研究者詳細 - 仲村　龍介

論文 - 仲村　龍介

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Transition in the nanoporous structure of iron oxides during the oxidation of iron nanoparticles and nanowires 査読国際誌

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

Acta Materialia 57 ( 14 ) 4261 - 4266 2009年8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 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

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Diffusion in intermetallic compounds and fabrication of hollow nanoparticles through Kirkendall effect 招待査読国際誌

Nakajima H., Nakamura R.

Journal of Nano Research 7 1 - 10 2009年7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：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

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Formation of a nano-hole via oxidation of metal nanoparticles 査読国際誌

Nakamura R., Nakajima H., Mori H.

Defect and Diffusion Forum 289-292 649 - 656 2009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（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

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Structural stability of hollow oxide nanoparticles at high temperatures 査読国際誌

Nakamura R., Nakajima H.

Journal of Physics: Conference Series 165 2009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（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

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Shrinkage of hollow nanoparticles of oxides of Cu and Ni at high temperatures 査読

Nakamura R., Nakajima H., Mori H.

Defect and Diffusion Forum 289-292 673 - 678 2009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（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

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Formation of a nano-pore during oxidation of metal nanoparticles 査読

Nakamura R., Tokozakura D., Lee J.G., Mori H., Nakajima H.

MetFoam 2007 - Proceedings of the 5th International Conference on Porous Metals and Metallic Foams 329 - 332 2008年11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（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.

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Shrinking of hollow Cu2O and NiO nanoparticles at high temperatures 査読国際誌

Nakamura R., Tokozakura D., Lee J.G., Mori H., Nakajima H.

Acta Materialia 56 ( 18 ) 5276 - 5284 2008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）

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

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Formation of hollow zinc oxide by oxidation and subsequent thermal treatment 査読国際誌

Lee J.G., Nakamura R., Tokozakura D., Nakajima H., Mori H., Lee J.H.

Solid State Phenomena 135 11 - 14 2008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（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

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Oxidation behaviour of Ni nanoparticles and formation process of hollow NiO 査読国際誌

Nakamura R., Lee J.G., Mori H., Nakajima H.

Philosophical Magazine 88 ( 2 ) 257 - 264 2008年1月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

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Formation of nano-scaled hollow oxide particles using oxidation reaction 査読国際誌

Nakamura R., Tokozakura D., Lee J.G., Mori H., Nakajima H.

TMS Annual Meeting 11 - 17 2007年12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：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.

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Transmission electron microscopy observation of oxide layer growth on Cu nanoparticles and formation process of hollow oxide particles 査読国際誌

Tokozakura D., Nakamura R., Nakajima H., Lee J.G., Mori H.

Journal of Materials Research 22 ( 10 ) 2930 - 2935 2007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）

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

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Hollow oxide formation by oxidation of Al and Cu nanoparticles 査読国際誌

Nakamura R., Tokozakura D., Nakajima H., Lee J.G., Mori H.

Journal of Applied Physics 101 ( 7 ) 074303.1 - 074303.7 2007年4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 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

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Supersaturated vacancies and vacancy complexes in rapidly solidified B2 aluminide ribbons 査読国際誌

Nakamura R., Yoshimi K., Tsurekawa S.

Materials Science and Engineering A 448-451 1036 - 1040 2007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）

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

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Formation of hollow ZnO through low-temperature oxidation of Zn nanoparticles 査読国際誌

Nakamura R., Lee J.G., Tokozakura D., Mori H., Nakajima H.

Materials Letters 61 ( 4-5 ) 1060 - 1063 2007年2月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：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

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Hollow amorphous formation via oxidation of Al nanoparticles at low temperatures 査読国際誌

Nakamura R., Lee J.G., Tokozakura D., Mori H., Nakajima H.

Materials Science Forum 544-545 347 - 350 2007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 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

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Oxidation behavior of Cu nanoparticles and formation of hollow Cu2O spheres 査読国際誌

Nakamura R., Tokozakura D., Lee J.G., Mori H., Nakajima H.

Materials Science Forum 561-565 ( PART 3 ) 1703 - 1706 2007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）

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

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Nanoscale surface self-patterning of FeAl single crystals by vacancy absorption process 査読国際誌

Yoshimi K., Tsunekane M., Nakamura R., Yamauchi A., Hanada S.

Applied Physics Letters 89 ( 7 ) 073110.1 - 073110.3 2006年8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 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

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Thermal analysis of lattice defects in LaNi5 査読国際誌

Nakamura R., Asano K., Yoshimi K., Iijima Y.

Journal of Alloys and Compounds 413 ( 1-2 ) 211 - 213 2006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）

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

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Effect of heat treatments on microstructure of rapidly solidified TiCo ribbons 査読国際誌

Yoshimi K., Yamauchi A., Nakamura R., Tsurekawa S., Hanada S.

Materials Research Society Symposium Proceedings 842 449 - 454 2005年8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）

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.

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Thermal analysis of relaxation processes of supersaturated vacancies in B2-type aluminides 査読国際誌

Nakamura R., Yoshimi K., Yamauchi A., Hanada S.

Materials Research Society Symposium Proceedings 842 535 - 540 2005年8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 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.

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