Concept of a spectrometer for resonant inelastic X‐ray scattering with parallel detection in incoming and outgoing photon energies

A spectrometer for resonant inelastic X‐ray scattering (RIXS) is proposed where imaging and dispersion actions in two orthogonal planes are combined to deliver a full two‐dimensional map of RIXS intensity in one shot with parallel detection at incoming hv_in and outgoing hv_out photon energies. Preliminary ray‐tracing simulations with a typical undulator beamline demonstrate a resolving power well above 11000 with both hv_in and hv_out near 930 eV, with a vast potential for improvement. Combining this instrument – nicknamed hv² spectrometer – with an X‐ray free‐electron laser source simplifies its technical implementation and enables efficient time‐resolved RIXS experiments.     

Single‐crystal X‐ray diffraction and resonant X‐ray magnetic scattering at helium‐3 temperatures in high magnetic fields at beamline P09 at PETRA III

The resonant scattering and diffraction beamline P09 at PETRA III at DESY is equipped with a 14 T vertical field split‐pair magnet. A helium‐3 refrigerator is available that can be fitted inside the magnet's variable‐temperature insert. Here the results of a series of experiments aimed at determining the beam conditions permitting operations with the He‐3 insert are presented. By measuring the tetragonal‐to‐orthorhombic phase transition occurring at 2.1 K in the Jahn–Teller compound TmVO₄, it is found that the photon flux at P09 must be attenuated down to 1.5 × 10⁹ photons s^?1 for the sample to remain at temperatures below 800 mK. Despite such a reduction of the incident flux and the subsequent use of a Cu(111) analyzer, the resonant X‐ray magnetic scattering signal at the Tm L_III absorption edge associated with the spin‐density wave in TmNi₂B₂C below 1.5 K is intense enough to permit a complete study in magnetic field and at sub‐Kelvin temperatures to be carried out.     

Soft X‐ray absorption spectroscopy and resonant inelastic X‐ray scattering spectroscopy below 100 eV: probing first‐row transition‐metal M‐edges in chemical complexes

X‐ray absorption and scattering spectroscopies involving the 3d transition‐metal K‐ and L‐edges have a long history in studying inorganic and bioinorganic molecules. However, there have been very few studies using the M‐edges, which are below 100 eV. Synchrotron‐based X‐ray sources can have higher energy resolution at M‐edges. M‐edge X‐ray absorption spectroscopy (XAS) and resonant inelastic X‐ray scattering (RIXS) could therefore provide complementary information to K‐ and L‐edge spectroscopies. In this study, M_2,3‐edge XAS on several Co, Ni and Cu complexes are measured and their spectral information, such as chemical shifts and covalency effects, are analyzed and discussed. In addition, M_2,3‐edge RIXS on NiO, NiF₂ and two other covalent complexes have been performed and different d–d transition patterns have been observed. Although still preliminary, this work on 3d metal complexes demonstrates the potential to use M‐edge XAS and RIXS on more complicated 3d metal complexes in the future. The potential for using high‐sensitivity and high‐resolution superconducting tunnel junction X‐ray detectors below 100 eV is also illustrated and discussed.     

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.     

Highly efficient beamline and spectrometer for inelastic soft X‐ray scattering at high resolution

The design, construction and commissioning of a beamline and spectrometer for inelastic soft X‐ray scattering at high resolution in a highly efficient system are presented. Based on the energy‐compensation principle of grating dispersion, the design of the monochromator–spectrometer system greatly enhances the efficiency of measurement of inelastic soft X‐rays scattering. Comprising two bendable gratings, the set‐up effectively diminishes the defocus and coma aberrations. At commissioning, this system showed results of spin‐flip, d–d and charge‐transfer excitations of NiO. These results are consistent with published results but exhibit improved spectral resolution and increased efficiency of measurement. The best energy resolution of the set‐up in terms of full width at half‐maximum is 108 meV at an incident photon energy tuned about the Ni L₃‐edge.     

A multiplexed high‐resolution imaging spectrometer for resonant inelastic soft X‐ray scattering spectroscopy

The optical design of a two‐dimensional imaging soft X‐ray spectrometer is described. A monochromator will produce a dispersed spectrum in a narrow vertical illuminated stripe (～2 µm wide by ～2 mm tall) on a sample. The spectrometer will use inelastically scattered X‐rays to image the extended field on the sample in the incident photon energy direction (vertical), resolving the incident photon energy. At the same time it will image and disperse the scattered photons in the orthogonal (horizontal) direction, resolving the scattered photon energy. The principal challenge is to design a system that images from the flat‐field illumination of the sample to the flat field of the detector and to achieve sufficiently high spectral resolution. This spectrometer provides a completely parallel resonant inelastic X‐ray scattering measurement at high spectral resolution (～30000) over the energy bandwidth (～5 eV) of a soft X‐ray absorption resonance.     

Origin of the X‐ray magnetic circular dichroism at the L‐edges of the rare‐earths in RxR1−x′Al2 systems

An X‐ray magnetic circular dichroism (XMCD) study performed at the rare‐earth L_2,3‐edges in the R_xR_1?x′Al₂ compounds is presented. It is shown that both R and R′ atoms contribute to the XMCD recorded at the L‐edges of the selected rare‐earth, either R or R′. The amplitude of the XMCD signal is not directly correlated to the magnetization or to the value of the individual (R, R′) magnetic moments, but it is related to the molecular field acting on the rare‐earth tuned in the photoabsorption process. This result closes a longstanding study of the origin of the XMCD at the L‐edge of the rare‐earths in multi‐component systems, allowing a full understanding of the exact nature of these signals.     

Zr and Ba edge phenomena in the scintillation intensity of fluorozirconate‐based glass‐ceramic X‐ray detectors

The energy‐dependent scintillation intensity of Eu‐doped fluorozirconate glass‐ceramic X‐ray detectors has been investigated in the energy range from 10 to 40 keV. The experiments were performed at the Advanced Photon Source, Argonne National Laboratory, USA. The glass ceramics are based on Eu‐doped fluorozirconate glasses, which were additionally doped with chlorine to initiate the nucleation of BaCl₂ nanocrystals therein. The X‐ray excited scintillation is mainly due to the 5d–4f transition of Eu²⁺ embedded in the BaCl₂ nanocrystals; Eu²⁺ in the glass does not luminesce. Upon appropriate annealing the nanocrystals grow and undergo a phase transition from a hexagonal to an orthorhombic phase of BaCl₂. The scintillation intensity is investigated as a function of the X‐ray energy, particle size and structure of the embedded nanocrystals. The scintillation intensity versus X‐ray energy dependence shows that the intensity is inversely proportional to the photoelectric absorption of the material, i.e. the more photoelectric absorption the less scintillation. At 18 and 37.4 keV a significant decrease in the scintillation intensity can be observed; this energy corresponds to the K‐edge of Zr and Ba, respectively. The glass matrix as well as the structure and size of the embedded nanocrystals have an influence on the scintillation properties of the glass ceramics.     

Multiple‐element spectrometer for non‐resonant inelastic X‐ray spectroscopy of electronic excitations

A multiple‐analyser‐crystal spectrometer for non‐resonant inelastic X‐ray scattering spectroscopy installed at beamline ID16 of the European Synchrotron Radiation Facility is presented. Nine analyser crystals with bending radii R = 1 m measure spectra for five different momentum transfer values simultaneously. Using a two‐dimensional detector, the spectra given by all analysers can be treated individually. The spectrometer is based on a Rowland circle design with fixed Bragg angles of about 88°. The energy resolution can be chosen between 30–2000 meV with typical incident‐photon energies of 6–13 keV. The spectrometer is optimized for studies of valence and core electron excitations resolving both energy and momentum transfer.     

Kinoform optics applied to X‐ray photon correlation spectroscopy

Moderate‐demagnification higher‐order silicon kinoform focusing lenses have been fabricated to facilitate small‐angle X‐ray photon correlation spectroscopy (XPCS) experiments. The geometric properties of such lenses, their focusing performance and their applicability for XPCS measurements are described. It is concluded that one‐dimensional vertical X‐ray focusing via silicon kinoform lenses significantly increases the usable coherent flux from third‐generation storage‐ring light sources for small‐angle XPCS experiments.     

Comparative study of multilayers used in monochromators for synchrotron‐based coherent hard X‐ray imaging

A systematic study is presented in which multilayers of different composition (W/Si, Mo/Si, Pd/B₄C), periodicity (from 2.5 to 5.5 nm) and number of layers have been characterized. In particular, the intrinsic quality (roughness and reflectivity) as well as the performance (homogeneity and coherence of the outgoing beam) as a monochromator for synchrotron radiation hard X‐ray micro‐imaging are investigated. The results indicate that the material composition is the dominating factor for the performance. By helping scientists and engineers specify the design parameters of multilayer monochromators, these results can contribute to a better exploitation of the advantages of multilayer monochromators over crystal‐based devices; i.e. larger spectral bandwidth and high photon flux density, which are particularly useful for synchrotron‐based micro‐radiography and ‐tomography.     

Sub‐microsecond‐resolved multi‐speckle X‐ray photon correlation spectroscopy with a pixel array detector

Small‐angle X‐ray photon correlation spectroscopy (XPCS) measurements spanning delay times from 826 ns to 52.8 s were performed using a photon‐counting pixel array detector with a dynamic range of 0–3 (2 bits). Fine resolution and a wide dynamic range of time scales was achieved by combining two modes of operation of the detector: (i) continuous mode, where data acquisition and data readout are performed in parallel with a frame acquisition time of 19.36 µs, and (ii) burst mode, where 12 frames are acquired with frame integration times of either 2.56 µs frame^?1 or 826 ns frame^?1 followed by 3.49 ms or 1.16 ms, respectively, for readout. The applicability of the detector for performing multi‐speckle XPCS was demonstrated by measuring the Brownian dynamics of 10 nm‐radius gold and 57 nm‐radius silica colloids in water at room temperature. In addition, the capability of the detector to faithfully record one‐ and two‐photon counts was examined by comparing the statistical distribution of photon counts with expected probabilities from the negative binomial distribution. It was found that in burst mode the ratio of 2 s to 1 s is markedly smaller than predicted and that this is attributable to pixel‐response dead‐time.     

Element‐selective X‐ray detected magnetic resonance: a novel application of synchrotron radiation

X‐ray detected magnetic resonance (XDMR) is a new element‐selective spectroscopy in which X‐ray magnetic circular dichroism is used to probe the resonant precession of spin and orbital magnetization components when a strong microwave pump field is applied perpendicularly to the static bias field. Experimental configurations suitable for detecting the very weak XDMR signal are compared. XDMR signatures were measured in yttrium iron garnet and related thin films on exciting not only the iron K‐edge but also the yttrium at diamagnetic sites. These measurements are shown to yield unique information regarding the wide‐angle precession of induced magnetization components involving either orbital p‐projected densities of states at the iron sites, or spin polarized d‐projected densities of states at the yttrium sites. Extending XDMR measurements into the millimeter wave range would make it possible to study paramagnetic systems routinely and investigate optical modes as well as acoustic modes in ferrimagnetic/antiferromagnetic systems.     

Application of a pnCCD in X‐ray diffraction: a three‐dimensional X‐ray detector

The first application of a pnCCD detector for X‐ray scattering experiments using white synchrotron radiation at BESSY II is presented. A Cd arachidate multilayer was investigated in reflection geometry within the energy range 7 keV < E < 35 keV. At fixed angle of incidence the two‐dimensional diffraction pattern containing several multilayer Bragg peaks and respective diffuse‐resonant Bragg sheets were observed. Since every pixel of the detector is able to determine the energy of every incoming photon with a resolution ΔE/E? 10^?2, a three‐dimensional dataset is finally obtained. In order to achieve this energy resolution the detector was operated in the so‐called single‐photon‐counting mode. A full dataset was evaluated taking into account all photons recorded within 10⁵ detector frames at a readout rate of 200 Hz. By representing the data in reciprocal‐space coordinates, it becomes obvious that this experiment with the pnCCD detector provides the same information as that obtained by combining a large number of monochromatic scattering experiments using conventional area detectors.     

Enhancement of measurement accuracy of X‐ray PIV in comparison with the micro‐PIV technique

The X‐ray PIV (particle image velocimetry) technique has been used as a non‐invasive measurement modality to investigate the haemodynamic features of blood flow. However, the extraction of two‐dimensional velocity field data from the three‐dimensional volumetric information contained in X‐ray images is technically unclear. In this study, a new two‐dimensional velocity field extraction technique is proposed to overcome technological limitations. To resolve the problem of finding a correction coefficient, the velocity field information obtained by X‐ray PIV and micro‐PIV techniques for disturbed flow in a concentric stenosis with 50% severity was quantitatively compared. Micro‐PIV experiments were conducted for single‐plane and summation images, which provide similar positional information of particles as X‐ray images. The correction coefficient was obtained by establishing the relationship between velocity data obtained from summation images (V_S) and centre‐plane images (V_C). The velocity differences between V_S and V_C along the vertical and horizontal directions were quantitatively analysed as a function of the geometric angle of the test model for applying the present two‐dimensional velocity field extraction technique to a conduit of arbitrary geometry. Finally, the two‐dimensional velocity field information at arbitrary positions could be successfully extracted from X‐ray images by using the correction coefficient and several velocity parameters derived from V_S.     

X‐Treme beamline at SLS: X‐ray magnetic circular and linear dichroism at high field and low temperature

X‐Treme is a soft X‐ray beamline recently built in the Swiss Light Source at the Paul Scherrer Institut in collaboration with École Polytechnique Fédérale de Lausanne. The beamline is dedicated to polarization‐dependent X‐ray absorption spectroscopy at high magnetic fields and low temperature. The source is an elliptically polarizing undulator. The end‐station has a superconducting 7 T–2 T vector magnet, with sample temperature down to 2 K and is equipped with an in situ sample preparation system for surface science. The beamline commissioning measurements, which show a resolving power of 8000 and a maximum flux at the sample of 4.7 × 10¹² photons s^?1, are presented. Scientific examples showing X‐ray magnetic circular and X‐ray magnetic linear dichroism measurements are also presented.     

Defect engineering by synchrotron radiation X‐rays in CeO2 nanocrystals

This work reports an unconventional defect engineering approach using synchrotron‐radiation‐based X‐rays on ceria nanocrystal catalysts of particle sizes 4.4–10.6 nm. The generation of a large number of oxygen‐vacancy defects (OVDs), and therefore an effective reduction of cations, has been found in CeO₂ catalytic materials bombarded by high‐intensity synchrotron X‐ray beams of beam size 1.5 mm × 0.5 mm, photon energies of 5.5–7.8 keV and photon fluxes up to 1.53 × 10¹² photons s^?1. The experimentally observed cation reduction was theoretically explained by a first‐principles formation‐energy calculation for oxygen vacancy defects. The results clearly indicate that OVD formation is mainly a result of X‐ray‐excited core holes that give rise to valence holes through electron down conversion in the material. Thermal annealing and subvalent Y‐doping were also employed to modulate the efficiency of oxygen escape, providing extra control on the X‐ray‐induced OVD generating process. Both the core‐hole‐dominated bond breaking and oxygen escape mechanisms play pivotal roles for efficient OVD formation. This X‐ray irradiation approach, as an alternative defect engineering method, can be applied to a wide variety of nanostructured materials for physical‐property modification.     

High‐efficiency coherence‐preserving harmonic rejection with crystal optics

This work reports a harmonic‐rejection scheme based on the combination of Si(111) monochromator and Si(220) harmonic‐rejection crystal optics. This approach is of importance to a wide range of X‐ray applications in all three major branches of modern X‐ray science (scattering, spectroscopy, imaging) based at major facilities, and especially relevant to the capabilities offered by the new diffraction‐limited storage rings. It was demonstrated both theoretically and experimentally that, when used with a synchrotron undulator source over a broad range of X‐ray energies of interest, the harmonic‐rejection crystals transmit the incident harmonic X‐rays on the order of 10^?6. Considering the flux ratio of fundamental and harmonic X‐rays in the incident beam, this scheme achieves a total flux ratio of harmonic radiation to fundamental radiation on the order of 10^?10. The spatial coherence of the undulator beam is preserved in the transmitted fundamental radiation while the harmonic radiation is suppressed, making this scheme suitable not only for current third‐generation synchrotron sources but also for the new diffraction‐limited storage rings where coherence preservation is an even higher priority. Compared with conventional harmonic‐rejection mirrors, where coherence is poorly preserved and harmonic rejection is less effective, this scheme has the added advantage of lower cost and footprint. This approach has been successfully utilized at the ultra‐small‐angle X‐ray scattering instrument at the Advanced Photon Source for scattering, imaging and coherent X‐ray photon correlation spectroscopy experiments. With minor modification, the harmonic rejection can be improved by a further five orders of magnitude, enabling even more performance capabilities.     

X‐ray powder diffraction at the XRD1 beamline at LNLS

Various upgrades have been completed at the XRD1 beamline at the Brazilian synchrotron light source (LNLS). The upgrades are comprehensive, with changes to both hardware and software, now allowing users of the beamline to conduct X‐ray powder diffraction experiments with faster data acquisition times and improved quality. The main beamline parameters and the results obtained for different standards are presented, showing the beamline ability of performing high‐quality experiments in transmission geometry. XRD1 operates in the 5.5–14 keV range and has a photon flux of 7.8 × 10⁹ photons s^?1 (with 100 mA) at 12 keV, which is one of the typical working energies. At 8 keV (the other typical working energy) the photon flux at the sample position is 3.4 × 10¹⁰ photons s^?1 and the energy resolution ΔE/E = 3 × 10^?4.