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Sample records for al k-edge xanes

  1. 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.

  2. 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

  3. Phosphorus K-edge XANES spectroscopy of mineral standards.

    PubMed

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

    2011-03-01

    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

  4. 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.

  5. K-edge shift and XANES investigation of laser driven reshock-compressed Aluminum

    NASA Astrophysics Data System (ADS)

    Benuzzi-Mounaix, Alessandra; Ravasio, Alessandra; Koenig, Michel; Festa, Floriane; Amadou, Nourou; Levy, Anna; Brambrink, Erik; Dorchies, Fabien; Peyrusse, Olivier; Mazevet, Stéphane; Recoules, Vanina; Hall, Tom

    2010-11-01

    The physical properties of warm dense matter, specially their structural properties, are still poorly known. In this work, K-edge shift and X-ray Absorption Near Edge Spectroscopy (XANES) of reshocked Aluminum have been investigated with the aim of bringing information on the evolution of its electronic structure. The experiment was performed at LULI where we used one long pulse (500 ps, IL 8 10^13 W/cm^2) to create the shock and a second picosecond beam (IL 10^17 W/cm^2) to generate an ultra-short broadband X-ray source near the Al K-edge. The spectra were registered by using two conical KAP Bragg crystals. By changing the delay between the two beams, we have been able to observe the modification of absorption spectra for different and extreme Al conditions, up to now unexplored (ρ <= 3 ρ0 and T <= 8 eV). The hydrodynamical Al conditions were measured by using VISARs interferometers and self-emission diagnostic. Experimental data are compared to various calculations.

  6. 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.

  7. 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.

  8. Phosphorus Speciation of Forest-soil Organic Surface Layers using P K-edge XANES Spectroscopy

    SciTech Connect

    J Prietzel; J Thieme; D Paterson

    2011-12-31

    The phosphorus (P) speciation of organic surface layers from two adjacent German forest soils with different degree of water-logging (Stagnosol, Rheic Histosol) was analyzed by P K-edge XANES and subsequent Linear Combination Fitting. In both soils, {approx}70% of the P was inorganic phosphate and {approx}30% organic phosphate; reduced P forms such as phosphonate were absent. The increased degree of water-logging in the Histosol compared to the Stagnosol did not affect P speciation.

  9. Phosphorus speciation of forest-soil organic surface layers using P K-edge XANES spectroscopy

    SciTech Connect

    Prietzel, Jörg; Thieme, Jürgen; Paterson, David

    2012-02-07

    The phosphorus (P) speciation of organic surface layers from two adjacent German forest soils with different degree of water-logging (Stagnosol, Rheic Histosol) was analyzed by P K-edge XANES and subsequent Linear Combination Fitting. In both soils, {approx} 70% of the P was inorganic phosphate and {approx} 30% organic phosphate; reduced P forms such as phosphonate were absent. The increased degree of water-logging in the Histosol compared to the Stagnosol did not affect P speciation.

  10. 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.

  11. Reference spectra of important adsorbed organic and inorganic phosphate binding forms for soil P speciation using synchrotron-based K-edge XANES spectroscopy.

    PubMed

    Prietzel, Jörg; Harrington, Gertraud; Häusler, Werner; Heister, Katja; Werner, Florian; Klysubun, Wantana

    2016-03-01

    Direct speciation of soil phosphorus (P) by linear combination fitting (LCF) of P K-edge XANES spectra requires a standard set of spectra representing all major P species supposed to be present in the investigated soil. Here, available spectra of free- and cation-bound inositol hexakisphosphate (IHP), representing organic P, and of Fe, Al and Ca phosphate minerals are supplemented with spectra of adsorbed P binding forms. First, various soil constituents assumed to be potentially relevant for P sorption were compared with respect to their retention efficiency for orthophosphate and IHP at P levels typical for soils. Then, P K-edge XANES spectra for orthophosphate and IHP retained by the most relevant constituents were acquired. The spectra were compared with each other as well as with spectra of Ca, Al or Fe orthophosphate and IHP precipitates. Orthophosphate and IHP were retained particularly efficiently by ferrihydrite, boehmite, Al-saturated montmorillonite and Al-saturated soil organic matter (SOM), but far less efficiently by hematite, Ca-saturated montmorillonite and Ca-saturated SOM. P retention by dolomite was negligible. Calcite retained a large portion of the applied IHP, but no orthophosphate. The respective P K-edge XANES spectra of orthophosphate and IHP adsorbed to ferrihydrite, boehmite, Al-saturated montmorillonite and Al-saturated SOM differ from each other. They also are different from the spectra of amorphous FePO4, amorphous or crystalline AlPO4, Ca phosphates and free IHP. Inclusion of reference spectra of orthophosphate as well as IHP adsorbed to P-retaining soil minerals in addition to spectra of free or cation-bound IHP, AlPO4, FePO4 and Ca phosphate minerals in linear combination fitting exercises results in improved fit quality and a more realistic soil P speciation. A standard set of P K-edge XANES spectra of the most relevant adsorbed P binding forms in soils is presented. PMID:26917141

  12. 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.

  13. 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

  14. 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. PMID:23657739

  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. PMID:25108733

  16. Nitrogen K-edge XANES - an overview of reference compounds used to identify unknown organic nitrogen in environmental samples.

    PubMed

    Leinweber, Peter; Kruse, Jens; Walley, Fran L; Gillespie, Adam; Eckhardt, Kai Uwe; Blyth, Robert I R; Regier, Tom

    2007-11-01

    The chemical nature of soil organic nitrogen (N) is still poorly understood and one-third to one-half of it is typically classified as ;unknown N'. Nitrogen K-edge XANES spectroscopy has been used to develop a systematic overview on spectral features of all major N functions in soil and environmental samples. The absolute calibration of the photon energy was completed using the 1s --> pi* transitions of pure gas-phase N(2). On this basis a library of spectral features is provided for mineral N, nitro N, amino acids, peptides, and substituted pyrroles, pyridines, imidazoles, pyrazoles, pyrazines, pyrimidines and purine bases. Although N XANES was previously considered ;non-destructive', effects of radiation damage were shown for two compound classes and an approach was proposed to minimize it. This new evidence is integrated into a proposal for the evaluation spectra from environmental samples with unknown composition. Thus a basis is laid to develop N K-edge XANES as a complementary standard research method to study the molecular composition and ecological functions of ;unknown N' in soil and the environment. PMID:17960033

  17. Optimizing experimental design, overcoming challenges, and gaining valuable information from the Sb K-edge XANES region

    SciTech Connect

    Fawcett, Skya E.; Gordon, Robert A.; Jamieson, Heather E.

    2009-10-05

    There are many challenges associated with collecting, processing, and interpreting high-energy XAS data. The most significant of these are broad spectra, minimal separation of edge positions, and high background owing to the Compton tail. Studies of the Sb system are a particular challenge owing to its complex bonding character and formation of mixed oxidation-state minerals. Furthermore, in environmental samples such as stream sediment containing mine waste, different Sb phases may coexist. Ways to overcome these challenges and achieve accurate and useful information are presented. Our investigations used Sb K-edge X-ray absorption near-edge spectroscopy (XANES) to elucidate Sb geochemical behavior. Several Sb mineral spectra are presented, including Sb sulfosalts, and contrasted based on the different hosting and coordination environments around the Sb atom in the crystal structure. These comparisons lead to the recognition of how the different hosting and coordination environments are manifested in the shape of the Sb mineral spectra. In fact from the shape of the spectra, the occupation of the Sb atom in a single or in multiple crystallographic sites, regardless of whether multiple phases are present in the sample, is discernible. Furthermore, we demonstrate that quantitative information can be derived from the XANES region using linear combination fitting of the derivative spectra, rather than the energy spectra. Particularly useful to the advancement of Sb research is the demonstration that a significant amount of information can be gained from the Sb K-edge XANES region.

  18. Ti K-edge EXAFS and XANES study on tektites from different strewnfields

    NASA Astrophysics Data System (ADS)

    Wang, L.; Furuta, T.; Okube, M.; Yoshiasa, A.

    2011-12-01

    The concentration and local structure of each element may have various kinds of information about the asteroid impact and mass extinction. Farges and Brown have discussed about the Ti local structure by XANES, and concluded that Ti in tektite occupies 4-coordinated site. EXAFS can be analyzed to give precise information about the distance from Ti to near neighbors. The XAFS measurement of Ti local structure was preformed at the beamline 9C of the Photon Factory in KEK, Tsukuba, Japan. The specimens of tektites are from different strewnfields, they are: indochinite, bediasite, hainanite, philippinite, australite and moldavite. Sample for comparison are Libya desert glass and suevite. The k3χ(k) function was transformed into the radial structure function (RSF) for Ti K-edge of six tektites. The RSF for the Ti atom in indochinite and bediasite are similar; hainanite, australite and philippinite are similar; and moldavite is discriminated from others. It indicates that they have the same local atomic environmental around the Ti atoms and extended structure respectively. Coordination numbers and radial structure function are determined by EXAFS analyses (Table 1). We classified the tektites in three types: in indochinite and bediasite, Ti occupies 4-coordinated tetrahedral site and Ti-O distances are 1.84-1.81 Å; in hainanite, australite and philippinite, Ti occupies 5-coordinated trigonal bi-pyramidal or tetragonal pyramidal site and Ti-O distances are 1.92-1.87 Å; in moldavite, Ti occupies the 6-coordinated octahedral site and Ti-O distance is 2.00-1.96 Å. Formation of tektites is related to the impact process. It is generally recognized that tektites were formed under higher temperature and high pressure. But through this study, local structures of Ti are differing in three strewnfields and even different locations of the same strewnfield. What caused the various local structures will be another topic of tektite studies. Local structure of Ti may be changed in

  19. Beyond muffin-tin model for theoretical analysis of As K-edge XANES of InAs

    NASA Astrophysics Data System (ADS)

    Smolentsev, Grigory; Soldatov, Alexander V.; Joly, Yves; Pascarelli, Sakura; Aquilanti, Guliana

    2006-11-01

    Three alternative approaches have been applied to calculate As K-edge XANES of InAs: multiple scattering (MS) theory, non-muffin-tin finite difference method (FDM) and full potential linearized augmented plane wave (FLAPW) method. Such combination allows to make the distinction between two types of non-muffin-tin effects. First, in the interstitial region the potential is not constant. Second, the covalent bonds increase the charge density between nearest atoms and lead to additional loss of spherical symmetry of the potential within MT spheres.

  20. Multiple Scattering Approach to Polarization Dependence of F K-Edge XANES Spectra for Highly Oriented Polytetrafluoroethylene (PTFE) Thin Film

    SciTech Connect

    Nagamatsu, S.; Ono, M.; Kera, S.; Okudaira, K. K.; Fujikawa, T.; Ueno, N.

    2007-02-02

    The polarization dependence of F K-edge X-ray absorption near edge structure (XANES) spectra of highly-oriented thin-film of polytetrafluoroethylene (PTFE) has been analyzed by using multiple scattering theory. The spectra show clear polarization dependence due to the highly-oriented structure. The multiple scattering calculations reflects a local structure around an absorbing atom. The calculated results obtained by considering intermolecular-interactions are in good agreement with the observed polarization-dependence. We have also analyzed structural models of the radiation damaged PTFE films.

  1. 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.

  2. 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. PMID:27379398

  3. Vanadium K-edge XANES in vanadium-bearing model compounds: a full multiple scattering study.

    PubMed

    Benzi, Federico; Giuli, Gabriele; Della Longa, Stefano; Paris, Eleonora

    2016-07-01

    A systematic study is presented on a set of vanadium-bearing model compounds, representative of the most common V coordination geometries and oxidation states, analysed by means of vanadium K-edge X-ray absorption near-edge spectroscopy calculations in the full multiple scattering (FMS) framework. Analysis and calibration of the free parameters of the theory under the muffin-tin approximation (muffin-tin overlap and interstitial potential) have been carried out by fitting the experimental spectra using the MXAN program. The analysis shows a correlation of the fit parameters with the V coordination geometry and oxidation state. By making use of this correlation it is possible to approach the study of unknown V-bearing compounds with useful preliminary information. PMID:27359143

  4. Sulfur K-edge XANES spectroscopy as a tool for understanding sulfur chemical state in anaerobic granular sludge

    NASA Astrophysics Data System (ADS)

    van Hullebusch, E.; Rossano, S.; Farges, F.; Lenz, M.; Labanowski, J.; Lagarde, P.; Flank, A.-M.; Lens, P.

    2009-11-01

    Sulfur is an essential biological element, yet its biochemistry in anaerobic biofilm is poorly understood because there are few tools for studying this element in biological systems. X-ray absorption spectroscopy provides a unique approach to determining the chemical speciation of sulfur in intact biological samples. When treating sulfate containing wastewaters in full scale up-flow anaerobic sludge bed bioreactors, microbial activity forms biofilms, consisting of a complex mixture of cells and associated extracellular substances as well as undefined inorganic precipitates. In addition to the anaerobic sludges, a large variety of model compounds of S (esp. sulfides) were investigated to find consistencies in the XANES that were used to model each "valence state" of S. The results confirmed that attributing a specific valence to most sulfides is impossible as we measured a continuum of edge shifts from sulfur "-2" to "-1", depending on the electronic structure of S in the probed sulfides. In the sludges, various sulfur hot spots were probed for speciation, despite photo-reduction was sometimes a problem. First, we index the main features of complex K-edge XANES spectra for S2--type units and sulfate units. Organic sulfur compounds were also shown to contribute significantly to the sulfur species present in some anaerobic granular sludge.

  5. 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.

  6. 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.

  7. Ca and S K-edge XANES studies of calcite-acid mine water interactions

    SciTech Connect

    Myneni, S.C.B.; Perera, R.C.C.

    1997-04-01

    Heavy metal-rich acidic waters (SO{sub 4}{sup 2{minus}}, AsO{sub 4}{sup 3{minus}}, SeO{sub 4}{sup 2{minus}}, Fe{sup 2+}, Fe{sup 3+}, Al{sup 3+}, Cu{sup 2+}, Zn{sup 2+}, Cd{sup 2+}) and related ochreous coatings are common around abandoned sulfide and coal mine sites. This is mainly caused by the natural weathering of pyrite (FeS{sub 2}), arsenopyrite (FeAsS), and other metal sulfide containing shales. Acid generation in the case of pyrite can be explained by a general reaction: FeS{sub 2} + 3.5 O{sub 2} + H{sub 2}O {leftrightarrow} Fe{sup 2+} + SO{sub 4}{sup 2{minus}} + 2H{sup +}. Also, these low pH waters interact with the soils, and mobilize their soluble elements. One of the common remediation strategies is to allow these acid waters to react with limestone (CaCO{sub 3}-rich rock) and neutralize the pH and precipitate out soluble metals. Yet, the associated problem is the precipitation of Fe and Al oxides and hydroxy sulfate coatings on limestone surfaces, which block calcite reactive sites, and make them ineffective a few hours after initiation of treatment. The main objectives of this research are to examine: (1) the chemistry of limestone surface coatings, and (2) their toxic metal uptake and the conditions that inhibit their formation. Previous molecular studies using X-ray diffraction, and vibrational spectroscopy on limestone surface coatings (sampled from Athens, OH) indicate that the surface-most layer (the layer in contact with water) is composed of schwertmannite (Fe(III)-hydroxy sulfate) like phases. However, white, X-ray amorphous; Al-, sulfate- and carbonate-rich; and Ca-poor phases appeared at the interface between the limestone and the iron oxide coatings. The structure, morphology, and coordination chemistry of component major and trace elements of these white precipitate phases have not previously been examined.

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

    NASA Astrophysics Data System (ADS)

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

    2014-08-01

    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.

  9. 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. PMID:27232988

  10. 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

    2015-01-01

    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. PMID:25426546

  11. 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.

  12. Formations of hydroxyapatite and inositol hexakisphosphate in poultry litter during the composting period: sequential fractionation, P K-edge XANES and solution (31)P NMR investigations.

    PubMed

    Hashimoto, Yohey; Takamoto, Akira; Kikkawa, Ren; Murakami, Keiichi; Yamaguchi, Noriko

    2014-05-20

    Little is known about how the solubility and chemical speciation of phosphorus (P) in poultry litters are altered during the composting period. This study investigated the quantitative and qualitative changes in organic P (Po) and inorganic P (Pi) compositions in poultry litters during the seven-day composting period using sequential extraction in combination with P K-edge X-ray absorption near-edge structure (XANES) and solution (31)P nuclear magnetic resonance (NMR) spectroscopy. The result of sequential extraction illustrated that the significant decrease of H2O-P by 55% in poultry litters occurred concomitantly with the increase of HCl-Pi and HCl-Po during the composting period (p < 0.05). X-ray diffraction results for poultry litter samples showed three distinct peaks indicative of hydroxyapatite. Phosphorus K-edge XANES confirmed the increase of hydroxyapatite during the composting period, corresponding to the increase of HCl-Pi determined by the sequential extraction. The NaOH-EDTA extraction for solution (31)P NMR revealed that myo-inositol hexakisphosphate (IHP) constituted about 80% of phosphate monoesters and was increased from 16 to 28% in the poultry litter during the composting period. The combined applications of chemical extraction and molecular-spectroscopic techniques determined that water-soluble P in poultry litter was transformed into less soluble phases, primarily hydroxyapatite and IHP, during the composting period. PMID:24735189

  13. Theory and X-ray Absorption Spectroscopy for Aluminum Coordination Complexes – Al K-Edge Studies of Charge and Bonding in (BDI)Al, (BDI)AlR2, and (BDI)AlX2 Complexes.

    PubMed

    Altman, Alison B; Pemmaraju, C D; Camp, Clément; Arnold, John; Minasian, Stefan G; Prendergast, David; Shuh, David K; Tyliszczak, Tolek

    2015-08-19

    Polarized aluminum K-edge X-ray absorption near edge structure (XANES) spectroscopy and first-principles calculations were used to probe electronic structure in a series of (BDI)Al, (BDI)AlX2, and (BDI)AlR2 coordination compounds (X = F, Cl, I; R = H, Me; BDI = 2,6-diisopropylphenyl-β-diketiminate). Spectral interpretations were guided by examination of the calculated transition energies and polarization-dependent oscillator strengths, which agreed well with the XANES spectroscopy measurements. Pre-edge features were assigned to transitions associated with the Al 3p orbitals involved in metal-ligand bonding. Qualitative trends in Al 1s core energy and valence orbital occupation were established through a systematic comparison of excited states derived from Al 3p orbitals with similar symmetries in a molecular orbital framework. These trends suggested that the higher transition energies observed for (BDI)AlX2 systems with more electronegative X(1-) ligands could be ascribed to a decrease in electron density around the aluminum atom, which causes an increase in the attractive potential of the Al nucleus and concomitant increase in the binding energy of the Al 1s core orbitals. For (BDI)Al and (BDI)AlH2 the experimental Al K-edge XANES spectra and spectra calculated using the eXcited electron and Core-Hole (XCH) approach had nearly identical energies for transitions to final state orbitals of similar composition and symmetry. These results implied that the charge distributions about the aluminum atoms in (BDI)Al and (BDI)AlH2 are similar relative to the (BDI)AlX2 and (BDI)AlMe2 compounds, despite having different formal oxidation states of +1 and +3, respectively. However, (BDI)Al was unique in that it exhibited a low-energy feature that was attributed to transitions into a low-lying p-orbital of b1 symmetry that is localized on Al and orthogonal to the (BDI)Al plane. The presence of this low-energy unoccupied molecular orbital on electron-rich (BDI)Al distinguishes

  14. 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

  15. 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.

  16. Ab initio x-ray absorption study of copper K-edge XANES spectra in Cu(II) compounds

    SciTech Connect

    Chaboy, Jesus; Munoz-Paez, Adela; Carrera, Flora; Merkling, Patrick; Marcos, Enrique Sanchez

    2005-04-01

    This work reports a theoretical study of the x-ray absorption near-edge structure spectra at the Cu K edge in several Cu(II) complexes with N-coordinating ligands showing a square-planar arrangement around metal cation. It is shown that single-channel multiple-scattering calculations are not able to reproduce the experimental spectra. The comparison between experimental data and ab initio computations indicates the need of including the contribution of two electronic configurations (3d{sup 9} and 3d{sup 10}L) to account for a proper description of the final state during the photoabsorption process. The best agreement between theory and experiment is obtained by considering a relative weight of 68% and 32% for the two absorption channels 3d{sup 10}L and 3d{sup 9}, respectively.

  17. 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.

  18. Investigation of Aluminate and Al2O3 Crystals and Melts at High Temperature Using XANES Spectroscopy

    SciTech Connect

    Neuville, Daniel R.; Roux, Jacques; Cormier, Laurent; Henderson, Grant S.; Ligny, Dominique de; Flank, Anne-Marie; Lagarde, Pierre

    2007-02-02

    Using X-ray absorption at the Al K-edge at high temperature, structural information was determined on Al2O3, CaAl2O4 (CA), Ca3Al2O6 (C3A) and CaAl2Si2O8 (anorthite) in the crystalline and liquid states (2380 K). Important changes are observed for Al2O3 where all oscillation in the XANES spectra disappear above the liquidus temperature. For the three other compositions some modifications of the XANES spectra can be attributed to changes in the Al coordination.

  19. An in situ Al K-edge XAS investigation of the local environment of H+- and Cu+-exchanged USY and ZSM-5 zeolites.

    PubMed

    Drake, Ian J; Zhang, Yihua; Gilles, Mary K; Teris Liu, C N; Nachimuthu, Ponnusamy; Perera, Rupert C C; Wakita, Hisanobu; Bell, Alexis T

    2006-06-22

    Aluminum coordination in the framework of USY and ZSM-5 zeolites containing charge-compensating cations (NH4+, H+, or Cu+) was investigated by Al K-edge EXAFS and XANES. This work was performed using a newly developed in-situ cell designed especially for acquiring soft X-ray absorption data. Both tetrahedrally and octahedrally coordinated Al were observed for hydrated H-USY and H-ZSM-5, in good agreement with 27Al NMR analyses. Upon dehydration, water desorbed from the zeolite, and octahedrally coordinated Al was converted progressively to tetrahedrally coordinated Al. These observations confirmed the hypothesis that the interaction of water with Brønsted acid protons can lead to octahedral coordination of Al without loss of Al from the zeolite lattice. When H+ is replaced with NH4+ or Cu+, charge compensating species that absorb less water, less octahedrally coordinated Al was observed. Analysis of Al K-edge EXAFS data indicates that the Al-O bond distance for tetrahedrally coordinated Al in dehydrated USY and ZSM-5 is 1.67 angstroms. Simulation of k3chi(k) for Cu+ exchanged ZSM-5 leads to an estimated distance between Cu+ and framework Al atoms of 2.79 angstroms. PMID:16800461

  20. Redox Reaction in Silicate Melts Monitored by ''Static'' In-Situ Fe K-Edge XANES up to 1180 deg. C

    SciTech Connect

    Wilke, Max; Partzsch, Georg M.; Welter, Edmund; Farges, Francois

    2007-02-02

    A new experimental setup to measure in-situ kinetics of redox reactions in silicate melts is presented. To study the progress of the Fe-redox reaction, the variation of the signal is recorded at an energy, where the difference between the spectra of the oxidized and reduced Fe in the melt is largest (''static XANES''). To control the redox conditions, the gas atmosphere could be changed between to types of gases using computer-controlled valves (N2:H2 and air, respectively). In this way, a number of reduction/oxidation cycles can be monitored in-situ and continuously. Applied at the Fe K-edge in molten silicates, we obtained a set of high quality data, which includes the very first steps of the redox reaction. An Avrami-type equation is used to investigate rate-controlling parameters for the iron oxidation/reduction kinetics for two melts (basaltic and Na trisilicate) for temperatures up to 1180 deg. C.

  1. Retention Mechanisms of Citric Acid in Ternary Kaolinite-Fe(III)-Citrate Acid Systems Using Fe K-edge EXAFS and L3,2-edge XANES Spectroscopy

    NASA Astrophysics Data System (ADS)

    Yang, Jianjun; Wang, Jian; Pan, Weinan; Regier, Tom; Hu, Yongfeng; Rumpel, Cornelia; Bolan, Nanthi; Sparks, Donald

    2016-05-01

    Organic carbon (OC) stability in tropical soils is strongly interlinked with multivalent cation interaction and mineral association. Low molecular weight organic acids (LMWOAs) represent the readily biodegradable OC. Therefore, investigating retention mechanisms of LMWOAs in mineral-cation-LMWOAs systems is critical to understanding soil C cycling. Given the general acidic conditions and dominance of kaolinite in tropical soils, we investigated the retention mechanisms of citric acid (CA) in kaolinite-Fe(III)-CA systems with various Fe/CA molar ratios at pH ~3.5 using Fe K-edge EXAFS and L3,2-edge XANES techniques. With Fe/CA molar ratios >2, the formed ferrihydrite mainly contributed to CA retention through adsorption and/or coprecipitation. With Fe/CA molar ratios from 2 to 0.5, ternary complexation of CA to kaolinite via a five-coordinated Fe(III) bridge retained higher CA than ferrihydrite-induced adsorption and/or coprecipitation. With Fe/CA molar ratios ≤0.5, kaolinite-Fe(III)-citrate complexation preferentially occurred, but less CA was retained than via outer-sphere kaolinite-CA complexation. This study highlighted the significant impact of varied Fe/CA molar ratios on CA retention mechanisms in kaolinite-Fe(III)-CA systems under acidic conditions, and clearly showed the important contribution of Fe-bridged ternary complexation on CA retention. These findings will enhance our understanding of the dynamics of CA and other LMWOAs in tropical soils.

  2. 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

    2013-09-01

    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. PMID:23924171

  3. Retention Mechanisms of Citric Acid in Ternary Kaolinite-Fe(III)-Citrate Acid Systems Using Fe K-edge EXAFS and L3,2-edge XANES Spectroscopy.

    PubMed

    Yang, Jianjun; Wang, Jian; Pan, Weinan; Regier, Tom; Hu, Yongfeng; Rumpel, Cornelia; Bolan, Nanthi; Sparks, Donald

    2016-01-01

    Organic carbon (OC) stability in tropical soils is strongly interlinked with multivalent cation interaction and mineral association. Low molecular weight organic acids (LMWOAs) represent the readily biodegradable OC. Therefore, investigating retention mechanisms of LMWOAs in mineral-cation-LMWOAs systems is critical to understanding soil C cycling. Given the general acidic conditions and dominance of kaolinite in tropical soils, we investigated the retention mechanisms of citric acid (CA) in kaolinite-Fe(III)-CA systems with various Fe/CA molar ratios at pH ~3.5 using Fe K-edge EXAFS and L3,2-edge XANES techniques. With Fe/CA molar ratios >2, the formed ferrihydrite mainly contributed to CA retention through adsorption and/or coprecipitation. With Fe/CA molar ratios from 2 to 0.5, ternary complexation of CA to kaolinite via a five-coordinated Fe(III) bridge retained higher CA than ferrihydrite-induced adsorption and/or coprecipitation. With Fe/CA molar ratios ≤0.5, kaolinite-Fe(III)-citrate complexation preferentially occurred, but less CA was retained than via outer-sphere kaolinite-CA complexation. This study highlighted the significant impact of varied Fe/CA molar ratios on CA retention mechanisms in kaolinite-Fe(III)-CA systems under acidic conditions, and clearly showed the important contribution of Fe-bridged ternary complexation on CA retention. These findings will enhance our understanding of the dynamics of CA and other LMWOAs in tropical soils. PMID:27212680

  4. Retention Mechanisms of Citric Acid in Ternary Kaolinite-Fe(III)-Citrate Acid Systems Using Fe K-edge EXAFS and L3,2-edge XANES Spectroscopy

    PubMed Central

    Yang, Jianjun; Wang, Jian; Pan, Weinan; Regier, Tom; Hu, Yongfeng; Rumpel, Cornelia; Bolan, Nanthi; Sparks, Donald

    2016-01-01

    Organic carbon (OC) stability in tropical soils is strongly interlinked with multivalent cation interaction and mineral association. Low molecular weight organic acids (LMWOAs) represent the readily biodegradable OC. Therefore, investigating retention mechanisms of LMWOAs in mineral-cation-LMWOAs systems is critical to understanding soil C cycling. Given the general acidic conditions and dominance of kaolinite in tropical soils, we investigated the retention mechanisms of citric acid (CA) in kaolinite-Fe(III)-CA systems with various Fe/CA molar ratios at pH ~3.5 using Fe K-edge EXAFS and L3,2-edge XANES techniques. With Fe/CA molar ratios >2, the formed ferrihydrite mainly contributed to CA retention through adsorption and/or coprecipitation. With Fe/CA molar ratios from 2 to 0.5, ternary complexation of CA to kaolinite via a five-coordinated Fe(III) bridge retained higher CA than ferrihydrite-induced adsorption and/or coprecipitation. With Fe/CA molar ratios ≤0.5, kaolinite-Fe(III)-citrate complexation preferentially occurred, but less CA was retained than via outer-sphere kaolinite-CA complexation. This study highlighted the significant impact of varied Fe/CA molar ratios on CA retention mechanisms in kaolinite-Fe(III)-CA systems under acidic conditions, and clearly showed the important contribution of Fe-bridged ternary complexation on CA retention. These findings will enhance our understanding of the dynamics of CA and other LMWOAs in tropical soils. PMID:27212680

  5. Retention mechanisms of citric acid in ternary kaolinite-Fe(III)-citrate acid systems using Fe K-edge EXAFS and L3,2-edge XANES spectroscopy

    DOE PAGESBeta

    Yang, Jianjun; Wang, Jian; Pan, Weinan; Regier, Tom; Hu, Yongfeng; Rumpel, Cornelia; Bolan, Nanthi; Sparks, Donald

    2016-05-23

    Organic carbon (OC) stability in tropical soils is strongly interlinked with multivalent cation interaction and mineral association. Low molecular weight organic acids (LMWOAs) represent the readily biodegradable OC. Therefore, investigating retention mechanisms of LMWOAs in mineral-cation-LMWOAs systems is critical to understanding soil C cycling. Given the general acidic conditions and dominance of kaolinite in tropical soils, we investigated the retention mechanisms of citric acid (CA) in kaolinite-Fe(III)-CA systems with various Fe/CA molar ratios at pH ~3.5 using Fe K-edge EXAFS and L-3,2-edge XANES techniques. With Fe/CA molar ratios >2, the formed ferrihydrite mainly contributed to CA retention through adsorption and/ormore » coprecipitation. With Fe/CA molar ratios from 2 to 0.5, ternary complexation of CA to kaolinite via a five-coordinated Fe(III) bridge retained higher CA than ferrihydrite-induced adsorption and/or coprecipitation. With Fe/CA molar ratios ≤ 0.5, kaolinite-Fe(III)-citrate complexation preferentially occurred, but less CA was retained than via outer-sphere kaolinite-CA complexation. This study highlighted the significant impact of varied Fe/CA molar ratios on CA retention mechanisms in kaolinite-Fe(III)-CA systems under acidic conditions, and clearly showed the important contribution of Fe-bridged ternary complexation on CA retention. In conclusion, these findings will enhance our understanding of the dynamics of CA and other LMWOAs in tropical soils.« less

  6. Combined Sulfur K-edge XANES Spectroscopy and Stable Isotope Analysis of Fulvic Acids and Groundwater Sulfate Identify Sulfur Cycling in a Karstic Catchment Area

    SciTech Connect

    Einsiedl,F.; Schafer, T.; Northrup, P.

    2007-01-01

    Chemical and isotope analyses on groundwater sulfate, atmospheric deposition sulfate and fulvic acids (FAs) associated sulfur were used to determine the S cycling in a karstic catchment area of the Franconian Alb, Southern Germany. Sulfur K-edge X-ray absorption near edge structure (XANES) spectroscopy provided information on the oxidation state and the mechanism of the incorporation of sulfur in FAs. During base flow {delta}{sup 34}S values of groundwater sulfate were slightly depleted to those of recent atmospheric sulfate deposition with mean amount-weighted {delta}{sup 34}S values of around + 3{per_thousand}. The {delta}{sup 18}O values of groundwater sulfate shifted to lower values compared to those of atmospheric deposition and indicated steadiness from base flow to peak flow. The reduced sulfur species (S{sub -1}/thiol; S{sub 0}/thiophene, disulfide, S{sub +2}2/sulfoxide) of soil FAs averaged around 49% of the total sulfur and {delta}{sup 34}S value in FAs was found to be 0.5{per_thousand}. The formation of polysulfides and thiols in FAs in concert with a decreasing isotope value of {delta}{sup 34}S in FAs with respect to those of atmospheric deposition sulfate suggests oxidation of H{sub 2}S, enriched in the {sup 32}S isotope, with organic material. The depletion of {delta}{sup 18}O-SO{sub 4}{sup 2-} by several per mil in groundwater sulfate with respect to those of atmospheric deposition is, therefore, consistent with the hypothesis that SO{sub 4}{sup 2-} has been cycled through the organic S pool as well as that groundwater sulfate is formed by oxidation of H{sub 2}S with organic matter in the mineral soil of the catchment area.

  7. Polarized XAFS study of Al K-edge for m-plane AlGaN films

    NASA Astrophysics Data System (ADS)

    Miyanaga, T.; Azuhata, T.; Nakajima, K.; Nagoya, H.; Hazu, K.; Chichibu, S. F.

    2014-04-01

    Local structures around Al atoms in high-quality m-plane AlxGa1-xN films (x=0.32 and 0.58) deposited on m-plane GaN substrates by the NH3 source molecular beam epitaxy method were investigated by Al K-edge X-ray absorption fine structure (XAFS) for the first time. XAFS spectra were measured using a linearly-polarized X-ray source from synchrotron radiation for three different directions; along the c-, a-, and m-axes. The interatomic distances along the a-axis are close to Ga-Ga distance in GaN, indicating that the local structures are strongly affected by GaN substrates. The localization of Al atoms was observed for the Al0.32Ga0.68N film.

  8. Distribution and oxidation state of Ge, Cu and Fe in sphalerite by μ-XRF and K-edge μ-XANES: insights into Ge incorporation, partitioning and isotopic fractionation

    NASA Astrophysics Data System (ADS)

    Belissont, Rémi; Muñoz, Manuel; Boiron, Marie-Christine; Luais, Béatrice; Mathon, Olivier

    2016-03-01

    Synchrotron-based microscale X-ray absorption near edge structure spectroscopy (μ-XANES) has been combined with X-ray fluorescence (μ-XRF) mapping to investigate Ge, Cu and Fe oxidation states in compositionally zoned Ge-rich sphalerite from the Saint-Salvy deposit (France). The present study aims at improving our understanding of substitution mechanisms and trace element uptake relative to Ge isotope fractionation in sphalerite. K-Edge XANES records of various Ge-, Cu- and Fe-bearing sulphides are presented for comparison with sphalerite, and ab initio calculations at the Ge K-edge complete our experimental data. The Ge K-edge spectra of the Ge-bearing sphalerite are identical to those of germanite, renierite and briartite, indicating the presence of tetrahedrally-coordinated Ge4+. In addition, Cu and Fe K-edge spectra suggest the presence of Cu+ and Fe2+, respectively, in the tetrahedral site. No significant differences in the oxidation states of Ge, Cu and Fe were observed within or between the zoning types or between the samples. The intake of Ge4+ in sphalerite may therefore occur in the tetrahedral divalent metal site via coupled substitutions charge-balanced by monovalent elements such as 3Zn2+ ↔ Ge4+ + 2Cu+, resulting in a strong Ge-Cu elemental correlation, or, when Ge does not correlate with monovalent elements, through the creation of lattice vacancies such as 2Zn2+ ↔ Ge4+ + □ (vacancy). The tetravalent state of Ge is compatible with temperature-related Ge isotopic fractionation and can explain the large range of δ74Ge measured in the Saint-Salvy sphalerite. Moreover, the exceptional enrichment in Ge and the large variations in the 'bulk' Ge contents in these sphalerites do not appear to be related to charge effects but would instead result from the effect of temperature-related partitioning.

  9. Mn K-Edge XANES and Kβ XES Studies of Two Mn–Oxo Binuclear Complexes: Investigation of Three Different Oxidation States Relevant to the Oxygen-Evolving Complex of Photosystem II

    PubMed Central

    Visser, Hendrik; Anxolabéhère-Mallart, Elodie; Bergmann, Uwe; Glatzel, Pieter; Robblee, John H.; Cramer, Stephen P.; Girerd, Jean-Jacques; Sauer, Kenneth; Klein, Melvin P.; Yachandra, Vittal K.

    2014-01-01

    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 Kβ X-ray emission spectroscopy (Kβ XES). The two manganese compounds are the di-μ-oxo compound [L′2MnIIIO2MnIVL′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-μ-oxo compound [LMnIIIOMnIIIL](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 MnIVMnIV species for the di-μ-oxo compound and the MnIIIMnIV and MnIVMnIV species for the mono-μ-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-μ-oxo and linear mono-μ-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, Kβ XES spectra show less dependence on ligand environment. The Kβ1,3 peak energies are comparable for the di-μ-oxo and mono

  10. 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. PMID:22284519

  11. 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.

  12. Electrochemically-Induced Redox Reactions in Basalt at High Pressure and Temperature: An Iron and Vanadium K-edge XANES Study

    NASA Astrophysics Data System (ADS)

    Kavner, A.; Walker, D.; Newville, M.; Sutton, S. R.

    2005-12-01

    An applied electric field across a silicate sample at high pressures and temperatures in a piston cylinder apparatus can generate a wide range of oxidation states of polyvalent cations within a single experiment. If two or more polyvalent cations are included, this technique can be used to cross-calibrate oxybarometers within a single experiment. The redox state of Fe and V within a partially melted basaltic silicate was manipulated in situ in a piston-cylinder experiment with a DC power supply providing a source and sink of electrons to the sample. A 1V electrical potential differential was applied across vanadium-doped and Fe-bearing synthetic basalt samples for 24 hrs. at 20 kbar and 1400°C in a specially-designed piston cylinder sample assembly. Three experiments were performed: a control sample with no applied voltage, one with bottom cathode and top anode, and a third with top cathode and bottom anode. Synchrotron-based x-ray absorption near edge structure (XANES) spectroscopy was used to provide spot analysis of iron and vanadium oxidation states with 5μm x 5μm spatial resolution throughout the recovered samples. Systematic spatial changes of increasing oxidation states of V and Fe were observed approaching the anode. The differences in oxidation states were mapped to a corresponding local effective oxygen fugacity by comparison and extension of a calibration of vanadium oxidation states as a function of controlled oxygen fugacity from a previous study (Sutton et al., 2005, GCA, vol. 69, pp. 2333-2348). The vanadium mapping indicates that a 1V potential drop across the sample induces effective oxygen fugacity perturbations in excess of ten orders of magnitude. The presence of both Fe and V within the same sample provides a wide range of oxygen fugacity cross-calibration in these recovered samples. A relationship between oxygen fugacity and electrochemical driving force is derived. The experimental results are in good agreement with the derived

  13. 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

  14. Application of Fe K-edge XANES determinations of Fe3+/totalFe in garnet to peridotite xenoliths from the Udachnaya Kimberlite

    NASA Astrophysics Data System (ADS)

    Yaxley, G. M.; Berry, A. J.; Woodland, A. B.; Kamenetsky, V. S.; Paterson, D.; de Jonge, M. D.; Howard, D. L.

    2012-04-01

    The garnet structure can accommodate both Fe2+ and Fe3+. Garnet Fe3+/∑Fe in kimberlite-bourne garnet peridotite xenoliths can be used to determine the oxygen fugacity (fO2) of the cratonic lithosphere. This is important as an indicator of diamond (versus carbonate) stability. In cratonic lithosphere the ƒO2 of peridotite is expected to broadly decrease with increasing depth, and is consistent with graphite or diamond stability. However metasomatic events may locally perturb this trend, possibly leading to oxidation that could result in diamond breakdown or resorption. Such events will usually be recorded by the coexisting garnet. Fe3+/∑Fe of garnets has traditionally been determined by Mössbauer Spectroscopy of powdered samples. This lacks spatial resolution and the data for each measurement take several days to acquire. X-ray Absorption Near Edge Structure (XANES) spectroscopy is now commonly being used to determine Fe3+/∑Fe in minerals, is capable of micron spatial resolution and spectra can be recorded in ~15 minutes. We have recently reported a new method for quantifying Fe3+/∑Fe from the XANES spectra of mantle garnets with an accuracy and precision comparable to Mössbauer Spectroscopy. We applied the XANES technique to investigate the ƒO2-depth variation in the Siberian Craton using a suite of fresh garnet lherzolites from the Udachnaya East kimberlite. Garnet Fe3+/∑Fe was detemined using XANES spectroscopy on the X-ray Fluorescence Microscopy beamline of the Australian Synchrotron. XANES spectra were recorded in fluorescence mode from garnets prepared as either polished thin sections or electron probe mounts. A calibration curve relating the spectra to Fe3+/∑Fe of mantle garnets previously analysed by Mössbauer spectroscopy allowed garnet unknowns to be quantified. Thermobarometry established that the samples range in pressure from 3.9-7.1 GPa and lie along a typical cratonic geotherm. Several samples exhibit elevated abundances of Ti, Zr

  15. Organic carbon and sulphur compounds in wetland soils: insights on structure and transformation processes using K-edge XANES and NMR spectroscopy

    NASA Astrophysics Data System (ADS)

    Jokic, Aleksander; Cutler, Jeffrey N.; Ponomarenko, Elena; van der Kamp, Garth; Anderson, Darwin W.

    2003-07-01

    X-ray absorption near-edge structure (XANES) and nuclear magnetic resonance (NMR) spectroscopy were used in combination to characterize organic carbon structures in a series of wetland soils in Saskatchewan, and XANES spectroscopy was also used to examine sulphur speciation in the soils. The organic C contents of most of the wetland soils are consistently higher by a factor of two to five times compared to adjacent well-drained soils. NMR analyses indicate that the organic matter in the wetland soils consists of predominantly aliphatic structures such as carbohydrates and long chain poly(methylene) units which are refractory structures found in plant waxes. The poly(methylene) structures have a significant capacity to sorb nonpolar organic molecules. The phenolic OH and carboxyl group content of the wetland soils studied is an additional significant factor in their sequestering ability for heavy metals or pesticides. Carbon XANES spectroscopy shows that the surface (˜10 nm) layer of particulate organic matter has a structure dominated by aromatic, carbohydrate and carboxylic acid-like material apparently derived from partially degraded lignin and cellulose polymers which are adsorbed onto clay minerals. The aliphatic structures remaining in this surface layer are probably recalcitrant (poly)methylene units. At a depth of ˜100 nm, the aliphatic content significantly increases suggesting the presence of more labile structures. The presence of these more labile aliphatic compounds may be due to slow decomposition rates in the wet, often cool environments present and to the protective action of the more refractory components in the surface ˜10 nm of the organic matter. Drying of the wetlands, either by draining or as a result of climate change, is likely to result in the rapid decomposition of these labile organic structures releasing carbon dioxide. Our data indicate that the preservation of the organic carbon compounds in these soils is a result of their presence

  16. Temperature dependence of Zr and Ti K-edge XANES spectra for para- and ferro-electric perovskite-type PbZrO3, PbTiO3 and BaTiO3

    NASA Astrophysics Data System (ADS)

    Yoshiasa, A.; Nakatani, T.; Hiratoko, T.; Tobase, T.; Nakatsuka, A.; Okube, M.; Arima, H.; Sugiyama, K.

    2016-05-01

    Zr and Ti K-edge XANES spectra of PbZrO3, PbTiO3 and BaTiO3 perovskite-type compounds were measured in the temperature range from 10K to 850K. Quantitative comparisons for the near-edge spectra were performed in a wide temperature range using the absorption intensity invariant point (AIIP) standardization. Clear temperature dependence for pre-edge shoulder is identified by the calculating the temperature difference of the XANES spectrum intensity. Decrease of pre-edge shoulder and peak intensity is observed only in the para- and ferro-electric phases and draw curves, not straight lines. The gradients for shoulder and pre-edge peak intensity are rich in a variety. The decrease in absorption of pre-edge peak and shoulder is speculated due to the shift from the off-centre position of the Zr atom with respect to the oxygen octahedron to center position. The Zr ion in the PbZrO3 para-electric phase has same temperature behaviors of Ti ions in the ferroelectric perovskite.

  17. Electronic defect states at the LaAlO3/SrTiO3 heterointerface revealed by O K-edge X-ray absorption spectroscopy.

    PubMed

    Palina, Natalia; Annadi, Anil; Asmara, Teguh Citra; Diao, Caozheng; Yu, Xiaojiang; Breese, Mark B H; Venkatesan, T; Ariando; Rusydi, Andrivo

    2016-05-18

    Interfaces of two dissimilar complex oxides exhibit exotic physical properties that are absent in their parent compounds. Of particular interest is insulating LaAlO3 films on an insulating SrTiO3 substrate, where transport measurements have shown a metal-insulator transition as a function of LaAlO3 thickness. Their origin has become the subject of intense research, yet a unifying consensus remains elusive. Here, we report evidence for the electronic reconstruction in both insulating and conducting LaAlO3/SrTiO3 heterointerfaces revealed by O K-edge X-ray absorption spectroscopy. For the insulating samples, the O K-edge XAS spectrum exhibits features characteristic of electronically active point defects identified as noninteger valence states of Ti. For conducting samples, a new shape-resonance at ∼540.5 eV, characteristic of molecular-like oxygen (empty O-2p band), is observed. This implies that the concentration of electronic defects has increased in proportion with LaAlO3 thickness. For larger defect concentrations, the electronic defect states are no longer localized at the Ti orbitals and exhibit pronounced O 2p-O 2p character. Our results demonstrate that, above a critical thickness, the delocalization of O 2p electronic states can be linked to the presence of oxygen vacancies and is responsible for the enhancement of conductivity at the oxide heterointerfaces. PMID:27146607

  18. XAS Study at Mo and Co K-Edges of the Sulfidation of a CoMo / Al2O3 Hydrotreating Catalyst

    NASA Astrophysics Data System (ADS)

    Pichon, C.; Gandubert, A. D.; Legens, C.; Guillaume, D.

    2007-02-01

    Because of its impact on environment, the removal of sulfur is an indispensable step, called hydrotreatment, in the refining of petroleum. One of the most commonly used hydrotreating catalysts is CoMo-type catalyst which is composed of molybdenum disulfide slabs promoted by cobalt atoms (CoMoS phase) and well dispersed on a high specific area alumina. As far as the highest sulfur content allowed in gasoline and diesel is continually decreasing, more and more efficient and active hydrotreating catalysts are required. In order to optimize the reactivity of the CoMo-type catalyst in hydrotreatment, a better understanding of the processes used to produce the active phase (CoMoS slabs) of the catalyst is necessary. The study reported here deals with the sulfiding mechanism of the slabs and the influence of temperature on the phenomenon. Ex situ X-ray absorption spectroscopy (XANES and EXAFS) was used to study the evolution of the structure of CoMo-type catalyst sulfided at various temperatures (from 293 to 873 K). XAS analysis was performed at both molybdenum and cobalt K-edges to obtain a cross-characterization of the sulfidation of the slabs. It evidenced the formation of various compounds, including two molybdenum oxides, MoS3 (or MoS3-like compound) and Co9S8, at specific steps of the sulfiding process. It showed the role of intermediate played by MoS3 (or MoS3-like compound) during the formation of the slabs and the competition between the appearance of promoted slabs (CoMoS phase) and Co9S8. At last, it leaded to the proposal of a mechanism for the sulfidation of the catalyst.

  19. XAS Study at Mo and Co K-Edges of the Sulfidation of a CoMo / Al2O3 Hydrotreating Catalyst

    SciTech Connect

    Pichon, C.; Gandubert, A. D.; Legens, C.; Guillaume, D.

    2007-02-02

    Because of its impact on environment, the removal of sulfur is an indispensable step, called hydrotreatment, in the refining of petroleum. One of the most commonly used hydrotreating catalysts is CoMo-type catalyst which is composed of molybdenum disulfide slabs promoted by cobalt atoms (CoMoS phase) and well dispersed on a high specific area alumina. As far as the highest sulfur content allowed in gasoline and diesel is continually decreasing, more and more efficient and active hydrotreating catalysts are required. In order to optimize the reactivity of the CoMo-type catalyst in hydrotreatment, a better understanding of the processes used to produce the active phase (CoMoS slabs) of the catalyst is necessary. The study reported here deals with the sulfiding mechanism of the slabs and the influence of temperature on the phenomenon. Ex situ X-ray absorption spectroscopy (XANES and EXAFS) was used to study the evolution of the structure of CoMo-type catalyst sulfided at various temperatures (from 293 to 873 K). XAS analysis was performed at both molybdenum and cobalt K-edges to obtain a cross-characterization of the sulfidation of the slabs. It evidenced the formation of various compounds, including two molybdenum oxides, MoS3 (or MoS3-like compound) and Co9S8, at specific steps of the sulfiding process. It showed the role of intermediate played by MoS3 (or MoS3-like compound) during the formation of the slabs and the competition between the appearance of promoted slabs (CoMoS phase) and Co9S8. At last, it leaded to the proposal of a mechanism for the sulfidation of the catalyst.

  20. Double conical crystal x-ray spectrometer for high resolution ultrafast x-ray absorption near-edge spectroscopy of Al K edge

    NASA Astrophysics Data System (ADS)

    Levy, A.; Dorchies, F.; Fourment, C.; Harmand, M.; Hulin, S.; Santos, J. J.; Descamps, D.; Petit, S.; Bouillaud, R.

    2010-06-01

    An x-ray spectrometer devoted to dynamical studies of transient systems using the x-ray absorption fine spectroscopy technique is presented in this article. Using an ultrafast laser-induced x-ray source, this optical device based on a set of two potassium acid phthalate conical crystals allows the extraction of x-ray absorption near-edge spectroscopy structures following the Al absorption K edge. The proposed experimental protocol leads to a measurement of the absorption spectra free from any crystal reflectivity defaults and shot-to-shot x-ray spectral fluctuation. According to the detailed analysis of the experimental results, a spectral resolution of 0.7 eV rms and relative fluctuation lower than 1% rms are achieved, demonstrated to be limited by the statistics of photon counting on the x-ray detector.

  1. The effect of zirconia content on the structure of zirconia-silica xerogels as determined by x-ray and neutron diffraction and Zr K-edge EXAFS and XANES

    NASA Astrophysics Data System (ADS)

    Mountjoy, G.; Anderson, R.; Newport, R. J.; Smith, M. E.

    2000-04-01

    We present combined x-ray and neutron diffraction, and extended x-ray absorption fine structure (EXAFS) and x-ray absorption near edge structure (XANES) results on a single set of (ZrO2 )x (SiO2 )1-x xerogel samples. In these samples, there is improved homogeneity of Zr compared to our previous study, due to greater dilution of the precursor Zr n-propoxide in propan-1-ol. Structural parameters obtained from model fitting of the diffraction and EXAFS data are compared with those in reference compounds. A qualitative comparison of XANES spectra is also made. The results show that for xicons/Journals/Common/geq" ALT="geq" ALIGN="TOP"/> 0.3 there is phase separation of ZrO2 and the Zr environment is similar to that in monoclinic ZrO2 and Zr hydroxide. For xicons/Journals/Common/leq" ALT="leq" ALIGN="TOP"/> 0.2 there is no phase separation, the SiO2 network is distorted and the Zr coordination is similar to that in Zr n-propoxide, with some Zr-Zr clustering.

  2. 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

  3. Carbon K-Edge XANES Spectromicroscopy of Natural Graphite

    SciTech Connect

    Brandes,J.; Cody, G.; Rumble, D.; Haberstroh, P.; Wirick, S.; Gelinas, Y.; Morais-Cabral, J.

    2008-01-01

    The black carbon continuum is composed of a series of carbon-rich components derived from combustion or metamorphism and characterized by contrasting environmental behavior and susceptibility to oxidation. In this work, we present a micro-scale density fractionation method that allows isolating the small quantities of soot-like and graphitic material usually found in natural samples. Organic carbon and {delta}{sup 13}C mass balance calculations were used to quantify the relative contributions of the two fractions to thermally-stable organic matter from a series of aquatic sediments. Varying proportions of soot-like and graphitic material were found in these samples, with large variations in {delta}{sup 13}C signatures suggesting important differences in their origin and/or dynamics in the environment.

  4. Properties of impurity-bearing ferrihydrite II: Insights into the surface structure and composition of pure, Al- and Si-bearing ferrihydrite from Zn(II) sorption experiments and Zn K-edge X-ray absorption spectroscopy

    NASA Astrophysics Data System (ADS)

    Cismasu, A. Cristina; Levard, Clément; Michel, F. Marc; Brown, Gordon E.

    2013-10-01

    Naturally occurring ferrihydrite often contains impurities such as Al and Si, which can impact its chemical reactivity with respect to metal(loid) adsorption and (in)organic or microbially induced reductive dissolution. However, the surface composition of impure ferrihydrites is not well constrained, and this hinders our understanding of the factors controlling the surface reactivity of these nanophases. In this study, we conducted Zn(II) adsorption experiments combined with Zn K-edge X-ray absorption spectroscopy measurements on pure ferrihydrite (Fh) and Al- or Si-bearing ferrihydrites containing 10 and 20 mol% Al or Si (referred to as 10AlFh, 20AlFh and 10SiFh, 20SiFh) to evaluate Zn(II) uptake in relation to Zn(II) speciation at their surfaces. Overall, Zn(II) uptake at the surface of AlFh is similar to that of pure Fh, and based on Zn K-edge EXAFS data, Zn(II) speciation at the surface of Fh and AlFh also appears similar. Binuclear bidentate IVZn-VIFe complexes (at ∼3.46 Å (2C[1]) and ∼3.25 Å (2C[2])) were identified at low Zn(II) surface coverages from Zn K-edge EXAFS fits. With increasing Zn(II) surface coverage, the number of second-neighbor Fe ions decreased, which was interpreted as indicating the formation of IVZn polymers at the ferrihydrite surface, and a deviation from Langmuir uptake behavior. Zn(II) uptake at the surface of SiFh samples was more significant than at Fh and AlFh surfaces, and was attributed to the formation of outer-sphere complexes (on average 24% of sorbed Zn). Although similar Zn-Fe/Zn distances were obtained for the Zn-sorbed SiFh samples, the number of Fe second neighbors was lower in comparison with Fh. The decrease in second-neighbor Fe is most pronounced for sample 20SiFh, suggesting that the amount of reactive surface Fe sites diminishes with increasing Si content. Although our EXAFS results shown here do not provide evidence for the existence of Zn-Al or Zn-Si complexes, their presence is not excluded for Zn-sorbed Al

  5. K-edge densitometer (KED)

    SciTech Connect

    Sprinkle, J.K.; Hansen, W.J.

    1993-02-11

    In 1979, a K-edge densitometer (KED) was installed by the Safeguards Assay group from Los Alamos National Laboratory in the PNC reprocessing plant at Tokai-mura, Japan. It uses an active nondestructive assay technique, KED, to measure the plutonium concentration of the product solution. The measurement uncertainty of an assay depends on the count time chosen, but can be 0.5% or better. The computer hardware and software were upgraded in 1992. This manual describes the operation of the instrument, with an emphasis on the user interface to the software.

  6. Compact K-edge densitometer

    SciTech Connect

    Cowder, L.R.; Klosterbuer, S.F.; Augustson, R.H.; Esmailpour, A.; Hawkins, R.; Kuhn, E.

    1984-05-01

    Los Alamos National Laboratory has designed, built, and is currently testing a compact K-edge densitometer for use by International Atomic Energy Agency (IAEA) inspectors. The unit, which can easily be moved from one location to another within a facility, is positioned outside a glovebox with the body of the instrument inserted into the glove. A fixture inside the glovebox fits around the body and positions a sample holder. A hand-held high-purity germanium detector powered by a battery pack and a Davidson portable multichannel analyzer (MCA) is used to measure the transmission through plutonium nitrate solutions at E/sub Y/ = 121.1 and 122.2 keV. The Davidson MCA is programmed to lead the user through the measurement procedure and perform all the data analyses. The instrument is currently installed at the Safeguards Analytical Laboratory, where IAEA personnel are evaluating its accuracy, ease of operation, and safety. 5 references, 5 figures, 5 tables.

  7. Al K-edge extended fine structures in X-ray emission spectra of aluminum metal and aluminum oxide measured by an electron probe microanalyzer (EPMA)

    NASA Astrophysics Data System (ADS)

    Tanuma, S.; Nishio, M.

    1998-03-01

    The radiative Auger satellite peaks of Al Kα for aluminum metal and aluminum oxide were measured over a small area using an electron probe microanalyzer (EPMA). The oscillation was found to be similar to the extended X-ray absorption fine structure (EXAFS) in the EPMA spectra, oscillation which was recently discovered by Hayashi et al. (1997) in the X-ray fluorescence (XRF) spectra. The measured EXAFS spectra with EPMA are in good agreement with those by Hayashi et al., but here the oscillation structure could be obtained in a few minutes over a small area by using EPMA.

  8. Effect of pressure and quench rate on V and Fe XANES spectra for synthetic basalt and andesitic glasses

    NASA Astrophysics Data System (ADS)

    Ardia, P.; Gerbode, C. N.; Hirschmann, M. M.; Newville, M.

    2010-12-01

    Multivalent elements are potential indicators of magmatic oxygen fugacity (fO2). Changes in oxidation state of V (2+, 3+, 4+, and 5+) and Fe (2+, 3+) influence chemical and physical behavior of melts. With proper calibration, XANES spectroscopy allows the direct measurement of V and Fe oxidation state through systematic variations in pre- and k-edge features. To investigate the pressure effect on V XANES pre- and k-edge features we conducted experiments with hydrous haplobasalt (Di40An42Ab18) doped with 0.5wt% V. Glasses were synthesized at three fixed buffers, reduced (IW: FeFeO), intermediate (NNO: NiNiO) and oxidized (RRO:RuRuO2), at 1400°C and pressures of 100 kPa, 0.5, 1.5, 3, 5, and 8 GPa for 2 hours. Glass compositions did not vary except for those at >1.5 GPa (IW, NNO) and >3 GPa (RRO), where minor cpx±gt crystals were present. The glasses were analyzed by XANES spectroscopy at the V k-edge using an undulator-based microprobe at Sector 13 GEOCARS of APS. Spectra were collected from 5400 to 5850eV with steps of 0.2 over the pre-edge region, normalized following Sutton et al. (GCA, 2005), and the pre- and k-edge intensity and position were compared. Results indicate that at each pressure the increase in fO2 is reflected by a positive shift of the pre- and k-edge, and an increase of the pre-edge intensity, consistent with previous studies. The pre-edge intensities of intermediate and oxidized glasses at 100 kPa are lower that predicted by Sutton et al. (GCA, 2005), possibly owing to a compositional effect on V XANES spectra. The effect is more pronounced at NNO and RRO at high pressure, perhaps suggesting a pressure-induced change in V coordination or possibly owing to slow kinetics of redox equilibration in our assembly. To observe the approach to equilibrium between external buffer and the liquid, we also conducted a time series experiment at NiNiO, 1.5 GPa, 1400°C with annealing times of 5, 30, 120, 360, and 1560 min. With time, the pre-edge intensity

  9. Sulfate formation on SOx trapping materials studied by Cu and S K-edge XAFS.

    PubMed

    Dathe, Hendrik; Jentys, Andreas; Lercher, Johannes A

    2005-03-21

    The elementary steps during oxidative chemisorption of SO2 by a novel composite material consisting of highly disordered benzene tri-carboxylate metal organic framework materials with Cu as central cation and BaCl2 as a second component (Ba/Cu-BTC) and by a conventional BaCO3/Al2O3/Pt based material were investigated. EXAFS analysis on the Cu K-edge in Ba/Cu-BTC indicates the opening of the majority of the Cu-Cu pairs present in the parent Cu-BTC. Compared to Cu-BTC, the BaCl2 loaded material has hardly any micropores and has higher disorder, but it has better accessibility of the Cu2+ cations. This results from the partial destruction of the MOF structure by reaction between BaCl2 and the Cu cations. The SO2 uptake in oxidative atmosphere was higher for the Ba/Cu-BTC sample than for the BaCO3/Al2O3/Pt based material. XRD showed that on Ba/Cu-BTC the formation of BaSO4 and CuSO4 occurs in parallel to the destruction of the crystalline structure. With BaCO3/Al2O3/Pt the disappearance of carbonates was accompanied with the formation of Ba- and Al-sulfates. XANES at the S K-edge was used to determine the oxidation states of sulfur and to differentiate between the sulfate species formed. At low temperatures (473 K) BaSO4 was formed preferentially (53 mol% BaSO4, 47 mol% CuSO4), while at higher temperatures (and higher sulfate loading) CuSO4 was the most abundant species (42 mol% BaSO4, 58 mol% CuSO4). In contrast, on the BaCO3/Al2O3/Pt based material the relative concentration of the sulfate species (i.e., BaSO4 and Al2(SO4)3) as function of the temperature remained constant. PMID:19791346

  10. Characterization of Oxygen Containing Functional Groups on Carbon Materials with Oxygen K-edge X-ray Absorption Near Edge Structure Spectroscopy

    SciTech Connect

    K Kim; P Zhu; L Na; X Ma; Y Chen

    2011-12-31

    Surface functional groups on carbon materials are critical to their surface properties and related applications. Many characterization techniques have been used to identify and quantify the surface functional groups, but none is completely satisfactory especially for quantification. In this work, we used oxygen K-edge X-ray absorption near edge structure (XANES) spectroscopy to identify and quantify the oxygen containing surface functional groups on carbon materials. XANES spectra were collected in fluorescence yield mode to minimize charging effect due to poor sample conductivity which can potentially distort XANES spectra. The surface functional groups are grouped into three types, namely carboxyl-type, carbonyl-type, and hydroxyl-type. XANES spectra of the same type are very similar while spectra of different types are significantly different. Two activated carbon samples were analyzed by XANES. The total oxygen contents of the samples were estimated from the edge step of their XANES spectra, and the identity and abundance of different functional groups were determined by fitting of the sample XANES spectrum to a linear combination of spectra of the reference compounds. It is concluded that oxygen K-edge XANES spectroscopy is a reliable characterization technique for the identification and quantification of surface functional groups on carbon materials.

  11. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2015-05-01

    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.

  13. 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.

  14. Local Structures around Si, Al and Na in Hydrated Silicate Glasses

    SciTech Connect

    Farges, Francois; Wispelaere, Sidoine de; Rossano, Stephanie; Munos, Manuel; Wilke, Max; Flank, Anne-Marie; Lagarde, Pierre

    2007-02-02

    XANES spectra were collected at the Si-, Al-, and Na K-edge in hydrous silicate glasses to understand the effect of water on the local structure around these cations. Around network forming Si and Al, no drastic changes are observed. Around Na, the dissolution of water creates more ordered environments in Al-bearing glasses and less ordered environment in Al-free glasses. Ab-initio XANES calculations were undertaken to understand the structural origins for these features. Based on these results, a bond valence model was refined that considers not only the present XANES experiments and models but also NMR information. The double percolation model refined explains, among others, the explosive properties of water-bearing hydrous melts, at the origin of a number of cataclysmic eruptions in subduction zones.

  15. 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. PMID:24046506

  16. On the Structure of the Iron K-Edge

    NASA Technical Reports Server (NTRS)

    Palmeri, P.; Mendoza, C.; Kallman, T. R.; Bautista, M. A.; White, Nicholas E. (Technical Monitor)

    2002-01-01

    It is shown that the commonly held view of a sharp Fe K edge must be modified if the decay pathways of the series of resonances converging to the K thresholds are adequately taken into account. These resonances display damped Lorentzian profiles of nearly constant widths that are smeared to impose continuity across the threshold. By modeling the effects of K damping on opacities, it is found that the broadening of the K edge grows with the ionization level of the plasma, and the appearance at high ionization of a localized absorption feature at 7.2 keV is identified as the Kbeta unresolved transition array.

  17. 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.

  18. 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.

  19. Electronic structure investigation of highly compressed aluminum with K edge absorption spectroscopy.

    PubMed

    Benuzzi-Mounaix, A; Dorchies, F; Recoules, V; Festa, F; Peyrusse, O; Levy, A; Ravasio, A; Hall, T; Koenig, M; Amadou, N; Brambrink, E; Mazevet, S

    2011-10-14

    The electronic structure evolution of highly compressed aluminum has been investigated using time resolved K edge x-ray absorption spectroscopy. A long laser pulse (500 ps, I(L)≈8×10(13) W/cm(2)) was used to create a uniform shock. A second ps pulse (I(L)≈10(17)  W/cm(2)) generated an ultrashort broadband x-ray source near the Al K edge. The main target was designed to probe aluminum at reshocked conditions up to now unexplored (3 times the solid density and temperatures around 8 eV). The hydrodynamical conditions were obtained using rear side visible diagnostics. Data were compared to ab initio and dense plasma calculations, indicating potential improvements in either description. This comparison shows that x-ray-absorption near-edge structure measurements provide a unique capability to probe matter at these extreme conditions and severally constrains theoretical approaches currently used. PMID:22107398

  20. Operando XAS study of the influence of CO and NO on methane oxidation by Pd/Al2O3

    NASA Astrophysics Data System (ADS)

    Marchionni, V.; Nachtegaal, M.; Petrov, A.; Kröcher, O.; Ferri, D.

    2016-05-01

    Methane oxidation on Pd/Al2O3 has been investigated using operando X-ray absorption spectroscopy (XAS) at the Pd K-edge. The influence of CO and NO on methane abatement has been addressed performing temperature programmed reaction runs while recording simultaneously XANES spectra. During CO oxidation Pd is reduced while methane conversion is shifted to higher temperature. NO strongly inhibits both CO and CH4 oxidation, despite the higher fraction of oxidized palladium.

  1. Photon counting spectral CT: improved material decomposition with K-edge-filtered x-rays

    NASA Astrophysics Data System (ADS)

    Shikhaliev, Polad M.

    2012-03-01

    voltage and Gd (Ek = 50.24 keV) was used for the 90 and 120 kVp tube voltages, respectively. The material selective CT images were also acquired with conventional Al filtration for comparison. The half-value layers of x-ray beams after K-edge and Al filtration were matched. The mean entrance skin exposure was 280 mR for all tube voltages and filters. The contrast-to-noise ratio (CNR) in material-decomposed images was approximately 30%-50% higher when K-edge filters were used instead of Al filters. It was concluded that K-edge filtration of x-rays provides substantial improvement of the CNR in material-selective PCSCT. Further optimization of K-edge filter materials, tube voltages, detector technology and energy bin settings will provide even higher CNR in decomposed images.

  2. 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). PMID:17429991

  3. Si K Edge Measurements of the ISM with Chandra

    NASA Astrophysics Data System (ADS)

    Schulz, Norbert S.; Corrales, Lia; Canizares, C. R.

    2016-01-01

    The Si K edge structure in X-ray spectra of the diffuse ISM is expected to exhibit substructure related to the fact that most absorption is due to silicates in dust. We surveyed high resolution X-ray spectra of a large number of bright low-mass X-ray binaries with column densities significantly larger than 10^22 cm^2. Using the to date unprecedented spectral resolution of the high energy transmission gratings onboard the Chandra X-ray observatory we find complex substructure in the Si K edge. The highest resolved spectra show two edges, one at the expected value for atomic, one at the value for most silicate compounds with the dominant contribution of the latter. There is specific subtructure from silicate optical depth caused by absorption and scattering. Some is also variable and can be attributed to ionized absorption in the vicinity of the X-ray sources.

  4. Spectral CT using multiple balanced K-edge filters.

    PubMed

    Rakvongthai, Yothin; Worstell, William; El Fakhri, Georges; Bian, Junguo; Lorsakul, Auranuch; Ouyang, Jinsong

    2015-03-01

    Our goal is to validate a spectral computed tomography (CT) system design that uses a conventional X-ray source with multiple balanced K-edge filters. By performing a simultaneously synthetic reconstruction in multiple energy bins, we obtained a good agreement between measurements and model expectations for a reasonably complex phantom. We performed simulation and data acquisition on a phantom containing multiple rods of different materials using a NeuroLogica CT scanner. Five balanced K-edge filters including Molybdenum, Cerium, Dysprosium, Erbium, and Tungsten were used separately proximal to the X-ray tube. For each sinogram bin, measured filtered vector can be defined as a product of a transmission matrix, which is determined by the filters and is independent of the imaging object, and energy-binned intensity vector. The energy-binned sinograms were then obtained by inverting the transmission matrix followed by a multiplication of the filter measurement vector. For each energy bin defined by two consecutive K-edges, a synthesized energy-binned attenuation image was obtained using filtered back-projection reconstruction. The reconstructed attenuation coefficients for each rod obtained from the experiment was in good agreement with the corresponding simulated results. Furthermore, the reconstructed attenuation coefficients for a given energy bin, agreed with National Institute of Standards and Technology reference values when beam hardening within the energy bin is small. The proposed cost-effective system design using multiple balanced K-edge filters can be used to perform spectral CT imaging at clinically relevant flux rates using conventional detectors and integrating electronics. PMID:25252276

  5. Spectral CT Using Multiple Balanced K-Edge Filters

    PubMed Central

    Rakvongthai, Yothin; Worstell, William; Fakhri, Georges El; Bian, Junguo; Lorsakul, Auranuch; Ouyang, Jinsong

    2015-01-01

    Our goal is to validate a spectral CT system design that uses a conventional X-ray source with multiple balanced K-edge filters. By performing a simultaneously synthetic reconstruction in multiple energy bins, we obtained a good agreement between measurements and model expectations for a reasonably complex phantom. We performed simulation and data acquisition on a phantom containing multiple rods of different materials using a NeuroLogica CT scanner. Five balanced K-edge filters including Molybdenum, Cerium, Dysprosium, Erbium, and Tungsten were used separately proximal to the X-ray tube. For each sinogram bin, measured filtered vector can be defined as a product of a transmission matrix, which is determined by the filters and is independent of the imaging object, and energy-binned intensity vector. The energy-binned sinograms were then obtained by inverting the transmission matrix followed by a multiplication of the filter measurement vector. For each energy bin defined by two consecutive K-edges, a synthesized energy-binned attenuation image was obtained using filtered back-projection reconstruction. The reconstructed attenuation coefficients for each rod obtained from the experiment was in good agreement with the corresponding simulated results. Furthermore, the reconstructed attenuation coefficients for a given energy bin, agreed with National Institute of Standards and Technology reference values when beam hardening within the energy bin is small. The proposed cost-effective system design using multiple balanced K-edge filters can be used to perform spectral CT imaging at clinically relevant flux rates using conventional detectors and integrating electronics. PMID:25252276

  6. Phosphorus dynamics in Swedish agricultural soils as influenced by fertilization and mineralogical properties: Insights gained from batch experiments and XANES spectroscopy.

    PubMed

    Eriksson, Ann Kristin; Hesterberg, Dean; Klysubun, Wantana; Gustafsson, Jon Petter

    2016-10-01

    The soil chemistry of phosphorus (P) is important for understanding the processes governing plant availability as well as the risk of environmental losses of P. The objective of this research was to investigate both the speciation and the pH-dependent solubility patterns of P in clayey agricultural soils in relation to soil mineralogy and fertilization history. The study focused on soil samples from six fields that were subjected to different P fertilization regimes for periods of 45 to 57years. Soil P speciation was analyzed by P K-edge XANES spectroscopy and chemical fractionation, sorption isotherms were constructed, and dissolved P was measured as a function of pH. The XANES fitting results showed that organic P and P adsorbed to Fe and Al (hydr)oxides were common P constituents in all soils. Calcium phosphates were identified in five of six soil samples. The XANES results also indicated an increase in P adsorbed to Al and to a lesser extent Fe (hydr)oxides as a result of fertilization. Moreover, the fluorescence intensity from the P K-edge XANES analysis was most strongly correlated with HCl-digestible P (r=0.81***). Consistent with the XANES analysis, laboratory sorption isotherm models showed that the Freundlich sorption coefficient (KF) was most closely related to oxalate-extractable Al. Greater proportions of Ca phosphate in two of the heavily fertilized soils in combination with enhanced PO4 solubilization upon sample acidification indicated neoformation of Ca-phosphate precipitates. The results for the unfertilized soil samples generally showed a minimum in dissolved PO4 between pH6.5 and 7.5, with increases particularly at lower pH. This behavior can be explained either by the dissolution of Al-hydroxide-type sorbents or Ca phosphates at lower pH. In fertilized soils, there was no consistent trend in pH-dependent solubilization of P, with a complex relationship to solid-phase speciation. To conclude, inorganic P species changed most dynamically in

  7. Simulating Cl K-edge X-ray absorption spectroscopy in MCl62- (M= U, Np, Pu) complexes and UOCl5- using time-dependent density functional theory

    SciTech Connect

    Govind, Niranjan; De Jong, Wibe A.

    2014-02-21

    We report simulations of the X-ray absorption near edge structure (XANES) at the Cl K-edge of actinide hexahalides MCl62- (M = U, Np, Pu) and the UOCl5- complex using linear-response time-dependent density functional theory (LR-TDDFT) extended for core excitations. To the best of our knowledge, these are the first calculations of the Cl K-edge spectra of NpCl62- and PuCl62-. In addition, the spectra are simulated with and without the environmental effects of the host crystal as well as ab initio molecular dynamics (AIMD) to capture the dynamical effects due to atomic motion. The calculated spectra are compared with experimental results, where available and the observed trends are discussed.

  8. Probing Warm Dense Matter electronic structure using X-ray absorption Near Edge Spectroscopy (XANES)

    NASA Astrophysics Data System (ADS)

    Benuzzi Mounaix, Alessandra

    2011-06-01

    The behavior and physical properties of warm dense matter, fundamental for various branches of physics including planetology and Inertial Confinement Fusion, are non trivial to simulate either theoretically, numerically or experimentally. Despite important progress obtained in the last decade on macroscopic characterization (e.g. equations of state), microscopic studies are today necessary to investigate finely the WDM structure changes, the phase transitions and to test physical hypothesis and approximations commonly used in calculations. In this work, highly compressed aluminum has been investigated with the aim of bringing information on the evolution of its electronic structure by using K-edge shift and XANES. The experiment was performed at LULI laboratory where we used one long pulse (500 ps, IL ~ 8 1013 W/cm2) to create a uniform shock and a second ps beam (IL ~ 1017 W/cm2) to generate an ultra-short broadband X-ray source near the Al K-edge. The spectra were registered by using two conical KAP Bragg crystals. The main target was designed to probe the Aluminum in reshocked conditions allowing us to probe and to test theories in an extreme regime up to now unexplored (ρ ~ 3 ρ0 and T ~ 8 eV). The hydrodynamical Al conditions were measured by using VISARs interferometers and self-emission diagnostics. By increasing the delay between the two beams, we have been able to observe the modification of absorption spectra for unloading Al conditions (ρ >= 0.5 g/cc), and to put in evidence the relocalization of the 3p valence electrons occurring in the metal-non metal transition. All data have been compared to ab initio and dense plasma calculations.

  9. Zn-K edge EXAFS study of human nails

    NASA Astrophysics Data System (ADS)

    Katsikini, M.; Mavromati, E.; Pinakidou, F.; Paloura, E. C.; Gioulekas, D.

    2009-11-01

    Extended X-ray absorption fine structure (EXAFS) spectroscopy at the Zn - K edge is applied for the study of the bonding geometry of Zn in human nails. The studied nail clippings belong to healthy donors and donors who suffer from lung diseases. Fitting of the first nearest neighboring shell of Zn reveals that it is bonded with N and S, at distances that take values in the ranges 2.00-2.04 Å and 2.23-2.28Å, respectively. Zn is four - fold coordinated and the ratio of the number of sulfur and nitrogen atoms (NS/NN) in the first coordination shell ranges from 0.52 to 1. The sample that belongs to the donor who suffers from lung fibrosis, a condition that is related to keratinization of the lung tissue, is characterized by the highest number of NS/NN. Simulation, using the FEFF8 code, of the Zn - K edge EXAFS spectra with models of tetrahedrally coordinated Zn with 1 (or 2) cysteine and 3 (or 2) histidines is satisfactory.

  10. Structural changes of nucleic acid base in aqueous solution as observed in X-ray absorption near edge structure (XANES)

    NASA Astrophysics Data System (ADS)

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

    2014-01-01

    X-ray absorption near edge structure (XANES) spectra for adenine-containing nucleotides, adenosine 5‧-monophosphate (AMP) and adenosine 5‧-triphosphate (ATP) in aqueous solutions at the nitrogen K-edge region were measured. The two intense peaks in XANES spectra are assigned to transitions of 1s electrons to the π∗ orbitals of different types of N atoms with particular bonding characteristics. The difference between their spectra is ascribed to protonation of a particular N atom. Similarity observed in XANES spectra of guanosine 5‧-monophosphate (GMP) and ATP is also interpreted as similar bonding characters of the N atoms in the nucleobase moiety.

  11. 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.

  12. K-Edge Subtraction Angiography with Synchrotron X-Rays

    SciTech Connect

    Giacomini, John C.

    1996-12-31

    The purpose of this project was to utilize dual energy, monochromatic X-rays produced from synchrotrons radiation in order to obtain noninvasive medical imaging. The application of synchrotrons radiation to medical imaging is based on the principle of iodine dichromography, first described by Bertil Jacobson of the Karolinska Institute in 1953. Medical imaging using synchrotrons radiation and K-edge dichromography was pioneered at Stanford University under the leadership of Dr. Ed Rubenstein, and the late Nobel Laureate in Physics, Dr. Robert Hofstadter. With progressive refinements in hardware, clinical-quality images were obtained of human coronary arteries utilizing peripheral injections of iodinated contrast agent. These images even now are far superior to those being presented by investigators using MRI as an imaging tool for coronary arteries. However, new supplies and instruments in the cardiac catheterization laboratory have served to transform coronary angiography into an outpatient procedure, with relatively little morbidity. We extended the principles learned with coronary angiography to noninvasive imaging of the human bronchial tree. For these images, we utilized xenon as the contrast agent, as it has a K-edge very similar to that of iodine. In this case, there is no true competing diagnostic test, and pulmonary neoplasm is an enormous public health concern. In early experiments, we demonstrated remarkably clear images of the human bronchial tree. These images have been shown internationally; however, funding difficulties primarily with the Department of Energy have not allowed for progression of this promising avenue of research. One potential criticism of the project is that in order to obtain these images, we utilized national laboratories. Some have questioned whether this would lead to a practical imaging modality. However, we have shown that the technology exists to allow for construction of a miniature storage ring, with a superconducting

  13. 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

    } region (690 cm{sup -2} per cm thickness), which is one of the lowest measured to date for tourmaline. The OH seems to be ordered strongly at the O3 site. The composition of this sample of olenite shows a trend toward the proposed olenite end-member formula, which contains only 1 OH group. The low content of F (0.01 apfu) is uncommon for natural Al-rich and Mg-poor tourmaline from granitic pegmatites. Synchrotron micro-XANES was used to detect the valence state of Fe in this crystal; it was found to have 93 {+-} 10% of the total Fe as Fe{sup 2+}. Optical absorption spectra show that the blue color is derived primarily from a combination of {sup [6]}Fe{sup 2+}, together with {sup [6]}Fe{sup 2+} interaction with a minor amount of {sup [6]}Fe{sup 3+}.

  14. Reducing radiation dose by application of optimized low-energy x-ray filters to K-edge imaging with a photon counting detector.

    PubMed

    Choi, Yu-Na; Lee, Seungwan; Kim, Hee-Joung

    2016-01-21

    K-edge imaging with photon counting x-ray detectors (PCXDs) can improve image quality compared with conventional energy integrating detectors. However, low-energy x-ray photons below the K-edge absorption energy of a target material do not contribute to image formation in the K-edge imaging and are likely to be completely absorbed by an object. In this study, we applied x-ray filters to the K-edge imaging with a PCXD based on cadmium zinc telluride for reducing radiation dose induced by low-energy x-ray photons. We used aluminum (Al) filters with different thicknesses as the low-energy x-ray filters and implemented the iodine K-edge imaging with an energy bin of 34-48 keV at the tube voltages of 50, 70 and 90 kVp. The effects of the low-energy x-ray filters on the K-edge imaging were investigated with respect to signal-difference-to-noise ratio (SDNR), entrance surface air kerma (ESAK) and figure of merit (FOM). The highest value of SDNR was observed in the K-edge imaging with a 2 mm Al filter, and the SDNR decreased as a function of the filter thicknesses. Compared to the K-edge imaging with a 2 mm Al filter, the ESAK was reduced by 66%, 48% and 39% in the K-edge imaging with a 12 mm Al filter for 50 kVp, 70 kVp and 90 kVp, respectively. The FOM values, which took into account the ESAK and SDNR, were maximized for 8, 6 to 8 and 4 mm Al filters at 50 kVp, 70 kVp and 90 kVp, respectively. We concluded that the use of an optimal low-energy filter thickness, which was determined by maximizing the FOM, could significantly reduce radiation dose while maintaining image quality in the K-edge imaging with the PCXD. PMID:26733235

  15. Reducing radiation dose by application of optimized low-energy x-ray filters to K-edge imaging with a photon counting detector

    NASA Astrophysics Data System (ADS)

    Choi, Yu-Na; Lee, Seungwan; Kim, Hee-Joung

    2016-01-01

    K-edge imaging with photon counting x-ray detectors (PCXDs) can improve image quality compared with conventional energy integrating detectors. However, low-energy x-ray photons below the K-edge absorption energy of a target material do not contribute to image formation in the K-edge imaging and are likely to be completely absorbed by an object. In this study, we applied x-ray filters to the K-edge imaging with a PCXD based on cadmium zinc telluride for reducing radiation dose induced by low-energy x-ray photons. We used aluminum (Al) filters with different thicknesses as the low-energy x-ray filters and implemented the iodine K-edge imaging with an energy bin of 34-48 keV at the tube voltages of 50, 70 and 90 kVp. The effects of the low-energy x-ray filters on the K-edge imaging were investigated with respect to signal-difference-to-noise ratio (SDNR), entrance surface air kerma (ESAK) and figure of merit (FOM). The highest value of SDNR was observed in the K-edge imaging with a 2 mm Al filter, and the SDNR decreased as a function of the filter thicknesses. Compared to the K-edge imaging with a 2 mm Al filter, the ESAK was reduced by 66%, 48% and 39% in the K-edge imaging with a 12 mm Al filter for 50 kVp, 70 kVp and 90 kVp, respectively. The FOM values, which took into account the ESAK and SDNR, were maximized for 8, 6 to 8 and 4 mm Al filters at 50 kVp, 70 kVp and 90 kVp, respectively. We concluded that the use of an optimal low-energy filter thickness, which was determined by maximizing the FOM, could significantly reduce radiation dose while maintaining image quality in the K-edge imaging with the PCXD.

  16. Portable X-Ray, K-Edge Heavy Metal Detector

    SciTech Connect

    Fricke, V.

    1999-10-25

    The X-Ray, K-Edge Heavy Metal Detection System was designed and built by Ames Laboratory and the Center for Nondestructive Evaluation at Iowa State University. The system uses a C-frame inspection head with an X-ray tube mounted on one side of the frame and an imaging unit and a high purity germanium detector on the other side. the inspection head is portable and can be easily positioned around ventilation ducts and pipes up to 36 inches in diameter. Wide angle and narrow beam X-ray shots are used to identify the type of holdup material and the amount of the contaminant. Precise assay data can be obtained within minutes of the interrogation. A profile of the containerized holdup material and a permanent record of the measurement are immediately available.

  17. Fragmentation of HCl following excitation at the chlorine K edge

    SciTech Connect

    Hansen, D.L.; Arrasate, M.E.; Cotter, J.P.

    1997-04-01

    A space-focused time-of-flight (TOF) mass spectrometer was used to study the relaxation dynamics of HCl following excitation in the vicinity of the Cl-K edge ({approximately}2.8 keV) using x-rays from B.L. 9.3.1. At the lowest resonant excitation to a {sigma}{sup *} antibonding orbital (1{sigma} {r_arrow} 6{sigma}), a significant fraction of the excited molecules decay by emission of a neutral H atom. While neutral-H emission has been observed for shallow core levels (e.g., Cl 2p in HCl), the authors believe this to be the first observation of neutral-atom emission as a significant decay channel following resonant excitation of a deep core hole. The dissociation of neutral hydrogen atoms raises the issue of how effectively dissociation competes with Auger decay in the relaxation of these deep core levels (i.e., Cl 1s). Graphical evidence is presented to support the dissociation agrument. In addition, trends in fractional ion yields from Photo-Ion Photo-Ion COincidence (PIPICO) spectra suggest the presence of post-collision interaction (PCI). While, electron spectroscopy studies are required to confirm the observation of this effect, the authors believe this to be the first evidence of PCI moderated dissociation in molecules.

  18. Structural investigation of lanthanoid coordination: a combined XANES and molecular dynamics study.

    PubMed

    D'Angelo, Paola; Zitolo, Andrea; Migliorati, Valentina; Mancini, Giordano; Persson, Ingmar; Chillemi, Giovanni

    2009-11-01

    This is the first systematic study exploring the potentiality of the X-ray absorption near edge structure (XANES) technique as a structural tool for systems containing lanthanoid(III) ions. A quantitative analysis of the XANES spectra at the K- and L(3)-edges has been carried out for three hydrated lanthanoid(III) ions, namely, Yb, Nd, and Gd, in aqueous solution and in the isostructural trifluoromethanesulfonate salts. The structural and dynamic properties of the hydrated lanthanoid(III) ions in aqueous solution have been investigated by a combined experimental-theoretical approach employing X-ray absorption spectroscopy and molecular dynamics (MD) simulations. This method allows one to perform a quantitative analysis of the XANES spectra of ionic solutions using a proper description of the thermal and structural fluctuations. XANES spectra have been computed starting from the MD trajectory, without carrying out any minimization in the structural parameter space. A comparative K- and L(3)-edge XANES data analysis is presented, demonstrating the clear advantages of the L(3)-edge XANES analysis over the K-edge studies for structural investigations of lanthanoid compounds. The second hydration shells provide a detectable contribution to the L(3)-edge spectra while the K-edge data are insensitive to the more distant coordination spheres because of the strong damping and broadening of the signal caused by the extremely large core hole widths. The XANES technique has been found to be a new valuable tool for the structural characterization of metal complexes both in the solid and in the liquid state, especially in the presence of low symmetry. PMID:19788258

  19. 2D XANES-XEOL mapping: observation of enhanced band gap emission from ZnO nanowire arrays

    NASA Astrophysics Data System (ADS)

    Wang, Zhiqiang; Guo, Xiaoxuan; Sham, Tsun-Kong

    2014-05-01

    Using 2D XANES-XEOL spectroscopy, it is found that the band gap emission of ZnO nanowire arrays is substantially enhanced i.e. that the intensity ratio between the band gap and defect emissions increases by more than an order of magnitude when the excitation energy is scanned across the O K-edge. Possible mechanisms are discussed.Using 2D XANES-XEOL spectroscopy, it is found that the band gap emission of ZnO nanowire arrays is substantially enhanced i.e. that the intensity ratio between the band gap and defect emissions increases by more than an order of magnitude when the excitation energy is scanned across the O K-edge. Possible mechanisms are discussed. Electronic supplementary information (ESI) available: XEOL spectra with different excitation energies. X-ray attenuation length vs. photon energy. Details of surface defects in ZnO NWs. The second O K-edge and Zn L-edge 2D XANES-XEOL maps. Comparison of the first and second TEY at O K-edge and Zn L-edge scans, respectively. Raman spectra of the ZnO NWs with different IBGE/IDE ratios. See DOI: 10.1039/c4nr01049c

  20. 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.

  1. Carbon K-Edge Scanning Transmission X-ray Spectromicroscopy (STXM) of Uranium Binding to Bacterial Cells

    NASA Astrophysics Data System (ADS)

    Gillow, J.; Wirick, S.; Feser, M.; Jacobsen, C.; Francis, A.

    2002-12-01

    The sorption of uranium by bacteria was studied by interrogation of the C K-absorption edge using scanning transmission x-ray spectromicroscopy (STXM). The unique imaging and spectroscopy capability of STXM was used to elucidate the chemical environment of C in the bacterial cell. Washed whole cells and cell wall preparations of bacteria commonly found in soil environments including Pseudomonas fluorescens, Bacillus subtilis, the facultative anaerobe Shewanella putrefaciens and the strict anaerobe Clostridium sp. were exposed to uranyl nitrate at pH 5. After washing to remove potential surface precipitates and non-bonded uranium the cells and walls were dried onto TEM gridx. Standards (uranyl salts and organic complexes), bacterial cells unexposed, and U-exposed cells were analyzed by STXM at 280-310 eV with the C K-edge x-ray absorption near-edge spectroscopy (XANES) examined for evidence of U in the C coordination environment. Principle spectral features of the bacteria included the 285 eV C=C and 288 eV C=O 1s-π * resonances due to the major C function groups that comprise the bacterial cell wall. There was no change in peak position of 1s-π * spectral features for whole cells or cell walls when U was present. This indicates that U does not exert an influence on the electron resonance of C when bonded as carboxylate species at the bacterial cell surface. This finding is supported by the analysis of uranyl citrate and uranyl alanine standards. The extended x-ray absorption fine structure spectroscopy region of the C K-edge of bacterial cells exposed to U shows slight changes in spectral features at >290 eV. Other absorption edges accessible by soft x-ray spectroscopy were examined; U was detected at it's NV (736.2 eV) and NIV (778.3 eV) edges however there was poor resolution of U associated with the bacteria. Analysis at the O K-edge (529 eV) provided evidence for metal-ligand interaction and forms the basis for further study to gain a molecular

  2. A XANES study of chromophores in archaeological glass

    NASA Astrophysics Data System (ADS)

    Arletti, Rossella; Quartieri, Simona; Freestone, Ian C.

    2013-04-01

    We applied X-ray absorption near edge spectroscopy (XANES) to obtain information on the origin of glass colour of several archaeological samples and on the oxidation conditions employed during their production. We studied a series of selected glass fragments—mainly from excavated primary and secondary production centres and dated to the first millennium AD—containing iron and manganese in a wide compositional range. In most of the studied samples iron is rather oxidised, while Mn K-edge XANES data show that, in all the studied glasses, Mn is mainly present in its reduced form (predominantly 2+), with the possible subordinate presence of Mn3+. The most oxidised samples are the HIMT (high iron manganese titanium) glasses, while the less oxidised ones belong to the primary natron glass series from the early Islamic tank furnaces at Bet Eliezer (Israel), and to the series coming from a Roman glass workshop excavated in Basinghall Street, London. In these glasses, iron is approximately equally distributed over the 2+ and 3+ oxidation states. The XANES analyses of two glasses which had been deliberately decolourized using Sb- and Mn-based decolourizers demonstrate that Sb is more effective than Mn as oxidant.

  3. 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

  4. Chemical Bonding In Amorphous Si Coated-carbon Nanotube As Anodes For Li ion Batteries: A XANES Study

    SciTech Connect

    Zhou, Jigang; Hu, Yongfeng; Li, Xiaolin; Wang, Chong M.; Zuin, Lucia

    2014-03-11

    The chemical bonding nature and its evolution upon electrochemical cycling in amorphous Si coated-carbon nanotube (Si-CNT) anode has been investigated using comprehensive X-ray absorption spectroscopy (XANES) at Si L- and K-edges along with C and O K-edges. The Si nanolayer on CNT is found to be anchored to CNT via Si-O-C bonding. This bond weakens upon electrochemical cycling accompanied with generation of Li2CO3 on the surface of Si-CNT. Those findings are crucial in designing further improved Si-C composite anode for lithium ion battery.

  5. Sparsity-regularized image reconstruction of decomposed K-edge data in spectral CT

    NASA Astrophysics Data System (ADS)

    Xu, Qiaofeng; Sawatzky, Alex; Anastasio, Mark A.; Schirra, Carsten O.

    2014-05-01

    The development of spectral computed tomography (CT) using binned photon-counting detectors has garnered great interest in recent years and has enabled selective imaging of K-edge materials. A practical challenge in CT image reconstruction of K-edge materials is the mitigation of image artifacts that arise from reduced-view and/or noisy decomposed sinogram data. In this note, we describe and investigate sparsity-regularized penalized weighted least squares-based image reconstruction algorithms for reconstructing K-edge images from few-view decomposed K-edge sinogram data. To exploit the inherent sparseness of typical K-edge images, we investigate use of a total variation (TV) penalty and a weighted sum of a TV penalty and an ℓ1-norm with a wavelet sparsifying transform. Computer-simulation and experimental phantom studies are conducted to quantitatively demonstrate the effectiveness of the proposed reconstruction algorithms.

  6. The origin of luminescence from di[4-(4-diphenylaminophenyl)phenyl]sulfone (DAPSF), a blue light emitter: an X-ray excited optical luminescence (XEOL) and X-ray absorption near edge structure (XANES) study.

    PubMed

    Zhang, Duo; Zhang, Hui; Zhang, Xiaohong; Sham, Tsun-Kong; Hu, Yongfeng; Sun, Xuhui

    2016-02-24

    The electronic structure and optical properties of di[4-(4-diphenylaminophenyl)phenyl]sulfone (denoted as DAPSF), a highly efficient fluorophor, have been investigated using X-ray excited optical luminescence (XEOL) and X-ray absorption near edge structure (XANES) spectroscopy at excitation energies across the C, N, O K-edges and the sulfur K-edge. The results indicate that the blue luminescence is mainly related to the sulfur functional group. PMID:26866785

  7. Determination of phosphorus speciation in dairy manure using XRD and XANES spectroscopy.

    PubMed

    Güngör, Kerem; Jürgensen, Astrid; Karthikeyan, K G

    2007-01-01

    Intensive manure application is an important source of diffuse phosphorus (P) pollution. Phosphorus availability from animal manure is influenced by its chemical speciation. The major objective of this study was to investigate the P speciation in raw and anaerobically digested dairy manure with an emphasis on the calcium (Ca) and magnesium (Mg) phosphate phases. Influent and effluent from an on-farm digester in Wisconsin were sampled and sieved, and the 25 to 53 microm size fraction was dried for X-ray powder diffraction (XRD) and P K-edge X-ray absorption near edge structure (XANES) analyses. Struvite (MgNH4PO4.6H2O) was identified in both the raw (influent) and anaerobically digested (effluent) manure using XRD. Qualitative analysis of P K-edge XANES spectra indicated that the Ca orthophosphate phases, except dicalcium phosphate anhydrous (DCPA) or monetite (CaHPO4), were not abundant in dairy manure. Linear combination fitting (LCF) of the P standard compounds showed that 57.0 and 43.0% of P was associated with DCPA and struvite, respectively, in the raw manure. In the anaerobically digested sample, 78.2% of P was present as struvite and 21.8% of P was associated with hydroxylapatite (HAp). The P speciation shifted toward Mg orthophosphates and least soluble Ca orthophosphates following anaerobic digestion. Similarity between the aqueous orthophosphate (aq-PO4), newberyite (MgHPO4.3H2O), and struvite spectra can cause inaccurate P speciation determination when dairy manure is analyzed solely using P K-edge XANES spectroscopy; however, XANES can be used in conjunction with XRD to quantify the distribution of inorganic P species in animal manure. PMID:17965388

  8. XANES and Raman spectrometry on glasses and crystals in the CAS system.

    NASA Astrophysics Data System (ADS)

    Neuville, N.; Cormier, C.; Flank, F.; Massiot, M.

    2003-04-01

    XANES and Raman spectrometry on glasses and crystals in the CAS system. DANIEL R. NEUVILLE1, LAURENT CORMIER2 ANNE-MARIE FLANK3 and DOMINIQUE MASSIOT4 1Laboratoire de physico-chimie des fluides géologiques, IPGP-CNRS-UMR7047, 4 place Jussieu, 75252 Paris 2Laboratoire de Minéralogie et de Cristallographie, Universités PARIS 6 et 7, IPGP, UMR CNRS 7590, 4 place Jussieu, 75252 Paris 3Laboratoire pour l’Utilisation du Rayonnement Electromagnétique, Bat. 209D, B.P. 34, 91898, Orsay Cedex France 4UPR 4212, CNRS-CRMHT1d, avenue de la recherche scientifique F-45071 Orléans Cedex 2. Calcium aluminate and aluminosilicate glasses are attractive materials for a wide range of technical applications due to their highly refractory nature, their excellent optical and mechanical properties. The CaO-Al2O3-SiO2 system (CAS) is remarkable since glasses with very few SiO2 content can be synthesized, contrary to alkali or Mg aluminosilicate glasses. We have synthesized more than 40 different glasses in the CAS system using quenching method and 15 glasses using laser heating. These glasses were studied using a Raman spectrometer T64000 from Jobin-Yvon-Dilor company, X-ray absorption spectroscopy at Si, Al, Ca K edges the SA32 and D44 beamlines at LURE and NMR-700MHz. Cormier et al (2000) have shown using X-ray and neutron diffraction that aluminium is in 4-fold coordination in this ternary system. In this present study, we present Raman and XANES obtained at room temperature for these glasses. On the join SiO2-CaAl2O4 glass, we observed a decrease in Raman frequency with increasing CaAl2O4 content for all the bands. In particular, we observed a big decrease in frequency for the T4 band near 1150 cm-1 assigned to T-O0 in T4 units. This decrease suggests that aluminium substitutes principally for Si4+ in the fully polymerized structural units (TO2) according with Neuville and Mysen (1996). On the join SiO2-Ca3Al2O7 (R=CaO/AL2O3=3), we observed a decrease for all bands with

  9. Inorganic iodine incorporation into soil organic matter: evidence from iodine K-edge X-ray absorption near-edge structure.

    PubMed

    Yamaguchi, Noriko; Nakano, Masashi; Takamatsu, Rieko; Tanida, Hajime

    2010-06-01

    The transformation of inorganic iodine (I(-) and IO(3)(-)) incubated in soils with varying amounts of organic matter (Andosols from the surface layer of an upland field and forest, as well as Acrisols from surface and subsurface layers of an upland field) was investigated by using the iodine K-edge X-ray absorption near-edge structure (XANES). After 60d of reaction, both I(-) and IO(3)(-) were transformed into organoiodine in surface soils containing sufficient amounts of organic matter, whereas IO(3)(-) remained unchanged in the subsurface soil of Acrisols with low organic matter contents. Transformation of IO(3)(-) into organoiodine was not retarded when the microbial activity in soil was reduced by gamma-ray irradiation, suggesting that microbial activity was not essential for the transformation of inorganic iodine into organoiodine. Soil organic matter has the ability to transform inorganic iodine into organoiodine. PMID:18640749

  10. Morphology-dependent luminescence from ZnO nanostructures - An X-ray excited optical luminescence study at the Zn K-edge

    SciTech Connect

    Lobacheva, Olga; Murphy, Michael W; Ko, Jun Young Peter; Sham, Tsun-Kong

    2009-08-28

    ZnO nanostructures have been synthesized by thermal evaporation on Si substrates. It is found that the morphologies of the nanostructures are governed by growth conditions such as temperature, carrier-gas flow rate, and the nature of the substrate (with and without a catalyst). We report X-ray excited optical luminescence from ZnO nanostructures of distinctly different morphologies in the energy and time domain using excitation photon energies across the Zn K-edge. X-ray excited optical luminescence (XEOL) and X-ray absorption near edge structure (XANES) study has clearly shown the morphology dependence of the ZnO optical properties. A correlation of luminescence with morphology, size, and crystallinity emerges.

  11. 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 Al³⁺•(H₂O)₆, and aqueous Al(OH)₄⁻

    SciTech Connect

    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, Al³⁺•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 Al³⁺•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 of the extended-XAFS region of the spectra for the K-edge of the crystalline and aqueous standards. The K-edge spectra and K-edge positions are predicted using time-dependent density functional theory (TDDFT). The TDDFT calculations for the K-edge XANES spectra reproduce the observed transitions in the experimental spectra of the four Al species. The KLII&III and KLI onsets and their corresponding chemical shifts for the four standards are estimated using the delta self-consistent field (ΔSCF) method. Research by JLF, NG, EJB, AV, TDS was supported by U.S. Department of Energy’s (DOE), Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences, and Biosciences. NG thanks Amity Andersen for help with the α-Al₂O₃ and tetrahedral sodium aluminate (NaAlO₂) clusters. All the calculations were performed using the Molecular Science Computing Capability at EMSL, a national scientific user facility sponsored by the U.S. Department of Energy’s Office of Biological and Environmental Research and located at

  12. Application of X-ray K-edge densitometry in D and D operations

    SciTech Connect

    Jensen, T.; Aljundi, T.; Gray, J.N. |

    1998-12-31

    K-edge densitometry is a nondestructive assay technique which provides accurate measurement of heavy metal contamination in pipes, containers, and other items encountered in D and D operations. A prototype mobile K-edge instrument has been built and demonstrated in several applications. Results from measurements of uranium in pipes and spent reactor fuel plates, and quantification of mercury and lead in waste drums are presented. In this report the authors briefly describe the theory behind K-edge densitometry. They follow that with a description of the prototype system they have developed, and a presentation of results from demonstrations of this system. They conclude with a discussion of the potential for application of K-edge analysis in D and D operations.

  13. 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.

  14. Interpretation of O K-edge EELS in zircon using a structural variation approach

    SciTech Connect

    Spence, John C.H; Jiang, Nan

    2009-12-01

    This work describes an approach to interpret the near-edge fine structure of electron energy-loss spectroscopy (EELS) of O K-edge in zircon using a structural variation method. The positions and intensities of several peaks in the O K-edge EELS spectrum are assigned to specific structural parameters. It suggests that the near-edge structures in EELS can be used to measure atomic structure changes.

  15. 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.

  16. Ce K edge XAS of ceria-based redox materials under realistic conditions for the two-step solar thermochemical dissociation of water and/or CO2.

    PubMed

    Rothensteiner, Matthäus; Sala, Simone; Bonk, Alexander; Vogt, Ulrich; Emerich, Hermann; van Bokhoven, Jeroen A

    2015-10-28

    X-ray absorption spectroscopy was used to characterise ceria-based materials under realistic conditions present in a reactor for solar thermochemical two-step water and carbon dioxide splitting. A setup suitable for in situ measurements in transmission mode at the cerium K edge from room temperature up to 1773 K is presented. Time-resolved X-ray absorption near-edge structure (XANES) data, collected for a 10 mol% hafnium-doped ceria sample (Ce0.9Hf0.1O2-δ) during reduction at 1773 K in a flow of inert gas and during re-oxidation by CO2 at 1073 K, enables the quantitative determination of the non-stoichiometry δ of the fluorite-type structure. XANES analysis suggests the formation of the hexagonal Ce2O3 phase upon reduction in 2% hydrogen/helium at 1773 K. We discuss the experimental limitations and possibilities of high-temperature in situ XAS at edges of lower energy as well as the importance of the technique for understanding and improving the properties of ceria-based oxygen storage materials for thermochemical solar energy conversion. PMID:26412705

  17. Probing the local environment of substitutional Al^{3+} in goethite using X-ray absorption spectroscopy and first-principles calculations

    NASA Astrophysics Data System (ADS)

    Ducher, Manoj; Blanchard, Marc; Vantelon, Delphine; Nemausat, Ruidy; Cabaret, Delphine

    2016-03-01

    We present experimental and calculated Al K-edge X-ray absorption near-edge structure (XANES) spectra of aluminous goethite with 10-33 mol% of AlOOH and diaspore. Significant changes are observed experimentally in the near- and pre-edge regions with increasing Al concentration in goethite. First-principles calculations based on density functional theory (DFT) reproduce successfully the experimental trends. This permits to identify the electronic and structural parameters controlling the spectral features and to improve our knowledge of the local environment of {Al}^{3+} in the goethite-diaspore partial solid solution. In the near-edge region, the larger peak spacing in diaspore compared to Al-bearing goethite is related to the nature (Fe or Al) of the first cation neighbours around the absorbing Al atom (Al*). The intensity ratio of the two near-edge peaks, which decreases with Al concentration, is correlated with the average distance of the first cations around Al* and the distortion of the {AlO}_6 octahedron. Finally, the decrease in intensity of the pre-edge features with increasing Al concentration is due to the smaller number of Fe atoms in the local environment of Al since Al atoms tend to cluster. In addition, it is found that the pre-edge features of the Al K-edge XANES spectra enable to probe indirectly empty 3 d states of Fe. Energetic, structural and spectroscopic results suggest that for Al concentrations around 10 mol%, Al atoms can be considered as isolated, whereas above 25 mol%, Al clusters are more likely to occur.

  18. C K-edge NEXAFS spectra of graphene with physical and chemical defects: a study based on density functional theory.

    PubMed

    Ehlert, Christopher; Unger, Wolfgang E S; Saalfrank, Peter

    2014-07-21

    Recently, C K-edge Near Edge X-ray Absorption Fine Structure (NEXAFS) spectra of graphite (HOPG) surfaces have been measured for the pristine material, and for HOPG treated with either bromine or krypton plasmas (Lippitz et al., Surf. Sci., 2013, 611, L1). Changes of the NEXAFS spectra characteristic for physical (krypton) and/or chemical/physical modifications of the surface (bromine) upon plasma treatment were observed. Their molecular origin, however, remained elusive. In this work we study by density functional theory, the effects of selected point and line defects as well as chemical modifications on NEXAFS carbon K-edge spectra of single graphene layers. For Br-treated surfaces, also Br 3d X-ray Photoelectron Spectra (XPS) are simulated by a cluster approach, to identify possible chemical modifications. We observe that some of the defects related to plasma treatment lead to characteristic changes of NEXAFS spectra, similar to those in experiment. Theory provides possible microscopic origins for these changes. PMID:24901898

  19. Real Time Observation of X-ray-Induced Surface Modification Using Simultaneous XANES and XEOL-XANES

    PubMed Central

    2013-01-01

    In experiments preliminary to the design of an X-ray-excited optical luminescence (XEOL)-based chemical mapping tool we have used X-ray micro (4.5 × 5.2 μm) and macro (1 × 6 mm) beams with similar total fluxes to assess the effects of a high flux density beam of X-rays at energies close to an absorption edge on inorganic surfaces in air. The near surface composition of corroded cupreous alloys was analyzed using parallel X-ray and optical photoemission channels to collect X-ray absorption near-edge structure (XANES) data at the Cu K edge. The X-ray fluorescence channel is characteristic of the composition averages over several micrometers into the surface, whereas the optical channel is surface specific to about 200 nm. While the X-ray fluorescence data were mostly insensitive to the X-ray dose, the XEOL-XANES data from the microbeam showed significant dose-dependent changes to the superficial region, including surface cleaning, changes in the oxidation state of the copper, and destruction of surface compounds responsible for pre-edge fluorescence or phosphorescence in the visible. In one case, there was evidence that the lead phase in a bronze had melted. Conversely, data from the macrobeam were stable over several hours. Apart from localized heating effects, the microbeam damage is probably associated with the O3 loading of the surface and increased reaction rate with atmospheric water vapor. PMID:24044633

  20. X-ray K-edge analysis of drain lines in Wilhelm Hall, Ames Laboratory

    SciTech Connect

    Jensen, T.; Whitmore, C. |

    1999-01-05

    From August 12--27, 1998 X-ray K-edge measurements were made on drain lines in seven rooms in Wilhelm Hall, Ames Laboratory. The purpose of these measurements was to determine the extent of thorium (and other heavy metal) contamination inside these pipes. The K-edge method is a noninvasive inspection technique that can provide accurate quantification of heavy metal contamination interior to an object. Of the seven drain lines inspected, one was found to have no significant contamination, three showed significant thorium deposits, two showed mercury contamination, and one line was found to contain mercury, thorium and uranium. The K-edge measurements were found to be consistent with readings from hand-held survey meters, and provided much greater detail on the location and amount of heavy metal contamination.

  1. K-edge ratio method for identification of multiple nanoparticulate contrast agents by spectral CT imaging

    PubMed Central

    Ghadiri, H; Ay, M R; Shiran, M B; Soltanian-Zadeh, H

    2013-01-01

    Objective: Recently introduced energy-sensitive X-ray CT makes it feasible to discriminate different nanoparticulate contrast materials. The purpose of this work is to present a K-edge ratio method for differentiating multiple simultaneous contrast agents using spectral CT. Methods: The ratio of two images relevant to energy bins straddling the K-edge of the materials is calculated using an analytic CT simulator. In the resulting parametric map, the selected contrast agent regions can be identified using a thresholding algorithm. The K-edge ratio algorithm is applied to spectral images of simulated phantoms to identify and differentiate up to four simultaneous and targeted CT contrast agents. Results: We show that different combinations of simultaneous CT contrast agents can be identified by the proposed K-edge ratio method when energy-sensitive CT is used. In the K-edge parametric maps, the pixel values for biological tissues and contrast agents reach a maximum of 0.95, whereas for the selected contrast agents, the pixel values are larger than 1.10. The number of contrast agents that can be discriminated is limited owing to photon starvation. For reliable material discrimination, minimum photon counts corresponding to 140 kVp, 100 mAs and 5-mm slice thickness must be used. Conclusion: The proposed K-edge ratio method is a straightforward and fast method for identification and discrimination of multiple simultaneous CT contrast agents. Advances in knowledge: A new spectral CT-based algorithm is proposed which provides a new concept of molecular CT imaging by non-iteratively identifying multiple contrast agents when they are simultaneously targeting different organs. PMID:23934964

  2. SR high-speed K-edge subtraction angiography in the small animal (abstract)

    NASA Astrophysics Data System (ADS)

    Takeda, T.; Akisada, M.; Nakajima, T.; Anno, I.; Ueda, K.; Umetani, K.; Yamaguchi, C.

    1989-07-01

    To assess the ability of the high-speed K-edge energy subtraction system which was made at beamline 8C of Photon Factory, Tsukuba, we performed an animal experiment. Rabbits were used for the intravenous K-edge subtraction angiography. In this paper, the actual images of the artery obtained by this system, are demonstrated. The high-speed K-edge subtraction system consisted of movable silicon (111) monocrystals, II-ITV, and digital memory system. Image processing was performed by 68000-IP computer. The monochromatic x-ray beam size was 50×60 mm. Photon energy above and below iodine K edge was changed within 16 ms and 32 frames of images were obtained sequentially. The rabbits were anaesthetized by phenobarbital and a 5F catheter was inserted into inferior vena cava via the femoral vein. 1.5 ml/kg of contrast material (Conlaxin H) was injected at the rate of 0.5 ml/kg/s. TV images were obtained 3 s after the starting point of injection. By using this system, the clear K-edge subtracted images were obtained sequentially as a conventional DSA system. The quality of the images were better than that obtained by DSA. The dynamical blood flow was analyzed, and the best arterial image could be selected from the sequential images. The structures of aortic arch, common carotid arteries, right subclavian artery, and internal thoracic artery were obtained at the chest. Both common carotid arteries and vertebral arteries were recorded at the neck. The diameter of about 0.3-0.4 mm artery could be clearly revealed. The high-speed K-edge subtraction system demonstrates the very sharp arterial images clearly and dynamically.

  3. 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.

  4. Magnetic circular x-ray dichroisms of Fe-Ni alloys at K edge.

    SciTech Connect

    Freeman, A. J.; Gofron, K. J.; Kimball, C. W.; Lee, P. L.; Montano, P. A.; Rao, F.; Wang, X.

    1997-04-03

    Magnetic Circular X-ray Dichroism (MCXD) studies at K edges of Fe-Ni alloys reveal changes of the MCXD signal with composition and crystal structure. We observe that the signal at the invar composition is of comparable strength as other compositions. Moreover, the edge position is strongly dependent on lattice constant. First principles calculations demonstrate that the shape and strength of the signal strongly depends on the crystal orientation, composition, and lattice constant. We find direct relation between the MCXD signal and the p DOS. We find that the MCXD at K edge probes the magnetism due to itinerant electrons.

  5. XAFS analysis for quantification of the gallium coordinations in Al2O3-supported Ga2O3 photocatalysts

    NASA Astrophysics Data System (ADS)

    Akatsuka, M.; Yoshida, T.; Yamamoto, N.; Yamamoto, M.; Ogawa, S.; Yagi, S.

    2016-05-01

    Ga2O3 loaded Al2O3 samples (Ga2O3/Al2O3) were prepared to change coordination structures around Ga atoms. Ga K-edge XANES spectra of the Ga2O3/Al2O3 samples showed two peaks assigned to Ga atoms having tetrahedral coordination structure (Ga(t)) and octahedral one (Ga(o)). Curve-fitting analysis of XANES spectra was carried out with a set of pseudo- Voight and arctangent functions, and the fractions of Ga(t) and Ga(o) were quantitatively estimated from the ratio of the peak areas. EXAFS curve-fitting analysis also evaluated the fractions of Ga(t) and Ga(o) and they were in good agreement with those obtained by XANES analysis. It was revealed that the fraction of Ga(t) increased with the decrease in the loading amount of Ga2O3 due to the interaction of Ga species with Al2O3. The fractions of Ga(t) and Ga(o) might relate to the photocatalytic activity for CO2 reduction with H2O over the Ga2O3/Al2O3 samples.

  6. XANES determination of magnesium speciation in shells of two marine bivalve molluscs

    NASA Astrophysics Data System (ADS)

    Clarke, L. J.; Finch, A. A.; Huthwelker, T.; Foster, L. C.; Kennedy, H. A.; Richardson, C. A.; Steaggles, H.

    2009-04-01

    Recent studies have demonstrated generally weak relationships between seawater temperature and Mg/Ca ratios in calcite marine bivalve mollusc shells, despite an expected thermodynamic control on Mg incorporation. Several studies have suggested that such weak relationships could be due to Mg being non-lattice bound and associated with the shell organic matrix. In this study we use XANES to investigate the structural state of Mg in the shells of two species of marine bivalve mollusc, Mytilus edulis and Pecten maximus. Both species of mollusc were cultured in laboratory constant-temperature aquaria. Mg K-edge XANES analyses were completed using the LUCIA beamline, then situated at the Swiss Light Source. Initially, Mg and S (as a proxy for the sulphated organic matrix) distributions were mapped using Synchrotron XRF within the new shell growth laid down during the culturing period. Subsequently, XANES were collected for different pixels within the maps that had contrasting Mg and S distributions. XANES spectra are consistent within the Pecten maximus shell, despite previous studies that have shown a marked heterogeneity of Mg/Ca ratios within this species, and are indicative of Mg being hosted in a calcite-type phase. In contrast, XANES of Mytilus edulis indicates that Mg is hosted predominantly in an organic-type phase. A simple two component numerical modelling will allow an assessment of the proportions of calcite and organic Mg hosts in the two species. Speciation studies using XANES thus indicate that Mg is hosted in different phases in the two marine bivalve mollusc species investigated in this study; such an observation clearly has implications for the application of Mg/Ca thermometry in these calcifying organisms.

  7. Neutralization of calcite in mineral aerosols by acidic sullur species collected in China and Japan studied by ca K-edge X-ray absorption near-edge structure.

    PubMed

    Takahashi, Yoshio; Miyoshi, Takuro; Higashi, Masayuki; Kamioka, Hikari; Kanai, Yutaka

    2009-09-01

    Calcium species in mineral aerosols collected simultaneously in Aksu (near the Taklimakan Desert), Qingdao (eastern China), and Tsukuba (Japan) during dust and nondust periods were determined using Ca K-edge X-ray absorption near-edge structure (XANES). From the fitting of XANES spectra, it was found that (i) calcite and gypsum were the main Ca species in the aerosol samples, and (ii) the gypsum fraction versus total Ca minerals [Gyp]/[Ca2+]t increased progressively in the order Aksu < Qingdao < Tsukuba. Surface-sensitive XANES in the conversion electron yield mode (CEY) showed that the gypsum is formed selectively at the surface of mineral aerosols for all the samples except for that taken in Aksu during the dust period. The decrease of the [Gyp]/[Ca2+]t ratio with an increase in particle size showed that the neutralization effect proceeds from the particle surface. For the Aksu sample in the dust period, however, (i) the [Gyp]/[Ca2+]t ratios obtained by XANES measured in the fluorescence (FL; regarded as bulk analysis) and CEY modes were similar and (ii) size dependence was not found, showing that neutralization is not important for the sample because of the large supply of mineral aerosol with little neutralization effect in Aksu. It was also found that the pH of the aerosol and the ratio of (NH4)2SO4 to gypsum were positively and negatively correlated with the Ca (or calcite) content, respectively. The speciation of Ca by XANES revealed the neutralization processes of acidic sulfur species by calcite during the long-range transport of mineral aerosols. PMID:19764213

  8. 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

    2016-04-01

    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. PMID:26959687

  9. Investigation of Prussian Blue Analogs by XMCD at the K-edge of transition metals

    NASA Astrophysics Data System (ADS)

    Bordage, A.; Nataf, L.; Baudelet, F.; Bleuzen, A.

    2016-05-01

    Despite transition metal (TM) K-edge x-ray magnetic circular dichroism (XMCD) seems an interesting tool to get magnetic and structural information at the atomic scale, the effects originating this signal are still poorly understood. We thus initiated a deep investigation of the TM K-edge XMCD using Prussian Blue analogs (PBA) as model-compounds. In a recent study of the NiFe PBA family, we demonstrated that the XMCD signals at the TM K-edges strongly vary with external (mechanical) or internal (chemical) pressure and so that they are highly sensitive to small structural distortions. Following these first results, we extended this approach to the MnFe and CoFe families to evaluate the effect of electronic parameters (number of unpaired electrons of the M II TM) on the XMCD signal. All the results set milestones in the disentanglement of the components originating the XMCD signals at the K-edge of TM and will eventually help in a better understanding of the photomagnetic properties of PBAs.

  10. An X-ray absorption spectroscopic study of the metal site preference in Al{sub 1-x}Ga{sub x}FeO{sub 3}

    SciTech Connect

    Walker, James D.S.; Grosvenor, Andrew P.

    2013-01-15

    Magnetoelectric materials have potential for being introduced into next generation technologies, especially memory devices. The AFeO{sub 3} (Pna2{sub 1}; A=Al, Ga) system has received attention to better understand the origins of magnetoelectric coupling. The magnetoelectric properties this system exhibits depend on the amount of anti-site disorder present, which is affected by the composition and the method of synthesis. In this study, Al{sub 1-x}Ga{sub x}FeO{sub 3} was synthesized by the ceramic method and studied by X-ray absorption spectroscopy. Al L{sub 2,3}-, Ga K-, and Fe K-edge spectra were collected to examine how the average metal coordination number changes with composition. Examination of XANES spectra from Al{sub 1-x}Ga{sub x}FeO{sub 3} indicate that with increasing Ga content, Al increasingly occupies octahedral sites while Ga displays a preference for occupying the tetrahedral site. The Fe K-edge spectra indicate that more Fe is present in the tetrahedral site in AlFeO{sub 3} than in GaFeO{sub 3}, implying more anti-site disorder is present in AlFeO{sub 3}. - Graphical abstract: Al{sub 1-x}Ga{sub x}FeO{sub 3} has been investigated by XANES. Through examination of Al L{sub 2,3}-, Ga K-, and Fe K-edge XANES spectra, it was found that more anti-site disorder of the Fe atoms is present in AlFeO{sub 3} compared to in GaFeO{sub 3}. Highlights: Black-Right-Pointing-Pointer Al{sub 1-x}Ga{sub x}FeO{sub 3} was investigated by X-ray absorption spectroscopy. Black-Right-Pointing-Pointer Ga prefers to occupy the tetrahedral site in Al{sub 1-x}Ga{sub x}FeO{sub 3}. Black-Right-Pointing-Pointer Fe prefers to occupy the octahedral sites in Al{sub 1-x}Ga{sub x}FeO{sub 3} as x increases. Black-Right-Pointing-Pointer More anti-site disorder is present in AlFeO{sub 3} compared to in GaFeO{sub 3.}.

  11. Ligand and Charge Dependence for Absorption Edge in XANES Spectra of TPP[Fe(Pc)L2]2 Systems

    NASA Astrophysics Data System (ADS)

    Takahashi, Kei; Watanabe, Akie; Niki, Kaori; Hanasaki, Noriaki; Kanda, Akinori; Fujikawa, Takashi

    We apply real space full multiple scattering theory to interpret the Fe K-edge XANES spectra of TPP[Fe(Pc)L2]2 (L = CN, Cl and Br) systems, which show the giant magnetoresistance (GMR) at the low temperatures. In the previous paper, we have reported the absorption edge shift of the XANES spectra, whose origin remains unclear, for TPP[Fe(Pc)L2]2 systems. In order to clarify the relation between the charge of the Fe atom, the local structure of the axial ligand and the XANES spectra, we improve the calculation of the XANES spectra by taking into account the wider region including the neighboring Fe(Pc)L2 and TPP molecules. Our multiple scattering analyses suggest that the spectral shape is strongly influenced by the distance between a central Fe and axial ligands L. The number of Fe 3d electrons obtained by density functional theory calculations show weak dependence on the axial ligands L. The EXAFS spectra, the polarization dependence and the temperature dependence of the XANES spectra are also discussed.

  12. 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.

  13. Ca K-Edge XAS as a Probe of Calcium Centers in Complex Systems

    PubMed Central

    2014-01-01

    Herein, Ca K-edge X-ray absorption spectroscopy (XAS) is developed as a means to characterize the local environment of calcium centers. The spectra for six, seven, and eight coordinate inorganic and molecular calcium complexes were analyzed and determined to be primarily influenced by the coordination environment and site symmetry at the calcium center. The experimental results are closely correlated to time-dependent density functional theory (TD-DFT) calculations of the XAS spectra. The applicability of this methodology to complex systems was investigated using structural mimics of the oxygen-evolving complex (OEC) of PSII. It was found that Ca K-edge XAS is a sensitive probe for structural changes occurring in the cubane heterometallic cluster due to Mn oxidation. Future applications to the OEC are discussed. PMID:25492398

  14. Hybrid-K-edge/X-ray Fluorescense Densitometry with Laser-Compton Scattered X-rays

    SciTech Connect

    Dr. Khalid Chouffani El Fassi

    2010-08-29

    The quantitative verification of the accountancy of fissile nuclear materials through independent measurements represents one of the key elements of nuclear materials Safeguards. Elemental probes of materials of interest to non-proliferation are critical to research strategy in order to identify sensitive advanced instrumentation detection technologies. Advanced instrumentation for material detection and accountability are needed for use in fuel cycle facilities for real-time in-process monitoring of separations-partitioning, fuels fabrication as well as for traditional safeguards activities. Radiation-based NDA (non-destructive analysis) techniques can provide some vital information about nuclear materials much more quickly, cheaply and safely than chemical or radio chemical analysis. Hybrid K-edge densitometry (HKED) is currently the most accurate nondestructive inspection technique that provides sensitive quantification of heavy metal contamination. HKED in a technique that exploits both K-edge absorption and X-ray fluorescence (XRF) and allows simultaneously greater elemental specificity and lower detection limits

  15. Carbon K edge spectroscopy of internal interface and defect states of chemical vapor deposited diamond films

    SciTech Connect

    Nithianandam, J.; Rife, J.C. ); Windischmann, H. )

    1992-01-06

    We have made carbon {ital K} edge reflectivity and absorption measurements using synchrotron radiation on diamond crystals and chemical vapor deposited diamond films to determine their electronic structures. Our spectra of diamond films show that both {ital sp}{sup 2} and {ital sp}{sup 3} bonded carbon atoms are formed during initial nucleation and growth. Transmission spectra of a diamond film with 30 nm diameter cystallites show striking features below the carbon {ital sp}{sup 3} {ital K} edge due to internal interface states and/or defects. We compare these absorption features to x-ray absorption spectra of clean diamond (111) surface, graphite, and hydrocarbon gases to understand surface chemistry involved in the deposition process.

  16. A Simple Algorithm for Finding All k-Edge-Connected Components

    PubMed Central

    Wang, Tianhao; Zhang, Yong; Chin, Francis Y. L.; Ting, Hing-Fung; Tsin, Yung H.; Poon, Sheung-Hung

    2015-01-01

    The problem of finding k-edge-connected components is a fundamental problem in computer science. Given a graph G = (V, E), the problem is to partition the vertex set V into {V1, V2,…, Vh}, where each Vi is maximized, such that for any two vertices x and y in Vi, there are k edge-disjoint paths connecting them. In this paper, we present an algorithm to solve this problem for all k. The algorithm preprocesses the input graph to construct an Auxiliary Graph to store information concerning edge-connectivity among every vertex pair in O(Fn) time, where F is the time complexity to find the maximum flow between two vertices in graph G and n = ∣V∣. For any value of k, the k-edge-connected components can then be determined by traversing the auxiliary graph in O(n) time. The input graph can be a directed or undirected, simple graph or multigraph. Previous works on this problem mainly focus on fixed value of k. PMID:26368134

  17. In situ and ex situ XANES study of nanodispersed Mo species in zeolites used in fine chemistry catalysis.

    PubMed

    Rentería, M; Traverse, A; Anunziata, O A; Lede, E J; Pierella, L; Requejo, F G

    2001-03-01

    Mo K-edge XANES experiments on Mo-containing zeolites at low Mo loading (1 and 2 wt% of Mo on H-ZSM-11, H-BETA and H-ZSM-5 catalysts), active in fine chemistry reactions, were performed ex situ as function of sample calcination temperature in air (in the range 773-973 K) or in situ at 873 and 973K under N2 flow. The results showed a 4-fold oxygen coordination for the incorporated Mo species in the activated (dehydrated) state. Combining these results with additional data evidences an almost total Mo exchange inside the zeolite channels. PMID:11512876

  18. 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.

  19. Kinetics of iron redox reaction in silicate melts: A high temperature Xanes study on an alkali basalt

    NASA Astrophysics Data System (ADS)

    Cochain, B.; Neuville, D. R.; de Ligny, D.; Roux, J.; Baudelet, F.; Strukelj, E.; Richet, P.

    2009-11-01

    In Earth and Materials sciences, iron is the most important transition element. Glass and melt properties are strongly affected by iron content and redox state with the consequence that some properties (i.e. viscosity, heat capacity, crystallization...) depend not only on the amounts of Fe2+ and Fe3+, but also on the coordination state of these ions. In this work we investigate iron redox reactions through XANES experiments at the K-edge of iron. Using a high-temperature heating device, pre-edge of XANES spectra exhibits definite advantages to make in-situ measurements and to determine the evolution of redox state with time, temperature and composition of synthetic silicate melts. In this study, new kinetics measurements are presented for a basalt melt from the 31,000-BC eruption of the Puy de Lemptegy Volcano in France. These measurements have been made between 773 K and at superliquidus temperatures up to 1923 K.

  20. Comparison of iodine K-edge subtraction and fluorescence subtraction imaging in an animal system

    NASA Astrophysics Data System (ADS)

    Zhang, H.; Zhu, Y.; Bewer, B.; Zhang, L.; Korbas, M.; Pickering, I. J.; George, G. N.; Gupta, M.; Chapman, D.

    2008-09-01

    K-Edge Subtraction (KES) utilizes the discontinuity in the X-ray absorption across the absorption edge of the selected contrast element and creates an image of the projected density of the contrast element from two images acquired just above and below the K-edge of the contrast element. KES has proved to be powerful in coronary angiography, micro-angiography, bronchography, and lymphatic imaging. X-ray fluorescence imaging is a successful technique for the detection of dilute quantities of elements in specimens. However, its application at high X-ray energies (e.g. at the iodine K-edge) is complicated by significant Compton background, which may enter the energy window set for the contrast material's fluorescent X-rays. Inspired by KES, Fluorescence Subtraction Imaging (FSI) is a technique for high-energy (>20 keV) fluorescence imaging using two different incident beam energies just above and below the absorption edge of a contrast element (e.g. iodine). The below-edge image can be assumed as a "background" image, which includes Compton scatter and fluorescence from other elements. The above-edge image will contain nearly identical spectral content as the below-edge image but will contain the additional fluorescence of the contrast element. This imaging method is especially promising with thick objects with dilute contrast materials, significant Compton background, and/or competing fluorescence lines from other materials. A quality factor is developed to facilitate the comparison. The theoretical value of the quality factor sets the upper limit that an imaging method can achieve when the noise is Poisson limited. The measured value of this factor makes two or more imaging methods comparable. Using the Hard X-ray Micro-Analysis (HXMA) beamline at the Canadian Light Source (CLS), the techniques of FSI and KES were critically compared, with reference to radiation dose, image acquisition time, resolution, signal-to-noise ratios, and quality factor.

  1. Neutral dissociation of hydrogen following photoexcitation of HCl at the chlorine K edge

    SciTech Connect

    Hansen, D.L.; Arrasate, M.E.; Martin, R.; Vanderford, B.; Lindle, D.W.; Cotter, J.; Neill, P.; Fisher, G.R.; Perera, R.C.; Leung, K.T.; Levin, J.C.; Sellin, I.A.; Simon, M.; Simon, M.; Uehara, Y.; Whitfield, S.B.

    1998-04-01

    Time-of-flight mass spectroscopy was used to study the relaxation dynamics of HCl following photoexcitation in the vicinity of the Cl K edge ({approximately}2.8keV) using monochromatic synchrotron radiation. At the lowest resonant excitation to the 6{sigma}{sup {asterisk}} antibonding orbital, almost half of the excited molecules decay by emission of a neutral H atom, mostly in coincidence with a highly charged Cl{sup n+} ion. The present work demonstrates that neutral-atom emission can be a significant decay channel for excited states with very short lifetimes (1 fs). {copyright} {ital 1998} {ital The American Physical Society}

  2. A Bremsstrahlung Spectrometer using k-edge and Differential Filters with Image plate dosimeters

    SciTech Connect

    Chen, C; Mackinnon, A; Beg, F; Chen, H; Key, M; King, J A; Link, A; MacPhee, A; Patel, P; Porkolab, M; Stephens, R; VanWoerkom, L; Akli, K; Freeman, R

    2008-05-02

    A Bremsstrahlung spectrometer using k-edge and differential filtering has been used with Image Plate dosimeters to measure the x-ray fluence from short-pulse laser/target interactions. An electron spectrometer in front of the Bremsstrahlung spectrometer deflects electrons from the x-ray line of sight and simultaneously measures the electron spectrum. The response functions were modeled with the Monte Carlo code Integrated Tiger Series 3.0 and the dosimeters calibrated with radioactive sources. Electron distributions with slope temperatures in the MeV range are inferred from the Bremsstrahlung spectra.

  3. A Bremsstrahlung spectrometer using k-edge and differential filters with image plate dosimeters

    SciTech Connect

    Chen, C. D.; Porkolab, M.; King, J. A.; Beg, F. N.; Key, M. H.; Chen, H.; Mackinnon, A. J.; MacPhee, A. G.; Patel, P. K.; Akli, K. U.; Stephens, R. B.; Freeman, R. R.; Link, A.; Van Woerkom, L. D.

    2008-10-15

    A Bremsstrahlung spectrometer using k-edge and differential filtering has been used with image plate dosimeters to measure the x-ray fluence from short-pulse laser/target interactions. An electron spectrometer in front of the Bremsstrahlung spectrometer deflects electrons from the x-ray line of sight and simultaneously measures the electron spectrum. The response functions were modeled with the Monte Carlo code INTEGRATED TIGER SERIES 3.0 and the dosimeters calibrated with radioactive sources. An electron distribution with a slope temperature of 1.3 MeV is inferred from the Bremsstrahlung spectra.

  4. Nb K-edge x-ray absorption investigation of the pressure induced amorphization in A-site deficient double perovskite La1/3NbO3.

    PubMed

    Marini, C; Noked, O; Kantor, I; Joseph, B; Mathon, O; Shuker, R; Kennedy, B J; Pascarelli, S; Sterer, E

    2016-02-01

    Nb K-edge x-ray absorption spectroscopy is utilized to investigate the changes in the local structure of the A-site deficient double perovskite La1/3NbO3 which undergoes a pressure induced irreversible amorphization. EXAFS results show that with increasing pressure up to 7.5 GPa, the average Nb-O bond distance decreases in agreement with the expected compression and tilting of the NbO6 octahedra. On the contrary, above 7.5 GPa, the average Nb-O bond distance show a tendency to increase. Significant changes in the Nb K-edge XANES spectrum with evident low energy shift of the pre-peak and the absorption edge is found to happen in La1/3NbO3 above 6.3 GPa. These changes evidence a gradual reduction of the Nb cations from Nb(5+) towards Nb(4+) above 6.3 GPa. Such a valence change accompanied by the elongation of the average Nb-O bond distances in the octahedra, introduces repulsion forces between non-bonding adjacent oxygen anions in the unoccupied A-sites. Above a critical pressure, the Nb reduction mechanism can no longer be sustained by the changing local structure and amorphization occurs, apparently due to the build-up of local strain. EXAFS and XANES results indicate two distinct pressure regimes having different local and electronic response in the La1/3NbO3 system before the occurence of the pressure induced amorphization at  ∼14.5 GPa. PMID:26742465

  5. Nb K-edge x-ray absorption investigation of the pressure induced amorphization in A-site deficient double perovskite La1/3NbO3

    NASA Astrophysics Data System (ADS)

    Marini, C.; Noked, O.; Kantor, I.; Joseph, B.; Mathon, O.; Shuker, R.; Kennedy, B. J.; Pascarelli, S.; Sterer, E.

    2016-02-01

    Nb K-edge x-ray absorption spectroscopy is utilized to investigate the changes in the local structure of the A-site deficient double perovskite La1/3NbO3 which undergoes a pressure induced irreversible amorphization. EXAFS results show that with increasing pressure up to 7.5 GPa, the average Nb-O bond distance decreases in agreement with the expected compression and tilting of the NbO6 octahedra. On the contrary, above 7.5 GPa, the average Nb-O bond distance show a tendency to increase. Significant changes in the Nb K-edge XANES spectrum with evident low energy shift of the pre-peak and the absorption edge is found to happen in La1/3NbO3 above 6.3 GPa. These changes evidence a gradual reduction of the Nb cations from Nb5+ towards Nb4+ above 6.3 GPa. Such a valence change accompanied by the elongation of the average Nb-O bond distances in the octahedra, introduces repulsion forces between non-bonding adjacent oxygen anions in the unoccupied A-sites. Above a critical pressure, the Nb reduction mechanism can no longer be sustained by the changing local structure and amorphization occurs, apparently due to the build-up of local strain. EXAFS and XANES results indicate two distinct pressure regimes having different local and electronic response in the La1/3NbO3 system before the occurence of the pressure induced amorphization at  ˜14.5 GPa.

  6. Second Generation Gold Nanobeacons for Robust K-Edge Imaging with Multi-Energy CT

    PubMed Central

    Schirra, Carsten O.; Senpan, Angana; Roessl, Ewald; Thran, Axel; Stacy, Allen J.; Wu, Lina; Proska, Roland; Pan, Dipanjan

    2012-01-01

    Spectral CT is the newest advancement in CT imaging technology, which enhances traditional CT images with the capability to image and quantify certain elements based on their distinctive K-edge energies. K-edge imaging feature recognizes high accumulations of targeted elements and presents them as colorized voxels against the normal grayscale X-ray background offering promise to overcome the relatively low inherent contrast within soft tissue and distinguish the high attenuation of calcium from contrast enhanced targets. Towards this aim, second generation gold nanobeacons (GNB2), which incorporate at least five times more metal than the previous generation was developed. The particles were synthesized as lipid-encapsulated, vascularly constrained (>120 nm) nanoparticle incorporating tiny gold nanoparticles (2–4 nm) within a polysorbate core. The choice of core material dictated to achieve a higher metal loading. The particles were thoroughly characterized by physicochemical techniques. This study reports one of the earlier examples of spectral CT imaging with gold nanoparticles demonstrating the potential for targeted in vitro and in vivo imaging and eliminates calcium interference with CT. The use of statistical image reconstruction shows high SNR may allow dose reduction and/or faster scan times. PMID:23185109

  7. Animal experiments by K-edge subtraction angiography by using SR (abstract)

    NASA Astrophysics Data System (ADS)

    Anno, I.; Akisada, M.; Takeda, T.; Sugishita, Y.; Kakihana, M.; Ohtsuka, S.; Nishimura, K.; Hasegawa, S.; Takenaka, E.; Hyodo, K.; Ando, M.

    1989-07-01

    Ischemic heart disease is one of the most popular and lethal diseases for aged peoples in the world, and is usually diagnosed by transarterial selective coronary arteriography. However, it is rather invasive and somewhat dangerous, so that the selective coronary arteriography is not feasible for prospective screening of coronary occlusive heart disease. Conventional digital subtraction angiography (DSA) is widely known as a relatively noninvasive and useful technique is making a diagnosis of arterial occlusive disease, especially in making the diagnosis of ischemic heart disease. Conventional intravenous subtraction angiography by temporal subtraction, however, has several problems when applying to the moving objects. Digital subtraction method using high-speed switching above and below the K edge could be the ideal approach to this solution. We intend to make a synchrotron radiation digital K-edge subtraction angiography in the above policy, and to apply it to the human coronary ischemic disease on an outpatient basis. The principles and experimental systems have already been described in detail by our coworkers. Our prototype experimental system is situated at the AR (accumulation ring) for TRISTAN project of high energy physics. The available beam size is 70 mm by 120 mm. The electron energy of AR is 6.5 GeV and average beam current is approximately 10 mA. This paper will show the animal experiments of our K-edge subtraction system, and discuss some problems and technical difficulties. Three dogs, weighing approximately 15 kg, were examined to evaluate the ability of our prototype synchrotron radiation DSA unit, that we are now constructing. The dogs were anaesthetized with pentobarbital sodium, intravenously (30 mg/kg). Six french-sized (1.52 mm i.d.) pigtail catheter with multiple side holes were introduced via the right femoral vein into the right atrium by the cutdown technique under conventional x-ray fluoroscopic control. Respiration of the dogs was

  8. Structural relaxation around substitutional Cr3+ in MgAl2O4

    NASA Astrophysics Data System (ADS)

    Juhin, Amélie; Calas, Georges; Cabaret, Delphine; Galoisy, Laurence; Hazemann, Jean-Louis

    2007-08-01

    The structural environment of a substitutional Cr3+ ion in a MgAl2O4 spinel has been investigated by Cr K -edge extended x-ray absorption fine structure and x-ray absorption near edge structure (XANES) spectroscopies. First-principles computations of the structural relaxation and of the XANES spectrum have been performed, with a good agreement with the experiment. The Cr-O distance is close to that in MgCr2O4 , indicating a full relaxation of the first neighbors, and the second shell of Al atoms relaxes partially. These observations demonstrate that Vegard’s law is not obeyed in the MgAl2O4-MgCr2O4 solid solution. Despite some angular site distortion, the local D3d symmetry of the B site of the spinel structure is retained during the substitution of Cr for Al. Here, we show that the relaxation is accommodated by strain-induced bond buckling, with angular tilts of the Mg-centered tetrahedra around the Cr-centered octahedron. By contrast, there is no significant alteration of the angles between the edge-sharing octahedra, which build chains aligned along the three fourfold axes of the cubic structure.

  9. NO binding kinetics in myoglobin investigated by picosecond Fe K-edge absorption spectroscopy

    PubMed Central

    Silatani, Mahsa; Lima, Frederico A.; Penfold, Thomas J.; Rittmann, Jochen; Reinhard, Marco E.; Rittmann-Frank, Hannelore M.; Borca, Camelia; Grolimund, Daniel; Milne, Christopher J.; Chergui, Majed

    2015-01-01

    Diatomic ligands in hemoproteins and the way they bind to the active center are central to the protein’s function. Using picosecond Fe K-edge X-ray absorption spectroscopy, we probe the NO-heme recombination kinetics with direct sensitivity to the Fe-NO binding after 532-nm photoexcitation of nitrosylmyoglobin (MbNO) in physiological solutions. The transients at 70 and 300 ps are identical, but they deviate from the difference between the static spectra of deoxymyoglobin and MbNO, showing the formation of an intermediate species. We propose the latter to be a six-coordinated domed species that is populated on a timescale of ∼200 ps by recombination with NO ligands. This work shows the feasibility of ultrafast pump–probe X-ray spectroscopic studies of proteins in physiological media, delivering insight into the electronic and geometric structure of the active center. PMID:26438842

  10. Photoabsorption and photoemission of magnesium diboride at the Mg K edge

    NASA Astrophysics Data System (ADS)

    Prince, K. C.; Feyer, V.; Tadich, A.; Thomsen, L.; Cowie, B. C. C.

    2009-10-01

    The Mg K edge photoabsorption spectrum and the B 1s, Mg 1s, Mg 2p and valence band photoemission spectra of polycrystalline magnesium diboride have been measured. The photoabsorption spectra of the diboride and the oxide, which is present as an impurity, were separated by measuring the Auger electron partial yield at electron energies characteristic of each phase. The spectra are consistent with published calculations of the density of unoccupied p symmetry states. Better agreement is obtained with calculations for the ground state of the system than with ones for the excited state. Valence band photoemission spectra were measured at photon energies corresponding to core resonances, but, within the signal to noise level of the spectra, no resonant enhancement was observed. This is consistent with the delocalized nature of the valence band.

  11. Exotic sources of x-rays for iodine K-edge angiography

    SciTech Connect

    Carr, R.

    1993-08-01

    Digital Subtractive Angiography (DSA) has been performed to image human coronary arteries using wiggler radiation from electron storage rings. The significant medical promise of this procedure motivates the development of smaller and less costly x-ray sources. Several exotic sources are candidates for consideration, using effects such as Cherenkov, channeling, coherent bremsstrahlung, laser backscattering, microundulator, parametric, Smith-Purcell, and transition radiation. In this work we present an analysis of these effects as possible sources of intense x-rays at the iodine K-edge at 33.169 key. The criteria we use are energy, efficiency, flux, optical properties, and technical realizability. For each of the techniques, we find that they suffer either from low flux, a low energy cutoff, target materials heating, too high electron beam energy requirement, optical mismatch to angiography, or a combination of these. We conclude that the foreseeable state-of-the-art favors a compact storage ring design.

  12. Three dimensional mapping of strontium in bone by dual energy K-edge subtraction imaging

    NASA Astrophysics Data System (ADS)

    Cooper, D. M. L.; Chapman, L. D.; Carter, Y.; Wu, Y.; Panahifar, A.; Britz, H. M.; Bewer, B.; Zhouping, W.; Duke, M. J. M.; Doschak, M.

    2012-09-01

    The bones of many terrestrial vertebrates, including humans, are continually altered through an internal process of turnover known as remodeling. This process plays a central role in bone adaptation and disease. The uptake of fluorescent tetracyclines within bone mineral is widely exploited as a means of tracking new tissue formation. While investigation of bone microarchitecture has undergone a dimensional shift from 2D to 3D in recent years, we lack a 3D equivalent to fluorescent labeling. In the current study we demonstrate the ability of synchrotron radiation dual energy K-edge subtraction (KES) imaging to map the 3D distribution of elemental strontium within rat vertebral samples. This approach has great potential for ex vivo analysis of preclinical models and human tissue samples. KES also represents a powerful tool for investigating the pharmokinetics of strontium-based drugs recently approved in many countries around the globe for the treatment of osteoporosis.

  13. K-edge and mirror filtered X-ray grating interferometers

    NASA Astrophysics Data System (ADS)

    Stutman, Dan; Finkenthal, Michael

    2012-07-01

    Talbot-Lau interferometers having good angular resolution and fringe contrast are needed for refraction imaging of biomedical objects with conventional X-ray tubes. To maximize angular resolution the interferometers must work in high Talbot orders, which in turn narrows the spectral region of good fringe contrast. To select this narrow region from the broad tube spectrum we study spectral filtering with K-edge absorbers or with grazing incidence X-ray mirrors. For instance, using a total reflection Au mirror at 2.7 mrad incidence in conjunction with a Mo tube at 50 kVp we obtain up to 30% contrast in the fifth Talbot order. The improved angular sensitivity and contrast achieved with quasi-monochromatic filtering enable single-exposure refraction imaging of soft tissues. The mirror filtering offers also a path for increasing the interferometer contrast at high X-ray energy.

  14. Measurement of an inverse Compton scattering source local spectrum using k-edge filters

    SciTech Connect

    Golosio, Bruno; Oliva, Piernicola; Carpinelli, Massimo; Endrizzi, Marco; Delogu, Pasquale; Pogorelsky, Igor; Yakimenko, Vitaly

    2012-04-16

    X-ray sources based on the inverse Compton scattering process are attracting a growing interest among scientists, due to their extremely fast pulse, quasi-monochromatic spectrum, and relatively high intensity. The energy spectrum of the x-ray beam produced by inverse Compton scattering sources in a fixed observation direction is a quasi-monochromatic approximately Gaussian distribution. The mean value of this distribution varies with the scattering polar angle between the electron beam direction and the x-ray beam observation direction. Previous works reported experimental measurements of the mean energy as a function of the polar angle. This work introduces a method for the measurement of the whole local energy spectrum (i.e., the spectrum in a fixed observation direction) of the x-ray beam yielded by inverse Compton scattering sources, based on a k-edge filtering technique.

  15. Local environment of metal ions in phthalocyanines: K-edge X-ray absorption spectra.

    PubMed

    Rossi, G; d'Acapito, F; Amidani, L; Boscherini, F; Pedio, M

    2016-09-14

    We report a detailed study of the K-edge X-ray absorption spectra of four transition metal phthalocyanines (MPc, M = Fe, Co, Cu and Zn). We identify the important single and multiple scattering contributions to the spectra in the extended energy range and provide a robust treatment of thermal damping; thus, a generally applicable model for the interpretation of X-ray absorption fine structure spectra is proposed. Consistent variations of bond lengths and Debye Waller factors are found as a function of atomic number of the metal ion, indicating a variation of the metal-ligand bond strength which correlates with the spatial arrangement and occupation of molecular orbitals. We also provide an interpretation of the near edge spectral features in the framework of a full potential real space multiple scattering approach and provide a connection to the local electronic structure. PMID:27510989

  16. Preliminary study of an angiographic and angio-tomographic technique based on K-edge filters

    SciTech Connect

    Golosio, Bruno; Brunetti, Antonio; Oliva, Piernicola; Carpinelli, Massimo; Luca Masala, Giovanni; Meloni, Francesco; Battista Meloni, Giovanni

    2013-08-14

    Digital Subtraction Angiography is commonly affected by artifacts due to the patient movements during the acquisition of the images without and with the contrast medium. This paper presents a preliminary study on an angiographic and angio-tomographic technique based on the quasi-simultaneous acquisition of two images, obtained using two different filters at the exit of an X-ray tube. One of the two filters (K-edge filter) contains the same chemical element used as a contrast agent (gadolinium in this study). This filter absorbs more radiation with energy just above the so called K-edge energy of gadolinium than the radiation with energy just below it. The other filter (an aluminium filter in this study) is simply used to suppress the low-energy contribution to the spectrum. Using proper calibration curves, the two images are combined to obtain an image of the contrast agent distribution. In the angio-tomographic application of the proposed technique two images, corresponding to the two filter types, are acquired for each viewing angle of the tomographic scan. From the two tomographic reconstructions, it is possible to obtain a three-dimensional map of the contrast agent distribution. The technique was tested on a sample consisting of a rat skull placed inside a container filled with water. Six small cylinders with 4.7 mm internal diameter containing the contrast medium at different concentrations were placed inside the skull. In the plain angiographic application of the technique, five out of six cylinders were visible, with gadolinium concentration down to 0.96%. In the angio-tomographic application, all six cylinders were visible, with gadolinium concentration down to 0.49%. This preliminary study shows that the proposed technique can provide images of the contrast medium at low concentration without most of the artifacts that are present in images produced by conventional techniques. The results encourage further investigation on the feasibility of a clinical

  17. Towards in-vivo K-edge imaging using a new semi-analytical calibration method

    NASA Astrophysics Data System (ADS)

    Schirra, Carsten; Thran, Axel; Daerr, Heiner; Roessl, Ewald; Proksa, Roland

    2014-03-01

    Flat field calibration methods are commonly used in computed tomography (CT) to correct for system imperfections. Unfortunately, they cannot be applied in energy-resolving CT when using bow-tie filters owing to spectral distortions imprinted by the filter. This work presents a novel semi-analytical calibration method for photon-counting spectral CT systems, which is applicable with a bow-tie filter in place and efficiently compensates pile-up effects at fourfold increased photon flux compared to a previously published method without degradation of image quality. The achieved reduction of the scan time enabled the first K-edge imaging in-vivo. The method employs a calibration measurement with a set of flat sheets of only a single absorber material and utilizes an analytical model to predict the expected photon counts, taking into account factors such as x-ray spectrum and detector response. From the ratios of the measured x-ray intensities and the corresponding simulated photon counts, a look-up table is generated. By use of this look-up table, measured photon-counts can be corrected yielding data in line with the analytical model. The corrected data show low pixel-to-pixel variations and pile-up effects are mitigated. Consequently, operations like material decomposition based on the same analytical model yield accurate results. The method was validated on a experimental spectral CT system equipped with a bow-tie filter in a phantom experiment and an in-vivo animal study. The level of artifacts in the resulting images is considerably lower than in images generated with a previously published method. First in-vivo K-edge images of a rabbit selectively depict vessel occlusion by an ytterbium-based thermoresponsive polymer.

  18. Experimental spectral measurements of heavy K-edge filtered beams for x-ray computed mammotomography

    PubMed Central

    Crotty, D J; McKinley, R L; Tornai, M P

    2012-01-01

    A dual modality computed mammotomography (CmT) and single photon emission computed tomography (SPECT) system for dedicated 3D breast imaging is in development. Using heavy K-edge filtration, the CmT component narrows the energy spectrum of the cone-shaped x-ray beam incident on the patient’s pendant, uncompressed breast. This quasi-monochromatic beam is expected to improve discrimination of tissue with similar attenuation coefficients while restraining absorbed dose to below that of dual view mammography. Previous simulation studies showed the optimal energy that maximizes dose efficiency for a 50/50% adipose/glandular breast is between 30 and 40 keV. This study experimentally validates these results using pre-breast and post-breast spectral measurements made under tungsten tube voltages between 40 and 100 kVp using filter materials with K-edge values ranging from 15 to 70 keV. Different filter material thicknesses are used, approximately equivalent to the 200th and 500th attenuating value layer (VL) thickness. Cerium (K = 40.4 keV) filtered post-breast spectra for 8–18 cm breasts are measured for a range of breast compositions. Figures of merit include mean beam energy, spectral full-width at tenth-maximum, beam hardening and dose for the range of breast sizes. Measurements corroborate simulation results, indicating that for a given dose, a 200th VL of cerium filtration may have optimal performance in the dedicated mammotomography paradigm. PMID:17228108

  19. Si K Edge Structure and Variability in Galactic X-Ray Binaries

    NASA Astrophysics Data System (ADS)

    Schulz, Norbert S.; Corrales, Lia; Canizares, Claude R.

    2016-08-01

    We survey the Si K edge structure in various absorbed Galactic low-mass X-ray binaries (LMXBs) to study states of silicon in the inter- and circum-stellar medium. The bulk of these LMXBs lie toward the Galactic bulge region and all have column densities above 1022 cm‑2. The observations were performed using the Chandra High Energy Transmission Grating Spectrometer. The Si K edge in all sources appears at an energy value of 1844 ± 0.001 eV. The edge exhibits significant substructure that can be described by a near edge absorption feature at 1849 ± 0.002 eV and a far edge absorption feature at 1865 ± 0.002 eV. Both of these absorption features appear variable with equivalent widths up to several mÅ. We can describe the edge structure using several components: multiple edge functions, near edge absorption excesses from silicates in dust form, signatures from X-ray scattering optical depths, and a variable warm absorber from ionized atomic silicon. The measured optical depths of the edges indicate much higher values than expected from atomic silicon cross sections and interstellar medium abundances, and they appear consistent with predictions from silicate X-ray absorption and scattering. A comparison with models also indicates a preference for larger dust grain sizes. In many cases, we identify Si xiii resonance absorption and determine ionization parameters between log ξ = 1.8 and 2.8 and turbulent velocities between 300 and 1000 km s‑1. This places the warm absorber in close vicinity of the X-ray binaries. In some data, we observe a weak edge at 1.840 keV, potentially from a lesser contribution of neutral atomic silicon.

  20. Killing of Bacillus Megaterium Spores by X-Rays at the Phosphorus K-Edge

    NASA Technical Reports Server (NTRS)

    Richmond, Robert C.; Frigo, Sean P.; Ehret, Charles F.; Rose, M. Franklin (Technical Monitor)

    2001-01-01

    This study continues a progression of experiments on the radiation-induced killing of bacterial spores that began at the Argonne National Laboratory in 1957. A series of aliquots of Bacillus megaterium spores were prepared onto polycarbonate filters and irradiated with photons of 2159 eV compared to 2140 eV energy on the 2-IDB beamline at the Advanced Photon Source. Flux density was approximately 10 photons/sec/mm . The phosphorous K-edge absorption spectrum in these spores was determined to peak at 2159 eV, wheras 2140 eV was determined to be outside that absorption spectrum. Spores on filters were irradiated at ambient conditions, and were either immediately plated for colony formation after irradiation, or were held for postirradiation exposure to oxygen prior to plating. Slopes of survival curves from the four conditions of irradiation, i.e., two photon energies each comparing immediate plating vs postirradiation holding, were used for quantitative determination of differences in rates of spore killing over a range of radiation doses. It was found that spores irradiated at the phosphorus K-edge were killed 20% more efficiently than when irradiated with 2140eV photons, and this was true for both immediate plating and postirradiation holding in air. Postirradiation holding in air increased killing efficiency by about 12% for both photon energies compared to plating immediately after irradiation. The increase of killing efficiency with postirradiation holding is less than expected from earlier experiments using relatively low-flux X-rays, and raises the possibility of dose-mitigation by radical-radical recombination in the case of high-flux X-rays from the synchrotron.

  1. Killing of Bacillus Megaterium Spores by X-rays at the Phosphorus K-edge

    NASA Technical Reports Server (NTRS)

    Richmond, Robert C.; Frigo, Sean P.; Ehret, Charles F.; Rose, M. Franklin (Technical Monitor)

    2001-01-01

    This study continues a progression of experiments on the radiation-induced killing of bacterial spores that began at the Argonne National Laboratory in 1957. A series of aliquots of Bacillus megaterium spores were prepared onto polycarbonate filters and irradiated with photons of 2159 eV compared to 2140 eV energy on the 2-IDB beamline at the Advanced Photon Source. Flux density was approximately 10(exp 18) photons/sec/sq mm. The phosphorous K-edge absorption spectrum in these spores was determined to peak at 2159 eV, wheras 2140 eV was determined to be outside that absorption spectrum. Spores on filters were irradiated at ambient conditions, and were either immediately plated for colony formation after irradiation, or were held for postirradiation exposure to oxygen prior to plating. Slopes of survival curves from the four conditions of irradiation, i.e., two photon energies each comparing immediate plating vs postirradiation holding, were used for quantitative determination of differences in rates of spore killing over a range of radiation doses. It was found that spores irradiated at the phosphorus K-edge were killed 20% more efficiently than when irradiated with 2140 eV photons, and this was true for both immediate plating and postirradiation holding in air. Postirradiation holding in air increased killing efficiency by about 12% for both photon energies compared to plating immediately after irradiation. The increase of killing efficiency with postirradiation holding is less than expected from earlier experiments using relatively low-flux X-rays, and raises the possibility of dose-mitigation by radical-radical recombination in the case of high-flux X-rays from the synchrotron.

  2. 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.

  3. New insights into the role of Mn and Fe in coloring origin of blue decorations of blue-and-white porcelains by XANES spectroscopy

    NASA Astrophysics Data System (ADS)

    Zhu, Jian; Luo, Wugan; Chen, Dongliang; Xu, Wei; Ming, Chaofang; Wang, Changsui; Wang, Lihua

    2013-04-01

    Blue and white porcelain is one of the most valuable ancient ceramics varieties in ancient China. It is well known for its beautiful blue decorations. However, the origin of its blue color has not been very clear till now. In this research, two blue and white porcelains from Jingdezhen, Jiangxi province were selected and Mn and Fe K-edge XANES spectra were recorded from blue decorations with or without transparent glaze. Results showed that Mn K-edge XANES features were almost identical between different samples while that of iron changed. The above findings indicated the positive role of iron in the variation of blue decorations. As for manganese, although more system researches were need, its negative role on the variations of the tone of blue decorations was obtained. On the other hand, the paper also revealed the XAFS results will be affect by the glaze layer above the pigment. These findings provided us more information to understand the coloring origin of blue decorations of blue-and-white porcelain by means of XANES spectroscopy.

  4. Femtosecond probing around the K-edge of a laser heated plasma using X-rays from betatron oscillations in a laser wakefield accelerator

    NASA Astrophysics Data System (ADS)

    Behm, Keegan; Zhao, Tony; Maksimchuk, Anatoly; Yanovsky, Victor; Nees, John; Mangles, Stuart; Krushelnick, Karl; Thomas, Alexander; CenterUltrafast Optical Science Team; Plasmas Group Team

    2015-11-01

    Presented here are data from a two-beam pump-probe experiment. We used synchrotron-like X-rays created by betatron oscillations to probe a thin metal foil that is pumped by the secondary laser beam. The Hercules Ti:Sapph laser facility was operated with a pulse duration of 34 fs and a power of 65 TW split to drive a laser wakefield accelerator and heat the secondary target. We observed opacity changes around the K-edge of thin foils as they were heated by an ultrafast pump laser. To understand how the opacity is changing with heating and expansion of the plasma, the delay between the two laser paths was adjusted on a fs and ps time scale. Experimental data for polyvinylidene chloride (PVDC) and aluminum show variations in opacity around the Cl and Al K-edges with changes in the probe delay. The transmitted synchrotron-like spectrum was measured using single photon counting on an X-ray CCD camera and was available on a shot-by-shot basis. The success of this work demonstrates a practical application for X-rays produced from betatron oscillations in a wakefield accelerator. The compact size of these ``table-top'' accelerators and the ultrashort nature of the generated X-ray pulses allows pump-probe experiments that can probe events that occur on the femtosecond time scale.

  5. 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.

    1994-12-31

    XANES (X-ray Absorption Near Edge Spectroscopy) has been employed to evaluate the efficacy of a process designed to encapsulate and reduce TcO{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 TcO{sub 4}{sup {minus}}. 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. The first investigation was to evaluate the effectiveness of a chemical reaction designed to slow the release of {sup 99}TcO{sub 4}{sup {minus}} in nuclear wasteform cements. The second investigation was to characterize the oxidation state of Se after microbial uptake from an aqueous solution by common soil bacteria, in order to provide information about the possible mechanisms of bioremediation.

  6. 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. PMID:23507250

  7. Model compound vulcanization studied by XANES

    NASA Astrophysics Data System (ADS)

    Taweepreda, W.; Nu-Mard, R.; Pattanasiriwisawa, W.; Songsiriritthigul, P.

    2009-11-01

    Squalene has been used as a model compound for the investigation of sulphur crosslink in the vulcanization process. The effects of the accelerator on the crosslink were deduced from the sulfur K-edge absorption spectra. The majority of the crosslinks for the squalene vulcanized with ZDEC or TMTD is likely disulfidic, while that vulcanized with CBS or MBTS is monosulfidic.

  8. 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.

  9. Prediction of Iron K-Edge Absorption Spectra Using Time-Dependent Density Functional Theory

    SciTech Connect

    George, S.DeBeer; Petrenko, T.; Neese, F.

    2009-05-14

    Iron K-edge X-ray absorption pre-edge features have been calculated using a time-dependent density functional approach. The influence of functional, solvation, and relativistic effects on the calculated energies and intensities has been examined by correlation of the calculated parameters to experimental data on a series of 10 iron model complexes, which span a range of high-spin and low-spin ferrous and ferric complexes in O{sub h} to T{sub d} geometries. Both quadrupole and dipole contributions to the spectra have been calculated. We find that good agreement between theory and experiment is obtained by using the BP86 functional with the CP(PPP) basis set on the Fe and TZVP one of the remaining atoms. Inclusion of solvation yields a small improvement in the calculated energies. However, the inclusion of scalar relativistic effects did not yield any improved correlation with experiment. The use of these methods to uniquely assign individual spectral transitions and to examine experimental contributions to backbonding is discussed.

  10. Demonstration of enhanced K-edge angiography using a cerium target x-ray generator

    SciTech Connect

    Sato, Eiichi; Tanaka, Etsuro; Mori, Hidezo; Kawai, Toshiaki; Ichimaru, Toshio; Sato, Shigehiro; Takayama, Kazuyoshi; Ido, Hideaki

    2004-11-01

    The cerium target x-ray generator is useful in order to perform enhanced K-edge angiography using a cone beam because K-series characteristic x rays from the cerium target are absorbed effectively by iodine-based contrast mediums. The x-ray generator consists of a main controller, a unit with a Cockcroft-Walton circuit and a fixed anode x-ray tube, and a personal computer. The tube is a glass-enclosed diode with a cerium target and a 0.5-mm-thick beryllium window. The maximum tube voltage and current were 65 kV and 0.4 mA, respectively, and the focal-spot sizes were 1.0x1.3 mm. Cerium K{alpha} lines were left using a barium sulfate filter, and the x-ray intensity was 0.48 {mu}C/kg at 1.0 m from the source with a tube voltage of 60 kV, a current of 0.40 mA, and an exposure time of 1.0 s. Angiography was performed with a computed radiography system using iodine-based microspheres. In coronary angiography of nonliving animals, we observed fine blood vessels of approximately 100 {mu}m with high contrasts.

  11. Molecular anisotropy effects in carbon K-edge scattering: depolarized diffuse scattering and optical anisotropy

    SciTech Connect

    Stone, Kevin H.

    2014-07-14

    Some polymer properties, such as conductivity, are very sensitive to short- and intermediate-range orientational and positional ordering of anisotropic molecular functional groups, and yet means to characterize orientational order in disordered systems are very limited. We demonstrate that resonant scattering at the carbon K-edge is uniquely sensitive to short-range orientation correlations in polymers through depolarized scattering at high momentum transfers, using atactic polystyrene as a well-characterized test system. Depolarized scattering is found to coexist with unpolarized fluorescence, and to exhibit pronounced anisotropy. We also quantify the spatially averaged optical anisotropy from low-angle reflectivity measurements, finding anisotropy consistent with prior visible, x-ray absorption, and theoretical studies. The average anisotropy is much smaller than that in the depolarized scattering and the two have different character. Both measurements exhibit clear spectral signatures from the phenyl rings and the polyethylene-like backbone. Discussion focuses on analysis considerations and prospects for using this depolarized scattering for studies of disorder in soft condensed matter.

  12. Photoabsorption spectra of potassium and rubidium near the K-edge

    SciTech Connect

    Azuma, Y.; Berry, H.G.; Cowan, P.L.

    1995-08-01

    We have used a high-temperature circulating heat-pipe absorption cell together with monochromatized X-ray beams at the X24A and X23A2 beam lines at the NSLS to obtain photoabsorption spectra of potassium and rubidium at their K- and KM-edges. The photon-energy ranges lay near 3600 eV and 15200 eV, respectively. We have also obtained first measurements of the LII and LIII edges in cesium. Although the K-edge photoabsorptions of the rare gases have been studied, there is little previous work on other atomic vapors. Most of the edges and resonance peaks that we observed have now been identified using Dirac Hartree-Fock calculations. As a check, we have compared these results with those obtained previously in closed-shell rare-gas absorption spectra. The absolute energies were obtained through a calibration of the X24A systems using measurements of several metal L-edges in the 3200-5000 eV energy range. We found that the 4p resonance in potassium is significantly enhanced compared with the corresponding situation in argon. Likewise, the 5p resonance in krypton is unresolved from the background ionization cross section, whereas it is well resolved in rubidium. As suggested by Amusia, these enhancements may be due to the enhanced potential seen in the excited state of the alkali systems as a result of the presence of an s-electron which reduces the nuclear shielding.

  13. Calibration of Energy-Specific TDDFT for Modeling K-edge XAS Spectra of Light Elements.

    PubMed

    Lestrange, Patrick J; Nguyen, Phu D; Li, Xiaosong

    2015-07-14

    X-ray absorption spectroscopy (XAS) has become a powerful technique in chemical physics, because of advances in synchrotron technology that have greatly improved its temporal and spectroscopic resolution. Our recent work on energy-specific time-dependent density functional theory (ES-TDDFT) allows for the direct calculation of excitation energies in any region of the absorption spectrum, from UV-vis to X-ray. However, the ability of different density functional theories to model X-ray absorption spectra (XAS) of light elements has not yet been verified for ES-TDDFT. This work is a calibration of the ability of existing DFT kernels and basis sets to reproduce experimental K-edge excitation energies. Results were compared against 30 different transitions from gas-phase experiments. We focus on six commonly used density functionals (BHandHLYP, B3LYP, PBE1PBE, BP86, HSE06, LC-ωPBE) and various triple-ζ basis sets. The effects of core and diffuse functions are also investigated. PMID:26575736

  14. Time-Dependent Density Functional Calculations of Ligand K-Edge X-Ray Absorption Spectra

    SciTech Connect

    DeBeer George, S.; Petrenko, T.; Neese, F.

    2007-07-10

    X-ray absorption spectra (XAS) at the Cl and S K edge and Mo L edge have been calculated at the TDDFT level for a series of dioxomolybdenum complexes LMoO{sub 2}X (L = hydrotris(3,5-dimethyl-1-pyrazolyl)borate, X = Cl, SCH{sub 2}Ph, OPh), which play an important role in modeling the catalytic cycle of the sulfite oxidase enzyme. Also, the XAS spectra of model molecules of the Mo complexes have been simulated and interpreted in terms of the Mo 4d orbital splitting, in order to find possible correlations with the spectral pattern of the complexes. Comparison with the available experimental data allows us to assess the performances of the present computational scheme to describe the core excitations in large bioinorganic systems. The theoretical interpretation of the spectral features of both the metal and ligand core excitations in terms of the oscillator strength distribution provides important insight into the covalency of the metal-ligand bond.

  15. Using X-ray, K-edge densitometry in spent fuel characterization

    SciTech Connect

    Jensen, T.; Aljundi, T.; Gray, J.N.

    1998-06-01

    There are instances where records for spent nuclear fuel are incomplete, as well as cases where fuel assemblies have deteriorated during storage. To bring these materials into compliance for long term storage will require determination of parameters such as enrichment, total fissionable material, and burnup. To obtain accurate estimates of these parameters will require the combination of information from different inspection techniques. A method which can provide an accurate measure of the total uranium in the spent fuel is X-ray K-edge densitometry. To assess the potential for applying this method in spent fuel characterization, the authors have measured the amount of uranium in stacks of reactor fuel plates containing nuclear materials of different enrichments and alloys. They have obtained good agreement with expected uranium concentrations ranging from 60 mg/cm{sup 2} to 3,000 mg/cm{sup 2}, and have demonstrated that these measurements can be made in a high radiation field (> 200 mR/hr).

  16. 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.

  17. Experimental and theoretical XANES of CdS{sub x}Se{sub 1−x} nanostructures

    SciTech Connect

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

    2014-03-31

    The morphology and electronic properties of the CdS{sub x}Se{sub 1−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 L{sub 3,2}-edges. The theoretical XANES spectra have been calculated using the density functional approach. It is found that the optical band-gap emission of these CdS{sub x}Se{sub 1−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 L{sub 3,2} 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.

  18. K-edge imaging with the XPAD3 hybrid pixel detector, direct comparison of CdTe and Si sensors

    NASA Astrophysics Data System (ADS)

    Cassol, F.; Portal, L.; Graber-Bolis, J.; Perez-Ponce, H.; Dupont, M.; Kronland, C.; Boursier, Y.; Blanc, N.; Bompard, F.; Boudet, N.; Buton, C.; Clémens, J. C.; Dawiec, A.; Debarbieux, F.; Delpierre, P.; Hustache, S.; Vigeolas, E.; Morel, C.

    2015-07-01

    We investigate the improvement from the use of high-Z CdTe sensors for pre-clinical K-edge imaging with the hybrid pixel detectors XPAD3. We compare XPAD3 chips bump bonded to Si or CdTe sensors in identical experimental conditions. Image performance for narrow energy bin acquisitions and contrast-to-noise ratios of K-edge images are presented and compared. CdTe sensors achieve signal-to-noise ratios at least three times higher than Si sensors within narrow energy bins, thanks to their much higher detection efficiency. Nevertheless Si sensors provide better contrast-to-noise ratios in K-edge imaging when working at equivalent counting statistics, due to their better estimation of the attenuation coefficient of the contrast agent. Results are compared to simulated data in the case of the XPAD3/Si detector. Good agreement is observed when including charge sharing between pixels, which have a strong impact on contrast-to-noise ratios in K-edge images.

  19. K-edge imaging with the XPAD3 hybrid pixel detector, direct comparison of CdTe and Si sensors.

    PubMed

    Cassol, F; Portal, L; Graber-Bolis, J; Perez-Ponce, H; Dupont, M; Kronland, C; Boursier, Y; Blanc, N; Bompard, F; Boudet, N; Buton, C; Clémens, J C; Dawiec, A; Debarbieux, F; Delpierre, P; Hustache, S; Vigeolas, E; Morel, C

    2015-07-21

    We investigate the improvement from the use of high-Z CdTe sensors for pre-clinical K-edge imaging with the hybrid pixel detectors XPAD3. We compare XPAD3 chips bump bonded to Si or CdTe sensors in identical experimental conditions. Image performance for narrow energy bin acquisitions and contrast-to-noise ratios of K-edge images are presented and compared. CdTe sensors achieve signal-to-noise ratios at least three times higher than Si sensors within narrow energy bins, thanks to their much higher detection efficiency. Nevertheless Si sensors provide better contrast-to-noise ratios in K-edge imaging when working at equivalent counting statistics, due to their better estimation of the attenuation coefficient of the contrast agent. Results are compared to simulated data in the case of the XPAD3/Si detector. Good agreement is observed when including charge sharing between pixels, which have a strong impact on contrast-to-noise ratios in K-edge images. PMID:26133567

  20. Photoabsorption study of Bacillus megaterium, DNA and Related Biological Materials in the Phosphorus K-edge Region

    NASA Technical Reports Server (NTRS)

    Frigo, Sean P.; McNulty,Ian; Richmond, Robert C.; Ehret, Charles F.

    2003-01-01

    We have measured the x-ray transmission spectra of several biologically related samples in the phosphorus K-edge absorption region. These include red phosphorus, hydrated sodium phosphate (Na3PO4 12 H2O), deoxyribonucleic acid (DNA), adenosinetriphosphate (ATP), diolylphosphatidyl choline (DOPC), and Bacillus megaterium spores. Red phosphorus essentially displays an edge-jump. All other spectra are similar in form and energy position, where each is dominated by a narrower, more intense first peak and a broader but less intense second peak. The corresponding K-edge absorption thresholds are shifted towards higher energy relative to that for red phosphorus, as expected for increasing degrees of phosphorus oxidation. The B.meguterium spectrum has aspects common to both the phosphate and DNA spectra and is therefore interpreted as a composite of spectra arising from DNA/RNA and phosphates within the spore. The B. megaterium spore spectrum provides needed information for resonant radiation damage studies in the phosphorus K-edge absorption region by identifying candidate photoexcitations. In addition, the absorption spectra will be useful in macromolecular crystallography studies employing anomalous dispersion effects at the phosphorus K-edge.

  1. Photoabsorption Study of Bacillus megaterium, DNA and Related Biological Materials in the Phosphorus K-edge Region

    NASA Technical Reports Server (NTRS)

    Frigo, Sean P.; McNulty, Ian; Richmond, Robert C.; Ehret, Charles F.

    2002-01-01

    We have measured the x-ray transmission spectra of several biologically related samples in the phosphorus K-edge absorption region. These include elemental red phosphorus, hydrated sodium phosphate (Na3PO4.12H2O), deoxyribonucleic acid (DNA), adenosinetriphosphate (ATP), diolylphosphatidyl choline (DOPC), and Bacillus megaterium spores. Elemental red phosphorus essentially displays an edge-jump. All other spectra are similar in form and energy position. Each spectrum for these substances is dominated by a narrower, more intense first peak and a broader but less intense second peak. The corresponding K-edge absorption thresholds are shifted towards higher energy relative to that for elemental red phosphorus, as expected for increasing degrees of phosphorus oxidation. The B. megaterium spectrum has aspects common to both the phosphate and DNA spectra and is therefore interpreted as a composite of spectra arising from DNA/RNA and phosphates within the spore. The B. megaterium spore spectrum provides needed information for resonant radiation damage studies in the phosphorus K-edge absorption region by identifying candidate photoexcitations. In addition,the absorption spectra will be useful in macromolecular crystallography studies employing anomalous dispersion effects at the phosphorus K-edge.

  2. XANES study of hydrogen incorporation in a Pd-capped Nb thin film

    SciTech Connect

    Ruckman, M.W.; Reisfeld, G.; Jisrawi, N.M.; Weinert, M.; Strongin, M.; Wiesmann, H.; Croft, M.; Sahiner, A.; Sills, D.; Ansari, P.

    1998-02-01

    X-ray absorption near-edge structure (XANES) measurements were used to probe the H-charging-induced electronic structure changes of a 2400 {Angstrom} Nb film capped with Pd. These results are discussed in terms of {ital ab initio} linear augmented plane-wave (LAPW) band-structure calculations for this material. The Pd-L{sub 3}-edge XANES clearly manifested the spectral (Pd-d state related) changes expected for Pd-hydride formation, a white line feature degradation, and the appearance of a Pd-H antibonding feature at 6 eV above the threshold. The Nb-L{sub 2,3} edge changes with H charging show a distinct enhancement of the white line strength; a feature 6 eV above the edges, associated with Nb-H antibonding states in analogy with the Pd results; the suppression of a threshold-onset feature of Nb metal; and a shift of the centrum of the white line feature towards the threshold. Comparison of the Nb sphere projection of the d{sub 3/2} component of the LAPW density of states (DOS) to the Nb-L{sub 2}-edge spectra yields good basic agreement with the observed spectral changes. In particular, the substantial theoretical reduction in the DOS at, and just above, the Fermi energy (E{sub f}) is directly related to the near threshold Nb-L{sub 2,3} spectral changes. The more modest white line enhancement in the theoretical DOS is noted and discussed. Nb-K-edge XANES are also discussed in terms of the Nb-site p-state projected LAPW DOS. This last comparison indicates a p-state reduction near E{sub f} upon H charging of the Nb. {copyright} {ital 1998} {ital The American Physical Society}

  3. 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.

  4. Manganese valence and coordination structure in Mn,Mg-codoped {gamma}-AlON green phosphor

    SciTech Connect

    Takeda, Takashi; Xie, Rong-Jun; Hirosaki, Naoto; Matsushita, Yoshitaka; Honma, Tetuso

    2012-10-15

    The valence and coordination structure of manganese in a Mn,Mg-codoped {gamma}-AlON spinel-type oxynitride green phosphor were studied by synchrotron X-ray diffraction and absorption fine structure measurements. The absorption edge position of the XANES revealed the bivalency of Mn. Two cation sites are available in the spinel structure for cation doping: a tetrahedral site and an octahedral site. The pre-edge of the XANES and the distance to the nearest neighbor atoms obtained from the EXAFS measurement showed that Mn was situated at the tetrahedral site. Rietveld analysis showed that the vacancy occupied the octahedral site. The preferential occupation of the tetrahedral site by Mn and the roles of N and Mg are discussed in relation to the spinel crystal structure. - Graphical Abstract: Fourier transform of EXAFS of Mn K-edge for Mn,Mg-codoped green phosphor and Mn coordination structure. Highlights: Black-Right-Pointing-Pointer Mn, Mg-codoped {gamma}-AlON green phosphor for white LED. Black-Right-Pointing-Pointer The valence of Mn is divalent. Black-Right-Pointing-Pointer Mn occupies the tetrahedral site in the spinel structure.

  5. 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 structure (µXANES) 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. PMID:24365942

  6. Demonstration of enhanced K-edge angiography utilizing a samarium x-ray generator

    NASA Astrophysics Data System (ADS)

    Sato, Eiichi; Tanaka, Etsuro; Mori, Hidezo; Kawai, Toshiaki; Inoue, Takashi; Ogawa, Akira; Izumisawa, Mitsuru; Takahashi, Kiyomi; Sato, Shigehiro; Ichimaru, Toshio; Takayama, Kazuyoshi

    2006-08-01

    The samarium-target x-ray tube is useful in order to perform cone-beam K-edge angiography because K-series characteristic x-rays from the samarium target are absorbed effectively by iodine-based contrast media. This generator consists of the following components: a constant high-voltage power supply, a filament power supply, a turbomolecular pump, and an x-ray tube. The x-ray tube is a demountable diode which is connected to the turbomolecular pump and consists of the following major devices: a samarium target, a tungsten hairpin cathode (filament), a focusing (Wehnelt) electrode, a polyethylene terephthalate x-ray window 0.25 mm in thickness, and a stainless-steel tube body. In the x-ray tube, the positive high voltage is applied to the anode (target) electrode, and the cathode is connected to the tube body (ground potential). In this experiment, the tube voltage applied was from 50 to 70 kV, and the tube current was regulated to within 0.10 mA by the filament temperature. The exposure time is controlled in order to obtain optimum x-ray intensity. The electron beams from the cathode are converged to the target by the focusing electrode, and bremsstrahlung x-rays were absorbed using a 50-µm-thick tungsten filter. The x-ray intensity was 1.04 μGy/s at 1.0 m from the x-ray source with a tube voltage of 60 kV and a tube current of 0.10 mA, and angiography was performed using a computed radiography system and iodine-based microspheres 15 µm in diameter. In angiography of non-living animals, we observed fine blood vessels of approximately 100 µm with high contrasts.

  7. 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. PMID:11505987

  8. XANES spectra of metal phytate compounds

    Technology Transfer Automated Retrieval System (TEKTRAN)

    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...

  9. Studies on effective atomic numbers, electron densities from mass attenuation coefficients near the K edge in some samarium compounds.

    PubMed

    Akman, F; Durak, R; Turhan, M F; Kaçal, M R

    2015-07-01

    The effective atomic numbers and electron densities of some samarium compounds were determined using the experimental total mass attenuation coefficient values near the K edge in the X-ray energy range from 36.847 up to 57.142 keV. The measurements, in the region from 36.847 to 57.142 keV, were done in a transmission geometry utilizing the Kα2, Kα1, Kβ1 and Kβ2 X-rays from different secondary source targets excited by the 59.54 keV gamma-photons from an Am-241 annular source. This paper presents the first measurement of the effective atomic numbers and electron densities for some samarium compounds near the K edge. The results of the study showed that the measured values were in good agreement with the theoretically calculated ones. PMID:25880612

  10. Probing single magnon excitations in Sr₂IrO₄ using O K-edge resonant inelastic x-ray scattering

    SciTech Connect

    Liu, X.; Dean, M. P. M.; Liu, J.; Chiuzbaian, S. G.; Jaouen, N.; Nicolaou, A.; Yin, W. G.; Rayan Serrao, C.; Ramesh, R.; Ding, H.; Hill, J. P.

    2015-04-28

    Resonant inelastic X-ray scattering (RIXS) at the L-edge of transition metal elements is now commonly used to probe single magnon excitations. Here we show that single magnon excitations can also be measured with RIXS at the K-edge of the surrounding ligand atoms when the center heavy metal elements have strong spin-orbit coupling. This is demonstrated with oxygen K-edge RIXS experiments on the perovskite Sr₂IrO₄, where low energy peaks from single magnon excitations were observed. This new application of RIXS has excellent potential to be applied to a wide range of magnetic systems based on heavy elements, for which the L-edge RIXS energy resolutions in the hard X-ray region is usually poor.

  11. Probing single magnon excitations in Sr₂IrO₄ using O K-edge resonant inelastic x-ray scattering

    DOE PAGESBeta

    Liu, X.; Dean, M. P. M.; Liu, J.; Chiuzbaian, S. G.; Jaouen, N.; Nicolaou, A.; Yin, W. G.; Rayan Serrao, C.; Ramesh, R.; Ding, H.; et al

    2015-04-28

    Resonant inelastic X-ray scattering (RIXS) at the L-edge of transition metal elements is now commonly used to probe single magnon excitations. Here we show that single magnon excitations can also be measured with RIXS at the K-edge of the surrounding ligand atoms when the center heavy metal elements have strong spin-orbit coupling. This is demonstrated with oxygen K-edge RIXS experiments on the perovskite Sr₂IrO₄, where low energy peaks from single magnon excitations were observed. This new application of RIXS has excellent potential to be applied to a wide range of magnetic systems based on heavy elements, for which the L-edgemore » RIXS energy resolutions in the hard X-ray region is usually poor.« less

  12. Comparison of quantitative k-edge empirical estimators using an energy-resolved photon-counting detector

    NASA Astrophysics Data System (ADS)

    Zimmerman, Kevin C.; Gilat Schmidt, Taly

    2016-03-01

    Using an energy-resolving photon counting detector, the amount of k-edge material in the x-ray path can be estimated using a process known as material decomposition. However, non-ideal effects within the detector make it difficult to accurately perform this decomposition. This work evaluated the k-edge material decomposition accuracy of two empirical estimators. A neural network estimator and a linearized maximum likelihood estimator with error look-up tables (A-table method) were evaluated through simulations and experiments. Each estimator was trained on system-specific calibration data rather than specific modeling of non-ideal detector effects or the x-ray source spectrum. Projections through a step-wedge calibration phantom consisting of different path lengths through PMMA, aluminum, and a k-edge material was used to train the estimators. The estimators were tested by decomposing data acquired through different path lengths of the basis materials. The estimators had similar performance in the chest phantom simulations with gadolinium. They estimated four of the five densities of gadolinium with less than 2mg/mL bias. The neural networks estimates demonstrated lower bias but higher variance than the A-table estimates in the iodine contrast agent simulations. The neural networks had an experimental variance lower than the CRLB indicating it is a biased estimator. In the experimental study, the k-edge material contribution was estimated with less than 14% bias for the neural network estimator and less than 41% bias for the A-table method.

  13. Co K-edge magnetic circular dichroism across the spin state transition in LaCoO3 single crystal

    NASA Astrophysics Data System (ADS)

    Efimov, V.; Ignatov, A.; Troyanchuk, I. O.; Sikolenko, V. V.; Rogalev, A.; Wilhelm, F.; Efimova, E.; Tiutiunnikov, S. I.; Karpinsky, D.; Kriventsov, V.; Yakimchuk, E.; Molodtsov, S.; Sainctavit, P.; Prabhakaran, D.

    2016-05-01

    We report on Co K-edge x-ray magnetic circular dichroism (XMCD) measurements of LaCoO3 single crystal in temperature range from 5 to 300 K and external magnetic field of 17 T. The response consists of pre-edge (at 7712 eV) and bi-polar peak (up at 7727, down at 7731 eV) with amplitudes, respectively, less than 10-3 and 10-2 of the Co K-edge jump. Using the sum rule the orbital magnetic moment of 4p Co is evaluated. Its temperature dependence reaches a maximum of (2.7 ± 0.9) x10-3 μB at 120 K, following the trend for the total magnetic moment on the Co obtained from the superconducting quantum interference device measurements. However, on warming from 25 to 120 K, the orbital magnetic moment of the 4p Co doubles while total magnetic moment of Co increases 10 times. First principle calculations are in order to relate the Co K-edge XMCD results to the orbital and spin moment of 3d Co.

  14. Three-dimensional labeling of newly formed bone using synchrotron radiation barium K-edge subtraction imaging

    NASA Astrophysics Data System (ADS)

    Panahifar, Arash; Swanston, Treena M.; Pushie, M. Jake; Belev, George; Chapman, Dean; Weber, Lynn; Cooper, David M. L.

    2016-07-01

    Bone is a dynamic tissue which exhibits complex patterns of growth as well as continuous internal turnover (i.e. remodeling). Tracking such changes can be challenging and thus a high resolution imaging-based tracer would provide a powerful new perspective on bone tissue dynamics. This is, particularly so if such a tracer can be detected in 3D. Previously, strontium has been demonstrated to be an effective tracer which can be detected by synchrotron-based dual energy K-edge subtraction (KES) imaging in either 2D or 3D. The use of strontium is, however, limited to very small sample thicknesses due to its low K-edge energy (16.105 keV) and thus is not suitable for in vivo application. Here we establish proof-of-principle for the use of barium as an alternative tracer with a higher K-edge energy (37.441 keV), albeit for ex vivo imaging at the moment, which enables application in larger specimens and has the potential to be developed for in vivo imaging of preclinical animal models. New bone formation within growing rats in 2D and 3D was demonstrated at the Biomedical Imaging and Therapy bending magnet (BMIT-BM) beamline of the Canadian Light Source synchrotron. Comparative x-ray fluorescence imaging confirmed those patterns of uptake detected by KES. This initial work provides a platform for the further development of this tracer and its exploration of applications for in vivo development.

  15. 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.

  16. Polycapillary-optics-based micro-XANES and micro-EXAFS at a third-generation bending-magnet beamline.

    PubMed

    Silversmit, Geert; Vekemans, Bart; Nikitenko, Sergey; Bras, Wim; Czhech, Viktoria; Zaray, Gyula; Szaloki, Imre; Vincze, Laszlo

    2009-03-01

    A focusing system based on a polycapillary half-lens optic has been successfully tested for transmission and fluorescence micro-X-ray absorption spectroscopy at a third-generation bending-magnet beamline equipped with a non-fixed-exit Si(111) monochromator. The vertical positional variations of the X-ray beam owing to the use of a non-fixed-exit monochromator were shown to pose only a limited problem by using the polycapillary optic. The expected height variation for an EXAFS scan around the Fe K-edge is approximately 200 microm on the lens input side and this was reduced to approximately 1 microm for the focused beam. Beam sizes (FWHM) of 12-16 microm, transmission efficiencies of 25-45% and intensity gain factors, compared with the non-focused beam, of about 2000 were obtained in the 7-14 keV energy range for an incoming beam of 0.5 x 2 mm (vertical x horizontal). As a practical application, an As K-edge micro-XANES study of cucumber root and hypocotyl was performed to determine the As oxidation state in the different plant parts and to identify a possible metabolic conversion by the plant. PMID:19240336

  17. Quantitative analysis of sulfur functional groups in natural organic matter by XANES spectroscopy

    NASA Astrophysics Data System (ADS)

    Manceau, Alain; Nagy, Kathryn L.

    2012-12-01

    Two new approaches to quantify sulfur functionalities in natural organic matter from S K-edge XANES spectroscopy are presented. In the first, the K-edge spectrum is decomposed into Gaussian and two arctangent functions, as in the usual Gaussian curve fitting (GCF) method, but the applicability of the model is improved by a rigorous simulation procedure that constrains the model-fit to converge toward chemically and physically realistic values. Fractions of each type of functionality are obtained after spectral decomposition by correcting Gaussian areas for the change in X-ray absorption cross-section with increasing oxidation state. This correction is made using published calibration curves and a new curve obtained in this study. Calibration-induced errors, inherent to the choice of a particular curve, are typically lower than 5% of total sulfur for oxidized species (e.g., sulfate), may reach 10% for organic reduced sulfur, and may be as high as 30-40% for inorganic reduced sulfur. A generic curve, which reduces the calibration-induced uncertainty by a factor of two on data collected to avoid X-ray overabsorption, is derived. In the second analytical scheme, the K-edge spectrum is partitioned into a weighted sum of component species, as in the usual linear combination fitting (LCF) method, but is fit to an extended database of reference spectra under the constraint of non-negativity in the loadings (Combo fit). The fraction of each sulfur functionality is taken as the sum of all positive fractions of references with similar oxidation state of sulfur. The two proposed methods are applied to eight humic and fulvic acids from the International Humic Substances Society (IHSS). The nature and fractions of sulfur functionalities obtained by the two analytical approaches are consistent with each other. The accuracy of the derived values, expressed as the difference in values of a fraction obtained on the same material by the two independent methods, is on average 4.5 ± 3

  18. 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.

  19. 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.

  20. Submicrometer hyperspectral X-ray imaging of heterogeneous rocks and geomaterials: applications at the Fe k-edge.

    PubMed

    De Andrade, Vincent; Susini, Jean; Salomé, Murielle; Beraldin, Olivier; Rigault, Cecile; Heymes, Thomas; Lewin, Eric; Vidal, Olivier

    2011-06-01

    Because of their complex genesis, rocks and geomaterials are commonly polycrystalline heterogeneous systems, with various scale-level chemical and structural heterogeneities. Like most other μ-analytical techniques relying on scanning instruments with pencil-beam, the X-ray absorption near edge structure (XANES) technique allows elemental oxidation states to be probed with high spatial resolution but suffers from long acquisition times, imposing practical limits on the field of view. Now, regions of interest of sample are generally several orders of magnitude larger than the beam size. Here, we show the potential of coupling XANES and full-field absorption radiographies with a large hard X-ray beam. Thanks to a new setup, which allows both the acquisition of a XANES image stack and the execution of polarization contrast imaging, 1 to 4 mega-pixel crystallographic orientations and Fe oxidation state mapping corrected from polarization effects are obtained in a couple of hours on polycrystalline materials with submicrometric resolution. The demonstration is first carried out on complex metamorphic rocks, where Fe(3+)/Fe(total) images reveal subtle redox variations within single mineralogical phases. A second application concerns a bentonite analogue considered for nuclear waste and CO(2) storage. Proportion mappings of finely mixed phases are extracted from hyperspectral data, imaging the spatial progress of reaction processes essential for the safety of such storage systems. PMID:21500858

  1. K-edge Subtraction Angiography with Synchrotron X-Rays: Final Technical Report, (February 1, 1984 to January 31, 1987)

    DOE R&D Accomplishments Database

    Hofstadter, R.

    1987-09-01

    The aim was the development of an angiographic method and appropriate equipment for imaging with x-rays the coronary arteries in a non-invasive manner. Successive steps involved studies with phantoms, live animals and finally with human subjects. Clinical evaluation of human coronary arteries remains a goal of this and a continuing project, and steps along the way to such an achievement are in process. Transvenous injection of a dye using the method of iodine dichromography near 33.2 keV, the K-edge of iodine, forms the basis of the method

  2. Sulfur K-edge X-ray absorption spectroscopy and time-dependent density functional theory of arsenic dithiocarbamates.

    PubMed

    Donahue, Courtney M; Pacheco, Juan S Lezama; Keith, Jason M; Daly, Scott R

    2014-06-28

    S K-edge X-ray absorption spectroscopy (XAS) and time-dependent density functional theory (TDDFT) calculations were performed on a series of As[S2CNR2]3 complexes, where R2 = Et2, (CH2)5 and Ph2, to determine how dithiocarbamate substituents attached to N affect As[S2CNR2]3 electronic structure. Complimentary [PPh4][S2CNR2] salts were also studied to compare dithiocarbamate bonding in the absence of As. The XAS results indicate that changing the orientation of the alkyl substituents from trans to cis (R2 = Et2vs. (CH2)5) yields subtle variations whereas differences associated with a change from alkyl to aryl are much more pronounced. For example, despite the differences in As 4p mixing, the first features in the S K-edge XAS spectra of [PPh4][S2CNPh2] and As[S2CNPh2]3 were both shifted by 0.3 eV compared to their alkyl-substituted derivatives. DFT calculations revealed that the unique shift observed for [PPh4][S2CNPh2] is due to phenyl-induced splitting of the π* orbitals delocalized over N, C and S. A similar phenomenon accounts for the shift observed for As[S2CNPh2]3, but the presence of two unique S environments (As-S and As···S) prevented reliable analysis of As-S covalency from the XAS data. In the absence of experimental values, DFT calculations revealed a decrease in As-S orbital mixing in As[S2CNPh2]3 that stems from a redistribution of electron density to S atoms participating in weaker As···S interactions. Simulated spectra obtained from TDDFT calculations reproduce the experimental differences in the S K-edge XAS data, which suggests that the theory is accurately modeling the experimental differences in As-S orbital mixing. The results highlight how S K-edge XAS and DFT can be used cooperatively to understand the electronic structure of low symmetry coordination complexes containing S atoms in different chemical environments. PMID:24811926

  3. Resonant inelastic X-ray scattering spectrometer with 25meV resolution at the Cu K -edge

    DOE PAGESBeta

    Ketenoglu, Didem; Harder, Manuel; Klementiev, Konstantin; Upton, Mary; Taherkhani, Mehran; Spiwek, Manfred; Dill, Frank-Uwe; Wille, Hans-Christian; Yavaş, Hasan

    2015-06-27

    An unparalleled resolution is reported with an inelastic X-ray scattering instrument at the CuK-edge. Based on a segmented concave analyzer, featuring single-crystal quartz (SiO2) pixels, the spectrometer delivers a resolution near 25meV (FWHM) at 8981eV. Besides the quartz analyzer, the performance of the spectrometer relies on a four-bounce Si(553) high-resolution monochromator and focusing Kirkpatrick–Baez optics. The measured resolution agrees with the ray-tracing simulation of an ideal spectrometer. The performance of the spectrometer is demonstrated by reproducing the phonon dispersion curve of a beryllium single-crystal.

  4. Overlap population diagram for ELNES and XANES: peak assignment and interpretation

    NASA Astrophysics Data System (ADS)

    Mizoguchi, Teruyasu

    2009-03-01

    This article reviews overlap population (OP) diagrams for electron energy loss near-edge structure (ELNES) and x-ray absorption near-edge structure (XANES). By using the OP diagrams, peaks in ELNES and XANES of MgO, ZnO, AlN, GaN, InN, and YBa2Cu3O7-x are interpreted in terms of cation-anion and cation-cation interactions. Common features are found in the OP diagrams for different edges. A reconstruction of the unoccupied electronic structure is demonstrated by aligning the different edges with the common features in the OP diagrams. The OP diagram is also applied to the Cu/Al2O3 hetero-interface to find the relationships among ELNES, atomic and electronic structures, and properties.

  5. Near-coincident K-line and K-edge energies as ionization diagnostics for some high atomic number plasmas

    SciTech Connect

    Pereira, N. R.; Weber, B. V.; Phipps, D. G.; Schumer, J. W.; Seely, J. F.; Carroll, J. J.; Vanhoy, J. R.; Slabkowska, K.; Polasik, M.

    2012-10-15

    For some high atomic number atoms, the energy of the K-edge is tens of eVs higher than the K-line energy of another atom, so that a few eV increase in the line's energy results in a decreasing transmission of the x-ray through a filter of the matching material. The transmission of cold iridium's Asymptotically-Equal-To 63.287 keV K{alpha}{sub 2} line through a lutetium filter is 7% lower when emitted by ionized iridium, consistent with an energy increase of {Delta}{epsilon} Asymptotically-Equal-To 10{+-}1 eV associated with the ionization. Likewise, the transmission of the K{beta}{sub 1} line of ytterbium through a near-coincident K-edge filter changes depending on plasma parameters that should affect the ionization. Systematic exploration of filter-line pairs like these could become a unique tool for diagnostics of suitable high energy density plasmas.

  6. Long-Range Chemical Sensitivity in the Sulfur K-Edge X-ray Absorption Spectra of Substituted Thiophenes

    PubMed Central

    2015-01-01

    Thiophenes are the simplest aromatic sulfur-containing compounds and are stable and widespread in fossil fuels. Regulation of sulfur levels in fuels and emissions has become and continues to be ever more stringent as part of governments’ efforts to address negative environmental impacts of sulfur dioxide. In turn, more effective removal methods are continually being sought. In a chemical sense, thiophenes are somewhat obdurate and hence their removal from fossil fuels poses problems for the industrial chemist. Sulfur K-edge X-ray absorption spectroscopy provides key information on thiophenic components in fuels. Here we present a systematic study of the spectroscopic sensitivity to chemical modifications of the thiophene system. We conclude that while the utility of sulfur K-edge X-ray absorption spectra in understanding the chemical composition of sulfur-containing fossil fuels has already been demonstrated, care must be exercised in interpreting these spectra because the assumption of an invariant spectrum for thiophenic forms may not always be valid. PMID:25116792

  7. Structure of Alkali Borate Glasses at High Pressure: B and Li K-Edge Inelastic X-Ray Scattering Study

    SciTech Connect

    Lee, Sung Keun; Eng, Peter J.; Mao, Ho-kwang; Meng, Yue; Shu, Jinfu

    2008-06-16

    We report the first in situ boron K-edge inelastic x-ray scattering (IXS) spectra for alkali borate glasses (Li{sub 2}B{sub 4}O{sub 7}) at high pressure up to 30 GPa where pressure-induced coordination transformation from three-coordinated to four-coordinated boron was directly probed. Coordination transformation (reversible upon decompression) begins around 5 GPa and the fraction of four-coordinated boron increases with pressure from about 50% (at 1 atm) to more than 95% (at 30 GPa) with multiple densification mechanisms, evidenced by three distinct pressure ranges for (d{sup [4]}B/dP){sub T}. The lithium K-edge IXS spectrum for Li-borate glasses at 5 GPa shows IXS features similar to that at 1 atm, suggesting that the Li environment does not change much with pressure up to 5 GPa. These results provide improved understanding of the structure of low-z glass at high pressure.

  8. Experimental results of use of triple-energy X-ray beam with K-edge filter in multi-energy imaging

    NASA Astrophysics Data System (ADS)

    Kim, D.; Lee, S.; Jeon, P.-H.

    2016-04-01

    Multi-energy imaging is useful for contrast enhancement of lesions, quantitative analysis of specific materials and material separation in the human body. Generally, dual-energy methods are applied to discriminating two materials, but this method cannot discriminate more than two materials. Photon-counting detectors provide spectral information from polyenergetic X-rays using multiple energy bins. In this work, we developed triple-energy X-ray beams using a filter with K-edge energy and applied them experimentally. The energy spectra of triple-energy X-ray beams were assessed by using a spectrometer. The designed triple-energy X-ray beams were validated by measuring quantitative evaluations with mean energy ratio (MER), contrast variation ratio (CVR) and exposure efficiency (EE). Then, triple-energy X-ray beams were used to extract density map of three materials, iodine (I), aluminum (Al) and polymethyl methacrylate (PMMA). The results of the thickness density maps obtained with the developed triple-energy X-ray beams were compared to those acquired using the photon-counting method. As a result, it was found experimentally that the proposed triple-energy X-ray beam technique can separate the three materials as well as the photon-counting method.

  9. XANES Demonstrates the Release of Calcium Phosphates from Alkaline Vertisols to Moderately Acidified Solution.

    PubMed

    Andersson, Karl O; Tighe, Matthew K; Guppy, Christopher N; Milham, Paul J; McLaren, Timothy I; Schefe, Cassandra R; Lombi, Enzo

    2016-04-19

    Calcium phosphate (CaP) minerals may comprise the main phosphorus (P) reserve in alkaline soils, with solubility dependent on pH and the concentration of Ca and/or P in solution. Combining several techniques in a novel way, we studied these phenomena by progressively depleting P from suspensions of two soils (low P) using an anion-exchange membrane (AEM) and from a third soil (high P) with AEM together with a cation-exchange membrane. Depletions commenced on untreated soil, then continued as pH was manipulated and maintained at three constant pH levels: the initial pH (pHi) and pH 6.5 and 5.5. Bulk P K-edge X-ray absorption near-edge structure (XANES) spectroscopy revealed that the main forms of inorganic P in each soil were apatite, a second more soluble CaP mineral, and smectite-sorbed P. With moderate depletion of P at pHi or pH 6.5, CaP minerals became more prominent in the spectra compared to sorbed species. The more soluble CaP minerals were depleted at pH 6.5, and all CaP minerals were exhausted at pH 5.5, showing that the CaP species present in these alkaline soils are soluble with decreases of pH in the range achievable by rhizosphere acidification. PMID:26974327

  10. Behavior and mechanism of arsenate adsorption on activated natural siderite: evidences from FTIR and XANES analysis.

    PubMed

    Zhao, Kai; Guo, Huaming

    2014-02-01

    Activated natural siderite (ANS) was used to investigate its characteristics and mechanisms of As(V) adsorption from aqueous solution. Batch tests were carried out to determine effects of contact time, initial As(V) concentration, temperature, pH, background electrolyte, and coexisting anions on As(V) adsorption. Arsenic(V) adsorption on ANS well-fitted pseudo-second-order kinetics. ANS showed a high-adsorption capacity of 2.19 mg/g estimated from Langmuir isotherm at 25 °C. Thermodynamic studies indicated that As(V) adsorption on ANS was spontaneous, favorable, and endothermic. ANS adsorbed As(V) efficiently in a relatively wide pH range between 2.0 and 10.0, although the removal efficiency was slightly higher in acidic conditions than that in basic conditions. Effects of background electrolyte and coexisting anions were not significant within the concentration ranges observed in high As groundwater. Results of XRD and Fe K-edge XANES analysis suggested ANS acted as an Fe(II)/(III) hybrid system, which was quite effective in adsorbing As from aqueous solution. There was no As redox transformation during adsorption, although Fe(II) oxidation occurred in the system. Two infrared bands at 787 and 872 cm(-1) after As(V) adsorption suggested that As(V) should be predominantly adsorbed on ANS via inner-sphere bidendate binuclear surface complexes. PMID:24014199

  11. Resonant inelastic X-ray scattering spectrometer with 25 meV resolution at the Cu K-edge.

    PubMed

    Ketenoglu, Didem; Harder, Manuel; Klementiev, Konstantin; Upton, Mary; Taherkhani, Mehran; Spiwek, Manfred; Dill, Frank Uwe; Wille, Hans Christian; Yavaş, Hasan

    2015-07-01

    An unparalleled resolution is reported with an inelastic X-ray scattering instrument at the Cu K-edge. Based on a segmented concave analyzer, featuring single-crystal quartz (SiO₂) pixels, the spectrometer delivers a resolution near 25 meV (FWHM) at 8981 eV. Besides the quartz analyzer, the performance of the spectrometer relies on a four-bounce Si(553) high-resolution monochromator and focusing Kirkpatrick-Baez optics. The measured resolution agrees with the ray-tracing simulation of an ideal spectrometer. The performance of the spectrometer is demonstrated by reproducing the phonon dispersion curve of a beryllium single-crystal. PMID:26134800

  12. K-edge photoabsorption cross section in metal oxides: Effect of vacancies in TiOx and VOx

    NASA Astrophysics Data System (ADS)

    Kutzler, F. W.; Ellis, D. E.

    1984-06-01

    The x-ray K-edge photoabsorption cross sections for TiO and VO have been calculated, with the use of the self-consistent one-electron local-density theory. Energy levels, charge distribution, and cross sections were obtained from a 27-atom "microcrystal," with a molecular-cluster approach in the discrete-variational method. A detailed comparison is made with experimental spectra for VOx; features of theory and experiment are in good agreement if one assumes a relaxation of the nearest-neighbor oxygen atoms for the O-vacancy cluster. Bound-to-bound transitions are found to contribute significantly to the near-edge structure for the defect crystal.

  13. Oxygen K-edge fine structures of water by x-ray Raman scattering spectroscopy under pressure conditions

    SciTech Connect

    Fukui, Hiroshi; Huotari, Simo; Andrault, Denis; Kawamoto, Tatsuhiko

    2007-10-07

    Fine structure of the oxygen K edge was investigated for water at ambient pressure, 0.16, 0.21, 0.27, 0.47, and 0.60 GPa using x-ray Raman scattering spectroscopy (XRS). Similarity in near-edge structures at 0.16 and 0.60 GPa suggests little difference in the electronic state of oxygen in the low-pressure and high-pressure forms of water. Yet, we observed significant variation of preedge structure of the XRS spectra with compression. The intensity of the preedge peak at 535.7 eV has a minimal value at around 0.3 GPa, indicating that the number of hydrogen bonding increases first and then decreases as a function of pressure.

  14. Automated Chemical Analysis of Internally Mixed Aerosol Particles Using X-ray Spectromicroscopy at the Carbon K-Edge

    SciTech Connect

    Gilles, Mary K; Moffet, R.C.; Henn, T.; Laskin, A.

    2011-01-20

    We have developed an automated data analysis method for atmospheric particles using scanning transmission X-ray microscopy coupled with near edge X-ray fine structure spectroscopy (STXM/NEXAFS). This method is applied to complex internally mixed submicrometer particles containing organic and inorganic material. Several algorithms were developed to exploit NEXAFS spectral features in the energy range from 278 to 320 eV for quantitative mapping of the spatial distribution of elemental carbon, organic carbon, potassium, and noncarbonaceous elements in particles of mixed composition. This energy range encompasses the carbon K-edge and potassium L2 and L3 edges. STXM/NEXAFS maps of different chemical components were complemented with a subsequent analysis using elemental maps obtained by scanning electron microscopy coupled with energy dispersive X-ray analysis (SEM/EDX). We demonstrate the application of the automated mapping algorithms for data analysis and the statistical classification of particles.

  15. Quantum Monte Carlo for the x-ray absorption spectrum of pyrrole at the nitrogen K-edge

    SciTech Connect

    Zubarev, Dmitry Yu.; Austin, Brian M.; Lester, William A. Jr.

    2012-04-14

    Fixed-node diffusion Monte Carlo (FNDMC) is used to simulate the x-ray absorption spectrum of a gas-phase pyrrole molecule at the nitrogen K-edge. Trial wave functions for core-excited states are constructed from ground-state Kohn-Sham determinants substituted with singly occupied natural orbitals from configuration interaction with single excitations calculations of the five lowest valence-excited triplet states. The FNDMC ionization potential (IP) is found to lie within 0.3 eV of the experimental value of 406.1 {+-} 0.1 eV. The transition energies to anti-bonding virtual orbitals match the experimental spectrum after alignment of IP values and agree with the existing assignments.

  16. Resonant inelastic X-ray scattering spectrometer with 25 meV resolution at the Cu K-edge

    PubMed Central

    Ketenoglu, Didem; Harder, Manuel; Klementiev, Konstantin; Upton, Mary; Taherkhani, Mehran; Spiwek, Manfred; Dill, Frank-Uwe; Wille, Hans-Christian; Yavaş, Hasan

    2015-01-01

    An unparalleled resolution is reported with an inelastic X-ray scattering instrument at the Cu K-edge. Based on a segmented concave analyzer, featuring single-crystal quartz (SiO2) pixels, the spectrometer delivers a resolution near 25 meV (FWHM) at 8981 eV. Besides the quartz analyzer, the performance of the spectrometer relies on a four-bounce Si(553) high-resolution monochromator and focusing Kirkpatrick–Baez optics. The measured resolution agrees with the ray-tracing simulation of an ideal spectrometer. The performance of the spectrometer is demonstrated by reproducing the phonon dispersion curve of a beryllium single-crystal. PMID:26134800

  17. Vulcanization reaction of squalene and S8 powder studied by Sulfur K-edge NEXAFS under liquid phase

    NASA Astrophysics Data System (ADS)

    Yagi, S.; Menjo, Y.; Tsukada, C.; Ogawa, S.; Kutluk, G.; Namatame, H.; Taniguchi, M.

    2015-03-01

    Vulcanized rubber materials are useful in our surroundings. However, detail structure and reaction are not revealed even in present. Since squalene molecule possesses some same properties compared with natural rubber, we have prepared the samples of vulcanized squalene at 140 °C for several hours. To understand the vulcanization reaction,sulfur K-edge NEXAFS measurements have been carried out for the vulcanized squalene under liquid phase with He-path system and fluorescence detection mode. Moreover, we have tried curve fitting analysis of NEXAFS spectra. The results indicate that the squalene has been vulcanized by the S8 molecule at 140 °C and the S8 molecule length is shortened from 8 to 5-6 after the vulcanization reaction.

  18. In situ structural changes of amorphous diopside (CaMgSi2O6) up to 20 GPa: A Raman and O K-edge X-ray Raman spectroscopic study

    NASA Astrophysics Data System (ADS)

    Moulton, Benjamin J. A.; Henderson, Grant S.; Fukui, Hiroshi; Hiraoka, Nozomu; de Ligny, Dominique; Sonneville, Camille; Kanzaki, Masami

    2016-04-01

    Diopside, CaMgSi2O6, is an important analogue for depolymerized silicate melts. We have used the complimentary spectroscopies, X-ray Raman Scattering (XRS), X-ray absorption near edge structure (XANES) and Raman, to investigate diopside glass in situ to 20 GPa. We observe a stark change in behavior of CaMgSi2O6 near 4 GPa that corresponds to a major change in the rate of inter-tetrahedral angle (∠Si-O-Si) closure. Below 4 GPa, the ∠Si-O-Si closes rapidly at 2-3°/GPa whereas above 4 GPa it decreases by ∼1°/GPa. A distinct shift to higher wavenumbers of the 870 and 905 cm-1 Raman bands are observed at 1.3 GPa suggesting that Q0 species have been completely converted to Q1 or higher Qn species. XRS measurements at the O K-edge suggest that [5]Si is formed by 3 GPa. This formation is accompanied by a rapid decrease in the ∠Si-O-Si and a decrease in Q0 species. A linear increase in the geometric mean of the high frequency envelope, the χb value, from 999 to 1018 cm-1 suggests that the conversion of NBO to BO is continuous up to 14 GPa. Above 14 GPa, the Raman spectra show an obvious negative shift in both, the high frequency peak maximum, and the χb position. Simultaneously, the low frequency envelope looses its asymmetry at 14 GPa. This may be explained by either a loss of a vibrational mode in the range 1000-1200 cm-1 and/or the formation of [6]Si. The structural evolution of CaMgSi2O6 correlates well with a major change in the compressibility and diffusivity around 5 GPa.

  19. Asymptotically-Equal-To 10 eV ionization shift in Ir K{alpha}{sub 2} from a near-coincident Lu K-edge

    SciTech Connect

    Pereira, N. R.; Weber, B. V.; Phipps, D.; Schumer, J. W.; Seely, J. F.; Carroll, J. J.; VanHoy, J. R.; Slabkowska, K.; Polasik, M.

    2012-10-15

    Close to an x-ray filter's K-edge the transmission depends strongly on the photon energy. For a few atom pairs, the K-edge of one is only a few tens of eV higher than a K-line energy of another, so that a small change in the line's energy becomes a measurable change in intensity behind such a matching filter. Lutetium's K-edge is Asymptotically-Equal-To 27 eV above iridium's K{alpha}{sub 2} line, Asymptotically-Equal-To 63.287 keV for cold Ir. A Lu filter reduces this line's intensity by Asymptotically-Equal-To 10 % when it is emitted by a plasma, indicating an ionization shift {Delta}E Asymptotically-Equal-To 10{+-}1 eV.

  20. Absolute determination of charge-coupled device quantum detection efficiency using Si K-edge x-ray absorption fine structure

    SciTech Connect

    Dunn, J; Steel, A B

    2012-05-06

    We report a method to determine the quantum detection efficiency and the absorbing layers on a front-illuminated charge-coupled device (CCD). The CCD under study, as part of a crystal spectrometer, measures intense continuum x-ray emission from a picosecond laser-produced plasma and spectrally resolves the Si K-edge x-ray absorption fine structure features due to the electrode gate structure of the device. The CCD response across the Si K-edge shows a large discontinuity as well as a number of oscillations that are identified individually and uniquely from Si, SiO{sub 2}, and Si{sub 3}N{sub 4} layers. From the spectral analysis of the structure and K-edge discontinuity, the active layer thickness and the different absorbing layers thickness can be determined precisely. A precise CCD detection model from 0.2-10 keV can be deduced from this highly sensitive technique.

  1. Vanadium speciation by XANES spectroscopy: a three-dimensional approach.

    PubMed

    Levina, Aviva; McLeod, Andrew I; Lay, Peter A

    2014-09-15

    A library of X-ray absorption near-edge structure (XANES) spectroscopic data for V(V), V(IV) and V(III) complexes with a broad range of biologically relevant ligand has been used to demonstrate that three-dimensional plots of key XANES parameters (pre-edge and edge energies; pre-edge and white line intensities) can be used for the prediction of V oxidation states and coordination numbers in biological or environmental matrices. The reliability of the technique has been demonstrated by re-analysis of the published XANES data for a V(V)-dependent bromoperoxidase. PMID:25088743

  2. Characterization of Darai Limestone Composition and Porosity Using Data-Constrained Modeling and Comparison with Xenon K-Edge Subtraction Imaging.

    PubMed

    Mayo, Sheridan C; Yang, Sam Y S; Pervukhina, Marina; Clennell, Michael B; Esteban, Lionel; Irvine, Sarah C; Siu, Karen K; Maksimenko, Anton S; Tulloh, Andrew M

    2015-08-01

    Data-constrained modeling is a method that enables three-dimensional distribution of mineral phases and porosity in a sample to be modeled based on micro-computed tomography scans acquired at different X-ray energies. Here we describe an alternative method for measuring porosity, synchrotron K-edge subtraction using xenon gas as a contrast agent. Results from both methods applied to the same Darai limestone sample are compared. Reasonable agreement between the two methods and with other porosity measurements is obtained. The possibility of a combination of data-constrained modeling and K-edge subtraction methods for more accurate sample characterization is discussed. PMID:26021343

  3. The Effect of Synthetic Method and Annealing Temperature on Metal Site Preference in Al1-xGaxFeO3

    SciTech Connect

    Walker, James D.S.; Grosvenor, Andrew P.

    2013-08-15

    Magnetoelectric materials couple both magnetic and electronic properties, making them attractive for use in multifunctional devices. The magnetoelectric AFeO3 compounds (Pna21; A = Al, Ga) have received attention as the properties of the system depend on composition as well as the synthetic method used. Al1–xGaxFeO3 (0 ≤ x ≤ 1) was synthesized by the sol–gel and coprecipitation methods and studied by X-ray absorption near-edge spectroscopy (XANES). Al L2,3⁻, Ga K-, and Fe K-edge XANES spectra were collected to examine how the average metal coordination number (CN) changes with the synthetic method. Al and Fe were found to prefer octahedral sites, while Ga prefers the tetrahedral site. It was found that composition played a larger role in determining site occupancies than synthetic method. Samples made by the sol–gel or ceramic methods (reported previously; Walker, J. D. S.; Grosvenor, A. P. J. Solid State Chem. 2013, 197, 147–153) showed smaller spectral changes than samples made via the coprecipitation method. This is attributed to greater ion mobility in samples synthesized via coprecipitation as the reactants do not have a long-range polymeric or oxide network during synthesis like samples synthesized via the sol–gel or ceramic method. Increasing annealing temperature increases the average coordination number of Al, and to a lesser extent Ga, while the average coordination number of Fe decreases. This study indicates that greater disorder is observed when the Al1–xGaxFeO3 compounds have high Al content, and when annealed at higher temperatures.

  4. Interlayer Potassium And Its Neighboring Atoms in Micas: Crystal-Chemical Modeling And Xanes Spectroscopy

    SciTech Connect

    Brigatti, M.F.; Malferrari, D.; Poppi, M.; Mottana, A.; Cibin, G.; Marcelli, A.; Cinque, G.

    2009-05-12

    A detailed description of the interlayer site in trioctahedral true micas is presented based on a statistical appraisal of crystal-chemical, structural, and spectroscopic data determined on two sets of trioctahedral micas extensively studied by both X-ray diffraction refinement on single crystals (SC-XRD) and X-ray absorption fine spectroscopy (XAFS) at the potassium K-edge. Spectroscopy was carried out on both random powders and oriented cleavage flakes, the latter setting taking advantage of the polarized character of synchrotron radiation. Such an approach (AXANES) is shown to be complementary to crystal-chemical investigation based on SC-XRD refinement. However, the results are not definitive as they focus on few samples having extreme features only (e.g., end-members, unusual compositions, and samples with extreme and well-identified substitution mechanisms). The experimental absorption K-edge (XANES) for potassium was decomposed by calculation and extrapolated into a full in-plane absorption component ({sigma}{parallel}) and a full out-of-plane absorption component ({sigma}{perpendicular}). These two patterns reflect different structural features: {sigma}{parallel}represents the arrangement of the atoms located in the mica interlayer space and facing tetrahedral sheets; {sigma}{perpendicular} is associated with multiple-scattering interactions entering deep into the mica structure, thus also reflecting interactions with the heavy atoms (essentially Fe) located in the octahedral sheet. The out-of-plane patterns also provide insights into the electronic properties of the octahedral cations, such as their oxidation states (e.g., Fe{sup 2+} and Fe{sup 3+}) and their ordering (e.g., trans- vs. cis-setting). It is also possible to distinguish between F- and OH-rich micas due to peculiar absorption features originating from the F vs. OH occupancy of the O4 octahedral site. Thus, combining crystal-chemical, structural, and spectroscopic information is shown to be a

  5. X-ray spectra from a cerium target and their application to cone beam K-edge angiography

    NASA Astrophysics Data System (ADS)

    Sato, Eiichi; Yamadera, Akira; Tanaka, Etsuro; Mori, Hidezo; Kawai, Toshiaki; Ito, Fumihito; Inoue, Takashi; Ogawa, Akira; Sato, Shigehiro; Takayama, Kazuyoshi; Onagawa, Jun; Ido, Hideaki

    2005-09-01

    The cerium-target x-ray tube is useful for performing cone beam K-edge angiography, because K-series characteristic x-rays from the cerium target are absorbed effectively by iodine-based contrast media. The x-ray generator consists of a main controller and a unit with a high-voltage circuit and a fixed anode x-ray tube. The tube is a glass-enclosed diode with a cerium target and a 0.5-mm-thick beryllium window. The maximum tube voltage and current are 65 kV and 0.4 mA, respectively, and the focal-spot sizes are 1.3×0.9 mm. Cerium K-series characteristic x-rays are left, using a 3.0-mm-thick aluminum filter, and the x-ray intensity is 19.9 μGy/s at 1.0 m from the source with a tube voltage of 60 kV and a current of 0.40 mA. Angiography is performed with a computed radiography system using iodine-based microspheres 15 μm in diameter. In angiography of nonliving animals, we observe fine blood vessels of approximately 100 μm with high contrasts.

  6. High-speed K-edge angiography achieved with tantalum K-series characteristic x rays (Honorable Mention Poster Award)

    NASA Astrophysics Data System (ADS)

    Sato, Eiichi; Tanaka, Etsuro; Mori, Hidezo; Kawai, Toshiaki; Inoue, Takashi; Ogawa, Akira; Sato, Shigehiro; Takayama, Kazuyoshi; Ido, Hideaki

    2005-04-01

    The tantalum plasma flash x-ray generator is useful in order to perform high-speed K-edge angiography using cone beams because Kα rays from the tantalum target are absorbed effectively by gadolinium-based contrast media. In the flash x-ray generator, a 150 nF condenser is charged up to 80 kV by a power supply, and flash x rays are produced by the discharging. The x-ray tube is a demountable diode, and the turbomolecular pump evacuates air from the tube with a pressure of approximately 1 mPa. Since the electric circuit of the high-voltage pulse generator employs a cable transmission line, the high-voltage pulse generator produces twice the potential of the condenser charging voltage. When the charging voltage was increased, the K-series characteristic x-ray intensities of tantalum increased. The K lines were clean and intense, and hardly any bremsstrahlung rays were detected. The x-ray pulse widths were approximately 100 ns, and the time-integrated x-ray intensity had a value of approximately 300 μGy at 1.0 m from the x-ray source with a charging voltage of 80 kV. Angiography was performed using a film-less computed radiography (CR) system and gadolinium-based contrast media. In angiography of non-living animals, we observed fine blood vessels of approximately 100 μm with high contrasts.

  7. Energy distribution measurement of narrow-band ultrashort x-ray beams via K-edge filters subtraction

    SciTech Connect

    Cardarelli, Paolo; Di Domenico, Giovanni; Marziani, Michele; Mucollari, Irena; Pupillo, Gaia; Sisini, Francesco; Taibi, Angelo; Gambaccini, Mauro

    2012-10-01

    The characterization of novel x-ray sources includes the measurement of the photon flux and the energy distribution of the produced beam. The aim of BEATS2 experiment at the SPARC-LAB facility of the INFN National Laboratories of Frascati (Rome, Italy) is to investigate possible medical applications of an x-ray source based on Thomson relativistic back-scattering. This source is expected to produce a pulsed quasi-monochromatic x-ray beam with an instantaneous flux of 10{sup 20} ph/s in pulses 10 ps long and with an average energy of about 20 keV. A direct measurement of energy distribution of this beam is very difficult with traditional detectors because of the extremely high photon flux. In this paper, we present a method for the evaluation of the energy distribution of quasi-monochromatic x-ray beams based on beam filtration with K-edge absorbing foils in the energy range of interest (16-22 keV). The technique was tested measuring the energy distribution of an x-ray beam having a spectrum similar to the expected one (SPARC-LAB Thomson source) by using a tungsten anode x-ray tube properly filtered and powered. The energy distribution obtained has been compared with the one measured with a HPGe detector showing very good agreement.

  8. Optimum design of multi-layer K-edge filter and multi-stage detectors for triple energy bone densitometer

    NASA Astrophysics Data System (ADS)

    Mazoochi, Alireza; Rahmani, Faezeh; Abbasi Davani, Fereydoun; Ghaderi, Ruhollah

    2014-03-01

    Dual X-ray bone densitometry may cause some errors in diagnosis due to heterogeneous distribution of adipose tissue. It is necessary to develop a more accurate technique to consider the effects of fat. In this research, a triple energy X-ray method has been introduced and conceptual design of a system consisting of 160 kV X-ray tube, multi-layer K-edge filter and multi-stage detector has been presented. Design calculations have been performed using MCNP4C Monte Carlo code to select the type of filters and detectors with the best thicknesses for better distinguishing materials. The energy peaks (37 keV, 50 keV and 105 keV) can be separated optimally with a multi-layer filter composed of barium (170 μm) and gadolinium (100 μm) as the first and second layers, respectively which are coated on a 1 mm aluminum plate placed between the source and tissue. The transmitted photons have been counted by a multi-stage linear array of detectors consisting of ZnSe(Te) and CsI(Tl) with 400 μm and 5 mm thicknesses, respectively. Monte Carlo simulations show that the triple energy X-ray technique has better accuracy than that of the standard dual energy X-ray technique.

  9. Site-Specific Studies on X-Ray Magnetic Circular Dichroism at Fe K Edge for Transition-Metal Ferrites

    NASA Astrophysics Data System (ADS)

    Matsumoto, Kenji; Saito, Fumikazu; Toyoda, Takeshi; Ohkubo, Koichi; Yamawaki, Koji; Mori, Takeharu; Hirano, Keiichi; Tanaka, Masahiko; Sasaki, Satoshi

    2000-10-01

    Experiments on X-ray magnetic circular dichroism (XMCD) were performed with synchrotron radiation for Zn and Mn-Zn ferrites (normal-spinel structure) and Ni, Co and Cu ferrites and magnetite (inverse-spinel structure). The inverse-spinel ferrites have positive-to-negative dispersion-type XMCD signals in the pre-edge region of the Fe K edge, which originate from Fe3+ ions in the A sites. There are no such signals for normal-spinel ferrites. Two kinds of negative-to-positive dispersion-type XMCD signals were observed in 7.119-7.125 keV and 7.122-7.129 keV regions of the main edge, which are caused by a mixture of Fe3+ and Fe2+ ions of the B sites in magnetite and Fe3+ ions of the B sites in the other inverse-spinel ferrites, respectively. The B-site origin of the XMCD main-edge spectra was also confirmed by observation of X-ray resonant magnetic scattering for the 222 reflection of Ni ferrite.

  10. High-resolution molybdenum K-edge X-ray absorption spectroscopy analyzed with time-dependent density functional theory.

    PubMed

    Lima, Frederico A; Bjornsson, Ragnar; Weyhermüller, Thomas; Chandrasekaran, Perumalreddy; Glatzel, Pieter; Neese, Frank; DeBeer, Serena

    2013-12-28

    X-ray absorption spectroscopy (XAS) is a widely used experimental technique capable of selectively probing the local structure around an absorbing atomic species in molecules and materials. When applied to heavy elements, however, the quantitative interpretation can be challenging due to the intrinsic spectral broadening arising from the decrease in the core-hole lifetime. In this work we have used high-energy resolution fluorescence detected XAS (HERFD-XAS) to investigate a series of molybdenum complexes. The sharper spectral features obtained by HERFD-XAS measurements enable a clear assignment of the features present in the pre-edge region. Time-dependent density functional theory (TDDFT) has been previously shown to predict K-pre-edge XAS spectra of first row transition metal compounds with a reasonable degree of accuracy. Here we extend this approach to molybdenum K-edge HERFD-XAS and present the necessary calibration. Modern pure and hybrid functionals are utilized and relativistic effects are accounted for using either the Zeroth Order Regular Approximation (ZORA) or the second order Douglas-Kroll-Hess (DKH2) scalar relativistic approximations. We have found that both the predicted energies and intensities are in excellent agreement with experiment, independent of the functional used. The model chosen to account for relativistic effects also has little impact on the calculated spectra. This study provides an important calibration set for future applications of molybdenum HERFD-XAS to complex catalytic systems. PMID:24197060

  11. Fe and S K-edge XAS determination of iron-sulfur species present in a range of acid sulfate soils: Effects of particle size and concentration on quantitative XANES determinations

    NASA Astrophysics Data System (ADS)

    Morgan, Kate E.; Burton, Edward D.; Cook, Perran; Raven, Mark D.; Fitzpatrick, Robert W.; Bush, Richard; Sullivan, Leigh A.; Hocking, Rosalie K.

    2009-11-01

    Acid sulfate soils (ASS) are soils and soft sediments in which sulfuric acid may be produced from iron sulfides or have been produced leaving iron oxyhydroxysulfates in amounts that have a long lasting effect on soil characteristics. If soil material is exposed to rotting vegetation or other reducing material, the Fe-oxyhydroxysulfates can be bacterially reduced to sulfides including disulfides (pyrite and marcasite), and Monosulfidic Black Ooze (MBO) a poorly characterised material known to be a mixture of iron sulfides (especially mackinawite) and organic matter. The chemistry of these environments is strongly affected by Fe and S cycling processes and herein we have sought to identify key differences in environments that occur as a function of Fe and S concentration. In addition to our chemical results, we have found that the effects of particle size on self absorption in natural sediments play an important role in the spectroscopic identification of the relative proportions of different species present.

  12. O K-edge x-ray magnetic circular dichroism of atomic O adsorbed on an ultrathin Co/Cu(100) film: Comparison with molecular CO on Co/Cu(100)

    NASA Astrophysics Data System (ADS)

    Amemiya, Kenta; Yokoyama, Toshihiko; Yonamoto, Yoshiki; Matsumura, Daiju; Ohta, Toshiaki

    2001-10-01

    We observed O K-edge x-ray magnetic circular dichroism (XMCD) of atomic O adsorbed on a fcc Co thin film grown epitaxially on Cu(100). The XMCD of c(2×2)O showed a negative sign at the O1s-->2p transition. The negative sign indicates parallel alignment of the O orbital moment with the substrate magnetization. This finding is in contrast to the CO/Co/Cu(100) case where a positive XMCD was observed at the O1s-->CO2π* transition. A possible explanation for this discrepancy is proposed referring to recent theoretical prediction [Pick et al., Phys. Rev. B 59, 4195 (1999)].

  13. SU-C-207-06: In Vivo Quantification of Gold Nanoparticles Using K-Edge Imaging Via Spectrum Shaping by Gold Filter

    SciTech Connect

    Chen, H; Cormack, R; Bhagwat, M; Berbeco, R

    2015-06-15

    Purpose: Gold nanoparticles (AuNP) are multifunctional platforms ideal for drug delivery, targeted imaging and radiosensitization. We have investigated quantitative imaging of AuNPs using on board imager (OBI) cone beam computed tomography (CBCT). To this end, we also present, for the first time, a novel method for k-edge imaging of AuNP by filter-based spectral shaping. Methods: We used a digital 25 cm diameter water phantom, embedded with 3 cm spheres filled with AuNPs of different concentrations (0 mg/ml – 16 mg/ml). A poly-energetic X-ray spectrum of 140 kVp from a conventional X-ray tube is shaped by balanced K-edge filters to create an excess of photons right above the K-edge of gold at 80.7 keV. The filters consist of gold, tin, copper and aluminum foils. The phantom with appropriately assigned attenuation coefficients is forward projected onto a detector for each energy bin and then integrated. FKD reconstruction is performed on the integrated projections. Scatter, detector efficiency and noise are included. Results: We found that subtracting the results of two filter sets (Filter A:127 µm gold foil with 254 µm tin, 330 µm copper and 1 mm aluminum, and Filter B: 635 µm tin with 264 µm copper and 1 mm aluminum), provides substantial image contrast. The resulting filtered spectra match well below 80.7 keV, while maintaining sufficient X-ray quanta just above that. Voxel intensities of AuNP containing spheres increase linearly with AuNP concentration. K-edge imaging provides 18% more sensitivity than the tin filter alone, and 38% more sensitivity than the gold filter alone. Conclusion: We have shown that it is feasible to quantitatively detect AuNP distributions in a patient-sized phantom using clinical CBCT and K-edge spectral shaping.

  14. Enhanced K-edge plasma angiography achieved with tungsten Kα rays utilizing gadolinium-based contrast media

    NASA Astrophysics Data System (ADS)

    Sato, Eiichi; Hayasi, Yasuomi; Germer, Rudolf; Kimura, Koji; Tanaka, Etsuro; Mori, Hidezo; Kawai, Toshiaki; Inoue, Takashi; Ogawa, Akira; Sato, Shigehiro; Takayama, Kazuyoshi; Ido, Hideaki

    2005-08-01

    The tungsten plasma flash x-ray generator is useful in order to perform high-speed enhanced K-edge angiography using cone beams because Kα rays from the tungsten target are absorbed effectively by gadolinium-based contrast media. In the flash x-ray generator, a 150 nF condenser is charged up to 80 kV by a power supply, and flash x-rays are produced by the discharging. The x-ray tube is a demountable diode, and the turbomolecular pump evacuates air from the tube with a pressure of approximately 1 mPa. Since the electric circuit of the high-voltage pulse generator employs a cable transmission line, the high-voltage pulse generator produces twice the potential of the condenser charging voltage. At a charging voltage of 80 kV, the estimated maximum tube voltage and current were approximately 160 kV and 40 kA, respectively. When the charging voltage was increased, the characteristic x-ray intensities of tungsten Kα lines increased. Using an ytterbium oxide filter, the Kα lines were clean, and hardly any Kβ lines and bremsstrahlung rays were detected. The x-ray pulse widths were approximately 60 ns, and the time-integrated x-ray intensity had a value of approximately 50 μGy at 1.0 m from the x-ray source with a charging voltage of 80 kV. Angiography was performed using a film-less computed radiography system and gadolinium-based contrast media. In angiography of non-living animals, we observed fine blood vessels of approximately 100 μm with high contrasts.

  15. Enhanced k-edge angiography utilizing a superfluorescent x-ray generator with a gadolinium-target tube

    NASA Astrophysics Data System (ADS)

    Sato, Eiichi; Germer, Rudolf; Obara, Haruo; Tanaka, Etsuro; Mori, Hidezo; Kawai, Toshiaki; Inoue, Takashi; Ogawa, Akira; Sato, Shigehiro; Takayama, Kazuyoshi

    2007-01-01

    The gadolinium plasma flash x-ray generator is useful for performing high-speed enhanced K-edge angiography using cone beams because K-series characteristic x-rays from the gadolinium target are absorbed effectively by iodine-based contrast media. In the flash x-ray generator, a 150 nF condenser is charged up to 80 kV by a power supply, and flash x-rays are produced by the discharging. The x-ray tube is a demountable cold-cathode diode, and the turbomolecular pump evacuates air from the tube with a pressure of approximately 1 mPa. Since the electric circuit of the high-voltage pulse generator employs a cable transmission line, the high-voltage pulse generator produces twice the potential of the condenser charging voltage. At a charging voltage of 80 kV, the estimated maximum tube voltage and current are approximately 160 kV and 40 kA, respectively. When the charging voltage was increased, the K-series characteristic x-ray intensities of gadolinium increased. Bremsstrahlung x-ray intensity rate decreased with increasing the charging voltage, and clean K lines were produced with a charging voltage of 80 kV. The x-ray pulse widths were approximately 100 ns, and the time-integrated x-ray intensity had a value of approximately 500 μGy at 1.0 m from the x-ray source with a charging voltage of 80 kV. Angiography was performed using a filmless computed radiography (CR) system and iodine-based contrast media. In the angiography of nonliving animals, we observed fine blood vessels of approximately 100 μm with high contrasts.

  16. K-edge angiography utilizing a tungsten plasma X-ray generator in conjunction with gadolinium-based contrast media

    NASA Astrophysics Data System (ADS)

    Sato, Eiichi; Hayasi, Yasuomi; Tanaka, Etsuro; Mori, Hidezo; Kawai, Toshiaki; Inoue, Takashi; Ogawa, Akira; Sato, Shigehiro; Takayama, Kazuyoshi; Onagawa, Jun; Ido, Hideaki

    2006-11-01

    The tungsten plasma flash X-ray generator is useful in order to perform high-speed enhanced K-edge angiography using cone beams because K-series characteristic X-rays from the tungsten target are absorbed effectively by gadolinium-based contrast media. In the flash X-ray generator, a 150 nF condenser is charged up to 80 kV by a power supply, and flash X-rays are produced by the discharging. The X-ray tube is a demountable diode, and the turbomolecular pump evacuates air from the tube with a pressure of approximately 1 mPa. Since the electric circuit of the high-voltage pulse generator employs a cable transmission line, the high-voltage pulse generator produces twice the potential of the condenser charging voltage. At a charging voltage of 80 kV, the estimated maximum tube voltage and current were approximately 160 kV and 40 kA, respectively. When the charging voltage was increased, the characteristic X-ray intensities of tungsten K α lines increased. The K α lines were clean, and hardly any bremsstrahlung rays were detected. The X-ray pulse widths were approximately 110 ns, and the time-integrated X-ray intensity had a value of approximately 0.35 mGy at 1.0 m from the X-ray source with a charging voltage of 80 kV. Angiography was performed using a film-less computed radiography (CR) system and gadolinium-based contrast media. In angiography of non-living animals, we observed fine blood vessels of approximately 100 μm with high contrasts.

  17. Enhanced K-edge Angiography Utilizing Tantalum Plasma X-ray Generator in Conjunction with Gadolinium-Based Contrast Media

    NASA Astrophysics Data System (ADS)

    Sato, Eiichi; Hayasi, Yasuomi; Kimura, Koji; Tanaka, Etsuro; Mori, Hidezo; Kawai, Toshiaki; Inoue, Takashi; Ogawa, Akira; Sato, Shigehiro; Takayama, Kazuyoshi; Onagawa, Jun; Ido, Hideaki

    2005-12-01

    The tantalum plasma flash X-ray generator is useful for performing high-speed enhanced K-edge angiography using cone beams because K-series characteristic X-rays from the tantalum target are absorbed effectively by gadolinium-based contrast media. In the flash X-ray generator, a 150 nF condenser is charged up to 80 kV by a power supply, and flash X-rays are produced by the discharging. The X-ray tube is a demountable cold-cathode diode, and the turbomolecular pump evacuates air from the tube with a pressure of approximately 1 mPa. Since the electric circuit of the high-voltage pulse generator employs a cable transmission line, the high-voltage pulse generator produces twice the potential of the condenser charging voltage. At a charging voltage of 80 kV, the estimated maximum tube voltage and current were approximately 160 kV and 40 kA, respectively. When the charging voltage was increased, the K-series characteristic X-ray intensities of cerium increased. The K lines were clean and intense, and hardly any bremsstrahlung rays were detected. The X-ray pulse widths were approximately 100 ns, and the time-integrated X-ray intensity had a value of approximately 300 μGy at 1.0 m from the X-ray source with a charging voltage of 80 kV. Angiography was performed using a filmless computed radiography (CR) system and gadolinium-based contrast media. In the angiography of nonliving animals, we observed fine blood vessels of approximately 100 μm with high contrasts.

  18. Calibration of scalar relativistic density functional theory for the calculation of sulfur K-edge X-ray absorption spectra.

    PubMed

    Debeer George, Serena; Neese, Frank

    2010-02-15

    Sulfur K-edge X-ray absorption spectroscopy has been proven to be a powerful tool for investigating the electronic structures of sulfur-containing coordination complexes. The full information content of the spectra can be developed through a combination of experiment and time-dependent density functional theory (TD-DFT). In this work, the necessary calibration is carried out for a range of contemporary functionals (BP86, PBE, OLYP, OPBE, B3LYP, PBE0, TPSSh) in a scalar relativistic (0(th) order regular approximation, ZORA) DFT framework. It is shown that with recently developed segmented all-electron scalar relativistic (SARC) basis sets one obtains results that are as good as with large, uncontracted basis sets. The errors in the calibrated transition energies are on the order of 0.1 eV. The error in calibrated intensities is slightly larger, but the calculations are still in excellent agreement with experiment. The behavior of full TD-DFT linear response versus the Tamm-Dancoff approximation has been evaluated with the result that two methods are almost indistinguishable. The inclusion of relativistic effects barely changes the results for first row transition metal complexes, however, the contributions become visible for second-row transition metals and reach a maximum (of an approximately 10% change in the calibration parameters) for third row transition metal species. The protocol developed here is approximately 10 times more efficient than the previously employed protocol, which was based on large, uncontracted basis sets. The calibration strategy followed here may be readily extended to other edges. PMID:20092349

  19. Development of a K-edge micro CT for the study of tumor angiogenesis in small animals

    NASA Astrophysics Data System (ADS)

    Baldazzi, G.; Bollini, D.; Gambaccini, M.; Golfieri, R.; Lollini, P. L.; Margotti, A.; Masetti, S.; Nicoletti, G.; Pancaldi, G.; Roma, L.; Rossi, P. L.; Zuffa, M.

    2006-03-01

    A new micro scanner CT for small animals - based on a couple of parallel quasi-monochromatic X-ray beams with different energies selectable - is under development. The aim of the study is the in vivo imaging of the tumor neo-angiogenesis pattern in an earlier diagnostic phase and the analysis of cancer growth and metastasis development in different tumor types on mice. As previously demonstrated1, the imaging system based on dual energy quasi- monochromatic X-ray beams provides higher sensitivity in detecting low concentrations of iodine contrast medium if compared to traditional polychromatic X-ray equipment. The K-edge dual energy radiology is a realistic candidate to recognize tumor neo- angiogenesis process in a very earlier stage, in which conventional systems are very poor in sensitivity. Moreover, the capability to select the energy of quasi-monochromatic beams enables the use of the Multi-Energy Quasi-Monochromatic technique. Tuning properly the energies allows maximizing the difference between linear absorption coefficients of healthy and pathological tissues increasing the contrast of pathologies. In order to optimize the contrast with this technique, one should know the X-ray energy regions where the absorption of healthy and pathological tissues eventually differs and that for each type of tumor under study. For this reason, the systematic X-ray characterization of many types of healthy and neoplastic human and mice tissues is in progress. The goal of this work is to obtain a catalog of liner attenuation coefficients of a variety of pathological tissues for respect to the healthy ones, finding any energy windows of radiological differentiation. In this paper, the theoretical methods are presented with development works and preliminary results.

  20. Inhibition of ammonia poisoning by addition of platinum to Ru/α-Al2 O3 for preferential CO oxidation in fuel cells.

    PubMed

    Sato, Katsutoshi; Yagi, Sho; Zaitsu, Shuhei; Kitayama, Godai; Kayada, Yuto; Teramura, Kentaro; Takita, Yusaku; Nagaoka, Katsutoshi

    2014-12-01

    In polymer electrolyte fuel cell (PEFC) systems, small amounts of ammonia (NH3 ) present in the reformate gas deactivate the supported ruthenium catalysts used for preferential oxidation (PROX) of carbon monoxide (CO). In this study, we investigated how the addition of a small amount of platinum to a Ru/α-Al2 O3 catalyst (Pt/Ru=1:9 w/w) affected the catalyst's PROX activity in both the absence and the presence of NH3 (130 ppm) under conditions mimicking the reformate conditions during steam reforming of natural gas. The activity of undoped Ru/α-Al2 O3 decreased sharply upon addition of NH3 , whereas Pt/Ru/α-Al2 O3 exhibited excellent PROX activity even in the presence of NH3 . Ruthenium K-edge X-ray absorption near-edge structure (XANES) spectra indicated that in the presence of NH3 , some of the ruthenium in the undoped catalyst was oxidized in the presence of NH3 , whereas ruthenium oxidation was not observed with Pt/Ru/α-Al2 O3 . These results suggest that ruthenium oxidation is retarded by the platinum, so that the catalyst shows high activity even in the presence of NH3 . PMID:25351412

  1. 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. PMID:23934494

  2. 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.

  3. Correlated NanoSIMS, TEM, and XANES Studies of Presolar Grains

    NASA Astrophysics Data System (ADS)

    Groopman, Evan Edward

    surrounded by turbostratic graphite within a low-density SN graphite grain. Nanocrystalline cores consisting of randomly-oriented 2-4 nm sheets of graphene and surrounded by concentric shells of graphite have been observed in high-density presolar graphite grains from Asymptotic Giant Branch stars, whose grains are typically microstructurally distinct from SN graphite grains. These vastly different stellar environments briefly formed similar nanocrystalline structures before diverging in the structure of their mantling graphite to be typical of AGB and SN grains. While relatively few correlated NanoSIMS and TEM studies have been performed previously, which this research thesis aims to expand, my collaborators and I also endeavored to add a third correlated technique, STXM/XANES, which had previously not been applied to presolar grains. XANES allows for the investigation of molecular bonds, which we used to help infer physical and chemical properties of stellar ejecta. I investigated the C K-edge and Ti L-edge of molecular bonds in both presolar graphite grains and their TiC subgrains. The presolar graphite grains, while overwhelmingly composed of aromatic C molecules, host a wide variety of minor organic molecules. Considering the large isotopic anomalies in the grains, these minor components are not likely due to contamination. I also investigated the valence state of Ti in Ti-rich subgrains and plan to work towards illuminating the effect that V in solid solution has upon the TiC bonds.

  4. 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.

  5. In situ total-electron-yield sulfur K-edge XAFS measurements during exposure of copper to an SO 2-containing humid atmosphere

    NASA Astrophysics Data System (ADS)

    Song, Inho; Rickett, Brett; Janavicius, Paul; Payer, Joe H.; Antonio, Mark R.

    1995-02-01

    A total-electron-yield (TEY) detector was designed and constructed for in situ X-ray absorption fine structure (XAFS) measurements of the sulfur-containing species formed during exposure of copper to a humid atmosphere containing SO 2. Using the detector, gas phase XAFS spectra were also collected for both dry and humid SO 2 atmospheres. This work presents the experimental technique and examples of the sulfur K-edge spectra collected during the study.

  6. Dynamical K Edge and Line Variations in the X-ray Spectrum of the Ultra-compact Binary 4U 0614+091

    NASA Astrophysics Data System (ADS)

    Schulz, N. S.; Nowak, M. A.; Chakrabarty, D.; Canizares, C. R.

    2010-12-01

    We observed the ultra-compact binary candidate 4U 0614+091 for a total of 200 ks with the high-energy transmission gratings on board the Chandra X-ray Observatory. The source is found at various intensity levels with spectral variations present. X-ray luminosities vary between 2.0 × 1036 erg s-1 and 3.5 × 1036 erg s-1. Continuum variations are present at all times and spectra can be fit well with a power-law component, a high kT blackbody component, and a broad line component near oxygen. The spectra require adjustments to the Ne K edge and in some occasions also to the Mg K edge. Once further resolved, the Ne K edge region appears variable in terms of optical depths and morphology. The edge vicinity reveals an average velocity smear of ~3500 km s-1 implying a characteristic radius of the order of <109 cm consistent with an ultra-compact binary nature. The variability proves that the excess is intrinsic to the source. The data seem to indicate excess column densities of up to several 1018 cm-2. However, there are some serious problems with an Ne I interpretation in ultra-compact disks and we need to consider alternative interpretations, which include a variable O VIII ionization edge, as likely candidates. We test such possibilities with existing observations. The prominent soft emission line complex near the O VIII Lyα position appears extremely broad and relativistic effects from near the innermost disk have to be included. Gravitationally broadened line fits also provide nearly edge-on angles of inclination consistent with the observed high dynamics near the Ne K edge. The emissions appear consistent with an ionized disk with ionization parameters of the order of 104 at radii of a few 107 cm. The line wavelengths with respect to O VIII Lyα are found variably blueshifted indicating more complex inner disk dynamics.

  7. 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.

  8. Vibrationally resolved NEXAFS at C and N K-edges of pyridine, 2-fluoropyridine and 2,6-difluoropyridine: A combined experimental and theoretical assessment.

    PubMed

    Baiardi, Alberto; Mendolicchio, Marco; Barone, Vincenzo; Fronzoni, Giovanna; Cardenas Jimenez, Gustavo Adolfo; Stener, Mauro; Grazioli, Cesare; de Simone, Monica; Coreno, Marcello

    2015-11-28

    In the present work, the near edge X-ray absorption spectroscopy (NEXAFS) spectra at both C and N K-edges of pyridine, 2-fluoropyridine, and 2,6-difluoropyridine have been studied both experimentally and theoretically. From an electronic point of view, both transition potential density functional theory and time-dependent density functional theory approaches lead to reliable results provided that suitable basis sets and density functionals are employed. In this connection, the global hybrid B3LYP functional in conjunction with the EPR-III basis set appears particularly suitable after constant scaling of the band positions. For the N K-edge, vertical energies obtained at these levels and broadened by symmetric Gaussian distributions provide spectra in reasonable agreement with the experiment. Vibronic contributions further modulate the band-shapes leading to a better agreement with the experimental results, but are not strictly necessary for semi-quantitative investigations. On the other hand, vibronic contributions are responsible for strong intensity redistribution in the NEXAFS C K-edge spectra, and their inclusion is thus mandatory for a proper description of experiments. In this connection, the simple vertical gradient model is particularly appealing in view of its sufficient reliability and low computational cost. For more quantitative results, the more refined vertical Hessian approach can be employed, and its effectiveness has been improved thanks to a new least-squares fitting approach. PMID:26627945

  9. Quasi in situ Ni K-edge EXAFS investigation of the spent NiMo catalyst from ultra-deep hydrodesulfurization of gas oil in a commercial plant.

    PubMed

    Hamabe, Yusuke; Jung, Sungbong; Suzuki, Hikotaro; Koizumi, Naoto; Yamada, Muneyoshi

    2010-07-01

    Ni species on the spent NiMo catalyst from ultra-deep hydrodesulfurization of gas oil in a commercial plant were studied by Ni K-edge EXAFS and TEM measurement without contact of the catalysts with air. The Ni-Mo coordination shell related to the Ni-Mo-S phase was observed in the spent catalyst by quasi in situ Ni K-edge EXAFS measurement with a newly constructed high-pressure chamber. The coordination number of this shell was almost identical to that obtained by in situ Ni K-edge EXAFS measurement of the fresh catalyst sulfided at 1.1 MPa. On the other hand, large agglomerates of Ni(3)S(2) were observed only in the spent catalyst by quasi in situ TEM/EDX measurement. MoS(2)-like slabs were sintered slightly on the spent catalyst, where they were destacked to form monolayer slabs. These results suggest that the Ni-Mo-S phase is preserved on the spent catalyst and Ni(3)S(2) agglomerates are formed by sintering of Ni(3)S(2) species originally present on the fresh catalyst. PMID:20567086

  10. In situ removal of carbon contamination from a chromium-coated mirror: ideal optics to suppress higher-order harmonics in the carbon K-edge region

    PubMed Central

    Toyoshima, Akio; Kikuchi, Takashi; Tanaka, Hirokazu; Mase, Kazuhiko; Amemiya, Kenta

    2015-01-01

    Carbon-free chromium-coated optics are ideal in the carbon K-edge region (280–330 eV) because the reflectivity of first-order light is larger than that of gold-coated optics while the second-order harmonics (560–660 eV) are significantly suppressed by chromium L-edge and oxygen K-edge absorption. Here, chromium-, gold- and nickel-coated mirrors have been adopted in the vacuum ultraviolet and soft X-ray branch beamline BL-13B at the Photon Factory in Tsukuba, Japan. Carbon contamination on the chromium-coated mirror was almost completely removed by exposure to oxygen at a pressure of 8 × 10−2 Pa for 1 h under irradiation of non-monochromated synchrotron radiation. The pressure in the chamber recovered to the order of 10−7 Pa within a few hours. The reflectivity of the chromium-coated mirror of the second-order harmonics in the carbon K-edge region (560–660 eV) was found to be a factor of 0.1–0.48 smaller than that of the gold-coated mirror. PMID:26524299

  11. Vibrationally resolved NEXAFS at C and N K-edges of pyridine, 2-fluoropyridine and 2,6-difluoropyridine: A combined experimental and theoretical assessment

    NASA Astrophysics Data System (ADS)

    Baiardi, Alberto; Mendolicchio, Marco; Barone, Vincenzo; Fronzoni, Giovanna; Cardenas Jimenez, Gustavo Adolfo; Stener, Mauro; Grazioli, Cesare; de Simone, Monica; Coreno, Marcello

    2015-11-01

    In the present work, the near edge X-ray absorption spectroscopy (NEXAFS) spectra at both C and N K-edges of pyridine, 2-fluoropyridine, and 2,6-difluoropyridine have been studied both experimentally and theoretically. From an electronic point of view, both transition potential density functional theory and time-dependent density functional theory approaches lead to reliable results provided that suitable basis sets and density functionals are employed. In this connection, the global hybrid B3LYP functional in conjunction with the EPR-III basis set appears particularly suitable after constant scaling of the band positions. For the N K-edge, vertical energies obtained at these levels and broadened by symmetric Gaussian distributions provide spectra in reasonable agreement with the experiment. Vibronic contributions further modulate the band-shapes leading to a better agreement with the experimental results, but are not strictly necessary for semi-quantitative investigations. On the other hand, vibronic contributions are responsible for strong intensity redistribution in the NEXAFS C K-edge spectra, and their inclusion is thus mandatory for a proper description of experiments. In this connection, the simple vertical gradient model is particularly appealing in view of its sufficient reliability and low computational cost. For more quantitative results, the more refined vertical Hessian approach can be employed, and its effectiveness has been improved thanks to a new least-squares fitting approach.

  12. Vibrationally resolved NEXAFS at C and N K-edges of pyridine, 2-fluoropyridine and 2,6-difluoropyridine: A combined experimental and theoretical assessment

    SciTech Connect

    Baiardi, Alberto; Mendolicchio, Marco; Barone, Vincenzo; Fronzoni, Giovanna; Cardenas Jimenez, Gustavo Adolfo; Stener, Mauro; Grazioli, Cesare; Simone, Monica de; Coreno, Marcello

    2015-11-28

    In the present work, the near edge X-ray absorption spectroscopy (NEXAFS) spectra at both C and N K-edges of pyridine, 2-fluoropyridine, and 2,6-difluoropyridine have been studied both experimentally and theoretically. From an electronic point of view, both transition potential density functional theory and time-dependent density functional theory approaches lead to reliable results provided that suitable basis sets and density functionals are employed. In this connection, the global hybrid B3LYP functional in conjunction with the EPR-III basis set appears particularly suitable after constant scaling of the band positions. For the N K-edge, vertical energies obtained at these levels and broadened by symmetric Gaussian distributions provide spectra in reasonable agreement with the experiment. Vibronic contributions further modulate the band-shapes leading to a better agreement with the experimental results, but are not strictly necessary for semi-quantitative investigations. On the other hand, vibronic contributions are responsible for strong intensity redistribution in the NEXAFS C K-edge spectra, and their inclusion is thus mandatory for a proper description of experiments. In this connection, the simple vertical gradient model is particularly appealing in view of its sufficient reliability and low computational cost. For more quantitative results, the more refined vertical Hessian approach can be employed, and its effectiveness has been improved thanks to a new least-squares fitting approach.

  13. Valence determination of rare earth elements in lanthanide silicates by L 3-XANES spectroscopy

    NASA Astrophysics Data System (ADS)

    Kravtsova, Antonina N.; Guda, Alexander A.; Goettlicher, Joerg; Soldatov, Alexander V.; Taroev, Vladimir K.; Kashaev, Anvar A.; Suvorova, Lyudmila F.; Tauson, Vladimir L.

    2016-05-01

    Lanthanide silicates have been hydrothermally synthesized using Cu and Ni containers. Chemical formulae of the synthesized compounds correspond to K3Eu[Si6O15] 2H2O, HK6Eu[Si10O25], K7Sm3[Si12O32], K2Sm[AlSi4O12] 0.375H2O, K4Yb2[Si8O21], K4Ce2[Al2Si8O24]. The oxidation state of lanthanides (Eu, Ce, Tb, Sm, Yb) in these silicates has been determined using XANES spectroscopy at the Eu, Ce, Tb, Sm, Yb, L 3- edges. The experimental XANES spectra were recorded using the synchrotron radiation source ANKA (Karlsruhe Institute of Technology) and the X-ray laboratory spectrometer Rigaku R- XAS. By comparing the absorption edge energies and white line intensities of the silicates with the ones of reference spectra the oxidation state of lanthanides Eu, Ce, Tb, Sm, Yb has been found to be equal to +3 in all investigated silicates except of the Ce-containing silicate from the run in Cu container where the cerium oxidation state ranges from +3 (Ce in silicate apatite and in a KCe silicate with Si12O32 layers) to +4 (starting CeO2 or oxidized Ce2O3).

  14. 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...

  15. XANES studies of chromate replacements in oxide films on aluminum

    SciTech Connect

    Davenport, A.J.; Aldykiewicz, A.J. Jr.; Isaacs, H.S.; Kendig, M.W.; Mundy, A.M.

    1991-12-31

    The chemistry of conversion coatings on aluminum containing chromate and non-toxic chromate replacements has been investigated using XANES. Chromate conversion coatings contain 20% 6-valent chromium which is gradually lost on immersion in a corrosive environment. The most promising alternative coatings are those based on phosphotungstate. The chemistry of these and coatings containing Mo, V, and Mn are discussed.

  16. XANES studies of chromate replacements in oxide films on aluminum

    SciTech Connect

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

    1991-01-01

    The chemistry of conversion coatings on aluminum containing chromate and non-toxic chromate replacements has been investigated using XANES. Chromate conversion coatings contain 20% 6-valent chromium which is gradually lost on immersion in a corrosive environment. The most promising alternative coatings are those based on phosphotungstate. The chemistry of these and coatings containing Mo, V, and Mn are discussed.

  17. K-edge x-ray dichroism investigation of Fe1-xCoxSi: Experimental evidence for spin polarization crossover

    NASA Astrophysics Data System (ADS)

    Hearne, G. R.; Diguet, G.; Baudelet, F.; Itié, J.-P.; Manyala, N.

    2015-04-01

    Both Fe and Co K-edge x-ray magnetic circular dichroism (XMCD) have been employed as element-specific probes of the magnetic moments in the composition series of the disordered ferromagnet Fe1-xCoxSi (for x=0.2, 0.3, 0.4, 0.5). A definitive single peaked XMCD profile occurs for all compositions at both Fe and Co K-edges. The Fe 4p orbital moment, deduced from the integral of the XMCD signal, has a steep dependence on x at low doping levels and evolves to a different (weaker) dependence at x≥0.3, similar to the behavior of the magnetization in the Co composition range studied here. It is systematically higher, by at least a factor of two, than the corresponding Co orbital moment for most of the composition series. Fine structure beyond the K-edge absorption (limited range EXAFS) suggests that the local order (atomic environment) is very similar across the series, from the perspective of both the Fe and Co absorbing atom. The variation in the XMCD integral across the Co composition range has two regimes, that which occurs below x=0.3 and then evolves to different behavior at higher doping levels. This is more conspicuously present in the Fe contribution. This is rationalized as the evolution from a half-metallic ferromagnet at low Co doping to that of a strong ferromagnet at x>0.3 and as such, spin polarization crossover occurs. The Fermi level is tuned from the majority spin band for x<0.3 where a strongly polarized majority spin electron gas prevails, to a regime where minority spin carriers dominate at higher doping. The evolution of the Fe-derived spin polarized (3d) bands, indirectly probed here via the 4p states, is the primary determinant of the doping dependence of the magnetism in this alloy series.

  18. 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.

  19. Resonant inelastic x-ray scattering study at the oxygen K-edge of corner-shared Sr2CuO3 cuprate

    NASA Astrophysics Data System (ADS)

    Kumar, Umesh; Schlappa, Justine; Zhou, Kejin; Singh, Surjeet; Strocov, Vladimir; Revcolevschi, Alexandre; Rønnow, Henrik; Johnston, Steven; Schmitt, Thorsten

    We present a resonant inelastic x-ray scattering (RIXS) study at the oxygen K-edge of the spin-chain system Sr2CuO3. We investigate this system using small cluster exact diagonalization calculations for a microscopic model that considers all the orbitals of Cu and O in CuO3-unit cell. Using a canonical parameter set, we compute the XAS and RIXS spectra in comparison to the experiment. This allows us to identify the dd- and charge transfer excitations in the observed spectrum. We also infer the presence of several low energy excitations that may be related to phononic and/or magnetic excitations.

  20. Auger electron and photoabsorption spectra of glycine in the vicinity of the oxygen K-edge measured with an X-FEL

    NASA Astrophysics Data System (ADS)

    Sanchez-Gonzalez, A.; Barillot, T. R.; Squibb, R. J.; Kolorenč, P.; Agaker, M.; Averbukh, V.; Bearpark, M. J.; Bostedt, C.; Bozek, J. D.; Bruce, S.; Carron Montero, S.; Coffee, R. N.; Cooper, B.; Cryan, J. P.; Dong, M.; Eland, J. H. D.; Fang, L.; Fukuzawa, H.; Guehr, M.; Ilchen, M.; Johnsson, A. S.; Liekhus-S, C.; Marinelli, A.; Maxwell, T.; Motomura, K.; Mucke, M.; Natan, A.; Osipov, T.; Östlin, C.; Pernpointner, M.; Petrovic, V. S.; Robb, M. A.; Sathe, C.; Simpson, E. R.; Underwood, J. G.; Vacher, M.; Walke, D. J.; Wolf, T. J. A.; Zhaunerchyk, V.; Rubensson, J.-E.; Berrah, N.; Bucksbaum, P. H.; Ueda, K.; Feifel, R.; Frasinski, L. J.; Marangos, J. P.

    2015-12-01

    We report the first measurement of the near oxygen K-edge auger spectrum of the glycine molecule. Our work employed an x-ray free electron laser as the photon source operated with input photon energies tunable between 527 and 547 eV. Complete electron spectra were recorded at each photon energy in the tuning range, revealing resonant and non-resonant auger structures. Finally ab initio theoretical predictions are compared with the measured above the edge auger spectrum and an assignment of auger decay channels is performed.

  1. Ligand K-edge XAS, DFT, and TDDFT analysis of pincer linker variations in Rh(i) PNP complexes: reactivity insights from electronic structure.

    PubMed

    Lee, Kyounghoon; Wei, Haochuan; Blake, Anastasia V; Donahue, Courtney M; Keith, Jason M; Daly, Scott R

    2016-06-14

    Here we report P K-edge, Cl K-edge, and Rh L3-edge X-ray absorption spectroscopy (XAS) data for Rh[C5H3N-2,6-(XP(t)Bu2)2]Cl, where X = O ((tBu)PONOP; ) or CH2 ((tBu)PNP; ). Solid-state XAS data for and were compared to density functional theory (DFT) and time-dependent density functional theory (TDDFT) calculations to identify how changing the PNP pincer linker from O to CH2 affected electronic structure and bonding at Rh(i). Pronounced differences in XAS peak intensities and energies were observed. The P K-edge XAS data revealed a large increase in Rh 4dx(2)-y(2) and P 3p orbital-mixing (Rh-P σ*) in compared to , and pronounced transition energy variations reflected marked differences in orbital energies and compositions. By comparison, the Cl K-edge XAS data revealed only subtle differences in Rh-Cl covalency, although larger splitting between the Rh-Cl π* and σ* transitions was observed in . Analysis of the occupied MOs from DFT (HOMO, HOMO-1, HOMO-2, and HOMO-3) and comparison to the unoccupied MOs involved in XAS revealed a relatively uniform energy increase (ca. 0.3-0.5 eV) for all five 4d-derived molecular orbitals in Rh((tBu)PNP)Cl () compared to Rh((tBu)PONOP)Cl (). The energy shift was relatively invariant with respect to differences in orbital symmetry, bonding type (σ or π), and orbital mixing, which suggested that the increase could be attributed to electrostatic effects. The change in d-orbital energies are consistent with known reactivity differences of Rh((tBu)PONOP)(+) and Rh((tBu)PNP)(+) towards CO, H2, and CH2Cl2, and are explained here by considering how d-orbital energies affect covalent L → M σ bonding and M → L π backbonding. PMID:27216135

  2. 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

  3. 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.

  4. 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.

  5. Formation of an SEI on a LiMn(2)O(4) Cathode during Room Temperature Charge-Discharge Cycling Studied by Soft X-Ray Absorption Spectroscopy at the Fluorine K-edge

    SciTech Connect

    Chung, K.Y.; Yang, X.; Yoon, W.-S.; Kim, K.-B.; Cho, B.-W.

    2011-11-01

    The solid electrolyte interface (SEI) formation on the surface of LiMn{sub 2}O{sub 4} electrodes during room temperature charge-discharge cycling was studied using soft X-ray absorption spectroscopy at the Fluorine (F) K-edge. LiMn{sub 2}O{sub 4} electrodes without any binder were prepared by electrostatic spray deposition to eliminate the signal originating from the PVDF binder in the F K-edge X-ray absorption spectra. The F K-edge absorption spectra show that the SEI layer forms at a very early stage of cycling. SEI growth takes place during discharge. In addition, LiF formation is accelerated if the discharge step follows a charge step. The F K-edge absorption spectra suggest that the major component of the SEI is LiF.

  6. X-ray absorption and reflection as probes of the GaN conduction bands: Theory and experiment of the N K-edge and Ga M{sub 2,3} edges

    SciTech Connect

    Lambrecht, W.R.L.; Rashkeev, S.N.; Segall, B.; Lawniczak-Jablonska, K.; Suski, T.; Gullikson, E.M.; Underwood, J.H.; Perera, R.C.C.; Rife, J.C.

    1997-12-31

    X-ray absorption and glancing angle reflectivity measurements in the energy range of the Nitrogen K-edge and Gallium M{sub 2,3} edges are reported. Linear muffin-tin orbital band-structure and spectral function calculations are used to interpret the data. Polarization effects are evidenced for the N-K-edge spectra by comparing X-ray reflectivity in s- and p-polarized light.

  7. XANES of Chromium in Sludges Used as Soil Ameliorants

    SciTech Connect

    Naftel, S.J.; Martin, R.R.; Sham, T.K.; Hart, B.; Powell, M.A.

    2010-12-01

    Samples of sewage sludges proposed for use as soil ameliorants in an Indo-Canadian project were tested for chromium content. Standard aqua regia extractions found one sludge to have excessive amounts of Cr. X-ray absorption near-edge structure (XANES) spectroscopy, however, indicated that the Cr was present in the relatively benign Cr(III) oxidation state in all the sludge samples.

  8. Local disorder investigation in NiS(2-x)Se(x) using Raman and Ni K-edge x-ray absorption spectroscopies.

    PubMed

    Marini, C; Joseph, B; Caramazza, S; Capitani, F; Bendele, M; Mitrano, M; Chermisi, D; Mangialardo, S; Pal, B; Goyal, M; Iadecola, A; Mathon, O; Pascarelli, S; Sarma, D D; Postorino, P

    2014-11-12

    We report on Raman and Ni K-edge x-ray absorption investigations of a NiS(2-x)Se(x) (with x = 0.00, 0.50/0.55, 0.60, and 1.20) pyrite family. The Ni K-edge absorption edge shows a systematic shift going from an insulating phase (x = 0.00 and 0.50) to a metallic phase (x = 0.60 and 1.20). The near-edge absorption features show a clear evolution with Se doping. The extended x-ray absorption fine structure data reveal the evolution of the local structure with Se doping which mainly governs the local disorder. We also describe the decomposition of the NiS(2-x)Se(x) Raman spectra and investigate the weights of various phonon modes using Gaussian and Lorentzian profiles. The effectiveness of the fitting models in describing the data is evaluated by means of Bayes factor estimation. The Raman analysis clearly demonstrates the disorder effects due to Se alloying in describing the phonon spectra of NiS(2-x)Se(x) pyrites. PMID:25320052

  9. Local disorder investigation in NiS2-xSex using Raman and Ni K-edge x-ray absorption spectroscopies

    NASA Astrophysics Data System (ADS)

    Marini, C.; Joseph, B.; Caramazza, S.; Capitani, F.; Bendele, M.; Mitrano, M.; Chermisi, D.; Mangialardo, S.; Pal, B.; Goyal, M.; Iadecola, A.; Mathon, O.; Pascarelli, S.; Sarma, D. D.; Postorino, P.

    2014-11-01

    We report on Raman and Ni K-edge x-ray absorption investigations of a NiS2-xSex (with x = 0.00, 0.50/0.55, 0.60, and 1.20) pyrite family. The Ni K-edge absorption edge shows a systematic shift going from an insulating phase (x = 0.00 and 0.50) to a metallic phase (x = 0.60 and 1.20). The near-edge absorption features show a clear evolution with Se doping. The extended x-ray absorption fine structure data reveal the evolution of the local structure with Se doping which mainly governs the local disorder. We also describe the decomposition of the NiS2-xSex Raman spectra and investigate the weights of various phonon modes using Gaussian and Lorentzian profiles. The effectiveness of the fitting models in describing the data is evaluated by means of Bayes factor estimation. The Raman analysis clearly demonstrates the disorder effects due to Se alloying in describing the phonon spectra of NiS2-xSex pyrites.

  10. Effect of x-ray energy dispersion in digital subtraction imaging at the iodine K-edge--A Monte Carlo study

    SciTech Connect

    Prino, F.; Ceballos, C.; Cabal, A.; Sarnelli, A.; Gambaccini, M.; Ramello, L.

    2008-01-15

    The effect of the energy dispersion of a quasi-monochromatic x-ray beam on the performance of a dual-energy x-ray imaging system is studied by means of Monte Carlo simulations using MCNPX (Monte Carlo N-Particle eXtended) version 2.6.0. In particular, the case of subtraction imaging at the iodine K-edge, suitable for angiographic imaging application, is investigated. The average energies of the two beams bracketing the iodine K-edge are set to the values of 31.2 and 35.6 keV corresponding to the ones obtained with a compact source based on a conventional x-ray tube and a mosaic crystal monochromator. The energy dispersion of the two beams is varied between 0 and 10 keV of full width at half-maximum (FWHM). The signal and signal-to-noise ratio produced in the simulated images by iodine-filled cavities (simulating patient vessels) drilled in a PMMA phantom are studied as a function of the x-ray energy dispersion. The obtained results show that, for the considered energy separation of 4.4 keV, no dramatic deterioration of the image quality is observed with increasing x-ray energy dispersion up to a FWHM of about 2.35 keV. The case of different beam energies is also investigated by means of fast simulations of the phantom absorption.

  11. Evidence for 5d-σ and 5d-π covalency in lanthanide sesquioxides from oxygen K-edge X-ray absorption spectroscopy.

    PubMed

    Altman, Alison B; Pacold, Joseph I; Wang, Jian; Lukens, Wayne W; Minasian, Stefan G

    2016-06-14

    The electronic structure in the complete series of stable lanthanide sesquioxides, Ln2O3 (Ln = La to Lu, except radioactive Pm), has been evaluated using oxygen K-edge X-ray absorption spectroscopy (XAS) with a scanning transmission X-ray microscope (STXM). The experimental results agree with recent synthetic, spectroscopic and theoretical investigations that provided evidence for 5d orbital involvement in lanthanide bonding, while confirming the traditional viewpoint that there is little Ln 4f and O 2p orbital mixing. However, the results also showed that changes in the energy and occupancy of the 4f orbitals can impact Ln 5d and O 2p mixing, leading to several different bonding modes for seemingly identical Ln2O3 structures. On moving from left to right in the periodic table, abrupt changes were observed for the energy and intensity of transitions associated with Ln 5d and O 2p antibonding states. These changes in peak intensity, which were directly related to the amounts of O 2p and Ln 5d mixing, were closely correlated to the well-established trends in the chemical accessibility of the 4f orbitals towards oxidation or reduction. The unique insight provided by the O K-edge XAS is discussed in the context of several recent theoretical and physical studies on trivalent lanthanide compounds. PMID:26979662

  12. X-ray Absorption Spectroscopy at the Sulfur K-Edge: A New Tool to Investigate the Biochemical Mechanisms of Neurodegeneration

    PubMed Central

    2012-01-01

    Sulfur containing molecules such as thiols, disulfides, sulfoxides, sulfonic acids, and sulfates may contribute to neurodegenerative processes. However, previous study in this field has been limited by the lack of in situ analytical techniques. This limitation may now be largely overcome following the development of synchrotron radiation X-ray absorption spectroscopy at the sulfur K-edge, which has been validated as a novel tool to investigate and image the speciation of sulfur in situ. In this investigation, we build the foundation required for future application of this technique to study and image the speciation of sulfur in situ within brain tissue. This study has determined the effect of sample preparation and fixation methods on the speciation of sulfur in thin sections of rat brain tissue, determined the speciation of sulfur within specific brain regions (brain stem and cerebellum), and identified sulfur specific markers of peroxidative stress following metal catalyzed reactive oxygen species production. X-ray absorption spectroscopy at the sulfur K-edge is now poised for an exciting new range of applications to study thiol redox, methionine oxidation, and the role of taurine and sulfatides during neurodegeneration. PMID:22860187

  13. Quantum simulation of thermally-driven phase transition and oxygen K-edge x-ray absorption of high-pressure ice

    PubMed Central

    Kang, Dongdong; Dai, Jiayu; Sun, Huayang; Hou, Yong; Yuan, Jianmin

    2013-01-01

    The structure and phase transition of high-pressure ice are of long-standing interest and challenge, and there is still a huge gap between theoretical and experimental understanding. The quantum nature of protons such as delocalization, quantum tunneling and zero-point motion is crucial to the comprehension of the properties of high-pressure ice. Here we investigated the temperature-induced phase transition and oxygen K-edge x-ray absorption spectra of ice VII, VIII and X using ab initio path-integral molecular dynamics simulations. The tremendous difference between experiments and the previous theoretical predictions is closed for the phase diagram of ice below 300 K at pressures up to 110 GPa. Proton tunneling assists the proton-ordered ice VIII to transform into proton-disordered ice VII where only thermal activated proton-transfer cannot occur. The oxygen K edge with its shift is sensitive to the order-disorder transition, and therefore can be applied to diagnose the dynamics of ice structures. PMID:24253589

  14. FORMATION OF CHROMATE CONVERSION COATINGS ON ALUMINUM AND ITS ALLOYS: AN IN SITU XANES STUDY.

    SciTech Connect

    SASAKI,K.; ISAACS,H.S.; JAFFCOATE,C.S.; BUCHHAIT,R.; LEGAT,V.; LEE,H.; SRINIVASAMURTHI,V.

    2001-09-02

    We used in situ X-ray adsorption near-edge structure (XANES) to investigate the formation of chromate conversion coatings on pure Al, commercial Al alloys (AA 1100, AA2024, and AA7075), and a series of binary Al-Cu alloys. The method employed a new electrochemical cell that can determine the ratio of hexavalent chromium (Cr(VI)) to total chromium (Cr(total)) speciation in conversion coatings as a function of exposure time to a chromate solution. The spectra showed that the initial Cr(VI)/Cr(total) ratios are greater than later ones for pure Al and AA1100, but not for AA2024 and AA7075. Measurements with Al-Cu alloys demonstrated that the difference observed in AA2024 and AA7075 may not be due to Cu alloying. The proportion of Cr(VI) in the coatings becomes approximately constant after 180 s of exposure for all the specimens examined even though the coatings continue to grow.

  15. EXAFS and XANES investigation of (Li, Ni) codoped ZnO thin films grown by pulsed laser deposition.

    PubMed

    Mino, Lorenzo; Gianolio, Diego; Bardelli, Fabrizio; Prestipino, Carmelo; Senthil Kumar, E; Bellarmine, F; Ramanjaneyulu, M; Lamberti, Carlo; Ramachandra Rao, M S

    2013-09-25

    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 Ni(0) 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. PMID:23988792

  16. A Monte Carlo simulation study of an improved K-edge log-subtraction X-ray imaging using a photon counting CdTe detector

    NASA Astrophysics Data System (ADS)

    Lee, Youngjin; Lee, Amy Candy; Kim, Hee-Joung

    2016-09-01

    Recently, significant effort has been spent on the development of photons counting detector (PCD) based on a CdTe for applications in X-ray imaging system. The motivation of developing PCDs is higher image quality. Especially, the K-edge subtraction (KES) imaging technique using a PCD is able to improve image quality and useful for increasing the contrast resolution of a target material by utilizing contrast agent. Based on above-mentioned technique, we presented an idea for an improved K-edge log-subtraction (KELS) imaging technique. The KELS imaging technique based on the PCDs can be realized by using different subtraction energy width of the energy window. In this study, the effects of the KELS imaging technique and subtraction energy width of the energy window was investigated with respect to the contrast, standard deviation, and CNR with a Monte Carlo simulation. We simulated the PCD X-ray imaging system based on a CdTe and polymethylmethacrylate (PMMA) phantom which consists of the various iodine contrast agents. To acquired KELS images, images of the phantom using above and below the iodine contrast agent K-edge absorption energy (33.2 keV) have been acquired at different energy range. According to the results, the contrast and standard deviation were decreased, when subtraction energy width of the energy window is increased. Also, the CNR using a KELS imaging technique is higher than that of the images acquired by using whole energy range. Especially, the maximum differences of CNR between whole energy range and KELS images using a 1, 2, and 3 mm diameter iodine contrast agent were acquired 11.33, 8.73, and 8.29 times, respectively. Additionally, the optimum subtraction energy width of the energy window can be acquired at 5, 4, and 3 keV for the 1, 2, and 3 mm diameter iodine contrast agent, respectively. In conclusion, we successfully established an improved KELS imaging technique and optimized subtraction energy width of the energy window, and based on

  17. Physical properties of the interstellar medium using high-resolution Chandra spectra: O K-edge absorption

    SciTech Connect

    Gatuzz, E.; Mendoza, C.; García, J.; Kallman, T. R.; Bautista, M. A.; Gorczyca, T. W. E-mail: claudio@ivic.gob.ve E-mail: manuel.bautista@wmich.edu E-mail: timothy.r.kallman@nasa.gov

    2014-08-01

    Chandra high-resolution spectra toward eight low-mass Galactic binaries have been analyzed with a photoionization model that is capable of determining the physical state of the interstellar medium. Particular attention is given to the accuracy of the atomic data. Hydrogen column densities are derived with a broadband fit that takes into account pileup effects, and in general are in good agreement with previous results. The dominant features in the oxygen-edge region are O I and O II Kα absorption lines whose simultaneous fits lead to average values of the ionization parameter of log ξ = –2.90 and oxygen abundance of A{sub O} = 0.70. The latter is given relative to the standard by Grevesse and Sauval, but rescaling with the revision by Asplund et al. would lead to an average abundance value fairly close to solar. The low average oxygen column density (N{sub O} = 9.2 × 10{sup 17} cm{sup –2}) suggests a correlation with the low ionization parameters, the latter also being in evidence in the column density ratios N(O II)/N(O I) and N(O III)/N(O I) that are estimated to be less than 0.1. We do not find conclusive evidence for absorption by any other compound but atomic oxygen in our oxygen-edge region analysis.

  18. 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

  19. DOPING AND BOND LENGTH CONTRIBUTIONS TO Mn K-EDGE SHIFT IN La1-xSrxMnO3 AND THEIR CORRELATION WITH ELECTRICAL TRANSPORT BEHAVIOUR.

    SciTech Connect

    PANDEY,S.K.; KHALID,S.; BINDU, R.; KUMAR, A.; PIMPALE, A.V.

    2006-12-04

    The experimental Mn K-edge x-ray absorption spectra of La{sub 1-x}Sr{sub x}MnO{sub 3}, x = 0 - 0.7 are compared with the band structure calculations using spin polarized density functional theory. It is explicitly shown that there is a correspondence between the inflection point on the absorption edge and the center of gravity of the unoccupied Mn 4p-band. This correspondence has been used to separate the doping and size contributions to edge shift due to variation in number of electrons in valence band and Mn-O bond lengths, respectively when Sr is doped into LaMnO{sub 3}. Such separation is helpful to find the localization behavior of charge carriers and to understand the observed transport properties and type of charge carrier participating in the conduction process in these compounds.

  20. Element-resolved orbital polarization in (III,Mn)As ferromagnetic semiconductors from K -edge x-ray magnetic circular dichroism

    NASA Astrophysics Data System (ADS)

    Wadley, P.; Freeman, A. A.; Edmonds, K. W.; van der Laan, G.; Chauhan, J. S.; Campion, R. P.; Rushforth, A. W.; Gallagher, B. L.; Foxon, C. T.; Wilhelm, F.; Smekhova, A. G.; Rogalev, A.

    2010-06-01

    Using x-ray magnetic circular dichroism (XMCD), we determine the element-specific character and polarization of unoccupied states near the Fermi level in (Ga,Mn)As and (In,Ga,Mn)As thin films. The XMCD at the AsK absorption edge consists of a single peak located on the low-energy side of the edge, which increases with the concentration of ferromagnetic Mn moments. The XMCD at the MnK edge is more detailed and is strongly concentration dependent, which is interpreted as a signature of hole localization for low Mn doping. The results indicate a markedly different character of the polarized holes in low-doped insulating and high-doped metallic films, with a transfer of the hole orbital magnetic moment from Mn to As sites on crossing the metal-insulator transition.

  1. X-ray absorption spectroscopy by full-field X-ray microscopy of a thin graphite flake: Imaging and electronic structure via the carbon K-edge

    PubMed Central

    Hitchock, Adam P; Ke, Xiaoxing; Van Tendeloo, Gustaaf; Ewels, Chris P; Guttmann, Peter

    2012-01-01

    Summary We demonstrate that near-edge X-ray-absorption fine-structure spectra combined with full-field transmission X-ray microscopy can be used to study the electronic structure of graphite flakes consisting of a few graphene layers. The flake was produced by exfoliation using sodium cholate and then isolated by means of density-gradient ultracentrifugation. An image sequence around the carbon K-edge, analyzed by using reference spectra for the in-plane and out-of-plane regions of the sample, is used to map and spectrally characterize the flat and folded regions of the flake. Additional spectral features in both π and σ regions are observed, which may be related to the presence of topological defects. Doping by metal impurities that were present in the original exfoliated graphite is indicated by the presence of a pre-edge signal at 284.2 eV. PMID:23016137

  2. X-ray natural linear dichroism of graphitic materials across the carbon K-edge: Correction for perturbing high-order harmonics

    NASA Astrophysics Data System (ADS)

    Jansing, C.; Mertins, H. C.; Gaupp, A.; Sokolov, A.; Gilbert, M. C.; Wahab, H.; Timmers, H.

    2016-05-01

    Reflectivity measurements on graphitic materials such as graphene at energies across the carbon K-edge are frustrated by significant intensity loss due to adventitious carbon on beamline mirrors. Such intensity reduction enhances effects due to perturbing high-order harmonics in the beam. These effects distort the actual structure of the reflectance curve. In order to overcome this limitation, a correction technique has been developed and demonstrated first with measurements for highly ordered pyrolytic graphite. The same approach may be applied to other graphitic materials such as graphene and it may be used with other synchrotron beamlines. The fraction of high-order harmonics was determined by passing the incident beam through a 87 nm thin silicon nitride absorber that can be well modeled. Using the corrected measurements the x-ray natural linear dichroism of the sample has been determined.

  3. Unraveling the nature of charge excitations in La2CuO4 with momentum-resolved Cu K-edge resonant inelastic X-ray scattering

    SciTech Connect

    Chen, Cheng-Chien

    2011-03-01

    Results of model calculations using exact diagonalization reveal the orbital character of states associated with different Raman loss peaks in Cu K-edge resonant inelastic X-ray scattering (RIXS) from La{sub 2}CuO{sub 4}. The model includes electronic orbitals necessary to highlight non-local Zhang-Rice singlet, charge transfer and d-d excitations, as well as states with apical oxygen 2p{sub z} character. The dispersion of these excitations is discussed with prospects for resonant final state wave-function mapping. A good agreement with experiments emphasizes the substantial multi-orbital character of RIXS profiles in the energy transfer range 1-6 eV.

  4. X-ray absorption spectra of nucleotides (AMP, GMP, and CMP) in liquid water solutions near the nitrogen K-edge

    NASA Astrophysics Data System (ADS)

    Ukai, Masatoshi; Yokoya, Akinari; Fujii, Kentaro; Saitoh, Yuji

    2010-07-01

    The X-ray absorption of nucleotides (adenosine-5'-monophosphate, guanosine 5'-monophosphate, and cytidine 5'-monophosphate) are measured in both water solutions and thin solid films at X-ray energies near the nitrogen K-edge in the 'water-window' region. Each spectrum corresponds to the selective excitation of a nucleobase site in a nucleotide, and thus has features similar to the spectrum of the corresponding nucleobase. An additional new peak in the energy region of the nitrogen 1s → π* resonance is observed for each nucleotide. No significant difference between the water solutions and thin solid films is found, which might be attributable to the hydrophobic properties of a nucleobase in a nucleotide.

  5. Position and flux stabilization of X-ray beams produced by double-crystal monochromators for EXAFS scans at the titanium K-edge.

    PubMed

    van Silfhout, Roelof; Kachatkou, Anton; Groppo, Elena; Lamberti, Carlo; Bras, Wim

    2014-03-01

    The simultaneous and active feedback stabilization of X-ray beam position and monochromatic beam flux during EXAFS scans at the titanium K-edge as produced by a double-crystal monochromator beamline is reported. The feedback is generated using two independent feedback loops using separate beam flux and position measurements. The flux is stabilized using a fast extremum-searching algorithm that is insensitive to changes in the synchrotron ring current and energy-dependent monochromator output. Corrections of beam height are made using an innovative transmissive beam position monitor instrument. The efficacy of the feedback stabilization method is demonstrated by comparing the measurements of EXAFS spectra on inhomogeneous diluted Ti-containing samples with and without feedback applied. PMID:24562562

  6. Fatigue of LiNi0.8Co0.15Al0.05O2 in commercial Li ion batteries

    NASA Astrophysics Data System (ADS)

    Kleiner, Karin; Dixon, Ditty; Jakes, Peter; Melke, Julia; Yavuz, Murat; Roth, Christina; Nikolowski, Kristian; Liebau, Verena; Ehrenberg, Helmut

    2015-01-01

    The degradation of LiNi0.8Co0.15Al0.05O2 (LNCAO), a cathode material in lithium-ion-batteries, was studied using in situ powder diffraction and in situ Ni K edge X-ray absorption spectroscopy (XAS). The fatigued material was taken from a 7 Ah battery which was cycled for 34 weeks under defined durability conditions. Meanwhile, a cell was stored, as reference, under controlled conditions without electrochemical treatment. The fatigued LNCAO used in this study showed a capacity loss of 26% ± 9% compared to the non-cycled material. During charge and discharge the local and the overall structure of LNCAO was investigated by X-ray near edge structure (XANES) analysis, the extended X-ray absorption fine structure (EXAFS) analysis and by using Rietveld refinement of in situ powder diffraction patterns. Both powder diffraction and XAS revealed additional, rhombohedral phases which do not change with electrochemical cycling. Moreover, a phase with the lattice parameters of fully lithiated LNCAO was still present in the fatigued material at high potentials, while it was absent in the non-fatigued reference material. The coexistence of these phases is described by domains within the LNCAO particles, in correlation with the observed fatigue.

  7. Tetrahalide Complexes of the [U(NR)(2)]2+ Ion: Synthesis, Theory, and Chlorine K-Edge X-ray Absorption Spectroscopy

    SciTech Connect

    Spencer, Liam P.; Yang, Ping; Minasian, Stefan G.; Jilek, Robert E.; Batista, Enrique R.; Boland, Kevin S.; Boncella, James M.; Conradson, S. D.; Clark, David L.; Hayton, Trevor W.; Kozimor, Stosh A.; Martin, Richard L.; MacInnes, Molly M.; Olson, Angela C.; Scott, Brian L.; Shuh, D. K.; Wilkerson, Marianne P.

    2013-02-13

    Synthetic routes to salts containing uranium bisimido tetrahalide anions [U(NR)(2)X-4](2-) (X = Cl-, Br-) and non-coordinating NEt4+ and PPh4+ countercations are reported. In general, these compounds can be prepared from U(NR)(2)I-2(THF)(x) (x = 2 and R = 'Bu, Ph; x = 3 and R = Me) upon addition of excess halide. In addition to providing stable coordination complexes with Cl-, the [U(NMe)(2)](2 +) cation also reacts with Br- to form stable [NEt4](2)[U(NMe)(2)Br-4] complexes. These materials were used as a platform to compare electronic structure and bonding in [U(NR)(2)](2+) with [UO2](2+). Specifically, Cl K-edge X-ray absorption spectroscopy (XAS) and both ground-state and time-dependent hybrid density functional theory (DFT and TDDFT) were used to probe U-Cl bonding interactions in [PPh4](2)[U((NBu)-Bu-t)(2)Cl-4] and [PPh4](2)[UO2Cl4]. The DFT and XAS results show the total amount of Cl 3p character mixed with the U 5f orbitals was roughly 7-10% per U-Cl bond for both compounds, which shows that moving from oxo to imido has little effect on orbital mixing between the U 5f and equatorial Cl 3p orbitals. The results are presented in the context of recent Cl K-edge XAS and DFT studies on other hexavalent uranium chloride systems with fewer oxo or imido ligands.

  8. Ligand K-edge x-ray absorption spectroscopy as a probe of ligand-metal bonding: Charge donation and covalency in copper-chloride systems

    SciTech Connect

    Shadle, S.E.; Hedman, B.; Solomon, E.I.; Hodgson, K.O.

    1994-09-14

    X-ray absorption spectra (XAS) have been measured at the chloride K-edge for a series of complexes containing chloride ligands bound to open shell d{sup 9} copper ions in order to probe ligand-metal bonding. The intensity of the pre-edge feature in these spectra reflects the covalency in the half-occupied d{sub x}{sup 2-}{sub y}{sup 2-} derived molecular orbital (HOMO) of the complex. The energy of the pre-edge feature as well as the energy of the rising absorption edge provides quantitative information about the covalency of the ligand-metal interaction, the charge donated by the chloride, and the energy of the copper d-manifold. The results demonstrate that ligand K-edge XAS features can be used to obtain information about ligand-metal bonding. The results also identify the chemical basis for trends in the XAS data for the following complexes: D{sub 4h} CuCl{sub 4}{sup 2-}, D{sub 2d} CuCl{sub 4}{sup 2-}, planar trans-CuCl{sub 2-} (pdmp){sub 2} (pdmp = N-phenyl-3,5-dimethylpyrazole), square pyramidal CuCl{sub 5}{sup 3-}, the planar dimer KCuCl{sub 3}, the distorted tetrahedral dimer (Ph{sub 4}P)CuCl{sub 3}, and two dimers with mixed ligation, one containing a bridging chloride, and the other, containing terminally bound chloride. Several of these results are supported by independent spectral data or by basic ligand field concepts. A geometric distortion from square planar to distorted tetrahedral results in a decrease in the chloride-copper HOMO covalency but an increase in the total charge donation by the chlorides. While the geometry can maximize the overlap for a highly covalent HOMO, this does not necessarily reflect the overall charge donation.

  9. Sulfur K-Edge XAS and DFT Calculations on NitrileHydratase: Geometric and Electronic Structure of the Non-heme Iron Active Site

    SciTech Connect

    Dey, Abhishek; Chow, Marina; Taniguchi, Kayoko; Lugo-Mas, Priscilla; Davin, Steven; Maeda, Mizuo; Kovacs, Julie A.; Odaka, Masafumi; Hodgson, Keith O.; Hedman, Britt; Solomon, Edward I.; /SLAC, SSRL

    2006-09-28

    The geometric and electronic structure of the active site of the non-heme iron enzyme nitrile hydratase (NHase) is studied using sulfur K-edge XAS and DFT calculations. Using thiolate (RS{sup -})-, sulfenate (RSO{sup -})-, and sulfinate (RSO{sub 2}{sup -})-ligated model complexes to provide benchmark spectral parameters, the results show that the S K-edge XAS is sensitive to the oxidation state of S-containing ligands and that the spectrum of the RSO- species changes upon protonation as the S-O bond is elongated (by {approx}0.1 {angstrom}). These signature features are used to identify the three cysteine residues coordinated to the low-spin Fe{sup III} in the active site of NHase as CysS{sup -}, CysSOH, and CysSO{sub 2}{sup -} both in the NO-bound inactive form and in the photolyzed active form. These results are correlated to geometry-optimized DFT calculations. The pre-edge region of the X-ray absorption spectrum is sensitive to the Z{sub eff} of the Fe and reveals that the Fe in [FeNO]{sup 6} NHase species has a Z{sub eff} very similar to that of its photolyzed Fe{sup III} counterpart. DFT calculations reveal that this results from the strong {pi} back-bonding into the {pi}* antibonding orbital of NO, which shifts significant charge from the formally t{sub 2}{sup 6} low-spin metal to the coordinated NO.

  10. Properties of impurity-bearing ferrihydrite I. Effects of Al content and precipitation rate on the structure of 2-line ferrihydrite

    SciTech Connect

    Cismasu, A. Cristina; Michel, F. Marc; Stebbins, Jonathan F.; Levard, Clément; Brown, Jr., Gordon E.

    2012-10-11

    The association of Al with ferrihydrite (Fh) may have a considerable effect on the composition, structure, and surface properties of Fh nanoparticles, and thus impact its reactivity and interaction with pollutant species. Aluminous Fh is abundant in natural environments, but the mode of association of Al with this nanomineral is not yet fully understood. Al{sup 3+} speciation may vary from true chemical substitution for Fe{sup 3+}, to adsorption or surface precipitation, and/or to formation of a mixture of two (or more) individual nanoscale phases. The conditions of formation (i.e. slow vs. rapid precipitation) may also affect the nature of Fh nanoparticles in terms of their crystallinity, phase purity, and Al speciation. In this study we used a variety of laboratory (TEM, NMR, ICP-AES) and synchrotron-based techniques (X-ray total scattering and PDF analysis, scanning transmission X-ray microscopy, Al K-edge XANES spectroscopy) to characterize two synthetic Al-bearing Fh series formed at different precipitation rates in the presence of 5-40 mol% Al. We find that Al is dominantly octahedrally coordinated in the synthetic Fh samples and that up to 20-30 mol% Al substitutes for Fe in the Fh structure, regardless of the synthesis method we used. Formation of separate aluminous phases (e.g., gibbsite) was most significant at Al concentrations above 30 mol% Al in slowly precipitated samples. However, small amounts (<6% of total Al) of Al-hydroxide phases were also detected by NMR spectroscopy in samples with lower Al content (as low as 15 mol% Al), particularly in the Fh series that was precipitated slowly. Furthermore, it appears that the amount of Al incorporated in Fh is not affected by the synthesis methods we used and is more likely controlled by the accumulated strain caused by Al substitution in the Fh lattice. Given the prevalence of naturally occurring aluminous ferrihydrite, assumptions about ferrihydrite reactivity in natural environments should consider the

  11. Copper, nickel and zinc speciation in a biosolid-amended soil: pH adsorption edge, μ-XRF and μ-XANES investigations.

    PubMed

    Mamindy-Pajany, Yannick; Sayen, Stéphanie; Mosselmans, J Frederick W; Guillon, Emmanuel

    2014-07-01

    Metal solid phase speciation plays an important role in the control of the long-term stability of metals in biosolid-amended soils. The present work used pH-adsorption edge experiments and synchrotron-based spectroscopy techniques to understand the solid phase speciation of copper, nickel and zinc in a biosolid-amended soil. Comparison of metal adsorption edges on the biosolid-amended soil and the soil sample showed that Cu, Ni, and Zn can be retained by both soil and biosolid components such as amorphous iron phases, organic matter and clay minerals. These data are combined with microscopic results to obtain structural information about the surface complexes formed. Linear combination fitting of K-edge XANES spectra of metal hot-spots indicated consistent differences in metal speciation between metals. While organic matter plays a dominant role in Ni binding in the biosolid-amended soil, it was of lesser importance for Cu and Zn. This study suggests that even if the metals can be associated with soil components (clay minerals and organic matter), biosolid application will increase metals retention in the biosolid-amended soil by providing reactive organic matter and iron oxide fractions. Among the studied metals, the long-term mobility of Ni could be affected by organic matter degradation while Cu and Zn are strongly associated with iron oxides. PMID:24899255

  12. 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.

  13. 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.

  14. First demonstration of 10 keV-width energy-discrimination K-edge radiography using a cadmium-telluride X-ray camera with a tungsten-target tube

    NASA Astrophysics Data System (ADS)

    Watanabe, Manabu; Sato, Eiichi; Abderyim, Purkhet; Abudurexiti, Abulajiang; Hagiwara, Osahiko; Matsukiyo, Hiroshi; Osawa, Akihiro; Enomoto, Toshiyuki; Nagao, Jiro; Sato, Shigehiro; Ogawa, Akira; Onagawa, Jun

    2011-05-01

    Energy-discrimination X-ray camera is useful to perform monochromatic radiography using polychromatic X-rays. This X-ray camera was developed to carry out K-edge radiography using cerium and gadolinium-based contrast media. In this camera, objects are irradiated by a cone beam from a tungsten-target X-ray generator, and penetrating X-ray photons are detected by a cadmium-telluride detector with amplifiers. Both optimal photon-energy level and energy width are selected using a multichannel analyzer, and the photon number is counted by a counter card. Radiography was performed by the detector scanning using an x- y stage driven by a two-stage controller, and radiograms were shown on a personal computer monitor. In radiography, tube voltage and current were 90 kV and 5.8 μA, respectively, and the X-ray intensity was 0.61 μGy/s at 1.0 m from the X-ray source. The K-edge energies of cerium and gadolinium are 40.3 and 50.3 keV, respectively, and 10 keV-width enhanced K-edge radiography was performed using X-ray photons with energies just beyond K-edge energies of cerium and gadolinium. Thus, cerium K-edge radiography was carried out using X-ray photons with an energy range from 40.3 to 50. 3 keV, and gadolinium K-edge radiography was accomplished utilizing photon energies ranging from 50.3 to 60.3 keV.

  15. 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,

  16. An unambiguous signature in molecular frame photoelectron angular distributions of core hole localization in fluorine K-edge photoionization of CF4

    NASA Astrophysics Data System (ADS)

    McCurdy, C. W.; Rescigno, T. N.; Trevisan, C. S.; Lucchese, R. R.

    2016-05-01

    Molecular Frame Photoelectron Angular Distributions (MFPADs) are calculated using the Complex Kohn variational method for core-hole ionization of the carbon and fluorines in CF4 at photoelectron energies below 15 eV. The angular distributions for localized versus delocalized core-hole creation on the four equivalent fluorines are radically different. A strong propensity for the dissociation to take place via the mechanism hν +CF4 -->CF 4 + +e- -->CF 3 + +F(1s-1) -->CF 3 + +F+ + 2e- in which a core excited neutral fluorine atom ionizes during or after dissociation creates the conditions for experimental observation of core hole localization. Comparison with recent unpublished experiments at the Advanced Light Source that measured the Recoil Frame Photoelectron Angular Distributions (averaged over CF3 rotations around the recoil axis) for fluorine K-edge ionization gives unambiguous evidence that these experiments directly observed the creation of an almost completely localized core hole on the dissociating fluorine atom when the molecule was initially photoionized. Work supported by USDOE, OBES Chemical Sciences, Geosciences, and Biosciences Division.

  17. Experimental and theoretical correlations between vanadium K-edge X-ray absorption and K[Formula: see text] emission spectra.

    PubMed

    Rees, Julian A; Wandzilak, Aleksandra; Maganas, Dimitrios; Wurster, Nicole I C; Hugenbruch, Stefan; Kowalska, Joanna K; Pollock, Christopher J; Lima, Frederico A; Finkelstein, Kenneth D; DeBeer, Serena

    2016-09-01

    A series of vanadium compounds was studied by K-edge X-ray absorption (XAS) and K[Formula: see text] X-ray emission spectroscopies (XES). Qualitative trends within the datasets, as well as comparisons between the XAS and XES data, illustrate the information content of both methods. The complementary nature of the chemical insight highlights the success of this dual-technique approach in characterizing both the structural and electronic properties of vanadium sites. In particular, and in contrast to XAS or extended X-ray absorption fine structure (EXAFS), we demonstrate that valence-to-core XES is capable of differentiating between ligating atoms with the same identity but different bonding character. Finally, density functional theory (DFT) and time-dependent DFT calculations enable a more detailed, quantitative interpretation of the data. We also establish correction factors for the computational protocols through calibration to experiment. These hard X-ray methods can probe vanadium ions in any oxidation or spin state, and can readily be applied to sample environments ranging from solid-phase catalysts to biological samples in frozen solution. Thus, the combined XAS and XES approach, coupled with DFT calculations, provides a robust tool for the study of vanadium atoms in bioinorganic chemistry. PMID:27251139

  18. Extended X- ray absorption fine structure study at the K-edge of copper in mixed ligand complexes having benzimidazole as one of the ligands

    NASA Astrophysics Data System (ADS)

    Hinge, V. K.; Joshi, S. K.; Nitin Nair, N.; Singh Verma, Vikram; Shrivastava, B. D.; Prasad, J.; Srivastava, K.

    2014-09-01

    Extended X-ray absorption fine structure (EXAFS) spectra have been studied at the K-edge of copper in some of its biologically important complexes, viz., [Cu(BzImH)4X2] and [Cu(BzIm)2], where X= Cl, Br, 1/2SO4, ClO4, NO3, and BzIm = Benzimidazolato anion. The spectra have been recorded using a bent crystal 0.4 m Cauchois-type transmission spectrograph. The positions of EXAFS maxima and minima have been used to determine the bond lengths in the complexes with the help of three different methods, namely, Levy's, Lytle's and Lytle, Sayers and Stern's (L.S.S.) methods. The phase uncorrected bond lengths have also been determined from Fourier transforms of the experimental spectra. The results obtained from these methods have been discussed and it has been found that the results obtained by L.S.S. method are comparable with the results obtained by Fourier transformation method and that these two methods give phase uncorrected bond lengths.

  19. K-edge magnetic circular dichroism of O in CO/Ni/Cu(001): Dependence on substrate magnetic anisotropy and its interpretation

    NASA Astrophysics Data System (ADS)

    Yokoyama, Toshihiko; Amemiya, Kenta; Miyachi, Mariko; Yonamoto, Yoshiki; Matsumura, Daiju; Ohta, Toshiaki

    2000-12-01

    O K-edge x-ray magnetic circular dichroism (XMCD) was investigated for molecular CO adsorbed on Ni thin films grown epitaxially on Cu(001). In the case of 10 monolayer (ML) Ni that shows perpendicular magnetic anisotropy (PMA), a relatively strong negative XMCD signal was observed at the O 1s-->CO 2π* transition. Since the CO 2π* orbital is partially filled due to hybridization of Ni 3d levels, this finding implies parallel alignment of the CO 2π* orbital moment with substrate Ni magnetization. The orbital moment is ascribed to the molecular orbital origin that is derived from degeneracy of the two π* orbitals. On the contrary, in the cases of in-plane magnetization of 6 ML and thick (>100 ML) Ni films, the XMCD signal at the CO 2π* resonance was found to be weak and positive. Although the origin of the orbital moment is not yet clear in the in-plane magnetization case, this indicates that the orbital moment shows antiparallel alignment with Ni. The direction of the CO 2π* orbital moment in PMA is interpreted with a framework of chemical bonding between CO and Ni.

  20. Cu K-edge X-ray Absorption Spectroscopy Reveals Differential Copper Coordimation Within Amyloid-beta Oligomers Compared to Amyloid-beta Monomers

    SciTech Connect

    J Shearer; P Callan; T Tran; V Szalai

    2011-12-31

    The fatal neurodegenerative disorder Alzheimer's disease (AD) has been linked to the formation of soluble neurotoxic oligomers of amyloid-{beta} (A{beta}) peptides. These peptides have high affinities for copper cations. Despite their potential importance in AD neurodegeneration few studies have focused on probing the Cu{sup 2+/1+} coordination environment within A{beta} oligomers. Herein we present a Cu K-edge X-ray absorption spectroscopic study probing the copper-coordination environment within oligomers of A{beta}(42) (sequence: DAEFRHDSGYEVHHQKLVFFAEDVGSNKGAIIGLMVGGVVIA). We find that the Cu{sup 2+} cation is contained within a square planar mixed N/O ligand environment within A{beta}(42) oligomers, which is similar to the copper coordination environment of the monomeric forms of {l_brace}Cu{sup II}A{beta}(40){r_brace} and {l_brace}Cu{sup II}A{beta}(16){r_brace}. Reduction of the Cu{sup 2+} cation within the A{beta}(42) oligomers to Cu{sup 1+} yields a highly dioxygen sensitive copper-species that contains Cu{sup 1+} in a tetrahedral coordination geometry. This can be contrasted with monomers of {l_brace}Cu{sup I}A{beta}(40){r_brace} and {l_brace}Cu{sup I}A{beta}(16){r_brace}, which contain copper in a dioxygen inert linear bis-histidine ligand environment [Shearer and Szalai, J. Am. Chem. Soc., 2008, 130, 17826]. The biological implications of these findings are discussed.

  1. Analysis of Flame Retardancy in Polymer Blends by Synchrotron X-ray K-edge Tomography and Interferometric Phase Contrast Movies.

    PubMed

    Olatinwo, Mutairu B; Ham, Kyungmin; McCarney, Jonathan; Marathe, Shashidhara; Ge, Jinghua; Knapp, Gerry; Butler, Leslie G

    2016-03-10

    Underwriters Laboratories 94 test bars have been imaged with X-ray K-edge tomography between 12 and 32 keV to assess the bromine and antimony concentration gradient across char layers of partially burnt samples. Phase contrast tomography on partially burnt samples showed gas bubbles and dark-field scattering ascribed to residual blend inhomogeneity. In addition, single-shot grating interferometry was used to record X-ray movies of test samples during heating (IR and flame) intended to mimic the UL 94 plastics flammability test. The UL 94 test bars were formulated with varying concentrations of a brominated flame retardant, Saytex 8010, and a synergist, Sb2O3, blended into high-impact polystyrene (HIPS). Depending on the sample composition, samples will pass or fail the UL 94 plastics flammability test. Tomography and interferometry imaging show differences that correlate with UL 94 performance. Key features such as char layer, gas bubble formation, microcracks, and dissolution of the flame retardant in the char layer regions are used in understanding the efficiency of the flame retardant and synergist. The samples that pass the UL 94 test have a thick, highly visible char layer as well as an interior rich in gas bubbles. Growth of gas bubbles from flame-retardant thermal decomposition is noted in the X-ray phase contrast movies. Also noteworthy is an absence of bubbles near the burning surface of the polymer; dark-field images after burning suggest a microcrack structure between interior bubbles and the surface. The accepted mechanism for flame retardant activity includes free radical quenching in the flame by bromine and antimony species. The imaging supports this as well as provides a fast inspection of other parameters, such as viscosity and surface tension. PMID:26846254

  2. In-operando synchronous time-multiplexed O K-edge x-ray absorption spectromicroscopy of functioning tantalum oxide memristors

    SciTech Connect

    Kumar, Suhas; Graves, Catherine E.; Strachan, John Paul Williams, R. Stanley; Kilcoyne, A. L. David; Tyliszczak, Tolek; Nishi, Yoshio

    2015-07-21

    Memristors are receiving keen interest because of their potential varied applications and promising large-scale information storage capabilities. Tantalum oxide is a memristive material that has shown promise for high-performance nonvolatile computer memory. The microphysics has been elusive because of the small scale and subtle physical changes that accompany conductance switching. In this study, we probed the atomic composition, local chemistry, and electronic structure of functioning tantalum oxide memristors through spatially mapped O K-edge x-ray absorption. We developed a time-multiplexed spectromicroscopy technique to enhance the weak and possibly localized oxide modifications with spatial and spectral resolutions of <30 nm and 70 meV, respectively. During the initial stages of conductance switching of a micrometer sized crosspoint device, the spectral changes were uniform within the spatial resolution of our technique. When the device was further driven with millions of high voltage-pulse cycles, we observed lateral motion and separation of ∼100 nm-scale agglomerates of both oxygen interstitials and vacancies. We also demonstrate a unique capability of this technique by identifying the relaxation behavior in the material during electrical stimuli by identifying electric field driven changes with varying pulse widths. In addition, we show that changes to the material can be localized to a spatial region by modifying its topography or uniformity, as against spatially uniform changes observed here during memristive switching. The goal of this report is to introduce the capability of time-multiplexed x-ray spectromicroscopy in studying weak-signal transitions in inhomogeneous media through the example of the operation and temporal evolution of a memristor.

  3. In-operando synchronous time-multiplexed O K-edge x-ray absorption spectromicroscopy of functioning tantalum oxide memristors

    NASA Astrophysics Data System (ADS)

    Kumar, Suhas; Graves, Catherine E.; Strachan, John Paul; Kilcoyne, A. L. David; Tyliszczak, Tolek; Nishi, Yoshio; Williams, R. Stanley

    2015-07-01

    Memristors are receiving keen interest because of their potential varied applications and promising large-scale information storage capabilities. Tantalum oxide is a memristive material that has shown promise for high-performance nonvolatile computer memory. The microphysics has been elusive because of the small scale and subtle physical changes that accompany conductance switching. In this study, we probed the atomic composition, local chemistry, and electronic structure of functioning tantalum oxide memristors through spatially mapped O K-edge x-ray absorption. We developed a time-multiplexed spectromicroscopy technique to enhance the weak and possibly localized oxide modifications with spatial and spectral resolutions of <30 nm and 70 meV, respectively. During the initial stages of conductance switching of a micrometer sized crosspoint device, the spectral changes were uniform within the spatial resolution of our technique. When the device was further driven with millions of high voltage-pulse cycles, we observed lateral motion and separation of ˜100 nm-scale agglomerates of both oxygen interstitials and vacancies. We also demonstrate a unique capability of this technique by identifying the relaxation behavior in the material during electrical stimuli by identifying electric field driven changes with varying pulse widths. In addition, we show that changes to the material can be localized to a spatial region by modifying its topography or uniformity, as against spatially uniform changes observed here during memristive switching. The goal of this report is to introduce the capability of time-multiplexed x-ray spectromicroscopy in studying weak-signal transitions in inhomogeneous media through the example of the operation and temporal evolution of a memristor.

  4. 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.

  5. Temperature and density dependence of XANES spectra in warm dense aluminum plasmas

    SciTech Connect

    Recoules, V.; Mazevet, S.

    2009-08-01

    Using ab initio molecular-dynamics simulations combined with linear-response theory, we calculate the density and temperature dependence of the x-ray absorption near-edge structure (XANES) of a dense aluminum plasma. At solid density and for temperatures increasing up to 6 eV, we see that the XANES spectrum loses its well-known room-temperature structure, first due to melting and second due to loss of correlation in the liquid. Similarly, as the density decreases and the system evolves from a liquid to a plasma, the XANES spectrum becomes less structured. As the density is further lowered and the system turns into an atomic fluid, a pre-edge forms as the 3p state becomes bound. We suggest that direct measurements of the XANES spectra in this density region is a unique opportunity to validate pressure ionization models routinely used in plasma physics modeling.

  6. XANES spectroscopic analysis of phosphorus speciation in alum-amended poultry litter.

    PubMed

    Seiter, Jennifer M; Staats-Borda, Kristin E; Ginder-Vogel, Matthew; Sparks, Donald L

    2008-01-01

    Aluminum sulfate (alum; Al(2)(SO(4))(3).14H(2)O) 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 ( approximately 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. PMID:18268311

  7. 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.

  8. Mercury speciation on three European mining districts by XANES techniques

    NASA Astrophysics Data System (ADS)

    Esbri, J. M.; Garcia-Noguero, E. M.; Guerrero, B.; Kocman, D.; Bernaus, A.; Gaona, X.; Higueras, P.; Alvarez, R.; Loredo, J.; Horvat, M.; Ávila, M.

    2009-04-01

    The mobility, bioavailability and toxicity of mercury in the environment depend on the chemical species in which is present in soil, sediments, water or air. In this work we used synchrotron radiation to determine mercury species in geological samples of three mercury mining districts: Almadén (Spain), Idria (Slovenia) and Asturias (Spain). The aim of this study was to find differences on mobility and bioavailability of mercury on three mining districts with different type of mineralization. For this porpoises we selected samples of ore, calcines, soils and stream sediments from the three sites, completely characterized by the Almadén School of Mines, Josef Stefan Institute of Ljubljana and Oviedo School of Mines. Speciation of mercury was carried out on Synchrotron Laboratories of Hamburg (HASYLAB) by XANES techniques. Spectra of pure compounds [HgCl2, HgSO4, HgO, CH3HgCl, Hg2Cl2 (calomel), HgSred (cinnabar), HgSblack (metacinnabar), Hg2NCl0.5(SO4)0.3(MoO4)0.1(CO3)0.1(H2O) (mosesite), Hg3S2Cl2 (corderoite), Hg3(SO4)O2 (schuetteite) y Hg2ClO (terlinguaite)] were obtained on transmittance mode. The number and type of the compounds required to reconstruct experimental spectra for each sample was obtained by PCA analysis and linear fitting of minimum quadratics of the pure compounds spectra. This offers a semiquantitative approach to the mineralogical constitution of each analyzed sample. The results put forward differences on the efficiency of roasting furnaces from the three studied sites, evidenced by the presence of metacinnabar on the less efficient (Almadén and Asturias) and absence on the most efficient (Idria). For the three studied sites, sulfide species (cinnabar and metacinnabar) were largely more abundant than soluble species (chlorides and sulfates). On the other hand, recent results on the mobility of both Hg and As on the target sites will be presented. These results correlate with the related chemical species found by XANES techniques.

  9. 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.

  10. φXANES: In vivo imaging of metal-protein coordination environments

    PubMed Central

    James, Simon A.; Hare, Dominic J.; Jenkins, Nicole L.; de Jonge, Martin D.; Bush, Ashley I.; McColl, Gawain

    2016-01-01

    We have developed an X-ray absorption near edge structure spectroscopy method using fluorescence detection for visualizing in vivo coordination environments of metals in biological specimens. This approach, which we term fluorescence imaging XANESXANES), allows us to spatially depict metal-protein associations in a native, hydrated state whilst avoiding intrinsic chemical damage from radiation. This method was validated using iron-challenged Caenorhabditis elegans to observe marked alterations in redox environment. PMID:26861174

  11. φXANES: In vivo imaging of metal-protein coordination environments.

    PubMed

    James, Simon A; Hare, Dominic J; Jenkins, Nicole L; de Jonge, Martin D; Bush, Ashley I; McColl, Gawain

    2016-01-01

    We have developed an X-ray absorption near edge structure spectroscopy method using fluorescence detection for visualizing in vivo coordination environments of metals in biological specimens. This approach, which we term fluorescence imaging XANESXANES), allows us to spatially depict metal-protein associations in a native, hydrated state whilst avoiding intrinsic chemical damage from radiation. This method was validated using iron-challenged Caenorhabditis elegans to observe marked alterations in redox environment. PMID:26861174

  12. φXANES: In vivo imaging of metal-protein coordination environments

    NASA Astrophysics Data System (ADS)

    James, Simon A.; Hare, Dominic J.; Jenkins, Nicole L.; de Jonge, Martin D.; Bush, Ashley I.; McColl, Gawain

    2016-02-01

    We have developed an X-ray absorption near edge structure spectroscopy method using fluorescence detection for visualizing in vivo coordination environments of metals in biological specimens. This approach, which we term fluorescence imaging XANESXANES), allows us to spatially depict metal-protein associations in a native, hydrated state whilst avoiding intrinsic chemical damage from radiation. This method was validated using iron-challenged Caenorhabditis elegans to observe marked alterations in redox environment.

  13. XANES Reveals the Flexible Nature of Hydrated Strontium in Aqueous Solution.

    PubMed

    D'Angelo, Paola; Migliorati, Valentina; Sessa, Francesco; Mancini, Giordano; Persson, Ingmar

    2016-05-01

    X-ray absorption near-edge structure (XANES) spectroscopy has been used to determine the structure of the hydrated strontium in aqueous solution. The XANES analysis has been carried out using solid [Sr(H2O)8](OH)2 as reference model. Classical and Car-Parrinello molecular dynamics (MD) simulations have been carried out and in the former case two different sets of Lennard-Jones parameters have been used for the Sr(2+) ion. The best performing theoretical approach has been chosen on the basis of the experimental results. XANES spectra have been calculated starting from MD trajectories, without carrying out any minimization of the structural parameters. This procedure allowed us to properly account for thermal and structural fluctuations occurring in the aqueous solution in the analysis of the experimental spectrum. A deconvolution procedure has been applied to the raw absorption data thus increasing the sensitivity of XANES spectroscopy. One of the classical MD simulations has been found to provide a XANES theoretical spectrum in better agreement with the experimental data. An 8-fold hydration complex with a Sr-O distance of 2.60 Å has been found to be compatible with the XANES data, in agreement with previous findings. However, the hydration shells of the strontium ions have been found to have a flexible nature with a fast ligand exchange rate between the first and second hydration shell occurring in the picosecond time scale. PMID:27065305

  14. XANES Data on Trace Quantities of Iron in Hydroxyapatite Structures

    NASA Astrophysics Data System (ADS)

    Tabor-Morris, A.; Schaefer, B.

    2003-03-01

    Trace elements such as iron are of interest in both biologically and geologically formed apatites. They are thought to occupy substitutional sites at the concentration of about 200 ppm. Most likely metal atoms replace the calcium atom in one of two non-equivalent calcium sites. The inorganic mineral structure hydroxyapatite (which comprises 30% of human and animal bone) consists of Ca_5(OH)(PO_4)3 in a hexagonal crystal structure designated in Herman-Maugin crystallography notation as P63/m or as Number 176 in the International Tables of Crystallography (ITC). Hydroxyapatite formed under geological conditions has the same crystal structure. Hydroxyapatite can also be fabricated synthetically, but has limitations in terms of crystal growth size. The experimental technique of X-ray Absorption Near Edge Structure (XANES) and X-ray Absorption Fine-structure Spectroscopy (XAFS) were used to evaluate the oxidation state of iron. Data was taken at the X-9B line at the National Synchrotron Light Source at Brookhaven National Laboratory.

  15. XANES Data on Metal Ions in Hydroxyapatite Structures

    NASA Astrophysics Data System (ADS)

    Schaefer, Beth; Tabor-Morris, Anne; Simons, Adrian

    2004-03-01

    The experimental technique of X-ray Absorption Near Edge Structure (XANES) was used to compare the absorption edges of different oxidation states of iron, strontium, lead, copper and zinc in the inorganic mineral structure hydroxyapatite and fluoroapatite. Trace elements such as iron, copper, zinc, lead and strontium are of interest in both biologically and geologically formed apatites. They are thought to occupy substitutional sites at the concentration of about 200 ppm. These metal atoms replace the calcium atom in one of two non-equivalent calcium sites. Hydroxyapatite consists of Ca _5 (OH)(PO_4)3 in a hexagonal crystal structure. Hydroxyapatite formed under geological conditions has the same crystal structure. Data was taken at the X-9B line at the National Synchrotron Light Source at Brookhaven National Laboratory. Samples were obtained from Dr. Susan G. Sheridan, at the University of Notre Dame, Dr. Catherine Skinner from Yale University, Dr. John Rakovan at Miami University in Ohio, Dr. Richard Riman at Rutgers University.

  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. Sulfur K-Edge X-Ray Absorption Spectroscopy And Density Functional Theory Calculations on Superoxide Reductase: Role of the Axial Thiolate in Reactivity

    SciTech Connect

    Dey, A.; Jenney, F.E.; Jr.; Adams, M.W.W.; Johnson, M.K.; Hodgson, K.O.; Hedman, B.; Solomon, E.I.

    2009-06-02

    Superoxide reductase (SOR) is a non-heme iron enzyme that reduces superoxide to peroxide at a diffusion-controlled rate. Sulfur K-edge X-ray absorption spectroscopy (XAS) is used to investigate the ground-state electronic structure of the resting high-spin and CN- bound low-spin FeIII forms of the 1Fe SOR from Pyrococcus furiosus. A computational model with constrained imidazole rings (necessary for reproducing spin states), H-bonding interaction to the thiolate (necessary for reproducing Fe-S bond covalency of the high-spin and low-spin forms), and H-bonding to the exchangeable axial ligand (necessary to reproduce the ground state of the low-spin form) was developed and then used to investigate the enzymatic reaction mechanism. Reaction of the resting ferrous site with superoxide and protonation leading to a high-spin FeIII-OOH species and its subsequent protonation resulting in H2O2 release is calculated to be the most energetically favorable reaction pathway. Our results suggest that the thiolate acts as a covalent anionic ligand. Replacing the thiolate with a neutral noncovalent ligand makes protonation very endothermic and greatly raises the reduction potential. The covalent nature of the thiolate weakens the FeIII bond to the proximal oxygen of this hydroperoxo species, which raises its pKa by an additional 5 log units relative to the pKa of a primarily anionic ligand, facilitating its protonation. A comparison with cytochrome P450 indicates that the stronger equatorial ligand field from the porphyrin results in a low-spin FeIII-OOH species that would not be capable of efficient H2O2 release due to a spin-crossing barrier associated with formation of a high-spin 5C FeIII product. Additionally, the presence of the dianionic porphyrin pi ring in cytochrome P450 allows O-O heterolysis, forming an FeIV-oxo porphyrin radical species, which is calculated to be extremely unfavorable for the non-heme SOR ligand environment. Finally, the 5C FeIII site that results

  18. Optimization of the K-edge imaging for vulnerable plaques using gold nanoparticles and energy-resolved photon counting detectors: a simulation study

    PubMed Central

    Alivov, Yahya; Baturin, Pavlo; Le, Huy Q.; Ducote, Justin; Molloi, Sabee

    2014-01-01

    We investigated the effect of different imaging parameters such as dose, beam energy, energy resolution, and number of energy bins on image quality of K-edge spectral computed tomography (CT) of gold nanoparticles (GNP) accumulated in an atherosclerotic plaque. Maximum likelihood technique was employed to estimate the concentration of GNP, which served as a targeted intravenous contrast material intended to detect the degree of plaque's inflammation. The simulations studies used a single slice parallel beam CT geometry with an X-ray beam energy ranging between 50 and 140 kVp. The synthetic phantoms included small (3 cm in diameter) cylinder and chest (33x24 cm2) phantom, where both phantoms contained tissue, calcium, and gold. In the simulation studies GNP quantification and background (calcium and tissue) suppression task were pursued. The X-ray detection sensor was represented by an energy resolved photon counting detector (e.g., CdZnTe) with adjustable energy bins. Both ideal and more realistic (12% FWHM energy resolution) implementations of photon counting detector were simulated. The simulations were performed for the CdZnTe detector with pixel pitch of 0.5-1 mm, which corresponds to the performance without significant charge sharing and cross-talk effects. The Rose model was employed to estimate the minimum detectable concentration of GNPs. A figure of merit (FOM) was used to optimize the X-ray beam energy (kVp) to achieve the highest signal-to-noise ratio (SNR) with respect to patient dose. As a result, the successful identification of gold and background suppression was demonstrated. The highest FOM was observed at 125 kVp X-ray beam energy. The minimum detectable GNP concentration was determined to be approximately 1.06 μmol/mL (0.21 mg/mL) for an ideal detector and about 2.5 μmol/mL (0.49 mg/mL) for more realistic (12% FWHM) detector. The studies show the optimal imaging parameters at lowest patient dose using an energy resolved photon counting detector

  19. 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.

  20. 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. PMID:27140156

  1. Sulfur K-Edge X-Ray Absorption Spectroscopy And Density Functional Theory Calculations on Superoxide Reduc Tase: Role of the Axial Thiolate in Reactivity

    SciTech Connect

    Dey, A.; Jenney, F.E., Jr.; Adams, M.W.; Johnson, M.K.; Hodgson, K.O.; Hedman, B.; Solomon, E.I.; /Stanford U., Chem. Dept. /Athens U. /SLAC, SSRL

    2007-10-26

    Superoxide reductase (SOR) is a non-heme iron enzyme that reduces superoxide to peroxide at a diffusion-controlled rate. Sulfur K-edge X-ray absorption spectroscopy (XAS) is used to investigate the ground-state electronic structure of the resting high-spin and CN{sup -} bound low-spin Fe{sup III} forms of the 1Fe SOR from Pyrococcus furiosus. A computational model with constrained imidazole rings (necessary for reproducing spin states), H-bonding interaction to the thiolate (necessary for reproducing Fe-S bond covalency of the high-spin and low-spin forms), and H-bonding to the exchangeable axial ligand (necessary to reproduce the ground state of the low-spin form) was developed and then used to investigate the enzymatic reaction mechanism. Reaction of the resting ferrous site with superoxide and protonation leading to a high-spin Fe{sup III}-OOH species and its subsequent protonation resulting in H2O2 release is calculated to be the most energetically favorable reaction pathway. Our results suggest that the thiolate acts as a covalent anionic ligand. Replacing the thiolate with a neutral noncovalent ligand makes protonation very endothermic and greatly raises the reduction potential. The covalent nature of the thiolate weakens the Fe{sup III} bond to the proximal oxygen of this hydroperoxo species, which raises its pKa by an additional 5 log units relative to the pK{sub a} of a primarily anionic ligand, facilitating its protonation. A comparison with cytochrome P450 indicates that the stronger equatorial ligand field from the porphyrin results in a low-spin Fe{sup III}-OOH species that would not be capable of efficient H2O2 release due to a spin-crossing barrier associated with formation of a high-spin 5C Fe{sup III} product. Additionally, the presence of the dianionic porphyrin {pi} ring in cytochrome P450 allows O-O heterolysis, forming an Fe{sup IV}-oxo porphyrin radical species, which is calculated to be extremely unfavorable for the non-heme SOR ligand

  2. Sulfur and iron speciation in gas-rich impact-melt glasses from basaltic shergottites determined by microXANES

    SciTech Connect

    Sutton, S.R.; Rao, M.N.; Nyquist, L.E.

    2008-04-28

    determine sulfur speciation (sulfide, sulfate or elemental sulfur) in these glasses, Gooding et al. and Burgess et al. carried out vacuum pyrolysis experiments on these GRIM glasses (also called Lith C) using quadrupole mass-spectrometric methods. They found that the evolved S-bearing gases from these samples consisted of both SO{sub 2} (from sulfate) and H{sub 2}S (from sulfide) in varying proportions. However, as mass-spectrometric studies do not provide details about spatial association of these S-species in these samples, we have studied the spatial distribution of sulfides and sulfates in GRIM glasses using sulfur K micro-XANES techniques in the present study. The microscale speciation of S may have important implications for the Rb-Sr isotope systematics of EET79001 Lith C glasses. In reference to oxidative weathering of surface basalts on Mars yielding secondary iron sulfates, Solberg and Burns examined a GRIM glass in EET79001 by Moessbauer spectroscopic techniques and showed that the percentage of Fe{sup 3+} in Lith C is <2%. They suggested that the Lith C contains very little Fe{sup 3+} despite the occurrence of oxidized sulfate in them, indicating that the conditions leading to the formation of these glasses were insufficiently oxidizing to produce Fe{sup 3+} from Fe{sup 2+} in these glasses. To understand the implications of these observations for the formation of the GRIM glasses, we determined the oxidation state of Fe in the GRIM glasses using Fe K micro-XANES techniques. The S and Fe K micro-XANES measurements were performed on thin sections from EET79001: 506 from Lith A and 507 from Lith B.

  3. Determination of CO, H{sub 2}O and H{sub 2} coverage by XANES and EXAFS on Pt and Au during water gas shift reaction.

    SciTech Connect

    Guo, N.; Fingland, B. R.; Williams, W. D.; Kispersky, V. F.; Jelic, J.; Delgass, W. N.; Ribeiro, F. H.; Meyer, R. J.; Miller, J. T.; Purdue Univ.; Univ. of Illinois

    2010-01-01

    The turn over rate (TOR) for the water gas shift (WGS) reaction at 200C, 7%CO, 9%CO{sub 2}, 22% H{sub 2}O, 37% H, and balance Ar, of 1.4 nm Au/Al{sub 2}O{sub 3} is approximately 20 times higher than that of 1.6 nm Pt.Al{sub 2}O{sub 3}. Operando EXFAS experiments at both the Au and Pt L{sub 3} edges reveal tht under reaction conditions, the catalysts are fully metallic. In the absence of adsorbates, the metal-metal bond distance of Pt and Au catalysts are 0.07 {angstrom} and 0.13 {angstrom} smaller than those of bulk Pt and Au foils, respectively. Adsorption of H{sub 2} or CO on the Pt catalysts leads to significantly longer Pt-Pt bond distances, while there is little change in the Au-Au bond distance with adsorbates. Adsorption of CO, H{sub 2} and H{sub 2}O leads to changes in the XANES spectra that can be used to determine the surface coverage of each adsorbate under reaction conditions. During WGS, the coverage of CO, H{sub 2}O and H{sub 2} are obtained by the linear combination fitting of the difference XANES or {Delta}XANES, spectra. Pt catalysts adsorb CO,H{sub 2} and H{sub 2}O more strongly than the Au, in agreement with the lower CO reaction order and higher reaction temperatures.

  4. Automated analysis of XANES: A feasibility study of Au reference compounds

    NASA Astrophysics Data System (ADS)

    Chang, S.-Y.; Molleta, L. B.; Booth, S. G.; Uehara, A.; Mosselmans, J. F. W.; Ignatyev, K.; Dryfe, R. A. W.; Schroeder, S. L. M.

    2016-05-01

    With the advent of high-throughput and imaging core level spectroscopies (including X-ray absorption spectroscopy, XAS, as well as electron energy loss spectroscopy, EELS), automated data processing, visualisation and analytics will become a necessity. As a first step towards these objectives we examined the possibilities and limitations of a simple automated XANES peak fitting procedure written in MATLAB, for the parametrisation of XANES features, including ionisation potentials as well as the energies and intensities of electronic transitions. Using a series of Au L3-edge XANES reference spectra we show that most of the relevant information can be captured through a small number of rules applied to constrain the fits. Uncertainty in this strategy arises mostly when the ionisation potential (IP) overlaps with weak electronic transitions or features in the continuum beyond the IP, which can result in ambiguity through multiple equally good fits.

  5. Nature of ThF bonding in crystalline and glassy states using EXAFS and XANES

    NASA Astrophysics Data System (ADS)

    Rao, K. J.; Wong, J.; Shafer, M. W.

    1984-11-01

    A binary glass of thorium and hafnium tetrafluorides (with dopant concentrations of LaF 3) has been investigated using EXAFS and XANES analysis of the L Ill edge spectra of thorium. Results of EXAFS analysis indicate that there is no change in the number of nearest neighbors of thorium ions. However, the intensity of the white line in XANES is significantly higher in the glass. This increase in intensity has been explained semiquantitatively in terms of enhanced covalency of ThF bonding. Since the coordination number of Th 4+ remains constant in both crystalline and glassy states, covalency enhancement seems to be a general characteristic of glassy state of ionic materials.

  6. An In Situ High Temperature Investigation of Cation Environments in Aluminate and Silicate Glasses and Liquids at the LUCIA Beamline

    SciTech Connect

    Neuville, Daniel R.; Roux, Jacques; Cormier, Laurent; Ligny, Dominique de; Flank, Anne-Marie; Lagarde, Pierre; Henderson, Grant S.

    2007-02-02

    The structure of crystals and melts were obtained at high temperature using X-ray absorption at the Ca K-edge on CaMgSi2O6 (diopside), CaAl2Si2O8 (anorthite), Ca3Al2O6 (C3A) and CaAl2O4 (CA) compositions. Important changes are observed above the liquidus temperature particularly for the C3A composition where all oscillations in the XANES spectra disappear. Important changes in the Ca K-edge XANES are also visible in the pre-edge region, with increasing temperature, for crystalline CaMgSi2O6.

  7. Resonant inelastic x-ray scattering on iso-C{sub 2}H{sub 2}Cl{sub 2} around the chlorine K-edge: Structural and dynamical aspects

    SciTech Connect

    Kawerk, Elie E-mail: ekawerk@units.it; Carniato, Stéphane; Journel, Loïc; Marchenko, Tatiana; Simon, Marc; Piancastelli, Maria Novella; Žitnik, Matjaž; Bučar, Klemen; Bohnic, Rok; and others

    2014-10-14

    We report a theoretical and experimental study of the high resolution resonant K{sub α} X-ray emission lines around the chlorine K-edge in gas phase 1,1-dichloroethylene. With the help of ab initio electronic structure calculations and cross section evaluation, we interpret the lowest lying peak in the X-ray absorption and emission spectra. The behavior of the K{sub α} emission lines with respect to frequency detuning highlights the existence of femtosecond nuclear dynamics on the dissociative Potential Energy Surface of the first K-shell core-excited state.

  8. Characterization of Sulfur Compounds in Coffee Beans by Sulfur K-XANES Spectroscopy

    NASA Astrophysics Data System (ADS)

    Lichtenberg, H.; Prange, A.; Modrow, H.; Hormes, J.

    2007-02-01

    In this `feasibility study' the influence of roasting on the sulfur speciation in Mexican coffee beans was investigated by sulfur K-XANES Spectroscopy. Spectra of green and slightly roasted beans could be fitted to a linear combination of `standard' reference spectra for biological samples, whereas longer roasting obviously involves formation of additional sulfur compounds in considerable amounts.

  9. EXAFS and XANES analysis of plutonium and cerium edges from titanate ceramics for fissile materials disposal.

    SciTech Connect

    Fortner, J. A.; Kropf, A. J.; Bakel, A. J.; Hash, M. C.; Aase, S. B.; Buck, E. C.; Chamerlain, D. B.

    1999-11-16

    We report x-ray absorption near edge structure (XANES) and extended x-ray absorption fine structure (EXAFS) spectra from the plutonium L{sub III} edge and XANES from the cerium L{sub II} edge in prototype titanate ceramic hosts. The titanate ceramics studied are based upon the hafnium-pyrochlore and zirconolite mineral structures and will serve as an immobilization host for surplus fissile materials, containing as much as 10 weight % fissile plutonium and 20 weight % (natural or depleted) uranium. Three ceramic formulations were studied: one employed cerium as a ''surrogate'' element, replacing both plutonium and uranium in the ceramic matrix, another formulation contained plutonium in a ''baseline'' ceramic formulation, and a third contained plutonium in a formulation representing a high-impurity plutonium stream. The cerium XANES from the surrogate ceramic clearly indicates a mixed III-IV oxidation state for the cerium. In contrast, XANES analysis of the two plutonium-bearing ceramics shows that the plutonium is present almost entirely as Pu(IV) and occupies the calcium site in the zirconolite and pyrochlore phases. The plutonium EXAFS real-space structure shows a strong second-shell peak, clearly distinct from that of PuO{sub 2}, with remarkably little difference in the plutonium crystal chemistry indicated between the baseline and high-impurity formulations.

  10. 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 ...

  11. 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.

  12. Characterization of Sulfur Compounds in Coffee Beans by Sulfur K-XANES Spectroscopy

    SciTech Connect

    Lichtenberg, H.; Hormes, J.; Prange, A.; Modrow, H.

    2007-02-02

    In this 'feasibility study' the influence of roasting on the sulfur speciation in Mexican coffee beans was investigated by sulfur K-XANES Spectroscopy. Spectra of green and slightly roasted beans could be fitted to a linear combination of 'standard' reference spectra for biological samples, whereas longer roasting obviously involves formation of additional sulfur compounds in considerable amounts.

  13. Arsenic speciation and phytoavailability in contaminated soils using a sequential extraction procedure and XANES spectroscopy.

    PubMed

    Niazi, Nabeel K; Singh, Balwant; Shah, Pushan

    2011-09-01

    In this study, a sequential extraction procedure (SEP) and X-ray absorption near edge structure (XANES) spectroscopy were used to determine the solid-phase speciation and phytoavailability of arsenic (As) of historically contaminated soils from As containing pesticides and herbicides and soils spiked with As in the laboratory. Brassica juncea was grown in the contaminated soils to measure plant available As in a glasshouse experiment. Arsenic associated with amorphous Fe oxides was found to be the dominant phase using both SEP and XANES spectroscopy. Arsenic predominantly existed in arsenate (As(V)) form in the soils; in a few samples As was also present in arsenite (As(III)) form or in scorodite mineral. Arsenic concentration in shoots showed significant (p < 0.001-0.05) correlations with the exchangeable As (r = 0.85), and amorphous Fe oxides associated As evaluated by the SEP (r = 0.67), and As associated with amorphous Fe oxides as determined by XANES spectroscopy (r = 0.51). The results show that As in both fractions was readily available for plant uptake and may pose a potential risk to the environment. The combination of SEP and XANES spectroscopy allowed us the quantitative speciation of As in the contaminated soils and the identification of valence and mineral forms of As. Such detailed knowledge on As speciation and availability is vital for management and rehabilitation of As-contaminated soils. PMID:21797214

  14. Local structure of Ge quantum dots determined by combined numerical analysis of EXAFS and XANES data.

    PubMed

    Zhang, Yuanpeng; Ersoy, Osman; Karatutlu, Ali; Little, William; Sapelkin, Andrei

    2016-01-01

    The sensitivity of X-ray absorption near-edge structure (XANES) to the local symmetry has been investigated in small (∼4 nm) matrix-free Ge quantum dots. The FDMNES package was used to calculate the theoretical XANES spectra that were compared with the experimental data of as-prepared and annealed nanoparticles. It was found that XANES data for an as-prepared sample can only be adequately described if the second coordination shell of the diamond-type structural model is included in the FDMNES calculations. This is in contrast to the extended X-ray absorption fine-structure data that show only the first-shell signal. These results suggest that, despite the high degree of disorder and a large surface-to-volume ratio, as-prepared small Ge quantum dots retain the diamond-type symmetry beyond the first shell. Furthermore, we utilized this sensitivity of XANES to the local symmetry to study annealed Ge quantum dots and found evidence for significant structural distortion which we attribute to the existence of surface disorder in the annealed oxygen-free Ge quantum dots. PMID:26698071

  15. The Atomic AXAFS and XANES Techniques as Applied to Heterogeneous Catalysis and Electrocatalysis

    SciTech Connect

    Ramaker, D.; Koningsberger, D

    2010-01-01

    X-Ray absorption spectroscopy (XAFS) is an attractive in situ and in operando technique. In recent years, the more conventional extended X-ray absorption fine structure (EXAFS) data analysis technique has been complemented by two newer analysis methods: the 'atomic' XAFS (AXAFS) technique, which analyzes the scattering from the absorber atom itself, and the {Delta}{mu} XANES technique, which uses a difference method to isolate the changes in the X-ray absorption near edge structure (XANES) due to adsorbates on a metal surface. With AXAFS it is possible to follow the electronic effect a support has on a metal particle; with {Delta}{mu} XANES it is possible to determine the adsorbate, the specific adsorption sites and adsorbate coverage on a metal catalyst. This unprecedented new information helps a great deal to unravel the complex kinetic mechanisms operating in working reactors or fuelcell systems. The fundamental principles and methodology for applying the AXAFS and {Delta}{mu} XANES techniques are given here, and then specific applications are summarized, including H adsorption on supported Pt in the gas phase, wateractivation at a Pt cathode and methanol oxidation at a Pt anode in an electrochemical cell, sulfur oxidation on Pt, and oxygenreduction on a Au/SnO{sub x} cathode. Finally, the future outlook for time and/or space resolved applications of these techniques is contemplated.

  16. Micro-XANES Measurements on Experimental Spinels and the Oxidation State of Vanadium in Spinel-Melt Pairs

    NASA Technical Reports Server (NTRS)

    Righter, K.; Sutton, S.R.; Newville, M.

    2004-01-01

    Spinel can be a significant host phase for V as well as other transition metals such as Ni and Co. However, vanadium has multiple oxidation states V(2+), V(3+), V(4+) or V(5+) at oxygen fugacities relevant to natural systems. We do know that D(V) spinel/melt is correlated with V and TiO2 content and fO2, but the uncertainty of the oxidation state under the range of natural conditions has made elusive a thorough understanding of D(V) spinel/melt. For example, V(3+) is likely to be stable in spinels, based on exchange with Al in experiments in the CaO-MgO-Al2O3-SiO2 system. On the other hand, it has been argued that V(4+) will be stable across the range of natural oxygen fugacities in nature. In order to gain a better understanding of D(V) spinel/melt we have equilibrated spinel-melt pairs at controlled oxygen fugacities, between HM to NNO, where V is present in the spinel at natural levels (approx. 300 ppm V). These spinel-melt pairs were analyzed using micro-XANES at the Advanced Photon Source at Argonne National Laboratory. The new results will be used together with spinel compositional data (Ti, V content) and oxygen fugacity, to unravel the effects of these variables on D(V) spinel/melt.

  17. Water-window soft x-ray high-harmonic generation up to the nitrogen K-edge driven by a kHz, 2.1 μm OPCPA source

    NASA Astrophysics Data System (ADS)

    Stein, Gregory J.; Keathley, Phillip D.; Krogen, Peter; Liang, Houkun; Siqueira, Jonathas P.; Chang, Chun-Lin; Lai, Chien-Jen; Hong, Kyung-Han; Laurent, Guillaume M.; Kärtner, Franz X.

    2016-08-01

    We report the generation of coherent water-window soft x-ray harmonics in a neon-filled semi-infinite gas cell driven by a femtosecond multi-mJ mid-infrared optical parametric chirped-pulse amplification (OPCPA) system at a 1 kHz repetition rate. The cutoff energy was extended to ∼450 eV with a 2.1 μm driver wavelength and a photon flux of ∼ 1.5× {10}6 photons/s/1% bandwidth was obtained at 350 eV. A comparable photon flux of ∼ 1.0× {10}6 photons/s/1% bandwidth was observed at the nitrogen K-edge of 410 eV. This is the first demonstration of water-window harmonic generation up to the nitrogen K-edge from a kHz OPCPA system. Finally, this system is suitable for time-resolved soft x-ray near-edge absorption spectroscopy. Further scaling of the driving pulse's energy and repetition rate is feasible due to the availability of high-power picosecond Yb-doped pump laser technologies, thereby enabling ultrafast, tabletop water-window x-ray imaging.

  18. In-plant measurements of gamma-ray transmissions for precise K-edge and passive assay of plutonium concentration and isotopic fractions in product solutions. Final report on TASTEX Task G

    SciTech Connect

    Russo, P.A.; Hsue, S.T.; Sprinkle, J.K. Jr.; Johnson, S.S.; Asakura, Y.; Kondo, I.; Masui, J.; Shoji, K.

    1982-08-01

    An instrument based upon high-resolution gamma-ray measurements has been tested for more than 1 year at the Tokai Reprocessing Facility for determination of plutonium concentration by K-edge absorption densitometry and for determination of plutonium isotopic fractions by transmission-corrected passive gamma-ray spectrometry. The nondestructive assay instrument was designed and built at Los Alamos National Laboratory for the Tokai Advanced Safeguards Technology Exercise (TASTEX). It was used at Tokai for the timely assay of more than 100 product solution samples during the TASTEX evaluations. The results were compared to reference values obtained by conventional destructive analysis of these samples. The precision and accuracy of plutonium concentrations measured by the K-edge technique are shown to be within 0.6% (1delta) in these applications. The precisions and accuracies of the isotopic fractions determined by these passive gamma-ray methods are shown to be within 0.4% for /sup 239/Pu, 1% for /sup 240/Pu and /sup 241/Pu, and 10% for /sup 242/Pu.

  19. Electron yield XAFS study of evaporated Co/Pd multilayers with various thickness ratios of Co to Pd sublayers: Simulations of the Co K-edge XAFS and fourier transforms

    SciTech Connect

    Choi, M. . Dept. of Physics); Joo, J.H. . Materials Design Lab.); Kim, S.K.; Kang, J.S.; Lee, Y.P. ); Shin, S.C. ); Heald, S.M.

    1992-01-01

    Electron-yield XAFS measurements using the NSLS were made on e-beam evaporated Co/Pd multilayers with various sublayer thicknesses and different thickness ratios of Co to Pd sublayers. The Co K-edge and the Pd K-edge XAFS data were obtained for the Co/Pd multilayers with sublayer thicknesses of 3[Angstrom]/ 4[Angstrom], 15[Angstrom]/4[Angstrom], 3[Angstrom]/15[Angstrom], 2.1[Angstrom]/13.5[Angstrom], and 2.2[Angstrom]/4.5[Angstrom]. Fourier transforms of Co K XAFS for most samples show a splitting of major peak, and the magnitude ratio of these split peaks varies systematically with the thickness ratio of the Pd sublayer to the Co sublayer, whereas the Fourier transforms of the Pd K XAFS for the same samples do not show a splitting of peaks. As a preliminary analysis, the Co K XAFS and the split peaks in the Fourier transform for the Co/Pd(3[Angstrom]/4[Angstrom]) case were simulated by using the FEFF calculations, and the Co K XAFS and the major peak in the fourier transform for the Co/Pd(15[Angstrom]/4[Angstrom]) case were also simulated consistently.

  20. Electron yield XAFS study of evaporated Co/Pd multilayers with various thickness ratios of Co to Pd sublayers: Simulations of the Co K-edge XAFS and fourier transforms

    SciTech Connect

    Choi, M.; Joo, J.H.; Kim, S.K.; Kang, J.S.; Lee, Y.P.; Shin, S.C.; Heald, S.M.

    1992-11-01

    Electron-yield XAFS measurements using the NSLS were made on e-beam evaporated Co/Pd multilayers with various sublayer thicknesses and different thickness ratios of Co to Pd sublayers. The Co K-edge and the Pd K-edge XAFS data were obtained for the Co/Pd multilayers with sublayer thicknesses of 3{Angstrom}/ 4{Angstrom}, 15{Angstrom}/4{Angstrom}, 3{Angstrom}/15{Angstrom}, 2.1{Angstrom}/13.5{Angstrom}, and 2.2{Angstrom}/4.5{Angstrom}. Fourier transforms of Co K XAFS for most samples show a splitting of major peak, and the magnitude ratio of these split peaks varies systematically with the thickness ratio of the Pd sublayer to the Co sublayer, whereas the Fourier transforms of the Pd K XAFS for the same samples do not show a splitting of peaks. As a preliminary analysis, the Co K XAFS and the split peaks in the Fourier transform for the Co/Pd(3{Angstrom}/4{Angstrom}) case were simulated by using the FEFF calculations, and the Co K XAFS and the major peak in the fourier transform for the Co/Pd(15{Angstrom}/4{Angstrom}) case were also simulated consistently.

  1. 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.

  2. Determination of Chemical States of Mercury on Activated Carbon Using XANES

    SciTech Connect

    Takaoka, Masaki; Takeda, Nobuo; Oshita, Kazuyuki; Yamamoto, Takashi; Tanaka, Tsunehiro; Uruga, Tomoya

    2007-02-02

    Although the adsorption of mercury vapor onto activated carbon is a widely used technology to prevent environmental release, the adsorption mechanism is not clearly understood. In this study, we determined the chemical states of mercury on two kinds of activated carbon using X-ray absorption near-edge spectroscopy (XANES) to elucidate the adsorption mechanism. The adsorption experiments of elemental mercury onto activated carbon were conducted under air and nitrogen atmospheres at temperatures of 20 and 160 deg. C. Two types of activated carbon were prepared. X-ray absorption fine structure (XAFS) measurements were carried out on beamline BL01B1 at SPring-8. Hg-LIII edge XANES spectra suggested that chemical adsorption of elemental mercury on the activated carbon occurred in the 20-160 deg. C temperature range. According to the XANES spectra, a difference occurred in the chemical states of mercury between AC no. 1 and AC no. 2. The Hg XANES spectra on AC no. 1 were similar to those of Hg2Cl2 and HgS, and the Hg XANES spectra on AC no. 2 were similar to that of HgO, which suggested that nitric acid treatment removed sulfur from AC no. 1 and functional groups that were strong oxidizers on the surface of AC no. 2 created HgO. According to the EXAFS oscillation, a difference occurred in the chemical states of mercury on AC no. 1 between 20 and 160 deg. C. We found that impurities and oxidant functional groups on activated carbon play key roles in mercury adsorption.

  3. Trends in Covalency for d- and f-Element Metallocene Dichlorides Identified Using Chlorine K-Edge X-Ray Absorption Spectroscopy and Time Dependent-Density Functional Theory

    SciTech Connect

    Kozimor, Stosh A.; Yang, Ping; Batista, Enrique R.; Boland, Kevin S.; Burns, Carol J.; Clark, David L.; Conradson, Steven D.; Martin, Richard L.; Wikerson, Marianne P.; Wolfsberg, Laura E.

    2009-09-02

    We describe the use of Cl K-edge X-ray Absorption Spectroscopy (XAS) and both ground state and time-dependent hybrid density functional theory (DFT) to probe electronic structure and determine the degree of orbital mixing in M-Cl bonds for (C5Me5)2MCl2 (M = Ti, 1; Zr, 2; Hf, 3; Th, 4; and U, 5), where we can directly compare a class of structurally similar compounds for d- and f-elements. We report direct experimental evidence for covalency in M-Cl bonding, including actinides, and offer insight into the relative roles of the valence f- and dorbitals in these systems. The Cl K-edge XAS data for the group IV transition metals, 1 – 3, show slight decreases in covalency in M-Cl bonding with increasing principal quantum number, in the order Ti > Zr > Hf. The percent Cl 3p character per M-Cl bond was experimentally determined to be 25, 23, and 22% per M-Cl bond for 1-3, respectively. For actinides, we find a shoulder on the white line for (C5Me5)2ThCl2, 4, and distinct, but weak pre-edge features for 2 (C5Me5)2UCl2, 5. The percent Cl 3p character in Th-Cl bonds in 4 was determined to be 14 %, with high uncertainty, while the U-Cl bonds in 5 contains 9 % Cl 3p character. The magnitudes of both values are approximately half what was observed for the transition metal complexes in this class of bent metallocene dichlorides. Using the hybrid DFT calculations as a guide to interpret the experimental Cl K-edge XAS, these experiments suggest that when evaluating An- Cl bonding, both 5f- and 6d-orbitals should be considered. For (C5Me5)2ThCl2, the calculations and XAS indicate that the 5f- and 6d-orbitals are nearly degenerate and heavily mixed. In contrast, the 5f- and 6d-orbitals in (C5Me5)2UCl2 are no longer degenerate, and fall in two distinct energy groupings. The 5f-orbitals are lowest in energy and split into a 5-over-2 pattern with the high lying U 6d-orbitals split in a 4-over-1 pattern, the latter of which is similar to the dorbital splitting in group IV transition

  4. 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.

  5. 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

  6. Experimental and Theoretical Comparison of the O K-Edge Non-Resonant Inelastic X-ray Scattering and X-ray Absorption Spectra of NaReO4

    SciTech Connect

    Bradley, Joseph A.; Yang, Ping; Batista, Enrique R.; Boland, Kevin S.; Burns, Carol J.; Clark, David L.; Conradson, Steven D.; Kozimor, Stosh A.; Martin, Richard L.; Seidler, Gerald T.; Scott, Brian L.; Shuh, David K.; Tyliszczak, T.; Wilkerson, Marianne P.; Wolfsberg, Laura E.

    2010-09-14

    Accurate X-ray absorption spectra (XAS) of first row atoms, e.g. O, are notoriously difficult to obtain due to the extreme sensitivity of the measurement to surface contamination, self-absorption, and saturation effects. Herein, we describe a comprehensive approach for determining reliable O K-edge XAS data for ReO41- and provide methodology for obtaining trustworthy and quantitative data on non-conducting molecular systems, even in the presence of surface contamination. This involves comparing spectra measured by non-resonant inelastic X-ray scattering (NRIXS), a bulk-sensitive technique that is not prone to X-ray self-absorption and provides exact peak intensities, with XAS spectra obtained by three different detection modes, namely total electron yield (TEY), fluorescence yield (FY), and scanning transmission X-ray microscopy (STXM). For ReO41-, TEY measurements were heavily influenced by surface contamination, while the FY and STXM data agree well with the bulk NRIXS analysis. These spectra all showed two intense pre-edge features indicative of the covalent interaction between the Re 5d and O 2p orbitals. Time dependent density functional theory calculations were used to assign these two peaks as O 1s excitations to the e and t2 molecular orbitals that result from Re 5d and O 2p covalent mixing in Td symmetry. Electronic structure calculations were used to determine the amount of O 2p character (%) in these molecular orbitals. Time-dependent density functional theory (TD-DFT) was also used to calculate the energies and intensities of the pre-edge transitions. Overall, under these experimental conditions, this analysis suggests that NRIXS, STXM, and FY operate cooperatively, providing a sound basis for validation of bulk-like excitation spectra and, in combination with electronic structure calculations, suggest that NaReO4 may serve as a well-defined O K-edge energy and intensity standard for future O K edge XAS studies.

  7. Experimental and Theoretical Comparison of the O K-Edge Nonresonant Inelastic X-ray Scattering and X-ray Absorption Spectra of NaReO[subscript 4

    SciTech Connect

    Bradley, Joseph A.; Yang, Ping; Batista, Enrique R.; Boland, Kevin S.; Burns, Carol J.; Clark, David L.; Conradson, Steven D.; Kozimor, Stosh A.; Martin, Richard L.; Seidler, Gerald T.; Scott, Brian L.; Shuh, David K.; Tyliszczak, Tolek; Wilkerson, Marianne P.; Wolfsberg, Laura E.

    2010-12-07

    Accurate X-ray absorption spectra (XAS) of first row atoms, e.g., O, are notoriously difficult to obtain due to the extreme sensitivity of the measurement to surface contamination, self-absorption, and saturation affects. Herein, we describe a comprehensive approach for determining reliable O K-edge XAS data for ReO{sub 4}{sup 1-} and provide methodology for obtaining trustworthy and quantitative data on nonconducting molecular systems, even in the presence of surface contamination. This involves comparing spectra measured by nonresonant inelastic X-ray scattering (NRIXS), a bulk-sensitive technique that is not prone to X-ray self-absorption and provides exact peak intensities, with XAS spectra obtained by three different detection modes, namely total electron yield (TEY), fluorescence yield (FY), and scanning transmission X-ray microscopy (STXM). For ReO{sub 4}{sup 1-}, TEY measurements were heavily influenced by surface contamination, while the FY and STXM data agree well with the bulk NRIXS analysis. These spectra all showed two intense pre-edge features indicative of the covalent interaction between the Re 5d and O 2p orbitals. Density functional theory calculations were used to assign these two peaks as O 1s excitations to the e and t{sub 2} molecular orbitals that result from Re 5d and O 2p covalent mixing in T{sub d} symmetry. Electronic structure calculations were used to determine the amount of O 2p character (%) in these molecular orbitals. Time dependent-density functional theory (TD-DFT) was also used to calculate the energies and intensities of the pre-edge transitions. Overall, under these experimental conditions, this analysis suggests that NRIXS, STXM, and FY operate cooperatively, providing a sound basis for validation of bulk-like excitation spectra and, in combination with electronic structure calculations, suggest that NaReO{sub 4} may serve as a well-defined O K-edge energy and intensity standard for future O K-edge XAS studies.

  8. 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.

  9. 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.

  10. 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.

  11. The new ID21 XANES full-field end-station at ESRF

    NASA Astrophysics Data System (ADS)

    Fayard, B.; Pouyet, E.; Berruyer, G.; Bugnazet, D.; Cornu, C.; Cotte, M.; De Andrade, V.; Di Chiaro, F.; Hignette, O.; Kieffer, J.; Martin, T.; Papillon, E.; Salomé, M.; Sole, V. A.

    2013-03-01

    A new X-ray absorption near-edge spectroscopy (XANES) full-field imaging station has been developed, installed and tested on beamline ID21 at the European Synchrotron Radiation Facility (ESRF). The set-up operates in the 2-9 keV energy range and allows for the simultaneous acquisition of up to 4.106 XANES spectra over large sample areas with preserved sub-micron spatial resolution. The versatile set-up is compatible with various types of cameras and magnifying objectives. It accommodates spatial resolutions ranging from 0.3 μm to 1.4 μm and fields of view from 600 μm up to 2 mm. The range of potential applications is broad: from geology, cultural heritage, environmental sciences to medicine.

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

    PubMed

    Hughes-Currie, Rosa B; Ivanovskikh, Konstantin V; R Wells, Jon-Paul; 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. PMID:26941175

  13. 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.

  14. Ni K-Edge XAS Suggests that Coordination of Ni II to the Unstructured Amyloidogenice Region of the Human Prion Protein Produces a Ni2 bis-u-hydroxo Dimer

    SciTech Connect

    Shearer,J.; Soh, P.

    2007-01-01

    Prion diseases are thought to be caused by the misfolding of the ubiquitous neuronal membrane prion protein (PrP) through an unknown mechanism that may involve Cu{sup II} coordination to the PrP. Previous work has utilized Ni{sup II} as a diamagnetic probe for Cu{sup II} coordination [C.E. Jones, M. Klewpatinond, S.R. Abdelraheim, D.R. Brown, J.H. Viles, J. Mol. Biol. 346 (2005) 1393-1407]. Herein we investigate Ni{sup II} coordination to the PrP fragment PrP(93-114) (AcN-GGTHSQWNKPSKPKTNMKHMAG) at pH = 10.0 by Ni K-edge X-ray absorption spectroscopy (XAS). We find that two equivalents of Ni{sup II} will coordinate to PrP(93-114) by UV/Vis titrations and mass spectrometry. Ni K-edge XAS data is consistent with Ni{sup II} ligated by five N/O based ligands (three N/O ligands at 2.01(2) {angstrom} and two at 1.855(2) {angstrom}). We were also able to locate a Ni-Ni vector at 3.1(1) {angstrom}, which suggests the two Ni{sup II} centers are contained in a bis-{mu}-hydroxo dimer. We therefore suggest that Ni{sup II} may not be a suitable diamagnetic mimic for Cu{sup II} coordination within the PrP since differential coordination modes for the two metals exist.

  15. 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.

  16. XANES analysis of organic residues produced from the UV irradiation of astrophysical ice analogs

    NASA Astrophysics Data System (ADS)

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

    2011-09-01

    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 nitrogen- and 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.

  17. Use of synchrotron XANES and Cr-doped coal to further confirm the vaporization of organically bound Cr and the formation of chromium(VI) during coal oxy-fuel combustion.

    PubMed

    Chen, Juan; Jiao, Facun; Zhang, Lian; Yao, Hong; Ninomiya, Yoshihiko

    2012-03-20

    Through the use of synchrotron XANES and Cr-doped brown coal, extensive efforts have been made to clarify the volatility of organically bound Cr during oxy-fuel combustion and the mode of occurrence and leachability of Cr in resulting fly ashes. As the continuation of our previous study using raw coal, the Cr-doped coal has been tested in this study to improve the signal-to-noise ratio for Cr K-edge XANES spectra, and hence the accuracy for Cr(VI) quantification. As has been confirmed, the abundant CO(2) as a balance gas for oxy-firing has the potential to inhibit the decomposition of organically bound Cr, thereby favoring its retention in solid ash. It also has the potential to promote the oxidation of Cr(III) to Cr(VI) to a minor extent. Increasing the oxygen partial pressure, particularly in the coexistence of HCl in flue gas, favored the oxidation of Cr(III) into gaseous Cr(VI)-bearing species such as CrO(2)Cl(2). Regarding the solid impurities including Na(2)SO(4) and CaO, Na(2)SO(4) has proven to preferentially capture the Cr(III)-bearing species at a low furnace temperature such as 600 °C. Its promoting effect on the oxidation of Cr(III) to Cr(VI), although thermodynamically available at the temperatures examined here, is negligible in a lab-scale drop tube furnace (DTF), where the particle residence time is extremely short. In contrast, CaO has proven facilitating the capture of Cr(VI)-bearing species particularly oxychloride vapors at 1000 °C, forming Ca chromate with the formulas of CaCrO(4) and Ca(3)(CrO(4))(2) via a direction stabilization of Cr(VI) oxychloride vapor by CaO particle or an indirect oxidation of Cr(III) via the initial formation of Ca chromite. The fly ash collected from the combustion of Cr-doped coal alone has a lower water solubility (i.e., 58.7%) for its Cr(VI) species, due to the formation of Ba/Pb chromate and/or the incorporation of Cr(VI) vapor into a slagging phase which is water-insoluble. Adding CaO to coal increased the

  18. The Speciation of Arsenic in Iron Oxides in Mine Wastes from the Giant Gold Mine, N.W.T.: Application of Synchrotron Micro-XRD and Micro-XANES at the Grain Scale

    SciTech Connect

    Walker,S.; Jamieson, H.; Lanzirotti, A.; Andrade, C.; Hall, G.

    2005-01-01

    Understanding the solid-phase speciation of arsenic in soils and sediments is important in evaluations of the potential mobility of arsenic and of its bio-availability in the environment. This is especially true in mine-influenced environments, where arsenic commonly is present at concentrations two and three orders of magnitude above quality criteria for soils and sediments. Arsenic-bearing particulates dispersed through hydraulic transport or aerosol emissions can represent a persistent source of contamination in sediments and soils adjacent to past mining and metallurgical operations. The stability and mobility of arsenic associated with these phases depend on the chemical form and oxidation state of the arsenic and the interaction with post-depositional geochemical conditions. The Giant mine in Yellowknife, Northwest Territories, roasted arsenic-bearing gold ore from 1949 to 1999. The roasting process decomposed arsenic-bearing sulfides (pyrite and arsenopyrite) to produce a calcine containing fine (generally <50 {micro}m) arsenic-bearing iron oxides. We have applied synchrotron As K-edge micro X-ray Absorption Near-Edge Structure ({micro}XANES) and {micro}XRD as part of a grain-by-grain mineralogical approach for the direct determination of the host mineralogy and oxidation state of As in these roaster-derived iron oxides. The grain-scale approach has resolved potential ambiguities that would have existed had only bulk XANES and XRD methods been applied. Using combined optical microscopy, electron microprobe and {micro}XRD, we have determined that the roaster-iron oxides are nanocrystalline grains of maghemite containing <0.5 to 7 wt.% As. Some of these arsenic-bearing nanocrystalline grains are a mixture of maghemite and hematite. All roaster iron oxides, including those present in 50-year-old tailings, contain mixtures of As{sup 5+} and As{sup 3+}. The persistence of As{sup 3+} in roaster-derived maghemite in shallow subareal (oxidized) shoreline tailings

  19. Micro-XANES Measurements on Experimental Spinels and the Oxidation State of Vanadium in Coexisting Spinel and Silicate Melt

    NASA Technical Reports Server (NTRS)

    Righter, K.; Sutton, S. R.; Newville, M.; Le. L.; Schwandt, C. S.

    2005-01-01

    Spinel can be a significant host phase for V which has multiple oxidation states V(sup 2+), V(sup 3+), V(sup 4+) or V(sup 5+) at oxygen fugacities relevant to natural systems. The magnitude of D(V) spinel/melt is known to be a function of composition, temperature and fO2, but the uncertainty of the oxidation state under the range of natural conditions has made elusive a thorough understanding of D(V) spinel/melt. For example, V(sup 3+) is likely to be stable in spinels, based on exchange with Al in experiments in the CaO-MgO-Al2O3-SiO2 system. On the other hand, it has been argued that V(sup 4+) will be stable across the range of natural oxygen fugacities in nature. In order to build on our previous work in more oxidized systems, we have carried out experiments at relatively reducing conditions from the FMQ buffer to 2 log fO2 units below the IW buffer. These spinel-melt pairs, where V is present in the spinel at natural levels (approx. 300 ppm V), were analyzed using an electron microprobe at NASA-JSC and micro- XANES at the Advanced Photon Source at Argonne National Laboratory. The new results will be used together with previous results to understand the valence of V in spinel-melt systems across 12 orders of magnitude of oxygen fugacity, and with application to natural systems.

  20. Using Solution- and Solid-State S K-edge X-ray Absorption Spectroscopy with Density Functional Theory to Evaluate M–S Bonding for MS42- (M = Cr, Mo, W) Dianions

    PubMed Central

    Olson, Angela C.; Keith, Jason M.; Batista, Enrique R.; Boland, Kevin S.; Daly, Scott R.; Kozimor, Stosh A.; MacInnes, Molly M.; Martin, Richard L.; Scott, Brian L.

    2014-01-01

    Herein, we have evaluated relative changes in M–S electronic structure and orbital mixing in Group 6 MS42- dianions using solid- and solution-phase S K-edge X-ray absorption spectroscopy (XAS; M = Mo, W), as well as density functional theory (DFT; M = Cr, Mo, W) and time-dependent density functional theory (TDDFT) calculations. To facilitate comparison with solution measurements (conducted in acetonitrile), theoretical models included gas-phase calculations as well as those that incorporated an acetonitrile dielectric, the latter of which provided better agreement with experiment. Two pre-edge features arising from S 1s → e* and t2* electron excitations were observed in the S K-edge XAS spectra and were reasonably assigned as 1A1 → 1T2 transitions. For MoS42-, both solution-phase pre-edge peak intensities were consistent with results from the solid-state spectra. For WS42-, solution- and solid-state pre-edge peak intensities for transitions involving e* were equivalent, while transitions involving the t2* orbitals were less intense in solution. Experimental and computational results have been presented in comparison to recent analyses of MO42- dianions, which allowed M–S and M–O orbital mixing to be evaluated as the principle quantum number (n) for the metal valence d orbitals increased (3d, 4d, 5d). Overall, the M–E (E = O, S) analyses revealed distinct trends in orbital mixing. For example, as the Group 6 triad was descended, e* (π*) orbital mixing remained constant in the M–S bonds, but increased appreciably for M–O interactions. For the t2* orbitals (σ* + π*), mixing decreased slightly for M–S bonding and increased only slightly for the M–O interactions. These results suggested that the metal and ligand valence orbital energies and radial extensions delicately influenced the orbital compositions for isoelectronic ME42- (E = O, S) dianions. PMID:25311904

  1. Using solution- and solid-state S K-edge X-ray absorption spectroscopy with density functional theory to evaluate M-S bonding for MS4(2-) (M = Cr, Mo, W) dianions.

    PubMed

    Olson, Angela C; Keith, Jason M; Batista, Enrique R; Boland, Kevin S; Daly, Scott R; Kozimor, Stosh A; MacInnes, Molly M; Martin, Richard L; Scott, Brian L

    2014-12-14

    Herein, we have evaluated relative changes in M-S electronic structure and orbital mixing in Group 6 MS4(2-) dianions using solid- and solution-phase S K-edge X-ray absorption spectroscopy (XAS; M = Mo, W), as well as density functional theory (DFT; M = Cr, Mo, W) and time-dependent density functional theory (TDDFT) calculations. To facilitate comparison with solution measurements (conducted in acetonitrile), theoretical models included gas-phase calculations as well as those that incorporated an acetonitrile dielectric, the latter of which provided better agreement with experiment. Two pre-edge features arising from S 1s → e* and t electron excitations were observed in the S K-edge XAS spectra and were reasonably assigned as (1)A1 → (1)T2 transitions. For MoS4(2-), both solution-phase pre-edge peak intensities were consistent with results from the solid-state spectra. For WS4(2-), solution- and solid-state pre-edge peak intensities for transitions involving e* were equivalent, while transitions involving the t orbitals were less intense in solution. Experimental and computational results have been presented in comparison to recent analyses of MO4(2-) dianions, which allowed M-S and M-O orbital mixing to be evaluated as the principle quantum number (n) for the metal valence d orbitals increased (3d, 4d, 5d). Overall, the M-E (E = O, S) analyses revealed distinct trends in orbital mixing. For example, as the Group 6 triad was descended, e* (π*) orbital mixing remained constant in the M-S bonds, but increased appreciably for M-O interactions. For the t orbitals (σ* + π*), mixing decreased slightly for M-S bonding and increased only slightly for the M-O interactions. These results suggested that the metal and ligand valence orbital energies and radial extensions delicately influenced the orbital compositions for isoelectronic ME4(2-) (E = O, S) dianions. PMID:25311904

  2. 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.

  3. Chromium in urban sediment particulates: an integrated micro-chemical and XANES study

    NASA Astrophysics Data System (ADS)

    Taylor, Kevin; Byrne, Patrick; Hudson-Edwards, Karen

    2015-04-01

    Chromium is generally common within the urban sediment cascade as a result of abundant industrial and transport-related sources. The risks that Cr-bearing particles pose to ecosystems and humans depend on the solid phase chemical speciation of Cr in the particles. In this study, we use bulk chemical digests, sequential chemical extraction analysis, electron microscopy, electron microprobe and microfocus XANES analysis to describe the solid-phase speciation of Cr in urban particulate matter from both aquatic sediment and road dust sediment (RDS) in Manchester, UK. Cr-bearing grains within RDS are predominantly iron oxide grains, commonly of goethite or haematite mineralogy, but Cr-bearing silicate glass grains are also present. Iron oxide glass grains most likely have sorbed Cr, and derive from the rusting of Cr-steel particles from vehicles. Electron microprobe analysis indicates concentrations of Cr up to 3200 μg/g in these grains, and XANES analysis indicates that Cr(III) is the dominant oxidation state, with some trace amounts of Cr(VI). Cr-bearing grains within aquatic sediments are dominated by alumino-silicate glass grains derived from industrial waste. These grains contain Cr-rich areas with up to 19% Cr2O3 and XANES analysis indicates that Cr is present as Cr(III). The dominance of Cr(III) in these urban particulate grains suggests limited bioavailability or toxicity. However, the presence within two markedly different grain types (iron oxides and silicate glasses) indicates that the long-term geochemical behaviour and environmental risk of RDS and the aquatic sediments studied are likely to be quite different. These findings highlight the importance of understanding sources of metal contaminants in urban environments and the geochemical processes that affect their transfer through the urban sediment cascade and the wider river basin.

  4. 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.

  5. 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. PMID:21997917

  6. Pd nanoparticles formation inside porous polymeric scaffolds followed by in situ XANES/SAXS

    NASA Astrophysics Data System (ADS)

    Longo, A.; Lamberti, C.; Agostini, G.; Borfecchia, E.; Lazzarini, A.; Liu, W.; Giannici, F.; Portale, G.; Groppo, E.

    2016-05-01

    Simultaneous time-resolved SAXS and XANES techniques were employed to follow in situ the formation of Pd nanoparticles from palladium acetate precursor in two porous polymeric supports: polystyrene (PS) and poly(4-vinyl-pyridine) (P4VP). In this study we have investigated the effect of the use of different reducing agents (H2 and CO) from the gas phase. These results, in conjunction with data obtained by diffuse reflectance IR (DRIFT) spectroscopy and TEM measurements, allowed us to unravel the different roles played by gaseous H2 and CO in the formation of the Pd nanoparticles for both PS and P4VP hosting scaffolds.

  7. Polarized XANES studies on the mechanical rubbing effect of poly(tetrafluoroethylene) and its model compound

    NASA Astrophysics Data System (ADS)

    Nagayama, K.; Mitsumoto, R.; Araki, T.; Ouchi, Y.; Seki, K.

    1995-02-01

    The structural change of the evaporated perfluorotetracosane (PFT) n-CF 3 (CF 2) 22CF 3 and poly(tetrafluoroethylene) (PTFE) (CF 2) n films by the mechanical rubbing process was examined with use of XANES spectroscopy. In the PTFE film the chains were almost parallel to the surface and were uniaxially realigned along the rubbing direction, while in the PFT film the chains after evaporation were oriented normal to the surface, and this orientation was hardly affected by the rubbing process. The chains of the PFT evaporated on the rubbed PTFE film aligned along the rubbing direction.

  8. Sulfur K-edge X-ray Absorption Spectroscopy and Density Functional Calculations on Mo(IV) and Mo(VI)=O Bis-dithiolenes: Insights into the Mechanism of Oxo Transfer in DMSO Reductase and Related Functional Analogues

    PubMed Central

    Tenderholt, Adam L.; Wang, Jun-Jieh; Szilagyi, Robert K.; Holm, Richard H.; Hodgson, Keith O.; Hedman, Britt; Solomon, Edward I.

    2010-01-01

    Sulfur K-edge X-ray absorption spectroscopy (XAS) and density functional theory (DFT) calculations have been used to determine the electronic structures of two Mo bis-dithiolene complexes, [Mo(OSi)(bdt)2]1− and [MoO(OSi)(bdt)2]1− where OSi = [OSiPh2tBu]1− and bdt = benzene-1,2-dithiolate(2−), that model the Mo(IV) and Mo(VI)=O states of the DMSO reductase family of molybdenum enzymes. These results show that the Mo(IV) complex undergoes metal-based oxidation unlike the Mo(IV) tris-dithiolene complexes, indicating that the dithiolene ligands are behaving innocently. Experimentally-validated calculations have been extended to model the oxo-transfer reaction coordinate using dimethylsulfoxide (DMSO) as a substrate. The reaction proceeds through a transition state (TS1) to an intermediate with DMSO weakly bound, followed by a subsequent transition state (TS2) which is the largest barrier of the reaction. The factors that control the energies of these transition states, the nature of the oxo transfer process, and the role of the dithiolene ligand are discussed. PMID:20499905

  9. Sulfur K-Edge XAS and DFT Calculations on [Fe4S4]2+Clusters: Effects of H-bonding and Structural Distortion on Covalency and SpinTopology

    SciTech Connect

    Dey, A.; Roche, C.L.; Walters, M.A.; Hodgson, K.O.; B., Hedman; Solomon, E.I.; /Stanford U., Chem. Dept. /SLAC, SSRL

    2006-09-28

    Sulfur K-edge X-ray absorption spectroscopy of a hydrogen-bonded elongated [Fe{sub 4}S{sub 4}]{sup 2+} cube is reported. The data show that this synthetic cube is less covalent than a normal compressed cube with no hydrogen bonding. DFT calculations reveal that the observed difference in electronic structure has significant contributions from both the cluster distortion and from hydrogen bonding. The elongated and compressed Fe{sub 4}S{sub 4} structures are found to have different spin topologies (i.e., orientation of the delocalized Fe{sub 2}S{sub 2} subclusters which are antiferromagnetically coupled to each other). It is suggested that the H-bonding interaction with the counterion does not contribute to the cluster elongation. A magneto-structural correlation is developed for the Fe{sub 4}S{sub 4} cube that is used to identify the redoxactive Fe{sub 2}S{sub 2} subclusters in active sites of HiPIP and ferredoxin proteins involving these clusters.

  10. Anisotropy of Chemical Bonds in Collagen Molecules Studied by X-ray Absorption Near-Edge Structure (XANES) Spectroscopy

    PubMed Central

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

    2012-01-01

    Collagen type I fibrils are the major building blocks of connective tissues. Collagen fibrils are anisotropic supra-molecular 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. PMID:22148847

  11. Metallization of warm dense SiO(2) studied by XANES spectroscopy.

    PubMed

    Denoeud, A; Benuzzi-Mounaix, A; Ravasio, A; Dorchies, F; Leguay, P M; Gaudin, J; Guyot, F; Brambrink, E; Koenig, M; Le Pape, S; Mazevet, S

    2014-09-12

    We investigate the evolution of the electronic structure of fused silica in a dense plasma regime using time-resolved x-ray absorption spectroscopy. We use a nanosecond (ns) laser beam to generate a strong uniform shock wave in the sample and a picosecond (ps) pulse to produce a broadband x-ray source near the Si K edge. By varying the delay between the two laser beams and the intensity of the ns beam, we explore a large thermodynamical domain with densities varying from 1 to 5  g/cm^{3} and temperatures up to 5 eV. In contrast to normal conditions where silica is a well-known insulator with a wide band gap of 8.9 eV, we find that shocked silica exhibits a pseudogap as a semimetal throughout this thermodynamical domain. This is in quantitative agreement with density functional theory predictions performed using the generalized gradient approximation. PMID:25259992

  12. 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.

  13. XANES studies of photocatalytic active species in nano TiO 2-SiO 2

    NASA Astrophysics Data System (ADS)

    Li Hsiung, Tung; Paul Wang, H.; Wang, H. C.

    2006-11-01

    Combined post-edge XANES (X-ray absorption near-edge structural) and 29Si magic angle spinning solid-state nuclear magnetic resonance (MAS SSNMR) observations show that Ti was dispersed in the frameworks of nano SiO 2 (synthesized with the sol-gel method). In addition, the nano TiO 2-SiO 2 photocatalyst have features such as A1 (4969 eV), A2 (4970.5 eV) and A3 (4972 eV) that can be attributed to 1s-to-3d transitions for four- (TiO 4), five- ((Ti=O)O 4), and six- (TiO 6) coordinated Ti species, respectively. The A2 ((Ti=O)O 4) in TiO 2-SiO 2 may be the main active species, for instance, in the photocatalytic decomposition of trace 2-chlorophenol in H 2O. This work exemplifies the utilization of XANES to reveal the active species in nano photocatalysts in detail.

  14. Spectral analysis by XANES reveals that GPNMB influences the chemical composition of intact melanosomes

    PubMed Central

    Haraszti, Tamas; Trantow, Colleen M.; Hedberg-Buenz, Adam; Grunze, Michael; Anderson, Michael G.

    2010-01-01

    Summary 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 to 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. Significance Of the large number of proteins known to be present in melanosomes, the majority are not known to visibly influence melanosome appearance. It remains largely unknown what role, if any, most of these proteins may have in pigment cell biology. This work demonstrates an approach for discovering previously undetectable melanosomal phenotypes through a combined use of synchrotron-based spectromicroscopy and genetics. Specifically, we demonstrate that GPNMB influences the carbon absorption spectra of melanosomes. A similar strategy might also be applied to discover new features of a wide range of additional organelles important to human health and disease. PMID:21029394

  15. Growth of Au@Pt coreshell nanoparticles: Probed by in-situ XANES and UV-visible spectroscopy

    NASA Astrophysics Data System (ADS)

    Nayak, C.; Bhattacharyya, K.; Tripathi, A. K.; Jha, S. N.; Bhattacharyya, D.; Sahoo, N. K.

    2016-05-01

    Au@Pt core shell nanoparticles have been synthesized by reducing Au and Pt chloride precursors with Block Co-polymer and Ascorbic acid. The growth and nucleation of Au@Pt nanoparticles have been investigated by in-situ time resolved XANES measurement which gives the evolution of the reduction process of the precursors. Linear combination fitting of the XANES spectra has been carried out to find the fraction of Au and Pt cations reduced at a particular reaction time. UV-Visible spectroscopy is used as a complementary technique which gives the changes in the Au SPR peak as Au@Pt core shell nanoparticles are formed.

  16. Valence state partitioning of V between pyroxene-melt: Effects of pyroxene and melt composition, and direct determination of V valence states by XANES. Application to Martian basalt QUE 94201 composition

    SciTech Connect

    Karner, J.M.; Papike, J.J.; Sutton, S.R.; Shearer, C.K.; Burger, P.; McKay, G.; Le, L.

    2009-01-13

    Experiments on a Martian basalt composition show that D{sub V} augite/melt is greater than D{sub V} pigeonite/melt in samples equilibrated under the same fO{sub 2} conditions. This increase is due to the increased availability of elements for coupled substitution with the V{sup 3+} or V{sup 4+} ions, namely Al and Na. for this bulk composition, both Al and Na are higher in concentration in augite compared with pigeonite; therefore more V can enter augite than pigeonite. Direct valence state determination by XANES shows that the V{sup 3+} and V{sup 4+} are the main V species in the melt at fO{sub 2} conditions of IW-1 to IW+3.5, whereas pyroxene grains at IW-1, IW, and IW+1 contain mostly V{sup 3+}. This confirms the idea that V{sup 3+} is more compatible in pyroxene than V{sup 4+}. The Xanes data also indicates that a small percentage of V{sup 2+} may exist in melt and pyroxene at IW-1. The similar valence of V in glass and pyroxene at IW-1 suggests that V{sup 2+} and V{sup 3+} may have similar compatibilities in pyroxene.

  17. Sulfur K-edge XAS and DFT Studies on NiII Complexes with Oxidized Thiolate Ligands: Implications for the Roles of Oxidized Thiolates in the Active Sites of Fe and Co Nitrile Hydratase

    PubMed Central

    Dey, Abhishek; Jeffrey, Stephen P.; Darensbourg, Marcetta; Hodgson, Keith O.; Hedman, Britt; Solomon, Edward I.

    2008-01-01

    S K-edge XAS data on a series of NiII complexes with thiolate (RS−) and oxidized thiolate (RSO2−) ligands are used to quantify Ni-S bond covalency and its change upon ligand oxidation. Analyses of these results using geometry optimized DFT calculations suggest that the Ni-S σ bonds do not weaken on ligand oxidation. Molecular orbital analysis indicates that these oxidized thiolate ligands use filled high lying S-O π* orbitals for strong σ donation. However, the RSO2− ligands are poor π donors as the orbital required for π interaction is is used in the S-O σ bond formation. The oxidation of the thiolate reduces the repulsion between electrons in the filled Ni t2 orbital and the thiolate out of plane π-donor orbital leading to shorter Ni-S bond length relative to a thiolate donor. The insights obtained from these results are relevant to the active sites of Fe and Co type nitrile hydratases (Nhase) that also have oxidized thiolate ligands. DFT calculations on models of the active site indicate that while the oxidation of these thiolates has a major effect in the axial ligand binding affinity of the Fe type Nhase (where there is both σ and π donation from the S ligands), it has only a limited effect on the sixth ligand binding affinity of the Co type Nhases (where there is only σ donation). These oxidized residues may also play a role in substrate binding and proton shuttling at the active site. PMID:17500514

  18. Low-Dose-Rate Computed Tomography System Utilizing 25 mm/s-Scan Silicon X-ray Diode and Its Application to Iodine K-Edge Imaging Using Filtered Bremsstrahlung Photons

    NASA Astrophysics Data System (ADS)

    Matsushita, Ryo; Sato, Eiichi; Yanbe, Yutaka; Chiba, Hiraku; Maeda, Tomoko; Hagiwara, Osahiko; Matsukiyo, Hiroshi; Osawa, Akihiro; Enomoto, Toshiyuki; Watanabe, Manabu; Kusachi, Shinya; Sato, Shigehiro; Ogawa, Akira; Onagawa, Jun

    2013-03-01

    A low-dose-rate X-ray computed tomography (CT) system is useful for reducing absorbed dose for patients. The CT system with a tube current of sub-mA was developed using a silicon X-ray diode (Si-XD). The Si-XD is a high-sensitivity Si photodiode (PD) selected for detecting X-ray photons, and the X-ray sensitivity of the Si-XD was twice as high as that of Si-PD cerium-doped yttrium aluminum perovskite [YAP(Ce)]. X-ray photons are directly detected using the Si-XD without a scintillator, and the photocurrent from the diode is amplified using current-voltage and voltage-voltage amplifiers. The output voltage is converted into logical pulses using a voltage-frequency converter with a maximum frequency of 500 kHz, and the frequency is proportional to the voltage. The pulses from the converter are sent to the differentiator with a time constant of 500 ns to generate short positive pulses for counting, and the pulses are counted using a counter card. Tomography is accomplished by repeated linear scans and rotations of an object, and projection curves of the object are obtained by the linear scan. The exposure time for obtaining a tomogram was 5 min at a scan step of 0.5 mm and a rotation step of 3.0°. The tube current and voltage were 0.55 mA and 60 kV, respectively, and iodine K-edge CT was carried out using filtered bremsstrahlung X-ray spectra with a peak energy of 38 keV.

  19. Quantifying X-Ray Pleochroism Effects in Synchrotron Micro-XANES Microanalyses of Elemental Oxidation States: Feldspar and Biotite

    NASA Technical Reports Server (NTRS)

    Delaney, J. S.; Dyar, M. D.; Sutton, S. R.

    2001-01-01

    X-ray pleochroism is a predictable source of scatter in synchrotron microXANES analyses of elemental oxidation states. The magnitude of the effect is illustrated and a procedure to compensate for it has been implemented, reducing errors significantly. Additional information is contained in the original extended abstract.

  20. Interpretation of Fe-XANES Pre-Edge Spectra: Predictions Based on Co and Fe Optical Spectra

    NASA Technical Reports Server (NTRS)

    Dyar, M. D.; Rossman, G. R.; Delaney, J. S.; Sutton, S. R.; Newville, M.

    2001-01-01

    Microanalysis of Fe-3+/Total(Fe) in extraterrestrial samples is important due to sample size constraints of sample return missions. We compare Fe XANES spectra with Co optical spectra that predict valence electron levels based on 'Z1' model. Additional information is contained in the original extended abstract.

  1. Characterization of the unoccupied and partially occupied states of TTF-TCNQ by XANES and first-principles calculations

    NASA Astrophysics Data System (ADS)

    Fraxedas, J.; Lee, Y. J.; Jiménez, I.; Gago, R.; Nieminen, R. M.; Ordejón, P.; Canadell, E.

    2003-11-01

    We report a combined experimental and theoretical study of the unoccupied electronic states of the neutral molecular organic materials TTF (tetrathiafulvalene) and TCNQ (7,7,8,8-tetracyano-p-quinodimethane) and of the one-dimensional metallic charge transfer salt TTF-TCNQ. The experimental density of states (DOS) is obtained by x-ray absorption near edge spectroscopy (XANES) with synchrotron light and the predicted DOS by means of first-principles density functional theory calculations. Most of the experimentally derived element-specific XANES features can be associated to molecular orbitals of defined symmetry. Because of the planar geometry of the TTF and TCNQ molecules and the polarization of the synchrotron light, the energy dependent σ or π character of the orbitals can be inferred from angular dependent XANES measurements. The present work represents the state of the art analysis of the XANES spectra of this type of materials and points out the need for additional work in order to elucidate the governing selection rules in the excitation process.

  2. 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.

  3. 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

  4. 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

  5. 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.

  6. 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.

  7. 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.

  8. Theoretical study of sulfur L-edge XANES of thiol protected gold nanoparticles.

    PubMed

    Nardelli, A; Fronzoni, G; Stener, M

    2011-01-14

    The Scalar Relativistic-Zero Order Regular Approximation-Time Dependent Density Functional Theory has been employed to study the sulfur L-edge XANES spectrum of the [Au(25)(SCH(3))(18)](+) model cluster, with the aim to reproduce and rationalize previous experimental data. The salient experimental features are properly described by the present calculation. The model cluster contains two different types of bidentate "staple" ligand thiol fragments, and it has been possible to assign the spectral features according to the different location of the initial core orbital on one of the two different fragments. This finding suggests that in the real nanoparticle two different non-equivalent type of sulfur bidentate ligands are present, arranged with the typical staple geometry. PMID:21031214

  9. Time resolved XANES illustrates a substrate-mediated redox process in Prussian blue cultural heritage materials

    NASA Astrophysics Data System (ADS)

    Gervais, Claire; Lanquille, Marie-Angélique; Moretti, Giulia; Réguer, Solenn

    2016-05-01

    The pigment Prussian blue is studied in heritage science because of its capricious fading behavior under light exposure. We show here that XANES can be used to study the photosensitivity of Prussian blue heritage materials despite X-ray radiation damage. We used an original approach based on X-ray photochemistry to investigate in depth the redox process of Prussian blue when it is associated with a cellulosic substrate, as in cyanotypes and watercolors. By modifying cation and proton contents of the paper substrate, we could tune both rate and extent of Prussian blue reduction. These results demonstrate that the photoreduction and fading of Prussian blue is principally mediated by the substrate and its interaction with the oxygen of the environment.

  10. Vanadium K Xanes Studies of EET79001 Impact-Melt Glasses Revisited

    NASA Technical Reports Server (NTRS)

    Sutton, S. R.; Rao, M. N.; Nyquist, L. E.; Ross, D. K.

    2016-01-01

    Some impact-melt glasses in shergottites are rich in Martian atmospheric noble gases and sulfur suggesting a possible association with regolith-derived secondary mineral assemblages in the shocked samples. Previously, we studied two glasses, # 506 (Lith C in Lith A) and # 507 (Lith C in Lith B) from EET79001 [1,2] and suggested that sulfur initially existed as sulfate in the glass precursor materials and, on shock-melting of the precursors, the sulfate was reduced to sulfides in the shock glasses. To examine the validity of this hypothesis, we used V K microXANES techniques to measure the valence states of vanadium in the Lith C glasses from Lith A and Lith B in EET79001 [3] to complement and com-pare with previous analogous measurements on,78 glass (Lith C in Lith A) [4,5]. We reported the preliminary results in [3]. Vanadium is ideal for addressing the redox issue because it has multiple valence states and is a well-studied element. Vanadium in basalts exists mostly as V(sup 3+), V(sup 4+) and V(sup 5+) in terrestrial samples, mainly as V(sup 3+) with minor V(sup 2+) and minor V(sup 4+) in lunar samples and as roughly equal mixtures of V(sup 3+) and V(sup 4+) in Martian meteorites. In this report, we discuss the application of the V K XANES results to decipher the nature of shock reduction occurring in the silicate glasses during the impact process.

  11. Probing Variable Amine/Amide Ligation in NiIIN2S2 Complexes Using Sulfur K-Edge and Nickel L-Edge X-ray Absorption Spectroscopies: Implications for the Active Site of Nickel Superoxide Dismutase

    SciTech Connect

    Shearer,J.; Dehestani, A.; Abanda, F.

    2008-01-01

    Nickel superoxide dismutase (NiSOD) is a recently discovered metalloenzyme that catalyzes the disproportionation of O2* into O2 and H2O2. In its reduced state, the mononuclear NiII ion is ligated by two cis-cysteinate sulfurs, an amine nitrogen (from the protein N-terminus), and an amide nitrogen (from the peptide backbone). Unlike many small molecule and metallopeptide-based NiN2S2 complexes, S-based oxygenation is not observed in NiSOD. Herein we explore the spectroscopic properties of a series of three NiIIN2S2 complexes (bisamine-ligated (bmmp-dmed)NiII, amine/amide-ligated (NiII(BEAAM)), and bisamide-ligated (NiII(emi))2) with varying amine/amide ligation to determine the origin of the dioxygen stability of NiSOD. Ni L-edge X-ray absorption spectroscopy (XAS) demonstrates that there is a progression in ligand-field strength with (bmmp-dmed)NiII having the weakest ligand field and (NiII(emi)2) having the strongest ligand field. Furthermore, these Ni L-edge XAS studies also show that all three complexes are highly covalent with (NiII(BEEAM)) having the highest degree of metal-ligand covalency of the three compounds studied. S K-edge XAS also shows a high degree of NiS covalency in all three complexes. The electronic structures of the three complexes were probed using both hybrid-DFT and multiconfigurational SORCI calculations. These calculations demonstrate that the nucleophilic Ni(3d)/S()* HOMO of these NiN2S2 complexes progressively decreases in energy as the amide-nitrogens are replaced with amine nitrogens. This decrease in energy of the HOMO deactivates the Ni-center toward O2 reactivity. Thus, the NiS bond is protected from S-based oxygenation explaining the enhanced stability of the NiSOD active-site toward oxygenation by dioxygen.

  12. Synchrotron Micro-XANES Measurements of Vanadium Oxidation State in Glasses as a Function of Oxygen Fugacity: Experimental Calibration of Data Relevant to Partition Coefficient Determination

    NASA Technical Reports Server (NTRS)

    Delaney, J. S.; Sutton, S. R.; Newville, M.; Jones, J. H.; Hanson, B.; Dyar, M. D.; Schreiber, H.

    2000-01-01

    Oxidation state microanalyses for V in glass have been made by calibrating XANES spectral features with optical spectroscopic measurements. The oxidation state change with fugacity of O2 will strongly influence partitioning results.

  13. 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

  14. XANES measurements of the rate of radiation damage to selenomethionine side chains

    PubMed Central

    Holton, James M.

    2009-01-01

    The radiation-induced disordering of selenomethionine (SeMet) side chains represents a significant impediment to protein structure solution. Not only does the increased B-factor of these sites result in a serious drop in phasing power, but some sites decay much faster than others in the same unit cell. These radiolabile SeMet side chains decay faster than high-order diffraction spots with dose, making it difficult to detect this kind of damage by inspection of the diffraction pattern. The selenium X-ray absorbance near-edge spectrum (XANES) from samples containing SeMet was found to change significantly after application of X-ray doses of 10–100 MGy. Most notably, the sharp ‘white line’ feature near the canonical Se edge disappears. The change was attributed to breakage of the Cγ—Se bond in SeMet. This spectral change was used as a probe to measure the decay rate of SeMet with X-ray dose in cryo-cooled samples. Two protein crystal types and 15 solutions containing free SeMet amino acid were examined. The damage rate was influenced by the chemical and physical condition of the sample, and the half-decaying dose for the selenium XANES signal ranged from 5 to 43 MGy. These decay rates were 34- to 3.8-fold higher than the rate at which the Se atoms interacted directly with X-ray photons, so the damage mechanism must be a secondary effect. Samples that cooled to a more crystalline state generally decayed faster than samples that cooled to an amorphous solid. The single exception was a protein crystal where a nanocrystalline cryoprotectant had a protective effect. Lowering the pH, especially with ascorbic or nitric acids, had a protective effect, and SeMet lifetime increased monotonically with decreasing sample temperature (down to 93 K). The SeMet lifetime in one protein crystal was the same as that of the free amino acid, and the longest SeMet lifetime measured was found in the other protein crystal type. This protection was found to arise from the folded

  15. 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

  16. 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.

  17. 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.

  18. 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.

  19. Polarized XANES studies on the rubbed polyimide for liquid crystal alignment; new applicability to the tribology of the polymer systems

    NASA Astrophysics Data System (ADS)

    Ouchi, Y.; Mori, I.; Sei, M.; Ito, E.; Araki, T.; Ishii, H.; Seki, K.; Kondo, K.

    1995-02-01

    The surface structure of rubbed polyimides, which is responsible for the homogeneous alignment of liquid crystal molecules, was examined with use of polarized XANES spectroscopy. Our first experiment was conducted on the odd-even effect of BPDA- Cn (bipenyl-3,3‧,4,4‧-tetracarboxylic dianhydride/ n-alkyl diamine) type polyimide; BPDA- Cn type polyimide with even number alkylene chain induces a large LC pretilt angle and the one with odd number alkylene chain does almost 0 degree LC pretilt angle. XANES spectra have successfully revealed the surface-structure difference between odd- and even-number BPDA polyimides, one is trans-cisoid type and the other is trans-transoid type, respectively.

  20. 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.

  1. 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.

  2. EXAFS/XANES studies of plutonium-loaded sodalite/glass waste forms

    NASA Astrophysics Data System (ADS)

    Richmann, Michael K.; Reed, Donald T.; Kropf, A. Jeremy; Aase, Scott B.; Lewis, Michele A.

    2001-09-01

    A sodalite/glass ceramic waste form is being developed to immobilize highly radioactive nuclear wastes in chloride form, as part of an electrochemical cleanup process. Two types of simulated waste forms were studied: where the plutonium was alone in an LiCl/KCl matrix and where simulated fission-product elements were added representative of the electrometallurgical treatment process used to recover uranium from spent nuclear fuel also containing plutonium and a variety of fission products. Extended X-ray absorption fine structure spectroscopy (EXAFS) and X-ray absorption near-edge spectroscopy (XANES) studies were performed to determine the location, oxidation state, and particle size of the plutonium within these waste form samples. Plutonium was found to segregate as plutonium(IV) oxide with a crystallite size of at least 4.8 nm in the non-fission-element case and 1.3 nm with fission elements present. No plutonium was observed within the sodalite in the waste form made from the plutonium-loaded LiCl/KCl eutectic salt. Up to 35% of the plutonium in the waste form made from the plutonium-loaded simulated fission-product salt may be segregated with a heavy-element nearest neighbor other than plutonium or occluded internally within the sodalite lattice.

  3. Conformation Analysis of Ferrocene and Decamethylferrocene via Full-Potential Modeling of XANES and XAFS Spectra.

    PubMed

    Bourke, J D; Islam, M T; Best, S P; Tran, C Q; Wang, F; Chantler, C T

    2016-07-21

    Recent high-accuracy X-ray absorption measurements of the sandwich organometallics ferrocene (Fc) and decamethylferrocene (DmFc) at temperatures close to liquid helium are compared with new full-potential modeling of X-ray absorption fine structure (XAFS) covering the near-edge region (XANES) and above up to k = 7 Å(-1). The implementation of optimized calculations of the oscillatory part of the spectrum from the package FDMX allows detailed study of the spectra in regions of the photoelectron momentum most sensitive to differences in the molecular stereochemistry. For Fc and DmFc, this corresponds to the relative rotation of the cyclopentadienyl rings. When applied to high-accuracy XAFS of Fc and DmFc, the FDMX theory gives clear evidence for the eclipsed conformation for Fc and the staggered conformation for DmFc for frozen solutions at ca. 15 K. This represents the first clear experimental assignment of the solution structures of Fc and DmFc and reveals the potential of high-accuracy XAFS for structural analysis. PMID:27391765

  4. Synchrotron study of the formation of nanoclusters in Al{sub 2}O{sub 3}/SiO{sub x}/Al{sub 2}O{sub 3}/SiO{sub x}/ Horizontal-Ellipsis /Si(100) multilayer nanostructures

    SciTech Connect

    Turishchev, S. Yu. Terekhov, V. A.; Koyuda, D. A.; Pankov, K. N.; Ershov, A. V.; Grachev, D. A.; Mashin, A. I.; Domashevskaya, E. P.

    2013-10-15

    Al{sub 2}O{sub 3}/SiO{sub x}/Al{sub 2}O{sub 3}/SiO{sub x}/ Horizontal-Ellipsis /Si(100) multilayer nanoperiodic structures (MNS) are studied by X-ray absorption near-edge structure spectroscopy (XANES). Experimental XANES spectroscopy spectra are obtained using synchrotron radiation. The formation of Si nanoclusters in the surface layers of the structures during their high-temperature annealing is observed. The structures featured intense size-dependent photoluminescence in the wavelength region near 800 nm. At the same time, it is shown that the formation of aluminum silicates is possible. The inversion effect of the intensity of the XANES spectra during the interaction of synchrotron radiation with MNSs is revealed.

  5. XANES, EXAFS and Kbeta spectroscopic studies of the oxygen-evolving complex in Photosystem II

    SciTech Connect

    Robblee, John H.

    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 S{sub 3} {r_arrow} [S{sub 4}] {r_arrow} S{sub 0} transition. Progress in instrumentation and flash sample preparation allowed us to apply Mn K{beta} X-ray emission spectroscopy (Kb XES) to this problem for the first time. The K{beta} 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 S{sub 2} {r_arrow} S{sub 3} transition, in contrast to the S{sub 0} {r_arrow} S{sub 1} and S{sub 1} {r_arrow} S{sub 2} transitions, does not involve a Mn-centered oxidation. This is rationalized by manganese {mu}-oxo bridge radical formation during the S{sub 2} {r_arrow} S{sub 3} transition. Using extended X-ray absorption fine structure (EXAFS) spectroscopy, the local environment of the Mn atoms in the S{sub 0} state has been structurally characterized. These results show that the Mn-Mn distance in one of the di-{mu}-oxo-bridged Mn-Mn moieties increases from 2.7 {angstrom} in the S{sub 1} state to 2.85 {angstrom} in the S{sub 0} state. Furthermore, evidence is presented that shows three di-{mu}-oxo binuclear Mn{sub 2} 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 S{sub 0} state have been investigated and a characteristic ''multiline'' signal in the S{sub 0} state has been discovered in the presence of methanol. This provides the first direct confirmation that the native S{sub 0} state is paramagnetic. In addition, this signal was simulated using parameters derived from three possible oxidation states of Mn in the S{sub 0

  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. 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.

  8. 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.

  9. Identification of Martian Regolith Sulfur Components in Shergottites Using Sulfur K Xanes and Fe/S Ratios

    NASA Technical Reports Server (NTRS)

    Sutton, S. R.; Ross, D. K.; Rao, M. N.; Nyquist, L. E.

    2014-01-01

    Based on isotopic anomalies in Kr and Sm, Sr-isotopes, S-isotopes, XANES results on S-speciation, Fe/S ratios in sulfide immiscible melts [5], and major element correlations with S determined in impact glasses in EET79001 Lith A & Lith B and Tissint, we have provided very strong evidence for the occurrence of a Martian regolith component in some impact melt glasses in shergottites. Using REE measurements by LA-ICP-MS in shergottite impact glasses, Barrat and co-workers have recently reported conflicting conclusions about the occurrence of Martian regolith components: (a) Positive evidence was reported for a Tissint impact melt, but (b) Negative evidence for impact melt in EET79001 and another impact melt in Tissint. Here, we address some specific issues related to sulfur speciation and their relevance to identifying Martian regolith components in impact glasses in EET79001 and Tissint using sulfur K XANES and Fe/S ratios in sulfide immiscible melts. XANES and FE-SEM measurements in approx. 5 micron size individual sulfur blebs in EET79001 and Tissint glasses are carried out by us using sub-micron size beams, whereas Barrat and coworkers used approx. 90 micron size laser spots for LA- ICP-MS to determine REE abundances in bulk samples of the impact melt glasses. We contend that Martian regolith components in some shergottite impact glasses are present locally, and that studying impact melts in various shergottites can give evidence both for and against regolith components because of sample heterogeneity.

  10. Synchrotron x-ray fluorescence microprobe: Quantification and mapping of mixed valence state samples using micro-XANES

    SciTech Connect

    Sutton, S.R. ); Bajt, S. Department of Applied Science, Brookhaven National Laboratory, Upton, New York 11973 ); Delaney, J. ); Schulze, D. ); Tokunaga, T. )

    1995-02-01

    The synchrotron x-ray fluorescence microprobe is a valuable instrument for quantification and mapping of mixed valence state samples with high spatial resolution and elemental sensitivity. A method has been developed for quantifying the proportions of Fe[sup 2+] and Fe[sup 3+] with 100 [mu]m spatial resolution and better than 100 ppm sensitivity using x-ray absorption near-edge structure (XANES). Applications of valence state mapping have been made to selenium in water-saturated sediments and manganese associated with wheat roots attacked by the take-all fungus.

  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. Recent advances and applications in the analysis of organic C and N using soft X-ray XANES

    NASA Astrophysics Data System (ADS)

    Gillespie, A. W.; Dynes, J.; Regier, T. Z.; Boyko, T.; Chevrier, D. K.; Peak, D.

    2014-12-01

    Determining the chemical speciation of carbon and nitrogen in environmental samples is important for understanding the role of organic matter in contamination mobility and nutrient cycling. Despite these important applications, bulk soft X-ray absorption spectroscopy, particularly at the carbon K-edge has not been extensively applied to environmental samples until recently. The primary reasons for this gap is the lack of beamline endstations that are suitable for 'dirty' samples and the technical challenges related to acquiring and normalizing spectra from dilute samples. X-ray absorption spectroscopy (XAS) at the C K-edge probes the local bonding environment of C and N. Bulk XAS techniques permit for high throughput, the study of whole soils and high sampling density. These analyses are complementary to X-ray transmission microscopy (STXM) techniques which are limited by low throughput, thin particles (<100 nm) and low sampling density. In many projects, these bulk XAS measurements may be essential to understanding large scale processes in soils such as the global C cycle. Technical challenges have been largely overcome through the use of customized energy selective silicon drift detectors which enable the carbon signal to be detected separately from the signals from higher order light such as oxygen (i.e., partial fluorescence yield). Accurate normalization is now possible using the X-ray scattering signal from Au coated Si wafers as the Io. The radiation dose was minimized using a monochromator slew scanning mode in conjunction with the development of software tools to automatically sample of multiple pristine spots on a sample. Technical developments and recent applications will be presented, showing how bulk C and N XAS is now positioned to contribute significantly to advancing the characterization of organic matter in soils and environmental samples.

  13. Localization and Speciation of Arsenic in Soil and Desert Plant Parkinsonia florida using μXRF and μXANES

    PubMed Central

    Castillo-Michel, Hiram; Hernandez-Viezcas, Jose; Dokken, Kenneth M.; Marcus, Matthew A.; Peralta-Videa, Jose R.; Gardea-Torresdey, Jorge L.

    2011-01-01

    Parkinsonia florida is a plant species native to the semi-desert regions of North America. The cultivation characteristics of this shrub/tree suggest that it could be used for phytoremediation purposes in semiarid regions. This work describes, through the use of synchrotron μXRF and μXANES techniques and ICP-OES, the arsenic (As) accumulation and distribution in P. florida plants grown in two soils spiked with As at 20 mg kg-1. Plants grown in a sandy soil accumulated at least twice more As in the roots compared to plants grown in a loamy soil. The lower As accumulation in plants grown in the loamy soil corresponded to a lower concentration of As in the water soluble fraction (WSF) of this soil. LC-ICP-MS speciation analysis showed only As(V) in the WSF from all treatments. In contrast, linear combination XANES speciation analysis from the root tissues showed As mainly present in the reduced As(III) form. Moreover, a fraction of the reduced As was found coordinating to S in a form consistent with As-Cys3. The percentage of As coordinated to sulfur was smaller for plants grown in the loamy soil when compared to the sandy soil. PMID:21842861

  14. Combined in situ XRD and in situ XANES studies on the reduction behavior of a rhenium promoted cobalt catalyst.

    PubMed

    Kumar, Nitin; Payzant, E A; Jothimurugesan, K; Spivey, J J

    2011-08-28

    A 10% Co-4% Re/(2% Zr/SiO(2)) catalyst was prepared by co-impregnation using a silica support modified by 2% Zr. The catalyst was characterized by temperature programmed reduction (TPR), in situ XRD and in situ XANES analysis where it was simultaneously exposed to H(2) using a temperature programmed ramp. The results showed the two step reduction of large crystalline Co(3)O(4) with CoO as an intermediate. TPR results showed that the reduction of highly dispersed Co(3)O(4) was facilitated by reduced rhenium by a H(2)-spillover mechanism. In situ XRD results showed the presence of both, Co-hcp and Co-fcc phases in the reduced catalyst at 400 °C. However, the Co-hcp phase was more abundant, which is thought to be the more active phase as compared to the Co-fcc phase for CO hydrogenation. CO hydrogenation at 270 °C and 5 bar pressure produces no detectable change in the phases during the time of experiment. In situ XANES results showed a decrease in the metallic cobalt in the presence of H(2)/CO, which can be attributed due to oxidation of the catalyst by reaction under these conditions. PMID:21743918

  15. Chemical imaging of single catalyst particles with scanning μ-XANES-CT and μ-XRF-CT.

    PubMed

    Price, S W T; Ignatyev, K; Geraki, K; Basham, M; Filik, J; Vo, N T; Witte, P T; Beale, A M; Mosselmans, J F W

    2015-01-01

    The physicochemical state of a catalyst is a key factor in determining both activity and selectivity; however these materials are often not structurally or compositionally homogeneous. Here we report on the 3-dimensional imaging of an industrial catalyst, Mo-promoted colloidal Pt supported on carbon. The distribution of both the active Pt species and Mo promoter have been mapped over a single particle of catalyst using microfocus X-ray fluorescence computed tomography. X-ray absorption near edge spectroscopy (XANES) and extended X-ray absorption fine structure revealed a mixed local coordination environment, including the presence of both metallic Pt clusters and Pt chloride species, but also no direct interaction between the catalyst and Mo promoter. We also report on the benefits of scanning μ-XANES computed tomography for chemical imaging, allowing for 2- and 3-dimensional mapping of the local electronic and geometric environment, in this instance for both the Pt catalyst and Mo promoter throughout the catalyst particle. PMID:25407850

  16. Speciation of sulfur in humic and fulvic acids using X-ray Absorption Near-Edge Structures (XANES) spectroscopy

    SciTech Connect

    Morra, M.J.; Fendorf, S.E.; Brown, P.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. 27 refs., 4 figs., 3 tabs.

  17. 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.

  18. 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.

  19. The effect of CO2 on the speciation of bromine in low-temperature geological solutions: an XANES study.

    PubMed

    Evans, K A; Mavrogenes, J; Newville, M

    2007-03-01

    CO(2)-rich solutions are common in geological environments. An XANES (X-ray absorption near-edge structure) study of Br in CO(2)-bearing synthetic fluid inclusions has revealed that Br exhibits a strong pre-edge feature at temperatures from 298 to 423 K. Br in CO(2)-free solutions does not show such a feature. The feature becomes smaller and disappears as temperature increases, but reappears when temperature is reduced. The size of the feature increases with increasing X(CO(2)) in the fluid inclusion, where X(CO(2)) is the mole fraction of CO(2) in the solution [n(CO(2))/(n(CO(2)) + n(H(2)(O)) + n(RbBr)); n indicates the number of moles]. The pre-edge feature is similar to that shown by covalently bonded Br, but observed and calculated concentrations of plausible Br-bearing covalent compounds (Br(2), CH(3)Br and HBr) are vanishingly small. An alternative possibility is that CO(2) affects the hydration of Br sufficiently that the charge density changes to favour the 1s-p level transitions that are thought to cause the pre-edge peak. The distance between the first two post-edge maxima in the XANES also decreases with increasing X(CO(2)). This is attributed to a CO(2)-related decrease in the polarity of the solvent. The proposed causes of the observed features are not integrated into existing geochemical models; thus CO(2)-bearing solutions could be predicted poorly by such models, with significant consequences for models of geological processes such as ore-formation and metamorphism. PMID:17317924

  20. Using X-ray microscopy and Hg L3 XANES to study Hg binding in the rhizosphere of Spartina cordgrass.

    PubMed

    Patty, Cynthia; Barnett, Brandy; Mooney, Bridget; Kahn, Amanda; Levy, Silvio; Liu, Yijin; Pianetta, Piero; Andrews, Joy C

    2009-10-01

    San Francisco Bay has been contaminated historically by mercury from mine tailings as well as contemporary industrial sources. Native Spartina foliosa and non-native S. alterniflora-hybrid cordgrasses are dominant florae within the SF Bay estuary environment. Understanding mercury uptake and transformations in these plants will help to characterize the significance of their roles in mercury biogeochemical cycling in the estuarine environment. Methylated mercury can be biomagnified up the food web, resulting in levels in sport fish up to 1 million times greater than in surrounding waters and resulting in advisories to limit fish intake. Understanding the uptake and methylation of mercury in the plant rhizosphere can yield insight into ways to manage mercury contamination. The transmission X-ray microscope on beamline 6-2 at the Stanford Synchrotron Radiation Lightsource (SSRL) was used to obtain absorption contrast images and 3D tomography of Spartina foliosa roots that were exposed to 1 ppm Hg (as HgCl2) hydroponically for 1 week. Absorption contrast images of micrometer-sized roots from S. foliosa revealed dark particles, and dark channels within the root, due to Hg absorption. 3D tomography showed that the particles are on the root surface, and slices from the tomographic reconstruction revealed that the particles are hollow, consistent with microorganisms with a thin layer of Hg on the surface. Hg L3 XANES of ground-up plant roots and Hg L3 micro-XANES from microprobe analysis of micrometer-sized roots (60-120 microm in size) revealed three main types of speciation in both Spartina species: Hg-S ligation in a form similar to Hg(II) cysteine, Hg-S bonding as in cinnabar and metacinnabar, and methylmercury-carboxyl bonding in a form similar to methylmercury acetate. These results are interpreted within the context of obtaining a "snapshot" of mercury methylation in progress. PMID:19848152

  1. New Highly Mixed Phases in Ball-Milled Cu/ZnO Catalysts as Established by EXAFS and XANES

    SciTech Connect

    Grandjean, Didier; Weckhuysen, Bert M.; Castricum, Hessel L.; Heuvel, Johannes C. van den

    2007-02-02

    AnXAFS investigation at both the Cu and Zn K-edge has allowed to unravel new highly mixed phases in Cu/ZnO catalysts prepared by ball-milling mixtures of Cu2O and ZnO under 3 different atmospheres of synthetic air (SA), SA+CO2 and CO2. The system milled in CO2 shows the disproportionation of Cu2O into Cu0, Cu1+ (cuprite Cu2O-type phase) and Cu2+ (tenorite CuO-type phase), while most of the Zn2+ is transformed into a nanocrystalline / amorphous ZnO-type zincite that forms a superficial mixture of oxide and carbonate phases. When synthetic air is added to the CO2 atmosphere, ball-milling results in the oxidation of part of the Cu1+ into Cu2+ with no Cu metal formed. In SA, a significant amount of Cu2+- and Zn2+-based phases react to form a nanocrystalline / amorphous Cu1-xZnxO solid solution that was never reported before. This distorted rock salt-like solid solution, in which Zn and Cu feature different octahedral environments, is formed by incorporation of Zn2+ in the Cu2O matrix and the concomitant oxidation of Cu1+ into Cu2+ and results from strong Cu/Zn interactions in the Cu/ZnO system.

  2. 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

  3. Valence state partitioning of vanadium between pyroxene-melt: effects of pyroxene and melt composition and direct determination of V valence by XANES

    SciTech Connect

    Karner, J.M.; Papike, J.J.; Sutton, S.R.; Shearer, C.K.; Burger, P.; McKay, G.; Le, L.

    2008-04-29

    This paper continues the study of the partitioning of multivalent elements between pyroxene-melt in synthetic charges of martian basalt QUE 94201 composition. Here we concentrate on the partitioning of V between augite/melt and pigeonite/melt. Previous studies have used the partitioning of V between minerals and melt to estimate the fO2 condition and setting of terrestrial and extraterrestrial lavas. Although the V partitioning studies have been successful in estimating fO{sub 2}, they provide no direct determination of V valence in the minerals or the melt. That information is now obtainable through XANES spectroscopy, and here we report XANES data on the same pyroxene grains that we measured the partitioning data.

  4. Inelastic scattering at the B K edge of hexagonal BN

    SciTech Connect

    Jia, J.J.; Callcott, T.A.; Zhou, L.

    1997-04-01

    Many recent soft x-ray fluorescence (SXF) studies have shown that inelastic scattering processes make important contributions to the observed spectra for excitation near the x-ray threshold. These effects are all attributed to a process, usually called an electronic Raman scattering (ERS) process, in which energy is lost to an electronic excitation. The theory has been described using second order perturbation theory by Tulkki and Aberg. In different materials, the detailed nature of the electronic excitation producing the energy loss may be very different. In crystalline Si, diamond and graphite, changes in spectral shape and dispersion of spectral features with variation of the excitation energy are observed, which are attributed to k conservation between the photoelectron generated in the excitation process and the valence hole remaining after the coupled emission process. Hence the process is strongly localized in k-space. In haxagonal boron nitride, which has a lattice and band structure very similar to graphite, inelastic scattering produces very different effects on the observed spectra. Here, the inelastic losses are coupled to a strong resonant elastic scattering process, in which the intermediate state is a localized core exciton and the final state is a localized valence exciton, so that the electronic excitation is strongly localized in real rather than reciprocal space.

  5. Selective catalytic reduction of NO over Fe-ZSM-5: mechanistic insights by operando HERFD-XANES and valence-to-core X-ray emission spectroscopy.

    PubMed

    Boubnov, Alexey; Carvalho, Hudson W P; Doronkin, Dmitry E; Günter, Tobias; Gallo, Erik; Atkins, Andrew J; Jacob, Christoph R; Grunwaldt, Jan-Dierk

    2014-09-17

    An in-depth understanding of the active site requires advanced operando techniques and the preparation of defined catalysts. We elucidate here the mechanism of the selective catalytic reduction of NO by NH3 (NH3-SCR) over a Fe-ZSM-5 zeolite catalyst. 1.3 wt % Fe-ZSM-5 with low nuclearity Fe sites was synthesized, tested in the SCR reaction and characterized by UV-vis, X-ray absorption near edge structure (XANES), and extended X-ray absorption fine structure (EXAFS) spectroscopy. Next, this defined Fe-zeolite catalyst was studied by complementary high-energy-resolution fluorescence-detected XANES (HERFD-XANES) and valence-to-core X-ray emission spectroscopy (V2C XES) under different model in situ and realistic working (operando) conditions identical to the catalyst test bench including the presence of water vapor. HERFD-XANES uncovered that the coordination (between 4 and 5), geometry (tetrahedral, partly 5-fold), and oxidation state of the Fe centers (reduced in NH3, partly in SCR mixture, slight reduction in NO) strongly changed. V2C XES supported by DFT calculations provided important insight into the chemical nature of the species adsorbed on Fe sites. The unique combination of techniques applied under realistic reaction conditions and the corresponding catalytic data unraveled the adsorption of ammonia via oxygen on the iron site. The derived reaction model supports a mechanism where adsorbed NOx reacts with ammonia coordinated to the Fe(3+) site yielding Fe(2+) whose reoxidation is slow. PMID:25105343

  6. 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

  7. XANES and IR spectroscopy study of the electronic structure and chemical composition of porous silicon on n- and p-type substrates

    SciTech Connect

    Lenshin, A. S. Kashkarov, V. M.; Seredin, P. V.; Spivak, Yu. M.; Moshnikov, V. A.

    2011-09-15

    The differences in the electronic structure and composition of porous silicon samples obtained under identical conditions of electrochemical etching on the most commonly used n- and p-type substrates with different conductivities are demonstrated by X-ray absorption near-edge spectroscopy (XANES) and Fourier transform IR spectroscopy (FTIR) methods. It is shown that significantly higher oxidation and saturation with hydrogen is observed for the porous layer on n-type substrates.

  8. 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.

  9. 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.

  10. 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. PMID:26835549

  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. PMID:27001695

  12. MICROSCANNING XRF, XANES, AND XRD STUDIES OF THEDECORATED SURFACE OF ROMAN TERRA SIGILLATA CERAMICS

    SciTech Connect

    Mirguet, C.; Sciau, P.; Goudeau, P.; Mehta, A.; Pianetta, P.; Liu, Z.; Tamura, N.

    2008-10-24

    Different microscanning synchrotron techniques were used to better understand the elaboration process and origins of Terra Sigillata potteries from the Roman period. A mixture Gallic slip sample cross-section showing red and yellow colors was studied. The small (micron) size of the X-ray beam available at Stanford Synchrotron Radiation Laboratory (SSRL) and Advanced Light Source (ALS) synchrotron sources, coupled with the use of a sample scanning stage allowed us to spatially resolve the distribution of the constitutive mineral phases related to the chemical composition. Results show that red color is a result of iron-rich hematite crystals and the yellow part is a result of the presence of Ti-rich rutile-type phase (brookite). Volcanic-type clay is at the origin of these marble Terra Sigillata.

  13. Studies of valence of selected rare earth silicides determined using Si K and Pd/Rh L2,3 XANES and LAPW numerical studies

    NASA Astrophysics Data System (ADS)

    Zajdel, P.; Kisiel, A.; Szytuła, A.; Goraus, J.; Balerna, A.; Banaś, A.; Starowicz, P.; Konior, J.; Cinque, G.; Grilli, A.

    2015-12-01

    We report on the investigation of Si and Pd/Rh chemical environments using X-ray Absorption Near Edge Spectroscopy in two different families of rare earth silicides R2PdSi3 (R = Ce, Nd, Tb, Dy, Ho, Er) and HoRh2-xPdxSi2 (x = 0, 0.5, 0.75, 1.0, 1.5, 1.8, 2.0). The Si K, Pd L3 and Rh L3 absorption edges were recorded in order to follow their changes upon the variation of 4f and 4d5s electron numbers. In both cases it was found that the Si K edge was shifted ≈0.5 eV toward lower energies, relative to pure silicon. In the first family, the shift decreases with increasing number of f-electrons, while the Si K edge remains constant upon rhodium-palladium substitution. In all cases the Pd L3 edge was shifted to higher energies relative to metallic Pd. No visible change in the Pd L3 position was observed either with a varying 4f electron count or upon Pd/Rh substitution. Also, the Rh L3 edge did not change. For two selected members, Ho2PdSi3 and HoPd2Si2, the Wien2K'09 (LDA + U) package was used to calculate the electronic structure and the absorption edges. Si K edges were reproduced well for both compounds, while Pd L3 only exhibited a fair agreement for the second compound. This discrepancy between the Pd L3 theory and experiment for the Ho2PdSi3 sample can be attributed to the specific ordered superstructure used in the numerical calculations. The observed changes indicate that despite possessing a formal inter-metallic character, the chemical bond between the R-Si and R-Pd interactions are different. The variation and the direction of the chemical shift of the Si K edge suggests a weak ionic character of the R-Si bonds, in agreement with the localized character of the 4f electrons. In turn, the changes of the Pd/Rh edge are consistent with a metallic band that is affected by its long range chemical environment.

  14. First approach to studies of sulphur electron DOS in prostate cancer cell lines and tissues studied by XANES

    NASA Astrophysics Data System (ADS)

    Kwiatek, Wojciech M.; Czapla, Joanna; Podgórczyk, Magdalena; Kisiel, Andrzej; Konior, Jerzy; Balerna, Antonella

    2011-10-01

    Urological cancers comprise approximately one-third of all cancers diagnosed in men worldwide and out of these, prostate cancer is the most common one ( WHO World Cancer Report, 2008). Several risk factors such as age, hormone levels, environmental conditions and family history are suspected to play a role in the onset of this disease of otherwise obscure aetiology. It is therefore the medical need that drives multidisciplinary research in this field, carried out by means of various experimental and theoretical techniques. Out of many relevant factors, it is believed that sulphur can take an important part in cancer transformations. We have investigated the prostate cancer cell lines and tissues, along with selected organic and inorganic compounds used as references, by the X-ray absorption fine structure spectroscopy near the sulphur edge energy region. Particularly, the comparison of the experimental results collected during XANES measurements and theoretical calculations of electron density of states with use of the FEFF8 code and LAPW (linearised augmented plane-wave) method has been performed and in this work the first results of our studies are presented.

  15. Polycapillary based μ-XAS and confocal μ-XANES at a bending magnet source of the ESRF

    NASA Astrophysics Data System (ADS)

    Silversmit, Geert; Vekemans, Bart; Nikitenko, Sergey; Tirez, Kristof; Bras, Wim; Brenker, Frank E.; Vincze, Laszlo

    2009-11-01

    Glass polycapillary optics are shown to be easy to use focusing optics for bending magnet XAS stations. These achromatic optics have acceptances of several mm horizontally and vertically, while their angular acceptances can be matched to the source divergence by the design of the polycapillary. A polycapillary half-lens based focusing system was successfully tested for transmission and fluorescence μ-XAS at the DUBBLE beamline (BM26A, ESRF) and the feasibility of confocal μ-XANES in fluorescence mode is presented. Transmission efficiencies of 25-45% with flux density gain factors of about 2000 and beam sizes of 10-20 μm were obtained in the 7-14 keV energy range. Although the polycapillary optic has a smoothly changing energy dependent transmission efficiency, the amplitude and shape of the EXAFS oscillations are not influenced by this. The focusing properties of the polycapillary lens cancel slight vertical motions of the incoming X-ray beam, resulting in a fixed μ-beam spot in the focal plane, making polycapillaries also suitable optic in combination with a non-fixed exit monochromator. In addition, by mounting a second polycapillary half-lens in front of an energy dispersive detector, a confocal set-up is obtained, which restricts the part of the sample seen by the detector to a microscopic volume of about 20×20×15 μm3 at the Fe K absorption edge for example.

  16. Effect of Precursor on the Electronic and Geometric Properties of Cobalt Nanoparticles Investigated by Co-K XANES and EXAFS

    SciTech Connect

    Palshin, Vadim; Silva, Rohini M. de; Hormes, Josef; Kumar, Challa S. S. R.

    2007-02-02

    By varying techniques and parameters in wet-chemical synthesis Co-nanoparticles different crystallographic structures (hcp, fcc and epsilon) can be synthesized. Co-K XANES and EXAFS spectra are very powerful tools to distinguish between those structures. In this study we are investigating for the first time the effect of the precursor molecule used for the synthesis on the electronic and geometric properties of cobalt nanoparticles. As precursors two organometallic cobalt complexes were used: alkyne-bridged dicobalthexacarbonyl [(Co2({mu}-HC{identical_to}CH)(CO)6] (ADH) and the well known dicobalt octacarbonyl [Co2(CO)8] (DCO). Both precursors were thermally decomposed under identical reaction conditions. Besides, effect of the precursor on the Co NPs was also investigated when two different types of surfactants are utilized in the reaction, oleic acid and n-trioctylphosphine. When only oleic acid was used as the surfactant, the XAFS analysis showed formation of fcc structure with ADH and hcp with DCO. When a combination of oleic acid and TOP were used, the crystal structure of CO NPs obtained is currently being analyzed.

  17. 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.

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

    PubMed

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

    2014-01-01

    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. PMID:25503313

  19. Direct determination of europium valence state by XANES in extraterrestrial merrillite: Implications for REE crystal chemistry and martian magmatism

    SciTech Connect

    Shearer, C.K.; Papike, J.J.; Burger, P.V.; Sutton, S.R.; McCubbin, F.M.; Newville, M.

    2012-03-15

    The relative proportion of divalent and trivalent Eu has proven to be a useful tool for estimating f{sub O{sub 2}} in various magmatic systems. However, in most cases, direct determination of the Eu valence state has not been made. In this study, direct determination of Eu valence by XANES and REE abundance in merrillite provide insights into the crystal chemistry of these phosphates and their ability to record conditions of magmatism. Merrillite strongly prefers Eu{sup 3+} to Eu{sup 2+}, with the average valence state of Eu ranging between 2.9 and 3 over approximately six orders of magnitude in f{sub O{sub 2}}. The dramatic shift in the REE patterns of merrillite in martian basaltic magmas, from highly LREE-depleted to LREE-enriched, parallels many other trace element and isotopic variations and reflects the sources for these magmas. The behavior of REE in the merrillite directly reflects the relationship between the eightfold-coordinated Ca1 site and adjacent sixfold Na and tetrahedral P sites that enables charge balancing through coupled substitutions.

  20. Elemental bioimaging and speciation analysis for the investigation of Wilson's disease using μXRF and XANES.

    PubMed

    Hachmöller, Oliver; Buzanich, Ana Guilherme; Aichler, Michaela; Radtke, Martin; Dietrich, Dörthe; Schwamborn, Kristina; Lutz, Lisa; Werner, Martin; Sperling, Michael; Walch, Axel; Karst, Uwe

    2016-07-13

    A liver biopsy specimen from a Wilson's disease (WD) patient was analyzed by means of micro-X-ray fluorescence (μXRF) spectroscopy to determine the elemental distribution. First, bench-top μXRF was utilized for a coarse scan of the sample under laboratory conditions. The resulting distribution maps of copper and iron enabled the determination of a region of interest (ROI) for further analysis. In order to obtain more detailed elemental information, this ROI was analyzed by synchrotron radiation (SR)-based μXRF with a beam size of 4 μm offering a resolution at the cellular level. Distribution maps of additional elements to copper and iron like zinc and manganese were obtained due to a higher sensitivity of SR-μXRF. In addition to this, X-ray absorption near edge structure spectroscopy (XANES) was performed to identify the oxidation states of copper in WD. This speciation analysis indicated a mixture of copper(i) and copper(ii) within the WD liver tissue. PMID:26999628

  1. In situ XANES study of the passive film formed on iron in borate buffer and in sodium acetate

    SciTech Connect

    Oblonsky, L.J.; Ryan, M.P.; Isaacs, S.

    1996-12-31

    The passive film formed on Fe in pH 8.4 borate buffer (0. 1 36 M) over a broad potential range was characterized by in situ XANES (x-ray absorption near edge structure). On stepping the potential to a value between -0.6 V and +0.4 V (MSE), a passive film forms without detectable dissolution. The edge position indicates that the valence state of Fe in the film is 10 {+-} 5% Fe{sup 2+} and 90 {+-} 5% Fe{sup 3+}. Formation of a passive film at potentials between -0.8 V and -0.65 V is associated with dissolution prior to passivation, and a lower average valence state of 17 {+-} 5% Fe{sup 2+} and 83 {+-} 5% Fe{sup 3+}. At -0.9 V, the Fe did not passivate. The passive film that forms in pH 8.2 sodium acetate (0.1 M) at +0.4 V gives an edge similar to the high potential passive film formed in borate buffer, but dissolution occurs prior to passivation.

  2. The darkening of zinc yellow: XANES speciation of chromium in artist;s paints after light and chemical exposures

    SciTech Connect

    Zanella, Luciana; Casadio, Francesca; Gray, Kimberly A.; Warta, Richard; Ma, Qing; Gaillard, Jean-François

    2012-03-14

    The color darkening of selected brushstrokes of the masterpiece A Sunday on La Grande Jatte - 1884 (by Georges Seurat) has been attributed to the alteration of the chromate pigment zinc yellow. The pigment originally displays a bright greenish-yellow color but may undergo, after aging, darkening to a dull, ocher tone. We used XANES to probe the oxidation state of Cr on paint reconstructions, and show that color changes are associated with the reduction of Cr(VI) to Cr(III). Paint mixtures containing the pigment and linseed oil to mimic mixtures used in La Grande Jatte were subjected to artificial aging in the presence of light, SO{sub 2}, and variable air humidity - 50 and 90% relative humidity. High relative humidity led to the largest degree of Cr(VI) reduction whereas low relative humidity promoted light-induced alterations. These results are corroborated by visible reflectance measurements on the same laboratory samples and contribute to a better understanding of the chemical reactivity of chromate pigments, which are present in many historical works of art.

  3. Arsenic Scavenging by Al-Substituted Ferrihydrites in a Circumneutral pH River Impacted by the Acid Mine Drainage of Carnoulès, Gard, France

    NASA Astrophysics Data System (ADS)

    ADRA, A.; Morin, G.; ona-Nguema, G.; Maillot, F.; Casiot, C.; Bruneel, O.

    2013-12-01

    Ferrihydrite (Fh) is a nanocrystalline ferric oxyhydroxide involved in the retention of pollutants in natural systems and in water-treatment processes. The status and properties of major chemical impurities in natural Fh is however still scarcely documented. Here we investigated the structure and reactivity of aluminum-rich Fh from river-bed sediments collected in a circumneutral river (pH 6-7) impacted by an arsenic-rich acid mine drainage (AMD). Extended X-ray absorption fine structure (EXAFS) spectroscopy at the Fe K-edge shows that Fh is the predominant mineral phase forming after neutralization of the AMD, in association with minor amount of schwertmannite transported from the AMD. EXAFS analysis indicates that Al(III) substitutes for Fe(III) ions into the Fh structure in the natural sediment samples, with local aluminum concentration within the 20-37×7 mol%Al range, in agreement with bulk chemical compositions. Synthetic aluminous Fh analogues prepared in the present study are found to be less Al-substituted (14-18×4 mol%Al). Finally, EXAFS analysis at the arsenic K-edge indicates that As(V) form similar inner-sphere surface complexes on the natural and synthetic Al-substituted Fh studied. Our results provide direct evidences for the scavenging of arsenic by natural Al- Fh, with possible implications for other pollutants in natural or engineered systems.

  4. Evidence for Germanene growth on epitaxial hexagonal (h)-AlN on Ag(1 1 1)

    NASA Astrophysics Data System (ADS)

    d'Acapito, F.; Torrengo, S.; Xenogiannopoulou, E.; Tsipas, P.; Marquez Velasco, J.; Tsoutsou, D.; Dimoulas, A.

    2016-02-01

    In this work, a structural analysis of Ge layers deposited by molecular beam epitaxy (MBE) on Ag(1 1 1) surfaces with and without an AlN buffer layer have been investigated by x-ray Absorption Spectroscopy (XAS) at the Ge-K edge. For the Ge layers deposited on h-AlN buffer layer on Ag(1 1 1) an interatomic Ge-Ge distance {{R}\\text{Ge-\\text{Ge}}}=2.38 Å is found, typical of 2-Dimensional Ge layers and in agreement with the theoretical predictions for free standing low-buckled Germanene presented in literature. First principles calculations, performed in the density functional theory (DFT) framework, supported the experimental RHEED and XAS findings, providing evidence for the epitaxial 2-D Ge layer formation on h-AlN/Ag(1 1 1) template.

  5. Evidence for Germanene growth on epitaxial hexagonal (h)-AlN on Ag(1 1 1).

    PubMed

    d'Acapito, F; Torrengo, S; Xenogiannopoulou, E; Tsipas, P; Marquez Velasco, J; Tsoutsou, D; Dimoulas, A

    2016-02-01

    In this work, a structural analysis of Ge layers deposited by molecular beam epitaxy (MBE) on Ag(1 1 1) surfaces with and without an AlN buffer layer have been investigated by x-ray Absorption Spectroscopy (XAS) at the Ge-K edge. For the Ge layers deposited on h-AlN buffer layer on Ag(1 1 1) an interatomic Ge-Ge distance [Formula: see text] Å is found, typical of 2-Dimensional Ge layers and in agreement with the theoretical predictions for free standing low-buckled Germanene presented in literature. First principles calculations, performed in the density functional theory (DFT) framework, supported the experimental RHEED and XAS findings, providing evidence for the epitaxial 2-D Ge layer formation on h-AlN/Ag(1 1 1) template. PMID:26751008

  6. X-ray absorption spectroscopy of aqueous aluminum-organic complexes.

    PubMed

    Hay, Michael B; Myneni, Satish C B

    2010-05-27

    Aqueous-phase X-ray absorption near-edge structure (XANES) spectra were collected on dissolved Al complexes with organic ligands, including desferrioxamine B, EDTA, acetohydroxamate, malate, oxalate, and salicylate. Spectral interpretations were made using the density functional theory-based modeling package StoBe. The goals of this work were to study the geometric and electronic structural characteristics of these complexes relative to Al(H(2)O)(6)(3+) and to examine the utility of the aqueous Al XANES technique as a tool for probing Al speciation and structure. In the case of EDTA, aqueous Fourier-transform infrared spectroscopy was also used to corroborate the structures of the Al(EDTA)(-) and AlOH(EDTA)(2-) complexes. Synthetic XANES spectra calculated with StoBe reproduced the observed spectral differences between Al(H(2)O)(6)(3+), Al(dfoB)(+), and Al(EDTA)(-). The narrower XANES feature observed for Al(dfoB)(+) relative to Al(H(2)O)(6)(3+) can be attributed to a weaker splitting of the Al 3p-O 2p interactions in the former, while Al(EDTA)(-) exhibits split Al 3p-ligand interactions that likely result from the mixed O/N coordination. In complexes with mixed aqua/organic-oxygen ligation (Al-acetohydroxamate, Al-malate, Al-oxalate, and Al-salicylate), spectra exhibit linear, systematic changes in peak width as a function of H(2)O to organic ligand ratio in the Al coordination sphere. These results highlight the sensitivity of the aqueous Al K-edge XANES spectrum to coordination environment and demonstrate its utility as an experimental probe for future studies of Al speciation in complex solutions. PMID:20443586

  7. 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

  8. ALS - resources

    MedlinePlus

    Resources - ALS ... The following organizations are good resources for information on amyotrophic lateral sclerosis : Muscular Dystrophy Association -- mda.org/disease/amyotrophic-lateral-sclerosis National Amyotrophic Lateral Sclerosis (ALS) Registry -- ...

  9. ALS Association

    MedlinePlus

    ... ALS. Find Out How Our Mission Leading the fight to treat and cure ALS through global research ... you participate, advocate, and donate, you advance the fight to find the cure and lead us toward ...

  10. 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

  11. Comparison of Synchrotron X-Ray Fluorescence Mapping and Micro-XANES to Bulk X-Ray Absorption Spectra in Metal-Contaminated Sediments

    SciTech Connect

    O'Day, P; Carroll, S A; Bajt, S

    2003-01-16

    Synchrotron X-ray absorption spectroscopy (XAS) is one of the few techniques that can supply molecular-scale information for a variety of elements at concentrations relevant to natural systems in non-vacuum conditions. Bulk XAS analysis supplies the dominant chemical bonding mode(s) for a specific element. In complex materials such as natural soils and sediments, however, the dominant mode may not necessarily be the most reactive because changes in speciation at surfaces may results in changes in reactivity. Our previous work at Naval Air Station (NAS) Alameda (CA) focused on in situ metal chemistry in surface and deep sediments, and the impact of metal mobility by sediment oxidation. Estuary sediments at the Alameda Naval Station Air in California have elevated metal concentrations that increase with increasing depth. The metal concentrations in these sediments are: Cd (10-350 ppm), Cr (200-1000 ppm), Cu (100-230 ppm), Pb (200-1200 ppm) and Zn (250-600 ppm). We have extensively characterized these sediments using bulk XAS and other non-synchrotron supporting methods [ 1]. In this experiment, we collected fluorescence element maps using synchrotron X-ray microprobe of unreacted and seawater-oxidized sediment samples from Alameda NAS to determine the spatial distribution and correlation of lead, zinc, and iron. We then compared micro-XANES spectra for lead and zinc collected with the X-ray microprobe to previously collected bulk XANES spectra. The results from our bulk XAS characterization of the sediments showed both oxide and sulfide components for the trace metals. However, the bulk XAS data were not able to identify the composition of the oxide component (i.e. carbonate or hydroxide), nor could absorbed species or solid solutions be definitively identified. Our objective in using micro-XANES and fluorescence element maps was to attempt a more precise identification of metal speciation in or on individual particles.

  12. In situ XANES & XRD Study of interphasial reaction between uncharged Li2FeSiO4 cathode and LiPF6-based electrolyte

    NASA Astrophysics Data System (ADS)

    Arthur, Z.; Chiu, H. C.; Lu, X.; Chen, N.; Emond, V.; Demopoulos, G. P.; Jiang, D. T.

    2016-05-01

    In situ synchrotron radiation XANES and XRD have been carried out on Li2FeSiO4 cathode material in a lithium-ion-battery (LIB) cell. The evolution of the long range lattice structure and the local iron oxidation state has been observed at a charging rate of C/20 for the formation cycle for one Lithium extraction; additional ex situ measurements of the pristine cathode material were taken for comparison. The observed spontaneous interaction between the cathode and the fluorinated electrolyte and the impact of subsequent cycling are discussed.

  13. Structure, Bonding, and Stability of Mercury Complexes with Thiolate and Thioether Ligands from High-Resolution XANES Spectroscopy and First-Principles Calculations.

    PubMed

    Manceau, Alain; Lemouchi, Cyprien; Rovezzi, Mauro; Lanson, Martine; Glatzel, Pieter; Nagy, Kathryn L; Gautier-Luneau, Isabelle; Joly, Yves; Enescu, Mironel

    2015-12-21

    We present results obtained from high energy-resolution L3-edge XANES spectroscopy and first-principles calculations for the structure, bonding, and stability of mercury(II) complexes with thiolate and thioether ligands in crystalline compounds, aqueous solution, and macromolecular natural organic matter (NOM). Core-to-valence XANES features that vary in intensity differentiate with unprecedented sensitivity the number and identity of Hg ligands and the geometry of the ligand environment. Post-Hartree-Fock XANES calculations, coupled with natural population analysis, performed on MP2-optimized Hg[(SR)2···(RSR)n] complexes show that the shape, position, and number of electronic transitions observed at high energy-resolution are directly correlated to the Hg and S (l,m)-projected empty densities of states and occupations of the hybridized Hg 6s and 5d valence orbitals. Linear two-coordination, the most common coordination geometry in mercury chemistry, yields a sharp 2p to 6s + 5d electronic transition. This transition varies in intensity for Hg bonded to thiol groups in macromolecular NOM. The intensity variation is explained by contributions from next-nearest, low-charge, thioether-type RSR ligands at 3.0-3.3 Å from Hg. Thus, Hg in NOM has two strong bonds to thiol S and k additional weak Hg···S contacts, or 2 + k coordination. The calculated stabilization energy is -5 kcal/mol per RSR ligand. Detection of distant ligands beyond the first coordination shell requires precise measurement of, and comparison to, spectra of reference compounds as well as accurate calculation of spectra for representative molecular models. The combined experimental and theoretical approaches described here for Hg can be applied to other closed-shell atoms, such as Ag(I) and Au(I). To facilitate further calculation of XANES spectra, experimental data, a new crystallographic structure of a key mercury thioether complex, Cartesian coordinates of the computed models, and examples of

  14. 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

  15. Using Fluorescence XANES Measurement to Correct the Content of Hexavalent Chromium in Chromate Conversion Coatings Determined by Diphenyl Carbazide Color Test

    SciTech Connect

    Nishino, Junichi; Ofuchi, Hironori; Taniguchi, Yosuke; Honma, Tetsuo; Sekikawa, Toshikazu; Otani, Haruka; Bando, Akio

    2007-01-19

    The Restriction of the use of certain Hazardous Substances (RoHS) directive will take effect on July 1 of this year. From that date, the use of chromate conversion coatings containing hexavalent chromium will not be permitted. By comparing the concentration of Cr6+ determined by the diphenyl carbazide color test and by fluorescence XANES (X-Ray Absorption Near Edge Structure) measurement, we can correct for the Cr6+ content of the color test. This will enable the use of the diphenyl carbazide color test to check product shipments in compliance with the RoHS directive.

  16. Fe-XANES analyses of Reykjanes Ridge basalts: Implications for oceanic crust's role in the solid Earth oxygen cycle

    NASA Astrophysics Data System (ADS)

    Shorttle, Oliver; Moussallam, Yves; Hartley, Margaret E.; Maclennan, John; Edmonds, Marie; Murton, Bramley J.

    2015-10-01

    The cycling of material from Earth's surface environment into its interior can couple mantle oxidation state to the evolution of the oceans and atmosphere. A major uncertainty in this exchange is whether altered oceanic crust entering subduction zones can carry the oxidised signal it inherits during alteration at the ridge into the deep mantle for long-term storage. Recycled oceanic crust may be entrained into mantle upwellings and melt under ocean islands, creating the potential for basalt chemistry to constrain solid Earth-hydrosphere redox coupling. Numerous independent observations suggest that Iceland contains a significant recycled oceanic crustal component, making it an ideal locality to investigate links between redox proxies and geochemical indices of enrichment. We have interrogated the elemental, isotope and redox geochemistry of basalts from the Reykjanes Ridge, which forms a 700 km transect of the Iceland plume. Over this distance, geophysical and geochemical tracers of plume influence vary dramatically, with the basalts recording both long- and short-wavelength heterogeneity in the Iceland plume. We present new high-precision Fe-XANES measurements of Fe3+ / ∑ Fe on a suite of 64 basalt glasses from the Reykjanes Ridge. These basalts exhibit positive correlations between Fe3+ / ∑ Fe and trace element and isotopic signals of enrichment, and become progressively oxidised towards Iceland: fractionation-corrected Fe3+ / ∑ Fe increases by ∼0.015 and ΔQFM by ∼0.2 log units. We rule out a role for sulfur degassing in creating this trend, and by considering various redox melting processes and metasomatic source enrichment mechanisms, conclude that an intrinsically oxidised component within the Icelandic mantle is required. Given the previous evidence for entrained oceanic crustal material within the Iceland plume, we consider this the most plausible carrier of the oxidised signal. To determine the ferric iron content of the recycled component ([Fe2O

  17. Combined In-Situ XRD and In-Situ XANES Studies on the Reduction Behavior of a Rhenium Promoted Cobalt Catalyst

    SciTech Connect

    Kumar, Nitin; Payzant, E Andrew; Jothimurugesan, K; Spivey, James J

    2011-01-01

    A 10% Co 4% Re/(2% Zr/SiO2) catalyst was prepared by co-impregnation using a silica support modified by 2% Zr. The catalyst was characterized by temperature programmed reduction (TPR), in situ XRD and in situ XANES analysis where it was simultaneously exposed to H2 using a temperature programmed ramp. The results showed the two step reduction of large crystalline Co3O4 with CoO as an intermediate. TPR results showed that the reduction of highly dispersed Co3O4 was facilitated by reduced rhenium by a H2-spillover mechanism. In situ XRD results showed the presence of both, Co-hcp and Co-fcc phases in the reduced catalyst at 400 C. However, the Co-hcp phase was more abundant, which is thought to be the more active phase as compared to the Co-fcc phase for CO hydrogenation. CO hydrogenation at 270 C and 5 bar pressure produces no detectable change in the phases during the time of experiment. In situ XANES results showed a decrease in the metallic cobalt in the presence of H2/CO, which can be attributed due to oxidation of the catalyst by reaction under these conditions.

  18. 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.

  19. Effect of metal ion on the structure and function of LiPDF: The study of the fine structure around the metal site using XANES

    NASA Astrophysics Data System (ADS)

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

    2010-07-01

    We used X-ray absorption near edge structure (XANES) spectroscopy to investigate the metal-dependent enzymatic activity of the peptide deformylase from Leptospira interrogans ( LiPDF). Ab initio full multiple scattering calculations performed by MXAN are applied to obtain the local structure of the cobalt-containing LiPDF (Co- LiPDF) and zinc-containing LiPDF (Zn- LiPDF) around the metal sites in pH9.0 buffer solution. The result shows the cobalt-wat1 (the bond water molecule) distance of Co- LiPDF is 1.89 Å, much shorter than that of Zn- LiPDF, 2.50 Å. That is an essential factor for its low catalytic activity.

  20. 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.

  1. Chemical Heterogeneity of a Large Cluster IDP: Clues to its Formation History Using X-ray Fluorescence Mapping and XANES Spectroscopy

    NASA Technical Reports Server (NTRS)

    Wirick, S.; Flynn, G. J.; Sutton, S.; Zolensky, M. E.

    2013-01-01

    Chondritic porous IDPs may be among the most primitive objects found in our solar system [1]. They consist of many micron to submicron minerals, glasses and carbonaceous matter [2,3,4,5,6,7] with > 10(exp 4) grains in a 10 micron cluster [8]. Speculation on the environment where these fine grained, porous IDPs formed varies with possible sources being presolar dusty plasma clouds, protostellar condensation, solar asteroids or comets [4,6,9]. Also, fine grained dust forms in our solar system today [10,11]. Isotopic anomalies in some particles in IDPs suggest an interstellar source[4,7,12]. IDPs contain relic particles left from the dusty plasma that existed before the protostellar disk formed and other grains in the IDPs formed later after the cold dense nebula cloud collapsed to form our protostar and other grains formed more recently. Fe and CR XANES spectroscopy is used here to investigate the oxygen environment in a large (>50 10 micron or larger sub-units) IDP. Conclusions: Analyzing large (>50 10 micron or larger sub-units) CP IDPs gives one a view on the environments where these fine dust grains formed which is different from that found by only analyzing the small, 10 micron IDPs. As with cluster IDP L2008#5 [3], L2009R2 cluster #13 appears to be an aggregate of grains that sample a diversity of solar and perhaps presolar environments. Sub-micron, grain by grain measurement of trace element contents and elemental oxidation states determined by XANES spectroscopy offers the possibility of understanding the environments in which these grains formed when compared to standard spectra. By comparing thermodynamic modeling of condensates with analytical data an understanding of transport mechanisms operating in the early solar system may be attained.

  2. 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.

  3. Zn distribution and speciation in zinc-containing steelmaking wastes by synchrotron radiation induced μ-XRF and μ-XANES spectroscopy

    NASA Astrophysics Data System (ADS)

    Wang, Lihua; Huang, Yuying; Lu, Xiaoming

    2013-04-01

    Zinc is an important element in steelmaking industry not only for its impact on environment but also for its hazardous influence to steel production. Collecting information about the chemical association of zinc in zinc-containing steelmaking wastes is fundamental for monitoring its behavior during further treatment. In the work presented here, the spatial distribution, and chemical forms of zinc in accumulated particles of zinc-containing steelmaking wastes, including electric arc furnace dust (EAFD) and basic oxygen furnace OG sludge (BOF OG), have been investigated using synchrotron radiation induced μ-XRF and μ-XANES spectroscopy. Results of μ-XRF analysis showed that zinc distributed in two ways. One was shared with iron and its distribution showed a positive correlation with that of iron. The other was accumulated in some well-defined hot spots with high amount and its distribution showed negative correlation with that of iron. For EAFD, results of μ-XANES spectroscopy indicated that zinc was mainly present in the form of ZnFe2O4 within the whole particles no matter the spots with high or low zinc content. Whereas for BOF OG, ZnFe2O4 was the main constituent in well-defined hot spots while in other regions zinc was mainly in the form of zinc carbonate. These results indicated that chemical reaction between zinc and other components occurred during the formation of accumulated OG sludge particles. If the above findings could be confirmed by more systematic investigations, it will provide valuable information for treating and utilizing these metallurgical residues.

  4. Phosphorus speciation in agro-industrial byproducts: sequential fractionation, solution (31)P NMR, and P K- and L(2,3)-edge XANES spectroscopy.

    PubMed

    Negassa, Wakene; Kruse, Jens; Michalik, Dirk; Appathurai, Narayana; Zuin, Lucia; Leinweber, Peter

    2010-03-15

    Little is known about P species in agro-industrial byproducts from developing countries, which may be either pollutants or valuable soil amendments. The present study speciated P in dry (COD) and wet (COW) coffee, sisal (SIS), barley malt (BEB) and sugar cane processing (FIC) byproducts, and filter cakes of linseed (LIC) and niger seed (NIC)with sequential fractionation, solution (31)P nuclear magnetic resonance (NMR) spectroscopy, and P K- and L(2,3)-edge X-ray absorption near-edge structure (XANES) spectroscopy. The sequential P fractionation recovered 59% to almost 100% of total P (P(t)), and more than 50% of P(t) was extracted by H(2)O and NaHCO(3) in five out of seven samples. Similarly, the NaOH + EDTA extraction for solution (31)P NMR recovered 48-94% of P(t). The (31)P NMR spectra revealed orthophosphate (6-81%), pyrophosphate (0-10%), and orthophosphate monoesters (6-94%). Orthophosphate predominated in COD, COW, SIS, and FIC, whereas BEB, UC, and NIC were rich in orthophosphate monoesters. The concentrations of P(i), and P(o) determined in the sequential and NaOH + EDTA extractions and (31)P NMR spectra were strongly and positively correlated (r = 0.88-1.00). Furthermore, the P K- and L(2,3)-edge XANES confirmed the H(2)SO(4)--P(i) detected in the sequential fractionation by unequivocal identification of Ca--P phases in a few samples. The results indicate that the combined use of all four analytical methods is crucial for comprehensive P speciation in environmental samples and the application of these byproducts to soil. PMID:20146464

  5. Design and performance of the ALS double-crystal monochromator

    SciTech Connect

    Jones, G.; Ryce, S.; Perera, R.C.C.

    1997-04-01

    A new {open_quotes}Cowan type{close_quotes} double-crystal monochromator, based on the boomerang design used at NSLS beamline X-24A, has been developed for beamline 9.3.1 at the ALS, a windowless UHV beamline covering the 1-6 keV photon-energy range. Beamline 9.3.1 is designed to simultaneously achieve the goals of high energy resolution, high flux, and high brightness at the sample. The mechanical design has been simplified, and recent developments in technology have been included. Measured mechanical precision of the monochromator shows significant improvement over existing designs. In tests with x-rays at NSLS beamline X-23 A2, maximum deviations in the intensity of monochromatic light were just 7% during scans of several hundred eV in the vicinity of the Cr K edge (6 keV) with the monochromator operating without intensity feedback. Such precision is essential because of the high brightness of the ALS radiation and the overall length of beamline 9.3.1 (26 m).

  6. Design and performance of the ALS double-crystal monochromator

    SciTech Connect

    Jones, G.; Ryce, S.; Perera, R.C.C.; Lindle, D.W. |; Karlin, B.A.; Woicik, J.C.

    1994-08-01

    A new ``Cowan type`` double-crystal monochromator, based on the boomerang design used at NSLS beamline X-24A, has been developed for beamline 9.3.1 at the ALS, a windowless UHV beamline covering the 1-6 keV photon-energy range. Beamline 9.3.1 is designed to simultaneously achieve the goals of high energy resolution, high flux, and high brightness at the sample. The mechanical design has been simplified, and recent developments in technology have been included. Measured mechanical precision of the monochromator shows significant improvement over existing designs. In tests with x-rays at NSLS beamline X-A, maximum deviations in the intensity of monochromatic light were just 7% during scans of several hundred eV in the vicinity of the Cr K edge (6 keV) with the monochromator operating without intensity feedback. Such precision is essential because of the high brightness of the ALS radiation and the overall length of beamline 9.3.1 (26 m).

  7. 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

  8. 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.

  9. Al Composites

    NASA Astrophysics Data System (ADS)

    Chandanayaka, Tharaka; Azarmi, Fardad

    2014-05-01

    In the present study, cold spraying technique was used to fabricate a metal matrix composite (MMC) that consists of Ni matrix and 20 vol.% Ni3Al particles at two different particle sizes as reinforcement. This study intends to investigate the effect of reinforcement particle size on microstructural and mechanical properties of cold sprayed MMCs. Two different Ni3Al powders with nominal particle size of -45 to +5 and +45 to 100 μm were used as reinforcement in this study. Cold sprayed Ni-Ni3Al samples were subjected to the microstructural observation and characterization prior to any mechanical testing. Then, samples were tested using nano-indentation, Knoop hardness, Vickers hardness, and Resonance frequency to evaluate their mechanical properties. No significant changes were observed in microstructural characteristics due to different particle sizes. The results obtained from a variety of mechanical testings indicated that the increasing reinforcement particle size resulted in the slight reduction of mechanical properties such as elastic modulus and hardness in cold sprayed MMCs. The mechanical interlock between deposited particles defines the bonding strength in cold sprayed samples. Small size particles have a higher velocity and impact resulting in stronger interlock between deformed particles.

  10. Electronic states of NO{sub 2}-exposed H-terminated diamond/Al{sub 2}O{sub 3} heterointerface studied by synchrotron radiation photoemission and X-ray absorption spectroscopy

    SciTech Connect

    Takahashi, Kazutoshi; Imamura, Masaki; Hirama, Kazuyuki; Kasu, Makoto

    2014-02-17

    The energy band-lineup and the electronic structure of NO{sub 2}-exposed H-terminated diamond/Al{sub 2}O{sub 3} heterointerface have been investigated by synchrotron radiation photoemission and x-ray absorption near-edge structure (XANES) measurements. It is found that the energy band-lineup is stagger-type, so-called type-II, with its valence band discontinuity of as high as 3.9 eV and its conduction band discontinuity of 2.7 eV. The valence band maximum of the H-terminated diamond surface is positioned at Fermi level as a result of high-density hole accumulation on the diamond side. The XANES measurement has shown that the oxygen-derived interface state locates at about 1–3 eV above the Fermi level.

  11. AL Amyloidosis

    PubMed Central

    2012-01-01

    Definition of the disease AL amyloidosis results from extra-cellular deposition of fibril-forming monoclonal immunoglobulin (Ig) light chains (LC) (most commonly of lambda isotype) usually secreted by a small plasma cell clone. Most patients have evidence of isolated monoclonal gammopathy or smoldering myeloma, and the occurrence of AL amyloidosis in patients with symptomatic multiple myeloma or other B-cell lymphoproliferative disorders is unusual. The key event in the development of AL amyloidosis is the change in the secondary or tertiary structure of an abnormal monoclonal LC, which results in instable conformation. This conformational change is responsible for abnormal folding of the LC, rich in β leaves, which assemble into monomers that stack together to form amyloid fibrils. Epidemiology AL amyloidosis is the most common type of systemic amyloidois in developed countries with an estimated incidence of 9 cases/million inhabitant/year. The average age of diagnosed patients is 65 years and less than 10% of patients are under 50. Clinical description The clinical presentation is protean, because of the wide number of tissues or organs that may be affected. The most common presenting symptoms are asthenia and dyspnoea, which are poorly specific and may account for delayed diagnosis. Renal manifestations are the most frequent, affecting two thirds of patients at presentation. They are characterized by heavy proteinuria, with nephrotic syndrome and impaired renal function in half of the patients. Heart involvement, which is present at diagnosis in more than 50% of patients, leading to restrictive cardiopathy, is the most serious complication and engages prognosis. Diagnostic methods The diagnosis relies on pathological examination of an involved site showing Congo red-positive amyloid deposits, with typical apple-green birefringence under polarized light, that stain positive with an anti-LC antibody by immunohistochemistry and/or immunofluorescence. Due to the

  12. New quaternary arsenide oxides with square planar coordination of gold(I) - structure, (197)Au Mössbauer spectroscopic, XANES and XPS characterization of Nd10Au3As8O10 and Sm10Au3As8O10.

    PubMed

    Bartsch, Timo; Niehaus, Oliver; Johrendt, Dirk; Kobayashi, Yasuhiro; Seto, Makoto; Abdala, Paula M; Bartsch, Manfred; Zacharias, Helmut; Hoffmann, Rolf-Dieter; Gerke, Birgit; Rodewald, Ute Ch; Pöttgen, Rainer

    2015-03-28

    The quaternary gold(I) arsenide oxides Nd10Au3As8O10 and Sm10Au3As8O10 were synthesized in sealed quartz ampoules from the rare earth (RE) elements, their appropriate sesquioxides, arsenic, arsenic(III) oxide and finely dispersed gold at maximum annealing temperatures of 1223 K. Both structures were refined from X-ray single crystal diffractometer data at room temperature and at 90 K. Nd10Au3As8O10 and Sm10Au3As8O10 crystallize with a new structure type that derives from the BaAl4 structure through distortions and formation of ordered vacancies. The structures consist of stacked polycationic [RE10O10](10+) layers with oxygen in tetrahedral rare earth coordination and polyanionic [Au(I)3(As2)4](10-) layers with gold in square planar or rectangular planar coordination of four arsenic dumbbells (255 pm As1-As2). In contrast to the well known ionic rare earth oxide layers, the gold arsenide layers rather show covalent bonding and account for the metallic nature of these two new arsenide oxides. This is confirmed by electronic structure calculations and resistivity measurements. The oxidation state of gold was investigated by (197)Au Mössbauer, X-ray absorption near edge structure (XANES) and photoelectron (XPS) spectroscopy. Due to missing comparative gold arsenide compounds, the monovalent gold phosphide oxides RE2AuP2O were measured for comparison. The XANES measurements additionally comprise monovalent gold arsenides REAuAs2. The XPS study contains BaAuAs as reference compound instead. Combination of all data clearly indicates Au(I), which was not observed in square planar coordination up to now. Temperature dependent magnetic susceptibility data show Curie-Weiss paramagnetism for Nd10Au3As8O10 and no magnetic ordering down to 2.5 K. Sm10Au3As8O10 shows the typical Van Vleck type paramagnetism for samarium compounds along with a transition to an antiferromagnetically ordered state at TN = 8.6 K. PMID:25716906

  13. Following the movement of Cu ions in a SSZ-13 zeolite during dehydration, reduction and adsorption: a combined in situ TP-XRD, XANES/DRIFTS study

    SciTech Connect

    Kwak, Ja Hun; Varga, Tamas; Peden, Charles HF; Gao, Feng; Hanson, Jonathan C.; Szanyi, Janos

    2014-05-05

    Cu-SSZ-13 has been shown to possess high activity and superior N2 formation selectivity in the selective catalytic reduction of NOx under oxygen rich conditions. Here, a combination of synchrotron-based (XRD and XANES) and vibrational (DRIFTS) spectroscopy tools have been used to follow the changes in the location and coordination environment of copper ions in a Cu-SSZ-13 zeolite during calcinations, reduction with CO, and adsorption of CO and H2O. XANES spectra collected during these procedures provides critical information not only on the variation in the oxidation state of the copper species in the zeolite structure, but also on the changes in the coordination environment around these ions as they interact with the framework, and with different adsorbates (H2O and CO). Time-resolved XRD data indicate the movement of copper ions and the consequent variation of the unit cell parameters during dehydration. DRIFT spectra provide information about the adsorbed species present in the zeolite, as well as the oxidation states of and coordination environment around the copper ions. A careful analysis of the asymmetric T-O-T vibrations of the CHA framework perturbed by copper ions in different coordination environments proved to be especially informative. The results of this study will aid the identification of the location, coordination and oxidation states of copper ions obtained during in operando catalytic studies. Financial support was provided by the US Department of Energy (DOE), Office of Energy Efficiency and Renewable Energy, Vehicle Technologies Program. Part of this work (sample preparation) was performed in the Environmental Molecular Sciences Laboratory (EMSL) at Pacific Northwest National Laboratory (PNNL). The EMSL is a national scientific user facility supported by the US DOE, Office of Biological and Environmental Research. PNNL is a multi-program national laboratory operated for the US DOE by Battelle. All of the spectroscopy work reported here was

  14. Comparison of Synchrotron MicroXANES Determination of Fe(3+)/Sigma Fe with Moessbauer Values for Clean Mineral Separates of Pyroxene from Martian Meteorites

    NASA Technical Reports Server (NTRS)

    Delaney, J. S.; Dyar, M. D.

    2003-01-01

    The oxidation state of Fe in Martian meteorites is a parameter of great interest and the ability to determine this value in micrometer scale samples is important. Intense, tunable x-ray sources at large synchrotron storage rings are being exploited to examine the Fe K-absorption edge with energy resolution of approx. 1-1.5eV in spots of 10x15 microns on thin sections of a wide variety of materials including several Martian meteorites. Synchrotron microXANES (SmX) spectroscopy is the technique that provides the most flexible capability for investigating Fe(3+)/Sigma Fe. Variation of Fe(3+)/Sigma Fe is manifested as a function of the energy of the pre-edge to the Fe absorption edge produced by the sample. SmX is at present the only technique that can be used with conventional polished thin sections. Data for a broad spectrum of minerals have been produced and indicate that SmX can be used with a large variety of samples types.

  15. Fischer Tropsch synthesis : influence of Mn on the carburization rates and activities of Fe-based catalysts by TPR-EXAFS/XANES and catalyst testing.

    SciTech Connect

    Ribeiro, M. C.; Jacobs, G.; Pendyala, R.; Davis, B. H.; Cronauer, D. C.; Kropf, A. J.; Marshall, C. L.

    2011-03-24

    Fe-based catalysts containing different amounts of Mn were tested for Fischer-Tropsch synthesis using a stirred tank reactor at 270 C, 1.21 MPa, and H{sub 2}:CO = 0.7. Catalyst activation by carburization with 10% CO/He was followed by Temperature Programmed Reduction/X-ray Absorption Spectroscopy (TPR-EXAFS/XANES) from room temperature to 300 C. {gamma}-Fe{sub 2}O{sub 3} was converted into iron carbides, whereas MnO{sub x} was reduced to oxygen deficient MnO. Mn hindered Fe carburization, such that the carburized catalyst displayed higher Fe{sub 3}O{sub 4} content than the catalyst without Mn. EXAFS fitting indicates that the carburized catalyst contained a mixture of Hgg carbide, Fe{sub 3}O{sub 4}, and Mn oxides. Increasing Mn content led to higher CH{sub 4} and light product selectivities, and lower light olefin selectivities. Higher and stable conversions were obtained with a catalyst containing an almost equimolar Fe/Mn ratio relative to the catalyst without Mn. Selectivity trends are attributed to the higher WGS rates observed on the FeMn catalysts, consistent with the structural differences observed.

  16. Synchrotron micro-XRF and micro-XANES confirmation of the uptake and translocation of TiO₂ nanoparticles in cucumber (Cucumis sativus) plants.

    PubMed

    Servin, Alia D; Castillo-Michel, Hiram; Hernandez-Viezcas, Jose A; Diaz, Baltazar Corral; Peralta-Videa, Jose R; Gardea-Torresdey, Jorge L

    2012-07-17

    Advances in nanotechnology have raised concerns about possible effects of engineered nanomaterials (ENMs) in the environment, especially in terrestrial plants. In this research, the impacts of TiO(2) nanoparticles (NPs) were evaluated in hydroponically grown cucumber (Cucumis sativus) plants. Seven day old seedlings were treated with TiO(2) NPs at concentrations varying from 0 to 4000 mg L(-1). At harvest, the size of roots and shoots were measured. In addition, micro X- ray fluorescence (micro-XRF) and micro X-ray absorption spectroscopy (micro-XAS), respectively, were used to track the presence and chemical speciation of Ti within plant tissues. Results showed that at all concentrations, TiO(2) significantly increased root length (average >300%). By using micro-XRF it was found that Ti was transported from the roots to the leaf trichomes, suggesting that trichomes are possible sink or excretory system for the Ti. The micro-XANES spectra showed that the absorbed Ti was present as TiO(2) within the cucumber tissues, demonstrating that the TiO(2) NPs were not biotransformed. PMID:22715806

  17. 3D Epitaxy of Graphene nanostructures in the Matrix of Ag, Al and Cu

    NASA Astrophysics Data System (ADS)

    Salamanca-Riba, Lourdes; Isaacs, Romaine; Wuttig, Manfred; Lemieux, Melburne; Hu, Liangbing; Iftekhar, Jaim; Rashkeev, Sergey; Kukla, Maija; Rabin, Oded; Mansour, Azzam

    2015-03-01

    Graphene nanostructures in the form ribbons were embedded in the lattice of metals such as Ag, Cu, and Al in concentrations up to 36.4 at.%, 21.8 at% and 10.5 at.%, respectively. These materials are called covetics. Raman scattering from Ag and Al covetics indicate variations in the intensity of peaks at ~ 1,300 cm-1 and 1,600 cm-1 with position on the sample. These peaks are associated with the D (defects) and G (graphite E2g mode) peaks of graphitic carbon with sp2 bonding and reveal various degrees of imperfections in the graphene layers. First principles calculations of the dynamic matrix of Ag and Al covetics show bonding between C and the metal. EELS mapping of the C-K edge and high resolution lattice images show that the graphene-like regions form ribbons with epitaxial orientation with the metal lattice of Ag and Al. The temperature dependences of the resistivites of Ag and Cu covetics are similar to those of the pure metals with only slight increase in resistivity. Films of Cu covetic deposited by e-beam evaporation and PLD show higher transmittance and resistance to oxidation than pure metal films of the same thickness indicating that copper covetic films can be used for transparent electrodes. Funded by DARPA/ARL Grant No. W911NF-13-1-0058, and ONR Award No N000141410042.

  18. Synchrotron EXAFS and XANES spectroscopy studies of transition aluminas doped with La and Cr for catalytic applications

    NASA Astrophysics Data System (ADS)

    Glazoff, Michael V.

    2016-04-01

    Transition aluminas doped with Cr find widespread application in the dehydrogenation catalysis industry, while La-stabilized transition aluminas are used extensively for high-temperature application as catalytic supports (Wefers and Misra in Oxides and hydroxides of aluminum, Alcoa Laboratories, Pittsburgh, 1987). In this work, detailed synchrotron XAFS spectroscopy studies were conducted to shed light upon the atomic mechanisms of surface and subsurface reconstructions and/or catalytic support stabilization of doped aluminas. It was demonstrated that in four transition aluminas doped with Cr, it is the atoms which are mostly in the state of oxidation Cr3+ and enter nanoparticles of Cr-bearing phases (Cr2O3 in the case of gamma- and chi-alumina). In the transition series aluminas: "gamma- chi- theta- eta-alumina," the change of properties (in particular, the dramatic increase in dehydrogenation catalytic activity and catalyst longevity and the coloration of samples) takes place because of the reduction in the average size of Cr clusters and their appearance on the Al2O3 surface, probably responsible for change in catalytic activity. It was demonstrated that in the samples of gamma-alumina doped with La any substantial change in the local coordination of the La atoms takes place only upon heating up to 1400 °C. This makes the La-stabilized gamma-alumina a perfect catalytic support for the numerous applications, e.g., catalytic three-way conversion of automobile exhaust gases. This change manifested itself in the form of increased La-O bond lengths and the La coordination number (from 8 to 12). Furthermore, it was demonstrated that the local environment of La in this new La-bearing phase cannot be explained in terms of the LaAlO3 formation. The absence of the La atoms in the second coordination sphere favors monoatomic distribution of La atoms on grain boundaries, proving that only very small amount of this rare earth material is required to achieve full

  19. Oxidative-reforming of model biogas over NiO/Al2O3 catalysts: The influence of the variation of support synthesis conditions

    NASA Astrophysics Data System (ADS)

    Asencios, Yvan J. O.; Elias, Kariny F. M.; Assaf, Elisabete M.

    2014-10-01

    In this study, nickel catalysts (20 wt%) supported on γ-Al2O3 were prepared by the impregnation method. The γ-Al2O3, was synthesized by precipitation of bayerite gel obtained from aluminum scrap. The synthetic conditions of the bayerite gel varied as follows: precipitation pH ranging from 6 to 7; ageing temperature ranging from 25 to 80 °C, the calcination temperature for all samples was 500 °C. The catalysts and the supports were analyzed by temperature programmed reduction (H2-TPR), X-ray diffraction (XRD), physisorption of N2 (BET), X-ray absorption near-edge structure (XANES) and scanning electron microscopy (SEM). Isopropanol decomposition reactions over the catalysts were carried out to evaluate their acidity. SEM images of the spent catalysts showed that the morphology of the carbon formed during the reaction is of the filamentous type. The TPR analysis of the catalysts showed the presence of NiO species weakly interacted with the support as well as stoichiometric and non-stoichiometric nickel aluminate, the reduction of these species was also observed by XANES analysis. XRD analysis of the fresh catalyst showed peaks assigned to NiO, NiAl2O4 and γ-Al2O3. The best catalysts (samples NiAl7-25 and NiAl7-80) synthesized in this report showed high stability and high conversion values (CH4 (70%) and CO2 (78%)). These catalysts showed better performance than the catalyst supported on commercial γ-Al2O3, which showed a high coke formation which affected the course of the reaction. The γ-Al2O3 synthesized from bayerite obtained at neutral pH conditions was the best support for nickel catalysts in the oxidative-reforming of model biogas.

  20. Experimental and Theoretical X-Ray Absorption Studies of Strain Effects in Films

    NASA Astrophysics Data System (ADS)

    Tyson, Trevor A.; Qian, Qing; Kao, Chi-Chang; Prellier, Wilfred

    2000-03-01

    From the pioneering work of Jin et al. [1], is was realized that the magnetoresistance of CMR films exhibits a strong thickness dependence. Recent theoretical work by Millis et al.[2], revealed that the Curie temperature of manganites is extremely sensitive to biaxial strain. The atomic details of the correlations between strain and magnetic properties present an area which has not been thoroughly explored. We find that the Mn K-Edge x-ray absorption near edge spectra (XANES) are strongly modified by local structural distortions such as Jahn-Teller (JT) distortions. We find that the measured asymmetry (JT induced) in the polarized XANES of Nd_0.5Sr_0.5MnO3 films correlates with the transition from charge ordering to metallic behavior [3]. Combined experimental and theoretical XANES and XAFS studies can be used to identify the structural phases present in films as a function of thickness. This work is supported by National Science Foundation Career Grant DMR-9733862 and by DOE Grant DE-FG02-97ER45665. [1] S. Jin et al., Appl. Phys. Lett. 67, 557 (1995)., [2] A. J. Millis et al., J. Appl. Phys. 83, 1588 (1998), [3] W. Prellier et al., Appl. Phys. Lett. 75, 397 (1999).

  1. [alpha]-Al[sub 2]O[sub 3] (0001) surfaces: Atomic and electronic structure

    SciTech Connect

    Gauntier, M.; Van, L.P.; Pollak, M.; Thromat, N.; Jollet, F.; Duraud, J.P. ); Renaud, G.; Villette, B. )

    1994-02-01

    New results on the ([radical]31 [times] [radical]31) R[+-]9[degree] reconstructed [alpha]-Al[sub 2]O[sub 3] (0001) surface, which can be obtained after heating at high temperature (1,400 C) under vacuum, are presented. The atomic structure has been studied by combining low-energy electron diffractometry and grazing incidence X-ray scattering. The surface structure is found to be perfectly commensurable with the underlying bulk lattice. The surface consists of hexagonal zones of two, nearly perfect, close-packed Al (111) planes separated by a defect of hexagonal periodicity with a parameter of 26.44 [angstrom]. This model is consistent with previous surface studies of this reconstruction. The electronic structure has been investigated using valence band photoemission spectroscopy, X-ray absorption spectroscopy at the O K edge, electron energy loss spectroscopy, and X-ray-induced Auger electron spectroscopy. Interpretation of these experimental data in the frame of a self-consistent, tight-binding calculation leads to the conclusion that the ([radical]31 [times] [radical]31) R[+-]9[degree] reconstructed surface is more covalent than the (1 [times] 1) surface. Significant changes in the Al-O hybridizations are observed; these are likely due to a difference in the interatomic distances along the [0001] axis (relaxations). The increase of covalent character is mainly due to a strong decrease of the Madelung field on the reconstructed surface.

  2. XRD and XAS structural study of CuAlO2 under high pressure.

    PubMed

    Pellicer-Porres, J; Segura, A; Ferrer-Roca, Ch; Polian, A; Munsch, P; Kim, D

    2013-03-20

    We present the results of x-ray diffraction and x-ray absorption spectroscopy experiments in CuAlO(2) under high pressure. We discuss the polarization dependence of the x-ray absorption near-edge structure at the Cu K-edge. XRD under high pressure evidences anisotropic compression, the a-axis being more compressible than the c-axis. EXAFS yields the copper-oxygen bond length, from which the only internal parameter of the delafossite structure is deduced. The combination of anisotropic compression and the internal parameter decrease results in a regularization of the AlO(6) octahedra. The anisotropic compression is related to the chemical trends observed in the lattice parameters when Al is substituted by other trivalent cations. Both experiments evidence the existence of an irreversible phase transition that clearly manifests at 35 ± 2 GPa. The structure of the high-pressure polymorph could not be determined, but it implies a change of the Cu environment, which remains anisotropic. Precursor effects are observed from the lowest pressures, which are possibly related to crystal breaking at a submicroscopic scale with partial reorientation of the crystallites. PMID:23423689

  3. Local structure investigation of Co doped ZnO thin films prepared by RF sputtering technique

    NASA Astrophysics Data System (ADS)

    Yadav, A. K.; Haque, S. Maidul; Shukla, D.; Phase, D. M.; Jha, S. N.; Bhattacharyya, D.

    2016-05-01

    Co doped ZnO thin films have been prepared using rf magnetron sputtering technique with varying Co doping concentration. GIXRD has been used to probe long range order and Zn, Co and Oxygen K-edge XAFS measurements have been used for investigating local structure around Zn and Co atoms. GIXRD results show wurzite structure of the samples while XANES and EXAFS results at Zn and Co K edge show that Co is going at Zn site in ZnO matrix and no other phase is present. These results are further confirmed by O K edge and Co L2,3 edge XANES measurements.

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

    DOE PAGESBeta

    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 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

  5. Discharge/charge reaction mechanisms of FeS2 cathode material for aluminum rechargeable batteries at 55°C

    NASA Astrophysics Data System (ADS)

    Mori, Takuya; Orikasa, Yuki; Nakanishi, Koji; Kezheng, Chen; Hattori, Masashi; Ohta, Toshiaki; Uchimoto, Yoshiharu

    2016-05-01

    The aluminum rechargeable battery is a desirable device for large-scale energy storage owing to the high capacity derived from the properties of the aluminum metal anode. The development of cathode materials is needed to compose battery systems. However, the design principles of the cathode materials have not been determined. We focus on the high capacity FeS2 cathode materials and investigate the discharge/charge reaction mechanisms in chloroaluminate ionic liquids as the electrolyte at 55°C. X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS) measurements are performed for the discharged and charged samples. S 3p-orbitals are shown to play an important role in the redox reactions from the results of the S and Fe K-edge XANES spectra. As a result of the redox reaction, FeS2 is transformed into low crystalline FeS and amorphous Al2S3, as shown by the XRD and S, Al, and Fe K-edge XANES spectra. This reaction mechanism is different from the reaction observed with lithium ion.

  6. [Surface studies of absorbents for the removal of SO[sub x] and NO[sub x

    SciTech Connect

    Cooper, B.R.; Montano, P.A.

    1989-01-01

    During this quarter, we continued to study the X-ray absorption spectra of copper compounds. Here we report measurements of the high resolution XANES and EXAFS spectra at the sulfur K-edge (E=2472 eV). Using these results together with the information from other investigations, we attempted to gain a better understanding of the complicated chemical adsorption process taking place on the CuO/Al[sub 2]O[sub 3] surface. In the modeling work we have made a major modification of our methodology that will enable us to treat the adsorption of the SO[sub 2] molecule on the CuO/Al[sub 2]O[sub 3] surface. This involves adoption of a hybrid technique in which we use our previously developed two-dimensional periodic FLMTO technique to model a clean surface, and then use a molecular cluster model to represent the local environment giving changes with the SO[sub 2] adsorption. Experimental Work: The XANES and EXAFS measurements at the sulfur K-edge were carried out on beamline X-19A of the National Synchrotron Light Source (NSLS).

  7. Study of Eu{sup 3+} → Eu{sup 2+} reduction in BaAl{sub 2}O{sub 4}:Eu prepared in different gas atmospheres

    SciTech Connect

    Rezende, Marcos V. dos S.; Valerio, Mário E.G.; Jackson, Robert A.

    2015-01-15

    Highlights: • The effect of different gas atmospheres on the Eu reduction process was studied. • The Eu reduction was monitored analyzing XANES region at the Eu L{sub III}-edge. • Hydrogen reducing agent are the most appropriate gas for Eu{sup 2+} stabilization. • Only a part of the Eu ions can be stabilized in the divalent state. • A model of Eu reduction process is proposed. - Abstract: The effect of different gas atmospheres such as H{sub 2}(g), synthetic air, carbon monoxide (CO) and nitrogen (N{sub 2}) on the Eu{sup 3+} → Eu{sup 2+} reduction process during the synthesis of Eu-doped BaAl{sub 2}O{sub 4} was studied using synchrotron radiation. The Eu{sup 3+} → Eu{sup 2+} reduction was monitored analyzing XANES region when the sample are excited at the Eu L{sub III}-edge. The results show that the hydrogen reducing agent are the most appropriate gas for Eu{sup 2+} stabilization in BaAl{sub 2}O{sub 4} and that only a part of the Eu ions can be stabilized in the divalent state. A model of Eu reduction process, based on the incorporation of charge compensation defects, is proposed.

  8. Fischer-Tropsch synthesis: study of the promotion of Pt on the reduction property of Co/Al2O3 catalysts by in situ EXAFS of Co K and Pt LIII edges and XPS.

    PubMed

    Jacobs, Gary; Chaney, John A; Patterson, Patricia M; Das, Tapan K; Maillot, Julie C; Davis, Burtron H

    2004-09-01

    The addition of platinum metal to cobalt/alumina-based Fischer-Tropsch synthesis (FTS) catalysts increases both the reduction rate and, consequently, the density of active cobalt sites. Platinum also lowers the temperature of the two-step conversion of cobalt oxide to cobalt metal observed in temperature programmed reduction (TPR) as Co3O4 to CoO and CoO to Co0. The interaction of the alumina support with cobalt oxide ultimately determines the active site density of the catalyst surface. This interaction can be controlled by varying the cobalt loading and dispersion, selecting supports with differing surface areas or pore sizes, or changing the noble metal promoter. However, the active site density is observed to depend primarily on the cluster size and extent of reduction, and there is a direct relationship between site density and FTS rate. In this work, in situ extended X-ray absorption fine structure (EXAFS) at the LIII edge of Pt was used to show that isolated Pt atoms interact with supported cobalt clusters without forming observable Pt--Pt bonds. K-edge EXAFS was also used to verify that the cobalt cluster size increases slightly for those systems with Pt promotion. X-ray absorption near-edge spectroscopy (XANES) was used to examine the remaining cobalt clusters after the first stage of TPR, and it revealed that the species were almost entirely cobalt (II) oxide. After the second stage of TPR to form cobalt metal, a residual oxide persists in the sample, and this oxide has been identified as cobalt (II) aluminate using X-ray photoelectron spectroscopy (XPS). Sequential in situ reduction of promoted and unpromoted systems was also monitored through XPS, and Pt was seen to increase the extent of cobalt reduction by a factor of two. PMID:15310958

  9. Zircon solubility and zirconium complexation in H2O+Na2O+SiO2±Al2O3 fluids at high pressure and temperature

    NASA Astrophysics Data System (ADS)

    Wilke, Max; Schmidt, Christian; Dubrail, Julien; Appel, Karen; Borchert, Manuela; Kvashnina, Kristina; Manning, Craig E.

    2012-10-01

    Zircon is an important host mineral for many high-field strength elements (HFSE), particularly Zr and Hf. Thus, its solubility in geologic fluids at high pressure and temperature plays an important role in terrestrial cycling of these elements during processes in the Earth's crust and mantle. We performed in-situ high-pressure, high-temperature measurements of zircon solubility in H2O-Na2Si3O7, H2O-Na2Si3O7+Al2O3, H2O-Na2Si2O5, H2O-NaAlSi3O8 fluids, as well as of baddeleyite solubility in H2O-NaOH fluids, by in-situ synchrotron radiation X-ray fluorescence analysis using hydrothermal diamond-anvil cells. Zirconium complexation in fluids in equilibrium with zircon was constrained by in-situ X-ray absorption near-edge structure (XANES) spectroscopy. Zircon solubility is strongly enhanced by addition of Na2Si3O7 to H2O. The degree of enhancement increases with Na2Si3O7 concentration. The Zr content of fluids containing 10 wt% Na2Si3O7 reached up to 86±2 ppm Zr at 550 °C and 400 MPa. At 30 wt% Na2Si3O7, the maximum Zr concentration was 997±6 ppm at 600 °C and 440 MPa. Zircon solubility in these fluids decreases considerably with pressure and increases slightly with temperature. Addition of Al2O3 decreases the zircon solubility. In H2O-NaAlSi3O8 fluids, the Zr concentrations are in the sub-ppm to ppm range. Zr concentrations in NaOH solutions in equilibrium with baddeleyite reached up to 390±2 ppm at 600 °C and 930 MPa and increase with pressure and temperature. In-situ XANES spectra collected on Zr in H2O-Na2Si3O7, H2O-Na2Si3O7+Al2O3, H2O-NaOH, and H2O-HCl fluids in equilibrium with zircon provide evidence for strong differences in the Zr complexation between these fluids. Comparison of XANES spectra to those of model compounds and ab-initio simulation of XANES spectra revealed [8]Zr for the HCl solution, [7]Zr for the NaOH solution, and [6]Zr for the Na-Al-silicate-bearing solutions. For the latter solutions, formation of alkali zircono-silicate complexes is

  10. Electronic structure of ZnO nanorods studied by angle-dependent x-ray absorption spectroscopy and scanning photoelectron microscopy

    NASA Astrophysics Data System (ADS)

    Chiou, J. W.; Jan, J. C.; Tsai, H. M.; Bao, C. W.; Pong, W. F.; Tsai, M.-H.; Hong, I.-H.; Klauser, R.; Lee, J. F.; Wu, J. J.; Liu, S. C.

    2004-05-01

    Angle-dependent x-ray absorption near-edge structure (XANES) and scanning photoelectron microscopy measurements were performed to differentiate local electronic structures at the tips and sidewalls of highly aligned ZnO nanorods. The overall intensity of the O K-edge XANES spectra is greatly enhanced for small photon incident angles. In contrast, the overall intensity of the Zn K-edge XANES is much less sensitive to the photon incident angle. Both valence-band photoemission and O K-edge XANES spectra show substantial enhancement of O 2p derived states near the valence band maximum and conduction band minimum, respectively. The spatially resolved Zn 3d core level spectra from tip and sidewall regions show the lack of chemical shift. All the results consistently suggest that the tip surfaces of the highly aligned ZnO nanorods are terminated by O ions and the nanorods are oriented in the [0001¯] direction.

  11. Microstructure and Electron Energy-Loss Spectroscopy Analysis of Interface Between Cu Substrate and Al2O3 Film Formed by Aerosol Deposition Method

    NASA Astrophysics Data System (ADS)

    Naoe, Kazuaki; Nishiki, Masashi; Sato, Keishi

    2014-12-01

    Aerosol deposition method is a technique to form dense films by impacting solid particles on a substrate at room temperature. To clarify the bonding mechanism between AD films and substrates, TEM observation and electron energy-loss spectroscopy (EELS) analysis of the interface between Al2O3 AD films and Cu substrates were conducted. The Al2O3 film was directly adhered to the Cu substrate without any void or crack. The film was composed of randomly oriented α-Al2O3 crystal grains of about 10-20 nm large. At the Al2O3/Cu interface, the lattice fringes of the film were recognized, and no interfacial layer with nanometer-order thickness could be found. EELS spectra near O- K edge obtained at the interface had the pre-peak feature at around 528 eV. According to previously reported experiments and theoretical calculations, this suggests interactions between Cu and O in Al2O3 at the interface. It is inferred that not only the anchoring effect but also the ionic bonding and covalent bonding that originates from the Cu-O interactions contribute to the bonding between Al2O3 AD films and Cu substrates.

  12. Structural, electronic structure, and band alignment properties at epitaxial NiO/Al2O3 heterojunction evaluated from synchrotron based X-ray techniques

    NASA Astrophysics Data System (ADS)

    Singh, S. D.; Nand, Mangla; Das, Arijeet; Ajimsha, R. S.; Upadhyay, Anuj; Kamparath, Rajiv; Shukla, D. K.; Mukherjee, C.; Misra, P.; Rai, S. K.; Sinha, A. K.; Jha, S. N.; Phase, D. M.; Ganguli, Tapas

    2016-04-01

    The valence band offset value of 2.3 ± 0.2 eV at epitaxial NiO/Al2O3 heterojunction is determined from photoelectron spectroscopy experiments. Pulsed laser deposited thin film of NiO on Al2O3 substrate is epitaxially grown along [111] direction with two domain structures, which are in-plane rotated by 60° with respect to each other. Observation of Pendellosung oscillations around Bragg peak confirms high interfacial and crystalline quality of NiO layer deposited on Al2O3 substrate. Surface related feature in Ni 2p3/2 core level spectra along with oxygen K-edge soft X-ray absorption spectroscopy results indicates that the initial growth of NiO on Al2O3 substrate is in the form of islands, which merge to form NiO layer for the larger coverage. The value of conduction band offset is also evaluated from the measured values of band gaps of NiO and Al2O3 layers. A type-I band alignment at NiO and Al2O3 heterojunction is also obtained. The determined values of band offsets can be useful in heterojunction based light emitting devices.

  13. Site partitioning of Cr3+ in the trichroic alexandrite BeAl2O4:Cr3+ crystal: contribution from x-ray absorption spectroscopy.

    PubMed

    Bordage, Amélie; Rossano, Stéphanie; Horn, Adolf Heinrich; Fuchs, Yves

    2012-06-01

    X-ray absorption spectroscopy measurements at the Cr K-edge of a trichroic crystal of alexandrite BeAl(2)O(4):Cr(3+) for different orientations of the crystal with respect to the polarization and direction of the x-ray incident beam have been performed. Analysis of the experimental spectra with the help of first-principles calculations of x-ray absorption spectra allowed us to estimate the proportion of chromium Cr(3+) cations among the two different octahedral sites of the alexandrite structure (70% in the C(s) site-30% in the C(i) site). The methodology presented in this work opens up new possibilities in the field of mineralogy for the study of complex minerals containing several sites potentially occupied by several transition elements or for solid solutions. PMID:22551549

  14. Site partitioning of Cr3+ in the trichroic alexandrite BeAl2O4:Cr3+ crystal: contribution from x-ray absorption spectroscopy

    NASA Astrophysics Data System (ADS)

    Bordage, Amélie; Rossano, Stéphanie; Horn, Adolf Heinrich; Fuchs, Yves

    2012-06-01

    X-ray absorption spectroscopy measurements at the Cr K-edge of a trichroic crystal of alexandrite BeAl2O4:Cr3+ for different orientations of the crystal with respect to the polarization and direction of the x-ray incident beam have been performed. Analysis of the experimental spectra with the help of first-principles calculations of x-ray absorption spectra allowed us to estimate the proportion of chromium Cr3+ cations among the two different octahedral sites of the alexandrite structure (70% in the Cs site-30% in the Ci site). The methodology presented in this work opens up new possibilities in the field of mineralogy for the study of complex minerals containing several sites potentially occupied by several transition elements or for solid solutions.

  15. Contrast in Metal-Ligand Effects on PtnM Electrocatalysts with M Equal Ru vs Mo and Sn As Exhibited by in Situ XANES and EXAFS Measurements in Methanol

    SciTech Connect

    Scott, F.; Mukerjee, S; Ramaker, D

    2010-01-01

    In situ X-ray absorption spectroscopy (XAS) measurements, at the Pt L{sub 3} edge (XANES and EXAFS), were carried out on carbon-supported Pt{sub n}Mo and PtSn electrocatalysts in an electrochemical cell in 1 M HClO{sub 4} with 0.3 M methanol. The CO, OH, and H relative adsorbate coverages on Pt are determined as a function of the applied potential via the {Delta}XANES technique and compared with comparable data previously reported for Pt{sub n}Ru. The more reactive Sn and Mo atoms on the Pt surface form the oxide over the potentials of interest, while Ru has variable oxide content depending on Ru island size and potential. The strength of the electronic ligand effect appears to increase in the order Ru < MoO{sub n} < SnO{sub n} < RuO{sub n}, where the Pt-CO bond strength is found to decrease and the Pt-OH bond strength increase with ligand effect. In the Sn and Mo bimetallics, the ligand effect is found to be sufficiently strong to allow CO replacement by H{sub 2} at low potentials. These widely different ligand effects may provide a straightforward explanation for the previously observed anode behavior in fuel cells: Pt{sub n}Mo better in reformate but Pt{sub n}Ru better in methanol.

  16. Understanding Sulfur Poisoning and Regeneration of Nickel Biomass Conditioning Catalysts using X-Ray Absorption Spectroscopy

    SciTech Connect

    Yung, M. M.; Cheah, S.; Kuhn, J. N.

    2013-01-01

    The production of biofuels can proceed via a biomass gasification to produce syngas, which can then undergo catalytic conditioning and reforming reactions prior to being sent to a fuel synthesis reactor. Catalysts used for biomass conditioning are plagued by short lifetimes which are a result of, among other things, poisoning. Syngas produced from biomass gasification may contain between 30-300 ppm H2S, depending on the feedstock and gasification conditions, and H2S is a key catalyst poison. In order to overcome catalyst poisoning, either an H2S-tolerant catalyst or an efficient regeneration protocol should be employed. In this study, sulfur K-edge X-ray absorption near edge spectroscopy (XANES) was used to monitor sulfur species on spent catalyst samples and the transformation of these species from sulfides to sulfates during steam and air regeneration on a Ni/Mg/K/Al2O3 catalyst used to condition biomass-derived syngas. Additionally, nickel K-edge EXAFS and XANES are used to examine the state of nickel species on the catalysts. Post-reaction samples showed the presence of sulfides on the H2S-poisoned nickel catalyst and although some gaseous sulfur species were observed to leave the catalyst bed during regeneration, sulfur remained on the catalyst and a transformation from sulfides to sulfates was observed. The subsequent H2 reduction led to a partial reduction of sulfates back to sulfides. A proposed reaction sequence is presented and recommended regeneration strategies are discussed.

  17. Mechanism of X-ray excited optical luminescence (XEOL) in europium doped BaAl2O4 phosphor.

    PubMed

    Rezende, Marcos V Dos S; Montes, Paulo J R; Andrade, Adriano B; Macedo, Zelia S; Valerio, Mário E G

    2016-06-29

    This paper reports a luminescence mechanism in Eu-doped BaAl2O4 excited with monochromatic X-rays (also known as X-ray excited optical luminescence - XEOL) from synchrotron radiation. The material was prepared via a proteic sol-gel methodology. The X-ray absorption near edge structures (XANES) at the Ba LIII- and Eu LIII-edges exhibit typical absorption spectra. XEOL spectra recorded in energy ranges, either around the Ba LIII- or Eu LIII-edges, showed important differences concerning the intensity of the Eu(2+) or Eu(3+) emission bands. Nevertheless, the total area under the XEOL spectra increases as the energy of the X-ray photons increases in both ranges (Ba LIII- and Eu LIII-edges). PMID:27306425

  18. Ferromagnetism in homogeneous (Al,Co)-codoped 4H-silicon carbides

    NASA Astrophysics Data System (ADS)

    Zhang, X. H.; Han, J. C.; Zhou, J. G.; Xin, C.; Zhang, Z. H.; Song, B.

    2014-08-01

    In view of the recent controversies on above room-temperature (RT) ferromagnetism (FM) in transition-metal (TM) doped silicon carbides (SiC), the present paper aims to shed some light on the natural origin of long-range magnetic order by investigating the (Al, Co)-doped 4H-SiC, both experimentally and theoretically. A combination of characterizations means including X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM) and X-ray absorption near-edge structure spectroscopy (XANES) measurement eliminated the presence of any nanoclusters or secondary phases as the source of FM. X-ray absorption near-edge structure spectroscopy analyses provided convincing evidence that no secondary phases such as Co metallic clusters were present when Co and Al are homogeneously inserted in the SiC matrix. RT FM originates from a composite mechanism based on the Ruderman-Kittel-Kasuya-Yosida, and double-exchange interactions. The dopant Al is found to stabilize the crystal structure as well as show the experimental possibility of tuning the magnetization by codoping.

  19. Towards advanced structural analysis of iron oxide clusters on the surface of γ-Al2O3 using EXAFS

    NASA Astrophysics Data System (ADS)

    Boubnov, Alexey; Roppertz, Andreas; Kundrat, Matthew D.; Mangold, Stefan; Reznik, Boris; Jacob, Christoph R.; Kureti, Sven; Grunwaldt, Jan-Dierk

    2016-11-01

    Iron oxide centres are structurally investigated in 0.1% Fe/γ-Al2O3, which is known as highly active catalyst, for instance in the oxidation of CO. The sample was characterised by using X-ray absorption spectroscopy (XAS) in terms of X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS), Mössbauer spectroscopy, X-ray diffraction (XRD) and transmission electron microscopy (TEM). These analyses evidenced high dispersion of the iron oxide entities without significant presence of bulk-like aggregates associated with the low Fe content of the catalyst. A library of structural models of Al2O3-supported surface Fe was created as input for EXAFS fitting. Additionally, several model structures of Fe substituting Al ions in bulk γ-Al2O3 were created with optimised geometry based on density-functional theory (DFT) calculations. From EXAFS refinement of the best 8 out of 24 models, it was found that the trivalent Fe ions are coordinated by 4-5 oxygen atoms and are located on octahedral lattice sites of the exposed surfaces of γ-Al2O3. These iron oxide species exist mainly as a mixture of monomeric and binuclear species and due to the low concentration represent suitable model systems as alternative to single crystal systems for structure-function relationships.

  20. Photoionization of the Fe lons: Structure of the K-Edge

    NASA Technical Reports Server (NTRS)

    Palmeri, P.; Mendoza, C.; Kallman, T.; Bautista, M.; White, Nicholas E. (Technical Monitor)

    2002-01-01

    X-ray absorption and emission features arising from the inner-shell transitions in iron are of practical importance in astrophysics due to the Fe cosmic abundance and to the absence of traits from other elements in the nearby spectrum. As a result, the strengths and energies of such features can constrain the ionization stage, elemental abundance, and column density of the gas in the vicinity of the exotic cosmic objects, e.g. active galactic nuclei (AGN) and galactic black hole candidates. Although the observational technology in X-ray astronomy is still evolving and currently lacks high spectroscopic resolution, the astrophysical models have been based on atomic calculations that predict a sudden and high step-like increase of the cross section at the K-shell threshold (see for instance. New Breit-Pauli R-matrix calculations of the photoionization cross section of the ground states of Fe XVII in the region near the K threshold are presented. They strongly support the view that the previously assumed sharp edge behaviour is not correct. The latter has been caused by the neglect of spectator Auger channels in the decay of the resonances converging to the K threshold. These decay channels include the dominant KLL channels and give rise to constant widths (independent of n). As a consequence, these series display damped Lorentzian components that rapidly blend to impose continuity at threshold, thus reformatting the previously held picture of the edge. Apparent broadened iron edges detected in the spectra of AGN and galactic black hole candidates seem to indicate that these quantum effects may be at least partially responsible for the observed broadening.