Croissy-sur-Seine, France


Croissy-sur-Seine, France
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Asahina S.,Tohoku University | Asahina S.,JEOL EUROPE SAS | Takami S.,Tohoku University | Otsuka T.,JEOL Ltd. | And 3 more authors.
ChemCatChem | Year: 2011

Development of new analytical tools for nanostructures directly contributes to the study of catalysts. By using scanning electron microscopy (SEM) with a newly designed signal enhancer, we study cubic and truncated octahedral cerium oxide (CeO2) nanoparticles, which are composed of smaller primary octahedral CeO2 and are formed through bond formation with hexanedioic acid. The signal enhancer is designed to efficiently collect secondary electrons of kinetic energy less than 10eV; thus, it greatly improves the S/N ratio. On the basis of the observed SEM images and electron backscattered diffraction patterns of the cross section of the nanoparticles, we discuss the formation mechanism of the nanoparticles and speculate that the primary CeO2 nanocrystals share their edges in the cubic nanoparticles and truncated octahedral nanoparticles. These results will contribute to the preparation of nanostructured metal oxide surfaces with controlled morphologies that could enhance catalytic activity. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Togashi T.,Tohoku University | Naka T.,Japan National Institute of Materials Science | Asahina S.,JEOL EUROPE SAS | Asahina S.,Tohoku University | And 3 more authors.
Dalton Transactions | Year: 2011

Magnetic nanoparticles (MNPs) have many potential biomedical applications. Improvements in their magnetic properties and solubility are necessary for these applications to realize their full potential. In this study, MNPs in the form of raspberry-like magnetite (Fe3O4) nanoparticle clusters, consisting of tiny Fe3O4 particles with a diameter of approximately 20 nm, were prepared under hydrothermal conditions at 200 °C in the presence of 3,4-dihydroxyhydroxysinnamic acid (DHCA). The primary particles were connected by DHCA molecules to form the clusters, which were well dispersed in water media because a COOH group from DHCA appeared on their surfaces. The cluster size could be tuned from 50 to 400 nm without changing the primary particle size by controlling the reaction time. Therefore, all prepared clusters displayed superparamagnetic properties at room temperature. In addition, the sensitivity of Fe3O4 to an external magnetic field could also be controlled by the cluster size. © 2011 The Royal Society of Chemistry.

Adschiri T.,Tohoku University | Takami S.,Tohoku University | Minami K.,Tohoku University | Yamagata T.,Japan Chemical Innovation Institute | And 10 more authors.
Materials Science Forum | Year: 2012

Various composite materials have been developed, but in many cases problems arise due to the combined materials such as fabrication becoming difficult because of the significant increase in viscosity, and transparency of the polymer is sacrificed. These issues can be overcome by controlling the nano-interface; however, this is considered as a difficult task since nanoparticles (NPs) easily aggregate in polymer matrices because of their high surface energy. Organic functionalization of inorganic NPs is required to increase affinity between NPs and polymers. For fabricating multi-functional materials, we proposed a new method to synthesize organic modified NPs by using supercritical water. Because organic molecules and metal salt aqueous solutions are miscible in supercritical water and water molecules serve as acid/base catalysts for the reactions, hybrid organic/inorganic NPs can be synthesized under the supercritical condition. The hybrid NPs show high affinity for the organic solvent and the polymer matrix, which leads to the fabrication of these super hybrid NPs. How to release the heat from the devices is the bottle neck of developing the future power devices, and thus nano hybrid materials of polymer and ceramics are required to achieve both high thermal conductivity and easy thin film flexible fabrication, namely trade-off functions. Surface modification of the BN particles via supercritical hydrothermal synthesis improves the affinity between BN and the polymers. This increases the BN loading ratio in the polymers, thus resulting in high thermal conductivity. Transparent dispersion of high refractive index NPs, such as TiO2 and ZrO2, in the polymers is required to fabricate optical materials. By adjusting the affinity between NPs and the polymers, we could fabricate super hybrid nanomaterials, which have flexiblility and high refractive index and transparency. © (2012) Trans Tech Publications, Switzerland.

Schmid H.,Leibniz Institute for New Materials | Schmid H.,University of Bonn | Okunishi E.,JEOL Ltd. | Oikawa T.,JEOL Europe SAS | Mader W.,University of Bonn
Micron | Year: 2012

ZnO with additions of Fe 2O 3 or In 2O 3 shows characteristic inversion domain structures. ZnO domains are separated by two types of inversion domain boundaries (IDBs): basal b-IDBs parallel to (0001) planes, and complementary pairs of three possible variants of pyramidal p-IDBs parallel to 2 1̄ 1̄ 5 lattice planes. The structure and composition of IDBs were investigated in a sophisticated aberration-corrected scanning transmission electron microscope (probe-corrected TEM/STEM). It is shown that Fe and In additions are essentially located in monolayers within the IDBs, and EELS electron spectroscopic imaging (ESI) as well as EDS spectroscopic imaging by X-rays (SIX) are capable of rapidly mapping the element distribution. With solid solubility of trivalent dopant species well below 1at.% within ZnO domains, the lateral spacings of b-IDBs are inversely proportional to the dopant concentration. Quantification of data acquired by ESI and SIX from well defined sample regions in STEM both confirm the assumption of one full monolayer of dopants per IDB. Atom columns of cations are well resolved in HAADF STEM imaging; experimental contrast intensities are approximately proportional to Z 1.6. Furthermore, annular bright-field (ABF)-STEM imaging is capable of resolving oxygen columns even in thick sample regions, thus providing highly localized information on atom positions and lattice distortions, and enables the construction of more reliable structure models of IDBs in doped ZnO. © 2011 Elsevier Ltd.

Gonzalez J.R.,University of Cordoba, Spain | Zhecheva E.,Bulgarian Academy of Science | Stoyanova R.,Bulgarian Academy of Science | Nihtianova D.,Bulgarian Academy of Science | And 6 more authors.
Physical Chemistry Chemical Physics | Year: 2015

An anatase nanotube array has been prepared with a special morphology: two concentric walls and a very small central cavity. The method used here to achieve the double-wall structure is a single-step anodization process under a voltage ramp. Thanks to this nanostructure, which is equivalent to a fractal electrode, the electrochemical behaviour is improved, and the specific capacity is higher in both lithium and sodium cells due to pseudocapacitance. The double-wall structure of the nanotube enhances the surface of TiO2 being in contact with the electrolyte solution, thus allowing an easy penetration of the alkali ions into the electrode active material. The occurrence of sodium titanate in the electrode material after electrochemical reaction with sodium is studied by using EPR, HRTEM and NMR experiments. © the Owner Societies 2015.

Jiang H.,Aalto University | Ruokolainen J.,Aalto University | Young N.,University of Oxford | Oikawa T.,JEOL Europe SAS | And 3 more authors.
Micron | Year: 2012

Applications relevant to carbon based nano-materials have been explored using a newly installed JEOL-2200FS field emission gun (FEG) (scanning) transmission electron microscope (S)TEM which is integrated with two CEOS aberration correctors for both the TEM image-forming and the STEM probe-forming lenses. The performance and utility of this newly commission hardware has been reviewed with a particular focus on operation at an acceleration voltage of 80. kV, thus bringing the primary electron beam voltage below the knock-on threshold for carbon materials and opening up a range of possibilities for the study of carbon-based nanostructures in the aberration-corrected electron microscope. The ability of the microscope to obtain both atomic TEM images and high-quality electron diffraction patterns from carbon nanotubes was demonstrated. The chiral structure of a double-walled carbon nanotube was determined from its diffraction pattern. The aberration corrected TEM imaging technique facilitates a unique approach to accurate determination of single-walled carbon nanotube diameters. On the other hand, the probe-corrected high angle annular dark field (HAADF) STEM imaging performance allows for the detection of single gold atoms at 80. kV and was used to study the graphite interlayer spacing in a multi-walled carbon nanotube. © 2011 Elsevier Ltd.

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