High-resolution X-ray Emission Research Articles

Consideration of the Potential of High Energy Resolution X-ray Absorption and X-ray Emission Experiments to Track Changes in Oxidation States on Nanoparticle Materials

Consideration of the Potential of High Energy Resolution X-ray Absorption and X-ray Emission Experiments to Track Changes in Oxidation States on Nanoparticle Materials

Magnetic microcalorimeter with paramagnetic temperature sensors and integrated dc-SQUID readout for high-resolution x-ray emission spectroscopy

We present two variants of a magnetic microcalorimeter with paramagnetic temperature sensors and integrated dc-superconducting quantum interference device readout for high-resolution x-ray emission spectroscopy. Each variant employs two overhanging gold absorbers with a sensitive area of 150 × 150 μm2 and a thickness of 3 μm, thus providing a thickness related quantum efficiency of >98% for photons up to 5 keV and >50% for photons up to 10 keV. The first variant operated nominally but suffered from Joule power dissipation of the Josephson junction shunt resistors, athermal phonon loss, and slew rate limitations of the overall setup. Overall, it only achieved an energy resolution of ΔEFWHM=8.9 eV for 5.9 keV photons. In the second variant, we introduced an innovative tetrapod absorber geometry as well as a membrane technique for diverting dissipated heat away from the temperature sensors. When all mitigations are applied optimally, the second variant achieves an energy resolution of ΔEFWHM=1.25(18) eV for 5.9 keV photons and hence provides the present best energy resolving power E/ΔEFWHM among all existing energy-dispersive detectors for soft and tender x-rays.

Hydrogen-Bonded Structures of Water Molecules in Hydroxy-Functionalized Nanochannels of Columnar Liquid Crystalline Nanostructured Membranes Studied by Soft X-ray Emission Spectroscopy.

Here, we report a synchrotron-based high-resolution soft X-ray emission spectroscopy study on hydrogen-bonded structures of water molecules in the self-organized, hydroxy-group-functionalized one-dimensional nanochannels of liquid crystalline nanostructured membranes. The water molecules confined in the uncharged hydroxy-functionalized nanochannels (which have a diameter of about 1.5 nm) exhibit hydrogen-bonded structures close to those of bulk liquid water, even directly interacting with diol groups. These hydrogen-bonded structures contrast with the more distorted hydrogen bonding of water molecules confined in self-organized channels with a diameter of 0.6 nm formed by an analogous nanostructured membrane with a cationic moiety, which was explained by the ability of the channel functional groups to donate and accept hydrogen bonds in a confined space and the nanochannel diameter.

High-Resolution X-ray Absorption and Emission Spectroscopy for Detailed Analysis of New CO2 Methanation Catalysts.

A new approach for the characterization of CO2 methanation catalysts prepared by thermal decomposition of a nickel MOF by hard X-ray photon-in/photon-out spectroscopy in form of high energy resolution fluorescence detected X-ray absorption near edge structure spectroscopy (HERFD-XANES) and valence-to-core X-ray emission (VtC-XES) is presented. In contrast to conventional X-ray absorption spectroscopy, the increased resolution of both methods allows a more precise phase determination of the final catalyst, which is influenced by the conditions during MOF decomposition.

High-resolution X-ray emission study for Xe^{54+} on Xe collisions

We report on an experiment conducted at the ESR storage ring aiming at the study of the X-ray emission of text {Xe}^{54+} ions colliding with Xe atoms at a beam energy of 50 MeV/u. The radiation resulting from the ion–atom interaction was observed using a high-resolution spectrometer based on metallic–magnetic calorimeter technology. In order to benchmark the capabilities of these detectors for high-precision atomic physics experiments, we identified several transitions from H-like and He-like xenon and determined their energies. Furthermore, the 1s-Lamb shift in text {Xe}^{53+} was estimated using the measured line energies. The results are compared with previous experimental studies and theoretical predictions.Graphicalabstract

A von Hamos full-cylindrical spectrometer based on striped Si/Ge crystal for advanced x-ray spectroscopy.

High-energy resolution core-level spectroscopies, including a group of different techniques to obtain element-specific information of the electronic structure around an absorption site, have become powerful tools for studying the chemical state, local geometric structure, and the nature of chemical bonding. High-resolution x-ray absorption and x-ray emission spectroscopies are well-established experimental techniques but have always been limited by the number of emitted photons and the limited acceptance of solid angles, as well as requiring high energy stability and repeatability for the whole experimental setup. A full-cylindrical x-ray spectrometer based on flexible HAPG (highly annealed pyrolitic graphite) mosaic crystals is an effective solution for the above issues. However, large-area HAPG remains expensive and is often not easy to access. Here, we present an alternative approach by using segmented single crystals (Si and Ge) with different orientations instead of the HAPG as a dispersive element. The proposed method drastically improved the energy resolution up to 0.2-2eV in the range of 2-10keV. High-pressure x-ray emission and resonant x-ray emission spectra are presented to demonstrate the capabilities of the instrument. The new design is particularly suitable for high-resolution spectroscopy applications at fourth-generation synchrotron radiation sources or free-electron lasers.

A laboratory X-ray emission spectrometer for phosphorus Kα and Kβ study of air-sensitive samples

We report a compact laboratory-based, high resolution X-ray emission spectrometer installed in a glovebox for simultaneous measurement of phosphorus Kα and Kβ spectra of air-sensitive materials.

Laser energy absorption and x-ray generation in nanowire arrays irradiated by relativistically intense ultra-high contrast femtosecond laser pulses

We report here on the results of comparative experimental measurements of laser energy absorption in a bulk and different morphology nanowire arrays interacting with relativistically intense, ultra-high temporal contrast femtosecond laser pulses. We compare polished, flat bulk samples with vertically and randomly oriented nanowires made of ZnO semiconductor material. The optical absorption of the 45° incident laser pulses of ∼40 fs duration with a central wavelength of 400 nm at intensities above 1019Wcm2 was determined using an integrating Ulbricht sphere. We demonstrate an almost twofold enhancement of absorption in both nanowire morphologies with an average of (79.6±1.9)% in comparison to the flat bulk sample of (45.8±1.9)%. The observed substantially enhanced absorption in nanowire arrays is also confirmed by high-resolution x-ray emission spectroscopy. The spectral analysis of the K-shell x-ray emission lines revealed that the He-like resonance line emission from highly ionized Zn (Zn28+) is only present in the case of nanowire arrays, whereas, for the flat bulk samples, only neutral and low charge states were observed. Our numerical simulations, based on radiative-collisional kinetic code FLYCHK, well reproduce the measured He-like emission spectrum and suggest that high charge state observed in nanowire arrays is due to substantially higher plasma temperature. Our results, which were measured for the first time with femtosecond laser pulses, can be used to benchmark theoretical models and numerical codes for the relativistic interaction of ultrashort laser pulses with nanowires.

High resolution x-ray emission spectrometer for multiple hard x-ray emission lines: Demonstration for Cu Kα and Kβ emissions.

We present a compact 3D printed x-ray emission spectrometer based on the von Hamos geometry that represents a significant upgrade to the existing von Hamos geometry-based miniature x-ray emission spectrometer (miniXES) [Mattern et al., Rev. Sci. Instrum. 83(2), 023901 (2012)]. The upgrades include the incorporation of a higher pixel density 500K detector for improved energy resolution and an enlarged sample area to accommodate a wider range of sample formats. The versatile spectrometer houses removable crystal holders that can be easily exchanged, as well as movable alignment eyelets that give flexibility in Bragg angle selection. Designed for ease of manufacture, all the components, except for the apertures, can be 3D printed and readily assembled. We describe its implementation in measurements of resonant and non-resonant Cu Kα and Kβ x-ray emission and report the theoretical and measured energy resolution and collected solid angle of the emission.

Ion Selectivity of Water Molecules in Subnanoporous Liquid-Crystalline Water-Treatment Membranes: A Structural Study of Hydrogen Bonding.

We demonstrate hydrogen‐bonded structures of water in self‐organized subnanoporous water treatment membranes obtained using synchrotron‐based high‐resolution soft X‐ray emission spectroscopy. The ion selectivity of these water treatment membranes is usually understood by the size compatibility of nanochannels in the membrane with the Stokes radius of hydrated ions, or by electrostatic interaction between charges inside the nanochannels and such ions. However, based on a comparison between the hydrogen‐bonded structures of water molecules in the nanochannels of the water treatment membrane and those surrounding the ions, we propose a definite contribution of structural consistency among the associated hydrogen‐bonded water molecules to the ion selectivity. Our observation delivers a novel concept to the design of water treatment membranes where water molecules in the nanochannel can be regarded as a part of the material that controls the ion selectivity.

Probing Sulfur Chemical and Electronic Structure with Experimental Observation and Quantitative Theoretical Prediction of Kα and Valence-to-Core Kβ X-ray Emission Spectroscopy.

An extensive experimental and theoretical study of the Kα and Kβ high-resolution X-ray emission spectroscopy (XES) of sulfur-bearing systems is presented. This study encompasses a wide range of organic and inorganic compounds, including numerous experimental spectra from both prior published work and new measurements. Employing a linear-response time-dependent density functional theory (LR-TDDFT) approach, strong quantitative agreement is found in the calculation of energy shifts of the core-to-core Kα as well as the full range of spectral features in the valence-to-core Kβ spectrum. The ability to accurately calculate the sulfur Kα energy shift supports the use of sulfur Kα XES as a bulk-sensitive tool for assessing sulfur speciation. The fine structure of the sulfur Kβ spectrum, in conjunction with the theoretical results, is shown to be sensitive to the local electronic structure including effects of symmetry, ligand type and number, and, in the case of organosulfur compounds, to the nature of the bonded organic moiety. This agreement between theory and experiment, augmented by the potential for high-access XES measurements with the latest generation of laboratory-based spectrometers, demonstrates the possibility of broad analytical use of XES for sulfur and nearby third-row elements. The effective solution of the forward problem, i.e., successful prediction of detailed spectra from known molecular structure, also suggests future use of supervised machine learning approaches to experimental inference, as has seen recent interest for interpretation of X-ray absorption near-edge structure (XANES).

Comparative study of the around-Fermi electronic structure of 5d metals and metal-oxides by means of high-resolution X-ray emission and absorption spectroscopies.

The composition of occupied and unoccupied electronic states in the vicinity of Fermi energies is vital for all materials and relates to their physical, chemical and mechanical properties. This work demonstrates how the combination of resonant and non-resonant X-ray emission spectroscopies supplemented with theoretical modelling allows for quantitative analysis of electronic states in 5d transition metal and metal-oxide materials. Application of X-rays provides element selectivity that, in combination with the penetrating properties of hard X-rays, allows determination of the composition of electronic states under working conditions, i.e. non-vacuum environment. Tungsten metal and tungsten oxide are evaluated to show the capability to simultaneously assess composition of around-band-gap electronic states as well as the character and magnitude of the crystal field splitting.

Multiple ionization X-ray satellites of Ti and its binary oxides in alpha particle PIXE

High energy resolution X-ray emission spectroscopy was used to study the multiple ionization satellites in the K X-ray spectra of titanium induced by target irradiation with MeV alpha particles. Beam energies of 3–5 MeV were used to explore the beam energy dependence. In addition, several titanium binary oxides excited with 5 MeV beam were measured to study also the chemical bonding effects on the multiple ionization satellites. Energy shifts and intensities of the satellites corresponding to one and two L-shell vacancies were determined from the measured spectra. The results will be used to refine the existing experimental alpha particle induced multiple ionization satellite database which is needed to improve the accuracy of PIXE analysis using alpha particle beams, including the PIXE mode of the Mars alpha particle X-ray spectrometers.

X-ray emission spectroscopy optimization for chemical speciation in laboratory

K X-ray emission spectra emitted from carbon, aluminum, silicon, phosphorus, titanium, chromium, and manganese compounds were measured, using a compact lab-scale flat crystal X-ray fluorescence spectrometer. The sensitivity of K X-ray transitions line-shape, relative to the atom's chemical speciation, is considered. Spectrometer's optimization concerning high energy resolution takes place for each measured fluorescence transition. The detected changes on the measured X-ray line-shapes allow extracting the chemical speciation of the emitting atom. In-lab high-resolution X-ray emission spectroscopy is shown to be a highly versatile technique for materials chemical characterization.

Experimental setup for the study of resonant inelastic X-ray scattering of organometallic complexes in gas phase.

A new setup has been designed and built to study organometallic complexes in gas phase at the third-generation Synchrotron radiation sources. This setup consists of a new homemade computer-controlled gas cell that allows us to sublimate solid samples by accurately controlling the temperature. This cell has been developed to be a part of the high-resolution X-ray emission spectrometer permanently installed at the GALAXIES beamline of the French National Synchrotron Facility SOLEIL. To illustrate the capabilities of the setup, the cell has been successfully used to record high-resolution Kα emission spectra of gas-phase ferrocene Fe(C5H5)2 and to characterize their dependence with the excitation energy. This will allow to extend resonant X-ray emission to different organometallic molecules.

Determination of Hexavalent Chromium Fractions in Plastics Using Laboratory-Based, High-Resolution X-ray Emission Spectroscopy.

Cr(VI) is a well-known human carcinogen with many water-soluble moieties. Its presence in both natural and man-made substances poses a risk to public health, especially when contamination of groundwater is possible. This has led the European Union and other jurisdictions to include Cr(VI) in restriction of hazardous substances regulations. However, for several important industrial and commercial purposes, analytical capability to characterize Cr(VI) is known to be insufficient for regulatory purposes. For example, advanced X-ray spectroscopies, particularly synchrotron-based X-ray absorption fine structure (XAFS) studies, have shown that species interconversion and under-extraction can be difficult to prevent in many existing liquid extraction protocols when applied to plastics, mining ores and tailings, and paint sludges. Here, we report that wavelength dispersive X-ray fluorescence spectroscopy taken at energy resolutions close to the theoretical limit imposed by the core-hole lifetime, generally called X-ray emission spectroscopy (XES) in the synchrotron community, can be used in the laboratory setting for noninvasive, analytical characterization of the Cr(VI)/Cr ratio in plastics. The selected samples have been part of ongoing efforts by standards development organizations to create improved Cr(VI) testing protocols, and the present work provides a direct proof-of-principle for the use of such extremely high-resolution laboratory WDXRF as an alternative to liquid extraction methods for regulatory compliance testing of Cr(VI) content. As a practical application of this work, we report a value for the Cr(VI) mass fraction of the new NIST Standard Reference Material 2859 Restricted Elements in Polyvinyl Chloride.

Relative L3 transition probabilities of titanium compounds as a function of the oxidation state using high-resolution X-ray emission spectrometry

The relative transition probabilities of the L3-fluorescence lines from different titanium oxides were determined using high-resolution X-ray emission spectrometry. A reliable deconvolution of the X-ray emission spectra, by means of both experimentally determined response functions and absorption correction, reduces the relative uncertainties of the relative transition probabilities to 10% for titanium and 15% for titanium dioxide. The relative L3 transition probability of metallic titanium amounts to 0.66 ± 0.07 for the Ll fluorescence line and 0.34 ± 0.07 for the Lα fluorescence line, respectively. Respective database values from existing literature vary up to a factor of 3, which shows that a determination of the fundamental parameters in the soft X-ray range with low uncertainties is needed in particular with respect to surface sensitive X-ray spectrometer methods. The relative L3 transition probability for titanium dioxide is slightly changed to 0.56 ± 0.08 for the Ll fluorescence line and 0.44 ± 0.08 for the group of fluorescence lines associated to the L3 transition of titanium dioxide that can be considered equivalent to the metal Lα fluorescence line.

Benchtop, High-Resolution XAFS and Xes Spectrometers As Tools for Electrochemical Research

Advanced x-ray spectroscopies allow the direct and element-specific interrogation of local electronic structure, yet their scientific impact is necessarily constrained by access limitations. This is particularly evident for x-ray absorption fine structure (XAFS) and x-ray emission spectroscopy (XES) techniques. Here, the technical capability afforded by a synchrotron x-ray facility allows researchers to answer basic or applied research questions and push the forefront of science. These national-lab scale sources often provide the only means to perform these techniques, consequently slowing progress on critical projects, and also largely excluding routine analytical characterization. Over the last four years, our group at the University of Washington has been developing several new families of lab-based instruments to expand the accessibility of advanced x-ray spectroscopies. [1-5] It is now possible to identify the electroactive element in a material and assess its oxidation state, spin state, and coordination chemistry – all with benchtop XAFS and XES. The feasibility of these studies is established by comparing performance of our benchtop instruments with various synchrotrons in the context of several electrochemical systems. From the standpoint of materials inquiry, we will present a variety of measurements of lithium ion batteries, valence-to-core XES results from a series of oxides, and preliminary efforts toward solution-phase measurements will be presented. The latter will be done with an eye toward future electrolyte analyses. William M. Holden, et al. “A Compact Dispersive Refocusing Rowland Circle X-ray Emission Spectrometer for Laboratory, Synchrotron and XFEL Applications”, Rev. Sci. Instrum 88, 073904 (2017). [DOI: 10.1063/1.4994739]T. Seidler, et al., “A Laboratory-based Hard X-ray Monochromator for High-Resolution X-ray Emission Spectroscopy and X-ray Absorption Near Edge Structure Measurements,” Review of Scientific Instruments 85, 113906 (2014). [DOI: 10.1063/1.4901599]T. Seidler, et al., “A Modern Laboratory XAFS Cookbook,” Journal of Physics: Conference Series 712, 012015 (2016). [ http://iopscience.iop.org/article/10.1088/1742-6596/712/1/012015]R. Mortensen, et al., “Benchtop Nonresonant X-ray Emission Spectroscopy: Coming Soon to Laboratories and Beamlines Near You,” Journal of Physics: Conference Series 712, 012036. (2016) [http://iopscience.iop.org/article/10.1088/1742-6596/712/1/012036]G.T. Seidler, “The Case for Analytical XAFS”, https://www.linkedin.com/pulse/case-benchtop-analytical-xafs-gerald-seidler

Extracting chemical information from high-resolution Kβ X-ray emission spectroscopy

High-resolution X-ray emission spectroscopy allows studying the chemical environment of a wide variety of materials. Chemical information can be obtained by fitting the X-ray spectra and observing the behavior of some spectral features. Spectral changes can also be quantified by means of statistical parameters calculated by considering the spectrum as a probability distribution. Another possibility is to perform statistical multivariate analysis, such as principal component analysis. In this work the performance of these procedures for extracting chemical information in X-ray emission spectroscopy spectra for mixtures of Mn2+ and Mn4+ oxides are studied. A detail analysis of the parameters obtained, as well as the associated uncertainties is shown. The methodologies are also applied for Mn oxidation state characterization of double perovskite oxides Ba1+xLa1−xMnSbO6 (with 0≤x≤0.7). The results show that statistical parameters and multivariate analysis are the most suitable for the analysis of this kind of spectra.

Chemical speciation using high energy resolution PIXE spectroscopy in the tender X-ray range

High energy resolution X-ray emission spectroscopy employing wavelength dispersive (WDS) crystal spectrometers can provide energy resolution on the level of core-hole lifetime broadening of the characteristic emission lines. While crystal spectrometers have been traditionally used in combination with electron excitation for major and minor element analysis, they have been rarely considered in proton induced X-ray emission (PIXE) trace element analysis mainly due to low detection efficiency. Compared to the simplest flat crystal WDS spectrometer the efficiency can be improved by employing cylindrically or even spherically curved crystals in combination with position sensitive X-ray detectors. When such spectrometer is coupled to MeV proton excitation, chemical bonding effects are revealed in the high energy resolution spectra yielding opportunity to extend the analytical capabilities of PIXE technique also towards chemical state analysis. In this contribution we will focus on the high energy resolution PIXE (HR-PIXE) spectroscopy in the tender X-ray range performed in our laboratory with our home-built tender X-ray emission spectrometer. Some general properties of high energy resolution PIXE spectroscopy in the tender X-ray range are presented followed by an example of sulfur speciation in biological tissue illustrating the capabilities as well as limitations of HR-PIXE method used for chemical speciation in the tender X-ray range.