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受賞国：日本国

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受賞国：日本国

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受賞国：日本国

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受賞国：日本国

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DOI： 10.14293/APMC13-2025-0153

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

There is great interest in the development of new multifunctional fluorescent-magnetic nanomaterials for use as multimodal diagnostic imaging probes and site-specific drug delivery tools. Metal nanoclusters (NCs) have been reported to possess either fluorescent or magnetic properties, but not both. In this paper, we report the synthesis and characterization of multifunctional fluorescent-magnetic Pt NCs. Our synthesized NCs (0.8 ± 0.2 nm in diameter) exhibit both bright red fluorescence (excitation: 535 nm, emission: 620 nm) and ferromagnetic behavior with hysteresis, which represents a noteworthy and significant advance in the development of Pt NCs. Our findings suggest the potential of our NCs to be applied in multimodal fluorescent-magnetic nanomaterials for biomedical applications.

DOI： 10.1021/acsomega.4c06765

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

Laser-powder bed fusion (LPBF) enables the fabrication of complex metallic components by manipulating various laser scan strategies to control microstructure and texture. Multiple thermal cycling and rapid solidification lead to non-equilibrium, non-uniform microstructure, and micro-segregation at the melt pool boundary (MPB), whose accurate location is still invisible by transmission electron microscopy (TEM), and quantitative concentration remains imprecise. In this study, we proposed a novel method to make it clear by controlling the crystallographic texture of 316 L stainless steel through unique LPBF processing parameters to obtain a single-crystal-like microstructure of the cellular structures along the laser scanning direction. The accurate location of the track-track MPB is distinguishable by means of the transverse and longitudinal cellular dislocation structures on both sides. The edge-on state of the track-track MPB makes the quantitative concentration analysis precisely using high-angle annular dark-field scanning TEM with energy-dispersive X-ray spectroscopy, which is in good agreement with the Scheil-Gulliver solidification simulations.

DOI： 10.1016/j.matchar.2024.114435

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ACS Applied Nano Materials  

Trigonal Fe<inf>2</inf>Si nanosheets, which are promising candidates for spintronic nanodevices, were synthesized at the Fe/amorphous (a-)SiO<inf>x</inf> thin film interface using electron irradiation. The formation of nanoscale silicide was confirmed at 90 K as well as at 298 K. Such a low-temperature synthesis of Fe<inf>2</inf>Si can be attributed to the dissociation of a-SiO<inf>x</inf> induced by electronic excitation; Si-O bonds dissociate through Auger decay of core-holes generated by electronic excitation, and then, dissociated Si atoms form Fe-Si bonds. The amount of Fe<inf>2</inf>Si formed at room temperature was greater than that at 90 K, suggesting that the atomic migration induced by electronic excitation involves a contribution of thermal energy. The amount of Fe<inf>2</inf>Si nanosheets produced indicates that the Si-O bonds are more easily dissociated by electronic excitation in a-SiO<inf>x</inf> rather than in a-SiO<inf>2</inf>. Formation of the Fe<inf>2</inf>Si nanosheets found in this study differs from the formation of an equiatomic FeSi phase predicted by thermodynamic models assuming diffusion at a planar Fe/Si interface. We propose a versatile route to selectively form metal silicide nanosheets in an electron irradiated area at temperatures below room temperature.

DOI： 10.1021/acsanm.4c02874

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

Element segregation and consequent phase separation are challenging problems in refractory high entropy alloys (RHEAs). In this study, thermodynamic parameters and calculation of phase diagrams (CALPHAD) were implemented for RHEA design to suppress segregation and phase separation. A novel non-equiatomic RHEA, Ti<inf>1</inf>(NbMoTa)<inf>2</inf>W<inf>0.5</inf> alloy, was designed with a minimized difference between liquidus and solidus temperatures (ΔT<inf>l−s</inf>) and a wide temperature range between solidus temperature and transformation temperature (ΔT<inf>single</inf>) and compared with equiatomic RHEA. As-cast Ti<inf>1</inf>(NbMoTa)<inf>2</inf>W<inf>0.5</inf> alloy maintained a single-phase body-centered cubic (BCC) structure, corresponding to the Scheil–Gulliver model, and segregation of constituent elements was suppressed owing to the minimized ΔT<inf>l−s</inf>. Ti<inf>1</inf>(NbMoTa)<inf>2</inf>W<inf>0.5</inf> alloy showed excellent strength (approximately 1100 MPa) and ductility (1.6 times higher than TiNbMoTaW alloy). This study demonstrated a novel approach for obtaining single-phase BCC-structured RHEAs with suppressed elemental segregation and phase separation by utilizing combined use of ΔT<inf>l−s</inf> and ΔT<inf>single</inf> as alloy design indexes.

DOI： 10.1016/j.scriptamat.2024.116260

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Materials Letters  

Ultra-rapid cooling of laser powder bed fusion (LPBF) generates a cellular solidification microstructure with submicron-sized periodicity accompanied by non-negligible segregation. In 316L austenitic stainless steel, an important corrosion-resistant alloy, the effect of segregation, particularly variations in Cr concentration, on the corrosion resistance of the LPBF product is unknown. Local valence analysis of the LPBF-produced 316L by electron energy-loss spectroscopy revealed no obvious changes in the energy-loss near-edge structures of Cr and Fe measured within the solidification cellular microstructure, at the cell boundary, or at the melt-pool boundary. This result indicates that solidification segregation in the LPBF-produced 316L is unlikely to affect the corrosion resistance of the material.

DOI： 10.1016/j.matlet.2024.136978

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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  

Sub-micro dislocation cellular structures formed during rapid solidification break the strength–ductility trade-off in laser powder bed fusion (LPBF)-processed 316L stainless steel through high-density dislocations and segregated elements or precipitates at the cellular boundaries. The high-density dislocation entangled at the cellular boundary accommodates solidification strains among the cellular structures and cooling stresses through elastoplastic deformation. Columnar grains with cellular structures typically form along the direction of thermal flux. However, the ultra-low misorientations between the adjacent cellular structures and their interactions with the cellular boundary formation remain unclear. In this study, we revealed the ultra-low misorientations between the cellular structures in LPBF-processed 316L stainless steel using conventional electron backscatter diffraction (EBSD), transmission Kikuchi diffraction (TKD), and transmission electron microscopy (TEM). The conventional EBSD and TKD analysis results could provide misorientation angles smaller than 2°, while the resolution mainly depends on the specimen quality and scanning step size, and so on. A TEM technique with higher spatial resolution provides accurate information between adjacent dislocation cells with misorientation angles smaller than 1°. This study presents evidence that the TEM method is the better and more precise analytical method for the misorientation measurement of the cellular structures and provides insights into measuring the small misorientation angles between adjacent dislocation cells and nanograins in nanostructured metals and alloys with ultrafine-grained microstructures.

DOI： 10.3390/ma17081851

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DOI： 10.1063/5.0192801

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Applied Physics Letters  

We investigate photoinduced phase transition of Ti 3 O 5 using the pump-probe method in an ultrafast electron microscope. We measured time-resolved electron diffraction patterns of single-crystal lamellae of Ti 3 O 5 excited by the femtosecond laser at the wavelength of 800 and 400 nm. Under 800 nm laser excitation, the photoinduced phase transition from the β-phase to the λ-phase with a similar timescale to previous measurements conducted using nanocrystals was observed. This indicates that the photoinduced phase transition is not a phenomenon influenced by the material surface, size, or boundary, but an intrinsic property in a bulk crystal of Ti 3 O 5 . The photoinduced phase transition was not detected, when excited by the laser at the wavelength of 400 nm. The results are discussed based on the electronic states of β- Ti 3 O 5 and λ- Ti 3 O 5 . The density of the dissociated interatomic bonds between Ti at the specific site should be an important factor for triggering the photoinduced phase transition.

DOI： 10.1063/5.0175450

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Materialia  

We propose a new mechanism of crystallization of amorphous alloy which is mediated by additional solute atoms produced by electronic excitation. For a freestanding Pd-19at%Si amorphous alloy film, electron irradiation causes subtle structural change. By contrast, extensive crystallization of Pd-19at%Si amorphous alloy sandwiched by amorphous (a-) SiO<inf>x</inf> films, i.e., a-SiO<inf>x</inf>/a-Pd-Si/a-SiO<inf>x</inf>, occurred by 75 keV and 200 keV electron irradiation. This crystallization was induced by irradiation not only at room temperature but also even at 90 K. It should be emphasized that the crystallization can be realized by 75 keV irradiation at 90 K via the electronic excitation; where both knock-on damage and a possible thermal crystallization can be excluded. A resultant product of the crystallization after electronic excitation (i.e., electron irradiation), hexagonal Pd<inf>2</inf>Si, differs from that of thermal annealing (orthorhombic Pd<inf>3</inf>Si). Evidence for decomposition of a-SiO<inf>x</inf> by electronic excitation contributes essentially to the crystallization of the a-Pd-Si in the composite film has been obtained in this study. Supply of dissociated Si to the a-Pd-Si layer may cause instability of the amorphous phase, which serves as the trigger for the remarkable structural change; i.e., additional solute atom mediated crystallization.

DOI： 10.1016/j.mtla.2023.101888

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Ecs Journal of Solid State Science and Technology  

Heterojunction p-GaN/n-ZnO light emitting diode (LED) structure using Eu-doped ZnO (ZnO:Eu) as an active component is demonstrated in order to realize low-cost and environmentally-friendly red LEDs with sharp linewidth and temperature stability against surrounding environment including operating temperature and injection current. Chemically stable Al<inf>2</inf>O<inf>3</inf> is inserted as an electron blocking layer between p-GaN and ZnO:Eu/n-ZnO in order to facilitate the injection of carriers into the ZnO:Eu active layer. Al<inf>2</inf>O<inf>3</inf> insertion with a moderate thickness (∼10 nm) facilitates the carrier recombination at the ZnO layer with comparatively low resistivity. Device characteristics of the p-GaN/Al<inf>2</inf>O<inf>3</inf>/ZnO:Eu/n-ZnO LED structures show red luminescence under current injection with reversed bias voltage originated from Eu³⁺ ions in the ZnO host. Detailed optical characteristics of the ZnO:Eu layer in the LED structures utilizing the combined excitation emission spectroscopy measurement enable the identification of the luminescence centers contributing to Eu luminescence under both indirect excitation and collisional excitation. The luminescence center contributing to Eu luminescence under indirect excitation via the ZnO host is different from that under collisional excitation, which would pave the way to understand the Eu luminescence mechanism in ZnO:Eu, and hence realize high-brightness LED structures based on rare-Earth doped ZnO as an active component.

DOI： 10.1149/2162-8777/ace655

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その他リンク： https://iopscience.iop.org/article/10.1149/2162-8777/ace655/pdf

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 Transactions  

Metal additive manufacturing enables producing complex geometric structures with high accuracy and breaks the design constraints of traditional manufacturing methods. Laser powder bed fusion, a typical additive manufacturing process, presents a challenge in experimentally understanding the nano-scaled microstructure-process relationship regarding the wide range of process parameters. In this study, we aim to reveal the novel nanoscale structural features by advanced scanning transmission electron microscopy to clarify the formation mechanisms in 316L stainless steel by laser powder bed fusion. Here we show that the slender columnar grains were confined to the centreline of the melt pool along the build direction, and the columnar cell structure at the side branching of the melt pool grew along orthogonal directions to follow drastic changes in thermal gradient across adjacent melt pools. Novel nano-scaled modulated structures have been observed in the dislocation cells parallel to the laser scan direction, which were mainly caused by the elastic strain involving the thermal gradient inside the melt pool and across adjacent melt pools as well as the effective strain field in the dislocation cell interiors. An in-depth understanding of microstructure developments is worthy of fabricating high-performance materials by controlling the additive manufacturing process.

DOI： 10.2320/matertrans.mt-me2022004

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Materials  

For this article, we studied the microstructure and solute segregation seen around the melt pool boundary of orientation-controlled 316L austenitic stainless steel produced by laser powder bed fusion, using transmission electron microscopy and energy-dispersive x-ray spectroscopy. We found that the solidification cellular microstructures could be visualized with the aid of solute segregation (Cr and Mo) during solidification. Mn–Si–O inclusions (10–15 nm in diameter) were distributed along the lamellar boundaries, as well as in the dislocation cell walls. It is believed that the grain growth of the inclusions can be effectively suppressed by rapid quenching during the laser powder-bed fusion process. A thin region without cellular microstructures was observed at the melt-pool boundary. The cellular spacing widened near the bottom of the melt-pool boundary, owing to the decrease in the cooling rate. Atomic-structure analysis at the lamellar boundary by high-resolution transmission electron microscopy revealed a local interfacial structure, which is complementary to the results of electron back-scatter diffraction.

DOI： 10.3390/ma16010218

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ACS Omega  

Thin films of V-doped Sb<inf>2</inf>Te<inf>3</inf>compounds were fabricated by co-deposition of Sb<inf>2</inf>Te<inf>3</inf>and V using rf-magnetron sputtering onto SrTiO<inf>3</inf>(001) substrates kept at 570 K. The microstructures of the films were characterized using transmission electron microscopy (TEM) and electron diffraction. The crystal structure of the sputtered film (Sb<inf>38</inf>V<inf>2</inf>Te<inf>60</inf>) is the Bi<inf>2</inf>Te<inf>3</inf>-type structure with lattice parameters of a = 0.44 ± 0.03 nm and c = 3.02 ± 0.02 nm. A combination of cross-sectional and plan-view TEM observations revealed the preferential orientation of the c axis in the film's normal direction. A thin amorphous layer exists between the Sb<inf>2</inf>Te<inf>3</inf>thin film and the SrTiO<inf>3</inf>substrate. The interfacial amorphous layer relaxes the strain between the thin film and the substrate, and hence, it should promote the growth of a low-index atomic plane with a low surface free energy (i.e., (0001) of the Sb<inf>2</inf>Te<inf>3</inf>). The onset of ferromagnetic order was detected at temperatures below 70 K. A remarkable increase in magnetization was detected in the film's normal direction, which corresponds to the magnetic easy axis (i.e., c axis of the Sb<inf>2</inf>Te<inf>3</inf>). V³⁺ions substituting Sb sites should contribute to ferromagnetism at low temperatures.

DOI： 10.1021/acsomega.2c05634

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Review B  

The intrinsic magnetic properties of nanoparticles (NPs) can be accurately determined using highly dispersed NPs in a matrix. In this paper, we study chemically ordered CoPt and FePt NPs with a diameter of 3 nm embedded in an amorphous carbon matrix. Although both alloys exhibit almost the same magnetic and crystallographic properties in the bulk materials, they are completely different as NPs. We show that their magnetic anisotropy differs greatly. To understand the origin of such a difference, a fine crystallographic structure study has been performed using extended x-ray absorption fine structure. In that respect, the atomic relaxations appear to be different in both nanoalloys. Ab initio calculations of the atomic relaxation shed light on these experimental results, showing that the wide distance distribution in Co sublattice should strongly alter the magnetic anisotropy of CoPt NPs.

DOI： 10.1103/PhysRevB.106.104420

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その他リンク： http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevB.106.104420/fulltext

担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Physical Chemistry C  

Structural defects in the layered compounds (Ta<inf>1-x</inf>Ti<inf>x</inf>)Se<inf>2</inf>(0 ≤ x ≤ 1), characterized by anisotropy in electrical conductivity, have been studied by cross-sectional observation using chemically sensitive high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). Intercalants were detected in the widest space between Se atoms across the van der Waals (vdW) gap, regardless of the Ti content (except TiSe<inf>2</inf>) or thermal history after the crystal growth. Binary TaSe<inf>2</inf>with both 3R and 2H structures includes a high density of stacking faults, while Ti addition stabilizes the 1T structure with no stacking faults. We show that the chemical composition dominates the structural defects in the (Ta<inf>1-x</inf>Ti<inf>x</inf>)Se<inf>2</inf>compounds. Substitution of Ta with Ti acts as a hole addition, which reduces the number of conduction electrons in the layer, while an intercalated atom in the vdW gap may not act as a donor of conduction electrons.

DOI： 10.1021/acs.jpcc.2c03943

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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 and Design  

The bimodal microstructure, which comprises ultrafine grains (UFGs) forming along the melt pool boundary and relatively coarse grains inside the melt pool, is a characteristic of the Sc-Zr-modified Al–Mg-based alloy (Scalmalloy) microstructure manufactured using laser powder bed fusion (LPBF). Focusing on this microstructural feature, we investigated the improvement in the mechanical properties of LPBF-fabricated Scalmalloy by tailoring the volume fraction of UFGs. Our approach was to decrease the laser hatch spacing (d) from 0.1 to 0.04 mm, while the volume fraction of UFGs increased from 34.6 ± 0.6 % (d = 0.1 mm) to 59.5 ± 0.5 % (d = 0.06 mm). The tensile yield stress increased from 296 ± 9 (d = 0.1 mm) to 380 ± 6 MPa (d = 0.06 mm), while maintaining a large elongation (14.8 % ± 1.2 %). The yield stress and elongation were superior to those of the cast counterparts by 2.9 and 4.0 times, respectively. In the sample with d = 0.04 mm, pores formed owing to excessive thermal energy input. Additionally, we investigated multiple strengthening mechanisms of the as-fabricated alloy. This is the first study to improve the mechanical properties of LPBF-fabricated Scalmalloy by optimizing the track-to-track interval and tuning the UFG fraction.

DOI： 10.1016/j.matdes.2022.110976

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Applied Physics  

Ferroelectric domain dynamics in Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 single crystals have been studied by in situ biasing high-voltage transmission electron microscopy with a direct electron detection camera. We have achieved time-resolved recording of polarization switching in real space on a 2.5 ms time scale. The reversible response of micrometer-scale domains was observed by applying an electric field of 1 kV/mm. Detailed analyses on smaller sized domains 100-500 nm in size revealed that the domain switching initiated at a corner of a rectangular domain and propagated inward rapidly. The switching proceeded within 60 ms and the maximum switching rate, as fast as 6-8 μm/s, was observed. The domain switching kinetics was classified as two-dimensional nucleation and growth mode based on the Kolmogolov-Avrami-Ishibashi model.

DOI： 10.1063/5.0064291

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ACS Omega  

Microelectronics based on Si requires metal silicide contacts. The ability to form platinum silicide (Pt2Si) by electronic excitation instead of thermal processes would benefit the field. We studied the effects of electron irradiation on Pt2Si formation in composite films-composed of Pt and amorphous silicon oxides (a-SiOx)-by transmission electron microscopy and electron diffraction. Pt2Si formed in Pt/a-SiOx bilayer and a-SiOx/Pt/a-SiOx sandwiched films by 75 keV electron irradiation, at 298 and 90 K. The reaction is attributable to dissociation of SiOx triggered by electronic excitation. In a-SiOx/Pt/a-SiOx sandwiched films, reflections of pure Pt were not present after irradiation, i.e., Pt was completely consumed in the reaction to form Pt2Si at 298 K. However, in Pt/a-SiOx bilayer films, unreacted Pt remained under the same irradiation conditions. Thus, it can be said that the extent of the interfacial area is the predominant factor in Pt2Si formation. The morphology of Pt islands extensively changed during Pt2Si formation even at 90 K. Coalescence and growth of metallic particles (Pt and Pt-Si) are not due to thermal effects during electron irradiation but to athermal processes accompanied by silicide formation. To maintain the reaction interface between metallic particles and the dissociation product (i.e., Si atoms) by electronic excitation, a considerable concomitant morphology change occurs. Elemental analysis indicates that the decrease in Si concentration near Pt is faster than the decrease in O concentration, suggesting formation of a Si depletion zone in the amorphous silicon oxide matrix associated with formation of Pt2Si.

DOI： 10.1021/acsomega.1c03604

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

A thermally impossible positive free energy reaction can proceed by electron-orbital-selective excitation. When the Si 2p core level is photo-excited in Pt/SiOx bilayer films, Coulomb repulsion at the final two-hole state localized in the valence band by an interatomic Auger transition induces dissociation of the O atom and formation of a Si-Pt bond. Consequently, Pt2Si silicide is formed by a positive free energy reaction. Under a single particle excitation of the valence band, low probability of the coexistence of the two-hole state for picosecond order suppresses to allow the reaction to proceed.

DOI： 10.1039/d0ra07151j

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

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

DOI： 10.1088/1361-6668/abaebf

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その他リンク： https://iopscience.iop.org/article/10.1088/1361-6668/abaebf/pdf

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

Overexpression of human epidermal growth factor receptor 2 (HER2) is associated with more frequent cancer recurrence and metastasis. Sensitive sensing of HER2 in living breast cancer cells is crucial in the early stages of cancer and to further understand its role in cells. Biomedical imaging has become an indispensable tool in the fields of early cancer diagnosis and therapy. In this study, we designed and synthesized platinum (Pt) nanocluster bionanoprobes with red emission (Ex/Em = 535/630 nm) for fluorescence imaging of HER2. Our Pt nanoclusters, which were synthesized using polyamidoamine (PAMAM) dendrimer and preequilibration, exhibited approximately 1% quantum yield and possessed low cytotoxicity, ultrasmall size, and excellent photostability. Furthermore, combined with ProteinA as an adapter protein, we developed Pt bionanoprobes with minimal nonspecific binding and utilized them as fluorescent probes for highly sensitive optical imaging of HER2 at the cellular level. More importantly, molecular probes with long-wavelength emission have allowed visualization of deep anatomical features because of enhanced tissue penetration and a decrease in background noise from tissue scattering. Our Pt nanoclusters are promising fluorescent probes for biomedical applications.

DOI： 10.1021/acsomega.0c02578

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

Ultra-high voltage electron microscopy is useful for research utilizing high-penetration thickness of electron beam, in situ observation, or irradiation effects by the particle characteristics of electrons. In this review, the importance of non-equilibrium materials science research by a combination with irradiation effects and in situ observation is shown, and examples of some research are introduced. For example, crystal-amorphous-crystalline phase transition in intermetallic compounds, non-equilibrium phase transition in pure metallic nanoparticles and nucleation and growth process of electron irradiation-induced crystallization in amorphous nanoparticles will be discussed. Finally, we want to suggest the importance of exploring non-equilibrium materials science based on dynamic structures which has been unexplored.

DOI： 10.1093/jmicro/dfaa042

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その他リンク： http://academic.oup.com/jmicro/article-pdf/69/6/331/34674627/dfaa042.pdf

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 Materials Science  

(K<inf>0.89</inf>Na<inf>0.11</inf>)(Nb<inf>0.85</inf>Ta<inf>0.15</inf>)O<inf>3</inf> thick films were epitaxially grown at 200 °C on (001)La:SrTiO<inf>3</inf> and (001)<inf>c</inf>SrRuO<inf>3</inf>//(001)SrTiO<inf>3</inf> substrates by hydrothermal method, and their crystal structures and electrical properties were investigated.Film thickness increased with deposition time and reached 6 µm in 10 h. High-temperature X-ray diffraction measurement showed that successive phase transitions from orthorhombic to tetragonal and from tetragonal to cubic phases take place at 120 and 400 °C, respectively. Microstructure analyses were performed by using electron microscopy, which revealed the existence of two types of stripe patterns with a width of 100 nm or less. In addition, scanning transmission electron microscopy–energy-dispersive X-ray spectroscopy elemental mapping showed that Nb/(Nb + Ta) ratio of the deposited films abruptly changed around 700 nm in thickness. Annealing at 500 °C led to the reduction in leakage current density from 10² to 10^–5 A/cm² at 30 kV/cm, showing that annealing is an effective way to improve insulation. Relative dielectric constant (ε<inf>r</inf>) decreased linearly with increasing frequency, reaching 450 at 10 kHz. Polarization–electric field hysteresis loop and field-induced stain curve were measured by piezoelectric force microscopy, which showed remanent polarization (P<inf>r</inf>) of 30 µC/cm² and piezoelectric constant (d<inf>33,PFM</inf>) of 70 pm/V. These results demonstrate that (K,Na)(Nb,Ta)O<inf>3</inf> thick films with superior electrical properties can be fabricated by the low-temperature deposition technique.

DOI： 10.1007/s10853-020-04663-x

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ACS Applied Nano Materials  

We observed an order-disorder transition confined to the interface of Pd@Co core-shell nanoparticles with a Pd core and Co shell. A local ordered region with the L1<inf>0</inf>- and L1<inf>2</inf>-type ordered structure 2-3 nm in size was formed in a ∼12 nm-sized particle. The local atomic order was only achieved in the narrow temperature range of 573-723 K, where the diffusion length is limited to a short-range comparable to the nearest-neighbor distance of the Co-Pd solid solution. Once the atom migration was activated (T ≥ 773 K), alloying of Co and Pd proceeded rapidly, and the ordered phase disappeared along with the core-shell structure. Namely, the stability of the ordered phase was diffusion controlled. Chemically sensitive atomic-resolution electron microscopy enabled detection of the local atomic order formed in a nanoparticle. Such local atomic order has the potential to enable tuning of the magnetic anisotropy of bimetallic nanomagnets, which may open a new route to realize ultrahigh-density magnetic storage media.

DOI： 10.1021/acsanm.9b02371

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ACS Omega  

Low-temperature crystal defect dynamics in Si has been studied by a newly developed cryo-high-voltage electron microscopy. The planar {113} defects of self-interstitial atoms were introduced at 94 K by 1 MeV electron irradiation with damage higher than 0.42 displacements per atom (dpa), unlike past findings. The defects once grew and then shrunk during the observation. We show that the nucleation and the dissociation dynamics of the {113} defects can be attributed to an athermal process, which is deduced from anomalously fast diffusion of self-interstitial atoms at a low temperature.

DOI： 10.1021/acsomega.9b03028

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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 Alloys and Compounds  

The authors regret that the printed version misses to cite a review paper which has been published. The correct and final version of figure captions and references is shown in this corrigendum. The authors would like to apologise for any inconvenience caused. Fig. 6. GI-XRD profiles for FeNi film (30 nm) on MgO(001) substrates annealed at 250–400 °C at heating rate of 50 °C/s for 20 hours. (a) Profiles in a narrow range around FeNi(001) and (200) peaks for samples. (b) Profiles in narrow range around FeNi(110) and (220) peaks for samples [38]. Fig. 7. Annealing-temperature dependence of S for FeNi films (30 nm) on MgO(001) substrates at a heating rate of 50 °C/s for 20 hours [38]. Fig. 10. Magnetization curves of FeNi films (5 and 30 nm) on MgO substrates annealed at 350 °C for 20 hours at heating rate of 50 °C/s. Magnetic field was applied in-plane (blue line and circles) and out-of-plane (red line and circles) to film plane. Insets show enlarged magnetization curve around 0 Oe [38]. [38] K. Takanashi, M. Mizuguchi, T. Kojima, T. Tashiro, J. Phys. D. 50 (2017) 483002.

DOI： 10.1016/j.jallcom.2019.02.165

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Materials Transactions  

Herein, the advantages of high-voltage scanning transmission electron microscopy (STEM) as a tool for structural characterization of micrometer-thick specimens are reported. Dislocations introduced in a wedge-shaped Si crystal were clearly observed by bright-field STEM operating at 1 MV. Many of the dislocations were straight and parallel to the ©110ª, ©112ª or ©113ª directions. The widths of the dislocations in the STEM images were almost constant at 1316 nm (i.e., 45 pixels) in the thickness range between 1 and 7.5 µm. The latest high-voltage STEM instrumentation is thus useful for imaging crystal defects in micrometer-thick materials, and enables multi-scale fields of view from a few nanometers squared to over 100µm²

DOI： 10.2320/matertrans.MC201801

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Review Materials  

Elastic strain and defects are important key words for controlling structure and properties in films. While epitaxial strain and misfit dislocations have been discussed in conventional films, the evolution of strain and defect can be significantly varied by nanocomposite strain and complicated defects in oxides. In the present study, long stacking faults with a spacing of 5-30 nm and a length of >500nm were self-organized by ex situ annealing highly strained nanocomposite films of YBa2Cu3O7-δ(YBCO)+BaMO3(M=Hf,Sn). It is surprising that the nonlocal nature of stacking faults, namely, the structural correlation over >500nm, was observed in spite of the local configuration of the nanocomposite interface. This kind of structural variation was not observed in the pure YBCO film without nanorods, even when the same annealing was performed. A strain energy analysis showed that the stacking fault formation led to the strain energy minimum by reducing the nanocomposite strain. The layered structure of YBCO stacking faults and the large nanocomposite strain realized the present nonlocal self-organization, which is not observed in the conventional systems with epitaxial strain and misfit dislocations.

DOI： 10.1103/PhysRevMaterials.3.013403

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IEEE Transactions on Magnetics  

There is a growing interest in the development of rare-earth element-free hard magnets. The L1<inf>0</inf> FeNi phase found in Fe-based meteorites is promising based on its high-magnetocrystalline anisotropy and saturation magnetization. Not only the production, but also the characterization of L1<inf>0</inf> FeNi phase is challenging due to similar X-ray scattering factors of Fe and Ni. Here, we report on the confirmation of L1<inf>0</inf> FeNi phase precipitated in a multi-phase FeNiSiBPCu alloy by anomalous X-ray diffraction (AXRD). This is a powerful technique, which can differentiate between ordered and disordered phases along with the elements present in a phase. We measured integrated X-ray intensity with energy near the Fe (7-7.2 keV) and Ni (8.25-8.4 keV) absorption edges for superlattice and fundamental reflections of L1<inf>0</inf> FeNi. A drastic change in integrated intensity with energy of X-ray was observed. Increase in intensity around superlattice reflection at Ni-absorption edge clearly confirms the presence of a chemically ordered L1<inf>0</inf> FeNi phase, but the results obtained at Fe edge are surprising. The analysis of AXRD results suggested that (110) diffraction peak of Fe<inf>2</inf>B phase overlaps with (001) of L1<inf>0</inf> FeNi. Understanding gained from AXRD results also allows us to estimate the long-range order parameter (S) from X-ray diffraction measurements.

DOI： 10.1109/TMAG.2018.2842057

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ACS Omega  

We report on extreme penetration power of relativistic electrons in a micrometer-thick gallium nitride epitaxial film and its application to probing threading dislocations, which were introduced during crystal growth. Maximum usable thickness of the specimen was quantitatively evaluated using high-voltage transmission electron microscopy (TEM) operating at 1 MV. The width of dislocation images was used as a measure for the evaluation of usable thickness. Superior maximum usable thickness was obtained in scanning transmission electron microscopy (STEM) than in TEM mode; the results were 6.9 μm for STEM and 4.4 μm for TEM. In STEM, dislocations can be imaged with an almost constant width of 15-20 nm in a wide thickness range 1-4 μm. The latest high-voltage STEM is thus useful for observing dislocations in micrometer-thick inorganic materials.

DOI： 10.1021/acsomega.8b02078

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Acta Materialia  

The synthesis of platinum silicide at a Pt/SiO<inf>x</inf> interface by photon irradiation was investigated using transmission electron microscopy. A platinum silicide, Pt<inf>2</inf>Si, was successfully formed at the Pt/SiO<inf>x</inf> interface by irradiation with 680 and 140 eV photons, but not by irradiation with 80 eV photons. Silicide formation was also induced by irradiation with electrons of energy 75 keV. The amount of silicide formed by photon irradiation was lower than the amount obtained by electron irradiation. Silicide formation by both photon and electron irradiation was accompanied by Si depletion in amorphous SiO<inf>x</inf>. The experimental results indicate that silicide formation is induced by electronic excitation. A possible mechanism for silicide formation is proposed on the basis of the results.

DOI： 10.1016/j.actamat.2018.05.045

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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 Alloys and Compounds  

FeNi films were directly deposited on MgO(001) substrates by co-sputtering and rapid thermal annealing (RTA). The formation of the L1<inf>0</inf> phase was investigated for films with different thicknesses and different annealing conditions by grazing incidence X-ray diffraction. For the FeNi films with a thickness of 5 nm, superlattice 001 and 110 peaks were observed after annealing at a heating rate of 50 °C/s, which indicates that three variants of L1<inf>0</inf> grains were formed in the films. The maximum long-range order parameter, which corresponded to a volume-averaged parameter, was approximately 0.11. For the FeNi films with a thickness of 30 nm, a superlattice 110 peak was only observed after annealing at a heating rate of 50 °C/s, and the formation of 001 textured grains was clarified. Magnetic properties also changed depending on the FeNi film structures. The formation mechanism of L1<inf>0</inf>-FeNi is discussed based on the strain caused by RTA in the FeNi films.

DOI： 10.1016/j.jallcom.2018.02.318

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Philosophical Magazine  

We have studied three-dimensional (3D) structures and growth processes of 14H-type long-period stacking order (LPSO) formed in Mg<inf>97</inf>Zn<inf>1</inf>Gd<inf>2</inf> cast alloys by single tilt-axis electron tomography (ET) using high-angle annular dark-field scanning transmission electron microscopy. Evolution of the solute-enriched stacking faults (SFs) and the 14H LPSO by ageing were visualised in 3D with a high spatial resolution in multi-scale fields of views from a few nanometres to ~10 μm. Lateral growth of the solute-enriched SFs and the LPSO in the (0 0 0 1)<inf>Mg</inf> plane is notable compared to the out-of-plane growth in the [0 0 0 1]<inf>Mg</inf> direction. The 14H LPSO grows at the cost of decomposition of the (Mg, Zn)<inf>3</inf>Gd-type precipitates, and accompany a change of in-plane edge angles from 30 to 60°. We have updated the Time–Temperature–Transformation diagram for precipitation in Mg<inf>97</inf>Zn<inf>1</inf>Gd<inf>2</inf> alloys: starting temperatures of both solute-enriched SFs and LPSO formation shifted to a shorter time side than those in the previous diagram.

DOI： 10.1080/14786435.2018.1468940

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担当区分：責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Philosophical Magazine  

The phase change induced by MeV electron irradiation in the intermetallic compound E9<inf>3</inf>–CoTi<inf>2</inf> was investigated using high-voltage electron microscopy. Under MeV electron irradiation, CoTi<inf>2</inf> was first transformed into an amorphous phase and, with continued irradiation, crystallite formation in the amorphous phase (i.e. formation of crystallites of a solid-solution phase within the amorphous phase) was induced. The critical temperature for amorphisation was around 250 K. The total dose (dpa) required for crystallite formation (i.e. that required for partial crystallisation) was high (i.e. 27–80 dpa) and, even after prolonged irradiation, the amorphous phase was retained in the irradiated sample. Such partial crystallisation behaviour of amorphous Co<inf>33</inf>Ti<inf>67</inf> was clearly different from the crystallisation behaviour (i.e. amorphous-to-solid solution, polymorphous transformation) of amorphous Cr<inf>67</inf>Ti<inf>33</inf> reported in the literature. A possible cause of the difference is discussed.

DOI： 10.1080/14786435.2018.1468941

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

Silver nanoparticles (AgNPs) and their assembled nanostructures such as core/satellite nanoassemblies are quite attractive in plasmonic-based applications. However, one biggest drawback of the AgNPs is the poor chemical stability which also greatly limits their applications. We report fine Au coating on synthesized quasi-spherical silver nanoparticles (AgNSs) with few atomic layers to several nanometers by stoichiometric method. The fine Au coating layer was confirmed by energy-dispersive X-ray spectroscopy elemental mapping and aberration-corrected high-angle annular dark-field scanning transmission electron microscopy. The optimized minimal thickness of Au coating layer on different sized AgNSs (22 nm Ag@0.9 nm Au, 44 nm Ag@1.8 nm Au, 75 nm Ag@2.9 nm Au, and 103 nm Ag@0.9 nm Au) was determined by extreme chemical stability tests using H<inf>2</inf>O<inf>2</inf>, NaSH, and H<inf>2</inf>S gas. The thin Au coating layer on AgNSs did not affect their plasmonic-based applications. The core/satellite assemblies based on Ag@Au NPs showed the comparable SERS intensity and uniformity three times higher than that of noncoated Ag core/satellites. The Ag@Au core/satellites also showed high stability in intracellular SERS imaging for at least two days, while the SERS of the noncoated Ag core/satellites decayed significantly. These spherical Ag@Au NPs can be widely used and have great advantages in plasmon-based applications, intracellular SERS probes, and other biological and analytical studies.

DOI： 10.1021/acsami.7b14976

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Japanese Journal of Applied Physics  

We have quantitatively evaluated the usable thickness of specimens in scanning transmission electron microscopy (STEM) at 1MV using a wedgeshaped Si(110) single crystal including artificially introduced high-density dislocations. The width of dislocation images was employed as a criterion for the quantitative evaluation of usable thickness. Superior usable thickness in STEM than in TEM was found; the obtained results were 14.7μm for STEM and 5.8μm for TEM. In particular, in STEM, dislocations can be observed as thin lines with 10-15nm width in the thickness range up to 10 μm. The latest high-voltage STEM is useful for imaging crystal defects in thick semiconductors.

DOI： 10.7567/JJAP.56.100304

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掲載種別：研究論文（学術雑誌）   出版者・発行元：The Carbon Society of Japan  

DOI： 10.7209/tanso.2017.55

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Aip Advances  

We have studied formation and stability of core-shell structures in epitaxial Au/Co nanoparticles (NPs) by using atomic-resolution scanning transmission electron microscopy. As the particle size reduces, number of NPs having Au-shell increases and their frequency of occurrence reached 65%. Au segregation proceeds during particle growth at 520 K. The core-shell structure formation is particle size-dependent; the critical diameter dividing the Au-shell and the Co-shell structures is about 11 nm, below which the Au-shell is stable. After annealing at 800 K for 3.6 ks, Au-shell NPs were conserved while the Co-shell NPs changed to two-phase structures with a planar interface separating Au and Co. There is a local energy minimum where the Co-shell NP is metastable in the as-deposited state. A simple model based on surface and interfacial energies suggests stability of Au-shell structures. Surface-segregation-induced phase separation in small NPs, due to low surface free energy of Au, will be responsible for the Au-shell formation.

DOI： 10.1063/1.4986905

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Applied Physics Letters  

The development of long-range order in disordered Co-Pt alloy nanoparticles has been atomically resolved in situ with an ultra-high voltage electron microscope equipped with a direct electron detection camera. Electron-irradiation-enhanced ordering occurred at 573 K with 1 MeV electrons at a dose rate of 8.9 × 10²⁴ e/m²s. High-speed (400 frames/s) imaging revealed fluctuations of the c-axis orientation of the L1<inf>0</inf>-type ordered structure. Specifically, the c-axis orientation changes occurred at 2.5-ms intervals. Thus, the atomic ordering rate at 573 K is deduced to be 3 × 10⁻¹⁷ m²/s, which is 10¹³ times higher than that estimated for interdiffusion in a bulk Co-Pt alloy. The observed kinetic ordering temperature of 573 K is significantly lower than that reported previously (>800 K). The low-temperature ordering may be the result of enhanced atom migration via excess vacancies, 10⁶ times higher than that at thermal equilibrium, introduced by the high-energy electron irradiation.

DOI： 10.1063/1.4980077

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

This paper reports the preliminary results of a new in-situ three-dimensional (3D) imaging system for observing plastic deformation behavior in a transmission electron microscope (TEM) as a directly relevant development of the recently reported straining-and-tomography holder [Sato K et al. (2015) Development of a novel straining holder for transmission electron microscopy compatible with single tilt-axis electron tomography. Microsc. 64: 369-375]. We designed an integrated system using the holder and newly developed straining and image-acquisition software and then developed an experimental procedure for in-situ straining and time-resolved electron tomography (ET) data acquisition. The software for image acquisition and 3D visualization was developed based on the commercially available ET software TEMographyTM. We achieved time-resolved 3D visualization of nanometer-scale plastic deformation behavior in a Pb-Sn alloy sample, thus demonstrating the capability of this system for potential applications in materials science.

DOI： 10.1093/jmicro/dfw109

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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  

Thermally induced crystallization processes for amorphous GeSn thin films with Sn concentrations beyond the solubility limit of the bulk crystal Ge-Sn binary system have been examined by X-ray photoelectron spectroscopy, grazing incidence X-ray diffraction, and (scanning) transmission electron microscopy. We paid special attention to the behavior of Sn before and after recrystallization. In the as-deposited specimens, Sn atoms were homogeneously distributed in an amorphous matrix. Prior to crystallization, an amorphous-to-amorphous phase transformation associated with the rearrangement of Sn atoms was observed during heat treatment; this transformation is reversible with respect to temperature. Remarkable recrystallization occurred at temperatures above 400 °C, and Sn atoms were ejected from the crystallized GeSn matrix. The segregation of Sn became more pronounced with increasing annealing temperature, and the ejected Sn existed as a liquid phase. It was found that the molten Sn remains as a supercooled liquid below the eutectic temperature of the Ge-Sn binary system during the cooling process, and finally, β-Sn precipitates were formed at ambient temperature.

DOI： 10.1063/1.4973121

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Applied Physics  

The microstructure of polycrystalline PbTe<inf>1-x</inf>Se<inf>x</inf>-ZnSe composite thin films has been studied by scanning transmission electron microscopy and electron diffraction. The films were prepared by the one-step synthesis method using simultaneous evaporation of PbTe and ZnSe. The nanocrystals of PbTe<inf>1-x</inf>Se<inf>x</inf> are formed in a ZnSe matrix. Tellurium concentration can be tuned by controlling the PbTe evaporation source temperatures between 753 K and 793 K. Binary PbSe nanocrystals were formed at 753 K, while ternary PbTe<inf>1-x</inf>Se<inf>x</inf> nanocrystals were formed at 793 K. The nanocrystals grow in a granular shape at the initial stage of film growth, and the morphology changes to nanowire-shape as the film grows, irrespective of the Te concentration. The ternary PbTe<inf>1-x</inf>Se<inf>x</inf> nanocrystals were composed of two phases with different Te concentration; Te-rich (Se-poor) granular crystals were formed near the bottom half parts of the film and Te-poor (Se-rich) nanowires were formed at the upper half parts of the film. Columnar ZnSe crystals contain high-density {111} stacking faults due to the low stacking fault energy of ZnSe. A balance of deposition and re-evaporation on the substrate during the film growth will be responsible for the resultant nanocrystal morphology.

DOI： 10.1063/1.4964874

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

One perovskite oxide, ASnO<inf>3</inf> (A = Sr, Ba), is a candidate for use as a transparent conductive oxide with high electron mobility in single crystalline form. However, the electron mobility of films grown on SrTiO<inf>3</inf> substrates does not reach the bulk value, probably because of dislocation scattering that originates from the large lattice mismatch. This study investigates the effect of insertion of bilayer BaSnO<inf>3</inf> / (Sr,Ba)SnO<inf>3</inf> for buffering this large lattice mismatch between La:BaSnO<inf>3</inf> and SrTiO<inf>3</inf> substrate. The insertion of 200-nm-thick BaSnO<inf>3</inf> on (Sr,Ba)SnO<inf>3</inf> bilayer buffer structures reduces the number of dislocations and improves surface smoothness of the films after annealing as proved respectively by scanning transmission electron microscopy and atomic force microscopy. A systematic investigation of BaSnO<inf>3</inf> buffer layer thickness dependence on Hall mobility of the electron transport in La:BaSnO<inf>3</inf> shows that the highest obtained value of mobility is 78 cm²V^-1s^-1 because of its fewer dislocations. High electron mobility films based on perovskite BaSnO<inf>3</inf> can provide a good platform for transparent-conducting-oxide electronic devices and for creation of fascinating perovskite heterostructures.

DOI： 10.1063/1.4953808

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

The microstructure of newly developed hard magnetic Fe<inf>42</inf>Ni<inf>41.3</inf>Si<inf>x</inf>B<inf>12-x</inf>P<inf>4</inf>Cu<inf>0.7</inf> (x = 2 to 8 at%) nanocrystalline alloy ribbons has been studied by transmission electron microscopy (TEM) and electron diffraction. A high-density polycrystalline grains, ∼30 nm in size, were formed in a ribbon after annealing at 673 K for 288 hours. Elemental mapping of the annealed specimen revealed the coexistence of three regions, Fe-rich, Ni-rich, and nearly equiatomic Fe-Ni, with areal fractions of 37%, 40%, and 23 %, respectively. The equiatomic L1<inf>0</inf>-type ordered phase of FeNi was detected in between the Fe and Ni-rich phases. The presence of superlattice reflections in nanobeam electron diffraction patterns confirmed the formation of the hard magnetic L1<inf>0</inf> phase beyond any doubt. The L1<inf>0</inf> phase of FeNi was detected in alloys annealed in the temperature range of 673 to 813 K. The present results suggest that the order-disorder transition temperature of L1<inf>0</inf> FeNi is higher than the previously reported value (593 K). The high diffusion rates of the constituent elements induced by the crystallization of an amorphous phase at relatively low temperature (∼673K) are responsible for the development of atomic ordering in FeNi.

DOI： 10.1063/1.4952968

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Materials Chemistry B  

Carbide precipitation in biomedical Co-Cr alloys significantly influences the performance in terms of mechanical properties and corrosion resistance. In this study, we examined the carbide precipitation associated with local solute partitioning in as-cast Co-Cr-W-based dental alloys at the micro- and nano-scale. Co-28Cr-9W-1Si (mass%) alloys with carbon concentrations ranging from 0.01 to 0.33 mass% were prepared. It was found that Cr, W, Si, and C segregated at the interdendritic regions of the face-centered cubic (fcc) γ-grain microstructures, resulting in precipitation; the amount of interdendritic precipitates was found to increase with increasing bulk carbon concentration. We identified, for the first time, the nanosized mixed-phase constituents, which were composed of ∼100 nm fine grains of the γ-phase and M<inf>23</inf>C<inf>6</inf>-type carbide, at the interdendritic regions of the high-carbon Co-Cr-W alloy. These nanosized M<inf>23</inf>C<inf>6</inf> carbides were produced with a cube-on-cube orientation relationship ([001]<inf>γ</inf>∥[001]<inf>M23C6</inf> and (100)<inf>γ</inf>∥(100)<inf>M23C6</inf>) with the surrounding submicron γ-grains, while the local morphology changed from equiaxed to plate-like morphology. Nanoscale partitioning of the alloying elements was considered to be the origin of the interdendritic nanostructured constituents. As such, the nanoscale elemental partitioning was observed to alter the local mechanical properties and to affect the corrosion resistance of the alloys. The observed results indicate the importance of local chemistry - which has not received sufficient attention to date - along with carbide precipitation in the optimization of alloy design for achieving desirable properties such as high strength, ductility, and corrosion resistance in dental Co-Cr-based cast alloys.

DOI： 10.1039/c6tb00040a

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Review B  

Crystal and electronic structures of BiFeO3 thin films (∼10 and ∼300 nm) grown on SrTiO3 substrate have been investigated in terms of BiFeO3 film thickness dependence using the advanced transmission electron microscopy (TEM) technique. Electron diffraction patterns of both BiFeO3 thin films acquired along [011]SrTiO3 cross sections clearly exhibited the existence of extra Bragg's reflections which are absent in that from SrTiO3. Structure factor calculations unambiguously revealed that the electron diffraction pattern corresponds to the [211] net pattern of rhombohedral BiFeO3. High-resolution TEM images combined with multislice simulation also demonstrated that the crystalline structure of both BiFeO3 films is rhombohedral. Electron energy loss spectroscopy results for both BiFeO3 thin films showed spectra with the characteristics of bulk BiFeO3, i.e., rhombohedral. The lattice mismatch of <2.5% between BiFeO3 and SrTiO3 found in a particular epitaxial relationship is considered to be the reason that BiFeO3 can grow by maintaining its bulk crystalline, i.e., rhombohedral, structure.

DOI： 10.1103/PhysRevB.93.064115

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Review B  

We study the enhanced spin relaxation time of Au nanoparticles in nanopillar-shaped double-barrier junction devices with a stacked Fe/MgO/Au-nanoparticle/MgO/Fe structure. The size of Au nanoparticles located in a current path is deduced from a transmission electron micrograph and the Coulomb blockade behavior in the current-voltage characteristics of the devices. A finite tunnel magnetoresistance (TMR) is observed above a critical current and is attributable to spin accumulation in Au nanoparticles. Based on a simple model of TMR due to spin accumulation in a nanoparticle, the spin relaxation time τs is estimated from the magnitude of the critical current. The temperature and bias-voltage region where TMR appears are determined from systematic observations, showing that the appearance of TMR is not associated with the Coulomb blockade but with spin accumulation. We find that the obtained τs is anomalously extended (∼800 ns) at low temperatures and abruptly decreases above a critical temperature. Interestingly, the critical temperature strongly depends on the size of the Au nanoparticles and is much lower than the effective temperature corresponding to the discrete energy spacing. A theoretical analysis for the spin relaxation of electrons with discrete energy levels shows that not only the anomalously extended spin relaxation time, but also the strong temperature dependence of τs arise from the broadening of discrete energy levels due to coupling with phonons in the surrounding matrix. Numerical calculations using reasonable parameter values well reproduce the observed temperature and size dependence of the spin relaxation time in Au nanoparticles.

DOI： 10.1103/PhysRevB.93.085402

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Materials Transactions  

Spatial configurations and lateral morphology of the 14H long-period stacking ordered (LPSO) phase have been studied by single tilt-axis electron tomography using high-voltage scanning transmission electron microscopy (STEM) operated at 1 MV. A "Quonset hut-like" lateral shape of the LPSO was found in a tomogram of a specimen as thick as 1.7 μ m. The reconstructed volume reveals spatial distribution of residual particulate precipitates of (Mg, Zn)<inf>3</inf>Gd phase 20-30 nm in diameters. The precipitates act as a source of solute elements for the formation and growth processes of 14H LPSO. 1 MV-STEM realizes enough resolution for imaging the morphology of LPSO as well as high electron transmittance (∼4.1 μ m) without any obvious electron irradiation damages on microstructures.

DOI： 10.2320/matertrans.M2016021

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

Chemically ordered hard magnetic L1<inf>0</inf>-FeNi phase of higher grade than cosmic meteorites is produced artificially. Present alloy design shortens the formation time from hundreds of millions of years for natural meteorites to less than 300hours. Electron diffraction detects four-fold 110 superlattice reflections and a high chemical order parameter (S≥0.8) for the developed L1<inf>0</inf>-FeNi phase. The magnetic field of more than 3.5kOe is required for the switching of magnetization. Experimental results along with computer simulation suggest that the ordered phase is formed due to three factors related to the amorphous state: high diffusion rates of the constituent elements at lower temperatures when crystallizing, a large driving force for precipitation of the L1<inf>0</inf> phase, and the possible presence of L1<inf>0</inf> clusters. Present results can resolve mineral exhaustion issues in the development of next-generation hard magnetic materials because the alloys are free from rare-earth elements, and the technique is well suited for mass production.

DOI： 10.1038/srep16627

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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 Nuclear Materials  

Nano-engineered 3C-SiC thin films, which possess columnar structures with high-density stacking faults and twins, were irradiated with 2 MeV Si ions at cryogenic and room temperatures. From cross-sectional transmission electron microscopy observations in combination with Monte Carlo simulations based on the Stopping and Range of Ions in Matter code, it was found that their amorphization resistance is six times greater than bulk crystalline SiC at room temperature. High-angle bright-field images taken by spherical aberration corrected scanning transmission electron microscopy revealed that the distortion of atomic configurations is localized near the stacking faults. The resultant strain field probably contributes to the enhancement of radiation tolerance of this material.

DOI： 10.1016/j.jnucmat.2015.06.036

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Microscopy  

We have developed a newly designed straining specimen holder for in situ transmission electron microscopy (TEM) compatible with high-angle single tilt-axis electron tomography. The holder can deform a TEM specimen under tensile stress with the strain rate between 1.5 × 10⁻⁶ and 5.2 × 10⁻³ s⁻¹. We have also confirmed that the maximum tilt angle of the specimen holder reaches ±60° with a rectangular shape aluminum specimen. The new specimen holder, termed as ‘straining and tomography holder’, will have wide range potential applications in materials science.

DOI： 10.1093/jmicro/dfv021

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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 Transactions  

This study has found that the Z-contrast of aberration-corrected high-angle annular dark field-scanning transmission electron microscopy (HAADF-STEM) images of solute enriched layers in Mg-TM-RE (TM:Zn, RE:Y, Gd) alloys is sensitive to the imaging conditions: The defocus and the focal depth. Consequently, the depth position of solute enriched layers in the projected direction shows strong effect on the Z-contrast around each layer. The blurring of the Z-contrast is preferentially observed in both sides region along (0001)Mg basal planes. The boundary position between HCP- And FCC-type stacking sequence at edge regions does not change by defocus. The permissible defocus amount is comparable to the focal depth. The aberration-corrected HAADF-STEM has short focal depth less than 10 nm, so that it is critical for interpreting image contrast that the thin foil thickness and the depth position of the nano-size structure such as the solute enriched layers. In turn, it can be presumed, by the blurring of the Z-contrast, that the depth position of the solute enriched layers in the projected direction. Thus, the focal depth of aberration-corrected HAADF-STEM is quite sensitive to the depth position of solute enriched layers in the thin foil of specimens and the defocus of the electron probe, so that the imaging condition of aberration-corrected HAADF-STEM is critical in order to interpret correctly the Z-contrast of the images.

DOI： 10.2320/matertrans.MAW201505

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Aip Advances  

A structural heterogeneity of the melt-spun Fe<inf>85.2</inf>Si<inf>2</inf>B<inf>8</inf>P<inf>4</inf>Cu<inf>0.8</inf> alloy has been studied by spherical aberration (C<inf>s</inf>) corrected high-resolution transmission electron microscopy. Hollow-cone illumination imaging revealed that the density of coherent scattering regions in the as-quenched Fe<inf>85.2</inf>Si<inf>2</inf>B<inf>8</inf>P<inf>4</inf>Cu<inf>0.8</inf> alloy is much higher than that in the Fe<inf>76</inf>Si<inf>9</inf>B<inf>10</inf>P<inf>5</inf> bulk metallic glass. According to the C<inf>s</inf>-corrected TEM, crystalline atomic clusters, typically of ∼1 nm in diameter, are densely distributed in an amorphous matrix of Fe<inf>85.2</inf>Si<inf>2</inf>B<inf>8</inf>P<inf>4</inf>Cu<inf>0.8</inf> alloy. Observation of four-fold and six-fold atomic arrangements of these clusters implies existence of Fe clusters with the body centered cubic structure. These Fe clusters must be responsible for the formation of ultrahigh-density α-Fe nanocrystals produced by post-annealing.

DOI： 10.1063/1.4923329

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

High-pressure polymorphs recovered in terrestrial craters are evidence of meteoroid impact events on the Earth's surface. Despite countless impact craters on the Moon, high-pressure polymorphs have not been reported to date in returned Apollo samples. On the other hand, recent studies report that the high-pressure polymorphs of silica, coesite, and stishovite occur in shocked lunar meteorites. We investigated regolith breccia 15299, which was returned by the Apollo 15 mission, using the combined techniques of focused ion beam (FIB), synchrotron Xray diffraction (XRD), and transmission electron microscopy (TEM). The regolith breccia 15299 studied here consists of a mafic impact melt breccia with millimeter-sized, coarse-grained, low-Ti basalt clasts. The mafic melt breccia consists of fragments of minerals (olivine, pyroxene, plagioclase, silica, and ilmenite) and glass. Several quartz, tridymite, and cristobalite grains of 10-100 mm across occur in the mafic impact melt breccia. Vesicular melt veins of less than ~200 mm wide cut across the mafic melt breccia matrix and mineral fragments. Some silica grains are entrained in the melt veins. One of the silica grains entrained in the melt veins consist of stishovite [a = 4.190(1), c = 2.674(1) Å, V = 46.95 ų, space group P4<inf>2</inf>/mnm] along with tridymite and silica glass. This is the first report of high-pressure polymorphs from returned lunar samples. TEM images show that the stishovite is needle-like in habit, and up to ~400 nm in size. Considering the lithologies and shock features of 15299, it is inferred that the stishovite possibly formed by the Imbrium impact or subsequent local impact event(s) in the Procellarum KREEP Terrane (PKT) of the nearside of the Moon.

DOI： 10.2138/am-2015-5290

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Materials  

We have studied three-dimensional (3D) configurations of dislocations in the β phase of a Ti-35mass%Nb alloy by means of single-axis tilt tomography using bright-field scanning transmission electron microscopy (BF-STEM). To visualize dislocations, the hh0 systematic reflections were excited throughout tilt-series acquisition with the maximum tilt angle of 70°. Dislocations in the β grains were clearly reconstructed by the weighted back-projection algorithm. The slip planes of the dislocations were deduced by rotating the reconstructed volumes with the aid of selected area electron diffraction patterns. It was found that BF-STEM images with relatively low contrasts, taken along low-order zone axes, are capable to reproduce and preserve the quality of reconstructed image of dislocations. We also found that tilt angles as low as 40° are practically acceptable to visualize 3D configurations of dislocations, while there exists limitation in resolution due to the existence of a large missing wedge.

DOI： 10.3390/ma8041924

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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 Experimental Nanoscience  

Catalytic activities of sonochemically prepared Au-core/Pd-shell-structured bimetallic nanoparticles (NPs) immobilised on TiO<inf>2</inf> were evaluated. Comparing with the mixture of monometallic Au and Pd NPs on TiO<inf>2</inf>, core/shell-immobilised catalysts exhibited higher activities for the partial reduction of nitrobenzene (NB) to aniline (AN), suggesting that the synergistic effect originating from the core/shell structure enhanced the catalytic activities. In the case of high Au/Pd ratios, where the Pd-shell thickness was calculated to be 0.5 nm or lower, infrared spectroscopic measurements of adsorbed CO showed that the Au cores were successfully covered with Pd shells. It was found that a thin Pd shell of one layer or two layers of Pd atoms effectively catalysed the reduction of NB under ambient temperature, whereas the formation of AN was not confirmed on monometallic Au NP-immobilised catalysts.

DOI： 10.1080/17458080.2013.824617

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

The majority of engineering steels are ferromagnetic and structurally inhomogeneous on scales ranging from nanometers to micrometers, and their physical properties depend on the three-dimensional (3D) features in their microstructures. Thus, obtaining a 3D image with a large field of view is desirable for transmission electron microscopy (TEM) based microstructure characterization in order to establish the relationship between the microstructure and the physical properties with a reasonable statistical relevancy. Here, we use a conventional sample preparation process, i.e., mechanical polishing followed by electropolishing, and optimizing experimental protocols for electron tomography (ET) of ferromagnetic materials, to carry out microstructural characterization of engineering steel. We determined that the sample thickness after the mechanical polishing step is a critical experimental parameter affecting the success rate of tilt-series image acquisitions. For example, for ferritic heat-resistant 9Cr steel, mechanical thinning down to 30 μm or less was necessary to acquire an adequate tilt-series image of the carbide precipitates in the annular dark-field scanning TEM (ADF-STEM) mode. However, acquiring tilt-series images of dislocation structures remains a challenge due to an unavoidable, significant electron beam deflection during specimen tilt, even with a thinned sample. To overcome the electron beam deflection problem, we evaluated several relatively accessible approaches including the "Low-Mag STEM and Lorentz TEM" modes. Although rarely used for ET, both modes reduce or even zero the objective lens current, likely weakening the magnetic interference between the ferromagnetic specimen and the objective lens magnetic field. The advantages and disadvantages of these experimental components are discussed.

DOI： 10.2355/isijinternational.55.623

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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 Transactions  

L1<inf>2</inf>-type TM<inf>6</inf>RE<inf>8</inf> clusters are distributed in enriched layers of LPSO (long period stacking ordered structure), and shrink in the [0001]<inf>Mg</inf> direction. The growth mechanism of LPSOs was investigated from the viewpoint of a local strain field. The strength of out-of plane normal strain of the enriched layer varied with the average radius of solute elements in the layer. The first principle calculation showed that there is a relationship between the average atomic radius of solute elements and the structural relaxation in the clusters. Zn conclusion, it is suggested that the difference of average atomic radius between Mg and solute elements controls the degree of the cluster shrinkage by the displacement of the solute elements, and that it is the dominant factor giving rise to the out-of plane normal strains of the enrichment layers.

DOI： 10.2320/matertrans.MH201404

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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：Physics Procedia  

A structural heterogeneity of a newly developed soft magnetic Fe<inf>81.2</inf>Co<inf>4</inf>Si<inf>0.5</inf>B9.5P4Cu0.8 melt-spun alloy has been studied by transmission electron microscopy (TEM) and electron diffraction. Hollow-cone dark-field TEM imaging revealed that the density of coherent scattering regions in the as-quenched Fe<inf>81.2</inf>Co<inf>4</inf>Si<inf>0.5</inf>B<inf>9.5</inf>P<inf>4</inf>Cu<inf>0.8</inf> alloy is as high as that in the Fe<inf>85.2</inf>Si<inf>2</inf>B<inf>8</inf>P<inf>4</inf>Cu<inf>0.8</inf> hetero-amorphous alloy (NANOMET^®). According to the aberration-corrected high-resolution TEM, crystalline atomic clusters, typically of ∼1 nm in diameter, are densely distributed in an amorphous matrix of Fe<inf>81.2</inf>Co<inf>4</inf>Si<inf>0.5</inf>B<inf>9.5</inf>P<inf>4</inf>Cu<inf>0.8</inf> alloy, while nanobeam electron diffraction detected weak Bragg reflections from Fe clusters with the body centered cubic structure. These results unambiguously reveal structural heterogeneity of the as-quenched Fe<inf>81.2</inf>Co<inf>4</inf>Si<inf>0.5</inf>B<inf>9.5</inf>P<inf>4</inf>Cu<inf>0.8</inf> alloy, which is similar to that observed in the NANOMET^®.

DOI： 10.1016/j.phpro.2015.12.154

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Materials Transactions  

Three-dimensional (3D) configurations of 14H long-period stacking ordered (LPSO) structures formed in Mg<inf>97</inf>Zn<inf>1</inf>Gd<inf>2</inf> cast alloys at intermediate stages of the formation process have been studied by single tilt-axis electron tomography using high-angle annular dark-field scanning transmission electron microscopy. Lateral morphology of the 14H LPSO is clearly visualized by reconstructing 3D volumes. An existence of "dent-shaped" area was found in a 3D reconstructed volume for the first time. The edge of LPSO shows a characteristic triangular shape with an angle of 60°, which indicates that the growth front is parallel to {112¯0}<inf>Mg</inf>. It is suggested that in-plane irregular or characteristic shapes are related to the lateral growth mechanism of LPSO. Electron tomography has proven to be an indispensable tool to characterize in-plane structural information of LPSO formed in α-Mg matrix.

DOI： 10.2320/matertrans.MH201406

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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 Transactions  

Using conventional transmission electron microscopy (TEM) and aberration-corrected high-angle annular dark field-scanning transmission electron microscopy (HAADF-STEM), compositional irregularity has been identified around long-period stacking order structures (LPSOs) in aged Mg<inf>97</inf>Zn<inf>1</inf>Y<inf>2</inf>alloys, which have coexistence of LPSO and α-Mg matrix. Elemental mappings show that compositional transition layers surround the growing LPSOs. The compositional transition layer includes solute atmosphere in the α-Mg matrix and transition layers of LPSOs with lower concentrations of solute elements. The Zn concentration in a transition layer of LPSO is higher than that of Y, which differs from the α-Mg matrix and LPSOs. The transition layer is an 18R-type stacking sequence. No transition layer was observed after the transformation from 18R-type to 14H-type LPSOs. These results indicate that the segregation of Zn is faster than that of Y, and that the transition layer is a non-stoichiometric 18R-type LPSO with Zn-rich lower concentration of the solute elements, which connects an 18R-type LPSO and an α-Mg matrix.

DOI： 10.2320/matertrans.MAW201413

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Materials Transactions  

Microstructure and phase decomposition of hexagonal α′ martensite in cold groove rolled (CGR) Ti-12 mass% V-2 mass% Al alloys have been studied by transmission electron microscopy and electron diffraction. Acicular structure of the α′ martensite changes into equiaxed α′ grains by CGR with a cold reduction of 75%. After aging at 573K for 500 h, local Moiré fringes disappear and diffraction rings become sharp due to recovery. However, Vickers hardness also increased in spite of the recovery. Partitioning of solute atoms and/or formation of fine precipitates can be possible cause for the observed age-hardening. Although a CGR alloy is characterized by a microstructure with polycrystalline equiaxed grains, following orientation relationship is locally observed between β precipitates and α grains after aging at 673 K: (101)β // (011̄1̄)α, [010]β // (101̄1)α. Electron tomography revealed a heterogeneous nucleation and growth of β precipitates in the deformed α′ matrix. © 2014 The Japan Institute of Metals and Materials.

DOI： 10.2320/matertrans.M2013463

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of the Ceramic Society of Japan  

Nanocomposite thin films composed of oriented Co<inf>50</inf>Pt <inf>44</inf>Cu<inf>6</inf> nanoparticles embedded in a MgO matrix has been synthesized by rf-magnetron co-sputtering onto NaCl(001) substrates kept at 620 K. As the sputtering power increases, (001) orientation is improved and atomic ordering is also promoted. However, superlattice reflections are quite weak and the ordered region is limited in local area of the nanoparticles, indicating low degree of order. Electron diffraction and elemental mapping revealed that additive Cu is alloyed with CoPt. We have also fabricated (Co <inf>26</inf>Fe<inf>20</inf>)Pt<inf>44</inf>Ag<inf>10</inf>SiO<inf>2</inf> nanocomposite thin films at 675K for comparison. Atomic ordering is promoted by Fe and Ag addition as well as higher substrate temperature; however, it was found that ternary element (Cu, Ag, Fe) addition into CoPt alloy is not so effective to promote atomic ordering. Origin of the slow ordering kinetics is discussed using thermodynamical parameters. © 2014 The Ceramic Society of Japan. All rights reserved.

DOI： 10.2109/jcersj2.122.317

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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 Materials Research  

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 Ta<inf>2</inf>O<inf>6.6</inf>S<inf>0.7</inf>, crystallizes into orthorhombic β-Ta<inf>2</inf>O<inf>5</inf> 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 Ta<inf>2</inf>O<inf>5</inf>, 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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physica Status Solidi B Basic Research  

SbBiTe alloys have been some of the most efficient thermoelectric materials near room temperature. Here we synthesized a complete nanocomposite using γ-ray irradiation, in which Au/AuTe<inf>2</inf> nanoparticles are dispersed uniformly without aggregation in the Sb<inf>1.6</inf>Bi<inf>0.4</inf>Te<inf>3</inf> matrix. The lattice thermal conductivity was significantly reduced mainly due to the increased number of interfaces for phonon scattering between the nanoparticles and the matrix phase, thereby resulting in clear enhancement of dimensionless figure of merit (ZT). The maximum ZT value of the Au/AuTe<inf>2</inf> nanoparticle-supported Sb<inf>1.6</inf>Bi<inf>0.4</inf>Te<inf>3</inf> nanocomposite was 1.01 at 423K, which is about 18% higher than the maximum ZT value of Sb<inf>1.6</inf>Bi<inf>0.4</inf>Te<inf>3</inf>. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

DOI： 10.1002/pssb.201349226

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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：Tetsu to Hagane Journal of the Iron and Steel Institute of Japan  

The majority of engineering steels are ferromagnetic and structually inhomogeneous on special scales ranging from nanometers to micrometers, and physical properties of engineering steels arise from three-dimensional (3D) features of the microstructure. Thus, obtaining 3D representation with a large field of view is desired for transmission electron microscopy (TEM) based microstructure characterization to establish microstructure - physical properties relationships with reasonable statistical relevancy. Here, we venture to use a conventional sample preparation process, i.e., mechanical polishing followed by electro-polishing, and experimental protocols optimization for electron tomography (ET) for ferromagnetic materials, especially engineering steels' microstructural characterization are carried out. We found that the sample thickness after the mechanical polishing step is a critical experimental parameter affecting the success rate of tilt-series image acquisition. For example, for a ferritic heat-resistant 9Cr steel with lath martensite structure, mechanically thinning down to 30 μm or thinner was necessary to acquire an adequate tilt-series image of carbide precipitates in the high-angle annular dark-field scanning TEM (HAADF-STEM) mode. On the other hand, tilt-series image acquisition from dislocation structures remains challenging because the electron beam deflection during specimen-tilt was unavoidable and significant in the HAADF-STEM mode. To overcome the electron beam deflection problem, we evaluate several relatively accessible approaches including the "Low-Mag and Lorentz" TEM/STEM modes; although they are rarely used for ET, both the modes reduce or even zero the objective lens current and likely weaken the magnetic interference between the ferromagnetic specimen and the objective lens magnetic field. The advantages and disadvantages of those experimental components are discussed.

DOI： 10.2355/tetsutohagane.100.889

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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：Key Engineering Materials  

Pb(Mg<inf>1/3</inf>Nb<inf>2/3</inf>)O<inf>3</inf> (PMN) thin films were prepared by metal organic decomposition (MOD) method. The effects of Pb content and annealing temperature on the crystallinity of PMN epitaxial thin films were investigated. The 10at% Pb-excess PMN film annealed at 973 K with facing the film surface against another STO substrate have improved its crystallinity compared with those under another conditions. © (2014) Trans Tech Publications, Switzerland.

DOI： 10.4028/www.scientific.net/KEM.582.19

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

Tetragonally structured barium titanate (BaTiO<inf>3</inf>) single crystals were irradiated using 635 MeV ²³⁸U⁺ ions to fluences of 1 × 10⁷, 5 × 10¹⁰ and 1.4 × 10 ¹² ions cm^-2 at room temperature. Irradiated samples were characterized using ion channeling, X-ray diffraction, helium ion microscopy and transmission electron microscopy. The results show that the ion-entry spot on the surface has an amorphous core of up to ∼10 nm in diameter, surrounded by a strained lattice structure. Satellite-like defects around smaller cores are also observed and are attributed to the imperfect epitaxial recrystallization of thermal-spike-induced amorphization. The critical value of the electronic stopping power for creating observable amorphous cores is determined to be ∼22 keV nm^-1. Molecular dynamics simulations show an amorphous track of ∼1.2 nm in radius under thermal energy deposition at 5 keV nm ^-1; the radius increases to ∼4.5 nm at 20 keV nm^-1. A linear fit of the core diameter as a function of the square root of the energy deposition rate suggests a reduction in the diameter by an average of ∼8.4 nm due to thermal recrystallization if electron-phonon coupling efficiency of 100% is assumed. The simulation also reveals details of the bonding environments and shows different densities of the amorphous zones produced at different energy deposition rates. © 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.actamat.2013.09.029

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.7567/JJAP.52.110120

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出版者・発行元：Japanese Journal of Applied Physics  

It has been reported that composition modulation is naturally formed in some of the epitaxially-grown thin films. Structural characterization of these materials is necessary for controlling their nanostructures precisely. Here, we prepared epitaxially-grown III-V semiconductor alloys and characterized their atomistic structures by means of diffraction crystallography and electron microscopy techniques. As a consequence, we found that the following quantum well structures are spontaneously formed: (1) ultrashort period lateral composition modulation (LCM) with a modulation period of ∼1 nm; (2) complex vertical composition modulated (VCM) structures consisting of two modulated structures with a different period (∼4 and ∼25 nm). The former LCM structure is created via nanoscale phase separation at the growth surface, while the shorter-period modulation in the later VCM structure is induced by rotating a substrate through an inhomogeneous distribution of the anion flux within a chamber. © 2013 The Japan Society of Applied Physics.

DOI： 10.7567/JJAP.52.110120

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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  

Formation of self-oriented and -elongated nanopores in annealed amorphous Nb<inf>2</inf>O<inf>5</inf> and Ta<inf>2</inf>O<inf>5</inf> 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 Nb<inf>2</inf>O<inf>5</inf> and Ta<inf>2</inf>O<inf>5</inf> was also studied. Additive tungsten atoms of a few atomic percent into Nb<inf>2</inf>O<inf>5</inf> and Ta<inf>2</inf>O<inf>5</inf> 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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Acta Materialia  

Biomedical Co-Cr-Mo (CCM) alloys have been commonly used for artificial hip and knee joint prostheses, but a need to improve their biomedical inertness and wear resistance has become widely recognized. The mechanical behavior of CCM alloys is dominated by strain-induced martensitic transformation (SIMT), which causes crack initiation during plastic deformation but dramatically enhances the wear resistance in practical use. To develop more reliable CCM alloys it is essential to clarify the factors affecting the occurrence of SIMT. In the present study we have focused on the effect of annealing twin boundaries (ATBs) on SIMT behavior. We have analyzed in detail the substructures near a parallel pair of ATBs after deformation under a stress preferential for slip parallel to the ATBs. Preferential formation of Z-hexagonal close-packed (HCP) phase at ATBs in metastable γ-face-centered cubic (FCC) phase was found by both scanning electron microscopy with electron backscattered diffraction (EBSD) analysis and transmission electron microscopy (TEM). High resolution TEM images indicated that thickening of the Z-HCP phase does not proceed regularly on every second atomic plane, which would form perfect Z-phase HCP structure, but irregularly leaving a high density of stacking faults. Furthermore, the thickness of the Z-HCP phase was found to be different at ATBs on the two sides of the twin. The difference was attributed to the internal stress due to strain incompatibility at the ATBs on the basis of residual stress analysis by the EBSD-Wilkinson method and phase-field simulation of solute segregation at ATBs. © 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.actamat.2012.11.041

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Review Letters  

In sharp contrast to previous studies on FeRh bulk, thin films, and nanoparticles, we report the persistence of ferromagnetic order down to 3 K for size-selected 3.3 nm diameter nanocrystals embedded into an amorphous carbon matrix. The annealed nanoparticles have a B2 structure with alternating atomic Fe and Rh layers. X-ray magnetic dichroism and superconducting quantum interference device measurements demonstrate ferromagnetic alignment of the Fe and Rh magnetic moments of 3 and 1μ<inf>B</inf>, respectively. The ferromagnetic order is ascribed to the finite-size induced structural relaxation observed in extended x-ray absorption spectroscopy. © 2013 American Physical Society.

DOI： 10.1103/PhysRevLett.110.087207

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Review Letters  

The atomic structure of CoPt and FePt nanoparticles (with a diameter between 2 and 5 nm) has been studied by transmission electron microscopy. The particles have been produced by a laser vaporization cluster source and annealed under vacuum in order to promote chemical ordering. For both alloys, we observe a coexistence of crystalline and multiply twinned particles with decahedral or icosahedral shapes. In addition to particles corresponding to a single L1 <inf>0</inf> ordered domain, we put into evidence that even small particles can display several L1<inf>0</inf> domains. In particular, the chemical order can be preserved across twin boundaries which can give rise to spectacular chemically ordered decahedral particles made of five L1<inf>0</inf> domains. The stability of such structures, which had been recently predicted from theoretical simulations, is thus unambiguously experimentally confirmed. © 2013 American Physical Society.

DOI： 10.1103/PhysRevLett.110.055501

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

Highly L1<inf>0</inf>-ordered FePt thin films with a strong (001) texture were successfully fabricated on amorphous substrates simply by co-sputtering and rapid thermal annealing at a low temperature of 400â°C. The morphology of FePt thin films depended strongly on the heating rate, changing from a continuous structure with an atomically flat surface to an island-like structure. The change of the morphology resulted in a drastic increase of coercivity, indicating that the magnetization process could be controlled by the heating condition. This fabrication method of ordered FePt thin films is favorable in view of the compatibility for a practical device fabrication process. © 2013 Author(s).

DOI： 10.1063/1.4821629

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

This study investigated modulation of the long period stacking order (LPSO) structure in aged Mg<inf>97</inf>Zn<inf>1</inf>Y<inf>2</inf> alloys using conventional transmission electron microscopy (TEM) and aberration-corrected high-angle annular dark field-scanning transmission electron microscopy (HAADF-STEM). The irregular stacking sequence of a fragment of 24R-type LPSO acts as a catalyst for the transformation from 18R- to 14H-type LPSO. The elementary step of the transformation from 18R- to 24R-type takes place by the ledge-pair movement on different (0001)<inf>Mg</inf> planes with Shockley partial dislocations. Each ledge has a transition region in front of it. The transition regions are HCP-type stacking sequence with lower Zn and Y concentrations than those of the FCC-type enrichment layer. The solute elements migrate easily in the region, where solute elements produce a kind of diffusion field. Therefore, structural modulation occurs by a mechanism resembling diffusionaldisplacive transformation. Local strain analysis using HAADF-STEM images has elucidated that lattice spacing of (0001)<inf>Mg</inf> in the FCC-type enrichment layer is shorter than that in the HCP-type transition region. These structural and compositional irregularities are an elementary step in the transformation of LPSO in Mg<inf>97</inf>Zn<inf>1</inf>Y<inf>2</inf> alloys. A diffusionaldisplacive type transformation mechanism in LPSO has been proposed. © 2013 The Japan Institute of Metals and Materials.

DOI： 10.2320/matertrans.MI201221

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Nanomaterials  

We report on atomic structure imaging of epitaxial L1CoPt nanoparticles using chemically sensitive high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). Highly ordered nanoparticles formed by annealing at 973 K show single-variant structure with perpendicular c-axis orientation, while multivariant ordered domains are frequently observed for specimens annealed at 873 K. It was found that the (001) facets of the multivariant particles are terminated by Co atoms rather than by Pt, presumably due to the intermediate stage of atomic ordering. Coexistence of single-variant particles and multivariant particles in the same specimen film suggests that the interfacial energy between variant domains be small enough to form such structural domains in a nanoparticle as small as 4 nm in diameter. © 2013 Kazuhisa Sato et al.

DOI： 10.1155/2013/679638

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Applied Physics Letters  

Fully epitaxial Co<inf>2</inf>Fe<inf>x</inf>Mn<inf>1-</inf> <inf>x</inf>Si(CFMS)/Ag/Co<inf>2</inf>Fe<inf>x</inf>Mn<inf>1</inf> <inf>-x</inf>Si current-perpendicular-to-plane giant magnetoresistive devices with various Fe/Mn ratios x and top CFMS layer thicknesses t <inf>CFMS</inf> were prepared. The highest magnetoresistance (MR) ratios, 58% at room temperature and 184% at 30 K, were observed in the sample with x = 0.4 and t<inf>CFMS</inf> = 3 nm. Enhancement of interface spin-asymmetry was suggested for x = 0.4 compared with that at x = 0. A MR ratio of 58% was also observed even in a very thin trilayer structure, CFMS(4 nm)/Ag(3 nm)/CFMS(2 nm), which is promising for a next-generation magnetic read sensor for high-density hard disk drives. © 2012 American Institute of Physics.

DOI： 10.1063/1.4772546

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Applied Physics Letters  

The atomic structure of extremely small cobalt (Co) nanoparticles embedded in an amorphous carbon (C) matrix has been studied by spherical aberration (C <inf>s</inf>) corrected high-resolution transmission electron microscopy and focal-series restoration. The Co nanoparticles, 1-3 nm in diameter, are crystalline with the face centered cubic structure, while the radial distribution function analysis revealed the existence of a Co-C bond. The reconstructed phase images of the exit-wave function clearly show the projected potential distribution within the Co nanoparticles. The C <inf>s</inf>-correction has hence a benefit to visualize embedded crystalline clusters unambiguously, which are responsible for the magnetotransport properties of the Co-C films. © 2012 American Institute of Physics.

DOI： 10.1063/1.4765362

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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 Nanoparticle Research  

We present a method using high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) to determine the chemical composition of bi-metallic nanoparticles. This method, which can be applied in a semi-automated way, allows large scale analysis with a statistical number of particles (several hundreds) in a short time. Once a calibration curve has been obtained, e.g., using energy-dispersive X-ray spectroscopy (EDX) measurements on a few particles, the HAADF integrated intensity of each particle can indeed be directly related to its chemical composition. After a theoretical description, this approach is applied to the case of iron-palladium nanoparticles (expected to be nearly stoichiometric) with a mean size of 8.3 nm. It will be shown that an accurate chemical composition histogram is obtained, i.e., the Fe content has been determined to be 49.0 at.% with a dispersion of 10.4 %. HAADF-STEM analysis represents a powerful alternative to fastidious single particle EDX measurements, for the compositional dispersion in alloy nanoparticles. © Springer Science+Business Media B.V. 2012.

DOI： 10.1007/s11051-012-1106-z

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Applied Physics Letters  

Gd-doped GaN (Ga <inf>1-x</inf>Gd <inf>x</inf>N) thin films were grown on a GaN(001) template by radio frequency plasma-assisted molecular beam epitaxy and characterized by means of x-ray diffraction (XRD) and transmission electron microscopy (TEM). Three samples with a different Gd composition were prepared in this study: x = 0.02, 0.05, and 0.08. XRD and TEM results revealed that the low Gd concentration GaN possesses the wurtzite structure. On the other hand, it was found that an ordered phase with a quadruple-periodicity along the [001] direction in the wurtzite structure is formed throughout the film with x = 0.08. We proposed the atomistic model for the superlattice structure observed here. © 2012 American Institute of Physics.

DOI： 10.1063/1.4751245

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

We investigated the graphitization of carbonized larch wood chars impregnated with aqueous solution of nickel acetate, using scanning electron microscopy (SEM), both in secondary and transmission modes, and high-resolution transmission electron microscopy (HRTEM). Heat treatment of the chars at 500 °C brought about homogeneous distribution of metallic Ni particles about 5 nm in size in the amorphous carbon matrix. Graphitization sporadically started at this temperature, and some of the Ni particles are aggregated. SEM observations on chars heat-treated at 900 °C suggested that graphitic nanoshells about 50-200 nm in diameter, formed by catalytic effects of the Ni particles, grow in a "meandering" manner inside the amorphous carbon matrix. Some graphitic protrusions are found to grow outwards. Upon removal of the residual amorphous carbon matrix, long chains of the graphitic nanoshells exhibited a three-dimensionally intertwined structure, while transmission SEM showed that the interior of the shells is empty. HRTEM images exhibited not only stacked graphitic layers, but also cross-sectional contrasts expected from the hexagonal net of the graphite structure. These findings are discussed from the viewpoints of processing parameters, such as the use of aqueous solutions and atmosphere, specific to the catalytic graphitization of lignocellulosic materials. © 2012 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.carbon.2012.03.016

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出版者・発行元：TMS Annual Meeting  

Hot deformation behavior and microstructural evolution of Ti-6A1-4V alloy in case of α' martensite starting microstructure were examined by comparing the case in equilibrium (α+β) starting microstructure. Compression test was carried out at 1173 K and 1273 K at strain rates of 0.001s ^-1 and 1s ^-1. In compression test in temperature region of (α+β), equiaxed grained structure is exhibited for both starting microstructures of α' martensite and equilibrium (α+β) after compression test. Then, distortion-less ultrafine grained microstructure is obtained in case of α' martensite starting microstructure after hot compression at condition of 1173 K-1s ^-1. While, the lamellar microstructure consisting of α phase and β phase is obtained after compression at 1273 K, which is above the β-transus of 1268 K, for both the cases of α' starting microstructure and as-received (α+β) starting microstructure. These results indicate that hot deformation behavior in the cases of α' martensite- and (α+β) starting microstructure is different especially at the temperature (1173 K) which is below the β-transus.

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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  

The effects of alloying elements (Ti, Nb, Ta, Cr, W, Re, Co and Si) on the phase equilibria among Ni (A1), Ni <inf>3</inf>Al (L1 <inf>2</inf>) and Ni <inf>3</inf>V (D0 <inf>22</inf>) phases were studied by means of microstructure observation and energy dispersive spectroscopy analysis on thin foils. It was found that the alloying elements can be classified into four categories: (a) Ti stabilizing the phases in the order: L1 <inf>2</inf> > D0 <inf>22</inf> > A1, (b) Nb and Ta stabilizing the phases: D0 <inf>22</inf> > L1 <inf>2</inf> > A1, (c) Cr, W, Re and Co stabilizing the phases: A1 > D0 <inf>22</inf> > L1 <inf>2</inf>, (d) Si stabilizing the phases: Al > L1 <inf>2</inf> > D0 <inf>22</inf>. The elements in the categories (a) and (b) raise the temperature of a eutectoid-type reaction (A1 → L1 <inf>2</inf> + D0 <inf>22</inf>) while the elements in the category (c) reduce the temperature. The alloying effects were examined in terms of mixing enthalpy and electron concentration. © 2011 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.intermet.2011.12.008

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

Suzuki segregation in Co-Ni-based superalloys is of longstanding interest. In this study, the development of widely extended stacking fault (SF) ribbons was confirmed in a Co-Ni-based superalloy aged at 973 K after deformation at room temperature, which supports the decrease in stacking fault energy (SFE) due to Suzuki segregation. In addition, the plastic deformation behaviors of Co-Ni-based superalloys with various Nb contents up to 3 wt.% were investigated focusing on the effect of Nb addition on dynamic strain-aging by Suzuki segregation. The negative strain-rate dependence of flow stress due to dynamic strain-aging became more significant with increasing Nb content; however, attempts to detect segregating elements by scanning transmission electron microscopy and energy-dispersive spectroscopy analysis were not successful. A phase-field simulation of Suzuki segregation suggested strong Ni depletion with segregation of Cr and Mo atoms at the SF, and the SFE can become negative as a consequence of the segregation. This agrees with the experimentally observed formation of wide SFs by the aging at 973 K after cold deformation. It is also suggested that Nb atoms are strongly depleted at SFs, and a small amount of Nb addition dramatically enhances Cr segregation, resulting in further decreases in the SFE, which is probably responsible for the observed enhancement of dynamic strain-aging by Nb addition. In addition, the local structural changes, such as short-range ordering and/or an in-plane ordering, accompanying the segregation were discussed as possible additional mechanisms for strain-aging enhancement. © 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.actamat.2012.01.054

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

Nanoporous Ta<inf>2</inf>O<inf>5</inf> films with oriented and elongated nanopores have been prepared by a technique which utilizes the accumulation of free volume during the crystallization of amorphous Ta<inf>2</inf>O<inf>5</inf> 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 Ta<inf>2</inf>O<inf>5</inf>. © 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.scriptamat.2011.10.033

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Thin Solid Films  

We report on the alloying of epitaxial Co/Pt core-shell nanoparticles using transmission electron microscopy (TEM) and electron diffraction. In as-deposited nanoparticles followed by in situ annealing at 823 K for 10.8 ks, high-angle annular dark-field (HAADF) imaging by scanning TEM (STEM) clearly revealed formation of Co-shell/Pt-core structures due to the large atomic number (Z) difference between Co (Z = 27) and Pt (Z = 78). We identified a formation of locally ordered areas of the L1 <inf>0</inf> ordered phase at the core of the nanoparticles. After ex situ annealing at 873 K for 0.6 ks, some of the ordered areas showed complicated contrasts in the HAADF-STEM images. Based on image simulations, we found that these atypical contrasts arise from the stacking of two orthogonal variants of the L1 <inf>0</inf> phase in the electron beam direction. Furthermore, the simulation showed that image contrast strongly reflects the structure of the variant located closer to the beam entrance rather than to the bottom side. Solid solution phase was formed by further annealing at 873 K for 3.6 ks, while high-density {111} stacking faults were observed inside the Co-Pt alloy nanoparticles. Magnetic coercivity remained at values as low as ∼ 15.9 kA/m at 300 K, irrespective of the formation of local L1 <inf>0</inf> ordered areas and/or a high-density stacking faults. © 2012 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.tsf.2012.01.004

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Philosophical Magazine Letters  

We report on the effect of cooling rate on the size-dependent atomic ordering of CoPt nanoparticles using aberration corrected high-resolution transmission electron microscopy. It was found that cooling rate plays a crucial role in promoting atomic ordering during the cooling process after annealing. Nanoparticles of 3 nm in diameter show the A1-disordered phase after annealing at 873K for 1 h followed by rapid cooling (110 K/min), while the L10-ordered phase is obtained when the cooling rate is slow (1.5 K/min). The disordered phase is also obtained by rapid cooling after annealing at 973K for 1 h. These results unambiguously indicate that the order-disorder transformation temperature is reduced to a temperature at least lower than 873K for CoPt nanoparticles smaller than 3 nm in diameter. The slow cooling process promotes the atomic ordering, which resulted in an enhancement of magnetic coercivity as high as 2200 Oe. This study demonstrates that hard magnetic properties of the CoPt nanoparticles can be improved by controlling the cooling rate after heat treatments. © 2012 Taylor & Francis.

DOI： 10.1080/09500839.2012.685188

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出版者・発行元：TMS Annual Meeting  

Atomic structures of hexagonal α' martensites in Ti-6mass%Al-4mass%V alloys have been studied by means of aberration corrected high-resolution transmission electron microscopy and electron diffraction. There observed differences in atomic structures of the {1011} -type twin boundaries of the α' martensites: stacking faults, a few atomic layers in width, was observed at the twin boundary for the as-quenched alloy after solution treatment at 1100°C (above the β transus), while the alloy solution treated at 950°C (below the β transus) showed a clear-cut twin boundary. The excellent ductility is observed in the latter alloy.

DOI： 10.1002/9781118356074.ch126

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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  

The effect of W on the nanovoid formation in annealed amorphous Al <inf>2</inf>O<inf>3</inf> was studied by transmission electron microscopy and molecular dynamics simulations. A comparison of the void formation behavior in electron-beam deposited Al<inf>2</inf>O<inf>3</inf> (without W) and resistance-heating deposited Al<inf>2</inf>O<inf>3</inf> (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 <inf>2</inf>O<inf>3</inf> showed that the introduction of W into amorphous Al<inf>2</inf>O<inf>3</inf> 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 Al<inf>2</inf>O<inf>3</inf> 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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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  

We report the first microscopic observation of complex precipitates coexisting with LPS phases in Mg<inf>97</inf>Zn<inf>1</inf>Y <inf>1.5</inf>Nd<inf>0.5</inf> (at %) alloy formed by aging at 473 K, and their effects on mechanical properties. It was found that the β' [space group Cmc2<inf>1</inf> , a = 0.68 nm], β<inf>1</inf>[space group Fm3m, a = 0.77 nm] phases and GP zones in α-Mg matrix are responsible for the peak hardness; which appeared after 30 h of annealing at 473 K, while large β<inf>1</inf> precipitates and GP zones appeared in an over-aged specimen. With the increase of the annealing temperature from 473 K to 523 K, stacking faults, together with GP zones appeared. It is proposed that the precipitates and GP-zones contribute simultaneously to the age-hardening process, and that GP zones are more stable at 473 K than 523 K. © 2010 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.intermet.2010.12.003

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Thin Solid Films  

We have studied order-disorder transformation in Fe-Pd alloy nanoparticles by in situ transmission electron microscopy (TEM) and electron diffraction. The transformation is size-dependent, and the transformation temperatures are lower than those of the bulk alloys. The transformation proceeds continuously but rather steeply as the temperature increases, which differs from the first-order transformation observed in a bulk alloy or gradual transformation predicted by simulations for nanoparticles. Experimental results indicated that the continuous nature can be attributed to the distribution of the transformation temperature due to the distributions of both particle size and alloy composition. Quantitative intensity analyses of nanobeam electron diffraction (NBD) patterns indicated the existence of short-range order (SRO) inside disordered nanoparticles. The SRO as well as particle size distribution are responsible for the remaining weak superlattice reflections above the transformation temperature. In situ high-resolution TEM (HRTEM) observation revealed the existence of the SRO, which was consistent with the results obtained by NBD. We show that the disorder may not necessarily proceed continuously from the surface toward the center of the nanoparticle. Ordering from the disordered phase upon cooling was also observed by in situ HRTEM, which can be attributed to growth of the SRO. © 2011 Elsevier B.V. All rights Reserved.

DOI： 10.1016/j.tsf.2010.12.246

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Proceedings of the National Academy of Sciences of the United States of America  

Microcrystals of coesite and stishovite were discovered as inclusions in amorphous silica grains in shocked melt pockets of a lunar meteorite Asuka-881757 by micro-Raman spectrometry, scanning electron microscopy, electron back-scatter diffraction, and transmission electron microscopy. These high-pressure polymorphs of SiO(2) in amorphous silica indicate that the meteorite experienced an equilibrium shock-pressure of at least 8-30 GPa. Secondary quartz grains are also observed in separate amorphous silica grains in the meteorite. The estimated age reported by the (39)Ar/(40)Ar chronology indicates that the source basalt of this meteorite was impacted at 3,800 Ma ago, time of lunar cataclysm; i.e., the heavy bombardment in the lunar surface. Observation of coesite and stishovite formed in the lunar breccias suggests that high-pressure impact metamorphism and formation of high-pressure minerals are common phenomena in brecciated lunar surface altered by the heavy meteoritic bombardment.

DOI： 10.1073/pnas.1009338108

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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 Science and Engineering A  

The microstructures, cold-rolling abilities, and mechanical properties of a Ti-6Al-4V alloy with a α' microstructure were examined, and compared with these properties in alloys with the (α + β) microstructure. The microstructure of a Ti-6Al-4V alloy solution treated at 1373. K followed by quenching (referred to as 1373. K STQ in the following) exhibits the acicular α' martensite microstructure. The alloy exhibits the (equilibrium α + α' martensite) bimodal microstructure when 1223. K solution treatment is carried out followed by quenching (referred to as 1223. K STQ). In contrast, Ti-6Al-4V alloys heat treated at 1373. K or 1223. K, followed by furnace cooling (referred to as 1373. K ST-FC and 1223. K ST-FC), exhibit a lamellar (α + β) microstructure and an equiaxed (α + β) microstructure, respectively. The strength of the STQ specimens was found to be higher than that of the ST-FC specimens. The 1223. K STQ specimen had excellent cold-rolling ability (more than 40% reduction) and higher tensile ductility than those of the ST-FC specimens. The excellent ductility of 1223. K STQ is thought to be due to the constituent phase of the single HCP phase (α' and α) and the fine equiaxed bimodal morphology. The compositional distribution of the V content enrichment and the decrease in the Al content in the α' martensitic region during solution treatment at 1223. K should contribute to the excellent ductility. This work therefore suggests a useful method for improving room-temperature ductility by using industrial Ti-6Al-4V alloys with the α' martensite microstructure. © 2010 Elsevier B.V.

DOI： 10.1016/j.msea.2010.10.070

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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 Physics Conference Series  

We have studied atomic ordering and magnetic properties of epitaxial FePd nanoparticles 3-14 nm in diameter. Thermal fluctuation of magnetic moment of L1<inf>0</inf>-FePd nanoparticles becomes prominent when particle size is smaller than about 8 nm. Atomic images of high-resolution transmission electron microscopy revealed the formation of the ordered phase in FePd nanoparticles as small as 4 nm in diameter, while the superlattice reflections were quite weak compared to those of the larger sized particles (>8nm). The experimental results indicate that the degradation of magnetic anisotropy is induced by the size-dependent decay of long-range atomic order. © Published under licence by IOP Publishing Ltd.

DOI： 10.1088/1742-6596/266/1/012042

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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 Transactions  

Fe and Si hybrid clusters are co-deposited on substrates in a double-glow-discharge-source-type plasma-gas-condensation system, and observed by transmission electron microscopy, scanning transmission electron microscopy, X-ray diffraction and Mössbauer spectroscopy. Core-shell Fe/Si clusters, in which chemically heterogeneous bcc Fe-Si cores are covered by amorphous-like Si shells, are obtained on the substrate when Fe and Si cluster nuclei collide with each other at an early stage (without setting the partition plate between the two sources). On the other hand, Fe and Si clusters are juxtaposed on the substrate when their nuclei collide with each other at a late stage (with setting of the partition plate). These results demonstrate that we can obtain various hybridized states of Fe and Si clusters bv controlline the collision staees. ©2010 The Japan Institute of Metals.

DOI： 10.2320/matertrans.M2010177

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Alloys and Compounds  

Microstructure and phase decomposition of α′ martensites in Ti-12 mass%V-2 mass%Al alloys have been studied by transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM). The as-quenched alloy showed an acicular structure of the hexagonal α′ martensite. Significant age-hardening was observed in the alloys after aging at 300 and 400 °C. A hardness, as high as 377 Hv, was obtained for the alloy after aging at 400 °C for 24 h. The age-hardening can be attributed to fine β precipitates nucleated inside primary α′-martensite plates. These fine acicular precipitates, about 50 nm in length, were identified using high-angle annular dark-field (HAADF) STEM as bright contrasts, indicating a vanadium-rich composition of the β precipitates. As the aging temperature increases, partitioning of vanadium becomes prominent, indicating phase decomposition towards the equilibrium α and β phases. Decomposition of the α′ martensite and formation of α/β two-phase structure were observed after aging at 500 °C for 24 h, which resulted in an abrupt decay of hardness. Plate-like three-dimensional shapes of large β precipitates have been revealed by HAADF-STEM electron tomography. © 2010 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jallcom.2010.07.127

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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  

The structural evolution, epitaxy, and sublimation temperature of silver nanoclusters (NCs) on TiO<inf>2</inf> (110) surfaces prepared in two different ways are reported here based on a combination of in situ reflection high energy electron diffraction characterization and ex situ electron imaging. It is shown that silver NCs deposited at room temperature on oxidized TiO<inf>2</inf> (110) surfaces are unable to form a single epitaxy prior to sublimation. When heated close to sublimation, two particle orientations dominate: (111) Ag∥(110) TiO<inf>2</inf>, [-110] Ag∥[001] TiO<inf>2</inf> and (112) Ag∥(110) TiO<inf>2</inf>, [-110] Ag∥[001] TiO<inf>2</inf>. Single twinned silver NCs are found to be stable even at temperatures close to sublimation. On the other hand, silver NCs prepared similarly on reduced TiO<inf>2</inf> (110) surfaces behave very differently when heated to higher temperatures. On the reduced surface, the NCs are able to evolve into a single epitaxy-(111) Ag∥(110) TiO<inf>2</inf>, [-110] Ag∥[001] TiO<inf>2</inf>. The sublimation temperature for silver NCs on the reduced surface is found to be less than those on the oxidized surface by about 35°. The epitaxy formed by annealing is the same as the one formed by depositing silver onto reduced TiO<inf>2</inf> (110) at 350 °C (>0.5 T<inf>m</inf> of Ag). © 2010 American Institute of Physics.

DOI： 10.1063/1.3296065

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Applied Catalysis B Environmental  

Bimetallic nanoparticles with a Au-core/Pd-shell structure were prepared and successfully immobilized on a TiO<inf>2</inf> surface using sonochemical method. When immobilizing the core/shell structured bimetallic nanoparticles with a Au/Pd molar ratio of 25/75, TiO<inf>2</inf> showed the highest activity for the photochemical H<inf>2</inf> evolution from ethanol aqueous solution. The activities of other two types of photocatalysts with the same Au/Pd molar ratio, TiO<inf>2</inf> immobilizing the mixture of Au and Pd monometallic nanoparticle, and TiO<inf>2</inf> immobilizing Au/Pd random alloy nanoparticles wherein Au and Pd atoms homogeneously located, were also evaluated. The dependence of the photocatalytic activities on the nanostructures of the immobilized bimetals was confirmed. © 2009 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.apcatb.2009.11.015

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Applied Physics  

We have studied three-dimensional shapes and distribution of FePd nanoparticles, prepared by electron beam deposition and postdeposition annealing, by means of single-axis tilt tomography using atomic number contrasts obtained by high-angle annular dark-field scanning transmission electron microscopy. Particle size, shape, and locations were reconstructed by weighted backprojection (WBP), as well as by simultaneous iterative reconstruction technique (SIRT). We have also estimated the particle size by simple extrapolation of tilt-series original data sets, which proved to be quite powerful. The results of the two algorithms for reconstruction have been compared quantitatively with those obtained by the extrapolation method and those independently reported by electron holography. It was found that the reconstructed intensity map by WBP contains a small amount of dotlike artifacts, which do not exist in the results by SIRT, and that the particle surface obtained by WBP is rougher than that by SIRT. We demonstrate, on the other hand, that WBP yields a better estimation of the particle size in the z direction than SIRT does, most likely due to the presence of a "missing wedge" in the original data set. © 2010 American Institute of Physics.

DOI： 10.1063/1.3280026

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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 Physics Conference Series  

CoFeB/MgO/CoFe/MgO/CoFeB double-barrier magnetic-tunnel junctions were fabricated using an ultrahigh vacuum magnetron sputtering system, and their magnetotransport properties were characterized at room temperature. After post-deposition annealing, the polarity of TMR changed from negative to positive with increasing bias voltage. A relatively high negative TMR ratio of 30% was obtained at a negative bias voltage. Furthermore, a unique bias voltage dependence of conductance was observed at room temperature. This behavior may be attributable to the large minority density of states caused by the interfacial oxidation of the middle CoFe layer. © 2010 IOP Publishing Ltd.

DOI： 10.1088/1742-6596/200/5/052009

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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：Key Engineering Materials  

Ti alloys are widely utilized for industrial applications due to their excellent mechanical properties combined with low density. In general, Ti alloys are classified as a, α+β and β alloys, with further subdivision into near α and metastable β alloys. Quite recently, we have presented new type structural α′ martensite (H.C.P.) Ti alloys with low Young's modulus, high strength and excellent ductility at room temperature. In this work, we examined the microstructure and mechanical properties of α′ martensite type Ti-V-Al alloy after cold- or hot working process. Then, we found that deformation behavior of α′ initial microstructure as compared with (α+β) initial microstructure was different based on the results of stress-strain curves and Processing Maps under the hot working process. Further, cold rolled α′ martensite microstructure exhibited the refined equiaxed dislocation cell structure, thereby resulting in high strength. This result suggests the new type deformation processing (for both cold- and hot work processing) utilizing α′ martensite in industrial Ti alloys. © (2010) Trans Tech Publications.

DOI： 10.4028/www.scientific.net/KEM.436.171

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記述言語：日本語   出版者・発行元：The Magnetics Society of Japan  

Perpendicularly magnetized magnetic tunnel junctions (MTJs) were fabricated by depositing thin L1₀-ordered FePt films on MgO(001) substrates using a UHV sputtering system, and the dependence of structural, magnetic, and magnetotransport properties of the junctions on the thickness of the FePt layers was investigated. A full epitaxial structure of MgO(001) sub./Cr/Pt/FePt/MgO/CoPt/Ta was observed. The tunnel magnetoresistance (TMR) ratio was measured to be 6% at room temperature, and magnetization switching was clearly observed in the thin FePt layer. Transmission electron microscopy (TEM) observations revealed that the interface between FePt, MgO, and CoPt layer has strain due to lattice mismatch, which might be a reason for the low TMR ratio.

DOI： 10.3379/msjmag.1003R047

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その他リンク： https://jlc.jst.go.jp/DN/JALC/00351380523?from=CiNii

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Tetsu to Hagane Journal of the Iron and Steel Institute of Japan  

The effect of Ti addition on phase equilibria among Ni (Al), Ni <inf>3</inf>Al (L1<inf>2</inf>) and Ni<inf>3</inf>V (D0<inf>22</inf>) phases at 950°C was investigated by means of TEM/EDS analysis on heat-treated alloys. The three-phase coexisting region of Al +L1<inf>2</inf>+D0<inf>22</inf> was found to exist around the composition of Ni-4A1-19V (at.%) in the Ni-Al-V ternary system. By addition of Ti into the ternary system the three-phase coexisting region was shifted to the Ni rich side. Ti partitioned most into the L1<inf>2</inf> phase and least into the Al phase. These results suggest that the addition of Ti stabilizes the L1<inf>2</inf> phase against D0<inf>22</inf> and Al phases.

DOI： 10.2355/tetsutohagane.96.386

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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 Transactions  

Microstructure and mechanical properties of cold groove rolled α' Ti-V-Al and Ti-V-Sn alloys were investigated. Microstructure after solution treatment at 1223 K and quenching into ice water showed the acicular martensitic structure of α' phase for (Ti-12mass%V)-2 mass%Al and (Ti-8 mass%V)-4mass%Sn alloys and (α' + α') phases for (Ti-12 mass%V)-6 mass%Sn alloy. After cold groove rolling at reduction of 75%, microstructure evolved into the equiaxed refined cell structure having the preferred rolling texture of 〈101̄0〈 parallel to rolling direction. After cold groove rolling, Young's modulus decreases to 47.5 GPa, in contrast, tensile strength increases to more than 1000 MPa accompanying with work nardening and gram rennement. © 2009 The Japan Institute of Metals.

DOI： 10.2320/matertrans.MA200912

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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 Microscopy  

Finely dispersed hard magnetic L1o-FePtCu nanoparticles with 〈100〉 orientation were directly synthesized by RF-sputtering on NaCl substrate at a temperature of 613 K. The maximum coercivity of the particles was 1.4 kOe (at RT). Degrees of atomic long-range order (LRO) for the L1o-FePtCu nanoparticles with different sizes were obtained using nanobeam electron diffraction technique. The decrease of LRO parameter became remarkable when the size became below 8 nm. The coercivity value also decreased with decreasing the particle size. The relation between the LRO parameter decrease and the coercivity decrease with particle size was discussed. © 2009 The Royal Microscopical Society.

DOI： 10.1111/j.1365-2818.2009.03234.x

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Review Letters  

We present experimental evidence of surface induced disordering at magnetic FeCoPd nanoparticles during the L10-A1 phase transition using high-resolution aberration-corrected electron microscopy and strain mapping. In situ electron diffraction studies show a narrow temperature range of fully ordered L10 structure. The order-disorder transition is size dependent and induces strong lattice deformation in outer part of the nanocrystals. The formation of unusually large strain of 20% is discussed in terms of core-shell structure formation with surface disordered layer and ordered core. © 2009 The American Physical Society.

DOI： 10.1103/PhysRevLett.103.115703

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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  

We report an in situ study of epitaxial island formation and alloying of FePd nanoparticles using reflection high-energy electron diffraction (RHEED) followed by ex situ atomic structure characterization. We used aberration corrected (AC) scanning transmission electron microscopy (STEM) with a high-angle annular dark field (HAADF) detector for the study of chemical ordering. The FePd nanoparticles were formed by sequential deposition of Pd and Fe onto NaCl substrates, which was then followed by heating to high temperatures to promote chemical ordering during a short period of annealing. We show that the epitaxial island growth and subsequent alloying of Fe into Pd can be clearly detected by RHEED. The high resolution and the atomic number (Z) contrast of AC HAADF-STEM allow a clear observation of nanometer-sized local chemical order in very small nanoparticles. The results revealed complex chemical structures at an intermediate stage of the ordering process with ordered regions of both L 10 and L 12 phases. © 2009 American Institute of Physics.

DOI： 10.1063/1.3122601

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Applied Physics Letters  

We prepared TlInGaAsN/TlInP quantum well structures using gas source molecular-beam epitaxy and characterized them by means of transmission electron microscopy and scanning transmission electron microscopy. It was found that naturally formed vertical quantum wells, so-called lateral composition modulation (LCM), with a periodicity of ∼1 nm are formed in TlInGaAsN layers. We discuss their formation process using a simple kinetic Ising model for layer-by-layer growth, and point out that the formation of ultrashort-period LCM is a universal phenomenon in most of epitaxially grown III-V semiconductor alloys. © 2009 American Institute of Physics.

DOI： 10.1063/1.3117507

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Applied Physics  

The atomic structure of FePd nanoparticles has been studied by spherical aberration (C<inf>s</inf>) corrected high-resolution transmission electron microscopy. The periodic arrangement of atoms arising from chemical order is clearly seen as bright contrast due to the small negative value of corrected C<inf>s</inf>. The amount of optimal defocus (Scherzer defocus) is markedly reduced by the small C<inf>s</inf> value. The interface between crystalline particles and the amorphous matrix can also be observed, free of imaging artifacts, at a small defocus value. The reconstructed phase image directly shows the projected potential distribution within the specimen and reveals the elemental differences due to chemical order. The clear-cut long-range order is lost when particle size is smaller than about 5 nm, at which locally ordered mixed-phase particles begin to dominate. © 2009 American Institute of Physics.

DOI： 10.1063/1.3074505

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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 Transactions  

Mg-0.7 at%Zn-1.4 at%Y alloys annealed at low temperatures after quenching in water from 520°C were studied by high-resolution transmission electron microscopy (HRTEM) and high-angle annular detector dark-field scanning transmission electron microscopy (HAADF-STEM). Stacking faults, thin bands of a 14H-type long period stacking (LPS) phase and relatively thick bands of LPS were precipitated in α-Mg crystalline grains by annealing at 300°C, 400°C and 500°, respectively. The precipitation of stacking faults, LPS phase and a supersaturated solid solution without any precipitates were reversibly transformed by annealing at low temperatures. It can be concluded that the stacking faults and LPS phase are stabilized by the segregation ot Zn and Y from a supersaturated solid solution. © 2009 The Japan Institute of Metals.

DOI： 10.2320/matertrans.MRP2008335

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記述言語：日本語   出版者・発行元：THE CARBON SOCIETY OF JAPAN  

Wood carbon prepared by nickel-catalyzed carbonization at 900°C followed by washing with acid for removal of the metal was oxidized in a muffle furnace at 480°C. This eliminated the amorphous region selectively, and the residual carbon became superior to a commercial electro-conductive carbon, Denka black, in the performance. Observations by scanning electron microscopy and transmission electron microscopy disclosed that the crystallite region in the original wood carbon had a novel graphitic nanostructure. It is noted that such a uniquely morphological graphitic carbon can be inexpensively and easily produced from woody biomass.

DOI： 10.7209/tanso.2009.169

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

Nanocomposite catalysts, consisting of Pd and magnetic maghemite, prepared by sonochemical reduction method showed high catalytic activities for the reduction of nitrobenzene. The used catalysts could be readily retrieved by magnets and be employed for further repetitive tests and verified the durability of the catalytic performance. Copyright © 2008 The Chemical Society of Japan.

DOI： 10.1246/cl.2008.922

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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 Science and Engineering C  

Lotus-type porous Fe-25 wt.%Cr, Fe-23 wt.%Cr-2 wt.%Mo alloys and type AISI 446 stainless steel were fabricated by continuous zone melting technique in pressurized hydrogen and helium gas. The porosity of the samples varied in the range 44-48% and the mean pore size values obtained (145-374 μm) are in the biomedical field desired range. The fabricated Lotus-type porous nickel-free stainless steel was nitrided at high temperature up to the nitrogen concentration of 1.0 wt.% and this amount resulted to be sufficient for maintaining almost single-phase austenitic structure at room temperature. The combination of very small magnetic susceptibility, light weight, mechanical properties close to the human cortical bone, together with the known good enough corrosion resistance of high nitrogen nickel-free stainless steel, makes this Lotus-type porous Fe-Cr-N alloys very attractive for bone implant applications. © 2007 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.msec.2007.01.010

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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  

The hard magnetic L 10 ordered phase formation in thin Pd and Fe bilayers prepared on MgO (001) substrate has been investigated by transmission electron microscopy using in situ annealing. The structures of as-deposited Fe/Pd and Pd/MgO interfaces were characterized by high-resolution transmission electron microscopy. Fast intermixing of Fe and Pd layers and immediate L 10 phase formation within the alloyed area was found at 673 K. The high-resolution observations indicated that the ordered region of the L 10 -FePd phase was formed in dispersed areas without a predetermined nucleation site. At 773 K, the growing ordered areas occasionally formed antiphase boundaries between the adjacent parts. The ordered L 10 -FePd thin layer contained translational domains with tetragonal c axis perpendicular to the substrate. © 2007 American Institute of Physics.

DOI： 10.1063/1.2826632

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担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Review B Condensed Matter and Materials Physics  

The size dependence of structural transition from multiple-twinned particles (MTP) to epitaxial face centered cubic nanocrystals was investigated for Ag nanoparticles formed on Si(001) surfaces by in situ reflection high-energy electron diffraction and ex situ transmission electron microscopy. The transition from MTP to nanocrystals was promoted by postdeposition annealing. Clear particle size dependence is found in the epitaxial formation temperatures (TE), which is about 2/3 of the calculated, size-dependent, melting temperature (TM) using the value of surface energy γS =1.2 J m2 for larger particles (>2 nm). Once nanocrystals are formed, they decay and disappear in a narrow temperature range between 795 and 850 K. No evidence of nanocrystal melting was detected from the reflection high-energy electron diffraction observations. © 2007 The American Physical Society.

DOI： 10.1103/PhysRevB.76.144113

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IEEE Transactions on Magnetics  

The effect of Co addition to magnetic properties of L1<inf>0</inf>-FePd nanoparticles is investigated. Nanocrystalline films with Fd-Co-Fe particles were prepared by electron-beam deposition and subsequent annealing to obtain the ordered L1<inf>0</inf> structure. The L1<inf>0</inf>-PdCoFe nanocrystals were formed up to 12 at % of Co concentrations with preferential c axis orientation. At higher Co concentrations, two-phase nanoparticles of L1<inf>0</inf> -PdCoFe and bcc-CoFe were formed. The saturation magnetization is increased with increasing the Co concentration. The saturation magnetization of L1 <inf>0</inf>-Pd<inf>51</inf>Co<inf>12</inf>Fe<inf>37</inf> nanoparticles is estimated as 1252 emu/cm³ at room temperature. Since it possesses a decrease of L1<inf>0</inf> ordering temperature together with an enhancement of preferential easy axis formation and an increase of saturation magnetization, the Co addition is demonstrated the beneficial impact to L1<inf>0</inf>-FePd nanoparticles. © 2007 IEEE.

DOI： 10.1109/TMAG.2007.893853

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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 Transactions  

Oriented and densely dispersed Ll<inf>0</inf>-FePtCu nanoparticles have been directly synthesized by co-evaporation of Fe, Pt and Cu using rfmagnetron sputtering onto NaCl substrate kept at 563-613 K without any post-deposition annealing. Formation of the L1<inf>0</inf>-type structure in the specimens fabricated as low a substrate temperature as 563 K (Fe<inf>40</inf>Pt <inf>50</inf>Cu<inf>10</inf>) was confirmed by electron microscopy and electron diffraction, while the coercivity measured at room temperature was very low and the intensity of the superlattice reflections was quite weak. The atomic ordering was promoted in the specimen fabricated at 613 K with a composition of Fe<inf>37</inf>Pt<inf>52</inf>Cu<inf>11</inf>, resulted in a higher coercivity exceeding 1 kOe at room temperature as well as appearance of clear superlattice reflections. In addition to the evolution of atomic ordering, (100) oriented growth was enhanced as the substrate temperature increased. Particle size dependence of long-range order (LRO) is considered to be responsible for the decrease of coercivity with particle size reduction as well as thermal fluctuation of magnetization. High coercivity was obtained for specimens with Cu concentration near 10at% under the present sputtering condition. The LRO in the FePtCu ternary phase is considered to sensitively depend on me alloy concentration. © 2007 The Japan Institute of Metals.

DOI： 10.2320/matertrans.48.903

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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 Magnetism and Magnetic Materials  

We investigated the compositional dependence of microstructure and the coercivity of FePt-M-B(M{double bond, short}Zr, Nb, La) sputter-deposited films. As-deposited ternary FePt-B films have an amorphous structure and low coercivity. After annealing at 923 K for 1.8 ks, ordered L1<inf>0</inf> FePt nanoparticles were observed. With the adding of the fourth element of M(Zr, Nb, La), the as-deposited films were also of the amorphous structure. After annealing at the same condition, the films show high coercivity of ∼520 kA/m and ordered L1<inf>0</inf> FePt phase are found. Compared with the ternary FePt-B films, the structure, coercivity and grain size vary with the additional element (M) and the compositions. The effects of additive elements on transformation to the L1<inf>0</inf>-ordered phase have been studied. © 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jmmm.2006.11.138

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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 Magnetism and Magnetic Materials  

L1<inf>0</inf>-type FePd nanoparticles with mean sizes between 4 and 15 nm in diameter have been fabricated by electron beam evaporation. Coercivity and remanence of FePd nanoparticles with sizes less than about 8 nm were quite low compared to the values for 10-nm-sized FePd nanoparticles. Both coercivity and remanence increased with decreasing the temperature, indicating the large suppression of the thermal agitation of the magnetic moment at lower temperatures. Superparamagnetic behavior appeared in zero-field-cooled (ZFC) and field-cooled (FC) temperature dependence of magnetization for about 6-nm-sized FePd nanoparticles. Disappearance of the hard magnetic properties in smaller sized FePd nanoparticles is attributed to the reduction of the long-range order (LRO) parameter of the L1<inf>0</inf>-structure as well as the thermal agitation of magnetic moment. © 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jmmm.2006.11.104

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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  

L 10 -PdCoFe nanoparticles were prepared by vapor deposition of the components and characterized by transmission electron microscopy and by superconducting quantum interference device magnetometry. Co addition to the Fe-Pd nanocrystals resulted in a strong perpendicular magnetic anisotropy and a reduction in the formation temperature of the ordered L 10 phase. Formation of the ordered phase was studied by in situ annealing of specimens inside the transmission electron microscope. L 10 phase formation started at 698 K, as evidenced by the appearance of 110 superlattice reflections in electron diffraction patterns. Co additions enhanced the magnetic easy axis alignment perpendicular to the film plane. The perpendicular maximum coercivity at room temperature was 1.75 kOe for L 10 -PdCoFe nanoparticles with an average size of 8 nm, and the magnetic coercivity decreased by increasing the Co concentration in the L 10 nanoparticles. © 2007 American Institute of Physics.

DOI： 10.1063/1.2434958

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Japanese Journal of Applied Physics Part 1 Regular Papers and Short Notes and Review Papers  

The microstructures of iron suicides synthesized by electron-beam evaporation were examined as a function of iron (Fe) deposition thickness on a silicon (Si) substrate. Si(100) substrates were prebaked at 923 K to clean their surface, and then an Fe thin film layer with a thickness of 2-10 nm was deposited. Transmission electron microscopy observations revealed that the atomistic structures of the as-deposited thin film layer depend on the Fe deposition thickness: amorphous layer (2nm) and crystalline Fe layer (4-10 nm). After thermal annealing at 1173 K for 2h, the deposited Fe atoms diffused into the Si substrate and formed iron silicides. It was found that both ε-FeSi and β-FeSi<inf>2</inf> exist at the deposition thickness of 2 nm, and that the amount of β-phase increases with the deposition thickness. Well-isolated iron silicide nanoparticles were obtained at deposition thicknesses less than 4 nm, whereas the deposition thickness of >10 nm was necessary for the formation of a continuous β-FeSi<inf>2</inf> layer on the Si substrate. We also examined the effects of prebaking temperature on the as-deposited thin film layer and annealing-induced iron suicide phases. © 2007 The Japan Society of Applied Physics.

DOI： 10.1143/JJAP.46.732

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出版者・発行元：Solid State Phenomena  

Isolated and oriented hard magnetic FePtCu ternary alloy nanoparticles with the L1<inf>0</inf>-type ordered structure have been directly fabricated by rf-magnetron sputtering onto NaCl substrate kept at 613K without any post-deposition annealing. Structure and morphology of those particles were studied by TEM. When the sputtering duration decreases, the particle size decreases and the particle areal number density increases. These nanoparticles have 〈100〉 orientation on the NaCl substrate. Alloy composition distribution from particle to particle examined by nano-beam elemental x-ray analysis was found to be quite small, which can be attributed to the homogeneous structure formed by co-deposition of Fe, Pt and Cu by sputtering. Thermal fluctuation of the magnetization becomes prominent in the specimen with the particle size smaller than about 10nm in diameter.

DOI： 10.4028/3-908451-33-7.129

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出版者・発行元：Solid State Phenomena  

Oriented and densely dispersed L1<inf>0</inf>-FePtCu nanoparticles have been directly synthesized by co-evaporation of Fe, Pt and Cu using rf-magnetron sputtering onto NaCl substrate kept at 563-613K without any post-deposition annealing. Under as low a substrate temperature as 563K, superlattice reflections of the L1<inf>0</inf> phase appeared in selected area electron diffraction pattern, while the intensity was quite weak. As the substrate temperature increased from 563K to 613K, 〈100〉 oriented growth as well as the atomic ordering were promoted, resulted in a large increase of coercivity.

DOI： 10.4028/3-908451-31-0.855

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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）  

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出版者・発行元：Solid State Phenomena  

The structure and magnetic properties of sequentially deposited Pd-Co and Pd-Co-Fe nanocrystals have been investigated by transmission electron microscopy (TEM) and superconducting quantum interference device magnetometer. The fcc structured PdCo alloy formation was found in binary Pd-Co nanostructured samples analysed by in situ TEM annealing. In ternary sample, the addition of Fe to Pd-Co resulted in a complex of Pd and FeCo nanoparticles. In situ TEM annealing of the ternary sample lead to the formation of Ll<inf>0</inf> ordered phase. It was found that the magnetic properties of the nanoparticles were improved by Fe addition to the Pd-Co nanoparticles.

DOI： 10.4028/3-908451-31-0.907

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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  

Oriented and well-isolated 14-nm -sized Fe41 Pd52 Cu7 ternary alloy nanoparticles with the L 10 -type ordered structure have been fabricated by the sequential deposition of Pd, Cu, and Fe on NaCl (001) substrate followed by postdeposition annealing. The annealing temperature required to obtain a high coercivity decreased by at least 50 K upon the addition of a small amount of Cu. Furthermore, it was revealed that a strong preferential c -axis orientation along the film normal direction was achieved by the addition of Cu, which resulted in a strong perpendicular magnetic anisotropy. The population of the nanoparticles with their c -axis oriented normal to the film plane was 74%. The alloy composition was independent of the particle size, as determined by energy dispersive x-ray spectroscopy using nanoprobe electrons. Nanobeam electron diffraction revealed that the axial ratio is constant for FePdCu nanoparticles with sizes between 10 and 25 nm. Interparticle magnetostatic and exchange interactions played an insignificant role in the isolated FePdCu nanoparticles. The correlation between their preferential c -axis orientation and magnetic properties is discussed based on the rotation magnetization of single magnetic domain particles. © 2006 American Institute of Physics.

DOI： 10.1063/1.2357420

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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  

We have synthesized epitaxially grown iron disilicide (FeSi<inf>2</inf>) nanoparticles using an electron-beam evaporation technique and characterized them by transmission electron microscopy (TEM). An Fe film was deposited on a Si(100) substrate, followed by thermal annealing at 1073 K for 2 h. It was found that epitaxially grown nanoparticles with an average size of ∼ 10 nm were formed just beneath the Si surface, suggesting that the deposited Fe atoms diffuse into the substrate. Every single phase of nanoparticles was examined in detail by TEM observation, nanobeam electron diffraction, and energy-dispersive x-ray spectroscopy. Plan-view and cross-sectional TEM observations revealed that these nanoparticles consist of α-, α-, and γ-FeSi <inf>2</inf>. It was found that the morphology of nanoparticles is closely related to the phases. The α and β phases consist of angled hemisphere and asymmetric triangle-shaped nanoparticles, respectively, while the γ phase consists of hemispherical or columnar-shaped nanoparticles. These particle morphologies are discussed with respect to the lattice mismatches between the particles and the matrix. © 2006 American Institute of Physics.

DOI： 10.1063/1.2209751

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Japanese Journal of Applied Physics Part 2 Letters  

A low-temperature synthesis of isolated and oriented L1<inf>0</inf>-FePtCu nanoparticles with high-density dispersion has been achieved by a conventional rf magnetron sputtering technique with a single crystal NaCl substrate. Hard magnetic L1<inf>0</inf>-type ordered phase with a coercivity of about 1.4 kOe is directly formed at substrate temperatures as low as 613 K without any post-deposition annealing. With a decrease in sputtering duration, particle size and interparticle distance decrease. These nanoparticles have 〈100〉 orientation on the NaCl substrate. The alloy compositional change from particle to particle is quite small. Although the atomic ordering is confirmed even at 563 K, the intensity of the superlattice reflections is very weak. The thermal fluctuation of magnetization becomes prominent in specimens with particle size smaller than about 10nm in diameter. © 2006 The Japan Society of Applied Physics.

DOI： 10.1143/JJAP.45.L608

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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 Materials Science  

We have synthesized iron silicides on a Si(111) substrate using an electron-beam evaporation technique in combination with thermal annealing. The microstructures, as a function of heating rate on annealing, were characterized by transmission electron microscopy (TEM). Bright-field plan-view TEM observations revealed that a discontinuous thin film is formed in the sample annealed rapidly, while complete separated nanoparticles were obtained in the specimen annealed slowly. Selected-area and nano-beam electron diffraction patterns indicated that the former and latter specimens mainly consist of iron monosilicide (ε-FeSi) and iron disilicide (β-FeSi<inf>2</inf>) phases, respectively. © 2006 Springer Science + Business Media, Inc.

DOI： 10.1007/s10853-006-7820-0

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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  

Oriented and well-isolated L 10 -FeCuPd ternary alloy nanoparticles have been fabricated by electron-beam evaporation followed by postdeposition annealing. A single L 10 phase was formed in the FeCuPd nanoparticles with (Fe+Cu) content lower than 48 at. %. A strong preferential c -axis orientation along the film normal direction was achieved by Cu addition, which leads to a strong perpendicular magnetic anisotropy. Also, a lowering of the ordering temperature by 50 K compared to the binary L 10 -FePd nanoparticles was achieved by Cu addition. By contrast, composite particles composed of the bcc Fe and the L 10 -FeCuPd were formed when the (Fe+Cu) content was higher than 52 at. %. Coexistence of the bcc Fe and the L 10 -FeCuPd was confirmed by high-resolution transmission electron microscopy and nanobeam electron diffraction. It was found that perpendicular magnetic anisotropy of the L 10 -FeCuPd nanoparticles on the NaCl substrate is sensitive to the alloy composition. © 2006 American Institute of Physics.

DOI： 10.1063/1.2165604

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Materials Transactions  

Disappearance of long-range atomic order in 10-nm-sized L1<inf>0</inf>-FePd (Fe-58 at%Pd) nanoparticles has been studied by electron diffraction using a specimen heating stage attached to a transmission electron microscope. Ordered structure is kept at lowest up to 949 K, while the intensity of superlattice reflection abruptly drops at 982 K. The transformation temperature decreases by about 80 K compared to that of the bulk alloy of Fe-58 at%Pd. Nanobeam electron diffraction from a particle shows a particle size dependence of the transformation temperature and the intensity of 110 superlattice reflection largely decreases below about 15 nm in diameter at 983 K. However, a weak intensity remains in the 110 superlattice reflection even at 983 K, which is attributed to short-range order in the nanoparticles. © 2006 The Japan Institute of Metals.

DOI： 10.2320/matertrans.47.59

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出版者・発行元：Journal of Ceramic Processing Research  

Atomic ordering of 10-nm-sized L1<inf>0</inf>-FePt, FePd and CoPt nanoparticles have been studied by transmission electron microscopy and electron diffraction. Proceeding of the atomic ordering was confirmed by the increase of coercivity as well as electron diffraction. Among these three kinds of L1 <inf>0</inf> nanoparticles, the atomic ordering reaction proceeded at the lowest temperature as low as 773 K for FePd nanoparticles. Coercivities of FePt and FePd nanoparticles largely increased with particle diameter and reached 10 kOe for 20-nm-sized FePt particles at room temperature. The large coercivity is attributed to the rotation magnetization of single-domain particles. For CoPt nanoparticles the observed coercivity was very small even after annealing at 1023 K for 1h. The slow rate of the L1<inf>0</inf> ordering can be attributed to the lowest T<inf>c</inf>/T<inf>m</inf> value in CoPt nanoparticles. L1 <inf>0</inf> ordering was also confirmed even in very small FePt particles as small as 2-3 nm in diameter. By contrast, FePd nanoparticles with sizes less than 5 nm showed disordered fcc even after annealing at 873 K. The coercivity of 4-nm-sized L1<inf>0</inf>-FePt nanoparticles were quite low and the observed largest coercivity was 490 Oe at 10 K after annealing at 873 K for 12 h.

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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  

The long-range order (LRO) parameter (S) of single isolated L 10 -FePd nanoparticle was determined by quantitative analysis of nanobeam electron diffraction (NBD) intensities and intensity calculations considering the multiple scattering of electrons. The obtained order parameters of the nanoparticles larger than 8 nm are distributed around the mean LRO parameter (S- =0.79) which was determined by selected area electron diffraction intensity analysis, while the parameters slightly decreased gradually as the particle size decreased below about 8 nm (S=0.60-0.73). The low degree of order in very small particles is responsible for the coercivity decrease of the L 10 nanoparticles in smaller-sized regions. Quantitative NBD intensity analysis is quite useful for the determination of the LRO parameter of individual L 10 -FePd single crystalline nanoparticle. Experimental conditions required for NBD analysis are presented in detail and the possible experimental errors of the determined LRO parameters are discussed. © 2005 American Institute of Physics.

DOI： 10.1063/1.1985973

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Applied Physics  

Long-range order (LRO) parameters of two-dimensional dispersed single-crystalline 10-nm -sized FePd nanoparticles with the L 10 structure have been determined accurately by electron diffraction in transmission electron microscopes (TEMs) under accelerating voltages of 300 kV and 1 kV. Diffraction patterns by exciting hh0 systematic reflections effectively reduced the numbers of diffracted beams and simplified the thickness dependence of intensity ratio I110 I220 for 110 and 220 reflections. Mean thickness of the nanoparticles was estimated to be 7.8 nm by electron holography. The relation between the intensity ratio and the order parameter was calculated on the basis of multiple-scattering intensity calculation. By comparing the relation and experimentally obtained intensity ratios, the order parameters of 0.65 and 0.79 were obtained using 300-kV TEM for FePd nanoparticles after annealing at 873 K for 3.6 and 36 ks, respectively. Also, the order parameter of 0.82 was obtained using 1-MV TEM for the same specimen annealed at 873 K for 36 ks. These order parameters were determined using the Debye-Waller factors for bulk Fe and Pd. The order parameter decreased about 7.3% when a very large Debye-Waller factor as large as 0.01 nm2 was assumed. A combination of electron diffraction under the conditions of hh0 systematic reflections and the diffraction experiment at the high accelerating voltage makes the LRO parameter analysis easy and correct. © 2005 American Institute of Physics.

DOI： 10.1063/1.1861987

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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  

Isolated nanoparticles composed of bcc-Fe and L1<inf>0</inf>-FePd have been fabricated by successive deposition of Pd and Fe onto NaCl substrate cleaved in air, and their structural characterization has been performed by transmission electron microscopy (TEM). Alloy composition was varied by changing the deposited Fe thickness in the thickness range between 2 and 7.5 nm with respect to the fixed Pd thickness of 1 nm. Post-deposition annealing lead to a formation of dual phase nanocomposite particles with the L1<inf>0</inf>-type ordered phase and the bcc-Fe phase within each particle. The particle size little changed on annealing at 873K, indicating that both alloying and atomic ordering reactions proceeded within each nanoparticle. The size of the bcc-Fe region in Fe/FePd nanoparticles was measured from TEM images and its relation to the change of the maximum energy product was discussed.

DOI： 10.4028/0-87849-980-6.275

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担当区分：責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Applied Physics  

The fabrication of exchange-coupled α-Fe/L1<inf>0</inf>-FePd nanocomposite particles, by annealing the Fe/Pd nanocomplex particles, was analyzed. It was observed that two regions composed of α-Fe and L1 <inf>0</inf>-FePd coexisted in each nanoparticle separated by a diffusion boundary. It was also observed that there was a gradual increase in the saturation magnetization with increase in the volume ratio of the α-Fe region. The results show that an exchange coupling existed between α-Fe and L1<inf>0</inf>-FePd crystallites connected coherently with each other within the nanoparticles.

DOI： 10.1063/1.1782963

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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  

Thin films of FePt nanoparticles were prepared by co-deposition of Fe and Pt on to amorphous C films kept at 350°C. As-prepared films were composed of disordered Fe-Pt nanoparticles with a fee structure, where twinned and multiply twinned Fe-Pt nanoparticles could be identified by transmission electron microscopy (TEM) and electron diffraction. Atomic ordering from fee to L1 <inf>0</inf> structure was followed by in-situ TEM observation during heating up to 750°C. Multiply twinned (fivefold) nanoparticles of the L1<inf>0</inf> FePt were observed for the first time by high-resolution TEM observation. In these nanoparticles the crystallographic c axes of L1<inf>0</inf> structure is oriented parallel to the film plane in each segment. The stability of the fivefold FePt nanoparticles is briefly discussed.

DOI： 10.1080/14786430410001678172

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.jmmm.2003.12.1004

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出版者・発行元：Journal of Magnetism and Magnetic Materials  

Oriented L1<inf>0</inf>-FePt nanoparticles with mean sizes as small as 12nm have been fabricated by electron beam evaporation. Atomic order parameter evaluated was as low as 0.55±0.02 in spite of the long-time annealing as long as 86.4ks at 873K. Magnetoanisotropy constant was estimated to be 1.2-1.4×10⁶J/m³, which was much smaller than that of bulk FePt. Residual magnetization showed a decay of about 3-4% at 300K. The relatively small values of magnetoanisotropy are closely related to the small order parameter, and thought to be responsible for residual magnetization decay at 300K. © 2003 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jmmm.2003.12.1044

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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）  

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Applied Physics  

An investigation on the variation of the particle size, particle density and its relation to the hard magnetic properties of FePt nanoparticles with respect to substrate surface morphologies and substrate temperatures was performed. At a substrate temperature below 573 K, densely dispersed FePt nanoparticles with a particle density of 10¹² cm ^-2 were obtained. It was found that for obtaining well-oriented and well-isolated L1<inf>0</inf>-FePt nanoparticles with large coercivity, substrate temperatures between 623 and 823 K were necessary.

DOI： 10.1063/1.1541641

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Applied Physics  

Isolated 10-nm-sized FePd nanoparticles were fabricated by electron-beam evaporation and postannealing above 773 K. FePd particles were epitaxially grown on a cleaved NaCl(001) substrate and were two-dimensionally dispersed on the substrate. Results showed that coalescence and growth of the particles were not prominent during annealing, indicating that the alloying and atomic ordering reactions proceeded mostly within each nanoparticle.

DOI： 10.1063/1.1568531

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Scripta Materialia  

Effects of particle size and additive element on atomic ordering of FePt nanoparticles have been examined by transmission electron microscopy and electron diffraction. Additive Ag deposited after the formation of Fe/Pt nanoparticles effectively reduces the ordering start temperature. The ordering reaction proceeds during the deposition at 673 K when the mean particle sizes are below 7 nm. © 2003 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.

DOI： 10.1016/S1359-6462(02)00605-X

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Materials Transactions  

Two-dimensionally dispersed L<inf>0</inf>-FePt nanoparticles as small as 12 nm with orientation was fabricated by electron-beam evaporation and post-annealing at 873 K. After a prolonged annealing at 873 K for 86.4 ks, the increase of coercivity was almost saturated and coercivity reached 434 kAm ^-1 at 300 K, which is very small compared to recent reports on FePt nanoparticles with sizes larger than 20 nm. Long-range order parameter of the fabricated nanoparticles was determined by electron diffraction at 200 kV taking the multiple scattering into consideration. Obtained order parameter remained 0.55 ± 0.02 for the nanoparticles with an axial ratio c/a of 0.961 ± 0.003. The low degree of order is thought to be responsible for the small coercivity. Effect of Debye-Waller factor on the order parameter was discussed.

DOI： 10.2320/matertrans.44.1518

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Applied Physics  

Oriented L1 <inf>0</inf>-FePt and FePd nanoparticles with coercivities as large as 5 kOe (FePt) and 3 kOe (FePd) were fabricated by alternating deposition of Pt(or Pd) and Fe nanoparticles and their annealing at the temperatures between 773 and 873 K on single crystal NaCl and MgO. Atomic ordering reactions and degrees of order towards the L1 <inf>0</inf>-structure formation in these nanoparticles were investigated by high resolution electron microscopy and electron diffraction, and magnetic coercivities at low temperature were also measured. The long range order parameter of the FePt nanoparticles was ∼0.56 even after annealing at 873 K for 24 h. The coercivity of the FePt nanoparticles at 100 K was as high as twice the room temperature value. The low degree of order in the L1 <inf>0</inf>-structure formation and the thermal effect on magnetization have been found in the present FePt and FePd nanoparticles. These are closely concerned with the origin of the coercivity values which are very small in comparison with those expected from the single magnetic domain theory. © 2002 American Institute of Physics.

DOI： 10.1063/1.1456446

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Japanese Journal of Applied Physics Part 2 Letters  

Nanoparticles of L1<inf>0</inf>-type ordered "FeAu", which does not exist in the equilibrium phase diagram, have been fabricated by annealing Fe/Au nano-complex particles with sizes of 20-30 nm. The structure of the nanoparticles was investigated by transmission electron microscopy. After annealing the Fe/Au particles with a mean composition of Fe-22 at% Au, Au-rich (more than 32at%) and Au-poor (less than 16 at%) regions were formed in most of the particles. The (110) lattice fringes of the L1<inf>0</inf>-type structure were frequently observed in the Au-rich regions where a dark contrast was always observed. The specimen showed ferromagnetic properties and its coercivity was increased up to about 40 kA/m by annealing. The formation of the ferromagnetic L1<inf>0</inf>-FeAu phase was discussed.

DOI： 10.1143/JJAP.41.L1

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Scripta Materialia  

The alloying reaction of Fe and Pt and the ordering reaction in nanometer-sized FePt particles was observed by in-situ TEM observation. At the initial stage of annealing, Fe started to dissolved into the Pt particles, then the ordering reaction started to occur simultaneously. These two reactions continued until all the Fe dissolved into the Pt during the annealing. The large magnetic coercivities as large as 815 kA/m were explained by the disappearance of the three-variants domains and the formation of crystallographic single domains.

DOI： 10.1016/S1359-6462(01)00914-9

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出版者・発行元：Journal of Ceramic Processing Research  

Atomically ordered FePt nanoparticles (L1<inf>0</inf>-type structure) covered with amorphous (a-) Al<inf>2</inf>O<inf>3</inf> have been fabricated. In this process, Fe particles were deposited on Pt "seed" particles which were epitaxially grown on (100) NaCl or MgO substrates. Annealing the a-Al<inf>2</inf>O<inf>3</inf>/Fe/Pt films at temperatures higher than 773 K leads to a formation of ordered nanoparticles with mutual fixed orientation in a monolayer form. Three variant ordered domains of the tetragonal L1<inf>0</inf> structure coexisted in a single nm-sized FePt particle, even in a particle as small as 7 nm. According to in-situ electron diffraction study, the degree of order of the ordered structure started to increase on annealing at 773 K and almost saturated on annealing at 873 K for 16 h. The magnetic coercivity varied depending on the particle size and the degree of order in the L1<inf>0</inf> structure formation. The perpendicular coercivity exceeded the in-plane one during the annealing. The in-plane coercivities of FePt nanoparticles measured both parallel to [100]<inf>MgO</inf> and [010]<inf>MgO</inf> directions were almost equal in numerical value. These results reflect the ordered domain formation process and the volume fraction of the domains. Remanent magnetization decay measured for the in-plane magnetization revealed a magnetic relaxation with the type of magnetic dipolar interaction between the FePt particles.

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Japanese Journal of Applied Physics  

Two-dimensionally dispersed 10 nm-sized Fe/Pd and Fe/Pt particles (nanoparticles) with orientations have been fabricated with the same condition using an electron-beam evaporation technique. Heat treatments at temperatures above 773 K lead to a formation of L1<inf>0</inf>-type (CuAu I-type) FePd and FePt ordered alloy particles with sizes as small as 10 nm. In the case of FePt nanoparticles, coercivity started to increase at 873 K, while in the case of FePd at 773 K. Moreover, in most of the FePd nanoparticles, their c-axes oriented normal to the film plane and the perpendicular coercivity reached as high as 1.2 kOe after annealing at 773 K for 1 h. This method can be applied to fabricate ultra-high density magneto-optical or vertical recording media under low annealing temperatures for the L1<inf>0</inf>-structure formation especially in the Fe-Pd system.

DOI： 10.1143/JJAP.39.L1121

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IEEE Transactions on Magnetics  

Isolated FePt particles were fabricated by taking advantage of overgrowth of Fe on Pt particles and subsequent annealing at 873K. The annealing lead to the formation of ordered tetragonal (L1<inf>0</inf>) FePt particles with three orthogonal variants. The average size of FePt particles could be adjusted to less than 10 nm and no significant grain coarsening occurred upon annealing due to the existence of an amorphous Al<inf>2</inf>O<inf>3</inf> layer. Nano-beam electron diffraction revealed that the lattice constant ratio c/a was approximately 0.97 for the annealed FePt particles with Fe composition close to 50 at.%.

DOI： 10.1109/20.908663

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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  

Thin films of oriented tetragonal FePt particles separated by amorphous alumina have been fabricated by electron beam evaporation. The ordering of the FePt particles without coarsening can be tailored by annealing conditions. The value of coercivity of the annealed film reached as high as 4.4 kOe. The perpendicular magnetic coercivity of the annealed film was slightly larger than in-plane coercivity. Some of the tetragonal FePt particles were found to have {111} twins and stacking faults. From our high-resolution electron microscopy observations, it was determined that central region of the ordered FePt particles tended to have oaxis perpendicular to the film plane. © 2000 American Institute of Physics.

DOI： 10.1063/1.372900

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Applied Physics Letters  

Thin films of oriented island-like crystallites of L1<inf>0</inf> FePt separated by amorphous (a-) Al<inf>2</inf>O<inf>3</inf> were fabricated. The process took advantage of the overgrowth of α-Fe on Pt "seed" particles epitaxially grown on (100) NaCl and MgO substrates and the ordering reaction between Fe and Pt upon annealing at temperatures higher than 500°C. The coercivities of the annealed (600°C for 6 h) a-Al<inf>2</inf>O<inf>3</inf>/Fe(1 nm)/Pt (1.5 nm) films on both the NaCl (100) and MgO (100) substrates are higher than 3.3 kOe. Transmission electron microscopy observation showed that the film consisted of oriented L1<inf>0</inf> FePt island-like crystals with an average size of 12 nm and a separation of 4 nm. It was found that any one of the three 〈100〉 axes of the fcc Pt parent particles could act as the tetragonal c axis of the L1<inf>0</inf> FePt superstructure and all three-variant ordered crystalline domains of the tetragonal L1<inf>0</inf> phase could exist in the small 10-nm-size FePt crystallites. The high magnetic coercivity of the film, with well-separated FePt particles, can be attributed to the ordering (L1<inf>0</inf>) as well as the oriented nature of the FePt crystallites. © 1999 American Institute of Physics.

DOI： 10.1063/1.125429

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担当区分：筆頭著者,　責任著者   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：The Magnetics Society of Japan  

Granular magnetic films composed of randomly oriented α-Fe nanoparticles on amorphous Al₂O₃ were synthesized by electron beam deposition. The nanocrystals were prepared by taking advantage of the growth of α-Fe on fcc-Au "used" nanoparticles. For films with an average Fe thickness of less than 1 nm, the resistivity was quite large (10⁴-10⁷ μΩcm). With these films, the temperature dependence of the resistivity ρ can be fitted by ρ = Aexp(α<i>T</i>^-1/2), where A and α are material constants. The films showed a magnetoresistance of about 1.4% in an applied field of 10 kOe at room temperature.

DOI： 10.3379/jmsjmag.23.1177

J-GLOBAL

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記述言語：英語   出版者・発行元：The Magnetics Society of Japan  

Granular thin films of oriented α-Fe nanoparticles were prepared by taking advantage of the epitaxial growth of α-Fe on <100> oriented Au "seed" nanoparticles, which were epitaxially grown on a (100) NaCl substrate. The crystallographic orientation between α-Fe and Au nanocrystals is <100>Au//<100>Fe with {010}Au//{011 }Fe. It is shown that this method can be applied to control the size and inter-particle distance of oriented Fe nanocrystals in granular films. Effects of the α-Fe particle size and inter-particle distance on the coercivity of the films have been studied.

DOI： 10.3379/jmsjmag.23.736

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Web of Science

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 Electron Microscopy  

Granular thin films of oriented α-Fe nanoparticles on a-Al<inf>2</inf>O<inf>3</inf> were fabricated by electron beam evaporation technique. The process took advantage of the overgrowth of α-Fe on Au or Pt 'seed' particles epitaxially grown on (100) NaCl substrates, which were later removed in distilled water. The crystallographic orientation between α-Fe and Au (Pt) nanocrystals was < 100>(Au(Pt))//<100>(Fe) with {010}(Au(Pt))//{011}(Fe). The magnetic coercivity of the oriented α-Fe particles was controllable by particle size and inter-particle distance. Annealing of the a-Al<inf>2</inf>O<inf>3</inf>/Fe/Pt films at temperatures higher than 500°C led to a formation of the ordered L1<inf>0</inf>-FePt phase. Any one of the three <100> axes of the fcc parent phase acted as the tetragonal c-axis of the L1<inf>0</inf> superstructure. Magnetic coercivities of a-Al<inf>2</inf>O<inf>3</inf>/Fe/Pt films were found to be largely increased by heat treatment. The coercivity of the annealed a-Al<inf>2</inf>O<inf>3</inf>/Fe/Pt films reached as high as 3.5 kOe with a squareness of 0.74. It has been shown that magnetic property can be improved by controlling orientation and structure of the magnetic particles.

DOI： 10.1093/oxfordjournals.jmicro.a023745

Scopus

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