X-ray Absorption Fine Structure Measurements Research Articles

VerSoX B07-B: a high-throughput XPS and ambient pressure NEXAFS beamline at Diamond Light Source.

The beamline optics and endstations at branch B of the Versatile Soft X-ray (VerSoX) beamline B07 at Diamond Light Source are described. B07-B provides medium-flux X-rays in the range 45-2200 eV from a bending magnet source, giving access to local electronic structure for atoms of all elements from Li to Y. It has an endstation for high-throughput X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine-structure (NEXAFS) measurements under ultrahigh-vacuum (UHV) conditions. B07-B has a second endstation dedicated to NEXAFS at pressures from UHV to ambient pressure (1 atm). The combination of these endstations permits studies of a wide range ofinterfaces and materials. The beamline and endstation designs are discussed in detail, as well as their performance and the commissioning process.

Anisotropic Local Structure of SrFe2-xNixAs2 (x = 0.00, 0.16, and 0.23) Superconductor Probed by Polarized X-ray Absorption Fine Structure Measurements.

We have investigated the effect of the Ni substitution on the local structure and the valence electronic states of the SrFe2-xNixAs2 (x = 0.00, 0.16, and 0.23) superconductor with a multi-edge extended X-ray absorption fine structure (EXAFS) and X-ray absorption near edge structure (XANES) spectroscopy. The As K-edge and Fe K-edge EXAFS measurements in the two polarizations (E‖ab and E‖c) show a clear change in the local structure with Ni concentration. The near-neighbor bondlengths and the related mean-square relative displacements (MSRDs) decrease as the Ni content increases. The polarized XANES spectra at the As, Fe and Ni K edges reveal a systematic change in the anisotropy of the valence electronic structure. The results suggest that the quasi 2D electronic structure of this system tends to become more isotropic as the Ni content increases. The local structure and the valence electronic states are discussed in the frame of the evolving electronic transport of the SrFe2-xNixAs2 system.

Single-shot X-ray absorption spectroscopy at X-ray free electron lasers

X-ray Absorption Spectroscopy (XAS) is a widely used X-ray diagnostic method for studying electronic and structural properties of matter. At first glance, the relatively narrow bandwidth and the highly fluctuating spectral structure of X-ray Free Electron Lasers (XFEL) sources seem to require accumulation over many shots to achieve high data quality. To date the best approach to implementing XAS at XFEL facilities has been using monochromators to scan the photon energy across the desired spectral range. While this is possible for easily reproducible samples such as liquids, it is incompatible with many important systems. Here, we demonstrate collection of single-shot XAS spectra over 10s of eV using an XFEL source, with error bars of only a few percent. We additionally show how to extend this technique over wider spectral ranges towards Extended X-ray Absorption Fine Structure measurements, by concatenating a few tens of single-shot measurements. Our results pave the way for future XAS studies at XFELs, in particular those in the femtosecond regime. This advance is envisioned to be especially important for many transient processes that can only be initiated at lower repetition rates, for difficult to reproduce excitation conditions, or for rare samples, such as those encountered in high-energy density physics.

Development of extremely high-temperature X-ray absorption fine structure measurement method for oxide samples

ABSTRACT Since the severe accident at Fukushima Daiichi Nuclear Power Plant, there has been an interest in the properties of oxide fuels in their near-melting temperature range. X-ray absorption fine structure (XAFS) is an effective method for understanding the fine structure and chemical bonding state of a sample; however, high-temperature XAFS measurements performed to date have been limited to 2000 K. We have developed a method for XAFS measurements of high-melting oxides above 2000 K. This method utilizes resistance heating of tungsten and confines the sample within a 0.06 mm slit to enable transmission-type XAFS measurements. We successfully performed an XAFS test with yttria-stabilized zirconia loaded at the tip of the slit and heated to 3000 K.

Elucidating diatomic catalysis for contaminants degradation: Role of multi-functional Fe/Co sites in peroxydisulfate activation

The application of catalysts with highly available active sites, such as single-atom catalysts (SACs), is a growing trend in peroxysulfate activation for organic contaminant degradation. However, the single functional active site of SACs limits its performance in such reactions involving multiple steps or reactants. For this issue, a Fe-Co diatomic catalyst (FeCo-N-C) with multi-functional active sites is synthesized to abate bisphenol A (BPA) using peroxydisulfate (PDS) as an oxidant. X-ray Absorption Fine Structure (XAFS) measurement confirms the successful construction of diatomic Fe-N4/Co-N4 sites. The FeCo-N-C exhibits a higher normalized reaction rate (2.07 × 105 min−1 mol−1) in BPA removal than previously reported SACs. Low-temperature electron paramagnetic resonance analysis reveals that Fe-N4 and Co-N4 process different intrinsic properties (spin states), which may lead to their diverse functions in the PDS activation process. The Co sites can significantly accelerate electron transfer and enhance the PDS adsorption abilities. As a complement, Fe sites perform better in the electrostatic interaction and destabilization of PDS. This study not only explains the synergy of multi-functional diatomic sites from the whole PDS activation process but provides a reliable reference for the elimination of emerging organic contaminants.

Site occupancies in a chemically complex σ-phase from the high-entropy Cr–Mn–Fe–Co–Ni system

Site occupancies in a single-phase σ-intermetallic compound of composition Cr46Mn15.2Fe16.3Co17Ni5.5 (in at.%) were studied. To the best of the authors’ knowledge, such a complex analysis with 5 elements occupying 5 different sites has never been tackled before and is addressed here using cutting edge X-ray diffraction techniques, absorption spectroscopy and simulations. Resonant powder diffraction data were collected at the K-edges of each of the five elements and the site occupancies were refined by a joint Rietveld analysis. Dispersion coefficients were retrieved independently from tabulated values, Kramers-Kronig relations and reference samples. Additional Extended X-ray Absorption Fine Structure (EXAFS) measurements were used to confirm the site occupancies and bond lengths. The site occupancies were independently obtained by a thermodynamic approach based on the enthalpies of formation of the 55 = 3125 configurations generated by the ordered distribution of the five components on the five sublattices, derived from a machine learning approach based on a DFT database. Overall, the calculations and experiments are in excellent agreement and reveal that the σ phase can accommodate a considerable degree of disorder, which consequences for thermodynamic modeling are discussed. The configurational entropy (S) of the σ phase represents 84% of that of a fully disordered alloy with the same composition, which is much larger than that expected for a fully ordered intermetallic phase (S = 0). The corresponding entropic stabilization is one of the reasons for the fact that the σ phase is one of the most important intermetallic that precipitates in high-entropy alloys and many engineering materials.

Kinetics of the catalytic oxidation of toluene over Mn,Cu co-doped Fe2O3: Ex situ XANES and EXAFS studies to investigate mechanism

In this study, the catalytic mechanism of Mn,Cu-Fe2O3 catalyst was directly determined through reaction kinetics coupled with surface characterization. The impact of operating conditions on the catalytic performance of Mn,Cu-Fe2O3 nanocomposite for toluene oxidation in a continuous fixed-bed reactor was investigated. It was found that Mn,Cu-Fe2O3 catalyst gave the best catalytic performance in toluene removal when the initial concentrations of toluene and oxygen were at 165 ppmv and 10% at a flow rate of 200 mL min−1, respectively. Subsequently, Power-law, Mars-van Krevelen, and Langmuir-Hinshelwood models were developed to describe the kinetics of the total toluene oxidation for both toluene- and oxygen-dependent mixtures in a range of temperatures. According to the results, the basic Power-law model could not properly represent the kinetics of toluene oxidation over the catalyst. Meanwhile, the Mars-van Krevelen model allows for determining the kinetic mechanism under the variation of C7H8 concentration. The Langmuir-Hinshelwood model is attainable to express the kinetics of the oxygen-involved reaction mechanism. Moreover, the change in the structure of Mn,Cu-Fe2O3 catalyst after the catalytic reaction was characterized by X-ray Absorption Near-edge Structure (XANES) and Extended X-ray Absorption Fine Structure (EXAFS) measurements to confirm the catalytic mechanism determined through reaction kinetics. The achieved results suggest the possibility of using various models to justify the correlation between model-simulated and experimental data for VOCs oxidation in a continuous-flow catalytic reactor.

Structural and optical properties of InP1-xSbx/n-InAs epilayers grown by gas source molecular beam epitaxy

High-resolution x-ray diffraction (HR-XRD), photoluminescence (PL), synchrotron radiation extended x-ray absorption fine-structure (SR-EXAFS) measurements are methodically analyzed for assessing the optical and structural properties of InP1−xSbx/n-InAs epifilms grown by gas-source molecular-beam epitaxy method. For InP0.63Sb0.37/n-InAs sample, the PL study has revealed two A1, A2 energy bands. The A1 band prevalent at low temperature is attributed to the recombination of carriers trapped in the tail states. The A2 band with nearly constant transition energy ∼ 0.46 eV is virtually temperature independent. In InP1−xSbx alloys, the energy peak of A1 band redshifted with temperature and showed strong compositional disorder. The A2 band, dominant at higher temperature with Gaussian-like line shape is ascribed to the deep-level transition as its behavior coincided with the signature of a configuration coordinate model. The deep level responsible for A2 band is possibly linked to the “vacancy-impurity” like complexes having ground and excited states in the energy band gap. The composition dependent analysis of SR-EXAFS data for InP1−xSbx/InAs samples has confirmed the maintenance of nearest neighbor In-P, In-Sb shell distances within the range of bulk binary materials’ bond lengths. We feel that our results of HR-XRD, PL and SR-EXAFS techniques have provided valuable information on the structural and optical characteristics of the InP1−xSbx/n-InAs (001) epilayers and can be extended to many other technologically important materials.

Coke-resistant NdFe0.7Ni0.3O3 perovskite catalyst with superior stability for dry reforming of ethane

Effects of A-site cation substitution and B-site active metal doping-segregation on physicochemical properties of Ni-doped perovskite-structured LnFe0.7Ni0.3O3 (Ln = La, Nd, Sm, Eu) catalysts and their catalytic performance for dry reforming of ethane (DRE) were studied. The DRE activity follows the trend: NdFe0.7Ni0.3O3 > SmFe0.7Ni0.3O3 > EuFe0.7Ni0.3O3 > LaFe0.7Ni0.3O3. The doping-segregation process of Ni was demonstrated by in-situ X-ray Diffraction (XRD) and X-ray Absorption Fine Structure (XAFS) measurements, which significantly improves the dispersion of Ni and enhance the interaction between metal and support. The results of temperature-programmed surface reactions (TPSR) and pulse reactions indicate that oxygen vacancies generated by the exsolution of Ni play an important role in the elimination of coke and shift the product from surface carbon to gaseous CO. According to the in-situ Raman experiments, the superior catalytic stability (no coke deposition or activity loss over 100 h) of NdFe0.7Ni0.3O3 is ascribed to its strong resistance towards carbon deposition.

Dispersion and stability mechanism of Pt nanoparticles on transition-metal oxides

The heterogeneous catalysts of Pt/transition-metal oxides are typically synthesized through calcination at 500 °C, and Pt nanoparticles are uniformly and highly dispersed when hydrogen peroxide (H2O2) is applied before calcination. The influence of H2O2 on the dispersion and the stability of Pt nanoparticles on titania-incorporated fumed silica (Pt/Ti–FS) supports was examined using X-ray absorption fine structure (XAFS) measurements at the Pt L3 and Ti K edges as well as density functional theory (DFT) calculations. The local structural and chemical properties around Pt and Ti atoms of Pt/Ti–FS with and without H2O2 treatment were monitored using in-situ XAFS during heating from room temperature to 500 °C. XAFS revealed that the Pt nanoparticles of H2O2-Pt/Ti–FS are highly stable and that the Ti atoms of H2O2-Pt/Ti–FS support form into a distorted-anatase TiO2. DFT calculations showed that Pt atoms bond more stably to oxidized–TiO2 surfaces than they do to bare- and reduced–TiO2 surfaces. XAFS measurements and DFT calculations clarified that the presence of extra oxygen atoms due to the H2O2 treatment plays a critical role in the strong bonding of Pt atoms to TiO2 surfaces.

A capillary sample cell used for in-situ SAXS, XRD, and XAFS measurements during hydrothermal synthesis

Hydrothermal synthesis was extensively used for the material preparation. In this paper, a capillary sample cell was designed for in-situ small angle X-ray scattering (SAXS), X-ray diffraction (XRD), and X-ray absorption fine structure (XAFS) studies during hydrothermal synthesis. Kalrez sealing ring was used to seal the liquid sample into a capillary. CO2 or inert gases were used as the pressure transmitting medium. A three-way valve was used to switch the liquid sample or the pressure transmitting medium. Sheathed heat-blocks were used to heat the capillary. The hydrothermal pressure can be up to 4.0 ± 0.1 MPa, and the hydrothermal temperature can reach to 600 ± 1 K. In-situ SAXS, XRD, and XAFS measurements during the hydrothermal synthesis of bismuth carbonate oxide confirm the feasibility that the capillary sample cell can be used for real-time structural characterization. Its application in Beijing Synchrotron Radiation Facility is expected to provide users with a new experimental research means.

Strain-Assisted Single Pt Sites on High-Curvature MoS 2 Surface for Ultrasensitive H 2 S Sensing

Strain-Assisted Single Pt Sites on High-Curvature MoS ₂ Surface for Ultrasensitive H ₂ S Sensing

A polycrystalline diamond micro-detector for X-ray absorption fine-structure measurements.

The microminiaturization of detectors used to record the intensity of X-ray beams is very favorable for combined X-ray experimental techniques. In this paper, chemical-vapor-deposited (CVD) polycrystalline diamond film was used to fabricate a micro-detector owing to its well controlled size, good thermostability, and appropriate conductivity. The preparation process and the main components of the CVD diamond micro-detector are described. The external dimensions of the packaged CVD diamond micro-detector are 15 mm × 7.8 mm × 5.8 mm. To demonstrate the performance of the detector, K-edge X-ray absorption fine-structure (XAFS) spectra of Cr, Fe, Cu, and Se foils were collected using the CVD diamond micro-detector and routine ion chamber. These XAFS measurements were performed at beamline 1W2B of Beijing Synchrotron Radiation Facility, covering an energy range from 5.5 to 13.5 keV. By comparison, it can be seen that the CVD diamond micro-detector shows a more excellent performance than the routine ion-chamber in recording these XAFS spectra. The successful application of the CVD diamond micro-detector in XAFS measurements shows its feasibility in recording X-ray intensity.

Analysis on Local Structure around Al Atoms in Al0.82In0.18N Alloy Grown on a GaN Substrate by X-ray Absorption Fine Structure Measurements

Analysis on Local Structure around Al Atoms in Al_0.82In_0.18N Alloy Grown on a GaN Substrate by X-ray Absorption Fine Structure Measurements

Effects of several ionic liquids on the structures and catalytic properties of double metal cyanides

A key challenge in the synthesis of catalyst is how to increase the catalytic property. Here Co(II)Fe(III) double metal cyanide (Co(II)Fe(III) DMC) had been prepared in presence with several typical kinds of ionic liquids(ILs), which were the ionic liquids with fluoroborate, fluorophosphate or -CF3, respectively. It is noteworthy that these ILs have shown significant influence on the catalytic performance of DMC for the epoxidation of styrene, and the Co(II)Fe(III) DMC catalyst modified with 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([BMIM]TF2N) show the highest catalytic efficiency. Then a series of techniques including infrared spectroscopy (IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), elemental analysis (EA), X-ray photoelectron spectroscopy (XPS), Thermogravimetric analysis (TGA), NH3-temperature programmed desorption (NH3-TPD), N2 adsorption–desorption measurement and X-ray absorption fine structure measurements(XAFS) have been used to explore the structures of Co(II)Fe(III) DMC + [BMIM]TF2N, respectively. Additionally, to further understand the influence of ionic liquid modifier, the mechanisms of the epoxidation of styrene with Co(II)Fe(III) DMC and Co(II)Fe(III) DMC + [BMIM]TF2N were probed by the density functional theory (DFT) based on the cluster model, respectively, unraveling the internal reason for the promotion of the catalyst performance. This understanding is critical to pave the way toward the design and preparation for novel catalysts.

Origin of magnetism in low energy Ni ion implanted ZnO thin films

ZnO films grown on Si(100) substrate through radio frequency (RF) sputtering are subjected to 100 keV Ni ion beam at different fluence (1×1016, 2.5×1016 and 5×1016 ions/cm2). High resolution X-ray diffraction revealed the increase in crystallite size and development of stress gradient in the ZnO thin films with the increasing Ni ion fluence. Ni implanted ZnO/Si(100) films exhibits room temperature ferromagnetism (RTFM) which is discussed via defect induced bound magnetic polaron model. Near-edge X-ray absorption fine-structure (NEXAFS) measurements at Ni L3,2-edge confirm the nature of implanted Ni ion inside the ZnO matrix. Further, NEXAFS at O K-edge revealed the onset of O(2p) with Ni(3d) orbital states, which is correlated with the observed RTFM.

Single-Atom Doping and High-Valence State for Synergistic Enhancement of NiO Electrocatalytic Water Oxidation.

The NiO-based electrocatalytic oxygen evolution reaction (OER) of water splitting is recognized as a promising approach to produce clean H2 fuel. However, the OER performance is still low, and especially, the overpotential is larger than 200mV at the current density of 10mA cm-2 . Herein, an Ir@IrNiO sample is prepared with single-atom (SA) Ir4+ doping and surface metallic Ir nanoparticles loaded onto the NiO. Owing to the bonding of the loaded Ir with surface-exposed Ni2+ , the nearby Ni atoms exist in the +3valence state, that is, the surface-loaded Ir particles behave like a stabilizer for the Ni3+ sites. Under the synergistic effect of SA Ir4+ and high-valance-state Ni3+ , the Ir@IrNiO nanostructure effectively reduces the overpotential to 195mV at acurrent density of 10mA cm-2 . Moreover, it gives an Ir-content-normalized current density of 0.0457 A mgIr -1 , 72.1 times higher than that of the best commercialized IrO2 (6.33 × 10-4 A mgIr -1 ), under the condition of 1.5V versus reversible hydrogen electrode. Operando Raman and X-ray absorption fine-structure (XAFS) measurements reveal that there are more surface-active species of Ni3+ , which adsorb and activate water molecules to form Ni3+ -*OH at low voltage, the intermediate of Ni4+ -•O is then formed at a relatively high bias voltage, and then the •O is transferred to the SA Ir4+ sites to generate Ir4+ -O-O with OH at increased voltage. This work can help design more SA-based highly active OER materials.

Mechanistic investigation and modeling of Cd immobilization by iron (hydr)oxide-humic acid coprecipitates

A molecular-scale understanding of aqueous metal adsorption onto humic acid-iron (hydr)oxide coprecipitates, and our ability to model these interactions, are lacking. Here, the molecular-scale mechanisms for Cd binding onto iron (hydr)oxide-humic acid (HA) composites were probed using X-ray absorption fine structure (XAFS) spectroscopy and surface complexation modeling (SCM). The immobilization of Cd in (hydr)oxide precipitation systems occurs predominantly through adsorption onto the freshly-formed (hydr)oxide nanoparticles, and SCM calculations suggest a specific surface area of 2400 m2/g available for Cd. The solution and XAFS measurements indicate that HA promotes the precipitation of both Fe clusters and Fe-Cd associations mainly through ligand exchange reactions. Site masking reactions result in a dramatic blockage of functional sites on HA and ~45% migration of the adsorbed Cd to iron (hydr)oxide binding sites at high HA:Fe mass ratios. A composite model that accounts for both site masking between Fe ions and HA and the increase of Fe hydroxyl sites simulate the distribution of Cd in the composites reasonably well. Overall, this study demonstrates that the Fe clusters play an overriding role for heavy metal stabilization in coprecipitation systems, while HA promotes the immobilization of Cd by facilitating the flocculation and dispersion of Fe clusters.

Combined EXAFS and MD study to elucidate defect behaviors and stage IV recovery mechanism in heavy ion irradiated molybdenum

The microstructural behaviors of materials control material properties and the recovery mechanism is a key to understanding the microstructural changes induced by irradiation. But the recovery mechanism of many metal materials is not fully understood through traditional research methods. By using Extended X-ray absorption fine-structure (EXAFS) measurements combined with Molecular Dynamics (MD) simulations, we studied the stage IV recovery process through investigating the behaviors of irradiation induced defects (caused by 104 MeV xenon ion beam irradiation) at an elevated temperature (~350 °C) in single crystal Molybdenum (Mo). We distinctly characterized self-interstitial dumbbell defect configurations and simulated their behaviors at this elevated temperature. EXAFS measurements, together with MD simulations and TEM observations, revealed that the mechanism of IV stage recovery is the migration of interstitial type defects (including dumbbells) rather than vacancy type defects. We also discussed the possible states of dumbbells after the stage IV recovery. These results further revealed the nature of the irradiated BCC structure (Mo).

Ｘ線吸収微細構造法を用いた有機金属気相成長法により成長した Sb 添加 AlN 中の Sb 原子近傍の局所構造解析

Ｘ線吸収微細構造法を用いた有機金属気相成長法により成長した Sb 添加 AlN 中の Sb 原子近傍の局所構造解析