X-ray Absorption Fine Structure Technique Research Articles

Evolution of local atomic structure accompanying devitrification of amorphous Ni-Zr alloy thin films

Thin film metallic glasses undergoing devitrification can form partially crystallized or fully crystallized materials with novel structural and magnetic properties. The development of desired and tunable properties of such systems drives the need to understand the mechanism of their thermal evolution at the atomic level. Co-sputtered amorphous Ni-Zr alloy thin films which were thermally annealed in steps of 200°C from room temperature up to 800°C, were observed to undergo an amorphous-to-crystalline transformation. Evolutions in local atomic structure, including oxide formation and depletion during this devitrification process, were determined using a combination of X-ray reflectivity (XRR), grazing incidence X-ray diffraction (GIXRD) and Extended X-ray Absorption Fine Structure (EXAFS) techniques. The most probable phase of the alloy was determined as Ni7Zr2; undergoing a polymorphous transformation. The slight oxide content in the films was also noted to decrease rapidly as annealing proceeded; leaving the crystallization pathway unhindered. modeling and analyses of XRR and GIXRD data showed that film thickness decreased with annealing while long range order increased. Pair distribution function peak widths were observed to decrease with annealing, indicating a control over structural disorder in the system as it transitioned from the amorphous to crystalline state. Partial atomic distribution in the environment of each constituent was examined at every stage of annealing through EXAFS measurements, which gave proper insight into atomic scale changes to the order present. Detailed analyses through these techniques gave coherent results, thus providing a true picture of the thermal evolution process of devitrification in this technologically useful material.

Structural and optical investigations on amorphous SnSe[formula omitted] alloy

The structural and optical properties of an amorphous SnSe9 alloy made using mechanical alloying were investigated through Extended X-ray Absorption Fine Structure and photoacoustic spectroscopy techniques. Average interatomic distances, average coordination numbers, disorder and asymmetry of the gij(r) functions, and also optical parameters such as Urbach and weak absorption tail energies and the optical gap were obtained. At 300 K, we found rSe–Se=2.388±0.002 Å and NSe–Se=1.96±0.04, for Se–Se pairs, and rSe–Sn=2.65±0.02 Å and NSe–Sn=0.35±0.04 for Se–Sn pairs. We determined a direct gap at Eg=1.51±0.02eV for SnSe9. Results indicated that the structure of SnSe9 is very different from those found in crystalline Sn–Se alloys, and the optical gap is the largest one considering amorphous alloys, being even larger than those found in some crystalline alloys of Sn–Se system.

Local structural study of α-MoO3 micro-strips using synchrotron X-ray diffraction and X-ray Absorption Spectroscopy at Mo K-edge

The orthorhombic MoO3 micro-strips sample was synthesized using microwave assisted chemical co-precipitation technique. Synchrotron X-ray Diffraction (SXRD) pattern and Rietveld Refinement was used to estimate structural parameter, crystallite size of sample. It reveals that the synthesized sample MoO3 crystallized as an orthorhombic phase. X-ray Absorption Spectroscopy (XAS) measurement, which comprises both X-ray Absorption Near Edge Structure (XANES) and Extended X-ray Absorption Fine Structure (EXAFS) techniques, have been carried out on Mo K-edge to probe the local structure of samples. Local structure is also confirmed from the SXRD and Raman spectra of sample. XAS measurement reveals that the first bond length of Mo-O and Mo-Mo is 1.69 and 3.42 Å in orthorhombic MoO3 respectively. Transmission electron microscopy and SAED patterns showed stripe-like structure and single-crystal formation of MoO3 respectively.

Development of Operando Polarization-Dependent Total Reflection Fluorescence X-ray Absorption Fine Structure Technique for Three-Dimensional Structure Determination of Active Metal Species on a Model Catalyst Surface under Working Conditions

Development of <i>Operando</i> Polarization-Dependent Total Reflection Fluorescence X-ray Absorption Fine Structure Technique for Three-Dimensional Structure Determination of Active Metal Species on a Model Catalyst Surface under Working Conditions

A comprehensive examination of the local- and long-range structure of Sb6O13 pyrochlore oxide

The crystal structure of the Sb6O13 oxide, exhibiting a defect pyrochlore crystal structure with atomic vacancies, has been studied using a complete set of state-of-the-art techniques. The degree of antimony disproportionation in Sb3+ and Sb5+ valence states has been directly determined around 36% and 64%, respectively, using X-ray absorption near edge structure (XANES). These findings are in excellent agreement with our Rietveld analysis of synchrotron X-ray (SXRD) and neutron powder diffraction (NPD) results. Moreover, the highly distorted Sb3+ coordination due to its lone electron pair has been critically revisited. The bonding distances and coordination of Sb3+ and Sb5+ species closely agree with an extensive dynamic and crystallographic determination using the Extended X-ray Absorption Fine Structure (EXAFS) technique. Most importantly, the specific local disorder of the two distinctive Sb ions has been crosschecked monitoring their unusual Debye–Waller factors.

Direct Conjugation of Resveratrol on Hydrophilic Gold Nanoparticles: Structural and Cytotoxic Studies for Biomedical Applications.

Strongly hydrophilic gold nanoparticles (AuNPs), functionalized with citrate and L-cysteine, were synthetized and used as Resveratrol (RSV) vehicle to improve its bioavailability. Two different conjugation procedures were investigated: the first by adding RSV during AuNPs synthesis (1) and the second by adding RSV after AuNPs synthesis (2). The two different conjugated systems, namely AuNPs@RSV1 and AuNPs@RSV2 respectively, showed good loading efficiency (η%): η1 = 80 ± 5% for AuNPs@RSV1 and η2 = 20 ± 3% for AuNPs@RSV2. Both conjugated systems were investigated by means of Dynamic Light Scattering (DLS), confirming hydrophilic behavior and nanodimension (<2RH> 1 = 45 ± 12 nm and <2RH> 2 = 170 ± 30 nm). Fourier Transform Infrared Spectroscopy (FT-IR), Synchrotron Radiation induced X-Ray Photoelectron Spectroscopy (SR-XPS) and Near Edge X-ray Absorption Fine Structure (NEXAFS) techniques were applied to deeply understand the hooking mode of RSV on AuNPs surface in the two differently conjugated systems. Moreover, the biocompatibility of AuNPs and AuNPs@RSV1 was evaluated in the concentration range 1.0–45.5 µg/mL by assessing their effect on breast cancer cell vitality. The obtained data confirmed that, at the concentration used, AuNPs do not induce cell death, whereas AuNPs@RSV1 maintains the same anticancer effects as the unconjugated RSV.

Direct measurements of copper speciation in basaltic glasses: understanding the relative roles of sulfur and oxygen in copper complexation in melts

Micro-analytical determination of copper (Cu) speciation in natural magmatic glasses, equilibrated below the nickel – nickel oxide (NNO) buffer, reveals that two copper species are commonly stabilized in such basaltic melts. X-ray absorption fine structure (XAFS) spectroscopic analysis of basaltic matrix glasses and melt inclusions (MI) from samples of mid-ocean ridge basalt (MORB), and from Nyamuragira, Etna and Kīlauea volcanoes shows that Cu complexes as both Cu(I)-sulfide and Cu(I)-oxide species in silicate melts. The proportion of each species correlates with the measured sulfur (S) abundance of the glass. In glasses with S abundances greater than ∼1000 ppm, Cu(I)-sulfide species are dominant, whereas in glasses with S abundances between 500 and 1000 ppm, both species are found to coexist. The Cu(I)-oxide species dominate at S concentrations below 500 ppm. In 1 atm S-free experimental glasses of basaltic composition that we analyzed, only Cu(I)-oxide species are detectable, regardless of the oxygen fugacity (fO2), even at relatively high fO2 values well above the NNO buffer. Our results demonstrate that XAFS techniques are highly sensitive in measuring Cu speciation in reduced (below NNO) basaltic glasses and that both oxide and sulfide complexes can be stabilized. The relative proportion of these two species is highly dependent on the concentration of S in the melt, and thus the Cu speciation in natural melts changes as S is lost from the melt by low pressure degassing.

Structural and magnetic studies on (Fe, Cu) co-doped ZnO nanocrystals

(Fe,Cu) co-doped ZnO nanocrystals have been prepared through wet chemical route using acetate based precursors over a wide concentration range. The samples have been characterized by X-ray fluorescence (XRF) measurements to find out the concentration of dopants while phase purity of the samples has been investigated by X-ray diffraction (XRD) and Transmission Electron Microscopy (TEM) measurements. To have further micro structural insight, the samples have subsequently been subjected to synchrotron radiation based X-ray absorption spectroscopy (XAS) measurements comprising of both X-ray near edge structure (XANES) and Extended X-ray Absorption Fine Structure (EXAFS) techniques. The results of the above measurements have been used to explain the magnetic properties of the samples which have further been corroborated by density functional theory (DFT) based electronic structure calculations. It has been observed that inclusion of Cu dopants in the samples in addition to Fe increases anti-ferromagnetic (AFM) correlation among the transition metal ions and thus decreases the ferromagnetic susceptibility of the samples.

Interaction of radionuclides with natural and manmade materials using XAFS technique

The X-ray absorption fine structure (XAFS) technology has exhibited a very unique application in the study of sorption mechanism, chemical species and microstructures of radionuclides at the natural solid-water interfaces. In this review, the interaction mechanism of radionuclides with clay minerals and nanomaterials under different environmental conditions are summarized from the XAFS spectroscopy analysis. The coordination number and the bond distances of radionuclides, the oxidation-reduction reactions, the influence of humic substances and microorganisms on the species and structures of radionuclides at molecule level are reviewed and compared. This review is helpful to understand the interactions of radionuclides with oxides, natural clay minerals and nanomaterials, which is also crucial to evaluate the physicochemical behaviors of radionuclides in the natural environment.

Photon-energy dependence of single-photon simultaneous core ionization and core excitation inCO2

We have studied the ${K}^{\ensuremath{-}2}V$ process corresponding to simultaneous $K$-shell ionization and $K$-shell excitation in the $\mathrm{C}{\mathrm{O}}_{2}$ molecule. We define these ${K}^{\ensuremath{-}2}V$ states as super shake-up, at variance with the ``conventional'' ${K}^{\ensuremath{-}1}{v}^{\ensuremath{-}1}V$ shake-up states. While the nature and evolution with photon energy of the conventional shake-up satellites has been the object of many studies, no such data on a large photon-energy range were previously reported on super shake-up. The $\mathrm{C}{\mathrm{O}}_{2}$ molecule is a textbook example because it exhibits two well-isolated ${K}^{\ensuremath{-}2}V$ resonances (with V being $2{\ensuremath{\pi}}_{u}^{*}$ and $5{\ensuremath{\sigma}}_{g}^{*}$) with different symmetries resulting from shake-up processes of different origin populated in comparable proportions. The variation of the excitation cross section of these two resonances with photon energy is reported, using two different experimental approaches, which sheds light on the excitation mechanisms. Furthermore, double-core-hole spectroscopy is shown to be able to integrate and even expand information provided by conventional single-core-hole X-ray Photoelectron Spectroscopy (XPS) and Near-Edge X-ray Absorption Fine Structure (NEXAFS) techniques, revealing, for instance, $g\ensuremath{-}g$ dipole forbidden transitions which are only excited in NEXAFS spectra through vibronic coupling.

Structural Analysis of Freshwater-Cultured Pearls with Different Lusters Using the Extended X-Ray Absorption Fine Structure Technique

The quality of freshwater-cultured pearls (Chamberlainia hainesiana) is determined by their luster, which is related to the content of the two CaCO3 mineral phases: aragonite and vaterite. The atomic structures of pearl samples were analyzed by the extended X-ray absorption fine structure (EXAFS) technique using synchrotron radiation to compare the atomic environment and atomic bonding around Ca atoms of high- and low-luster pearls. The Ca K-edge EXAFS spectra of the pearl samples were determined and interpreted in terms of the photoelectron wave number and the distance between Ca atoms and neighboring atoms. From the results, the wave oscillation of high-luster pearls is less than that of low-luster pearls. This indicates the presence of the aragonite phase in high-luster pearls and a combination of aragonite and vaterite phases in low-luster pearls, especially in the fi rst and second shells of Ca atoms. It can be concluded that the different lusters of freshwater-cultured pearls are related to the different CaCO3 phases in their structures.

Local Structural Analysis of Amorphous In-Ga-Zn-O Thin Films by Total Reflection Fluorescence X-ray Absorption Fine Structure Technique

Local Structural Analysis of Amorphous In-Ga-Zn-O Thin Films by Total Reflection Fluorescence X-ray Absorption Fine Structure Technique

Electronic aspects of formation and properties of local structures around Mn in Cd1−xMnxTe1−ySey

Local electronic and structural features around Mn in Cd1−xMnxTe0.97Se0.03 (x = 0.02; 0.05; 0.1; y = 0.03) were studied by means of X-ray Absorption Fine Structure (XAFS) techniques. Manganese ions with an average valence 2+, are found to be well incorporated into the host CdTe lattice, with clear preference for Te atoms as the first neighbors. However, Mn and Te are found to form two essentially different types of bonds, one short, strong and directional (cubic MnTe-alike bond), and three much longer, predominantly ionic in nature (hexagonal MnTe-alike bonds), thereby distorting the tetrahedral coordination around Mn. The origin of peculiar Mn–Te bonds distribution and details of their nature and strength are further elaborated by employing the first principle electronic structure calculations. That way a thorough insight in impact of the Mn–Te bond length variation on the electronic structure of the compound is obtained. The relations established between the local structures and electronic properties offer a reliable procedure for detailed analysis of the structural and electronic consequences of the 3d-transition metals (TM) incorporation in II–VI semiconductor host. Clear distinction between various influences makes the procedure easily adoptable also to the studies of TM impurities in other semiconductors.

In situ XANES and EXAFS Analysis of Redox Active Fe Center Ionic Liquids

In situ X-Ray Absorption Near Edge Spectroscopy (XANES) and Extended X-Ray Absorption Fine Structure (EXAFS) techniques are applied to a metal center ionic liquid undergoing oxidation and reduction in a three electrode spectroscopic cell. Determination of the extent of reduction under negative bias on the working electrode and the extent of oxidation are determined after pulse voltammetry to quiescence. While the ionic liquid undergoes full oxidation, it undergoes only partial reduction, likely due to transport issues on the timescale of the experiment. Nearest neighbor Fe-O distances in the fully oxidized state match well to expected values for similarly coordinated solids, but reduction does not result in an extension of the Fe-O bond length, as would be expected from comparisons to the solid phase. Instead, little change in bond length is observed. We suggest that this may be due to a more complex interaction between the monodentate ligands of the metal center anion and the surrounding charge cloud, rather than straightforward electrostatics between the metal center and the nearest neighbor grouping.

Direct Observation of Active Nickel Oxide Cluster in Nickel–Borate Electrocatalyst for Water Oxidation by In Situ O K-Edge X-ray Absorption Spectroscopy

In situ O K-edge X-ray absorption fine structure (XAFS) spectroscopy was applied to investigate the electronic and structural change in the nickel–borate (Ni–Bi) electrocatalyst during the oxygen evolution reaction (OER). An absorption peak was observed around 528.7 eV at 1.0 V versus Ag/AgCl in a potassium borate aqueous solution, which relates with the formation of nanoscale order domains of edge-sharing NiO6 octahedra in the Ni–Bi electrocatalyst. XAFS spectra were measured with variation of the electrode potential from 0.3 up to 1.0 V. The measured absorption peaks suggest that the quantity of NiO6 octahedra increased in correlation with the OER current; however, when the potential was changed downward, the XAFS absorption peak assigned to NiO6 octahedra remained constant, even at the electrode potential for no OER current. This difference implies that the water oxidation catalysis proceeds at the domain edge of NiO6 octahedra. The XAFS technique provides the first successful direct probing of the act...

Anisotropic distortions in Sb doped CePt4Ge12

We investigated the local structure of the Sb doped skutterudite CePt4Ge12-xSbx using the Extended X-ray Absorption Fine Structure Technique (EXAFS). As the concentration of Sb is increased the disorder around Ce increases rapidly, and for x = 3, the peak for the nearest neighbor (Ce-Ge) is no longer observed. In contrast, for the Pt site, the disorder of the nearest neighbors is small even for x = 3. Thus the distortions are anisotropic and appear to be mainly in the plane of the Ce-Ge bonds and Ge4 rings. The increased disorder about Ce will decrease the lattice thermal conductivity at low temperatures, and likely is part of the reason for improved thermoelectric properties for the x = 1 sample.

Structural analysis of [Bmim]2CuCl4 ionic liquids in the presence of water and ethanol by XAFS technique

The structure of [Bmim]2CuCl4 ionic liquids (Bmim: 1-butyl-3-methylimidazolium) with different ratios of H2O and C2H5OH was investigated using X-ray absorption fine structure (XAFS) technique. In this study, XAFS was employed to directly probe the conformational variations of copper ions in [Bmim]2CuCl4 with the addition of either water or ethanol. XAFS analysis confirmed that the structure of ionic liquids gradually transformed from tetrahedral to octahedral configuration with the increase in ratio of H2O. Our results also showed that water molecules coordinated with the copper ions of [Bmim]2CuCl4, leading to the conformational change in ionic liquids. However, the XAFS spectra of [Bmim]2CuCl4/C2H5OH indicated no coordination of anhydrous ethanol with the copper ions of [Bmim]2CuCl4. The structure of [Bmim]2CuCl4 ionic liquids is maintained as the tetrahedral configuration in presence of ethanol. Therefore, anhydrous ethanol causes little variation in the structure of ionic liquids and it is a good solvent for the dilution of ionic liquids.

The electronic structure of homogeneous ferromagnetic (Ga, Mn)N epitaxial films

X-ray Absorption Fine Structure (XAFS) techniques, namely, X-ray Near Edge Structure (XANES), Extended XAFS (EXAFS), and Anomalous X-ray Diffraction (AXRD) were used to investigate the local atomic and electronic structure of (Ga, Mn)N magnetic layers with Mn concentrations of up to 10% grown by Molecular Beam Epitaxy. The XANES and AXRD analysis prove the Mn incorporation on substitutional GaN lattice sites. EXAFS results indicate the good quality of the structure under examination, although 0.5 nitride atom vacancies were found. The Wien2k code was applied to interpret the XANES spectra quantitatively, i.e., to determine the electronic structure of the Mn atoms. It was shown that accounting for the core-hole effect is necessary to reconstruct effectively the XANES spectra. Conducted charge density analysis based on DFT calculations identified the valency of Mn atom to be of 2.4+.

Characteristics of a tapered undulator for the X-rayabsorption fine-structure technique at PLS-II.

An in-vacuum undulator (IVU) with a tapered configuration was installed in the 8C nanoprobe/XAFS beamlime (BL8C) of the Pohang Light Source in Korea for hard X-ray nanoprobe and X-ray absorption fine-structure (XAFS) experiments. It has been operated in planar mode for the nanoprobe experiments, while gap-scan and tapered modes have been used alternatively for XAFS experiments. To examine the features of the BL8C IVU for XAFS experiments, spectral distributions were obtained theoretically and experimentally as functions of the gap and gap taper. Beam profiles at a cross section of the X-ray beam were acquired using a slit to visualize the intensity distributions which depend on the gap, degree of tapering and harmonic energies. To demonstrate the effect of tapering around the lower limit of the third-harmonic energy, V K-edge XAFS spectra were obtained in each mode. Owing to the large X-ray intensity variation around this energy, XAFS spectra of the planar and gap-scan modes show considerable spectral distortions in comparison with the tapered mode. This indicates that the tapered mode, owing to the smooth X-ray intensity profile at the expense of the highest and most stable intensity, can be an alternative for XAFS experiments where the gap-scan mode gives a considerable intensity variation; it is also suitable for quick-XAFS scanning.

Hydration and coordination structure of d-block metals formed by the confinement effect of carbon micropores

We have studied the structure around a metal ion such as zinc and copper restricted in the micropores of carbon materials with the X-ray absorption fine structure (XAFS) technique and adsorption isotherm analyses. We succeeded in revealing the dehydrated structure of zinc ions confined in the micropores of activated carbon fibers (ACFs) and carbon nanotubes (CNTs) whose pore widths are below 1 nm. XAFS spectra and adsorption isotherms of zinc ions at 303 K strongly indicate that the dehydrated structure can be stably formed even in a micropore whose pore width is less than the diameter of a spherically hydrated zinc ion, where the dehydrated ions can be stabilized by the strong potential well of the carbon micropores. Also, we studied the local structure around a copper ion of copper acetate restricted in the micropore of two kinds of ACFs by the XAFS technique. The results obtained indicate the elongation of the Cu–Cu distance of the dinuclear copper complex because of the distortion or the reduction in the number of bridging carboxylates inside the micropore. We could understand the specific formation of hydration or coordination structure formed in micropores by using d-block elements as probe metal ions. [TANSO 2013 (No. 260) 297–305.]