

Matsubayashi G., Nakamura R., Tsuchiya H., Fujimoto S., Nakajima H.

Materials Science Forum 658 232 - 235 2010年1月

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

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Formation of hollow and porous nanostructures of iron oxides via oxidation of iron nanoparticles and nanowires 査読

Nakamura R., Nakajima H.

Materials Science Forum 658 197 - 200 2010年1月

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

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Formation of oxide nanotubes via oxidation of Fe, Cu and Ni nanowires and their structural stability: Difference in formation and shrinkage behavior of interior pores 査読国際誌

Nakamura R., Matsubayashi G., Tsuchiya H., Fujimoto S., Nakajima H.

Acta Materialia 57 ( 17 ) 5046 - 5052 2009年10月

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

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