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Werheit H.,University of Duisburg - Essen | Filipov V.,Frantsevich Institute for Problems of Materials Science | Kuhlmann U.,University of Duisburg - Essen | Kuhlmann U.,Pirelli SpA | And 8 more authors.
Science and Technology of Advanced Materials | Year: 2010

We present Raman spectra of numerous icosahedral boron-rich solids having the structure of α-rhombohedral, β-rhombohedral, α-tetragonal, β-tetragonal, YB66, orthorhombic or amorphous boron. The spectra were newly measured and, in some cases, compared with reported data and discussed. We emphasize the importance of a high signal-to-noise ratio in the Raman spectra for detecting weak effects evoked by the modification of compounds, accommodation of interstitial atoms and other structural defects. Vibrations of the icosahedra, occurring in all the spectra, are interpreted using the description of modes in α-rhombohedral boron by Beckel et al. The Raman spectrum of boron carbide is largely clarified. Relative intra- and inter-icosahedral bonding forces are estimated for the different structural groups and for vanadium-doped β-rhombohedral boron. The validity of Badger's rule is demonstrated for the force constants of inter-icosahedral B-B bonds, whereas the agreement is less satisfactory for the intra-icosahedral B-B bonds. © 2010 National Institute for Materials Science.

Shiroyama T.,National Institute for MaterialsScience | Abe T.,National Institute for MaterialsScience | Takahashi Y.,National Institute for MaterialsScience | Hono K.,National Institute for MaterialsScience
IEEE Transactions on Magnetics | Year: 2013

We have studied the microstructures and magnetic properties of FePt-segregant granular films to achieve an ideal media structure on glass substrates for thermally assisted magnetic recording. Although FePt-C granular films show an excellent in-plane structure, it does not have a good surface roughness. Meanwhile, FePt-SiO2 granular films have a smooth surface and an interconnected in-plane microstructure. Therefore, to obtain both a surface with a small roughness and well-isolated small columnar grains, we have selected four metal oxides, MOx (M=Nb, W, Zr and Al) as segregants, which are expected to have a driving force for the phase separation between FePt-C and FePt-SiO2 based on thermodynamic evaluation. In this paper, we introduce the ground for selecting these materials as segregants and then show the microstructure and magnetic properties of FePt-MOx granular films. © 2013 IEEE.

PubMed | National Institute for MaterialsScience
Type: Journal Article | Journal: Physical chemistry chemical physics : PCCP | Year: 2011

The optical use of colloidal silicon nanocrystals (Si NCs) has gained increasing attention for its possible contributions to building a sustainable society that ideally uses resources and energy with high efficiency without causing damage to the environment or human health. Si wafers (E(g) 1.1 eV) dominate modern microelectronics as an impressive electronic material, but they exhibit relatively poor optical performance owing to an indirect bandgap structure. Interestingly, however, full control of the size distribution and surface chemistry of the NCs yields size-dependent light emission in a very wide range from near-ultraviolet through visible to near-infrared wavelengths. In addition to such unique luminescence properties, Si exhibits a high chemical affinity to covalent linkages with carbon, oxygen, and nitrogen, thereby producing almost unlimited variations in organic-Si NCs architectures hybridized at the molecular level. To achieve this goal, I note some parameters, including interfacial chemistry, that are emerging as important elements for increasing our understanding of the effect of quantum confinement in nanostructured Si and for realizing efficient fluorescence emission. This article covers new aspects of derivatives of Si NCs in applications that utilize their optical absorption and emission features.

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