A miniature X‐ray emission spectrometer (miniXES) for high‐pressure studies in a diamond anvil cell

Core–shell X‐ray emission spectroscopy (XES) is a valuable complement to X‐ray absorption spectroscopy (XAS) techniques. However, XES in the hard X‐ray regime is much less frequently employed than XAS, often as a consequence of the relative scarcity of XES instrumentation having energy resolutions comparable with the relevant core‐hole lifetimes. To address this, a family of inexpensive and easily operated short‐working‐distance X‐ray emission spectrometers has been developed. The use of computer‐aided design and rapid prototype machining of plastics allows customization for various emission lines having energies from ～3 keV to ～10 keV. The specific instrument described here, based on a coarsely diced approximant of the Johansson optic, is intended to study volume collapse in Pr metal and compounds by observing the pressure dependence of the Pr Lα emission spectrum. The collection solid angle is ～50 msr, roughly equivalent to that of six traditional spherically bent crystal analyzers. The miniature X‐ray emission spectrometer (miniXES) methodology will help encourage the adoption and broad application of high‐resolution XES capabilities at hard X‐ray synchrotron facilities.     

The multi‐purpose hard X‐ray beamline BL10 at the DELTA storage ring

The layout and the characteristics of the hard X‐ray beamline BL10 at the superconducting asymmetric wiggler at the 1.5 GeV Dortmund Electron Accelerator DELTA are described. This beamline is equipped with a Si(111) channel‐cut monochromator and is dedicated to X‐ray studies in the spectral range from ～4 keV to ～16 keV photon energy. There are two different endstations available. While X‐ray absorption studies in different detection modes (transmission, fluorescence, reflectivity) can be performed on a designated table, a six‐axis kappa diffractometer is installed for X‐ray scattering and reflectivity experiments. Different detector set‐ups are integrated into the beamline control software, i.e. gas‐filled ionization chambers, different photodiodes, as well as a Pilatus 2D‐detector are permanently available. The performance of the beamline is illustrated by high‐quality X‐ray absorption spectra from several reference compounds. First applications include temperature‐dependent EXAFS experiments from liquid‐nitrogen temperature in a bath cryostat up to ～660 K by using a dedicated furnace. Besides transmission measurements, fluorescence detection for dilute sample systems as well as surface‐sensitive reflection‐mode experiments are presented.     

Chemical speciation via X‐ray emission spectra

Since the early days of X‐ray spectrometry, X‐ray emission and fluorescence spectra have been used to investigate chemical speciation, e.g. the dependence on the formal oxidation state. Laboratory wavelength‐dispersive spectrometers have adequate resolution for these measurements. However, almost all studies have employed empirical methods to interpret the spectra. We aim to place such methods on a quantitative basis by means of efficient ab initio calculations of the X‐ray emission line shapes based on a self‐consistent, real‐space Green's function approach, as implemented in the X‐ray spectroscopy code FEFF8.2. Calculations are presented for the phosphorus K‐M_{2, 3}, and the chromium L‐series emission lines for a selection of simple compounds. These lines exhibit changes depending on the oxidation state and on the neighboring atoms in the compounds that can be observed with instruments available in many XRF laboratories. The calculated spectra, as modified by convolution with a model monochromator response function, are compared with measured spectra. Simulated and measured spectra are found to be in reasonable agreement, and show that the approach has the potential to yield quantitative information about the chemical state. Copyright © 2006 John Wiley & Sons, Ltd.     

Early commissioning results for spectroscopic X‐ray Nano‐Imaging Beamline BL 7C sXNI at PLS‐II

For spectral imaging of chemical distributions using X‐ray absorption near‐edge structure (XANES) spectra, a modified double‐crystal monochromator, a focusing plane mirrors system and a newly developed fluorescence‐type X‐ray beam‐position monitoring and feedback system have been implemented. This major hardware upgrade provides a sufficiently stable X‐ray source during energy scanning of more than hundreds of eV for acquisition of reliable XANES spectra in two‐dimensional and three‐dimensional images. In recent pilot studies discussed in this paper, heavy‐metal uptake by plant roots in vivo and iron's phase distribution in the lithium–iron–phosphate cathode of a lithium‐ion battery have been imaged. Also, the spatial resolution of computed tomography has been improved from 70 nm to 55 nm by means of run‐out correction and application of a reconstruction algorithm.     

Si PIN X‐ray photon counter

A Si PIN detector for visible light detection, instead of a Geiger‐Müller tube, is applied to X‐ray photon counting. We counted radiation from a checking source of a Geiger‐Müller counter with a Si PIN counter and with a Geiger‐Müller counter. White X‐ray of energy up to 20 keV emitted from a pyroelectric X‐ray emitter was also counted, and the Si PIN X‐ray counter showed a similar curve of count rate versus source distance in both measurements. Pulse counting was performed by spectroscopy circuits. An audio digitizer with computer software for signal processing was also used to simplify the photon counter. A plot of count rate versus time was obtained with this setup. With simple pulse counting circuits, Si PIN X‐ray counters have advantages such as compact structure, low cost and easy application. Copyright © 2011 John Wiley & Sons, Ltd.     

Elemental mapping of frozen‐hydrated cells with cryo‐scanning X‐ray fluorescence microscopy

Visualizing the elemental distributions of cells and tissues is of growing importance in biology and medical science because such data deepen our understanding of the behavior of metal‐binding proteins and ions. Elemental mapping by X‐ray fluorescence analysis with a hard X‐ray nanobeam is very well suited for this purpose owing to its high sensitivity and high resolution. Using this technique, samples must be prepared without artifacts that are caused by treatments such as chemical fixation and staining procedures. In many studies of elemental mapping, sample preparation is not explicitly considered. To overcome this deficiency, we developed a cryo‐scanning X‐ray fluorescence microscope and installed it in the second experimental hutch of BL29XUL of SPring‐8. We used it to observe frozen‐hydrated cells that had been fixed by a quick‐freezing technique to preserve elemental data of the living state at an X‐ray energy of 11.5 keV. The distributions of K, Ca, Fe, Cu and Zn were successfully visualized. The distributions of these elements (especially those of K, Ca and Fe) differed from those in cells fixed with paraformaldehyde. Copyright © 2010 John Wiley & Sons, Ltd.     

The stopped‐drop method: a novel setup for containment‐free and time‐resolved measurements

A novel setup for containment‐free time‐resolved experiments at a free‐hanging drop is reported. Within a dead‐time of 100 ms a drop of mixed reactant solutions is formed and the time evolution of a reaction can be followed from thereon by various techniques. As an example, a small‐angle X‐ray scattering study on the formation mechanism of EDTA‐stabilized CdS both at a synchrotron and a laboratory X‐ray source is presented here. While the evolution can be followed with one drop only at a synchrotron source, a stroboscopic mode with many drops is preferable for the laboratory source.     

First experiments on the Australian Synchrotron Imaging and Medical beamline,including investigations of the effective source size in respect of X‐ray imaging

The Imaging and Medical beamline at the Australian Synchrotron achieved `first light' in December 2008. Here, the first experiments performed on the beamline are reported, which involved both X‐ray imaging and tomography studies for a range of samples. The use of a plastic‐edge phantom for quantitative measurements of contrast and resolution proved to be very instructive and helped to confirm certain parameter values such as the effective horizontal source size, detector resolution and average X‐ray energy for the polychromatic beam.     

Direct nano‐scale patterning of Ag films using hard X‐ray induced oxidation

The morphological change of silver nano‐particles (AgNPs) exposed to an intense synchrotron X‐ray beam was investigated for the purpose of direct nano‐scale patterning of metal thin films. AgNPs irradiated by hard X‐rays in oxygen ambient were oxidized and migrated out of the illuminated region. The observed X‐ray induced oxidation was utilized to fabricate nano‐scale metal line patterns using sectioned WSi₂/Si multilayers as masks. Lines with a width as small as 21 nm were successfully fabricated on Ag films on silicon nitride. Au/Ag nano‐lines were also fabricated using the proposed method.     

Study of radiation damage induced by 12 keV X‐rays in MOS structures built on high‐resistivity n‐type silicon

Imaging experiments at the European X‐ray Free Electron Laser (XFEL) require silicon pixel sensors with extraordinary performance specifications: doses of up to 1 GGy of 12 keV photons, up to 10⁵ 12 keV photons per 200 µm × 200 µm pixel arriving within less than 100 fs, and a time interval between XFEL pulses of 220 ns. To address these challenges, in particular the question of radiation damage, the properties of the SiO₂ layer and of the Si–SiO₂ interface, using MOS (metal‐oxide‐semiconductor) capacitors manufactured on high‐resistivity n‐type silicon irradiated to X‐ray doses between 10 kGy and 1 GGy, have been studied. Measurements of capacitance/conductance–voltage (C/G–V) at different frequencies, as well as of thermal dielectric relaxation current (TDRC), have been performed. The data can be described by a dose‐dependent oxide charge density and three dominant radiation‐induced interface states with Gaussian‐like energy distributions in the silicon band gap. It is found that the densities of the fixed oxide charges and of the three interface states increase up to dose values of approximately 10 MGy and then saturate or even decrease. The shapes and the frequency dependences of the C/G–V measurements can be quantitatively described by a simple model using the parameters extracted from the TDRC measurements.     

A microfocus X‐ray fluorescence beamline at Indus‐2 synchrotron radiation facility

A microfocus X‐ray fluorescence spectroscopy beamline (BL‐16) at the Indian synchrotron radiation facility Indus‐2 has been constructed with an experimental emphasis on environmental, archaeological, biomedical and material science applications involving heavy metal speciation and their localization. The beamline offers a combination of different analytical probes, e.g. X‐ray fluorescence mapping, X‐ray microspectroscopy and total‐external‐reflection fluorescence characterization. The beamline is installed on a bending‐magnet source with a working X‐ray energy range of 4–20 keV, enabling it to excite K‐edges of all elements from S to Nb and L‐edges from Ag to U. The optics of the beamline comprises of a double‐crystal monochromator with Si(111) symmetric and asymmetric crystals and a pair of Kirkpatrick–Baez focusing mirrors. This paper describes the performance of the beamline and its capabilities with examples of measured results.     

Accurate standard‐based quantification of X‐ray fluorescence data using metal‐contaminated plant tissue

Quantitative X‐ray fluorescence (XRF) measurements have been conducted on naturally lead‐contaminated samples. The calibration procedure using the ratio of fluorescence to Compton scattered radiation was investigated using Monte Carlo simulation. Experimental results with low‐energy photons (14 keV) and simulations show a very good linearity of the fluorescence to Compton ratio as a function of metal concentration. Lead (Pb), iron (Fe) and zinc (Zn) are measured in samples of Phaseolus vulgaris (bean seeds) that have been grown using a nutritive solution with different Pb dopings. Naturally contaminated samples are thus obtained. The calibration must be done for fixed conditions of X‐ray energy and scattering angle, while X‐ray beam intensity and detector to sample distance can change from one sample to another. Simulation allows to evaluate the matrix effect on the calibration curve, and shows that linearity is preserved even in the presence of other heavy elements in the fluorescence spectrum. However, calibration must be done using samples with similar matrix as it affects the slope of the curve. Copyright © 2010 John Wiley & Sons, Ltd.     

Combining CdTe and Si detectors for Energy‐Dispersive X‐Ray Fluorescence

Most energy‐dispersive X‐ray fluorescence (EDXRF) instruments use Si diodes as X‐ray detectors. These provide very high energy resolution, but their sensitivity falls off at energies of 10–20 keV. They are well suited for measuring the K lines of elements with Z < 40, but for heavier elements, one must use K lines at low efficiency or use L or M lines that often overlap other lines. Either is a challenge for accurate quantitative analysis. CdTe detectors offer much higher efficiency at high energy but poorer energy resolution compared with Si diodes. In many important EDXRF measurements, both high and low Z elements are present. In this paper, we will compare the precision and accuracy of systems using the following: (1) a high resolution Si detector, (2) a high efficiency CdTe detector, and (3) a composite system using both detectors. We will show that CdTe detectors generally offer better analytical results than even a high resolution silicon drift detectors for K lines greater than 20 or 25 keV, whereas the high resolution Si detectors are much better at lower energies. We will also show the advantages of a combined system, using both detectors. Although a combined system would be more expensive, the increased accuracy, precision, and throughput will often outweigh the small increase in cost and complexity. The systems will be compared for representative applications that include both high and low Z elements. Copyright © 2012 John Wiley & Sons, Ltd.     

HAXPES beamline PES‐BL14 at the Indus‐2 synchrotron radiation source

The Hard X‐ray Photo‐Electron Spectroscopy (HAXPES) beamline (PES‐BL14), installed at the 1.5 T bending‐magnet port at the Indian synchrotron (Indus‐2), is now available to users. The beamline can be used for X‐ray photo‐emission electron spectroscopy measurements on solid samples. The PES beamline has an excitation energy range from 3 keV to 15 keV for increased bulk sensitivity. An in‐house‐developed double‐crystal monochromator [Si (111)] and a platinum‐coated X‐ray mirror are used for the beam monochromatization and manipulation, respectively. This beamline is equipped with a high‐energy (up to 15 keV) high‐resolution (meV) hemispherical analyzer with a microchannel plate and CCD detector system with SpecsLab Prodigy and CasaXPS software. Additional user facilities include a thin‐film laboratory for sample preparation and a workstation for on‐site data processing. In this article, the design details of the beamline, other facilities and some recent scientific results are described.     

Performances of a metallic magnetic calorimeter for the measurement of hard X‐ray emission intensities

The energy spectrum analysis of X‐ray intensities with semiconductor detectors is often difficult because their energy resolution is usually not good enough to separate the different X‐ray lines. Metallic magnetic calorimeters (MMCs) can be an alternative; they can offer both high energy resolution and high intrinsic detection efficiency from 0 to 100 keV. MMCs are thermal detectors; that is to say, the energy of each absorbed photon is measured as a temperature elevation. At very low temperature, typically few tens of mK, a very large pulse height‐to‐noise ratio can be obtained that is an essential condition for high energy resolution. We are involved in the development of MMCs for metrology applications such as the determination of hard X‐ray emission intensities. For that purpose, we conceived an MMC with an energy resolution of 57 eV around 30 keV. The absorber is made of gold providing high intrinsic detection efficiency even for a small volume, greater than 90% below 60 keV. We will describe the physical principle and the practical realisation of this detector and discuss its performances by analysing the energy spectrum obtained from a ¹³³Ba source. Preliminary outcomes of relative emission intensities of the K X‐ray of cesium are presented and compared with other experimental data and theoretical calculations. Copyright © 2012 John Wiley & Sons, Ltd.     

Chemical effects on x‐ray fluorescence yield of Ag+ compounds

X‐ray fluorescence measurements were carried out for silver metal and a number of silver compounds containing Ag⁺ ions such as Ag₂CO₃, Ag₂SO₄, AgNO₃, AgCl, AgBr and AgI using 59.6 keV γ‐rays, emitted from ²⁴¹Am, as the excitation source, to evaluate the value of Kβ/Kα x‐ray intensity ratio. For silver metal the value of this parameter is found to be 0.206 ± 0.003 and wide variations, 0.190 ≤ Kβ/Kα≤ 0.207, were observed for these compounds. The results are explained in terms of the charge transfer occurring between Ag⁺ and the coordinating anions. Copyright © 2005 John Wiley & Sons, Ltd.     

The materials science X‐ray beamline BL8 at the DELTA storage ring

The hard X‐ray beamline BL8 at the superconducting asymmetric wiggler at the 1.5 GeV Dortmund Electron Accelerator DELTA is described. This beamline is dedicated to X‐ray studies in the spectral range from ～1 keV to ～25 keV photon energy. The monochromator as well as the other optical components of the beamline are optimized accordingly. The endstation comprises a six‐axis diffractometer that is capable of carrying heavy loads related to non‐ambient sample environments such as, for example, ultrahigh‐vacuum systems, high‐pressure cells or liquid‐helium cryostats. X‐ray absorption spectra from several reference compounds illustrate the performance. Besides transmission measurements, fluorescence detection for dilute sample systems as well as surface‐sensitive reflection‐mode experiments have been performed. The results show that high‐quality EXAFS data can be obtained in the quick‐scanning EXAFS mode within a few seconds of acquisition time, enabling time‐resolved in situ experiments using standard beamline equipment that is permanently available. The performance of the new beamline, especially in terms of the photon flux and energy resolution, is competitive with other insertion‐device beamlines worldwide, and several sophisticated experiments including surface‐sensitive EXAFS experiments are feasible.     

A high‐energy‐resolution resonant inelastic X‐ray scattering spectrometer at ID20 of the European Synchrotron Radiation Facility

An end‐station for resonant inelastic X‐ray scattering and (resonant) X‐ray emission spectroscopy at beamline ID20 of ESRF – The European Synchrotron is presented. The spectrometer hosts five crystal analysers in Rowland geometry for large solid angle collection and is mounted on a rotatable arm for scattering in both the horizontal and vertical planes. The spectrometer is optimized for high‐energy‐resolution applications, including partial fluorescence yield or high‐energy‐resolution fluorescence detected X‐ray absorption spectroscopy and the study of elementary electronic excitations in solids. In addition, it can be used for non‐resonant inelastic X‐ray scattering measurements of valence electron excitations.     

In situ electrochemical high‐energy X‐ray diffraction using a capillary working electrode cell geometry

The ability to generate new electrochemically active materials for energy generation and storage with improved properties will likely be derived from an understanding of atomic‐scale structure/function relationships during electrochemical events. Here, the design and implementation of a new capillary electrochemical cell designed specifically for in situ high‐energy X‐ray diffraction measurements is described. By increasing the amount of electrochemically active material in the X‐ray path while implementing low‐Z cell materials with anisotropic scattering profiles, an order of magnitude enhancement in diffracted X‐ray signal over traditional cell geometries for multiple electrochemically active materials is demonstrated. This signal improvement is crucial for high‐energy X‐ray diffraction measurements and subsequent Fourier transformation into atomic pair distribution functions for atomic‐scale structural analysis. As an example, clear structural changes in LiCoO₂ under reductive and oxidative conditions using the capillary cell are demonstrated, which agree with prior studies. Accurate modeling of the LiCoO₂ diffraction data using reverse Monte Carlo simulations further verifies accurate background subtraction and strong signal from the electrochemically active material, enabled by the capillary working electrode geometry.     

On‐line optical and X‐ray spectroscopies with crystallography: an integrated approach for determining metalloprotein structures in functionally well defined states

X‐ray‐induced redox changes can lead to incorrect assignments of the functional states of metals in metalloprotein crystals. The need for on‐line monitoring of the status of metal ions (and other chromophores) during protein crystallography experiments is of growing importance with the use of intense synchrotron X‐ray beams. Significant efforts are therefore being made worldwide to combine different spectroscopies in parallel with X‐ray crystallographic data collection. Here the implementation and utilization of optical and X‐ray absorption spectroscopies on the modern macromolecular crystallography (MX) beamline 10, at the SRS, Daresbury Laboratory, is described. This beamline is equipped with a dedicated monolithic energy‐dispersive X‐ray fluorescence detector, allowing X‐ray absorption spectroscopy (XAS) measurements to be made in situ on the same crystal used to record the diffraction data. In addition, an optical microspectrophotometer has been incorporated on the beamline, thus facilitating combined MX, XAS and optical spectroscopic measurements. By uniting these techniques it is also possible to monitor the status of optically active and optically silent metal centres present in a crystal at the same time. This unique capability has been applied to observe the results of crystallographic data collection on crystals of nitrite reductase from Alcaligenes xylosoxidans, which contains both type‐1 and type‐2 Cu centres. It is found that the type‐1 Cu centre photoreduces quickly, resulting in the loss of the 595 nm peak in the optical spectrum, while the type‐2 Cu centre remains in the oxidized state over a much longer time period, for which independent confirmation is provided by XAS data as this centre has an optical spectrum which is barely detectable using microspectrophotometry. This example clearly demonstrates the importance of using two on‐line methods, spectroscopy and XAS, for identifying well defined redox states of metalloproteins during crystallographic data collection.