Synchrotron‐based spectroscopy of X‐ray channeling through hollow capillary microchannels inside glass plates

Here, soft X‐ray synchrotron radiation transmitted through microchannel plates is studied experimentally. Fine structures of reflection and XANES Si L‐edge spectra detected on the exit of silicon glass microcapillary structures under conditions of total X‐ray reflection are presented and analyzed. The phenomenon of the interaction of channeling radiation with unoccupied electronic states and propagation of X‐ray fluorescence excited in the microchannels is revealed. Investigations of the interaction of monochromatic radiation with the inner‐shell capillary surface and propagation of fluorescence radiation through hollow glass capillary waveguides contribute to the development of novel X‐ray focusing devices in the future.     

Interference phenomena of synchrotron radiation in TEY spectra for silicon‐on‐insulator structure

The general matrix theory of the photoelectron/fluorescence excitation in anisotropic multilayer films at the total reflection condition of X‐rays has been developed. In a particular case the theory has been applied to explain the oscillation structure of L_2,3 XANES spectra for a SiO₂/Si/SiO₂/c‐Si sample in the pre‐edge region which has been observed by a sample current technique at glancing angles of synchrotron radiation. Remarkably the phase of the oscillations is reversed by a ～2° angle variation. The observed spectral features are found to be a consequence of waveguide mode creation in the middle layer of strained Si, which changes the radiation field amplitude in the top SiO₂ layer. The fit of the data required the correction of the optical constants for Si and SiO₂ near the Si L_2,3‐edges.     

Scanning transmission X‐ray microscopy probe for in situ mechanism study of graphene‐oxide‐based resistive random access memory

Here, an in situ probe for scanning transmission X‐ray microscopy (STXM) has been developed and applied to the study of the bipolar resistive switching (BRS) mechanism in an Al/graphene oxide (GO)/Al resistive random access memory (RRAM) device. To perform in situ STXM studies at the C K‐ and O K‐edges, both the RRAM junctions and the I₀ junction were fabricated on a single Si₃N₄ membrane to obtain local XANES spectra at these absorption edges with more delicate I₀ normalization. Using this probe combined with the synchrotron‐based STXM technique, it was possible to observe unique chemical changes involved in the BRS process of the Al/GO/Al RRAM device. Reversible oxidation and reduction of GO induced by the externally applied bias voltages were observed at the O K‐edge XANES feature located at 538.2 eV, which strongly supported the oxygen ion drift model that was recently proposed from ex situ transmission electron microscope studies.     

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.     

Effect of gamma irradiation on X‐ray absorption and photoelectron spectroscopy of Nd‐doped phosphate glass

X‐ray absorption near‐edge structure (XANES) and X‐ray photoelectron spectroscopy (XPS) of Nd‐doped phosphate glasses have been studied before and after gamma irradiation. The intensity and the location of the white line peak of the L₃‐edge XANES of Nd are found to be dependent on the ratio O/Nd in the glass matrix. Gamma irradiation changes the elemental concentration of atoms in the glass matrix, which affects the peak intensity of the white line due to changes in the covalence of the chemical bonds with Nd atoms in the glass (structural changes). Sharpening of the Nd 3d_5/2 peak profile in XPS spectra indicates a deficiency of oxygen in the glasses after gamma irradiation, which is supported by energy‐dispersive X‐ray spectroscopy measurements. The ratio of non‐bridging oxygen to total oxygen in the glass after gamma radiation has been found to be correlated to the concentration of defects in the glass samples, which are responsible for its radiation resistance as well as for its coloration.     

Augmentation of the step‐by‐step Energy‐Scanning EXAFS beamline BL‐09 to continuous‐scan EXAFS mode at INDUS‐2 SRS

An innovative scheme to carry out continuous‐scan X‐ray absorption spectroscopy (XAS) measurements similar to quick‐EXAFS mode at the Energy‐Scanning EXAFS beamline BL‐09 at INDUS‐2 synchrotron source (Indore, India), which is generally operated in step‐by‐step scanning mode, is presented. The continuous XAS mode has been implemented by adopting a continuous‐scan scheme of the double‐crystal monochromator and on‐the‐fly measurement of incident and transmitted intensities. This enabled a high signal‐to‐noise ratio to be maintained and the acquisition time was reduced to a few seconds from tens of minutes or hours. The quality of the spectra (signal‐to‐noise level, resolution and energy calibration) was checked by measuring and analysing XAS spectra of standard metal foils. To demonstrate the energy range covered in a single scan, a continuous‐mode XAS spectrum of copper nickel alloy covering both Cu and Ni K‐edges was recorded. The implementation of continuous‐scan XAS mode at BL‐09 would expand the use of this beamline in in situ time‐resolved XAS studies of various important systems of current technological importance. The feasibility of employing this mode of measurement for time‐resolved probing of reaction kinetics has been demonstrated by in situ XAS measurement on the growth of Ag nanoparticles from a solution phase.     

Operando QEXAFS studies of Ni2P during thiophene hydrodesulfurization: direct observation of Ni—S bond formation under reaction conditions

Structural changes in Ni₂P/MCM‐41 were followed by quick extended X‐ray absorption fine structure (QEXAFS) and were directly related to changes in X‐ray absorption near‐edge structure (XANES) which had been used earlier for the study of the active catalyst phase. An equation is proposed to correct the transient QEXAFS spectra up to second‐order in time to remove spectral distortions induced by structural changes occurring during measurements. A good correlation between the corrected QEXAFS and the XANES spectral changes was found, giving support to the conclusions derived from the XANES in the previous work, namely that the formation of a Ni—S bond in a surface NiPS phase is involved in the active site for the hydrodesulfurization reaction.     

An attempt at kidney stone analysis with the application of synchrotron radiation

X‐ray absorption near‐edge spectroscopy (XANES) is a spectroscopic technique using synchrotron light to determine the valence state of excited atoms as well as the electronegativity of their neighbouring atoms. XANES spectra can provide information about the chemical bond in the second coordination shell of the excited atom. In this study, XANES spectra of unknown compounds from human kidney stones were recorded around the K‐edges of sulfur, phosphorus and calcium. The XANES results agree well with the diffractogram data of the same stones obtained through an X‐ray powder diffraction (XRPD) technique. By comparing the measurement techniques presented here, it is shown that XANES requires a smaller amount of each sample than XRPD for analysis.     

X‐ray absorption near‐edge structure anomalous behaviour in structures with buried layers containing silicon nanocrystals

Substructure and phase composition of silicon suboxide films containing silicon nanocrystals and implanted with carbon have been investigated by means of the X‐ray absorption near‐edge structure technique with the use of synchrotron radiation. It is shown that formation of silicon nanocrystals in the films' depth (more than 60 nm) and their following transformation into silicon carbide nanocrystals leads to abnormal behaviour of the X‐ray absorption spectra in the elementary silicon absorption‐edge energy region (100–104 eV) or in the silicon oxide absorption‐edge energy region (104–110 eV). This abnormal behaviour is connected to X‐ray elastic backscattering on silicon or silicon carbide nanocrystals located in the silicon oxide films depth.     

Application of Synchrotron X‐Ray Microbeam Spectroscopy to the Determination of Metal Distribution and Speciation in Biological Tissues

Abstract

Resolving the distribution and speciation of metal(loid)s within biological environmental samples is essential for understanding bioavailability, trophic transfer, and environmental risk. We used synchrotron x‐ray microspectroscopy to analyze a range of samples that had been exposed to metal(loid) contamination. Microprobe x‐ray fluorescence elemental mapping (µSXRF) of decomposing rhizosphere microcosms consisting of Ni‐ and U‐contaminated soil planted with wheat (Triticum aestivum) showed the change in Ni and U distribution over a 27‐day period, with a progressive movement of U into decaying tissue. µSXRF maps showed the micrometer‐scale distribution of Ca, Mn, Fe, Ni, and U in roots of willow (Salix nigra L.) growing on a former radiological settling pond, with U located outside of the epidermis and Ni inside the cortex. X‐ray computed tomography (CMT) of woody tissue of this same affected willow showed that small points of high Ni fluorescence observed previously are actually a Ni‐rich substance contained within an individual xylem vessel. µSXRF and x‐ray absorption near‐edge spectroscopy (XANES) linked the elevated Se concentrations in sediments of a coal fly ash settling pond with oral deformities of bullfrog tadpoles (Rana catesbeiana). Se distribution was localized within the deformed mouthparts, and with an oxidation state of Se (?II) consistent with organo‐Se compounds, it suggests oral deformities are caused by incorporation of Se into proteins. The range of tissues analyzed in this study highlight the applicability of synchrotron X‐ray microspectroscopic techniques to biological tissues and the study of metal(loid) bioavailability.     

Magnesium K‐edge XANES spectroscopy of geological standards

Magnesium K‐edge X‐ray absorption near‐edge structure (XANES) spectra have been investigated to develop a systematic understanding of a suite of Mg‐bearing geological materials such as silicate and carbonate minerals, sediments, rocks and chemical reagents. For the model compounds the Mg XANES was found to vary widely between compounds and to provide a fingerprint for the form of Mg involved in geologic materials. The energy positions and resonance features obtained from these spectra can be used to specify the dominant molecular host site of Mg, thus shedding light on Mg partitioning and isotope fractionation in geologic materials and providing a valuable complement to existing knowledge of Mg geochemistry.     

Iron speciation in ancient Attic pottery pigments: a non‐destructive SR‐XAS investigation

The present work reports a detailed investigation on the speciation of iron in the pigments of decorated pottery fragments of cultural heritage relevance. The fragments come from the Gioiosa Guardia archaeological site in the area of the `Strait of Messina' (Sicily, Southern Italy), and date back to VI–V century BC. The purpose of this study is to characterize the main pigmenting agents responsible for the dark‐red coloration of the specimens using non‐destructive analytical techniques such as synchrotron radiation X‐ray absorption spectroscopy (SR‐XAS), a well established technique for cultural heritage and environmental subjects. Absorption spectra were collected at the Fe K‐edge on the Italian beamline for absorption and diffraction (BM8‐GILDA) at the European Synchrotron Radiation Facility in Grenoble (France). In order to determine the speciation of Fe in the samples, principal component analysis and least‐squares fitting procedures were applied to the near‐edge part of the absorption spectra (XANES). Details on the local structure around the Fe sites were obtained by analyzing the extended part of the spectra (EXAFS). Furthermore, an accurate determination of the average Fe oxidation state was carried out through analysis of the pre‐edge peaks of the absorption spectra. Samples resulted composed of an admixture of Fe₂O₃ (hematite or maghemite) and magnetite (Fe₃O₄), occurring in different relative abundance in the dark‐ and light‐colored areas of the specimens. The results obtained are complementary to information previously obtained by means of instrumental neutron activation analysis, Fourier transform infrared absorbance and time‐of‐flight neutron diffraction.     

Colouration mechanism of underglaze copper‐red decoration porcelain (AD 13th–14th century), China

Underglaze copper‐red decoration, i.e. the copper colourant used to paint diversified patterns on the surface of a body and then covered by transparent glaze and fired at high temperature in a reductive firing environment, is famous all over the world. However, the red colouration mechanism generated by underglaze copper remains unclear. In particular, the fact that the edges of the red patterns are orange has been ignored in previous research. Here, non‐destructive analysis has been carried out on a precious fragment of early underglaze red porcelain using synchrotron radiation X‐ray fluorescence, X‐ray absorption near‐edge spectroscopy (XANES) and reflection spectrometry techniques. The results suggest that the copper content in the red region is higher than that in the orange region, and other colour generation elements do not have obvious content difference, indicating that the colour generation effect of the underglaze red product is related to the copper content. XANES analysis shows that the valence states of copper in the red and orange regions are similar and metal copper contributes to their hues. The results of reflection spectrometry demonstrate that tiny orange hues could be attributed to the Mie scatting effect. Therefore, light‐scattering effects should be considered when researching the colouration mechanism of underglaze red.     

Phosphorus L2,3‐edge XANES: overview of reference compounds

Synchrotron‐based X‐ray absorption near‐edge structure (XANES) spectroscopy is becoming an increasingly used tool for the element speciation in complex samples. For phosphorus (P) almost all XANES measurements have been carried out at the K‐edge. The small number of distinctive features at the P K‐edge makes in some cases the identification of different P forms difficult or impossible. As indicated by a few previous studies, the P L_2,3‐edge spectra were richer in spectral features than those of the P K‐edge. However, experimentally consistent spectra of a wide range of reference compounds have not been published so far. In this study a library of spectral features is presented for a number of mineral P, organic P and P‐bearing minerals for fingerprinting identification. Furthermore, the effect of radiation damage is shown for three compounds and measures are proposed to reduce it. The spectra library provided lays a basis for the identification of individual P forms in samples of unknown composition for a variety of scientific areas.     

A setup for synchrotron‐radiation‐induced total reflection X‐ray fluorescence and X‐ray absorption near‐edge structure recently commissioned at BESSY II BAMline

An automatic sample changer chamber for total reflection X‐ray fluorescence (TXRF) and X‐ray absorption near‐edge structure (XANES) analysis in TXRF geometry was successfully set up at the BAMline at BESSY II. TXRF and TXRF‐XANES are valuable tools for elemental determination and speciation, especially where sample amounts are limited (<1 mg) and concentrations are low (ng ml^?1 to µg ml^?1). TXRF requires a well defined geometry regarding the reflecting surface of a sample carrier and the synchrotron beam. The newly installed chamber allows for reliable sample positioning, remote sample changing and evacuation of the fluorescence beam path. The chamber was successfully used showing accurate determination of elemental amounts in the certified reference material NIST water 1640. Low limits of detection of less than 100 fg absolute (10 pg ml^?1) for Ni were found. TXRF‐XANES on different Re species was applied. An unknown species of Re was found to be Re in the +7 oxidation state.     

K‐edge XANES analysis of sulfur compounds: an investigation of the relative intensities using internal calibration

Sulfur K‐edge XANES (X‐ray absorption near‐edge structure) spectroscopy is an excellent tool for determining the speciation of sulfur compounds in complex matrices. This paper presents a method to quantitatively determine the kinds of sulfur species in natural samples using internally calibrated reference spectra of model compounds. Owing to significant self‐absorption of formed fluorescence radiation in the sample itself the fluorescence signal displays a non‐linear correlation with the sulfur content over a wide concentration range. Self‐absorption is also a problem at low total absorption of the sample when the sulfur compounds are present as particles. The post‐edge intensity patterns of the sulfur K‐edge XANES spectra vary with the type of sulfur compound, with reducing sulfur compounds often having a higher post‐edge intensity than the oxidized forms. In dilute solutions (less than 0.3–0.5%) it is possible to use sulfur K‐edge XANES reference data for quantitative analysis of the contribution from different species. The results show that it is essential to use an internal calibration system when performing quantitative XANES analysis. Preparation of unknown samples must take both the total absorption and possible presence of self‐absorbing particles into consideration.     

On the correlation between the X‐ray absorption chemical shift and the formal valence state in mixed‐valence manganites

Here the correlation between the chemical shift in X‐ray absorption spectroscopy, the geometrical structure and the formal valence state of the Mn atom in mixed‐valence manganites are discussed. It is shown that this empirical correlation can be reliably used to determine the formal valence of Mn, using either X‐ray absorption spectroscopy or resonant X‐ray scattering techniques. The difficulties in obtaining a reliable comparison between experimental XANES spectra and theoretical simulations on an absolute energy scale are revealed. It is concluded that the contributions from the electronic occupation and the local structure to the XANES spectra cannot be separated either experimentally or theoretically. In this way the geometrical and electronic structure of the Mn atom in mixed‐valence manganites cannot be described as a bimodal distribution of the formal integer Mn³⁺ and Mn⁴⁺ valence states corresponding to the undoped references.     

Thorough small‐angle X‐ray scattering analysis of the instability of liquid micro‐jets in air

Liquid jets are of interest, both for their industrial relevance and for scientific applications (more important, in particular for X‐rays, after the advent of free‐electron lasers that require liquid jets as sample carrier). Instability mechanisms have been described theoretically and by numerical simulation, but confirmed by few experimental techniques. In fact, these are mainly based on cameras, which is limited by the imaging resolution, and on light scattering, which is hindered by absorption, reflection, Mie scattering and multiple scattering due to complex air/liquid interfaces during jet break‐up. In this communication it is demonstrated that synchrotron small‐angle X‐ray scattering (SAXS) can give quantitative information on liquid jet dynamics at the nanoscale, by detecting time‐dependent morphology and break‐up length. Jets ejected from circular tubes of different diameters (100–450 µm) and speeds (0.7–21 m s^?1) have been explored to cover the Rayleigh and first wind‐induced regimes. Various solvents (water, ethanol, 2‐propanol) and their mixtures have been examined. The determination of the liquid jet behaviour becomes essential, as it provides background data in subsequent studies of chemical and biological reactions using SAXS or X‐ray diffraction based on synchrotron radiation and free‐electron lasers.     

Synchrotron XANES and ED‐XRF analyses of fine‐paste ware from 13th to 14th century maritime Southeast Asia

The combination of energy dispersive X‐ray fluorescence (ED‐XRF) and synchrotron X‐ray absorption near‐edge structure (XANES) provides the detailed composition of fine‐paste ware (FPW) kendis, dated back to 13th–14th century maritime Southeast Asia. Sources of clay and production sites were classified according to Al₂O₃, SiO₂, α‐Fe₂O₃ and γ‐Fe₂O₃ as well as trace elements. The similarities based on these components provided another evidence of a trade route between Kota Cina in North Sumatra of Indonesia and Kok Moh on Satingphra Peninsula, a well‐known production area in present‐day Thailand. In additions, the uniquely large contribution of α‐Fe₂O₃ in XANES spectra suggests that Nakhon Si Thammarat province of Thailand could also be one of FPW production areas in maritime Southeast Asia. Copyright © 2017 John Wiley & Sons, Ltd.     

In vivo high‐resolution synchrotron radiation imaging of collagen‐induced arthritis in a rodent model

In vivo microstructures of the affected feet of collagen‐induced arthritic (CIA) mice were examined using a high‐resolution synchrotron radiation (SR) X‐ray refraction technique with a polychromatic beam issued from a bending magnet. The CIA models were obtained from six‐week‐old DBA/1J mice that were immunized with bovine type II collagen and grouped as grades 0–3 according to a clinical scoring for the severity of arthritis. An X‐ray shadow of a specimen was converted into a visual image on the surface of a CdWO₄ scintillator that was magnified using a microscopic objective lens before being captured with a digital charge‐coupled‐device camera. Various changes in the joint microstructure, including cartilage destruction, periosteal born formation, articular bone thinning and erosion, marrow invasion by pannus progression, and widening joint space, were clearly identified at each level of arthritis severity with an equivalent pixel size of 2.7 µm. These high‐resolution features of destruction in the CIA models have not previously been available from any other conventional imaging modalities except histological light microscopy. However, thickening of the synovial membrane was not resolved in composite images by the SR refraction imaging method. In conclusion, in vivo SR X‐ray microscopic imaging may have potential as a diagnostic tool in small animals that does not require a histochemical preparation stage in examining microstructural changes in joints affected with arthritis. The findings from the SR images are comparable with standard histopathology findings.