In-situ X-ray diffraction study on β-CrOOH at high pressure and high-temperature

ABSTRACT

High pressure hydrous phases with distorted rutile-type structure have attracted much interest as potential water reservoirs in the Earth’s mantle. An in-situ X-ray diffraction study of β-CrOOH was performed at high pressures of up to 6.2?GPa and high-temperatures of up to 700?K in order to clarify the temperature effect on compression behaviors of β-CrOOH. The P-V-T data fitted to a Birch–Murnaghan equation of state yielded the following results: isothermal bulk modulus K_T0?=?191(4)?GPa, temperature derivative (?K_T/?T)_P?=??0.04(2)?GPa?K^?1, and volumetric thermal expansion coefficient α?=?3.3(2)?×?10^?5?K^?1. In this study, at 300?K, the a-axis became less compressible at pressures above 1–2?GPa. We found that the pressure where the slopes of a/b and a/c ratios turned positive increased with temperature. This is the first experimental study indicating the temperature dependence of the change in the axial compressibility in distorted rutile-type M³⁺OOH.     

Optical characteristics of one-dimensional photonic crystals composed of high-aspect-ratio Si walls fabricated on V-grooved wafer

We demonstrate optical properties of one-dimensional photonic crystals (PC), which are fabricated using high-aspect-ratio etching on a V-grooved silicon wafer. The measured transmission spectrum has an obvious band gap; the suppression is over 30 dB. The quite small insertion loss of 1.9 dB is achieved by induced coupled plasma (ICP) cryogenic etching and direct coupling to the optical fiber aligned in the V-groove. We also successfully observed peaks originating from a localized cavity mode. Such a microcavity enables control of the light, which qualifies photonic crystal as a fundamental structure of optical functional devices. These results lead to achievement of integrated Si-based photonic circuits.     

Strain distribution and electronic states in stacked InAs/GaAs quantum dots with dot spacing 0–

We have calculated the strain distribution and electronic structures in stacked InAs/GaAs quantum dots (QDs) with the dot spacing 6–. We used the elastic continuum theory for the strain distribution, and the 8-band k·p theory for the electronic structures. For the triply stacked QDs, the light-hole (LH) component of the hole ground state increases with decreasing the dot spacing. The LH component in the columnar QD (dot spacing ) reaches 21.1% which is 4.8 times larger than that in the single QD due to the reduction of the biaxial strain. Further increase of the LH component (up to 28.6%) is obtained in the fivefold-stacked columnar QD. This result suggests a possibility of increase in the TM-mode transition in the columnar QDs.     

Synthesis of Al–Cr decagonal quasicrystal nanoparticles and their temperature of phase transformation to stable crystal phase

The synthesis of Al–Cr single quasicrystal (QC) nanoparticles of the decagonal phase was achieved by introducing an advanced gas flow evaporation method. By obtaining successive electron diffraction patterns for single-QC nanoparticles, the phase transformation temperature of a single-QC nanoparticle was determined to be 700 °C. It was also determined that part of the QC nanoparticle decomposed into hex-Al₈Cr₅ and Al during the phase transformation. Since the grain growth did not occur during the phase transformation in the present experiment, the inherent phase transformation temperature could be measured.     

Characterization of calcium carbonate polymorphs with Ca K edge X-ray absorption fine structure spectroscopy

Ca K edge X-ray absorption fine structure (XAFS) spectroscopy was utilized for the characterization and quantification of calcium carbonate polymorphs and their mixtures. The advantage of the XAFS is the small sample quantity required for measurements, and a flexible sample environment. The near-edge XAFS spectra of calcite, aragonite and vaterite were measured with the conversion electron yield (CEY) method, and the obtained spectra showed characteristic features that can be utilized as fingerprints. The quantification of mixed polymorphs was examined by using a linear combination fitting of reference XAFS spectra. Though the quality of the fits was satisfactory, discrepancies in the evaluated values were observed between those with X-ray diffraction (XRD) and XAFS. The nonuniformity of samples may be enhanced by the surface sensitivity of the CEY method.     

XPS for in situ observation of an Ag electrode on a solid electrolyte used as oxygen sensor

The Ag electrode surface of a solid electrolyte in its working state has been studied by X-ray photoelectron spectroscopy. The nature of the AgO system on the electrode is dependent on the temperature. There are three types of AgO systems at 400°C. Type 1 with an O is binding energy of 532.6 eV only appeared at 325°C. However, when the temperature was raised to 400°C, types II and III (with BEs 531.1 and 529.2 eV) appeared. These O is signals are discussed in detail.     

Low energy electron attenuation length studies in thin amorphous carbon films

The results of experiments on low energy electrons passing through thin amorphous carbon films are reported. For electron energies between 50 and 3000 eV, electron attenuation lengths were determined by electron transmission measurements through carbon films of thicknesses between 81 and 210 Å. The density of these amorphous carbon films was also obtained by a sink—float method and found to be 1.90 ± 0.05 g cm^?3. The electron attenuation length for inelastic scattering was found to increase monotonically from approximately 10 to 55 Å over the 50 to 3000 eV range. Over the 500–3000 eV energy region, the results are in good agreement with mean free paths calculated using optically measured dielectric functions.