Katsuaki Watanabe

Microcalorimeter-type energy dispersive X-ray spectrometer for a transmission electron microscope

A new energy dispersive X-ray spectrometer (EDS) with a microcalorimeter detector equipped with a transmission electron microscope (TEM) has been developed for high- accuracy compositional analysis in the nanoscale. A superconducting transition-edge-sensor-type microcalorimeter is applied as the detector. A cryogen-free cooling system, which consists of a mechanical and a dilution refrigerator, is selected to achieve long-term temperature stability. In order to mount these detector and refrigerators on a TEM, the cooling system is specially designed such that these two refrigerators are separated. Also, the detector position and arrangement are carefully designed to avoid adverse affects between the superconductor detector and the TEM lens system. Using the developed EDS system, at present, an energy resolution of 21.92 eV full-width-at-half maximum has been achieved at the Cr K alpha line. This value is about seven times better than that of the current typical commercial Si(Li) detector, which is usually around 140 eV. The developed microcalorimeter EDS system can measure a wide energy range, 1-20 keV, at one time with this high energy resolution that can resolve peaks from most of the elements. Although several further developments will be needed to enable practical use, highly accurate compositional analysis with high energy resolution will be realized by this microcalorimeter EDS system.

Direct transformation of graphite to cubic diamond observed in a laser-heated diamond anvil cell

Graphite samples are heated in a diamond anvil cell with a CO2 laser above 11 GPa. A light transparent phase has appeared after heating, which is quenchable at ambient conditions. The Raman spectrum shows that the phase is a fine-grained cubic diamond. Images by a high resolution transmission electron microscope indicate that the diamond has twins and stacking faults of nanometer size. The electron diffraction pattern shows that the stacking fault cannot be explained by a diamond polytype such as a hexagonal diamond. The cathodoluminescence pattern exhibits the “band-A” emission, which is derived from the defects of the cubic diamond.

Elemental behaviour during the process of corrosion of sekishu glazed roof-tiles affected by Lecidea s.lat. sp. (crustose lichen)

Abstract Elemental behaviour, during the process of weathering of glazed sekishu roof-tiles affected by Lecidea s.lat. sp. (a crustose lichen), was investigated using optical and fluorescence microscopy, field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy. Sekishu roof tiles have an opaque reddish brown glaze on their surfaces which consist of an alkali feldspar-type X-ray amorphous glass recrystallized at 1200°C. Optical and fluorescence microscopy revealed the presence of corrosion pits (at a depth of ~50 μm) at the lichen-glaze interface. Elemental mapping by FE-SEM identified the concentrations of Ti and Fe in the section of the glazed tile analysed. The behaviour of C was correlated with those elements, suggesting the possibility of biomineralization.

Development of an energy dispersive spectrometer for a transmission electron microscope utilizing a TES microcalorimeter array

A high‐energy‐resolution energy dispersive spectrometer (EDS) utilizing a TES (transition edge sensor) microcalorimeter array is developed for a transmission electron microscope (TEM). The goals of the development are (1) an energy range of 0.3–10 keV, (2) an energy resolution of FWHM <10 eV, (3) a maximum counting rate of 3 kcps, and (4) a cryogen‐free cooling system. We adopted a dilution refrigerator (DR) pre‐cooled by a Gifford‐McMahon (GM) refrigerator to cool the TES microcalorimeter to ∼100 mK. In order to avoid micro phonics of GM fridge to propagate to the TEM, pressurized He gas is circulated between the DR and the GM to reject heat from the DR. The GM is mechanically well isolated from the TEM. In oder to obtain 3 kcps counting rate, we utilize a ten pixel TES array and read out the signals in parallel wtih ten analog signal channels from cryogenic to room temperature electronics. One of the pixels can be always irradiated by a radio isotope for energy calibration. As the first step, we have at...

Nanoscale pseudobrookite layer in the surface glaze of a Japanese sekishu roof tile

Abstract The mineralogy of the glazed surfaces of Japanese sekishu roof tiles covered by a crustose lichen − Lecidella asema (Nyl.) Knoph & Hertel − was investigated using transmission electron microscopy (TEM). The study sought to identify the Ti-Fe mineral observed as a low concentration of Ti and Fe in a previous study of the glazed surfaces of the same roof tile. The TEM analysis revealed that: (1) a thin layer of the Ti-Fe mineral pseudobrookite exists on the glaze surface; (2) the pseudobrookite consists of well-ordered single crystals, continuously and widely distributed on the glaze surface.

Nanostructural evidence at the phase boundary of A-and C-type antiferromagnetic phases in Nd1-xSrxMnO3 crystals

A weak ferromagnetic phase appears around the phase boundary between the A-type and C-type antiferromagnetic phases in overdoped Nd1−xSrxMnO3 crystals (0.6≤x≤0.7). We investigated the crystal structure and the magnetic domain structure around the phase boundary, by powder synchrotron x-ray diffractometry and transmission electron microscopy. The phase boundary exists between x = 0.62 in the phase separation region where the A-type and C-type antiferromagnetic phases coexist and x = 0.625 in the C-type antiferromagnetic phase. By transmission electron microscopy, the orbital-disordered nanodomains in the C-type antiferromagnetic matrix phase were only observed in the vicinity of the phase boundary in the C-type antiferromagnetic phase. This is a nanoscale inhomogeneity but is not a conventional phase separation for manganites. We also successfully observed magnetic domain structures in the weak ferromagnetic phase by Lorentz electron microscopy. Moreover, we found that the ferromagnetic correlation becomes a short-range correlation when the orbital-disordered nanodomains appear. We consider that the orbital-disordered nanodomains interfere with the long-range ferromagnetic correlation.

Novel ternary Y-B-C compound: Y10+xB7C10-x (x ? 0.1)

A novel ternary Y-B-C compound Y10+xB7C10-x is established. Y10+xB7C10-x has a monoclinic crystal structure with space group C2/c (No.15) and lattice constants a = 1.1273(14) nm, b = 1.1159(14) nm, c = 2.3566(30) nm and β = 98.15(2)°. Y10+xB7C10-x crystal rods were grown by floating zone technique and consisted of a predominant crystal phase and impurity phases. A small crystal having sufficient quality for single crystal XRD analysis could be selected. Structure refinement achieved a final R1 = 0.044 for 1660 independent reflections with Fo > 4s(Fo). 10 Y sites, 8 B sites, 9 C sites and one C/Y mixed occupancy site with about 0.9/0.1 occupation ratio were assigned. The unit chemical formula is Y10+xB7C10-x (x≈0.1), and the unit cell contains 8 formula units. Y10+xB7C10-x has a layer structure: Y-C double layers, in which Y and C bond alternatively like in the NaCl structure, spread parallel to the (001) plane and stack along the c-axis. The Y-C double layer is connected to the neighboring Y-C double layers via C-B-C chains or C-B-B-C chains. This structure was confirmed by electron diffraction and high-resolution electron microscopy. Magnetic susceptibility measurement indicated that the Y10+xB7C10-x phase has no superconductivity above 2 K. A minor superconducting phase with Tc=7.5 K was observed, but ascribed to an unidentified impurity phase.