Spectroscopic studies for identifying the chemical states of the periostracum of the Corbicula species in Lake Biwa.

Corbicula clam shells consist of thin periostracum and calcareous layers made of calcium carbonate (CaCO3). Depending on habitat conditions, the shell exhibits various colorations, such as yellow, brown, and black. The chemical state of the periostracum of the Corbicula species in Lake Biwa was studied by X-ray absorption fine structure (XAFS) and Raman scattering spectroscopies. Fe K-edge X-ray absorption near edge structure (XANES) revealed that the Fe3+ intensity increases as the color of the shell changes from yellow to black. Raman spectra suggested that quinone-based polymers cover the yellow shell, and the black shell is further covered by dihydroxyphenylalanine (DOPA) rings of amino acid derivatives. From Fe K-edge extended X-ray absorption fine structure (EXAFS), it was found that Fe3+ in the periostracum was surrounded by five to six oxygen atoms with an average Fe-O ligand distance of 2.0 Å. Accordingly, a tris-DOPA-Fe3+ complex is formed, which is responsible for the periostracum's black color.

Correlation between crystal structure and magnetism in PLD grown epitaxial films of ε-Fe2O3 on GaN.

In the present paper we discuss correlations between crystal structure and magnetic properties of epitaxial ε-Fe2O3 films grown on GaN. The large magnetocrystalline anisotropy and room temperature multiferroic properties of this exotic iron oxide polymorph, make it a perspective material for the development of low power consumption magnetic media storage devices. Extending our recent progress in PLD growth of ε-Fe2O3 on the surface of technologically important nitride semiconductors, we apply reciprocal space tomography by electron and x-ray diffraction to investigate the break of crystallographic symmetry occurring at the oxide-nitride interface resulting in the appearance of anisotropic crystallographic disorder in the sub-100 nm ε-Fe2O3 films. The orthorhombic-on-hexagonal nucleation scenario is shown responsible for the development of a peculiar columnar structure observed in ε-Fe2O3 by means of HRTEM and AFM. The complementary information on the direct and reciprocal space structure of the columnar ε-Fe2O3 films is obtained by various techniques and correlated to their magnetic properties. The peculiar temperature dependence of magnetization studied by the small-field magnetization derivative method and by neutron diffraction reveals the existence of a magnetic softening below 150 K, similar to the one observed earlier solely in nanoparticles. The magnetization reversal in ε-Fe2O3 films probed by X-ray magnetic circular dichroism is found different from the behavior of the bulk averaged magnetization measured by conventional magnetometry. The presented results fill the gap between the numerous studies performed on randomly oriented ε-Fe2O3 nanoparticles and much less frequent investigations of epitaxial epsilon ferrite films with lattice orientation fixed by the substrate.

Enhanced oxygen reduction activity of platinum subnanocluster catalysts through charge redistribution.

Single-size platinum Pt6 subnanoclusters exhibit superior mass-specific and surface-specific activities for the oxygen reduction reaction. The enhanced activity is attributed to polarized electron distributions based on rigorous structure characterization by X-ray absorption fine structure spectroscopy and density functional theory.

Magnetization reversal in YIG/GGG(111) nanoheterostructures grown by laser molecular beam epitaxy.

Thin (4-20 nm) yttrium iron garnet (Y3Fe5O12, YIG) layers have been grown on gadolinium gallium garnet (Gd3Ga5O12, GGG) 111-oriented substrates by laser molecular beam epitaxy in 700-1000 °C growth temperature range. The layers were found to have atomically flat step-and-terrace surface morphology with step height of 1.8 Å characteristic for YIG(111) surface. As the growth temperature is increased from 700 to 1000 °C the terraces become wider and the growth gradually changes from layer by layer to step-flow regime. Crystal structure studied by electron and X-ray diffraction showed that YIG lattice is co-oriented and laterally pseudomorphic to GGG with small rhombohedral distortion present perpendicular to the surface. Measurements of magnetic moment, magneto-optical polar and longitudinal Kerr effect (MOKE), and X-ray magnetic circular dichroism (XMCD) were used for study of magnetization reversal for different orientations of magnetic field. These methods and ferromagnetic resonance studies have shown that in zero magnetic field magnetization lies in the film plane due to both shape and induced anisotropies. Vectorial MOKE studies have revealed the presence of an in-plane easy magnetization axis. In-plane magnetization reversal was shown to occur through combination of reversible rotation and abrupt irreversible magnetization jump, the latter caused by domain wall nucleation and propagation. The field at which the flip takes place depends on the angle between the applied magnetic field and the easy magnetization axis and can be described by the modified Stoner-Wohlfarth model taking into account magnetic field dependence of the domain wall energy. Magnetization curves of individual tetrahedral and octahedral magnetic Fe3+ sublattices were studied by XMCD.

Translocation of 133Cs administered to Cryptomeria japonica wood.

To reveal the in planta behaviour of caesium (Cs), the stable isotope 133Cs was administered into 3-year-old Cryptomeria japonica seedlings by the application of 133CsCl aqueous solution to the bark surface. The administered 133Cs was quantified by ICP-MS measurements, which showed transportation of 133Cs in an ascending direction in the stem. Distribution of 133Cs was visualized using freeze-fixed C. japonica woody stem samples and cryo-time-of-flight secondary ion mass spectrometry/scanning electron microscopy (cryo-TOF-SIMS/SEM) analysis. Cryo-TOF-SIMS/SEM visualization suggested that 133Cs was rapidly transported radially by ray parenchyma cells followed by axial transportation by pith and axial parenchyma cells. Adsorption experiments using powdered C. japonica wood samples and X-ray absorption fine structure (XAFS) analysis suggested that 133Cs was in the hydrated state following its deposition into tracheid cell walls.

Protein crystallography beamline BL2S1 at the Aichi synchrotron.

The protein crystallography beamline BL2S1, constructed at one of the 5 T superconducting bending-magnet ports of the Aichi synchrotron, is available to users associated with academic and industrial organizations. The beamline is mainly intended for use in X-ray diffraction measurements of single-crystals of macromolecules such as proteins and nucleic acids. Diffraction measurements for crystals of other materials are also possible, such as inorganic and organic compounds. BL2S1 covers the energy range 7-17 keV (1.8-0.7 Å) with an asymmetric-cut curved single-crystal monochromator [Ge(111) or Ge(220)], and a platinum-coated Si mirror is used for vertical focusing and as a higher-order cutoff filter. The beamline is equipped with a single-axis goniometer, a CCD detector, and an open-flow cryogenic sample cooler. High-pressure protein crystallography with a diamond anvil cell can also be performed using this beamline.

Nanoclusters first: a hierarchical phase transformation in a novel Mg alloy.

The Mg-Y-Zn ternary alloy system contains a series of novel structures known as long-period stacking ordered (LPSO) structures. The formation process and its key concept from a viewpoint of phase transition are not yet clear. The current study reveals that the phase transformation process is not a traditional spinodal decomposition or structural transformation but, rather a novel hierarchical phase transformation. In this transformation, clustering occurs first, and the spatial rearrangement of the clusters induce a secondary phase transformation that eventually lead to two-dimensional ordering of the clusters. The formation process was examined using in situ synchrotron radiation small-angle X-ray scattering (SAXS). Rapid quenching from liquid alloy into thin ribbons yielded strongly supersaturated amorphous samples. The samples were heated at a constant rate of 10 K/min. and the scattering patterns were acquired. The SAXS analysis indicated that small clusters grew to sizes of 0.2 nm after they crystallized. The clusters distributed randomly in space grew and eventually transformed into a microstructure with two well-defined cluster-cluster distances, one for the segregation periodicity of LPSO and the other for the in-plane ordering in segregated layer. This transformation into the LPSO structure concomitantly introduces the periodical stacking fault required for the 18R structures.

Initial stages of high-temperature CaF2/Si(001) epitaxial growth studied by surface X-ray diffraction.

Surface X-ray diffraction was applied to study structure of the fluorite-silicon interface forming upon epitaxial growth of CaF2 on Si(001) surface kept at 750 degrees C. Samples with CaF2 coverage of 1.5-4 (110)-monolayers were grown and in-situ characterized using synchrotron radiation. The 3 x 1-like surface reconstruction was observed in agreement with the previous studies by electron diffraction. Interestingly, a well pronounced splitting of the fractional x 1/3 reflections was revealed. This splitting was ascribed to the effect of antiphase domain boundaries in the row-like structure of the interface layer. The in-plane integrated intensities were used to reconstruct two-dimensional atomic structure of the high-temperature CaF2/Si(001) interface.

Ga and As composition profiles in InP/GaInAs/InP heterostructures--x-ray CTR scattering and cross-sectional STM measurements.

Changes of composition profiles in GaInAs layers sandwiched by InP, due to the layer thicknesses, were measured by the x-ray CTR scattering and cross-sectional STM techniques. Both techniques showed quite similar results, which indicates that the x-ray CTR scattering measurements and analyses give us correct composition profiles both for group-III and group-V atoms in the buried heterostructures non-destructively. Limits of the CTR analysis are discussed, especially on the spatial resolution and composition grading below the bottom interface.