Shigeru Suehara

Oxyfluoride tellurite glasses doped by erbium: thermal analysis, structural organization and spectral properties

Abstract The effects of fluorine substitution in zinc tellurite glass system doped with rare earths on the spectral properties of the Er 3+ ions are investigated. Differential thermal analysis, vibrational spectroscopies studies and in situ high-temperature X-ray diffraction measurements have been considered in term of fluorine influence. As a function of composition, we have principally measured optical absorption, spontaneous emission, and lifetime measurements. Judd–Ofelt intensity parameters of Er 3+ in these host glasses were determined and used to calculate radiative transition rates and lifetimes. The bulk composition variation and addition of fluoride compounds in tellurite glasses result among others, in broad emission spectra, improved emission lifetime and difference in relative band intensities compared to pure oxide glass.

Ultra-high-resolution HVEM (H-1500) newly constructed at NIRIM: I. Instrumentation

Abstract Basic specifications and some experimental data of a new ultra-high-resolution HVEM (Hitachi H-1500), with a maximum accelerating voltage of 1300 kV, are described. A lattice fringe image of 0.07 nm is obtained from thin gold film, indicating excellent mechanical and electrical stability of the microscope. Spherical and chromatic aberration coefficients of the objective lens are 1.85 and 3.4 mm, respectively, at 1300 kV; and a theoretical point-to-point resolution, defined by the first-zero point of the contrast transfer function (CTF) curve under the Scherzer condition, is about 0.104 nm. A crystal structure image of silicon, in which each silicon site is observed as a black dot, is successfully obtained and the image agrees fairly with the results of computer simulations based on the above optical parameters.

Dynamic Breathing of CO2 by Hydrotalcite

The carbon cycle of carbonate solids (e.g., limestone) involves weathering and metamorphic events, which usually occur over millions of years. Here we show that carbonate anion intercalated layered double hydroxide (LDH), a class of hydrotalcite, undergoes an ultrarapid carbon cycle with uptake of atmospheric CO2 under ambient conditions. The use of (13)C-labeling enabled monitoring by IR spectroscopy of the dynamic exchange between initially intercalated (13)C-labeled carbonate anions and carbonate anions derived from atmospheric CO2. Exchange is promoted by conditions of low humidity with a half-life of exchange of ~24 h. Since hydrotalcite-like clay minerals exist in Nature, our finding implies that the global carbon cycle involving exchange between lithosphere and atmosphere is much more dynamic than previously thought.

Spectral properties of Er3+ doped oxyfluoride tellurite glasses

The glass forming capability, glass structural organization and optical properties have been examined in rare-earth doped oxyfluoride zinc tellurite glass system. As a function of composition, differential thermal analysis, vibrational spectra, optical absorption, spontaneous emission and lifetime measurements have been analyzed in term of fluorine influence. The bulk composition variation and addition of fluoride compounds in tellurite glasses result among others, broad emission spectra compared to silicate glasses, in improved emission lifetime and slight difference in relative band intensities compared to pure oxide glass.

Investigation of glass formation and color properties in the P2O5–TeO2–ZnO system

Abstract The compositional dependence of glass-forming tendency and thermal properties was investigated for the P2O5–TeO2–ZnO system with the aid of an automatic sample preparation system including a batch-preparing apparatus and a multi-sample casting machine. The samples exhibited a variety of colors, such as transparent, yellow, wine red and brown depending on composition. Analyses with scanning electron microscopy and X-ray photoelectron spectroscopy revealed that the reddish coloration results from a colloidal suspension of nanometer-sized elemental Te particles.

Ultra-high-resolution HVEM (H-1500) newly constructed at NIRIM. II: Application to materials

Abstract We have recently constructed an ultra-high-resolution HVEM (H-1500), whose specifications are introduced in part I of this series. The point-to-point resolving power of the microscope is 1.0 A at an accelerating voltage of 1300 kV and 1.25 A at 1000 kV. Using the microscope at 1000 kV we have succeeded in imaging clearly not only Zr atoms but also oxygen atoms in zirconia ( ZrO 2 ). The contrast of oxygen atoms in a high- T c superconductor YBa 2 Cu 3 O 7− x is locally discriminated from that of cations in the image. A real structure image of Si [110] incidence is obtained at 1300 kV with a dark contrast at the Si atom sites and then used to analyze the structure at an initial stage of the damage due to electron irradiation.

EXAFS AND RDF STUDIES OF TEO2-LI2O GLASSES

Local arrangements around Te atoms in TeO 2 -Li 2 O glasses with four different Li 2 O contents (15, 20, 25, and 30 mol %) are observed by Te K EXAFS spectroscopy and x-ray diffraction by making use of synchrotron radiation. EXAFS results based on the two-shell fitting method indicate that interatomic distances of Te-O in axial (ax) sites decrease from 0.208 to 0.197 nm with increasing Li 2 O contents, while distances between tellurium atom and oxygen atoms in equatorial (eq) sites change slightly from 0.190 to 0.188 nm. Total coordination numbers seem to decrease slightly with increasing Li 2 O contents. These results suggest the coordination states of tellurium atoms are changed from TeO 4 trigonal bipyramids to TeO 3+1 polyhedra and TeO 3 trigonal pyramids. RDF results also suggest the change of coordination states of tellurium atoms. TeO 3+1 polyhedra in glasses are considered to be connected at the vertices with Te- eq O ax -Te or Te- ax O ax -Te linkage as seen in crystalline α-Li 2 Te 2 O 5 .

Interlayer bonding energy of layered minerals: Implication for the relationship with friction coefficient

The frictional strength of layered minerals is an important component of fault slip physics. A low-friction coefficient of these minerals has been attributed to the interlayer bonding energy (ILBE) of their weak interlayer bonding. The ILBE used for discussing the friction coefficient is based on a simple electrostatic calculation; however, the values should be revisited by precise calculations based on quantum mechanics. In this study, the ILBEs of layered minerals were calculated by using the density functional theory (DFT) method with van der Waals correction. The ILBEs calculated by the simple electrostatic method for hydrogen-bonding minerals such as kaolinite, lizardite, gibbsite, and brucite strongly overestimated the reliable energies calculated by the DFT method. This result should be ascribed to the inaccurate approximation of the point charges at the basal plane. A linear relationship between the experimentally measured friction coefficients of layered minerals and the ILBEs determined by the simple method was not confirmed by using the reliable ILBEs calculated by our DFT method. The results, however, do not remove the possibility of a relationship between interlayer bonding energy and the friction coefficient because the latter, used for comparing the former, was obtained through experiments conducted under various conditions.

Roughness study of ion-irradiated silica glass surface

Abstract We have investigated the surface roughness of ion-irradiated silica glass by the use of atomic force microscopy (AFM). Highly polished synthetic silica glass was irradiated with 120 keV Ar+ ion at a dose range of1 × 1012−1 × 1017ions/cm2. The surface roughens progressively at an ion dose up to1 × 1014ions/cm2, whereas smoothing occurs at an ion dose above1 × 1014ions/cm2. The smoothing in the high dose region is attributed to the viscous relaxation induced by ion beam. As to roughening in the low dose region, two mechanisms both sputtering and compaction has been discussed. The roughening is thought of the compaction of the partial region in which each of the ion impacts cause structural changes.

Valence-band spectra of hydrogenated diamond (111) surface

Abstract Boron-doped semiconducting diamond thin films were epitaxially grown on a natural diamond (111) single crystal by microwave-plasma-assisted chemical vapor deposition. We investigated chemisorption of hydrogen on the diamond surface by X-ray photoemission spectroscopy measurements and first-principles molecular orbital calculations. By comparison between the experimental and calculated spectra, we conclude that hydrogen termination of the epitaxially grown diamond (111) surface is in the form of the CH3 group.