Growth of ZnO thin films on c-plane Al2O3 by molecular beam epitaxy using ozone as an oxygen source

The growth of c-axis oriented ZnO thin films on c-plane Al₂O₃ via molecular beam epitaxy (MBE) using dilute ozone (O₃) as an oxygen source was investigated. Four-circle X-ray diffraction (XRD) indicates that films grown at 350 °C are epitaxial with respect to the substrate, but with a broad in-plane and out-of-plane mosaic. The films were highly conductive and n-type. Epitaxial film growth required relatively high Zn flux and O₃/O₂ pressure. The growth rate decreased rapidly as growth temperature was increased above 350 °C. The drop in growth rate with temperature reflects the low sticking coefficient of Zn at moderately high temperatures and limited ozone flux for the oxidation of the Zn metal. Characterization of the films included atomic force microscopy (AFM), X-ray diffraction, photoluminescence, and Hall measurements. These results show that molecular beam epitaxy of ZnO using ozone is rate limited by the ozone flux for growth temperatures above 350 °C.     

Plasmonic-based colorimetric and spectroscopic discrimination of acetic and butyric acids produced by different types of Escherichia coli through the different assembly structures formation of gold nanoparticles

We present a plasmonic-based strategy for the colourimetric and spectroscopic differentiation of various organic acids produced by bacteria. The strategy is based on our discovery that particular concentrations of dl-lactic, acetic, and butyric acids induce different assembly structures, colours, and optical spectra of gold nanoparticles. We selected wild-type (K-12 W3110) and genetically-engineered (JHL61) Escherichia coli (E. coli) that are known to primarily produce acetic and butyric acid, respectively. Different assembly structures and optical properties of gold nanoparticles were observed when different organic acids, obtained after the removal of acid-producing bacteria, were mixed with gold nanoparticles. Moreover, at moderate cell concentrations of K-12 W3110 E. coli, which produce sufficient amounts of acetic acid to induce the assembly of gold nanoparticles, a direct estimate of the number of bacteria was possible based on time-course colour change observations of gold nanoparticle aqueous suspensions. The plasmonic-based colourimetric and spectroscopic methods described here may enable onsite testing for the identification of organic acids produced by bacteria and the estimation of bacterial numbers, which have applications in health and environmental sciences.     

Na3SbS4: A Solution Processable Sodium Superionic Conductor for All‐Solid‐State Sodium‐Ion Batteries

All‐solid‐state sodium‐ion batteries that operate at room temperature are attractive candidates for use in large‐scale energy storage systems. However, materials innovation in solid electrolytes is imperative to fulfill multiple requirements, including high conductivity, functional synthesis protocols for achieving intimate ionic contact with active materials, and air stability. A new, highly conductive (1.1 mS cm^?1 at 25 °C, E_a=0.20 eV) and dry air stable sodium superionic conductor, tetragonal Na₃SbS₄, is described. Importantly, Na₃SbS₄ can be prepared by scalable solution processes using methanol or water, and it exhibits high conductivities of 0.1–0.3 mS cm^?1. The solution‐processed, highly conductive solidified Na₃SbS₄ electrolyte coated on an active material (NaCrO₂) demonstrates dramatically improved electrochemical performance in all‐solid‐state batteries.     

Structural evolution in microbial polyesters

The crystallization behavior of microbially synthesized poly(3-hydroxybutyrate) (PHB) and its copolymers [P(HB-co-HHx)] containing 2.5, 3.4, and 12 mol % 3-hydroxyhexanoate (HHx) comonomer and the melting of the resultant crystals were studied in detail using time-resolved small-angle X-ray scattering and differential scanning calorimetry. The polyesters were found to undergo primary crystallization as well as secondary crystallization. In the primary crystallization, the thicknesses of the lamellar crystals were sensitive to the crystallization temperature, but no thickening was observed throughout the entire crystallization at a given temperature. The thickness of the lamellar crystals in the PHB homopolymer was always larger than that of the amorphous layers. In the copolymers, by contrast, the randomly distributed HHx comonomer units were found to be excluded from the lamellar crystals into the amorphous regions during the isothermal crystallization process. This interrupted the crystallization of the copolymer chains, resulting in the formation of lamellar crystals with thicknesses smaller than those of the amorphous layers. The lamellar crystals in the copolymers had lower electron densities compared to those formed in the PHB homopolymer. On the other hand, secondary crystallization favorably occurred during the later stage of isothermal crystallization in competition with the continuous primary crystallization, forming secondary crystals in amorphous regions, in particular in the amorphous layers between the primarily formed lamellar crystal stacks. Compared to the primarily formed lamellar crystals, the secondary crystals had short-range-ordered structures of smaller size, a broader size distribution, and a lower electron density.     

Radial Fourier multipliers in high dimensions

Given a fixed p≠2, we prove a simple and effective characterization of all radial multipliers of FL^p( \mathbbR^d ) \mathcal{F}{L^p}\left( {{\mathbb{R}^d}} \right) , provided that the dimension d is sufficiently large. The method also yields new L ^q space-time regularity results for solutions of the wave equation in high dimensions.     

Influence of the Ga addition on optical properties of Pr in Ge–Sb–Se glasses

Absorption and emission spectra for the ³H₄↔(³F₂, ³H₆) transition of Pr³⁺ ions embedded in Ge–Sb–Se glasses turned out to change systematically upon the introduction of a small amout of Ga. Clear blueshift of the absorption peak wavelengths together with the decrease of absorption cross-section was evident in these glasses containing Ga. We believe that the Ga addition into the conventional covalent selenide glasses makes chemical bonds between rare earth atoms and Se atoms more ionic due to preferential location of the GaSe₄ tetrahedra at the second coordination shell of a rare earth atom. Taking into consideration the hypersensitive nature of the Pr³⁺: ³H₄↔³F₂ transition, the observed blueshift may manifest the enhanced ionicity of the chemical bonds between Pr and Se in the current Ga-containing glasses.     

Compositional dependences on the mechanism of upconversion in Nd3+/Tm3+ co-doped chalcohalide glasses

Mechanisms of the compositional dependence of blue emission from Nd³⁺/Tm³⁺ co-doped Ge–Ga–S–CsBr chalcohalide glasses were investigated. The blue upconversion emissions (centered at 475 nm) due to the Tm³⁺: ¹G₄ → ³H₆ transition decreased as the CsBr/Ga ratio in glasses while the other upconversion emissions from the Nd³⁺ ions increased. Changes in the local environment of rare-earth ions incurred by the CsBr addition significantly increased the excited state absorption within Nd³⁺ ions. This resulted in the decrease in the Nd³⁺ → Tm³⁺ energy transfer rates that led to the large decrease in blue upconversion emission.     

Thermal decomposition mechanism of Ba(DPM)2

We have investigated the thermal decomposition behavior of Ba(DPM)₂ using thermogravimetry (TG), mass spectrometry (MS), ultraviolet (UV) absorption and in-situ Fourier transform infrared (FTIR) spectroscopy. FTIR has been used particularly for direct monitoring of the bond dissociation order in the metal complex by thermal treatment in either N₂ or O₂. TG analysis shows that the ambient gas has a significant effect on the weight loss patterns of Ba(DPM)₂. The chemical bonds of Ba(DPM)₂ begin to decompose at low temperatures below 50 °C and are sequentially dissociated when the temperature is raised. The C-C(CH₃)₃ and the Ba-O bonds are decomposed most easily at low temperatures, followed by the C-H bond, but the stable C-C and C-O bonds do not dissociate until the total complex is gasified. The decomposition sequence of the chemical bonds in Ba(DPM)₂ is similar to that of Sr(DPM)₂ but differs from that of Ti(O-iPr)₂(DPM)₂ which is decomposed in the sequence of C(CH₃)₃ > C-H and C-O > Ti-O. The major difference in the decomposition sequence between Ba and Ti complexes can be seen to derive from the intrinsic character of the individual metal-oxygen bond as observed by UV spectroscopy.     

Stabilization of Cs/Re trapping filters using magnesium phosphate ceramics

The present study a promising method for stabilizing spent filters trapping cesium and technetium by using magnesium phosphate ceramics. Simulated spent filters were fabricated by vaporizing nonradioactive cesium and rhenium (a surrogate of Tc) through the voloxidizer. In order to reveal the characteristics of spent filters, phase structures and thermal stability were analyzed by using X-ray diffraction (XRD), X-ray photoelectron spectroscopy, and thermogravimetric analysis techniques. Waste forms were fabricated by crushing spent filters and mixing them with magnesium oxide and potassium phosphate. Characterizations of the waste forms were performed by the analyses of compressive strength, apparent porosity, XRD, and scanning electron microscopy. The waste forms showed the excellent mechanical property compared with that of ordinary Portland cement, with the highest compressive strength of 38.1 MPa in the sample with 30 wt% of Cs-filter. Microstructural analysis suggests that waste materials are encapsulated by the binding matrix composed of magnesium potassium phosphate. The results of characterization suggest that fabricating a sound and durable waste form is possible with magnesium phosphate ceramics.