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Interface resolved magnetism at metal–organic (Fe/Alq) interfaces under x-ray standing wave condition
No full textA resistively-heated dynamic diamond anvil cell (RHdDAC) for fast compression x-ray diffraction experiments at high temperatures
No full textA resistively-heated dynamic diamond anvil cell (RHdDAC) setup is presented. The setup enables the dynamic compression of samples at high temperatures by employing a piezoelectric actuator for pressure control and internal heaters for high temperature. The RHdDAC facilitates the precise control of compression rates and was tested in compression experiments at temperatures up to 1400 K and pressures of ∼130 GPa. The mechanical stability of metallic glass gaskets composed of a FeSiB alloy was examined under simultaneous high-pressure/high-temperature conditions. High-temperature dynamic compression experiments on HO ice and (Mg, Fe)O ferropericlase were performed in combination with time-resolved x-ray diffraction measurements to characterize crystal structures and compression behaviors. The employment of high brilliance synchrotron radiation combined with two fast GaAs LAMBDA detectors available at the Extreme Conditions Beamline (P02.2) at PETRA III (DESY) facilitates the collection of data with excellent pressure resolution. The pressure–temperature conditions achievable with the RHdDAC combined with its ability to cover a wide range of compression rates and perform tailored compression paths offers perspectives for a variety of future experiments under extreme conditions
Observation of the fastest chemical processes in the radiolysis of water
No full textElementary processes associated with ionization of liquid water provide a framework for understanding radiation-matter interactions in chemistry and biology. Although numerous studies have been conducted on the dynamics of the hydrated electron, its partner arising from ionization of liquid water, H2O+, remains elusive. We used tunable femtosecond soft x-ray pulses from an x-ray free electron laser to reveal the dynamics of the valence hole created by strong-field ionization and to track the primary proton transfer reaction giving rise to the formation of OH. The isolated resonance associated with the valence hole (H2O+/OH) enabled straightforward detection. Molecular dynamics simulations revealed that the x-ray spectra are sensitive to structural dynamics at the ionization site. We found signatures of hydrated-electron dynamics in the x-ray spectrum
Anisotropic and heterogeneous dynamics in an aging colloidal gel
No full textWe investigate the out-of-equilibrium dynamics of a colloidal gel obtained by quenching a suspension of soft polymer-coated gold nanoparticles close to and below its gelation point using X-ray Photon Correlation Spectroscopy (XPCS). A faster relaxation process emergent from the localized motions of the nanoparticles reveals a dynamically-arrested network at the nanoscale as a key signature of the gelation process. We find that the slower network dynamics is hyperdiffusive with a compressed exponential form, consistent with stress-driven relaxation processes. Specifically, we use direction-dependent correlation functions to characterize the anisotropy in dynamics. We show that the anisotropy is greater for the gel close to its gelation point than at lower temperatures, and the anisotropy decreases as the gel ages. We quantify the anisotropic dynamical heterogeneities emergent in such a stress-driven dynamical system using higher order intensity correlations, and demonstrate that the aging phenomenon contributes significantly to the properties evaluated by the fluctuations in the intensity correlations. Our results provide important insights into the structural origin of the emergent anisotropic and cooperative heterogeneous dynamics, and we discuss analogies with previous work on other soft disordered systems
Thermomechanical response of thickly tamped targets and diamond anvil cells under pulsed hard x-ray irradiation
No full textIn the laboratory study of extreme conditions of temperature and density, the expo22sure of matter to high intensity radiation sources has been of central importance. Here23 we interrogate the performance of multi-layered targets in experiments involving high24 intensity, hard x-ray irradiation, motivated by the advent of extremely high bright25ness hard x-ray sources, such as free electron lasers and 4th-generation synchrotron26 facilities. Intense hard x-ray beams can deliver signicant energy in targets having27 thick x-ray transparent layers (tampers) around samples of interest, for the study28 of novel states of matter and materials' dynamics. Heated-state lifetimes in such29 targets can approach the microsecond level, regardless of radiation pulse duration,30 enabling the exploration of conditions of local thermal and thermodynamic equilib31rium at extreme temperature in solid density matter. The thermal and mechanical32 response of such thick layered targets following x-ray heating, including hydrody33namic relaxation and heat ow on picosecond to millisecond timescales, is modeled34 using radiation hydrocode simulation, nite element analysis, and thermodynamic35 calculations. Assessing the potential for target survival over one or more exposures,36 and resistance to damage arising from heating and resulting mechanical stresses, this37 study doubles as an investigation into the performance of diamond-anvil high pres38sure cells under high x-ray uences. Long used in conjunction with synchrotron x-ray39 radiation and high power optical lasers, the strong connement aorded by such cells40 suggests novel applications at emerging high intensity x-ray facilities and new routes41 to studying thermodynamic equilibrium states of warm, very dense matter
Influence of Nb-doping on the local structure and thermoelectric properties of transparent thin films
No full textTransparent n-type niobium-doped titanium dioxide thin films (TiO2:1.5 at.%Nb) with pronouncedthermoelectric properties were produced from a composite Ti:Nb target by reactive magnetron sputtering.The thin films were comprehensively characterized by X-ray diffraction, X-ray photoelectronspectroscopy, optical spectroscopy, electrical conductivity, and thermoelectric measurement techniques.The local structure of the thin films was investigated in detail by X-ray absorption spectroscopy at the Tiand Nb K-edges. A set of radial distribution functions were extracted from the simultaneous analysis ofEXAFS data at two absorption edges using the reverse Monte Carlo method. It was found that Nb dopantatoms modify the local environment of the films, but their average structure remains close to that of theanatase phase. This conclusion is also supported by the ab initio simulations of XANES. A very highabsolute Seebeck coefficient (S = 155 mV/K) for n-type TiO2 was achieved with Nb doping, yielding amaximum power factor and thermoelectric figure of merit of 0.5 mW m-1 K-2 and 0.18 at a temperatureof 300 K, respectively, for a 150 nm thick film. From frequency-domain thermoreflectance experiments, athermal conductivity value of 1.3 W m-1 K-1 was obtained for the optimized TiO2:Nb film
Nuclear quantum effects in state-selective scattering from ring polymer molecular dynamics
No full textWe present an efficient method to obtain initial state-selective cross sections for bimolecular reactions that can account for certain nuclear quantum effects by employing the ring polymer molecular dynamics approach. The method combines the well known quasiclassical trajectory (QCT) approach with the description of the system in an extended ring polymer phase space. Employing the prototypical Mu/H/D + H2(v = 0, 1) reactions as a benchmark, we show that the presented approach does not violate zero-point energy constraints and that it can also capture the contributions of tunneling through the v = 1 vibrationally adiabatic barrier present for the Mu + H2(v = 1) reaction. This is a significant improvement over the QCT approach with only a small increase in numerical cost
Synthesis and characterization of , and core/shell nanowire heterostructures
No full textLayered 2D van der Waals (vdW) materials such as graphene and transition metal dichalcogenides have recently gained a great deal of scientific attention due to their unique properties and prospective applications in various fields such as electronics and optoelectronics, sensors and energy. As a direct bandgap semiconductor in both bulk and monolayer forms, ReS stands out for its unique distorted octahedral structure that results in distinctive anisotropic physical properties; however, only a few scalable synthesis methods for few-layer ReS have been proposed thus far. Here, the growth of high-quality few-layer ReS is demonstrated via sulfurization of a pre-deposited rhenium oxide coating on different semiconductor material nanowires (GaN, ZnS, ZnO). As-produced core-shell heterostructures were characterized by X-ray diffraction, scanning and transmission electron microscopy, micro-Raman spectroscopy and X-ray absorption spectroscopy. Experimental characterizations were supported by total energy calculations of the electronic structure of ReS nanosheets and GaN, ZnS, and ZnO substrates. Our results demonstrate the potential of using nanowires as a template for the growth of layered vdW materials to create novel core-shell heterostructures for energy applications involving photocatalytic and electrocatalytic hydrogen evolution
Opportunities for Structure Determination Using X-ray Free-electron Laser Pulses
No full textOne of the exciting prospects enabled by the short, intense pulses of X-ray free-electron lasers (XFELs) is the determination of near-atomic resolution structures of biomolecules and their complexes without the need of crystallisation or cryo-cooling. Using femtosecond pulses that freeze all atomic motion could open up entirely new capabilities and insights into the dynamics, function and interaction of many systems in structural biology. Meeting this goal requires methodological advances beyond those that have already been recently made at XFEL facilities. Here, some of the challenges and opportunities are discussed, starting from considerations of the interactions of X-rays with materials. The destructive nature of XFEL pulses restricts high-resolution imaging experiments to a single shot from a single sample, yet three-dimensional information is needed to properly interpret images from unsectioned samples. This requires the means to obtain multiple-view images of a unique object, such as a cell, in a single pulse or to average data from many reproducible objects as in crystallography or single-particle diffractive imaging. A potential method is presented for the former case and, in addition to the requirement of high peak brightness, the performance in the latter case is dependent on the highest average brightness achievable with future XFEL sources
A laser powder bed fusion system for in situ x-ray diffraction with high-energy synchrotron radiation
No full textIn Laser Powder Bed Fusion (LPBF) the highly localized energy input by the laser leads to hightemperature gradients. Combined with the inherent cycles of re-melting and solidifying of thematerial, they can result in high mechanical stresses. These stresses can cause distortion andcracking within the component. In situ diffraction experiments with high-energy synchrotronradiation allow an analysis of the lattice spacing during the LPBF process and provide insightinto the dynamics of stress generation and texture evolution. In this work, an LPBF system forthe purpose of synchrotron X-ray diffraction experiments during the manufacturing process ofmulti-layer components with simple geometries is described. Moreover, results from diffractionexperiments at the HEMS beamline P07 at PETRA-III, DESY, Hamburg, Germany arepresented. Components with a length of ls = 20 mm and width of ws = 2.5 mm consisting of100 layers with a layer thickness of Δz = 50 μm were produced using the nickel-base alloyInconel 625 as powder material. Diffraction experiments were carried out in situ at samplingrates of f = 10 Hz with a synchrotron radiation beam size of 750 × 70 μm². The presentedexperimental setup allows for the observation of arbitrary measuring positions in the sample intransmission mode while gathering full diffraction rings. Thus, new possibilities for theobservation of the dynamic evolution of strains, stresses and textures during the LPBF processare provided