Synchrotron Experiments Research Articles

Magnetodielectric effects inA-site cation-ordered chromate spinelsLiMCr4O8(M=Gaand In)

We report the occurrence of a magnetodielectric effect and its correlation with structure and magnetism in the $A$-site ordered chromate spinel oxides $\mathrm{Li}M\mathrm{C}{\mathrm{r}}_{4}{\mathrm{O}}_{8}$ ($M=\mathrm{Ga}$, In). In addition to magnetic and dielectric measurements, temperature dependent synchrotron and neutron diffraction experiments have been carried out for the Ga compound. The results are compared and contrasted with that of a corresponding conventional $B$-site magnetic chromate spinel oxide, $\mathrm{ZnC}{\mathrm{r}}_{2}{\mathrm{O}}_{4}$. Like $\mathrm{ZnC}{\mathrm{r}}_{2}{\mathrm{O}}_{4}$, the $A$-site ordered chromate spinels exhibit a magnetodielectric effect at the magnetic ordering temperature (${T}_{\mathrm{N}}\ensuremath{\sim}13--15\phantom{\rule{0.16em}{0ex}}\mathrm{K}$), resulting from magnetoelastic coupling through a spin Jahn-Teller effect. While the presence of a broad magnetic anomaly, associated with a short-range magnetic ordering (${T}_{\mathrm{SO}}\ensuremath{\sim}45\phantom{\rule{0.16em}{0ex}}\mathrm{K}$) in $\mathrm{ZnC}{\mathrm{r}}_{2}{\mathrm{O}}_{4}$, does not cause any dielectric anomaly, a sharp change in dielectric constant has been observed in $\mathrm{LiInC}{\mathrm{r}}_{4}{\mathrm{O}}_{8}$ at the magnetic anomaly, which is associated with the opening of a spin gap (${T}_{\mathrm{SG}}\ensuremath{\sim}60\phantom{\rule{0.16em}{0ex}}\mathrm{K}$). Contrary to the In compound, a broad dielectric anomaly exists at the onset of short-range antiferromagnetic ordering (${T}_{\mathrm{SO}}\ensuremath{\sim}55\phantom{\rule{0.16em}{0ex}}\mathrm{K}$) in $\mathrm{LiGaC}{\mathrm{r}}_{4}{\mathrm{O}}_{8}$. The differences in dielectric behavior of these compounds have been discussed in terms of breathing distortion of the $\mathrm{C}{\mathrm{r}}_{4}$ tetrahedra.

The new barium compound Ba4Al7+x : formation and crystal structure

Abstract Combining laboratory X-ray powder diffraction with in-situ high-temperature synchrotron experiments and differential scanning calorimetry, it has been shown that Ba21Al40, Ba3Al5, Ba7Al10 and Ba4Al5 decompose peritectically at 914, 826, 756, and 732°C, respectively. In addition, a new binary compound with the composition Ba4Al7+x (x = 0.17) and the formation temperature of 841°C was found. The initial structural model (space group P63/mmc, a = 6.0807(1), c = 39.2828(8) Å) with four Ba and five Al crystallographic positions was developed. It is based on the intergrowth concept involving the neighboring Ba21Al40 and Ba3Al5 phases and the derived atomic arrangement is subsequently refined using X-ray diffraction data. The crystal structures of all phases in the Ba–Al system, except BaAl4, exhibit Kagomé nets of aluminum atoms resembling those observed for the B atoms in the Laves phases AB 2. In the crystal structure of Ba4Al7+x , single Kagomé layers alternate with double slabs (MgZn2 motif) along [001] and are separated by Ba cations. Intergrowth features of Ba4Al7+x are discussed together with the neighboring Ba–Al compounds and Sr5Al9.

Timepix3 as X-ray detector for time resolved synchrotron experiments

The Timepix3 ASIC can be used very effectively for time resolved experiments at synchrotron facilities. We have carried out characterizations with the synchrotron beam in order to determine the time resolution and other characteristics such as the energy resolution, charge sharing and signals overlapping. The best time resolution achieved is 19ns FWHM for 12keV photons and 350V bias voltage. The time resolution shows dependency on the photon energy as well as on the chip and acquisition parameters.

Sapphire hard X-ray Fabry-Perot resonators for synchrotron experiments.

Hard X-ray Fabry-Perot resonators (FPRs) made from sapphire crystals were constructed and characterized. The FPRs consisted of two crystal plates, part of a monolithic crystal structure of Al2O3, acting as a pair of mirrors, for the backward reflection (0 0 0 30) of hard X-rays at 14.3147 keV. The dimensional accuracy during manufacturing and the defect density in the crystal in relation to the resonance efficiency of sapphire FPRs were analyzed from a theoretical standpoint based on X-ray cavity resonance and measurements using scanning electron microscopic and X-ray topographic techniques for crystal defects. Well defined resonance spectra of sapphire FPRs were successfully obtained, and were comparable with the theoretical predictions.

Quantitative characterization of X-ray lenses from two fabrication techniques with grating interferometry.

Refractive X-ray lenses are in use at a large number of synchrotron experiments. Several materials and fabrication techniques are available for their production, each having their own strengths and drawbacks. We present a grating interferometer for the quantitative analysis of single refractive X-ray lenses and employ it for the study of a beryllium point focus lens and a polymer line focus lens, highlighting the differences in the outcome of the fabrication methods. The residuals of a line fit to the phase gradient are used to quantify local lens defects, while shape aberrations are quantified by the decomposition of the retrieved wavefront phase profile into either Zernike or Legendre polynomials, depending on the focus and aperture shape. While the polymer lens shows better material homogeneity, the beryllium lens shows higher shape accuracy.

Ptychographic coherent diffractive imaging with orthogonal probe relaxation.

Ptychography is a scanning coherent diffractive imaging (CDI) technique that relies upon a high level of stability of the illumination during the course of an experiment. This is particularly an issue for coherent short wavelength sources, where the beam intensity is usually tightly focused on the sample in order to maximize the photon flux density on the illuminated region of the sample and thus a small change in the beam position results in a significant change in illumination of the sample. We present an improved ptychographic method that allows for limited stability of the illumination wavefront and thus significantly improve the reconstruction quality without additional prior knowledge. We have tested our reconstruction method in a proof of concept experiment, where the beam instability of a visible light source was emulated using a piezo driven mirror, and also in a short wavelength microscopy CDI setup using a high harmonic generation source in the extreme ultraviolet range. Our work shows a natural extension of the ptychography method that paves the way to use ptychographic imaging with any limited pointing stability coherent source such as free electron or soft X-ray lasers and improve reconstruction quality of long duration synchrotron experiments.

Evaluating scintillator performance in time-resolved hard X-ray studies at synchrotron light sources.

The short pulse duration, small effective source size and high flux of synchrotron radiation is ideally suited for probing a wide range of transient deformation processes in materials under extreme conditions. In this paper, the challenges of high-resolution time-resolved indirect X-ray detection are reviewed in the context of dynamic synchrotron experiments. In particular, the discussion is targeted at two-dimensional integrating detector methods, such as those focused on dynamic radiography and diffraction experiments. The response of a scintillator to periodic synchrotron X-ray excitation is modelled and validated against experimental data collected at the Diamond Light Source (DLS) and European Synchrotron Radiation Facility (ESRF). An upper bound on the dynamic range accessible in a time-resolved experiment for a given bunch separation is calculated for a range of scintillators. New bunch structures are suggested for DLS and ESRF using the highest-performing commercially available crystal LYSO:Ce, allowing time-resolved experiments with an interframe time of 189 ns and a maximum dynamic range of 98 (6.6 bits).

The role of mesophases in the ordering of polymers

The role played by mesophases in the ordering of polymers, namely if they are either competitors with the more stable crystal structures, or they act as precursors of subsequent crystallization, has been analyzed in two kinds of systems: (a) isotactic polypropylene and copolymers with 1-pentene, as representative of forming solid mesophases, and (b) liquid crystalline polymers with biphenyl mesogens (polybibenzoates and esters of hydroxypropylcellulose with different acids including the biphenyl group). Variable-temperature synchrotron experiments have been the primary tool in order to evaluate the formation and stability of those mesophases as function of composition, chemical structure and crystallization conditions (mainly the cooling rate). The results show, in the first case, that the mesophase forming rate depends strongly on comonomer content, and that these solid mesophases are really competitors with the 3D phases. Additionally, a rather complicated polymorphic behavior is exhibited by the 1-pentene copolymers at intermediate contents, where the mesophase is a competitor with both trigonal and monoclinic crystals. On the contrary, in the case of liquid crystalline mesophases these are precursors of the eventual subsequent crystallization. Moreover, correlation lengths and phase behavior in hydroxypropylcellulose esters were found to depend strongly on the degree of substitution, in such a way that differentiation between the mesophase and the isotropic amorphous profile becomes increasingly difficult.

On the Carbon Solubility in Expanded Austenite and Formation of Hägg Carbide in AISI 316 Stainless Steel

The carbon solubility in expanded austenite is investigated by controlled low temperature gaseous through-carburizing of AISI 316 stainless steel thin foils with thermogravimetry and synchrotron powder diffraction analysis. Carburizing is carried out in C2H2–H2–N2 and CO–H2–N2 atmospheres at 380–420 °C and 465–470 °C, respectively. Hägg carbide (χ-M5C2) develops when the carbon content in the expanded austenite exceeds the metastable solubility limit; the transformation of carbon expanded austenite into Hägg carbide occurs irrespective of carburizing temperature in the investigated temperature range (380–470 °C). The maximum solubility of carbon in expanded austenite (380 °C) is found to correspond to an occupancy (yC) of 0.220 of the interstitial octahedral sites of the austenite lattice (i.e., 4.74 wt% C). Decomposition of Hägg carbide into M7C3 occurs upon prolonged carburizing treatment or thermal exposure in inert atmosphere (in situ synchrotron experiments).

Oxide film defects in Al alloys and the formation of hydrogen- related porosity

Double oxide film defects have also been held responsible for the origins of hydrogen porosity, where hydrogen dissolved in the Al melt passes into the interior atmosphere of the double oxide film defect causing it to inflate. However, this is in opposition to long- established evidence that H cannot readily diffuse through aluminium oxide. To investigate this further, samples of commercial purity Al were first degassed to remove their initial H content, and then heated to above their melting point and held in atmospheres of air and nitrogen respectively, to determine any differences in H pick-up. The experiment showed that samples held in an oxidising atmosphere, and having an oxide skin, picked up significantly less H than when the samples were held in a nitrogen atmosphere, which resulted in the formation of AlN in cracks in the oxide skin of the sample. It is suggested that double oxide film defects can give rise to hydrogen-related porosity, but this occurs more quickly when the oxygen in the original oxide film defect has been consumed by reaction with the surrounding melt and nitrogen reacts to form AlN, which is more permeable to H than alumina, more easily allowing the oxide film defect to give rise to a hydrogen pore. This is used to interpret results from an earlier synchrotron experiment, in which a small pore was seen to grow into a larger pore, while an adjacent large pore remained at a constant size.

In-vacuum long-wavelength macromolecular crystallography.

Structure solution based on the weak anomalous signal from native (protein and DNA) crystals is increasingly being attempted as part of synchrotron experiments. Maximizing the measurable anomalous signal by collecting diffraction data at longer wavelengths presents a series of technical challenges caused by the increased absorption of X-rays and larger diffraction angles. A new beamline at Diamond Light Source has been built specifically for collecting data at wavelengths beyond the capability of other synchrotron macromolecular crystallography beamlines. Here, the theoretical considerations in support of the long-wavelength beamline are outlined and the in-vacuum design of the endstation is discussed, as well as other hardware features aimed at enhancing the accuracy of the diffraction data. The first commissioning results, representing the first in-vacuum protein structure solution, demonstrate the promising potential of the beamline.

Signal-to-noise criterion for free-propagation imaging techniques at free-electron lasers and synchrotrons.

We propose a signal-to-noise criterion which predicts whether a feature of a given size and scattering strength, placed inside a larger object, can be retrieved with two common X-ray imaging techniques: coherent diffraction imaging and projection microscopy. This criterion, based on how efficiently these techniques detect the scattered photons and validated through simulations, shows in general that projection microscopy can resolve smaller phase differences and features than coherent diffraction imaging. Our criterion can be used to design optimized imaging experiments and perform feasibility studies for sensitive biological materials in free-electron lasers, where the number of photons per pulse is limited, or in synchrotron experiments, for both techniques.

Controlling the emission profile of an H2discharge lamp to simulate interstellar radiation fields

Context. Microwave discharge hydrogen-flow lamps have been used for more than half a century to simulate interstellar ultraviolet radiation fields in the laboratory. Recent discrepancies between identical measurements in different laboratories, as well as clear wavelength dependent results obtained in monochromatic (synchrotron) experiments, hint at a more elaborate dependence on the exact discharge settings than assumed so far.Aims. We have investigated systematically two lamp geometries in full dependence of a large number of different running conditions and the spectral emission patterns are characterized for the first time with fully calibrated absolute flux numbers.Methods. A sophisticated plasma lamp calibration set-up has been used to record the vacuum-ultraviolet emission spectra with a spectral resolution of 0.5 nm and bandwidth of 1.6 nm in the 116–220 nm region. Spectra are compared with the output of a calibrated D2 -lamp which allows a derivation of absolute radiance values.Results. The general findings of over 200 individual measurements are presented, illustrating how the lamp emission pattern depends on i) microwave power; ii) gas and gas mixing ratios; iii) discharge lamp geometry; iv) cavity positioning; and v) gas pressure.

A large surface X-ray camera based on XPAD3/CdTe single chip hybrids

The XPAD3 chip bump-bonded to a Si sensor has been widely used in preclinical micro-computed tomography and in synchrotron experiments. Although the XPAD3 chip is linear up to 60 keV, the performance of the XPAD3/Si hybrid detector is limited to energies below 30 keV, for which detection efficiencies remain above 20%. To overcome this limitation on detection efficiency in order to access imaging at higher energies, we decided to develop a camera based on XPAD3 single chips bump-bonded to high-Z CdTe sensors. We will first present the construction of this new camera, from the first tests of the single chip hybrids to the actual mechanical assembly. Then, we will show first images and stability tests performed on the D2AM beam line at ESRF synchrotron facility with the fully assembled camera.

Grating-based interferometry and hybrid photon counting detectors: Towards a new era in X-ray medical imaging

Progress in X-ray medical imaging and advances in detector developments have always been closely related. Similarly, a strong connection exists between innovations in synchrotron imaging and their implementation on table-top X-ray tube setups. The transfer of phase-based imaging to X-ray tubes can provide table-top setups with improved contrast between areas of low attenuation differences, by exploiting the unit decrement of the real part of the refractive index. Medical imaging is a potential application for such a system. Originally developed for synchrotron experiments, the novel generation of hybrid photon counting detectors is becoming increasingly popular due to their unique characteristics, such as small pixel size, negligible dark noise, fast counting and adjustable energy thresholds. Furthermore, novel room temperature semiconductor materials such as Cd(Zn)Te can provide higher quantum efficiency. In the first part of this article we review phase-contrast techniques and recent research towards medical applications. In the second part we present results and evaluate the potential of combining a table-top Talbot grating interferometry system with latest generation hybrid photon counting detectors.

X-ray induced fragmentation dynamics of doubly charged L-alanine in gas phase

SynopsisThe molecular fragmentation of doubly charged L-alanine in gas phase was studied in radiation synchrotron experiments. In this presentation, we summarize our theoretical study on the dynamics of this fragmentation, using various computational methods. We show that in practice the ground state MD simulations are able to statistically reproduce the experimental results of the photo-fragmentation initiated at the excited state.

Degradation Mechanism Analysis of 18650-Type Lithium-Ion Battery: A Hard X-Ray Photoelectron Spectroscopic Investigation

Introduction Establishment of lifetime prediction methodology for Li-ion batteries (LIBs) is strongly required in order to prolong the lifetime of LIBs and to use LIBs in safe. While “square root (SQRT) law” has been proposed to predict the lifetime of LIBs based on the growth mechanism of solid electrolyte interphases (SEIs) [1], the SQRT law cannot describe the degradation behavior precisely in whole period of LIB operation, especially near the end stage of degradation, because the detailed mechanism of degradation remains unknown. We, therefore, investigated the detailed structure of SEIs in heavily deteriorated anodes by Hard X-ray photoelectron spectroscopy (HAXPES) technique [2] that enables us to investigate the chemical composition of the whole SEIs in non-destructive way, and then, we discuss the reason of deviation from the SQRT law. Experimental A commercial 18650-type LIB cell, which consists of a graphite anode, Li(Ni1/3Mn1/3Co1/3)O2 cathode, and LiPF6 in a mixture solvent of EC, PC, EMC and DMC as electrolyte, was used in this study. Cells were charged and discharged with 1C rate (0, 100, 200 and 500cycles) at 25ºC. The cells were then disassembled in an argon glove box, in which the oxygen and water contents were maintained below 1 ppm. Then the electrodes were washed with highly purified DMC to remove the residual electrolyte components. After washing, the electrodes were vacuum-dried to evaporate the solvents and then transferred to the analysis chamber by using a transfer vessel. The HAXPES measurements were carried out at the BL46XU beamline at SPring-8. The photon energy of incident X-rays was 14 keV. The X-ray take-off angle was 80º Results and discussion Figure 1(a) shows the change of discharge capacity retention as a function of SQRT of the number of charge/discharge cycle. Although discharge capacity retention was proportional to SQRT up to 300cycles, a sudden reduction was observed around 300 cycles. We show the pictures of disassembled anodes after cycle tests in Fig. 1(b). We observed the inhomogeneous degradation in anode sheet especially on 500 cycled. At the outside, the surface of the anode layer was discolored to blue, and at the inside, we observed the depositions. We, then, investigated the distribution of SEI growth on the anode sheet in addition to the cycle dependence of SEI growth. Figures 1(c) and (d) show C 1s spectra obtained by using 14 keV HAXPES. We can easily find the graphite peak (283.9 eV) was observed in all samples by using 14 keV HAXPES. In XPS spectra with Al Kα incident X-rays (hv = 1486.6eV), this graphite peak wasn’t observed in almost all samples. This indicates that the probing depth of 14 keV HAXPES is larger than thickness of SEI, thus 14 keV HAXPES detected whole SEI and a part of the graphite exists underneath SEI formed on all the anodes in the depth direction. In order to look the difference in cycle dependence of SEI growth between the outside and inside of an anode sheet, we focused on the intensity of graphite peak. In Fig. 1(c), we observed that the intensity of graphite peak gradually decreases with increasing cycles. This indicates that the SEI gradually grew with increasing cycles at the outside. On the other hand, in Fig. 1(d), sudden decrease in the intensity of graphite peak was observed on 500 cycled, though the intensity of graphite peak hardly changes on 100 and 200 cycled. This result suggests that SEI dramatically grew between 200 and 500 cycles at the inside. This behavior coincides with the sudden reduction of discharge capacity retention. From these results, one reason for the sudden reduction of discharge capacity retention was considered to be caused by the irreversible loss of Li due to rapid SEI growth at the inside of anode sheet. At the meeting, we will also discuss about the variation of the chemical composition of SEI and the factor of rapid SEI growth. Acknowledgement The synchrotron experiments were carried out on beamline BL46XU at SPring-8 with approvals from Japan synchrotron radiation institute (JASRI) (Proposal No. 2014B1903). Reference [1] H. Yoshida et al ., Electrochemistry 71, 1018 (2003). [2] M. Matsumoto et al,. 226thECS meeting A5-422. Figure caption Fig.1 (a) Cycle dependence of discharge capacity retention. (b) Pictures of disassembled anodes after cycle tests. (c) and (d) C 1s spectra obtained by using 14 keV HAXPES at the outside and at the inside of an anode sheet, respectively. Figure 1

Online remote control systems for static and dynamic compression and decompression using diamond anvil cells.

The ability to remotely control pressure in diamond anvil cells (DACs) in accurate and consistent manner at room temperature, as well as at cryogenic and elevated temperatures, is crucial for effective and reliable operation of a high-pressure synchrotron facility such as High Pressure Collaborative Access Team (HPCAT). Over the last several years, a considerable effort has been made to develop instrumentation for remote and automated pressure control in DACs during synchrotron experiments. We have designed and implemented an array of modular pneumatic (double-diaphragm), mechanical (gearboxes), and piezoelectric devices and their combinations for controlling pressure and compression/decompression rate at various temperature conditions from 4 K in cryostats to several thousand Kelvin in laser-heated DACs. Because HPCAT is a user facility and diamond cells for user experiments are typically provided by users, our development effort has been focused on creating different loading mechanisms and frames for a variety of existing and commonly used diamond cells rather than designing specialized or dedicated diamond cells with various drives. In this paper, we review the available instrumentation for remote static and dynamic pressure control in DACs and show some examples of their applications to high pressure research.

DIOPTAS: a program for reduction of two-dimensional X-ray diffraction data and data exploration

The amount of data collected during synchrotron X-ray diffraction (XRD) experiments is constantly increasing. Most of the time, the data are collected with image detectors, which necessitates the use of image reduction/integration routines to extract structural information from measured XRD patterns. This step turns out to be a bottleneck in the data processing procedure due to a lack of suitable software packages. In particular, fast-running synchrotron experiments require online data reduction and analysis in real time so that experimental parameters can be adjusted interactively. Dioptas is a Python-based program for on-the-fly data processing and exploration of two-dimensional X-ray diffraction area detector data, specifically designed for the large amount of data collected at XRD beamlines at synchrotrons. Its fast data reduction algorithm and graphical data exploration capabilities make it ideal for online data processing during XRD experiments and batch post-processing of large numbers of images.

ALICE—An advanced reflectometer for static and dynamic experiments in magnetism at synchrotron radiation facilities.

We report on significant developments of a high vacuum reflectometer (diffractometer) and spectrometer for soft x-ray synchrotron experiments which allows conducting a wide range of static and dynamic experiments. Although the chamber named ALICE was designed for the analysis of magnetic hetero- and nanostructures via resonant magnetic x-ray scattering, the instrument is not limited to this technique. The versatility of the instrument was testified by a series of pilot experiments. Static measurements involve the possibility to use scattering and spectroscopy synchrotron based techniques (photon-in photon-out, photon-in electron-out, and coherent scattering). Dynamic experiments require either laser or magnetic field pulses to excite the spin system followed by x-ray probe in the time domain from nano- to femtosecond delay times. In this temporal range, the demagnetization/remagnetization dynamics and magnetization precession in a number of magnetic materials (metals, alloys, and magnetic multilayers) can be probed in an element specific manner. We demonstrate here the capabilities of the system to host a variety of experiments, featuring ALICE as one of the most versatile and demanded instruments at the Helmholtz Center in Berlin-BESSY II synchrotron center in Berlin, Germany.