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Sample records for near-edge structure xanes

  1. Microanalysis of iron oxidation state in iron oxides using X Ray Absorption Near Edge Structure (XANES)

    NASA Technical Reports Server (NTRS)

    Sutton, S. R.; Delaney, J.; Bajt, S.; Rivers, M. L.; Smith, J. V.

    1993-01-01

    An exploratory application of x ray absorption near edge structure (XANES) analysis using the synchrotron x ray microprobe was undertaken to obtain Fe XANES spectra on individual sub-millimeter grains in conventional polished sections. The experiments concentrated on determinations of Fe valence in a suite of iron oxide minerals for which independent estimates of the iron speciation could be made by electron microprobe analysis and x ray diffraction.

  2. XANES (X-ray Absorption Near Edge Structure) investigation of cerium as an inhibitor for Al alloys

    SciTech Connect

    Davenport, A.J.; Isaacs, H.S. ); Kendig, M.W. . Science Center)

    1991-01-01

    Cerium ions are under investigation as possible replacements for toxic chromates. The use of cerium ions as corrosion inhibitors for aluminum alloys is investigated using XANES (x-ray absorption near edge structure). On immersion in a dilute solution of cerium ions, cerium is incorporated into the oxide films on aluminum alloys in either the 3- or 4-valent state depending upon the alloy and on the surface preparation. 7 refs., 2 figs.

  3. Anisotropy of chemical bonds in collagen molecules studied by X-ray absorption near-edge structure (XANES) spectroscopy.

    PubMed

    Lam, Raymond S K; Metzler, Rebecca A; Gilbert, Pupa U P A; Beniash, Elia

    2012-03-16

    Collagen type I fibrils are the major building blocks of connective tissues. Collagen fibrils are anisotropic supramolecular structures, and their orientation can be revealed by polarized light microscopy and vibrational microspectroscopy. We hypothesized that the anisotropy of chemical bonds in the collagen molecules, and hence their orientation, might also be detected by X-ray photoemission electron spectromicroscopy (X-PEEM) and X-ray absorption near-edge structure (XANES) spectroscopy, which use linearly polarized synchrotron light. To test this hypothesis, we analyzed sections of rat-tail tendon, composed of parallel arrays of collagen fibrils. The results clearly indicate that XANES-PEEM is sensitive to collagen fibril orientation and, more specifically, to the orientations of carbonyl and amide bonds in collagen molecules. These data suggest that XANES-PEEM is a promising technique for characterizing the chemical composition and structural organization at the nanoscale of collagen-based connective tissues, including tendons, cartilage, and bone.

  4. Interaction between Pt nanoparticles and carbon nanotubes An X-ray absorption near edge structures (XANES) study

    NASA Astrophysics Data System (ADS)

    Zhou, Jigang; Zhou, Xingtai; Sun, Xuhui; Li, Ruying; Murphy, Michael; Ding, Zhifeng; Sun, Xueliang; Sham, Tsun-Kong

    2007-04-01

    The interaction between Pt and carbon in Pt nanoparticles (NPs)-carbon nanotubes (CNTs) composite has been investigated with Pt M 3-edge and C K-edge X-ray absorption near edge structures (XANES) recorded in surface-sensitive total electron yield (TEY) and bulk-sensitive fluorescence yield (FLY). XANES in TEY shows that Pt NPs on CNTs have a fcc structure and the white-line features of the XANES strongly support that the crystalline Pt NPs interact with CNTs through synergic bonding involving charge redistribution between C 2p-derived states and Pt 5d bands. Such interaction facilitates the immobilization of Pt NPs on CNT surface without generating oxygenated functional groups.

  5. Reduced chromium in olivine grains from lunar basalt 15555 - X-ray Absorption Near Edge Structure (XANES)

    NASA Technical Reports Server (NTRS)

    Sutton, S. R.; Jones, K. W.; Gordon, B.; Rivers, M. L.; Bajt, S.; Smith, J. V.

    1993-01-01

    The oxidation state of Cr in 200-micron regions within individual lunar olivine and pyroxene grains from lunar basalt 15555 was inferred using X-ray Absorption Near Edge Structure (XANES). Reference materials had previously been studied by optical absorption spectroscopy and included Cr-bearing borosilicate glasses synthesized under controlled oxygen fugacity and Cr-doped olivines. The energy dependence of XANES spectral features defined by these reference materials indicated that Cr is predominantly divalent in the lunar olivine and trivalent in the pyroxene. These results, coupled with the apparent f(02)-independence of partitioning coefficients for Cr into olivine, imply that the source magma was dominated by divalent Cr at the time of olivine crystallization.

  6. Reduced chromium in olivine grains from lunar basalt 15555 - X-ray Absorption Near Edge Structure (XANES)

    NASA Technical Reports Server (NTRS)

    Sutton, S. R.; Jones, K. W.; Gordon, B.; Rivers, M. L.; Bajt, S.; Smith, J. V.

    1993-01-01

    The oxidation state of Cr in 200-micron regions within individual lunar olivine and pyroxene grains from lunar basalt 15555 was inferred using X-ray Absorption Near Edge Structure (XANES). Reference materials had previously been studied by optical absorption spectroscopy and included Cr-bearing borosilicate glasses synthesized under controlled oxygen fugacity and Cr-doped olivines. The energy dependence of XANES spectral features defined by these reference materials indicated that Cr is predominantly divalent in the lunar olivine and trivalent in the pyroxene. These results, coupled with the apparent f(02)-independence of partitioning coefficients for Cr into olivine, imply that the source magma was dominated by divalent Cr at the time of olivine crystallization.

  7. Drug-nanocarrier interaction--tracking the local structure of calcium silicate upon ibuprofen loading with X-ray absorption near edge structure (XANES).

    PubMed

    Guo, Xiaoxuan; Wu, Jin; Yiu, Yun-Mui; Hu, Yongfeng; Zhu, Ying-Jie; Sham, Tsun-Kong

    2013-09-28

    The interaction between drug carrier and drug molecules is fundamental for the study of drug delivery, drug targeting, and drug release. Until now, little has been known about the interaction at the molecular level. X-Ray absorption near edge structure (XANES) spectroscopy is a sensitive tool for identifying this interaction. Herein, we report the use of calcium and silicon K-edge X-ray absorption near edge structure (XANES) spectroscopy to investigate how drug molecules interact with different functional groups in calcium silicate hydrate and anhydrous calcium silicate nanocarriers with different morphologies. Significant changes are observed in the XANES spectra after drug loading; ibuprofen (IBU) loading leads to the ordering of silicates locally and there is loss of hydrates during the IBU loading processes.

  8. Speciation of sulfur in humic and fulvic acids using X-ray absorption near-edge structure (XANES) spectroscopy

    NASA Astrophysics Data System (ADS)

    Morra, Matthew J.; Fendorf, Scott E.; Brown, Paul D.

    1997-02-01

    Sulfur species in soils and sediments have previously been determined indirectly using destructive techniques. A direct and more accurate method for S speciation would improve our understanding of S biogeochemistry. X-ray absorption near edge structure (XANES) spectroscopy was performed on purified humic and fulvic acids from terrestrial and aquatic environments. This methodology allows direct determination of S species using the relationship that exists with the energy required for core electron transitions and in some cases, correlation with additional spectral features. Soil, peat, and aquatic humic acids were dominated by sulfonates with an oxidation state of +5, but also contained ester-bonded sulfates with an oxidation state of +6. Leonardite humic acid contained ester-bonded sulfate and an unidentified S compound with an oxidation state of +4.0. In contrast, high-valent S in soil, peat, and aquatic fulvic acids was exclusively in the form of sulfonic acids. Reduced S species were also present in both humic and fulvic acids. XANES is a valuable method for the speciation of S in humic materials and of potential use in S speciation of unfractionated soils.

  9. Interaction of Nanostructured Calcium Silicate Hydrate with Ibuprofen Drug Molecules: X-ray Absorption Near Edge Structure (XANES) Study at the Ca, Si and O K-edge

    NASA Astrophysics Data System (ADS)

    Guo, X. X.; Sham, T. K.; Zhu, Y. J.; Hu, Y. F.

    2013-04-01

    Mesoporous calcium silicate hydrate (CSH) nanostructure has been proven to be bioactive and biocompatible, and has a bright future in the application of bone treatment among other applications. X-ray absorption near edge structure (XANES) is a powerful tool for the study of the interactions of calcium silicate hydrates with drug molecules because it is element specific and it probes the unoccupied electronic states. Herein, we report the use of the calcium, silicon and oxygen K-edge XANES spectroscopy to identify how drug molecules interact with different groups in calcium silicate hydrate mesoporous nano-carriers with different morphologies. Significant changes are observed in XANES spectra after drug loading into the calcium silicate hydrate system, especially at the Si and O K-edge. The implications of these findings are discussed.

  10. Nitrogen K-edge X-ray absorption near edge structure (XANES) spectra of purine-containing nucleotides in aqueous solution.

    PubMed

    Shimada, Hiroyuki; Fukao, Taishi; Minami, Hirotake; Ukai, Masatoshi; Fujii, Kentaro; Yokoya, Akinari; Fukuda, Yoshihiro; Saitoh, Yuji

    2014-08-07

    The N K-edge X-ray absorption near edge structure (XANES) spectra of the purine-containing nucleotide, guanosine 5'-monophosphate (GMP), in aqueous solution are measured under various pH conditions. The spectra show characteristic peaks, which originate from resonant excitations of N 1s electrons to π* orbitals inside the guanine moiety of GMP. The relative intensities of these peaks depend on the pH values of the solution. The pH dependence is explained by the core-level shift of N atoms at specific sites caused by protonation and deprotonation. The experimental spectra are compared with theoretical spectra calculated by using density functional theory for GMP and the other purine-containing nucleotides, adenosine 5'-monophosphate, and adenosine 5'-triphosphate. The N K-edge XANES spectra for all of these nucleotides are classified by the numbers of N atoms with particular chemical bonding characteristics in the purine moiety.

  11. Light-induced relaxation of photolyzed carbonmonoxy myoglobin: a temperature-dependent x-ray absorption near-edge structure (XANES) study.

    PubMed

    Arcovito, A; Lamb, D C; Nienhaus, G U; Hazemann, J L; Benfatto, M; Della Longa, S

    2005-04-01

    X-ray absorption near-edge structure (XANES) spectra at the Fe K-edge have been measured and compared on solution samples of horse carbonmonoxy-myoglobin and its photoproducts, prepared by two different photolysis protocols: 1), extended illumination at low temperature (15 K) by white light; and 2), slow-cool from 140 to 10 K at a rate of 0.5 K/min while illuminating the sample with a 532-nm continuous-wave laser source. CO recombination has been followed while increasing the temperature at a rate of 1.2 K/min. After extended illumination at 15 K, a single process is observed, corresponding to CO recombination from a completely photolyzed species with CO bound to the primary docking site (formally B-state, in agreement with previous x-ray diffraction studies). The temperature peak for this single process is approximately 50 K. Using slow-cool illumination, data show a two-state recombination curve, the two temperature peaks being roughly assigned to 50 K and 110 K. These results are in good agreement with previous FTIR studies using temperature-derivative spectroscopy. The XANES spectroscopic markers probe structural differences between the photoproduct induced by extended illumination at 15 K and the photoproduct induced by slow-cool illumination. These differences in the XANES data have been interpreted as due to light-induced Fe-heme relaxation that does not involve CO migration from the B-state. A quantitative description of the unrelaxed and relaxed B-states, including the measurements of the Fe-N(p), Fe-N(His), and Fe-CO distances, and the out-of-plane Fe displacement, has been obtained via a procedure (MXAN) recently developed by us. This work shows that XANES, being able to extract both kinetic and structural parameters in a single experiment, is a powerful tool for structural dynamic studies of proteins.

  12. X-ray absorption near-edge structure (XANES) spectroscopy study of the interaction of silver ions with Staphylococcus aureus, Listeria monocytogenes, and Escherichia coli.

    PubMed

    Bovenkamp, Gudrun Lisa; Zanzen, Ulrike; Krishna, Katla Sai; Hormes, Josef; Prange, Alexander

    2013-10-01

    Silver ions are widely used as antibacterial agents, but the basic molecular mechanism of this effect is still poorly understood. X-ray absorption near-edge structure (XANES) spectroscopy at the Ag LIII, S K, and P K edges reveals the chemical forms of silver in Staphylococcus aureus and Escherichia coli (Ag(+) treated). The Ag LIII-edge XANES spectra of the bacteria are all slightly different and very different from the spectra of silver ions (silver nitrate and silver acetate), which confirms that a reaction occurs. Death or inactivation of bacteria was observed by plate counting and light microscopy. Silver bonding to sulfhydryl groups (Ag-S) in cysteine and Ag-N or Ag-O bonding in histidine, alanine, and DL-aspartic acid was detected by using synthesized silver-amino acids. Significantly lower silver-cysteine content, coupled with higher silver-histidine content, in Gram-positive S. aureus and Listeria monocytogenes cells indicates that the peptidoglycan multilayer could be buffering the biocidal effect of silver on Gram-positive bacteria, at least in part. Bonding of silver to phosphate groups was not detected. Interaction with DNA or proteins can occur through Ag-N bonding. The formation of silver-cysteine can be confirmed for both bacterial cell types, which supports the hypothesis that enzyme-catalyzed reactions and the electron transport chain within the cell are disrupted.

  13. X-Ray Absorption Near-Edge Structure (XANES) Spectroscopy Study of the Interaction of Silver Ions with Staphylococcus aureus, Listeria monocytogenes, and Escherichia coli

    PubMed Central

    Zanzen, Ulrike; Krishna, Katla Sai; Hormes, Josef

    2013-01-01

    Silver ions are widely used as antibacterial agents, but the basic molecular mechanism of this effect is still poorly understood. X-ray absorption near-edge structure (XANES) spectroscopy at the Ag LIII, S K, and P K edges reveals the chemical forms of silver in Staphylococcus aureus and Escherichia coli (Ag+ treated). The Ag LIII-edge XANES spectra of the bacteria are all slightly different and very different from the spectra of silver ions (silver nitrate and silver acetate), which confirms that a reaction occurs. Death or inactivation of bacteria was observed by plate counting and light microscopy. Silver bonding to sulfhydryl groups (Ag-S) in cysteine and Ag-N or Ag-O bonding in histidine, alanine, and dl-aspartic acid was detected by using synthesized silver-amino acids. Significantly lower silver-cysteine content, coupled with higher silver-histidine content, in Gram-positive S. aureus and Listeria monocytogenes cells indicates that the peptidoglycan multilayer could be buffering the biocidal effect of silver on Gram-positive bacteria, at least in part. Bonding of silver to phosphate groups was not detected. Interaction with DNA or proteins can occur through Ag-N bonding. The formation of silver-cysteine can be confirmed for both bacterial cell types, which supports the hypothesis that enzyme-catalyzed reactions and the electron transport chain within the cell are disrupted. PMID:23934494

  14. Nitrogen K-edge X-ray absorption near edge structure (XANES) spectra of purine-containing nucleotides in aqueous solution

    SciTech Connect

    Shimada, Hiroyuki; Fukao, Taishi; Minami, Hirotake; Ukai, Masatoshi; Fujii, Kentaro; Yokoya, Akinari; Fukuda, Yoshihiro; Saitoh, Yuji

    2014-08-07

    The N K-edge X-ray absorption near edge structure (XANES) spectra of the purine-containing nucleotide, guanosine 5{sup ′}-monophosphate (GMP), in aqueous solution are measured under various pH conditions. The spectra show characteristic peaks, which originate from resonant excitations of N 1s electrons to π* orbitals inside the guanine moiety of GMP. The relative intensities of these peaks depend on the pH values of the solution. The pH dependence is explained by the core-level shift of N atoms at specific sites caused by protonation and deprotonation. The experimental spectra are compared with theoretical spectra calculated by using density functional theory for GMP and the other purine-containing nucleotides, adenosine 5{sup ′}-monophosphate, and adenosine 5{sup ′}-triphosphate. The N K-edge XANES spectra for all of these nucleotides are classified by the numbers of N atoms with particular chemical bonding characteristics in the purine moiety.

  15. Sulfur poisoning mechanism of steam reforming catalysts: an X-ray absorption near edge structure (XANES) spectroscopic study.

    PubMed

    Chen, Yongsheng; Xie, Chao; Li, Yan; Song, Chunshan; Bolin, Trudy B

    2010-06-07

    The present XANES study aims at elucidating the roles of carbon deposits and metal sulfides in the catalyst deactivation in steam reforming reactions with the presence of sulfur. CeO(2)-Al(2)O(3)-supported Ni and Rh-based catalysts were tested in steam reforming of liquid hydrocarbon fuel containing 350 ppm sulfur for H(2) production at 800 degrees C. The Rh catalyst demonstrated much better sulfur tolerance than the Ni catalyst. XANES revealed that there are various sulfur species (metal sulfide, sulfonate, sulfate and organic sulfide) on the used Ni and Rh catalysts. Metal sulfide and organic sulfide are the dominant sulfur species on the Ni catalyst whereas sulfonate and sulfate predominate on the Rh catalyst. Meanwhile organic sulfide and sulfate are also observed on the support alone. Furthermore, there are more carbon deposits formed in the presence of sulfur on both catalysts. More carboxyl groups occur on the carbon deposits formed on the same catalyst when there is no sulfur in the fuel. From correlation analysis of the amounts of nickel sulfide and carbon deposits along with the relative catalytic activity loss, we conclude that sulfur causes the initial deactivation of the Ni catalyst by metal sulfide formation in the first few hours while build-up of carbon deposits contributes mainly to the subsequent deactivation.

  16. Diurnal Variation and Spatial Distribution Effects on Sulfur Speciation in Aerosol Samples as Assessed by X-Ray Absorption Near-Edge Structure (XANES)

    PubMed Central

    Pongpiachan, Siwatt; Thumanu, Kanjana; Na Pattalung, Warangkana; Hirunyatrakul, Phoosak; Kittikoon, Itthipon; Ho, Kin Fai; Cao, Junji

    2012-01-01

    This paper focuses on providing new results relating to the impacts of Diurnal variation, Vertical distribution, and Emission source on sulfur K-edge XANES spectrum of aerosol samples. All aerosol samples used in the diurnal variation experiment were preserved using anoxic preservation stainless cylinders (APSCs) and pressure-controlled glove boxes (PCGBs), which were specially designed to prevent oxidation of the sulfur states in PM10. Further investigation of sulfur K-edge XANES spectra revealed that PM10 samples were dominated by S(VI), even when preserved in anoxic conditions. The “Emission source effect” on the sulfur oxidation state of PM10 was examined by comparing sulfur K-edge XANES spectra collected from various emission sources in southern Thailand, while “Vertical distribution effects” on the sulfur oxidation state of PM10 were made with samples collected from three different altitudes from rooftops of the highest buildings in three major cities in Thailand. The analytical results have demonstrated that neither “Emission source” nor “Vertical distribution” appreciably contribute to the characteristic fingerprint of sulfur K-edge XANES spectrum in PM10. PMID:22988545

  17. Use of X-ray absorption near edge structure (XANES) to identify physisorption and chemisorption of phosphate onto ferrihydrite-modified diatomite.

    PubMed

    Xiong, Wenhui; Peng, Jian; Hu, Yongfeng

    2012-02-15

    This paper presents a novel technique integrating bulk-sensitive and surface-sensitive XANES methods to distinguish between physisorption and chemisorption for phosphate adsorption onto ferrihydrite-modified diatomite (FHMD). XANES P K-edge, L-edge, and Fe M-edge spectra were obtained for reference samples (K(2)HPO(4) and FePO(4)·2H(2)O) and test samples (phosphate adsorbed onto FHMD (FHMD-Ps) and Si-containing ferrihydrite (FHYD-Ps)). A resolvable pre-edge peak in the P K-edge spectra of FHMD-Ps and FHYD-Ps provided direct evidence for the formation of P-O-Fe(III) coordination and the occurrence of chemisorption. The resemblance between the P L-edge spectra of K(2)HPO(4) and FHMD-Ps and the marked difference between the spectra of FHMD-Ps and FePO(4)·2H(2)O indicated the intact existence of the adsorbate and the adsorbent. The similarity between Fe M-edge spectra of FHMD and FHMD-Ps and the difference between the spectra of FHMD-Ps and FePO(4)·2H(2)O confirmed the findings from P L-edge analyses. Therefore, chemisorption and physisorption coexisted during phosphate adsorption onto FHMD. Phosphate chemisorption occurred in the deeper zone of FHMD (from 50 nm to 5 μm); whereas physisorption occurred in the zone of FHMD shallower than 50 nm since the probing depth of XANES P K-edge method is 5 μm and that of P L-edge and Fe M-edge methods is 50 nm. Copyright © 2011 Elsevier Inc. All rights reserved.

  18. Small copper clusters studied by x-ray absorption near-edge structure

    NASA Astrophysics Data System (ADS)

    Oyanagi, H.; Sun, Z. H.; Jiang, Y.; Uehara, M.; Nakamura, H.; Yamashita, K.; Orimoto, Y.; Zhang, L.; Lee, C.; Fukano, A.; Maeda, H.

    2012-04-01

    The local structure of copper nanoparticles grown in organic solution by reducing Cu(II) hexafluoroacetylacetonate [Cu(hfac)2] was studied as-grown by the Cu K-edge x-ray absorption near-edge structure (XANES). Comparison of the experimental XANES spectra with reference materials indicated small copper clusters are formed by ligand-exchange with oleylamine and subsequent reducing by diphenylsilane. The multiple-scattering (MS) calculation for various model clusters consisting of 13-135 atoms suggests that small (13-19 atom) Cu clusters are stabilized without a large deformation.

  19. Three Dimensional Mapping of Nicle Oxidation States Using Full Field Xray Absorption Near Edge Structure Nanotomography

    SciTech Connect

    Nelson, G.J.; Chu, Y.; Harris, W.M.; Izzo, J.R.; Grew, K.N., Chiu, W.K.S.; Yi, J.; Andrews, J.C.; Liu, Y., Pierro, P.

    2011-04-28

    The reduction-oxidation cycling of the nickel-based oxides in composite solid oxide fuel cells and battery electrodes is directly related to cell performance. A greater understanding of nickel redox mechanisms at the microstructural level can be achieved in part using transmission x-ray microscopy (TXM) to explore material oxidation states. X-ray nanotomography combined with x-ray absorption near edge structure (XANES) spectroscopy has been applied to study samples containing distinct regions of nickel and nickel oxide (NiO) compositions. Digitally processed images obtained using TXM demonstrate the three-dimensional chemical mapping and microstructural distribution capabilities of full-field XANES nanotomography.

  20. Structural analysis of sulfur in natural rubber using X-ray absorption near-edge spectroscopy.

    PubMed

    Pattanasiriwisawa, Wanwisa; Siritapetawee, Jaruwan; Patarapaiboolchai, Orasa; Klysubun, Wantana

    2008-09-01

    X-ray absorption near-edge spectroscopy (XANES) has been applied to natural rubber in order to study the local environment of sulfur atoms in sulfur crosslinking structures introduced in the vulcanization process. Different types of chemical accelerators in conventional, semi-efficient and efficient vulcanization systems were investigated. The experimental results show the good sensitivity and reproducibility of XANES to characterize the local geometry and electronic environment of the sulfur K-shell under various conditions of vulcanization and non-vulcanization of natural rubber. Several applications of XANES in this study demonstrate an alternative way of identifying sulfur crosslinks in treated natural rubber based on differences in their spectra and oxidation states.

  1. Local structure and dynamics of hemeproteins by X-ray absorption near edge structure spectroscopy.

    PubMed

    Arcovito, Alessandro; della Longa, Stefano

    2012-07-01

    X-ray absorption near edge structure (XANES) spectroscopy is a synchrotron radiation technique sensitive to the local structure and dynamics around the metal site of a heme containing protein. Advances in detection techniques and theoretical/computational platforms in the last 15 years allowed the use of XANES as a quantitative probe of the key structural determinants driving functional changes, both in a concerted way with protein crystallography and EXAFS (extended X-ray absorption fine structure), or as a stand-alone method to apply in the crystal state as well as in solution. Moreover, the local dynamics of the heme site has been deeply investigated, on one hand, coupling XANES to classical photolysis experiments at cryogenic temperatures; on the other hand, the intrinsic property of the synchrotron radiation to induce radiolysis events, has been exploited to investigate specific cryotrapped intermediates, using X-rays both as a pump and a probe. Insights on the XANES method and some specific examples are presented to illustrate these topics. Copyright © 2012 Elsevier Inc. All rights reserved.

  2. X-ray absorption near edge structure/electron energy loss near edge structure calculation using the supercell orthogonalized linear combination of atomic orbitals method

    NASA Astrophysics Data System (ADS)

    Ching, Wai-Yim; Rulis, Paul

    2009-03-01

    Over the last eight years, a large number of x-ray absorption near edge structure (XANES) and/or electron energy loss near edge structure (ELNES) spectroscopic calculations for complex oxides and nitrides have been performed using the supercell-OLCAO (orthogonalized linear combination of atomic orbitals) method, obtaining results in very good agreement with experiments. The method takes into account the core-hole effect and includes the dipole matrix elements calculated from ab initio wavefunctions. In this paper, we describe the method in considerable detail, emphasizing the special advantages of this method for large complex systems. Selected results are reviewed and several hitherto unpublished results are also presented. These include the Y K edge of Y ions segregated to the core of a Σ31 grain boundary in alumina, O K edges of water molecules, C K edges in different types of single walled carbon nanotubes, and the Co K edge in the cyanocobalamin (vitamin B12) molecule. On the basis of these results, it is argued that the interpretation of specific features of the calculated XANES/ELNES edges is not simple for complex material systems because of the delocalized nature of the conduction band states. The long-standing notion of the 'fingerprinting' technique for spectral interpretation of experimental data is not tenable. A better approach is to fully characterize the structure under study, using either crystalline data or accurate ab initio modeling. Comparison between calculated XANES/ELNES spectra and available measurements enables us to ascertain the validity of the modeled structure. For complex crystals or structures, it is necessary to use the weighted sum of the spectra from structurally nonequivalent sites for comparison with the measured data. Future application of the supercell-OLCAO method to complex biomolecular systems is also discussed.

  3. X-ray absorption near edge structure/electron energy loss near edge structure calculation using the supercell orthogonalized linear combination of atomic orbitals method.

    PubMed

    Ching, Wai-Yim; Rulis, Paul

    2009-03-11

    Over the last eight years, a large number of x-ray absorption near edge structure (XANES) and/or electron energy loss near edge structure (ELNES) spectroscopic calculations for complex oxides and nitrides have been performed using the supercell-OLCAO (orthogonalized linear combination of atomic orbitals) method, obtaining results in very good agreement with experiments. The method takes into account the core-hole effect and includes the dipole matrix elements calculated from ab initio wavefunctions. In this paper, we describe the method in considerable detail, emphasizing the special advantages of this method for large complex systems. Selected results are reviewed and several hitherto unpublished results are also presented. These include the Y K edge of Y ions segregated to the core of a Σ31 grain boundary in alumina, O K edges of water molecules, C K edges in different types of single walled carbon nanotubes, and the Co K edge in the cyanocobalamin (vitamin B(12)) molecule. On the basis of these results, it is argued that the interpretation of specific features of the calculated XANES/ELNES edges is not simple for complex material systems because of the delocalized nature of the conduction band states. The long-standing notion of the 'fingerprinting' technique for spectral interpretation of experimental data is not tenable. A better approach is to fully characterize the structure under study, using either crystalline data or accurate ab initio modeling. Comparison between calculated XANES/ELNES spectra and available measurements enables us to ascertain the validity of the modeled structure. For complex crystals or structures, it is necessary to use the weighted sum of the spectra from structurally nonequivalent sites for comparison with the measured data. Future application of the supercell-OLCAO method to complex biomolecular systems is also discussed.

  4. Investigation of the mica x-ray absorption near-edge structure spectral features at the Al K-edge

    NASA Astrophysics Data System (ADS)

    Wu, Ziyu; Marcelli, A.; Cibin, G.; Mottana, A.; Della Ventura, G.

    2003-10-01

    Near-edge features of Al x-ray absorption near-edge structure (XANES) spectra in aluminosilicate compounds with mixed coordination number are usually assigned to a fourfold coordinated site contribution followed by a sixfold coordinated site contribution that is displaced towards higher energy because of the increasing ligand nucleus potentials, neglecting possible contributions due to bond distance variations and local geometrical distortion. Here we present and discuss the Al K-edge XANES spectra of synthetic micas with either fourfold coordinated Al (phlogopite), or with sixfold coordinated Al (polylithionite), as well as with mixed coordination (preiswerkite). Multiple scattering simulations of XANES spectra demonstrate that octahedral contributions may overlap the tetrahedral ones so that the lower energy structures in mixed coordination compounds may be associated with the octahedral sites. This unexpected behaviour can be described as due to the effect of a significant reduction of the ligand field strength (i.e. large local distortion and Al-O bond distances).

  5. Application toward Confocal Full-Field Microscopic X-ray Absorption Near Edge Structure Spectroscopy.

    PubMed

    Tack, Pieter; Vekemans, Bart; Laforce, Brecht; Rudloff-Grund, Jennifer; Hernández, Willinton Y; Garrevoet, Jan; Falkenberg, Gerald; Brenker, Frank; Van Der Voort, Pascal; Vincze, Laszlo

    2017-02-07

    Using X-ray absorption near edge structure (XANES) spectroscopy, information on the local chemical structure and oxidation state of an element of interest can be acquired. Conventionally, this information can be obtained in a spatially resolved manner by scanning a sample through a focused X-ray beam. Recently, full-field methods have been developed to obtain direct 2D chemical state information by imaging a large sample area. These methods are usually in transmission mode, thus restricting the use to thin and transmitting samples. Here, a fluorescence method is displayed using an energy-dispersive pnCCD detector, the SLcam, characterized by measurement times far superior to what is generally applicable. Additionally, this method operates in confocal mode, thus providing direct 3D spatially resolved chemical state information from a selected subvolume of a sample, without the need of rotating a sample. The method is applied to two samples: a gold-supported magnesia catalyst (Au/MgO) and a natural diamond containing Fe-rich inclusions. Both samples provide XANES spectra that can be overlapped with reference XANES spectra, allowing this method to be used for fingerprinting and linear combination analysis of known XANES reference compounds.

  6. Quantitative measurement of the reduction of platinum(IV) complexes using X-ray absorption near-edge spectroscopy (XANES).

    PubMed

    Hall, Matthew D; Daly, Helen L; Zhang, Jenny Z; Zhang, Mei; Alderden, Rebecca A; Pursche, Daniel; Foran, Garry J; Hambley, Trevor W

    2012-06-01

    The platinum(II) drugs cisplatin, carboplatin and oxaliplatin are usefully employed against a range of malignancies, but toxicities and resistance have spurred the search for improved analogs. This has included investigation of the platinum(IV) oxidation state, which provides greater kinetic inertness. It is generally accepted that Pt(IV) complexes must be reduced to Pt(II) for activation. As such, the ability to monitor reduction of Pt(IV) complexes is critical to guiding the design of candidates, and providing mechanistic understanding. Here we report in full that the white line height of X-ray absorption near-edge spectra (XANES) of Pt complexes, normalized to the post-edge minima, can be used to quantitatively determine the proportion of each oxidation state in a mixture. A series of Pt(IV) complexes based on the Pt(II) complexes cisplatin and transplatin were prepared with chlorido, acetato or hydroxido axial ligands, and studies into their reduction potential and cytotoxicity against A2780 human ovarian cancer cells were performed, demonstrating the relationship between reduction potential and cytotoxicity. Analysis of white line height demonstrated a clear and consistent difference between Pt(II) (1.52 ± 0.05) and Pt(IV) (2.43 ± 0.19) complexes. Reduction of Pt(IV) complexes over time in cell growth media and A2780 cells was observed by XANES, and shown to correspond with their reduction potentials and cytotoxicities. We propose that this method is useful for monitoring reduction of metal-based drug candidates in complex biological systems.

  7. Sulfur speciation in heavy petroleums: Information from X-ray absorption near-edge structure

    NASA Astrophysics Data System (ADS)

    Waldo, Geoffrey S.; Carlson, Robert M. K.; Moldowan, J. Michael; Peters, Kenneth E.; Penner-hahn, James E.

    1991-03-01

    The chemical speciation of sulfur in heavy petroleums, petroleum source rock extracts, and source rock pyrolysis products was studied using X-ray absorption near-edge structure (XANES) spectroscopy. The good energy resolution (ca. 0.5 eV) at the sulfur K edge and the strong dependence of XANES on the sulfur environment combine to give excellent sensitivity to changes in the electronic and structural environment of the sulfur. This has permitted identification and approximate quantitation of different classes of sulfur-containing compounds (e.g., sulfur, sulfides (including disulfides and polysulfides as a group), thiophenes, sulfoxides, sulfones, sulfinic acids, sulfonic acids, and sulfate) in a series of petroleums and petroleum source rocks. Our results indicate that the sulfur speciation of geological samples can be correlated with differences in source depositional environment, thermal maturity, and aromaticity. We report organosulfur compositions for the asphaltene, maltene, and liquid Chromatographie fractions of two sulfur-rich oils. In addition, we find that the organosulfur species in some, but not all, oils are subject to oxidation upon storage and thus may also be susceptible to oxidation in shallow reservoirs exposed to oxic waters. This work illustrates the utility of XANES as a direct spectroscopic probe for the quantitative determination of sulfur species in geological samples.

  8. Solving local structure around dopants in metal nanoparticles with ab initio modeling of X-ray absorption near edge structure

    DOE PAGES

    Timoshenko, J.; Shivhare, A.; Scott, R. W.; ...

    2016-06-30

    We adopted ab-initio X-ray Absorption Near Edge Structure (XANES) modelling for structural refinement of local environments around metal impurities in a large variety of materials. Our method enables both direct modelling, where the candidate structures are known, and the inverse modelling, where the unknown structural motifs are deciphered from the experimental spectra. We present also estimates of systematic errors, and their influence on the stability and accuracy of the obtained results. We illustrate our approach by following the evolution of local environment of palladium atoms in palladium-doped gold thiolate clusters upon chemical and thermal treatments.

  9. Solving local structure around dopants in metal nanoparticles with ab initio modeling of X-ray absorption near edge structure.

    PubMed

    Timoshenko, Janis; Shivhare, Atal; Scott, Robert W J; Lu, Deyu; Frenkel, Anatoly I

    2016-07-20

    We adopted ab initio X-ray absorption near edge structure (XANES) modeling for structural refinement of local environments around metal impurities in a large variety of materials. Our method enables both direct modeling, where the candidate structures are known, and the inverse modeling, where the unknown structural motifs are deciphered from the experimental spectra. We present also estimates of systematic errors, and their influence on the stability and accuracy of the obtained results. We illustrate our approach by revealing the evolution of local environment of palladium atoms in palladium-doped gold thiolate clusters upon chemical and thermal treatments.

  10. Influence of the local atomic structure in the X-ray absorption near edge spectroscopy of neptunium oxo ions.

    PubMed

    Lozano, Janeth M; Clark, David L; Conradson, Steven D; Den Auwer, Christophe; Fillaux, Clara; Guilaumont, Dominique; Keogh, D Webster; Mustre de Leon, Jose; Palmer, Phillip D; Simoni, Eric

    2009-11-28

    Experimental L(III) X-ray absorption near edge structure (XANES) spectra of the distorted octahedral neptunium oxo ions NpO(2)(OH)(4)(2-), NpO(4)(OH)(2)(3-), and NpO(6)(6-) are interpreted using relativistic full multiple scattering calculations of the X-ray absorption process. In this series of compounds, the neptunium cation exhibits two different oxidation states, VI and VII, with coordination spheres from di- to tetra oxo for the first two compounds. The comparison between calculated XANES spectra using the feff code and experimental ones shows that the main features in the spectra are determined by the local coordination around the actinide metal center. Furthermore, the projected density of electronic states (DOS) calculated from the XANES simulations using the feff code are compared to calculations using ADF code. They are both discussed in terms of molecular orbitals and qualitative evolution of bonding within this series of compounds.

  11. 3D Imaging of Nickel Oxidation States using Full Field X-ray Absorption Near Edge Structure Nanotomography

    SciTech Connect

    Nelson, George; Harris, William; Izzo, John; Grew, Kyle N.

    2012-01-20

    Reduction-oxidation (redox) cycling of the nickel electrocatalyst phase in the solid oxide fuel cell (SOFC) anode can lead to performance degradation and cell failure. A greater understanding of nickel redox mechanisms at the microstructural level is vital to future SOFC development. Transmission x-ray microscopy (TXM) provides several key techniques for exploring oxidation states within SOFC electrode microstructure. Specifically, x-ray nanotomography and x-ray absorption near edge structure (XANES) spectroscopy have been applied to study samples of varying nickel (Ni) and nickel oxide (NiO) compositions. The imaged samples are treated as mock SOFC anodes containing distinct regions of the materials in question. XANES spectra presented for the individual materials provide a basis for the further processing and analysis of mixed samples. Images of composite samples obtained are segmented, and the distinct nickel and nickel oxide phases are uniquely identified using full field XANES spectroscopy. Applications to SOFC analysis are discussed.

  12. Near-edge structures from first principles all-electron Bethe-Salpeter equation calculations.

    PubMed

    Olovsson, W; Tanaka, I; Puschnig, P; Ambrosch-Draxl, C

    2009-03-11

    We obtain x-ray absorption near-edge structures (XANES) by solving the equation of motion for the two-particle Green's function for the electron-hole pair, the Bethe-Salpeter equation (BSE), within the all-electron full-potential linearized augmented plane wave method (FPLAPW). The excited states are calculated for the Li K-edge in the insulating solids LiF, Li(2)O and Li(2)S, and absorption spectra are compared with independent particle results using the random phase approximation (RPA), as well as supercell calculations using the core-hole approximation within density functional theory (DFT). The binding energies of strongly bound excitations are determined in the materials, and core-exciton wavefunctions are demonstrated for LiF.

  13. The speciation of soluble sulphur compounds in bacterial culture fluids by X-ray absorption near edge structure spectroscopy.

    PubMed

    Franz, Bettina; Lichtenberg, Henning; Hormes, Josef; Dahl, Christiane; Prange, Alexander

    2009-11-01

    Over the last decade X-ray absorption near edge structure (XANES) spectroscopy has been used in an increasing number of microbiological studies. In addition to other applications it has served as a valuable tool for the investigation of the sulphur globules deposited intra- or extracellularly by certain photo- and chemotrophic sulphur-oxidizing (Sox) bacteria. For XANES measurements, these deposits can easily be concentrated by filtration or sedimentation through centrifugation. However, during oxidative metabolism of reduced sulphur compounds, such as sulphide or thiosulphate, sulphur deposits are not the only intermediates formed. Soluble intermediates such as sulphite may also be produced and released into the medium. In this study, we explored the potential of XANES spectroscopy for the detection and speciation of sulphur compounds in culture supernatants of the phototrophic purple sulphur bacterium Allochromatium vinosum. More specifically, we investigated A. vinosum DeltasoxY, a strain with an in frame deletion of the soxY gene. This gene encodes an essential component of the thiosulphate-oxidizing Sox enzyme complex. Improved sample preparation techniques developed for the DeltasoxY strain allowed for the first time not only the qualitative but also the quantitative analysis of bacterial culture supernatants by XANES spectroscopy. The results thus obtained verified and supplemented conventional HPLC analysis of soluble sulphur compounds. Sulphite and also oxidized organic sulphur compounds were shown by XANES spectroscopy to be present, some of which were not seen when standard HPLC protocols were used.

  14. Nitrogen K-edge x-ray absorption near edge structure of pyrimidine-containing nucleotides in aqueous solution

    SciTech Connect

    Shimada, Hiroyuki Minami, Hirotake; Okuizumi, Naoto; Sakuma, Ichiro; Ukai, Masatoshi; Fujii, Kentaro; Yokoya, Akinari; Fukuda, Yoshihiro; Saitoh, Yuji

    2015-05-07

    X-ray absorption near edge structure (XANES) was measured at energies around the N K-edge of the pyrimidine-containing nucleotides, cytidine 5′-monophosphate (CMP), 2′-deoxythymidine 5′-monophosphate (dTMP), and uridine 5′-monophosphate (UMP), in aqueous solutions and in dried films under various pH conditions. The features of resonant excitations below the N K-edge in the XANES spectra for CMP, dTMP, and UMP changed depending on the pH of the solutions. The spectral change thus observed is systematically explained by the chemical shift of the core-levels of N atoms in the nucleobase moieties caused by structural changes due to protonation or deprotonation at different proton concentrations. This interpretation is supported by the results of theoretical calculations using density functional theory for the corresponding nucleobases in the neutral and protonated or deprotonated forms.

  15. Nitrogen K-edge x-ray absorption near edge structure of pyrimidine-containing nucleotides in aqueous solution.

    PubMed

    Shimada, Hiroyuki; Minami, Hirotake; Okuizumi, Naoto; Sakuma, Ichiro; Ukai, Masatoshi; Fujii, Kentaro; Yokoya, Akinari; Fukuda, Yoshihiro; Saitoh, Yuji

    2015-05-07

    X-ray absorption near edge structure (XANES) was measured at energies around the N K-edge of the pyrimidine-containing nucleotides, cytidine 5'-monophosphate (CMP), 2'-deoxythymidine 5'-monophosphate (dTMP), and uridine 5'-monophosphate (UMP), in aqueous solutions and in dried films under various pH conditions. The features of resonant excitations below the N K-edge in the XANES spectra for CMP, dTMP, and UMP changed depending on the pH of the solutions. The spectral change thus observed is systematically explained by the chemical shift of the core-levels of N atoms in the nucleobase moieties caused by structural changes due to protonation or deprotonation at different proton concentrations. This interpretation is supported by the results of theoretical calculations using density functional theory for the corresponding nucleobases in the neutral and protonated or deprotonated forms.

  16. Study on Coloration Mechanism of Chinese Ancient Ceramics by X-ray Absorption Near-edge Structure

    NASA Astrophysics Data System (ADS)

    Peng, Y. H.; Xie, Z.; He, J. F.; Liu, Q. H.; Pan, Z. Y.; Cheng, W. R.; Wei, S. Q.

    2013-04-01

    The Fe K-edge X-ray absorption near-edge structure (XANES) spectra of a series of ceramic shards were measured by fluorescence mode to reveal the color-generating techniques of Chinese porcelain. The analysis disclosed relationships among the chemical form of the iron, the firing conditions and the colors of the ceramics. The results indicate that the coloration for different ceramics depend on the valence states of iron as the main color element in glaze and the proportion of Fe2+ and Fe3+ was attributed to the baking technology. The findings provide important information for archaeologist on the coloration researches.

  17. Characterization of As-Doped p-Type ZnO by X-ray Absorption Near-Edge Structure Spectroscopy: Theory

    SciTech Connect

    Limpijumnong, S.; Smith, M. F.; Zhang, S. B.

    2006-01-01

    Vaithianathan et al. [Appl. Phys. Lett. 88, 112103 (2006)] measured x-ray absorption near-edge structure (XANES) of As-doped ZnO and analyzed it as evidence for As{sub o} acceptors. However, upon carrying out first principles calculations, we found that the simulated XANES spectrum for As{sub o} is very different from that observed. Instead, the simulated spectrum for As{sub Zn}-2V{sub Zn} defect complex, which is predicted to be an acceptor [S. Limpijumnong et al., Phys. Rev. Lett. 92, 155504 (2004)], is far more consistent with the XANES data. The combination of our study, with the XANES of Vaithianathan et al. might be, until now, the strongest support for the As{sub Zn}-2V{sub Zn} model.

  18. X-ray absorption near-edge structure of selenium in the Cu-In-Se system

    NASA Astrophysics Data System (ADS)

    Wolska, A.; Bacewicz, R.; Filipowicz, J.; Attenkofer, K.

    2001-05-01

    The x-ray absorption near edge structure (XANES) of selenium is investigated in the crystals with compositions from the pseudobinary cut line Cu2Se-In2Se3. This includes CuInSe2, indium-rich ternary compounds (Cu2In4Se7, CuIn3Se5, CuIn5Se8, CuIn7Se11) and α-In2Se3. The absorption at the K and L3/L2 edges of selenium has been measured using synchrotron radiation. Two theoretical approaches are used to the interpretation of the experimental data: the band structure calculation and the real-space multiple-scattering (RSMS) method. In the first one, the angular momentum projected densities of states at Se sites are calculated for CuInSe2 and α-In2Se3 for the energies up to 17 eV above the conduction band minimum by the LMTO-ASA method. The RSMS approach represented by the FEFF8 code is used to calculate the XANES spectra for the phases with tetragonal symmetry. Clusters up to 160 atoms are used in the calculations. The influence of different structural factors on the selenium XANES is studied.

  19. Ab initio x-ray absorption near-edge structure study of Ti K-edge in rutile.

    PubMed

    Chaboy, J; Nakajima, N; Tezuka, Y

    2007-07-04

    This work reports a theoretical x-ray absorption near-edge structure (XANES) spectroscopy study at the Ti K-edge in TiO(2) rutile. We present detailed ab initio computations of the Ti K-edge XANES spectrum performed within the multiple-scattering framework. An extensive discussion is presented concerning the size of the cluster needed to reproduce the experimental spectrum, especially regarding the split main absorption line. In addition, the role of the exchange and correlation potential (ECP) in reproducing all the experimental XANES features is discussed. The best agreement between experimental data and computations is obtained by using real ECP potentials, i.e. the energy-dependent Dirac-Hara exchange potential, or by using only the real part of the energy-dependent Hedin-Lundqvist complex potential, together with an additional imaginary constant to account for the core-hole lifetime and the experimental resolution. The addition of the imaginary part of the HL potential worsens the agreement between the experimental and calculated spectra, indicating the failure of the complex part of the Hedin-Lundqvist ECP in accounting for the electron damping in these systems.

  20. Li K-edge X-ray absorption near edge structure spectra for a library of lithium compounds applied in lithium batteries

    NASA Astrophysics Data System (ADS)

    Wang, Dongniu; Zuin, Lucia

    2017-01-01

    Lithium ion batteries (LIB) have achieved great success as energy supply systems in portable devices and in electrical vehicles. Identifying the local chemical structures of elemental lithium in lithium compounds is beneficial for improving understanding of battery components and performance. Herein, a library of Li K-edge X-ray absorption near edge structure (XANES) of lithium compounds relevant to Li-ion batteries is reported. Materials described include lithium metals (anode), Li-containing cathodes, electrolytes and solid electrolyte interphase (SEI). The results illustrate the characteristic spectral features stemming from the various electronic structures and chemical environment of lithium atoms for each and every possible battery component. XANES spectra of Sn based anode after discharging reveal the appearance of Li2CO3 on electrode surface. X-ray damage on sensitive lithium species is also assessed; the results reveal that more attention should be paid to irradiation effects to conduct XANES measurements for battery materials properly.

  1. Structural Disorder in Colloidal InAs and CdSe Nanocrystals Observed by X-Ray Absorption Near-Edge Spectroscopy

    SciTech Connect

    Hamad, K.S.; Hamad, K.S.; Roth, R.; Roth, R.; Rockenberger, J.; Rockenberger, J.; Alivisatos, A.P.; Alivisatos, A.P.; van Buuren, T.

    1999-10-01

    We report the observation of size dependent structural disorder by x-ray absorption near-edge spectroscopy (XANES) in InAs and CdSe nanocrystals 17{endash}80thinspthinsp{Angstrom} in diameter. XANES of the In and Cd M{sub 4,5} edges yields features that are sharp for the bulk solid but broaden considerably as the size of the particle decreases. FEFF7 multiple-scattering simulations reproduce the size dependent broadening of the spectra if a bulklike surface reconstruction of a spherical nanocrystal model is included. This illustrates that XANES is sensitive to the structure of the entire nanocrystal including the surface. {copyright} {ital 1999} {ital The American Physical Society }

  2. Structural studies of Ba1-xLaxTiO3 using X-ray absorption near-edge spectroscopy

    NASA Astrophysics Data System (ADS)

    Kamon-in, O.; Pattanasiriwisawa, W.; Yangthaisong, A.; Srilomsak, S.

    2009-11-01

    La-doped barium titanate (Ba1-xLaxTiO3) is an important electronic ceramic material used in a wide variety of applications including in multilayer capacitor, transducers, ferroelectric thin film memories, and positive temperature coefficient resistor (PTCR). In this work, we investigated the changes of the local atomic structure around barium and titanium ions of Ba1-xLaxTiO3 compounds prepared by solid state reaction using X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS). The X-ray Absorption Near-Edge Structure (XANES) spectra at the Ti K-edge (4966 eV) and Ba LIII-edge (5247 eV) were analyzed. Our findings suggest that La3+ doping can modify the degree of covalency of the Ti-O bonds, but cause no change in the BaTiO3 unit cell volume and the atomic coordinate around Ti4+, Ba2+ions.

  3. Spectroscopic study of X-ray absorption near-edge structure of chemical states of Pt catalyst during growth of single-walled carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Kumakura, Makoto; Kozawa, Akinari; Saida, Takahiro; Naritsuka, Shigeya; Maruyama, Takahiro

    2017-06-01

    Growth of single-walled carbon nanotubes (SWCNTs) by alcohol catalytic chemical vapor deposition with the assistance of Pt as a catalyst is a useful technique because small-diameter SWCNTs are prepared under low ethanol pressure. In the study reported here, we carried out spectroscopy of X-ray absorption near-edge structure (XANES) to investigate the chemical bonding states of the Pt catalyst during SWCNT growth. Pt L3-edge XANES spectra of the Pt catalyst showed that it was reduced during pre-heating and remained metallic during SWCNT growth. This indicates that carbon atoms dissociated from the ethanol molecules did not dissolve into the Pt catalyst particles, but diffused on their surface and formed SWCNTs. Based on the XANES results, a model of Pt-catalyzed SWCNT growth is proposed.

  4. Structural evolution of fluorinated graphene upon molten-alkali treatment probed by X-ray absorption near-edge structure spectroscopy

    NASA Astrophysics Data System (ADS)

    Liang, Xianqing; Pan, Deyou; Lao, Ming; Liang, Shuiying; Huang, Dan; Zhou, Wenzheng; Guo, Jin

    2017-05-01

    The structural evolution of fluorinated graphene (FG) nanosheets upon molten-alkali treatment has been systematically investigated utilizing X-ray absorption near-edge structure (XANES) spectroscopy. It is found that the hydroxyl groups can progressively displace fluorine atoms to form covalent bonds to the graphene sheets under designed molten-alkali condition. The XANES spectra also reveal the formation of epoxide groups through intramolecular dehydration of neighbouring hydroxyl groups after substitution reaction. At high alkali-FG weight ratio, the restoration of the π-conjugated structure in graphene sheets can be observed due to the gradual decomposition of epoxide groups. Our experimental results indicate that the surface chemistry and electronic structure of hydroxyl-functionalized FG (HFG) can be readily tuned by varying the ratio of reactants.

  5. Speciation of Gold Nanoparticles by Ex Situ Extended X-ray Absorption Fine Structure and X-ray Absorption Near Edge Structure.

    PubMed

    Giorgetti, Marco; Aquilanti, Giuliana; Ballarin, Barbara; Berrettoni, Mario; Cassani, Maria Cristina; Fazzini, Silvia; Nanni, Daniele; Tonelli, Domenica

    2016-07-05

    A combined X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) methodology is here presented on a series of partially and fully reduced Au(III) samples. This allows monitoring the relative fraction of Au(III) and Au(0) in the studied samples, displaying a consistent and independent outcome. The strategy followed is based, for the first time, on two structural models that can be fitted simultaneously, and it evaluates the correlation among strongly correlated parameters such as coordination number and the Debye-Waller factor. The results of the present EXAFS and XANES approach can be extended to studies based on X-ray absorption spectroscopy experiments for the in situ monitoring of the formation of gold nanoclusters.

  6. X-ray structure analysis of a metalloprotein with enhanced active-site resolution using in situ x-ray absorption near edge structure spectroscopy.

    PubMed

    Arcovito, Alessandro; Benfatto, Maurizio; Cianci, Michele; Hasnain, S Samar; Nienhaus, Karin; Nienhaus, G Ulrich; Savino, Carmelinda; Strange, Richard W; Vallone, Beatrice; Della Longa, Stefano

    2007-04-10

    X-ray absorption spectroscopy is exquisitely sensitive to the coordination geometry of an absorbing atom and therefore allows bond distances and angles of the surrounding atomic cluster to be measured with atomic resolution. By contrast, the accuracy and resolution of metalloprotein active sites obtainable from x-ray crystallography are often insufficient to analyze the electronic properties of the metals that are essential for their biological functions. Here, we demonstrate that the combination of both methods on the same metalloprotein single crystal yields a structural model of the protein with exceptional active-site resolution. To this end, we have collected an x-ray diffraction data set to 1.4-A resolution and Fe K-edge polarized x-ray absorption near edge structure (XANES) spectra on the same cyanomet sperm whale myoglobin crystal. The XANES spectra were quantitatively analyzed by using a method based on the multiple scattering approach, which yielded Fe-heme structural parameters with +/-(0.02-0.07)-A accuracy on the atomic distances and +/-7 degrees on the Fe-CN angle. These XANES-derived parameters were subsequently used as restraints in the crystal structure refinement. By combining XANES and x-ray diffraction, we have obtained an cyanomet sperm whale myoglobin structural model with a higher precision of the bond lengths and angles at the active site than would have been possible with crystallographic analysis alone.

  7. Cerium valence in cerium-exchanged Preyssler`s heteropolyanion through x-ray absorption near-edge structure

    SciTech Connect

    Antonio, M.R.; Soderholm, L.

    1994-12-21

    The sodium ion in the heteropolytungstate known as the Preyssler anion, [NaP{sub 5}W{sub 30}O{sub 110}]{sup 14{minus}}, was exchanged with cerium from aqueous solutions of ammonium ceric nitrate, [NH{sub 4}]{sub 2}Ce{sup IV}(NO{sub 3}){sub 6}, as described by Creaser et al. The valence of cerium in this heteropolyanion was determined through Ce L-edge XANES, X-ray absorption near-edge structure. The XANES results demonstrate that cerium is trivalent in the Ce-exchanged Preyssler heteropolyanion in the solid state and in aqueous solution (1 M H{sub 2}SO{sub 4}) at rest potential and after constant-potential, bulk electrolysis at-0.55 V vs SCE. The encapsulated sodium ion of the Preyssler anion was shown to be directly exchangeable with Ce{sup III} by prolonged (48 h), high temperature (165 {degrees}C) aqueous treatments with either Ce(NO{sub 3}){sub 3}{lg_bullet}6H{sub 2}O or CeCl{sub 3}{lg_bullet}7H{sub 2}O in Teflon-lined pressure vessels.

  8. [Chlorine speciation and concentration in cultivated soil in the northeastern China studied by X-ray absorption near edge structure].

    PubMed

    Li, Jing; Lang, Chun-Yan; Ma, Ling-Ling; Xu, Dian-Dou; Zheng, Lei; Lu, Yu-Nanz; Cui Li-Rui; Zhang, Xiao-Meng

    2014-10-01

    A procedure has been proposed to determine chlorine speciation and concentration in soil with X-ray absorption near edge structure (XANES), and this method was applied to study the cultivated soil (bog, dark brown and black cultivated soil) in the Northeastern China. Qualitative analysis was carried out by least-squares fitting of sample spectra with standard spectra of three model compounds (NaCl, 3-chloropropionic acid, chlorophenol red). Linear correlation between the absolute fluorescence intensity of a series of NaCl standards and the Cl concentration was used as quantification standard for measuring the total Cl concentration in samples. The detection limits,relative standard deviation (RSD), recoveries were 2 mg · kg(-1), 0%-5% and 77%-133%, respectively. The average concentration of total Cl was 19 mg · kg(-1). The average relative content was as high as 61% of organochlorine with the concentration of 1-2 times as high as the concentration of inorganic chloride. The distribution trend of the total Cl, inorganic chloride and organic chlorine in different types of soil was: bog arable soil > dark brown soil > black soil. In conclusion, XANES is a reliable method to nondestructively characterize the speciation and concentration of chlorine in soil, which would provide some basic data for the future study of the chlorine's biogeochemical transformations.

  9. X-ray absorption near-edge structure micro-spectroscopy study of vanadium speciation in Phycomyces blakesleeanus mycelium.

    PubMed

    Žižić, Milan; Dučić, Tanja; Grolimund, Daniel; Bajuk-Bogdanović, Danica; Nikolic, Miroslav; Stanić, Marina; Križak, Strahinja; Zakrzewska, Joanna

    2015-09-01

    Vanadium speciation in the fungus Phycomyces blakesleeanus was examined by X-ray absorption near-edge structure (XANES) spectroscopy, enabling assessment of oxidation states and related molecular symmetries of this transition element in the fungus. The exposure of P. blakesleeanus to two physiologically important vanadium species (V(5+) and V(4+)) resulted in the accumulation of this metal in central compartments of 24 h old mycelia, most probably in vacuoles. Tetrahedral V(5+), octahedral V(4+), and proposed intracellular complexes of V(5+) were detected simultaneously after addition of a physiologically relevant concentration of V(5+) to the mycelium. A substantial fraction of the externally added V(4+) remained mostly in its original form. However, observable variations in the pre-edge-peak intensities in the XANES spectra indicated intracellular complexation and corresponding changes in the molecular coordination symmetry. Vanadate complexation was confirmed by (51)V NMR and Raman spectroscopy, and potential binding compounds including cell-wall constituents (chitosan and/or chitin), (poly)phosphates, DNA, and proteins are proposed. The evidenced vanadate complexation and reduction could also explain the resistance of P. blakesleeanus to high extracellular concentrations of vanadium.

  10. Micro-X-ray absorption near edge structure spectroscopy investigations of baroque tin-amalgam mirrors at BESSY using a capillary focusing system

    NASA Astrophysics Data System (ADS)

    Bartoll, J.; Röhrs, S.; Erko, A.; Firsov, A.; Bjeoumikhov, A.; Langhoff, N.

    2004-10-01

    An elliptically shaped glass monocapillary with a spatial resolution of 5 μm has been used for the fine focusing of the pre-focused X-ray beam produced by the graded-crystal monochromator beamline, KMC-2. The flux density gain of 50 was experimentally measured. The microprobe has been used in the energy range of 3.5-15 keV. Micro-X-ray fluorescence analysis (μXFA) and micro-X-ray absorption near edge structure spectroscopy (μXANES) measurements on test samples and investigations of baroque tin-amalgam mirrors were done.

  11. In Situ X-ray Absorption Near-Edge Structure Spectroscopy of ZnO Nanowire Growth During Chemical Bath Deposition

    SciTech Connect

    McPeak, Kevin M.; Becker, Matthew A.; Britton, Nathan G.; Majidi, Hasti; Bunker, Bruce A.; Baxter, Jason B.

    2010-12-03

    Chemical bath deposition (CBD) offers a simple and inexpensive route to deposit semiconductor nanostructures, but lack of fundamental understanding and control of the underlying chemistry has limited its versatility. Here we report the first use of in situ X-ray absorption spectroscopy during CBD, enabling detailed investigation of both reaction mechanisms and kinetics of ZnO nanowire growth from zinc nitrate and hexamethylenetetramine (HMTA) precursors. Time-resolved X-ray absorption near-edge structure (XANES) spectra were used to quantify Zn(II) speciation in both solution and solid phases. ZnO crystallizes directly from [Zn(H{sub 2}O){sub 6}]{sup 2+} without long-lived intermediates. Using ZnO nanowire deposition as an example, this study establishes in situ XANES spectroscopy as an excellent quantitative tool to understand CBD of nanomaterials.

  12. Cationic exchange in nanosized ZnFe{sub 2}O{sub 4} spinel revealed by experimental and simulated near-edge absorption structure

    SciTech Connect

    Stewart, S. J.; Figueroa, S. J. A.; Ramallo Lopez, J. M.; Requejo, F. G.; Marchetti, S. G.; Bengoa, J. F.; Prado, R. J.

    2007-02-15

    The nonequilibrium cation site occupancy in nanosized zinc ferrites ({approx}6-13 nm) with different degree of inversion ({approx}0.2 to 0.4) was investigated using Fe and Zn K-edge x-ray absorption near edge spectroscopy (XANES) and extended x-ray absorption fine structure, and magnetic measurements. The very good agreement between experimental and ab initio calculations on the Zn K-edge XANES region clearly shows the large Zn{sup 2+}(A){yields}Zn{sup 2+}[B] transference that takes place in addition to the well-identified Fe{sup 3+}[B]{yields}Fe{sup 3+}(A) one, without altering the long-range structural order. XANES spectra features as a function of the spinel inversion were shown to depend on the configuration of the ligand shells surrounding the absorbing atom. This XANES approach provides a direct way to sense cationic inversion in these Zn-containing spinel ferrites. We also demonstrated that a mechanical crystallization takes place on nanocrystalline spinel that causes an increase of both grain and magnetic sizes and, simultaneously, generates a significant augment of the inversion.

  13. X-ray absorption near-edge structure of GaN with high Mn concentration grown on SiC

    NASA Astrophysics Data System (ADS)

    Sancho-Juan, O.; Cantarero, A.; Garro, N.; Cros, A.; Martínez-Criado, G.; Salomé, M.; Susini, J.; Olguín, D.; Dhar, S.

    2009-07-01

    By means of x-ray absorption near-edge structure (XANES) several Ga1-xMnxN (0.03near-edge structure, we have performed ab initio calculations using the full potential linear augmented plane wave method as implemented in the Wien2k code. The calculations show the appearance of a Mn bonding \\mathrm {t_{2}}\\uparrow band localized in the gap region, and the corresponding anti-bonding state \\mathrm {t_{2}}\\downarrow , which seem to be responsible for the double structure which appears at the pre-edge absorption region. The shoulders and main absorption peak of the XANES spectra are attributed to transitions from the Mn(1s) band to the conduction bands, which are partially dipole allowed because of the Mn(4p) contribution to these bands.

  14. High repetition rate laser produced soft x-ray source for ultrafast x-ray absorption near edge structure measurements.

    PubMed

    Fourmaux, S; Lecherbourg, L; Harmand, M; Servol, M; Kieffer, J C

    2007-11-01

    Recent progress in high intensity ultrafast laser systems provides the opportunity to produce laser plasma x-ray sources exhibiting broad spectrum and high average x-ray flux that are well adapted to x-ray absorption measurements. In this paper, the development of a laser based x-ray absorption near edge structure (XANES) beamline exhibiting high repetition rate by using the Advanced Laser Light Source (ALLS) facility 100 Hz laser system (100 mJ, 35 fs at 800 nm) is presented. This system is based on a broadband tantalum solid target soft x-ray source and a grazing incidence grating spectrometer in the 1-5 nm wavelength range. To demonstrate the high potential of this laser based XANES technique in condensed matter physics, material science, or biology, measurements realized with several samples are presented: VO2 vanadium L edge, Si3N4 nitrogen K edge, and BPDA/PPD polyimide carbon K edge. The characteristics of this laser based beamline are discussed in terms of brightness, signal to noise ratio, and compared to conventional synchrotron broadband x-ray sources which allow achieving similar measurements. Apart from the very compact size and the relative low cost, the main advantages of such a laser based soft x-ray source are the picosecond pulse duration and the perfect synchronization between this x-ray probe and a laser pulse excitation which open the way to the realization of time resolved x-ray absorption measurements with picosecond range time resolution to study the dynamics of ultrafast processes and phase transition.

  15. High repetition rate laser produced soft x-ray source for ultrafast x-ray absorption near edge structure measurements

    SciTech Connect

    Fourmaux, S.; Lecherbourg, L.; Harmand, M.; Servol, M.; Kieffer, J. C.

    2007-11-15

    Recent progress in high intensity ultrafast laser systems provides the opportunity to produce laser plasma x-ray sources exhibiting broad spectrum and high average x-ray flux that are well adapted to x-ray absorption measurements. In this paper, the development of a laser based x-ray absorption near edge structure (XANES) beamline exhibiting high repetition rate by using the Advanced Laser Light Source (ALLS) facility 100 Hz laser system (100 mJ, 35 fs at 800 nm) is presented. This system is based on a broadband tantalum solid target soft x-ray source and a grazing incidence grating spectrometer in the 1-5 nm wavelength range. To demonstrate the high potential of this laser based XANES technique in condensed matter physics, material science, or biology, measurements realized with several samples are presented: VO{sub 2} vanadium L edge, Si{sub 3}N{sub 4} nitrogen K edge, and BPDA/PPD polyimide carbon K edge. The characteristics of this laser based beamline are discussed in terms of brightness, signal to noise ratio, and compared to conventional synchrotron broadband x-ray sources which allow achieving similar measurements. Apart from the very compact size and the relative low cost, the main advantages of such a laser based soft x-ray source are the picosecond pulse duration and the perfect synchronization between this x-ray probe and a laser pulse excitation which open the way to the realization of time resolved x-ray absorption measurements with picosecond range time resolution to study the dynamics of ultrafast processes and phase transition.

  16. Iron K-edge X-ray absorption near-edge structure spectroscopy of aerodynamically levitated silicate melts and glasses

    DOE PAGES

    Alderman, O. L. G.; Wilding, M. C.; Tamalonis, A.; ...

    2017-01-26

    Here, the local structure about Fe(II) and Fe(III) in silicate melts was investigated in-situ using iron K-edge X-ray absorption near-edge structure (XANES) spectroscopy. An aerodynamic levitation and laser heating system was used to allow access to high temperatures without contamination, and was combined with a chamber and gas mixing system to allow the iron oxidation state, Fe3+/ΣFe, to be varied by systematic control of the atmospheric oxygen fugacity. Eleven alkali-free, mostly iron-rich and depolymerized base compositions were chosen for the experiments, including pure oxide FeO, olivines (Fe,Mg)2SiO4, pyroxenes (Fe,Mg)SiO3, calcic FeO-CaSiO3, and a calcium aluminosilicate composition, where total iron contentmore » is denoted by FeO for convenience. Melt temperatures varied between 1410 and 2160 K and oxygen fugacities between FMQ – 2.3(3) to FMQ + 9.1(3) log units (uncertainties in parentheses) relative to the fayalite-magnetite-β-quartz (FMQ) buffer.« less

  17. Minerals discovered in paleolithic black pigments by transmission electron microscopy and micro-X-ray absorption near-edge structure

    NASA Astrophysics Data System (ADS)

    Chalmin, E.; Vignaud, C.; Salomon, H.; Farges, F.; Susini, J.; Menu, M.

    2006-05-01

    Analysis of archeological materials aims to rediscover the know-how of prehistoric men by determining the nature of the painting matter, its preparation mode, and the geographic origin of its raw materials. The preparation mode of the painting matter of the paleolithic rock art apparently consisted of mixing, grinding, and also heat-treatment. In this study, we focus on black pigments and more particularly manganese oxides. Using the combined approach of transmission electron microscopy (TEM) and Mn K-edge X-ray absorption near-edge structure (XANES) spectroscopy, we analyzed a variety of archeological black painted samples. The studied pigments arise from the caves of Ekain (Basque country, Spain), Labastide and Gargas (Hautes-Pyrénées, France). In addition, a black “crayon” (i.e., a “pen”) from the cave of Combe Saunière (Dordogne, France) was also investigated. From the analysis of these painting matters, several unusual minerals have been identified as black pigment, such as manganite, groutite, todorokite and birnessite. These conclusions enable us to estimate the technical level of paleolithic artists: they didn’t use heat-treatment to prepare black painting matter. Consequently, the unusual mineralogy found in some of these pigments suggests that some of the manganese ores are coming from geological settings that are sometimes relatively far away from the Dordogne and Basque region such as in Ariège (central-oriental Pyrénées).

  18. Aluminum incorporation in Ti{sub 1-x}Al{sub x}N films studied by x-ray absorption near-edge structure

    SciTech Connect

    Gago, R.; Redondo-Cubero, A.; Endrino, J. L.; Jimenez, I.; Shevchenko, N.

    2009-06-01

    The local bonding structure of titanium aluminum nitride (Ti{sub 1-x}Al{sub x}N) films grown by dc magnetron cosputtering with different AlN molar fractions (x) has been studied by x-ray absorption near-edge structure (XANES) recorded in total electron yield mode. Grazing incidence x-ray diffraction (GIXRD) shows the formation of a ternary solid solution with cubic structure (c-Ti{sub 1-x}Al{sub x}N) that shrinks with the incorporation of Al and that, above a solubility limit of xapprox0.7, segregation of w-AlN and c-Ti{sub 1-x}Al{sub x}N phases occurs. The Al incorporation in the cubic structure and lattice shrinkage can also be observed using XANES spectral features. However, contrary to GIXRD, direct evidence of w-AlN formation is not observed, suggesting a dominance and surface enrichment of cubic environments. For x>0.7, XANES shows the formation of Ti-Al bonds, which could be related to the segregation of w-AlN. This study shows the relevance of local-order information to assess the atomic structure of Ti{sub 1-x}Al{sub x}N solutions.

  19. Point defects in hexagonal BN, BC{sub 3} and BC{sub x}N compounds studied by x-ray absorption near-edge structure

    SciTech Connect

    Caretti, Ignacio; Jimenez, Ignacio

    2011-07-15

    The generation of point defects in highly oriented pyrolytic boron nitride (HOPBN) after Ar{sup +} ion bombardment in ultrahigh vacuum and subsequent exposure to air was studied by angle-resolved x-ray absorption near edge structure (XANES). The pristine HOPBN showed well-oriented boron nitride (BN) basal planes parallel to the surface, with a negligible amount of defects. Amorphization of the BN structure took place after Ar{sup +} sputtering, as indicated by the broadening of the XANES spectra and significant decrease of the characteristic {pi}* states. Following air exposure, the XANES analysis revealed a spontaneous reorganization of the sample structure. The appearance of four new B1s {pi}* excitonic peaks indicates an oxygen decoration process of the nitrogen vacancies created by ion bombardment. A core-level shift model is presented to support this statement. This model is successfully extended to the case of oxygen substitutional defects in hexagonal BC{sub 3} and BC{sub x}N (0 < x < 4) materials, which can be applied to any B-based sp{sup 2}-bonded honeycomb structure.

  20. Quantitative analysis of deconvolved X-ray absorption near-edge structure spectra: a tool to push the limits of the X-ray absorption spectroscopy technique.

    PubMed

    D'Angelo, Paola; Migliorati, Valentina; Persson, Ingmar; Mancini, Giordano; Della Longa, Stefano

    2014-09-15

    A deconvolution procedure has been applied to K-edge X-ray absorption near-edge structure (XANES) spectra of lanthanoid-containing solid systems, namely, hexakis(dmpu)praseodymium(III) and -gadolinium(III) iodide. The K-edges of lanthanoids cover the energy range 38 (La)-65 (Lu) keV, and the large widths of the core-hole states lead to broadening of spectral features, reducing the content of structural information that can be extracted from the raw X-ray absorption spectra. Here, we demonstrate that deconvolution procedures allow one to remove most of the instrumental and core-hole lifetime broadening in the K-edge XANES spectra of lanthanoid compounds, highlighting structural features that are lost in the raw data. We show that quantitative analysis of the deconvolved K-edge XANES spectra can be profitably used to gain a complete local structural characterization of lanthanoid-containing systems not only for the nearest neighbor atoms but also for higher-distance coordination shells.

  1. Local structure and La L1 and L3-edge XANES spectra of lanthanum complex oxides.

    PubMed

    Asakura, Hiroyuki; Shishido, Tetsuya; Teramura, Kentaro; Tanaka, Tsunehiro

    2014-06-16

    La L1 and L3-edge X-ray absorption near-edge structure (XANES) of various La oxides were classified according to the local configuration of La. We found a correlation between both of the areas of the pre-edge peaks of the La L1-edge XANES spectra and the full width at half-maximum of white line of La L3-edge XANES spectra and the local configuration of La. Theoretical calculation of the XANES spectra and local density of states reveals the difference of La L1 and L3-edge XANES spectra of various La compounds is related to the p-d hybridization of the unoccupied band and broadening of the d band of La induced by the difference of local configuration. In addition, simplified bond angle analysis parameters defined by the angles of the La atom and the two adjacent oxygen atoms are correlated to the pre-edge peak intensity of the La L1-edge XANES spectra. These results indicate that quantitative analysis of La L1 and L3-edge XANES spectra could be an indicator of the local structure of La materials.

  2. Dynamic study of sub-micro sized LiFePO4 cathodes by in-situ tender X-ray absorption near edge structure

    NASA Astrophysics Data System (ADS)

    Wang, Dongniu; Wang, Huixin; Yang, Jinli; Zhou, Jigang; Hu, Yongfeng; Xiao, Qunfeng; Fang, Haitao; Sham, Tsun-Kong

    2016-01-01

    Olivine-type phosphates (LiMPO4, M = Fe, Mn, Co) are promising cathode materials for lithium-ion batteries that are generally accepted to follow first order equilibrium phase transformations. Herein, the phase transformation dynamics of sub-micro sized LiFePO4 particles with limited rate capability at a low current density of 0.14 C was investigated. An in-situ X-ray Absorption Near Edge Structure (XANES) measurement was conducted at the Fe and P K-edge for the dynamic studies upon lithiation and delithiation. Fe K-edge XANES spectra demonstrate that not only lithium-rich intermediate phase LixFePO4 (x = 0.6-0.75), but also lithium-poor intermediate phase LiyFePO4 (y = 0.1-0.25) exist during the charge and discharge, respectively. Furthermore, during charge and discharge, a fluctuation of the FePO4 and LiFePO4 fractions obtained by liner combination fitting around the imaginary phase fractions followed Faraday's law and the equilibrium first-order two-phase transformation versus reaction time is present, respectively. The charging and discharging process has a reversible phase transformation dynamics with symmetric structural evolution routes. P K-edge XANES spectra reveal an enrichment of PF6-1 anions at the surface of the electrode during charging.

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

    PubMed

    Fittschen, U; Guilherme, A; Böttger, S; Rosenberg, D; Menzel, M; Jansen, W; Busker, M; Gotlib, Z P; Radtke, M; Riesemeier, H; Wobrauschek, P; Streli, C

    2016-05-01

    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.

  4. Iron speciation in human cancer cells by K-edge total reflection X-ray fluorescence-X-ray absorption near edge structure analysis

    NASA Astrophysics Data System (ADS)

    Polgári, Zs.; Meirer, F.; Sasamori, S.; Ingerle, D.; Pepponi, G.; Streli, C.; Rickers, K.; Réti, A.; Budai, B.; Szoboszlai, N.; Záray, G.

    2011-03-01

    X-ray absorption near edge structure (XANES) analysis in combination with synchrotron radiation induced total reflection X-ray fluorescence (SR-TXRF) acquisition was used to determine the oxidation state of Fe in human cancer cells and simultaneously their elemental composition by applying a simple sample preparation procedure consisting of pipetting the cell suspension onto the quartz reflectors. XANES spectra of several inorganic and organic iron compounds were recorded and compared to that of different cell lines. The XANES spectra of cells, independently from the phase of cell growth and cell type were very similar to that of ferritin, the main Fe store within the cell. The spectra obtained after CoCl 2 or NiCl 2 treatment, which could mimic a hypoxic state of cells, did not differ noticeably from that of the ferritin standard. After 5-fluorouracil administration, which could also induce an oxidative-stress in cells, the absorption edge position was shifted toward higher energies representing a higher oxidation state of Fe. Intense treatment with antimycin A, which inhibits electron transfer in the respiratory chain, resulted in minor changes in the spectrum, resembling rather the N-donor Fe-α,α'-dipyridyl complex at the oxidation energy of Fe(III), than ferritin. The incorporation of Co and Ni in the cells was followed by SR-TXRF measurements.

  5. Core-hole effect on XANES and electronic structure of minor actinide dioxides with fluorite structure

    NASA Astrophysics Data System (ADS)

    Suzuki, Chikashi; Nishi, Tsuyoshi; Nakada, Masami; Akabori, Mitsuo; Hirata, Masaru; Kaji, Yoshiyuki

    2012-02-01

    The authors investigated theoretically core-hole effects on X-ray absorption near-edge structures (XANES) of Np and Am LIII in neptunium dioxide (NpO2) and americium dioxide (AmO2) with CaF2-type crystal lattices using the all-electron full-potential linearized augmented plane-wave (FP-LAPW) method. The peak creation mechanism of XANES was shown by examining the electronic structures of these oxides, which indicated that core-hole screening was more marked for AmO2 than for NpO2 because of the difference in the charge transfer between these oxides. Furthermore, the results of charge density analysis suggested that the white line was assigned to the quasi-bound state composed of the localized Np d or Am d components and O components, and that the tail structure was created as a result of delocalized standing waves between the Np or Am atoms.

  6. X-ray absorption near edge structure study on Acutolysin-C, a zinc-metalloproteinase from Agkistrodon acutus venom: Insight into the acid-inactive mechanism

    NASA Astrophysics Data System (ADS)

    Zhao, Wei; Chu, Wangsheng; Li, Shujun; Liu, Yiwei; Gao, Bin; Niu, Liwen; Teng, Maikun; Benfatto, Maurizio; Hu, Tiandou; Wu, Ziyu

    2007-11-01

    Acutolysin-C, a snake-venom zinc metalloproteinase, displays a distinct pH-dependent proteolytic activity, which has been tentatively assigned to a structural change of the zinc-containing catalytic center. In this work we compare X-ray absorption near-edge structure (XANES) experimental spectra at the Zn K-edge and theoretical calculations of solutions at different pH values. The experimental data show clear differences confirmed by a best fit using the MXAN procedure. The results show that, when pH decreases from pH 8.0 to pH 3.0, the zinc-coordinating catalytic water molecule moves far from the Glu143 residue that is considered to play an essential role in the proteolytic process. Data suggests that this is the possible mechanism that deactivates the metalloproteinase.

  7. Single shot near edge x-ray absorption fine structure spectroscopy in the laboratory

    SciTech Connect

    Mantouvalou, I. Witte, K.; Martyanov, W.; Jonas, A.; Grötzsch, D.; Kanngießer, B.; Streeck, C.; Löchel, H.; Rudolph, I.; Erko, A.; Stiel, H.

    2016-05-16

    With the help of adapted off-axis reflection zone plates, near edge X-ray absorption fine structure spectra at the C and N K-absorption edge have been recorded using a single 1.2 ns long soft X-ray pulse. The transmission experiments were performed with a laser-produced plasma source in the laboratory rendering time resolved measurements feasible independent on large scale facilities. A resolving power of E/ΔE ∼ 950 at the respective edges could be demonstrated. A comparison of single shot spectra with those collected with longer measuring time proves that all features of the used reference samples (silicon nitrate and polyimide) can be resolved in 1.2 ns. Hence, investigations of radiation sensitive biological specimen become possible due to the high efficiency of the optical elements enabling low dose experiments.

  8. Near-edge X-ray absorption fine structure spectroscopy of MDI and TDI polyurethane polymers

    SciTech Connect

    Urquhart, S.G.; Smith, A.P.; Ade, H.W.; Hitchcock, A.P.; Rightor, E.G.; Lidy, W.

    1999-06-03

    The sensitivity of near-edge X-ray absorption fine structure (NEXAFS) to differences in key chemical components of polyurethane polymers is presented. Carbon is NEXAFS spectra of polyurethane polymers made from 4,4{prime}-methylene di-p-phenylene isocyanate (MDI) and toluene diisocyanate (TDI) isocyanate monomers illustrate that there is an unambiguous spectroscopic fingerprint for distinguishing between MDI-based and TDI-based polyurethane polymers. NEXAFS spectra of MDI and TDI polyurea and polyurethane models show that the urea and carbamate (urethane) linkages in these polymers can be distinguished. The NEXAFS spectroscopy of the polyether component of these polymers is discussed, and the differences between the spectra of MDI and TDI polyurethanes synthesized with polyether polyols of different molecular composition and different molecular weight are presented. These polymer spectra reported herein provide appropriate model spectra to represent the pure components for quantitative microanalysis.

  9. PT L 3 near edge structure of halogen-bridged mixed-valence pt complexes and pd-pt mixed-metal complexes

    NASA Astrophysics Data System (ADS)

    Tanino, H.; Oyanagi, H.; Yamashita, M.; Kobayashi, K.

    1985-03-01

    X-ray absorption near edge structure (XANES) of halogen-bridged mixed-valence Pt complexes and halogen-bridged Pd-Pt mixed-metal complexes have been measured using synchrotron radiation with a high energy resolution. In Pd-Pt mixed metal complexes, we demonstrate that the degree of the valence is estimated from the intensity of the white line at the Pt L 3 edge. In the mixed-valence complexes, the electron system is proved to be the Peierls insulator with a charge density wave of renormalized d electrons of Pt, where the total valence of Pt IV- and Pt 11 is conserved without excess electrons from ligands or anions.

  10. Near-Edge X-ray Absorption Fine Structure Spectroscopy of Diamondoid Thiol Monolayers on Gold

    SciTech Connect

    Willey, T M; Fabbri, J; Lee, J I; Schreiner, P; Fokin, A A; Tkachenko, B A; Fokina, N A; Dahl, J; Carlson, B; Vance, A L; Yang, W; Terminello, L J; van Buuren, T; Melosh, N

    2007-11-27

    Diamondoids, hydrocarbon molecules with cubic-diamond-cage structures, have unique properties with potential value for nanotechnology. The availability and ability to selectively functionalize this special class of nanodiamond materials opens new possibilities for surface-modification, for high-efficiency field emitters in molecular electronics, as seed crystals for diamond growth, or as robust mechanical coatings. The properties of self-assembled monolayers (SAMs) of diamondoids are thus of fundamental interest for a variety of emerging applications. This paper presents the effects of thiol substitution position and polymantane order on diamondoid SAMs on gold using near-edge X-ray absorption fine structure spectroscopy (NEXAFS) and X-ray photoelectron spectroscopy (XPS). A framework to determine both molecular tilt and twist through NEXAFS is presented and reveals highly ordered diamondoid SAMs, with the molecular orientation controlled by the thiol location. C 1s and S 2p binding energies are lower in adamantane thiol than alkane thiols on gold by 0.67 {+-} 0.05 eV and 0.16 {+-} 0.04 eV respectively. These binding energies vary with diamondoid monolayer structure and thiol substitution position, consistent with different amounts of steric strain and electronic interaction with the substrate. This work demonstrates control over the assembly, in particular the orientational and electronic structure, providing a flexible design of surface properties with this exciting new class of diamond clusters.

  11. Three-dimensional local structure of photoexcited Cu diimine complex refined by quantitative XANES analysis.

    SciTech Connect

    Smolentsev, G.; Soldatov, A. V.; Chen, L. X.; Chemical Sciences and Engineering Division; Southern Federal Univ.; Northwestern Univ.

    2008-05-28

    The structural details of [Cu(dmp){sub 2}]{sup +} (dmp = 2,9-dimethyl-1,10-phenanthroline) at its metal-to-ligand charge-transfer (MLCT) excited-state in acetonitrile were extracted using quantitative analysis of Cu K-edge X-ray adsorption near edge structure (XANES). The study combines two techniques: fitting experimental XANES spectra with a multidimensional interpolation approximation, and calculating theoretical XANES spectra with molecular potentials beyond the muffin-tin approximation. The results of the study show that the best fit of the experimental XANES data must include a solvent molecule binding to the Cu with a short Cu-N distance of 2.00 {angstrom}. This confirms that the formation of an exciplex is responsible for the excited-state quenching in coordinating solvents, such as acetonitrile. Moreover, the calculations suggest that the formation of this exciplex state is accompanied by significant rocking distortions of the dmp ligands resulting in a 108{sup o} angle between the N(solvent)-Cu bond and the C{sub 2} symmetry axis of the dmp ligand. This combined approach allows us to extract molecular configurations that would otherwise be missed in a conventional qualitative XANES analysis.

  12. Engineering the Near-Edge Electronic Structure of SnSe through Strains

    NASA Astrophysics Data System (ADS)

    Wu, Yabei; Xia, Weiyi; Gao, Weiwei; Ren, Wei; Zhang, Peihong

    2017-09-01

    The discovery of the unprecedented figure of merit Z T of SnSe has sparked a large number of studies on the fundamental physics of this material and further improvement through guided materials design and optimization. Motivated by its rich chemical-bonding characters, unusual multivalley electronic structure, and the sensitivity of the band-edge states to lattice strains, we carry out accurate quasiparticle calculations for the low-temperature phase SnSe under strains. We illustrate how the band-edge states can be engineered by lattice strains, including the size and the nature of the band gap, the positions of the band extrema in the Brillouin zone, and the control of the number of electron and/or hole valleys. The distinct atomic origin and orientation of the wave functions of the different band-edge states dictates the relative shift in their band energy, enabling active control of the near-edge electronic structure of this material. Our work demonstrates that strain engineering is a promising way to manipulate the low-energy electronic structure of SnSe, which can have profound influences on the optical and transport properties of this material.

  13. Extraction of local coordination structure in a low-concentration uranyl system by XANES.

    PubMed

    Zhang, Linjuan; Zhou, Jing; Zhang, Jianyong; Su, Jing; Zhang, Shuo; Chen, Ning; Jia, Yunpeng; Li, Jiong; Wang, Yu; Wang, Jian Qiang

    2016-05-01

    Obtaining structural information of uranyl species at an atomic/molecular scale is a critical step to control and predict their physical and chemical properties. To obtain such information, experimental and theoretical L3-edge X-ray absorption near-edge structure (XANES) spectra of uranium were studied systematically for uranyl complexes. It was demonstrated that the bond lengths (R) in the uranyl species and relative energy positions (ΔE) of the XANES were determined as follows: ΔE1 = 168.3/R(U-Oax)(2) - 38.5 (for the axial plane) and ΔE2 = 428.4/R(U-Oeq)(2) - 37.1 (for the equatorial plane). These formulae could be used to directly extract the distances between the uranium absorber and oxygen ligand atoms in the axial and equatorial planes of uranyl ions based on the U L3-edge XANES experimental data. In addition, the relative weights were estimated for each configuration derived from the water molecule and nitrate ligand based on the obtained average equatorial coordination bond lengths in a series of uranyl nitrate complexes with progressively varied nitrate concentrations. Results obtained from XANES analysis were identical to that from extended X-ray absorption fine-structure (EXAFS) analysis. XANES analysis is applicable to ubiquitous uranyl-ligand complexes, such as the uranyl-carbonate complex. Most importantly, the XANES research method could be extended to low-concentration uranyl systems, as indicated by the results of the uranyl-amidoximate complex (∼40 p.p.m. uranium). Quantitative XANES analysis, a reliable and straightforward method, provides a simplified approach applied to the structural chemistry of actinides.

  14. Multiple-scattering calculations of the uranium {ital L}{sub 3}-edge x-ray-absorption near-edge structure

    SciTech Connect

    Hudson, E.A.; Rehr, J.J.; Bucher, J.J.

    1995-11-15

    A theoretical study of the uranium {ital L}{sub 3}-edge x-ray absorption near-edge structure (XANES) is presented for several uranium compounds, including oxides, intermetallics, uranyl fluoride, and {alpha}-uranium. Calculations were performed using FEFF6, an {ital ab} {ital initio} multiple-scattering (MS) code that includes the most important features of current theories. The results, which account for both the fine structure {chi} and the atomiclike background {mu}{sub 0} of the absorption coefficient {mu}, are compared to new and previously measured experimental spectra, reavealing very good agreement for most systems. For several compounds, a more detailed theoretical analysis determined the influence of cluster size and scattering order upon the calculated spectra. Results indicate that MS paths and scattering paths that include rather distant atoms make significant contributions for UO{sub 2}, whereas XANES for crystals with lower symmetry and density can be modeled using only shorter single-scattering paths. In most cases, assumption of a screened final state in the calculation gives better agreement with experiment than use of an unscreened final state. The successful modeling of spectra for a variety of different uranium compounds, with differing spectral features, indicates that the semirelativistic treatment of XANES used here is adequate even for heavy elements. The well-known resonance, observed experimentally for uranyl (UO{sub 2}{sup 2+}) compounds {approx}15 eV above the white line, is successfully modeled here for the first time, using multiple-scattering paths within the O-U-O axial bonds. Overlapping muffin-tin spheres were required in the calculation, probably as a result of the short uranyl axial bonds.

  15. Electronic structure and optical properties of 2,5,8,11-tetra-tert-butylperylene polyhedral crystals from x-ray absorption near-edge structure and x-ray excited optical luminescence studies

    NASA Astrophysics Data System (ADS)

    Lv, Jingyu; Ko, Peter J. Y.; Zhang, Ying; Liu, Lijia; Zhang, Xiujuan; Zhang, Xiaohong; Sun, Xuhui; Sham, T. K.

    2011-06-01

    X-ray absorption near-edge structure (XANES) and x-ray excited optical luminescence (XEOL) have been used to study the optical properties of 2,5,8,11-tetra-tert-butylperylene (TBPe) polyhedral crystals with morphology varies from cube to rhombic dodecahedron. Benefit from the high resolution of synchrotron radiation spectroscopy, C 1s to π∗ and σ∗ transitions from different carbon sites in TBPe can be clearly distinguished in the carbon K-edge XANES. XEOL studies reveal that different crystals exhibit multiple emission bands with different branching ratio. It is also found that all the polyhedral crystals exhibit a weak luminescence in the near infrared, which is absent in the powder sample.

  16. Radiation effects in water ice: a near-edge x-ray absorption fine structure study.

    PubMed

    Laffon, C; Lacombe, S; Bournel, F; Parent, Ph

    2006-11-28

    The changes in the structure and composition of vapor-deposited ice films irradiated at 20 K with soft x-ray photons (3-900 eV) and their subsequent evolution with temperatures between 20 and 150 K have been investigated by near-edge x-ray absorption fine structure spectroscopy (NEXAFS) at the oxygen K edge. We observe the hydroxyl OH, the atomic oxygen O, and the hydroperoxyl HO(2) radicals, as well as the oxygen O(2) and hydrogen peroxide H(2)O(2) molecules in irradiated porous amorphous solid water (p-ASW) and crystalline (I(cryst)) ice films. The evolution of their concentrations with the temperature indicates that HO(2), O(2), and H(2)O(2) result from a simple step reaction fuelled by OH, where O(2) is a product of HO(2) and HO(2) a product of H(2)O(2). The local order of ice is also modified, whatever the initial structure is. The crystalline ice I(cryst) becomes amorphous. The high-density amorphous phase (I(a)h) of ice is observed after irradiation of the p-ASW film, whose initial structure is the normal low-density form of the amorphous ice (I(a)l). The phase I(a)h is thus peculiar to irradiated ice and does not exist in the as-deposited ice films. A new "very high density" amorphous phase-we call I(a)vh-is obtained after warming at 50 K the irradiated p-ASW ice. This phase is stable up to 90 K and partially transforms into crystalline ice at 150 K.

  17. Polarized XANES Monitors Femtosecond Structural Evolution of Photoexcited Vitamin B12

    DOE PAGES

    Miller, Nicholas A.; Deb, Aniruddha; Alonso-Mori, Roberto; ...

    2017-01-30

    Ultrafast, polarization-selective time-resolved X-ray absorption near-edge structure (XANES) was used to characterize the photochemistry of vitamin B12, cyanocobalamin (CNCbl), in solution. Cobalamins are important biological cofactors involved in methyl transfer, radical rearrangement, and light-activated gene regulation, while also holding promise as light-activated agents for spatiotemporal controlled delivery of therapeutics. We introduce polarized femtosecond XANES, combined with UV–visible spectroscopy, to reveal sequential structural evolution of CNCbl in the excited electronic state. Femtosecond polarized XANES provides the crucial structural dynamics link between computed potential energy surfaces and optical transient absorption spectroscopy. Polarization selectivity can be used to uniquely identify electronic contributions andmore » structural changes, even in isotropic samples when well-defined electronic transitions are excited. Our XANES measurements reveal that the structural changes upon photoexcitation occur mainly in the axial direction, where elongation of the axial Co–CN bond and Co–NIm bond on a 110 fs time scale is followed by corrin ring relaxation on a 260 fs time scale. In conclusion, these observations expose features of the potential energy surfaces controlling cobalamin reactivity and deactivation.« less

  18. Polarized XANES Monitors Femtosecond Structural Evolution of Photoexcited Vitamin B12.

    PubMed

    Miller, Nicholas A; Deb, Aniruddha; Alonso-Mori, Roberto; Garabato, Brady D; Glownia, James M; Kiefer, Laura M; Koralek, Jake; Sikorski, Marcin; Spears, Kenneth G; Wiley, Theodore E; Zhu, Diling; Kozlowski, Pawel M; Kubarych, Kevin J; Penner-Hahn, James E; Sension, Roseanne J

    2017-02-08

    Ultrafast, polarization-selective time-resolved X-ray absorption near-edge structure (XANES) was used to characterize the photochemistry of vitamin B12, cyanocobalamin (CNCbl), in solution. Cobalamins are important biological cofactors involved in methyl transfer, radical rearrangement, and light-activated gene regulation, while also holding promise as light-activated agents for spatiotemporal controlled delivery of therapeutics. We introduce polarized femtosecond XANES, combined with UV-visible spectroscopy, to reveal sequential structural evolution of CNCbl in the excited electronic state. Femtosecond polarized XANES provides the crucial structural dynamics link between computed potential energy surfaces and optical transient absorption spectroscopy. Polarization selectivity can be used to uniquely identify electronic contributions and structural changes, even in isotropic samples when well-defined electronic transitions are excited. Our XANES measurements reveal that the structural changes upon photoexcitation occur mainly in the axial direction, where elongation of the axial Co-CN bond and Co-NIm bond on a 110 fs time scale is followed by corrin ring relaxation on a 260 fs time scale. These observations expose features of the potential energy surfaces controlling cobalamin reactivity and deactivation.

  19. Effects of strain relaxation in Pr0.67Sr0.33MnO3 films probed by polarization dependent X-ray absorption near edge structure

    DOE PAGES

    zhang, Bangmin; Chen, Jingsheng; Venkatesan, T.; ...

    2016-01-28

    In this study, the Mn K edge X-ray absorption near edge structure (XANES) of Pr0.67Sr0.33MnO3 films with different thicknesses on (001) LaAlO3 substrate were measured, and the effects of strain relaxation on film properties were investigated. The films experienced in-plane compressive strain and out-of-plane tensile strain. Strain relaxation evolved with the film thickness. In the polarization dependent XANES measurements, the in-plane (parallel) and out-of-plane (perpendicular) XANES spectrocopies were anisotropic with different absorption energy Er. The resonance energy Er along two directions shifted towards each other with increasing film thickness. Based on the X-ray diffraction results, it was suggested that themore » strain relaxation weakened the difference of the local environment and probability of electronic charge transfer (between Mn 3d and O 2p orbitals) along the in-plane and out-of-plane directions, which was responsible for the change of Er. XANES is a useful tool to probe the electronic structures, of which the effects on magnetic properties with the strain relaxation was also been studied.« less

  20. Effects of strain relaxation in Pr0.67Sr0.33MnO3 films probed by polarization dependent X-ray absorption near edge structure

    SciTech Connect

    zhang, Bangmin; Chen, Jingsheng; Venkatesan, T.; Sun, Cheng -Jun; Heald, Steve M.; Chow, Gan Moog; Yang, Ping; Chi, Xiao; Lin, Weinan

    2016-01-28

    In this study, the Mn K edge X-ray absorption near edge structure (XANES) of Pr0.67Sr0.33MnO3 films with different thicknesses on (001) LaAlO3 substrate were measured, and the effects of strain relaxation on film properties were investigated. The films experienced in-plane compressive strain and out-of-plane tensile strain. Strain relaxation evolved with the film thickness. In the polarization dependent XANES measurements, the in-plane (parallel) and out-of-plane (perpendicular) XANES spectrocopies were anisotropic with different absorption energy Er. The resonance energy Er along two directions shifted towards each other with increasing film thickness. Based on the X-ray diffraction results, it was suggested that the strain relaxation weakened the difference of the local environment and probability of electronic charge transfer (between Mn 3d and O 2p orbitals) along the in-plane and out-of-plane directions, which was responsible for the change of Er. XANES is a useful tool to probe the electronic structures, of which the effects on magnetic properties with the strain relaxation was also been studied.

  1. Temperature dependent electronic structure of Pr{sub 0.67}Sr{sub 0.33}MnO{sub 3} film probed by X-ray absorption near edge structure

    SciTech Connect

    Zhang, Bangmin; Sun, Cheng-Jun E-mail: msecgm@nus.edu.sg; Heald, Steve M.; Chen, Jing-Sheng; Moog Chow, Gan E-mail: msecgm@nus.edu.sg; Venkatesan, T.

    2014-05-07

    The Mn K edge X-ray absorption near edge structures (XANES) of Pr{sub 0.67}Sr{sub 0.33}MnO{sub 3} film (100 nm) on (001) LaAlO{sub 3} substrate was measured at different temperatures to probe the MnO{sub 6} octahedron distortion and corresponding electronic structure. The absorption of high temperature paramagnetic-insulator phase differed from that of the low temperature ferromagnetic-metal phase. The temperature-dependent absorption intensity of Mn K edge XANES was correlated with the relaxation of distorted MnO{sub 6} octahedron, which changed the crystal field acting on the Mn site and the related electronic structure and properties. At low temperature, the splitting of Mn majority e{sub g} orbitals decreased and the density of states above the Fermi level increased in the relaxed MnO{sub 6} octahedron, as reflected by a wider separation between two sub-peaks in the pre-edge XANES spectra.

  2. Chemical forms of sulfur in geological and archeological asphaltenes from Middle East, France, and Spain determined by sulfur K- and L-edge X-ray absorption near-edge structure spectroscopy

    NASA Astrophysics Data System (ADS)

    Sarret, Géraldine; Connan, Jacques; Kasrai, Masoud; Bancroft, G. Michael; Charrié-Duhaut, Armelle; Lemoine, Sylvie; Adam, Pierre; Albrecht, Pierre; Eybert-Bérard, Laurent

    1999-11-01

    Asphaltene samples extracted from archeological and geological bitumens from the Middle East, France, and Spain were studied by sulfur K- and L-edge X-ray absorption near-edge structure (XANES) spectroscopy in combination with isotopic analyses (δ 13C and δD). Within each series, the samples were genetically related by their δ 13C values. The gross and elemental composition and the δD values were used to characterize the weathering state of the samples. Sulfur K- and L-edge XANES results show that in all the samples, dibenzothiophenes are the dominant forms of sulfur. In the least oxidized asphaltenes, minor species include disulfides, alkyl and aryl sulfides, and sulfoxides. With increasing alteration the proportion of oxidized sulfur (sulfoxides, sulfones, sulfonates and sulfates) increases, whereas the disulfide and sulfide content decreases. This evolution is observed in all the series, regardless of the origin of the asphaltenes. This work illustrates the advantages of XANES spectroscopy as a selective probe for determining sulfur speciation in natural samples. It also shows that S K- and L-edge XANES spectroscopy are complementary for identifying the oxidized and reduced forms of sulfur, respectively.

  3. Geometric Structure Determination of N694C Lipoxygenase: A Comparative XAS Near-Edge and EXAFS Study

    PubMed Central

    Sarangi, Ritimukta; Hocking, Rosalie K.; Neidig, Michael L.; Benfatto, Maurizio; Holman, Theodore R; Solomon, Edward I.; Hodgson, Keith O.; Hedman, Britt

    2008-01-01

    The mononuclear non-heme iron active site of N694C soybean lipoxygenase (sLO1) has been investigated in the resting ferrous form using a combination of Fe K-pre-edge, near-edge (using MXAN full multiple-scattering approach) and EXAFS methods. The results indicate that the active site is six coordinate (6C) with a large perturbation in the first shell bond distances in comparison to the more ordered octahedral site in wild type sLO1. Upon mutation of the asparigine to cystiene, the short Fe-O interaction with asparigine is replaced by a weak Fe-(H2O) which leads to a distorted 6C site with an effective 5C ligand field. In addition, it is shown that near-edge multiple scattering analysis can give important three-dimensional structural information, which usually cannot be accessed using EXAFS analysis. It is further shown that relative to EXAFS, near-edge analysis is more sensitive to partial coordination numbers and can be potentially used as a tool for structure determination in a mixture of chemical species. PMID:18656914

  4. Studies on the Structural Transformation of Pt Clusters with Adsorbed Hydrogen on α-Al2O3(0001) Using Multiple Scattering Approach to Pt L3-edge Polarized X-Ray Absorption Near Edge Structure Spectra for the Pt Cluster

    NASA Astrophysics Data System (ADS)

    Ohtani, Kunihiro

    1998-03-01

    The X-ray absorption near edge structure (XANES) or the Extended X-ray absorption fine structure (EXAFS) study with polarization dependence is useful for determining the structures of the metal clusters. We have calculated Pt L3-edge XANES spectra for various structures of Pt clusters with adsorbed hydrogen, such as the one-layer-thick raft, and the hemispherical and spherical structures on α-Al2O3(0001), using the full multiple scattering approach. Comparison of the calculated results with the experimental results have yielded important information. With an increase in the spherically symmetric character of Pt clusters, the influence of Pt-support interaction on the XANES spectra decreases, that is, the hydrogen-Pt interaction plays a dominant role in such cases. We expect that Pt clusters with the one-layer-thick raft, or hemispherical structures are on the top site of surface oxygen atoms.

  5. X-ray absorption near-edge structure study on the configuration of Cu 2+ /histidine complexes at different pH values

    NASA Astrophysics Data System (ADS)

    Mei-Juan, Yu; Yu, Wang; Wei, Xu

    2016-04-01

    The local configurations around metal ions in metalloproteins are of great significance for understanding their biological functions. Cu2+/histidine (His) is a typical complex existing in many metalloproteins and plays an important role in lots of physiological functions. The three-dimensional (3D) structural configurations of Cu2+/His complexes at different pH values (2.5, 6.5, and 8.5) are quantitatively determined by x-ray absorption near-edge structure (XANES). Generally Cu2+/His complex keeps an octahedral configuration consisting of oxygen atoms from water molecules and oxygen or nitrogen atoms from histidine molecules coordinated around Cu2+. It is proved in this work that the oxygen atoms from water molecules, when increasing the pH value from acid to basic value, are gradually substituted by the Ocarboxyl, Nam, and Nim from hisitidine molecules. Furthermore, the symmetries of Cu2+/His complexes at pH 6.5 and pH 8.5 are found to be lower than at pH 2.5. Project supported by the National Natural Science Foundation of China (Grant No. 11205186).

  6. Full-Field Calcium K-Edge X-ray Absorption Near-Edge Structure Spectroscopy on Cortical Bone at the Micron-Scale: Polarization Effects Reveal Mineral Orientation.

    PubMed

    Hesse, Bernhard; Salome, Murielle; Castillo-Michel, Hiram; Cotte, Marine; Fayard, Barbara; Sahle, Christoph J; De Nolf, Wout; Hradilova, Jana; Masic, Admir; Kanngießer, Birgit; Bohner, Marc; Varga, Peter; Raum, Kay; Schrof, Susanne

    2016-04-05

    Here, we show results on X-ray absorption near edge structure spectroscopy in both transmission and X-ray fluorescence full-field mode (FF-XANES) at the calcium K-edge on human bone tissue in healthy and diseased conditions and for different tissue maturation stages. We observe that the dominating spectral differences originating from different tissue regions, which are well pronounced in the white line and postedge structures are associated with polarization effects. These polarization effects dominate the spectral variance and must be well understood and modeled before analyzing the very subtle spectral variations related to the bone tissue variations itself. However, these modulations in the fine structure of the spectra can potentially be of high interest to quantify orientations of the apatite crystals in highly structured tissue matrices such as bone. Due to the extremely short wavelengths of X-rays, FF-XANES overcomes the limited spatial resolution of other optical and spectroscopic techniques exploiting visible light. Since the field of view in FF-XANES is rather large the acquisition times for analyzing the same region are short compared to, for example, X-ray diffraction techniques. Our results on the angular absorption dependence were verified by both site-matched polarized Raman spectroscopy, which has been shown to be sensitive to the orientation of bone building blocks and by mathematical simulations of the angular absorbance dependence. As an outlook we further demonstrate the polarization based assessment of calcium-containing crystal orientation and specification of calcium in a beta-tricalcium phosphate (β-Ca3(PO4)2 scaffold implanted into ovine bone. Regarding the use of XANES to assess chemical properties of Ca in human bone tissue our data suggest that neither the anatomical site (tibia vs jaw) nor pathology (healthy vs necrotic jaw bone tissue) affected the averaged spectral shape of the XANES spectra.

  7. Sulfur species in source rock bitumen before and after hydrous pyrolysis determined by X-ray absorption near-edge structure

    USGS Publications Warehouse

    Bolin, Trudy B.; Birdwell, Justin E.; Lewan, Michael; Hill, Ronald J.; Grayson, Michael B.; Mitra-Kirtley, Sudipa; Bake, Kyle D.; Craddock, Paul R.; Abdallah, Wael; Pomerantz, Andrew E.

    2016-01-01

    The sulfur speciation of source rock bitumen (chloroform-extractable organic matter in sedimentary rocks) was examined using sulfur K-edge X-ray absorption near-edge structure (XANES) spectroscopy for a suite of 11 source rocks from around the world. Sulfur speciation was determined for both the native bitumen in thermally immature rocks and the bitumen produced by thermal maturation of kerogen via hydrous pyrolysis (360 °C for 72 h) and retained within the rock matrix. In this study, the immature bitumens had higher sulfur concentrations than those extracted from samples after hydrous pyrolysis. In addition, dramatic and systematic evolution of the bitumen sulfur moiety distributions following artificial thermal maturation was observed consistently for all samples. Specifically, sulfoxide sulfur (sulfur double bonded to oxygen) is abundant in all immature bitumen samples but decreases substantially following hydrous pyrolysis. The loss in sulfoxide sulfur is associated with a relative increase in the fraction of thiophene sulfur (sulfur bonded to aromatic carbon) to the extent that thiophene is the dominant sulfur form in all post-pyrolysis bitumen samples. This suggests that sulfur moiety distributions might be used for estimating thermal maturity in source rocks based on the character of the extractable organic matter.

  8. New methodological approach for the vanadium K-edge X-ray absorption near-edge structure interpretation: application to the speciation of vanadium in oxide phases from steel slag.

    PubMed

    Chaurand, Perrine; Rose, Jérôme; Briois, Valérie; Salome, Murielle; Proux, Olivier; Nassif, Vivian; Olivi, Luca; Susini, Jean; Hazemann, Jean-Louis; Bottero, Jean-Yves

    2007-05-17

    This paper presents a comparison between several methods dedicated to the interpretation of V K-edge X-ray absorption near-edge structure (XANES) features. V K-edge XANES spectra of several V-bearing standard compounds were measured in an effort to evaluate advantages and limits of each method. The standard compounds include natural minerals and synthetic compounds containing vanadium at various oxidation state (from +3 to +5) and in different symmetry (octahedral, tetrahedral, and square pyramidal). Correlations between normalized pre-edge peak area and its centroid position have been identified as the most reliable method for determining quantitative and accurate redox and symmetry information for vanadium. This methodology has been previously developed for the Fe K edge. It is also well adapted for the V K edge and is less influenced by the standard choice than other methods. This methodology was applied on an "environmental sample," i.e., a well-crystallized leached steel slag containing vanadium as traces. Micro-XANES measurements allowed elucidating the microdistribution of vanadium speciation in leached steel slag. The vanadium exhibits an important evolution from the unaltered to the altered phases. Its oxidation state increases from +3 to +5 together with the decrease of its symmetry (from octahedral to tetrahedral).

  9. Near-edge x-ray absorption fine structure measurements using a laboratory-scale XUV source

    NASA Astrophysics Data System (ADS)

    Peth, Christian; Barkusky, Frank; Mann, Klaus

    2008-05-01

    We present a compact setup for near-edge x-ray absorption spectroscopy at the carbon K-edge based on a laser-driven plasma source. To generate the required broad-band emission in the spectral range of the 'water window' (λ = 2.2-4.4 nm) a krypton gas puff target was used. The table-top setup consisting basically of the laser-plasma source and a flat-field spectrometer can be used for near-edge x-ray absorption fine structure experiments in transmission as well as reflection under grazing incidence conditions (ReflEXAFS). The latter method offers the advantage that thin film preparation is not necessary and that the surface sensitivity is strongly enhanced. The results obtained for thin polymer films show good agreement with synchrotron data. Furthermore, we use the ReflEXAFS method to investigate changes in the chemical composition of PMMA induced by extreme ultraviolet (EUV) radiation. The spectra indicate a loss of the carbonyl functional group upon irradiation as well as crosslinking effects at high EUV radiation doses.

  10. XANES spectra of metal phytate compounds

    USDA-ARS?s Scientific Manuscript database

    Metal speciation of phosphate and metal-phosphate interactions can be investigated by molecular-scale X-ray absorption near edge structure (XANES) spectroscopic analysis. Much of the effort, however, has been focused on inorganic P speciation (i. e. metal-orthophosphate interactions). Phytate (inosi...

  11. Solvation structure of Zn(2+) and Cu(2+) ions in acetonitrile: a combined EXAFS and XANES study.

    PubMed

    D'Angelo, Paola; Migliorati, Valentina

    2015-03-12

    The solvation structure of Zn(2+) and Cu(2+) in acetonitrile has been determined by a combined approach using both X-ray absorption near edge structure (XANES) and the extended X-ray absorption fine structure (EXAFS) spectroscopy. For the former cation, an octahedral geometry of the acetonitrile solvate complex has been found with a Zn-N distance of 2.12(1) Å. For the Cu(2+) solvates the EXAFS technique has been found to be not able to provide a conclusive determination of the coordination numbers and polyhedral environment, while the analysis of the XANES spectra unambiguously shows the existence of an axially elongated square pyramidal coordination, ruling out the previously proposed octahedral Jahn-Teller (JT) distorted geometry. The Cu-N distances obtained are 2.00(1) and 2.28(2) Å for the equatorial and axial ligands, respectively, and the EXAFS and XANES techniques find values of the bond distances in good agreement. The XANES technique has proven to be extremely powerful in providing a reliable resolution of solution structure for dynamic ion complexes.

  12. Near Edge X-Ray Absorption Fine Structure Spectroscopy with X-Ray Free-Electron Lasers

    SciTech Connect

    Bernstein, D.P.; Acremann, Y.; Scherz, A.; Burkhardt, M.; Stohr, J.; Beye, M.; Schlotter, W.F.; Beeck, T.; Sorgenfrei, F.; Pietzsch, A.; Wurth, W.; Fohlisch, A.; /Hamburg U.

    2009-12-11

    We demonstrate the feasibility of Near Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy on solids by means of femtosecond soft x-ray pulses from a free-electron laser (FEL). Our experiments, carried out at the Free-Electron Laser at Hamburg (FLASH), used a special sample geometry, spectrographic energy dispersion, single shot position-sensitive detection and a data normalization procedure that eliminates the severe fluctuations of the incident intensity in space and photon energy. As an example we recorded the {sup 3}D{sub 1} N{sub 4,5}-edge absorption resonance of La{sup 3+}-ions in LaMnO{sub 3}. Our study opens the door for x-ray absorption measurements on future x-ray FEL facilities.

  13. Theory and the Experimental Confirmation of the Local Electronic Structure of the Multiferroic PbVO3, a New Member of PbTiO3 Family, Studied by X-ray Near Edge Absorption Structure: I

    NASA Astrophysics Data System (ADS)

    Alam, Sher; Ahmad, Javed; Ohya, Yutaka; Dong, Chungli; Hsu, Chih-Chin; Lee, Jyh-Fu; Mutsuhiro, Shima; Miki, Kazuki; Al-Deyab, Salem S.; Guo, Jinghua; Nishimura, Chikashi

    2012-07-01

    Recently, an interesting multiferroic system PbVO3 [A. A. Belik et al.: Chem. Mater. 17 (2005) 269] has been successfully prepared using a high-pressure and high-temperature technique. The crystallographic features of PbVO3 were reported. In this note, we concentrate on the theoretical and the experimental X-ray near edge absorption structure (XANES) spectra by considering the K-edge of Vanadium. The tetragonality (c/a=1.229 at 300 K) of PbVO3 is the largest in the PbTiO3 family of compounds. Thus, one is led naturally to examine the effects of the changes in the tetragonality and axial oxygen position on the electronic structure (i.e., XANES spectrum). We study these effects in two ways. At a given temperature, we vary the tetragonality and the axial oxygen position, and quantify the changes in terms of the XANES difference spectrum. Secondly, we compute the XANES spectra at three different temperatures, namely, 90, 300, and 530 K, and quantify the changes in terms of the difference spectrum. We note that in this compound the tetragonality increases almost monotonically with temperature from 12 to 570 K, without transition to the cubic phase under ambient pressure. A key objective of the current investigation is to gain an understanding of various absorption features in the vicinity of the K-edge of V, in terms of valence, local site symmetry, local coordination geometry, local bond distances, charge transfer, and local projected density of states. We consider both the polarized and unpolarized XANES spectra, theoretically. The experiment was performed on the polycrystalline material after the theoretical investigation. In short, we have performed a local electronic study, theoretical as well as experimental, which complements the crystallographic features reported recently for PbVO3. The local electronic study given here is supplemented and enhanced by the O-K edge results indicated in the accompanying Paper II, which gives both the experimental and theoretical

  14. Geometric Structure Determination of N694C Lipoxygenase: a Comparative Near-Edge X-Ray Absorption Spectroscopy And Extended X-Ray Absorption Fine Structure Study

    SciTech Connect

    Sarangi, R.; Hocking, R.K.; Neidig, M.L.; Benfatto, M.; Holman, T.R.; Solomon, E.I.; Hodgson, K.O.; Hedman, B.

    2009-05-27

    The mononuclear nonheme iron active site of N694C soybean lipoxygenase (sLO1) has been investigated in the resting ferrous form using a combination of Fe-K-pre-edge, near-edge (using the minuit X-ray absorption near-edge full multiple-scattering approach), and extended X-ray absorption fine structure (EXAFS) methods. The results indicate that the active site is six-coordinate (6C) with a large perturbation in the first-shell bond distances in comparison to the more ordered octahedral site in wild-type sLO1. Upon mutation of the asparigine to cystiene, the short Fe-O interaction with asparigine is replaced by a weak Fe-(H{sub 2}O), which leads to a distorted 6C site with an effective 5C ligand field. In addition, it is shown that near-edge multiple scattering analysis can give important three-dimensional structural information, which usually cannot be accessed using EXAFS analysis. It is further shown that, relative to EXAFS, near-edge analysis is more sensitive to partial coordination numbers and can be potentially used as a tool for structure determination in a mixture of chemical species.

  15. Probing the structure of iron at extreme conditions by X-ray absorption near-edge structure calculations

    NASA Astrophysics Data System (ADS)

    Raji, A. T.; Scandolo, S.; Härting, M.; Britton, D. T.

    2013-03-01

    We present the K-edge X-ray absorption near edge spectra of hexagonal-closed packed iron at pressure and temperature conditions relevant to Earth's mantle conditions. The calculated spectra have been obtained using the first-principles scheme based on the continued-fraction approach and norm-conserving pseudopotentials. The atomic configurations used for the X-ray absorption near edge spectroscopy calculations were obtained from classical molecular dynamics simulations, using an optimized embedded-atom potential. We compare our calculated spectra to recently available experiment results (R. Boehler, H.G. Musshoff, R. Ditz, G. Aquilanti, and A. Trapananti, Rev. Sci. Instrum. 80 (2009), pp. 045103-045108) and identify the main features of the spectra that may indicate onset of melting in iron.

  16. A New Look at the Structural and Magnetic Properties of Potassium Neptunate K2NpO4 Combining XRD, XANES Spectroscopy, and Low-Temperature Heat Capacity

    PubMed Central

    2017-01-01

    The physicochemical properties of the potassium neptunate K2NpO4 have been investigated in this work using X-ray diffraction, X-ray absorption near edge structure (XANES) spectroscopy at the Np-L3 edge, and low-temperature heat capacity measurements. A Rietveld refinement of the crystal structure is reported for the first time. The Np(VI) valence state has been confirmed by the XANES data, and the absorption edge threshold of the XANES spectrum has been correlated to the Mössbauer isomer shift value reported in the literature. The standard entropy and heat capacity of K2NpO4 have been derived at 298.15 K from the low-temperature heat capacity data. The latter suggest the existence of a magnetic ordering transition around 25.9 K, most probably of the ferromagnetic type. PMID:28437069

  17. O K-energy loss near-edge structure change induced by tantalum impurity in monoclinic hafnium oxide

    SciTech Connect

    Yang, Mino; Baik, Hionsuck; Ivanovskaya, Viktoria; Colliex, Christian; Benayad, Anass

    2011-03-01

    The present paper reports the energy loss near-edge structure (ELNES) study of monoclinic HfO{sub 2} (m-HfO{sub 2}) and tantalum doped m-HfO{sub 2} (Ta{sub 0.1}Hf{sub 0.9}O{sub 2}) thin films prepared by radio frequency magnetron co-sputtering method. A change in the O K-ELNES spectra was observed as the amount of dopant increases. In order to precise the common features and the differences as a function of Ta defect nature (substitutional or interstitial) in HfO{sub 2}, the O K-ELNES were commented with respect to density functional theory calculations implemented in Vienna ab initio simulation package code. The calculated Ta doped HfO{sub 2} band structure showed that substitutional tantalum is the dominant defect and the spectral differences between doped and non-doped HfO{sub 2} are mainly originated from the change in the local cation distribution around the oxygen atoms.

  18. Effect of the van der Waals interaction on the electron energy-loss near edge structure theoretical calculation.

    PubMed

    Katsukura, Hirotaka; Miyata, Tomohiro; Tomita, Kota; Mizoguchi, Teruyasu

    2017-07-01

    The effect of the van der Waals (vdW) interaction on the simulation of the electron energy-loss near edge structure (ELNES) by a first-principles band-structure calculation is reported. The effect of the vdW interaction is considered by the Tkatchenko-Scheffler scheme, and the change of the spectrum profile and the energy shift are discussed. We perform calculations on systems in the solid, liquid and gaseous states. The transition energy shifts to lower energy by approximately 0.1eV in the condensed (solid and liquid) systems by introducing the vdW effect into the calculation, whereas the energy shift in the gaseous models is negligible owing to the long intermolecular distance. We reveal that the vdW interaction exhibits a larger effect on the excited state than the ground state owing to the presence of an excited electron in the unoccupied band. Moreover, the vdW effect is found to depend on the local electron density and the molecular coordination. In addition, this study suggests that the detection of the vdW interactions exhibited within materials is possible by a very stable and high resolution observation. Copyright © 2016 Elsevier B.V. All rights reserved.

  19. Near-edge X-ray absorption fine-structure spectroscopy of naphthalene diimide-thiophene co-polymers

    SciTech Connect

    Gann, Eliot; McNeill, Christopher R.; Szumilo, Monika; Sirringhaus, Henning; Sommer, Michael; Maniam, Subashani; Langford, Steven J.; Thomsen, Lars

    2014-04-28

    Near-edge X-ray absorption fine-structure (NEXAFS) spectroscopy is an important tool for probing the structure of conjugated polymer films used in organic electronic devices. High-performance conjugated polymers are often donor-acceptor co-polymers which feature a repeat unit with multiple functional groups. To facilitate better application of NEXAFS spectroscopy to the study of such materials, improved understanding of the observed NEXAFS spectral features is required. In order to examine how the NEXAFS spectrum of a donor-acceptor co-polymer relates to the properties of the sub-units, a series of naphthalene diimide-thiophene-based co-polymers have been studied where the nature and length of the donor co-monomer has been systematically varied. The spectra of these materials are compared with that of a thiophene homopolymer and naphthalene diimide monomer enabling peak assignment and the influence of inter-unit electronic coupling to be assessed. We find that while it is possible to attribute peaks within the π* manifold as arising primarily due to the naphthalene diimide or thiophene sub-units, very similar dichroism of these peaks is observed indicating that it may not be possible to separately probe the molecular orientation of the separate sub-units with carbon K-edge NEXAFS spectroscopy.

  20. Parameters Influencing Sulfur Speciation in Environmental Samples Using Sulfur K-Edge X-Ray Absorption Near-Edge Structure

    PubMed Central

    Pongpiachan, Siwatt; Thumanu, Kanjana; Kositanont, Charnwit; Schwarzer, Klaus; Prietzel, Jörg; Hirunyatrakul, Phoosak; Kittikoon, Itthipon

    2012-01-01

    This paper aims to enhance the credibility of applying the sulfur K-edge XANES spectroscopy as an innovative “fingerprint” for characterizing environmental samples. The sensitivities of sulfur K-edge XANES spectra of ten sulfur compound standards detected by two different detectors, namely, Lytle detector (LyD) and Germanium detector (GeD), were studied and compared. Further investigation on “self-absorption” effect revealed that the maximum sensitivities of sulfur K-edge XANES spectra were achieved when diluting sulfur compound standards with boron nitride (BN) at the mixing ratio of 0.1%. The “particle-size” effect on sulfur K-edge XANES spectrum sensitivities was examined by comparing signal-to-noise ratios of total suspended particles (TSP) and particulate matter of less than 10 millionths of a meter (PM10) collected at three major cities of Thailand. The analytical results have demonstrated that the signal-to-noise ratios of sulfur K-edge XANES spectra were positively correlated with sulfate content in aerosols and negatively connected with particle sizes. The combination of hierarchical cluster analysis (HCA) and principal component analysis (PCA) has proved that sulfur K-edge XANES spectrum can be used to characterize German terrestrial soils and Andaman coastal sediments. In addition, this study highlighted the capability of sulfur K-edge XANES spectra as an innovative “fingerprint” to distinguish tsunami backwash deposits (TBD) from typical marine sediments (TMS). PMID:23193498

  1. Obtaining X-ray absorption near-edge structure for transition metal oxides via the Bethe-Salpeter equation

    NASA Astrophysics Data System (ADS)

    Liang, Yufeng; Vinson, John; Pemmaraju, Sri; Shirley, Eric; Prendergast, David

    Transition metal oxides are an important class of materials featured with strongly correlated effects. Most interesting and yet to-be-unveiled physics is associated with the metal 3d orbitals, which can be probed by X-ray absorption near-edge spectroscopy. A thorough interpretation of the x-ray spectroscopy is often accompanied with first-principles simulations of structures, electronic properties and the corresponding x-ray spectra. However, the simulation for TMOs is particularly challenging with the localized 3d orbitals. Most previous studies relied on the ground-state calculations without the core-hole as a compromise. Other treated the excited atom as a charged impurity but the calculated spectra turn out to be even more deviated from experiments. Here, we present the first study for the O K-edge for several typical TMOs via solving the Bethe-Salpeter equation (BSE). We have found that electron-core-hole interactions can alter the absorption spectra significantly. Our study helps to disentangle core-hole effects from the intrinsic electron correlations and hence facilitates the development of more advanced many-electron theories.

  2. The use of C-near edge X-ray absorption fine structure spectroscopy for the elaboration of chemistry in lignocellulosics

    Treesearch

    Lucian A. Lucia; Hiroki Nanko; Alan W. Rudie; Doug G. Mancosky; Sue Wirick

    2006-01-01

    The research presented elucidates the oxidation chemistry occurring in hydrogen peroxide bleached kraft pulp fibers by employing carbon near edge x-ray absorption fine structure spectroscopy (C-NEXAFS). C-NEXAFS is a soft x-ray technique that selectively interrogates atomic moieties using photoelectrons (Xrays) of variable energies. The X1A beam line at the National...

  3. Novel visualization studies of lignocellulosic oxidation chemistry by application of C-near edge X-ray absorption fine structure spectroscopy

    Treesearch

    Douglas G. Mancosky; Lucian A. Lucia; Hiroki Nanko; Sue Wirick; Alan W. Rudie; Robert Braun

    2005-01-01

    The research presented herein is the first attempt to probe the chemical nature of lignocellulosic samples by the application of carbon near edge X-ray absorption fine structure spectroscopy (C-NEXAFS). C-NEXAFS is a soft X-ray technique that principally provides selective interrogation of discrete atomic moieties using photoelectrons of variable energies. The X1A beam...

  4. XANES: Solid state mineral analysis

    NASA Astrophysics Data System (ADS)

    Bell, Peter M.

    Researchers in the field of mineral physics have become aware of new analytical techniques for studying the electronic structure of solids; one such technique is the X ray absorption fine structure (XFAS) method. In this technique the fine structure of the X ray K-edge, for example, can b e employed as a critical probe of t h e intricacies of a crystal structure (P. A. Lee, P. H. Citrin, P. Eisenberger, and B. M. Kincaid, Rev. Mod. Phys., 53, 799, 1981).A similar, related technique, X ray absorption near-edge spectroscopy (XANES), is a relatively unknown method of studying the electronic structure of solids. XANES is new, and due to its complex nature, data on all but very simple solids have not yet been applied rigorously. Among the first XANES results on minerals is the recent study reported by G. Knapp, B. Veal, H. Pan, and T. Klipper (Solid State Comm. 44, 1343, 1982) on perovskites, magnesiowustites, and other 3d oxides in the zircon and spinel groups. The interpretation of these results is still semiquantitative, being based on ground state and basic selection rule considerations. The results show, however, a strong correlation between near-edge spectra and crystal structure.

  5. Calculation and Interpretation of XANES

    NASA Astrophysics Data System (ADS)

    Ravel, B.; Rehr, J. J.

    1997-03-01

    A real space multiple-scattering (MS) approach for ab initio calculations and for the interpretation of x-ray absorption near edge structure (XANES) is presented. The method is based on full-MS calculations of the electron density matrix ρ(E). Our approach uses the exact Rehr-Albers [Phys. Rev. B, 41, 8139, (1990)] separable representation of the free propagator G together with atomic scattering t-matrices from uc(FEFF7) [Phys. Rev. B52, 2995 (1995)]. This method yields a parallel treatment both of XANES and local electronic structure, including local densities of states (LDOS) and charge transfer. With this method XANES for large clusters can be calculated efficiently. A scattering theoretic interpretation is presented using the separation of both XANES and LDOS into central site and scattering parts, i.e., μ(E)=μ_c(E)[1+\\chi(E)] and ρ(E)=ρ_c(E)[1+\\chi(E)], where \\chi(E) is the XAFS function and both μc and ρc are smooth backgrounds. Charge transfer is interpreted in terms of the scattering part \\chi, and hence is related to features in XANES. Calculations for several materials are presented and compared with LMTO band-structure calculations and with experiment.

  6. Experimental and ab initio investigations of the x-ray absorption near edge structure of orthorhombic LuMnO3

    NASA Astrophysics Data System (ADS)

    Hu, Y.; Borca, C. N.; Kleymenov, E.; Nachtegaal, M.; Delley, B.; Janousch, M.; Dönni, A.; Tachibana, M.; Kitazawa, H.; Takayama-Muromachi, E.; Kenzelmann, M.; Niedermayer, C.; Lippert, T.; Wokaun, A.; Schneider, C. W.

    2012-06-01

    X-ray near edge absorption spectroscopy was used to probe the electronic structure of multiferroic orthorhombic LuMnO3 polycrystalline samples and strained, twin-free orthorhombic (1-10) LuMnO3 films grown by pulsed laser deposition on (1-10) YAlO3 substrates. For all o-LuMnO3 samples x-ray near edge absorption spectroscopy spectra reveal that the pre-edge structure is influenced by the increase in MnO6 distortion as a result of the smaller Re-ion or film strain. Furthermore there is clear evidence of anisotropic Mn-O bonding and Mn orbital ordering along the c- and [110] direction. The experimental film and bulk data are in agreement with ab initio simulations.

  7. Electronic structure of individual hybrid colloid particles studied by near-edge X-ray absorption fine structure (NEXAFS) spectroscopy in the X-ray microscope.

    PubMed

    Henzler, Katja; Guttmann, Peter; Lu, Yan; Polzer, Frank; Schneider, Gerd; Ballauff, Matthias

    2013-02-13

    The electronic structure of individual hybrid particles was studied by nanoscale near-edge X-ray absorption spectromicroscopy. The colloidal particles consist of a solid polystyrene core and a cross-linked poly-N-(isopropylacrylamide) shell with embedded crystalline titanium dioxide (TiO(2)) nanoparticles (d = 6 ± 3 nm). The TiO(2) particles are generated in the carrier network by a sol-gel process at room temperature. The hybrid particles were imaged with photon energy steps of 0.1 eV in their hydrated environment with a cryo transmission X-ray microscope (TXM) at the Ti L(2,3)-edge. By analyzing the image stacks, the obtained near-edge X-ray absorption fine structure (NEXAFS) spectra of our individual hybrid particles show clearly that our synthesis generates TiO(2) in the anastase phase. Additionally, our spectromicroscopy method permits the determination of the density distribution of TiO(2) in single carrier particles. Therefore, NEXAFS spectroscopy combined with TXM presents a unique method to get in-depth insight into the electronic structure of hybrid materials.

  8. [Distribution and speciation of Pb in Arabidopsis thaliana shoot and rhizosphere soil by in situ synchrotron radiation micro X-ray fluorescence and X-ray absorption near edge structure].

    PubMed

    Shen, Ya-Ting

    2014-03-01

    In order to investigate plant reacting mechanism with heavy metal stress in organ and tissue level, synchrotron radiation micro X-ray fluorescence (micro-SRXRF) was used to determine element distribution characteristics of K, Ca, Mn, Fe, Cu, Zn, Pb in an Arabidopsis thaliana seedling grown in tailing dam soil taken from a lead-zinc mine exploration area. The results showed a regular distribution characters of K, Ca, Fe, Cu and Zn, while Pb appeared not only in root, but also in a leaf bud which was beyond previously understanding that Pb mainly appeared in plant root. Pb competed with Mn in the distribution of the whole seedling. Pb may cause the increase of oxidative stress in root and leaf bud, and restrict Mn absorption and utilization which explained the phenomenon of seedling death in this tailing damp soil. Speciation of Pb in Arabidopsis thaliana and tailing damp rhizosphere soil were also presented after using PbL3 micro X-ray absorption near edge structure (micro-XANES). By comparison of PbL3 XANES peak shape and peak position between standard samples and rhizosphere soil sample, it was demonstrated that the tailing damp soil was mainly formed by amorphous forms like PbO (64.2%), Pb (OH)2 (28.8%) and Pb3O4 (6.3%) rather than mineral or organic Pb speciations. The low plant bioavailability of Pb demonstrated a further research focusing on Pb absorption and speciation conversion is needed, especially the role of dissolve organic matter in soil which may enhance Pb bioavailability.

  9. Combined speciation analysis by X-ray absorption near-edge structure spectroscopy, ion chromatography, and solid-phase microextraction gas chromatography-mass spectrometry to evaluate biotreatment of concentrated selenium wastewaters.

    PubMed

    Lenz, Markus; van Hullebusch, Eric D; Farges, François; Nikitenko, Sergei; Corvini, Philippe F X; Lens, Piet N L

    2011-02-01

    In this study we evaluate the potential of anaerobic granular sludge as an inoculum for the bioremediation of selenium-contaminated waters using species-specific analytical methods. Solid species formed by microbial reduction were investigated using X-ray absorption near-edge structure (XANES) spectroscopy at the selenium K-edge. Furthermore, dissolved selenium species were specifically determined by ion chromatography (IC) and solid-phase microextraction gas chromatography-mass spectrometry (SPME-GC-MS). Least-squares linear combination of the XANES spectra for samples incubated with the highest selenate/selenite concentrations (10(-3) M) show the predominance of elemental selenium and a Se(-I) selenide, such as ferroselite, the thermodynamically most stable iron selenide. In contrast, elemental selenium and Se(-II) selenides are the main species detected at the lower selenate/selenite concentrations. In each repeated fed batch incubation, most aqueous selenite anions were converted into solid selenium species, regardless of the type of electron donor used (acetate or H(2)/CO(2)) and the selenium concentration applied. On the other hand, at higher concentrations of selenate (10(-4) and 10(-3) M), significant amounts of the oxyanion remained unconverted after consecutive incubations. SPME-GC-MS demonstrated selenium alkylation with both electron donors investigated, as dimethyl selenide (DMSe) and dimethyl diselenide (DMDSe). Selenite was even more alkylated in the presence of H(2)/CO(2) (maximum 2156 μg of Se/L of DMSe + DMDSe) as compared to acetate (maximum 50 μg of Se/L). In contrast, selenate was less alkylated using both electron donors (maximum 166 and 3 μg of Se/L, respectively). The high alkylation potential for selenite limits its bioremediation in selenium laden waters involving H(2)/CO(2) as the electron donor despite the fact that nontoxic elemental selenium and thermodynamically stable metal selenide species are formed.

  10. Effect of atomic vibrations in XANES: polarization-dependent damping of the fine structure at the Cu K-edge of (creat)2CuCl4.

    PubMed

    Šipr, Ondřej; Vackář, Jiří; Kuzmin, Alexei

    2016-11-01

    Polarization-dependent damping of the fine structure in the Cu K-edge spectrum of creatinium tetrachlorocuprate [(creat)2CuCl4] in the X-ray absorption near-edge structure (XANES) region is shown to be due to atomic vibrations. These vibrations can be separated into two groups, depending on whether the respective atoms belong to the same molecular block; individual molecular blocks can be treated as semi-rigid entities while the mutual positions of these blocks are subject to large mean relative displacements. The effect of vibrations can be efficiently included in XANES calculations by using the same formula as for static systems but with a modified free-electron propagator which accounts for fluctuations in interatomic distances.

  11. Quantitative investigation of two metallohydrolases by X-ray absorption spectroscopy near-edge spectroscopy

    NASA Astrophysics Data System (ADS)

    Zhao, W.; Chu, W. S.; Yang, F. F.; Yu, M. J.; Chen, D. L.; Guo, X. Y.; Zhou, D. W.; Shi, N.; Marcelli, A.; Niu, L. W.; Teng, M. K.; Gong, W. M.; Benfatto, M.; Wu, Z. Y.

    2007-09-01

    The last several years have witnessed a tremendous increase in biological applications using X-ray absorption spectroscopy (BioXAS), thanks to continuous advancements in synchrotron radiation (SR) sources and detector technology. However, XAS applications in many biological systems have been limited by the intrinsic limitations of the Extended X-ray Absorption Fine Structure (EXAFS) technique e.g., the lack of sensitivity to bond angles. As a consequence, the application of the X-ray absorption near-edge structure (XANES) spectroscopy changed this scenario that is now continuously changing with the introduction of the first quantitative XANES packages such as Minut XANES (MXAN). Here we present and discuss the XANES code MXAN, a novel XANES-fitting package that allows a quantitative analysis of experimental data applied to Zn K-edge spectra of two metalloproteins: Leptospira interrogans Peptide deformylase ( LiPDF) and acutolysin-C, a representative of snake venom metalloproteinases (SVMPs) from Agkistrodon acutus venom. The analysis on these two metallohydrolases reveals that proteolytic activities are correlated to subtle conformation changes around the zinc ion. In particular, this quantitative study clarifies the occurrence of the LiPDF catalytic mechanism via a two-water-molecules model, whereas in the acutolysin-C we have observed a different proteolytic activity correlated to structural changes around the zinc ion induced by pH variations.

  12. How water molecules affect the catalytic activity of hydrolases - A XANES study of the local structures of peptide deformylase

    NASA Astrophysics Data System (ADS)

    Cui, Peixin; Wang, Yu; Chu, Wangsheng; Guo, Xiaoyun; Yang, Feifei; Yu, Meijuan; Zhao, Haifeng; Dong, Yuhui; Xie, Yaning; Gong, Weimin; Wu, Ziyu

    2014-12-01

    Peptide deformylase (PDF) is a prokaryotic enzyme that catalyzes the deformylation of nascent peptides generated during protein synthesis and water molecules play a key role in these hydrolases. Using X-ray absorption near edge spectroscopy (XANES) and ab initio calculations we accurately probe the local atomic environment of the metal ion binding in the active site of PDF at different pH values and with different metal ions. This new approach is an effective way to monitor existing correlations among functions and structural changes. We show for the first time that the enzymatic activity depends on pH values and metal ions via the bond length of the nearest coordinating water (Wat1) to the metal ion. Combining experimental and theoretical data we may claim that PDF exhibits an enhanced enzymatic activity only when the distance of the Wat1 molecule with the metal ion falls in the limited range from 2.15 to 2.55 Å.

  13. [Effect of Long-Term Fertilization on Organic Nitrogen Functional Groups in Black Soil as Revealed by Synchrotron-Based X-Ray Absorption Near-Edge Structure Spectroscopy].

    PubMed

    Li, Hui; Gao, Qiang; Wang, Shuai; Zhu, Ping; Zhang, Jin-jing; Zhao, Yi-dong

    2015-07-01

    Nitrogen (N) is a common limiting nutrient in crop production. The N content of soil has been used as an important soil fertility index. Organic N is the major form of N in soil. In most agricultural surface soils, more than 90% of total N occurs in organic forms. Therefore, understanding the compositional characteristics of soil organic N functional groups can provide the scientific basis for formulating the reasonable farmland management strategies. Synchrotron radiation soft X-ray absorption near-edge structure (N K-edge XANES) spectroscopy is the most powerful tool to characterize in situ organic N functional groups compositions in soil. However, to our most knowledge, no studies have been conducted to examine the organic N functional groups compositions of soil using N K-edge XANES spectroscopy under long-term fertilization practices. Based on a long-term field experiment (started in 1990) in a black soil (Gongzhuling, Northeast China), we investigated the differences in organic N functional groups compositions in bulk soil and clay-size soil fraction among fertilization patterns using synchrotron-based N K- edge XANES spectroscopy. Composite soil samples (0-20 cm) were collected in 2008. The present study included six treatments: farmland fallow (FALL), no-fertilization control (CK), chemical nitrogen, phosphorus, and potassium fertilization (NPK), NPK in combination with organic manure (NPKM), 1.5 times of NPKM (1.5 NPKM), and NPK in combination with maize straw (NPKS). The results showed that N K-edge XANES spectra of all the treatments under study exhibited characteristic absorption peaks in the ranges of 401.2-401.6 and 402.7-403.1 eV, which were assigned as amides/amine-N and pyrrole-N, respectively. These characteristic absorption peaks were more obvious in clay-size soil fraction than in bulk soil. The results obtained from the semi-quantitative analysis of N K-edge XANES spectra indicated that the relative proportion of amides/amine-N was the highest

  14. Calculation of near-edge x-ray-absorption fine structure at finite temperatures: spectral signatures of hydrogen bond breaking in liquid water.

    PubMed

    Hetényi, Balázs; De Angelis, Filippo; Giannozzi, Paolo; Car, Roberto

    2004-05-08

    We calculate the near-edge x-ray-absorption fine structure of H(2)O in the gas, hexagonal ice, and liquid phases using heuristic density-functional based methods. We present a detailed comparison of our results with experiment. The differences between the ice and water spectra can be rationalized in terms of the breaking of hydrogen bonds around the absorbing molecule. In particular the increase in the pre-edge absorption feature from ice to water is shown to be due to the breaking of a donor hydrogen bond. We also find that in water approximately 19% of hydrogen bonds are broken. (c) 2004 American Institute of Physics.

  15. C 1s Near Edge X-ray Absorption Fine Structure (NEXAFS) of substituted benzoic acids: a theoretical and experimental study

    SciTech Connect

    Baldea,I.; Schimmelpfennig, B.; Plaschke, M.; Rothe, J.; Schirmer, J.; Trofimov, A.; Fanghaenel, T.

    2007-01-01

    Ab initio calculations are performed to explain the discrete transitions in experimental C 1s-NEXAFS (near edge X-ray absorption fine structure) spectra of various benzoic acid derivates. Transition energies and oscillator strengths of the contributing C 1s-{pi}* excitations are computed using the ADC(2) (second-order algebraic-diagrammatic construction) method. This method is demonstrated to be well suited for the finite electronic systems represented by these simple organic acids. There is good agreement between experiment and theory reproducing all the relevant spectral features. Some transitions can only be assigned based on a theoretical foundation. Remaining discrepancies between experimental and computed spectra are discussed.

  16. Cyclic voltammetry and near edge X-ray absorption fine structure spectroscopy at the Ag L3-edge on electrochemical halogenation of Ag layers on Au(111)

    NASA Astrophysics Data System (ADS)

    Endo, Osamu; Nakamura, Masashi

    2011-05-01

    One to three layers of Ag grown on a Au(111) electrode were studied by cyclic voltammetry in chloride and bromide solutions and by ex-situ near-edge X-ray absorption fine structure spectroscopy at the Ag L3-edge (Ag L3-NEXAFS). The one and two layers obtained by underpotential deposition exhibited reduced intensity at the absorption edge in the Ag L3-NEXAFS spectra, which suggests the gain of d-electrons in these layers. The cyclic voltammograms and the Ag L3-NEXAFS spectra indicate that the second and third layers of Ag halogenated at positive potentials, whereas the first layer remained in metallic form.

  17. Exact Multiple Scattering XANES Calculations

    NASA Astrophysics Data System (ADS)

    Ravel, B.; Rehr, J. J.

    1996-03-01

    Ab initio calculations of X-ray absorption near-edge structure (XANES), are made by inverting the full multiple-scattering (MS) matrix G=(1-G_0t)-1G_0. Our approach uses the fast, quickly convergent Rehr-Albers(J.J. Rehr and R.C. Albers, Phys. Rev. B, 41), 8139, (1990) separable representation of the free electron propagator G0 together with atomic scattering t-matrices from the FEFF6 code,(S. I. Zabinsky, et al., Phys. Rev. B52), 2995 (1995). which are calculated within the muffin-tin approximation with overlapped atom potentials. With this technique XANES spectra and its polarization dependence can be calculated in reasonable cpu time on large clusters. Good agreement with the XANES spectra of several sample compounds is obtained. This strategy is also used to determine the local densities of states ρ(E, r ) from the full MS matrix. From ρ(E, r ) we calculate the Fermi energies and estimate charge transfer for our sample clusters. The prospect of quantitative analysis of XANES spectra and its preedge features is discussed.

  18. A XANES and Raman investigation of sulfur speciation and structural order in Murchison and Allende meteorites

    NASA Astrophysics Data System (ADS)

    Bose, M.; Root, R. A.; Pizzarello, S.

    2017-03-01

    Insoluble organic matter (IOM) and hydrothermally treated IOM extracted from two carbonaceous chondrites, Murchison and Allende, was studied using sulfur K-edge XANES (X-ray absorption near edge structure) and μ-Raman spectroscopy, with the aim to understand their IOM's sulfur speciation and structural order, and how aqueous alteration or thermal metamorphism may have transformed these materials. We found that the sulfur-functional group chemistry of both the Murchison IOM and hydrothermally treated IOM samples have a large chemical variability ranging from oxidation states of S-2 to S+6, and exhibit a transformation in their oxidation state after the hydrothermal treatment (HT) to produce thiophenes and thiol compounds. Sulfoxide and sulfite peaks are also present in Murchison. Sulfates considered intrinsic to Murchison are most likely preaccretionary in nature, and not a result of reactions with water at high temperatures on the asteroid parent body. We argue that the reduced sulfides may have formed in the CM parent body, while the thiophenes and thiol compounds are a result of the HT. Micro-Raman spectra show the presence of aliphatic and aromatic moieties in Murchison's material as observed previously, which exhibits no change after HT. Because the Murchison IOM was modified, as seen by XANES analysis, absence of a change observed using micro-Raman indicated that although the alkyl carbons of IOM were cleaved, the aromatic network was not largely modified after HT. By contrast, Allende IOM contains primarily disulfide and elemental sulfur, no organic sulfur, and shows no transformation after HT. This nontransformation of Allende IOM after HT would indicate that parent body alteration of sulfide to sulfate is not feasible up to temperatures of 300°C. The reduced sulfur products indicate extreme secondary chemical processing from the precursor compounds in its parent body at temperatures as high as 624°C, as estimated from μ-Raman D band parameters. The

  19. Characterization of atmospheric aerosols using Synchroton radiation total reflection X-ray fluorescence and Fe K-edge total reflection X-ray fluorescence-X-ray absorption near-edge structure

    NASA Astrophysics Data System (ADS)

    Fittschen, U. E. A.; Meirer, F.; Streli, C.; Wobrauschek, P.; Thiele, J.; Falkenberg, G.; Pepponi, G.

    2008-12-01

    In this study a new procedure using Synchrotron total reflection X-ray fluorescence (SR-TXRF) to characterize elemental amounts in atmospheric aerosols down to particle sizes of 0.015 um is presented. The procedure was thoroughly evaluated regarding bounce off effects and blank values. Additionally the potential of total reflection X-ray fluorescence-X-ray absorption near edge structure (SR-TXRF-XANES) for speciation of FeII/III down to amounts of 34 pg in aerosols which were collected for 1 h is shown. The aerosols were collected in the city of Hamburg with a low pressure Berner impactor on Si carriers covered with silicone over time periods of 60 and 20 min each. The particles were collected in four and ten size fractions of 10.0-8.0 μm, 8.0-2.0 μm, 2.0-0.13 μm 0.13-0.015 μm (aerodynamic particle size) and 15-30 nm, 30-60 nm, 60-130 nm, 130-250 nm, 250-500 nm, 0.5-1 μm, 1-2 μm, 2-4 μm, 4-8 μm, 8-16 μm. Prior to the sampling "bounce off" effects on Silicone and Vaseline coated Si carriers were studied with total reflection X-ray fluorescence. According to the results silicone coated carriers were chosen for the analysis. Additionally, blank levels originating from the sampling device and the calibration procedure were studied. Blank levels of Fe corresponded to 1-10% of Fe in the aerosol samples. Blank levels stemming from the internal standard were found to be negligible. The results from the Synchroton radiation total reflection X-ray fluorescence analysis of the aerosols showed that 20 min of sampling time gave still enough sample material for elemental determination of most elements. For the determination of the oxidation state of Fe in the aerosols different Fe salts were prepared as a reference from suspensions in isopropanol. The results from the Fe K-edge Synchroton radiation total reflection X-ray fluorescence-X-ray absorption near-edge structure analysis of the aerosol samples showed that mainly Fe(III) was present in all particle size fractions.

  20. Near-edge study of gold-substituted YBa2Cu3O(7-delta)

    NASA Technical Reports Server (NTRS)

    Ruckman, Mark W.; Hepp, Aloysius F.

    1991-01-01

    The valence of Cu and Au in YBa2Au0.3Cu2.7O7-delta was investigated using X-ray absorption near edge structure (XANES). X-ray and neutron diffraction studies indicate that Au goes on the Cu(1) site and Cu K-edge XANES shows that this has little effect on the oxidation state of the remaining copper. The Au L3 edge develops a white line feature whose position lies between that of trivalent gold oxide and monovalent potassium gold cyanide, and whose height relative to the edge step is smaller than in the two reference compounds. The appearance of the Au L3 edge suggests that fewer Au 3d states are involved in forming the Au-O bond in YBa2Au0.3Cu2.7O7-delta than in trivalent gold oxide.

  1. Near-edge study of gold-substituted YBa2Cu3O(7-delta)

    NASA Technical Reports Server (NTRS)

    Ruckman, Mark W.; Hepp, Aloysius F.

    1991-01-01

    The valence of Cu and Au in YBa2Au0.3Cu2.7O7-delta was investigated using X-ray absorption near edge structure (XANES). X-ray and neutron diffraction studies indicate that Au goes on the Cu(1) site and Cu K-edge XANES shows that this has little effect on the oxidation state of the remaining copper. The Au L3 edge develops a white line feature whose position lies between that of trivalent gold oxide and monovalent potassium gold cyanide, and whose height relative to the edge step is smaller than in the two reference compounds. The appearance of the Au L3 edge suggests that fewer Au 3d states are involved in forming the Au-O bond in YBa2Au0.3Cu2.7O7-delta than in trivalent gold oxide.

  2. Near-edge study of gold-substituted YBa2Cu3O(7-delta)

    NASA Technical Reports Server (NTRS)

    Ruckman, Mark W.; Hepp, Aloysius F.

    1991-01-01

    The valence of Cu and Au in YBa2Au0.3Cu2.7O7-delta was investigated using x-ray absorption near edge structure (XANES). X-ray and neutron diffraction studies indicate that Au goes on the Cu(1) site and Cu K-edge XANES shows that this has little effect on the oxidation state of the remaining copper. The Au L3 edge develops a white line feature whose position lies between that of trivalent gold oxide and monovalent potassium gold cyanide, and whose height relative to the edge step is smaller than in the two reference compounds. The appearance of the Au L3 edge suggests that fewer Au 3d states are involved in forming the Au-O bond in YBa2Au0.3Cu2.7O7-delta than in trivalent gold oxide.

  3. Solid state synthesis of layered sodium manganese oxide for sodium-ion battery by in-situ high energy X-ray diffraction and X-ray absorption near edge spectroscopy [Solid state synthesis of layered sodium manganese oxide for sodium-ion battery by in-situ HEXRD and XANES

    DOE PAGES

    Ma, Tianyuan; Xu, Gui -Liang; Zeng, Xiaoqiao; ...

    2016-12-07

    In situ high energy X-ray diffraction (HEXRD) and in situ X-ray absorption near edge spectroscopy (XANES) were carried out to understand the soild state synthesis of NaxMnO2, with particular interest on the synthesis of P2 type Na2/3MnO2. It was found that there were multi intermediate phases formed before NaMnO2 appeared at about 600 °C. And the final product after cooling process is a combination of O'3 NaMnO2 with P2 Na2/3MnO2. A P2 type Na2/3MnO2 was synthesized at reduced temperature (600 °C). The influence of Na2CO3 impurity on the electrochemical performance of P2 Na2/3MnO2 was thoroughly investigated in our work. Itmore » was found that the content of Na2CO3 can be reduced by optimizing Na2CO3/MnCO3 ratio during the solid state reaction or other post treatment such as washing with water. Lastly, we expected our results could provide a good guide for future development of high performance cathode materials for sodium-ion batteries.« less

  4. Temperature dependent evolution of the local electronic structure of atmospheric plasma treated carbon nanotubes: Near edge x-ray absorption fine structure study

    SciTech Connect

    Roy, S. S.; Papakonstantinou, P.; Okpalugo, T. I. T.; Murphy, H.

    2006-09-01

    Near edge x-ray absorption fine structure (NEXAFS) spectroscopy has been employed to obtain the temperature dependent evolution of the electronic structure of acid treated carbon nanotubes, which were further modified by dielectric barrier discharge plasma processing in an ammonia atmosphere. The NEXAFS studies were performed from room temperature up to 900 deg. C. The presence of oxygen and nitrogen containing functional groups was observed in C K edge, N K edge, and O K edge NEXAFS spectra of the multiwalled carbon nanotubes. The N K edge spectra revealed three types of {pi}* features, the source of which was decisively identified by their temperature dependent evolution. It was established that these features are attributed to pyridinelike, NO, and graphitelike structures, respectively. The O K edge indicated that both carbonyl (C=O), {pi}*(CO), and ether C-O-C, {sigma}*(CO), functionalities were present. Upon heating in a vacuum to 900 deg. C the {pi}*(CO) resonances disappeared while the {sigma}*(CO) resonances were still present confirming their higher thermal stability. Heating did not produce a significant change in the {pi}* feature of the C K edge spectrum indicating that the tabular structure of the nanotubes is essentially preserved following the thermal decomposition of the functional groups on the nanotube surface.

  5. Percolative superconductivity in La{sub 2}CuO{sub 4.06} by lattice granularity patterns with scanning micro x-ray absorption near edge structure

    SciTech Connect

    Poccia, Nicola; Chorro, Matthieu; Ricci, Alessandro; Xu, Wei; Marcelli, Augusto; Campi, Gaetano; Bianconi, Antonio

    2014-06-02

    The simplest cuprate superconductor La{sub 2}CuO{sub 4+y} with mobile oxygen interstitials exhibits a clear phase separation. It is known that oxygen interstitials enter into the rocksalt La{sub 2}O{sub 2+y} spacer layers forming oxygen interstitials rich puddles and poor puddles but only recently a bulk multiscale structural phase separation has been observed by using scanning micro X-ray diffraction. Here we get further information on their spatial distribution, using scanning La L{sub 3}-edge micro X-ray absorption near edge structure. Percolating networks of oxygen rich puddles are observed in different micrometer size portions of the crystals. Moreover, the complex surface resistivity shows two jumps associated to the onset of intra-puddle and inter-puddles percolative superconductivity. The similarity of oxygen doped La{sub 2}CuO{sub 4+y}, with the well established phase separation in iron selenide superconductors is also discussed.

  6. Femtosecond laser-induced modification of potassium-magnesium silicate glasses: An analysis of structural changes by near edge x-ray absorption spectroscopy

    NASA Astrophysics Data System (ADS)

    Seuthe, T.; Höfner, M.; Reinhardt, F.; Tsai, W. J.; Bonse, J.; Eberstein, M.; Eichler, H. J.; Grehn, M.

    2012-05-01

    The effects of femtosecond laser pulse irradiation on the glass structure of alkaline silicate glasses were investigated by x-ray absorption near edge structure spectroscopy using the beamline of the Physikalisch-Technische Bundesanstalt at the electron synchrotron BESSY II in Berlin (Germany) by analyzing the magnesium K-edge absorption peak for different laser fluences. The application of fluences above the material modification threshold (2.1 J/cm2) leads to a characteristic shift of ˜1.0 eV in the K-edge revealing a reduced (˜3%) mean magnesium bond length to the ligated oxygen ions (Mg-O) along with a reduced average coordination number of the Mg ions.

  7. Pyrimidine and halogenated pyrimidines near edge x-ray absorption fine structure spectra at C and N K-edges: experiment and theory

    SciTech Connect

    Bolognesi, P.; O'Keeffe, P.; Ovcharenko, Y.; Coreno, M.; Avaldi, L.; Feyer, V.; Plekan, O.; Prince, K. C.; Zhang, W.; Carravetta, V.

    2010-07-21

    The inner shell excitation of pyrimidine and some halogenated pyrimidines near the C and N K-edges has been investigated experimentally by near edge x-ray absorption fine structure spectroscopy and theoretically by density functional theory calculations. The selected targets, 5-Br-pyrimidine, 2-Br-pyrimidine, 2-Cl-pyrimidine, and 5-Br-2-Cl-pyrimidine, allow the effects of the functionalization of the pyrimidine ring to be studied either as a function of different halogen atoms bound to the same molecular site or as a function of the same halogen atom bound to different molecular sites. The results show that the individual characteristics of the different spectra of the substituted pyrimidines can be rationalized in terms of variations in electronic and geometrical structures of the molecule depending on the localization and the electronegativity of the substituent.

  8. Pyrimidine and halogenated pyrimidines near edge x-ray absorption fine structure spectra at C and N K-edges: experiment and theory.

    PubMed

    Bolognesi, P; O'Keeffe, P; Ovcharenko, Y; Coreno, M; Avaldi, L; Feyer, V; Plekan, O; Prince, K C; Zhang, W; Carravetta, V

    2010-07-21

    The inner shell excitation of pyrimidine and some halogenated pyrimidines near the C and N K-edges has been investigated experimentally by near edge x-ray absorption fine structure spectroscopy and theoretically by density functional theory calculations. The selected targets, 5-Br-pyrimidine, 2-Br-pyrimidine, 2-Cl-pyrimidine, and 5-Br-2-Cl-pyrimidine, allow the effects of the functionalization of the pyrimidine ring to be studied either as a function of different halogen atoms bound to the same molecular site or as a function of the same halogen atom bound to different molecular sites. The results show that the individual characteristics of the different spectra of the substituted pyrimidines can be rationalized in terms of variations in electronic and geometrical structures of the molecule depending on the localization and the electronegativity of the substituent.

  9. Analysis of the near-edge X-ray-absorption fine-structure of anthracene: A combined theoretical and experimental study

    SciTech Connect

    Klues, Michael; Witte, Gregor; Hermann, Klaus

    2014-01-07

    The near-edge fine structure of the carbon K-edge absorption spectrum of anthracene was measured and theoretically analyzed by density functional theory calculations implemented in the StoBe code. It is demonstrated that the consideration of electronic relaxation of excited states around localized core holes yields a significant improvement of the calculated excitation energies and reproduces the experimentally observed fine structure well. The detailed analysis of excitation spectra calculated for each symmetry inequivalent excitation center allows in particular to examine the influence of chemical shifts and core hole effects on the excitation energies. Moreover, the visualization of final states explains the large variations in the oscillator strength of various transitions as well as the nature of Rydberg-states that exhibit a notable density of states below the ionization potentials.

  10. An x-ray absorption near edge structure spectroscopy study of metal coordination in Co(II)-substituted Carcinus maenas hemocyanin.

    PubMed Central

    Della Longa, S; Bianconi, A; Palladino, L; Simonelli, B; Congiu Castellano, A; Borghi, E; Barteri, M; Beltramini, M; Rocco, G P; Salvato, B

    1993-01-01

    High-resolution x-ray absorption near edge structure spectroscopy was used to characterize the metal sites in three different cobalt-substituted derivatives of Carcinus maenas hemocyanin (Hc), including a mononuclear cobalt, a dinuclear cobalt and a copper-cobalt hybrid derivative. Co(II) model complexes with structures exemplifying octahedral, trigonal bipyramidal, pseudo-tetrahedral, and square planar geometries were also studied. The results provide structural information about the metal binding site(s) in the Co-Hcs that extend earlier results from EPR and optical spectroscopy (Bubacco et al. 1992. Biochemistry. 31: 9294-9303). Experimental spectra were compared to those calculated for atomic clusters of idealized geometry, generated using a multiple scattering approach. The energy of the dipole forbidden 1s-->3d transition and of the absorption edge in the spectra for all cobalt Hc derivatives confirmed the cobaltous oxidation state which rules out the presence of an oxygenated site. Comparisons between data and simulations showed that the mononuclear and dinuclear Co(II) derivatives, as well as the hybrid derivative, contain four-coordinate Co(II) in distorted tetrahedral sites. Although the spectra for Co(II) in dinuclear metal sites more closely resemble the simulated spectrum for a tetrahedral complex than do spectra for the mononuclear derivative, the Co(II) sites in all derivatives are very similar. The Cu K-edge high resolution x-ray absorption near edge structure spectrum of the hybrid Cu-Co-Hc resembles that of deoxy-Hc demonstrating the presence of three-coordinate Cu(I). PMID:8312502

  11. An x-ray absorption near edge structure spectroscopy study of metal coordination in Co(II)-substituted Carcinus maenas hemocyanin.

    PubMed

    Della Longa, S; Bianconi, A; Palladino, L; Simonelli, B; Congiu Castellano, A; Borghi, E; Barteri, M; Beltramini, M; Rocco, G P; Salvato, B

    1993-12-01

    High-resolution x-ray absorption near edge structure spectroscopy was used to characterize the metal sites in three different cobalt-substituted derivatives of Carcinus maenas hemocyanin (Hc), including a mononuclear cobalt, a dinuclear cobalt and a copper-cobalt hybrid derivative. Co(II) model complexes with structures exemplifying octahedral, trigonal bipyramidal, pseudo-tetrahedral, and square planar geometries were also studied. The results provide structural information about the metal binding site(s) in the Co-Hcs that extend earlier results from EPR and optical spectroscopy (Bubacco et al. 1992. Biochemistry. 31: 9294-9303). Experimental spectra were compared to those calculated for atomic clusters of idealized geometry, generated using a multiple scattering approach. The energy of the dipole forbidden 1s-->3d transition and of the absorption edge in the spectra for all cobalt Hc derivatives confirmed the cobaltous oxidation state which rules out the presence of an oxygenated site. Comparisons between data and simulations showed that the mononuclear and dinuclear Co(II) derivatives, as well as the hybrid derivative, contain four-coordinate Co(II) in distorted tetrahedral sites. Although the spectra for Co(II) in dinuclear metal sites more closely resemble the simulated spectrum for a tetrahedral complex than do spectra for the mononuclear derivative, the Co(II) sites in all derivatives are very similar. The Cu K-edge high resolution x-ray absorption near edge structure spectrum of the hybrid Cu-Co-Hc resembles that of deoxy-Hc demonstrating the presence of three-coordinate Cu(I).

  12. The Ti environment in natural hibonite: XANES spectroscopy and computer modelling

    NASA Astrophysics Data System (ADS)

    Kravtsova, Antonina N.; Soldatov, Alexander V.; Walker, Andrew M.; Berry, Andrew J.

    2016-05-01

    The local atomic structure around Ti in Ti-bearing hibonite (CaAl12O19) was studied using X-ray absorption near-edge structure (XANES) spectroscopy and computer modelling. Structural models of the direct substitution of Al by Ti3+, Al by Ti4+ charge balanced by the coupled substitution of Mg2+ for Al, and small Ti clusters were considered. The Ti K-XANES spectra of natural hibonite with different Ti concentration were recorded. Theoretical Ti K- XANES spectra for structural models of hibonite were calculated. It was shown that the theoretical Ti K-XANES spectra for a model with Ti at the five-coordinated M2 site are in agreement with the experimental XANES spectra of hibonite with low concentrations of Ti, while the theoretical spectra for a structural model of clustered Ti are in agreement with the experimental spectra of hibonite with higher Ti contents.

  13. Structural Properties and Charge Distribution of the Sodium Uranium, Neptunium, and Plutonium Ternary Oxides: A Combined X-ray Diffraction and XANES Study.

    PubMed

    Smith, Anna L; Martin, Philippe; Prieur, Damien; Scheinost, Andreas C; Raison, Philippe E; Cheetham, Anthony K; Konings, Rudy J M

    2016-02-15

    The charge distributions in α-Na2UO4, Na3NpO4, α-Na2NpO4, Na4NpO5, Na5NpO6, Na2PuO3, Na4PuO5, and Na5PuO6 are investigated in this work using X-ray absorption near-edge structure (XANES) spectroscopy at the U-L3, Np-L3, and Pu-L3 edges. In addition, a Rietveld refinement of monoclinic Na2PuO3, in space group C2/c, is reported for the first time, and the existence of the isostructural Na2NpO3 phase is revealed. In contrast to measurements in solution, the number of published XANES data for neptunium and plutonium solid phases with a valence state higher than IV is very limited. The present results cover a wide range of oxidation states, namely, IV to VII, and can serve as reference for future investigations. The sodium actinide series show a variety of local coordination geometries, and correlations between the shape of the XANES spectra and the local structural environments are discussed herein.

  14. Investigation of Pb species in soils, celery and duckweed by synchrotron radiation X-ray absorption near-edge structure spectrometry

    NASA Astrophysics Data System (ADS)

    Luo, Liqiang; Shen, Yating; Liu, Jian; Zeng, Yuan

    2016-08-01

    The Pb species play a key role in its translocation in biogeochemical cycles. Soils, sediments and plants were collected from farmlands around Pb mines, and the Pb species in them was identified by X-ray absorption near-edge structure spectrometry. In soils, Pb5(PO4)3Cl and Pb3(PO4)2 were detected, and in sediments, Pb-fulvic acids (FAs) complex was identified. A Pb complex with FA fragments was also detected in celery samples. We found that (1) different Pb species were present in soils and sediments; (2) the Pb species in celery, which was grown in sediments, was different from the species present in duckweed, which grew in water; and (3) a Pb-FA-like compound was present in celery roots. The newly identified Pb species, the Pb-FA-like compound, may play a key role in Pb tolerance and translocation within plants.

  15. Impact of local strain on Ti-L₂,₃ electron energy-loss near-edge structures of BaTiO₃: a first-principles multiplet study.

    PubMed

    Ootsuki, Shirou; Ikeno, Hidekazu; Umeda, Yuji; Yonezawa, Yu; Moriwake, Hiroki; Kuwabara, Akihide; Kido, Osamu; Ueda, Satoko; Tanaka, Isao; Fujikawa, Yoshinori; Mizoguchi, Teruyasu

    2014-06-01

    Identification of local strains is crucial because the local strains largely influence the ferroelectric property of BaTiO₃. The effects of local strains induced by external pressures on the Ti-L₂,₃ electron energy-loss near-edge structure (ELNES) of BaTiO₃ were theoretically investigated using first-principles multiplet calculations. We revealed that the effects appear in the position of the spectral threshold, namely the spectrum shifts to lower and higher energy sides by the tensile and compressive pressures, respectively. We concluded that conventional ELNES observations can identify only large strains induced by -10 GPa, and 0.1 eV energy resolution is required to identify ±2% of strains.

  16. Time-resolved near-edge x-ray absorption fine structure spectroscopy on photo-induced phase transitions using a tabletop soft-x-ray spectrometer

    NASA Astrophysics Data System (ADS)

    Grossmann, P.; Rajkovic, I.; Moré, R.; Norpoth, J.; Techert, S.; Jooss, C.; Mann, Klaus

    2012-05-01

    We present a table-top soft-x-ray spectrometer for the wavelength range λ = 1-5 nm based on a stable laser-driven x-ray source, making use of a gas-puff target. With this setup, optical light-pump/soft-x-ray probe near-edge x-ray absorption fine structure (NEXAFS) experiments with a temporal resolution of about 230 ps are feasible. Pump-probe NEXAFS measurements were carried out in the "water-window" region (2.28 nm-4.36 nm) on the manganite Pr0.7Ca0.3MnO3, investigating diminutive changes of the oxygen K edge that derive from an optically induced phase transition. The results show the practicability of the table-top soft-x-ray spectrometer on demanding investigations so far exclusively conducted at synchrotron radiation sources.

  17. Near-edge x-ray absorption fine structure spectroscopy at atmospheric pressure with a table-top laser-induced soft x-ray source

    SciTech Connect

    Kühl, Frank-Christian Müller, Matthias Schellhorn, Meike; Mann, Klaus; Wieneke, Stefan; Eusterhues, Karin

    2016-07-15

    The authors present a table-top soft x-ray absorption spectrometer, accomplishing investigations of the near-edge x-ray absorption fine structure (NEXAFS) in a laboratory environment. The system is based on a low debris plasma ignited by a picosecond laser in a pulsed krypton gas jet, emitting soft x-ray radiation in the range from 1 to 5 nm. For absorption spectroscopy in and around the “water window” (2.3–4.4 nm), a compact helium purged sample compartment for experiments at atmospheric pressure has been constructed and tested. NEXAFS measurements on CaCl{sub 2} and KMnO{sub 4} samples were conducted at the calcium and manganese L-edges, as well as at the oxygen K-edge in air, atmospheric helium, and under vacuum, respectively. The results indicate the importance of atmospheric conditions for an investigation of sample hydration processes.

  18. Particle Formation from Pulsed Laser Irradiation of SootAggregates studied with scanning mobility particle sizer, transmissionelectron microscope and near-edge x-ray absorption fine structure.

    SciTech Connect

    Michelsen, Hope A.; Tivanski, Alexei V.; Gilles, Mary K.; vanPoppel, Laura H.; Dansson, Mark A.; Buseck, Peter R.; Buseck, Peter R.

    2007-02-20

    We investigated the physical and chemical changes induced in soot aggregates exposed to laser radiation using a scanning mobility particle sizer, a transmission electron microscope, and a scanning transmission x-ray microscope to perform near-edge x-ray absorption fine structure spectroscopy. Laser-induced nanoparticle production was observed at fluences above 0.12 J/cm(2) at 532 nm and 0.22 J/cm(2) at 1064 nm. Our results indicate that new particle formation proceeds via (1) vaporization of small carbon clusters by thermal or photolytic mechanisms, followed by homogeneous nucleation, (2) heterogeneous nucleation of vaporized carbon clusters onto material ablated from primary particles, or (3) both processes.

  19. Time dependent density functional theory study of the near-edge x-ray absorption fine structure of benzene in gas phase and on metal surfaces.

    PubMed

    Asmuruf, Frans A; Besley, Nicholas A

    2008-08-14

    The near-edge x-ray absorption fine structure of benzene in the gas phase and adsorbed on the Au(111) and Pt(111) surfaces is studied with time dependent density functional theory. Excitation energies computed with hybrid exchange-correlation functionals are too low compared to experiment. However, after applying a constant shift the spectra are in good agreement with experiment. For benzene on the Au(111) surface, two bands arising from excitation to the e(2u)(pi(*)) and b(2g)(pi(*)) orbitals of benzene are observed for photon incidence parallel to the surface. On Pt(111) surface, a broader band arises from excitation to benzene orbitals that are mixed with the surface and have both sigma(*)(Pt-C) and pi(*) characters.

  20. Communication: Near edge x-ray absorption fine structure spectroscopy of aqueous adenosine triphosphate at the carbon and nitrogen K-edges.

    PubMed

    Kelly, Daniel N; Schwartz, Craig P; Uejio, Janel S; Duffin, Andrew M; England, Alice H; Saykally, Richard J

    2010-09-14

    Near edge x-ray absorption fine structure (NEXAFS) spectroscopy at the nitrogen and carbon K-edges was used to study the hydration of adenosine triphosphate in liquid microjets. The total electron yield spectra were recorded as a function of concentration, pH, and the presence of sodium, magnesium, and copper ions (Na(+)/Mg(2+)/Cu(2+)). Significant spectral changes were observed upon protonation of the adenine ring, but not under conditions that promote π-stacking, such as high concentration or presence of Mg(2+), indicating that NEXAFS is insensitive to the phenomenon. Intramolecular inner-sphere association of Cu(2+) did create observable broadening of the nitrogen spectrum, whereas outer-sphere association with Mg(2+) did not.

  1. Adsorption and stability of malonic acid on rutile TiO2 (110), studied by near edge X-ray absorption fine structure and photoelectron spectroscopy

    NASA Astrophysics Data System (ADS)

    Syres, Karen L.; Thomas, Andrew G.; Graham, Darren M.; Spencer, Ben F.; Flavell, Wendy R.; Jackman, Mark J.; Dhanak, Vinod R.

    2014-08-01

    The adsorption of malonic acid on rutile TiO2 (110) has been studied using photoelectron spectroscopy and C K-edge, near edge X-ray fine structure spectroscopy (NEXAFS). Analysis of the O 1s and Ti 2p spectra suggest that the molecule adsorbs dissociatively in a doubly-bidentate adsorption geometry as malonate. The data are unable to distinguish between a chelating bonding mode with the backbone of the molecule lying along the [001] azimuth or a bridging geometry along the direction. Work carried out on a wiggler beamline suggests that the molecule is unstable under irradiation by high-flux synchrotron radiation from this type of insertion device.

  2. Time-resolved near-edge x-ray absorption fine structure spectroscopy on photo-induced phase transitions using a tabletop soft-x-ray spectrometer.

    PubMed

    Grossmann, P; Rajkovic, I; Moré, R; Norpoth, J; Techert, S; Jooss, C; Mann, Klaus

    2012-05-01

    We present a table-top soft-x-ray spectrometer for the wavelength range λ = 1-5 nm based on a stable laser-driven x-ray source, making use of a gas-puff target. With this setup, optical light-pump/soft-x-ray probe near-edge x-ray absorption fine structure (NEXAFS) experiments with a temporal resolution of about 230 ps are feasible. Pump-probe NEXAFS measurements were carried out in the "water-window" region (2.28 nm-4.36 nm) on the manganite Pr(0.7)Ca(0.3)MnO(3), investigating diminutive changes of the oxygen K edge that derive from an optically induced phase transition. The results show the practicability of the table-top soft-x-ray spectrometer on demanding investigations so far exclusively conducted at synchrotron radiation sources.

  3. Mechanistic insights on the electronic properties and electronic/atomic structure aspects in orthorhombic SrVO3 thin films: XANES-EXAFS study.

    PubMed

    Sharma, Aditya; Varshney, Mayora; Cheol Lim, Weon; Shin, Hyun-Joon; Pal Singh, Jitendra; Ok Won, Sung; Hwa Chae, Keun

    2017-03-01

    Correlations among the B-O6 octahedra distortions, existing polymorphous phases, band structures and electronic conductivities of ABO3 perovskites are matters for debate and require a deep understanding of their local atomic/electronic structures and diverse assets. In this study, to illustrate the distortion in V-O6 octahedra and its implication on the band structure and electronic properties, spectroscopic investigations on the RF-sputtering grown insulating SrVO3 thin films were employed using X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS). V K-edge and V L3,2-edge XANES, along with atomic multiplet calculations, have confirmed the 4+ oxidation state of V ions in the pristine and annealed SrVO3 thin films. Lower t2g/eg peak intensity ratio and smaller energy separation between t2g and eg peaks in the O K-edge XANES spectra, compared to the VO2 reference sample, have confirmed a larger V-O6 distortion in the orthorhombic SrVO3 thin films. Moreover, from the EXAFS data analysis, the local orthorhombic structure has been identified in the pristine and annealed SrVO3 thin films, compelling significant distortion in the V-O6 octahedra. Dimerization in the vanadium chains and V-V twisting, caused by V-O6 octahedra distortion, manifests a miscellaneous ligand field interaction between O 2p and V 3d orbitals and facilitates (i) a larger separation between the bonding and antibonding d‖ orbitals and (ii) an upward shift of the π* band in the band structure, leading to larger band gaps in the insulating SrVO3 thin films. Our spectroscopy results may open up new avenues for the mechanism of insulating/conducting character in other complicated perovskite materials using XANES-EXAFS.

  4. Solid state synthesis of layered sodium manganese oxide for sodium-ion battery by in-situ high energy X-ray diffraction and X-ray absorption near edge spectroscopy [Solid state synthesis of layered sodium manganese oxide for sodium-ion battery by in-situ HEXRD and XANES

    SciTech Connect

    Ma, Tianyuan; Xu, Gui -Liang; Zeng, Xiaoqiao; Li, Yan; Ren, Yang; Sun, Chengjun; Heald, Steve M.; Jorne, Jacob; Amine, Khalil; Chen, Zonghai

    2016-12-07

    In situ high energy X-ray diffraction (HEXRD) and in situ X-ray absorption near edge spectroscopy (XANES) were carried out to understand the soild state synthesis of NaxMnO2, with particular interest on the synthesis of P2 type Na2/3MnO2. It was found that there were multi intermediate phases formed before NaMnO2 appeared at about 600 °C. And the final product after cooling process is a combination of O'3 NaMnO2 with P2 Na2/3MnO2. A P2 type Na2/3MnO2 was synthesized at reduced temperature (600 °C). The influence of Na2CO3 impurity on the electrochemical performance of P2 Na2/3MnO2 was thoroughly investigated in our work. It was found that the content of Na2CO3 can be reduced by optimizing Na2CO3/MnCO3 ratio during the solid state reaction or other post treatment such as washing with water. Lastly, we expected our results could provide a good guide for future development of high performance cathode materials for sodium-ion batteries.

  5. Surface Structure and Chemical Switching of Thioctic Acid Adsorbed on Au(111) as Observed Using Near-Edge X-ray Absorption Fine Structure

    SciTech Connect

    Meulenberg, R W; van Buuren, T; Vance, A L; Terminello, L J; Willey, T M; Bostedt, C; Fadley, C S

    2004-01-06

    Thioctic acid (alpha-lipoic acid) is a molecule with a large disulfide-containing base, a short alkyl-chain with four CH{sub 2} units, and a carboxyl termination. Self-assembled monolayer (SAM) films of thioctic acid adsorbed on Au(111) have been investigated with near-edge x-ray absorption fine structure (NEXAFS) spectroscopy and x-ray photoelectron spectroscopy (XPS) to determine film quality, bonding and morphology. Using standard preparation protocols for SAMs, that is, dissolving thioctic acid in ethanol and exposing gold to the solution, results in poor films. These films are highly disordered, contain a mixture of carboxyl and carboxylate terminations, have more than monolayer coverage, and exhibit unbound disulfide. Conversely, forming films by dissolving 1 mmol thioctic acid into 5% acetic acid in ethanol (as previously reported with carboxyl-terminated alkyl-thiols) forms ordered monolayers with small amounts of unbound sulfur. NEXAFS indicates tilted over endgroups with the carboxyl group normal on average 38{sup o} from the surface normal. Slight dichroism in other features indicates alkyl chains statistically more upright than prostrate on the surface. Reflection-absorption Fourier transform infrared (RA-FTIR) spectra indicate hydrogen bonding between neighboring molecules. In such well-formed monolayers, a stark reorientation occurs upon deprotonation of the endgroup by rinsing in a KOH solution. The carboxylate plane normal is now about 66{sup o} from sample normal, a much more upright orientation. Data indicate this reorientation may also cause a more upright orientation to the alkyl portion of the molecules.

  6. A XANES study of the structural role of lead in glazes from decorated tiles, XVI to XVIII century manufacture

    NASA Astrophysics Data System (ADS)

    Figueiredo, M. O.; Silva, T. P.; Veiga, J. P.

    2006-05-01

    Aged lead-rich, tin-opacified glazes from polychrome tiles manufactured in the 16th 18th century were studied to ascertain the structural role of lead. Glaze fragments with white, blue, yellow, brown and green colouring were analysed using non-destructive X-ray techniques, both laboratorial X-ray diffraction to identify crystalline components and synchrotron-based. Elemental analyses by synchrotron radiation X-ray fluorescence were performed at the former LURE photon microprobe (line D15A at DCI, in Orsay). The instrumental set-up of beamline BM29 at the ESRF, in Grenoble, was applied to collect X-ray absorption spectra at the Pb L3-edge. Natural minerals and synthetics with known crystal structure were used as model oxy-compounds to configure different formal valences and coordinations of lead ions by oxygen anions, and to interpret the effects upon details of X-ray absorption near-edge spectroscopy (XANES) spectra. Experimental evidence supports the general conclusion that lead is hosted by the glassy matrix, irrespective of the glaze colour. Furthermore, it was concluded that lead ions assume coordinations higher than usual for silica glasses, acting as network modifiers in the silica-lime-alkali glasses of ancient tile glazes.

  7. Vanadium bisimide bonding investigated by X-ray crystallography, 51V and 13C nuclear magnetic resonance spectroscopy, and V L(3,2)-edge X-ray absorption near-edge structure spectroscopy.

    PubMed

    La Pierre, Henry S; Minasian, Stefan G; Abubekerov, Mark; Kozimor, Stosh A; Shuh, David K; Tyliszczak, Tolek; Arnold, John; Bergman, Robert G; Toste, F Dean

    2013-10-07

    Syntheses of neutral halide and aryl vanadium bisimides are described. Treatment of VCl2(NtBu)[NTMS(N(t)Bu)], 2, with PMe3, PEt3, PMe2Ph, or pyridine gave vanadium bisimides via TMSCl elimination in good yield: VCl(PMe3)2(N(t)Bu)2 3, VCl(PEt3)2(N(t)Bu)2 4, VCl(PMe2Ph)2(N(t)Bu)2 5, and VCl(Py)2(N(t)Bu)2 6. The halide series (Cl-I) was synthesized by use of TMSBr and TMSI to give VBr(PMe3)2(N(t)Bu)2 7 and VI(PMe3)2(N(t)Bu)2 8. The phenyl derivative was obtained by reaction of 3 with MgPh2 to give VPh(PMe3)2(N(t)Bu)2 9. These neutral complexes are compared to the previously reported cationic bisimides [V(PMe3)3(N(t)Bu)2][Al(PFTB)4] 10, [V(PEt3)2(N(t)Bu)2][Al(PFTB)4] 11, and [V(DMAP)(PEt3)2(N(t)Bu)2][Al(PFTB)4] 12 (DMAP = dimethylaminopyridine, PFTB = perfluoro-tert-butoxide). Characterization of the complexes by X-ray diffraction, (13)C NMR, (51)V NMR, and V L(3,2)-edge X-ray absorption near-edge structure (XANES) spectroscopy provides a description of the electronic structure in comparison to group 6 bisimides and the bent metallocene analogues. The electronic structure is dominated by π bonding to the imides, and localization of electron density at the nitrogen atoms of the imides is dictated by the cone angle and donating ability of the axial neutral supporting ligands. This phenomenon is clearly seen in the sensitivity of (51)V NMR shift, (13)C NMR Δδ(αβ), and L3-edge energy to the nature of the supporting phosphine ligand, which defines the parameters for designing cationic group 5 bisimides that would be capable of breaking stronger σ bonds. Conversely, all three methods show little dependence on the variable equatorial halide ligand. Furthermore, this analysis allows for quantification of the electronic differences between vanadium bisimides and the structurally analogous mixed Cp/imide system CpV(N(t)Bu)X2 (Cp = C5H5(1-)).

  8. Refinement of DNA structures through near-edge X-ray absorption fine structure analysis: applications on guanine and cytosine nucleobases, nucleosides, and nucleotides.

    PubMed

    Hua, Weijie; Gao, Bin; Li, Shuhua; Agren, Hans; Luo, Yi

    2010-10-21

    In this work we highlight the potential of NEXAFS—near-edge X-ray absorption fine structure—analysis to perform refinements of hydrogen-bond structure in DNA. For this purpose we have carried out first-principle calculations of the N1s NEXAFS spectra of the guanine and cytosine nucleobases and their tautomers, nucleosides, and nucleotides in the gas phase, as well as for five crystal structures of guanine, cytosine, or guanosine. The spectra all clearly show imine (π1*) and amine (π2*) nitrogen absorption bands with a characteristic energy difference (Δ). Among all of the intramolecule covalent connections, the tautomerism of hydrogens makes the largest influence, around ±0.4−0.5 eV change of Δ, to the spectra due to a switch of single−double bonds. Deoxyribose and ribose sugars can cause at most 0.2 eV narrowing of Δ, while the phosphate groups have nearly negligible effects on the spectra. Two kinds of intermolecule interactions are analyzed, the hydrogen bonds and the stacking effect, by comparing “compressed” and “expanded” models or by comparing models including or excluding the nearest stacking molecules. The shortening of hydrogen-bond length by 0.2−0.3 Å can result in the reduction of Δ by 0.2−0.8 eV. This is because the hydrogen bonds make the electrons more delocalized, and the amine and imine nitrogens become less distinguishable. Moreover, the hydrogen bond has a different ability to influence the spectra of different crystals, with guanine crystals as the largest (change by 0.8 eV) and the guanosine crystal as the smallest (change by 0.2 eV). The stacking has negligible effects on the spectra in all studied systems. A comparison of guanosine to guanine crystals shows that the sugars in the crystal could create “blocks” in the π-and hydrogen bonds network of bases and thus makes the imine and amine nitrogens more distinguishable with a larger Δ. Our theoretical calculations offer a good match with experimental findings

  9. Low-temperature adsorption of H2S on Ni(001) studied by near-edge- and surface-extended-x-ray-absorption fine structure

    NASA Astrophysics Data System (ADS)

    McGrath, R.; MacDowell, A. A.; Hashizume, T.; Sette, F.; Citrin, P. H.

    1989-11-01

    The adsorption of H2S on Ni(001) has been studied with surface-extended x-ray-absorption fine structure and near-edge x-ray-absorption fine structure (NEXAFS) using the AT&T Bell Laboratories X15B beamline at the National Synchrotron Light Source. At 95 K and full saturation coverage, ~0.45 monolayer (ML) of S atoms in fourfold-hollow sites are produced, characteristic of room-temperature adsorption, accompanied by ~0.05 ML of oriented molecular H2S. Both these atomic and molecular chemisorbed species are buried under ~0.9 ML of disordered physisorbed H2S. No evidence for HS is found. Above 190 K the two molecular H2S phases desorb, leaving only dissociated S. These findings differ from previously reported interpretations of data obtained with high-resolution electron-energy-loss spectroscopy. They also exemplify the utility of NEXAFS for identifying and quantifying atomic and molecular surface species even when their difference involves only H and the two species coexist.

  10. Near-Edge X-ray Absorption Fine Structure Studies of Electrospun Poly(dimethylsiloxane)/Poly (methyl methacrylate)/Multiwall Carbon Nanotube Composites

    PubMed Central

    Winter, A. Douglas; Larios, Eduardo; Alamgir, Faisal M.; Jaye, Cherno; Fischer, Daniel; Campo, Eva M.

    2014-01-01

    This work describes the near conduction band edge structure of electrospun mats of MWCNT-PDMS-PMMA by near edge X-Ray absorption fine structure (NEXAFS) spectroscopy. Effects of adding nanofillers of different sizes were addressed. Despite observed morphological variations and inhomogeneous carbon nanotube distribution, spun mats appeared homogeneous under NEXAFS analysis. Spectra revealed differences in emissions from glancing and normal spectra; which may evidence phase separation within the bulk of the micron-size fibers. Further, dichroic ratios show polymer chains did not align, even in the presence of nanofillers. Addition of nanofillers affected emissions in the C-H, C=O and C-C regimes, suggesting their involvement in interfacial matrix-carbon nanotube bonding. Spectral differences at glancing angles between pristine and composite mats suggest that geometric conformational configurations are taking place between polymeric chains and carbon nanotubes. These differences appear to be carbon nanotube-dimension dependent, and are promoted upon room temperature mixing and shear flow during electrospinning. CH-π bonding between polymer chains and graphitic walls, as well as H-bonds between impurities in the as-grown CNTs and polymer pendant groups are proposed bonding mechanisms promoting matrix conformation. PMID:24308286

  11. Low-temperature adsorption of H sub 2 S on Ni(001) studied by near-edge-- and surface-extended--x-ray-absorption fine structure

    SciTech Connect

    McGrath, R.; MacDowell, A.A.; Hashizume, T.; Sette, F.; Citrin, P.H. )

    1989-11-15

    The adsorption of H{sub 2}S on Ni(001) has been studied with surface-extended x-ray-absorption fine structure and near-edge x-ray-absorption fine structure (NEXAFS) using the AT T Bell Laboratories X15B beamline at the National Synchrotron Light Source. At 95 K and full saturation coverage, {similar to}0.45 monolayer (ML) of S atoms in fourfold-hollow sites are produced, characteristic of room-temperature adsorption, accompanied by {similar to}0.05 ML of oriented molecular H{sub 2}S. Both these atomic and molecular chemisorbed species are buried under {similar to}0.9 ML of disordered physisorbed H{sub 2}S. No evidence for HS is found. Above 190 K the two molecular H{sub 2}S phases desorb, leaving only dissociated S. These findings differ from previously reported interpretations of data obtained with high-resolution electron-energy-loss spectroscopy. They also exemplify the utility of NEXAFS for identifying and quantifying atomic and molecular surface species even when their difference involves only H and the two species coexist.

  12. Near Edge X-Ray Absorption and X-Ray Photoelectron Diffraction Studies of the Structural Environment of Ge-Si Systems

    NASA Astrophysics Data System (ADS)

    Castrucci, P.; Gunnella, R.; Pinto, N.; Bernardini, R.; de Crescenzi, M.; Sacchi, M.

    Near edge X-ray absorption spectroscopy (XAS), X-ray photoelectron diffraction (XPD) and Auger electron diffraction (AED) are powerful techniques for the qualitative study of the structural and electronic properties of several systems. The recent development of a multiple scattering approach to simulating experimental spectra opened a friendly way to the study of structural environments of solids and surfaces. This article reviews recent X-ray absorption experiments using synchrotron radiation which were performed at Ge L edges and core level electron diffraction measurements obtained using a traditional X-ray source from Ge core levels for ultrathin Ge films deposited on silicon substrates. Thermodynamics and surface reconstruction have been found to play a crucial role in the first stages of Ge growth on Si(001) and Si(111) surfaces. Both techniques show the occurrence of intermixing processes even for room-temperature-grown Ge/Si(001) samples and give a straightforward measurement of the overlayer tetragonal distortion. The effects of Sb as a surfactant on the Ge/Si(001) interface have also been investigated. In this case, evidence of layer-by-layer growth of the fully strained Ge overlayer with a reduced intermixing is obtained when one monolayer of Sb is predeposited on the surface.

  13. Near-edge X-ray absorption fine structure studies of electrospun poly(dimethylsiloxane)/poly(methyl methacrylate)/multiwall carbon nanotube composites.

    PubMed

    Winter, A Douglas; Larios, Eduardo; Alamgir, Faisal M; Jaye, Cherno; Fischer, Daniel; Campo, Eva M

    2013-12-23

    This work describes the near conduction band edge structure of electrospun mats of multiwalled carbon nanotube (MWCNT)-polydimethylsiloxane-poly(methyl methacrylate) by near edge X-ray absorption fine structure (NEXAFS) spectroscopy. Effects of adding nanofillers of different sizes were addressed. Despite observed morphological variations and inhomogeneous carbon nanotube distribution, spun mats appeared homogeneous under NEXAFS analysis. Spectra revealed differences in emissions from glancing and normal spectra, which may evidence phase separation within the bulk of the micrometer-size fibers. Further, dichroic ratios show polymer chains did not align, even in the presence of nanofillers. Addition of nanofillers affected emissions in the C-H, C═O, and C-C regimes, suggesting their involvement in interfacial matrix-carbon nanotube bonding. Spectral differences at glancing angles between pristine and composite mats suggest that geometric conformational configurations are taking place between polymeric chains and carbon nanotubes. These differences appear to be carbon nanotube-dimension dependent and are promoted upon room temperature mixing and shear flow during electrospinning. CH-π bonding between polymer chains and graphitic walls, as well as H-bonds between impurities in the as-grown MWCNTs and polymer pendant groups are proposed bonding mechanisms promoting matrix conformation.

  14. Investigation of the fine structure around the copper site in copper/zinc superoxide dismutase by XANES combined with ab initio calculations

    NASA Astrophysics Data System (ADS)

    Wang, Yu; Jin, Sheng; Li, Jiong; Zhou, Jing; Zhang, Linjuan; Wang, Jianqiang; Zhang, Shuo; Wei, Xiangjun; Jiang, Zheng; Huang, Yuying; Cui, Peixin; Zhao, Haifeng; Chu, Wangsheng

    2017-08-01

    Copper/zinc superoxide dismutase (CuZnSOD) is an important enzyme that plays a crucial role in protecting oxygen-metabolizing cells against harmful effects of superoxide free-radicals. In this work, the three-dimensional local structure around the copper-binding site in pH 7.0 buffer solution was determined using X-ray absorption near-edge spectroscopy (XANES) combined with ab initio calculations in the framework of the multiple-scattering theory performed by MXAN. Extremely accurate bond distances and bond angle information between ligands were returned. The result confirmed that the copper ion binds four conserved His residues and a water molecule in CuZnSOD and prefers a five-coordinated in a distorted square pyramidal geometry.

  15. Probing the Ordering of Semiconducting Fluorene-Thiophene Copolymer Surfaces on Rubbed Polyimide Substrates by Near-Edge X-ray Absorption Fine Structure

    SciTech Connect

    Pattison,L.; Hexemer, A.; Kramer, E.; Krishnan, S.; Petroff, P.; Fischer, D.

    2006-01-01

    The temperature-dependent alignment of semiconducting liquid crystalline fluorene-thiophene copolymer (F8T2) thin film surfaces was investigated using the near-edge X-ray absorption fine structure (NEXAFS) technique. Partial electron yield spectra were recorded over a range of temperatures in order to observe directly the surface orientation as the polymer is heated and cooled through glass, crystal, and liquid crystal phases. In addition, samples annealed under varying processing conditions and quenched to room temperature were analyzed. The NEXAFS data show that (a) in thin F8T2 films at all temperatures the polymer backbone lies in the plane of the substrate, (b) the fluorene and thiophene rings are rotated randomly about the molecular axis, (c) orientation of the polymer backbone can be controlled using a rubbed polyimide alignment layer as a template for liquid crystal orientation, and (d) under proper annealing conditions there is strong temperature-dependent alignment of the copolymer main-chain axis to the rubbing direction which extends from the polyimide/F8T2 interface all the way to the F8T2 surface. The surface alignment does not disappear after annealing at temperatures {approx}30 K above the bulk nematic to isotropic transition.

  16. Near-edge X-ray Absorption Fine Structure (NEXAFS) Spectroscopy study on Chlorinated Graphene through Plasma-based Surface Functionalization

    NASA Astrophysics Data System (ADS)

    Zhang, Xu; Schiros, Theanne; Nordlund, Dennis; Shin, Yong Cheol; Kong, Jing; Dresselhaus, Mildred; Palacios, Tomas; MIT/Columbia University/SLAC Collaboration

    2015-03-01

    Plasma-based chlorination is a promising technique to realize controllable doping in graphene, while maintaining its high mobility. Meanwhile, synchrotron-based X-ray spectroscopy provides us a sensitive probe to investigate the surface states of functionalizing dopants in graphene. Here, we systematically studied the electronic states of chlorinated graphene on different substrates, including surface binding energy, dopant concentration and work function shift by use of Near Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy, XPS and photoemission threshold measurements. The concentration of absorbed chlorine is high enough to generate a distinct NEXAFS resonance at 286.2 eV (1s -> π* transition for C-Cl bonds). It is remarkable that the sp2 carbon core-hole exciton (291.85eV) retained its sharpness even after treatment, indicating the long-range periodicity in graphene is largely preserved. This distinguishes our approach as a noninvasive and effective doping method. The interaction between Cl and graphene also exhibits strong substrate effects: for Cu, graphene's Fermi level is shifted downwards by 0.35eV, while for graphene on SiO2, the much (4-5 times) higher chlorine concentration causes EF to shift by 0.9eV.

  17. Interaction of Isophorone with Pd(111): A Combination of Infrared Reflection-Absorption Spectroscopy, Near-Edge X-ray Absorption Fine Structure, and Density Functional Theory Studies.

    PubMed

    Dostert, Karl-Heinz; O'Brien, Casey P; Riedel, Wiebke; Savara, Aditya; Liu, Wei; Oehzelt, Martin; Tkatchenko, Alexandre; Schauermann, Swetlana

    2014-12-04

    Atomistic level understanding of interaction of α,β-unsaturated carbonyls with late transition metals is a key prerequisite for rational design of new catalytic materials with the desired selectivity toward C=C or C=O bond hydrogenation. The interaction of this class of compounds with transition metals was investigated on α,β-unsaturated ketone isophorone on Pd(111) as a prototypical system. In this study, infrared reflection-absorption spectroscopy (IRAS), near-edge X-ray absorption fine structure (NEXAFS) experiments, and density functional theory calculations including van der Waals interactions (DFT+vdW) were combined to obtain detailed information on the binding of isophorone to palladium at different coverages and on the effect of preadsorbed hydrogen on the binding and adsorption geometry. According to these experimental observations and the results of theoretical calculations, isophorone adsorbs on Pd(111) in a flat-lying geometry at low coverages. With increasing coverage, both C=C and C=O bonds of isophorone tilt with respect to the surface plane. The tilting is considerably more pronounced for the C=C bond on the pristine Pd(111) surface, indicating a prominent perturbation and structural distortion of the conjugated π system upon interaction with Pd. Preadsorbed hydrogen leads to higher tilting angles of both π bonds, which points to much weaker interaction of isophorone with hydrogen-precovered Pd and suggests the conservation of the in-plane geometry of the conjugated π system. The results of the DFT+vdW calculations provide further insights into the perturbation of the molecular structure of isophorone on Pd(111).

  18. Interaction of Isophorone with Pd(111): A Combination of Infrared Reflection–Absorption Spectroscopy, Near-Edge X-ray Absorption Fine Structure, and Density Functional Theory Studies

    PubMed Central

    2014-01-01

    Atomistic level understanding of interaction of α,β-unsaturated carbonyls with late transition metals is a key prerequisite for rational design of new catalytic materials with the desired selectivity toward C=C or C=O bond hydrogenation. The interaction of this class of compounds with transition metals was investigated on α,β-unsaturated ketone isophorone on Pd(111) as a prototypical system. In this study, infrared reflection–absorption spectroscopy (IRAS), near-edge X-ray absorption fine structure (NEXAFS) experiments, and density functional theory calculations including van der Waals interactions (DFT+vdW) were combined to obtain detailed information on the binding of isophorone to palladium at different coverages and on the effect of preadsorbed hydrogen on the binding and adsorption geometry. According to these experimental observations and the results of theoretical calculations, isophorone adsorbs on Pd(111) in a flat-lying geometry at low coverages. With increasing coverage, both C=C and C=O bonds of isophorone tilt with respect to the surface plane. The tilting is considerably more pronounced for the C=C bond on the pristine Pd(111) surface, indicating a prominent perturbation and structural distortion of the conjugated π system upon interaction with Pd. Preadsorbed hydrogen leads to higher tilting angles of both π bonds, which points to much weaker interaction of isophorone with hydrogen-precovered Pd and suggests the conservation of the in-plane geometry of the conjugated π system. The results of the DFT+vdW calculations provide further insights into the perturbation of the molecular structure of isophorone on Pd(111). PMID:26089998

  19. Chemical analysis for optimal synthesis of ferrihydrite-modified diatomite using soft X-ray absorption near-edge structure spectroscopy

    NASA Astrophysics Data System (ADS)

    Xiong, Wenhui; Peng, Jian; Hu, Yongfeng

    2009-12-01

    Effects of process parameters such as concentrations of FeCl2, NaOH, and drying temperature on the formation mechanism and chemical characteristics of ferrihydrite-modified diatomite are studied by using X-ray absorption near-edge structure spectroscopy. The spectra were recorded in total electron yield mode and/or fluorescence yield mode to investigate the chemical nature of Fe and Si on the surface and/or in the bulk of ferrihydrite-modified diatomite, respectively. It was found that only the surface SiO2 was partially dissolved in the NaOH solution with stirring and heating, whereas the bulk of diatomite seemed to be preserved. The dissolved Si was incorporated into the structure of ferrihydrite to form the 2-line Si-containing ferrihydrite on the surface of diatomite. The crystalline degree of ferrihydrite increased with the increasing FeCl2 concentration and the Brunauer-Emmett-Teller specific surface area of ferrihydrite-modified diatomite decreased with the increasing FeCl2 concentration. The crystalline degree of ferrihydrite decreased with the increase of NaOH concentration. The high temperature calcination caused an energy shift in the Si L-edge spectra to the high energy side and a transformation of Si-containing ferrihydrite to crystallized hematite might occur when ferrihydrite-modified diatomite is calcined at 900°C. In this study, the optimal synthesis conditions for the ferrihydrite-modified diatomite with the least crystalline Si-containing ferrihydrite and the highest surface area were found to be as the follows: 0.5 M FeCl2 solution, 6 M NaOH solution and drying temperature of 50°C.

  20. Near-edge X-ray absorption fine structure (NEXAFS) spectroscopy for mapping nano-scale distribution of organic carbon forms in soil: Application to black carbon particles

    NASA Astrophysics Data System (ADS)

    Lehmann, Johannes; Liang, Biqing; Solomon, Dawit; Lerotic, Mirna; LuizãO, Flavio; Kinyangi, James; SchäFer, Thorsten; Wirick, Sue; Jacobsen, Chris

    2005-03-01

    Small-scale heterogeneity of organic carbon (C) forms in soils is poorly quantified since appropriate analytical techniques were not available up to now. Specifically, tools for the identification of functional groups on the surface of micrometer-sized black C particles were not available up to now. Scanning Transmission X-ray Microscopy (STXM) using synchrotron radiation was used in conjunction with Near-Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy to investigate nano-scale distribution (50-nm resolution) of C forms in black C particles and compared to synchrotron-based FTIR spectroscopy. A new embedding technique was developed that did not build on a C-based embedding medium and did not pose the risk of heat damage to the sample. Elemental sulfur (S) was melted to 220°C until it polymerized and quenched with liquid N2 to obtain a very viscous plastic S in which the black C could be embedded until it hardened to a noncrystalline state and was ultrasectioned. Principal component and cluster analysis followed by singular value decomposition was able to resolve distinct areas in a black carbon particle. The core of the studied biomass-derived black C particles was highly aromatic even after thousands of years of exposure in soil and resembled the spectral characteristics of fresh charcoal. Surrounding this core and on the surface of the black C particle, however, much larger proportions of carboxylic and phenolic C forms were identified that were spatially and structurally distinct from the core of the particle. Cluster analysis provided evidence for both oxidation of the black C particle itself as well as adsorption of non-black C. NEXAFS spectroscopy has great potential to allow new insight into black C properties with important implications for biogeochemical cycles such as mineralization of black C in soils and sediments, and adsorption of C, nutrients, and pollutants as well as transport in the geosphere, hydrosphere, and atmosphere.

  1. Composition-dependent structure of polycrystalline magnetron-sputtered V–Al–C–N hard coatings studied by XRD, XPS, XANES and EXAFS

    PubMed Central

    Krause, Bärbel; Darma, Susan; Kaufholz, Marthe; Mangold, Stefan; Doyle, Stephen; Ulrich, Sven; Leiste, Harald; Stüber, Michael; Baumbach, Tilo

    2013-01-01

    V–Al–C–N hard coatings with high carbon content were deposited by reactive radio-frequency magnetron sputtering using an experimental combinatorial approach, deposition from a segmented sputter target. The composition-dependent coexisting phases within the coating were analysed using the complementary methods of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), X-ray absorption near-edge spectroscopy (XANES) and extended X-ray absorption fine-structure spectroscopy (EXAFS). For the analysis of the X-ray absorption near-edge spectra, a new approach for evaluation of the pre-edge peak was developed, taking into account the self-absorption effects in thin films. Within the studied composition range, a mixed face-centred cubic (V,Al)(C,N) phase coexisting with a C–C-containing phase was observed. No indication of hexagonal (V,Al)(N,C) was found. The example of V–Al–C–N demonstrates how important a combination of complementary methods is for the detection of coexisting phases in complex multi-element coatings. PMID:24046506

  2. Composition-dependent structure of polycrystalline magnetron-sputtered V-Al-C-N hard coatings studied by XRD, XPS, XANES and EXAFS.

    PubMed

    Krause, Bärbel; Darma, Susan; Kaufholz, Marthe; Mangold, Stefan; Doyle, Stephen; Ulrich, Sven; Leiste, Harald; Stüber, Michael; Baumbach, Tilo

    2013-08-01

    V-Al-C-N hard coatings with high carbon content were deposited by reactive radio-frequency magnetron sputtering using an experimental combinatorial approach, deposition from a segmented sputter target. The composition-dependent coexisting phases within the coating were analysed using the complementary methods of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), X-ray absorption near-edge spectroscopy (XANES) and extended X-ray absorption fine-structure spectroscopy (EXAFS). For the analysis of the X-ray absorption near-edge spectra, a new approach for evaluation of the pre-edge peak was developed, taking into account the self-absorption effects in thin films. Within the studied composition range, a mixed face-centred cubic (V,Al)(C,N) phase coexisting with a C-C-containing phase was observed. No indication of hexagonal (V,Al)(N,C) was found. The example of V-Al-C-N demonstrates how important a combination of complementary methods is for the detection of coexisting phases in complex multi-element coatings.

  3. Dysprosium compounds studied by resonant inelastic X-ray scattering and high-resolution X-ray absorption near edge structure spectroscopy.

    PubMed

    Zhou, K J; Cui, M Q; Hua, W; Ma, C Y; Zhao, Y D; Huang, Y Y; He, W; Wu, Z Y

    2008-11-15

    A set of resonant inelastic X-ray scattering (RIXS) studies focusing on the 2p64f(n)-->2p54f(n)5d1(2p54f(n+1)5d0)-->2p63d94f(n)5d1(2p63d94f(n+1)5d0) channel of dysprosium in Dy metal, Dy2O3, DyNi3 and Dy25Fe18 compounds have been carried out. Data showed with high statistics and resolution, the different delocalization degree of the 5d band of dysprosium in these compounds, e.g., decreasing from Dy metal to DyNi3, Dy25Fe18 and to dysprosium oxide, in agreement with the high-resolution XANES (HRXANES) spectra. Band structure calculations performed on Dy metal and Dy2O3 confirm both RIXS and HRXANES results in the increasing delocalization of the dysprosium 5d band in Dy metal with respect to Dy2O3. The 5d orbital occupancies of DyNi3 and Dy25Fe18 alloys have been also studied by comparison of the HRXANES white line (WL) area with the behavior of the final states energy position in RIXS spectra and we show that DyNi3 has a higher 5d orbital occupancy than Dy25Fe18.

  4. The C 1s and N 1s near edge x-ray absorption fine structure spectra of five azabenzenes in the gas phase

    SciTech Connect

    Vall-llosera, G.; Gao, B.; Kivimaeki, A.; Coreno, M.; Alvarez Ruiz, J.; Simone, M. de; Aagren, H.; Rachlew, E.

    2008-01-28

    Near edge x-ray absorption fine structure spectra have been measured and interpreted by means of density functional theory for five different azabenzenes (pyridine, pyridazine, pyrimidine, pyrazine, and s-triazine) in the gas phase. The experimental and theoretical spectra at the N 1s and C 1s edges show a strong resonance assigned to the transition of the 1s electron in the respective N or C atoms to the lowest unoccupied molecular orbital with {pi}* symmetry. As opposed to the N 1s edge, at the C 1s edge this resonance is split due to the different environments of the core hole atom in the molecule. The shift in atomic core-level energy due to a specific chemical environment is explained with the higher electronegativity of the N atom compared to the C atom. The remaining resonances below the ionization potential (IP) are associated to {sigma} or {pi} orbitals with mixed valence/Rydberg character. Upon N addition, a reduction of intensity is observed in the Rydberg region at both edges as compared to the intensity in the continuum. Above the IP one or more resonances are seen and ascribed here to transitions to {sigma}* orbitals. Calculating the experimental and theoretical {delta}{sub {pi}} term values at both edges, we observe that they are almost the same within {+-}1 eV as expected for isoelectronic bonded pairs. The term values of the {pi}* and {sigma}* resonances are discussed in terms of the total Z number of the atoms participating in the bond.

  5. Chemical bonding, interface strength, and oxygen K electron-energy-loss near-edge structure of the Cu/Al{sub 2}O{sub 3} interface

    SciTech Connect

    Mizoguchi, Teruyasu; Sasaki, Takeo; Matsunaga, Katsuyuki; Ikuhara, Yuichi; Tanaka, Shingo; Kohyama, Masanori; Yamamoto, Takahisa

    2006-12-15

    Chemical bondings and oxygen K electron-energy-loss near-edge structures (ELNES) of oxygen terminated Cu/Al{sub 2}O{sub 3} heterointerfaces with hollow and on-top configurations were theoretically investigated by using a first principles orthogonalized linear combination of atomic orbitals method. From the chemical bonding analysis, it was found that the hollow configuration has stronger ionic and covalent bondings as compared with the on-top configuration, and the weakness of the on-top configuration originates from the strong antibonding interactions between an interfacial oxygen and the second near neighbor Cu. Detailed analysis using overlap population diagrams revealed the formation mechanism of the strong antibonding interactions in the on-top configuration. In the oxygen K ELNES calculation, a prepeak feature appears in both configurations and it was predicted that the prepeak for the on-top configuration is larger than that for the hollow configuration. The overlap population diagrams elucidated that the prepeak is mainly composed of the O-Cu antibonding interactions, and the larger prepeak of the on-top configuration originates from the larger O-Cu interactions. The dependence of O-K ELNES on the direction of the momentum transfer vector was also discussed. Knowledge of the responsible direction of the momentum transfer vector in relation to the interface orientation was concluded to be indispensable in order to discuss detailed profiles of the ELNES from metal/ceramic heterointerfaces. This study reveals the effect of the atomic configuration of the interface to the chemical bondings, interface strength, and ELNES.

  6. Systematic Oxidation of Polystyrene by Ultraviolet-Ozone, Characterized by Near-Edge X-ray Absorption Fine Structure and Contact Angle

    SciTech Connect

    Klein,R.; Fischer, D.; Lenhart, J.

    2008-01-01

    The process of implanting oxygen in polystyrene (PS) via exposure to ultraviolet-ozone (UV-O) was systematically investigated using the characterization technique of near-edge X-ray absorption fine structure (NEXAFS). Samples of PS exposed to UV-O for 10-300 s and washed with isopropanol were analyzed using the carbon and oxygen K-edge NEXAFS partial electron yields, using various retarding bias voltages to depth-profile the oxygen penetration into the surface. Evaluation of reference polymers provided a scale to quantify the oxygen concentration implanted by UV-O treatment. We find that ozone initially reacts with the double bonds on the phenyl rings, forming carbonyl groups, but within 1 min of exposure, the ratio of double to single oxygen bonds stabilizes at a lower value. Oxygen penetrates the film with relative ease, creating a fairly uniform distribution of oxygen within at least the first 4 nm (the effective depth probed by NEXAFS here). Before oxygen accumulates in large concentrations, however, it preferentially degrades the uppermost layer of the film by removing oxygenated low-molecular-weight oligomers. The failure to accumulate high concentrations of oxygen is seen in the nearly constant carbon edge jump, the low concentration of oxygen even at 5 min exposure (58% of that in poly(4-acetoxystyrene), the polymer with the most similarities to UV-O-treated PS), and the relatively high contact angles. At 5 min exposure the oxygen concentration contains ca. 7 atomic % oxygen. The oxygen species that are implanted consist predominantly of single O-C bonds and double OC bonds but also include a small fraction of O-H. UV-O treatment leads a plateau after 2 min exposure in the water contact angle hysteresis, at a value of 67 {+-} 2, due primarily to chemical heterogeneity. Annealing above Tg allows oxygenated species to move short distances away from the surface but not diffuse further than 1-2 nm.

  7. Spectroscopic analysis of small organic molecules: A comprehensive near-edge x-ray-absorption fine-structure study of C{sub 6}-ring-containing molecules

    SciTech Connect

    Kolczewski, C.; Puettner, R.; Martins, M.; Schlachter, A.S.; Snell, G.; Sant'Anna, M.M.; Hermann, K.; Kaindl, G.

    2006-01-21

    We report high-resolution C 1s near-edge x-ray-absorption fine-structure (NEXAFS) spectra of the C{sub 6}-ring-containing molecules benzene (C{sub 6}H{sub 6}), 1,3- and 1,4-cyclohexadiene (C{sub 6}H{sub 8}), cyclohexene (C{sub 6}H{sub 10}), cyclohexane (C{sub 6}H{sub 12}), styrene (C{sub 8}H{sub 8}), and ethylbenzene (C{sub 8}H{sub 10}) which allow us to examine the gradual development of delocalization of the corresponding {pi} electron systems. Due to the high experimental resolution, vibrational progressions can be partly resolved in the spectra. The experimental spectra are compared with theoretical NEXAFS spectra obtained from density-functional theory calculations where electronic final-state relaxation is accounted for. The comparison yields very good agreement between theoretical spectra and experimental results. In all cases, the spectra can be described by excitations to {pi}*- and {sigma}*-type final-state orbitals with valence character, while final-state orbitals of Rydberg character make only minor contributions. The lowest C 1s{yields}1{pi}* excitation energy is found to agree in the (experimental and theoretical) spectra of all molecules except for 1,3-cyclohexadiene (C{sub 6}H{sub 8}) where an energy smaller by about 0.6 eV is obtained. The theoretical analysis can explain this result by different binding properties of this molecule compared to the others.

  8. Near-Edge X-ray Absorption Fine Structure Imaging of Spherical and Flat Counterfaces of Ultrananocrystalline Diamond Tribological Contacts: A Correlation of Surface Chemistry and Friction

    SciTech Connect

    A Konicek; C Jaye; M Hamilton; W Sawyer; D Fischer; R Carpick

    2011-12-31

    A recently installed synchrotron radiation near-edge X-ray absorption fine structure (NEXAFS) full field imaging electron spectrometer was used to spatially resolve the chemical changes of both counterfaces from an ultra-nanocrystalline diamond (UNCD) tribological contact. A silicon flat and Si{sub 3}N{sub 4} sphere were both coated with UNCD, and employed to form two wear tracks on the flat in a linear reciprocating tribometer. The first wear track was produced using a new, unconditioned sphere whose surface was thus conditioned during this first experiment. This led to faster run-in and lower friction when producing a second wear track using the conditioned sphere. The large depth of field of the magnetically guided NEXAFS imaging detector enabled rapid, large area spectromicroscopic imaging of both the spherical and flat surfaces. Laterally resolved NEXAFS data from the tribological contact area revealed that both substrates had an as-grown surface layer that contained a higher fraction of sp{sup 2}-bonded carbon and oxygen which was mechanically removed. Unlike the flat, the film on the sphere showed evidence of having graphitic character, both before and after sliding. These results show that the graphitic character of the sphere is not solely responsible for low friction and short run-in. Rather, conditioning the sphere, likely by removing asperities and passivating dangling bonds, leads to lower friction with less chemical modification of the substrate in subsequent tests. The new NEXAFS imaging spectroscopy detector enabled a more complete understanding of the tribological phenomena by imaging, for the first time, the surface chemistry of the spherical counterface which had been in continual contact during wear track formation.

  9. Characterization of Functionalized Self-Assembled Monolayers and Surface-Attached Interlocking Molecules Using Near-Edge X-ray Absorption Fine Structure Spectroscopy

    SciTech Connect

    Willey, Trevor M.

    2004-04-01

    Quantitative knowledge of the fundamental structure and substrate binding, as well as the direct measurement of conformational changes, are essential to the development of self-assembled monolayers (SAMs) and surface-attached interlocking molecules, catenanes and rotaxanes. These monolayers are vital to development of nano-mechanical, molecular electronic, and biological/chemical sensor applications. This dissertation investigates properties of functionalized SAMs in sulfur-gold based adsorbed molecular monolayers using quantitative spectroscopic techniques including near-edge x-ray absorption fine structure spectroscopy (NEXAFS) and x-ray photoelectron spectroscopy (XPS). The stability of the gold-thiolate interface is addressed. A simple model SAM consisting of dodecanethiol adsorbed on Au(111) degrades significantly in less than 24 hours under ambient laboratory air. S 2p and O 1s XPS show the gold-bound thiolates oxidize to sulfinates and sulfonates. A reduction of organic material on the surface and a decrease in order are observed as the layer degrades. The effect of the carboxyl vs. carboxylate functionalization on SAM structure is investigated. Carboxyl-terminated layers consisting of long alkyl-chain thiols vs. thioctic acid with short, sterically separated, alkyl groups are compared and contrasted. NEXAFS shows a conformational change, or chemical switchability, with carboxyl groups tilted over and carboxylate endgroups more upright. Surface-attached loops and simple surface-attached rotaxanes are quantitatively characterized, and preparation conditions that lead to desired films are outlined. A dithiol is often insufficient to form a molecular species bound at each end to the substrate, while a structurally related disulfide-containing polymer yields surface-attached loops. Similarly, spectroscopic techniques show the successful production of a simple, surface-attached rotaxane that requires a ''molecular riveting'' step to hold the mechanically attached

  10. Infrared and X-ray Absorption Near Edge Structure Spectroscopy Analyses of the Titan Haze Simulation (THS) Aerosols Produced at Low Temperature (200 K)

    NASA Astrophysics Data System (ADS)

    Sciamma-O'Brien, Ella; Salama, Farid

    2016-10-01

    We present our latest results on the Titan Haze Simulation (THS) experiment developed on the COSmIC simulation chamber at NASA Ames. In Titan's atmosphere, a complex organic chemistry induced by UV radiation and electron bombardment occurs between N2 and CH4 and leads to the production of larger molecules and solid aerosols. In the THS, Titan's chemistry is simulated by pulsed plasma in the stream of a supersonic expansion, at Titan-like temperature (200 K). The residence time of the gas in the pulsed plasma discharge is ~3 µs, hence the chemistry is truncated allowing us to probe the first and intermediate steps of the chemistry, by adding heavier precursors into the initial N2-CH4 gas mixture. Experiments have been performed in different gas mixtures from the simpler N2-CH4 (98:2 and 95:5), to more complex mixtures: N2-CH4-C2H2 (91:5:4 and 94.5:5:0.5), N2-CH4-C6H6 (90:5:5) and N2-CH4-C2H2-C6H6 (86:5:4:5). Both the gas and solid phases have been analyzed using a combination of in situ and ex situ diagnostics.A recent mass spectrometry analysis of the gas phase demonstrated that the THS is a unique tool to monitor the different steps of the N2-CH4 chemistry [1]. The results of the solid phase study are consistent with the chemical growth evolution observed in the gas phase. The solid phase products are in the form of grains produced in volume and not from interaction on the substrate's surface. Scanning Electron Microscopy images have shown that more complex mixtures produce larger aggregates (100-500 nm in N2-CH4, up to 5 µm in N2-CH4-C2H2-C6H6). Moreover, the morphology of the grains seems to depend on the precursors, a finding that could have an impact on Titan haze microphysical models. We will present the latest results of the infrared and x-ray absorption near edge structure spectroscopic measurements that have been performed on all four mixtures. These results provide information on the nature of the different functional groups present in our samples as

  11. Ligand binding processes in hemoglobin. Chemical reactivity of iron studied by XANES spectroscopy.

    PubMed Central

    Pin, S; Valat, P; Cortes, R; Michalowicz, A; Alpert, B

    1985-01-01

    K-absorption edge of coordinated ions exhibits a fine structure (through the use of XANES, or x-ray absorption near edge structures) that reflects the electronic repartition and the chemical reactivity of these ions. Comparative analysis of iron K-absorption-edge shape for hemoglobin derivatives with different ligand affinity suggests strongly that in hemoglobin, iron-forms with high and low affinity are highly improbable. PMID:4092074

  12. Density functional theory simulation of the L2,3 XANES spectra

    NASA Astrophysics Data System (ADS)

    Alperovich, I.; Soldatov, A. V.; Moonshiram, D.; Pushkar, Yu. N.

    2012-07-01

    A method for the theoretical simulation of X-ray absorption near edge structure (XANES) spectra at the Ru L2,3 edges has been developed using relativistic density functional theory (DFT) calculations. The effect of the parameters of DFT calculations on the shape of theoretical curves has been comparatively analyzed for XANES spectra of a water oxidation catalyst and hexaammineruthenium complexes. Recommendations for the choice of the best parameters ensuring good agreement with the experimental data, including the most correct exchange-correlation potential, have been made.

  13. Electronic structure and optical properties of CdS{sub x}Se{sub 1−x} solid solution nanostructures from X-ray absorption near edge structure, X-ray excited optical luminescence, and density functional theory investigations

    SciTech Connect

    Murphy, M. W.; Yiu, Y. M. Sham, T. K.; Ward, M. J.; Liu, L.; Hu, Y.; Zapien, J. A.; Liu, Yingkai

    2014-11-21

    The electronic structure and optical properties of a series of iso-electronic and iso-structural CdS{sub x}Se{sub 1−x} solid solution nanostructures have been investigated using X-ray absorption near edge structure, extended X-ray absorption fine structure, and X-ray excited optical luminescence at various absorption edges of Cd, S, and Se. It is found that the system exhibits compositions, with variable local structure in-between that of CdS and CdSe accompanied by tunable optical band gap between that of CdS and CdSe. Theoretical calculation using density functional theory has been carried out to elucidate the observations. It is also found that luminescence induced by X-ray excitation shows new optical channels not observed previously with laser excitation. The implications of these observations are discussed.

  14. Unraveling the solid-liquid-vapor phase transition dynamics at the atomic level with ultrafast x-ray absorption near-edge spectroscopy.

    PubMed

    Dorchies, F; Lévy, A; Goyon, C; Combis, P; Descamps, D; Fourment, C; Harmand, M; Hulin, S; Leguay, P M; Petit, S; Peyrusse, O; Santos, J J

    2011-12-09

    X-ray absorption near-edge spectroscopy (XANES) is a powerful probe of electronic and atomic structures in various media, ranging from molecules to condensed matter. We show how ultrafast time resolution opens new possibilities to investigate highly nonequilibrium states of matter including phase transitions. Based on a tabletop laser-plasma ultrafast x-ray source, we have performed a time-resolved (∼3  ps) XANES experiment that reveals the evolution of an aluminum foil at the atomic level, when undergoing ultrafast laser heating and ablation. X-ray absorption spectra highlight an ultrafast transition from the crystalline solid to the disordered liquid followed by a progressive transition of the delocalized valence electronic structure (metal) down to localized atomic orbitals (nonmetal-vapor), as the average distance between atoms increases.

  15. X-ray absorption near edge spectroscopy at the Mn K-edge in highly homogeneous GaMnN diluted magnetic semiconductors

    NASA Astrophysics Data System (ADS)

    Sancho-Juan, O.; Cantarero, A.; Martínez-Criado, G.; Olguín, D.; Garro, N.; Cros, A.; Salomé, M.; Susini, J.; Dhar, S.; Ploog, K.

    We have studied by X-ray absorption spectroscopy the local environment of Mn in highly homogeneous Ga1-xMnxN (0.06 < x < 0.14) thin epilayers grown by molecular beam epitaxy on [0001] SiC substrates. The measurements were performed in fluorescence mode around the Ga and Mn K-edges. In this report, we focus our attention to the X-ray absorption near edge spectroscopy (XANES) results. The comparison of the XANES spectra corresponding to the Ga and Mn edges indicates that Mn is substitutional to Ga in all samples studied. The XANES spectra measured at the Mn absorption edge shows in the near-edge region a double peak and a shoulder below the absorption edge and the main absorption peak after the edge, separated around 15 eV above the pre-edge structure. We have compared the position of the edge with that of MnO (Mn2+) and Mn2O3 (Mn3+). All samples studied present the same Mn oxidation state, 2+. In order to interprete the near-edge structure, we have performed ab initio calculations with a 2 × 2 × 1 supercell (?6% Mn) using the full potential linear augmented plane wave method as implemented in the Wien2k code. The calculations show the appearance of Mn anti-bonding t2g bands, which are responsible for the pre-edge absorption. The shoulder and main absorption peaks are due to transitions from the valence band 1s-states of Mn to the p-contributions of the conduction bands.

  16. Structural investigations of PuIII phosphate by X-ray diffraction, MAS-NMR and XANES spectroscopy

    NASA Astrophysics Data System (ADS)

    Popa, Karin; Raison, Philippe E.; Martel, Laura; Martin, Philippe M.; Prieur, Damien; Solari, Pier L.; Bouëxière, Daniel; Konings, Rudy J. M.; Somers, Joseph

    2015-10-01

    PuPO4 was prepared by a solid state reaction method and its crystal structure at room temperature was solved by powder X-ray diffraction combined with Rietveld refinement. High resolution XANES measurements confirm the +III valence state of plutonium, in agreement with valence bond derivation. The presence of the americium (as β- decay product of plutonium) in the +III oxidation state was determined based on XANES spectroscopy. High resolution solid state 31P NMR agrees with the XANES results and the presence of a solid-solution.

  17. Speciation and long- and short-term molecular-level dynamics of soil organic sulfur studied by X-ray absorption near-edge structure spectroscopy.

    PubMed

    Solomon, Dawit; Lehmann, Johannes; de Zarruk, Katrin Knoth; Dathe, Julia; Kinyangi, James; Liang, Biqing; Machado, Stephen

    2011-01-01

    We investigated speciation, oxidative state changes, and long- and short-term molecular-level dynamics of organic S after 365 d of aerobic incubation with and without the addition of sugarcane residue using XANES spectroscopy. Soil samples were collected from the upper 15 cm of undisturbed grasslands since 1880, from undisturbed grasslands since 1931, and from cultivated fields since 1880 in the western United States. We found three distinct groups of organosulfur compounds in these grassland-derived soils: (i) strongly reduced (S to S) organic S that encompasses thiols, monosulfides, disulfides, polysulfides, and thiophenes; (ii) organic S in intermediate oxidation (S to S) states, which include sulfoxides and sulfonates; and (iii) strongly oxidized (S) organic S, which comprises ester-SO-S. The first two groups represent S directly linked to C and accounted for 80% of the total organic S detected by XANES from the undisturbed soils. Aerobic incubation without the addition of sugarcane residue led to a 21% decline in organanosulfur compounds directly linked to C and to up to an 82% increase inorganic S directly bonded to O. Among the C-bonded S compounds, low-valence thiols, sulfides, thiophenic S, and intermediate-valence sulfoxide S seem to be highly susceptible to microbial attack and may represent the most reactive components of organic S pool in these grassland soils. Sulfonate S exhibited a much lower short-term reactivity. The incorporation of sugarcane residue resulted in an increase in organosulfur compounds directly bonded to C at the early stage of incubation. However, similar to soils incubated without residue addition, the proportion of organic S directly linked to C continued to decline with increasing duration of aerobic incubation, whereas the proportion of organic S directly bonded to O showed a steady rise. American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America.

  18. Speciation and Long- and Short-term Molecular-level Dynamics of Soil Organic Sulfur Studied by X-ray Absorption Near-Edge Structure Spectroscopy

    SciTech Connect

    D Solomon; J Lehmann; K Knoth de Zarruk; J Dathe; J Kinyangi; B Liang; S Machado

    2011-12-31

    We investigated speciation, oxidative state changes, and long- and short-term molecular-level dynamics of organic S after 365 d of aerobic incubation with and without the addition of sugarcane residue using XANES spectroscopy. Soil samples were collected from the upper 15 cm of undisturbed grasslands since 1880, from undisturbed grasslands since 1931, and from cultivated fields since 1880 in the western United States. We found three distinct groups of organosulfur compounds in these grassland-derived soils: (i) strongly reduced (S{sup 0} to S{sup 1+}) organic S that encompasses thiols, monosulfides, disulfides, polysulfides, and thiophenes; (ii) organic S in intermediate oxidation (S{sup 2+} to S{sup 5+}) states, which include sulfoxides and sulfonates; and (iii) strongly oxidized (S{sup 6+}) organic S, which comprises ester-SO{sub 4}-S. The first two groups represent S directly linked to C and accounted for 80% of the total organic S detected by XANES from the undisturbed soils. Aerobic incubation without the addition of sugarcane residue led to a 21% decline in organanosulfur compounds directly linked to C and to up to an 82% increase inorganic S directly bonded to O. Among the C-bonded S compounds, low-valence thiols, sulfides, thiophenic S, and intermediate-valence sulfoxide S seem to be highly susceptible to microbial attack and may represent the most reactive components of organic S pool in these grassland soils. Sulfonate S exhibited a much lower short-term reactivity. The incorporation of sugarcane residue resulted in an increase in organosulfur compounds directly bonded to C at the early stage of incubation. However, similar to soils incubated without residue addition, the proportion of organic S directly linked to C continued to decline with increasing duration of aerobic incubation, whereas the proportion of organic S directly bonded to O showed a steady rise.

  19. Extended x-ray absorption fine structure spectroscopy and x-ray absorption near edge spectroscopy study of aliovalent doped ceria to correlate local structural changes with oxygen vacancies clustering

    SciTech Connect

    Shirbhate, S. C.; Acharya, S. A.; Yadav, A. K.

    2016-04-04

    This study provides atomic scale insight to understand the role of aliovalent dopants on oxygen vacancies clustering and dissociation mechanism in ceria system in order to enhance the performance of oxy-ion conductor. Dopants induced microscale changes in ceria are probed by extended X-ray absorption fine structure spectroscopy, X-ray absorption near edge spectra, and Raman spectroscopy. The results are explored to establish a correlation between atomic level structural changes (coordination number, interatomic spacing) → formation of dimer and trimer type cation-oxygen vacancies defect complex (intrinsic and extrinsic) → dissociation of oxygen vacancies from defect cluster → ionic conductivity temperature. It is a strategic approach to understand key physics of ionic conductivity mechanism in order to reduce operating temperature of electrolytes for intermediate temperature (300–450 °C) electrochemical devices for the first time.

  20. Determining the Sulfur species in the dispersants Corexit 9500A and 9527A applying S K-edge XANES spectroscopy

    NASA Astrophysics Data System (ADS)

    Bovenkamp-Langlois, Lisa; Roy, Amitava

    2016-05-01

    The dispersants Corexit 9500A and 9527A were used extensively during the Deepwater Horizon oil spill in the Gulf of Mexico. Sulfur K-edge X-ray absorption near edge structure (XANES) spectroscopy was used to investigate the dispersants for the sulfur based components. The main sulfur containing component should be dioctyl sodium sulfosuccinate (DOSS). S K-edge XANES analysis shows that indeed the major sulfur species in both kinds of Corexit (9500A and 9527A) is sulfonic acid which is a part of DOSS. In addition some fraction of sulfone was detected.

  1. First-principles calculations of Zn-K XANES in Ca-deficient hydroxyapatite.

    PubMed

    Murata, Hidenobu; Shitara, Kazuki; Tanaka, Isao; Nakahira, Atsushi; Mizoguchi, Teruyasu; Matsunaga, Katsuyuki

    2010-09-29

    The local environment of substitutional Zn(2+) in Ca-deficient hydroxyapatite (HAp) was investigated using experimental and theoretical analyses of the x-ray absorption near edge structure (XANES). For Zn-K XANES calculations, two situations of Zn(2+) were considered. One was Zn(2+) substituted for Ca sites in perfect HAp, and the other was a Ca-deficient HAp model of substitutional Zn(2+) associated with a Ca(2+) vacancy charge compensated by two protons. The model of Zn(2+) in perfect HAp did not reproduce the experimental Zn-K XANES spectrum. In contrast, the Ca-deficient HAp model agreed well with the experimental spectrum. This indicates that substitutional Zn(2+) in Ca-deficient HAp is associated with the Ca(2+) vacancy complex in HAp.

  2. Nondestructive Speciation Depth Profiling of Complex TiOx Nanolayer Structures by Grazing Incidence X-ray Fluorescence Analysis and Near Edge X-ray Absorption Fine Structure Spectroscopy.

    PubMed

    Pollakowski, Beatrix; Beckhoff, Burkhard

    2015-08-04

    An important challenge of modern material science is the depth-sensitive and nondestructive analysis of the chemical binding state of complex structures consisting of multiple thin layers. In general, the correlation of the material functionality and underlying chemical and physical properties is the key question in view of directed device development, performance, and quality control. It has been shown that the combined method grazing incidence X-ray fluorescence analysis (GIXRF) and near edge X-ray absorption fine structure spectroscopy (NEXAFS) can significantly contribute to the nondestructive chemical analysis of buried thin films and interface structures regarding chemical speciation. Recently, we have enhanced the method to allow for a depth-resolved analysis of multilayered nanoscaled thin film structures. By means of appropriate model systems, the methodology has been developed and successfully validated. The model systems basically consist of a carbon cap layer, two titanium layers differing in their oxidation states and separated by a thin carbon layer, and a silicon substrate covered with molybdenum and a carbon layer. A differential approach has been developed to derive the chemical species of each of the titanium layers.

  3. X-ray absorption near edge spectroscopy with a superconducting detector for nitrogen dopants in SiC

    PubMed Central

    Ohkubo, M.; Shiki, S.; Ukibe, M.; Matsubayashi, N.; Kitajima, Y.; Nagamachi, S.

    2012-01-01

    Fluorescence-yield X-ray absorption fine structure (FY-XAFS) is extensively used for investigating atomic-scale local structures around specific elements in functional materials. However, conventional FY-XAFS instruments frequently cannot cover trace light elements, for example dopants in wide gap semiconductors, because of insufficient energy resolution of semiconductor X-ray detectors. Here we introduce a superconducting XAFS (SC-XAFS) apparatus to measure X-ray absorption near-edge structure (XANES) of n-type dopant N atoms (4 ×1019 cm−3) implanted at 500°C into 4H-SiC substrates annealed subsequently. The XANES spectra and ab initio multiple scattering calculations indicate that the N atoms almost completely substitute for the C sites, associated with a possible existence of local CN regions, in the as-implanted state. This is a reason why hot implantation is necessary for dopant activation in ion implantation. The SC-XAFS apparatus may play an important role in improving doping processes for energy-saving wide-gap semiconductors and other functional materials. PMID:23152937

  4. Speciation of sulfur from filamentous microbial mats from sulfidic cave springs using X-ray absorption near-edge spectroscopy.

    PubMed

    Engel, Annette Summers; Lichtenberg, Henning; Prange, Alexander; Hormes, Josef

    2007-04-01

    Most transformations within the sulfur cycle are controlled by the biosphere, and deciphering the abiotic and biotic nature and turnover of sulfur is critical to understand the geochemical and ecological changes that have occurred throughout the Earth's history. Here, synchrotron radiation-based sulfur K-edge X-ray absorption near-edge structure (XANES) spectroscopy is used to examine sulfur speciation in natural microbial mats from two aphotic (cave) settings. Habitat geochemistry, microbial community compositions, and sulfur isotope systematics were also evaluated. Microorganisms associated with sulfur metabolism dominated the mats, including members of the Epsilonproteobacteria and Gammaproteobacteria. These groups have not been examined previously by sulfur K-edge XANES. All of the mats consisted of elemental sulfur, with greater contributions of cyclo-octasulfur (S8) compared with polymeric sulfur (Smicro). While this could be a biological fingerprint for some bacteria, the signature may also indicate preferential oxidation of Smicro and S8 accumulation. Higher sulfate content correlated to less S8 in the presence of Epsilonproteobacteria. Sulfur isotope compositions confirmed that sulfur content and sulfur speciation may not correlate to microbial metabolic processes in natural samples, thereby complicating the interpretation of modern and ancient sulfur records.

  5. Existence of Fe{sup 4+} ions in Co{sub 2.25}Fe{sub 0.75}O{sub 4} spinel ferrite confirmed from SXRD and XANES spectroscopy

    SciTech Connect

    Panda, Manas Ranjan Bhowmik, R. N.; Sinha, A. K.

    2015-06-24

    The Co{sub 2.25}Fe{sub 0.75}O{sub 4} ferrite composition has been prepared by chemical co-precipitation route. The as-prepared sample after annealing at 900°C in air formed single phase cubic spinel structure. Synchrotron X-ray diffraction and X-ray absorption near edge structure (XANES) measurements were used to study charge states of the cations in octahedral and tetrahedral sites of the cubic spinel structure. Raman spectra indicated normal cubic spinel structure. XANES data suggested the existence of Fe{sup 4+} ions in the spinel structure.

  6. Structural investigations of Pu{sup III} phosphate by X-ray diffraction, MAS-NMR and XANES spectroscopy

    SciTech Connect

    Popa, Karin; Raison, Philippe E.; Martel, Laura; Martin, Philippe M.; Solari, Pier L.; Bouëxière, Daniel; Konings, Rudy J.M.; Somers, Joseph

    2015-10-15

    PuPO{sub 4} was prepared by a solid state reaction method and its crystal structure at room temperature was solved by powder X-ray diffraction combined with Rietveld refinement. High resolution XANES measurements confirm the +III valence state of plutonium, in agreement with valence bond derivation. The presence of the americium (as β{sup −} decay product of plutonium) in the +III oxidation state was determined based on XANES spectroscopy. High resolution solid state {sup 31}P NMR agrees with the XANES results and the presence of a solid-solution. - Graphical abstract: A full structural analysis of PuPO{sub 4} based on Rietveld analysis of room temperature X-ray diffraction data, XANES and MAS NMR measurements was performed. - Highlights: • The crystal structure of PuPO{sub 4} monazite is solved. • In PuPO{sub 4} plutonium is strictly trivalent. • The presence of a minute amount of Am{sup III} is highlighted. • We propose PuPO{sub 4} as a potential reference material for spectroscopic and microscopic studies.

  7. The competitive growth of cubic domains in Ti(1-x)AlxN films studied by diffraction anomalous near-edge structure spectroscopy.

    PubMed

    Pinot, Y; Tuilier, M-H; Pac, M-J; Rousselot, C; Thiaudière, D

    2015-11-01

    Titanium and aluminium nitride films deposited by magnetron sputtering generally grow as columnar domains made of oriented nanocrystallites with cubic or hexagonal symmetry depending on Al content, which are embedded in more disordered grain boundaries. The substitution of Al atoms for Ti in the cubic lattice of the films improves their resistance to wear and oxidation, allowing their use as protective coatings. Ti K-edge X-ray absorption spectroscopy, which probes both crystallized and more disordered grain boundaries, and X-ray diffraction anomalous fine structure, which is sensitive to short- and long-range order within a given crystallized domain, are carried out on a set of Ti(1-x)AlxN films deposited by magnetron sputtering on Si substrates. Attention is paid to the shape of the pre-edge region, which is sensitive to the symmetry of the site occupied by Ti atoms, either octahedral in face-centred-cubic Ti-rich (TiN, Ti0.54Al0.46N) samples or tetrahedral in hexagonal-close-packed Al-rich (Ti0.32Al0.68N) films. In order to obain information on the titanium environment in the well crystallized areas, subtraction of the smooth part of the energy-dependent structure factor for the Bragg reflections is applied to the pre-edge region of the diffraction anomalous data in order to restore their spectroscopic appearance. A flat pre-edge is related to the typical octahedral environment of Ti atoms for cubic reflections. The difference observed between pre-edge spectra associated with face-centred-cubic 200 and 111 Bragg reflections of Ti0.54Al0.46N is assigned to Ti enrichment of 111 large well ordered domains compared with the more disordered 200 ones. The sharp peak observed in the spectrum recorded from the hexagonal 002 peak of Ti0.32Al0.68N can be regarded as a standard for the pure tetrahedral Ti environment in hexagonal-close-packed nitride.

  8. Near-edge band structures and band gaps of Cu-based semiconductors predicted by the modified Becke-Johnson potential plus an on-site Coulomb U

    SciTech Connect

    Zhang, Yubo; Zhang, Jiawei; Wang, Youwei; Gao, Weiwei; Abtew, Tesfaye A.; Zhang, Peihong E-mail: wqzhang@mail.sic.ac.cn; Zhang, Wenqing E-mail: wqzhang@mail.sic.ac.cn

    2013-11-14

    Diamond-like Cu-based multinary semiconductors are a rich family of materials that hold promise in a wide range of applications. Unfortunately, accurate theoretical understanding of the electronic properties of these materials is hindered by the involvement of Cu d electrons. Density functional theory (DFT) based calculations using the local density approximation or generalized gradient approximation often give qualitative wrong electronic properties of these materials, especially for narrow-gap systems. The modified Becke-Johnson (mBJ) method has been shown to be a promising alternative to more elaborate theory such as the GW approximation for fast materials screening and predictions. However, straightforward applications of the mBJ method to these materials still encounter significant difficulties because of the insufficient treatment of the localized d electrons. We show that combining the promise of mBJ potential and the spirit of the well-established DFT + U method leads to a much improved description of the electronic structures, including the most challenging narrow-gap systems. A survey of the band gaps of about 20 Cu-based semiconductors calculated using the mBJ + U method shows that the results agree with reliable values to within ±0.2 eV.

  9. Quadrupole transition in the Dy L{sub 3} edge observed by lifetime-broadening-suppressed XANES spectroscopy

    SciTech Connect

    Hayashi, Hisashi; Takeda, Rumi; Kawata, Masaki; Udagawa, Yasuo; Kawamura, Naomi; Watanabe, Yasuhiro; Nanao, Susumu

    2004-10-15

    Lifetime-broadening-suppressed x-ray absorption near edge structure (LBS-XANES) spectroscopy is applied to the Dy L{sub 3} edge, where multiplet nature of the final state as well as lifetime-broadening distorts the band shape. It was found that, by determining appropriate final state density function from observed the L{alpha} band shape, LBS-XANES spectra can be obtained and 2p{yields}4f quadrupole transition is unequivocally observed as a separate peak. It has been proved from the present results that LBS-XANES spectroscopy is very versatile; transitions with multiplet final states can be studied by the use of hard x-rays and forbidden transitions obscured by intense dipole-allowed transitions can be revealed. Implications for resonant inelastic x-ray scattering (RIXS) spectra are also discussed in terms of RIXS contour plot and the Kramers-Heisenberg equation.

  10. Orientation of graphitic planes during the bias-enhanced nucleation of diamond on silicon: An x-ray absorption near-edge study

    SciTech Connect

    Jimenez, I.; Mar Garcia, M.; Albella, J.M.; Terminello, L.J.

    1998-11-01

    The bias-enhanced nucleation of diamond on Si(100) is studied by angle-dependent x-ray absorption near-edge spectroscopy (XANES). During diamond nucleation, a graphitic phase is also detected. The angle dependence of the XANES signal shows that the graphitic basal planes are oriented perpendicular to the surface. Implications of this result on the mechanism of bias-enhanced nucleation are discussed.{copyright} {ital 1998 American Institute of Physics.}

  11. Phosphorus K-edge XANES spectroscopy of mineral standards

    PubMed Central

    Ingall, Ellery D.; Brandes, Jay A.; Diaz, Julia M.; de Jonge, Martin D.; Paterson, David; McNulty, Ian; Elliott, W. Crawford; Northrup, Paul

    2011-01-01

    Phosphorus K-edge X-ray absorption near-edge structure (XANES) spectroscopy was performed on phosphate mineral specimens including (a) twelve specimens from the apatite group covering a range of compositional variation and crystallinity; (b) six non-apatite calcium-rich phosphate minerals; (c) 15 aluminium-rich phosphate minerals; (d) ten phosphate minerals rich in either reduced iron or manganese; (e) four phosphate minerals rich in either oxidized iron or manganese; (f) eight phosphate minerals rich in either magnesium, copper, lead, zinc or rare-earth elements; and (g) four uranium phosphate minerals. The identity of all minerals examined in this study was independently confirmed using X-ray powder diffraction. Minerals were distinguished using XANES spectra with a combination of pre-edge features, edge position, peak shapes and post-edge features. Shared spectral features were observed in minerals with compositions dominated by the same specific cation. Analyses of apatite-group minerals indicate that XANES spectral patterns are not strongly affected by variations in composition and crystallinity typical of natural mineral specimens. PMID:21335905

  12. Phosphorus K-edge XANES Spectroscopy of Mineral Standards

    SciTech Connect

    E Ingall; J Brandes; J Diaz; M de Jonge; D Paterson; I McNulty; C Elliott; P Northrup

    2011-12-31

    Phosphorus K-edge X-ray absorption near-edge structure (XANES) spectroscopy was performed on phosphate mineral specimens including (a) twelve specimens from the apatite group covering a range of compositional variation and crystallinity; (b) six non-apatite calcium-rich phosphate minerals; (c) 15 aluminium-rich phosphate minerals; (d) ten phosphate minerals rich in either reduced iron or manganese; (e) four phosphate minerals rich in either oxidized iron or manganese; (f) eight phosphate minerals rich in either magnesium, copper, lead, zinc or rare-earth elements; and (g) four uranium phosphate minerals. The identity of all minerals examined in this study was independently confirmed using X-ray powder diffraction. Minerals were distinguished using XANES spectra with a combination of pre-edge features, edge position, peak shapes and post-edge features. Shared spectral features were observed in minerals with compositions dominated by the same specific cation. Analyses of apatite-group minerals indicate that XANES spectral patterns are not strongly affected by variations in composition and crystallinity typical of natural mineral specimens.

  13. XANES, EXAFS and photoluminescence investigations on the amorphous Eu:HfO2.

    PubMed

    Sharma, Aditya; Varshney, Mayora; Shin, Hyun-Joon; Chae, KeunHwa; Won, Sung Ok

    2017-02-15

    We report detailed investigations on the local electronic/atomic structure and photoluminescence properties of chemically synthesized Eu:HfO2 powders. X-ray diffraction (XRD), X-ray absorption near edge structure (XANES), extended X-ray absorption fine structure (EXAFS) and photoluminescence (PL) measurements were performed to analyze the crystal structure, local atomic/electronic structure and luminescence properties of the samples. No crystalline phases were detected with Cu Kα (λ=1.5418Å) based XRD; however, local monoclinic structure was confirmed by the Hf L-edge XANES and EXAFS. O K-edge XANES spectral features could be deconvoluted with doublets and triplets in eg and t2g orbitals, respectively, which ascribed to the local monoclinic structure for all of the samples. Eu M5,4-edge XANES confirmed the pre-dominancy of Eu(3+) ions in the HfO2 samples with a fractional amount of Eu(2+) ions. PL spectra revealed the electric dipole allowed ((5)D0-(7)F0,2,4) emission properties of Eu:HfO2 samples. The orange-red emission is ascribed to the Eu interstitial/surface segregation induced defects. Copyright © 2016. Published by Elsevier B.V.

  14. XANES, EXAFS and photoluminescence investigations on the amorphous Eu:HfO2

    NASA Astrophysics Data System (ADS)

    Sharma, Aditya; Varshney, Mayora; Shin, Hyun-Joon; Chae, KeunHwa; Won, Sung Ok

    2017-02-01

    We report detailed investigations on the local electronic/atomic structure and photoluminescence properties of chemically synthesized Eu:HfO2 powders. X-ray diffraction (XRD), X-ray absorption near edge structure (XANES), extended X-ray absorption fine structure (EXAFS) and photoluminescence (PL) measurements were performed to analyze the crystal structure, local atomic/electronic structure and luminescence properties of the samples. No crystalline phases were detected with Cu Kα (λ = 1.5418 Å) based XRD; however, local monoclinic structure was confirmed by the Hf L-edge XANES and EXAFS. O K-edge XANES spectral features could be deconvoluted with doublets and triplets in eg and t2g orbitals, respectively, which ascribed to the local monoclinic structure for all of the samples. Eu M5,4-edge XANES confirmed the pre-dominancy of Eu3 + ions in the HfO2 samples with a fractional amount of Eu2 + ions. PL spectra revealed the electric dipole allowed (5D0-7F0,2,4) emission properties of Eu:HfO2 samples. The orange-red emission is ascribed to the Eu interstitial/surface segregation induced defects.

  15. Surface metallization on Si(001) at elevated temperatures studied by angle-resolved photoemission spectroscopy and near-edge x-ray absorption fine structure: Effect of thermal adatoms

    NASA Astrophysics Data System (ADS)

    Jeon, C.; Hwang, C. C.; Kang, T.-H.; Kim, K.-J.; Kim, B.; Kim, Y.; Noh, D. Y.; Park, C.-Y.

    2009-10-01

    We report the metallization of the Si(001)2×1 surface at elevated temperatures using angle-resolved photoemission spectroscopy (ARPES) and near-edge x-ray absorption fine structure (NEXAFS). A metallic state (Sm) over the EF , which corresponds to the empty (π∗) state of the 2×1 asymmetric dimer model, increases in the ARPES spectra, while the π∗ state decreases in the NEXAFS spectra with increasing temperature. Since Sm is observed even at 400 K, the structural phase transition at ˜900K [Phys. Rev. Lett. 91, 126103 (2003); Phys. Rev. Lett. 77, 3869 (1996)] is not related to the metallization. Thermal excitation seems to be too small to detect in ARPES in initial stage of the metallization and cannot account for the different behavior of Sm and the filled surface state of the up-dimer upon oxidation. We suggest, based on the existence of Sm even at 400 K and the oxidation behavior, that the metallization is attributed to thermal adatoms.

  16. A high-resolution near-edge x-ray absorption fine structure investigation of the molecular orientation in the pentacene/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) pentacene/system.

    PubMed

    Casu, M B; Cosseddu, P; Batchelor, D; Bonfiglio, A; Umbach, E

    2008-01-07

    We present x-ray photoemission spectroscopy and highly resolved near-edge x-ray absorption fine structure spectroscopy measurements taken on pentacene thin films of different thicknesses deposited on a spin coated poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) substrate. Thin films of pentacene were prepared by using organic molecular beam deposition in situ using strictly controlled evaporation conditions. Our investigations show that pentacene thin films on PEDOT:PSS are characterized by upright standing molecules. Due to the strong dichroic behavior, the calculated values of the molecular orientation give a clear indication not only of the real molecular arrangement in the films but also of a high orientational order. This high degree of molecular orientation order is a characteristic already of the first layer. The films show the tendency to grow on the PEDOT:PSS substrate following an island-fashion mode, with a relatively narrow intermixing zone at the interface between the pentacene and the polymer blend. The peculiarity of the growth of pentacene on PEDOT:PSS is due to the fact that the substrate does not offer any template for the nucleated films and thus exerts a lateral order toward the crystal structure arrangement. Under these conditions, the upright orientation of the molecules in the films minimizes the energy required for the system stability.

  17. X-ray Absorption Near Edge Structure Spectroscopy to Resolve the in Vivo Chemistry of the Redox-Active Indazolium trans-[Tetrachlorobis(1H-indazole)ruthenate(III)] (KP1019)

    PubMed Central

    2013-01-01

    Indazolium trans-[tetrachlorobis(1H-indazole)ruthenate(III)] (1, KP1019) and its analogue sodium trans-[tetrachlorobis(1H-indazole)ruthenate(III)] (2, KP1339) are promising redox-active anticancer drug candidates that were investigated with X-ray absorption near edge structure spectroscopy. The analysis was based on the concept of the coordination charge and ruthenium model compounds representing possible coordinations and oxidation states in vivo. 1 was investigated in citrate saline buffer (pH 3.5) and in carbonate buffer (pH 7.4) at 37 °C for different time intervals. Interaction studies on 1 with glutathione in saline buffer and apo-transferrin in carbonate buffer were undertaken, and the coordination of 1 and 2 in tumor tissues was studied too. The most likely coordinations and oxidation states of the compound under the above mentioned conditions were assigned. Microprobe X-ray fluorescence of tumor thin sections showed the strong penetration of ruthenium into the tumor tissue, with the highest concentrations near blood vessels and in the edge regions of the tissue samples. PMID:23282017

  18. Determination of Mn Valence from X-Ray Absorption Near Edge Structure and Study of Magnetic Behavior in Hole-Doped (Nd 1- xCa x)MnO 3System

    NASA Astrophysics Data System (ADS)

    Liu, R. S.; Wu, J. B.; Chang, C. Y.; Lin, J. G.; Huang, C. Y.; Chen, J. M.; Liu, R. G.

    1996-08-01

    The Mn valence in (Nd1-xCax)MnO3(x= 0-0.5) has been successfully determined using Mn 2p-edge X-ray absorption near edge structure spectra. Moreover, we have measured the magnetic properties across the series (Nd1-xCax)MnO3; the results show that the perovskite NdMnO3is an antiferromagnet with two Néel temperatures (TN) of 14 and 60 K, respectively. By replacement of Nd3+with Ca2+, the mixed compounds (Nd1-xCax)MnO3became ferromagnetic with a Curie temperature of around 130 K (TC) forxin the range 0.1-0.3. Furthermore, two weak antiferromagnetic transitions withTN's of around 30 and 75 K, respectively, embedded in the matrix of the ferromagnet have also been discovered in the rangex= 0.2-0.3. Forx≥ 0.4, the samples change to antiferromagnetic withTN's of around 30 K together with a weak broad ferromagnetic transition withTC's of around 130 K. It is also important to note that the charge-ordering-induced antiferromagnetic transition at the temperature (TCO) 250 K was observed in the samples ofx= 0.4 and 0.5.

  19. Interrogation of Surface, Skin, and Core Orientation in Thermotropic Liquid-Crystalline Copolyester Moldings by Near-Edge X-ray Absorption Fine Structure and Wide-Angle X-ray Scattering

    SciTech Connect

    Rendon,S.; Bubeck, R.; Thomas, L.; Burghardt, W.; Hexemer, A.; Fischer, D.

    2007-01-01

    Injection molding thermotropic liquid-crystalline polymers (TLCPs) usually results in the fabrication of molded articles that possess complex states of orientation that vary greatly as a function of thickness. 'Skin-core' morphologies are often observed in TLCP moldings. Given that both 'core' and 'skin' orientation states may often differ both in magnitude and direction, deconvolution of these complex orientation states requires a method to separately characterize molecular orientation in the surface region. A combination of two-dimensional wide-angle X-ray scattering (WAXS) in transmission and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy is used to probe the molecular orientation in injection molded plaques fabricated from a 4,4'-dihydroxy-{alpha}-methylstilbene (DH{alpha}MS)-based thermotropic liquid crystalline copolyester. Partial electron yield (PEY) mode NEXAFS is a noninvasive ex situ characterization tool with exquisite surface sensitivity that samples to a depth of 2 nm. The effects of plaque geometry and injection molding processing conditions on surface orientation in the regions on- and off- axis to the centerline of injection molded plaques are presented and discussed. Quantitative comparisons are made between orientation parameters obtained by NEXAFS and those from 2D WAXS in transmission, which are dominated by the microstructure in the skin and core regions. Some qualitative comparisons are also made with 2D WAXS results from the literature.

  20. X-ray absorption near edge structure spectroscopy to resolve the in vivo chemistry of the redox-active indazolium trans-[Tetrachlorobis(1H-indazole)ruthenate(III)] (KP1019).

    PubMed

    Hummer, Alfred A; Heffeter, Petra; Berger, Walter; Filipits, Martin; Batchelor, David; Büchel, Gabriel E; Jakupec, Michael A; Keppler, Bernhard K; Rompel, Annette

    2013-02-14

    Indazolium trans-[tetrachlorobis(1H-indazole)ruthenate(III)] (1, KP1019) and its analogue sodium trans-[tetrachlorobis(1H-indazole)ruthenate(III)] (2, KP1339) are promising redox-active anticancer drug candidates that were investigated with X-ray absorption near edge structure spectroscopy. The analysis was based on the concept of the coordination charge and ruthenium model compounds representing possible coordinations and oxidation states in vivo. 1 was investigated in citrate saline buffer (pH 3.5) and in carbonate buffer (pH 7.4) at 37 °C for different time intervals. Interaction studies on 1 with glutathione in saline buffer and apo-transferrin in carbonate buffer were undertaken, and the coordination of 1 and 2 in tumor tissues was studied too. The most likely coordinations and oxidation states of the compound under the above mentioned conditions were assigned. Microprobe X-ray fluorescence of tumor thin sections showed the strong penetration of ruthenium into the tumor tissue, with the highest concentrations near blood vessels and in the edge regions of the tissue samples.

  1. XANES and EXAFS study of Au-substituted YBa2Cu3O(7-delta)

    NASA Technical Reports Server (NTRS)

    Ruckman, Mark W.; Hepp, Aloysius F.

    1990-01-01

    The near-edge structure (XANES) of the Au L3 and Cu K edges of YBa2Au(0.3)Cu(2.7)O(7-delta) was studied. X ray diffraction suggests that Au goes on the Cu(1) site and XANES shows that this has little effect on the oxidation state of the remaining copper. The gold L3 edge develops a white line feature whose position lies between that of trivalent gold oxide (Au2O3) and monovalent potassium gold cyanide (KAu(CN)2) and whose intensity relative to the edge step is smaller than in the two reference compounds. The L3 EXAFS for Au in the superconductor resembles that of Au2O3. However, differences in the envelope of the Fourier filtered component for the first shell suggest that the local structure of the Au in the superconductor is not equivalent to Au2O3.

  2. K-edge XANES investigation of octakis(DMSO)lanthanoid(III) complexes in DMSO solution and solid iodides.

    PubMed

    D'Angelo, Paola; Migliorati, Valentina; Spezia, Riccardo; De Panfilis, Simone; Persson, Ingmar; Zitolo, Andrea

    2013-06-14

    The potential of high energy XANES (X-ray absorption near edge structure) as a tool for the structural analysis of lanthanoid-containing systems has been explored. The K-edge XANES spectra of La(3+), Gd(3+), and Lu(3+) ions both in DMSO solution and solid octakis(DMSO)lanthanoid(III) iodides have been analysed. Although the K-edges of lanthanoids cover the energy range of 38 (La) to 65 (Lu) keV, the large widths of the core hole states do not appreciably reduce the potential structural information of the XANES data. We show that, for lanthanoid compounds, accurate structural parameters are obtained from the analysis of K-edge XANES signals if a deconvolution procedure is carried out. We found that in solid octakis(DMSO)lanthanoid(III) iodides the Ln(3+) ions are coordinated by eight DMSO ligands arranged in a quite symmetric fashion. In DMSO solution the Ln(3+) ions retain a regular eight-coordination structure and the coordination number does not change along the series. In contrast to when in water the second coordination shell has been found to provide a negligible contribution to the XANES spectra of Ln(3+) ions in DMSO solution.

  3. K-edge XANES investigation of octakis(DMSO)lanthanoid(III) complexes in DMSO solution and solid iodides

    PubMed Central

    D’Angelo, Paola; Migliorati, Valentina; Spezia, Riccardo; De Panfilis, Simone; Persson, Ingmar; Zitolo, Andrea

    2014-01-01

    The potentiality of high energy XANES (X-ray absorption near edge structure) as a structural tool for lanthanoid-containing systems has been explored. The K-edge XANES spectra of La3+, Gd3+, and Lu3+ ions both in DMSO solution and solid octakis(DMSO) lanthanoid(III) iodides have been analysed. Although the K-edges of lanthanoids cover the energy range 38 (La) to 65 (Lu) keV, the large widths of the core hole states do not appreciably reduce the potential structural information of XANES data. We show that, for lanthanoid compounds, accurate structural parameters are obtained from the analysis of K-edge XANES signal if a deconvolution procedure is carried out. We found that in solid octakis(DMSO) lanthanoid(III) iodides the Ln3+ ions are coordinated by eight DMSO ligands arranged in a quite symmetric fashion. In DMSO solution the Ln3+ ions retain a regular eight-coordination structure and the coordination number does not change along the series. At variance with water the second coordination shell has been found to provide a negligible contribution to the XANES spectra of Ln3+ ions in DMSO solution. PMID:23657739

  4. Linear combination of XANES for quantitative analysis of Ti-Si binary oxides.

    PubMed

    Lee, J S; Kim, W B; Choi, S H

    2001-03-01

    A new method is demonstrated for the quantification of Ti-O-Si and Ti-O-Ti bonds in Ti-Si binary oxides. It is based on the linear combination of two reference X-ray absorption near-edge structure (XANES) spectra at the Ti K edge. The proper selection of a Ti-O-Si reference material is most important for the successful application of this method. Three Ti-Si binary oxide systems have been analysed by the new method: Ti-Si mixed oxides, titania supported on silica and Ti-substituted MCM-41 (crystalline mesoporous molecular sieve material invented by Mobil) with various Ti contents.

  5. B K-Edge XANES of Superstructural Units in Borate Glasses

    SciTech Connect

    Sipr, O.; Simunek, A.; Rocca, F.

    2007-02-02

    The potential of x-ray absorption near-edge structure (XANES) spectroscopy for studying medium range order in borate glasses is assessed by theoretical modelling of the spectra. B K edge XANES is calculated in case that B atoms are located in isolated BO3 and BO4 units and in case that B atom are located in superstructural units of 9-15 atoms. It is found that boroxol ring and diborate and ditriborate superstructural units give rise to spectra which differ from spectra obtained by a mere superposition of spectra of isolated BO3 and BO4 units. On the other hand, spectra of pentaborate and triborate units do not differ significantly from spectra of isolated BO3 and BO4.

  6. Spectral Analysis by XANES Reveals that GPNMB Influences the Chemical Composition of Intact Melanosomes

    SciTech Connect

    T Haraszti; C Trantow; A Hedberg-Buenz; M Grunze; M Anderson

    2011-12-31

    GPNMB is a unique melanosomal protein. Unlike many melanosomal proteins, GPNMB has not been associated with any forms of albinism, and it is unclear whether GPNMB has any direct influence on melanosomes. Here, melanosomes from congenic strains of C57BL/6J mice mutant for Gpnmb are compared to strain-matched controls using standard transmission electron microscopy and synchrotron-based X-ray absorption near-edge structure analysis (XANES). Whereas electron microscopy did not detect any ultrastructural changes in melanosomes lacking functional GPNMB, XANES uncovered multiple spectral phenotypes. These results directly demonstrate that GPNMB influences the chemical composition of melanosomes and more broadly illustrate the potential for using genetic approaches in combination with nano-imaging technologies to study organelle biology.

  7. The determination of dopant ion valence distributions in insulating crystals using XANES measurements.

    PubMed

    Hughes-Currie, Rosa B; Ivanovskikh, Konstantin V; Wells, Jon-Paul R; Reid, Michael F; Gordon, Robert A

    2016-04-06

    Ytterbium-doped wide-bandgap fluoride crystals CaF2, SrF2 and NaMgF3 have been measured using x-ray absorption near edge structure (XANES) on the L3 edge to determine the ratio of trivalent to divalent Yb ions present in the crystals. This study improves upon previous XANES measurements of dopant ion valency by taking into account the x-ray emission transition probabilities for the divalent and trivalent species instead of simply assuming that the relative concentrations may be determined by the ratio of the x-ray excitation band areas. Trivalent to divalent ratios as high as 5 are inferred even at low total dopant ion concentrations of 0.05 mol% Yb.

  8. The determination of dopant ion valence distributions in insulating crystals using XANES measurements

    NASA Astrophysics Data System (ADS)

    Hughes-Currie, Rosa B.; Ivanovskikh, Konstantin V.; Wells, Jon-Paul R.; Reid, Michael F.; Gordon, Robert A.

    2016-04-01

    Ytterbium-doped wide-bandgap fluoride crystals CaF2, SrF2 and NaMgF3 have been measured using x-ray absorption near edge structure (XANES) on the L3 edge to determine the ratio of trivalent to divalent Yb ions present in the crystals. This study improves upon previous XANES measurements of dopant ion valency by taking into account the x-ray emission transition probabilities for the divalent and trivalent species instead of simply assuming that the relative concentrations may be determined by the ratio of the x-ray excitation band areas. Trivalent to divalent ratios as high as 5 are inferred even at low total dopant ion concentrations of 0.05 mol% Yb.

  9. Electrosynthesis of ZnO nanorods and nanotowers: Morphology and X-ray Absorption Near Edge Spectroscopy studies

    NASA Astrophysics Data System (ADS)

    Sigircik, Gokmen; Erken, Ozge; Tuken, Tunc; Gumus, Cebrail; Ozkendir, Osman M.; Ufuktepe, Yuksel

    2015-06-01

    Deposition mechanism of nano-structured ZnO films has been investigated in the absence and presence of chloride ions from aqueous solution. The resulting opto-electronic properties were interpreted extensively, using X-ray diffraction (XRD), X-ray Absorption Near Edge Spectroscopy (XANES), field emission scanning electron microscopy (FE-SEM), UV-Visible spectroscopy and four probe techniques. The ZnO deposition is mass transport controlled process and the interaction of chloride ions with the surface has great influence on diffusion kinetics, considering the substantial species (Zn2+ and OH-) involved in the construction of ZnO film. This effect does not change major lattice parameters, as shown with detailed analysis of XRD data. However, the texture coefficient (Tc) (0 0 2) value is higher in presence of chloride ions containing synthesis solution which gave vertically aligned, well defined and uniformly dispersed nanorods structure. The calculated Eg values are in the range 3.28-3.41 eV and 3.22-3.31 eV for ZnO nanorods and nanotowers synthesized at different deposition periods, respectively. Furthermore, the charge mobility values regarding the deposition periods were measured to be in the ranges from 130.4 to 449.2 cm2 V-1 s-1 and 126.2 to 204.7 cm2 V-1 s-1 for nanorods and nanotowers, respectively. From XANES results, it was shown that the Zn K-edge spectrum is dominated by the transition of Zn 1s core electrons into the unoccupied Zn 4p states of the conduction band. Comparing the rod and tower nano-structured ZnO thin films, the excitation behavior of valence band electrons is different. Moreover, the density states of Zn 4p are higher for ZnO nanorods.

  10. Mn K-edge XANES spectroscopy of a photosynthetic O2-evolving complex. High-quality pre-edge features and distinct fine structures in the S1- and S2-states.

    PubMed

    Kusunoki, M; Ono, T; Matsushita, T; Oyanagi, H; Inoue, Y

    1990-10-01

    High-resolution XANES (X-ray Absorption Near Edge Structure) spectroscopy for Mn in the S1 and S2 states of the spinach photosynthetic O2-evolving complex revealed distinct features in K-edge spectra, when a high signal-to-noise (S/N) ratio of ca. 80 with a low and constant background-to-signal (B/S) ratio of 0.15 to 0.18 was attained. Six features resolved in each S-state spectrum involve a pre-edge feature due to 1s----3d transitions, a main-edge feature possibly due to 1s----4s transitions and four fine structures superimposed on the principal absorption bands due to 1s----4p* transitions. The high-quality pre-edge features were analyzed according to a parametric ligand-field theory in comparison with those of some typical authentic Mn complexes. It was deduced that i) all of the four Mn ions in the S1-state are octahedrally coordinated and two of them constitute a di-mu-oxo bridged Mn(III, III) dimeric subunit; ii) the bridged Mn(III) ions are further bridged by a deprotonated water dimer, (HOHOH)-, and coordinated by imidazole-N and carboxylate-O- on the opposite side of the Mn atom from the di-mu-oxo bridge; iii) the other two Mn ions exist in the form of Mn(III) monomeric subunits; and iv) upon the S1----S2 transition, only the bridged Mn(III,III) is oxidized to Mn(III,IV). The distinct change in the principal absorption band shape upon the S1----S2 transition is briefly discussed to obtain the XANES evidence for a tetrameric Mn-cluster.

  11. Inherent size effects on XANES of nanometer metal clusters: Size-selected platinum clusters on silica

    SciTech Connect

    Dai, Yang; Gorey, Timothy J.; Anderson, Scott L.; Lee, Sungsik; Lee, Sungwon; Seifert, Soenke; Winans, Randall E.

    2016-12-12

    X-ray absorption near-edge structure (XANES) is commonly used to probe the oxidation state of metal-containing nanomaterials, however, as the particle size in the material drops below a few nanometers, it becomes important to consider inherent size effects on the electronic structure of the materials. In this paper, we analyze a series of size-selected Ptn/SiO2 samples, using X-ray photoelectron spectroscopy (XPS), low energy ion scattering, grazing-incidence small angle X-ray scattering, and XANES. The oxidation state and morphology are characterized both as-deposited in UHV, and after air/O2 exposure and annealing in H2. Here, the clusters are found to be stable during deposition and upon air exposure, but sinter if heated above ~150 °C. XANES shows shifts in the Pt L3 edge, relative to bulk Pt, that increase with decreasing cluster size, and the cluster samples show high white line intensity. Reference to bulk standards would suggest that the clusters are oxidized, however, XPS shows that they are not. Instead, the XANES effects are attributable to development of a band gap and localization of empty state wavefunctions in small clusters.

  12. Inherent size effects on XANES of nanometer metal clusters: Size-selected platinum clusters on silica

    DOE PAGES

    Dai, Yang; Gorey, Timothy J.; Anderson, Scott L.; ...

    2016-12-12

    X-ray absorption near-edge structure (XANES) is commonly used to probe the oxidation state of metal-containing nanomaterials, however, as the particle size in the material drops below a few nanometers, it becomes important to consider inherent size effects on the electronic structure of the materials. In this paper, we analyze a series of size-selected Ptn/SiO2 samples, using X-ray photoelectron spectroscopy (XPS), low energy ion scattering, grazing-incidence small angle X-ray scattering, and XANES. The oxidation state and morphology are characterized both as-deposited in UHV, and after air/O2 exposure and annealing in H2. Here, the clusters are found to be stable during depositionmore » and upon air exposure, but sinter if heated above ~150 °C. XANES shows shifts in the Pt L3 edge, relative to bulk Pt, that increase with decreasing cluster size, and the cluster samples show high white line intensity. Reference to bulk standards would suggest that the clusters are oxidized, however, XPS shows that they are not. Instead, the XANES effects are attributable to development of a band gap and localization of empty state wavefunctions in small clusters.« less

  13. Analyzing organic sulfur in coal/char: Integrated mild gasification/XANES methods. Technical report, 1 March--31 May 1994

    SciTech Connect

    Palmer, S.R.; Huffman, G.P.

    1994-09-01

    The overall goal of this study is to improve the understanding of sulfur in coals/chars via the use of combined advanced non-destructive and advanced destructive methods of sulfur analysis. This study combines selective oxidation, analytical pyrolysis, and sulfur X-ray Absorption Near Edge Structure Spectroscopy (XANES) analysis. Samples with a wide variety of sulfur contents, (0.63% to 4.40%) have been prepared for use in this study. This includes steam gasification chars, oxidized coals and desulfurized coals as well of the original unaltered coals. Mild pyrolysis and preliminary XANES data shows that the sulfur chemistry of gasification chars is significantly different from that of the original coals. Mild pyrolysis of the samples that were oxidized with peroxyacetic acid showed that the level of simple thiophene structures observed in the pyrolysis products declines with increasing levels of oxidation. Sulfur XANES spectra of treated samples showed various effects depending on the treatment severity. For the less severely treated samples (demineralization and solvent extraction), the XANES spectra were similar, although not identical, to the untreated coal spectra, whereas the more severe treatments (steam at 450 C; peroxyacetic acid at 25 C) showed preferential oxidation of one or more sulfur-bearing phases in the original coal. Additional samples have recently been examined by XANES and W-band EPR and the data is currently being processed and evaluated.

  14. Combined Carbon, Nitrogen, and Oxygen XANES Spectroscopy on Hydrated and Anhydrous Interplanetary Dust Particles

    NASA Technical Reports Server (NTRS)

    Feser, M.; Wirick, S.; Flynn, G. J.; Keller, L. P.

    2003-01-01

    Interplanetary dust particles (IDPs) collected from the Earth s stratosphere generally contain percent-level concentrations of organic matter. This organic matter in IDPs is important for several reasons: 1) some IDPs contain interstellar organic matter, identified by high D/H or N-15, providing the opportunity to characterize this interstellar material, 2) comparison of the organic matter in anhydrous IDPs to that in hydrated IDPs can help establish the effects of parent body aqueous alteration, and, 3) IDPs are believed to have delivered to the surface of the early Earth pre-biotic organic matter important for the origin of life. X-Ray Absorption Near-Edge Structure (XANES) spectroscopy provides information on the functional groups present in a sample, and XANES can be performed on the nano-scale, comparable to the size of some of the sub-units of the IDPs. The energies of the XANES transitions are diagnostic of the type of bonding of the C, N, and O, allowing identification of the functional groups present in the sample. As part of our ongoing effort to characterize the organic matter in the IDPs, we have performed carbon- and oxygen- and the first nitrogen-XANES spectroscopy on two IDPs and acid-insoluble residue from the CM2 meteorite Murchison.

  15. Combined Carbon, Nitrogen, and Oxygen XANES Spectroscopy on Hydrated and Anhydrous Interplanetary Dust Particles

    NASA Technical Reports Server (NTRS)

    Feser, M.; Wirick, S.; Flynn, G. J.; Keller, L. P.

    2003-01-01

    Interplanetary dust particles (IDPs) collected from the Earth s stratosphere generally contain percent-level concentrations of organic matter. This organic matter in IDPs is important for several reasons: 1) some IDPs contain interstellar organic matter, identified by high D/H or N-15, providing the opportunity to characterize this interstellar material, 2) comparison of the organic matter in anhydrous IDPs to that in hydrated IDPs can help establish the effects of parent body aqueous alteration, and, 3) IDPs are believed to have delivered to the surface of the early Earth pre-biotic organic matter important for the origin of life. X-Ray Absorption Near-Edge Structure (XANES) spectroscopy provides information on the functional groups present in a sample, and XANES can be performed on the nano-scale, comparable to the size of some of the sub-units of the IDPs. The energies of the XANES transitions are diagnostic of the type of bonding of the C, N, and O, allowing identification of the functional groups present in the sample. As part of our ongoing effort to characterize the organic matter in the IDPs, we have performed carbon- and oxygen- and the first nitrogen-XANES spectroscopy on two IDPs and acid-insoluble residue from the CM2 meteorite Murchison.

  16. XANES studies of oxidation states of sulfur in aquatic and soil humic substances

    SciTech Connect

    Xia, K.; Weesner, F.; Bleam, W.F.; Helmke, P.A.; Bloom, P.R.; Skyllberg, U.L.

    1998-09-01

    Sulfur K-edge x-ray absorption near-edge structure spectroscopy (XANES) was used to identify multiple organic S oxidation states in aquatic and soil humic substances. The XANES results suggest that S in humic substances exists in four major oxidation groups similar to sulfate ester, sulfonate, sulfoxide, and thiol-sulfide. Thiol S cannot be separated from sulfide X and must be considered as a single thiol-sulfide peak. The second derivative spectra suggest the existence of thiophene and sulfone S. The relative quantities of each major S form in humic samples were estimated based on the integrated cross section of each s {r_arrow} p transition peak corresponding to different S oxidation states in the S K-edge XANES spectra. The XANES results of the four humic samples used in this study appear to reflect the environmental settings where the humic substances originally formed. The percentage of the most reduced organic S (thiol-sulfide and possibly thiophene) in humic substances follows the sequence:aquatic samples > organic soil sample > mineral soil sample. The percentage of most oxidized S (sulfate group) was the greatest in the humic substance from a mineral soil and the lowest in the aquatic humic substances.

  17. XRD and XANES study of some Cu-doped MnBi materials

    NASA Astrophysics Data System (ADS)

    Mishra, Ashutosh; Patil, Harsha

    2016-10-01

    High purity MnBi low temperature phase has been prepared and analyzed using X- ray diffraction (XRD) and X-ray absorption near edge structure (XANES) measurements. The X-ray diffraction measurements were carried out using Bruker D8 Advance X-ray diffractometer. The X-rays were produced using a sealed tube and the wavelength of X-ray was 154 nm (Cu K-alpha). and X-rays were detected using a fast counting detector based on Silicon strip technology (Bruker LynxEye detector)[1]. and the X-ray absorption spectra has emerged as a powerful technique for local structure determination, which can be applied to any type of material. The X-ray absorption measurements of two Cu-doped MnBi alloys have been performed at the recently developed BL-8 Dispersive EXAFS beam line at 2.5 GeV Indus-2 synchrotron at RRCAT, Indore, India[2]. The X-ray absorption near edge structure (XANES) data obtained has been processed using data analysis program Athena. The energies of the K absorption edge, chemical shifts, edge-widths, shifts of the principal absorption maximum in the alloys have been determined.

  18. Characterization of phosphorus species in biosolids and manures using XANES spectroscopy.

    PubMed

    Shober, Amy L; Hesterberg, Dean L; Sims, J Thomas; Gardner, Sheila

    2006-01-01

    Identification of the chemical P species in biosolids or manures will improve our understanding of the long-term potential for P loss when these materials are land applied. The objectives of this study were to determine the P species in dairy manures, poultry litters, and biosolids using X-ray absorption near-edge structure (XANES) spectroscopy and to determine if chemical fractionation techniques can provide useful information when interpreted based on the results of more definitive P speciation studies. Our XANES fitting results indicated that the predominant forms of P in organic P sources included hydroxylapatite, PO(4) sorbed to Al hydroxides, and phytic acid in lime-stabilized biosolids and manures; hydroxylapatite, PO(4) sorbed on ferrihydrite, and phytic acid in lime- and Fe-treated biosolids; and PO(4) sorbed on ferrihydrite, hydroxylapatite, beta-tricalcium phosphate (beta-TCP), and often PO(4) sorbed to Al hydroxides in Fe-treated and digested biosolids. Strong relationships existed between the proportions of XANES PO(4) sorbed to Al hydroxides and NH(4)Cl- + NH(4)F-extractable P, XANES PO(4) sorbed to ferrihydrite + phytic acid and NaOH-extractable P, and XANES hydroxylapatite + beta-TCP and dithionite-citrate-bicarbonate (DCB)- + H(2)SO(4)-extractable P (r(2) = 0.67 [P = 0.01], 0.78 [P = 0.01], and 0.89 [P = 0.001], respectively). Our XANES fitting results can be used to make predictions about long-term solubility of P when biosolids and manures are land applied. Fractionation techniques indicate that there are differences in the forms of P in these materials but should be interpreted based on P speciation data obtained using more advanced analytical tools.

  19. Characterization of Phosphorus Species in Biosolids and Manures Using XANES Spectroscopy

    SciTech Connect

    Shober,A.; Hesterberg, D.; Sims, J.; Gardner, S.

    2006-01-01

    Received for publication March 10, 2006. Identification of the chemical P species in biosolids or manures will improve our understanding of the long-term potential for P loss when these materials are land applied. The objectives of this study were to determine the P species in dairy manures, poultry litters, and biosolids using X-ray absorption near-edge structure (XANES) spectroscopy and to determine if chemical fractionation techniques can provide useful information when interpreted based on the results of more definitive P speciation studies. Our XANES fitting results indicated that the predominant forms of P in organic P sources included hydroxylapatite, PO{sub 4} sorbed to Al hydroxides, and phytic acid in lime-stabilized biosolids and manures; hydroxylapatite, PO{sub 4} sorbed on ferrihydrite, and phytic acid in lime- and Fe-treated biosolids; and PO{sub 4} sorbed on ferrihydrite, hydroxylapatite, {beta}-tricalcium phosphate ({beta}-TCP), and often PO{sub 4} sorbed to Al hydroxides in Fe-treated and digested biosolids. Strong relationships existed between the proportions of XANES PO{sub 4} sorbed to Al hydroxides and NH{sub 4}Cl- + NH{sub 4}F-extractable P, XANES PO{sub 4} sorbed to ferrihydrite + phytic acid and NaOH-extractable P, and XANES hydroxylapatite + {beta}-TCP and dithionite-citrate-bicarbonate (DCB)- + H{sub 2}SO{sub 4}-extractable P ({gamma}{sup 2} = 0.67 [P = 0.01], 0.78 [P = 0.01], and 0.89 [P = 0.001], respectively). Our XANES fitting results can be used to make predictions about long-term solubility of P when biosolids and manures are land applied. Fractionation techniques indicate that there are differences in the forms of P in these materials but should be interpreted based on P speciation data obtained using more advanced analytical tools.

  20. Probing the Orientation of Electrostatically Immobilized Protein G B1 by Time of Flight Secondary Ion Spectrometry, Sum Frequency Generation and Near-edge X-Ray Adsorption Fine Structure Spectroscopy

    PubMed Central

    Baio, Joe E.; Weidner, Tobias; Baugh, Loren; Gamble, Lara J.; Stayton, Patrick S.; Castner, David G.

    2011-01-01

    To fully develop techniques that provide an accurate description of protein structure at a surface, we must start with a relatively simple model system before moving on to increasingly complex systems. In this study, x-ray photoelectron spectroscopy (XPS), sum frequency generation spectroscopy (SFG), near-edge x-ray adsorption fine structure (NEXAFS) spectroscopy, and time-of-flight secondary ion mass spectrometry (ToF-SIMS) were used to probe the orientation of Protein G B1 (6 kDa) immobilized onto both amine (NH3+) and carboxyl (COO−) functionalized gold. Previously, we have shown that we could successful control orientation of a similar Protein G fragment via a cysteine-maleimide bond. In this investigation, to induce opposite end-on orientations, a charge distribution was created within the Protein G B1 fragment by first substituting specific negatively charged amino acids with neutral amino acids and then immobilizing the protein onto two oppositely charged self-assembled monolayer (SAM) surfaces (NH3+ and COO−). Protein coverage, on both surfaces, was monitored by the change in the atomic % N, as determined by XPS. Spectral features within the SFG spectra, acquired for the protein adsorbed onto a NH3+-SAM surface, indicates that this electrostatic interaction does induce the protein to form an oriented monolayer on the SAM substrate. This corresponded to the polarization dependence of the spectral feature related to the NEXAFS N1s to π* transition of the β-sheet peptide bonds within the protein layer. ToF-SIMS data demonstrated a clear separation between the two samples based on the intensity differences of secondary ions stemming from amino acids located asymmetrically within Protein G B1 (Methionine: 62 and 105 m/z; Tyrosine: 107 and 137 m/z; Leucine: 86 m/z). For a more quantitative examination of orientation, we developed a ratio comparing the sum of the intensities of secondary-ions stemming from the amino acid residues at either end of the protein

  1. Contribution of molecular dynamics simulations and ab initio calculations to the interpretation of Mg K-edge experimental XANES in K(2)O-MgO-3SiO(2) glass.

    PubMed

    Trcera, Nicolas; Rossano, Stéphanie; Madjer, Karim; Cabaret, Delphine

    2011-06-29

    The structural environment of Mg in a K-bearing silicate glass of composition K(2)MgSi(3)O(8) is investigated by x-ray absorption near-edge structure (XANES) spectroscopy at the Mg K-edge. XANES calculations are performed using a plane-wave electronic structure code, and a structural model obtained by classical molecular dynamics coupled to ab initio relaxation. Bond valence theory is used to validate plausible environments within the structural models. Comparison between the experimental and calculated spectra enables us to conclude that the Mg atoms are located in distorted tetrahedral sites. Site distortions are found to be correlated to the theoretical shift of the XANES edge position.

  2. The Electronic Properties and L3 XANES of Au and Nano-Au

    SciTech Connect

    Yiu, Y.M.; Zhang, P.; Sham, T.K.

    2004-04-20

    The electronic properties of Au crystal and nano Au have been investigated by theory and experiment. Molecularly capped nano-Au was synthesized using the two-phase method. Au nano-particles have been characterized by X-Ray Diffraction (XRD) and Transmission Electron Microscopy (TEM). They retain the fcc crystal structure. Their sizes have been determined to be in a range from 5.5 nm to 1.7 nm. The L3 X-ray Absorption Near Edge Structure (XANES) of nano-Au and Au foil have been recorded using synchrotron radiation, and examined by theoretical calculation based on the first principles. Both theory and experiment show that the nano-Au particles have essentially all the Au L3 XANES features of bulk Au in the near edge region with less pronounced resonance peaks. It is also shown that nano Au exhibits lower 4f binding energy than bulk Au in good agreement with quantum confined Au systems reported previously.

  3. XANES study of Fe-implanted strontium titanate

    NASA Astrophysics Data System (ADS)

    Lobacheva, O.; Goncharova, L. V.; Chavarha, M.; Sham, T. K.

    2014-03-01

    Properties of strontium titanate SrTiO3 (STO) depend to a great extent on the substitutional dopants and defects of crystal structure. The ion beam implantation method was used for doping STO (001) crystals with Fe at different doses. Implanted samples were then annealed at 350°C in oxygen to induce recrystallization and remove oxygen vacancies produced during ion implantation process. The effect of Fe doping and post-implantation annealing was studied by X-ray Absorption Near Edge Spectroscopy (XANES) method and Superconducting Quantum Interference Device (SQUID). XANES allowed to monitor the change in structure of STO crystals and in the local environment of Fe following the implantation and annealing steps. SQUID measurements revealed correlation between magnetic moment and Fe implantation dose. Ferromagnetic hysteresis was observed on selected Fe-implanted STO at 5 K. The observed magnetic properties can be correlated with the several Fe oxide phases in addition to the presence of O/Ti vacancies.

  4. XANES study of Fe-implanted strontium titanate

    SciTech Connect

    Lobacheva, O.; Goncharova, L. V.; Chavarha, M.; Sham, T. K.

    2014-03-31

    Properties of strontium titanate SrTiO{sub 3} (STO) depend to a great extent on the substitutional dopants and defects of crystal structure. The ion beam implantation method was used for doping STO (001) crystals with Fe at different doses. Implanted samples were then annealed at 350°C in oxygen to induce recrystallization and remove oxygen vacancies produced during ion implantation process. The effect of Fe doping and post-implantation annealing was studied by X-ray Absorption Near Edge Spectroscopy (XANES) method and Superconducting Quantum Interference Device (SQUID). XANES allowed to monitor the change in structure of STO crystals and in the local environment of Fe following the implantation and annealing steps. SQUID measurements revealed correlation between magnetic moment and Fe implantation dose. Ferromagnetic hysteresis was observed on selected Fe-implanted STO at 5 K. The observed magnetic properties can be correlated with the several Fe oxide phases in addition to the presence of O/Ti vacancies.

  5. In Situ XANES Study of CuO/TiO2 Thin Films During Photodegradation of Methylene Blue

    SciTech Connect

    Hsiung Tungli; Wang, H. Paul; Wei Yuling

    2007-02-02

    Speciation of copper in the CuO/TiO2 thin film (synthesized by the doctor-blade deposition method) during photocatalytic decomposition of methylene blue has been studied by in situ X-ray absorption near-edge structural (XANES) spectroscopy. During the UV/VIS radiation (90 min), in the presence of methylene blue, a decrease of Cu(II) and an increases of Cu(0) and Cu(I) fractions in the CuO/TiO2 thin film are observed by in situ XANES. The r-space Fourier transformation EXAFS (extend X-ray absorption fine structural) spectra also show that the bond distance of Cu-O in the thin film is decreased by 0.03 A during photocatalytic degradation of methylene blue.

  6. Experimental and theoretical XANES of CdSxSe1-x nanostructures

    NASA Astrophysics Data System (ADS)

    Yiu, Y. M.; Murphy, M. W.; Liu, L.; Hu, Y.; Sham, T. K.

    2014-03-01

    The morphology and electronic properties of the CdSxSe1-x nanostructures with varying alloy compositions have been acquired experimentally by X-ray Absorption Near-Edge Structures (XANES) at the Cd, Se and S K-edge and L3,2-edges. The theoretical XANES spectra have been calculated using the density functional approach. It is found that the optical band-gap emission of these CdSxSe1-x nano-ribbons can be tuned to the range between that of pure CdS (2.43 eV) and CdSe (1.74 eV) by changing the S and Se ratio. This gradual shift in (optical and structural) properties from CdS character to CdSe character is also seen in the electronic structures. The densities of states and band structures show that with the addition of Se replacing S in CdS, the band gap shrinks. The K and L3,2 edges of Cd, Se, and S of the XANES structures of both the CdS and CdSe in B4 (wurtzite) and B3 (cubic zinc-blende) structures have been calculated and compared.

  7. XANES mapping of organic sulfate in three scleractinian coral skeletons

    NASA Astrophysics Data System (ADS)

    Cuif, Jean-Pierre; Dauphin, Yannicke; Doucet, Jean; Salome, Murielle; Susini, Jean

    2003-01-01

    The presence and localization of organic sulfate within coral skeletons are studied by using X-ray absorption near edge structure spectroscopy (XANES) fluorescence. XANES spectra are recorded from four reference sulfur-bearing organic molecules: three amino acids (H-S-C bonds in cysteine; C-S-C bonds in methionine; one disulfide bond C-S-S-C bonds in cystine) and a sulfated sugar (C-SO 4 bonds in chondroitin sulfate). Spectral responses of three coral skeletons show that the sulfated form is extremely dominant in coral aragonite, and practically exclusive within both centres of calcification and the surrounding fibrous tissues of coral septa. Mapping of S-sulfate concentrations in centres and fibres gives us direct evidence of high concentration of organic sulfate in centres of calcification. Additionally, a banding pattern of S-sulfate is visible in fibrous part of the coral septa, evidencing a biochemical zonation that corresponds to the step-by-step growth of fibres.

  8. First Principles Fe L2,3-Edge and O K-Edge XANES and XMCD Spectra for Iron Oxides.

    PubMed

    Sassi, Michel; Pearce, Carolyn I; Bagus, Paul S; Arenholz, Elke; Rosso, Kevin M

    2017-09-21

    X-ray absorption near edge structure (XANES) and X-ray magnetic circular dichroism (XMCD) spectroscopies are tools in widespread use for providing detailed local atomic structure, oxidation state, and magnetic structure information for materials and organometallic complexes. Analysis of these spectra for transition metal L-edges is routinely performed on the basis of ligand-field multiplet theory because one- and two-particle mean field ab initio methods typically cannot describe the multiplet structure. Here we show that multireference configuration interaction (MRCI) calculations can satisfactorily reproduce measured XANES spectra for a range of complex iron oxide materials including hematite and magnetite. MRCI Fe L2,3-edge XANES and XMCD spectra of Fe(II)O6, Fe(III)O6 and Fe(III)O4 in magnetite are found to be in very good qualitative agreement with experiment and multiplet calculations. Point charge embedding and small distortions of the first shell oxygen ligands have only small effects. Oxygen K-edge XANES/XMCD spectra for magnetite investigated by a real-space Green's function approach completes the very good qualitative agreement with experiment. Material-specific differences in local coordination and site symmetry are well reproduced, making the approach useful for assigning spectral features to specific oxidation states and coordination environments.

  9. PROCEEDINGS ON SYNCHROTRON RADIATION: Transfer characterization of sulfur from coal-burning emission to plant leaves by PIXE and XANES

    NASA Astrophysics Data System (ADS)

    Bao, Liang-Man; Zhang, Gui-Lin; Zhang, Yuan-Xim; Li, Yan; Lin, Jun; Liu, Wei; Cao, Qing-Chen; Zhao, Yi-Dong; Ma, Chen-Yan; Han, Yong

    2009-11-01

    The impact of coal-burning emission on sulfur in camphor leaves was investigated using Proton Induced X-ray Emission (PIXE) and synchrotron radiation technique X-ray Absorption Near-Edge Structure (XANES) spectroscopy. The PIXE results show that the sulfur concentrations in the leaves collected at the polluted site are significantly higher than those in controls. The Sulfur XANES spectra show the presence of organic (disulfides, thiols, thioethers, sulfonates and sulfoxides) and inorganic sulfur (sulfates) in the leaves. The inorganic sulfur in the leaves of camphor tree polluted by coal combustion is 15% more than that of the control site. The results suggest that the long-term coal-burning pollution resulted in an enhanced content of the total sulfur and sulfate in the leaves, and the uptake of sulfur by leaves had exceeded the metabolic requirement of plants and the excess of sulfur was stored as SO2-4. It can monitor the sulfur pollution in atmosphere.

  10. XANES spectral changes for discotic liquid crystals of bis[1,2-bis(3,4-dioctyloxyphenyl) ethanedione dioximato]Ni(II)

    NASA Astrophysics Data System (ADS)

    Yokomizo, Mitsutoshi; Kurisaki, Tsutomu; Yamaguchi, Toshio; Wakita, Hisanobu; Oka-Inagaki, Yoshio; Ohta, Kazuchika

    The one-dimensional stacking structures of a liquid crystal Ni complex- [1,2-bis(3,4-dialkoxyphenyl)ethanedione dioximato]Ni(II), [Ni{(C8O)4dpg}2],which shows thermochromism, (see Fig. 1) have been investigated over a temperature range from room temperature to 220°C by analyzing X-ray absorption near-edge structure (XANES) spectra together with a DV-X[alpha] molecular orbital calculation. The thermochromic character of the complex is discussed through the structural change with temperature in Ni--Ni and Ni to ligand atom interactions.

  11. Diamond xenolith and matrix organic matter in the Sutter's Mill meteorite measured by C-XANES

    NASA Astrophysics Data System (ADS)

    Kebukawa, Yoko; Zolensky, Michael E.; Kilcoyne, A. L. David; Rahman, Zia; Jenniskens, Peter; Cody, George D.

    2014-11-01

    The Sutter's Mill (SM) meteorite fell in El Dorado County, California, on April 22, 2012. This meteorite is a regolith breccia composed of CM chondrite material and at least one xenolithic phase: oldhamite. The meteorite studied here, SM2 (subsample 5), was one of three meteorites collected before it rained extensively on the debris site, thus preserving the original asteroid regolith mineralogy. Two relatively large (10 μm sized) possible diamond grains were observed in SM2-5 surrounded by fine-grained matrix. In the present work, we analyzed a focused ion beam (FIB) milled thin section that transected a region containing these two potential diamond grains as well as the surrounding fine-grained matrix employing carbon and nitrogen X-ray absorption near-edge structure (C-XANES and N-XANES) spectroscopy using a scanning transmission X-ray microscope (STXM) (Beamline 5.3.2 at the Advanced Light Source, Lawrence Berkeley National Laboratory). The STXM analysis revealed that the matrix of SM2-5 contains C-rich grains, possibly organic nanoglobules. A single carbonate grain was also detected. The C-XANES spectrum of the matrix is similar to that of insoluble organic matter (IOM) found in other CM chondrites. However, no significant nitrogen-bearing functional groups were observed with N-XANES. One of the possible diamond grains contains a Ca-bearing inclusion that is not carbonate. C-XANES features of the diamond-edges suggest that the diamond might have formed by the CVD process, or in a high-temperature and -pressure environment in the interior of a much larger parent body.

  12. EXAFS and XANES structural characterization of bimetallic AuPd vapor derived catalysts

    NASA Astrophysics Data System (ADS)

    Balerna, A.; Evangelisti, C.; Schiavi, E.; Vitulli, G.; Bertinetti, L.; Martra, G.; Mobilio, S.

    2013-04-01

    Using an innovative procedure known as metal vapor synthesis (MVS) to prepare bimetallic catalysts, starting from Au and Pd vapors, [AuPd] co-evaporated and [Au][Pd] separately evaporated bimetallic catalysts were achieved. After being tested, the catalytic activity and selectivity of the [AuPd] catalyst turned out to be higher than the [Au][Pd] ones. Using EXAFS spectroscopy it was shown that, in the [AuPd] samples, small bimetallic AuPd nanoparticles were present, having an Au rich core surrounded by an AuPd alloyed shell while in the [Au][Pd] sample there was the presence of monometallic Au and Pd nanoparticles showing some alloying only in the boundary regions. The EXAFS results were also qualitatively confirmed by the XANES spectra.

  13. Experimental station for laser-based picosecond time-resolved x-ray absorption near-edge spectroscopy

    NASA Astrophysics Data System (ADS)

    Dorchies, F.; Fedorov, N.; Lecherbourg, L.

    2015-07-01

    We present an experimental station designed for time-resolved X-ray Absorption Near-Edge Spectroscopy (XANES). It is based on ultrashort laser-plasma x-ray pulses generated from a table-top 100 mJ-class laser at 10 Hz repetition rate. A high transmission (10%-20%) x-ray beam line transport using polycapillary optics allows us to set the sample in an independent vacuum chamber, providing high flexibility over a wide spectral range from 0.5 up to 4 keV. Some XANES spectra are presented, demonstrating 1% noise level in only ˜1 mn and ˜100 cumulated laser shots. Time-resolved measurements are reported, indicating that the time resolution of the entire experimental station is 3.3 ± 0.6 ps rms.

  14. XANES Identification of Plutonium Speciation in RFETS Samples

    SciTech Connect

    LoPresti, V.; Conradson, S.D.; Clark, D.L.

    2009-06-03

    Using primarily X-ray absorption near edge spectroscopy (XANES) with standards run in tandem with samples, probable plutonium speciation was determined for 13 samples from contaminated soil, acid-splash or fire-deposition building interior surfaces, or asphalt pads from the Rocky Flats Environmental Technology Site (RFETS). Save for extreme oxidizing situations, all other samples were found to be of Pu(IV) speciation, supporting the supposition that such contamination is less likely to show mobility off site. EXAFS analysis conducted on two of the 13 samples supported the validity of the XANES features employed as determinants of the plutonium valence.

  15. Characterization of extracellular polymeric substances in the biofilms of typical bacteria by the sulfur K-edge XANES spectroscopy.

    PubMed

    Lin, Huirong; Ye, Chengsong; Lv, Lu; Zheng, Clark Renjun; Zhang, Shenghua; Zheng, Lei; Zhao, Yidong; Yu, Xin

    2014-08-01

    A combined approach of physicochemical extraction and sulfur K-edge X-ray absorption near-edge structure (XANES) spectroscopy was applied to characterize the extracellular polymeric substances (EPS) of typical bacterial biofilms in this study. Physicochemical analysis showed variation of the contents of DNA, polysaccharide and protein in different fractions of EPS in different mediums. The sulfur K-edge XANES analysis yielded a variety of spectra. Spectral fitting of the XANES spectra utilizing a large set of model compounds showed that there was more reduced sulfur in both LB-EPS (loosely bound EPS) and TB-EPS (tightly bound EPS) of all the biofilms in LB medium than in R2A medium. More oxidized sulfur was identified in LB-EPS than that in TB-EPS, suggesting different niches and physiological heterogeneity in the biofilms. Our results suggested that the sulfur K-edge XANES can be a useful tool to analyze the sulfur speciation in EPS of biofilms.

  16. Near Edge X-ray Absorption Spectroscopy of Polymers

    NASA Astrophysics Data System (ADS)

    Dhez, Olivier; Ade, Harald; Urquhart, Stephen

    2001-03-01

    Synthetic and natural polymers exhibit a rich carbon, nitrogen and oxygen K-edge Near Edge X-ray Absorption Fine Structure (NEXAFS). The spectroscopic variations with chemical structure and composition are interesting in their own right. In addition, the large spectroscopic variability can be utilized for the compositional analysis of materials. This is particularly useful for high spatial resolution NEXAFS microanalysis at lateral spatial resolutions exceeding that achievable with more traditional compositional analysis tools such as Infrared and NMR spectroscopy. To increase our understanding of NEXAFS spectra and to start a database for microanalysis, we acquired carbon NEXAFS spectra of the following polymers: polycarbonate, poly(oxybenzoate-co-2,6oxynaphthoate), poly (p-phenylene terephtalamide), toluene diisocyanate polyurethane, toluene diisocyanate polyurea, 4,4'-methylene di-p-phenylene isocyanate polyurethane, 4,4'-methylene di-p-phenylene isocyanate polyurea, poly(ether ether ketone), poly(alpha-methylstyrene), poly-styrene, poly bromostyrene, poly(2-vinyl styrene), polyethylene, poly(ethylene oxide), polypropylene, poly(propylene oxide), polyisobutylene, ethylene propylene rubber, poly(methyl -metacrylate). These spectra were obtained in transmission with an energy resolution of 150 meV. The energy scale was carefully calibrated in-situ utilizing C02 gas as a reference. Spectral assignments are made based on model compounds and theoretical calculations.

  17. Standard Protocol and Quality Assessment of Soil Phosphorus Speciation by P K-Edge XANES Spectroscopy.

    PubMed

    Werner, Florian; Prietzel, Jörg

    2015-09-01

    Phosphorus (P) in soils is most often bound as phosphate to one or more of the following four elements or compounds: calcium, aluminum, iron, and soil organic matter. A promising method for direct P speciation in soils is synchrotron-based X-ray absorption near edge structure (XANES) spectroscopy at the K-edge of P. However, the quality of this method is debated controversially, partly because a standard protocol for reproducible spectrum deconvolution is lacking and minor modifications of the applied deconvolution procedure can lead to considerable changes in the P speciation results. On the basis of the observation that appropriate baseline correction and edge-step normalization are crucial for correct linear combination (LC) fitting results, we established a standard protocol for the deconvolution and LC fitting of P K-edge XANES spectra. We evaluated the quality of LC fits obtained according to this standard protocol with 16 defined dilute (2 mg P g(-1)) ternary mixtures of aluminum phosphate, iron phosphate, hydroxyapatite, and phytic acid in a quartz matrix. The LC fitting results were compared with the contribution of the different P compounds to total P in the various mixtures. Compared to using a traditional LC fitting procedure, our standard protocol reduced the fitting error by 6% (absolute). However, P portions smaller than 5% should be confirmed with other methods or excluded from the P speciation results. A publicly available database of P K-edge XANES reference spectra was initiated.

  18. XANES Analysis of Organic Residues Produced from the UV Irradiation of Astrophysical Ice Analogs

    NASA Technical Reports Server (NTRS)

    Nuevo, M.; Milam, S N.; Sandford, S A.; De Gregorio, B T.; Cody, G D.; Kilcoyne, A L.

    2011-01-01

    Organic residues formed in the laboratory from the ultraviolet (UV) photo-irradiation or ion bombardment of astrophysical ice analogs have been extensively studied for the last 15 years with a broad suite of techniques, including infrared (IR) and UV spectroscopies, as well as mass spectrometry. Analyses of these materials show that they consist of complex mixtures of organic compounds stable at room temperature, mostly soluble, that have not been fully characterized. However, the hydrolysis products of these residues have been partly identified using chromatography techniques, which indicate that they contain molecular precursors of prebiotic interest such as amino acids, nitrile-bearing compounds, and amphiphilic compounds. In this study, we present the first X-ray absorption near-edge structure (XANES) spectroscopy measurements of three organic residues made from the UV irradiation of ices having different starting compositions. XANES spectra confirm the presence of different chemical functions in these residues, and indicate that they are rich in nitrogenand oxygen-bearing species. These data can be compared with XANES measurements of extraterrestrial materials. Finally, this study also shows how soft X rays can alter the chemical composition of samples.

  19. XANES Analysis of Organic Residues Produced from the UV Irradiation of Astrophysical Ice Analogs

    NASA Technical Reports Server (NTRS)

    Nuevo, M.; Milam, S N.; Sandford, S A.; De Gregorio, B T.; Cody, G D.; Kilcoyne, A L.

    2011-01-01

    Organic residues formed in the laboratory from the ultraviolet (UV) photo-irradiation or ion bombardment of astrophysical ice analogs have been extensively studied for the last 15 years with a broad suite of techniques, including infrared (IR) and UV spectroscopies, as well as mass spectrometry. Analyses of these materials show that they consist of complex mixtures of organic compounds stable at room temperature, mostly soluble, that have not been fully characterized. However, the hydrolysis products of these residues have been partly identified using chromatography techniques, which indicate that they contain molecular precursors of prebiotic interest such as amino acids, nitrile-bearing compounds, and amphiphilic compounds. In this study, we present the first X-ray absorption near-edge structure (XANES) spectroscopy measurements of three organic residues made from the UV irradiation of ices having different starting compositions. XANES spectra confirm the presence of different chemical functions in these residues, and indicate that they are rich in nitrogenand oxygen-bearing species. These data can be compared with XANES measurements of extraterrestrial materials. Finally, this study also shows how soft X rays can alter the chemical composition of samples.

  20. Ab-initio Calculation of the XANES of Lithium Phosphates and LiFePO4

    NASA Astrophysics Data System (ADS)

    Yiu, Y. M.; Yang, Songlan; Wang, Dongniu; Sun, Xueliang; Sham, T. K.

    2013-04-01

    Lithium iron phosphate has been regarded as a promising cathode material for the next generation lithium ion batteries due to its high specific capacity, superior thermal and cyclic stability [1]. In this study, the XANES (X-ray Absorption Near Edge Structure) spectra of lithium iron phosphate and lithium phosphates of various compositions at the Li K, P L3,2, Fe M3,2 and O K-edges have been simulated self-consistently using ab-initio calculations based on multiple scattering theory (the FEFF9 code) and DFT (Density Functional Theory, the Wien2k code). The lithium phosphates under investigation include LiFePO4, γ-Li3PO4, Li4P2O7 and LiPO3. The calculated spectra are compared to the experimental XANES recorded in total electron yield (TEY) and fluorescence yield (FLY). This work was carried out to assess the XANES of possible phases presented in LiFePO4 based Li ion battery applications [2].

  1. Structural investigation of high-valent manganese-salen complexes by UV/Vis, Raman, XANES, and EXAFS spectroscopy.

    PubMed

    Feth, Martin P; Bolm, Carsten; Hildebrand, Jens P; Köhler, Manuela; Beckmann, Oliver; Bauer, Matthias; Ramamonjisoa, Rivo; Bertagnolli, Helmut

    2003-03-17

    XANES and EXAFS spectroscopic studies at the Mn-K- and Br-K-edge of reaction products of (S,S)-(+)-N,N'-bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexanediaminomanganese(III) chloride ([(salen)Mn(III)Cl], 1) and (S,S)-(+)-N,N'-bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexanediaminomanganese(III) bromide ([(salen)Mn(III)Br], 2) with 4-phenylpyridine N-oxide (4-PPNO) and 3-chloroperoxybenzoic acid (MCPBA) are reported. The reaction of the Mn(III) complexes with two equivalents of 4-PPNO leads to a hexacoordinated compound, in which the manganese atom is octahedrally coordinated by four oxygen/nitrogen atoms of the salen ligand at an average distance of approximately 1.90 A and two additional, axially bonded oxygen atoms of the 4-PPNO at 2.25 A. The oxidation state of this complex was determined as approximately +IV by a comparative study of Mn(III) and Mn(V) reference compounds. The green intermediate obtained in reactions of MCPBA and solutions of 1 or 2 in acetonitrile was investigated with XANES, EXAFS, UV/Vis, and Raman spectroscopy, and an increase of the coordination number of the manganese atoms from 4 to 5 and the complete abstraction of the halide was observed. A formal oxidation state of IV was deduced from the relative position of the pre-edge 1s-->3d feature of the X-ray absorption spectrum of the complex. The broad UV/Vis band of this complex in acetonitrile with lambda(max)=648 nm was consistent with a radical cation structure, in which a MCPBA molecule was bound to the Mn(IV) central atom. An oxomanganese(V) or a dimeric manganese(IV) species was not detected.

  2. Structure of assemblies of metal nanowires in mesoporous alumina membranes studied by EXAFS, XANES, X-ray diffraction and SAXS.

    PubMed

    Benfield, Robert E; Grandjean, Didier; Dore, John C; Esfahanian, Hamid; Wu, Zhonghua; Kröll, Michael; Geerkens, Marcus; Schmid, Günter

    2004-01-01

    Mesoporous alumina membranes ("anodic aluminium oxide", or "AAO") are made by anodic oxidation of aluminium metal. These membranes contain hexagonal arrays of parallel non-intersecting cylindrical pores perpendicular to the membrane surface. By varying the anodisation voltage, the pore diameters are controllable within the range 5-250 nm. We have used AAO membranes as templates for the electrochemical deposition of metals within the pores to produce nanowires. These represent assemblies of one-dimensional quantum wires with prospective applications in electronic, optoelectronic and magnetic devices. Detailed characterisation of the structures of these nanowire assemblies on a variety of length scales is essential to understand their physical properties and evaluate their possible applications. We have used EXAFS, XANES, WAXS, high energy X-ray diffraction and SAXS to study their structure and bonding. In this paper we report the results of our studies of four different nanowire systems supported in AAO membranes. These are the ferromagnetic metals iron and cobalt, the superconducting metal tin, and the semiconductor gallium nitride. Iron nanowires in pores of diameter over the range 12 nm-72 nm are structurally very similar to bcc bulk iron. They have a strong preferred orientation within the alumina pores. Their XANES shows significant differences from that of bulk iron, showing that the electronic structure of the iron nanowires depends systematically on their diameter. Cobalt nanowires are composed of a mixture of hcp and fcc phases, but the ratio of the two phases does not depend in a simple way on the pore diameter or preparation conditions. In bulk cobalt, the fcc beta-phase is normally stable only at high temperatures. Strong preferred orientation of the c-axis in the pores was found. Tin nanowires in alumina membranes with pores diameters between 12 nm and 72 nm have a tetragonal beta-structure at ambient temperature and also at 80 K. Magnetic

  3. XANES: observation of quantum confinement in the conduction band of colloidal PbS quantum dots

    NASA Astrophysics Data System (ADS)

    Demchenko, I. N.; Chernyshova, M.; He, X.; Minikayev, R.; Syryanyy, Y.; Derkachova, A.; Derkachov, G.; Stolte, W. C.; Piskorska-Hommel, E.; Reszka, A.; Liang, H.

    2013-04-01

    The presented investigations aimed at development of inexpensive method for synthesized materials suitable for utilization of solar energy. This important issue was addressed by focusing, mainly, on electronic local structure studies with supporting x-ray diffraction (XRD) and transmission electron microscopy (TEM) analysis of colloidal galena nano-particles (NPs) and quantum dots (QDs) synthesized using wet chemistry under microwave irradiation. Performed x-ray absorption near edge structure (XANES) analysis revealed an evidence of quantum confinement for the sample with QDs, where the bottom of the conduction band was shifted to higher energy. The QDs were found to be passivated with oxides at the surface. Existence of sulfate/sulfite and thiosulfate species in pure PbS and QDs, respectively, was identified.

  4. Combining µXANES and µXRD mapping to analyse the heterogeneity in calcium carbonate granules excreted by the earthworm Lumbricus terrestris.

    PubMed

    Brinza, Loredana; Schofield, Paul F; Hodson, Mark E; Weller, Sophie; Ignatyev, Konstantin; Geraki, Kalotina; Quinn, Paul D; Mosselmans, J Frederick W

    2014-01-01

    The use of fluorescence full spectral micro-X-ray absorption near-edge structureXANES) mapping is becoming more widespread in the hard energy regime. This experimental method using the Ca K-edge combined with micro-X-ray diffraction (µXRD) mapping of the same sample has been enabled on beamline I18 at Diamond Light Source. This combined approach has been used to probe both long- and short-range order in calcium carbonate granules produced by the earthworm Lumbricus terrestris. In granules produced by earthworms cultured in a control artificial soil, calcite and vaterite are observed in the granules. However, granules produced by earthworms cultivated in the same artificial soil amended with 500 p.p.m. Mg also contain an aragonite. The two techniques, µXRD and µXANES, probe different sample volumes but there is good agreement in the phase maps produced.

  5. General Method for Determination of the Surface Composition in Bimetallic Nanoparticle Catalysts from the L Edge X-ray Absorption Near-Edge Spectra

    SciTech Connect

    Wu, Tiapin; Childers, David; Gomez, Carolina; Karim, Ayman M.; Schweitzer, Neil; Kropf, Arthur; Wang, Hui; Bolin, Trudy B.; Hu, Yongfeng; Kovarik, Libor; Meyer, Randall; Miller, Jeffrey T.

    2012-10-08

    Bimetallic PtPd on silica nano-particle catalysts have been synthesized and their average structure determined by Pt L3 and Pd K-edge extended X-ray absorption finestructure (EXAFS) spectroscopy. The bimetallic structure is confirmed from elemental line scans by STEM for the individual 1-2 nm sized particles. A general method is described to determine the surface composition in bimetallic nanoparticles even when both metals adsorb, for example, CO. By measuring the change in the L3 X-ray absorption near-edge structure (XANES) spectra with and without CO in bimetallic particles and comparing these changes to those in monometallic particles of known size the fraction of surface atoms can be determined. The turnover rates (TOR) and neopentane hydrogenolysis and isomerization selectivities based on the surface composition suggest that the catalytic and spectroscopic properties are different from those in monometallic nano-particle catalysts. At the same neo-pentane conversion, the isomerization selectivity is higher for the PtPd catalyst while the TOR is lower than that of both Pt and Pd. As with the catalytic performance, the infrared spectra of adsorbed CO are not a linear combination of the spectra on monometallic catalysts. Density functional theory calculations indicate that the Pt-CO adsorption enthalpy increases while the Pd-CO bond energy decreases. The ability to determine the surface composition allows for a better understanding of the spectroscopic and catalytic properties of bimetallic nanoparticle catalysts.

  6. Re and Br X-ray absorption near-edge structure study of the ground and excited states of [ReBr(CO)3(bpy)] interpreted by DFT and TD-DFT calculations.

    PubMed

    Záliš, Stanislav; Milne, Chris J; El Nahhas, Amal; Blanco-Rodríguez, Ana María; van der Veen, Renske M; Vlček, Antonín

    2013-05-20

    X-ray absorption spectra of fac-[ReBr(CO)3(bpy)] near the Re L3- and Br K-edges were measured in a steady-state mode as well as time-resolved at 630 ps after 355 nm laser pulse excitation. Relativistic spin-orbit time-dependent density functional theory (TD-DFT) calculations account well for the shape of the near-edge absorption (the ″white line″) of the ground-state Re spectrum, assigning the lowest-lying transitions as core-to-ligand metal-to-ligand charge transfer from Re 2p(3/2) into predominantly π*(bpy) molecular orbitals (MOs) containing small 5d contributions, followed in energy by transitions into π* Re(CO)3 and delocalized σ*/π* MOs. Transitions gain their intensities from Re 5d and 6s participation in the target orbitals. The 5d character is distributed over many unoccupied MOs; the 5d contribution to any single empty MO does not exceed 29%. The Br K-edge spectrum is dominated by the ionization edge and multiple scattering features, the pre-edge electronic transitions being very weak. Time-resolved spectra measured upon formation of the lowest electronic excited state show changes characteristic of simultaneous Re and Br electronic depopulation: shifts of the Re and Br edges and the Re white line to higher energies and emergence of new intense pre-edge features that are attributed by TD-DFT to transitions from Re 2p(3/2) and Br 1s orbitals into a vacancy in the HOMO-1 created by electronic excitation. Experimental spectra together with quantum chemical calculations provide a direct evidence for a ReBr(CO)3 → bpy delocalized charge transfer character of the lowest excited state. Steady-state as well as time-resolved Re L3 spectra of [ReCl(CO)3(bpy)] and [Re(Etpy)(CO)3(bpy)](+) are very similar to those of the Br complex, in agreement with similar (TD) DFT calculated transition energies as well as delocalized excited-state spin densities and charge changes upon excitation.

  7. µ-XANES AND µ-XRF INVESTIGATIONS OF METAL BINDING MECHANISMS IN BIOSOLIDS

    EPA Science Inventory

    Micro-X-ray fluorescence (µ-XRF) microprobe analysis and micro-X-ray absorption near edge spectroscopy (µ-XANES) were employed to identify Fe and Mn phases and their association with selected toxic elements in two biosolids (limed composted and Nu-Earth) containing low ...

  8. µ-XANES AND µ-XRF INVESTIGATIONS OF METAL BINDING MECHANISMS IN BIOSOLIDS

    EPA Science Inventory

    Micro-X-ray fluorescence (µ-XRF) microprobe analysis and micro-X-ray absorption near edge spectroscopy (µ-XANES) were employed to identify Fe and Mn phases and their association with selected toxic elements in two biosolids (limed composted and Nu-Earth) containing low ...

  9. Ge L{sub 3}-edge x-ray absorption near-edge structure study of structural changes accompanying conductivity drift in the amorphous phase of Ge{sub 2}Sb{sub 2}Te{sub 5}

    SciTech Connect

    Mitrofanov, K. V.; Kolobov, A. V. Fons, P.; Wang, X.; Tominaga, J.; Tamenori, Y.; Uruga, T.; Ciocchini, N.; Ielmini, D.

    2014-05-07

    A gradual uncontrollable increase in the resistivity of the amorphous phase of phase-change alloys, such as Ge{sub 2}Sb{sub 2}Te{sub 5}, known as drift, is a serious technological issue for application of phase-change memory. While it has been proposed that drift is related to structural relaxation, no direct structural results have been reported so far. Here, we report the results of Ge L{sub 3}-edge x-ray absorption measurements that suggest that the drift in electrical conductivity is associated with the gradual conversion of tetrahedrally coordinated Ge sites into pyramidal sites, while the system still remains in the amorphous phase. Based on electronic configuration arguments, we propose that during this process, which is governed by the existence of lone-pair electrons, the concentration of free carriers in the system decreases resulting in an increase in resistance despite the structural relaxation towards the crystalline phase.

  10. Structure and Composition of Cu Doped CdSe Nanocrystals Using Soft X-ray Absorption Spectroscopy

    SciTech Connect

    Meulenberg, R W; van Buuren, T; Hanif, K M; Willey, T M; Strouse, G F; Terminello, L J

    2004-06-04

    The local structure and composition of Cu ions dispersed in CdSe nanocrystals is examined using soft x-ray absorption near edge spectroscopy (XANES). Using Cu L-edge XANES and X-ray photoelectron measurements (XPS), we find that the Cu ions exist in the Cu(I) oxidation state. We also find that the observed Cu L-edge XANES signal is directly proportional to the molar percent of Cu present in our final material. Se L-edge XANES indicates changes in the Se density of states with Cu doping, due to a chemical bonding effect, and supports a statistical doping mechanism. Photoluminescence (PL) measurements indicate the Cu ions may act as deep electron traps. We show that XANES, XPS, and PL are a powerful combination of methods to study the electronic and chemical structure of dopants in nanostructured materials.

  11. Analyzing organic sulfur in coal/char: Integrated mild degradation/XANES methods. Final technical report, September 1, 1993--November 30, 1994

    SciTech Connect

    Palmer, S.R.; Huffman, G.P.

    1994-12-31

    The overall goal of this study is to improve the understanding of sulfur in coals/chars via the use of combined advanced nondestructive and advanced destructive methods of sulfur analysis. This study combines selective oxidation, analytical pyrolysis, and sulfur X-ray Absorption Near Edge Structure Spectroscopy (XANES) analysis. Samples with a wide variety of sulfur contents, (0.63%--4.40%) have been prepared for use in this study. This includes steam gasification chars, oxidized coals and desulfurized coals as well of the original unaltered coals. Mild pyrolysis and XANES data shows that the sulfur chemistry of gasification chars is significantly different from that of the original coals. Mild pyrolysis of the samples that were oxidized with peroxyacetic acid showed that the level of simple thiophene structures observed in the pyrolysis products declines with increasing levels of oxidation. Sulfur XANES spectra of treated samples showed various effects depending on the treatment severity. The XANES spectra of less severely treated samples were similar, although not identical, to the untreated coal spectra. XANES of gasification chars indicated conversion of pyrite to pyrrhotite, removal of organic sulfide sulfur and dissolution of soluble inorganic sulfur species during gasification. Mild oxidation with peroxyacetic acid results in preferential oxidation of sulfide forms before thiophene forms but increasing oxidation severity leads to virtually all sulfur species being oxidized. Good agreement between W-band EPR and XANES data for aromatic sulfur contents were obtained. The TPR analysis of coal indicated that organic sulfur was present as alkyl-aryl sulfide, aryl-aryl sulfides, simple thiophenes and condensed thiophenes. TPR shows that non-thiophenic compounds are removed by PAA oxidation, and that the longer the oxidation is performed the greater is the removal of non-thiophenic sulfur structures.

  12. Nickel site distribution and clustering in synthetic double-chain silicates by experimental and theoretical XANES spectroscopy

    NASA Astrophysics Data System (ADS)

    Giuli, Gabriele; Paris, Eleonora; Ziyu, Wu; Berrettoni, Mario; della Ventura, Giancarlo; Mottana, Annibale

    2000-09-01

    The crystal-chemical role of Ni in synthetic potassium-richterites within the join K(CaNa)Mg4Ni[Si8O22](OH)2-K(CaNa)Ni5[Si8O22](OH)2 has been investigated by XAS (x-ray-absorption spectroscopy). From a structural point of view these materials are classified as double-chain silicates and belong to the amphiboles group. X-ray absorption near-edge structure (XANES) spectra recorded at the Ni K edge show variations that can be related to the Ni-Mg substitution at the octahedral M sites of these amphi-boles. Theoretical XANES spectra, calculated on the basis of the multiple-scattering theory, reproduce very well the experimental spectra, and allow us to understand the relationships between XANES features and the chemical and structural environments around the photoabsorbing ion. The combination of XAS experiments and theoretical calculations provides information on the Ni partitioning between the three octahedral sites and on the local chemistry around the absorber.

  13. X-ray fluorescence mapping and micro-XANES spectroscopic characterization of exhaust particulates emitted from auto engines burning MMT-added gasoline.

    PubMed

    Mölders, N; Schilling, P J; Wong, J; Roos, J W; Smith, I L

    2001-08-01

    The elemental distribution and compositional homogeneity in auto exhaust particulates emitted from methylcyclopentadienyl manganese tricarbonyl-(MMT-)added gasoline engines have been investigated using a newly installed synchrotron X-ray microprobe. Two representative groups of exhaust particulate matter, as defined in a recent bulk X-ray absorption fine structure (XAFS) spectroscopic study at the Mn K-edge, were studied. The micro-X-ray absorption near-edge structure (XANES) spectra indicate a relatively homogeneous distribution of phases within a given particulate sample, down to a spatial extent of 40 microm (the resolution of microprobe). The micro-XANES also enabled analysis of several areas which displayed compositions different from the bulk sample, supporting the general theory describing manganese species formation in the exhaust. The ability to evaluate small regions also enabled direct verification of manganese sulfate from the S XANES despite the vast excess of sulfur present in other forms. The presence of a chloride compound, introduced through the sample dilution air and engine intake air, was also revealed. The study demonstrates the value of the combined X-ray microfluorescence with excitation by polychromatic radiation for elemental mapping and micro-XANES spectroscopy for chemical speciation in the study of dilute environmental materials containing low-Z constituents such as Cl, S, and P.

  14. The role of trace metallic elements in neurodegenerative disorders: quantitative analysis using XRF and XANES spectroscopy.

    PubMed

    Ide-Ektessabi, Ari; Rabionet, Mariona

    2005-07-01

    The present paper focuses on the analysis of trace metallic elements and their role in neurodegenerative disorders. The use of synchrotron radiation microbeams allows investigation of pathological tissues from Alzheimer's disease, Parkinson's disease and Amyotrophic lateral sclerosis cases in a nondestructive manner and at cellular level. By employing X-ray absorption near edge structure (XANES) technique, the chemical state of the investigated elements can be determined, while energy-selective X-ray fluorescence spectroscopy provides the spatial distribution of each element in each oxidative state selectively. The investigated tissues (derived from human, monkey and mouse specimens) show distinct imbalances of metallic elements such as Zn and Cu as well as Fe(2+)/Fe(3+) redox pair, which point to oxidative stress as a crucial factor in the development or progress of these neurodegenerative diseases.

  15. XAF/XANES studies of plutonium-loaded sodalite/glass composite waste forms.

    SciTech Connect

    Aase, S. B.; Kropf, A. J.; Lewis, M. A.; Reed, D. T.; Richmann, M. K.

    1999-07-14

    A sodalite/glass ceramic waste form has been developed to immobilize highly radioactive nuclear wastes in chloride form, as part of an electrochemical cleanup process. Simulated waste forms have been fabricated which contain plutonium and are representative of the salt from the electrometallurgical process to recover uranium from spent nuclear fuel. X-ray absorption fine structure spectroscopy (XAFS) and x-ray absorption near-edge spectroscopy (XANES) studies were performed to determine the location, oxidation state and form of the plutonium within these waste forms. Plutonium, in the non-fission-element case, was found to segregate as plutonium(IV) oxide with a crystallite size of at least 20 nm. With fission elements present, the crystallite size was about 2 nm. No plutonium was observed within the sodalite or glass in the waste form.

  16. EXAFS and XANES analysis of oxides at the nanoscale

    PubMed Central

    Kuzmin, Alexei; Chaboy, Jesús

    2014-01-01

    Worldwide research activity at the nanoscale is triggering the appearance of new, and frequently surprising, materials properties in which the increasing importance of surface and interface effects plays a fundamental role. This opens further possibilities in the development of new multifunctional materials with tuned physical properties that do not arise together at the bulk scale. Unfortunately, the standard methods currently available for solving the atomic structure of bulk crystals fail for nanomaterials due to nanoscale effects (very small crystallite sizes, large surface-to-volume ratio, near-surface relaxation, local lattice distortions etc.). As a consequence, a critical reexamination of the available local-structure characterization methods is needed. This work discusses the real possibilities and limits of X-ray absorption spectroscopy (XAS) analysis at the nanoscale. To this end, the present state of the art for the interpretation of extended X-ray absorption fine structure (EXAFS) is described, including an advanced approach based on the use of classical molecular dynamics and its application to nickel oxide nanoparticles. The limits and possibilities of X-ray absorption near-edge spectroscopy (XANES) to determine several effects associated with the nanocrystalline nature of materials are discussed in connection with the development of ZnO-based dilute magnetic semiconductors (DMSs) and iron oxide nanoparticles. PMID:25485137

  17. Diversity in C-Xanes Spectra Obtained from Carbonaceous Solid Inclusions from Monahans Halite

    NASA Technical Reports Server (NTRS)

    Kebukawa, Y.; Zolensky, M. E.; Fries, M.; Kilcoyne, A. L. D.; Rahman, Z.; Cody, G. D.

    2014-01-01

    Monahans meteorite (H5) contains fluid inclusion- bearing halite (NaCl) crystals [1]. Microthermometry and Raman spectroscopy showed that the fluid in the inclusions is an aqueous brine and they were trapped near 25degC [1]. Their continued presence in the halite grains requires that their incorporation into the H chondrite asteroid was post metamorphism [2]. Abundant solid inclusions are also present in the halites. The solid inclusions include abundant and widely variable organics [2]. Analyses by Raman microprobe, SEM/EDX, synchrotron X-ray diffraction and TEM reveal that these grains include macromolecular carbon similar in structure to CV3 chondrite matrix carbon, aliphatic carbon compounds, olivine (Fo99-59), high- and low-Ca pyroxene, feldspars, magnetite, sulfides, lepidocrocite, carbonates, diamond, apatite and possibly the zeolite phillipsite [3]. Here we report organic analyses of these carbonaceous residues in Monahans halite using C-, N-, and O- X-ray absorption near edge structure (XANES). Samples and Methods: Approximately 100 nm-thick sections were extracted with a focused ion beam (FIB) at JSC from solid inclusions from Monahans halite. The sections were analyzed using the scanning transmission X-ray microscope (STXM) on beamline 5.3.2.2 at the Advanced Light Source, Lawrence Berkeley National Laboratory for XANES spectroscopy. Results and Discussion: C-XANES spectra of the solid inclusions show micrometer-scale heterogeneity, indicating that the macromolecular carbon in the inclusions have complex chemical variations. C-XANES features include 284.7 eV assigned to aromatic C=C, 288.4-288.8 eV assigned to carboxyl, and 290.6 eV assigned to carbonate. The carbonyl features obtained by CXANES might have been caused by the FIB used in sample preparation. No specific N-XANES features are observed. The CXANES spectra obtained from several areas in the FIB sections include type 1&2 chondritic IOM like, type 3 chondritic IOM like, and none of the above

  18. 279 - Xanes Studies on UV-Irradiated Interstellar Ice Analogs: A Comparison to STARDUST Samples

    NASA Technical Reports Server (NTRS)

    Milam, Stefanie N.; Cody, George D.; Kilcoyne, A. L. David; Nuevo, Michel; Sandford, Scott A.; Stroud, Rhonda M.; DeGregorio, Bradley T.

    2010-01-01

    We present C-, N-, and O-XANES (X-ray Absorption Near-Edge Spectroscopy) results of organic residues produced in the laboratory from the UV irradiation of astrophysical ice analogs containing H20, CO, CH30H, NH31 in order to mimic processes that may occur in cold icy bodies of the outer Solar System, particularly in comets, Such analyses showed that laboratory-formed organic residues mainly consist of a solid phase and an oily phase. C-XANES analysis of the solid phase suggests a rich distribution of organic functionalities, among which carbonyl groups, C=C bonds, and alcohols are present. Results from N-XANES indicate the possible presence of amide, amine, and nitrile groups, The O-XANES spectra confirmed the a-bearing groups, These results are compared with the XANES spectra obtained from STARDUST cometary samples,

  19. Ca L2,3-edge XANES and Sr K-edge EXAFS study of hydroxyapatite and fossil bone apatite.

    PubMed

    Zougrou, I M; Katsikini, M; Brzhezinskaya, M; Pinakidou, F; Papadopoulou, L; Tsoukala, E; Paloura, E C

    2016-08-01

    Upon burial, the organic and inorganic components of hard tissues such as bone, teeth, and tusks are subjected to various alterations as a result of interactions with the chemical milieu of soil, groundwater, and presence of microorganisms. In this study, simulation of the Ca L 2,3-edge X-ray absorption near edge structure (XANES) spectrum of hydroxyapatite, using the CTM4XAS code, reveals that the different symmetry of the two nonequivalent Ca(1) and Ca(2) sites in the unit cell gives rise to specific spectral features. Moreover, Ca L 2,3-edge XANES spectroscopy is applied in order to assess variations in fossil bone apatite crystallinity due to heavy bacterial alteration and catastrophic mineral dissolution, compared to well-preserved fossil apatite, fresh bone, and geologic apatite reference samples. Fossilization-induced chemical alterations are investigated by means of Ca L 2,3-edge XANES and scanning electron microscopy (SEM) and are related to histological evaluation using optical microscopy images. Finally, the variations in the bonding environment of Sr and its preference for substitution in the Ca(1) or Ca(2) sites upon increasing the Sr/Ca ratio is assessed by Sr K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy.

  20. Ca L2,3-edge XANES and Sr K-edge EXAFS study of hydroxyapatite and fossil bone apatite

    NASA Astrophysics Data System (ADS)

    Zougrou, I. M.; Katsikini, M.; Brzhezinskaya, M.; Pinakidou, F.; Papadopoulou, L.; Tsoukala, E.; Paloura, E. C.

    2016-08-01

    Upon burial, the organic and inorganic components of hard tissues such as bone, teeth, and tusks are subjected to various alterations as a result of interactions with the chemical milieu of soil, groundwater, and presence of microorganisms. In this study, simulation of the Ca L 2,3-edge X-ray absorption near edge structure (XANES) spectrum of hydroxyapatite, using the CTM4XAS code, reveals that the different symmetry of the two nonequivalent Ca(1) and Ca(2) sites in the unit cell gives rise to specific spectral features. Moreover, Ca L 2,3-edge XANES spectroscopy is applied in order to assess variations in fossil bone apatite crystallinity due to heavy bacterial alteration and catastrophic mineral dissolution, compared to well-preserved fossil apatite, fresh bone, and geologic apatite reference samples. Fossilization-induced chemical alterations are investigated by means of Ca L 2,3-edge XANES and scanning electron microscopy (SEM) and are related to histological evaluation using optical microscopy images. Finally, the variations in the bonding environment of Sr and its preference for substitution in the Ca(1) or Ca(2) sites upon increasing the Sr/Ca ratio is assessed by Sr K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy.

  1. The chemical sensitivity of X-ray spectroscopy: high energy resolution XANES versus X-ray emission spectroscopy of substituted ferrocenes.

    PubMed

    Atkins, Andrew J; Bauer, Matthias; Jacob, Christoph R

    2013-06-07

    X-ray spectroscopy at the metal K-edge is an important tool for understanding catalytic processes and provides insight into the geometric and electronic structures of transition metal complexes. In particular, X-ray emission-based methods such as high-energy resolution fluorescence detection (HERFD), X-ray absorption near-edge spectroscopy (XANES) and valence-to-core X-ray emission spectroscopy (V2C-XES) hold the promise of providing increased chemical sensitivity compared to conventional X-ray absorption spectroscopy. Here, we explore the ability of HERFD-XANES and V2C-XES spectroscopy to distinguish substitutions beyond the directly coordinated atoms for the example of ferrocene and selected ferrocene derivatives. The experimental spectra are assigned and interpreted through the use of density functional theory (DFT) calculations. We find that while the pre-edge peaks in the HERFD-XANES spectra are affected by substituents at the cyclopentadienyl ring containing π-bonds [A. J. Atkins, Ch. R. Jacob and M. Bauer, Chem.-Eur. J., 2012, 18, 7021], the V2C-XES spectra are virtually unchanged. The pre-edge in HERFD-XANES probes the weak transition to unoccupied metal d-orbitals, while the V2C-XES spectra are determined by dipole-allowed transitions from occupied ligand orbitals to the 1s core hole. The latter turn out to be less sensitive to changes beyond the first coordination shell.

  2. Investigation of soil legacy phosphorus transformation in long-term agricultural fields using sequential fractionation, P K-edge XANES and solution P NMR spectroscopy.

    PubMed

    Liu, Jin; Hu, Yongfeng; Yang, Jianjun; Abdi, Dalel; Cade-Menun, Barbara J

    2015-01-06

    Understanding legacy phosphorus (P) build-up and draw-down from long-term fertilization is essential for effective P management. Using replicated plots from Saskatchewan, Canada, with P fertilization from 1967 to 1995 followed by either P fertilization or P cessation (1995-2010), soil P was characterized in surface and subsurface layers using sequential fractionation, P K-edge X-ray absorption near-edge structure (XANES) and solution (31)P nuclear magnetic resonance (P NMR) spectroscopy. Legacy P from a 28-year build-up was sufficient for 15 years of wheat cultivation, resulting in no significant differences in crop yield in 2010. In surface soils, soil test (Olsen) P decreased significantly in unfertilized plots compared with 1995, which was reflected in declining aluminum (hydr)oxide-associated inorganic P by fractionation and XANES. Furthermore, XANES analysis revealed a decrease of calcium-associated P in 2010-unfertilized soils at both depths and an increase of Fe (hydr)oxides-associated P in the 2010-fertilized and -unfertilized surface soils relative to the 1995 soils. Increased total organic P and orthophosphate diesters by P NMR and accumulated inositol hexaphosphate by XANES were observed in surface soils with P fertilization cessation. In subsurface soils, few legacy P transformations were detected. These results provide important information about legacy P to improve agricultural sustainability while mitigating water quality deterioration.

  3. XANES Speciation of P in Environmental Samples: An Assessment of Filter Media for on-Site Wastewater Treatment

    SciTech Connect

    Eveborn, D.; Gustafsson, J; Hesterberg, D; Hillier, S

    2009-01-01

    X-ray absorption near edge structure (XANES) spectroscopy is a useful technique for characterization of chemical species of phosphorus in complex environmental samples. To develop and evaluate bed filters as sustainable on-site wastewater treatment solutions, our objective in this study was to determine the chemical forms of accumulated phosphorus in a selection of promising filter materials: Filtralite P, Filtra P, Polonite, Absol, blast furnace slag, and wollastonite. Full-scale operational wastewater-treatment systems were sampled and in addition, filter samples collected from laboratory studies provided access to additional media and complementary samples. Phosphorus species were characterized using phosphorus K-edge XANES spectroscopy, complemented by X-ray powder diffraction (XRPD) and attenuated total reflectance Fourier-transform infrared spectroscopy (ATR-FTIR). No systematic differences could be seen in the results between laboratory- and full-scale samples. All six filter media contained significant amounts of crystalline calcium phosphates. Some samples also contained amorphous calcium phosphate (>60% of total P in Absol). In Filtralite P and blast furnace slag, more than 35% of the accumulated phosphorus was associated with Fe or Al. Both the power and shortcomings of XANES analysis for characterizing P species in these filter media are discussed.

  4. Aqueous U(VI) interaction with magnetite nanoparticles in a mixed flow reactor system: HR-XANES study

    NASA Astrophysics Data System (ADS)

    Pidchenko, I.; Heberling, F.; Kvashnina, KO; Finck, N.; Schild, D.; Bohnert, E.; Schäfer, T.; Rothe, J.; Geckeis, H.; Vitova, T.

    2016-05-01

    The redox variations and changes in local atomic environment of uranium (U) interacted with the magnetite nanoparticles were studied in a proof of principle experiment by the U L3 and M4 edges high energy resolution X-ray absorption near edge structure (HR-XANES) technique. We designed and applied a mixed flow reactor (MFR) set-up to maintain dynamic flow conditions during U-magnetite interactions. Formation of hydrolyzed, bi- and poly-nuclear U species were excluded by slow continuous injection of U(VI) (10-6 M) and pH control integrated in the MFR set-up. The applied U HR-XANES technique is more sensitive to minor changes in the U redox states and bonding compared to the conventional XANES method. Major U(VI) contribution in uranyl type of bonding is found in the magnetite nanoparticles after three days operation time of the MFR. Indications for shortening of the U-Oaxial bond length for the magnetite compared to the maghemite system are present too.

  5. Ru L[subscript 2,3] XANES theoretical simulation with DFT: A test of the core-hole treatment

    SciTech Connect

    Alperovich, Igor; Moonshiram, Dooshaye; Soldatov, Alexander; Pushkar, Yulia

    2012-10-09

    Density functional theory (DFT)-based relativistic calculations were performed to model the Ru L-edge X-ray absorption near edge structure (XANES) spectra of the hexaammineruthenium complex [Ru(NH{sub 3}){sub 6}]{sup 3+} and 'blue dimer' water oxidation catalyst, cis,cis- [(bpy){sub 2}(H{sub 2}O)Ru{sup III}ORu{sup III}(OH{sub 2})(bpy){sub 2}]{sup 4+} (bpy is 2,2-bipyridine). Two computational approaches were compared: simulations without the core-hole and by modeling of the core-hole within the Z+1 approximation. Good agreement between calculated and experimental XANES spectra is achieved without including the core-hole. Simulations with algorithms beyond the Z+1 approximation were only possible in a framework of the scalar relativistic treatment. Time-dependent DFT (TD-DFT) was used to compute the Ru L-edge spectrum for [Ru(NH{sub 3}){sub 6}]{sup 3+} model compound. Three different core-hole treatments were compared in a real-space full multiple scattering XANES modeling within the Green function formalism (implemented in the FEFF9.5 package) for the [Ru(Mebimpy)(bpm)(H{sub 2}O)]{sup 2+} complex. The latter approaches worked well in cases where spin-orbit treatment of relativistic effects is not required.

  6. On the origin of the differences in the Cu K-edge XANES of isostructural and isoelectronic compounds.

    PubMed

    Sipr, O; Rocca, F; Fornasini, P

    2009-06-24

    Cu K-edge x-ray absorption near-edge structure (XANES) spectra of trigonal (3R) CuScO(2) and CuLaO(2) and of hexagonal (2H) CuScO(2) were investigated experimentally and theoretically, in order to study differences between spectra of isostructural and isoelectronic compounds. Significant differences were found in the Cu K-edge XANES of 3R CuScO(2) and 3R CuLaO(2); these differences can be understood by considering the calculated polarization dependence of the XANES spectra and the differences between the phaseshifts of Sc and La. Spectra of the 3R and 2H polytypes of CuScO(2) differ only weakly and the difference originates from the long-range order. The pre-edge peak around 8980 eV is generated by the same mechanism as the pre-edge peak in Cu(2)O, i.e. involving scattering by the Cu atoms in the plane which is perpendicular to the O-Cu-O axis.

  7. Surface complexation and precipitate geometry for aqueous Zn(II) sorption on ferrihydrite: II. XANES analysis and simulation

    USGS Publications Warehouse

    Waychunas, G.A.; Fuller, C.C.; Davis, J.A.; Rehr, J.J.

    2003-01-01

    X-ray absorption near-edge spectroscopy (XANES) analysis of sorption complexes has the advantages of high sensitivity (10- to 20-fold greater than extended X-ray absorption fine structure [EXAFS] analysis) and relative ease and speed of data collection (because of the short k-space range). It is thus a potentially powerful tool for characterization of environmentally significant surface complexes and precipitates at very low surface coverages. However, quantitative analysis has been limited largely to "fingerprint" comparison with model spectra because of the difficulty of obtaining accurate multiple-scattering amplitudes for small clusters with high confidence. In the present work, calculations of the XANES for 50- to 200-atom clusters of structure from Zn model compounds using the full multiple-scattering code Feff 8.0 accurately replicate experimental spectra and display features characteristic of specific first-neighbor anion coordination geometry and second-neighbor cation geometry and number. Analogous calculations of the XANES for small molecular clusters indicative of precipitation and sorption geometries for aqueous Zn on ferrihydrite, and suggested by EXAFS analysis, are in good agreement with observed spectral trends with sample composition, with Zn-oxygen coordination and with changes in second-neighbor cation coordination as a function of sorption coverage. Empirical analysis of experimental XANES features further verifies the validity of the calculations. The findings agree well with a complete EXAFS analysis previously reported for the same sample set, namely, that octahedrally coordinated aqueous Zn2+ species sorb as a tetrahedral complex on ferrihydrite with varying local geometry depending on sorption density. At significantly higher densities but below those at which Zn hydroxide is expected to precipitate, a mainly octahedral coordinated Zn2+ precipitate is observed. An analysis of the multiple scattering paths contributing to the XANES

  8. Evaluation of iron-containing carbon nanotubes by near edge X-ray absorption technique

    NASA Astrophysics Data System (ADS)

    Osorio, A. G.; Bergmann, C. P.

    2015-10-01

    The synthesis of carbon nanotubes (CNTs) via Chemical Vapor Deposition method with ferrocene results in CNTs filled with Fe-containing nanoparticles. The present work proposes a novel route to characterize the Fe phases in CNTs inherent to the synthesis process. CNTs were synthesized and, afterwards, the CNTs were heat treated at 1000 °C for 20 min in an inert atmosphere during a thermogravimetric experiment. X-Ray Absorption Spectroscopy (XAS) experiments were performed on the CNTs before and after the heat treatment and, also, during the heat treatment, e.g., in situ tests were performed while several Near-Edge X-Ray Absorption (XANES) spectra were collected during the heating of the samples. The XAS technique was successfully applied to evaluate the phases encapsulated by CNTs. Phase transformations of the Fe-based nanoparticles were also observed from iron carbide to metallic iron when the in situ experiments were performed. Results also indicated that the applied synthesis method guarantees that Fe phases are not oxidize. In addition, the results show that heat treatment under inert atmosphere can control which phase remains encapsulated by the CNTs.

  9. Direct Determination of Oxidation States of Uranium in Mixed-Valent Uranium Oxides Using Total Reflection X-ray Fluorescence X-ray Absorption Near-Edge Spectroscopy.

    PubMed

    Sanyal, Kaushik; Khooha, Ajay; Das, Gangadhar; Tiwari, M K; Misra, N L

    2017-01-03

    Total reflection X-ray fluorescence (TXRF)-based X-ray absorption near-edge spectroscopy has been used to determine the oxidation state of uranium in mixed-valent U3O8 and U3O7 uranium oxides. The TXRF spectra of the compounds were measured using variable X-ray energies in the vicinity of the U L3 edge in the TXRF excitation mode at the microfocus beamline of the Indus-2 synchrotron facility. The TXRF-based X-ray absorption near-edge spectroscopy (TXRF-XANES) spectra were deduced from the emission spectra measured using the energies below and above the U L3 edge in the XANES region. The data processing using TXRF-XANES spectra of U(IV), U(V), and U(VI) standard compounds revealed that U present in U3O8 is a mixture of U(V) and U(VI), whereas U in U3O7 is mixture of U(IV) and U(VI). The results obtained in this study are similar to that reported in literature using the U M edge. The present study has demonstrated the possibility of application of TXRF for the oxidation state determination and elemental speciation of radioactive substances in a nondestructive manner with very small amount of sample requirement.

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

    SciTech Connect

    Piskorska-Hommel, E.; Winiarski, M. J.; Kunert, G.; Falta, J.; Demchenko, I. N.; Roshchupkina, O. D.; Grenzer, J.; Hommel, D.; Holý, V.

    2015-02-14

    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+.

  11. Li K-Edge XANES Spectra of Lithium Niobate and Lithium Tantalite

    SciTech Connect

    Mizota, H.; Ito, Y.; Tochio, T.; Handa, K.; Takekawa, S.; Kitamura, K.

    2007-02-02

    The x-ray emission with the single crystal of lithium niobate (LiNbO3) or lithium tantalite (LiTaO3) by thermal changes in a vacuum system is closely concerned with the electronic state of each crystal. Therefore, lithium K-edge x-ray absorption near edge structures (XANES) spectra of these materials were measured in the region from 50 eV to 90 eV by means of total electron yield method (T.E.Y.), using the extremely soft x-ray. Samples were powder of lithium carbonate (Li2CO3) and single crystal of lithium fluoride (LiF), LiNbO3 and LiTaO3 in order to compare the shapes of these XANES spectra. Various peak structures appear in these spectra in the range from 55 eV to 80 eV and each spectrum has different shapes as a result of the difference of bond length and bond angles for the atoms which are in less than 60 nm from the absorbing atom. The relationship between these spectra and the electronic states was discussed by FEFF 8.

  12. Investigation of damaged interior walls using synchrotron-based XPS and XANES.

    PubMed

    Poo-arporn, Yingyot; Thachepan, Surachai; Palangsuntikul, Rungtiva

    2015-01-01

    Evidence of internal sulfate attack in field exposure was demonstrated by the damaged interior wall of a three-year-old house situated in Nakhon Ratchasima Province, Thailand. Partial distension of the mortar was clearly observed together with an expansion of a black substance. Removal of the black substance revealed a dense black layer. This layer was only found in the vicinity of the damaged area, suggesting that this black material is possibly involved in the wall cracking. By employing synchrotron-based X-ray photoelectron spectroscopy (XPS) and X-ray absorption near-edge structure (XANES) techniques, the unknown sample was chemically identified. The S 2p and O 1s XPS results mutually indicated the existence of sulfate species in the materials collected from the damaged area. The XANES results indicated the presence of ferrous (II) sulfate, confirming sulfate-induced expansion and cracking. The sulfate attack in the present case appeared to physically affect the structure whereas the chemical integrity at the molecular level of the calcium silicate hydrate phase was retained since there was a lack of spectroscopic evidence for calcium sulfate. It was speculated that internal sulfate probably originated from the contaminated aggregates used during the construction. The current findings would be beneficial for understanding the sulfate-attack mechanism as well as for future prevention against sulfate attack during construction.

  13. High Pressure XANES studies on Mn dopeHigh Pressure XANES studies on Mn doped Bi2 Te3

    NASA Astrophysics Data System (ADS)

    Light, Brian; Kumar, Ravhi; Baker, Jason; Dharmalingam, Prabhakaran; Park, Changyong; Unlv Team; Hpcat; Carnegie Institute Of Washington Collaboration

    Bi2Te3, Bi2Se3, and Sb2Te3 are narrow band-gap semiconductors have been extensively studied along with their alloys due to their promising technological applications as thermoelectric materials. More recently pressure induced superconductivity and structural transition have been observed in these materials around 7 GPa [1, 2]. Here we have performed high pressure x-ray near edge spectroscopy (XANES) measurements at Bi L-III edge on Mn (0.1) doped Bi2Te3 samples to understand the variation of the Bi valence across the pressure induced superconductivity regime. We have inferred notable changes in the Bi valence at high pressure conditions. The results will be discussed in detail. Work at the University of Nevada Las Vegas (ALC) is funded by U.S. Department of Energy Award DE-SC0001928. Portions of this work were performed at HPCAT (Sector 16), Advanced Photon Source (APS), Argonne National Laboratory. HPCAT is supported by DOE-BES, DOE-NNSA, NSF, and the W.M. Keck Foundation. APS is supported by DOE-BES, under Contract No. DE-AC02-06CH1135.

  14. Total electron yield XANES of zinc-blende MnTe

    NASA Astrophysics Data System (ADS)

    Iwanowski, R. J.; Welter, E.; Janik, E.

    2008-09-01

    The electronic structure and chemical bond of zinc-blende (zb) MnTe have been studied by using total-electron-yield (TEY) X-ray absorption near-edge structure (XANES) spectroscopy. Close resemblances of the shape of Mn K-edge XANES in zb-MnTe and in Zn 1- xMn xTe [A. Titov, X. Biquard, D. Halley, S. Kuroda, E. Bellet-Amalric, H. Mariette, J. Cibert, A.E. Merad, G. Merad, M.B. Kanoun, E. Kulatov, Yu.A. Uspenskii, Phys. Rev. B 72 (2005) 115209] indicated predominant influence of the 1st coordination shell. In particular, identical single-peak pre-edge structure for both cases was mainly ascribed to the Mn 1s-3d/4p weakly allowed dipole transitions. The quantitative analysis of XANES in zb-MnTe concerned the observed chemical shift of Mn K-edge threshold energy and a magnitude of the relevant cation-anion charge transfer (or effective cation charge), q(Mn-Te) [calculated after M. Kitamura, H. Chen, J. Phys. Chem. Solids 52 (1991) 731]. It also provided a comparison with our earlier X-ray absorption studies of Zn 1- xMn xB alloys (B = S, Se). The estimated charge transfer within the chemical bond of zb-MnTe enabled us to complete the q(Mn-B) versus chalcogen ligand (B = S, Se, Te) dependence and to interpret it in terms of p-d hybridization and a contribution of Mn 3d electrons to the overall charge transfer.

  15. High resolution near edge x-ray spectroscopy

    SciTech Connect

    Haemaelaeinen, K.; Siddons, D.P.; Berman, L.E.; Kao, C.C.; Hastings, J.B.

    1992-12-01

    A technique to suppress the core-hole lifetime broadening in near- edge x-ray spectroscopy is presented. A simple theoretical explanation based on total energy conservation in the fluorescence process is given to explain the improved resolution. The experimental arrangement is shown together with an application to the L{sub III} edge of dysprosium. Furthermore, the application of high-resolution fluorescence spectroscopy in the study of magnetism is presented. The spin-resolved absorption spectra from MnF{sub 2} are shown as an example.

  16. High resolution near edge x-ray spectroscopy

    SciTech Connect

    Haemaelaeinen, K.; Siddons, D.P.; Berman, L.E.; Kao, C.C.; Hastings, J.B.

    1992-01-01

    A technique to suppress the core-hole lifetime broadening in near- edge x-ray spectroscopy is presented. A simple theoretical explanation based on total energy conservation in the fluorescence process is given to explain the improved resolution. The experimental arrangement is shown together with an application to the L[sub III] edge of dysprosium. Furthermore, the application of high-resolution fluorescence spectroscopy in the study of magnetism is presented. The spin-resolved absorption spectra from MnF[sub 2] are shown as an example.

  17. The blue of iron in mineral pigments: a Fe K-edge XANES study of vivianite

    NASA Astrophysics Data System (ADS)

    Figueiredo, M. O.; Silva, T. P.; Veiga, J. P.

    2010-05-01

    Iron is a powerful chromophore element whose pigmenting properties were the first to be recognized among transition metals. The interest in blue iron minerals as pigments for painting was enhanced with the use of vivianite—a natural hydrated ferrous phosphate, Fe3(PO4)2ṡ8H2O—which in medieval Europe became an alternative to the expensive lapis lazuli, (Na, Ca)4(AlSiO4)3(SO4, Cl, S), a member of the ultramarines whose appreciated blue tone is due to the presence of sulfur polyanions. Conversely, vivianite coloring is attributed to the intervalence charge transfer (IVCT) Fe2+-Fe3+ that in later decades was studied by optical techniques and Mössbauer spectroscopy. However, the aging of blue vivianite pigments in old paintings has become a serious concern for conservators, but the aging process still awaits a satisfactory explanation. As an input to this problem, an X-ray absorption near-edge structure (XANES) study at the Fe K-edge of vivianite with different colors and origins was undertaken at the European Synchrotron Radiation Facility using the instrumental facilities of beamline ID-21. The analysis of pre-edge features corroborates previous data on the origin of vivianite color and emphasizes the need for a precautious assessment of iron speciation on the exclusive basis of XANES data. Actual results are discussed and further work is outlined.

  18. Evaluation of hexavalent chromium extraction method EPA method 3060A for soils using XANES spectroscopy.

    PubMed

    Malherbe, Julien; Isaure, Marie-Pierre; Séby, Fabienne; Watson, Russell P; Rodriguez-Gonzalez, Pablo; Stutzman, Paul E; Davis, Clay W; Maurizio, Chiara; Unceta, Nora; Sieber, John R; Long, Stephen E; Donard, Olivier F X

    2011-12-15

    Hexavalent chromium (Cr(VI)) occurrence in soils is generally determined using an extraction step to transfer it to the liquid phase where it is more easily detected and quantified. In this work, the performance of the most common extraction procedure (EPA Method 3060A) using NaOH-Na(2)CO(3) solutions is evaluated using X-ray absorption near edge structure spectroscopy (XANES), which enables the quantification of Cr(VI) directly in the solid state. Results obtained with both methods were compared for three solid samples with different matrices: a soil containing chromite ore processing residue (COPR), a loamy soil, and a paint sludge. Results showed that Cr(VI) contents determined by the two methods differ significantly, and that the EPA Method 3060A procedure underestimated the Cr(VI) content in all studied samples. The underestimation is particularly pronounced for COPR. Low extraction yield for EPA Method 3060A was found to be the main reason. The Cr(VI) present in COPR was found to be more concentrated in magnetic phases. This work provides new XANES analyses of SRM 2701 and its extraction residues for the purpose of benchmarking EPA 3060A performance.

  19. A XANES study of Cu speciation in high-temperature brines using synthetic fluid inclusions

    SciTech Connect

    Berry, Andrew J.; Hack, Alistair C.; Mavrogenes, John A.; Newville, Matthew; Sutton, Stephen R.

    2010-12-03

    Cu K-edge X-ray absorption near edge structure (XANES) spectra were recorded from individual synthetic brine fluid inclusions as a function of temperature up to 500 C. The inclusions serve as sample cells for high-temperature spectroscopic studies of aqueous Cu-Cl speciation. Cu{sup +} and Cu{sup 2+} can both be identified from characteristic pre-edge features. Mixed oxidation states can be deconvoluted using linear combinations of Cu{sup +} and Cu{sup 2+} spectra. This work illustrates how complex Cu XANES spectra can be interpreted successfully. Cu{sup 2+} is the stable oxidation state in solution at room temperature and Cu{sup +} at high temperatures. The change in oxidation state with temperature was completely reversible. Cu{sup +} was found to occur exclusively as the linear species [CuCl{sub 2}]{sup -} in solutions containing KCl with Cu:Cl ratios up to 1:6. In the absence of K{sup +}, there is evidence for higher order coordination of Cu{sup +}, in particular the tetrahedral complex [CuCl{sub 4}]{sup 3-}. The importance of such complexes in natural ore-forming fluids is yet to be determined, but may explain the vapor-phase partitioning of Cu as a Cl complex from a Cl-rich brine.

  20. Assessing sulfur redox state and distribution in abyssal serpentinites using XANES spectroscopy

    NASA Astrophysics Data System (ADS)

    Debret, Baptiste; Andreani, Muriel; Delacour, Adélie; Rouméjon, Stéphane; Trcera, Nicolas; Williams, Helen

    2017-05-01

    Sulfur is one of the main redox sensitive and volatile elements involved in chemical transfers between earth surface and the deep mantle. At mid-oceanic ridges, sulfur cycle is highly influenced by serpentinite formation which acts as a sink of sulfur under various oxidation states (S2-, S-, S0 and S6+). Sulfur sequestration in serpentinites is usually attributed to the crystallization of secondary minerals, such as sulfides (e.g. pyrite, pyrrhotite) or sulfates (e.g. anhydrite). However, the role of serpentine minerals as potential sulfur carriers is not constrained. We investigate the distribution and redox state of sulfur at micro-scale combining in situ spectroscopic (X-ray absorption near-edge structure: XANES) and geochemical (SIMS) measurements in abyssal serpentinites from the SWIR (South West Indian Ridge), the Rainbow and the MARK (Mid-Atlantic Ridge, Kane Fracture Zone) areas. These serpentinites are formed in different tectono-metamorphic settings and provide a meaningful database to understand the fate of sulfur during seafloor serpentinization. XANES spectra of serpentinite powders show that the sulfur budget of the studied samples is dominated by oxidized sulfur (S6+ / ∑ S = 0.6- 1) although sulfate micro-phases, such as barite and anhydrite, are absent. Indeed, μ-XANES analyses of mesh, bastite and antigorite veins in thin sections and of serpentine grains rather suggest the presence of S6+ ions incorporated into serpentine minerals. The structural incorporation of S in serpentine minerals is also supported by X-ray fluorescence mapping revealing large areas (1600 μm2) of serpentinite where S is homogeneously distributed. Our observations show that serpentine minerals can incorporate high S concentrations, from 140 to 1350 ppm, and that this can account for 60 to 100% of the sulfur budget of abyssal serpentinites. Serpentine minerals thus play an important role in S exchanges between the hydrosphere and the mantle at mid-oceanic ridges and may

  1. The status of strontium in biological apatites: an XANES investigation.

    PubMed

    Bazin, D; Daudon, M; Chappard, Ch; Rehr, J J; Thiaudière, D; Reguer, S

    2011-11-01

    Osteoporosis represents a major public health problem and increases patient morbidity through its association with fragility fractures. Among the different treatments proposed, strontium-based drugs have been shown to increase bone mass in postmenopausal osteoporosis patients and to reduce fracture risk. While the localization of Sr(2+) cations in the bone matrix has been extensively studied, little is known regarding the status of Sr(2+) cations in natural biological apatite. In this investigation the local environment of Sr(2+) cations has been investigated through XANES (X-ray absorption near-edge structure) spectroscopy in a set of pathological and physiological apatites. To assess the localization of Sr(2+) cations in these biological apatites, numerical simulations using the ab initio FEFF9 X-ray spectroscopy program have been performed. The complete set of data show that the XANES part of the absorption spectra may be used as a fingerprint to determine the localization of Sr(2+) cations versus the mineral part of calcifications. More precisely, it appears that a relationship exists between some features present in the XANES part and a Sr(2+)/Ca(2+) substitution process in site (I) of crystal apatite. Regarding the data, further experiments are needed to confirm a possible link between the relationship between the preparation mode of the calcification (cellular activity for physiological calcification and precipitation for the pathological one) and the adsorption mode of Sr(2+) cations (simple adsorption or insertion). Is it possible to draw a line between life and chemistry through the localization of Sr in apatite? The question is open for discussion. A better structural description of these physiological and pathological calcifications will help to develop specific therapies targeting the demineralization process in the case of osteoporosis.

  2. Theoretical analysis of x-ray-absorption near-edge fine structure at the O and metal K edges of LaFeO{sub 3} and LaCoO{sub 3}

    SciTech Connect

    Wu, Z.Y.; Pedio, M.; Cimino, R.; Mobilio, S. |; Barman, S.R. |; Maiti, K.; Sarma, D.D. |

    1997-07-01

    We present experimental x-ray-absorption spectra at the oxygen and 3d transition-metal K edges of LaFeO{sub 3} and LaCoO{sub 3}. We interpret the experimental results in terms of detailed theoretical calculations based on multiple-scattering theory. Along with providing an understanding of the origin of various experimental features, we investigate the effects of structural distortions and the core-hole potential in determining the experimental spectral shape. The results indicate that the core-hole potential as well as many-body effects within the valence electrons do not have any strong effect on the spectra suggesting that the spectral features can be directly interpreted in terms of the electronic structure of such compounds. {copyright} {ital 1997} {ital The American Physical Society}

  3. Use of micro-XANES to speciate chromium in airborne fine particles in the Sacramento Valley

    SciTech Connect

    Michelle L. Werner; Peter S. Nico; Matthew A. Marcus; Cort Anastasio

    2007-07-15

    While particulate matter (PM) in the atmosphere can lead to a wide array of negative health effects, the cause of toxicity is largely unknown. One aspect of PM that likely affects health is the chemical composition, in particular the transition metals within the particles. Chromium is one transition metal of interest due to its two major oxidation states, with Cr(III) being much less toxic compared to Cr(VI). Using microfocused X-ray absorption near edge structure (micro-XANES), we analyzed the Cr speciation in fine particles (diameters {le} 2.5 {mu}m) collected at three sites in the Sacramento Valley of northern California: Sacramento, a large urban area, Davis, a small city, and Placerville, a rural area. These are several major stationary sources of Cr within 24 km of the site including chrome-plating plants, power plants and incinerators. The microfocused X-ray beam enables us to look at very small areas on the filter with a resolution of typically 5-7 micrometers. With XANES we are able to not only distinguish between Cr(VI) and Cr(III), but also to identify different types of Cr(III) and more reduced Cr species. At all of our sampling sites the main Cr species were Cr(III), with Cr(OH){sub 3} or a Cr-Fe, chromite-like, phase being the dominant species. Cr(VI)-containing particles were found only in the most urban site. All three sites contained some reduced Cr species, either Cr(0) or Cr{sub 3}C{sub 2}, although these were minor components. This work demonstrates that micro-XANES can be used as a minimally invasive analytical tool to investigate the composition of ambient PM. 32 refs., 6 figs.

  4. Local structure of indium oxynitride from x-ray absorption spectroscopy

    SciTech Connect

    T-Thienprasert, J.; Onkaw, D.; Rujirawat, S.; Limpijumnong, S.; Nukeaw, J.; Sungthong, A.; Porntheeraphat, S.; Singkarat, S.

    2008-08-04

    Synchrotron x-ray absorption near edge structures (XANES) measurements of In L{sub 3} edge is used in conjunction with first principles calculations to characterize rf magnetron sputtered indium oxynitride at different O contents. Good agreement between the measured and the independently calculated spectra are obtained. Calculations show that the XANES spectra of this alloy are sensitive to the coordination numbers of the In atoms, i.e., fourfold for indium nitride-like structures and sixfold for indium oxide-like structures, but not to the substitution of nearest neighbor N by O or vice versa.

  5. C-C bond unsaturation degree in monosubstituted ferrocenes for molecular electronics investigated by a combined near-edge x-ray absorption fine structure, x-ray photoemission spectroscopy, and density functional theory approach

    SciTech Connect

    Boccia, A.; Lanzilotto, V.; Marrani, A. G.; Zanoni, R.; Stranges, S.; Alagia, M.; Fronzoni, G.; Decleva, P.

    2012-04-07

    We present the results of an experimental and theoretical investigation of monosubstituted ethyl-, vinyl-, and ethynyl-ferrocene (EtFC, VFC, and EFC) free molecules, obtained by means of synchrotron-radiation based C 1s photoabsorption (NEXAFS) and photoemission (C 1s XPS) spectroscopies, and density functional theory (DFT) calculations. Such a combined study is aimed at elucidating the role played by the C-C bond unsaturation degree of the substituent on the electronic structure of the ferrocene derivatives. Such substituents are required for molecular chemical anchoring onto relevant surfaces when ferrocenes are used for molecular electronics hybrid devices. The high resolution C 1s NEXAFS spectra exhibit distinctive features that depend on the degree of unsaturation of the hydrocarbon substituent. The theoretical approach to consider the NEXAFS spectrum made of three parts allowed to disentangle the specific contribution of the substituent group to the experimental spectrum as a function of its unsaturation degree. C 1s IEs were derived from the experimental data analysis based on the DFT calculated IE values for the different carbon atoms of the substituent and cyclopentadienyl (Cp) rings. Distinctive trends of chemical shifts were observed for the substituent carbon atoms and the substituted atom of the Cp ring along the series of ferrocenes. The calculated IE pattern was rationalized in terms of initial and final state effects influencing the IE value, with special regard to the different mechanism of electron conjugation between the Cp ring and the substituent, namely the {sigma}/{pi} hyperconjugation in EtFC and the {pi}-conjugation in VFC and EFC.

  6. C-C bond unsaturation degree in monosubstituted ferrocenes for molecular electronics investigated by a combined near-edge x-ray absorption fine structure, x-ray photoemission spectroscopy, and density functional theory approach

    NASA Astrophysics Data System (ADS)

    Boccia, A.; Lanzilotto, V.; Marrani, A. G.; Stranges, S.; Zanoni, R.; Alagia, M.; Fronzoni, G.; Decleva, P.

    2012-04-01

    We present the results of an experimental and theoretical investigation of monosubstituted ethyl-, vinyl-, and ethynyl-ferrocene (EtFC, VFC, and EFC) free molecules, obtained by means of synchrotron-radiation based C 1s photoabsorption (NEXAFS) and photoemission (C 1s XPS) spectroscopies, and density functional theory (DFT) calculations. Such a combined study is aimed at elucidating the role played by the C-C bond unsaturation degree of the substituent on the electronic structure of the ferrocene derivatives. Such substituents are required for molecular chemical anchoring onto relevant surfaces when ferrocenes are used for molecular electronics hybrid devices. The high resolution C 1s NEXAFS spectra exhibit distinctive features that depend on the degree of unsaturation of the hydrocarbon substituent. The theoretical approach to consider the NEXAFS spectrum made of three parts allowed to disentangle the specific contribution of the substituent group to the experimental spectrum as a function of its unsaturation degree. C 1s IEs were derived from the experimental data analysis based on the DFT calculated IE values for the different carbon atoms of the substituent and cyclopentadienyl (Cp) rings. Distinctive trends of chemical shifts were observed for the substituent carbon atoms and the substituted atom of the Cp ring along the series of ferrocenes. The calculated IE pattern was rationalized in terms of initial and final state effects influencing the IE value, with special regard to the different mechanism of electron conjugation between the Cp ring and the substituent, namely the σ/π hyperconjugation in EtFC and the π-conjugation in VFC and EFC.

  7. Extended spin-polarized x-ray absorption near-edge spectra of MnO

    SciTech Connect

    Hayashi, Hisashi; Kawata, Masaki; Udagawa, Yasuo; Kawamura, Naomi; Nanao, Susumu

    2004-10-01

    We present Mn K{beta}(3p{yields}1s) emission data as a contour map over wide energy ranges in both excitation and emission. It is demonstrated that spin-polarized x-ray absorption near edge structure (SPXANES) can be deduced by analyzing the data in terms of a formula derived from the Kramers-Heisenberg equation. The SPXANES spectra thus obtained are considerably different from those by conventional method, but are consistent with an anticipation from Hund's rule, and the overall spectral shapes as well as peak positions agree well with a theoretical calculation.

  8. Intracellular nanoparticles mass quantification by near-edge absorption soft X-ray nanotomography

    PubMed Central

    Conesa, Jose Javier; Otón, Joaquín; Chiappi, Michele; Carazo, Jose María; Pereiro, Eva; Chichón, Francisco Javier; Carrascosa, José L.

    2016-01-01

    We used soft X-ray three-dimensional imaging to quantify the mass of superparamagnetic iron oxide nanoparticles (SPION) within whole cells, by exploiting the iron oxide differential absorption contrast. Near-edge absorption soft X-ray nanotomography (NEASXT) combines whole-cell 3D structure determination at 50 nm resolution, with 3D elemental mapping and high throughput. We detected three-dimensional distribution of SPIONs within cells with 0.3 g/cm3 sensitivity, sufficient for detecting the density corresponding to a single nanoparticle. PMID:26960695

  9. Intracellular nanoparticles mass quantification by near-edge absorption soft X-ray nanotomography.

    PubMed

    Conesa, Jose Javier; Otón, Joaquín; Chiappi, Michele; Carazo, Jose María; Pereiro, Eva; Chichón, Francisco Javier; Carrascosa, José L

    2016-03-10

    We used soft X-ray three-dimensional imaging to quantify the mass of superparamagnetic iron oxide nanoparticles (SPION) within whole cells, by exploiting the iron oxide differential absorption contrast. Near-edge absorption soft X-ray nanotomography (NEASXT) combines whole-cell 3D structure determination at 50 nm resolution, with 3D elemental mapping and high throughput. We detected three-dimensional distribution of SPIONs within cells with 0.3 g/cm(3) sensitivity, sufficient for detecting the density corresponding to a single nanoparticle.

  10. Near-edge X-ray refraction fine structure microscopy

    DOE PAGES

    Farmand, Maryam; Celestre, Richard; Denes, Peter; ...

    2017-02-06

    We demonstrate a method for obtaining increased spatial resolution and specificity in nanoscale chemical composition maps through the use of full refractive reference spectra in soft x-ray spectro-microscopy. Using soft x-ray ptychography, we measure both the absorption and refraction of x-rays through pristine reference materials as a function of photon energy and use these reference spectra as the basis for decomposing spatially resolved spectra from a heterogeneous sample, thereby quantifying the composition at high resolution. While conventional instruments are limited to absorption contrast, our novel refraction based method takes advantage of the strongly energy dependent scattering cross-section and can seemore » nearly five-fold improved spatial resolution on resonance.« less

  11. Understanding the Zr and Si interdispersion in Zr1-xSixO2 mesoporous thin films by using FTIR and XANES spectroscopy.

    PubMed

    Andrini, Leandro; Angelomé, Paula C; Soler-Illia, Galo J A A; Requejo, Félix G

    2016-06-14

    Zr-Si mixed mesoporous oxides were obtained in a wide range of proportions, from 0 to 30% and from 70 to 100% of Si, using Si(OEt)4 and ZrCl4 as precursors and Pluronic F127 as a template. The oxide mesostructure was characterized by transmission electron microscopy and 2D-small angle X-ray scattering. Fourier transform infrared spectroscopy measurements suggested a local homogeneous interdispersion of both cations. Further selective studies using X-ray Absorption Near Edge Structure (XANES) spectroscopy for separately Zr and Si local environments, allowed for demonstrating that the Zr coordination varies from close to 7 to 6, when its concentration in the mixed oxide is reduced. In addition, it was possible to determine that in mixed oxides with low Zr concentrations, Zr can fit into the spaces occupied by Si in SiO2 pure oxide. An equivalent XANES result was obtained for Si, which is also compatible with the information obtained by FTIR. Furthermore, the Zr-O distance varied from close to 2.2 Å to 1.7 Å when the Zr concentration decreased. Finally, our study also demonstrates the usefulness of XANES to selectively assess the local structure (coordination, symmetry and chemical state) of specific atoms in nanostructured systems.

  12. Analyzing organic sulfur in coal/char: Integrated mild degradation/XANES methods. [Quarterly] technical report, December 1, 1993--February 28, 1994

    SciTech Connect

    Palmer, S.R.; Huffman, G.P.

    1994-06-01

    The cost effective removal of sulfur from coal has been very difficult to accomplish. Perhaps the single most important reason for this is the fact that the organic sulfur in coal remains very poorly characterized. The overall goal of this study is to improve our understanding of sulfur in coals/chars via the use of combined advanced non-destructive and advanced destructive methods of sulfur analysis. This study combines selective oxidation, analytical pyrolysis, and sulfur X-ray Absorption Near Edge Structure Spectroscopy (XANES) analysis. Examination of samples that were oxidized with peroxyacetic acid using the analytical pyrolysis technique showed that the level of simple thiophene structures observed in the pyrolysis products declines with increasing levels of oxidation. Sulfur XANES spectra of treated samples showed various effects depending on the treatment severity. For the less severely treated samples (demineralization and solvent extraction), the XANES spectra were similar, although not identical, to the untreated coal spectra, whereas the more severe treatments (steam at 450{degree}C; peroxyacetic acid at 25{degree}C) showed preferential oxidation of one or more sulfur-bearing phases in the original coal.

  13. Studies by Near Edge X-ray Absorption Spectroscopies of Bonding Dynamics at the Graphene/Guanine Interface - A Proposal for High Mobility, Organic Graphene Field Effect Transistors

    DTIC Science & Technology

    2015-07-01

    AFRL-AFOSR-UK-TR-2015-0034 Studies by Near Edge X-ray Absorption Spectroscopies of Bonding Dynamics at the Graphene/Guanine...April 2015 4. TITLE AND SUBTITLE Studies by Near Edge X-ray Absorption Spectroscopies of Bonding Dynamics at the Graphene/Guanine Interface - A...native graphene on SiC when used with the Si- terminated surface. Structural and chemical analysis suggest healthy dielectric epilayers, suggesting

  14. Micro-XANES Determination of Fe Oxidation State in MORB and its Relationship to Water Content

    NASA Astrophysics Data System (ADS)

    Posner, E. S.; Cottrell, E.; Kelley, K. A.; Ruebush, E.

    2009-12-01

    We report the oxidation state of iron and H2O content for a global suite of mid-ocean ridge basalt (MORB) glasses in order to assess the relationship between water and oxidation state in mantle-derived basalts unaffected by subduction zone processes. Fe3+/ΣFe ratios were determined with Fe K-edge μX-ray absorption near-edge structure spectroscopy (μXANES). Fe oxidation state was previously determined with microcolorimetry and/or direct titration on a subset of the samples. Fe3+/ΣFe ratios determined using the Mossbauer-based μXANES basalt calibration averaged 0.16±0.01 (n=46) and negatively correlate with MgO suggesting the influence of olivine fractionation. The subset of samples also analyzed by colorimetry ranged from 0.04-0.15 compared to 0.13-0.17 with XANES (n=27) and those also analyzed by direct titration ranged from 0.09-0.14 compared to 0.14-0.17 with XANES (n=9). To investigate the cause of these offsets, Fe3+/ΣFe ratios were determined directly by Mossbauer spectroscopy on two hand-picked, aphyric MORB glass separates and were found to be identical within error to values determined by μXANES. Experimentally equilibrated basaltic glasses from the original study of Kress and Carmichael (CMP, 1991), for which Fe3+/ΣFe ratios were determined by microcolorimetry, were also found to yield Fe3+/ΣFe ratios identical to those determined by μXANES within error. Acid digestion of olivine microphenocrysts in natural MORB samples may lead to an offset between XANES, which samples only glass, and wet-chemical determinations of Fe3+/ΣFe ratios. For example, acid digestion of 20% Fo85 olivine is sufficient to cause the observed offset between XANES and direct titration. Total H2O content, determined with FTIR on the same suite of glasses, shows no correlation with iron oxidation state globally (n=46) or locally within a cogenetic suite (n=10, CHEPR, EPR 6°-13° N, 6-9wt% MgO). In contrast, subduction-influenced back-arc basin (BABB) settings show clear

  15. Trichroism in energy-loss near-edge structure spectroscopy: Polarization dependence of near-edge fine structures

    SciTech Connect

    Le Bosse, Jean-Claude; Epicier, Thierry; Chermette, Henry

    2007-08-15

    The goal of this paper is to relate the current of inelastically scattered electrons collected in a transmission electron microscope (TEM) to the double differential electron energy-loss cross section. Up to now, this relationship, which depends on the point symmetry around the probed atom site, has been essentially studied in a situation called dichroism. This situation can be encountered when a principal threefold, fourfold, or sixfold rotation axis through the probed atom site exists. The electron energy-loss cross section is then a linear combination of longitudinal and transversal cross sections, and the weights of these components are cos{sup 2} {theta}{sub q} and sin{sup 2} {theta}{sub q}, where {theta}{sub q} is the angle between the scattering wave vector q and the principal rotation axis. The first aim of this paper is to find the dependence on q of the cross section in all other cases, that is to say, when the symmetry around the probed atom site is described with one of the eight low symmetry point groups C{sub 1}, S{sub 2}, C{sub 1h}, C{sub 2}, C{sub 2h}, C{sub 2v}, D{sub 2}, and D{sub 2h}. In these eight cases of low symmetry, three distinct situations called trichroism can be distinguished. In these situations, the cross section is expressed in terms of the cross sections obtained for six, four, or three particular orientations of the scattering wave vector. The second aim of this paper is to provide an expression of the inelastically scattered electron current collected in a TEM for these three situations of trichroism. This current is expressed in terms of experimental parameters, such as the incident beam convergence, the collector acceptance, the electron beam kinetic energy, and the sample orientation. As in the case of dichroism, magic conditions can be found, for which the collected current becomes independent of the single-crystal sample orientation. The case of the C K edge in the nonstoichiometric V{sub 6}C{sub 5} metallic carbide with a trigonal symmetry is given as an illustration.

  16. Substitution behavior of x(Na0.5K0.5)NbO3-(1 - x)BaTiO3 ceramics for multilayer ceramic capacitors by a near edge x-ray absorption fine structure analysis

    NASA Astrophysics Data System (ADS)

    Ha, Jooyeon; Ryu, Jiseung; Lee, Heesoo

    2014-06-01

    The doping effect of (Na0.5K0.5)NbO3 (NKN) as alternatives for rare-earth elements on the electrical properties of BaTiO3 has been investigated, in terms of their substitution behavior. The dielectric constant of a specimen with x = 0.05 was about 79% higher than that of pure BaTiO3, and the temperature coefficient of capacitance was satisfied by the X7R specification. The specimen with x = 0.05 showed the lowest tetragonality among the four compositions and had a fine grain size of <2 μm. Although the addition of NKN decreased the specimen's tetragonality, the electrical properties were enhanced by the formation of defect dipoles and conduction electrons, which resulted from an acceptor and donor substitution behavior. Through O K-edge near edge x-ray absorption fine structure spectroscopy, the practical substitution behavior was defined by the change in Ti 3d orbital states. The energy separation of the Ti 3d orbitals was more apparent with the specimen of x = 0.05, which is related to the donor level from the donor substitution of Nb5+ ion for Ti-sites. Therefore, the simultaneous substitution of Na+/K+ and Nb5+ ions into BaTiO3 can improve dielectric properties, based on the charge-transfer process.

  17. Comparison of Nickel XANES Spectra and Elemental Maps from a Ureilite, a LL3.8 Ordinary Chondrite, Two Carbonaceous Chondrites and Two Large Cluster IDPs

    NASA Technical Reports Server (NTRS)

    Wirick, S.; Flynn, G. J.; Sutton, S.; Zolensky, M. E.

    2014-01-01

    Nickel in the extraterrestrial world is commonly found in both Fe-Ni sulfide and Fe-Ni met-al forms [1] and in the pure metal state in the interior of iron meteorites where it is not easily oxidized. Ni is also found in olivine, pyroxene and glasses and in some melts the partitioning of Ni between the olivines and glass is controlled by the amount of S in the melt [2]. Its most common valence state is Ni(2+) but Ni also occurs as Ni(0), Ni(+), and Ni(3+) and rarely as Ni(2-), Ni(1-) and Ni(4+) [3]. It's valence state in olivines is Ni(2+) in octa-hedral coordination on the M1 site and rarely on the M2 site.[4]. The chemical sensitivity of X-ray absorp-tion near-edge structure (XANES) spectroscopy is well established and can be used to determine not only va-lence states but also coordination sites [5]. We report here Ni XANES spectroscopy and elemental maps collected from 2 carbonaceous chondrites, 2 large clus-ter IDPs, 1 ureilite and 1 LL3 orginary chondrite.Using XANES it may be possible to find a common trait in the large cluster IDPs that will also be found in mete-orite samples.

  18. In-situ reflection-XANES study of ZDDP and MoDTC lubricant films formed on steel and diamond like carbon (DLC) surfaces

    NASA Astrophysics Data System (ADS)

    Morina, Ardian; Zhao, Hongyuan; Mosselmans, J. Fred W.

    2014-04-01

    Chemical characterisation of boundary lubricated interfaces is essential for developing mechanistic models that describe lubricant additive interactions with the surface and their effect on tribological performance. In this study the potential for using the synchrotron-based reflection mode X-ray absorption spectroscopy (XAS) technique for in-situ chemical characterisation of lubricant films has been studied. Thermal films formed from zinc dialkyl dithio phosphate (ZDDP) and molybdenum dialkyl dithio carbamate (MoDTC) lubricant additives have been formed and analysed in-situ using the X-ray absorption near edge structure (XANES) spectroscopy technique. The surface sensitivity of this approach was improved by doing the analysis in reflection mode, enabling analysis of only top layer (up to around 10 nm) of the solid surface. In addition, in-lubro analysis of pre-formed tribofilms from the same additives was done using non-vacuum conditions. The results are discussed in conjunction with XANES and X-ray photoelectron spectroscopy (XPS) analysis of similar additives published in the literature. The results obtained are consistent with the existing ZDDP and MoDTC literature and provide some new insight into intermediate species not reported before. The advantages and disadvantages of the developed XANES methodology for in-situ surface chemical analysis of lubricated conditions are discussed.

  19. Antimony leaching and chemical species analyses in an industrial solid waste: Surface and bulk speciation using ToF-SIMS and XANES.

    PubMed

    Kappen, P; Ferrando-Miguel, G; Reichman, S M; Innes, L; Welter, E; Pigram, P J

    2017-05-05

    The surface chemistry and bulk chemical speciation of solid industrial wastes containing 8wt-% antimony (Sb) were investigated using synchrotron X-ray Absorption Near Edge Structure (XANES) and Time-of-Flight Ion Secondary Mass Spectrometry (ToF-SIMS). Leaching experiments were conducted in order to better understand the behavior of Sb in waste streams and to inform regulatory management of antimony-containing wastes. The experiments also demonstrate how a combination of XANES and ToF-SIMS adds value to the field of waste investigations. Leaching treatments (acid and base) were performed at a synchrotron over 24h time periods. Surface analyses of the wastes before leaching showed the presence of Sb associated with S and O. Bulk analyses revealed Sb to be present, primarily, as trivalent sulfide species. Both acid and base leaching did not change the antimony speciation on the solid. Leaching transferred about 1% of the total Sb into solution where Sb was found to be present as Sb(V). XANES data showed similarities between leachate and FeSbO4. During base leaching, the Sb content in solution gradually increased over time, and potential desorption mechanisms are discussed.

  20. XANES evidence of arsenate removal from water with magnetic ferrite.

    PubMed

    Tu, Yao-Jen; You, Chen-Feng; Chang, Chien-Kuei; Wang, Shan-Li

    2013-05-15

    Arsenic (As) in groundwater and surface water is a worldwide problem possessing a serious threat to public health. In this study, a magnetic ferrite, was synthesized and investigated for its As(V) removal efficiency. The adsorption of As(V) by magnetic ferrite exhibited an L-shaped nonlinear isotherm, suggesting limiting binding sites on the adsorbent surface. The As K-edge X-Ray Absorption Near-Edge Structure (XANES) revealed that the adsorbed As(V) on ferrite was not reduced to more toxic As(III) by Fe(2+) in the ferrite structure. The maximum As adsorption capacity of ferrite was 14 mg/g at pH 3 and decreased with increasing pH due to enhanced electrostatic repulsion between As(V) and the adsorbent surface. Desorption of As(V) using six different acid and salt solutions showed that the desorption rate decreased in an order of H3PO4 > Na3PO4 > H2SO4 > Na2SO4 > HCl > HNO3. These results suggest that magnetic ferrite without surface modification is an effective adsorbent for removing As(V) from water, which was confirmed by the effective removal of As(V) from contaminated groundwater using this material. The used material can then be recovered using a magnet because of its paramagnetism; the adsorbed As(V) on the material can be recovered using H3PO4 or Na3PO4 solutions.

  1. First Ti-XANES analyses of refractory inclusions from Murchison

    SciTech Connect

    Simon, S.B.; Sutton, S.R.; Grossman, L.

    2009-03-23

    Ti valence in refractory phases is an important recorder of redox conditions in the early solar nebula. We report the valence of Ti in pyroxene, spinel and hibonite in spinel-hibonite and spinel-pyroxene inclusions and in a coarse hibonite grain. A system of solar composition is so reducing that Ti{sup 3+} and Ti{sup 4+} can coexist, making the valence of Ti a valuable indicator of f{sub O2} conditions during formation of nebular materials. The Ti{sup 3+}/Ti{sup 4+} ratios observed in the Ti-rich phases fassaite and rhoenite in coarse-grained refractory inclusions from CV3 chondrites have been shown to be quantitatively consistent with formation in a gas of solar composition (log f{sub O2} = IW-6.8), but these are the only objects in chondrites for which this is the case. Here, we report the valence of Ti in various phases in refractory inclusions from the Murchison CM2 chondrite. The second-highest temperature, major-element-bearing phase predicted to condense from a gas of solar composition, hibonite (ideally CaAl{sub 12}O{sub 19}), can contain significant amounts of Ti, but the hibonite structure can have oxygen vacancies, so calculation of Ti valence from stoichiometry of electron probe analyses is not recommended for hibonite. To date, the only reported measurement of Ti valence in meteoritic hibonite was done by electron spin resonance, on coarse crystals from a Murchison hibonite-perovskite-melilite inclusion. Spinel and most of the pyroxene in CM inclusions contain too little Ti for derivation of Ti{sup 3+}/Ti{sup 4+} ratios from electron probe analyses. X-ray absorption near edge spectroscopy (XANES), however, allows determination of Ti valence in relatively Ti-poor phases. In the present work, we apply synchrotron microXANES to a large hibonite grain from Murchison and to spinel-hibonite (sp-hib) and spinel-pyroxene (sp-pyx) inclusions from Murchison, refractory materials whose Ti{sup 3+}/Ti{sup 4+} ratios have not been previously measured. Analysis of

  2. Mn K-edge XANES study of the La1-xCaxMnO3 colossal magnetoresistive manganites

    NASA Astrophysics Data System (ADS)

    Ignatov, A. Yu.; Ali, N.; Khalid, S.

    2001-07-01

    We report Mn K-edge x-ray absorption near edge structure (XANES) calculations of the La1-xCaxMnO3 manganites considering three pair correlations, according to the three fundamental degrees of freedom governing their unusual electronic properties, namely, the electronic structure of the unoccupied states probed by the Mn K-edge profile versus (i) local atomic distortions; (ii) local magnetic ordering; and (iii) the charge-transfer nature of the Mn-O bonds. The calculations are accompanied by Mn K-edge XANES measurements in the temperature range 30-300 K. The main features of the absorption edge can be qualitatively reproduced in terms of single-electron multiple-scattering calculations for an 87-atom cluster. Lattice polaronic distortions in La0.7Ca0.3MnO3 are simulated assuming a strongly distorted orthorhombic structure above and an almost undistorted rhombohedral structure below Tc. The results roughly reproduce the energy ``shift'' across Tc observed experimentally. Mn K-edge spin-polarized XANES spectra of the x=0, 0.3, and 1 samples are presented. An energy splitting between the majority- and minority-spin spectra of 0.5-1.1 eV contributes to the total XANES broadening below the Néel (Curie) temperature. A small feature B3 standing approximately 6 eV above the main absorption peak is beyond the scope of single-electron calculations; it is assigned to a shake-up transition. To illustrate, the calculated Mn K edge is obtained as the convolution product of the single-electron XANES and the spectrum of many-body excitations in the Mn-O electronic states upon the sudden switching on of the Mn 1s core hole. We investigate the charge-transfer (CT) versus. Mott-Hubbard-type ground state using the Ud, Δ, and the Tdp parameters determined by previous Mn 2p x-ray photoemission spectroscopy measurements and find that LaMnO3 should be viewed as a CT-type insulator with a substantial O 2p component in the ground state. In light of these results the controversial issue of

  3. In Situ XANES of U and Th in Silicate Liquids at High Pressure and Temperature

    NASA Astrophysics Data System (ADS)

    Mallmann, G.; Wykes, J.; Berry, A.; O'Neill, H. S.; Cline, C. J., II; Turner, S.; Rushmer, T. A.

    2016-12-01

    Although the chemical environments of elements in silicate melts at specific conditions of temperature, pressure and oxygen fugacity (fO2) are often inferred from measurements after quenching the melts to glasses, it is widely recognized that changes may occur during the quenching process, making measurements in situ at high pressure and temperature highly desirable. A case of importance in geochemistry is the speciation of uranium in silicate melts as a function of pressure. Evidence from mineral-melt partitioning and XANES (X-ray Absorption Near-Edge Structure) spectroscopy of glasses suggests that U5+ may be stable at low pressures in the Earth's crust (along with U4+ or U6+, depending on fO2) where basaltic liquids crystallize, but not in the Earth's upper mantle where peridotite partially melts to produce such liquids. To test these observations we recorded in situ transmission U and Th L3-edge XANES spectra of U and Th-doped silicate liquids at 1.6 GPa and 1350°C using the D-DIA apparatus at the X-ray Absorption Spectroscopy Beamline of the Australian Synchrotron. Data for thorium, which occurs exclusively as a tetravalent cation under terrestrial fO2 conditions, were collected as a `control' to monitor for changes in coordination. The cell assembly consisted of a boron-epoxy cube as pressure medium, alumina sleeve and cylindrical graphite heater. The starting mix, a powdered synthetic average MORB silicate glass doped with 2 wt.% of U and Th, was loaded into San Carlos olivine capsules along with solid oxygen buffers (either Re-ReO2 or Ru-RuO2) in a sandwich arrangement. The capsule was then placed inside the graphite heater and insulated with crushable MgO powder. Temperature was monitored using a type D thermocouple. U and Th L3-edge XANES spectra were recorded throughout the heating/compression cycle and then after quenching. Our preliminary assessment indicates that the U-XANES spectra recorded for the liquid in situ at high pressure and temperature and

  4. Oxidation of shallow conduit magma: Insight from μ-XANES analysis on volcanic ash particle

    NASA Astrophysics Data System (ADS)

    Miwa, T.; Ishibashi, H.; Iguchi, M.

    2014-12-01

    Redox state of magma is important to understand dynamics of volcanic eruptions because magma properties such as composition of degassed volatiles, stability field of minerals, and rheology of magma depend on redox state. To evaluate redox state of magma, Fe3+/ΣFe ratio [= Fe3+/( Fe3++ Fe2+)] of volcanic glass has been measured non-destructively by Fe-K edge μ-XANES (micro X-ray Absorption Near Edge Structure) spectroscopy (e.g., Cottrell and Kelly, 2011). We performed textural, compositional, and Fe-K edge μ-XANES analyses on volcanic ash to infer oxidation process of magma at shallow conduit during eruption at Bromo Volcano, Indonesia. The volcanic ash particles were collected in 24th March 2011 by real-time sampling from ongoing activity. The activity was characterized by strombolian eruption showing magma head ascended to near the ground surface. The ash sample contains two type of volcanic glasses named as Brown and Black glasses (BrG and BlG), based on their color. Textual analysis shows microlite crystallinities are same in the two type of glasses, ranging from 0 to 3 vol.%. EPMA analyses show that all of the glasses have almost identical andesitic composition with SiO2 = 60 wt.%. In contrast, Fe-K edge μ-XANES spectra with the analytical method by Ishibashi et al. (in prep) demonstrate that BrG (Fe3+/ΣFe = 0.20-0.26) is more oxidized than BlG (Fe3+/ΣFe = 0.32-0.60). From combination of the glass composition, the measured Fe3+/ΣFe ratio and 1060 degree C of temperature (Kress and Carmichael, 1991), the oxygen fugacities are estimated to be NNO and NNO+4 for BrG and BlG, respectively. The volcanic glasses preserve syn-eruptive physicochemical conditions by rapid quenching due to their small size ranging from 125 to 250 μm. Our results demonstrate that BrG and BlG magmas are textually and chemically identical but their redox conditions are different at the eruption. The oxidation of magma can be caused by following two processes; 1) diffusive transport

  5. A theoretical approach to La L(1)-edge XANES spectra of La complex oxides and their local configuration.

    PubMed

    Asakura, Hiroyuki; Shishido, Tetsuya; Teramura, Kentaro; Tanaka, Tsunehiro

    2015-04-28

    The characteristic peaks (pre-edge peaks) in the La L1-edge X-ray absorption near edge structure (XANES) of various La complex oxides were analyzed by both experimental and theoretical approaches. The pre-edge peak areas are correlated with the bond angle analysis (BAA) parameter, which we proposed as an indicator of the centrosymmetry or disorder of the local configuration of the La site. The origin of the pre-edge peak and the parameterization criteria of the BAA parameter were evaluated using theoretical calculations based on molecular orbital theory and multiple scattering theory. The theoretical calculations showed that the origin of the pre-edge peak at the La L1-edge is electric dipole transition from 2s to unoccupied states generated by p-d hybridization. Medium-scale theoretical simulations of the La L1-edge XANES spectra of thousands of virtual La aqueous complex models verified that the parameterization criteria of the BAA parameter are applicable to local configuration analysis of La.

  6. A theoretical approach to La L1-edge XANES spectra of La complex oxides and their local configuration

    NASA Astrophysics Data System (ADS)

    Asakura, Hiroyuki; Shishido, Tetsuya; Teramura, Kentaro; Tanaka, Tsunehiro

    2015-04-01

    The characteristic peaks (pre-edge peaks) in the La L1-edge X-ray absorption near edge structure (XANES) of various La complex oxides were analyzed by both experimental and theoretical approaches. The pre-edge peak areas are correlated with the bond angle analysis (BAA) parameter, which we proposed as an indicator of the centrosymmetry or disorder of the local configuration of the La site. The origin of the pre-edge peak and the parameterization criteria of the BAA parameter were evaluated using theoretical calculations based on molecular orbital theory and multiple scattering theory. The theoretical calculations showed that the origin of the pre-edge peak at the La L1-edge is electric dipole transition from 2s to unoccupied states generated by p-d hybridization. Medium-scale theoretical simulations of the La L1-edge XANES spectra of thousands of virtual La aqueous complex models verified that the parameterization criteria of the BAA parameter are applicable to local configuration analysis of La.

  7. Humic sulfur in eutrophic bay sediments: Characterization by sulfur stable isotopes and K-edge XANES spectroscopy

    NASA Astrophysics Data System (ADS)

    Zhu, Mao-Xu; Chen, Liang-Jin; Yang, Gui-Peng; Huang, Xiang-Li; Ma, Chen-Yan

    2014-02-01

    Organic sulfur (OS) is an important sedimentary sulfur pool in marine sediments and chemical extractions are often used for quantification of various OS pools, however, OS sources and mechanisms of OS formation are not well understood. In this study, sulfur stable isotope and sulfur X-ray absorption near edge structure (XANES) spectroscopy were combined to investigate the sources and speciation of humic-acid sulfur (HA-S) and fulvic-acid sulfur (FA-S) in sediments of eutrophic Jiaozhou Bay. Whilst there may be some indication that eutrophication has enhanced FA-S burial in the sediment, this has not substantially modified the characteristically low humic sulfur (i.e., HA-S + FA-S) contents of the sediments. Sulfur isotopic compositions indicate that both HA-S and FA-S are mixtures of diagenetic and biosynthetic OS in origin; HA-S is dominated by biosynthetic sulfur and FA-S by diagenetic source. Sulfur isotopic compositions and contents of pyrite and diagenetic OS indicate that inhibition of sulfurization by pyrite formation, if any, appears insignificant. XANES analysis suggests that the contents of high oxidized OS (i.e., sulfones and ester-sulfates) and strongly reduced OS species are comparable in the HA-S, whereas the FA-S is dominated by strongly reduced OS as a result of enhanced sulfurization.

  8. Utilization of 'elemental' sulfur by different phototrophic sulfur bacteria (Chromatiaceae, Ectothiorhodospiraceae): A sulfur K-edge XANES spectroscopy study

    NASA Astrophysics Data System (ADS)

    Franz, B.; Lichtenberg, H.; Dahl, C.; Hormes, J.; Prange, A.

    2009-11-01

    Phototrophic sulfur bacteria are generally able to use elemental sulfur as an electron donor for anoxygenic photosynthesis. Elemental sulfur is mainly a mixture of cyclo-octasulfur and polymeric sulfur. The purple sulfur bacterium Allochromatium vinosum strongly prefers the polymeric sulfur fraction showing that sulfur speciation has a strong influence on availability of elemental sulfur. X-ray absorption near edge structure (XANES) spectroscopy was used to investigate whether polymeric sulfur is also the preferred sulfur species in other purple sulfur bacteria belonging to the families Chromatiaceae and Ecothiorodospiraceae. The cultures were fed with 50 mM of elemental sulfur consisting of 68% polymeric sulfur and 30% cyclo-octasulfur. In all cultures, elemental sulfur was converted into intra- or extracellular sulfur globules, respectively, and further oxidized to sulfate. Sulfate concentrations were determined by HPLC and turbidometric assays, respectively. However, the added elemental sulfur was only partly used by the bacteria, one part of the 'elemental sulfur' remained in the cultures and was not taken up. XANES spectroscopy revealed that only the polymeric sulfur fraction was taken up by all cultures investigated. This strongly indicates that polymeric 'chain-like' sulfur is the form preferably used by phototrophic sulfur bacteria.

  9. 3D local structure around copper site of rabbit prion-related protein: Quantitative determination by XANES spectroscopy combined with multiple-scattering calculations

    NASA Astrophysics Data System (ADS)

    Cui, P. X.; Lian, F. L.; Wang, Y.; Wen, Yi; Chu, W. S.; Zhao, H. F.; Zhang, S.; Li, J.; Lin, D. H.; Wu, Z. Y.

    2014-02-01

    Prion-related protein (PrP), a cell-surface copper-binding glycoprotein, is considered to be responsible for a number of transmissible spongiform encephalopathies (TSEs). The structural conversion of PrP from the normal cellular isoform (PrPC) to the post-translationally modified form (PrPSc) is thought to be relevant to Cu2+ binding to histidine residues. Rabbits are one of the few mammalian species that appear to be resistant to TSEs, because of the structural characteristics of the rabbit prion protein (RaPrPC) itself. Here we determined the three-dimensional local structure around the C-terminal high-affinity copper-binding sites using X-ray absorption near-edge structure combined with ab initio calculations in the framework of the multiple-scattering (MS) theory. Result shows that two amino acid resides, Gln97 and Met108, and two histidine residues, His95 and His110, are involved in binding this copper(II) ion. It might help us understand the roles of copper in prion conformation conversions, and the molecular mechanisms of prion-involved diseases.

  10. HERFD-XANES and XES as complementary operando tools for monitoring the structure of Cu-based zeolite catalysts during NOx-removal by ammonia SCR

    NASA Astrophysics Data System (ADS)

    Günter, T.; Doronkin, D. E.; Carvalho, H. W. P.; Casapu, M.; Grunwaldt, J.-D.

    2016-05-01

    In this article, we demonstrate the potential of hard X-ray techniques to characterize catalysts under working conditions. Operando high energy resolution fluorescence detected (HERFD) XANES and valence to core (vtc) X-ray emission spectroscopy (XES) have been used in a spatially-resolved manner to study Cu-zeolite catalysts during the standard-SCR reaction and related model conditions. The results show a gradient in Cu oxidation state and coordination along the catalyst bed as the reactants are consumed. Vtc-XES gives complementary information on the direct adsorption of ammonia at the Cu sites. The structural information on the catalyst shows the suitability of X-ray techniques to understand catalytic reactions and to facilitate catalyst optimization.

  11. A valence state evaluation of a positive electrode material in an Li-ion battery with first-principles K- and L-edge XANES spectral simulations and resonance photoelectron spectroscopy

    NASA Astrophysics Data System (ADS)

    Kubobuchi, Kei; Mogi, Masato; Matsumoto, Masashi; Baba, Teruhisa; Yogi, Chihiro; Sato, Chikai; Yamamoto, Tomoyuki; Mizoguchi, Teruyasu; Imai, Hideto

    2016-10-01

    X-ray absorption near edge structure (XANES) analysis is an element-specific method for proving electronic state mostly in the field of applied physics, such as battery and catalysis reactions, where the valence change plays an important role. In particular, many results have been reported for the analysis of positive electrode materials of Li-ion batteries, where multiple transition materials contribute to the reactions. However, XANES analysis has been limited to identifying the valence state simply in comparison with reference materials. When the shape of XANES spectra shows complicated changes, we were not able to identify the valence states or estimate the valence quantitatively, resulting in insufficient reaction analysis. To overcome such issues, we propose a valence state evaluation method using K- and L-edge XANES analysis with first-principles simulations. By using this method, we demonstrated that the complicated reaction mechanism of Li(Ni1/3Co1/3Mn1/3)O2 can be successfully analyzed for distinguishing each contribution of Ni, Co, Mn, and O to the redox reactions during charge operation. In addition to the XANES analysis, we applied resonant photoelectron spectroscopy (RPES) and diffraction anomalous fine structure spectroscopy (DAFS) with first-principles calculations to the reaction analysis of Co and Mn, which shows no or very little contribution to the redox. The combination of RPES and first-principles calculations successfully enables us to confirm the contribution of Co at high potential regions by electively observing Co 3d orbitals. Through the DAFS analysis, we deeply analyzed the spectral features of Mn K-edges and concluded that the observed spectral shape change for Mn does not originate from the valence change but from the change in distribution of wave functions around Mn upon Li extraction.

  12. The irradiation of ammonia ice studied by near edge x-ray absorption spectroscopy

    SciTech Connect

    Parent, Ph.; Bournel, F.; Lasne, J.; Laffon, C.; Carniato, S.; Lacombe, S.; Strazzulla, G.; Gardonio, S.; Lizzit, S.; Kappler, J.-P.; Joly, L.

    2009-10-21

    A vapor-deposited NH{sub 3} ice film irradiated at 20 K with 150 eV photons has been studied with near-edge x-ray absorption fine structure (NEXAFS) spectroscopy at the nitrogen K-edge. Irradiation leads to the formation of high amounts (12%) of molecular nitrogen N{sub 2}, whose concentration as a function of the absorbed energy has been quantified to 0.13 molecule/eV. The stability of N{sub 2} in solid NH{sub 3} has been also studied, showing that N{sub 2} continuously desorbs between 20 and 95 K from the irradiated ammonia ice film. Weak concentrations (<1%) of other photoproducts are also detected. Our NEXAFS simulations show that these features own to NH{sub 2}, N{sub 2}H{sub 2}, and N{sub 3}{sup -}.

  13. PREFACE: Proceedings of the First International Workshop on the Theoretical Calculation of ELNES and XANES (TEX2008) (Nagoya, Japan, 2-4 July 2008) Proceedings of the First International Workshop on the Theoretical Calculation of ELNES and XANES (TEX2008) (Nagoya, Japan, 2-4 July 2008)

    NASA Astrophysics Data System (ADS)

    Tanaka, Isao; Mizoguchi, Teruyasu; Yamamoto, Tomoyuki

    2009-03-01

    Both electron energy loss near edge structure (ELNES) spectroscopy and x-ray absorption near edge structure (XANES) spectroscopy provide information on the local structural and chemical environments of selected elements of interest. Recent technological progress in scanning transmission electron microscopy has enabled ELNES measurements with atomic column spatial resolution. Very dilute concentrations (nanograms per milliliter or ppb level) of dopants can be observed using third-generation synchrotron facilities when x-ray fluorescence is measured with highly efficient detectors. With such technical developments, ELNES and XANES have become established as essential tools in a large number of fields of natural science, including condensed matter physics, chemistry, mineralogy and materials science. In addition to these developments in experimental methodology, notable progress in reproducing spectra using theoretical methods has recently been made. Using first-principles methods, one can analyze and interpret spectra without reference to experiment. This is quite important since we are often interested in the analysis of exotic materials or specific atoms located at lattice discontinuities such as surfaces and interfaces, where appropriate experimental data are difficult to obtain. Using the structures predicted by reliable first-principles calculations, one can calculate theoretical ELNES and XANES spectra without too much difficulty even in such cases. Despite the fact that ELNES and XANES probe the same phenomenon—essentially the electric dipole transition from a core orbital to an unoccupied band—there have not been many opportunities for researchers in the two areas to meet and discuss. Theoretical calculations of ELNES spectra have been mainly confined to the electron microscopy community. On the other hand, the theory of XANES has been developed principally by researchers in the x-ray community. Publications describing the methods have been written more

  14. Sulphur XANES Analysis of Cultured Human Prostate Cancer Cells

    NASA Astrophysics Data System (ADS)

    Kwiatek, W. M.; Podgórczyk, M.; Paluszkiewicz, Cz.; Balerna, A.; Kisiel, A.

    2008-08-01

    Prostate cancer is one of the most commonly diagnosed cancers in men throughout the world. It is believed that changes to the structure of protein binding sites, altering its metabolism, may play an important role in carcinogenesis. Sulphur, often present in binding sites, can influence such changes through its chemical speciation. Hence there is a need for precise investigation of coordination environment of sulphur. X-ray absorption near edge structure spectroscopy offers such possibility. Cell culture samples offer histologically well defined areas of good homogeneity, suitable for successful and reliable X-ray absorption near edge structure analysis. This paper presents sulphur speciation data collected from three different human prostate cancer cell lines (PC-3, LNCaP and DU-145). Sulphur X-ray absorption near edge structure analysis was performed on K-edge structure. The spectra of cells were compared with those of cancerous tissue and with organic substances as well as inorganic compounds.

  15. Speciation of magnesium in monohydrocalcite: XANES, ab initio and geochemical modeling

    NASA Astrophysics Data System (ADS)

    Fukushi, Keisuke; Suzuki, Yuma; Kawano, Jun; Ohno, Takeshi; Ogawa, Masahiro; Yaji, Toyonari; Takahashi, Yoshio

    2017-09-01

    Monohydrocalcite (MHC: CaCO3·H2O), a rare carbonate mineral formed under surface conditions, is usually observed in nature as containing a variable amount of Mg, with a 0.007-0.45 Mg/Ca mole ratio. The variable Mg composition in MHC is anticipated as a promising proxy to assess paleo-hydrochemistry especially in saline lakes. Although the roles of Mg on the formation and stability of MHC have been studied intensively, the Mg speciation in MHC has remained unclear and controversial. This study examined Mg speciation in MHC using X-ray absorption near edge structure (XANES), ab initio molecular simulation, and geochemical modeling. Mg-XANES spectra of MHC with different Mg/Ca ratios prepared from mixing solutions of Na2CO3, CaCl2 and MgCl2 revealed that the Mg in MHC is a mixture of amorphous Mg carbonate (AMC) and other Mg containing phase. The contribution of AMC to total Mg is negatively correlated to the crystallinity of MHC. Results show that AMC might play a protective role in the crystallization and the transformation to stable calcium carbonates. Ab initio calculation of Mg2+ substitution into MHC showed that a limited amount of Mg2+ can be incorporated into the MHC structure. Six-fold coordination of Mg2+ is substituted for eight-fold coordination of Ca2+ in the MHC structure. The other type of Mg in MHC revealed from the XANES analyses most likely corresponds to the structural Mg in MHC. The contribution of the structural Mg is almost constant at 0.06 in Mg/Ca, representing the limit of solid solubility of Mg in MHC. The solubility products of the MHC with the limit of solid solubility of Mg and the AMC associated with MHC were estimated from the reacted solution compositions. Prediction of the Mg/Ca ratio as a function of the initial solution conditions using solubility reasonably reproduces the observed apparent Mg/Ca ratios in MHC from the present study and earlier studies. The apparent Mg/Ca ratio of MHC is useful to elucidate water chemistry

  16. micro-XANES and micro-XRF investigations of metal binding mechanisms in biosolids.

    PubMed

    Hettiarachchi, G M; Scheckel, K G; Ryan, J A; Sutton, S R; Newville, M

    2006-01-01

    Micro-X-ray fluorescence (micro-XRF) microprobe analysis and micro-X-ray absorption near-edge structure (micro-XANES) spectroscopy were employed to identify Fe and Mn phases and their association with selected metals in two biosolids (limed composted [LC] and Nu-Earth) before and after treatment to remove organic carbon (OC). Spatial correlations derived from elemental mapping of XRF images showed strong correlations between Fe and Cd, Cr, Pb, or Zn (r2= 0.65-0.92) before and after removal of most of the OC. The strong correlation between Fe and Cu that was present in intact samples disappeared after OC removal, suggesting that Cu was associated with OC coatings that may have been present on Fe compounds. Except for Fe and Cr, the spatial correlations of metals with Mn were improved after treatment to remove OC, indicating that the treatment may have altered more than the OC in the system. The Fe micro-XANES spectra of the intact biosolids sample showed that every point had varying mixtures of Fe(II and III) species and no two points were identical. The lack of uniformity in Fe species in the biosolids sample illustrates the complexity of the materials and the difficulty of studying biosolids using conventional analytical tools or chemical extraction techniques. Still, these microscopic observations provide independent information supporting the previous laboratory and field hypothesis that Fe compounds play a major role in retention of environmentally important trace elements in biosolids. This could be due to co-precipitation of the metals with Fe, adsorption of metals by Fe compounds, or a combination of both mechanisms.

  17. The Valence of Iron in CM Chondrite Serpentine as Measured by Synchrotron Xanes

    NASA Technical Reports Server (NTRS)

    Mikouchi, T.; Zolensky, Michael E.; Satake, W.; Le, L.

    2012-01-01

    Fe-bearing phyllosilicates are the dominant product of aqueous alteration in carbonaceous chondrites, and serpentine is the most abundant phyllosilicate in CM2 chondrites that are the most abundant carbonaceous chondrite. Browning et al. predicted that Fe(3+)/(sum of Fe) ratios of serpentine in CM chondrites should change with progressive alteration. They proposed that progressive CM alteration is best monitored by evaluating the progress of Si and Fe3+ substitutions that necessarily attend the transition from end-member cronstedtite to serpentine. Their proposed Mineralogic Alteration Index, 2-(Fe(3+)/(2-Si)), was intended to highlight and utilize the relevant ex-change information in the stoichiometric phyllosilicate formulas based upon the coupled substitution of 2(Fe(3+), Al) = Si + (Mg, Fe(2+)...) in serpentine. The value of this ratio increases as alteration proceeds. We always wanted to directly test Browning s pre-diction through actual measurements of the Fe3+ con-tent of serpentine at the micron scale appropriate to EPMA analyses (Zega et al. have measured it at much finer scale), and this test can now be made using Synchrotron Radiation X-ray Absorption Near-Edge Structure (SR-XANES). Thus, we have recently begun investigation with CMs that span a large portion of the range of observed aqueous alteration, and we first analyzed Murray, Nogoya, and ALH84029 by SR-XANES. However, we did not find clear correlation between Fe3+/(sum of Fe) ratios of serpentine and their alteration degrees. We thus analyzed serpentine in three more CMs and here report their Fe3+/(sum of Fe) ratios in comparison with our previous results.

  18. Polarized XANES and EXAFS spectroscopic investigation into copper(II) complexes on vermiculite

    NASA Astrophysics Data System (ADS)

    Furnare, Luca J.; Vailionis, Arturas; Strawn, Daniel G.

    2005-11-01

    Interaction of heavy metals with clay minerals can dominate solid-solution reactions in soil, controlling the fate of the metals in the environment. In this study we used powdered and polarized extended X-ray absorption fine structure (EXAFS) spectroscopy and X-ray absorption near edge spectroscopy (XANES) to investigate Cu sorbed on Llano vermiculite and compare the results to reported Cu sorption mechanism on Wyoming (WY) smectite and reduced South African (SA) vermiculite. Analysis of the Cu K-edge spectra revealed that Cu sorbed on Llano vermiculite at high ionic strength ( I) has the greatest degree of covalent bond character, followed by Cu sorbed on montmorillonite at high I, and Cu sorbed on reduced SA vermiculite at high I. Cu sorbed on clay minerals at low I has the least covalent character. EXAFS data from Cu sorbed Ca- and K-equilibrated Llano vermiculites showed the presence of a second-shell Al, Si, or Mg backscatterer at 3.02 Å. This distance is consistent with Cu sorbing via a corner-sharing monodentate or bidentate bond. Polarized XANES and EXAFS results revealed that the angle between the Cu atom and the mineral sorption sites is 68° with respect to the [001] direction. From the bond angle and the persistence of the second-shell backscatterer when the interlayer is collapsed (K-equilibration), we conclude that Cu adsorption on the Llano vermiculite is not occurring in the interlayer but rather Cu is adsorbing onto the edges of the vermiculite. Results from this research provide evidence that Cu forms inner-sphere and outer-sphere complexes on clay minerals, and does not form the vast multinuclear surface precipitates that have been observed for Co, Zn, and Ni.

  19. Chemical species of sulfur in prostate cancer cells studied by XANES spectroscopy

    NASA Astrophysics Data System (ADS)

    Czapla, Joanna; Kwiatek, Wojciech M.; Lekki, Janusz; Dulińska-Litewka, Joanna; Steininger, Ralph; Göttlicher, Jörg

    2013-12-01

    The role of sulfur in prostate cancer progression may be significant for understanding the process of carcinogenesis. This work, based on X-ray Absorption Near Edge Structure (XANES) spectroscopy, is focused on determination of sulfur chemical species occurring in prostate cancer cell lines. The experimental material consisted of four commercially available cell lines: three from metastasized prostate cancer (PC3, LNCaP, and DU145) and one, used as a control, from the non-tumourigenic peripheral zone of the prostate (PZ-HPV-7). The experiment was performed at the SUL-X beamline of the synchrotron radiation source ANKA, Karlsruhe (Germany). The K-edge XANES spectra of sulfur were analyzed by deconvolution in order to establish sulfur species that occur in prostate cancer cells and to find out whether there are any differences in their content between various cell lines. Experimental spectra were fitted in two ways: with two Gaussian peaks and one arctangent step function, and additionally by a Linear Combination Fit with spectra of reference compounds in order to obtain quantitative chemical information. All fitting procedures were performed with the Athena code (Ravel and Newville, 2005) and the results of deconvolution were used to determine the fraction of each sulfur form. The results of data analysis showed that cell lines from different metastasis had different ratio of reduced to oxidized sulfur species. The LCF analysis demonstrated that the highest content of GSH, one of the most important sulfur-bearing compounds in cells, was observed in DU145 cells. These findings may confirm the hypothesis of changes in redox balance in case of cancer initiation and progression.

  20. X-ray studies on optical and structural properties of ZnO nanostructured thin films

    NASA Astrophysics Data System (ADS)

    Larcheri, S.; Armellini, C.; Rocca, F.; Kuzmin, A.; Kalendarev, R.; Dalba, G.; Graziola, R.; Purans, J.; Pailharey, D.; Jandard, F.

    2006-01-01

    X-ray absorption near-edge fine structure (XANES) studies have been carried out on nanostructured ZnO thin films prepared by atmospheric pressure chemical vapour deposition (APCVD). Films have been characterized by X-ray diffraction (XRD) and optical luminescence spectroscopy exciting with laser light (PL) or X-ray (XEOL). According to XRD measurements, all the APCVD samples reveal a highly (002) oriented crystalline structure. The samples have different thickness (less than 1 μm) and show significant shifts of the PL and XEOL bands in the visible region. Zn K-edge XANES spectra were recorded using synchrotron radiation at BM08 of ESRF (France), by detecting photoluminescence yield (PLY) and X-ray fluorescence yield (FLY). The differences between the PLY- and FLY-XANES confirm the possibility of studying the local environment in the luminescence centres and to correlate the structural and optical properties of ZnO nanostructured samples.

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

    SciTech Connect

    Apblett, Christopher A.; Stewart, David M.; Fryer, Robert T.; Sell, Julia C.; Pratt, Harry D. III; Anderson, Travis M.; Meulenberg, Robert W.

    2015-10-23

    We apply in situ X-Ray Absorption Near Edge Spectroscopy (XANES) and Extended X-Ray Absorption Fine Structure (EXAFS) techniques to a metal center ionic liquid undergoing oxidation and reduction in a three electrode spectroscopic cell. Furthermore, the 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. Finally, 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.

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

    DOE PAGES

    Apblett, Christopher A.; Stewart, David M.; Fryer, Robert T.; ...

    2015-10-23

    We apply in situ X-Ray Absorption Near Edge Spectroscopy (XANES) and Extended X-Ray Absorption Fine Structure (EXAFS) techniques to a metal center ionic liquid undergoing oxidation and reduction in a three electrode spectroscopic cell. Furthermore, the 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 similarlymore » 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. Finally, 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.« less

  3. Environmental impacts of steel slag reused in road construction: a crystallographic and molecular (XANES) approach.

    PubMed

    Chaurand, Perrine; Rose, Jerome; Briois, Valérie; Olivi, Luca; Hazemann, Jean-Louis; Proux, Olivier; Domas, Jérémie; Bottero, Jean-Yves

    2007-01-31

    Basic oxygen furnace (BOF) steel slag is a residue from the basic oxygen converter in steel-making operations, and is partially reused as an aggregate for road constructions. Although BOF slag is an attractive building material, its long-term behaviour and the associated environmental impacts must be taken into account. Indeed BOF slag is mainly composed of calcium, silicon and iron but also contains trace amounts of potential toxic elements, specifically chromium and vanadium, which can be released. The present research focuses (i) on the release of Cr and V during leaching and (ii) on their speciation within the bearing phase. Indeed the mobility and toxicity of heavy metals strongly depend on their speciation. Leaching tests show that only low amounts of Cr, present at relatively high concentration in steel slag, are released while the release of V is significantly high. X-ray absorption near-edge structure (XANES) spectroscopy indicates that Cr is present in the less mobile and less toxic trivalent form and that its speciation does not evolve during leaching. On the contrary, V which is predominantly present in the 4+ oxidation state seems to become oxidized to the pentavalent form (the most toxic form) during leaching.

  4. Distribution and oxidation state of copper in the cell walls of treated wood examined by synchrotron based XANES and XFM

    Treesearch

    Samuel L. Zelinka; Grant T. Kirker; Joseph E. Jakes; Leandro Passarini; Barry Lai

    2016-01-01

    Recently, synchrotron based X-ray fluorescence microscopy (XFM) and X-ray absorption near edge spectroscopy (XANES) were used to examine the metal fastener corrosion in copper-treated wood. XFM is able to map the copper concentration in the wood with a spatial resolution of 0.5 µm and is able to quantify the copper concentration to within 0.05 µg cm-3...

  5. Aluminium K-Edge XANES Study of Mica Preiswerkite

    SciTech Connect

    Wu, Z.; Marcelli, A.; Cibin, G.; Mottana, A.; Della Ventura, G.; /SLAC, SSRl

    2006-10-27

    We present the Al K-edge XANES spectrum of synthetic mica with mixed fourfold coordinated and sixfold coordinated Al (preiswerkite). Experimental analysis and multiple scattering simulations of XANES spectra demonstrate that octahedral contributions may overlap the tetrahedral ones so that the lower energy structures in mixed coordination compounds may be associated to Al octahedral site. This unexpected behavior can be explained as due to a large local distortion of the Al octahedral site.

  6. Amorphisation mechanism of a flint aggregate during the alkali-silica reaction: X-ray diffraction and X-ray absorption XANES contributions

    SciTech Connect

    Verstraete, J.; Khouchaf, L.; Bulteel, D.; Garcia-Diaz, E.; Flank, A.M; Tuilier, M.H

    2004-04-01

    Flint samples at different stages of the Alkali-Silica Reaction were prepared and analyzed by X-ray diffraction (XRD) and silicon K-edge X-ray absorption near edge structure techniques (XANES). The results are compared to those of measurements performed on alpha quartz c-SiO{sub 2} and rough flint aggregate. The molar fraction of Q{sub 3} sites is determined as a function of the time of reaction. Up to 14 h of attack, the effect of the reaction seems of little importance. From 30 to 168 h, we showed an acceleration of the effect of the reaction on the crystal structure of the aggregate resulting in an amorphisation of the crystal. During this period, the amorphous fraction increases linearly with the number of Q{sub 3} sites. The results of the XANES confirm the amorphisation of the aggregate during the reaction and show the presence of silicon in a tetrahedral environment of oxygen whatever the time of attack.

  7. High-Resolution Fe XANES Pre-Edge Spectroscopy of Micas

    NASA Astrophysics Data System (ADS)

    Tucker, J. M.; Dyar, M. D.; Gunter, M.; Delaney, J. S.; Lanzirotti, A.

    2009-12-01

    Fe XANES (X-Ray Absorption Near-Edge Structure) spectroscopy has the potential to yield information on Fe valence states and coordination geometry in minerals at microscales smaller than 10 μm. In this study, component peaks in Fe-Kα XANES pre-edge spectra of micas with varying compositions are examined to relate area-weighted pre-edge peaks present at the three optical orientations to Fe3+/Fe2+ ratios, cation site occupancies and mica structural features. Samples studied include three dioctahedral (Fe occupancy in M2 only) and three trioctahedral micas (Fe occupancy in both M1 and M2) with well-known chemistries: two illites, one muscovite, one annite, and two phlogopites with Fe3+/total Fe ranging from 11% to 75%. Mössbauer data determined that Fe3+and Fe2+ were present in the M sites of all samples except one tetra-ferriphlogopite, which is dominated by tetrahedral Fe3+ with a small amount of octahedral Fe3+. Samples were mounted on goniometer heads and the three optical orientations were determined using a spindle stage. XANES spectra were acquired with polarized x-rays parallel to each of the three optical orientations. Incident x-rays were tuned using a Si(311) monochromator at beamline X26A at the National Synchrotron Light Source at Brookhaven National Laboratory. XANES spectra were collected in fluorescence mode using a 9-element high purity Ge solid state detector array. Spectra were edge-step normalized and corrected for self-absorption using the FLUO algorithm. Differences between the tetra-ferriphlogopite spectra and the other high Fe3+ samples allow peaks due to tetrahedral Fe3+ and octahedral Fe3+ to be identified. The energy of the tetrahedral Fe3+ peak is higher by ~0.5 eV in the X direction than in Y and Z and its area is also much greater in the X orientation, suggesting that those transitions are favored perpendicular to c. Comparison of spectra of the other dioctahedral and trioctahedral micas allows peaks due to Fe3+ and Fe2+ in M1 and M2

  8. Adsorption of boric acid on pure and humic acid coated am-Al(OH)3: A boron K-edge XANES study.

    PubMed

    Xu, Dani; Peak, Derek

    2007-02-01

    The fate and mobility of boric acid in the environment is largely controlled by adsorption reactions with soil organic matter and soil minerals to form surface complexes (Soil Sci Soc. Am. J. 1991, 55, 1582; Geochim. Cosmochim. Acta 2002, 67, 2551; Soil Sci. Soc. Am. J. 1995, 59, 405; Environ. Sci. Technol. 1995, 29, 302). In this study, boric acid adsorption on pure am-Al(OH)3 and 5% (w/w) humic acid (HA) coated am-Al(OH)3 were investigated both as a function of pH (4.5-11) and initial boric acid concentration (0-4.5 mmol L(-1)). Batch adsorption isotherm experiments were also conducted with samples exposed to atmospheric CO2 and anaerobic (N2) conditions to examine the effects of dissolved CO2 on boric acid adsorption. Boron (B) K-edge X-ray absorption near-edge structure (XANES) spectroscopy was used to investigate the coordination of boric acid adsorbed at mineral/water interfaces. The XANES spectra of boric acid adsorption samples showed that both trigonally and tetrahedrally coordinated B complexes were present on the mineral surface. Both macroscopic and spectroscopic experiments revealed that the combination of HA coating on am-Al(OH)3 and dissolved CO2 decreased boric acid adsorption compared to adsorption on pure am-Al(OH)3.

  9. Study of Cu chemical state inside single neurons from Parkinson's disease and control substantia nigra using the micro-XANES technique.

    PubMed

    Chwiej, Joanna; Adamek, Dariusz; Szczerbowska-Boruchowska, Magdalena; Krygowska-Wajs, Anna; Bohic, Sylvain; Lankosz, Marek

    2008-01-01

    Parkinson's disease (PD) is referred to as idiopathic disorder, which means that its causes have not been found yet. However, a few processes such as oxidative stress, protein aggregation and mitochondrial dysfunction are suspected to lead to the atrophy and death of substantia nigra (SN) neurons in case of this neurodegenerative disorder. Cu is a trace element whose role in the pathogenesis of PD is widely discussed. The investigation of Cu oxidation state inside single nerve cells from SN of PD and control cases may shed some new light on the role of this element in PD. The differences in Cu chemical state were investigated with the use of X-ray absorption near edge structure (XANES) spectroscopy. The least-square fitting method was applied for the analysis of XANES spectra. The comparison of the positions of white line, multiple scattering and pre-edge peak maximum at the energy scale did not reveal the existence of differences in Cu chemical state between PD and control samples. However, it was found that most of the Cu inside SN neurons occurs in tetrahedral environment and probably as Cu(II).

  10. Measurement of sulfur L2,3 and carbon K edge XANES in a polythiophene film using a high harmonic supercontinuum.

    PubMed

    Johnson, A S; Miseikis, L; Wood, D A; Austin, D R; Brahms, C; Jarosch, S; Strüber, C S; Ye, P; Marangos, J P

    2016-11-01

    We use a high harmonic generated supercontinuum in the soft X-ray region to measure X-ray absorption near edge structure (XANES) spectra in polythiophene (poly(3-hexylthiophene)) films at multiple absorption edges. A few-cycle carrier-envelope phase-stable laser pulse centered at 1800 nm was used to generate a stable soft X-ray supercontinuum, with amplitude gating limiting the generated pulse duration to a single optical half-cycle. We report a quantitative transmission measurement of the sulfur L2,3 edge over the range 160-200 eV and the carbon K edge from 280 to 330 eV. These spectra show all the features previously reported in the XANES spectra of polythiophene, but for the first time they are measured with a source that has an approximately 1 fs pulse duration. This study opens the door to measurements that can fully time-resolve the photoexcited electronic dynamics in these systems.

  11. Measurement of sulfur L2,3 and carbon K edge XANES in a polythiophene film using a high harmonic supercontinuum

    PubMed Central

    Johnson, A. S.; Miseikis, L.; Wood, D. A.; Austin, D. R.; Brahms, C.; Jarosch, S.; Strüber, C. S.; Ye, P.; Marangos, J. P.

    2016-01-01

    We use a high harmonic generated supercontinuum in the soft X-ray region to measure X-ray absorption near edge structure (XANES) spectra in polythiophene (poly(3-hexylthiophene)) films at multiple absorption edges. A few-cycle carrier-envelope phase-stable laser pulse centered at 1800 nm was used to generate a stable soft X-ray supercontinuum, with amplitude gating limiting the generated pulse duration to a single optical half-cycle. We report a quantitative transmission measurement of the sulfur L2,3 edge over the range 160–200 eV and the carbon K edge from 280 to 330 eV. These spectra show all the features previously reported in the XANES spectra of polythiophene, but for the first time they are measured with a source that has an approximately 1 fs pulse duration. This study opens the door to measurements that can fully time-resolve the photoexcited electronic dynamics in these systems. PMID:27822487

  12. Near-edge X-ray absorption spectroscopy signature of image potential states in multilayer epitaxial graphene

    NASA Astrophysics Data System (ADS)

    Coelho, P. M.; dos Reis, D. D.; Matos, M. J. S.; Mendes-de-Sa, T. G.; Goncalves, A. M. B.; Lacerda, R. G.; Malachias, A.; Magalhaes-Paniago, R.

    2016-02-01

    Single layer behavior in multilayer epitaxial graphene has been a matter of intense investigation. This is due to the layer decoupling that occurs during growth of graphene on some types of substrates, such as carbon-terminated silicon carbide. We show here that near-edge X-ray absorption spectroscopy can be used to observe the signature of this decoupling. To this end, samples of multilayer graphene from silicon carbide sublimation were grown with different degrees of decoupling. Raman spectroscopy was used to infer the degree of structural decoupling. X-ray grazing-incidence diffraction and scanning tunneling microscopy showed that growth initiates with the presence of bilayer graphene commensurate structures, while layer decoupling is associated to the formation of incommensurate structures observed for longer sublimation time. Near-edge X-ray absorption spectroscopy was used to probe the electronic states above the Fermi energy. Besides the σ* and π* empty states, image potential states are observed and show a clear change of intensity as a function of incident angle. These image potential states evolve from a graphite- to graphene-like behavior as a function of growth time and can be used to infer the degree of structural coupling among layers.

  13. Manganese speciation in Diplodon chilensis patagonicus shells: a XANES study

    NASA Astrophysics Data System (ADS)

    Soldati, A. L.; Vicente-Vilas, V.; Goettlicher, J.; Jacob, D. E.

    2009-04-01

    century, resolving the environmental signal annually and even seasonally (Soldati et al., 2008b). High resolution trace elemental analysis by LA-ICPMS and EPMA in the shells show that elements like Mg and Mn are related to the seasonal pattern and can be enriched along the organic-rich annual shell growth lines. Thus, these elements could possibly be bound organically instead of occupying a defined site in the crystal lattice of the calcium carbonate phase. LA-ICP-MS results show that Mn concentrations in these Diplodon shells range between 1000-300 g/g and 100-10 g/g and that the areas of enrichment are in the micrometer range. Raman and XRD measurements at high spatial resolution failed in recognizing whether the Mn is in carbonate solid solution or not. Therefore, speciation techniques like X-ray absorption fine structure (XAFS) spectroscopy with a high lateral resolution are required to address this question. Prior to XAFS spectroscopy the samples were mapped with the intensity of the Mn Kα fluorescence emission line in order to locate the Mn rich areas of interest. Because of the Mn concentrations in the sub % range the XAFS spectra at the positions of interest have been recorded in fluorescence mode using a 7 element Si(Li) detector. This study focuses on the near edge (XANES: X-ray absorption near edge structure) part of the spectra. For data evaluation, XANES spectra of reference substances were additionally measured in order to get first hints to Mn valence and bonding. As standards were used Mn and Mn rich carbonates, Mn oxides with Mn in different oxidation states, and Mn in organic compounds (Mn-porphyrin and Mn-acetate). The XAFS measurements have been carried out at the SUL-X beamline of the synchrotron radiation source ANKA of the Forschungszentrum Karlsruhe. Data evaluation is ongoing. References MEIBOM, A., CUIF, J.P., HOULBREQUE, F., MOSTEFAOUI, S., DAUPHIN, Y., MEIBOM; K.L. & DUNBAR, R. (2008). Compositional variations at ultra-structure length scales

  14. Sulfur K-edge XANES and acid volatile sulfide analyses of changes in chemical speciation of S and Fe during sequential extraction of trace metals in anoxic sludge from biogas reactors.

    PubMed

    Shakeri Yekta, Sepehr; Gustavsson, Jenny; Svensson, Bo H; Skyllberg, Ulf

    2012-01-30

    The effect of sequential extraction of trace metals on sulfur (S) speciation in anoxic sludge samples from two lab-scale biogas reactors augmented with Fe was investigated. Analyses of sulfur K-edge X-ray absorption near edge structure (S XANES) spectroscopy and acid volatile sulfide (AVS) were conducted on the residues from each step of the sequential extraction. The S speciation in sludge samples after AVS analysis was also determined by S XANES. Sulfur was mainly present as FeS (≈ 60% of total S) and reduced organic S (≈ 30% of total S), such as organic sulfide and thiol groups, in the anoxic solid phase. Sulfur XANES and AVS analyses showed that during first step of the extraction procedure (the removal of exchangeable cations), a part of the FeS fraction corresponding to 20% of total S was transformed to zero-valent S, whereas Fe was not released into the solution during this transformation. After the last extraction step (organic/sulfide fraction) a secondary Fe phase was formed. The change in chemical speciation of S and Fe occurring during sequential extraction procedure suggests indirect effects on trace metals associated to the FeS fraction that may lead to incorrect results. Furthermore, by S XANES it was verified that the AVS analysis effectively removed the FeS fraction. The present results identified critical limitations for the application of sequential extraction for trace metal speciation analysis outside the framework for which the methods were developed. Copyright © 2011 Elsevier B.V. All rights reserved.

  15. EXAFS, XANES, and DFT study of the mixed-valence compound YMn2O5 : Site-selective substitution of Fe for Mn

    NASA Astrophysics Data System (ADS)

    Wunderlich, F.; Leisegang, T.; Weißbach, T.; Zschornak, M.; Stöcker, H.; Dshemuchadse, J.; Lubk, A.; Führlich, T.; Welter, E.; Souptel, D.; Gemming, S.; Seifert, G.; Meyer, D. C.

    2010-07-01

    In YMn2O5 , the Mn atoms occupy two nonequivalent Wyckoff sites within the unit cell exhibiting different oxygen coordinations, i.e., the system can be characterized as a mixed-valence compound. For the formation of the orthorhombic crystal structure, Jahn-Teller distortions are assumed to play an important role. In this study, we aimed at the investigation of the crystal structure changes upon the substitution of Mn by the non-Jahn-Teller cation Fe3+ . Therefore, we synthesized a series of YMn2-xFexO5 powder samples with x=0 , 0.5, and 1 by a citrate technique. We utilized extended x-ray absorption fine structure (EXAFS) and x-ray absorption near-edge structure (XANES) analysis as well as density-functional theory (DFT) to investigate the two nonequivalent Wyckoff sites within the orthorhombic crystal structure (confirmed for all compositions) occupied by transition-metal atoms. For quantitative determination of structural short-range order, all plausible options of substitution of Fe for Mn are discussed. On the basis of these evaluations, the EXAFS and XANES behavior is analyzed and appropriate crystallographic weights are assigned to the subset of structural models in accordance with the experimental data. From EXAFS analysis, using multiple-scattering theory, we conclude only the 4h Wyckoff site to be occupied by Fe [occupancy refined is (100±3)% in case of x=1 ]. Furthermore, taking the XANES spectra into account, we are able to verify the EXAFS results and additionally explain the differences in the MnK XANES spectra in dependence on x to be caused by changes in the dipole transitions to 4p final states. From quantitative pre-edge analysis an oxidation number of +4 for the Mn atom for x=1 is determined whereas the Fe valence is shown to be unchanged. Since the substitution process only involves one Wyckoff site, the experimentally observed limit to a maximum amount of x=1 is explained. Additionally, a possible disorder, discussed in the literature, is not

  16. A XANES and EXAFS Study of Hydration and Ion Pairing in Ambient Aqueous MnBr[subscript 2] Solutions

    SciTech Connect

    Chen, Yongsheng; Fulton, John L.; Partenheimer, Walter

    2008-09-25

    Extended X-ray absorption fine structure (EXAFS) and X-ray absorption near edge structure (XANES) spectroscopies were used to probe the first-shell coordination structure of Mn(II) in aqueous MnBr{sub 2} solutions at ambient conditions from very dilute to the near saturation limit. The Mn K-edge EXAFS spectra for 0.05 and 0.2 m solutions showed that there was no Br(-I) in the first shell, and that the Mn(II) was fully hydrated with six water molecules in an octahedral arrangement. In contrast, for 6 m solution, the coordination number of water was reduced to about 5, and an average of about one bromine atom was present in the first shell as a contact ion pair. The 1s {yields} 4p transition at 6545.5 eV confirmed the observation of Mn-Br contact ion pairs at high concentrations and the 1s {yields} 3d transition at 6539.5 eV showed that the first shell coordination symmetry remained octahedral even in the presence of Mn-Br ion pairs.

  17. EXAFS and XANES investigation of (Li, Ni) codoped ZnO thin films grown by pulsed laser deposition

    NASA Astrophysics Data System (ADS)

    Mino, Lorenzo; Gianolio, Diego; Bardelli, Fabrizio; Prestipino, Carmelo; Senthil Kumar, E.; Bellarmine, F.; Ramanjaneyulu, M.; Lamberti, Carlo; Ramachandra Rao, M. S.

    2013-09-01

    Ni doped, Li doped and (Li, Ni) codoped ZnO thin films were successfully grown using a pulsed laser deposition technique. Undoped and doped ZnO thin films were investigated using extended x-ray absorption fine structure (EXAFS) and x-ray absorption near edge spectroscopy (XANES). Preliminary investigations on the Zn K-edge of the undoped and doped ZnO thin films revealed that doping has not influenced the average Zn-Zn bond length and Debye-Waller factor. This shows that both Ni and Li doping do not appreciably affect the average local environment of Zn. All the doped ZnO thin films exhibited more than 50% of substitutional Ni, with a maximum of 77% for 2% Ni and 2% Li doped ZnO thin film. The contribution of Ni metal to the EXAFS signal clearly reveals the presence of Ni clusters. The Ni-Ni distance in the Ni0 nanoclusters, which are formed in the film, is shorter with respect to the reference Ni metal foil and the Debye-Waller factor is higher. Both facts perfectly reflect what is expected for metal nanoparticles. At the highest doping concentration (5%), the presence of Li favors the growth of a secondary NiO phase. Indeed, 2% Ni and 5% Li doped ZnO thin film shows %Nisub = 75 ± 11, %Nimet = 10 ± 8, %NiO = 15 ± 8. XANES studies further confirm that the substitutional Ni is more than 50% in all the samples. These results explain the observed magnetic properties.

  18. Ab initio and experimental pre-edge investigations of the Mn K -edge XANES in oxide-type materials

    NASA Astrophysics Data System (ADS)

    Farges, François

    2005-04-01

    Mn K edge ab initio FEFF8.2 calculations of the pre-edge features of the x-ray-absorption near-edge structure (XANES) region were undertaken for a series of Mn-bearing oxide-type compounds. The aim of the study is to provide a reliable method for determining quantitative and accurate redox and symmetry information for manganese. In agreement with multiplet calculations by Glatzel and co-workers, FEFF8.2 predicts a doublet and a triplet for Mn(II) and Mn(III) in octahedral symmetry, respectively, in agreement with high-resolution XANES experiments. Site distortion increases notably the contribution from dipolar transitions and, consequently, the pre-edge feature integrated area. An even more intense pre-edge feature is calculated and measured for the Td symmetry (singletlike). For Mn(IV), a triplet is predicted and measured for the Oh symmetry. However, additional transitions are found in Mn(IV)-rich compounds, that are related to metal-metal transitions. These transitions overlap strongly with the “true pre-edge,” making extraction of redox and symmetry information for Mn(IV) more challenging. However, a model of the pre-edge with pseudo-Voigt functions of fixed calculated width (based on core-hole lifetime and experimental resolution) helps to separate the contributions related to first-neighbor symmetry from those of the metal-metal pairs. Application to multivalent defective manganese oxide materials suggests that the pre-edge information varies linearly as a function of Mn redox state or symmetry but varies nonlinearly as a function of both parameters. Finally, the polymerization of the manganese networks can be estimated from the metal-metal transitions found in the pre-edge region.

  19. XANES spectroscopy as a tool to trace phosphorus transformation during soil genesis and mountain ecosystem development from lake sediments

    NASA Astrophysics Data System (ADS)

    Giguet-Covex, C.; Poulenard, J.; Chalmin, E.; Arnaud, F.; Rivard, C.; Jenny, J.-P.; Dorioz, J.-M.

    2013-10-01

    The aim of this study is to investigate phosphorus (P) species modifications triggered by soil genesis and mountain ecosystem development after glacial retreat using a lake sediment archive (Lake Anterne, North French Alps). Five lake sediment samples, representative of different stages of soil and ecosystem development, were selected for P speciation analyses. Furthermore, a sequence of current soils from the catchment was analyzed to better constrain our interpretations of the lacustrine archive. Synchrotron techniques (X-ray Fluorescence (XRF) mapping and P K-edge X-ray absorption near edge structure (XANES) spectroscopy) were applied to lake sediments, soils, and standards (mineral and organic) to distinguish between different P species. The results show that soil development during the first millennia of the Holocene triggered increased P species diversity. At the onset of the Holocene, P was present as apatite when rocks and leptosols dominated the catchment. Pedogenic processes then led to apatite dissolution and the formation of large amounts of P on metal/clay-organic complexes. P geochemistry during the main step of soil genesis (early leptosols dominated by apatite, low weathered cambisols with P mainly adsorbed on iron oxides, highly weathered podzols with large amounts of P on Al/Fe/clay organic complexes) is thus clearly recorded in lake sediments. P K-edge XANES spectroscopy is particularly relevant as qualitative method to study P species in soils and lake sediments at high spatial resolution. Such resolution is needed to reveal the diversity of small P particles and like this better characterize the P cycle and improve our understanding of ecosystem evolution.

  20. Sulphur Speciation and Turnover in Soils: Evidence from Sulphur K-Edge XANES Spectroscopy and Isotope Dilution Studies

    SciTech Connect

    Zhao,F.; Lehmann, J.; Solomon, D.; Fox, M.; McGrath, S.

    2005-01-01

    Sulphur K-edge X-ray absorption near edge structure (XANES) spectroscopy was used to quantify S species in humic substance extracts from ten soils from the UK, China and New Zealand, which differ in land use and agricultural management. XANES spectroscopy showed the presence of most reduced (sulphides, disulphides, thiols and thiophenes), intermediate (sulphoxides and sulphonates) and highly oxidised S (ester sulphates) forms, with the three groups representing 14-32%, 33-50% and 22-53% of the organic S in the humic substance extracts, respectively. Land use had a profound influence on the relative proportions of S species. Well-drained arable soils generally had a higher proportion of organic S present in the most oxidised form than the grassland soils collected nearby, whereas paddy soils showed a more reduced profile due to episodic flooding. In the Broadbalk Classical Experiment at Rothamsted, reversion of an arable system to grassland or woodland in the 1880s resulted in an increase of the most reduced and intermediate S species at the expense of the most oxidised S species. Long-term applications of farmyard manure to an arable plot also shifted S species from the most oxidised to the intermediate and the most reduced species. Sulphur immobilization and gross mineralization were determined in seven soils using the {sup 35}S isotope dilution method. Gross mineralization during a 53-day incubation correlated more closely with the amounts of the most reduced and intermediate S species than with the most oxidised S species, suggesting that the former (C-bonded S) were the main source of organic S for mineralization in the short-term.

  1. Sulphur Speciation and Turnover in Soils: Evidence from Sulfur K-Edge XANES Spectroscopy and Isotope Dilution Studies

    SciTech Connect

    Zhao,F.; Lehmann, J.; Solomon, D.; Fox, M.; McGrath, S.

    2006-01-01

    Sulphur K-edge X-ray absorption near edge structure (XANES) spectroscopy was used to quantify S species in humic substance extracts from ten soils from the UK, China and New Zealand, which differ in land use and agricultural management. XANES spectroscopy showed the presence of most reduced (sulphides, disulphides, thiols and thiophenes), intermediate (sulphoxides and sulphonates) and highly oxidised S (ester sulphates) forms, with the three groups representing 14-32%, 33-50% and 22-53% of the organic S in the humic substance extracts, respectively. Land use had a profound influence on the relative proportions of S species. Well-drained arable soils generally had a higher proportion of organic S present in the most oxidised form than the grassland soils collected nearby, whereas paddy soils showed a more reduced profile due to episodic flooding. In the Broadbalk Classical Experiment at Rothamsted, reversion of an arable system to grassland or woodland in the 1880s resulted in an increase of the most reduced and intermediate S species at the expense of the most oxidised S species. Long-term applications of farmyard manure to an arable plot also shifted S species from the most oxidised to the intermediate and the most reduced species. Sulphur immobilisation and gross mineralisation were determined in seven soils using the {sup 35}S isotope dilution method. Gross mineralisation during a 53-day incubation correlated more closely with the amounts of the most reduced and intermediate S species than with the most oxidised S species, suggesting that the former (C-bonded S) were the main source of organic S for mineralisation in the short-term.

  2. Ab initio and experimental pre-edge investigations of the Mn K-edge XANES in oxide-type materials

    SciTech Connect

    Farges, Francois

    2005-04-15

    Mn K edge ab initio FEFF8.2 calculations of the pre-edge features of the x-ray-absorption near-edge structure (XANES) region were undertaken for a series of Mn-bearing oxide-type compounds. The aim of the study is to provide a reliable method for determining quantitative and accurate redox and symmetry information for manganese. In agreement with multiplet calculations by Glatzel and co-workers, FEFF8.2 predicts a doublet and a triplet for Mn(II) and Mn(III) in octahedral symmetry, respectively, in agreement with high-resolution XANES experiments. Site distortion increases notably the contribution from dipolar transitions and, consequently, the pre-edge feature integrated area. An even more intense pre-edge feature is calculated and measured for the T{sub d} symmetry (singletlike). For Mn(IV), a triplet is predicted and measured for the O{sub h} symmetry. However, additional transitions are found in Mn(IV)-rich compounds, that are related to metal-metal transitions. These transitions overlap strongly with the 'true pre-edge', making extraction of redox and symmetry information for Mn(IV) more challenging. However, a model of the pre-edge with pseudo-Voigt functions of fixed calculated width (based on core-hole lifetime and experimental resolution) helps to separate the contributions related to first-neighbor symmetry from those of the metal-metal pairs. Application to multivalent defective manganese oxide materials suggests that the pre-edge information varies linearly as a function of Mn redox state or symmetry but varies nonlinearly as a function of both parameters. Finally, the polymerization of the manganese networks can be estimated from the metal-metal transitions found in the pre-edge region.

  3. First-principles XANES simulations of spinel zinc ferrite with a disordered cation distribution

    SciTech Connect

    Nakashima, Seisuke; Fujita, Koji; Tanaka, Katsuhisa; Hirao, Kazuyuki; Yamamoto, Tomoyuki; Tanaka, Isao

    2007-05-01

    Theoretical calculations of Zn K and Fe K x-ray absorption near-edge structures (XANES) using a first-principles method have been performed to evaluate the degree of cation disordering in spinel zinc ferrite (ZnFe{sub 2}O{sub 4}) thin film prepared by a sputtering method, ZnFe{sub 2}O{sub 4} thin films annealed at elevated temperatures, and ZnFe{sub 2}O{sub 4} bulk specimen prepared by a solid-state reaction. Using the full-potential linearized augmented plane-wave + local orbitals method, a theoretical spectrum is generated for the tetrahedral and octahedral environments for each of the two cations. The experimental XANES spectrum of the thin film annealed at 800 deg. C as well as that of bulk specimen is successfully reproduced by using either the theoretical spectrum for Zn{sup 2+} on the tetrahedral site (A site) or that for Fe{sup 3+} on the octahedral site (B site), which is indicative of the normal spinel structure. For the as-deposited film, on the other hand, excellent agreement between theoretical and experimental spectra is obtained by considering the presence of either ion in both the A and B sites. The degree of cation disordering, x, defined as [Zn{sub 1-x}{sup 2+}Fe{sub x}{sup 3+}]{sub A}[Zn{sub x}{sup 2+}Fe{sub 2-x}{sup 3+}]{sub B}O{sub 4}, is estimated to be approximately 0.6 in the as-deposited film, which is consistent with the analysis of the extended x-ray absorption fine structure on the Zn K edge. Curious magnetic properties as we previously observed for the as-deposited thin film--i.e., ferrimagnetic behaviors accompanied by large magnetization at room temperature and cluster spin-glass-like behavior--are discussed in connection with disordering of Zn{sup 2+} and Fe{sup 3+} ions in the spinel-type structure.

  4. Pressure-Induced Amorphisation in San Carlos Olivine: a XANES Study.

    NASA Astrophysics Data System (ADS)

    Kantor, I.; Torchio, R.

    2014-12-01

    Olivine (Mg,Fe)2SiO4 is one of the main rock-forming minerals of the Earth crust and is often used as a model compound of the whole silicate part of our planet. In equilibrium conditions in the Earth interior olivine undergoes a series of phase transitions and further breaks into ferropericlase and bridgmanite phases at about 25 GPa. All these transitions are responsible for major seismic discontinuities in the Earth. However, if olivine in compressed at temperature that is too low to overcome kinetic barrier, it preserves its original structureuntil ~35 GPa and then gradually becomes amorphous. This transformation have been observed before by mean of X-ray diffraction and Raman spectroscopy, but very little is known about the amorphisation mechanism and the local structure of (Mg,Fe)2SiO4 glass under high pressure. We performed a combined XANES and Raman spectroscopic study of a pressure-induced amorphisation is natural olivine sample (Mg0.92Fe0.08)2SiO4 from San Carlos location. Despite the fact that this natural sample has very low iron concentration and therefore absorption jump was quite small (about 0.06), a decent quality XANES spectra were recorded in transmission mode on the energy-dispercive beamline ID24 at the ESRF usind a diamond anvil cell technique. The amorphisation process can be clearly seen in Raman spectra as a significant broadening and further disappearance of the Raman peaks starting from 35-40 GPa, in perfect agreement with the previous literature data. The most interesting result is a dramatic change of the near-edge structure of X-ray absorption spectra. Since XAS is sensitive to the local structure only, one would not expect significant changes in spectra (apart for some broadening) if only long-range order in the material is lost. Our experimental results indicate that pressure-induced amorphisation in olivine is accomplished with a significant variation of the local atomic structure around Fe cation, probably forming effective

  5. Study of XANES near Ta-L edges in LiTaO3 through thermal wave, fluorescence and first principles

    NASA Astrophysics Data System (ADS)

    Kane, S. R.; Kumar, Shailendra; Ghosh, Haranath; Singh, Ajit Kumar; Tiwari, M. K.

    2016-01-01

    X-ray absorption near-edge spectra (XANES) of Ta-L2 and L3 edges in LiTaO3 (LTO) crystals are measured by measuring amplitude and phase of thermal waves generated within the LTO crystal, using pyroelectric property of LTO. Thus, LTO crystal is used both as a sample as well as sensor material. XANES of Ta-L edges in LTO are also measured by fluorescence. XANES spectra from fluorescence and first-principles simulations agree excellently well. The onset of the pre-edge region of XANES, measured by both techniques, extends below the edge by about 50 eV. This pre-edge onset of absorption is explained in terms of the core-hole lifetime effect on near-edge absorption using density functional theory. However, detailed nature of XANES peaks near Ta-L3 and Ta-L2 absorption edges, measured by thermal waves and fluorescence, differ. Possible origins of these differences are discussed.

  6. Study of the Warm Dense Matter with XANES spectroscopy - Applications to planetary interiors

    NASA Astrophysics Data System (ADS)

    Denoeud, Adrien

    With the recent discovery of many exoplanets, modelling the interior of these celestial bodies is becoming a fascinating scientific challenge. In this context, it is crucial to accurately know the equations of state and the macroscopic and microscopic physical properties of their constituent materials in the Warm Dense Matter regime (WDM). Moreover, planetary models rely almost exclusively on physical properties obtained using first principles simulations based on density functional theory (DFT) predictions. It is thus of paramount importance to validate the basic underlying mechanisms occurring for key planetary constituents (metallization, dissociation, structural modifications, phase transitions, etc....) as pressure and temperature both increase. In this work, we were interested in two materials that can be mainly found in the Earth-like planets: silica, or SiO2, as a model compound of the silicates that constitute the major part of their mantles, and iron, which is found in abundance in their cores. These two materials were compressed and brought to the WDM regime by using strong shock created by laser pulses during various experiments performed on the LULI2000 (Palaiseau, France) and the JLF (Livermore, US) laser facilities and on the LCLS XFEL (Stanford, US). In order to penetrate this dense matter and to have access to its both ionic and electronic structures, we have probed silica and iron with time-resolved X-ray Absorption Near Edge Structure (XANES). In parallel with these experiments, we performed quantum molecular dynamics simulations based on DFT at conditions representative of the region investigated experimentally so as to extract the interesting physical processes and comprehend the limits of the implemented models. In particular, these works allowed us to highlight the metallization processes of silica in temperature and the structural changes of its liquid in density, as well as to more constrain the melting curve of iron at very high pressures.

  7. Supervised Machine Learning-Based Determination of Three-Dimensional Structure of Metallic Nanoparticles.

    PubMed

    Timoshenko, Janis; Lu, Deyu; Lin, Yuewei; Frenkel, Anatoly I

    2017-09-29

    Tracking the structure of heterogeneous catalysts under operando conditions remains a challenge due to the paucity of experimental techniques that can provide atomic-level information for catalytic metal species. Here we report on the use of X-ray absorption near edge structure (XANES) spectroscopy and supervised machine learning (SML) for refining the three-dimensional geometry of metal catalysts. SML is used to unravel the hidden relationship between the XANES features and catalyst geometry. To train our SML method, we rely on ab-initio XANES simulations. Our approach allows one to solve the structure of a metal catalyst from its experimental XANES, as demonstrated here by reconstructing the average size, shape and morphology of well-defined platinum nanoparticles. This method is applicable to the determination of the nanoparticle structure in operando studies and can be generalized to other nanoscale systems. It also allows on-the-fly XANES analysis, and is a promising approach for high-throughput and time-dependent studies.

  8. Supervised Machine-Learning-Based Determination of Three-Dimensional Structure of Metallic Nanoparticles

    DOE PAGES

    Timoshenko, Janis; Lu, Deyu; Lin, Yuewei; ...

    2017-09-29

    Tracking the structure of heterogeneous catalysts under operando conditions remains a challenge due to the paucity of experimental techniques that can provide atomic-level information for catalytic metal species. Here we report on the use of X-ray absorption near edge structure (XANES) spectroscopy and supervised machine learning (SML) for refining the three-dimensional geometry of metal catalysts. SML is used to unravel the hidden relationship between the XANES features and catalyst geometry. To train our SML method, we rely on ab-initio XANES simulations. Our approach allows one to solve the structure of a metal catalyst from its experimental XANES, as demonstrated heremore » by reconstructing the average size, shape and morphology of well-defined platinum nanoparticles. This method is applicable to the determination of the nanoparticle structure in operando studies and can be generalized to other nanoscale systems. In conclusion, it also allows on-the-fly XANES analysis, and is a promising approach for high-throughput and time-dependent studies.« less

  9. XANES characterization of UO2/Mo(Pd) thin films as models for epsilon-particles in spent nuclear fuel

    NASA Astrophysics Data System (ADS)

    Denecke, M. A.; Petersmann, T.; Marsac, R.; Dardenne, K.; Vitova, T.; Prüßmann, T.; Borchert, M.; Bösenberg, U.; Falkenberg, G.; Wellenreuther, G.

    2013-04-01

    X-ray absorption near edge structure (XANES) is recorded for nano- and micro-particles formed in Mo doped UO2 thin films (TFs) prepared by in situ sputter co-deposition and 1000°C tempering. These UO2/Mo TFs are intended to serve as synthetic models for epsilon-particles in spent nuclear fuel. We find that when Si is used as substrate, nano-sized zero-valent Mo particles form as desired. However, these are embedded in USi3, which forms at the high temper temperatures. Micron-sized Mo-particles are formed when SiO2 is used as substrate. Using focussed X-ray beams of varying size (500μm, 25μm and 5μm), these particles are characterized to be predominantly hexavalent Mo oxides, potentially with tetrahedral coordinated [Mo(VI)O4]2- at the surface and a MoO3-like phase in the bulk. These TFs are poor synthetic models for spent fuel epsilon-particles but do offer the opportunity to study changes in surface structures in response to stress/charge as a function of particle size.

  10. STXM-XANES Analysis of Organic Matter in Dark Clasts and Halite Crystals in Zag and Monahans Meteorites

    NASA Technical Reports Server (NTRS)

    Kebukawa, Y.; Zolensky, M. E.; Fries, M.; Nakato, A.; Kilcoyne, A. L. D.; Takeichi, Y.; Suga, H.; Miyamoto, C.; Rahman, Z.; Kobayashi, K.; Mase, K.; Takahashi, Y.

    2016-01-01

    Zag and Monahans meteorites (H5) contains xenolithic dark clasts and halite (NaCl) crystals [e.g., 1]. The proposed source of the H chondrites is asteroid 6 Hebe [2]. The modern orbits of 1 Ceres and 6 Hebe essentially cross, with aphelion/perihelion of Ceres and Hebe of 2.99/2.55 and 2.91/1.94 AU (Astronomical Units), respectively. Therefore, Ceres might be the source of the clasts and halite in Zag and Monahans meteorites. Recent results from NASA's Dawn mission shows that bright spots in Ceres's crater may be hydrated magnesium sulfate with some water ice, and an average global surface contains ammoniated phyllosilicates that is likely of outer Solar System origin. One dark clast and all halite crystals in Zag and Monahans meteorites contain carbon-rich particles. We report organic analyses of these carbon-rich particles using carbon, nitrogen, and oxygen X-ray absorption near edge structure (C-, N-, and O-XANES), in order to constrain the origin of the clast and halite crystals.

  11. SORPTION OF ARSENATE AND ARSENITE ON RUO2 X H2O: ANALYSIS OF SORBED PHASE OXIDATION STATE BY XANES IN ADVANCED PHOTON SOURCE ACTIVITY REPORT 2002

    EPA Science Inventory

    The sorption reactions of arsenate (As(V)) and arsenite (As(III)) on RuO2 x H2O were examined by X-ray Absorption Near Edge Spectroscopy (XANES) to elucidate the solid state speciation of sorbed As. At all pH values studied (pH 4-8), RuO2 x H

  12. SORPTION OF ARSENATE AND ARSENITE ON RUO2 X H2O: ANALYSIS OF SORBED PHASE OXIDATION STATE BY XANES IN ADVANCED PHOTON SOURCE ACTIVITY REPORT 2002

    EPA Science Inventory

    The sorption reactions of arsenate (As(V)) and arsenite (As(III)) on RuO2 x H2O were examined by X-ray Absorption Near Edge Spectroscopy (XANES) to elucidate the solid state speciation of sorbed As. At all pH values studied (pH 4-8), RuO2 x H

  13. Environmental applications of XANES: Speciation of {Tc} in cement after chemical treatment and Se after bacterial uptake

    SciTech Connect

    Shuh, D.K.; Kaltsoyannis, N.; Bucher, J.J.

    1994-03-01

    XANES (X-ray Absorption Near Edge Spectroscopy) has been employed to evaluate the efficacy of a process designed to encapsulate and reduce {Tc}O{sub 4}{sup {minus}} in cement matrices, thereby immobilizing {Tc}. The oxidation state of Se following.bioremediation of Se by bacteria has also been determined by XANES. The XANES measurements were performed at the Stanford Synchrotron Radiation Laboratory (SSRL) and the National Synchrotron Light Source (NSLS) at the respective K edges of {Tc} (21.0 keV) and Se (12.7 keV). Comparison of the XANES spectra of Tc in untreated cement to Tc in slag treated cement and to the chemical shifts of reference materials, shows that the oxidation state of {Tc} is the same in both cements. Thus, the addition of a reducing agent to the cement formulation does not significantly reduce the {Tc}O{sub 4} The common soil bacterium, Bacillus subtilis, is known to incorporate Se on or within the cell wall when exposed to a SE(IV) solution. The Se XANES spectra of B. subtilis, as well as bacillus isolated from selenium rich soil, show that the organisms reduce selenite to the red allotrope of elemental Se.

  14. Phosphorus Speciation in Manure and Manure-Amended Soils Using XANES Spectroscopy

    SciTech Connect

    Sato,S.; Solomon, D.; Hyland, C.; Ketterings, Q.; Lehmann, J.

    2005-01-01

    Previous studies suggested an increase in the proportion of calcium phosphates (CaP) of the total phosphorus (P) pool in soils with a long-term poultry manure application history versus those with no or limited application histories. To understand and predict long-term P accumulation and release dynamics in these highly amended soils, it is important to understand what specific P species are being formed. We assessed forms of CaP formed in poultry manure and originally acidic soil in response to different lengths of mostly poultry manure applications using P K-edge X-ray absorption near-edge structure (XANES) spectroscopy. Phosphorus K-edge XANES spectra of poultry manure showed no evidences of crystalline P minerals but dominance of soluble CaP species and free and weakly bound phosphates (aqueous phosphate and phosphate adsorbed on soil minerals). Phosphate in an unamended neighboring forest soil (pH 4.3) was mainly associated with iron (Fe) compounds such as strengite and Fe-oxides. Soils with a short-term manure history contained both Fe-associated phosphates and soluble CaP species such as dibasic calcium phosphate (DCP) and amorphous calcium phosphate (ACP). Long-term manure application resulted in a dominance of CaP forms confirming our earlier results obtained with sequential extractions, and a transformation from soluble to more stable CaP species such as {beta}-tricalcium calcium phosphate (TCP). Even after long-term manure application (>25 yr and total P in soil up to 13 307 mg kg{sup -1}), however, none of the manure-amended soils showed the presence of crystalline CaP. With a reduction or elimination of poultry manure application to naturally acidic soils, the pH of the soil is likely to decrease, thereby increasing the solubility of Ca-bonded inorganic P minerals. Maintaining a high pH is therefore an important strategy to minimize P leaching in these soils.

  15. XANES analysis of organic residues formed from the UV irradiation of astrophysical ice analogs and comparison with Stardust samples

    NASA Astrophysics Data System (ADS)

    Nuevo, Michel; Milam, Stefanie; Sandford, Scott; Cody, George; Kilcoyne, David; de Gregorio, Bradley; Stroud, Rhonda

    The NASA Stardust mission successfully collected authentic cometary grains from Comet 81P/Wild 2.1,2 X-ray absorption near-edge structure (XANES) analysis of these samples in-dicates that a number of them contains O-rich and N-rich organic materials, consisting of a broad variety of functional groups: carbonyls, C=C bonds, aliphatic chains, amines, amides, etc.3 One component of these organics contains very little aromatic carbon and resembles the organic residues produced by the irradiation of interstellar/cometary ice analogs. Stardust sam-ples were also recently shown to contain the amino acid glycine.4 Organic residues produced from the UV irradiation of astrophysical ice analogs are already known to contain a large suite of prebiotic molecules including amino acids,5-7 and amphiphilic compounds (fatty acids).8 In this work, residues were produced in the laboratory from the UV irradiation of mixtures of ices containing H2 O, CH3 OH, CO, and NH3 in relative proportions 100:50:1:1 at 7 K. Additional residues were produced from mixtures with no NH3 , and mixtures containing alkanes and/or naphthalene (C10 H8 ). C-, N-, and O-XANES spectra of these residues were measured in order to assess their organic functional group chemistry and overall atomic composition, as well as their C/N/O ratios. The first results indicate the presence of a number of chemical bonds and functions, namely, carbonyls, C=C bonds, alcohols, amides, amines, and nitrile groups, whose relative proportions are compared with XANES measurements of Stardust samples.9 References: 1. Brownlee, D. E., et al., Science, 314, 1711 (2006). 2. Sandford, S. A., et al., Science, 314, 1720 (2006). 3. Cody, G. D., et al., Meteoritics & Planet. Sci., 43, 353 (2008). 4. Elsila, J. E., et al., Meteoritics & Planet. Sci., 44, 1323 (2009). 5. Bernstein, M. P., et al., Nature, 416, 401 (2002). 6. Muñoz Caro, G. M., et al., Nature, 416, 403 (2002). n 7. Nuevo, M., et al., Orig. Life Evol. Biosph., 38, 37 (2008). 8

  16. Fe-bearing Olenite with Tetrahedrally Coordinated Al from an Abyssal Pegmatite at Kutna Hora, Czech Republic: Structure, Crystal Chemistry, Optical and XANES Spectra

    SciTech Connect

    Cempirek,J.; Novak, M.; Ertl, A.; Hughes, J.; Rossman, G.; Dyar, M.

    2006-01-01

    The pale blue rim of olenite on a black crystal of olenite-schorl tourmaline from an abyssal pegmatite at the locality Kuklik, near Kutna Hora, Czech Republic, has been chemically and structurally characterized. The optimized formula, calculated using chemical and structural data, is {sup X}(Na{sub 0.54}Ca{sub 0.14}K{sub 0.01}{D'Alembertian}{sub 0.31}){sup Y}(Al{sub 2.15}Fe{sup 2+}{sub 0.06}Ti{sup 4+}{sub 0.01}) {sup Z}(Al{sub 5.90}Mg{sub 0.10}) {sup T}(Si{sub 5.60}Al{sub 0.40})B{sub 3}O{sub 27} {sup V}[(OH){sub 2.49}O{sub 0.51}] {sup W}(O{sub 0.99}F{sub 0.01}), with {alpha} 15.8838(3), c 7.1056(2) {angstrom} and R = 0.017. The relatively short bond-length, 1.992 {angstrom}, confirms the high content of Al at the Y site ({approx}2.1 atoms per formula unit, apfu). It is similar to that of olenite from the type locality, though the olenite from Kuklik contains significant amounts of Fe at the Y site, and significant amounts of {sup [4]}Al ({approx}0.4 apfu) instead of {sup [4]}B in the T site. This finding is supported by results of the structure determination, which show an enlarged bond-length of {approx}1.626 {angstrom}. This sample of olenite shows that nonstoichiometric content of Si does not always imply {sup [4]}B in aluminous tourmaline. No H could be found at the O1 site by refinement, and the spherical distribution of electron density in the difference-Fourier map around the O1 site supports the conclusion that this site is only or mainly occupied by O and not by OH. On a bond-angle distortion ({sigma}{sub oct}{sup 2} of the ZO{sub 6} octahedron) - distance diagram, the olenite from Kuklik lies between compositions containing 3 (OH) at the V site, and natural buergerite, which contains 0.3 (OH) and 2.7 O at the V site (O3 site). The (OH) content with {approx}2.5 (OH) pfu, which was calculated for a charge-balanced formula, is in a good agreement with these findings and with the integrated intensity of the OH overtones in the 7000 cm{sup -1

  17. XANES Spectroscopic Analysis of Phosphorus Speciation in Alum-Amended Poultry Litter

    SciTech Connect

    Seiter,J.; Staats-Borda, K.; Ginder-Vogel, M.; Sparks, D.

    2008-01-01

    Aluminum sulfate (alum; Al2(SO4)3{center_dot}14H2O) is used as a chemical treatment of poultry litter to reduce the solubility and release of phosphate, thereby minimizing the impacts on adjacent aquatic ecosystems when poultry litter is land applied as a crop fertilizer. The objective of this study was to determine, through the use of X-ray absorption near edge structure (XANES) spectroscopy and sequential extraction, how alum amendments alter P distribution and solid-state speciation within the poultry litter system. Our results indicate that traditional sequential fractionation procedures may not account for variability in P speciation in heterogeneous animal manures. Analysis shows that NaOH-extracted P in alum amended litters is predominantly organic ({approx}80%), whereas in the control samples, >60% of NaOH-extracted P was inorganic P. Linear least squares fitting (LLSF) analysis of spectra collected of sequentially extracted litters showed that the P is present in inorganic (P sorbed on Al oxides, calcium phosphates) and organic forms (phytic acid, polyphosphates, and monoesters) in alum- and non-alum-amended poultry litter. When determining land application rates of poultry litter, all of these compounds must be considered, especially organic P. Results of the sequential extractions in conjunction with LLSF suggest that no P species is completely removed by a single extractant. Rather, there is a continuum of removal as extractant strength increases. Overall, alum-amended litters exhibited higher proportions of Al-bound P species and phytic acid, whereas untreated samples contained Ca-P minerals and organic P compounds. This study provides in situ information about P speciation in the poultry litter solid and about P availability in alum- and non-alum-treated poultry litter that will dictate P losses to ground and surface water systems.

  18. Full multiple scattering analysis of XANES at the Cd L3 and O K edges in CdO films combined with a soft-x-ray emission investigation

    SciTech Connect

    Demchenko, I. N.; Denlinger, J. D.; Chernyshova, M.; Yu, K. M.; Speaks, D. T.; Olalde-Velasco, P.; Hemmers, O.; Walukiewicz, W.; Derkachova, A.; Lawniczak-Jablonska, K.

    2010-07-05

    X-ray absorption near edge structure (XANES) at the cadmium L3 and oxygen K edges for CdO thin films grown by pulsed laser deposition method, is interpreted within the real-space multiple scattering formalism, FEFF code. The features in the experimental spectra are well reproduced by calculations for a cluster of about six and ten coordination shells around the absorber for L3 edge of Cd and K edge of O, respectively. The calculated projected electronic density of states is found to be in good agreement with unoccupied electronic states in experimental data and allows to conclude that the orbital character of the lowest energy of the conductive band is Cd-5s-O-2p. The charge transfer has been quantified and not purely ionic bonding has been found. Combined XANES and resonant inelastic x-ray scattering measurements allow us to determine the direct and indirect band gap of investigated CdO films to be {approx}2.4-eV and {approx}0.9-eV, respectively.

  19. Ce(III) and Ce(IV) (re)distribution and fractionation in a laterite profile from Madagascar: Insights from in situ XANES spectroscopy at the Ce LIII-edge

    NASA Astrophysics Data System (ADS)

    Janots, Emilie; Bernier, Felix; Brunet, Fabrice; Muñoz, Manuel; Trcera, Nicolas; Berger, Alfons; Lanson, Martine

    2015-03-01

    The distribution of trivalent and tetravalent cerium, Ce(III) and Ce(IV) respectively, in a lateritic profile from Madagascar, has been characterized by X-ray-absorption near-edge structure (XANES) spectroscopy at the Ce LIII-edge on the LUCIA beamline (SOLEIL synchrotron, France). XANES spectra were acquired on bulk-rock samples as well as on specific lateritic minerals or polymineral zones (in-situ measurements) of the tonalite bedrock and the three overlying weathered horizons (C-, B- and A-horizons). Geochemically, the bedrock, and the A- and C-horizons show similar rare earth element content (REE = 363-405 mg/kg). They also display the same positive Ce-anomaly (CeCN/Ce∗ = 1.12-1.45), which is therefore likely to be inherited from the bedrock. In the B-horizon, the higher REE content (REE = 2194 mg/kg) and the larger Ce-anomaly (CeCN/Ce∗ = 4.26) are consistent with an accumulation zone caused by the evaporation of groundwater during the dry season. There is a good agreement between the Ce(III)/Cetotal ratio (XCe(III)) deduced from the positive Ce-anomaly (bulk-rock geochemical data) and that derived from XANES spectroscopy on the same bulk-rock samples (BR-XCe(III)-XANES) in the bedrock, and the C- and B-horizons. In the A-horizon, XANES measurements on bulk rock and minerals revealed a higher BR-XCe(III)-XANES (up to 100%) compared to the XCe(III) deduced from geochemical data (XCe(III) = 79%). The preservation of a positive Ce-anomaly in the A-horizon suggests that the Ce mobilization and redistribution during weathering occurred with no significant Ce fractionation from other trivalent REE. Remarkably, the only investigated sample where cerianite is observed belongs to the B-horizon. Within this horizon, Ce oxidation state varies depending on the microstructural position (porosity, cracks, clay-rich groundmass). The highest Ce(IV) concentrations are measured in cerianite (and aluminophosphates) localized in pores at the vicinity of Mn-rich domains (XCe(III)-XANES

  20. In situ X-ray near-edge absorption spectroscopy investigation of the state of charge of all-vanadium redox flow batteries.

    PubMed

    Jia, Chuankun; Liu, Qi; Sun, Cheng-Jun; Yang, Fan; Ren, Yang; Heald, Steve M; Liu, Yadong; Li, Zhe-Fei; Lu, Wenquan; Xie, Jian

    2014-10-22

    Synchrotron-based in situ X-ray near-edge absorption spectroscopy (XANES) has been used to study the valence state evolution of the vanadium ion for both the catholyte and anolyte in all-vanadium redox flow batteries (VRB) under realistic cycling conditions. The results indicate that, when using the widely used charge-discharge profile during the first charge process (charging the VRB cell to 1.65 V under a constant current mode), the vanadium ion valence did not reach V(V) in the catholyte and did not reach V(II) in the anolyte. Consequently, the state of charge (SOC) for the VRB cell was only 82%, far below the desired 100% SOC. Thus, such incompletely charged mix electrolytes results in not only wasting the electrolytes but also decreasing the cell performance in the following cycles. On the basis of our study, we proposed a new charge-discharge profile (first charged at a constant current mode up to 1.65 V and then continuously charged at a constant voltage mode until the capacity was close to the theoretical value) for the first charge process that achieved 100% SOC after the initial charge process. Utilizing this new charge-discharge profile, the theoretical charge capacity and the full utilization of electrolytes has been achieved, thus having a significant impact on the cost reduction of the electrolytes in VRB.

  1. Correlated NanoSIMS, TEM, and XANES Studies of Presolar Grains

    NASA Astrophysics Data System (ADS)

    Groopman, Evan Edward

    The objective of this thesis is to describe the correlated study of individual presolar grains via Nano-scale Secondary Ion Mass Spectrometry (NanoSIMS), Transmission Electron Microscopy (TEM), and Scanning Transmission X-ray Microscopy (STXM) utilizing X-ray Absorption Near Edge Structure (XANES), with a focus on connecting these correlated laboratory studies to astrophysical phenomena. The correlated isotopic, chemical, and microstructural studies of individual presolar grains provide the most detailed description of their formation environments, and help to inform astrophysical models and observations of stellar objects. As a part of this thesis I have developed and improved upon laboratory techniques for micromanipulating presolar grains and embedding them in resin for ultramicrotomy after NanoSIMS analyses and prior to TEM characterization. The new methods have yielded a 100% success rate and allow for the specific correlation of microstructural and isotopic properties of individual grains. Knowing these properties allows for inferences to be made regarding the condensation sequences and the origins of the stellar material that condensed to form these grains. NanoSIMS studies of ultramicrotomed sections of presolar graphite grains have revealed complex isotopic heterogeneities that appear to be primary products of the grains' formation environments and not secondary processing during the grains' lifetimes. Correlated excesses in 15N and 18O were identified as being carried by TiC subgrains within presolar graphite grains from supernovae (SNe). These spatially-correlated isotopic anomalies pinpoint the origin of the material that formed these grains: the inner He/C zone. Complex microstructures and isotopic heterogeneities also provide evidence for mixing in globular SN ejecta, which is corroborated by models and telescopic observations. In addition to these significant isotopic discoveries, I have also observed the first reported nanocrystalline core

  2. Tailoring the crystal structure of TiO{sub 2} thin films from the anatase to rutile phase

    SciTech Connect

    Kotake, Haruka; Jia, Junjun; Nakamura, Shin-ichi; Shigesato, Yuzo; Okajima, Toshihiro

    2015-07-15

    TiO{sub 2} films with various Sn concentrations were deposited on quartz substrates using rf reactive magnetron sputtering. The crystal structure was investigated by using x-ray diffraction, Raman spectroscopy, and transmission electron microscopy, and the chemical states of Ti and Sn were analyzed by x-ray absorption near edge structure (XANES) spectroscopy. Without Sn doping, TiO{sub 2} films change the crystal structure from rutile to anatase as the total gas pressure increases in the sputtering deposition. On the other hand, Sn doping induces the transformation of TiO{sub 2} crystalline structure from anatase to rutile phase, where the XANES spectra implied that Sn substitutes into Ti site of rutile TiO{sub 2}. Atomic force microscope analyses revealed that the Sn-doped TiO{sub 2} films exhibited a flat surface with the roughness of approximately 2 nm.

  3. Combined sulfur K-edge XANES-EXAFS study of the effect of protonation on the sulfate tetrahedron in solids and solutions.

    PubMed

    Pin, S; Huthwelker, T; Brown, M A; Vogel, F

    2013-09-05

    Sulfur K-edge X-ray absorption spectroscopy (XAS) has been used to distinguish between aqueous and solid sulfates and to investigate changes in their speciation. Data have been collected for tetrahedrally coordinated S in K2SO4 and KHSO4 solids and aqueous solutions. With a first qualitative analysis of the X-ray absorption near-edge structure (XANES) spectra, it has been observed that those for solids are much more structured and distinguishable from those of aqueous solutions. The protonation state has a strong effect on the white line of sulfates and has been assigned to the different charge delocalization in the samples, the effect of the solvating water molecules and multiple scattering effects. In the extended X-ray absorption fine structure (EXAFS) spectra, the backscattering from the first O shell dominated the EXAFS fine structure function, χ(k), but the nonlinear multiple scattering contributions occurring in the first coordination shell are significant and must be considered in the EXAFS analysis. The intensity of these contributions strongly depend on the symmetry of the system. For a distorted tetrahedron, the intensity of the multiple scattering contributions is less than that found in a regular tetrahedron. The FEFF code has been used to model the contributions of the multiple-scattering processes. The observed experimental evidence in the XAS data can be used to distinguish between sulfates in solids and liquids. This is applicable to many chemical, geochemical, and biological systems.

  4. Insights into molecular chemistry of Chiapas amber using infrared-light microscopy, PIXE/RBS, and sulfur K-edge XANES spectroscopy

    NASA Astrophysics Data System (ADS)

    Riquelme, Francisco; Northrup, Paul; Ruvalcaba-Sil, José Luis; Stojanoff, Vivian; Peter Siddons, D.; Alvarado-Ortega, Jesús

    2014-07-01

    Chiapas amber is a natural occurring fossil resin structurally composed of long macromolecule chains with semicrystalline phases associated with both fossil and polymerization process. The most conspicuous characteristic of this fossil polymer is that it preserves ancient organic inclusions. In the present work, PIXE/RBS spectrometry (particle-induced X-ray emission/Rutherford backscattering) were combined with complementary K-edge XANES spectroscopy (X-ray absorption near-edge structure) to identify the amount of sulfur in Chiapas amber. Initially, the amber samples were examined using infrared reflected photomicrography. Amber is transparent to infrared light and so embedded plants and animals are easily visible, showing them in extraordinary detail, as if they were immersed in a water-like solution. The PIXE/RBS data show that the proportion of sulfur in amber is significantly higher than that found in recently formed resins, consistent with the biogeochemical process that transforms the resin into amber during long-term burial in geological deposits. The sulfur K-edge XANES spectra from amber confirm the sulfur abundance and reveal sulfur species in the reduced and intermediate oxidation states in amber. Almost no oxidized sulfur was found, whereas the recent resins show mostly oxidized sulfur fractions. This indicates that labile oxidized sulfur decays during fossilization and resin maturation must occur under conditions of oxygen depletion. The implications of the presence of sulfur in amber for organic preservation is also discussed here. Sulfur compounds work as a polymer additive that promotes intense resin solidification. This restricts the early oxidant-specific biodegradation of the embedded biomatter and, over geological time, provides greater stability against chemical changes.

  5. Electronic and atomic structures of quasi-one-dimensional K{sub 0.3}MoO{sub 3}

    SciTech Connect

    Huang, C.H.; Jan, J.C.; Chiou, J.W.; Tsai, H.M.; Pao, C.W.; Du, C.H.; Pong, W.F.; Tsai, M.-H.; Tang, M.T.; Lee, J.J.; Lee, J.F.

    2005-04-04

    The electronic and atomic structures of quasi-one-dimensional blue bronze K{sub 0.3}MoO{sub 3} were investigated by polarization-dependent O K-edge x-ray absorption near-edge structure (XANES) and Mo K-edge extended x-ray absorption fine structure (EXAFS) measurements at various temperature and applied voltages. The O K-edge XANES spectra suggest that the number of unoccupied O 2p-Mo 4d hybridized states increases and decreases with temperature, respectively, below and above a critical temperature of 180 K. The along b-axis electric current measurements show a threshold applied voltage, beyond which the current increases rapidly. The Mo K-edge EXAFS measurements show that the Mo-O bond lengths are insensitive to the temperature even beyond 180 K.

  6. Boron carbides formed by coevaporation of B and C atoms: Vapor reactivity, B{sub x}C{sub 1-x} composition, and bonding structure

    SciTech Connect

    Caretti, I.; Albella, J. M.; Jimenez, I.

    2008-05-01

    Boron carbides (B{sub x}C{sub 1-x}) in thin film form have been synthesized in a high vacuum by coevaporation of B and C atoms from independent sources, allowing a study of the whole composition range from pure B films to pure C films. The relationship between the impinging B/C atomic fluxes and the film composition has been studied, providing information on the chemical reactivity between the B and C vapors. The composition was determined with x-ray emission energy dispersion spectroscopy and x-ray absorption near edge spectroscopy (XANES). Finally, the bonding structure of the films has been determined by XANES, showing a change from structures based on B{sub 12}-icosahedral units for the B-rich samples to hexagonal-like structures for the C-rich samples. The study shows that the structural transition takes place for x{approx}0.5.

  7. Properties of pure and sulfided NiMoO{sub 4} and CoMoO{sub 4} catalysts: TPR, XANES and time-resolved XRD studies

    SciTech Connect

    Chaturvedi, S.; Rodriguez, J.A.; Hanson, J.C.; Albornoz, A.; Brito, J.L.

    1998-12-31

    X-ray absorption near-edge spectroscopy (XANES) was used to characterize the structural and electronic properties of a series of cobalt- and nickel-molybdate catalysts (AMoO{sub 4}.nH{sub 2}O, {alpha}-AMoO{sub 4}, {beta}-AMoO{sub 4}; A=Co or Ni). The results of XANES indicate that the Co and Ni atoms are in octahedral sites in all these compounds, while the coordination of Mo varies from octahedral in the {alpha}-phases to tetrahedral in the {beta}-phases and hydrate. Time-resolved x-ray diffraction shows a direct transformation of the hydrates into the {beta}-AMoO{sub 4} compounds (following a kinetics of first order) at temperatures between 200 and 350{degrees}C. This is facilitated by the similarities that the AMoO{sub 4}.nH{sub 2}O and H{sub 2} at temperatures between 400 and 600{degrees}C, forming gaseous water oxides in which the oxidation state of Co and Ni remains +2 while that of Mo is reduced to +5 or +4. After exposing {alpha}-NiMoO{sub 4} and {beta}-NiMoO{sub 4} to H{sub 2}S, both metals get sulfided and a NiMoS{sub x} phase is formed. For the {beta} phase of NiMoO{sub 4} the sulfidation of Mo is more extensive than for the {alpha} phase, making the former a better precursor for catalysts of hydrodesulfurization reactions.

  8. International Conference on the Structure of Surfaces (ICSOS-1) (1st) Held in Berkeley, California on August 13-16, 1984

    DTIC Science & Technology

    1984-08-16

    D.K. Saldin and J.B. Pendry Near-Edge X-Ray Absorption Spectroscopy D17 D.K. Saldin , D.D. Vvedensky and J.B. Pendry The Structure of Organic...Pendry and D.K. Saldin LEED, XANES and the Structure of Disordered Surfaces 9:10 E2 M. Ringger, H.R. Hidber, R. Schiogl, P. Oelhafen, H.-J...of Physics University of Rome Sendai 980 P22a A. Moro, 2 JAPAN 00185 Roma ITALY 0222-22-1800, ext. 3239 Dilano K. Saldin Massimo Simonetta Imperial

  9. Local atomic structure investigation of AlFeCuCrMgx (0.5, 1, 1.7) high entropy alloys: X-ray absorption spectroscopy study

    NASA Astrophysics Data System (ADS)

    Maulik, Ornov; Patra, N.; Bhattacharyya, D.; Jha, S. N.; Kumar, Vinod

    2017-02-01

    The present paper reports local atomic structure investigation of novel AlFeCuCrMgx (x=0.5, 1, 1.7) high entropy alloys (HEAs) produced by mechanical alloying using Fe, Cr and Cu K-edge X-ray absorption near edge spectroscopy (XANES) and extended x-ray absorption fine structure (EXAFS) spectroscopy. XANES spectra measured at Fe and Cr K-edges resemble that of the respective pure metal foils, while the spectrum measured at Cu K-edge manifests the presence of some other phases in the as-milled alloys. The radial distribution functions (RDFs) obtained from Fourier transformation of EXAFS spectra support the formation of disordered BCC structure.

  10. Mn K-edge XANES and Kbeta XES studies of two Mn-oxo binuclear complexes: investigation of three different oxidation states relevant to the oxygen-evolving complex of photosystem II.

    PubMed

    Visser, H; Anxolabéhère-Mallart, E; Bergmann, U; Glatzel, P; Robblee, J H; Cramer, S P; Girerd, J J; Sauer, K; Klein, M P; Yachandra, V K

    2001-07-25

    Two structurally homologous Mn compounds in different oxidation states were studied to investigate the relative influence of oxidation state and ligand environment on Mn K-edge X-ray absorption near-edge structure (XANES) and Mn Kbeta X-ray emission spectroscopy (Kbeta XES). The two manganese compounds are the di-mu-oxo compound [L'2Mn(III)O2Mn(IV)L'2](ClO4)3, where L' is 1,10-phenanthroline (Cooper, S. R.; Calvin, M. J. Am. Chem. Soc. 1977, 99, 6623-6630) and the linear mono-mu-oxo compound [LMn(III)OMn(III)L](ClO4)2, where L- is the monoanionic N,N-bis(2-pyridylmethyl)-N'-salicylidene-1,2-diaminoethane ligand (Horner, O.; Anxolabéhère-Mallart, E.; Charlot, M. F.; Tchertanov, L.; Guilhem, J.; Mattioli, T. A.; Boussac, A.; Girerd, J.-J. Inorg. Chem. 1999, 38, 1222-1232). Preparative bulk electrolysis in acetonitrile was used to obtain higher oxidation states of the compounds: the Mn(IV)Mn(IV) species for the di-mu-oxo compound and the Mn(III)Mn(IV) and Mn(IV)Mn(IV) species for the mono-mu-oxo compound. IR, UV/vis, EPR, and EXAFS spectra were used to determine the purity and integrity of the various sample solutions. The Mn K-edge XANES spectra shift to higher energy upon oxidation when the ligand environment remains similar. However, shifts in energy are also observed when only the ligand environment is altered. This is achieved by comparing the di-mu-oxo and linear mono-mu-oxo Mn-Mn moieties in equivalent oxidation states, which represent major structural changes. The magnitude of an energy shift due to major changes in ligand environment can be as large as that of an oxidation-state change. Therefore, care must be exercised when correlating the Mn K-edge energies to manganese oxidation states without taking into account the nature of the ligand environment and the overall structure of the compound. In contrast to Mn K-edge XANES, Kbeta XES spectra show less dependence on ligand environment. The Kbeta1,3 peak energies are comparable for the di-mu-oxo and mono

  11. Simple algorithm to determine the near-edge smoke boundaries with scanning lidar.

    PubMed

    Kovalev, Vladimir A; Newton, Jenny; Wold, Cyle; Hao, Wei Min

    2005-03-20

    We propose a modified algorithm for the gradient method to determine the near-edge smoke plume boundaries using backscatter signals of a scanning lidar. The running derivative of the ratio of the signal standard deviation (STD) to the accumulated sum of the STD is calculated, and the location of the global maximum of this function is found. No empirical criteria are required to determine smoke boundaries; thus the algorithm can be used without a priori selection of threshold values. The modified gradient method is not sensitive to the signal random noise at the far end of the lidar measurement range. Experimental data obtained with the Fire Sciences Laboratory lidar during routine prescribed fires in Montana were used to test the algorithm. Analysis results are presented that demonstrate the robustness of this algorithm.

  12. Evolution of phosphorus complexation and mineralogy during (hydro)thermal treatments of activated and anaerobically digested sludge: Insights from sequential extraction and P K-edge XANES.

    PubMed

    Huang, Rixiang; Tang, Yuanzhi

    2016-09-01

    (Hydro)thermal treatments of sewage sludge is a promising option that can simultaneously target safe waste disposal, energy recovery, and nutrient recovery/recycling. The speciation of phosphorus (P) in sludge is of great relevance to P reclamation/recycling and soil application of sludge-derived products, thus it is critical to understand the effects of different treatment techniques and conditions on P speciation. This study systematically characterized P speciation (i.e. complexation and mineral forms) in chars derived from pyrolysis and hydrothermal carbonization (HTC) of municipal sewage sludges. Combined sequential extraction and P K-edge X-ray absorption near edge structure (XANES) spectroscopy analysis revealed the dependence of P transformation on treatment conditions and metal composition in the feedstocks. Pyrolysis of sludges decreased the relative abundance of phytic acid while increased the abundance of Al-associated P. HTC thoroughly homogenized and exposed P for interaction with various metals/minerals, with the final P speciation closely related to the composition/speciation of metals and their affinities to P. Results from this study revealed the mechanisms of P transformation during (hydro)thermal treatments of sewage sludges, and might be applicable to other biosolids. It also provided fundamental knowledge basis for the design and selection of waste management strategies for better P (re)cycling and reclamation.

  13. XANES-EXAFS analysis of se solid-phase reaction products formed upon contacting Se(IV) with FeS2 and FeS.

    PubMed

    Breynaert, E; Bruggeman, C; Maes, A

    2008-05-15

    The solid-phase Se speciation after short-term (3 weeks) contact of selenite [Se(IV)] oxyanions with pyrite (FeS2) and troilite (FeS) was investigated using X-ray absorption spectroscopy (XAS; X-ray absorption near-edge spectroscopy-extended X-ray absorption fine structure (XANES-EXAFS)). It was found that the nature of the sulfide mineral dictates the final speciation since respectively Se(0) and FeSe(x) were formed, meaning that the reaction mechanism is different and that these phases cannot be regarded as geochemically similar. The experimental results support the previously proposed sorption/ reduction mechanism for the reaction of selenite with pyrite. In the presence of troilite the reduction proceeds through the intermediate formation of Se(0) by reduction of selenite with dissolved sulfide. XAS data recorded for the FeS2 and FeS were compared with different Se reference phases, ranging in oxidation state from -II to +IV, used for validation of the XAS analysis methodology. This methodology can in principle be used to analyze Se phases formed in "in situ" geochemical conditions such as high-level radioactive waste disposal facilities.

  14. Combination of first-principles molecular dynamics and XANES simulations for LiCoO2-electrolyte interfacial reactions in a lithium-ion battery

    NASA Astrophysics Data System (ADS)

    Tamura, Tomoyuki; Kohyama, Masanori; Ogata, Shuji

    2017-07-01

    We performed a first-principles molecular dynamics (FPMD) simulation of the interfacial reactions between a LiCoO2 electrode and a liquid ethylene carbonate (EC) electrolyte. For configurations during the FPMD simulation, we also performed first-principles Co K-edge x-ray absorption near-edge structure (XANES) simulations, which can properly reproduce the bulk and surface spectra of LiCoO2. We observed strong absorption of an EC molecule on the LiCoO2 {110} surface, involving ring opening of the molecule, bond formation between oxygen atoms in the molecule and surface Co ions, and emission of one surface Li ion, while all the surface Co ions remain Co3 +. The surface Co ions having the bond with an oxygen atom in the molecule showed remarkable changes in simulated K-edge spectra which are similar to those of the in situ observation under electrolyte soaking [D. Takamatsu et al., Angew. Chem., Int. Ed. 51, 11597 (2012), 10.1002/anie.201203910]. Thus, the local environmental changes of surface Co ions due to the reactions with an EC molecule can explain the experimental spectrum changes.

  15. IN SITU STUDIES OF CORROSION USING X-RAY ABSORPTION NEAR SPECTROSCOPY (XANES)

    SciTech Connect

    ISAACS, H.S.; SCHMUKI, P.; VIRTANEN, S.

    2001-03-25

    Applications of x-ray absorption near-edge spectroscopy (XANES) and the design of cells for in situ corrosion studies are reviewed. Passive films studies require very thin metal or alloy layers be used having a thickness of the order of the films formed because of penetration of the x-ray beam into the metal substrate. The depth of penetration in water also limits the thickness of solutions that can be used because of water reduces the x-ray intensity. Solution thickness must also be limited in studies of conversion layer formation studies because the masking of the Cr in solution. Illustrative examples are taken from the anodic behavior of Al-Cr alloys, the growth of passive films on Fe and stainless steels, and the formation of chromate conversion layers on Al.

  16. Various Arsenic Network Structures in 112-Type Ca1-xLaxFe1-yPdyAs2 Revealed by Synchrotron X-ray Diffraction Experiments.

    PubMed

    Tamura, Shinya; Katayama, Naoyuki; Yamada, Yuto; Sugiyama, Yuki; Sugawara, Kento; Sawa, Hiroshi

    2017-03-06

    Two novel 112-type palladium-doped iron arsenides were synthesized and identified using comprehensive studies involving synchrotron X-ray diffraction and X-ray absorption near-edge structure (XANES) experiments. Whereas in-plane arsenic zigzag chains were found in the 112-type superconducting iron arsenide Ca1-xLaxFeAs2 with maximum Tc = 34 K, deformed arsenic network structures appeared in other 112-type materials, such as longitudinal arsenic zigzag chains in CaFe1-yPdyAs2 (y ∼ 0.51) and arsenic square sheets constructed via hypervalent bonding in Ca1-xLaxFe1-yPdyAs2 (x ∼ 0.31, y ∼ 0.30). As K-edge XANES spectra clarified the similar oxidization states around FeAs4 tetrahedrons, alluding to possible parents for high-Tc 112-type iron arsenide superconductors.

  17. Progressive Oxidation of Pyrite in Five Bituminous Coal Samples: An As XANES and 57Fe Mossbauer Spectroscopic Study

    SciTech Connect

    Kolker,A.; Huggins, F.

    2007-01-01

    Naturally occurring pyrite commonly contains minor substituted metals and metalloids (As, Se, Hg, Cu, Ni, etc.) that can be released to the environment as a result of its weathering. Arsenic, often the most abundant minor constituent in pyrite, is a sensitive monitor of progressive pyrite oxidation in coal. To test the effect of pyrite composition and environmental parameters on the rate and extent of pyrite oxidation in coal, splits of five bituminous coal samples having differing amounts of pyrite and extents of As substitution in the pyrite, were exposed to a range of simulated weathering conditions over a period of 17 months. Samples investigated include a Springfield coal from Indiana (whole coal pyritic S = 2.13 wt.%; As in pyrite = detection limit (d.l.) to 0.06 wt.%), two Pittsburgh coal samples from West Virginia (pyritic S = 1.32-1.58 wt.%; As in pyrite = d.l. to 0.34 wt.%), and two samples from the Warrior Basin, Alabama (pyritic S = 0.26-0.27 wt.%; As in pyrite = d.l. to 2.72 wt.%). Samples were collected from active mine faces, and expected differences in the concentration of As in pyrite were confirmed by electron microprobe analysis. Experimental weathering conditions in test chambers were maintained as follows: (1) dry Ar atmosphere; (2) dry O{sub 2} atmosphere; (3) room atmosphere (relative humidity {approx}20-60%); and (4) room atmosphere with samples wetted periodically with double-distilled water. Sample splits were removed after one month, nine months, and 17 months to monitor the extent of As and Fe oxidation using As X-ray absorption near-edge structure (XANES) spectroscopy and {sup 57}Fe Mossbauer spectroscopy, respectively. Arsenic XANES spectroscopy shows progressive oxidation of pyritic As to arsenate, with wetted samples showing the most rapid oxidation. {sup 57}Fe Mossbauer spectroscopy also shows a much greater proportion of Fe{sup 3+} forms (jarosite, Fe{sup 3+} sulfate, FeOOH) for samples stored under wet conditions, but much less

  18. Progressive oxidation of pyrite in five bituminous coal samples: An As XANES and 57Fe Mössbauer spectroscopic study

    USGS Publications Warehouse

    Kolker, Allan; Huggins, Frank E.

    2007-01-01

    Naturally occurring pyrite commonly contains minor substituted metals and metalloids (As, Se, Hg, Cu, Ni, etc.) that can be released to the environment as a result of its weathering. Arsenic, often the most abundant minor constituent in pyrite, is a sensitive monitor of progressive pyrite oxidation in coal. To test the effect of pyrite composition and environmental parameters on the rate and extent of pyrite oxidation in coal, splits of five bituminous coal samples having differing amounts of pyrite and extents of As substitution in the pyrite, were exposed to a range of simulated weathering conditions over a period of 17 months. Samples investigated include a Springfield coal from Indiana (whole coal pyritic S = 2.13 wt.%; As in pyrite = detection limit (d.l.) to 0.06 wt.%), two Pittsburgh coal samples from West Virginia (pyritic S = 1.32–1.58 wt.%; As in pyrite = d.l. to 0.34 wt.%), and two samples from the Warrior Basin, Alabama (pyritic S = 0.26–0.27 wt.%; As in pyrite = d.l. to 2.72 wt.%). Samples were collected from active mine faces, and expected differences in the concentration of As in pyrite were confirmed by electron microprobe analysis. Experimental weathering conditions in test chambers were maintained as follows: (1) dry Ar atmosphere; (2) dry O2 atmosphere; (3) room atmosphere (relative humidity ∼20–60%); and (4) room atmosphere with samples wetted periodically with double-distilled water. Sample splits were removed after one month, nine months, and 17 months to monitor the extent of As and Fe oxidation using As X-ray absorption near-edge structure (XANES) spectroscopy and 57Fe Mössbauer spectroscopy, respectively. Arsenic XANES spectroscopy shows progressive oxidation of pyritic As to arsenate, with wetted samples showing the most rapid oxidation. 57Fe Mössbauer spectroscopy also shows a much greater proportion of Fe3+ forms (jarosite, Fe3+ sulfate, FeOOH) for samples stored under wet conditions, but much less

  19. Short Range Order Signature in Crystalline and Amorphous GeSbTe Xanes Spectra

    NASA Astrophysics Data System (ADS)

    Raty, Jean-Yves; Otjacques, C. Éline; Pekoz, Rengin; Bichara, Christophe; Lordi, Vince

    2011-03-01

    A new implementation of XANES spectra calculations within DFT and PAW potentials is used to compute the XANES spectra of various amorphous and crystalline GeSbTe structures. A clear correlation between the local order, either tetrahedral or distorted octahedral, and the shape of the XANES signal is observed. These calculations provide a new interpretation of past XANES measurements, relating essentially the phase change mechanism to a moderate modification of the local environment of the Ge atoms. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. This work was supported by the Belgian PAI 3/42 program and the FNRS-FRFC.

  20. Electronic structure of KD2xH2(1-x)PO4 studied by soft x-ray absorption and emission spectroscopies

    SciTech Connect

    Kucheyev, S O; Bostedt, C F; van Buuren, T; Willey, T M; Land, T A; Terminello, L J; Felter, T E; Hamza, A V; Demos, S G; Nelson, A J

    2004-04-27

    The surface and bulk electronic structure of tetragonal (at 300 K) and orthorhombic (at 77 K) KD{sub 2x}H{sub 2(1-x)}PO{sub 4} single crystals (so-called KDP and DKDP), with a deuteration degree x of 0.0, 0.3, and 0.6, is studied by soft x-ray absorption near-edge structure (XANES) and non-resonant soft x-ray emission (XES) spectroscopies. High-resolution O K-edge, P L{sub 2,3}-edge, and K L{sub 2,3}-edge XANES and XES spectra reveal that the element-specific partial density of states in the conduction and valence bands is essentially independent of deuteration x. We give assignment of XANES and XES peaks based on previous molecular orbital and band-structure calculations. Projected densities of states in the conduction band also appear to be essentially identical for tetragonal (at 300 K) and orthorhombic (at 77 K) phases, consistent with previous band structure calculations. However, a decrease in sample temperature from 300 to 77 K results in an {approx} 0.5 eV shift in the valence band edge (probed by XES), with negligible changes to the conduction band edge (probed by XANES). Results also show that high-intensity x-ray irradiation results in decomposition of these hydrogen-bonded materials into water and KPO{sub 3} cyclo- and polyphosphates.

  1. X-ray absorption near-edge spectroscopy in bioinorganic chemistry: Application to M–O2 systems

    PubMed Central

    Sarangi, Ritimukta

    2012-01-01

    Metal K-edge X-ray absorption spectroscopy (XAS) has been extensively applied to bioinorganic chemistry to obtain geometric structure information on metalloprotein and biomimetic model complex active sites by analyzing the higher energy extended X-ray absorption fine structure (EXAFS) region of the spectrum. In recent years, focus has been on developing methodologies to interpret the lower energy K-pre-edge and rising-edge regions (XANES) and using it for electronic structure determination in complex bioinorganic systems. In this review, the evolution and progress of 3d-transition metal K-pre-edge and rising-edge methodology development is presented with particular focus on applications to bioinorganic systems. Applications to biomimetic transition metal–O2 intermediates (M = Fe, Co, Ni and Cu) are reviewed, which demonstrate the power of the method as an electronic structure determination technique and its impact in understanding the role of supporting ligands in tuning the electronic configuration of transition metal–O2 systems. PMID:23525635

  2. High-precision determination of iron oxidation state in silicate glasses using XANES

    SciTech Connect

    Cottrell, Elizabeth; Kelley, Katherine A.; Lanzirotti, Antonio; Fischer, Rebecca A.

    2009-11-04

    Fe K-edge X-ray absorption near-edge structure (XANES) and Moessbauer spectra were collected on natural basaltic glasses equilibrated over a range of oxygen fugacity (QFM - 3.5 to QFM + 4.5). The basalt compositions and fO{sub 2} conditions were chosen to bracket the natural range of redox conditions expected for basalts from mid-ocean ridge, ocean island, back-arc basin, and arc settings, in order to develop a high-precision calibration for the determination of Fe{sup 3+}/{Sigma}Fe in natural basalts. The pre-edge centroid energy, corresponding to the 1s {yields} 3d transition, was determined to be the most robust proxy for Fe oxidation state, affording significant advantages compared to the use of other spectral features. A second-order polynomial models the correlation between the centroid and Fe{sup 3+}/{Sigma}Fe, yielding a precision of {+-} 0.0045 in Fe{sup 3+}/{Sigma}Fe for glasses with Fe{sup 3+}/{Sigma}Fe > 8%, which is comparable to the precision of wet chemistry. This high precision relies on a Si (311) monochromator to better define the Fe{sup 2+} and Fe{sup 3+} transitions, accurate and robust modeling of the pre-edge feature, dense fO{sub 2}-coverage and compositional appropriateness of reference glasses, and application of a non-linear drift correction. Through re-analysis of the reference glasses across three synchrotron beam sessions, we show that the quoted precision can be achieved (i.e., analyses are reproducible) across multiple synchrotron beam sessions, even when spectral collection conditions (detector parameters or sample geometry) change. Rhyolitic glasses were also analyzed and yield a higher centroid energy at a given Fe{sup 3+}/{Sigma}Fe than basalts, implying that major variations in melt structure affect the relationship between centroid position and Fe{sup 3+}/{Sigma}Fe, and that separate calibrations are needed for the determination of oxidation state in basalts and rhyolites.

  3. XANES, EXAFS and Kbeta spectroscopic studies of the oxygen-evolving complex in Photosystem II

    SciTech Connect

    Robblee, John Henry

    2000-12-01

    A key question for the understanding of photosynthetic water oxidation is whether the four oxidizing equivalents necessary to oxidize water to dioxygen are accumulated on the four Mn ions of the oxygen evolving complex (OEC), or whether some ligand-centered oxidations take place before the formation and release of dioxygen during the S3 → [S4] → S0 transition. Progress in instrumentation and flash sample preparation allowed us to apply Mn Kβ X-ray emission spectroscopy (Kb XES) to this problem for the first time. The Kβ XES results, in combination with Mn X-ray absorption near-edge structure (XANES) and electron paramagnetic resonance (EPR) data obtained from the same set of samples, show that the S2 → S3 transition, in contrast to the S0 → S1 and S1 → S2 transitions, does not involve a Mn-centered oxidation. This is rationalized by manganese μ-oxo bridge radical formation during the S2 → S3 transition. Using extended X-ray absorption fine structure (EXAFS) spectroscopy, the local environment of the Mn atoms in the S0 state has been structurally characterized. These results show that the Mn-Mn distance in one of the di-μ-oxo-bridged Mn-Mn moieties increases from 2.7 Å in the S1} state to 2.85 Å in the S0 state. Furthermore, evidence is presented that shows three di-μ-oxo binuclear Mn2 clusters may be present in the OEC, which is contrary to the widely held theory that two such clusters are present in the OEC. The EPR properties of the S0 state have been investigated and a characteristic ''multiline'' signal in the S0 state has been discovered in the presence of methanol. This provides the first direct confirmation that the native S0 state is paramagnetic. In addition, this signal was simulated using parameters derived from three possible oxidation

  4. XANES studies of titanium dioxide nanoparticles synthesized by using Peltophorum pterocarpum plant extract

    NASA Astrophysics Data System (ADS)

    Saravanan, S.; Balamurugan, M.; Lippitz, A.; Fonda, E.; Swaraj, S.

    2016-12-01

    The preparation and characterization of a Titanium dioxide (TiO2) by a simple, cost effective, facile and eco-friendly green synthesis method using Peltophorum pterocarpum plant extract is presented. The green synthesized nanoparticles were characterized using X-ray diffraction (XRD), Raman spectroscopy, High-resolution transmission electron microscopy (HR-TEM) and X-ray absorption near edge spectroscopy (XANES). XRD results show that the prepared TiO2 NPs were significantly crystalline with various percentages of anatase and rutile phases. The nanoparticles were found to have different diameters ranging from 20 to 80 nm. No evidence of any intermediate or different TiO2 phases were found in XANES measurements performed at the Ti K- and L-edge. It is shown that the TiO2 NPs with high uniformity, high surface area and minimum aggregation can be prepared with relative ease and the desired anatase: rutile phase ratio can be obtained by controlling the experimental conditions.

  5. Electronic and Chemical State of Aluminum from the Single- (K) and Double-Electron Excitation (KLII&III, KLI) X-ray Absorption Near-Edge Spectra of α-Alumina, Sodium Aluminate, Aqueous Al(3+)·(H2O)6, and Aqueous Al(OH)4(-).

    PubMed

    Fulton, John L; Govind, Niranjan; Huthwelker, Thomas; Bylaska, Eric J; Vjunov, Aleksei; Pin, Sonia; Smurthwaite, Tricia D

    2015-07-02

    We probe, at high energy resolution, the double electron excitation (KLII&II) X-ray absorption region that lies approximately 115 eV above the main Al K-edge (1566 eV) of α-alumina and sodium aluminate. The two solid standards, α-alumina (octahedral) and sodium aluminate (tetrahedral), are compared to aqueous species that have the same Al coordination symmetries, Al(3+)·6H2O (octahedral) and Al(OH)4(-) (tetrahedral). For the octahedral species, the edge height of the KLII&III-edge is approximately 10% of the main K-edge; however, the edge height is much weaker (3% of K-edge height) for Al species with tetrahedral symmetry. For the α-alumina and aqueous Al(3+)·6H2O the KLII&III spectra contain white line features and extended absorption fine structure (EXAFS) that mimics the K-edge spectra. The KLII&III-edge feature interferes with an important region in the EXAFS spectra of the crystalline and aqueous standards. The K-edge spectra and K-edge energy positions are predicted using time-dependent density functional theory (TDDFT). The TDDFT calculations for the K-edge X-ray absorption near-edge spectra (XANES) reproduce the observed transitions in the experimental spectra of the four Al species. The KLII&II and KLI onsets and their corresponding chemical shifts for the four standards are estimated using the delta self-consistent field (ΔSCF) method.

  6. XANES Measurements of Cr Valence in Olivine and their Applications to Planetary Basalts (Invited)

    NASA Astrophysics Data System (ADS)

    Bell, A. S.; Burger, P.; Le, L.; Shearer, C. K.; Papike, J.; Sutton, S. R.; Newville, M.; Jones, J. H.

    2013-12-01

    The oxidation state and partitioning behavior of trace Cr in terrestrial and planetary basaltic magmas has long been a subject of petrologic inquiry. We have performed a series of experiments designed to examine the relationship between oxygen fugacity and the ratio of divalent to trivalent Cr present in olivine crystals grown from a basaltic liquid. The experimental olivine crystals were grown at fO2 values ranging from IW-1 to IW+3.4. The melt composition used in this work was modeled after the bulk composition of the primitive, basaltic martian meteorite Yamato 980459 (Y-98). Chromium valence in the olivine crystals was measured with X-ray-Absorption-Near-Edge-Spectroscopy (XANES) at the Advanced Photon Source, Argonne National Laboratory. Chromium K-edge XANES data were acquired with the x-ray microprobe of GSECARS beamline 13-ID-E. Beam focusing was accomplished with dynamically-figured Kirkpatrick-Baez focusing mirrors; this configuration yielded a beam focused to a final spot size of ~ 4 μm2. Results from the XANES measurements indicate that the ratio of divalent to trivalent Cr in the olivine is systematically correlated with fO2 in a manner that is consistent with the expected redox systematics for Cr2+- Cr3+ in the melt. In this way, measurements of the Cr2+/Cr3+ in olivine phenocrysts can indirectly reveal information about the Cr valence ratio and fO2 the liquid from which it grew even in the absence of a quenched melt phase. Although the results from the experiments presented in this work specifically apply to the Yamato 98 parental liquid, the concepts and XANES analytical techniques used in this study present a novel, generalized methodology that may be applicable to any olivine-bearing basalt. Furthermore, the XANES based measurements are made on a micron-scale, thus potential changes of the Cr2+/Cr3+ in the melt occurring during crystallization may be recorded in detail.

  7. Near-Edge X-ray Absorption Fine Structure within Multilevel Coupled Cluster Theory.

    PubMed

    Myhre, Rolf H; Coriani, Sonia; Koch, Henrik

    2016-06-14

    Core excited states are challenging to calculate, mainly because they are embedded in a manifold of high-energy valence-excited states. However, their locality makes their determination ideal for local correlation methods. In this paper, we demonstrate the performance of multilevel coupled cluster theory in computing core spectra both within the core-valence separated and the asymmetric Lanczos implementations of coupled cluster linear response theory. We also propose a visualization tool to analyze the excitations using the difference between the ground-state and excited-state electron densities.

  8. Combining state-of-the-art experiment and ab initio calculations for a better understanding of the interplay between valence, magnetism and structure in Eu compounds at high pressure

    SciTech Connect

    Souza-Neto, N. M.; Haskel, D.; dos Reis, R. D.; Gandra, F. C. G.

    2016-07-26

    Here, we describe how first principle calculations can play a key role in the interpretation of X-ray absorption near-edge structure (XANES) and X-ray magnetic circular dichroism (XMCD) spectra for a better understanding of emergent phenomena in condensed matter physics at high applied pressure. Eu compounds are used as case study to illustrate the advantages of this methodology, ranging from studies of electronic charge transfer probed by quadrupolar and dipolar contributions, to accurately determining electronic valence, and to inform about the influence of pressure on RKKY interactions and magnetism. This description should help advance studies where the pressure dependence of XANES and XMCD data must be tackled with the support of theoretical calculations for a proper understanding of the electronic properties of materials.

  9. Combining state-of-the-art experiment and ab initio calculations for a better understanding of the interplay between valence, magnetism and structure in Eu compounds at high pressure

    SciTech Connect

    Souza-Neto, N. M.; Haskel, D.; dos Reis, R. D.; Gandra, F. C. G.

    2016-07-26

    Here, we describe how first principle calculations can play a key role in the interpretation of X-ray absorption near-edge structure (XANES) and X-ray magnetic circular dichroism (XMCD) spectra for a better understanding of emergent phenomena in condensed matter physics at high applied pressure. Eu compounds are used as case study to illustrate the advantages of this methodology, ranging from studies of electronic charge transfer probed by quadrupolar and dipolar contributions, to accurately determining electronic valence, and to inform about the influence of pressure on RKKY interactions and magnetism. This description should help advance studies where the pressure dependence of XANES and XMCD data must be tackled with the support of theoretical calculations for a proper understanding of the electronic properties of materials.

  10. Synchrotron WAXS and XANES studies of silica (SiO2) powders synthesized from Indonesian natural sands

    NASA Astrophysics Data System (ADS)

    Muchlis, Khairanissa; Aini Fauziyah, Nur; Soontaranon, Siriwat; Limpirat, Wanwisa; Pratapa, Suminar

    2017-01-01

    In this study, we have investigated polymorphic silica (SiO2) powders using, Wide Angle X-ray Scattering (WAXS) and X-Ray Absorption Near Edge Spectroscopy (XANES), laboratory X-Ray Diffraction (XRD) instruments. The WAXS and XANES spectra were collected using synchrotron radiation at Synchrotron Light Research Institute (SLRI), Nakhon Ratchasima, Thailand. The silica powders were obtained by processing silica sand from Tanah Laut, South Kalimantan, Indonesia. Purification process of silica sand was done by magnetic separation and immersion with HCl. The purification step was needed to reduce impurity or undesirable non Si elements. Three polymorphs of silica were produced, i.e. amorphous phase (A), quartz (B), and cristobalite (C). WAXS profile for each phase was presented in terms of intensity vs. 2θ prior to analyses. Both XRD (λCuKα=1.54056 Å) and WAXS (λ=1.09 Å) patttern show that (1) A sample contains no crystallites, (2) B sample is monophasic, contains only quartz, and (3) C sample contains cristobalite and trydimite. XRD quantitative analysis using Rietica gave 98,8 wt% cristobalite, while the associated WAXS data provided 98.7 wt% cristobalite. Si K-edge XANES spectra were measured at energy range 1840 to 1920 eV. Qualitatively, the pre-edge and edge features for all phases are similar, but their main peaks in the post-edge region are different.

  11. Use of HERFD-XANES at the U L3- and M4-Edges To Determine the Uranium Valence State on [Ni(H2O)4]3[U(OH,H2O)(UO2)8O12(OH)3].

    PubMed

    Bès, René; Rivenet, Murielle; Solari, Pier-Lorenzo; Kvashnina, Kristina O; Scheinost, Andreas C; Martin, Philippe M

    2016-05-02

    We report and discuss here the unambiguous uranium valence state determination on the complex compound [Ni(H2O)4]3[U(OH,H2O)(UO2)8O12(OH)3] by using high-energy-resolution fluorescence detection-X-ray absorption near-edge structure spectroscopy (HERFD-XANES). The spectra at both U L3- and M4-edges confirm that all five nonequivalent U atoms are solely in the hexavalent form in this compound, as previously suggested by bond-valence-sum analysis and X-ray diffraction pattern refinement. Moreover, the presence of the preedge feature, due to the 2p3/2-5f quadrupole transition, has been observed in the U L3-edge HERFD-XANES spectrum, in agreement with theoretical and experimental observations of other uranium-based compounds. Recently, this feature has been proposed as a possible tool to determine the uranium oxidation state in a manner similar to that of 3d and 4d metals. Nevertheless, this feature is also very sensitive to the uranium local environment, as revealed by our theoretical calculations, and consequently could not be used to attribute without ambiguity the uranium valence state. In contrast, U M4-edge HERFD-XANES appears to be the most straightforward and reliable way to assess the uranium valence state in very complex materials such as [Ni(H2O)4]3[U(OH,H2O)(UO2)8O12(OH)3] or a mixture of compounds.

  12. Magnetic structures of FeTiO{sub 3}-Fe{sub 2}O{sub 3} solid solution thin films studied by soft X-ray magnetic circular dichroism and ab initio multiplet calculations

    SciTech Connect

    Hojo, H. E-mail: fujita@dipole7.kuic.kyoto-u.ac.jp; Fujita, K. E-mail: fujita@dipole7.kuic.kyoto-u.ac.jp; Matoba, T.; Tanaka, K.; Ikeno, H.; Mizoguchi, T.; Tanaka, I.; Nakamura, T.; Takeda, Y.; Okane, T.

    2014-03-17

    The solid solutions between ilmenite (FeTiO{sub 3}) and hematite (α-Fe{sub 2}O{sub 3}) have recently attracted considerable attention as a spintronic material due to their interesting magnetic and electrical properties. In this study, the electronic and magnetic structures of epitaxially grown 0.6FeTiO{sub 3}·0.4Fe{sub 2}O{sub 3} solid solution thin films were investigated by combining x-ray absorption near-edge structure (XANES), x-ray magnetic circular dichroism (XMCD) for two different crystallographic projections, and first-principles theoretical calculations. The Fe L-edge XANES and XMCD spectra reveal that Fe is in the mixed-valent Fe{sup 2+}–Fe{sup 3+} states while Fe{sup 2+} ions are mainly responsible for the magnetization. Moreover, the experimental Fe L-edge XANES and XMCD spectra change depending on the incident x-ray directions, and the theoretical spectra explain such spectral features. We also find a large orbital magnetic moment, which can originate the magnetic anisotropy of this system. On the other hand, although the valence state of Ti was interpreted to be 4+ from the Ti L-edge XANES, XMCD signals indicate that some electrons are present in the Ti-3d orbital, which are coupled antiparallel to the magnetic moment of Fe{sup 2+} ions.

  13. Synthesis and structural characterization of zinc titanates

    NASA Astrophysics Data System (ADS)

    Akgül, Güvenç

    2013-04-01

    The aim of this study is to accurately obtain of local atomic structures of zinc titanates (ZnTiO3 and Zn2TiO4). Samples have been synthesized by the ball milling method using mixture of high purity ZnO and TiO2 powders. X-ray diffraction (XRD), X-ray absorption near edge structure (XANES), and extended X-ray absorption fine structure (EXAFS) techniques have been used to probe crystal and local structures of the synthesized powders. They have been found to exhibit very high crystallinity. In addition, the EXAFS results have showed that the ball milling is a quite effective method to fabricate highly crystalline nanosized powders. The obtained results are presented in detail.

  14. Crystal structure and electronic and thermal properties of TbFeAsO0.85

    NASA Astrophysics Data System (ADS)

    Kaurav, N.; Chung, Y. T.; Kuo, Y. K.; Liu, R. S.; Chan, T. S.; Chen, J. M.; Lee, J.-F.; Sheu, H.-S.; Wang, X. L.; Dou, S. X.; Lee, S. I.; Shi, Y. G.; Belik, A. A.; Yamaura, K.; Takayama-Muromachi, E.

    2009-05-01

    The crystal structure and the electronic and thermal properties of a high-quality polycrystalline TbFeAsO0.85 sample made by a high-pressure technique are investigated. The crystal structure, as determined by synchrotron X-ray powder diffraction, possesses a tetragonal unit cell (space group: P4/nmm) with lattice parameters of a =b=3.8851 Å and c =8.3630 Å. In order to elucidate the electronic structure and oxidation states of corresponding elements, X-ray absorption near-edge structure (XANES) spectra are presented. The XANES spectra confirm that the oxidation states of Fe, As, and Tb in the TbFeAsO0.85 sample are ˜Fe2+, ˜As3-, and ˜Tb3+, respectively, which are consistent with the previously reported band structure calculations. The n-type character of the charge carriers as revealed from XANES spectra is corroborated by the negative sign of the Seebeck coefficient (S) in the present study. The heat capacity (CP) measurement shows an anomaly in the vicinity of the superconducting transition temperature (Tc=42.5 K), which confirms the bulk nature of the superconductivity in this material.

  15. Mn K-edge XANES studies of La1-xAxMnO3 systems (A=Ca, Ba, Pb)

    NASA Astrophysics Data System (ADS)

    Bridges, F.; Booth, C. H.; Anderson, M.; Kwei, G. H.; Neumeier, J. J.; Snyder, J.; Mitchell, J.; Gardner, J. S.; Brosha, E.

    2001-06-01

    We present Mn K-edge x-ray absorption near-edge structure (XANES) data for a number of manganite systems as a function of temperature. The 1s absorption edge for the Ca-substituted samples is very sharp, almost featureless, and shifts uniformly upwards with increasing Ca content. The interpretation of this result is controversial because the lack of structure appears difficult to reconcile with a mixture of Mn+3 and Mn+4 ions or with several different Mn-O bond lengths at high T. We propose a possible solution in terms of covalency and considerable overlap of the Mn p states (mostly Mn 4p). The manganite preedge structure is quite similar to that for a large number of other Mn compounds, with two or three small peaks that are ascribed to 1s-3d weakly allowed dipole transitions plus possibly a small quadrupole component. The weak dipole transitions are explained as arising from a hybridization of the Mn 4p state of the excited atom with an odd symmetry combination of Mn 3d states on adjacent Mn atoms. The first preedge peak A1 has a small shift to higher energy with increasing valence while the next peak A2 is nearly independent of dopant concentration at 300 K. However, for the colossal magnetoresistance (CMR) samples the A2 preedge peak shifts to a lower energy below the ferromagnetic transition temperature Tc, resulting in a decrease in the A2-A1 splitting by ~0.4 eV. This indicates a change in the higher-energy 3d bands, most likely the minority spin eg, plus some change in covalency. In addition, the amplitudes are temperature dependent for the CMR materials, with the change in A1, A2 correlated with the change in sample magnetization. For the charge ordered (CO) sample, the analysis suggests that the change in the preedge is produced by a distortion that increases below TCO. We discuss these results in terms of some of the theoretical models that have been proposed and other recent XANES studies.

  16. Correlation between bonding structure and microstructure in fullerenelike carbon nitride thin films

    SciTech Connect

    Gago, R.; Abendroth, B.; Moeller, W.; Jimenez, I.; Neidhardt, J.; Hultman, L.; Caretti, I.

    2005-03-15

    The bonding structure of highly ordered fullerenelike (FL) carbon nitride (CN{sub x}) thin films has been assessed by x-ray absorption near-edge spectroscopy (XANES). Samples with different degrees of FL character have been analyzed to discern spectral signatures related to the FL microstructure. The XANES spectra of FL-CN{sub x} films resemble that of graphitic CN{sub x}, evidencing the sp{sup 2} hybridization of both C and N atoms. The FL structure is achieved with the promotion of N in threefold positions over pyridinelike and cyanidelike bonding environments. In addition, the relative {pi}{sup *}/{sigma}* XANES intensity ratio at the C(1s) edge is independent of the FL character, while it decreases {approx}40% at the N(1s) edge with the formation of FL arrangements. This result indicates that there is no appreciable introduction of C-sp{sup 3} hybrids with the development of FL structures and, additionally, that a different spatial localization of {pi} electrons at C and N sites takes place in curved graphitic structures. The latter has implications for the elastic properties of graphene sheets and could, as such, explain the outstanding elastic properties of FL-CN{sub x}.

  17. Lead hydro sodalite [Pb2(OH)(H2O)3]2[Al3Si3O12]2: synthesis and structure determination by combining X-ray rietveld refinement, 1H MAS NMR FTIR and XANES spectroscopy.

    PubMed

    Eiden-Assmann, S; Schneider, A M; Behrens, P; Wiebcke, M; Engelhardt, G; Felsche, J

    2000-01-01

    Ion exchange of the sodium hydro sodalites [Na3(H2O)4]2-[Al3Si3O12]2 [Na4(H3O2)]2[Al3Si3O12]2 and [Na4(OH)]2[Al3Si3O12]2 with aqueous Pb(NO3)2 solutions yielded, whichever reactant sodalite phase was used, the same lead hydro sodalite, [Pb2(OH)-(H2O)3]2[Al3Si3O12]2. Thus, in the case of the non-basic reactant [Na3(H2O)4]2-[Al3Si3O12]2 an overexchange occurs with respect to the number of nonframework cationic charges. Rietveld structure refinement of the lead hydro sodalite based on powder X-ray diffraction data (cubic, a = 9.070 A, room temperature, space group P43n) revealed that the two lead cations within each polyhedral sodalite cage form an orientationally disordered dinuclear [Pb2(micro-OH)(micro-H2O)(H2O)2]3+ complex. Due to additional lead framework oxygen bonds the coordination environment of each metal cation (CN 3+3) is approximately spherical, and clearly the lead 6s electron lone pair is stereochemically inactive. This is also suggested by the absence of a small peak at 13.025 keV, attributed in other Pb2+-O compounds to an electronic 2p-6s transition, in the PbL3 edge XANES spectrum. 1H MAS NMR and FTIR spectra show that the hydrogen atoms of the aqua hydroxo complex (which could not be determined in the Rietveld analysis) are involved in hydrogen bonds of various strengths.

  18. Effect of Fe(II)/Ce(III) dosage ratio on the structure and anion adsorptive removal of hydrothermally precipitated composites: Insights from EXAFS/XANES, XRD and FTIR.

    PubMed

    Chubar, Natalia; Gerda, Vasyl; Banerjee, Dipanjan; Yablokova, Ganna

    2017-02-01

    In this work, we present material chemistry in the hydrothermal synthesis of new complex structure materials based on various dosage ratios of Fe and Ce (1:0, 2:1, 1:1, 1:2, 0:1), characterize them by the relevant methods that allow characterization of both crystalline and amorphous phases and correlate their structure/surface properties with the adsorptive performance of the five toxic anions. The applied synthesis conditions resulted in the formation of different compounds of Fe and Ce components. The Fe-component was dominated by various phases of Fe hydrous oxides, whereas the Ce-component was composed of various phases of Ce carbonates. The presence of two metal salts in raw materials resulted in the formation of a mesoporous structure and averaged the surface area compared to one metal-based material. The surface of all Fe-Ce composites was abundant in Fe component phases. Two-metal systems showed stronger anion removal performance than one-metal materials. The best adsorption was demonstrated by Fe-Ce based materials that had low crystallinity, that were rich in phases and that exhibited surfaces were abundant in greater number of surface functional groups. Notably, Fe extended fine structures simulated by EXAFS in these better adsorbents were rich from oscillations from both heavy and light atoms. This work provides new insights on the structure of composite inorganic materials useful to develop their applications in adsorption and catalysis. It also presents new inorganic anion exchangers with very high removal potential to fluoride and arsenate.

  19. Amyloid-β peptide active site: theoretical Cu K-edge XANES study

    NASA Astrophysics Data System (ADS)

    Chaynikov, A. P.; Soldatov, M. A.; Streltsov, V.; Soldatov, A. V.

    2013-04-01

    This article is dedicated to the local atomic structure analysis of the copper binding site in amyloid-β peptide. Here we considered two possible structural models that were previously obtained by means of EXAFS analysis and density functional theory simulations. We present the calculations of Cu K-edge XANES spectra for both models and make comparison of these spectra with experiment.

  20. Solid state synthesis of layered sodium manganese oxide for sodium-ion battery by in-situ high energy X-ray diffraction and X-ray absorption near edge spectroscopy

    NASA Astrophysics Data System (ADS)

    Ma, Tianyuan; Xu, Gui-Liang; Zeng, Xiaoqiao; Li, Yan; Ren, Yang; Sun, Chengjun; Heald, Steve M.; Jorne, Jacob; Amine, Khalil; Chen, Zonghai

    2017-02-01

    In situ high energy X-ray diffraction (HEXRD) and in situ X-ray absorption near edge spectroscopy (XANES) were carried out to understand the solid state synthesis of NaxMnO2, with particular interest on the synthesis of P2 type Na2/3MnO2. It was found that there were multi intermediate phases formed before NaMnO2 appeared at about 600 °C. And the final product after cooling process is a combination of O‧3 NaMnO2 with P2 Na2/3MnO2. A P2 type Na2/3MnO2 was synthesized at reduced temperature (600 °C). The influence of Na2CO3 impurity on the electrochemical performance of P2 Na2/3MnO2 was thoroughly investigated in our work. It was found that the content of Na2CO3 can be reduced by optimizing Na2CO3/MnCO3 ratio during the solid state reaction or other post treatment such as washing with water. We expected our results could provide a good guide for future development of high performance cathode materials for sodium-ion batteries.

  1. [XANES study of lead speciation in duckweed].

    PubMed

    Chu, Bin-Bin; Luo, Li-Qiang; Xu, Tao; Yuan, Jing; Sun, Jian-Ling; Zeng, Yuan; Ma, Yan-Hong; Yi, Shan

    2012-07-01

    Qixiashan lead-zinc mine of Nanjing was one of the largest lead zinc deposits in East China Its exploitation has been over 50 years, and the environmental pollution has also been increasing. The lead concentration in the local environment was high, but lead migration and toxic mechanism has not been clear. Therefore, biogeochemistry research of the lead zinc mine was carried out. Using ICP-MS and Pb-L III edge XANES, lead concentration and speciation were analyzed respectively, and duckweed which can tolerate and enriched heavy metals was found in the pollution area. The results showed that the lead concentration of duckweed was 39.4 mg x kg(-1). XANES analysis and linear combination fit indicated that lead stearate and lead sulfide accounted for 65% and 36.9% respectively in the lead speciation of duckweed, suggesting that the main lead speciation of duckweed was sulfur-containing lead-organic acid.

  2. Determination of the local structure of CsBi4-xPbxTe6 (x = 0, 0.5) by X-ray absorption spectroscopy.

    PubMed

    Wakita, Takanori; Paris, Eugenio; Mizokawa, Takashi; Hacisalihoglu, Muammer Yasin; Terashima, Kensei; Okazaki, Hiroyuki; Proux, Olivier; Kieffer, Isabelle; Lahera, Eric; Del Net, William; Olivi, Luca; Takano, Yoshihiko; Muraoka, Yuji; Yokoya, Takayoshi; Saini, Naurang L

    2016-09-14

    We have studied the local structure and valence electronic unoccupied states of thermoelectric CsBi4Te6 and superconducting CsBi3.5Pb0.5Te6 (Tc ∼ 3 K) by extended X-ray absorption fine structure (EXAFS) and X-ray absorption near edge structure (XANES) measurements. The Bi-L3 edge EXAFS reveals wide Bi-Te distance distribution for both compounds indicating complex atomic arrangements in the studied system. The mean square relative displacements (MSRDs) of the Bi-Te bond distances appear largely increased in Pb substituted system due to larger overall local disorder, however, one of the Bi-Te bonds shows a reduced disorder. On the other hand, the Bi-L3 edge XANES is hardly affected by Pb substitution while the Te-L1 edge XANES reveals increased density of unoccupied Te 5p states. This suggests that the carriers introduced by the Pb substitution in CsBi4-xPbxTe6 preferentially goes on Te sites. Similarly, the Cs-L3 edge XANES also shows small changes due to Pb-substitution and reduced local disorder indicated by the reduced width of the Cs-L3 edge white line. We have also shown that the X-ray photoemission spectroscopy (XPS) measurements on various electronic core levels are in a qualitative agreement with the XANES results. These findings are consistent with carrier doping and a reduced disorder in one direction to be likely factors to drive the thermoelectric CsBi4Te6 into a bulk superconductor by Pb-substitution in CsBi4-xPbxTe6.

  3. Polychrome glass from Etruscan sites: first non-destructive characterization with synchrotron μ-XRF, μ-XANES and XRPD

    NASA Astrophysics Data System (ADS)

    Arletti, R.; Vezzalini, G.; Quartieri, S.; Ferrari, D.; Merlini, M.; Cotte, M.

    2008-07-01

    This work is devoted to the characterization of a suite of very rare, highly decorated and coloured glass vessels and beads from the VII to the IV century BC. The most serious difficulty in developing this study was that any sampling even micro-sampling was absolutely forbidden. As a consequence, the mineralogical and chemical nature of chromophores and opacifiers present in these Iron Age finds were identified by means of the following synchrotron-based, strictly non-destructive, techniques: micro X-ray fluorescence (μ-XRF), Fe K-edge micro X-ray absorption near edge spectroscopy (μ-XANES) and X-ray powder diffraction (XRPD). The μ-XRF mapping evidenced high levels of Pb and Sb in the yellow decorations and the presence of only Sb in the white and light-blue ones. Purple and black glass show high amounts of Mn and Fe, respectively. The XRPD analyses confirmed the presence of lead and calcium antimonates in yellow, turquoise and white decorations. Fe K-edge μ-XANES spectra were collected in different coloured parts of the finds, thus enabling the mapping of the oxidation state of these elements across the samples. In most of the samples iron is present in the reduced form Fe2+ in the bulk glass of the vessels, and in the oxidized form Fe3+ in the decorations, indicating that these glass artefacts were produced in at least two distinct processing steps under different furnace conditions.

  4. Clarifying the chemical state of additives in membranes for polymer electrolyte fuel cells by X-ray absorption fine structure

    NASA Astrophysics Data System (ADS)

    Tanuma, Toshihiro; Itoh, Takanori

    2016-02-01

    Cerium and manganese compounds are used in the membrane for polymer electrolyte fuel cells (PEFCs) as radical scavengers to mitigate chemical degradation of the membrane. The chemical states of cerium and manganese in the membrane were investigated using a fluorescence X-ray absorption fine structure (XAFS) technique. Membrane electrode assemblies (MEAs) were subjected to open circuit voltage (OCV) condition, under which hydroxyl radicals attack the membrane; a shift in absorption energy in X-ray absorption near edge structure (XANES) spectra was compared between Ce- and Mn-containing membranes before and after OCV testing. In the case of the Ce-containing MEA, there was no significant difference in XANES spectra before and after OCV testing, whereas in the case of the Mn-containing MEA, there was an obvious shift in XANES absorption energy after OCV testing, indicating that Mn atoms with higher valence state than 2+ exist in the membrane after OCV testing. This can be attributed to the difference in the rate of reduction; the reaction of Ce4+ with ·OOH is much faster than that of Mn3+ with ·OOH, leaving some of the Mn atoms with higher valence state. It was confirmed that cerium and manganese redox couples reduced the attack from radicals, mitigating membrane degradation.

  5. Electronic structure of Pb1-xBaxZr0.65Ti0.35O3 ferroelectric compounds probed by soft x-ray absorption spectroscopy

    NASA Astrophysics Data System (ADS)

    Mastelaro, V. R.; Neves, P. P.; Michalowicz, A.; Eiras, J. A.

    2007-06-01

    O K and Ti L2,3 x-ray absorption near-edge spectra (XANES) of Pb1-xBaxZr0.65Ti0.35O3 (PBZT) ferroelectric ceramic compounds with x varying from 0.0 to 0.40 were obtained. The XANES spectra at the O K edge were compared with ab initio calculations based on the structures obtained by x-ray diffraction, using the FEFF 8.2 code. The different features observed in the XANES spectra of PBZT samples were quite well reproduced with the calculations, especially for x<=0.20. However, for x>0.20 the ab initio calculations do not match the experimental spectra, indicating that for these Ba concentrations, the structural model deduced from powder x-ray diffraction does not reflect the actual local structure around oxygen atoms. Based on calculations of the local partial electron density of states (DOS), the main features of the O K-edge experimental spectra were assigned primarily to the hybridization between O 2p-Ti 3d, Pb 6p and Ba 5d orbitals. The differences in the ferroelectric character of the end-member x = 0.0 and 0.40 sample compositions has been interpreted as due to the decrease of the hybridization between Pb 6p and O 2p orbitals caused by the substitution of Pb2+ by Ba2+ atoms.

  6. Approximating the near-edge mass absorption coefficients for Ni using an ultra-thin bimetal foil

    SciTech Connect

    Alkire, Randall W.

    2016-11-01

    In an effort to improve the characteristics of a fluorescing metal-foil-based beam position monitor, a new bimetal ultra-thin (0.98/0.67 µm) Ti–Ni foil was introduced to replace an existing single-element ultra-thin 0.5 µm thick Cr foil. During characterization it was determined that absorption measurements on the bimetal foil could be used to fit the Ni mass absorption coefficients accurately in the vicinity of the NiKedge. Comparison with experimental results from the literature demonstrated that the fitting procedure produced coefficients with uncertainties of the order of ±1%. Once determined, these fit coefficients allowed the thickness of an independently mounted 8 µm thick Ni foil to be computed from absorption measurements instead of relying on a tool-based measurement of the foil thickness. Using the 8 µm thick foil, a continuous map of Ni mass absorption coefficients was produced at 1 eV resolution throughout the near-edge region. Lastly, this high-resolution map marks a significant improvement over the existing NIST XCOM or FFAST database mass absorption coefficients, which have estimated errors of 10–20% for the near-edge region.

  7. Approximating the near-edge mass absorption coefficients for Ni using an ultra-thin bimetal foil

    DOE PAGES

    Alkire, Randall W.

    2016-11-01

    In an effort to improve the characteristics of a fluorescing metal-foil-based beam position monitor, a new bimetal ultra-thin (0.98/0.67 µm) Ti–Ni foil was introduced to replace an existing single-element ultra-thin 0.5 µm thick Cr foil. During characterization it was determined that absorption measurements on the bimetal foil could be used to fit the Ni mass absorption coefficients accurately in the vicinity of the NiKedge. Comparison with experimental results from the literature demonstrated that the fitting procedure produced coefficients with uncertainties of the order of ±1%. Once determined, these fit coefficients allowed the thickness of an independently mounted 8 µm thickmore » Ni foil to be computed from absorption measurements instead of relying on a tool-based measurement of the foil thickness. Using the 8 µm thick foil, a continuous map of Ni mass absorption coefficients was produced at 1 eV resolution throughout the near-edge region. Lastly, this high-resolution map marks a significant improvement over the existing NIST XCOM or FFAST database mass absorption coefficients, which have estimated errors of 10–20% for the near-edge region.« less

  8. Electronic structure and local atomic arrangement of transition metal ions in nanoporous iron-substituted nickel phosphates, VSB-1 and VSB-5.

    PubMed

    Kim, Tae Woo; Oh, Eun-Jin; Jhung, Sung Hwa; Chang, Jong-San; Hwang, Seong-Ju

    2010-01-01

    The electronic structure and local atomic arrangement of transition metal ions in nanoporous iron-substituted nickel phosphates VSB-1 and VSB-5 have been investigated using X-ray absorption near-edge structure (XANES) spectroscopy at Fe K- and Ni K-edges. The Fe K-edge XANES study clearly demonstrated that substituted iron ions were stabilized in octahedral nickel sites of nanoporous nickel phosphate lattice. A comparison with several Fe-references revealed that the substituted irons have mixed Fe2+/Fe3+ oxidation state with the average valence of +2.8-3.0. According to the Ni K-edge XANES analysis, the aliovalent substitution of Ni2+ with Fe2+/Fe3+ induced a slight reduction of divalent nickel ions in VSB-5 to meet a charge balance. On the contrary, Fe substitution for the VSB-1 phase did not cause notable decrease in the oxidation state of nickel ions, which would be related either to the accompanying decrease of pentavalent phosphorus cations or to the increase of oxygen anions. In conclusion, the present findings clearly demonstrated that the nanoporous lattice of nickel phosphate can accommodate effectively iron ions in its octahedral nickel sites.

  9. Pressure dependence of the local structure of iridium ditelluride across the structural phase transition

    NASA Astrophysics Data System (ADS)

    Paris, E.; Joseph, B.; Iadecola, A.; Marini, C.; Ishii, H.; Kudo, K.; Pascarelli, S.; Nohara, M.; Mizokawa, T.; Saini, N. L.

    2016-04-01

    The local structure of IrTe2 has been studied by iridium L3-edge x-ray absorption spectroscopy (XAS) measurements as a function of pressure, performed at two temperatures (100 and 295 K) across the structural phase transition at ˜270 K. Extended x-ray absorption fine structure (EXAFS) and x-ray absorption near-edge structure (XANES) spectra show pressure-dependent anomalies, suggesting phase transitions that are characterized by different local atomic displacements. The high-temperature phase of IrTe2 (trigonal at 295 K) reveals a clear anomaly in the Ir-Te correlations at ˜4 GPa, while the low-temperature phase (at 100 K) shows a smaller change at ˜6 GPa, likely to be associated with transitions in lower-symmetry phases. XANES spectra, measuring higher-order atomic correlations, also show nonlinear pressure dependence in the local geometry at the anomalous pressures. These nonlinear changes suggest that IrTe2 goes through lower local symmetry phases with increasing pressure.

  10. Olivine-melt relationships and syneruptive redox variations in the 1959 eruption of Kīlauea Volcano as revealed by XANES

    USGS Publications Warehouse

    Helz, Rosalind L.; Cottrell, Elizabeth; Brounce, Maryjo N.; Kelley, Katherine A.

    2017-01-01

    The 1959 summit eruption of Kīlauea Volcano exhibited high lava fountains of gas-rich, primitive magma, containing olivine + chromian spinel in highly vesicular brown glass. Microprobe analysis of these samples shows that euhedral rims on olivine phenocrysts, in direct contact with glass, vary significantly in forsterite (Fo) content, at constant major-element melt composition, as do unzoned groundmass olivine crystals. Ferric/total iron (Fe+ 3/FeT)ratios for matrix and interstitial glasses, plus olivine-hosted glass inclusions in eight 1959 scoria samples have been determined by micro X-ray absorption near-edge structure spectroscopy (μ-XANES). These data show that much of the variation in Fo content reflects variation in oxidation state of iron in the melt, which varies with sulfur concentration in the glass and (locally) with proximity to scoria edges in contact with air. Data for 24 olivine-melt pairs in the better-equilibrated samples from later in the eruption show KD averaging 0.280 ± 0.03 for the exchange of Fe and Mg between olivine and melt, somewhat displaced from the value of 0.30 ± 0.03 given by Roeder and Emslie (1970). This may reflect the low SiO2 content of the 1959 magmas, which is lower than that in most Kīlauea tholeiites. More broadly, we show the potential of μ-XANES and electron microprobe to revisit and refine the value of KD in natural systems.The observed variations of Fe+ 3/FeT ratios in the glasses reflect two distinct processes. The main process, sulfur degassing, produces steady decrease of the Fe+ 3/FeT ratio. Melt inclusions in olivine are high in sulfur (1060–1500 ppm S), with Fe+ 3/FeT = 0.160–0.175. Matrix glasses are degassed (mostly S < 200 ppm) with generally lower Fe+ 3/FeT(0.114–0.135). Interstitial glasses within clumps of olivine crystals locally show intermediate levels of sulfur and Fe+ 3/FeT ratio. The correlation suggests that (1) the 1959 magma was significantly reduced by sulfur

  11. Olivine-melt relationships and syneruptive redox variations in the 1959 eruption of Kīlauea Volcano as revealed by XANES

    NASA Astrophysics Data System (ADS)

    Helz, R. T.; Cottrell, E.; Brounce, M. N.; Kelley, K. A.

    2017-03-01

    The 1959 summit eruption of Kīlauea Volcano exhibited high lava fountains of gas-rich, primitive magma, containing olivine + chromian spinel in highly vesicular brown glass. Microprobe analysis of these samples shows that euhedral rims on olivine phenocrysts, in direct contact with glass, vary significantly in forsterite (Fo) content, at constant major-element melt composition, as do unzoned groundmass olivine crystals. Ferric/total iron (Fe+ 3/FeT)ratios for matrix and interstitial glasses, plus olivine-hosted glass inclusions in eight 1959 scoria samples have been determined by micro X-ray absorption near-edge structure spectroscopy (μ-XANES). These data show that much of the variation in Fo content reflects variation in oxidation state of iron in the melt, which varies with sulfur concentration in the glass and (locally) with proximity to scoria edges in contact with air. Data for 24 olivine-melt pairs in the better-equilibrated samples from later in the eruption show KD averaging 0.280 ± 0.03 for the exchange of Fe and Mg between olivine and melt, somewhat displaced from the value of 0.30 ± 0.03 given by Roeder and Emslie (1970). This may reflect the low SiO2 content of the 1959 magmas, which is lower than that in most Kīlauea tholeiites. More broadly, we show the potential of μ-XANES and electron microprobe to revisit and refine the value of KD in natural systems. The observed variations of Fe+ 3/FeT ratios in the glasses reflect two distinct processes. The main process, sulfur degassing, produces steady decrease of the Fe+ 3/FeT ratio. Melt inclusions in olivine are high in sulfur (1060-1500 ppm S), with Fe+ 3/FeT = 0.160-0.175. Matrix glasses are degassed (mostly S < 200 ppm) with generally lower Fe+ 3/FeT (0.114-0.135). Interstitial glasses within clumps of olivine crystals locally show intermediate levels of sulfur and Fe+ 3/FeT ratio. The correlation suggests that (1) the 1959 magma was significantly reduced by sulfur degassing during the eruption

  12. Local structural variation with oxygen fugacity in Fe2SiO4+x fayalitic iron silicate melts

    DOE PAGES

    Alderman, O.L.G.; Lazareva, L.; Wilding, M. C.; ...

    2017-01-07

    Here, the structure of molten Fe2SiO4+x has been studied using both high-energy X-ray diffraction and Fe K-edge X-ray absorption near-edge structure (XANES) spectroscopy, combined with aerodynamic levitation and laser beam heating. A wide range of Fe3+ contents were accessed by varying the levitation and atmospheric gas composition. Diffraction measurements were made in the temperature (T) and oxygen partial pressure ranges 1624(21) < T < 2183(94) K (uncertainties in parentheses) and –5.6(3) < ΔFMQ < +2.8(5) log units (relative to the Fayalite-Magnetite-Quartz buffer). Iron K-edge XANES measurements covered the ranges 1557(33) < T < 1994(36) K and –2.1(3) < ΔFMQ XANES spectra varied between 0.15(1) and 0.40(2). While these agree in some cases with semi-empirical models, notable discrepancies are discussed in the context of the redox kinetics and the limitations in both the models and in the calibrations used to derive oxidation state from XANES spectra. XANES pre-edge peak areas imply average Fe–O coordination numbers, nFeO, close to 5 for all Fe3+/ΣFe. Diffraction measurements yielded values of 4.4(2) < nFeO < 4.7(1). There is limited evidence for a linear trend nFeO(x) = 4.46(3) + 0.4(1)x. Asymmetric Fe–O bond length distributions peak at around 1.96 Å and have a shoulder arising from longer interatomic distances. Mean rFeO lie close to 2.06 Å, consistent with nFeO close to 5. These observations suggest that Fe2+ is less efficient at stabilizing tetrahedral Fe3+ compared to large monovalent alkali cations. Comparison of in-situ XANES estimates of Fe3+/ΣFe in the melts to those of the quenched solids obtained from XANES as well as Mössbauer spectroscopy indicate rapid oxidation during cooling, enabled by stirring of the melt by the levitation gas flow. As such, the oxidation state of hot komatiitic and other highly fluid melts may not be

  13. Local structural variation with oxygen fugacity in Fe2SiO4+x fayalitic iron silicate melts

    NASA Astrophysics Data System (ADS)

    Alderman, O. L. G.; Lazareva, L.; Wilding, M. C.; Benmore, C. J.; Heald, S. M.; Johnson, C. E.; Johnson, J. A.; Hah, H.-Y.; Sendelbach, S.; Tamalonis, A.; Skinner, L. B.; Parise, J. B.; Weber, J. K. R.

    2017-04-01

    The structure of molten Fe2SiO4+x has been studied using both high-energy X-ray diffraction and Fe K-edge X-ray absorption near-edge structure (XANES) spectroscopy, combined with aerodynamic levitation and laser beam heating. A wide range of Fe3+ contents were accessed by varying the levitation and atmospheric gas composition. Diffraction measurements were made in the temperature (T) and oxygen partial pressure ranges 1624(21) < T < 2183(94) K (uncertainties in parentheses) and -5.6(3) < ΔFMQ < +2.8(5) log units (relative to the Fayalite-Magnetite-Quartz buffer). Iron K-edge XANES measurements covered the ranges 1557(33) < T < 1994(36) K and -2.1(3) < ΔFMQ < +4.4(3) log units. Fe3+ contents, x = Fe3+/ΣFe, estimated directly from the pre-edge peaks of the XANES spectra varied between 0.15(1) and 0.40(2). While these agree in some cases with semi-empirical models, notable discrepancies are discussed in the context of the redox kinetics and the limitations in both the models and in the calibrations used to derive oxidation state from XANES spectra. XANES pre-edge peak areas imply average Fe-O coordination numbers, nFeO, close to 5 for all Fe3+/ΣFe. Diffraction measurements yielded values of 4.4(2) < nFeO < 4.7(1). There is limited evidence for a linear trend nFeO(x) = 4.46(3) + 0.4(1)x. Asymmetric Fe-O bond length distributions peak at around 1.96 Å and have a shoulder arising from longer interatomic distances. Mean rFeO lie close to 2.06 Å, consistent with nFeO close to 5. These observations suggest that Fe2+ is less efficient at stabilizing tetrahedral Fe3+ compared to large monovalent alkali cations. Comparison of in-situ XANES estimates of Fe3+/ΣFe in the melts to those of the quenched solids obtained from XANES as well as Mössbauer spectroscopy indicate rapid oxidation during cooling, enabled by stirring of the melt by the levitation gas flow. As such, the oxidation state of hot komatiitic and other highly fluid melts may not be retained, even during

  14. Solvation structure of the halides from x-ray absorption spectroscopy

    NASA Astrophysics Data System (ADS)

    Antalek, Matthew; Pace, Elisabetta; Hedman, Britt; Hodgson, Keith O.; Chillemi, Giovanni; Benfatto, Maurizio; Sarangi, Ritimukta; Frank, Patrick

    2016-07-01

    Three-dimensional models for the aqueous solvation structures of chloride, bromide, and iodide are reported. K-edge extended X-ray absorption fine structure (EXAFS) and Minuit X-ray absorption near edge (MXAN) analyses found well-defined single shell solvation spheres for bromide and iodide. However, dissolved chloride proved structurally distinct, with two solvation shells needed to explain its strikingly different X-ray absorption near edge structure (XANES) spectrum. Final solvation models were as follows: iodide, 8 water molecules at 3.60 ± 0.13 Å and bromide, 8 water molecules at 3.40 ± 0.14 Å, while chloride solvation included 7 water molecules at 3.15 ± 0.10 Å, and a second shell of 7 water molecules at 4.14 ± 0.30 Å. Each of the three derived solvation shells is approximately uniformly disposed about the halides, with no global asymmetry. Time-dependent density functional theory calculations simulating the chloride XANES spectra following from alternative solvation spheres revealed surprising sensitivity of the electronic state to 6-, 7-, or 8-coordination, implying a strongly bounded phase space for the correct structure during an MXAN fit. MXAN analysis further showed that the asymmetric solvation predicted from molecular dynamics simulations using halide polarization can play no significant part in bulk solvation. Classical molecular dynamics used to explore chloride solvation found a 7-water solvation shell at 3.12 (-0.04/+0.3) Å, supporting the experimental result. These experiments provide the first fully three-dimensional structures presenting to atomic resolution the aqueous solvation spheres of the larger halide ions.

  15. Influence of carbon content and nitrogen vacancies on the bonding structure and mechanical performance of graphite-like BC{sub x}N thin films

    SciTech Connect

    Caretti, Ignacio; Jimenez, Ignacio

    2012-09-15

    X-ray absorption near edge structure (XANES) was used to investigate two sets of graphite-like BC{sub x}N thin films with similar B:C:N ratios but different amounts of nitrogen vacancies, which become oxygen-filled in the surface-most region. The two sets of samples were grown on Si (100) at room temperature by ion beam assisted deposition using two different ion/atom ratios. Nitrogen vacancy defects were detected in the B1s XANES spectra due to an oxygen decoration mechanism taking place at the film surface, which is correctly described by a core-level shift model. Analysis of the O1s XANES spectra showed two different types of oxygen incorporation in the samples under study. The tribomechanical properties of the BC{sub x}N samples were tested by the pin-on-disk technique, revealing the substantial role played by both the carbon intake in the hexagonal BCN planes and the concentration of nitrogen vacancies generated during the growth.

  16. Solution spectroelectrochemical cell for in situ X-ray absorption fine structure

    SciTech Connect

    Antonio, M.R.; Soderholm, L.; Song, I.

    1995-06-12

    A purpose-built spectroelectrochemical cell for in situ fluorescence XAFS (X-ray Absorption Fine Structure) measurements of bulk solution species during constant-potential electrolysis is described. The cell performance was demonstrated by the collection of europium L{sub 3}-edge XANES (X-ray Absorption Near Edge Structure) throughout the course of electrolysis of an aqueous solution of EuCl{sub 3}{center_dot}6H{sub 2}O in 1 M H{sub 2}SO{sub 4}. The europium L{sub 3}-edge resonances reported here for the Eu{sup III} and Eu{sup II} ions demonstrate that their 2p{sub 3/2} {yields} 5d electronic transition probabilities are not the same.

  17. Structural studies of advanced functional materials by synchrotron-based x-ray absorption spectroscopy: BL5.2 at SLRI, Thailand

    NASA Astrophysics Data System (ADS)

    Kidkhunthod, Pinit

    2017-09-01

    This paper highlights the use of the x-ray absorption spectroscopy (XAS) as a local structural tool unlike x-ray diffraction for selected atoms in advanced functional materials including energy storage materials, dielectric materials and thermoelectric materials. The information concerning the oxidation states and local atomic structure around probing atoms will be revealed using x-ray absorption near edge structure (XANES) and extended x-ray absorption fine structure (EXAFS). The XAS beamline: BL5.2 at the Synchrotron Light Research Institute (SLRI) (public organization), Thailand, and its characteristic including available of measured energy ranges, examples of measured spectra of Mg, S and Ti K-edge XAS are also presented. In addition, in situ XAS set up and experiment carried out at this beamline are also outlined. Invited talk at 5th Thailand International Nanotechnology Conference (Nano Thailand-2016), 27-29 November 2016, Nakhon Ratchasima, Thailand.

  18. Electronic structure of Al-doped ZnO transparent conductive thin films studied by x-ray absorption and emission spectroscopies

    SciTech Connect

    Huang, W. H.; Sun, S. J.; Chiou, J. W.; Chou, H.; Chan, T. S.; Lin, H.-J.; Kumar, Krishna; Guo, J.-H.

    2011-11-15

    This study used O K-, Zn L{sub 3}-, Zn K-, and Al K-edges x-ray absorption near-edge structure (XANES) and O K-edge x-ray emission spectroscopy (XES) measurements to investigate the electronic structure of transparent Al-doped ZnO (AZO) thin film conductors. The samples were prepared on glass substrates at a low temperature near 77 K by using a standard RF sputtering method. High-purity Ne (5N) was used as the sputtering gas. The crystallography of AZO thin films gradually transformed from the ZnO wurtize structure to an amorphous structure during sample deposition, which suggests the suitability to grow on flexible substrates, eliminating the severe degradation due to fragmentation by repeated bending. The O K- and Zn L{sub 3}-edges XANES spectra of AZO thin films revealed a decrease in the number of both O 2p and Zn 3d unoccupied states when the pressure of Ne was increased from 5 to 100 mTorr. In contrast, Al K-edges XANES spectra showed that the number of unoccupied states of Al 3p increased in conjunction with the pressure of Ne, indicating an electron transfer from Al to O atoms, and suggesting that Al doping increases the negative effective charge of oxygen ions. XES and XANES spectra of O 2p states at the O K-edge also revealed that Al doping not only raised the conduction-band-minimum, but also increased the valence-band-maximum and the band-gap. The results indicate that the reduction in conductivity of AZO thin films is due to the generation of ionic characters, the increase in band-gap, and the decrease in density of unoccupied states of oxygen.

  19. Coordination structure of adsorbed Zn(II) at Water-TiO2 interfaces

    SciTech Connect

    He, G.; Pan, G.; Zhang, M.; Waychunas, G.A.

    2011-01-15

    The local structure of aqueous metal ions on solid surfaces is central to understanding many chemical and biological processes in soil and aquatic environments. Here, the local coordination structure of hydrated Zn(II) at water-TiO{sub 2} interfaces was identified by extended X-ray absorption fine structure (EXAFS) and X-ray absorption near-edge structure (XANES) spectroscopy combined with density functional theory (DFT) calculations. A nonintegral coordination number of average {approx}4.5 O atoms around a central Zn atom was obtained by EXAFS analysis. DFT calculations indicated that this coordination structure was consistent with the mixture of 4-coordinated bidentate binuclear (BB) and 5-coordinated bidentate mononuclear (BM) metastable equilibrium adsorption (MEA) states. The BB complex has 4-coordinated Zn, while the monodentate mononuclear (MM) complex has 6-coordinated Zn, and a 5-coordinated adsorbed Zn was found in the BM adsorption mode. DFT calculated energies showed that the lower-coordinated BB and BM modes were thermodynamically more favorable than the higher-coordinated MM MEA state. The experimentally observed XANES fingerprinting provided additional direct spectral evidence of 4- and 5-coordinated Zn-O modes. The overall spectral and computational evidence indicated that Zn(II) can occur in 4-, 5-, and 6-oxygen coordinated sites in different MEA states due to steric hindrance effects, and the coexistence of different MEA states formed the multiple coordination environments.

  20. Predictions of the near edge transport shortfall in DIII-D L-mode plasmas using the trapped gyro-Landau-fluid model

    SciTech Connect

    Kinsey, J. E.; Staebler, G. M.; Candy, J.; Petty, C. C.; Waltz, R. E.; Rhodes, T. L.

    2015-01-15

    Previous studies of DIII-D L-mode plasmas have shown that a transport shortfall exists in that our current models of turbulent transport can significantly underestimate the energy transport in the near edge region. In this paper, the Trapped Gyro-Landau-Fluid (TGLF) drift wave transport model is used to simulate the near edge transport in a DIII-D L-mode experiment designed to explore the impact of varying the safety factor on the shortfall. We find that the shortfall systematically increases with increasing safety factor and is more pronounced for the electrons than for the ions. Within the shortfall dataset, a single high current case has been found where no transport shortfall is predicted. Reduced neutral beam injection power has been identified as the key parameter separating this discharge from other discharges exhibiting a shortfall. Further analysis shows that the energy transport in the L-mode near edge region is not stiff according to TGLF. Unlike the H-mode core region, the predicted temperature profiles are relatively more responsive to changes in auxiliary heating power. In testing the fidelity of TGLF for the near edge region, we find that a recalibration of the collision model is warranted. A recalibration improves agreement between TGLF and nonlinear gyrokinetic simulations performed using the GYRO code with electron-ion collisions. The recalibration only slightly impacts the predicted shortfall.

  1. HgL(3) XANES Study of Mercury Methylation in Shredded Eichhornia Crassipes

    SciTech Connect

    Rajan, M.; Darrow, J.; Hua, M.; Barnett, B.; Mendoza, M.; Greenfield, B.K.; Andrews, J.C.

    2009-05-21

    Eichhornia crassipes (water hyacinth) is a non-native plant found in abundance in the Sacramento-San Joaquin River Delta (hereafter called Delta). This species has become a problem, clogging waterways and wetlands. Water hyacinth are also known to accumulate mercury. Recent attempts to curb its proliferation have included shredding with specialized boats. The purpose of this research is to better understand the ability of water hyacinth to phytoremediate mercury and to determine the effect of shredding and anoxic conditions on mercury speciation in plant tissue. In the field assessment, total mercury levels in sediment from the Dow Wetlands in the Delta were found to be 0.273 {+-} 0.070 ppm Hg, and levels in hyacinth roots and shoots from this site were 1.17 {+-} 0.08 ppm and 1.03 {+-} 0.52 ppm, respectively, indicating bioaccumulation of mercury. Plant samples collected at this site were also grown in nutrient solution with 1 ppm HgCl{sub 2} under (1) aerobic conditions, (2) anaerobic conditions, and (3) with shredded plant material only. The greatest accumulation was found in the roots of whole plants. Plants grown in these conditions were also analyzed at Stanford Synchrotron Radiation Laboratory using Hg L{sub 3} X-ray Absorption Near Edge Spectroscopy (XANES), a method to examine speciation that is element-specific and noninvasive. Least-squares fitting of the XANES data to methylated and inorganic mercury(II) model compounds revealed that in plants grown live and aerobically, 5 {+-} 3% of the mercury was in the form of methylmercury, in a form similar to methylmercury cysteine. This percentage increased to 16 {+-} 4% in live plants grown anaerobically and to 22 {+-} 6% in shredded anaerobic plants. We conclude that shredding of the hyacinth plants and, in fact, subjection of plants to anaerobic conditions (e.g., as in normal decay, or in crowded growth conditions) increases mercury methylation. Mechanical removal of the entire plant is significantly more

  2. Hg L3 XANES study of mercury methylation in shredded Eichhornia crassipes.

    PubMed

    Rajan, Michael; Darrow, Jeannine; Hua, Michael; Barnett, Brandy; Mendoza, Miguel; Greenfield, Ben K; Andrews, Joy C

    2008-08-01

    Eichhornia crassipes (water hyacinth) is a non-native plant found in abundance in the Sacramento-San Joaquin River Delta (hereafter called Delta). This species has become a problem, clogging waterways and wetlands. Water hyacinth are also known to accumulate mercury. Recent attempts to curb its proliferation have included shredding with specialized boats. The purpose of this research is to better understand the ability of water hyacinth to phytoremediate mercury and to determine the effect of shredding and anoxic conditions on mercury speciation in plant tissue. In the field assessment, total mercury levels in sediment from the Dow Wetlands in the Delta were found to be 0.273 +/- 0.070 ppm Hg, and levels in hyacinth roots and shoots from this site were 1.17 +/- 0.08 ppm and 1.03 +/- 0.52 ppm, respectively, indicating bioaccumulation of mercury. Plant samples collected at this site were also grown in nutrient solution with 1 ppm HgCl2 under (1) aerobic conditions, (2) anaerobic conditions, and (3)with shredded plant material only. The greatest accumulation was found in the roots of whole plants. Plants grown in these conditions were also analyzed at Stanford Synchrotron Radiation Laboratory using Hg L3 X-ray Absorption Near Edge Spectroscopy (XANES), a method to examine speciation that is element-specific and noninvasive. Least-squares fitting of the XANES data to methylated and inorganic mercury(II) model compounds revealed that in plants grown live and aerobically, 5 +/- 3% of the mercury was in the form of methylmercury, in a form similar to methylmercury cysteine. This percentage increased to 16 +/- 4% in live plants grown anaerobically and to 22 +/- 6% in shredded anaerobic plants. We conclude that shredding of the hyacinth plants and, in fact, subjection of plants to anaerobic conditions (e.g., as in normal decay, or in crowded growth conditions) increases mercury methylation. Mechanical removal of the entire plant is significantly more expensive than

  3. Structure and phase formation behavior and dielectric and magnetic properties of lead iron tantalate-lead zirconate titanate multiferroic ceramics

    SciTech Connect

    Wongmaneerung, R.; Tipakontitikul, R.; Jantaratana, P.; Bootchanont, A.; Jutimoosik, J.; Yimnirun, R.; Ananta, S.

    2016-03-15

    Highlights: • The multiferroic ceramics consisted of PFT and PZT. • Crystal structure changed from cubic to mixedcubic and tetragonal with increasing PZT content. • Dielectric showed the samples underwent a typical relaxor ferroelectric behavior. • Magnetic properties showed very interesting behavior with square saturated magnetic hysteresis loops. - Abstract: Multiferroic (1 − x)Pb(Fe{sub 0.5}Ta{sub 0.5})O{sub 3}–xPb(Zr{sub 0.53}Ti{sub 0.47})O{sub 3} (or PFT–PZT) ceramics were synthesized by solid-state reaction method. The crystal structure and phase formation of the ceramics were examined by X-ray diffraction (XRD). The local structure surrounding Fe and Ti absorbing atoms was investigated by synchrotron X-ray Absorption Near-Edge Structure (XANES) measurement. Dielectric properties were studied as a function of frequency and temperature using a LCR meter. A vibrating sample magnetometer (VSM) was used to determine the magnetic hysteresis loops. XRD study indicated that the crystal structure of the sample changed from pure cubic to mixed cubic and tetragonal with increasing PZT content. XANES measurements showed that the local structure surrounding Fe and Ti ions was similar. Dielectric study showed that the samples underwent a typical relaxor ferroelectric behavior while the magnetic properties showed very interesting behavior with square saturated magnetic hysteresis loops.

  4. Probing Covalency in the UO3 Polymorphs by U M4 edge HR- XANES

    NASA Astrophysics Data System (ADS)

    Podkovyrina, Y.; Pidchenko, I.; Prüßmann, T.; Bahl, S.; Göttlicher, J.; Soldatov, A.; Vitova, T.

    2016-05-01

    Local atomic and electronic structure investigations of uranium trioxide (UO3) crystalline phases performed by the U M4 edge HR-XANES technique is presented. The experimental U M4 edge HR-XANES spectra of α-UO3, β-UO3 and γ-UO3 polymorphic phases are compared with spectra of uranate (CaU2O7) and uranyl (UO3•1-2(H2O)) compounds. We describe a finger print approach valuable for characterization of variations of U-O axial bond lengths. Theoretical calculations of spectra using full-multiple-scattering theory (FEFF9.6 code) are performed. We have tested and selected input parameters, which provide best agreement between experimental and calculated spectra.

  5. Local structure in magnetostrictive melt-spun Fe80Ga20 alloys

    NASA Astrophysics Data System (ADS)

    Pascarelli, S.; Ruffoni, M. P.; Sato Turtelli, R.; Kubel, F.; Grössinger, R.

    2008-05-01

    We perform a detailed investigation of the local atomic structure in highly magnetostrictive α-FeGa melt-spun ribbons. By using extended x-ray absorption fine structure (EXAFS) analysis at the Fe and GaK edges coupled to x-ray diffraction (XRD) and to ab initio full multiple scattering calculations of the x-ray absorption near edge structure (XANES), we test for the presence of different local defect structures proposed in literature as being responsible for the large magnetostriction in these alloys. XRD shows that the ribbons crystallize in the A2 phase. Invisible by XRD, the presence of small Ga clusters is excluded by both EXAFS and XANES since no first shell Ga-Ga bonds are detected. However, EXAFS analysis of the second coordination shell around Ga clearly provides evidence for the presence of one highly strained (+4%) Ga-Ga pair and five Ga-Fe pairs, among the six crystallographically equivalent ⟨001⟩ atomic pairs. This conclusion supports recent total energy calculations that assign the large magnetostriction in these alloys to the strain caused by the rotation of the magnetization in the vicinity of such defects.

  6. Magnetite biomineralization in Magnetospirillum gryphiswaldense: time-resolved magnetic and structural studies.

    PubMed

    Fdez-Gubieda, M Luisa; Muela, Alicia; Alonso, Javier; García-Prieto, Ana; Olivi, Luca; Fernández-Pacheco, Rodrigo; Barandiarán, José Manuel

    2013-04-23

    Magnetotactic bacteria biosynthesize magnetite nanoparticles of high structural and chemical purity that allow them to orientate in the geomagnetic field. In this work we have followed the process of biomineralization of these magnetite nanoparticles. We have performed a time-resolved study on magnetotactic bacteria Magnetospirillum gryphiswaldense strain MSR-1. From the combination of magnetic and structural studies by means of Fe K-edge X-ray absorption near edge structure (XANES) and high-resolution transmission electron microscopy we have identified and quantified two phases of Fe (ferrihydrite and magnetite) involved in the biomineralization process, confirming the role of ferrihydrite as the source of Fe ions for magnetite biomineralization in M. gryphiswaldense. We have distinguished two steps in the biomineralization process: the first, in which Fe is accumulated in the form of ferrihydrite, and the second, in which the magnetite is rapidly biomineralized from ferrihydrite. Finally, the XANES analysis suggests that the origin of the ferrihydrite could be at bacterial ferritin cores, characterized by a poorly crystalline structure and high phosphorus content.

  7. A Structural Investigation of Hydrous and Anhydrous Rare-Earth Phosphates.

    PubMed

    Rafiuddin, Mohamed Ruwaid; Grosvenor, Andrew P

    2016-10-03

    Rhabdophane- (REPO4·nH2O; RE = La to Dy), monazite- (REPO4; RE = La to Gd), and xenotime-type (REPO4 and RE'PO4·nH2O; RE = Tb to Lu and Y; RE' = Ho to Lu and Y) rare-earth phosphate materials are being considered for a number of applications including as photonic materials, for biolabeling studies, and as potential nuclear wasteforms. Structural studies of hydrous rare-earth phosphates are rather limited when compared to anhydrous rare-earth phosphates. In this study, rhabdophane- (REPO4·nH2O; RE = La, Nd, Sm, Gd, and Dy) and xenotime-type (REPO4·nH2O; RE = Y and Yb) materials were synthesized by a precipitation-based method and investigated using X-ray diffraction (XRD) and X-ray absorption near-edge spectroscopy (XANES). Examination of the powder XRD data from rhabdophane-type materials has confirmed that the rhabdophane structure crystallizes in the monoclinic crystal system rather than the hexagonal structure that has most often been reported. Materials adopting the rhabdophane- or xenotime-type structure were studied as a function of temperature to understand how the structure varies with increasing annealing temperature. Local structural information was obtained by collecting P K- and RE L1-edge XANES spectra. Examination of P K-edge XANES spectra from rhabdophane- and xenotime-type materials revealed changes in the local environment around P as a function of temperature. These changes were attributed to the removal of water from these structures as a result of high temperature annealing.

  8. Changes in local surface structure and Sr depletion in Fe-implanted SrTiO3 (001)

    NASA Astrophysics Data System (ADS)

    Lobacheva, O.; Yiu, Y. M.; Chen, N.; Sham, T. K.; Goncharova, L. V.

    2017-01-01

    Local surface structure of single crystal strontium titanate SrTiO3 (001) samples implanted with Fe in the range of concentrations between 2 × 1014 to 2 × 1016 Fe/cm2 at 30 keV has been investigated. In order to facilitate Fe substitution (doping), implanted samples were annealed in oxygen at 350 °C. Sr depletion was observed from the near-surface layers impacted by the ion-implantation process, as revealed by Rutherford Backscattering Spectrometry (RBS), X-ray photoelectron spectroscopy (XPS), X-ray Absorption Near Edge Spectroscopy (XANES), and Atomic Force Microscopy (AFM). Hydrocarbon contaminations on the surface may contribute to the mechanisms of Sr depletion, which have important implications for Sr(Ti1-xFex)O3-δ materials in gas sensing applications.

  9. Size- and support-dependent evolution of the oxidation state and structure by oxidation of subnanometer cobalt clusters.

    PubMed

    Yin, Chunrong; Zheng, Fan; Lee, Sungsik; Guo, Jinghua; Wang, Wei-Cheng; Kwon, Gihan; Vajda, Viktor; Wang, Hsien-Hau; Lee, Byeongdu; DeBartolo, Janae; Seifert, Sönke; Winans, Randall E; Vajda, Stefan

    2014-09-18

    Size-selected subnanometer cobalt clusters with 4, 7, and 27 cobalt atoms supported on amorphous alumina and ultrananocrystalline diamond (UNCD) surfaces were oxidized after exposure to ambient air. Grazing incidence X-ray absorption near-edge spectroscopy (GIXANES) and near-edge X-ray absorption fine structure (NEXAFS) were used to characterize the clusters revealed a strong dependency of the oxidation state and structure of the clusters on the surface. A dominant Co(2+) phase was identified in all samples. However, XANES analysis of cobalt clusters on UNCD showed that ∼10% fraction of a Co(0) phase was identified for all three cluster sizes and about 30 and 12% fraction of a Co(3+) phase in 4, 7, and 27 atom clusters, respectively. In the alumina-supported clusters, the dominating Co(2+) component was attributed to a cobalt aluminate, indicative of a very strong binding to the support. NEXAFS showed that in addition to strong binding of the clusters to alumina, their structure to a great extent follows the tetrahedral morphology of the support. All supported clusters were found to be resistant to agglomeration when exposed to reactive gases at elevated temperatures and atmospheric pressure.

  10. Size- and Support-Dependent Evolution of the Oxidation State and Structure by Oxidation of Subnanometer Cobalt Clusters

    SciTech Connect

    Yin, Chunrong; Zheng, Fan; Lee, Sungsik; Guo, Jinghua; Wang, Wei-Cheng; Kwon, Gihan; Vajda, Viktor; Wang, Hsien-Hau; Lee, Byeongdu; DeBartolo, Janae; Seifert, Sönke; Winans, Randall E.; Vajda, Stefan

    2014-09-18

    Size-selected subnanometer cobalt clusters with 4, 7 and 27 cobalt atoms supported on amorphous alumina and ultrananocrystalline diamond (UNCD) surfaces were oxidized after exposure to ambient air. Grazing incidence X-ray absorption near edge spectroscopy (GIXANES) and near edge X-ray absorption fine structure (NEXAFS) used to characterize the clusters revealed a strong dependency of the oxidation state and structure of the clusters on the surface. A dominant Co2+ phase was identified in all samples. However, form XANES analysis, on UNCD about 10% fraction of Co0 phase was identified for all three cluster sizes and about 30% and 12% fraction of Co3+ phase in 4, 7 and 27 atoms, respectively. In the alumina-supported clusters, the dominating Co2+ component was attributed to cobalt aluminate, indicative of a very strong binding to the support. NEXAFS showed that in addition to strong binding of the clusters to alumina, their structure in great extent follows the tetrahedral morphology of the support. The supported clusters of all three sizes were found resistant to agglomeration when exposed to reactive gases at elevated temperatures and atmospheric pressure.

  11. Copper blue in an ancient glass bead: a XANES study

    NASA Astrophysics Data System (ADS)

    Veiga, J. P.; Figueiredo, M. O.

    2006-06-01

    The blue colour in ancient soda-lime glasses has been attributed to the presence of copper and/or cobalt but the origin of different shades is not yet fully interpreted. As a contribution to this question, a non-destructive X-ray absorption study at [ Cu]K-edge was undertaken on the blue (turquoise) layer from a “Nueva Cadiz” type tubular glass bead dated pre-XVII century where copper is the unique colouring agent. Minerals configuring two distinct blue tonalities due to Cu (2+) in similar square coordination were selected as basic model compounds: azurite, which is a classical navy-blue pigment used in ancient wall paintings over plaster, and chalcanthite, displaying exactly the same turquoise-blue tonality of tubular glass beads manufactured since the Egyptian Antiquity. Theoretical modelling of the XAFS spectra was undertaken using the FEFF code. The IFEFFIT software package was used for fitting the calculated spectra to experimental data. EXAFS results are discussed in view of the crystal structures of copper minerals chosen to model the speciation state and structural situation of that element prevailing in the turquoise-blue archaeological glass. Special attention is focused on the difficulties in theoretical modelling [ Cu]K-XANES spectra of ancient glasses with different colourings.

  12. Anomalous structural behavior in the metamagnetic transition of FeRh thin films from a local viewpoint

    NASA Astrophysics Data System (ADS)

    Wakisaka, Yuki; Uemura, Yohei; Yokoyama, Toshihiko; Asakura, Hiroyuki; Morimoto, Hiroyuki; Tabuchi, Masao; Ohshima, Daiki; Kato, Takeshi; Iwata, Satoshi

    2015-11-01

    The metamagnetic transition in FeRh thin films has been investigated via temperature-dependent x-ray-absorption fine-structure spectroscopy in order to gain correlations between magnetization and local electronic and geometric structures. According to the Fe and Rh K -edge x-ray-absorption near-edge structure (XANES), strong hybridization between Fe and Rh was revealed to exist. This Fe-Rh hybridization was observed to decrease during the phase transition from the antiferromagnetic (AFM) to ferromagnetic (FM) phases from the systematic change in the Fe K -edge XANES. In addition, only the Debye-Waller factor of the Fe-Fe pair in the AFM phase was observed to be considerably enhanced when compared with that in the FM phase, which was ascribed to local structural fluctuation inherent in the AFM phase. By considering the different features of the exchange interactions in Fe-Rh and Fe-Fe, this anomalous behavior is interpreted as being consistent with the recent theoretical study proposing the local fluctuations of spin and structure. Therefore, we consider that the local spin and Fe-Fe distance fluctuations play an important role in driving the metamagnetic transition, whereas the Fe-Rh hybridization correlates with the static stability of each magnetic phase.

  13. The effect of nitrogen incorporation on the bonding structure of hydrogenated carbon nitride films

    SciTech Connect

    Camero, M.; Buijnsters, J. G.; Gomez-Aleixandre, C.; Gago, R.; Caretti, I.; Jimenez, I.

    2007-03-15

    This work describes the composition and bonding structure of hydrogenated carbon nitride (a-CN{sub x}:H) films synthesized by electron cyclotron resonance chemical vapor deposition using as precursor gases argon, methane, and nitrogen. The composition of the films was derived from Rutherford backscattering and elastic recoil detection analysis and the bonding structure was examined by infrared (IR) spectroscopy and x-ray absorption near edge spectroscopy (XANES). By varying the nitrogen to methane ratio in the applied gas mixture, polymeric a-CN{sub x}:H films with N/C contents varying from 0.06 to 0.49 were obtained. Remarkably, the H content of the films ({approx}40 at. %) was rather unaffected by the nitrogenation process. The different bonding states as detected in the measured XANES C(1s) and N(1s) spectra have been correlated with those of a large number of reference samples. The XANES and IR spectroscopy results indicate that N atoms are efficiently incorporated into the amorphous carbon network and can be found in different bonding environments, such as pyridinelike, graphitelike, nitrilelike, and amino groups. The nitrogenation of the films results in the formation of N-H bonding environments at the cost of C-H structures. Also, the insertion of N induces a higher fraction of double bonds in the structure at the expense of the linear polymerlike chains, hence resulting in a more cross-linked solid. The formation of double bonds takes place through complex C=N structures and not by formation of graphitic aromatic rings. Also, the mechanical and tribological properties (hardness, friction, and wear) of the films have been studied as a function of the nitrogen content. Despite the major modifications in the bonding structure with nitrogen uptake, no significant changes in these properties are observed.

  14. Electronic structure and conductivity of nanocomposite metal (Au,Ag,Cu,Mo)-containing amorphous carbon films

    SciTech Connect

    Endrino, Jose L.; Horwat, David; Gago, Raul; Andersson, Joakim; Liu, Y.S.; Guo, Jinghua; Anders, Andre

    2008-05-14

    In this work, we study the influence of the incorporation of different metals (Me = Au, Ag, Cu, Mo) on the electronic structure of amorphous carbon (a-C:Me) films. The films were produced at room temperature using a novel pulsed dual-cathode arc deposition technique. Compositional analysis was performed with secondary neutral mass spectroscopy whereas X-ray diffraction was used to identify the formation of metal nanoclusters in the carbon matrix. The metal content incorporated in the nanocomposite films induces a drastic increase in the conductivity, in parallel with a decrease in the band gap corrected from Urbach energy. The electronic structure as a function of the Me content has been monitored by x-ray absorption near edge structure (XANES) at the C K-edge. XANES showed that the C host matrix has a dominant graphitic character and that it is not affected significantly by the incorporation of metal impurities, except for the case of Mo, where the modifications in the lineshape spectra indicated the formation of a carbide phase. Subtle modifications of the spectral lineshape are discussed in terms of nanocomposite formation.

  15. Influence of substituents on the N K X-ray absorption near-edge structure of pyrrole derivatives

    NASA Astrophysics Data System (ADS)

    Hennig, C.; Hallmeier, K. H.; Bach, A.; Bender, S.; Franke, R.; Hormes, J.; Szargan, R.

    1996-08-01

    The X-ray absorption and electron yield spectra of monomeric pyrrole including derivatives with different substituents, thiazole and oxazole have been investigated. Inductive and mesomeric effects on the spectral features are discussed. Inductive effects create energy shifts of the π ∗ resonances: mesomeric effects cause a splitting and energy shifts of the π ∗ resonances.

  16. X-ray absorption near-edge structure study on positive electrodes of degraded lithium-ion battery

    NASA Astrophysics Data System (ADS)

    Shikano, Masahiro; Kobayashi, Hironori; Koike, Shinji; Sakaebe, Hikari; Saito, Yoshiyasu; Hori, Hironobu; Kageyama, Hiroyuki; Tatsumi, Kuniaki

    18650-type cylindrical cells using LiNi 1/3Mn 1/3Co 1/3O 2 (NMC) and hard carbon as positive and negative electrode material, respectively, were fabricated and degraded by cycle tests. The capacity of the cells remained more than 95% and 85% after cycle tests at 25 and 50 °C, respectively. After the cycle tests, Li-deficient cubic phase was observed on the surface of NMC. This phenomenon should be related to the degradation mechanism of this type of cell.

  17. Air annealing effects on lattice structure, charge state distribution of cations, and room temperature ferrimagnetism in the ferrite composition Co2.25Fe0.75O4

    NASA Astrophysics Data System (ADS)

    Ranjan Panda, Manas; Bhowmik, R. N.; Singh, Harishchandra; Singh, M. N.; Sinha, A. K.

    2015-03-01

    The ferrite composition Co2.25Fe0.75O4 has been prepared by chemical coprecipitation route. The as-prepared material has been annealed at different temperatures to investigate thermal activated changes in structural phase, charge states of cations, and room temperature magnetic properties. Synchrotron x-ray diffraction (SXRD) patterns have shown splitting of cubic spinel structure into Fe-rich and Co-rich phases for annealing temperature up to 800 °C. Single phase cubic spinel structure has been stabilized at annealing temperature 900 °C. The existence of Fe4+ ions, as confirmed from x-ray absorption near edge structure spectroscopy (XANES), is the new information for spinel ferrite. Raman spectra indicated normal spinel structure. The results of SXRD, XANES and Raman spectra have been used to estimate distribution of Co and Fe ions in spinel structure. The variation in population of Co and Fe ions and phase instability has affected the magnetic properties. The sample annealed at 800 °C shows maximum coercivity (∼567 Oe) and squareness (∼0.38), whereas the single-phased sample showed lowest values of ferrimagnetic parameters. The tuning of magnetic parameters by thermal activated structural phase variation of a hetero-structured magnetic system appears to be a new technique for the development of magnetic materials.

  18. Distribution of trace element in Japanese red coral Paracorallium japonicum by μ-XRF and sulfur speciation by XANES: Linkage between trace element distribution and growth ring formation

    NASA Astrophysics Data System (ADS)

    Trong Nguyen, Luan; Rahman, Mohammad Azizur; Maki, Teruya; Tamenori, Yusuke; Yoshimura, Toshihiro; Suzuki, Atsushi; Iwasaki, Nozomu; Hasegawa, Hiroshi

    2014-02-01

    This study investigated the distribution of magnesium (Mg), phosphorus (P), sulfur (S) and strontium (Sr) using micro X-ray fluorescence (μ-XRF), and the speciation of S using X-ray absorption near edge spectroscopy (XANES) along the annual growth rings in the skeleton of Japanese red coral Paracorallium japonicum. The Mg, P and S distribution in μ-XRF mapping images correspond to the dark and light bands along the annual growth rings in microscopic images of the coral skeleton. The μ-XRF mapping data showed a positive correlation (r = 0.6) between P and S distribution in the coral skeleton. A contrasting distribution pattern of S and Mg along the axial skeleton of P. japonicum indicates a weak negative correlation (r = -0.2) between these two elements. The distribution pattern of S, P and Mg in the axial skeleton of P. japonicum reveals linkage between the trace element distribution and the formation of dark/light bands along the annual growth rings. Sulfur and P were distributed in the organic matrix rich dark bands, while Mg was distributed in the light bands of the annual growth rings. XANES analysis showed that inorganic sulfate is the major species of S in the skeleton of P. japonicum with a ratio of 1:20 for organic and inorganic sulfate.

  19. The effect of site geometry, Ti content and Ti oxidation state on the Ti K-edge XANES spectrum of synthetic hibonite

    NASA Astrophysics Data System (ADS)

    Doyle, P. M.; Berry, A. J.; Schofield, P. F.; Mosselmans, J. F. W.

    2016-08-01

    The Al-rich oxide hibonite (CaAl12O19) is modeled to be the second mineral to condense from a gas of solar composition and is found within calcium-aluminum-rich inclusions and the matrix of chondritic meteorites. Both Ti3+ and Ti4+ are reported in meteoritic hibonite, so hibonite has been proposed as a single mineral oxybarometer that could be used to elucidate conditions within the first 0.2 Myrs of the Solar System. Synthetic hibonites with Ti3+/(Ti3+ + Ti4+) (hereafter Ti3+/ΣTi) ranging between 0 and 1 were prepared as matrix-matched standards for meteoritic hibonite. The largest yield of both Ti-free and Ti-bearing hibonite at ∼1300 and ∼1400 °C was obtained by a single sinter under reducing conditions. In situ micro-beam Ti K-edge X-ray absorption near edge structure (XANES) spectra were recorded from the synthetic hibonites, as well as from terrestrial hibonite. Spectral features in the post-crest region were shown to correlate with the Ti4+ content. Furthermore, Ti4+ on the M2 trigonal bipyramidal and the adjoining M4 octahedral sites appears to cause variability in the post-crest region as a function of orientation. For this suite of synthetic hibonites it was observed that the pre-edge peak region is not influenced by orientation, but is controlled by Ti3+/ΣTi, site geometry and/or Ti concentration. In particular, the pre-edge peak intensities reflect Ti coordination environment and distortion of the M4 octahedral site. Therefore, although pre-edge peak intensities have previously been used to determine Ti3+/ΣTi in meteoritic minerals, we excluded use of the pre-edge peak intensities for quantifying Ti valence states in hibonite. The energy of the absorption edge at a normalized intensity of 0.8 (E0.8) and the energy of the minimum between the pre-edge region and the absorption edge (Em1) were found to vary systematically with Ti3+/ΣTi. Ti3+/ΣTi in hibonite as a function of Em1 was modeled by a quadratic function that may be used to quantify Ti3

  20. Electronic and atomic structures of the Sr3Ir4Sn13 single crystal: A possible charge density wave material

    PubMed Central

    Wang, H.-T.; Srivastava, M. K.; Wu, C.-C.; Hsieh, S.-H.; Wang, Y.-F.; Shao, Y.-C.; Liang, Y.-H.; Du, C.-H.; Chiou, J.-W.; Cheng, C.-M.; Chen, J.-L.; Pao, C.-W.; Lee, J.-F.; Kuo, C. N.; Lue, C. S.; Wu, M.-K.; Pong, W.-F.

    2017-01-01

    X-ray scattering (XRS), x-ray absorption near-edge structure (XANES) and extended x-ray absorption fine structure (EXAFS) spectroscopic techniques were used to study the electronic and atomic structures of the high-quality Sr3Ir4Sn13 (SIS) single crystal below and above the transition temperature (T* ≈ 147 K). The evolution of a series of modulated satellite peaks below the transition temperature in the XRS experiment indicated the formation of a possible charge density wave (CDW) in the (110) plane. The EXAFS phase derivative analysis supports the CDW-like formation by revealing different bond distances [Sn1(2)-Sn2] below and above T* in the (110) plane. XANES spectra at the Ir L3-edge and Sn K-edge demonstrated an increase (decrease) in the unoccupied (occupied) density of Ir 5d-derived states and a nearly constant density of Sn 5p-derived states at temperatures T < T* in the (110) plane. These observations clearly suggest that the Ir 5d-derived states are closely related to the anomalous resistivity transition. Accordingly, a close relationship exists between local electronic and atomic structures and the CDW-like phase in the SIS single crystal. PMID:28106144

  1. Electronic and atomic structures of the Sr3Ir4Sn13 single crystal: A possible charge density wave material

    NASA Astrophysics Data System (ADS)

    Wang, H.-T.; Srivastava, M. K.; Wu, C.-C.; Hsieh, S.-H.; Wang, Y.-F.; Shao, Y.-C.; Liang, Y.-H.; Du, C.-H.; Chiou, J.-W.; Cheng, C.-M.; Chen, J.-L.; Pao, C.-W.; Lee, J.-F.; Kuo, C. N.; Lue, C. S.; Wu, M.-K.; Pong, W.-F.

    2017-01-01

    X-ray scattering (XRS), x-ray absorption near-edge structure (XANES) and extended x-ray absorption fine structure (EXAFS) spectroscopic techniques were used to study the electronic and atomic structures of the high-quality Sr3Ir4Sn13 (SIS) single crystal below and above the transition temperature (T* ≈ 147 K). The evolution of a series of modulated satellite peaks below the transition temperature in the XRS experiment indicated the formation of a possible charge density wave (CDW) in the (110) plane. The EXAFS phase derivative analysis supports the CDW-like formation by revealing different bond distances [Sn1(2)-Sn2] below and above T* in the (110) plane. XANES spectra at the Ir L3-edge and Sn K-edge demonstrated an increase (decrease) in the unoccupied (occupied) density of Ir 5d-derived states and a nearly constant density of Sn 5p-derived states at temperatures T < T* in the (110) plane. These observations clearly suggest that the Ir 5d-derived states are closely related to the anomalous resistivity transition. Accordingly, a close relationship exists between local electronic and atomic structures and the CDW-like phase in the SIS single crystal.

  2. Effect of Fe-substitution on the structure and magnetism of single crystals Mn2-xFexBO4

    NASA Astrophysics Data System (ADS)

    Platunov, M. S.; Kazak, N. V.; Knyazev, Yu. V.; Bezmaternykh, L. N.; Moshkina, E. M.; Trigub, A. L.; Veligzhanin, A. A.; Zubavichus, Y. V.; Solovyov, L. A.; Velikanov, D. A.; Ovchinnikov, S. G.

    2017-10-01

    Single crystalline Mn2-xFexBO4 with x = 0.3, 0.5, 0.7 grown by the flux method have been studied by means of X-ray diffraction and X-ray absorption spectroscopy at both Mn and Fe K edges. The compounds were found to crystallize in an orthorhombic warwickite structure (sp. gr. Pnam). The lattice parameters change linearly with x thus obeying the Vegard's law. The Fe3+ substitution for Mn3+ has been deduced from the X-ray absorption near-edge structure (XANES) spectra. Two energy positions of the absorption edges have been observed in Mn K-edge XANES spectra indicating the presence of manganese in two different oxidation states. Extended X-ray absorption fine structure (EXAFS) analysis has shown the reduction of local structural distortions upon Fe substitution. The magnetization data have revealed a spin-glass transition at TSG = 11, 14 and 18 K for x = 0.3, 0.5 and 0.7, respectively.

  3. The local structure and ferromagnetism in Fe-implanted SrTiO3 single crystals

    NASA Astrophysics Data System (ADS)

    Lobacheva, O.; Chavarha, M.; Yiu, Y. M.; Sham, T. K.; Goncharova, L. V.

    2014-07-01

    We report a connection between the local structure of low-level Fe impurities and vacancies as the cause of ferromagnetic behavior observed in strontium titanate single crystals (STO), which were implanted with Fe and Si ions at different doses then annealed in oxygen. The effects of Fe doping and post-implantation annealing of STO were studied by X-ray Absorption Near Edge Structure (XANES) spectroscopy and Superconducting Quantum Interference Device magnetometry. XANES spectra for Fe and Ti K- and L-edge reveal the changes in the local environment of Fe and Ti following the implantation and annealing steps. The annealing in oxygen atmosphere partially healed implantation damages and changed the oxidation state of the implanted iron from metallic Fe0 to Fe2+/Fe3+ oxide. The STO single crystals were weak ferromagnets prior to implantation. The maximum saturation moment was obtained after our highest implantation dose of 2 × 1016 Fe atom/cm2, which could be correlated with the metallic Fe0 phases in addition to the presence of O/Ti vacancies. After recrystallization annealing, the ferromagnetic response disappears. Iron oxide phases with Fe2+ and Fe3+ corresponding to this regime were identified and confirmed by calculations using Real Space Multiple Scattering program (FEFF9).

  4. The structure of graphite oxide: investigation of its surface chemical groups.

    PubMed

    Lee, D W; De Los Santos V, L; Seo, J W; Leon Felix, L; Bustamante D, A; Cole, J M; Barnes, C H W

    2010-05-06

    The structure of graphite oxide (GO) has been systematically studied using various tools such as SEM, TEM, XRD, Fourier transform infrared spectroscopy (FT-IR), X-ray photoemission spectroscopy (XPS), (13)C solid-state NMR, and O K-edge X-ray absorption near edge structure (XANES). The TEM data reveal that GO consists of amorphous and crystalline phases. The XPS data show that some carbon atoms have sp(3) orbitals and others have sp(2) orbitals. The ratio of sp(2) to sp(3) bonded carbon atoms decreases as sample preparation times increase. The (13)C solid-state NMR spectra of GO indicate the existence of -OH and -O- groups for which peaks appear at 60 and 70 ppm, respectively. FT-IR results corroborate these findings. The existence of ketone groups is also implied by FT-IR, which is verified by O K-edge XANES and (13)C solid-state NMR. We propose a new model for GO based on the results; -O-, -OH, and -C=O groups are on the surface.

  5. The local structure and ferromagnetism in Fe-implanted SrTiO₃ single crystals

    SciTech Connect

    Lobacheva, O. Chavarha, M.; Yiu, Y. M.; Sham, T. K.; Goncharova, L. V.

    2014-07-07

    We report a connection between the local structure of low-level Fe impurities and vacancies as the cause of ferromagnetic behavior observed in strontium titanate single crystals (STO), which were implanted with Fe and Si ions at different doses then annealed in oxygen. The effects of Fe doping and post-implantation annealing of STO were studied by X-ray Absorption Near Edge Structure (XANES) spectroscopy and Superconducting Quantum Interference Device magnetometry. XANES spectra for Fe and Ti K- and L-edge reveal the changes in the local environment of Fe and Ti following the implantation and annealing steps. The annealing in oxygen atmosphere partially healed implantation damages and changed the oxidation state of the implanted iron from metallic Fe⁰ to Fe²⁺/Fe³⁺ oxide. The STO single crystals were weak ferromagnets prior to implantation. The maximum saturation moment was obtained after our highest implantation dose of 2×10¹⁶ Fe atom/cm², which could be correlated with the metallic Fe⁰ phases in addition to the presence of O/Ti vacancies. After recrystallization annealing, the ferromagnetic response disappears. Iron oxide phases with Fe²⁺ and Fe³⁺ corresponding to this regime were identified and confirmed by calculations using Real Space Multiple Scattering program (FEFF9).

  6. High-temperature annealing effects on multiwalled carbon nanotubes: electronic structure, field emission and magnetic behaviors.

    PubMed

    Ray, Sekhar Chandra; Pao, Chih-Wen; Tsai, Huang-Ming; Chen, Huang-Chin; Chen, Yu-Shin; Wu, Shang-Lun; Ling, Dah-Chin; Lin, I-Nan; Pong, Way-Faung; Gupta, Sanju; Giorcelli, Mauro; Bianco, Stefano; Musso, Simone; Tagliaferro, Alberto

    2009-12-01

    This work elucidates the effects of high-temperature annealing on the microscopic and electronic structure of multiwalled carbon nanotubes (MWCNTs) using high-resolution transmission electron microscopy, micro-Raman spectroscopy, X-ray diffraction, X-ray absorption near-edge structure (XANES) and valence-band photoemission spectroscopy (VBPES), respectively. The field emission and magnetization behaviors are also presented. The results of annealing are as follows: (1) MWCNTs tend to align in the form of small fringes along their length, promote graphitization and be stable in air, (2) XANES indicates an enhancement in oxygen content on the sample, implying that it can be adopted for sensing and storing oxygen gas, (3) the electron field emission current density (J) is enhanced and the turn-on electric field (E(TOE)) reduced, suggesting potential use in field emission displays and as electron sources in microwave tube amplifiers and (4) as-grown MWCNTs with embedded iron nanoparticles exhibits significantly higher coercivity approximately 750 Oe than its bulk counterpart (Fe(bulk) approximately 0.9 Oe), suggesting its potential use as low-dimensional high-density magnetic recording media.

  7. Relating Electronic and Geometric Structure of Atomic Layer Deposited BaTiO3 to its Electrical Properties

    PubMed Central

    2016-01-01

    Atomic layer deposition allows the fabrication of BaTiO3 (BTO) ultrathin films with tunable dielectric properties, which is a promising material for electronic and optical technology. Industrial applicability necessitates a better understanding of their atomic structure and corresponding properties. Through the use of element-specific X-ray absorption near edge structure (XANES) analysis, O K-edge of BTO as a function of cation composition and underlying substrate (RuO2 and SiO2) is revealed. By employing density functional theory and multiple scattering simulations, we analyze the distortions in BTO’s bonding environment captured by the XANES spectra. The spectral weight shifts to lower energy with increasing Ti content and provides an atomic scale (microscopic) explanation for the increase in leakage current density. Differences in film morphologies in the first few layers near substrate–film interfaces reveal BTO’s homogeneous growth on RuO2 and its distorted growth on SiO2. This work links structural changes to BTO thin-film properties and provides insight necessary for optimizing future BTO and other ternary metal oxide-based thin-film devices. PMID:27009677

  8. Relating electronic and geometric structure of atomic layer deposited BaTiO3 to its electrical properties

    SciTech Connect

    Torgersen, Jan; Acharya, Shinjita; Dadlani, Anup Lal; Petousis, Ioannis; Kim, Yongmin; Trejo, Orlando; Nordlund, Dennis; Prinz, Fritz B.

    2016-03-24

    Atomic layer deposition allows the fabrication of BaTiO3 (BTO) ultrathin films with tunable dielectric properties, which is a promising material for electronic and optical technology. Industrial applicability necessitates a better understanding of their atomic structure and corresponding properties. Through the use of element-specific X-ray absorption near edge structure (XANES) analysis, O K-edge of BTO as a function of cation composition and underlying substrate (RuO2 and SiO2) is revealed. By employing density functional theory and multiple scattering simulations, we analyze the distortions in BTO’s bonding environment captured by the XANES spectra. The spectral weight shifts to lower energy with increasing Ti content and provides an atomic scale (microscopic) explanation for the increase in leakage current density. Differences in film morphologies in the first few layers near substrate–film interfaces reveal BTO’s homogeneous growth on RuO2 and its distorted growth on SiO2. As a result, this work links structural changes to BTO thin-film properties and provides insight necessary for optimizing future BTO and other ternary metal oxide-based thin-film devices.

  9. Probing local structure of co doped polyvinylidene fluoride-ZnO thin films using X-ray absorption spectroscopy

    NASA Astrophysics Data System (ADS)

    Dey, Rajkumar; Yadav, Ashok Kumar; Bhunia, Ritamay; Jha, Shambhu Nath; Bhattacharyya, Dibyendu; Hussain, Shamima; Bhar, Radhaballav; Pal, Arun Kumar

    2017-05-01

    Nanocrystalline ZnO doped with cobalt (CoxZn1 - xO) as a filler was added to polyvinylidene fluoride (PVDF) host matrix to produce a free-standing flexible composite film by sol-gel technique. Three different amounts of cobalt (x = 0.01, 0.04, 0.07) were used in the above synthesis. The as-deposited and the poled composite Co-ZnO/PVDF films were subjected to extensive study by X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy. Detailed information regarding the valence states of the host and the filler ions in the samples was derived from XPS and XANES (X-ray absorption near edge structure) studies. Local structures surrounding the Zn and Co sites were obtained from EXAFS (Extended X-ray absorption fine structure) data analysis. Combined XPS, XANES and EXAFS studies confirm that substitution of Zn sites by Co ions in wurtzite ZnO lattice without forming any significant metallic cluster phase in the samples.

  10. Relating electronic and geometric structure of atomic layer deposited BaTiO3 to its electrical properties

    DOE PAGES

    Torgersen, Jan; Acharya, Shinjita; Dadlani, Anup Lal; ...

    2016-03-24

    Atomic layer deposition allows the fabrication of BaTiO3 (BTO) ultrathin films with tunable dielectric properties, which is a promising material for electronic and optical technology. Industrial applicability necessitates a better understanding of their atomic structure and corresponding properties. Through the use of element-specific X-ray absorption near edge structure (XANES) analysis, O K-edge of BTO as a function of cation composition and underlying substrate (RuO2 and SiO2) is revealed. By employing density functional theory and multiple scattering simulations, we analyze the distortions in BTO’s bonding environment captured by the XANES spectra. The spectral weight shifts to lower energy with increasing Timore » content and provides an atomic scale (microscopic) explanation for the increase in leakage current density. Differences in film morphologies in the first few layers near substrate–film interfaces reveal BTO’s homogeneous growth on RuO2 and its distorted growth on SiO2. As a result, this work links structural changes to BTO thin-film properties and provides insight necessary for optimizing future BTO and other ternary metal oxide-based thin-film devices.« less

  11. Relating Electronic and Geometric Structure of Atomic Layer Deposited BaTiO3 to its Electrical Properties.

    PubMed

    Torgersen, Jan; Acharya, Shinjita; Dadlani, Anup Lal; Petousis, Ioannis; Kim, Yongmin; Trejo, Orlando; Nordlund, Dennis; Prinz, Fritz B

    2016-04-21

    Atomic layer deposition allows the fabrication of BaTiO3 (BTO) ultrathin films with tunable dielectric properties, which is a promising material for electronic and optical technology. Industrial applicability necessitates a better understanding of their atomic structure and corresponding properties. Through the use of element-specific X-ray absorption near edge structure (XANES) analysis, O K-edge of BTO as a function of cation composition and underlying substrate (RuO2 and SiO2) is revealed. By employing density functional theory and multiple scattering simulations, we analyze the distortions in BTO's bonding environment captured by the XANES spectra. The spectral weight shifts to lower energy with increasing Ti content and provides an atomic scale (microscopic) explanation for the increase in leakage current density. Differences in film morphologies in the first few layers near substrate-film interfaces reveal BTO's homogeneous growth on RuO2 and its distorted growth on SiO2. This work links structural changes to BTO thin-film properties and provides insight necessary for optimizing future BTO and other ternary metal oxide-based thin-film devices.

  12. Quick extended x-ray absorption fine structure instrument with millisecond time scale, optimized for in situ applications

    SciTech Connect

    Khalid, S.; Caliebe, W.; Siddons, P.; So, I.; Clay, b.; Hanson, J.; Wang, Q.; Frenkel, A.; Marinkovicl, N.; Hould, N.; ginder-Vogel, M.; Landrot, G.L.; Sparks, D.L.; Ganjoo, A.

    2010-01-19

    In order to learn about in situ structural changes in materials at subseconds time scale, we have further refined the techniques of quick extended x-ray absorption fine structure (QEXAFS) and quick x-ray absorption near edge structure (XANES) spectroscopies at beamline X18B at the National Synchrotron Light Source. The channel cut Si (111) monochromator oscillation is driven through a tangential arm at 5 Hz, using a cam, dc motor, pulley, and belt system. The rubber belt between the motor and the cam damps the mechanical noise. EXAFS scan taken in 100 ms is comparable to standard data. The angle and the angular range of the monochromator can be changed to collect a full EXAFS or XANES spectrum in the energy range 4.7-40.0 KeV. The data are recorded in ascending and descending order of energy, on the fly, without any loss of beam time. The QEXAFS mechanical system is outside the vacuum system, and therefore changing the mode of operation from conventional to QEXAFS takes only a few minutes. This instrument allows the acquisition of time resolved data in a variety of systems relevant to electrochemical, photochemical, catalytic, materials, and environmental sciences.

  13. Quick extended x-ray absorption fine structure instrument with millisecond time scale, optimized for in situ applications.

    PubMed

    Khalid, S; Caliebe, W; Siddons, P; So, I; Clay, B; Lenhard, T; Hanson, J; Wang, Q; Frenkel, A I; Marinkovic, N; Hould, N; Ginder-Vogel, M; Landrot, G L; Sparks, D L; Ganjoo, A

    2010-01-01

    In order to learn about in situ structural changes in materials at subseconds time scale, we have further refined the techniques of quick extended x-ray absorption fine structure (QEXAFS) and quick x-ray absorption near edge structure (XANES) spectroscopies at beamline X18B at the National Synchrotron Light Source. The channel cut Si (111) monochromator oscillation is driven through a tangential arm at 5 Hz, using a cam, dc motor, pulley, and belt system. The rubber belt between the motor and the cam damps the mechanical noise. EXAFS scan taken in 100 ms is comparable to standard data. The angle and the angular range of the monochromator can be changed to collect a full EXAFS or XANES spectrum in the energy range 4.7-40.0 KeV. The data are recorded in ascending and descending order of energy, on the fly, without any loss of beam time. The QEXAFS mechanical system is outside the vacuum system, and therefore changing the mode of operation from conventional to QEXAFS takes only a few minutes. This instrument allows the acquisition of time resolved data in a variety of systems relevant to electrochemical, photochemical, catalytic, materials, and environmental sciences.

  14. Electronic structure and field emission properties of nitrogen doped graphene nano-flakes (GNFs:N) and carbon nanotubes (CNTs:N)

    NASA Astrophysics Data System (ADS)

    Ray, Sekhar C.; Pong, W. F.; Papakonstantinou, P.

    2016-09-01

    Substitution of hetero-atom doping is a promising route to modulate the outstanding material properties of carbon nanotubes and graphene for customized applications. Nitrogen-doping has been introduced to ensure tunable work-function, enhanced n-type carrier concentration, diminished surface energy, and manageable polarization. Along with the promising assessment of N-doping effects, research on the N-doped carbon based composite structures is emerging for the synergistic integration with various functional materials. Nitrogen undoped/doped graphene nano-flakes (GNFs/GNFs:N) and multiwall carbon nano-tubes (MWCNTs/MWCNTs:N) are used for comparative study of their electronic/bonding structure along with their defects state. X-ray absorption near edge structure (XANES) spectroscopy shows that the GNFs:N produce mainly pyridine like structure; whereas MWCNTs:N shows graphitic nitrogen atoms are attached with the carbon lattice. The ID/IG ratio obtained from Raman spectroscopy shows that the defects is higher in MWCNTs:N than GNFs:N. The electron field emission result shows that the turn on electric field is lower (higher electron emission current) in case of MWCNTs:N than GNFs:N and are good agreement with XANES and the results obtained from Raman spectra.

  15. Combining state-of-the-art experiment and ab initio calculations for a better understanding of the interplay between valence, magnetism and structure in Eu compounds at high pressure

    DOE PAGES

    Souza-Neto, N. M.; Haskel, D.; dos Reis, R. D.; ...

    2016-07-26

    Here, we describe how first principle calculations can play a key role in the interpretation of X-ray absorption near-edge structure (XANES) and X-ray magnetic circular dichroism (XMCD) spectra for a better understanding of emergent phenomena in condensed matter physics at high applied pressure. Eu compounds are used as case study to illustrate the advantages of this methodology, ranging from studies of electronic charge transfer probed by quadrupolar and dipolar contributions, to accurately determining electronic valence, and to inform about the influence of pressure on RKKY interactions and magnetism. This description should help advance studies where the pressure dependence of XANESmore » and XMCD data must be tackled with the support of theoretical calculations for a proper understanding of the electronic properties of materials.« less

  16. Structural Investigation of Au Catalysts on TiO2-SiO2 Supports: Nature of the Local Structure of Ti and Au Atoms by EXAFS and XANES

    SciTech Connect

    Schwartz,V.; Mullins, D.; Yan, W.; Zhu, H.; Dai, S.; Overbury, S.

    2007-01-01

    X-ray absorption spectroscopy (XAS) was utilized to investigate both the Au particle size on several supports composed by silica and titanium oxide, and the coordination of TiO2 in the support phase. Particularly, we wanted to utilize the technique to probe mixing in the support phase, by using different synthetic methods such as by functionalizing silica or by ALD (atomic layer deposition) techniques as prepared in our laboratories, and the growth and stability of Au nanoparticles deposited on these supports. The study using cosynthesis techniques to dope bulk mesoporous SiO2 with TiO2 resulted in TiO2 being dispersed in the SiO2 matrix; however, a second phase starts forming as the TiO2 content increases as indicated by the EXAFS Ti-O shell shift in position and increase of coordination number. On the supports prepared by cosynthesis, Au particles were smaller and more stable. The study using the surface sol-gel technique for deposition of single monolayers of an oxide such as TiO2 produced Ti environments in which the Ti-O shell and the next two Ti-Ti shells lie on the same position as expected for an anatase structure. Although undercoordinated, the presence of the Ti-Ti shells indicate that the titania species are not molecularly dispersed on the SiO2 surface as hypothesized, but there is indeed a cross-linking of the titania moieties.

  17. Structural investigation of Au catalysts on TiO2-SiO2 supports - on the nature of the local structure of Ti and Au atoms by EXAFS and XANES

    SciTech Connect

    Schwartz, Viviane; Mullins, David R; Yan, Wenfu; Zhu, Haoguo; Dai, Sheng

    2007-01-01

    X-ray absorption spectroscopy (XAS) was utilized to investigate both the Au particle size on several supports composed by silica and titanium oxide, and the coordination of TiO2 in the support phase. Particularly, we wanted to utilize the technique to probe mixing in the support phase, by using different synthetic methods such as by functionalizing silica or by ALD (atomic layer deposition) techniques as prepared in our laboratories, and the growth and stability of Au nanoparticles deposited on these supports. The study using cosynthesis techniques to dope bulk mesoporous SiO2 with TiO2 resulted in TiO2 being dispersed in the SiO2 matrix; however, a second phase starts forming as the TiO2 content increases as indicated by the EXAFS Ti-O shell shift in position and increase of coordination number. On the supports prepared by cosynthesis, Au particles were smaller and more stable. The study using the surface sol-gel technique for deposition of single monolayers of an oxide such as TiO2 produced Ti environments in which the Ti-O shell and the next two Ti-Ti shells lie on the same position as expected for an anatase structure. Although undercoordinated, the presence of the Ti-Ti shells indicate that the titania species are not molecularly dispersed on the SiO2 surface as hypothesized, but there is indeed a cross-linking of the titania moieties.

  18. A structural study of bone changes in knee osteoarthritis by synchrotron-based X-ray fluorescence and X-ray absorption spectroscopy techniques

    NASA Astrophysics Data System (ADS)

    Sindhupakorn, Bura; Thienpratharn, Suwittaya; Kidkhunthod, Pinit

    2017-10-01

    Osteoarthritis (OA) is characterized by degeneration of articular cartilage and thickening of subchondral bone. The present study investigated the changing of biochemical components of cartilage and bone compared between normal and OA people. Using Synchrotron-based X-ray fluorescence (SR-XRF) and X-ray absorption spectroscopy (XAS) techniquesincluding X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) were employed for the bone changes in kneeosteoarthritisstudies. The bone samples were collected from various osteoarthritis patients with both male and female in the ages range between 20 and 74 years old. SR-XRF results excited at 4240 eV for Ca elements show a majority three main groups, based on their XRF intensities, 20-36 years, 40-60 years and over 70 years, respectively. By employing XAS techniques, XANES features can be used to clearly explain in term of electronic transitions occurring in bone samples which are affected from osteoarthritis symptoms. Moreover, a structural change around Ca ions in bone samples is obviously obtained by EXAFS results indicating an increase of Ca-amorphous phase when the ages increase.

  19. Predictions of the near edge transport shortfall in DIII-D L-mode plasmas using the trapped gyro-Landau-fluid model [Predictions of the near edge transport shortfall in DIII-D L-mode plasmas using the TGLF model

    SciTech Connect

    Kinsey, Jon E.; Staebler, Gary M.; Candy, Jefferey M.; Petty, Craig C.; Rhodes, Terry L.; Waltz, Ronald E.

    2015-01-14

    Previous studies of DIII-D L-mode plasmas have shown that a transport shortfall exists in that our current models of turbulent transport can significantly underestimate the energy transport in the near edge region. In this paper, the Trapped Gyro-Landau-Fluid (TGLF) drift wave transport model is used to simulate the near edge transport in a DIII-D L-mode experiment designed to explore the impact of varying the safety factor on the shortfall. We find that the shortfall systematically increases with increasing safety factor and is more pronounced for the electrons than for the ions. Within the shortfall dataset, a single high current case has been found where no transport shortfall is predicted. Reduced neutral beam injection power has been identified as the key parameter separating this discharge from other discharges exhibiting a shortfall. Further analysis shows that the energy transport in the L-mode near edge region is not stiff according to TGLF. Unlike the H-mode core region, the predicted temperature profiles are relatively more responsive to changes in auxiliary heating power. In testing the fidelity of TGLF for the near edge region, we find that a recalibration of the collision model is warranted. A recalibration improves agreement between TGLF and nonlinear gyrokinetic simulations performed using the GYRO code with electron-ion collisions. As a result, the recalibration only slightly impacts the predicted shortfall.

  20. Predictions of the near edge transport shortfall in DIII-D L-mode plasmas using the trapped gyro-Landau-fluid model [Predictions of the near edge transport shortfall in DIII-D L-mode plasmas using the TGLF model

    DOE PAGES

    Kinsey, Jon E.; Staebler, Gary M.; Candy, Jefferey M.; ...

    2015-01-14

    Previous studies of DIII-D L-mode plasmas have shown that a transport shortfall exists in that our current models of turbulent transport can significantly underestimate the energy transport in the near edge region. In this paper, the Trapped Gyro-Landau-Fluid (TGLF) drift wave transport model is used to simulate the near edge transport in a DIII-D L-mode experiment designed to explore the impact of varying the safety factor on the shortfall. We find that the shortfall systematically increases with increasing safety factor and is more pronounced for the electrons than for the ions. Within the shortfall dataset, a single high current casemore » has been found where no transport shortfall is predicted. Reduced neutral beam injection power has been identified as the key parameter separating this discharge from other discharges exhibiting a shortfall. Further analysis shows that the energy transport in the L-mode near edge region is not stiff according to TGLF. Unlike the H-mode core region, the predicted temperature profiles are relatively more responsive to changes in auxiliary heating power. In testing the fidelity of TGLF for the near edge region, we find that a recalibration of the collision model is warranted. A recalibration improves agreement between TGLF and nonlinear gyrokinetic simulations performed using the GYRO code with electron-ion collisions. As a result, the recalibration only slightly impacts the predicted shortfall.« less

  1. Speciation Mapping of Environmental Samples Using XANES Imaging

    EPA Science Inventory

    Fast X-ray detectors with large solid angles and high dynamic ranges open the door to XANES imaging, in which millions of spectra are collected to image the speciation of metals at micrometre resolution, over areas up to several square centimetres. This paper explores how such mu...

  2. Speciation Mapping of Environmental Samples Using XANES Imaging

    EPA Science Inventory

    Fast X-ray detectors with large solid angles and high dynamic ranges open the door to XANES imaging, in which millions of spectra are collected to image the speciation of metals at micrometre resolution, over areas up to several square centimetres. This paper explores how such mu...

  3. Effects of Composition on Fe XANES Redox Calibrations in Glasses

    NASA Astrophysics Data System (ADS)

    McCanta, M. C.; Dyar, M. D.; Breves, E.

    2013-12-01

    The oxidation state of volcanic materials on a planet reflects the degree of oxidation of the magma source region and, possibly, the additional effects of magma interaction with the near surface environment. Constraining fO2 in geologic samples can be both difficult and subject to large uncertainties, with the choice of oxybarometer often limited by the phase assemblage present. Many current methods for estimating magmatic fO2 rely on Fe2+/Fe3+ partitioning in silicate melts or between crystals and melt as a function of fO2 (e.g., Sack et al., 1980; Kress and Carmichael, 1991). However, use of oxybarometers is limited by the difficulty in measuring Fe2+/Fe3+ ratios in situ at micro-scales. Fe titration and Mössbauer techniques allow for bulk measurements but require large amounts of material and do not allow for investigation of zoning or fO2 variations at microscales. Synchrotron micro-XANES spectroscopy (SmX), which uses the shape of the Fe K absorption XANES edge, offers great promise making these measurements on standard thin sections. However, because melt composition and structure have an effect on Fe3+/ΣFe (e.g., Kilinc et al., 1983; Borisov and McCammon, 2010), especially under oxidizing conditions, SmX requires calibration samples with compositions similar to those of the unknowns being studied. To address this need, a suite of 33 synthetic glasses covering a wide range of geologically-relevant compositions was generated under varying fO2 conditions. Runs were conducted in a 1-atm gas mixing furnace using the Pt (fO2 ≥ QFM) or Re (fO2 < QFM) wire-loop technique. Three oxygen fugacities were considered for each composition: air, quartz-fayalite-magnetite (QFM), and iron-wustite (IW). The fO2 values were fixed either by flowing air or an H2-CO2 gas mixture pegged at the QFM or IW buffer for the maximum temperature of an experiment with the gas composition held constant during quench. Samples were held above their melting temperatures for 6 hours, drop

  4. Carbon monoxide binding to the heme group at the dimeric interface modulates structure and copper accessibility in the Cu,Zn superoxide dismutase from Haemophilus ducreyi: in silico and in vitro evidences.

    PubMed

    Chillemi, Giovanni; De Santis, Serena; Falconi, Mattia; Mancini, Giordano; Migliorati, Valentina; Battistoni, Andrea; Pacello, Francesca; Desideri, Alessandro; D'Angelo, Paola

    2012-01-01

    X-ray absorption near-edge structure (XANES) spectroscopy and molecular dynamics (MD) simulations have been jointly applied to the study of the Cu,Zn superoxide dismutase from Haemophilus ducreyi (HdSOD) in interaction with the carbon monoxide molecule. The configurational flexibility of the Fe(II)-heme group, intercalated between the two subunits, has been sampled by MD simulations and included in the XANES data analysis without optimization in the structural parameter space. Our results provide an interpretation of the observed discrepancy in the Fe-heme distances as detected by extended X-ray absorption fine structure (EXAFS) spectroscopy and the classical XANES analysis, in which the structural parameters are optimized in a unique structure. Moreover, binding of the CO molecule to the heme induces a long range effect on the Cu,Zn active site, as evidenced by both MD simulations and in vitro experiments. MD simulation of the CO bound system, in fact, highlighted a structural rearrangement of the protein-protein hydrogen bond network in the region of the Cu,Zn active site, correlated with an increase in water accessibility at short distance from the copper atom. In line, in vitro experiments evidenced an increase of copper accessibility to a chelating agent when the CO molecule binds to the heme group, as compared to a heme deprived HdSOD. Altogether, our results support the hypothesis that the HdSOD is a heme-sensor protein, in which binding to small gaseous molecules modulates the enzyme superoxide activity as an adaptive response to the bacterial environment.

  5. Behavior of redox-sensitive elements during weathering of granite in subtropical area using X-ray absorption fine structure spectroscopy

    NASA Astrophysics Data System (ADS)

    Zhang, Zhuo-Jun; Liu, Cong-Qiang; Zhao, Zhi-Qi; Cui, Li-Feng; Liu, Wen-Jing; Liu, Tao-Ze; Liu, Bao-Jian; Fan, Bai-Ling

    2015-06-01

    The variation in chemical compositions of regolith along a weathering profile developed on a granite substrate in Jiangxi province, in southern China, was investigated in this paper, with the aim to characterize the speciation of redox-sensitive elements and to evaluate their mobility and redistribution during chemical weathering. Mass balance calculations indicate titanium (Ti) is the most immobile element in this weathering profile. A new method, X-ray absorption fine structure (XAFS) spectroscopy, was used to determine the speciation of Fe and Mn along the profile. Fe K-edge X-ray absorption near edge structure (XANES) spectra show Fe in saprolith is stabilized mainly in the state of Fe(III), suggesting Fe is as immobile as conservative elements during granite weathering. Mn K-edge XANES spectra show Mn (III/IV) oxides are reduced to Mn(II) in surface soil, where soil organic matter (SOM) acts as an important reductant. Although Ce, Co and V were unable to be analysed by XAFS, their concentrations have significant correlations with that of Mn, indicating that the mobilization and redistribution of Ce, Co and V may also be governed by redox condition. All in all, the results suggest that redox process impacts significantly on the redistribution of Mn, Ce, Co and V along the profile. The successful application of XAFS in the study on migration of redox-sensitive elements during granite chemical weathering has provided valuable information for the understanding and evaluating the geochemical behavior of elements in the environment.

  6. X-ray diffraction and X-ray K-absorption near edge studies of Copper (II) Micro cyclic Carbamide complexes.

    NASA Astrophysics Data System (ADS)

    Malviya, P. K.; Sharma, P.; Mishra, A.; Bhalse, D.

    2016-10-01

    Synthesis of metal complexes [Cu (Carbamide)] (X = Br, Cl, NO3, SO4,CH3COO) by the chemical root method. The XRD data have been recorded at DAE, IUC Indore.XANES spectra have been recorded at the K-edge of Cu using the dispersive beam line at 2.5GeV Indus-2 synchrotron radiation source RRCAT (Raja Ramanna Center for Advance Technology), Indore, India. XRD and XANES data have been analysed using the computer software Origin 8.0 professional and Athena. X-ray diffraction studies of all the complexes are indicative of their crystalline nature. The crystalline size of the samples is estimated using the Scherer's formula. The values of the chemical shifts suggest that copper is in oxidation state +2 in all of the complexes.

  7. Peculiarities of the electronic structure and phase composition of amorphous (SiO2) x (a-Si: H) x-1 composite films according to X-ray spectroscopy data

    NASA Astrophysics Data System (ADS)

    Terekhov, V. A.; Parinova, E. V.; Domashevskaya, E. P.; Sadchikov, A. S.; Terukov, E. I.; Undalov, Yu. K.; Sen'kovskii, B. V.; Turishchev, S. Yu.

    2015-10-01

    Amorphous (SiO2) x (a-Si: H) x-1 composite films have been deposited from plasma of dc magnetron discharge switched on and off for variable periods of time. The electronic structure and phase composition of obtained films were studied by methods of ultrasoft X-ray emission spectroscopy (USXES) and X-ray absorption near edge structure (XANES) spectroscopy using synchrotron radiation. The results of a qualitative and semiquantitative analysis of the phase composition of films with the use of a special method of computer simulation showed that the content of amorphous a-Si: H clusters in SiO2 matrix can be varied within wide limits by changing the period of dc magnetron discharge switching. It is established that the formation of a large number of silicon nanoclusters in the (SiO2) x (a-Si: H) x-1 composite film leads to the appearance of anomalies in the XANES spectra, which are related to the scattering of synchrotron radiation on nanoclusters with dimensions comparable to the radiation wavelength near the X-ray absorption edge of silicon.

  8. Investigation of the Structural Stability of Ion-Implanted Gd2Ti2-xSnxO7 Pyrochlore-Type Oxides by Glancing Angle X-ray Absorption Spectroscopy

    SciTech Connect

    Aluri, Esther Rani; Hayes, John R.; Walker, James D.S.; Grosvenor, Andrew P.

    2016-03-24

    Rare-earth titanate and stannate pyrochlore-type oxides have been investigated in the past for the sequestration of nuclear waste elements because of their resistance to radiation-induced structural damage. In order to enhance this property, it is necessary to understand the effect of radioactive decay of the incorporated actinide elements on the local chemical environment. In this study, Gd2Ti2–xSnxO7 materials have been implanted with Au– ions to simulate radiation-induced structural damage. Glancing angle X-ray absorption near-edge spectroscopy (GA-XANES), glancing angle X-ray absorption fine structure (GA-EXAFS) analysis, and powder X-ray diffraction have been used to investigate changes in the local coordination environment of the metal atoms in the damaged surface layer. Examination of GA-XANES/EXAFS spectra from the implanted Gd2Ti2–xSnxO7 materials collected at various glancing angles allowed for an investigation of how the local coordination environment around the absorbing atoms changed at different depths in the damaged surface layer. This study has shown the usefulness of GA-XANES to the examination of ion-implanted materials and has suggested that Gd2Ti2–xSnxO7 becomes more susceptible to ion-beam-induced structural damage with increasing Sn concentration.

  9. X-ray and photoelectron spectroscopy of the structure, reactivity, and electronic structure of semiconductor nanocrystals

    SciTech Connect

    Hamad, Kimberly Sue

    2000-01-01

    Semiconductor nanocrystals are a system which has been the focus of interest due to their size dependent properties and their possible use in technological applications. Many chemical and physical properties vary systematically with the size of the nanocrystal and thus their study enables the investigation of scaling laws. Due to the increasing surface to volume ratio as size is decreased, the surfaces of nanocrystals are expected to have a large influence on their electronic, thermodynamic, and chemical behavior. In spite of their importance, nanocrystal surfaces are still relatively uncharacterized in terms of their structure, electronic properties, bonding, and reactivity. Investigation of nanocrystal surfaces is currently limited by what techniques to use, and which methods are suitable for nanocrystals is still being determined. This work presents experiments using x-ray and electronic spectroscopies to explore the structure, reactivity, and electronic properties of semiconductor (CdSe, InAs) nanocrystals and how they vary with size. Specifically, x-ray absorption near edge spectroscopy (XANES) in conjunction with multiple scattering simulations affords information about the structural disorder present at the surface of the nanocrystal. X-ray photoelectron spectroscopy (XPS) and ultra-violet photoelectron spectroscopy (UPS) probe the electronic structure in terms of hole screening, and also give information about band lineups when the nanocrystal is placed in electric contact with a substrate. XPS of the core levels of the nanocrystal as a function of photo-oxidation time yields kinetic data on the oxidation reaction occurring at the surface of the nanocrystal.

  10. Origin of improved scintillation efficiency in (Lu,Gd)3(Ga,Al)5O12:Ce multicomponent garnets: An X-ray absorption near edge spectroscopy study

    NASA Astrophysics Data System (ADS)

    Wu, Yuntao; Luo, Jialiang; Nikl, Martin; Ren, Guohao

    2014-01-01

    In the recent successful improvement of scintillation efficiency in Lu3Al5O12:Ce driven by Ga3+ and Gd3+ admixture, the "band-gap engineering" and energy level positioning have been considered the valid strategies so far. This study revealed that this improvement was also associated with the cerium valence instability along with the changes of chemical composition. By utilizing X-ray absorption near edge spectroscopy technique, tuning the Ce3+/Ce4+ ratio by Ga3+ admixture was evidenced, while it was kept nearly stable with the Gd3+ admixture. Ce valence instability and Ce3+/Ce4+ ratio in multicomponent garnets can be driven by the energy separation between 4f ground state of Ce3+ and Fermi level.

  11. Local Structure of Cerium in Aluminophosphate and Silicophosphate Glasses

    SciTech Connect

    J Rygel; Y Chen; C Pantano; T Shibata; J Du; L Kokou; R Woodman; J Belcher

    2011-12-31

    The local structure of cerium in two systematic compositional series of glasses, nominally CeP{sub 3}O{sub 9}-AlP{sub 3}O{sub 9} and CeP{sub 3}O{sub 9}-SiP{sub 2}O{sub 7}, was interrogated using X-ray photoelectron spectroscopy (XPS) and X-ray absorption fine structure (XAFS) spectroscopy. XPS revealed that, for glasses melted in air, {>=}95% of cerium ions are Ce{sup 3+}. This was independently confirmed using X-ray absorption near edge spectroscopy (XANES). Ce K-edge extended X-ray absorption fine structure (EXAFS) has been used to determine the local structure of Ce{sup 3+}. Near the metaphosphate composition, cerium was found to have an average cerium coordination number of {approx}7.0 and an average cerium-oxygen bond length of 2.41 {angstrom}. The average cerium coordination number and average cerium-oxygen bond distance were found to increase with decreasing cerium concentration in both compositional series. Rare-earth clustering is suggested based on numerical calculations for glasses containing {>=}14 and {>=}15 mol% Ce{sub 2}O{sub 3} for the aluminophosphate and silicophosphate series, respectively.

  12. Local Structure of Cerium in Aluminophosphate and Silicophosphate Glasses

    SciTech Connect

    Rygel, Jennifer L.; Chen, Yongsheng; Pantano, Carlo G.; Shibata, Tomohiro; Du, Jincheng; Kokou, Leopold; Woodman, Robert; Belcher, James

    2011-09-20

    The local structure of cerium in two systematic compositional series of glasses, nominally CeP{sub 3}O{sub 9}-AlP{sub 3}O{sub 9} and CeP{sub 3}O{sub 9}-SiP{sub 2}O{sub 7}, was interrogated using X-ray photoelectron spectroscopy (XPS) and X-ray absorption fine structure (XAFS) spectroscopy. XPS revealed that, for glasses melted in air, {>=}95% of cerium ions are Ce{sup 3+}. This was independently confirmed using X-ray absorption near edge spectroscopy (XANES). Ce K-edge extended X-ray absorption fine structure (EXAFS) has been used to determine the local structure of Ce{sup 3+}. Near the metaphosphate composition, cerium was found to have an average cerium coordination number of {approx}7.0 and an average cerium-oxygen bond length of 2.41 {angstrom}. The average cerium coordination number and average cerium-oxygen bond distance were found to increase with decreasing cerium concentration in both compositional series. Rare-earth clustering is suggested based on numerical calculations for glasses containing {>=}14 and {>=}15 mol% Ce{sub 2}O{sub 3} for the aluminophosphate and silicophosphate series, respectively.

  13. Probing local structure of pyrochlore lead zinc niobate with synchrotron x-ray absorption spectroscopy technique

    NASA Astrophysics Data System (ADS)

    Kanchiang, Kanokwan; Pramchu, Sittichain; Yimnirun, Rattikorn; Pakawanit, Phakkhananan; Ananta, Supon; Laosiritaworn, Yongyut

    2013-08-01

    Local structure of lead zinc niobate (PZN) ceramic, synthesized via B-site oxide precursor route in atmospheric pressure, was investigated using synchrotron x-ray absorption spectroscopy (XAS) technique. The x-ray absorption near-edge structure (XANES) simulation was first carried out. The XANES simulation results indicate that the PZN ceramic is in pyrochlore phase having Zn2+ substituted on Nb5+ site. Afterwards, the extended x-ray absorption fine structure (EXAFS) analysis was performed to extract the bond length information between Zn2+ and its neighboring atoms. From the EXAFS fitting, the bond length between Zn2+ and Pb2+ in the pyrochlore phase was found to be longer than the previously reported bond length in the perovskite phase. Further, with the radial distribution information of Zn2+'s neighboring atoms, the formation energies along the precursor-to-pyrochlore and precursor-to-perovskite reaction paths were calculated using the density functional theory (DFT). The calculated results show that the formation energy of the perovskite phase is noticeably higher than that of the pyrochlore phase, which is influenced by the presence of energetic Pb2+ lone pair, as the perovskite phase has shorter Zn2+ to Pb2+ bonding. This therefore suggests the steric hindrance of Pb2+ lone pair and the mutual interactions between Pb2+ lone pair and Zn2+ are main causes of the instability of lead zinc niobate in the perovskite structure and confirm the efficacy of XAS and DFT analysis in revealing local structural details of complex pyrochlore materials.

  14. Synchrotron-based P K-edge XANES spectroscopy reveals rapid changes of phosphorus speciation in the topsoil of two glacier foreland chronosequences

    NASA Astrophysics Data System (ADS)

    Prietzel, Jörg; Dümig, Alexander; Wu, Yanhong; Zhou, Jun; Klysubun, Wantana

    2013-05-01

    Phosphorus (P) is a crucial element for life on Earth, and the bioavailability of P in terrestrial ecosystems, which is dependent on the soil P stock and its speciation, may limit ecosystem productivity and succession. In our study, for the first time a direct speciation of soil P in two glacier foreland chronosequences has been conducted using synchrotron-based X-ray Absorption Near-Edge Structure (XANES) spectroscopy. The chronosequences are located in the forefields of Hailuogou Glacier (Gongga Shan, China) and Damma Glacier (Swiss Alps). The age since deglaciation of the investigated soils ranges from 0 to 120 years at Hailuogou, and from 15 to >700 years at Damma. Differences in climate conditions (cooler at Damma, in contrast to Hailuogou precluding the establishment of forest in advanced ecosystem succession stages) and in the chemical composition of the parent material result in different soil contents of total P and Fe/Al oxyhydroxides, which are much smaller at Damma than at Hailuogou. Nevertheless, both chronosequences show similar trends of their topsoil P status with increasing soil age. Our study reveals a rapid change of topsoil P speciation in glacier retreat areas already during initial stages of pedogenesis: Initially dominating bedrock-derived apatite-P and Al-bound P is depleted; Fe-bound P and particularly organically-bound P is accumulated. Organic P strongly dominates in the topsoil of the mature soils outside the proglacial area of Damma Glacier (age 700-3000 years), and already 50 years after deglacation in the topsoil of the retreat area of Hailuogou Glacier. A key factor for the change in topsoil P speciation is the establishment of vegetation, resulting in soil organic matter (SOM) accumulation as well as accelerated soil acidification and apatite dissolution by organic acids, which are produced by SOM-degrading micro-organisms, mykorrhiza fungi, and plant roots. Particularly the succession of grassland to forest seems to accelerate the

  15. Mg coordination in biogenic carbonates constrained by theoretical and experimental XANES

    NASA Astrophysics Data System (ADS)

    Yoshimura, Toshihiro; Tamenori, Yusuke; Takahashi, Osamu; Nguyen, Luan T.; Hasegawa, Hiroshi; Iwasaki, Nozomu; Kuroyanagi, Azumi; Suzuki, Atsushi; Kawahata, Hodaka

    2015-07-01

    Incorporation of magnesium into biogenic calcium carbonate is widely used to infer the conditions of mineral growth. From a mineralogical perspective, the dominant chemical environment of Mg and whether Mg replaces calcium by ideal substitution in biogenic CaCO3 are still debated, however. Here we show that energy positions and resonance features in experimental and theoretical XANES spectra can be used to identify the dominant molecular host site. In all biogenic calcite, which is produced by foraminifera, corals, bivalves, and brachiopods, the local environment of Mg indicated that it is incorporated primarily as a structural substitute for calcium in the crystal lattice, but in aragonitic coral and bivalves a pronounced effect of the organic fraction or disordered phases was observed. These differences among CaCO3 polymorphs suggest that physicochemical parameters affect the final composition of biogenic calcite, but in aragonite-secreting organisms, there may be physiological controls on Mg concentrations in biogenic aragonite.

  16. Iron in Silicate Glasses: Systematic Analysis of Pre-Edge And Xanes Features

    SciTech Connect

    Farges, F.; Rossano, S.; Wilke, M.; Lefrere, Y.; Brown, G.E., Jr.; /SLAC, SSRL

    2006-10-27

    A large number (67) of silicate glasses containing variable amounts of iron oxide were studied by high-resolution XANES spectroscopy at the Fe K-edge to determine an accurate method to derive redox information from pre-edge features. The glass compositions studied mimic geological magmas, ranging from basaltic to rhyolitic, dry and hydrous, with variable quench rates. The studied glasses also include more chemically simple calco-sodic silicate glass compositions. The Fe contents range from 30 wt.% to less than 2000 ppm. For most of the series of composition studied, the pre-edge information varies linearly with redox, even under high-resolution conditions. The average coordination of Fe(II) is often similar to its Fe(III) counterpart except in highly polymerized glasses because of the strong influence exerted by the tetrahedral framework on iron's sites. Natural volcanic glasses (from various volcanoes around the world) show similar variations. The average coordination of Fe(II) is often comprised between 4.5 and 5. Fe(III) shows larger variations in coordination (4 to 6, depending on composition). Bond valence models are proposed to predict the average coordination of Fe based on composition. Molecular dynamics simulations (Born-Mayer-Huggins) potentials were carried out on some compositions to estimate the magnitude of disorder effects (both static and thermal) in the XAFS analysis. XANES calculations based on the MD simulations and FEFF 8.2 show large variations in the local structures around Fe. Also, 5-coordinated Fe(III) is found to be an important moiety in ferrisilicate glasses. For Fe(II), discrepancies between glass and melt are larger and are related to its greater structural relaxation at T{sub g}. Also, a strong destructive interference between network formers and modifiers explain the relatively weak intensity of the next-nearest neighbors contributions in the experimental spectra.

  17. Chemical and structural characterization of copper adsorbed on mosses (Bryophyta).

    PubMed

    González, Aridane G; Jimenez-Villacorta, Felix; Beike, Anna K; Reski, Ralf; Adamo, Paola; Pokrovsky, Oleg S

    2016-05-05

    The adsorption of copper on passive biomonitors (devitalized mosses Hypnum sp., Sphagnum denticulatum, Pseudoscleropodium purum and Brachythecium rutabulum) was studied under different experimental conditions such as a function of pH and Cu concentration in solution. Cu assimilation by living Physcomitrella patents was also investigated. Molecular structure of surface adsorbed and incorporated Cu was studied by X-ray Absorption Spectroscopy (XAS). Devitalized mosses exhibited the universal adsorption pattern of Cu as a function of pH, with a total binding sites number 0.05-0.06 mmolg(dry)(-1) and a maximal adsorption capacity of 0.93-1.25 mmolg(dry)(-1) for these devitalized species. The Extended X-ray Absorption Fine Structure (EXAFS) fit of the first neighbor demonstrated that for all studied mosses there are ∼4.5 O/N atoms around Cu at ∼1.95 Å likely in a pseudo-square geometry. The X-ray Absorption Near Edge Structure (XANES) analysis demonstrated that Cu(II)-cellulose (representing carboxylate groups) and Cu(II)-phosphate are the main moss surface binding moieties, and the percentage of these sites varies as a function of solution pH. P. patens exposed during one month to Cu(2+) yielded ∼20% of Cu(I) in the form of Cu-S(CN) complexes, suggesting metabolically-controlled reduction of adsorbed and assimilated Cu(2+).

  18. NanoSIMS, TEM, and XANES studies of a unique presolar supernova graphite grain

    SciTech Connect

    Groopman, Evan; Bernatowicz, Thomas; Zinner, Ernst; Nittler, Larry R.

    2014-07-20

    We report on isotopic and microstructural investigations of a unique presolar supernova (SN) graphite grain, referred to as G6, isolated from the Orgueil CI chondrite. G6 contains complex heterogeneities in its isotopic composition and in its microstructure. Nano-scale secondary ion mass spectrometer isotope images of ultramicrotome sections reveal heterogeneities in its C, N, and O isotopic compositions, including anomalous shell-like structures. Transmission electron microscope studies reveal a nanocrystalline core surrounded by a turbostratic graphite mantle, the first reported nanocrystalline core from a low-density SN graphite grain. Electron diffraction analysis shows that the nanocrystalline core consists of randomly oriented 2-4 nm graphene particles, similar to those in cores of high-density (HD) presolar graphite grains from asymptotic giant branch stars. G6's core also exhibits evidence for planar stacking of these graphene nano-sheets with a domain size up to 4.5 nm, which was unobserved in the nanocrystalline cores of HD graphite grains. We also report on X-ray absorption near-edge structure measurements of G6. The complex isotopic- and micro-structure of G6 provides evidence for mixing and/or granular transport in SN ejecta.

  19. Linear-Response and Real-Time Time-Dependent Density Functional Theory Studies of Core-Level Near-Edge X-Ray Absorption.

    PubMed

    Lopata, K; Van Kuiken, B E; Khalil, M; Govind, N

    2012-09-11

    We discuss our implementation and application of time-dependent density functional theory (TDDFT) to core-level near-edge absorption spectroscopy, using both linear-response (LR) and real-time (RT) approaches. We briefly describe our restricted excitation window TDDFT (REW-TDDFT) approach for core excitations, which has also been reported by other groups. This is followed by a detailed discussion of real-time TDDFT techniques tailored to core excitations, including obtaining spectral information through delta-function excitation, postprocessing time-dependent signals, and resonant excitation through quasi-monochromatic excitation. We present results for the oxygen K-edge of water and carbon monoxide; the carbon K-edge of carbon monoxide; the ruthenium L3-edge for the hexaamminerutheium(III) ion, including scalar relativistic corrections via the zeroth order regular approximation (ZORA); and the carbon and fluorine K-edges for a series of fluorobenzenes. In all cases, the calculated spectra are found to be in reasonable agreement with experimental results, requiring only a uniform shift ranging from -4 eV to +19 eV, i.e., on the order of a few percent of the excitation energy. Real-time TDDFT visualization of excited state charge densities is used to visually examine the nature of each excitation, which gives insight into the effects of atoms bound to the absorbing center.

  20. Local structure of cobalt nanoparticles synthesized by high heat flux plasma process

    NASA Astrophysics Data System (ADS)

    Orpe, P. B.; Paris, E.; Balasubramanian, C.; Joseph, B.; Mukherjee, S.; Di Gioacchino, D.; Marcelli, A.; Saini, N. L.

    2017-08-01

    We have used high heat flux plasma synthesis process to grow Co those for the morphology, stoichiometry and the local structure as a function of plasma current. We find that the nanoparticles produced by the thermal plasma method have different shapes and size distribution with the plasma current being a key parameter in controlling the formation of composition, morphology and crystalline structure. X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) measurements at Co K-edge have revealed formation of metal and metal oxide nanoparticles with the composition mainly depending on the arc current. While low plasma current appears to produce nanoparticles solely of CoO with a small amount of Co metal, the high plasma current tends to produce nanoparticles of CoO and Co3O4 oxides with increased amount of Co metal. The results are consistent with the morphological and structural analysis, showing nanoparticles of different shapes and size depending on the arc current.

  1. A first-principle calculation of the XANES spectrum of Cu{sup 2+} in water

    SciTech Connect

    La Penna, G.; Minicozzi, V.; Morante, S.; Stellato, F.; Rossi, G. C.

    2015-09-28

    The progress in high performance computing we are witnessing today offers the possibility of accurate electron density calculations of systems in realistic physico-chemical conditions. In this paper, we present a strategy aimed at performing a first-principle computation of the low energy part of the X-ray Absorption Spectroscopy (XAS) spectrum based on the density functional theory calculation of the electronic potential. To test its effectiveness, we apply the method to the computation of the X-ray absorption near edge structure part of the XAS spectrum in the paradigmatic, but simple case of Cu{sup 2+} in water. In order to keep into account the effect of the metal site structure fluctuations in determining the experimental si