No abstract

To investigate the sorption mechanism of cesium (Cs) into clay minerals, high-resolution (scanning) transmission electron microscopy (TEM/STEM) imaging of Cs in mica (phlogopite) has been conducted. Platy phlogopite powders were immersed in a cesium chloride (CsCl) solution to achieve Cs(+)-K(+) ion-exchange at the interlayer regions in phlogopite. To observe many phlogopite particles with the incident electron beam parallel to the mica layers, cross-sectional thin specimens were prepared from sedimented particles using a focused ion beam. High-angle annular dark-field imaging with STEM is superior to conventional high-resolution TEM (HRTEM) for visualizing Cs at interlayer sites even in thicker crystal regions and/or at lower magnification due to the intense Z-contrast of Cs. However, HRTEM is also practical for estimating the concentration of Cs at the interlayer site from the thickness dependence of the contrast at the interlayer region. Cs sorption of micas was previously thought to be localized mainly at the frayed-edge sites of mica crystals. However, the present observations indicate that Cs substitution of K occurs not around crystal edges but deep inside the crystals along specific interlayer regions.

No abstract

Interfacial chemistry and band offsets of HfO2 films grown on Si(100) substrates are investigated using high-resolution angle-resolved photoelectron spectroscopy and are correlated with interfacial structures revealed by transmission electron microscope. Hf 4f and O 1s spectra show similar chemical shifts indicating the existence of a double layer structure consisting of a HfO2, upper layer and a SiO2-rich Hf1−xSixO2 lower layer. Two types of valence band offsets are clearly determined by a double subtraction method to be 3.0 and 3.8 eV that can be attributed to ΔEv1 for the upper layer HfO2/Si and ΔEv2 for the lower layer Hf1−xSixO2/Si, respectively.

The influence of intracrystalline organic macromolecules on the microstructure and properties of host crystals has been investigated by micro-and macroscopic analyses for several biogenic calcites: prisms in the outer layers of pearl oysters (Pinctada fucata), oysters (Crassostrea nippona), and pen shells (Atrina pectinata); folia in the inner layers of C. nippona and scallops (Patinopecten yessoensis); and coccoliths of Pleurochrysis carterae. Thermogravimetric analysis showed that the three prisms contain more intracrystalline organic matter than the folia and coccolith. Transmission electron microscopy (TEM) revealed that Fresnel contrasts, which probably correspond to the intracrystalline organic macromolecules, are distributed inhomogeneously and partition the calcite crystals into subgrains with small misorientations in the prisms of P. f ucata and C. nippona. From peak broadening in powder X-ray diffraction (XRD), we found a large variance of lattice spacing (Δd/d) in the two prisms. On the other hand, intracrystalline macromolecules in the prisms of A. pectinata are distributed rather homogeneously and do not influence the crystal structure, as revealed by diffraction contrast in TEM. XRD of the prisms in A. pectinata indicates significantly smaller Δd/d than that for the other two prisms. In the folia and coccolith, intracrystalline macromolecules were scarcely observed in TEM, and the estimated Δd/d is small. ■ INTRODUCTIONBiominerals often possess well-regulated structures with superior properties. 1,2 Such superiority may be ascribed to the fact that biominerals are not pure inorganic crystals because they contain a certain amount of organic matter. Mollusk shells, for example, contain organic components of up to 5% of the entire weight, 3 which may influence the polymorph selection, 4,5 morphology, 6 and mechanical properties 1 of biominerals.Calcium carbonate crystals are the most abundant biominerals. Calcite, one of the polymorphs of calcium carbonate, is the most thermodynamically stable polymorph under ambient conditions, but it is mechanically weak because of the perfect {104} cleavage planes. Biogenic calcite is, however, much more resistant to fractures than abiotic calcite because {104} cleavage planes generally do not develop at the fractures. This is attributed to the existence of organic matter within the crystals, 7 but it has not been elucidated at the atomic scale how organic matter modifies the calcite crystals to prevent the cleavages.The relationships between intracrystalline organic matter and calcium carbonate crystals have been investigated using X-ray diffraction (XRD). High-resolution synchrotron XRD analysis indicated that anisotropic lattice distortion and crystallite size exist in the calcite prismatic layers of bivalves, and the anisotropy has been ascribed to intracrystalline organic matter. 8 However, although XRD techniques can quantitatively estimate such anisotropy in the whole specimens, they do not tell us the actual interaction between organic matter and crystals at...