Yolk–Shell‐Structured Cu/Fe@γ‐Fe2O3 Nanoparticles Loaded Graphitic Porous Carbon for the Oxygen Reduction Reaction

Core–shell Cu/γ‐Fe₂O₃@C and yolk–shell‐structured Cu/Fe@γ‐Fe₂O₃@C particles are prepared by a facile synthesis method using copper oxide as template particles, resorcinol‐formaldehyde as the carbon precursor, and iron nitrate solution as the iron source via pyrolysis. With increasing carbonization temperature and time, solid γ‐Fe₂O₃ cores are formed and then transformed into Fe@γ‐Fe₂O₃ yolk–shell‐structured particles via Ostwald ripening under nitrogen gas flow. The composition variations are studied, and the formation mechanism is proposed for the generation of the hollow and yolk–shell‐structured metal and metal oxides. Moreover, highly graphitic carbons can be obtained by etching the metal and metal oxide nanoparticles through an acid treatment. The electrocatalytic activity for oxygen reduction reaction is investigated on Cu/γ‐Fe₂O₃@C, Cu/Fe@γ‐Fe₂O₃@C, and graphitic carbons, indicating comparable or even superior performance to other Fe‐based nanocatalysts.     

A three‐crystal spectrometer for high‐energy resolution fluorescence‐detected X‐ray absorption spectroscopy and X‐ray emission spectroscopy at SSRF

A Johann‐type spectrometer for the study of high‐energy resolution fluorescence‐detected X‐ray absorption spectroscopy, X‐ray emission spectroscopy and resonant inelastic X‐ray scattering has been developed at BL14W1 X‐ray absorption fine structure spectroscopy beamline of Shanghai Synchrotron Radiation Facility. The spectrometer consists of three crystal analyzers mounted on a vertical motion stage. The instrument is scanned vertically and covers the Bragg angle range of 71.5–88°. The energy resolution of the spectrometer ranges from sub‐eV to a few eV. The spectrometer has a solid angle of about 1.87 × 0^?3 of 4π sr, and the overall photons acquired by the detector could be 10⁵ counts per second for the standard sample. The performances of the spectrometer are illustrated by the three experiments that are difficult to perform with the conventional absorption or emission spectroscopy. Copyright © 2016 John Wiley & Sons, Ltd.     

A convolutional neural network approach to calibrating the rotation axis for X‐ray computed tomography

This paper presents an algorithm to calibrate the center‐of‐rotation for X‐ray tomography by using a machine learning approach, the Convolutional Neural Network (CNN). The algorithm shows excellent accuracy from the evaluation of synthetic data with various noise ratios. It is further validated with experimental data of four different shale samples measured at the Advanced Photon Source and at the Swiss Light Source. The results are as good as those determined by visual inspection and show better robustness than conventional methods. CNN has also great potential for reducing or removing other artifacts caused by instrument instability, detector non‐linearity, etc. An open‐source toolbox, which integrates the CNN methods described in this paper, is freely available through GitHub at tomography/xlearn and can be easily integrated into existing computational pipelines available at various synchrotron facilities. Source code, documentation and information on how to contribute are also provided.     

A compact permanent‐magnet system for measuring magnetic circular dichroism in resonant inelastic soft X‐ray scattering

A compact and portable magnet system for measuring magnetic dichroism in resonant inelastic soft X‐ray scattering (SX‐RIXS) has been developed at the beamline BL07LSU in SPring‐8. A magnetic circuit composed of Nd–Fe–B permanent magnets, which realised ～0.25 T at the center of an 11 mm gap, was rotatable around the axis perpendicular to the X‐ray scattering plane. Using the system, a SX‐RIXS spectrum was obtained under the application of the magnetic field at an angle parallel, nearly 45° or perpendicular to the incident X‐rays. A dedicated sample stage was also designed to be as compact as possible, making it possible to perform SX‐RIXS measurements at arbitrary incident angles by rotating the sample stage in the gap between the magnetic poles. This system enables facile studies of magnetic dichroism in SX‐RIXS for various experimental geometries of the sample and the magnetic field. A brief demonstration of the application is presented.     

SUT‐NANOTEC‐SLRI beamline for X‐ray absorption spectroscopy

The SUT‐NANOTEC‐SLRI beamline was constructed in 2012 as the flagship of the SUT‐NANOTEC‐SLRI Joint Research Facility for Synchrotron Utilization, co‐established by Suranaree University of Technology (SUT), National Nanotechnology Center (NANOTEC) and Synchrotron Light Research Institute (SLRI). It is an intermediate‐energy X‐ray absorption spectroscopy (XAS) beamline at SLRI. The beamline delivers an unfocused monochromatic X‐ray beam of tunable photon energy (1.25–10 keV). The maximum normal incident beam size is 13 mm (width) × 1 mm (height) with a photon flux of 3 × 10⁸ to 2 × 10¹⁰ photons s^?1 (100 mA)^?1 varying across photon energies. Details of the beamline and XAS instrumentation are described. To demonstrate the beamline performance, K‐edge XANES spectra of MgO, Al₂O₃, S₈, FeS, FeSO₄, Cu, Cu₂O and CuO, and EXAFS spectra of Cu and CuO are presented.     

Pump−probe experiments at the TEMPO beamline using the low‐α operation mode of Synchrotron SOLEIL

The SOLEIL synchrotron radiation source is regularly operated in special filling modes dedicated to pump–probe experiments. Among others, the low‐α mode operation is characterized by shorter pulse duration and represents the natural bridge between 50 ps synchrotron pulses and femtosecond experiments. Here, the capabilities in low‐α mode of the experimental set‐ups developed at the TEMPO beamline to perform pump–probe experiments with soft X‐rays based on photoelectron or photon detection are presented. A 282 kHz repetition‐rate femtosecond laser is synchronized with the synchrotron radiation time structure to induce fast electronic and/or magnetic excitations. Detection is performed using a two‐dimensional space resolution plus time resolution detector based on microchannel plates equipped with a delay line. Results of time‐resolved photoelectron spectroscopy, circular dichroism and magnetic scattering experiments are reported, and their respective advantages and limitations in the framework of high‐time‐resolution pump–probe experiments compared and discussed.     

Electrochemical behaviour of sputtered c-V2O5 and LiCoO2 thin films for solid state lithium microbatteries

Here are reported for the first time electrochemical data on all-solid-state lithium microbatteries using crystalline sputtered V₂O₅ thin films as cathode materials and LiPON as solid electrolyte. The stable specific capacity of 30 µAh/cm² found with a 2.4 µm thick film competes very well with the best values obtained for solid state microbatteries using amorphous films. With the challenge of decreasing the temperature of heat treatment for sputtered LiCoO₂ thin films, we show that a temperature of 500 °C combined with an optimized bias sputtering (-50 V) allows to get highly crystalline deposits, to minimize the presence of Co₃O₄ and to suppress any trace of the cubic phase. At the same time the theoretical specific capacity is reached in the 4.2 V-3 V range and a good cycling behaviour is achieved with a high capacity of 50 µAh/cm²/µm after 140 cycles at 10 µA.cm².     

Quantum phase diagram for homogeneous Bose‐Einstein condensate

We calculate the quantum phase transition for a homogeneous Bose gas in the plane of s‐wave scattering length a_s and temperature T. This is done by improving a one‐loop result near the interaction‐free Bose‐Einstein critical temperature T_c⁽⁰⁾ with the help of recent high‐loop results on the shift of the critical temperature due to a weak atomic repulsion based on variational perturbation theory. The quantum phase diagram shows a nose above T_c⁽⁰⁾, so that we predict the existence of a reentrant transition above T_c⁽⁰⁾, where an increasing repulsion leads to the formation of a condensate.     

(Mo + N) codoped TiO2 for enhanced visible-light photoactivity

A series of Ti_1−xMo_xO_2−yN_y samples were prepared by using sol-gel method and characterized by X-ray diffraction, transmission electron microscopy and UV-vis absorption spectroscopy. All Ti_1−xMo_xO_2−yN_y samples are anatase phase. It is found that Mo, N mono-doping can increase visible light absorption, while (Mo + N) co-doping can greatly enhance absorption in whole visible region. Results of our first-principles band structure calculations reveal that (Mo + N)-doping, especially passivated co-doping can increase the up-limit of dopant concentration and create more impurity bands in the band gap of TiO₂, which leads to a greatly increase of its visible-light absorption without a decrease of its redox potential. It reveals that (Mo + N) co-doped TiO₂ is promising for a photocatalyst with high photocalystic activity under visible light.     

Convergence of mixed finite element approximations for the shallow arch problem

Summary The stability and convergence of mixed finite element methods are investigated, for an equilibrium problem for thin shallow elastic arches. The problem in its standard form contains two terms, corresponding to the contributions from the shear and axial strains, with a small parameter. Lagrange multipliers are introduced, to formulate the problem in an alternative mixed form. Questions of existence and uniqueness of solutions to the standard and mixed problems are addressed. It is shown that finite element approximations of the mixed problem are stable and convergent. Reduced integration formulations are equivalent to a mixed formulation which in general is distinct from the formulation shown to be stable and convergent, except when the order of polynomial interpolationt of the arch shape satisfies 1tmin (2,r) wherer is the order of polynomial approximation of the unknown variables.