Abstract: Topological superconductivity is of great contemporary interest and has been proposed in doped Bi₂Se₃, in which electron-donating atoms such as Cu, Sr or Nb have been intercalated into the Bi₂Se₃structure. For Nb_{<italic>x</italic>}Bi₂Se₃, with<italic>T</italic>_c ~ 3 K, it is assumed in the literature that Nb is inserted in the van der Waals gap. However, in this work an alternative origin for the superconductivity in Nb-doped Bi₂Se₃is established. In contrast to previous reports, it is deduced that Nb intercalation in Bi₂Se₃does not take place. Instead, the superconducting behaviour in samples of nominal composition Nb_{<italic>x</italic>}Bi₂Se₃results from the (BiSe)_1.10NbSe₂misfit phase that is present in the sample as an impurity phase for small<italic>x</italic>(0.01 ≤ <italic>x</italic> ≤ 0.10) and as a main phase for large<italic>x</italic>(<italic>x</italic> = 0.50). The structure of this misfit phase is studied in detail using a combination of X-ray diffraction and transmission electron microscopy techniques.

Abstract: Our study compares short-range order parameters refined from the diffuse scattering in single-crystal X-ray and single-crystal electron diffraction data. Nb0.84CoSb was chosen as a reference material. The correlations between neighbouring vacancies and the displacements of Sb and Co atoms were refined from the diffuse scattering using a Monte Carlo refinement in DISCUS. The difference between the Sb and Co displacements refined from the diffuse scattering and the Sb and Co displacements refined from the Bragg reflections in single-crystal X-ray diffraction data is 0.012 (7) angstrom for the refinement on diffuse scattering in single-crystal X-ray diffraction data and 0.03 (2) angstrom for the refinement on the diffuse scattering in single-crystal electron diffraction data. As electron diffraction requires much smaller crystals than X-ray diffraction, this opens up the possibility of refining short-range order parameters in many technologically relevant materials for which no crystals large enough for single-crystal X-ray diffraction are available.

Abstract: Gold nanoparticles are studied extensively due to their unique optical and catalytical properties. Their exact shape determines the properties and thereby the possible applications. Electron tomography is therefore often used to examine the three-dimensional (3D) shape of nanoparticles. However, since the acquisition of the experimental tilt series and the 3D reconstructions are very time consuming, it is difficult to obtain statistical results concerning the 3D shape of nanoparticles. Here, we propose a new approach for electron tomography that is based on artificial neural networks. The use of a new reconstruction approach enables us to reduce the number of projection images with a factor of 5 or more. The decrease in acquisition time of the tilt series and use of an efficient reconstruction algorithm allows us to examine a large amount of nanoparticles in order to retrieve statistical results concerning the 3D shape.

Abstract: Recent studies are concisely reviewed, in which X-ray beams of (sub)micrometre to millimetre dimensions have been used for non-destructive analysis and characterization of pigments, minute paint samples, and/or entire paintings from the seventeenth to the early twentieth century painters. The overview presented encompasses the use of laboratory and synchrotron radiation-based instrumentation and deals with the use of several variants of X-ray fluorescence (XRF) as a method of elemental analysis and imaging, as well as with the combined use of X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS). Microscopic XRF is a variant of the method that is well suited to visualize the elemental distribution of key elements, mostly metals, present in paint multi-layers, on the length scale from 1 to 100 μm inside micro-samples taken from paintings. In the context of the characterization of artists pigments subjected to natural degradation, the use of methods limited to elemental analysis or imaging usually is not sufficient to elucidate the chemical transformations that have taken place. However, at synchrotron facilities, combinations of μ-XRF with related methods such as μ-XAS and μ-XRD have proven themselves to be very suitable for such studies. Their use is often combined with microscopic Fourier transform infra-red spectroscopy and/or Raman microscopy since these methods deliver complementary information of high molecular specificity at more or less the same length scale as the X-ray microprobe techniques. Since microscopic investigation of a relatively limited number of minute paint samples, taken from a given work of art, may not yield representative information about the entire artefact, several methods for macroscopic, non-invasive imaging have recently been developed. Those based on XRF scanning and full-field hyperspectral imaging appear very promising; some recent published results are discussed.

Abstract: The orientation relationships (ORs), segregation behavior and morphologies of beta precipitate in an over aged Al-Mg-Si-Cu alloy are systematically characterized by atomic resolution high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM). Six different ORs and two morphologies, i.e. rod-and lath-like are revealed for beta precipitates, and Cu segregation at the (beta/alpha-Al interface is observed in all these precipitates. The rod-like beta precipitate has multiple beta-angles ranging from 6.1 to 14.1 degrees and non-uniform Cu segregation at the (beta/alpha-Al interface, while the lath-like beta precipitate has a constant beta-angle of 0 degrees and a periodic Cu segregation. These different ORs are explained to be attributable to the rotation of QP lattice, a near-hexagonal network of Si columns formed within beta precipitates, which causes different lattice matching of beta with alpha-Al lattice. These findings provide new insights in controlling the precipitation hardening and mechanical properties of this type of alloys. (C) 2018 Elsevier B.V. All rights reserved.

Abstract: The intensity distributions of the coherent and partially coherent x-rays passed through a poly-capillary lens have been computed at the focal plane. The computations showed that at the appropriate experimental conditions the interference phenomenon does affect the intensity distribution. In the case of the coherent input radiation with the photon energy of 0.1 keV, the interference fringes were observed, while the non-coherent x-ray radiation produced no interference-like intensity distributions.

Abstract: The 2,2′-diaminodiethylamine (DEN) functional group can be expected to have ideal properties for the chelation of transition metals and their collection from aqueous solutions, independent of the alkali and alkaline earth ions concentration. Introducing DEN into cellulose filters allows straightforward preconcentration of trace cations by a simple filtration step, and the DEN-filter constitutes a suitable target for X-ray fluorescence (XRF) analysis. The linearity between the XRF-response on the loaded DEN-filter and the trace cation concentration in the solution appears excellent, up to a total filter capacity of ca. 3 μeq.cm−2. The detection limits are around 0.5 μg. l−1 in most practical cases. Accuracy and precision are around 10%. The applicability of the proposed procedure is illustrated on a comparative basis by XRF-analysis of drinking water and surface water, after preconcentration by DEN-filtration and by alternative procedures.

Abstract: Activated carbon fibers for indoor air purification were investigated by means of pressure drop and adsorption capacity. The Darcy-Forchheimer law combined with Computational Fluid Dynamics (CFD) modelling was deployed to simulate the pressure drop over an activated carbon fiber (ACF) filter with varying filter thickness. The CFD model was later combined with adsorption modelling to simulate breakthrough profiles of acetaldehyde adsorption on the ACF-filter. The adsorption model incorporates mass transfer resistance and adsorption equilibrium. It assumes local equilibrium between gas phase and solid phase. The latter was investigated for three different adsorption isotherms: linear, Langmuir and Freundlich adsorption. Successful agreement between model simulations and experimental data was obtained, using the Freundlich adsorption model. The numerical model could provide valuable insights and allows to continuously improve the design of filtration devices.

Abstract: Recent technological advances resulted in high-quality superconducting metallic nanofilms and nanowires. The physical properties of such nanostructures are governed by the size-quantization of the transverse electron spectrum. This has a substantial impact on the basic superconducting characteristics, e.g., the order parameter, the critical temperature and the critical magnetic field. In the present paper we give an overview of our theoretical results on this subject. Based on a numerical self-consistent solution of the Bogoliubov-de Gennes equations, we investigate how the superconducting properties are modified in the quantum-size regime.