The MYTHEN detector for X-ray powder diffraction experiments at the Swiss Light Source

A synergic approach of X-ray powder diffraction and Raman spectroscopy for crystal structure determination of 2,3-thienoimide capped oligothiophenes

This work presents a Raman based approach for the rapid identification of the molecular conformation in a series of new 2,3-thienoimide capped quaterthiophenes.

Tutorial on X-ray photon counting detector characterization

BACKGROUND

Recent advances in photon counting detection technology have led to significant research interest in X-ray imaging.

OBJECTIVE

As a tutorial level review, this paper covers a wide range of aspects related to X-ray photon counting detector characterization.

METHODS

The tutorial begins with a detailed description of the working principle and operating modes of a pixelated X-ray photon counting detector with basic architecture and detection mechanism. Currently available methods and techniques for charactering major aspects including energy response, noise floor, energy resolution, count rate performance (detector efficiency), and charge sharing effect of photon counting detectors are comprehensively reviewed. Other characterization aspects such as point spread function (PSF), line spread function (LSF), contrast transfer function (CTF), modulation transfer function (MTF), noise power spectrum (NPS), detective quantum efficiency (DQE), bias voltage, radiation damage, and polarization effect are also remarked.

RESULTS

A cadmium telluride (CdTe) pixelated photon counting detector is employed for part of the characterization demonstration and the results are presented.

CONCLUSIONS

This review can serve as a tutorial for X-ray imaging researchers and investigators to understand, operate, characterize, and optimize photon counting detectors for a variety of applications.

Atomic pair distribution function at the Brazilian Synchrotron Light Laboratory: application to the Pb1-xLaxZr0.40Ti0.60O3 ferroelectric system

This work reports the setting up of the X-ray diffraction and spectroscopy beamline at the Brazilian Synchrotron Light Laboratory for performing total scattering experiments to be analyzed by atomic pair distribution function (PDF) studies. The results of a PDF refinement for Al₂O₃ standard are presented and compared with data acquired at a beamline of the Advanced Photon Source, where it is common to perform this type of experiment. A preliminary characterization of the Pb_1-xLa_xZr_0.40Ti_0.60O₃ ferroelectric system, with x = 0.11, 0.12 and 0.15, is also shown.

High-throughput powder diffraction measurement system consisting of multiple MYTHEN detectors at beamline BL02B2 of SPring-8

In this study, we developed a user-friendly automatic powder diffraction measurement system for Debye-Scherrer geometry using a capillary sample at beamline BL02B2 of SPring-8. The measurement system consists of six one-dimensional solid-state (MYTHEN) detectors, a compact auto-sampler, wide-range temperature control systems, and a gas handling system. This system enables to do the automatic measurement of temperature dependence of the diffraction patterns for multiple samples. We introduced two measurement modes in the MYTHEN system and developed new attachments for the sample environment such as a gas handling system. The measurement modes and the attachments can offer in situ and/or time-resolved measurements in an extended temperature range between 25 K and 1473 K and various gas atmospheres and pressures. The results of the commissioning and performance measurements using reference materials (NIST CeO₂ 674b and Si 640c), V₂O₃ and Ti₂O₃, and a nanoporous coordination polymer are presented.

Coherent Nanotwins and Dynamic Disorder in Cesium Lead Halide Perovskite Nanocrystals

Crystal defects in highy luminescent colloidal nanocrystals (NCs) of CsPbX₃ perovskites (X = Cl, Br, I) are investigated. Here, using X-ray total scattering techniques and the Debye scattering equation (DSE), we provide evidence that the local structure of these NCs always exhibits orthorhombic tilting of PbX₆ octahedra within locally ordered subdomains. These subdomains are hinged through a two-/three-dimensional (2D/3D) network of twin boundaries through which the coherent arrangement of the Pb ions throughout the whole NC is preserved. The density of these twin boundaries determines the size of the subdomains and results in an apparent higher-symmetry structure on average in the high-temperature modification. Dynamic cooperative rotations of PbX₆ octahedra are likely at work at the twin boundaries, causing the rearrangement of the 2D or 3D network, particularly effective in the pseudocubic phases. An orthorhombic, 3D γ-phase, isostructural to that of CsPbBr₃ is found here in as-synthesized CsPbI₃ NCs.

Dismantling the "Red Wall" of Colloidal Perovskites: Highly Luminescent Formamidinium and Formamidinium-Cesium Lead Iodide Nanocrystals

Colloidal nanocrystals (NCs) of APbX₃-type lead halide perovskites [A = Cs⁺, CH₃NH₃⁺ (methylammonium or MA⁺) or CH(NH₂)₂⁺ (formamidinium or FA⁺); X = Cl^-, Br^-, I^-] have recently emerged as highly versatile photonic sources for applications ranging from simple photoluminescence down-conversion (e.g., for display backlighting) to light-emitting diodes. From the perspective of spectral coverage, a formidable challenge facing the use of these materials is how to obtain stable emissions in the red and infrared spectral regions covered by the iodide-based compositions. So far, red-emissive CsPbI₃ NCs have been shown to suffer from a delayed phase transformation into a nonluminescent, wide-band-gap 1D polymorph, and MAPbI₃ exhibits very limited chemical durability. In this work, we report a facile colloidal synthesis method for obtaining FAPbI₃ and FA-doped CsPbI₃ NCs that are uniform in size (10-15 nm) and nearly cubic in shape and exhibit drastically higher robustness than their MA- or Cs-only cousins with similar sizes and morphologies. Detailed structural analysis indicated that the FAPbI₃ NCs had a cubic crystal structure, while the FA_0.1Cs_0.9PbI₃ NCs had a 3D orthorhombic structure that was isostructural to the structure of CsPbBr₃ NCs. Bright photoluminescence (PL) with high quantum yield (QY > 70%) spanning red (690 nm, FA_0.1Cs_0.9PbI₃ NCs) and near-infrared (near-IR, ca. 780 nm, FAPbI₃ NCs) regions was sustained for several months or more in both the colloidal state and in films. The peak PL wavelengths can be fine-tuned by using postsynthetic cation- and anion-exchange reactions. Amplified spontaneous emissions with low thresholds of 28 and 7.5 μJ cm^-2 were obtained from the films deposited from FA_0.1Cs_0.9PbI₃ and FAPbI₃ NCs, respectively. Furthermore, light-emitting diodes with a high external quantum efficiency of 2.3% were obtained by using FAPbI₃ NCs.

Dismantling the "Red Wall" of Colloidal Perovskites: Highly Luminescent Formamidinium and Formamidinium-Cesium Lead Iodide Nanocrystals

Colloidal nanocrystals (NCs) of APbX₃-type lead halide perovskites [A = Cs⁺, CH₃NH₃⁺ (methylammonium or MA⁺) or CH(NH₂)₂⁺ (formamidinium or FA⁺); X = Cl^-, Br^-, I^-] have recently emerged as highly versatile photonic sources for applications ranging from simple photoluminescence down-conversion (e.g., for display backlighting) to light-emitting diodes. From the perspective of spectral coverage, a formidable challenge facing the use of these materials is how to obtain stable emissions in the red and infrared spectral regions covered by the iodide-based compositions. So far, red-emissive CsPbI₃ NCs have been shown to suffer from a delayed phase transformation into a nonluminescent, wide-band-gap 1D polymorph, and MAPbI₃ exhibits very limited chemical durability. In this work, we report a facile colloidal synthesis method for obtaining FAPbI₃ and FA-doped CsPbI₃ NCs that are uniform in size (10-15 nm) and nearly cubic in shape and exhibit drastically higher robustness than their MA- or Cs-only cousins with similar sizes and morphologies. Detailed structural analysis indicated that the FAPbI₃ NCs had a cubic crystal structure, while the FA_0.1Cs_0.9PbI₃ NCs had a 3D orthorhombic structure that was isostructural to the structure of CsPbBr₃ NCs. Bright photoluminescence (PL) with high quantum yield (QY > 70%) spanning red (690 nm, FA_0.1Cs_0.9PbI₃ NCs) and near-infrared (near-IR, ca. 780 nm, FAPbI₃ NCs) regions was sustained for several months or more in both the colloidal state and in films. The peak PL wavelengths can be fine-tuned by using postsynthetic cation- and anion-exchange reactions. Amplified spontaneous emissions with low thresholds of 28 and 7.5 μJ cm^-2 were obtained from the films deposited from FA_0.1Cs_0.9PbI₃ and FAPbI₃ NCs, respectively. Furthermore, light-emitting diodes with a high external quantum efficiency of 2.3% were obtained by using FAPbI₃ NCs.

Complexation of oxethazaine with 2-hydroxypropyl-β-cyclodextrin: increased drug solubility, decreased cytotoxicity and analgesia at inflamed tissues

Objectives

Oxethazaine (OXZ) is one of the few local anaesthetics that provides analgesia at low pH, but presents poor solubility, cytotoxicity and no parenteral formulations. To address these issues, we aimed to prepare OXZ host-guest inclusion complex with hydroxypropyl-beta-cyclodextrin (HP-β-CD).

Methods

The inclusion complex was formed by co-solubilization, followed by a job plot analysis to determine stoichiometry of complexation and dialysis equilibrium analysis (based on UV/VIS absorption and fluorescence profiles of OXZ). Complex formation was confirmed by phase-solubility data, X-ray, Scanning Electron Microscopy and DOSY-1H-NMR experiments. In vitro cytotoxicity was analysed by MTT test in 3T3 fibroblasts. In vivo analgesia was tested by Von Frey test (inflammatory wounds – rats).

Key findings

Oxethazaine complexed (1 : 1 molar ratio) with HP-β-CD, as indicated by loss of OZX crystalline structure (X-ray) and strong host: guest interaction (NMR, K = 198/m), besides increased solubility. In vitro cell survival improved with the complex (IC50 OXZ = 28.9 μm, OXZ : HP-β-CD = 57.8 μm). In addition, the complex (0.1% OXZ) promoted in vivo analgesia for the same time that 2% lidocaine/epinephrine did.

Conclusion

Our results show that complexation improved physicochemical and biological properties of OXZ, allowing its application to inflamed tissues by parenteral routes.

Systematic study of the crystallization process of CrAPO-5 using in situ high resolution X-ray diffraction

Systematic study of the hydrothermal crystallization process of CrAPO-5 by in situ high resolution X-ray powder diffraction (HRXRD).

XDS: a flexible beamline for X-ray diffraction and spectroscopy at the Brazilian synchrotron

The majority of the beamlines at the Brazilian Synchrotron Light Source Laboratory (LNLS) use radiation produced in the storage-ring bending magnets and are therefore currently limited in the flux that can be used in the harder part of the X-ray spectrum (above ∼10 keV). A 4 T superconducting multipolar wiggler (SCW) was recently installed at LNLS in order to improve the photon flux above 10 keV and fulfill the demands set by the materials science community. A new multi-purpose beamline was then installed at the LNLS using the SCW as a photon source. The XDS is a flexible beamline operating in the energy range between 5 and 30 keV, designed to perform experiments using absorption, diffraction and scattering techniques. Most of the work performed at the XDS beamline concentrates on X-ray absorption spectroscopy at energies above 18 keV and high-resolution diffraction experiments. More recently, new setups and photon-hungry experiments such as total X-ray scattering, X-ray diffraction under high pressures, resonant X-ray emission spectroscopy, among others, have started to become routine at XDS. Here, the XDS beamline characteristics, performance and a few new experimental possibilities are described.

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.

A total scattering Debye function analysis study of faulted Pt nanocrystals embedded in a porous matrix

Faulted face-centred cubic platinum nanocrystals, grown within a nanoporous silica matrix, have been extensively characterized by the Debye function analysis method applied to wide-angle synchrotron X-ray total scattering data. A method for building databases of sampled interatomic distances of weakly faulted materials is proposed, maintaining statistical significance and allowing complete populations of differently sized and shaped nanocrystals to be used within theDEBUSSYapproach. This study suggests that anisotropic Pt nanoclusters are formed in the presence of a shape-directing (templating) agent, and tentatively describes the effects of post-synthetic temperature treatments on fault probability, size, shape and dispersion of the nanocrystal populations. Surface relaxation effects are also observed in the smallest particles.

White luminescence achieved by a multiple thermochromic emission in a hybrid organic-inorganic compound based on 3-picolylamine and copper(i) iodide

Three copper(i) complexes have been obtained by the reaction of CuI with 3-picolylamine in acetonitrile solution and characterized by X-ray powder diffraction, both from synchrotron and laboratory radiation. Photophysical investigations in the solid state revealed highly efficient thermally-activated delayed fluorescence (TADF) with photoluminescence quantum yields (PLQYs) up to 18%. Notably, the complex [Cu₂I₂(3pica)]_∞ displays a strong luminescence thermochromism due to the presence of both ^1,3(X + M)LCT excited states and a lower-lying cluster-centered (³CC) one, leading to multiple emission at room temperature; as a result, a white luminescence is achieved with a PLQY of 4.5%.

Accurate unrestrained DDM refinement of crystal structures from highly distorted and low-resolution powder diffraction data

The structure of benzene:ethane co-crystal at 90 K is refined with anisotropic displacement parameters without geometric restraints from high-resolution synchrotron X-ray powder diffraction (XRPD) data using the derivative difference method (DDM) with properly chosen weighting schemes. The average C-C bond precision achieved is 0.005 Å and the H-atom positions in ethane are refined independently. A new DDM weighting scheme is introduced that compensates for big distortions of experimental data. The results are compared with density functional theory (DFT) calculations reported by Maynard-Casely et al. [(2016). IUCrJ, 3, 192-199] where a rigid-body Rietveld refinement was also applied to the same dataset due to severe distortions of the powder pattern attributable to experimental peculiarities. For the crystal structure of 2-aminopyridinium fumarate-fumaric acid formerly refined applying 77 geometric restraints by Dong et al. [(2013). Acta Cryst. C69, 896-900], an unrestrained DDM refinement using the same XRPD pattern surprisingly gave two times narrower dispersion of interatomic distances.

Facile usage of a MYTHEN 1K with a Huber 5021 diffractometer and angular calibration inoperandoexperiments

A facile usage of a MYTHEN 1K detector with a Huber 5021 six-circle diffractometer is described in detail. A mechanical support has been custom designed for the first time to combine the MYTHEN 1K detector with a point detector, which can be used as a reference point for each individual pixel of the MYTHEN 1K during measurements. The MYTHEN 1K is mounted on the arm of the 2θ circle of the Huber diffractometer with an intrinsic angular resolution of ∼0.0038°, and its pitch angle can be automatically adjusted with an accuracy of 0.0072°. Standard procedures are discussed for its calibration. Programs have been written in theSPECenvironment for simultaneous data conversion, integration and acquisition. The X-ray powder diffraction patterns of standard samples were measured in the Debye–Scherrer geometry and matched well with those of references. The angular shift due to sample-to-center displacement in the `flat-plate transmission' geometry, which is frequently employed inoperandoexperiments, has been successfully investigated and can be efficiently corrected. Oneoperandoexperiment using the MYTHEN 1K is presented. This work provides a straightforward procedure to use the MYTHEN 1K detector properly in Debye–Scherrer geometry, and could facilitate its application at other synchrotron facilities.

Locating Organic Guests in Inorganic Host Materials from X-ray Powder Diffraction Data

Can the location of the organic structure-directing agent (SDA) inside the channel system of a zeolite be determined experimentally in a systematic manner? In an attempt to answer this question, we investigated six borosilicate zeolites of known framework structure (SSZ-53, SSZ-55, SSZ-56, SSZ-58, SSZ-59, and SSZ-60), where the location of the SDA had only been simulated using molecular modeling techniques in previous studies. From synchrotron powder diffraction data, we were able to retrieve reliable experimental positions for the SDA by using a combination of simulated annealing (global optimization) and Rietveld refinement. In this way, problems arising from data quality and only partially compatible framework and SDA symmetries, which can lead to indecipherable electron density maps, can be overcome. Rietveld refinement using geometric restraints were then performed to optimize the positions and conformations of the SDAs. With these improved models, it was possible to go on to determine the location of the B atoms in the framework structure. That is, two pieces of information that are key to the understanding of zeolite synthesis-the location of the organic SDA in the channel system and of the positions adopted by heteroatoms in the silicate framework-can be extracted from experimental data using a systematic strategy. In most cases, the locations of the SDAs determined experimentally compare well with those simulated with molecular modeling, but there are also some clear differences, and the reason for these differences can be understood. The approach is generally applicable, and has also been used to locate organic guests, linkers, and ligands in metal-organic compounds.

A sample cell for in situ electric-field-dependent structural characterization and macroscopic strain measurements

When studying electro-mechanical materials, observing the structural changes during the actuation process is necessary for gaining a complete picture of the structure-property relationship as certain mechanisms may be meta-stable during actuation. In situ diffraction methods offer a powerful and direct means of quantifying the structural contributions to the macroscopic strain of these materials. Here, a sample cell is demonstrated capable of measuring the structural variations of electro-mechanical materials under applied electric potentials up to 10 kV. The cell is designed for use with X-ray scattering techniques in reflection geometry, while simultaneously collecting macroscopic strain data using a linear displacement sensor. The results show that the macroscopic strain measured using the cell can be directly correlated with the microscopic response of the material obtained from diffraction data. The capabilities of the cell have been successfully demonstrated at the Powder Diffraction beamline of the Australian Synchrotron and the potential implementation of this cell with laboratory X-ray diffraction instrumentation is also discussed.

A co-crystal between benzene and ethane: a potential evaporite material for Saturn's moon Titan

Using synchrotron X-ray powder diffraction, the structure of a co-crystal between benzene and ethane formed in situ at cryogenic conditions has been determined, and validated using dispersion-corrected density functional theory calculations. The structure comprises a lattice of benzene molecules hosting ethane molecules within channels. Similarity between the intermolecular interactions found in the co-crystal and in pure benzene indicate that the C-H⋯π network of benzene is maintained in the co-crystal, however, this expands to accommodate the guest ethane molecules. The co-crystal has a 3:1 benzene:ethane stoichiometry and is described in the space group [Formula: see text] with a = 15.977 (1) Å and c = 5.581 (1) Å at 90 K, with a density of 1.067 g cm(-3). The conditions under which this co-crystal forms identify it is a potential that forms from evaporation of Saturn's moon Titan's lakes, an evaporite material.

Ru/Al Multilayers Integrate Maximum Energy Density and Ductility for Reactive Materials

Established and already commercialized energetic materials, such as those based on Ni/Al for joining, lack the adequate combination of high energy density and ductile reaction products. To join components, this combination is required for mechanically reliable bonds. In addition to the improvement of existing technologies, expansion into new fields of application can also be anticipated which triggers the search for improved materials. Here, we present a comprehensive characterization of the key parameters that enables us to classify the Ru/Al system as new reactive material among other energetic systems. We finally found that Ru/Al exhibits the unusual integration of high energy density and ductility. For example, we measured reaction front velocities up to 10.9 (±0.33) ms⁻¹ and peak reaction temperatures of about 2000 °C indicating the elevated energy density. To our knowledge, such high temperatures have never been reported in experiments for metallic multilayers. In situ experiments show the synthesis of a single-phase B2-RuAl microstructure ensuring improved ductility. Molecular dynamics simulations corroborate the transformation behavior to RuAl. This study fundamentally characterizes a Ru/Al system and demonstrates its enhanced properties fulfilling the identification requirements of a novel nanoscaled energetic material.

Note: An X-ray powder diffractometer with a wide scattering-angle range of 72° using asymmetrically positioned one-dimensional detectors

An X-ray powder diffractometer has been developed for a time-resolved measurement without the requirement of a scattering angle (2θ) scan. Six one-dimensional detector modules are asymmetrically arranged in a vertical line at a designed distance of 286.5 mm. A detector module actually covers a diffraction angle of about 12° with an angular resolution of 0.01°. A diffracted intensity pattern is simultaneously recorded in a 2θ angular range from 1.63° to 74.37° in a "one shot" measurement. We tested the performance of the diffractometer with reference CeO2 powders and demonstrated diffraction measurements from an operating lithium-air battery.

Understanding Inhomogeneous Reactions in Li-Ion Batteries: Operando Synchrotron X-Ray Diffraction on Two-Layer Electrodes

To understand inhomogeneous reactions perpendicular to the current collector in an electrode for batteries, a method combining operando synchrotron X-ray diffraction and two-layer electrodes with different porosities is developed. The two layers are built using two different active materials (LiNi_0.80Co_0.15Al_0.05O₂ and LiMn₂O₄), therefore, tracing each diffraction pattern reveals which active material is reacting during the electrochemical measurement in transmission mode. The results demonstrate that the active material close to the separator is obviously more active than that one close to the current collector in the case of low porosity electrodes. This inhomogeneity should be due to the rate-limitation and especially to low average ionic conductivity of the electrolyte in the porous electrode because the current flows first mainly into the electrode regions close to the separator. The inhomogeneity is found to be mitigated by the adjustment of the electrode density and thus porosity. Hence, the novel operando method reveals a clear inhomogeneous reaction perpendicular to the current collector.

Structural evolution of Ag–Cu nano-alloys confined between AlN nano-layers upon fast heating

The paper presents a first comprehensive experimental investigation of the structural evolution of eutectic Ag–Cu nano-alloys, as confined between inert AlN barriers in a nano-multilayered configuration, upon fast heating.

Pressure-induced oversaturation and phase transition in zeolitic imidazolate frameworks with remarkable mechanical stability

ZIF-7/9 are shown be able to withstand high hydrostatic pressure unaffected by metal substitution, whilst retaining porosity and structural integrity.

Diffuse scattering and partial disorder in complex structures

The study of single-crystal diffuse scattering (SCDS) goes back almost to the beginnings of X-ray crystallography. Because SCDS arises from two-body correlations, it contains information about local (short-range) ordering in the sample, information which is often crucial in the attempt to relate structure to function. This review discusses the state of the field, including detectors and data collection and the modelling of SCDS using Monte Carlo and ab initio techniques. High-quality, three-dimensional volumes of SCDS data can now be collected at synchrotron light sources, allowing ever more detailed and quantitative analyses to be undertaken, and opening the way to approaches such as three-dimensional pair distribution function studies (3D-PDF) and automated refinement of a disorder model, powerful techniques that require large volumes of low-noise data.

Lattice parameters and site occupancy factors of magnetite–maghemite core–shell nanoparticles. A critical study

The size-driven expansion and oxidation-driven contraction phenomena of nonstoichiometric magnetite–maghemite core–shell nanoparticles have been investigated by the total scattering Debye function approach. Results from a large set of samples are discussed in terms of significant effects on the sample average lattice parameter and on the possibility of deriving the sample average oxidation level from accurate, diffraction-based, cell values. Controlling subtle experimental effects affecting the measurement of diffraction angles and correcting for extra-sample scattering contributions to the pattern intensity are crucial issues for accurately estimating lattice parameters and cation vacancies. The average nanoparticle stoichiometry appears to be controlled mainly by iron depletion of octahedral sites. A simple law with a single adjustable parameter, well correlating lattice parameter, stoichiometry and size effects of all the nanoparticles present in the whole set of samples used in this study, is proposed.

Solving the structures of light-atom compounds with powder charge flipping

While the powder charge flipping (pCF) algorithm has been applied successfully to a variety of inorganic compounds, reports on its application to organic structures, in particular those consisting of light atoms only, are rare. To investigate the reason for this apparent incongruity, a series of light-atom structures were tested using the pCF algorithm implemented in the programSuperflip. The data sets, which covered varying degrees of reflection overlap, had resolutions of approximately 1 Å, and the structures ranged from 40 to 136 atoms per unit cell. Both centrosymmetric and noncentrosymmetric structures were investigated. A modified pCF approach, which was developed in a separate study, was tested on several compounds whose structures could not be solved by applying the basic pCF algorithm inSuperflip. The results show that organic structures with no heavy atoms and low symmetry do indeed test the limits of the pCF algorithm inSuperflip. The study has allowed a few guidelines for approaching such problems to be formulated.

High energy resolution off-resonant spectroscopy for x-ray absorption spectra free of self-absorption effects

X-ray emission spectra recorded in the off-resonant regime carry information on the density of unoccupied states. It is known that by employing the Kramers-Heisenberg formalism, the high energy resolution off-resonant spectroscopy (HEROS) is equivalent to the x-ray absorption spectroscopy (XAS) technique and provides the same electronic state information. Moreover, in the present Letter we demonstrate that the shape of HEROS spectra is not modified by self-absorption effects. Therefore, in contrast to the fluorescence-based XAS techniques, the recorded shape of the spectra is independent of the sample concentration or thickness. The HEROS may thus be used as an experimental technique when precise information about specific absorption features and their strengths is crucial for chemical speciation or theoretical evaluation.

An “Off-axis” Mn–Mn bond in Mn2(CO)10 at high pressure

Pressure induces an “off-axis” Mn–Mn bond in crystals of Mn₂(CO)₁₀, but no eclipsing of the equatorial carbonyls was observed.

Deep sub micrometer imaging of defects in copper pillars by X-ray tomography in a SEM

The potential of X-ray nanotomography hosted in a SEM in presented in this paper. In order to improve the detail detectability of this system, which is directly related to the X-ray source size, thin metal layers have been studied and installed in the equipment. A 3D resolution pattern has been created in order to determine the smallest detectable features by this setup. This sample is a 25 μm diameter copper pillar in which size-controlled holes have been milled using a plasma-focused ion beam. This pattern has then been scanned and the resulting 3D reconstruction demonstrates that the instrument is able to detect 500 nm diameter voids in a copper interconnection, as used in 3D integration.

The Materials Science beamline upgrade at the Swiss Light Source

The Materials Science beamline at the Swiss Light Source has been operational since 2001. In late 2010, the original wiggler source was replaced with a novel insertion device, which allows unprecedented access to high photon energies from an undulator installed in a medium-energy storage ring. In order to best exploit the increased brilliance of this new source, the entire front-end and optics had to be redesigned. In this work, the upgrade of the beamline is described in detail. The tone is didactic, from which it is hoped the reader can adapt the concepts and ideas to his or her needs.

A scanning CCD detector for powder diffraction measurements

Several different approaches have traditionally been used for detection of X-ray powder diffraction patterns, including area detectors, point detectors and position-sensitive detectors. Each has advantages. This paper discusses use of a low-cost CCD detector attached to a diffractometer arm, where line-by-line readout of the CCD is coupled to continuous motion of the arm. When this type of detector is used and where X-ray optics are employed to focus the source image onto the detector plane both high-resolution and rapid measurements can be performed, with data collection over a complete 2θ range. This is particularly advantageous for synchrotron applications but valuable also for Guinier diffractometer laboratory instruments. Peak resolutions are shown to be moderately better than what can be obtained with a position-sensitive detector and significantly better than with an area detector. Many samples have intrinsically broadened peak shapes for which little improvement in data quality could be obtained with an analyzer-crystal detector. With comparable numbers of modules, these CCD data collection speeds can be close to those with position-sensitive detectors, but without the low-angle asymmetry seen in the latter.

Advances in exploiting preferred orientation in the structure analysis of polycrystalline materials

In an attempt to overcome the reflection overlap problem, which is the primary hindrance to structure determination from powder diffraction data, an experimental approach that exploits preferred orientation was developed some years ago. Now both the experimental setup and the data analysis procedure have been optimized, with the result that the quality of the extracted reflection intensities has been improved significantly and the synchrotron beamtime required for the data collection reduced. The one-dimensional Si microstrip detector Mythen II on the Materials Science beamline at the Swiss Light Source and new features in the data analysis softwareMAUD[Lutterotti, Matthies & Wenk (1999).IUCr Commission on Powder Diffraction Newsletter, No. 21, pp. 14–15] have made these improvements possible. The main changes in the experimental setup are (1) using an optimized set of sample orientations, (2) placing the detector such that both positive and negative 2θ angles are measured simultaneously, and (3) introducing an additional sample tilt angle, to measure data that cannot be accessed otherwise. On the data analysis side, the programMAUDis now used for both the determination of the orientation of the crystallites and the intensity extraction. The evaluation of data obtained from a textured zirconium phosphate pyridinium sample shows a significant improvement in the reliability of the structure factor amplitudes derived from overlapping reflections.

Study of threading dislocation density reduction in AlGaN epilayers by Monte Carlo simulation of high-resolution reciprocal-space maps of a two-layer system

High-resolution X-ray diffraction in coplanar and noncoplanar geometries has been used to investigate the influence of an SiNxnano-mask in the reduction of the threading dislocation (TD) density of high-quality AlGaN epitaxial layers grown on sapphire substrates. Our developed model, based on a Monte Carlo method, was applied to the simulation of the reciprocal-space maps of a two-layer system. Good agreement was found between the simulation and the experimental data, leading to an accurate determination of the dislocation densities as a function of the overgrowth layer thickness. The efficiency of the SiNxnano-mask was defined as the ratio of the TD densities in the AlGaN layers below and above the mask. A significant improvement in the AlGaN layer quality was achieved by increasing the overgrowth layer thickness, and a TD density reduction scaling law was established.

Capturing dynamics with Eiger, a fast-framing X-ray detector

Eiger is the next-generation single-photon-counting pixel detector following the widely used Pilatus detector. Its smaller pixel size of 75 µm × 75 µm, higher frame rate of up to 22 kHz, and practically zero dead-time (~4 µs) between exposures will further various measurement methods at synchrotron sources. In this article Eiger's suitability for X-ray photon correlation spectroscopy (XPCS) is demonstrated. By exploiting its high frame rate, complementary small-angle X-ray scattering (SAXS) and XPCS data are collected in parallel to determine both the structure factor and collective diffusion coefficient of a nano-colloid suspension. For the first time, correlation times on the submillisecond time scale are accessible with a large-area pixel detector.