281 research outputs found

    SAXSDOG: open software for real-time azimuthal integration of 2D scattering images

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    In situ small- and wide-angle scattering experiments at synchrotrons often result in massive quantities of data within just seconds. Especially during such beamtimes, processing of the acquired data online, without appreciable delay, is key to obtaining feedback on the failure or success of the experiment. This had led to the development of SAXSDOG, a Python-based environment for real-time azimuthal integration of large-area scattering images. The software is primarily designed for dedicated data pipelines: once a scattering image is transferred from the detector onto the storage unit, it is automatically integrated and pre-evaluated using integral parameters within milliseconds. The control and configuration of the underlying server-based processes is achieved via a graphical user interface, SAXSLEASH, which visualizes the resulting 1D data together with integral classifiers in real time. SAXSDOG further includes a portable ‘take-home’ version for users that runs on standalone computers, enabling its use in laboratories or at the preferred workspace

    In situ electrochemical grazing incidence small angle X-ray scattering: From the design of an electrochemical cell to an exemplary study of fuel cell catalyst degradation

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    Nowadays, electrochemistry has a considerable technological impact, involving fuel cells, super capacitors and batteries. These devices are based on complex architectures, which complicates monitoring their evolution in situ under operating conditions to reveal the reasons for reduced lifetime and performances. Here, we present a design of a multipurpose electrochemical cell for grazing incidence small and wide angle X-ray scattering (GISAXS and GIWAXS) where the environment for operating conditions can be recreated. We focus on proton exchange membrane fuel cells (PEMFCs) which operational conditions are simulated by means of potentiodynamic-based accelerated stress tests, applied to a thin film of Pt nanoparticles representing a model system of a benchmark catalyst. Two different upper potentials are used to mimic fuel cell operating conditions: at 1.0 V RHE the catalyst film preserves its initial morphology, while at 1.5 V RHE (simulating fuel cell start-up/shut-down cycles) significant coarsening has been observed. The initial dimension of the Pt particles of 4.0 nm increases to 8.7 nm due to the predominant process of coalescence and final Ostwald ripening. In parallel, the distance between the particles increases, the catalyst film (9 nm thick) becomes thinner at first and exhibit a higher roughness at the end

    High-throughput asymmetric double-crystal monochromator of the SAXS beamline at ELETTRA.

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    A new high-flux wiggler beamline for fast time-resolved small-angle X-ray scattering (SAXS) based on double-focusing optics has recently commenced operation at the 2 GeV third-generation storage ring ELETTRA at Trieste, Italy. Its non-dispersive double-crystal monochromator contains three pairs of interchangeable asymmetrically cut flat Si(111)-crystal pairs, each of which is optimized for high throughput at one of the three fixed energies 5.4, 8 and 16 keV. To cope with the severe thermal power load produced by a 57-pole wiggler on the first crystal of each pair (up to 5.4 W mm−2 and 700 W under normal incidence, for 400 mA), grazing angles of 2° and optimized back-cooling have been chosen. This solution allows simultaneously a gain of 2.5–3.0 in throughput and, accordingly, in flux density. Finite-element analysis as well as commissioning tests showed that the cooling layout functions very satisfactorily, and that up to 5 × 1012 photons s−1 are available at the sample (at 8 keV and 250 mA), as predicted

    Imaging with high Dynamic using an Ionization Chamber

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    In this work a combination of an ionization chamber with one-dimensional spatial resolution and a MicroCAT structure will be presented. The combination between gas gain operations and integrating front-end electronics yields a dynamic range as high as eight to nine orders of magnitude. Therefore this device is well suitable for medical imaging or applications such as small angle x-ray scattering, where the requirements on the dynamic of the detector are exceptional high. Basically the described detector is an ionization chamber adapted to fan beam geometry with an active area of 192 cm and a pitch of the anode strips of 150 micrometer. In the vertical direction beams as high as 10 mm can be accepted. Every read-out strip is connected to an analogue integrating electronics channel realized in a custom made VLSI chip. A MicroCAT structure utilized as a shielding grid enables frame rates as high as 10kHz. The high dynamic range observed stems from the fact that the MicroCAT enables active electron amplification in the gas. Thus a single photon resolution can be obtained for low photon fluxes even with the integrating electronics. The specialty of this device is that for each photon flux the gas amplification can be adjusted in such a fashion that the maximum DQE value is achieved.Comment: 7 pages, 12 figures, distilled by OpenOffice.org 3.

    In Situ Study of Nanoporosity Evolution during Dealloying AgAu and CoPd by Grazing-Incidence Small-Angle X-ray Scattering

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    Electrochemical dealloying has become a standard technique to produce nanoporous network structures of various noble metals, exploiting the selective dissolution of one component from an alloy. While achieving nanoporosity during dealloying has been intensively studied for the prime example of nanoporous Au from a AgAu alloy, dealloying from other noble-metal alloys has been rarely investigated in the scientific literature. Here, we study the evolution of nanoporosity in the electrochemical dealloying process for both CoPd and AgAu alloys using a combination of in situ grazing-incidence small-angle X-ray scattering (GISAXS), kinetic Monte Carlo (KMC) simulations, and scanning transmission electron microscopy (STEM). When comparing dealloying kinetics, we find a more rapid progression of the dealloying front for CoPd and also a considerably slower coarsening of the nanoporous structure for Pd in relation to Au. We argue that our findings are natural consequences of the effectively higher dealloying potential and the higher interatomic binding energy for the CoPd alloy. Our results corroborate the understanding of electrochemical dealloying on the basis of two rate equations for dissolution and surface diffusion and suggest the general applicability of this dealloying mechanism to binary alloys. The present study contributes to the future tailoring of structural size in nanoporous metals for improved chemical surface activity

    Control of silver-polymer aggregation mechanism by primary particle spatial correlations in dynamic fractal-like geometry

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    Silver nanocrystals have been prepared by reacting silver nitrate with ascorbic acid in aqueous solution containing a low concentration of a commercial polynaphtalene sulphonate polymer (Daxad 19). Various crystalline morphologies have been obtained simply by tuning the reaction temperature. We have investigated the nanoparticle formation mechanism at three different temperatures by in situ and time resolved Small Angle X ray Scattering measurements. By modeling the scattering intensity with interacting spherical particles in a fractal-like polymer-Ag matrix, we found signatures of nucleation, growth and assembly of primary particles of about 15-20 nm. We observed how the time evolution of both spatial correlations between primary particles and the dynamic fractal geometry of the polymer-Ag matrix could influence and determine both the aggregation mechanism and the morphology of forming nanostructures in solution

    Development of a two-dimensional virtual pixel X-ray imaging detector for time-resolved structure research

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    An interpolating two-dimensional X-ray imaging detector based on a single photon counter with gas amplification by GEM (gas electron multiplier) structures is presented. The detector system can be used for time-resolved structure research down to the microsecond-time domain. The prototype detector has been tested at the SAXS beamline at ELETTRA synchrotron light source with a beam energy of 8 keV to test its capabilities in the rough beamline environment. The imaging performance is examined with apertures and standard diffraction targets. Finally, the application in a time-resolved lipid temperature jump experiment is presented.Comment: 10 pages, 14 figures, accepted for publication in J. Synchrotron Rad, revised version, paper shortened, minor change

    Mechanism of Li2S formation and dissolution in Lithium-Sulphur batteries

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    Insufficient understanding of the mechanism that reversibly converts sulphur into lithium sulphide (Li2S) via soluble polysulphides (PS) hampers the realization of high performance lithium-sulphur cells. Typically Li2S formation is explained by direct electroreduction of a PS to Li2S; however, this is not consistent with the size of the insulating Li2S deposits. Here, we use in situ small and wide angle X-ray scattering (SAXS/WAXS) to track the growth and dissolution of crystalline and amorphous deposits from atomic to sub-micron scales during charge and discharge. Stochastic modelling based on the SAXS data allows quantification of the chemical phase evolution during discharge and charge. We show that Li2S deposits predominantly via disproportionation of transient, solid Li2S2 to form primary Li2S crystallites and solid Li2S4 particles. We further demonstrate that this process happens in reverse during charge. These findings show that the discharge capacity and rate capability in Li-S battery cathodes are therefore limited by mass transport through the increasingly tortuous network of Li2S / Li2S4 / carbon pores rather than electron transport through a passivating surface film
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