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Sample records for polarized cu k-edge

  1. 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.

  2. 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

  3. 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.

  4. 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.

  5. 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.

  6. 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

  7. 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

  8. 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.

  9. 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.

  10. 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.

  11. 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

  12. Polarization dependence of charge-transfer excitations in La2CuO4

    NASA Astrophysics Data System (ADS)

    Lu, Li; Chabot-Couture, Guillaume; Hancock, Jason; Vajk, Owen; Yu, Guichuan; Ishii, Kenji; Mizuki, Jun'ichiro; Casa, Diego; Gog, Thomas; Greven, Martin

    2006-03-01

    We have carried out an extensive resonant inelastic x-ray scattering (RIXS) study of La2CuO4 at the Cu K-edge. Multiple charge-transfer excitations have been identified using the incident photon energy dependence of the cross section and studied carefully with polarizations E//c and E //ab. An analysis of the incident photon energy dependence, the polarization dependence, as well as the K-edge absorption spectra, indicates that the RIXS spectra reveal rich physics about the K-edge absorption process and momentum-dependent charge-transfer excitations in cuprates.

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. 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)].

  19. Polarized X-ray absorption fine structure of La 2CuO 4-y single crystal

    NASA Astrophysics Data System (ADS)

    Oyanagi, Hiroyuki; Oka, Kunihiko; Unoki, Hiromi; Nishihara, Yoshikazu; Murata, Keizo; Matsushita, Tadashi; Tokumoto, Madoka; Kimura, Yoichi

    1989-06-01

    Polarized X-ray absorption fine structure (XAFS) has been measured on the Cu K-edge for undoped La2CuO4-y bulk single crystal (15 × 20 × 3 mm) grown by the top-seeded solution growth method. Strong polarization dependence observed in the near-edge and EXAFS regions demonstrates the quasi-2D character of the CuO2 plane in terms of both electron states and local structure.

  20. 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.

  1. Many-electron effects in anomalous elastic scattering of linearly polarized x-ray photons by Xe near the K-edge

    NASA Astrophysics Data System (ADS)

    Hopersky, A. N.; Yavna, V. A.; Popov, V. A.

    1997-11-01

    Within the non-relativistic approximation the effect of radial monopole rearrangement of electron shells within the field of a vacancy and of the processes of one-photon double excitation - ionization on the differential cross section of anomalous non-zero-angle elastic scattering of linearly polarized x-ray photons by the Xe atom in the region of its 1s-shell ionization threshold is studied. Theoretical results for the anomalous dispersion region of scattering demonstrate a strong dependence of the cross section value on the approximation used.

  2. 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.

  3. 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

  4. Magnetic Nature of the 500 meV peak in La2−xSrxCuO4 Observed with Resonant Inelastic X-ray Scattering at the Cu K-edge

    SciTech Connect

    Hill, J.P.; Ellis, D.S.; Kim, J.; Wakimoto, S.; Birgeneau, R.J.; Shvyd’ko, Y.; Casa, D.; Gog, T.; Ishii, K.; Ikeuchi, K.; Paramekanti, A.; Kim, Y.-J.

    2010-02-15

    We present a comprehensive study of the temperature and doping dependence of the 500 meV peak observed at q = ({pi},0) in resonant inelastic x-ray scattering (RIXS) experiments on La{sub 2}CuO{sub 4}. The intensity of this peak persists above the Neel temperature (T{sub N} = 320 K), but decreases gradually with increasing temperature, reaching zero at around T = 500 K. The peak energy decreases with temperature in close quantitative accord with the behavior of the two-magnon B{sub 1g} Raman peak in La{sub 2}CuO{sub 4} and, with suitable rescaling, agrees with the Raman peak shifts in EuBa{sub 2}Cu{sub 3}O{sub 6} and K{sub 2}NiF{sub 4}. The overall dispersion of this excitation in the Brillouin zone is found to be in agreement with theoretical calculations for a two-magnon excitation. Upon doping, the peak intensity decreases analogous to the Raman mode intensity and appears to track the doping dependence of the spin-correlation length. Taken together, these observations strongly suggest that the 500 meV mode is magnetic in character and is likely a two-magnon excitation.

  5. Incident energy and polarization-dependent resonant inelastic x-ray scattering study of La2CuO4

    NASA Astrophysics Data System (ADS)

    Lu, L.; Hancock, J. N.; Chabot-Couture, G.; Ishii, K.; Vajk, O. P.; Yu, G.; Mizuki, J.; Casa, D.; Gog, T.; Greven, M.

    2006-12-01

    We present a detailed Cu K -edge resonant inelastic x-ray scattering (RIXS) study of the Mott insulator La2CuO4 in the 1-7eV energy loss range. As initially found for the high-temperature superconductor HgBa2CuO4+δ , the spectra exhibit a multiplet of weakly dispersive electron-hole excitations, which are revealed by utilizing the subtle dependence of the cross section on the incident photon energy. The close similarity between the fine structures for in-plane and out-of-plane polarizations is indicative of the central role played by the 1s core hole in inducing charge excitations within the CuO2 planes. On the other hand, we observe a polarization dependence of the spectral weight, and careful analysis reveals two separate features near 2eV that may be related to different charge-transfer processes. The polarization dependence indicates that the 4p electrons contribute significantly to the RIXS cross section. Third-order perturbation arguments and a shake-up of valence excitations are then applied to account for the final-energy resonance in the spectra. As an alternative scenario, we discuss fluorescence-like emission processes due to 1s→4p transitions into a narrow continuum 4p band.

  6. 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.

  7. 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.

  8. 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

  9. 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.

  10. 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

  11. 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.

  12. 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.

  13. 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

  14. 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.

  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. 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.

  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. 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

  19. 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

  20. 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.

  1. High spin polarization and the origin of unique ferromagnetic ground state in CuFeSb

    NASA Astrophysics Data System (ADS)

    Sirohi, Anshu; Singh, Chandan K.; Thakur, Gohil S.; Saha, Preetha; Gayen, Sirshendu; Gaurav, Abhishek; Jyotsna, Shubhra; Haque, Zeba; Gupta, L. C.; Kabir, Mukul; Ganguli, Ashok K.; Sheet, Goutam

    2016-06-01

    CuFeSb is isostructural to the ferro-pnictide and chalcogenide superconductors and it is one of the few materials in the family that are known to stabilize in a ferromagnetic ground state. Majority of the members of this family are either superconductors or antiferromagnets. Therefore, CuFeSb may be used as an ideal source of spin polarized current in spin-transport devices involving pnictide and the chalcogenide superconductors. However, for that the Fermi surface of CuFeSb needs to be sufficiently spin polarized. In this paper we report direct measurement of transport spin polarization in CuFeSb by spin-resolved Andreev reflection spectroscopy. From a number of measurements using multiple superconducting tips we found that the intrinsic transport spin polarization in CuFeSb is high (˜47%). In order to understand the unique ground state of CuFeSb and the origin of large spin polarization at the Fermi level, we have evaluated the spin-polarized band structure of CuFeSb through first principles calculations. Apart from supporting the observed 47% transport spin polarization, such calculations also indicate that the Sb-Fe-Sb angles and the height of Sb from the Fe plane are strikingly different for CuFeSb than the equivalent parameters in other members of the same family thereby explaining the origin of the unique ground state of CuFeSb.

  2. 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.

  3. 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.

  4. Influence of Optical Properties on the Spin Polarization of Cu3P Photoelectrons

    NASA Astrophysics Data System (ADS)

    Chassé, A.; Niebergall, L.

    We have investigated the influence of optical properties of Cu(001) on the spin polarization in Cu3p photoelectron diffraction patterns. The refraction and absorption of light have been taken into account in the calculation of the dipole transition matrix element. Therefore, a general polarization vector of light is defined within a macroscopic theory of electromagnetic fields. Results are shown and discussed for Cu3p photoelectrons excited by linearly or circularly polarized light, respectively. It is shown that the optical behavior of crystals may cause a symmetry breaking in the angular dependence of the photoelectron intensity. Besides, there are strong quantitative changes in the related spin polarization of Cu3p photoelectrons.

  5. 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.

  6. 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.

  7. 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.

  8. 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

  9. 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.

  10. 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.

  11. The enhanced spontaneous dielectric polarization in Ga doped CuFeO{sub 2}

    SciTech Connect

    Shi, Liran; Wei, Meng; Huang, Junwei; Chen, Borong; Shang, Cui; Xia, Zhengcai Long, Zhuo; Ouyang, Zhongwen; Xia, Nianming

    2014-11-07

    The magnetic and dielectric polarization properties of the single crystal samples of CuFe{sub 1−x}Ga{sub x}O{sub 2} (x = 0 and 0.02) are investigated. Experimental results show that the magnetization and dielectric polarizations are anisotropy and coupled together. Compared with pure CuFeO{sub 2}, in the case with the magnetic field parallel to the c axis, a field-induced phase transition with a hysteresis is clearly observed between the five-sublattice (5SL) and three-sublattice (3SL) phases. Specially, an obvious spontaneous dielectric polarization is observed in CuFe{sub 0.98}Ga{sub 0.02}O{sub 2} in a lower magnetic field region, indicating that the Ga doping has an effect on the enhancement of spontaneous dielectric polarization. Based on the dilution effect, change of exchange interaction, and partial release of the spin frustration due to the structural modulation of the Ga ion dopant, the origin of the magnetization, and spontaneous polarization characteristics are discussed and the complete dielectric polarization diagrams are assumed.

  12. Spin polarization and exchange coupling of Cu and Mn atoms in paramagnetic CuMn diluted alloys induced by a Co layer

    SciTech Connect

    Abes, M.; Arena, D.; Atkinson, D.; Tanner, B.K.; Charlton, T.R.; Langridge, S.; Hase, T.P.A.; Ali, M.; Marrows, C.H.; Hickey, B.J.; Neudert, Al; Hicken, R.J.; Wilkins, S.B.; Mirone, A.; Lebegue, S.

    2010-11-09

    Using the surface, interface, and element specificity of x-ray resonant magnetic scattering in combination with x-ray magnetic circular dichroism, we have spatially resolved the magnetic spin polarization, and the associated interface proximity effect, in a Mn-based high-susceptibility material close to a ferromagnetic Co layer. We have measured the magnetic polarization of Mn and Cu3d electrons in paramagnetic CuMn alloy layers in [Co/Cu(x)/CuMn/Cu(x)]{sub 20} multilayer samples with varying copper layer thicknesses from x=0 to 25 {angstrom}. The size of the Mn and CuL{sub 2,3} edge dichroism shows a decrease in the Mn-induced polarization for increasing copper thickness indicating the dominant interfacial nature of the Cu and Mn spin polarization. The Mn polarization is much higher than that of Cu. Evidently, the Mn moment is a useful probe of the local spin density. Mn atoms appear to be coupled antiferromagnetically with the Co layer below x = 10 {angstrom} and ferromagnetically coupled above. In contrast, the interfacial Cu atoms remain ferromagnetically aligned to the Co layer for all thicknesses studied.

  13. Cu(2)ZnSnS(4) nanocrystal dispersions in polar liquids.

    PubMed

    Tosun, B Selin; Chernomordik, Boris D; Gunawan, Aloysius A; Williams, Bryce; Mkhoyan, K Andre; Francis, Lorraine F; Aydil, Eray S

    2013-05-01

    Cu(2)ZnSnS(4) (CZTS) nanocrystals sterically stabilized with oleic acid and oleylamine ligands and dispersed in nonpolar organic liquids have been extracted into, and electrostatically stabilized in, polar liquids by covering their surfaces with S(2-). PMID:23519191

  14. 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.

  15. Depth-selective measurements of induced magnetic polarization in the Cu layer of Gd/Cu multilayers by [superscript 119] Sn Mössbauer Spectroscopy

    SciTech Connect

    Ohkochi, T.; Hosoito, N.; Mibu, K.

    2010-07-20

    We performed {sup 119}Sn Moessbauer spectroscopic measurements on Gd/Cu multilayers with {sup 119}Sn probing atoms. The Cu layers are delta-doped with Sn probes at a certain depth. Hyperfine fields are observed in the Moessbauer spectra at low temperatures below the Curie temperature of the Gd layers. From the temperature-dependent measurements, the hyperfine field is found to be proportional to the spontaneous magnetization of the Gd layer. The result indicates that the Gd magnetization induces magnetic polarization in the Cu layers. The hyperfine field per Gd magnetization is found to be {approx}40 kOe/{mu}{sub B(Gd)}, regardless of the position of the {sup 119}Sn atoms and the Cu thickness (20-40 {angstrom}), suggesting that the magnetic polarization in the Cu layer is uniform at any depth from the Gd/Cu interface.

  16. 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

  17. 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

  18. 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

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

    NASA Astrophysics Data System (ADS)

    Shikhaliev, Polad M.

    2012-03-01

    Photon counting spectral computed tomography (PCSCT) provides material selective CT imaging at a single CT scan and fixed tube voltage. The PCSCT data are acquired in several energy ranges (bins) arranged over the x-ray spectrum. The quasi-monoenergetic CT images are acquired in these energy bins and are used for material decomposition. The PCSCT exhibits inherent limitations when material decomposition is performed using energy bins. For effective material decomposition, the energy bins used for material decomposition should be sufficiently narrow and well separated. However, when narrow bins are used, a large fraction of the detected x-ray counts is lost and statistical noise is increased. Alternatively, the x-ray spectrum can be split into a few larger bins with no gap in between and all detected x-ray photons can be used for material decomposition. However, in this case the energy bins are too wide and not well separated, which results in suboptimal material decomposition. The above contradictory requirements can be resolved if the x-ray photons are physically removed from the regions of the energy spectrum between the energy bins. Such a selective removal can be performed using filtration of the x-ray beam by high-Z filter materials with appropriate positions of K-edge energies. The K-edge filtration of x-rays can, therefore, provide necessary gaps between the energy bins with no dose penalty to the patient. In the current work, we proposed using selective K-edge filtration of x-rays in PCSCT and performed the first experimental investigation of this approach. The PCSCT system included a cadmium zinc telluride semiconductor detector with 2 × 256 pixels and 1 × 1 mm2 pixel size, and five energy bins. The CT phantom had 14 cm diameter and included contrast elements of iodine, gold and calcifications with clinically relevant concentrations. The tube voltages of 60, 90 and 120 kVp were used. K-edge filters based on Ba (Ek = 37.44 keV) were used for a 60 kVp tube

  20. 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.

  1. 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.

  2. 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.

  3. Magnetism and magnetoelectricity in the polar oxide α-Cu2V2O7

    NASA Astrophysics Data System (ADS)

    Lee, Y.-W.; Jang, T.-H.; Dissanayake, S. E.; Lee, Seunghun; Jeong, Yoon H.

    2016-01-01

    Single crystals of the orthorhombic polar oxide α-Cu2V2O7 with space group Fdd2 are synthesized and their physical properties are measured. Neutron powder diffraction is also performed on a polycrystal sample to extract the magnetic structure. The ground state is shown to be weakly ferromagnetic, that is, collinearly antiferromagnetic in the a-direction with a small remanent magnetization in the c-direction. When an external magnetic field is applied in the c-direction, further spin canting, accompanied by the induced electric polarization, occurs. It is demonstrated that the magnetoelectric effect in α-Cu2V2O7 is adequately described if spin-dependent p\\text-d hybridization due to spin-orbit coupling as well as magnetic domain effects are simultaneously taken into account. We discuss the implication of the present result in the search for materials with multiferroicity and/or magnetoelectricity.

  4. Self-Assembly of Glycine on Cu (001): The tale of Temperature and Polarity

    NASA Astrophysics Data System (ADS)

    Xu, Lifang; Xu, Jing; Lin, Zheshuai; Meng, Sheng; Wang, Enge

    Glycine on Cu(001) is used as an example to illustrate the critical role of molecular polarity and finite temperature effect in self-assembly of bio-molecules at a metal surface. A unified picture for glycine self-assembly on Cu(001) is derived based on full polarity compensation considerations. Temperature plays a non-trivial role: the ground-state structure at 0 K is absent at room temperature, where intermolecular hydrogen bonding overweighs competing molecule-substrate interactions. The unique p(2×4) structure predicted as the most stable structure was confirmed by ab initio molecular dynamics simulations, whose scanning tunneling microscopy images and anisotropic free-electron-like dispersion are in excellent agreement with experiments. Moreover, the rich self-assembling patterns including the heterochiral and homochiral phases, and their interrelationships are entirely governed by the same mechanism.

  5. 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

  6. 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.

  7. 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.

  8. 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

  9. 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.

  10. 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}

  11. 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.

  12. 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.

  13. Polarized Raman spectroscopy of Cu-poor and Zn-rich single-crystal Cu2ZnSnSe4

    NASA Astrophysics Data System (ADS)

    Nam, Dahyun; Kim, Jungcheol; Lee, Jae-Ung; Nagaoka, Akira; Yoshino, Kenji; Cha, Wonsuk; Kim, Hyunjung; Hwang, In Chul; Yoon, Kyung Byung; Cheong, Hyeonsik

    2014-10-01

    Cu2ZnSnSe4 (CZTSe) is a p-type semiconductor which has been developed as an absorber layer of polycrystalline thin film solar cells. Generally, Cu-poor and Zn-rich compositions tend to give the highest solar conversion efficiencies. Raman spectroscopy has been used to detect secondary phases such as ZnSe and Cu2SnSe3 in CZTSe thin films. However, the fundamental phonon modes in single-crystal CZTSe with a composition matching that of high-efficiency thin film solar cells have not yet been fully understood. We performed polarized Raman measurements on Cu-poor and Zn-rich single-crystal CZTSe and identified 12 peaks, including two low-frequency peaks. By comparing the polarization dependence of the Raman peaks with a group theoretical analysis, we concluded that the crystal structure of CZTSe single-crystal is kesterite and made appropriate peak assignments.

  14. Defect-induced Nonpolar-to-polar Transition at the Surface of CuInSe2

    SciTech Connect

    Jaffe, John E.; Zunger, Alex

    2003-09-10

    In contrast to zinc-blende semiconductors, where the nonpolar (110) surface has the lowest energy, our first-principles calculations on the chalcopyrite semiconductor CuInSe2 reveal that facets terminated by the (112)-cation and -Se polar surfaces are lower in energy than the unfaceted (110) plane, despite the resulting increased surface area. This explains the hitherto puzzling existence of polar microfacets on nominally nonpolar (110) chalcopyrite surfaces. The extraordinary stability of these polar facets originates from the effective neutralization of surface charge by low-energy ordered CuIn antisite or Cu vacancy surface defects, while the relaxed but defect-free (112) surface is metallic and much higher in energy. We explain the low carrier density of the observed faceted surface in terms of autocompensation between opposite-polarity facets.

  15. 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

  16. 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.

  17. 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

  18. Polarized Raman scattering study of kesterite type Cu2ZnSnS4 single crystals

    NASA Astrophysics Data System (ADS)

    Guc, Maxim; Levcenko, Sergiu; Bodnar, Ivan V.; Izquierdo-Roca, Victor; Fontane, Xavier; Volkova, Larisa V.; Arushanov, Ernest; Pérez-Rodríguez, Alejandro

    2016-01-01

    A non-destructive Raman spectroscopy has been widely used as a complimentary method to X-ray diffraction characterization of Cu2ZnSnS4 (CZTS) thin films, yet our knowledge of the Raman active fundamental modes in this material is far from complete. Focusing on polarized Raman spectroscopy provides important information about the relationship between Raman modes and CZTS crystal structure. In this framework the zone-center optical phonons of CZTS, which is most usually examined in active layers of the CZTS based solar cells, are studied by polarized resonant and non-resonant Raman spectroscopy in the range from 60 to 500 cm-1 on an oriented single crystal. The phonon mode symmetry of 20 modes from the 27 possible vibrational modes of the kesterite structure is experimentally determined. From in-plane angular dependences of the phonon modes intensities Raman tensor elements are also derived. Whereas a strong intensity enhancement of the polar E and B symmetry modes is induced under resonance conditions, no mode intensity dependence on the incident and scattered light polarization configurations was found in these conditions. Finally, Lyddane-Sachs-Teller relations are applied to estimate the ratios of the static to high-frequency optic dielectric constants parallel and perpendicular to c-optical axis.

  19. Polarized Raman scattering study of kesterite type Cu2ZnSnS4 single crystals

    PubMed Central

    Guc, Maxim; Levcenko, Sergiu; Bodnar, Ivan V.; Izquierdo-Roca, Victor; Fontane, Xavier; Volkova, Larisa V.; Arushanov, Ernest; Pérez-Rodríguez, Alejandro

    2016-01-01

    A non-destructive Raman spectroscopy has been widely used as a complimentary method to X-ray diffraction characterization of Cu2ZnSnS4 (CZTS) thin films, yet our knowledge of the Raman active fundamental modes in this material is far from complete. Focusing on polarized Raman spectroscopy provides important information about the relationship between Raman modes and CZTS crystal structure. In this framework the zone–center optical phonons of CZTS, which is most usually examined in active layers of the CZTS based solar cells, are studied by polarized resonant and non-resonant Raman spectroscopy in the range from 60 to 500 cm−1 on an oriented single crystal. The phonon mode symmetry of 20 modes from the 27 possible vibrational modes of the kesterite structure is experimentally determined. From in-plane angular dependences of the phonon modes intensities Raman tensor elements are also derived. Whereas a strong intensity enhancement of the polar E and B symmetry modes is induced under resonance conditions, no mode intensity dependence on the incident and scattered light polarization configurations was found in these conditions. Finally, Lyddane-Sachs-Teller relations are applied to estimate the ratios of the static to high-frequency optic dielectric constants parallel and perpendicular to c-optical axis. PMID:26776727

  20. Polarized Raman scattering study of kesterite type Cu2ZnSnS4 single crystals.

    PubMed

    Guc, Maxim; Levcenko, Sergiu; Bodnar, Ivan V; Izquierdo-Roca, Victor; Fontane, Xavier; Volkova, Larisa V; Arushanov, Ernest; Pérez-Rodríguez, Alejandro

    2016-01-01

    A non-destructive Raman spectroscopy has been widely used as a complimentary method to X-ray diffraction characterization of Cu2ZnSnS4 (CZTS) thin films, yet our knowledge of the Raman active fundamental modes in this material is far from complete. Focusing on polarized Raman spectroscopy provides important information about the relationship between Raman modes and CZTS crystal structure. In this framework the zone-center optical phonons of CZTS, which is most usually examined in active layers of the CZTS based solar cells, are studied by polarized resonant and non-resonant Raman spectroscopy in the range from 60 to 500 cm(-1) on an oriented single crystal. The phonon mode symmetry of 20 modes from the 27 possible vibrational modes of the kesterite structure is experimentally determined. From in-plane angular dependences of the phonon modes intensities Raman tensor elements are also derived. Whereas a strong intensity enhancement of the polar E and B symmetry modes is induced under resonance conditions, no mode intensity dependence on the incident and scattered light polarization configurations was found in these conditions. Finally, Lyddane-Sachs-Teller relations are applied to estimate the ratios of the static to high-frequency optic dielectric constants parallel and perpendicular to c-optical axis. PMID:26776727

  1. Development of a graphite polarization analyzer for resonant inelastic x-ray scattering

    SciTech Connect

    Gao Xuan; Burns, Clement; Li Chengyang; Casa, Diego; Upton, Mary; Gog, Thomas; Kim, Jungho

    2011-11-15

    Resonant inelastic x-ray scattering (RIXS) is a powerful technique for studying electronic excitations in correlated electron systems. Current RIXS spectrometers measure the changes in energy and momentum of the photons scattered by the sample. A powerful extension of the RIXS technique is the measurement of the polarization state of the scattered photons which contains information about the symmetry of the excitations. This long-desired addition has been elusive because of significant technical challenges. This paper reports the development of a new diffraction-based polarization analyzer which discriminates between linear polarization components of the scattered photons. The double concave surface of the polarization analyzer was designed as a good compromise between energy resolution and throughput. Such a device was fabricated using highly oriented pyrolytic graphite for measurements at the Cu K-edge incident energy. Preliminary measurements on a CuGeO{sub 3} sample are presented.

  2. Polarized Rayleigh and Raman Study of single CuO Nanowire

    NASA Astrophysics Data System (ADS)

    Lu, Qiujie; Wu, Jian; Gutierrez, Humberto; Russin, Timothy; Eklund, Peter

    2009-03-01

    Crystalline CuO is an interesting Ferroelectric and Ferromagnetic system which we have recently grown in nanowire (NW) form. In this paper, we present results of Raman and Rayleigh scattering studies of individual CuO NWs to probe optical antenna effects that we first discovered in GaP NWs. We have shown that these antenna effects can, in general, strongly mask Raman selection rules in semiconducting nanowires[1]. Using a microRaman spectrometer, polarized light scattering experiments (backscattering geometry) were carried on NWs suspended over holes in a TEM grid. TEM was therefore also used to identify the growth axis and determine the NW diameter. As a function of the angle q between the NW axis and the incident laser field, we collect the Rayleigh scattering intensity as well as the Raman LO and TO optical phonon scattering intensity. These results can then be used to quantify the optical antenna effects in the CuO system. NWs of different diameters, from 70nm to 200 nm were studied; the results depend dramatically on the NW diameter. Our results will be compared to EM calculations based on the DDA approximation. This work is supported by NSF NIRT, grant DMR-0304178. [1] Chen G. Jian Wu, etc., Nano Lett. 2008 Vol.8 pp. 1341-1346.

  3. Magnetic properties of O2 adsorbed on Cu(100): A spin-polarized metastable He beam study

    NASA Astrophysics Data System (ADS)

    Kurahashi, M.; Sun, X.; Yamauchi, Y.

    2012-12-01

    Magnetic properties of O2 adsorbed on Cu(100) were investigated by monitoring the spin dependence in Penning ionization of metastable He(23S) under external magnetic fields of 0-5 T. A clear spin polarization was found for the 3σg and 1πu orbitals of physisorbed O2 under external fields, while the spin polarization disappeared when O2 was changed into the chemisorbed state at >50 K. The magnetic susceptibility at the surface of multilayer and monolayer of physisorbed O2 on Cu(100) was similar to that for the bulk liquid O2. Observed exchange splittings and spin polarization suggest that a physisorbed O2 molecule has a magnetic moment close to that for an isolated O2 molecule even at submonolayer coverages, while a density functional theory calculation predicts a much reduced magnetic moment for O2 directly adsorbed on Cu(100).

  4. 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

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. 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

  11. 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

  12. 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.

  13. 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

  14. 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.

  15. 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.

  16. 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.

  17. Optical Properties of CuInSe2 Bulk Material Characterized by a Fixed Polarizer-Rotating Analyzer Spectroscopic Ellipsometer

    NASA Astrophysics Data System (ADS)

    Hidalgo, M. L.; Lachab, M.; Zouaoui, A.; Alhamed, M.; Llinares, C.; Peyrade, J. P.; Galibert, J.

    1997-03-01

    In the present paper, we have investigated the optical properties of CuInSe2 single and polycrystals using a broad band fixed polarizer-rotating analyzer spectroscopic ellipsometer (RAE) in the spectral range 250 to 1700 nm. The wavelength dependence of CuInSe2 optical constants was studied assuming a two-phase system: the ambient medium and the sample. We have determined interband transition energies near and above the bandgap by a detailed analysis of the absorption spectrum and through the third joint-density-of-states (JDOS) derivative computation. Measurements were carried out on nearly-stoichiometric and In-rich CuInSe2 substrates.

  18. The growth of heteroepitaxial CuInSe{sub 2} on free-standing N-polar GaN

    SciTech Connect

    Shih, Cheng-Hung; Lo, Ikai You, Shuo-Ting; Tsai, Cheng-Da; Tseng, Bae-Heng; Chen, Yun-Feng; Chen, Chiao-Hsin; Lee, Chuo-Han; Lee, Wei-I; Hsu, Gary Z. L.

    2014-12-15

    We report that chalcopyrite CuInSe{sub 2} thin films were grown on free-standing N-polar GaN (0001{sup -}) by molecular beam epitaxy. X-ray diffraction showed that the CuInSe{sub 2} thin film was grown in (112) orientation, and its peak of rocking curve with full width at half maximum of about 897.8 arc-sec indicated the epitaxial growth of CuInSe{sub 2} (112) film on N-polar GaN. Microstructure analysis of the CuInSe{sub 2 } showed that the large lattice mismatch (28.5%) between CuInSe{sub 2 } and GaN is accommodated by domain matching, and no interface reaction occurs between CuInSe{sub 2} and GaN. Our experimental results show that GaN is stable for the epitaxial growth of CuInSe{sub 2} thin film, which exhibits a promising potential for optoelectronic applications.

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

    NASA Astrophysics Data System (ADS)

    Bovenkamp-Langlois, Lisa; Roy, Amitava

    2016-05-01

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

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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

  6. 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.

  7. 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).

  8. 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.

  9. 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.

  10. 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

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. Local Structure of CuIn3Se5

    SciTech Connect

    Chang, C. H.; Wei, S. H.; Leyarovska, N.; Johnson, J. W.; Zhang, S. B.; Stanbery, B. J.; Anderson, T. J.

    2000-01-01

    The results of a detailed EXAFS study of the Cu-K, In-K, and Se-K edges CuIn3Se5 are reported. The Cu and In first nearest neighbor local structures were found to be almost identical to those in CuInSe2.

  16. 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.

  17. 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

  18. 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.

  19. 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.

  20. 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

  1. 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.

  2. Binding mechanism of Cu(II) at the clay-water interface by powder and polarized EXAFS spectroscopy

    NASA Astrophysics Data System (ADS)

    Schlegel, Michel L.; Manceau, Alain

    2013-07-01

    The sorption mechanism of Cu(II) on the 2:1 magnesian clay hectorite, the 2:1 aluminous clay montmorillonite, and the 1:1 aluminous clay kaolinite was investigated at pH 5.4-6.0 and 0.5 M NaCl ionic strength by solution chemistry and powder and polarized XANES and EXAFS spectroscopy. Divalent copper was not photoreduced under the intense synchrotron X-ray beam and retained its usual square (bi)pyramidal coordination with four equatorial oxygens (Oeq) at 1.93-1.96 Å and one to two axial oxygens (Oax) at 2.56-2.58 Å. The angular dependence of XANES spectra, the measured angle of 57-58° between the Cu-Oeq atomic pair and the direction perpendicular to the clay layer plane ([0 0 1]∗), and the detection and polarization dependence of neighboring Al/Mg and Si cationic shells, together indicate that Cu(II) is bonded to the edges of the clay layers as an inner-sphere complex. Based on the number of Mg/Al and Si nearest neighbors, the Cu(Oeq)4(Oax)1-2 polyhedron is attached to the clay surface by sharing one to three edges with the structural Al/Mg octahedra and zero to three corners with the Si/Al tetrahedra. Copper has an unusually high coordination on the two dioctahedral aluminous clays, explained by the presence at their surface of distorted empty cavities which can accommodate irregular coordination polyhedra. The steric match between the distorted empty octahedral cavities and the Jahn-Teller distorted Cu polyhedra provides a rationale to explain the higher affinity of Cu(II) for Al octahedral sheets, including the hydrargillite sheet of lithiophorite ([Al,Li][MnO2]O2[OH]2) as observed in nature.

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

    PubMed Central

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

    2014-01-01

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

  4. 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

  5. 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.

  6. 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

  7. Cu,Zn-Superoxide Dismutase-Mediated Redox Regulation of Jumonji Domain Containing 3 Modulates Macrophage Polarization and Pulmonary Fibrosis.

    PubMed

    He, Chao; Larson-Casey, Jennifer L; Gu, Linlin; Ryan, Alan J; Murthy, Shubha; Carter, A Brent

    2016-07-01

    M2 macrophages are implicated in the development of pulmonary fibrosis as they generate profibrotic signals. The polarization process, at least in part, is regulated by epigenetic modulation. Because Cu,Zn-superoxide dismutase-induced H2O2 can polarize macrophages to a profibrotic M2 phenotype, we hypothesized that modulation of the redox state of the cell is involved in the epigenetic modulation of the macrophage phenotype. In this study, we show that signal transducer and activator of transcription 6 (STAT6) regulates Jumonji domain containing (Jmjd) 3, a histone H3 lysine 27 demethylase, and mutation of a redox-sensitive cysteine in STAT6 attenuates jmjd3 expression. Moreover, Jmjd3 deficiency abrogates profibrotic M2 gene expression. Treatment with leflunomide, which reduces mitochondrial reactive oxygen species production and tyrosine phosphorylation, inhibits jmjd3 expression and M2 polarization, as well as development of a fibrotic phenotype. Taken together, these observations provide evidence that the redox regulation of Jmjd3 is a unique regulatory mechanism for Cu,Zn-superoxide dismutase-mediated profibrotic M2 polarization. Furthermore, leflunomide, which reduces reactive oxygen species production and tyrosine phosphorylation, may prove to be therapeutic in the treatment of asbestos-induced pulmonary fibrosis. PMID:26699812

  8. 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

  9. Spin-polarization properties and electronic structure of the ordered c(2 × 2) MnCu/Cu(1 1 0) surface alloy.

    PubMed

    Wang, C; Stojić, N; Binggeli, N

    2014-10-01

    The spin-ordering and electronic properties of the c(2 × 2) MnCu/Cu(1 1 0) surface alloy are investigated by means of ab initio density-functional calculations. We first address the magnetic ground state and the robustness of the spin-polarization properties. The lowest-energy state is found to be ferromagnetic with a very low Curie temperature, showing that the paramagnetic phase should be established in this system at room temperature. The calculated trends obtained for the various spin structures considered indicate that the local Mn-spin moment and resulting reduced work function as well as Mn-outward buckling should persist in the paramagnetic phase. We then address the electronic surface-band structure of the paramagnetic phase close to the Fermi energy, in connection with the interpretation of recent angle-resolved-photoemission-spectroscopy experiments at room temperature. Our calculations account for an intriguing new surface-band feature observed experimentally near the [Formula: see text] point upon alloy formation, and provide a microscopic interpretation for this feature and for the alloy-induced changes in the Cu(1 1 0) Shockley surface state. PMID:25158692

  10. Spin polarized low energy electron microscopy of quantum well resonances in Fe films on the Cu-covered W(110) surface.

    PubMed

    Wu, Qiang; Altman, M S

    2013-07-01

    Spin polarized low energy electron microscopy has been used to investigate the quantum size effect (QSE) in electron reflectivity from Fe films grown on a pseudomorphic Cu layer on a W(110) surface. Intensity oscillations caused by the QSE as functions of Fe film thickness and incident electron energy identify quantum well resonance conditions in the film. Evaluation of these intensity oscillations using the phase accumulation model provides information on the unoccupied spin polarized band structure in the Fe film above the vacuum level. We also find evidence that the presence of the non-magnetic Cu layer shifts spin polarized quantum well resonances in the Fe layer uniformly downward in energy by 1.1eV compared to Fe/W(110) films without an interface Cu layer, suggesting that the Cu layer gives a small degree of control over the quantum well resonances. PMID:23628648

  11. 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.

  12. 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

  13. 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

  14. Polar Kerr Effect Measurements of YBa_2Cu_3O_6+x: Evidence for Broken Symmetry Near the Pseudogap Temperature

    SciTech Connect

    Xia, Jing

    2011-08-24

    Polar Kerr effect in the high-Tc superconductor YBa{sub 2}Cu{sub 3}O{sub 6+x} was measured at zero magnetic field with high precision using a cyogenic Sagnac fiber interferometer. We observed non-zero Kerr rotations of order {approx} 1 {micro}rad appearing near the pseudogap temperature T*, and marking what appears to be a true phase transition. Anomalous magnetic behavior in magnetic-field training of the effect suggests that time reversal symmetry is already broken above room temperature.

  15. Mechanical, spin polarized electronic and magnetic properties of TmX(X = Cu, Ag): First principle study

    NASA Astrophysics Data System (ADS)

    Chand, Satish; Singh, R. P.; Govindan, A.; Singh, S. K.

    2015-10-01

    To study the mechanical, spin polarized electronic and magnetic behavior of TmX(X = Cu, Ag), full-potential linear augmented plane wave plus local orbital method has been used. The lattice parameter (a0), bulk modulus (B0) and its first-order pressure derivative (B0') have been calculated using optimization method. Mechanical properties have been studied in terms of elastic constants (Cij), Young's modulus (Y), shear modulus (G) and Poisson's ratio (v) at ambient temperature and pressure which are found to be consistent with available experimental/theoretical values. Electronic properties have been investigated in terms of band structure and density of state histograms for spin up and spin down channel. Electronic and magnetic behavior of TmX shows that studied materials are metallic ferromagnets with high spin polarization in which Tm-f state electrons are contributed mainly.

  16. 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.

  17. 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

  18. 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

  19. 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.

  20. 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

  1. 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.

  2. Microstructure and anodic polarization behavior of experimental Ag-18Cu-15Pd-12Au alloy in aqueous sulfide solution.

    PubMed

    Endo, Kazuhiko; Ohno, Hiroki; Asakura, Shukuji

    2003-05-01

    The anodic corrosion behavior of an experimental Ag-15Pd-18Cu-12Au alloy in 0.1% Na(2)S solution in relation to its microstructure was investigated using potentiodynamic and potentiostatic polarization techniques with analyses of corrosion products by X-ray diffractometry, Auger electron spectroscopy, and X-ray photoelectron spectroscopy. The role of Pd in improvement of the corrosion resistance was also investigated. In the potential/current density curve, three distinct current peaks, at -520 mV (peak I), -425 mV (peak II) and -175 mV (peak III), were observed. The Ag-rich alpha(2) matrix with coarse Cu and Pd-rich lamellae was the most corrosion-susceptible region, and this region was preferentially corroded at peak I with the formation of granular deposits of Ag(2)S. A small amount of Ag-Cu mixed sulfide deposited on the Cu and Pd-rich coarse particles and dissolution of Ag as AgO(-) might have occurred in parallel with Ag(2)S formation at peak II. Enrichment of Pd on the alloy surface occurred at peak III due to preferential dissolution of Ag and Cu. A high level of corrosion resistance was attained with the formation of a thin Pd-rich sulfide film, which enhanced the passivity of the alloy in an alkaline sulfide solution. It was found that passivity is an important phenomenon not only for base metal alloys but also for noble metal alloys to maintain high levels of resistance to corrosion and tarnishing in sulfide environments. PMID:15348446

  3. 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.

  4. High-sensitivity determination of Zn(II) and Cu(II) in vitro by fluorescence polarization

    NASA Astrophysics Data System (ADS)

    Thompson, Richard B.; Maliwal, Badri P.; Feliccia, Vincent; Fierke, Carol A.

    1998-04-01

    Recent work has suggested that free Cu(II) may play a role in syndromes such as Crohn's and Wilson's diseases, as well as being a pollutant toxic at low levels to shellfish and sheep. Similarly, Zn(II) has been implicated in some neural damage in the brain resulting from epilepsy and ischemia. Several high sensitivity methods exist for determining these ions in solution, including GFAAS, ICP-MS, ICP-ES, and electrochemical techniques. However, these techniques are generally slow and costly, require pretreatment of the sample, require complex instruments and skilled personnel, and are incapable of imaging at the cellular and subcellular level. To address these shortcomings we developed fluorescence polarization (anisotropy) biosensing methods for these ions which are very sensitivity, highly selective, require simple instrumentation and little pretreatment, and are inexpensive. Thus free Cu(II) or Zn(II) can be determined at picomolar levels by changes in fluorescence polarization, lifetime, or wavelength ratio using these methods; these techniques may be adapted to microscopy.

  5. 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

  6. 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.

  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. 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

  9. Polarity driven morphology of CeO2(1 0 0) islands on Cu(1 1 1)

    NASA Astrophysics Data System (ADS)

    Stetsovych, O.; Beran, J.; Dvořák, F.; Mašek, K.; Mysliveček, J.; Matolín, V.

    2013-11-01

    Thin ceria films supported by metal substrates represent important model systems for reactivity studies in heterogeneous catalysis. Here we report the growth study of the polar CeO2(1 0 0) phase as part of a mixed CeO2(1 1 1)-CeO2(1 0 0) thin film supported by Cu(1 1 1). The two ceria phases grow on different areas of the substrate, what allows a reliable growth characterization of the CeO2(1 0 0) islands on Cu(1 1 1). Scanning tunneling microscopy measurements reveal CeO2(1 0 0) to grow in the form of highly dispersed three dimensional (3D) islands on a CeO2(1 0 0) interfacial layer. The CeO2(1 0 0) islands exhibit a 2 × 2 surface reconstruction. The presence of the surface reconstruction together with the highly dispersed growth of CeO2(1 0 0) islands corresponds to the requirement for compensation of the surface dipole moment on the CeO2(1 0 0). CeO2(1 0 0) islands are further characterized by reflection high energy electron diffraction yielding their epitaxial relations with respect to the Cu(1 1 1) substrate. The growth of well characterized CeO2(1 0 0) islands supported by Cu(1 1 1) represents a starting point for developing a novel template for structure-related reactivity studies of ceria based model catalysts.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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

  16. 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.

  17. 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.

  18. 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

  19. 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.

  20. 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.

  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. 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.

  3. 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

  4. 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.

  5. 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.

  6. 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

  7. PMMA interlayer-modulated memory effects by space charge polarization in resistive switching based on CuSCN-nanopyramids/ZnO-nanorods p-n heterojunction.

    PubMed

    Cheng, Baochang; Zhao, Jie; Xiao, Li; Cai, Qiangsheng; Guo, Rui; Xiao, Yanhe; Lei, Shuijin

    2015-01-01

    Resistive switching (RS) devices are commonly believed as a promising candidate for next generation nonvolatile resistance random access memory. Here, polymethylmethacrylate (PMMA) interlayer was introduced at the heterointerface of p-CuSCN hollow nanopyramid arrays and n-ZnO nanorod arrays, resulting in a typical bipolar RS behavior. We propose the mechanism of nanostructure trap-induced space charge polarization modulated by PMMA interlayer. At low reverse bias, PMMA insulator can block charges through the heterointerface, and V(-)Cu and V(+)o trapped states are respectively created on both sides of PMMA, resulting in a high resistance state (HRS) due to wider depletion region. At high reverse bias, however, electrons and holes can cross PMMA interlayer by Fowler-Nordeim tunneling due to a massive tilt of energy band, and then inject into the traps of ZnO and CuSCN, respectively. V(+)Cu and V(-)O trapped states are created, resulting in the formation of degenerate semiconductors on both sides of PMMA. Therefore, quantum tunneling and space charge polarization lead to a low resistance state (LRS). At relatively high forward bias, subsequently, the trapped states of V(-)Cu and V(+)o are recreated due to the opposite injection of charges, resulting in a recovery of HRS. The introduction of insulating interlayer at heterointerface, point a way to develop next-generation nonvolatile memories. PMID:26648249

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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

  16. 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.

  17. High resolution short focal distance Bent Crystal Laue Analyzer for copper K edge x-ray absorption spectroscopy

    SciTech Connect

    Kujala, N. G.; Barrea, R. A.; Karanfil, C.

    2011-06-15

    We have developed a compact short focal distance Bent Crystal Laue Analyzer (BCLA) for Cu speciation studies of biological systems with specific applications to cancer biology. The system provides high energy resolution and high background rejection. The system is composed of an aluminum block serving as a log spiral bender for a 15 micron thick Silicon 111 crystal and a set of soller slits. The energy resolution of the BCLA--about 14 eV at the Cu K{alpha} line-- allows resolution of the Cu K{alpha}{sub 1} and CuK{alpha}{sub 2} lines. The system is easily aligned by using a set of motorized XYZ linear stages. Two operation modes are available: incident energy scans (IES) and emission energy scans (EES). IES allows scanning of the incident energy while the BCLA system is maintained at a preselected fixed position - typically CuK{alpha}{sub 1} line. EES is used when the incident energy is fixed and the analyzer is scanned to provide the peak profile of the emission lines of Cu.

  18. High resolution short focal distance Bent Crystal Laue Analyzer for copper K edge x-ray absorption spectroscopy

    PubMed Central

    Kujala, N. G.; Karanfil, C.; Barrea, R. A.

    2011-01-01

    We have developed a compact short focal distance Bent Crystal Laue Analyzer (BCLA) for Cu speciation studies of biological systems with specific applications to cancer biology. The system provides high energy resolution and high background rejection. The system is composed of an aluminum block serving as a log spiral bender for a 15 micron thick Silicon 111 crystal and a set of soller slits. The energy resolution of the BCLA—about 14 eV at the Cu Kα line— allows resolution of the Cu Kα1 and CuKα2 lines. The system is easily aligned by using a set of motorized XYZ linear stages. Two operation modes are available: incident energy scans (IES) and emission energy scans (EES). IES allows scanning of the incident energy while the BCLA system is maintained at a preselected fixed position—typically CuKα1 line. EES is used when the incident energy is fixed and the analyzer is scanned to provide the peak profile of the emission lines of Cu. PMID:21721673

  19. Incorrect DFT-GGA predictions of the stability of non-stoichiometric/polar dielectric surfaces: the case of Cu2O(111).

    PubMed

    Nilius, Niklas; Fedderwitz, Hanna; Groß, Boris; Noguera, Claudine; Goniakowski, Jacek

    2016-03-01

    Scanning tunneling microscopy (STM) and hybrid density functional theory (DFT) have been used to study the stability and electronic characteristics of the Cu2O(111) surface. We challenge previous interpretations of its structure and composition and show that only appropriate (hybrid) calculations can correctly account for the relative thermodynamic stability of stoichiometric versus Cu-deficient terminations. Our theoretical finding of the stoichiometric surface to be most stable at oxygen-lean conditions is confirmed by an excellent matching between STM spectroscopy data and the calculated surface electronic structure. Beyond the specific case of the Cu2O(111) surface, and beyond the known deficiencies of GGA-based approaches in the description of oxide electronic structures, our work highlights the risk of an erroneous evaluation of the surface stability, in cases where the energetics and electronic characteristics are strongly coupled, as in a wide class of polar and/or non-stoichiometric oxide surfaces. PMID:26876056

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. 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

  5. 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

  6. 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

  7. 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

  8. 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.

  9. 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.

  10. High resolution polarized Cu L3 XAS of high temperature superconductors: correlations between the symmetry of d holes and the critical temperature

    NASA Astrophysics Data System (ADS)

    Flank, A. M.; Lagarde, P.; Bianconi, A.; Castrucci, P.; Fabrizi, A.; Pompa, M.; Katayama-Yoshida, H.; Calestani, G.

    1990-06-01

    High resolution polarized Cu L3 X-ray absorption spectra of single crystals and of highly oriented pellets of high Tc superconductors of the bismuth kind have been measured by using synchrotron radiation at Super-ACO. We have investigated the energy splitting Δ between the in-plane and out-of-plane 2p → 3d transition. We find that the splitting Δ as well as the intensity of the Eparallelz component is correlated with the critical temperature of the superconducting systems for each class of superconductors.

  11. 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.

  12. 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

  13. 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

  14. 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.

  15. PMMA interlayer-modulated memory effects by space charge polarization in resistive switching based on CuSCN-nanopyramids/ZnO-nanorods p-n heterojunction

    PubMed Central

    Cheng, Baochang; Zhao, Jie; Xiao, Li; Cai, Qiangsheng; Guo, Rui; Xiao, Yanhe; Lei, Shuijin

    2015-01-01

    Resistive switching (RS) devices are commonly believed as a promising candidate for next generation nonvolatile resistance random access memory. Here, polymethylmethacrylate (PMMA) interlayer was introduced at the heterointerface of p-CuSCN hollow nanopyramid arrays and n-ZnO nanorod arrays, resulting in a typical bipolar RS behavior. We propose the mechanism of nanostructure trap-induced space charge polarization modulated by PMMA interlayer. At low reverse bias, PMMA insulator can block charges through the heterointerface, and and trapped states are respectively created on both sides of PMMA, resulting in a high resistance state (HRS) due to wider depletion region. At high reverse bias, however, electrons and holes can cross PMMA interlayer by Fowler-Nordeim tunneling due to a massive tilt of energy band, and then inject into the traps of ZnO and CuSCN, respectively. and trapped states are created, resulting in the formation of degenerate semiconductors on both sides of PMMA. Therefore, quantum tunneling and space charge polarization lead to a low resistance state (LRS). At relatively high forward bias, subsequently, the trapped states of and are recreated due to the opposite injection of charges, resulting in a recovery of HRS. The introduction of insulating interlayer at heterointerface, point a way to develop next-generation nonvolatile memories. PMID:26648249

  16. Polarization-dependent infrared reflectivity study of Sr2.5Ca11.5Cu24O41 under pressure: Charge dynamics, charge distribution, and anisotropy

    DOE PAGESBeta

    Frank, S.; Huber, A.; Ammerahl, U.; Hücker, M.; Kuntscher, C. A.

    2014-12-18

    We present a polarization-dependent infrared reflectivity study of the spin-ladder compound Sr₂̣₅Ca₁₁̣₅Cu₂₄O₄₁ under pressure. The optical response is strongly anisotropic, with the highest reflectivity along the ladders/chains (E∥c) revealing a metallic character. For the polarization direction perpendicular to the ladder plane, an insulating behavior is observed. With increasing pressure the optical conductivity for E∥c shows a strong increase, which is most pronounced below 2000cm⁻¹. According to the spectral weight analysis of the E∥c optical conductivity the hole concentration in the ladders increases with increasing pressure and tends to saturate at high pressure. At ~7.5 GPa the number of holes permore » Cu atom in the ladders has increased by Δδ=0.09(±0.01), and the Cu valence in the ladders has reached the value +2.33. Thus, the optical data suggest that Sr₂̣₅Ca₁₁̣₅Cu₂₄O₄₁ remains electronically highly anisotropic up to high pressure, also at low temperatures.« less

  17. PMMA interlayer-modulated memory effects by space charge polarization in resistive switching based on CuSCN-nanopyramids/ZnO-nanorods p-n heterojunction

    NASA Astrophysics Data System (ADS)

    Cheng, Baochang; Zhao, Jie; Xiao, Li; Cai, Qiangsheng; Guo, Rui; Xiao, Yanhe; Lei, Shuijin

    2015-12-01

    Resistive switching (RS) devices are commonly believed as a promising candidate for next generation nonvolatile resistance random access memory. Here, polymethylmethacrylate (PMMA) interlayer was introduced at the heterointerface of p-CuSCN hollow nanopyramid arrays and n-ZnO nanorod arrays, resulting in a typical bipolar RS behavior. We propose the mechanism of nanostructure trap-induced space charge polarization modulated by PMMA interlayer. At low reverse bias, PMMA insulator can block charges through the heterointerface, and and trapped states are respectively created on both sides of PMMA, resulting in a high resistance state (HRS) due to wider depletion region. At high reverse bias, however, electrons and holes can cross PMMA interlayer by Fowler-Nordeim tunneling due to a massive tilt of energy band, and then inject into the traps of ZnO and CuSCN, respectively. and trapped states are created, resulting in the formation of degenerate semiconductors on both sides of PMMA. Therefore, quantum tunneling and space charge polarization lead to a low resistance state (LRS). At relatively high forward bias, subsequently, the trapped states of and are recreated due to the opposite injection of charges, resulting in a recovery of HRS. The introduction of insulating interlayer at heterointerface, point a way to develop next-generation nonvolatile memories.

  18. 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

  19. 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

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. 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

  5. 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.

  6. 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

  7. 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

  8. 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

  9. 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

  10. 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

  11. Polarized X-Ray Absorption Spectroscopy Studies of Copper in High Temperature Superconductors

    NASA Astrophysics Data System (ADS)

    Mini, Susan M.

    One can take advantage of the linearly polarized nature of the x-rays from a synchrotron to study the electronic and structural properties of single crystals or magnetically aligned powders. Since the advent of layered copper oxide compounds as high temperature superconductors (1) the structures of La_{rm 2-x}Sr _{rm x}CuO _4, Nd_{rm 2-x }Ce_{rm x}CuO _4 and YBa_2Cu _3O_{rm 7-y} have been of extreme interest. In this study, the powder samples of these compounds were magnetically aligned such that the electric vector was either perpendicular or parallel to the crystallographic c axis. The results of polarized XANES (X-ray Absorption Near Edge Spectroscopy) measurements at the copper K-edge (8979 eV) of all three structures will be presented. The EXAFS (Extended X-ray Absorption Fine Structure) of magnetically aligned YBa_2Cu _3O_{6.9} were used to characterize the local structure as well as study the structural changes of the Cu1-O4 and Cu2-O4 bonds in as a function of temperature (20 to 300 K). In this manner, the Cu1-O4 and Cu2-O4 bonds, which are thought to play a role in the superconductivity of the sample, are distinguishable. The complementary technique of XANES is used to study the electronic structure of the superconducting copper oxides as well as alkali cuprates M^{ rm I}CuO_2 (M = Na, K, Rb and Cs) and rare earth copper oxides RE _2CuO_4 (RE = Pr, Nd, Sm, Eu and Gd). A method (2) for determining the effective charge is described and applied to the copper oxides. ftn 1. J. G. Bednorz and K. A. Muller; Z Phys. B64, 189 (1986). 2. E. E. Alp, G L. Goodman, L. Soderholm, S.M. Mini, M. Ramanathan, G. K. Shenoy and A. S. Bommannavar, J.Phys. Condens, Matter 1, 6463 (1989).

  12. 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

  13. 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

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. 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

  19. 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.

  20. 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.

  1. 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.

  2. Atomic structure of a polar ceramic/metal interface: {l_brace}222{r_brace}MgO/Cu

    SciTech Connect

    Benedek, R.; Shashkov, D.A.; Seidman, D.N.; Muller, D.A.; Silcox, J.; Chisholm, M.F.; Yang, L.H.

    1998-02-01

    {l_brace}222{r_brace}MgO/Cu is one of the most extensively characterized ceramic/metal interfaces, in view of the atom probe field ion microscopy, Z-contrast Scanning Transmission Electron Microscopy (STEM), and spatially resolved Electron energy loss spectroscopy (EELS) measurements performed by the present authors, as well as the high resolution electron microscopy (HREM) of this system by others. Atomistic simulations with local density functional theory (LDFT) and Molecular Dynamics (MD) have been performed to gain additional insight into the structure of this interface. This presentation describes an interface interatomic potential for {l_brace}222{r_brace}MgO/Cu derived from LDFT total energy calculations, and its application to structural properties, including the terminating species, the absence of dislocation standoff, and the symmetry of the interfacial dislocation network.

  3. Design and performance of a 4.5GHz circularly polarized YBa 2Cu 3O 7 microstrip antenna

    NASA Astrophysics Data System (ADS)

    Zhu, M. H.; Cao, B. S.; Zhang, X. X.; Li, W. H.; Yuan, H. J.; Wang, Y. J.; Zhang, L. W.; Dong, D. J.; Liu, M. L.; Cui, D. F.; He, M.; Zhou, Y. L.; Liu, T. J.

    1997-08-01

    A 4.5GHz circularly polarized YBCO microstrip antenna was designed and fabricated. Measurements showed that at 77K the superconducting antenna had about 3dB gain improvement over the comparable silver antenna, in agreement with the calculated results using the modified Green function method.

  4. Crystal-field polarization and the insulating gap in FeO, CoO, NiO, and La sub 2 CuO sub 4 (US). [FeO; CoO; NiO; La d2CuO d ix

    SciTech Connect

    Norman, M.R. )

    1991-07-15

    An orbital polarization correction to local spin density (LSD) theory is developed in a crystal field basis, and applied to FeO, CoO, NiO, and La{sub 2}CuO{sub 4}. The result is a substantial enhancement of the LSD band gap for NiO, and the creation of an insulating ground state for FeO, CoO, and La{sub 2}CuO{sub 4}.

  5. 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.

  6. Micro-Structural Properties of YBa2Cu3O(7-x)/ZnO Nanorods on SrTiO3.

    PubMed

    Jin, Zhenlan; Park, Changin; Song, Kyu Jeong; Kang, Sukil; Ko, Kyeong-Eun; Park, Chan; Ko, Rock Kil; Han, S W

    2015-01-01

    We examined the local structural and the interfacial properties of YBa2Cu3O(7-x) (YBCO)/ZnO nanorods on SrTiO3 (STO) substrates using various measurements. Vertically aligned ZnO nanorods were synthesized on STO substrates using a catalyst-free metal-organic chemical vapor deposition. YBCO films were deposited ex-situ on the ZnO nanorods/STO templates using a DC magnetron sputtering deposition. X-ray diffraction revealed that the YBCO films were crystallized along their c-axes on the ZnO nanorods/STO templates. Transmission electron microscopy measurements demonstrated that YBCO filled the space between ZnO nanorods and that both interfaces of YBCO/ZnO nanorods and ZnO nanorods/STO were quite clean with no disorder. Polarization-dependent extended X-ray absorption fine structure measurements at the Cu K edge showed extra disorder in the CuO2 planes of YBCO/ZnO nanorods/STO, compared with that of YBCO/STO. The superconductivity transition temperature (T(c)) of YBCO/ZnO nanorods/STO was approximately 50 K whereas that of YBCO/STO was 93 K. The decrease of T(c) of YBCO/ZnO nanorods/STO was ascribed to the structural disorder of CuO2 planes as well as grain boundaries in the YBCO films. PMID:26328417

  7. 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

  8. 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.

  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. 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.

  12. 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.

  13. 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

  14. 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

  15. 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.

  16. 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

  17. 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

  18. Polaroid H-sheet as a polarizer for 33 keV X-rays

    NASA Astrophysics Data System (ADS)

    Collins, S. P.

    1997-07-01

    It is shown that Polaroid H-sheet (iodine-doped polyvinyl alcohol) can be used to good effect as a fixed-wavelength polarizer for 33.17 keV X-ray beams. Iodine K-edge dichroic spectra of HN22 and HN38 sheets are presented, and the HN22 is used to demonstrate X-ray polarization analysis and polarization rotation.

  19. 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

  20. Visible-light photocatalysis in Cu2Se nanowires with exposed {111} facets and charge separation between (111) and (1[combining macron]1[combining macron]1[combining macron]) polar surfaces.

    PubMed

    Liu, Bin; Ning, Lichao; Zhao, Hua; Zhang, Congjie; Yang, Heqing; Liu, Shengzhong Frank

    2015-05-28

    The search for active narrow band gap semiconductor photocatalysts that directly split water or degrade organic pollutants under solar irradiation remains an open issue. We synthesized Cu2Se nanowires with exposed {111} facets using ethanol and glycerol as morphology controlling agents. The {111} facets were found to be the active facets for decomposing organic contaminants in the entire solar spectrum. Based on the polar structure of the Cu2Se {111} facets, a charge separation model between polar (111) and (1[combining macron]1[combining macron]1[combining macron]) surfaces is proposed. The internal electric field between polar (111) and (1[combining macron]1[combining macron]1[combining macron]) surfaces created by spontaneous polarization drives charge separation. The reduction and oxidation reactions occur on the positive (111) and negative (1[combining macron]1[combining macron]1[combining macron]) polar surfaces, respectively. This suggests the surface-engineering of narrow band gap semiconductors as a strategy to fabricate photocatalysts with high reactivity in the entire solar spectrum. The charge separation model can deepen the understanding of charge transfer in other semiconductor nanocrystals with high photocatalytic activities and offer guidance to design more effective photocatalysts as well as new types of solar cells, photoelectrodes and photoelectric devices. PMID:25920433

  1. 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.

  2. 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.

  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

    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

  4. 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

  5. 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.

  6. 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.

  7. 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.

  8. Change of the In-Plane Cu-O Bond Distribution in La(2)CuO(4.1) Across T(C)

    SciTech Connect

    Leon, J.Mustre de; Acosta-Alejandro, M.; Conradson, S.D.; Bishop, A.R.

    2009-05-26

    Cu K-edge X-ray absorption fine structure (XAFS) on La{sub 2}CuO{sub 4.1} has been used to study the radial Cu-O distribution function across the superconducting transition. Fits to the isolated Cu-O XAFS signal show the presence of a non-Gaussian distribution function for temperatures away from the superconducting transition temperature. However, this distribution becomes more harmonic in the vicinity of the superconducting transition temperature T{sub c}. The results provide evidence for the coupling between the local atomic dynamics and the particles involved in the superconductivity.

  9. 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

  10. 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

  11. 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

  12. Observation of current polarity effect in stressing as-formed sub-micron Al-Si-Cu/TiW/TiSi 2 contacts

    NASA Astrophysics Data System (ADS)

    Chen, Li-Zen; Hsu, Klaus Y.-J.

    1999-06-01

    Formation of good silicide contacts becomes more important but difficult as the contact size continues shrinking toward the deep sub-micron regime. At the same time, higher current density, which may easily appear in small regions, could pose strong impact to the long-term reliability of sub-micron contacts. In this work, high current density stress experiments were conducted on the Al-Si-Cu/TiW/TiSi 2 contacts with the size ranging from 0.5×0.5 μm 2 down to 0.25×0.25 μm 2. The self-aligned silicide contacts were formed by using collimated sputtering, E-beam lithography, RTA, and RIE techniques. The silicide contacts were sintered at 400°C for 30 min. Cross-bridge Kelvin resistor structures were formed for electrical stressing and contact resistance measurement. One-way and two-way stressings were performed at high current density (˜10 7 A/cm 2) and the contact resistance was measured periodically at low current density during the stressing to monitor the evolution. It was found that the initial resistance of as-formed contacts was higher than expected. This is probably due to the difficulty of forming good interfaces in the small contact region by sputtering and that the sintering temperature may not be high enough to smear out the imperfection. The stressing was found to anneal the contacts. With electrons flowing from metal layer into the contact window, the contact resistance was reduced more efficiently than with reverse current of the same density. Stressed first by reverse current then by normal current, the resistance showed a two-step reduction with a significant transition at the switch of current polarity. For prolonged stressing, the contacts were gradually degraded and the reverse current induced more severe damage. These observations indicate strong electromigration effect at the small contacts.

  13. Atomic structure of PtCu nanoparticles in PtCu/C catalysts prepared by simultaneous and sequential deposition of components on carbon support

    NASA Astrophysics Data System (ADS)

    Bugaev, L. A.; Srabionyan, V. V.; Pryadchenko, V. V.; Bugaev, A. L.; Avakyan, L. A.; Belenov, S. V.; Guterman, V. E.

    2016-05-01

    Nanocatalysts PtCu/C with different distribution of components in bimetallic PtCu nanoparticles (NPs) were synthesized by simultaneous and sequential deposition of Cu and Pt on carbon support. Electrochemical stability of the obtained samples PtCu/C was studied using the cyclic voltammetry. Characterization of atomic structure of as prepared PtCu NPs and obtained after acid treatment was performed by Pt L 3- and Cu K-edge EXAFS using the technique for determining local structure parameters of the absorbing atom under strong correlations among them. EXAFS derived parameters were used for generation of structural models of PtCu NPs by the method of cluster simulations. Within this approach, the models of atomic structure of PtCu NPs obtained by the two methods of synthesis, before and after post treatment and after two months from their preparation were revealed.

  14. 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

  15. Atomic Resolution Mapping of the Excited-State Electronic Structure of Cu2O with Time-Resolved X-Ray Absorption Spectroscopy

    SciTech Connect

    Hillyard, Patrick B.; Kuchibhatla, Satyanarayana V N T; Glover, T. E.; Hertlein, M. P.; Huse, N.; Nachimuthu, Ponnusamy; Saraf, Laxmikant V.; Thevuthasan, Suntharampillai; Gaffney, Kelly J.

    2009-09-29

    We have used time-resolved soft x-ray spectroscopy to investigate the electronic structure of optically excited cuprous oxide at the O K-edge and the Cu L3-edge. The 400 nm optical excitation shifts the Cu and O absorptions to lower energy, but does not change the integrated x-ray absorption significantly for either edge. The constant integrated x-ray absorption cross-section indicates that that the conduction band and valence band edges have very similar Cu 3d and O 2p orbital contributions. The 2.1 eV optical band gap of Cu2O significantly exceeds the one eV shift in the Cu L3- and O K-edges absorption edges induced by optical excitation, demonstrating the importance of core-hole excitonic effects and valence electron screening in the x-ray absorption process.

  16. Atomic resolution mapping of the excited-state electronic structure of Cu2O with time-resolved x-ray absorption spectroscopy

    SciTech Connect

    Hillyard, P. W.; Kuchibhatla, S. V. N. T.; Glover, T. E.; Hertlein, M. P.; Huse, Nils; Nachimuthu, P.; Saraf, L. V.; Thevuthasan, S.; Gaffney, K. J.

    2010-05-02

    We have used time-resolved soft x-ray spectroscopy to investigate the electronic structure of optically excited cuprous oxide at the O K-edge and the Cu L3-edge. The 400 nm optical excitation shifts the Cu and O absorptions to lower energy, but does not change the integrated x-ray absorption significantly for either edge. The constant integrated x-ray absorption cross-section indicates that the conduction-band and valence-band edges have very similar Cu 3d and O 2p orbital contributions. The 2.1 eV optical band gap of Cu2O significantly exceeds the one eV shift in the Cu L3- and O K-edges absorption edges induced by optical excitation, demonstrating the importance of core-hole excitonic effects and valence electron screening in the x-ray absorption process.

  17. 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.

  18. 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.

  19. 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

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. Dielectric function and magneto-optical Voigt constant of Cu2O: A combined spectroscopic ellipsometry and polar magneto-optical Kerr spectroscopy study

    NASA Astrophysics Data System (ADS)

    Haidu, Francisc; Fronk, Michael; Gordan, Ovidiu D.; Scarlat, Camelia; Salvan, Georgeta; Zahn, Dietrich R. T.

    2011-11-01

    Cuprous oxide is a highly interesting material for the emerging field of transparent oxide electronics. In this work the energy dispersion of the dielectric function of Cu2O bulk material is revised by spectroscopic ellipsometry measurements in an extended spectral range from 0.73 to 10 eV. For the first time, the magneto-optical Kerr effect was measured in the spectral range from 1.7 to 5.5 eV and the magneto-optical Voigt constant of Cu2O was obtained by numerical calculations from the magneto-optical Kerr effect spectra and the dielectric function.

  6. 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

  7. 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.

  8. Analyzing Particle Size Effects in ZnS:Cu using X-ray Absorption Spectroscopy

    NASA Astrophysics Data System (ADS)

    Medling, Scott; Kozina, M.; Jiang, Y.; Balaban, B.; Bridges, F.; Carter, S.

    2009-11-01

    We report XAS measurements on ZnS:Cu,Mn phosphor materials of various particle sizes, 1-25μm. These materials exhibit electroluminescence (EL) at AC voltages of order 100V for ˜25μm particles, but only from small points associated with CuS nanoprecipitates (which form along the 111 plane in ZnS); here the local electric fields are enhanced by a factor of about 100. To enable lower-voltage applications, it is desirable to make smaller particles so devices can be thinner. We investigated the local structure for smaller particles produced by mill-grinding to determine why grinding leads to reduced AC EL. The K-edge EXAFS data show a decreased Cu-S first peak amplitude for the ground particle samples, but little change for Mn-S or Zn-S peaks. The XANES data show a large change in the structure of the Cu K-edge for smaller particles but not for either the host Zn or Mn dopant edges. Clearly grinding affects the environment about Cu, in the CuS precipitates, much more than the ZnS host lattice. Possibly the ZnS particles fracture preferentially through the CuS precipitates or the ZnS particles are partially sheared along the 111 plane.

  9. 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

  10. 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.

  11. 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.

  12. 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

  13. 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.

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

    NASA Technical Reports Server (NTRS)

    Ruckman, Mark W.; Hepp, Aloysius F.

    1991-01-01

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

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

    NASA Technical Reports Server (NTRS)

    Ruckman, Mark W.; Hepp, Aloysius F.

    1991-01-01

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

  16. The XAS model of dissolved Cu(II) and its significance to biological electron transfer

    NASA Astrophysics Data System (ADS)

    Frank, Patrick; Benfatto, Maurizio; Hedman, Britt; Hodgson, Keith O.

    2009-11-01

    The standard model for dissolved Cu(II) portrays the complex ion as an axially elongated, equatorially planar octahedron. Using EXAFS and MXAN analyses of copper K-edge XAS spectra, new structural models for dissolved [Cu(aq)]2+ and [Cu(amm)]2+ have been determined. These structures uniformly depart from the octahedral model in favour of an axially elongated square pyramidal core. MXAN results also indicate that the equatorial ligands need not be coplanar with copper. Further structural elements include a -z axially localized scatterer at ~3 Å. Even more distant scatterers imply second shell solvent organization, which can vary with the medium. Preliminary results from new extended, k = 18 Å-1, higher resolution copper K-edge XAS data sets are reported. The low symmetry of dissolved Cu(II) ion contradicts the central thesis of the rack-induced bonding hypothesis of copper electron transfer proteins. The asymmetry of biological copper is not a frozen vibronic excited state enforced by a rigid protein scaffold, but is entirely in harmony with the structural ground state of the dissolved aqueous Cu(II) complex ion.

  17. 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

  18. 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

  19. 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

  20. 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.

  1. 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

  2. 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.

  3. Spectromicroscopy Study of the Organic Molecules Utilizing Polarized Radiation

    SciTech Connect

    Hsu, Y.J.; Wei, D.H.; Yin, G.C.; Chung, S.C.; Hu, W.S.; Tao, Y.T.

    2004-05-12

    Spectromicroscopy combined with polarized synchrotron radiation is a powerful tool for imaging and characterizing the molecular properties on surface. In this work we utilized the photoemission electron microscopy (PEEM) with linear polarized radiation provided by an elliptically polarized undulator to investigate the molecular orientations of pentacene on self-assembled monolayer (SAMs) modified gold surface and to observe the cluster domain of mixed monolayers after reorganization on silver. Varying the electric vector parallel or perpendicular to the surface, the relative intensity of {pi}* and {sigma}* transition in carbon K-edge can be used to determine the orientation of the planar-shaped pentacene molecule or long carbon chain of carboxylic acids which are important for organic semiconductor.

  4. Local surrounding of vanadium atoms in CuCr1 - x V x S2: X-ray absorption spectroscopy analysis

    NASA Astrophysics Data System (ADS)

    Smirnova, Yu. O.; Smolentsev, N. Yu.; Guda, A. A.; Soldatov, M. A.; Kvashnina, K. O.; Glatzel, P.; Korotaev, E. V.; Soldatov, A. V.; Mazalov, L. N.

    2013-03-01

    In the present work local surrounding of vanadium atoms in layered copper-chromium disulfides CuCr1 - x V x S2 is investigated using high-resolution X-ray absorption spectroscopy above vanadium K-edge. Based on experimental and theoretically simulated spectra comparison it is shown that vanadium atoms replace chromium ones even at high concentrations of vanadium and that they are in 3+ oxidation state.

  5. Local structure study of (In{sub 0.95−x}Fe{sub x}Cu{sub 0.05}){sub 2}O{sub 3} thin films using x-ray absorption spectroscopy

    SciTech Connect

    Ren, Yuan; Xing, Yaya; Ma, Guanxiong; Wang, Shiqi; An, Yukai Liu, Jiwen; Zhao, Xingliang

    2015-07-15

    The (In{sub 0.95−x}Fe{sub x}Cu{sub 0.05}){sub 2}O{sub 3} (x = 0.06, 0.08, 0.15, and 0.20) films prepared by RF-magnetron sputtering were investigated by the combination of x-ray absorption spectroscopy (XAS) at Fe, Cu, and O K-edge. Although the Fe and O K-edge XAS spectra show that the Fe atoms substitute for the In sites of In{sub 2}O{sub 3} lattice for all the films, the Cu K-edge XAS spectra reveal that the codoped Cu atoms are separated to form the Cu metal clusters. After being annealed in air, the Fe atoms are still substitutionally incorporated into the In{sub 2}O{sub 3} lattice, while the Cu atoms form the CuO secondary phases. With the increase of Fe concentration, the bond length R{sub Fe-O} shortens and the Debye–Waller factor σ{sup 2}{sub Fe-O} increases in the first coordination shell of Fe, which are attributed to the relaxation of oxygen environment around the substitutional Fe ions. The forming of Cu relating secondary phases in the films is due to high ionization energy of Cu atoms, leading that the Cu atoms are energetically much harder to be oxidized to substitute for the In sites of In{sub 2}O{sub 3} lattice than Fe atoms. These results provide new experimental guidance in the preparation of the codoped In{sub 2}O{sub 3} based dilute magnetic oxides.

  6. EXAFS analysis of a human Cu,Zn SOD isoform focused using non-denaturing gel electrophoresis

    NASA Astrophysics Data System (ADS)

    Chevreux, Sylviane; Solari, Pier Lorenzo; Roudeau, Stéphane; Deves, Guillaume; Alliot, Isabelle; Testemale, Denis; Hazemann, Jean Louis; Ortega, Richard

    2009-11-01

    Isoelectric point isoforms of a metalloprotein, copper-zinc superoxide dismutase (CuZnSOD), separated on electrophoresis gels were analyzed using X-ray Absorption Spectroscopy. Mutations of this protein are involved in familial cases of amyotrophic lateral sclerosis. The toxicity of mutants could be relied to defects in the metallation state. Our purpose is to establish analytical protocols to study metallation state of protein isoforms such as those from CuZnSOD. We previously highlighted differences in the copper oxidation state between CuZnSOD isoforms using XANES. Here, we present the first results for EXAFS analyses performed at Cu and Zn K-edge on the majoritary expressed isoform of human CuZnSOD separated on electrophoresis gels.

  7. 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.

  8. 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

  9. 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

  10. 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.

  11. Antiferromagnetically Spin Polarized Oxygen Observed in Magnetoelectric TbMn2O5

    NASA Astrophysics Data System (ADS)

    Beale, T. A. W.; Wilkins, S. B.; Johnson, R. D.; Bland, S. R.; Joly, Y.; Forrest, T. R.; McMorrow, D. F.; Yakhou, F.; Prabhakaran, D.; Boothroyd, A. T.; Hatton, P. D.

    2010-08-01

    We report the direct measurement of antiferromagnetic spin polarization at the oxygen sites in the multiferroic TbMn2O5, through resonant soft x-ray magnetic scattering. This supports recent theoretical models suggesting that the oxygen spin polarization is key to the magnetoelectric coupling mechanism. The spin polarization is observed through a resonantly enhanced diffraction signal at the oxygen K edge at the commensurate antiferromagnetic wave vector. Using the fdmnes code we have accurately reproduced the experimental data. We have established that the resonance arises through the spin polarization on the oxygen sites hybridized with the square based pyramid Mn3+ ions. Furthermore we have discovered that the position of the Mn3+ ion directly influences the oxygen spin polarization.

  12. Depth profile of the ferromagnetic order in a YBa2Cu3O7/La2/3Ca1/3MnO3 superlattice on a LSAT substrate: A polarized neutron reflectometry study

    NASA Astrophysics Data System (ADS)

    Uribe-Laverde, M. A.; Satapathy, D. K.; Marozau, I.; Malik, V. K.; Das, S.; Sen, K.; Stahn, J.; Rühm, A.; Kim, J.-H.; Keller, T.; Devishvili, A.; Toperverg, B. P.; Bernhard, C.

    2013-03-01

    Using polarized neutron reflectometry (PNR) we have investigated a [YBa2Cu3O7(10 nm)/La2/3Ca1/3MnO3(9 nm)]10 (YBCO/LCMO) superlattice grown by pulsed laser deposition on a La0.3Sr0.7Al0.65Ta0.35O3 (LSAT) substrate. Due to the high structural quality of the superlattice and the substrate, the specular reflectivity signal extends with a high signal-to-background ratio beyond the fourth-order superlattice Bragg peak. This allows us to obtain more detailed and reliable information about the magnetic depth profile than in previous PNR studies on similar superlattices that were partially impeded by problems related to the low-temperature structural transitions of the SrTiO3 substrates. In agreement with the previous reports, our PNR data reveal a strong magnetic proximity effect showing that the depth profile of the magnetic potential differs significantly from the one of the nuclear potential that is given by the YBCO and LCMO layer thickness. We present fits of the PNR data using different simple blocklike models for which either a large ferromagnetic moment is induced on the YBCO side of the interfaces or the ferromagnetic order is suppressed on the LCMO side. We show that a good agreement with the PNR data and with the average magnetization as obtained from dc magnetization data can only be obtained with the latter model where a so-called depleted layer with a strongly suppressed ferromagnetic moment develops on the LCMO side of the interfaces. We also show that the PNR data are still compatible with the presence of a small, ferromagnetic Cu moment of 0.25μB on the YBCO side that was previously identified with x-ray magnetic circular dichroism and x-ray resonant magnetic reflectometry measurements on the same superlattice [D. K. Satapathy , Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.108.197201 108, 197201 (2012)]. We discuss that the depleted layer thus should not be mistaken with a “dead” layer that is entirely nonmagnetic but rather may contain a

  13. Apical Cu-O bond in YBa{sub 2}Cu{sub 3}O{sub 7-{delta}} superconductors by XAFS

    SciTech Connect

    Stern, E.A.; Qian, M.; Yacoby, Y.; Heald, S.M.; Maeda, H.

    1993-04-01

    Careful Cu K-edge X-ray absorption fine structure (XAFS) measurements on oriented powders of YBa{sub 2}CU{sub 3}O{sub 7{minus}} were made as a function of temperature, of {delta}, {Tc} method of preparation and grain size. The XAFS data were analyzed for the Cu(1) - O(4) apical bond distance distribution. AU samples indicated evidence for a double-peak in the distribution with a splitting of 0.1{Angstrom}, with the clearest case for the {delta} {approx} 0 samples occurring for the {Tc} = 89K 20{mu}m grain samples and the least clear one for the 5{mu}m grain {Tc} = 93K sample. There is no significant temperature dependence of the splitting. Because the XAFS evidence for the splitting depends on a small signal, it is prudent to verify its existence by other independent measurements.

  14. Impact of S fertilizers on pore-water Cu dynamics and transformation in a contaminated paddy soil with various flooding periods.

    PubMed

    Yang, Jianjun; Zhu, Shenhai; Zheng, Cuiqing; Sun, Lijuan; Liu, Jin; Shi, Jiyan

    2015-04-01

    Impact of S fertilization on Cu mobility and transformation in contaminated paddy soils has been little reported. In this study, we investigated the dynamics and transformation of dissolved and colloidal Cu in the pore water of a contaminated paddy soil after applying ammonium sulphate (AS) and sulfur coated urea (SCU) with various flooding periods (1, 7 and 60 days). Compared to the control soil, the AS-treated soil released more colloidal and dissolved Cu over the entire flooding period, while the SCU-treated soil had lower colloidal Cu after 7-day flooding but higher colloidal and dissolved Cu after 60-day flooding. Microscopic X-ray fluorescence (μ-XRF) analysis found a close relationship between Fe and Cu distribution on soil colloids after 60-day flooding, implying the formation of colloidal Fe/Cu sulphide coprecipitates. Cu K-edge X-ray absorption near-edge structure (XANES) spectroscopy directly revealed the transformation of outer-sphere complexed Cu(II) species to Cu(II) sulphide and reduced Cu2O in the colloids of S-treated soils after 60-day flooding. These results demonstrated the great influence of S fertilization on pore-water Cu mobility by forming Cu sulphide under flooding conditions, which facilitated our understanding and control of Cu loss in contaminated paddy soils under S fertilization. PMID:25603292

  15. 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.

  16. 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.

  17. The adsorption geometry and chemical state of lysine on Cu{110}

    NASA Astrophysics Data System (ADS)

    Eralp, Tugce; Shavorskiy, Andrey; Held, Georg

    2011-02-01

    Chemisorbed layers of lysine adsorbed on Cu{110} have been studied using X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. XPS indicates that the majority (70%) of the molecules in the saturated layer at room temperature (coverage 0.27 ML) are in their zwitterionic state with no preferential molecular orientation. After annealing to 420 K a less densely packed layer is formed (0.14 ML), which shows a strong angular dependence in the characteristic π-resonance of oxygen K edge NEXAFS and no indication of zwitterions in XPS. These experimental results are best compatible with molecules bound to the substrate through the oxygen atoms of the (deprotonated) carboxylate group and the two amino groups involving Cu atoms in three different close packed rows. This μ4 bonding arrangement with an additional bond through the ɛ-amino group is different from geometries previously suggested for lysine on Cu{110}.

  18. Local atomic structure and oxidation processes of Cu(I) binding site in amyloid beta peptide: XAS Study

    NASA Astrophysics Data System (ADS)

    Kremennaya, M. A.; Soldatov, M. A.; Stretsov, V. A.; Soldatov, A. V.

    2016-05-01

    There are two different motifs of X-ray absorption spectra for Cu(I) K-edge in amyloid-β peptide which could be due to two different configurations of local Cu(I) environment. Two or three histidine ligands can coordinate copper ion in varying conformations. On the other hand, oxidation of amyloid-β peptide could play an additional role in local copper environment. In order to explore the peculiarities of local atomic and electronic structure of Cu(I) binding sites in amyloid-β peptide the x-ray absorption spectra were simulated for various Cu(I) environments including oxidized amyloid-β and compared with experimental data.

  19. An investigation of the electronic structure of Cu{sub 2}FeSn{sub 3-x}Ti{sub x}S{sub 8} (0{<=}x{<=}3) thiospinel spin-crossover materials by X-ray absorption spectroscopy and electronic structure calculations

    SciTech Connect

    Hayes, John R.; Grosvenor, Andrew P.

    2013-01-15

    The spin-crossover (SCO) transition is an interesting phenomenon in which a metal center transitions from a low-spin state to a high-spin state (or vice versa) upon some external perturbation. Only a few studies have investigated the SCO transition in crystalline compounds and the Cu{sub 2}FeSn{sub 3-x}Ti{sub x}S{sub 8} thiospinels present an opportunity for such a study. Fe K-XANES has been used to investigate the changes in the electronic structure of these materials as Ti is substituted for Sn. The room-temperature Fe K-edge XANES spectra showed that the pre-edge intensity increased with increasing Ti content as a result of the Fe-S bond becoming more covalent. Ti K- and S K-edge XANES spectra confirmed this analysis. Electronic structure calculations were also performed to aid in the interpretation of the XANES spectra. Temperature-dependent Fe K-edge XANES spectra were further collected to study the SCO transition and showed that the main-edge features decreased in intensity with decreasing temperature, corresponding to variations in the average Fe{sup 2+} spin-state. - Graphical abstract: The Cu{sub 2}FeSn{sub 3-x}Ti{sub x}S{sub 8} spin-crossover materials have been investigated by XANES. The pre-edge region of the Fe K-edge spectra increases with greater Ti incorporation because of the Fe-S bonds becoming more covalent. Highlights: Black-Right-Pointing-Pointer Cu{sub 2}FeSn{sub 3-x}Ti{sub x}S{sub 8} thiospinels were investigated by XANES. Black-Right-Pointing-Pointer The covalency of the Fe-S and Ti-S bonds increases with greater Ti incorporation. Black-Right-Pointing-Pointer T-dependent Fe K-edge XANES spectra were collected to investigate SCO transitions. Black-Right-Pointing-Pointer Covalent bonding makes study of the SCO transition difficult by Fe K-edge XANES. Black-Right-Pointing-Pointer The bonding interactions were investigated through examination of S K-edge spectra.

  20. Polarization developments

    SciTech Connect

    Prescott, C.Y.

    1993-07-01

    Recent developments in laser-driven photoemission sources of polarized electrons have made prospects for highly polarized electron beams in a future linear collider very promising. This talk discusses the experiences with the SLC polarized electron source, the recent progress with research into gallium arsenide and strained gallium arsenide as a photocathode material, and the suitability of these cathode materials for a future linear collider based on the parameters of the several linear collider designs that exist.

  1. Neuronal polarization.

    PubMed

    Takano, Tetsuya; Xu, Chundi; Funahashi, Yasuhiro; Namba, Takashi; Kaibuchi, Kozo

    2015-06-15

    Neurons are highly polarized cells with structurally and functionally distinct processes called axons and dendrites. This polarization underlies the directional flow of information in the central nervous system, so the establishment and maintenance of neuronal polarization is crucial for correct development and function. Great progress in our understanding of how neurons establish their polarity has been made through the use of cultured hippocampal neurons, while recent technological advances have enabled in vivo analysis of axon specification and elongation. This short review and accompanying poster highlight recent advances in this fascinating field, with an emphasis on the signaling mechanisms underlying axon and dendrite specification in vitro and in vivo. PMID:26081570

  2. Polarization Aberrations

    NASA Technical Reports Server (NTRS)

    Mcguire, James P., Jr.; Chipman, Russell A.

    1990-01-01

    The analysis of the polarization characteristics displayed by optical systems can be divided into two categories: geometrical and physical. Geometrical analysis calculates the change in polarization of a wavefront between pupils in an optical instrument. Physical analysis propagates the polarized fields wherever the geometrical analysis is not valid, i.e., near the edges of stops, near images, in anisotropic media, etc. Polarization aberration theory provides a starting point for geometrical design and facilitates subsequent optimization. The polarization aberrations described arise from differences in the transmitted (or reflected) amplitudes and phases at interfaces. The polarization aberration matrix (PAM) is calculated for isotropic rotationally symmetric systems through fourth order and includes the interface phase, amplitude, linear diattenuation, and linear retardance aberrations. The exponential form of Jones matrices used are discussed. The PAM in Jones matrix is introduced. The exact calculation of polarization aberrations through polarization ray tracing is described. The report is divided into three sections: I. Rotationally Symmetric Optical Systems; II. Tilted and Decentered Optical Systems; and Polarization Analysis of LIDARs.

  3. Polar Bear

    USGS Publications Warehouse

    Amstrup, S.D.; DeMaster

    1988-01-01

    Polar bears are long-lived, late-maturing carnivores that have relatively low rates of reproduction and natural mortality. Their populations are susceptible to disturbance from human activities, such as the exploration and development of mineral resources or hunting. Polar bear populations have been an important renewable resource available to coastal communities throughout the Arctic for thousands of years.

  4. Polarized rainbow.

    PubMed

    Können, G P; de Boer, J H

    1979-06-15

    The Airy theory of the rainbow is extended to polarized light. For both polarization directions a simple analytic expression is obtained for the intensity distribution as a function of the scattering angle in terms of the Airy function and its derivative. This approach is valid at least down to droplet diameters of 0.3 mm in visible light. The degree of polarization of the rainbow is less than expected from geometrical optics; it increases with droplet size. For a droplet diameter >1 mm the locations of the supernumerary rainbows are equal for both polarization directions, but for a diameter <1 mm the supernumerary rainbows of the weaker polarization component are located between those in the strong component. PMID:20212586

  5. Synthesis, structure, ultrafast kinetics, and light-induced dynamics of CuHETPHEN chromophores.

    PubMed

    Kohler, Lars; Hayes, Dugan; Hong, Jiyun; Carter, Tyler J; Shelby, Megan L; Fransted, Kelly A; Chen, Lin X; Mulfort, Karen L

    2016-06-14

    Five heteroleptic Cu(i)bis(phenanthroline) chromophores with distinct variation in the steric bulk at the 2,9-phenanthroline position were synthesized using the HETPHEN method, and their ground and excited state properties are described. Analysis of the crystal structures reveals a significant distortion from tetrahedral geometry around the Cu(i) centre which is attributed to favourable aromatic interactions between the two phenanthroline ligands. Ultrafast and nanosecond transient optical spectroscopies reveal that the excited state lifetime can be tuned across two orders of magnitude up to 74 nanoseconds in acetonitrile by changing the 2,9-substituent from hydrogen to sec-butyl. X-ray transient absorption spectroscopy at the Cu K-edge confirmed Cu(i) oxidation to Cu(ii) and revealed a decrease of the Cu-N bond lengths in the excited state. The ground and excited state characterization presented here will guide the integration of CuHETPHEN chromophores into complex electron donor-acceptor architectures. PMID:26924711

  6. Preparation and characterization of a (Cu,Zn)-pMMO from Methylococcus capsulatus (Bath).

    PubMed

    Chen, Chang-Li; Chen, Kelvin H-C; Ke, Shyue-Chu; Yu, Steve S-F; Chan, Sunney I

    2004-12-01

    We report the preparation of a (Cu,Zn)-particulate methane monooxygenase (pMMO) in which the bulk of the copper ions of the electron-transfer clusters (E-clusters) has been replaced by divalent Zn ions. The Cu and Zn contents in the (Cu,Zn)-pMMO were determined by both inductively coupled plasma mass spectroscopy (ICP-MS) and X-ray absorption K-edge spectroscopy. Further characterization of the (Cu,Zn)-pMMO was provided by pMMO-activity assays as well as low-temperature electron paramagnetic resonance (EPR) spectroscopy following reductive titration and incubation in air or air/propylene mixtures. The pMMO-activity assays indicated that the (Cu,Zn)-pMMO was no longer capable of supporting catalytic turnover of hydrocarbon substrates. However, the EPR studies revealed that the catalytic cluster (C-cluster) copper ions in the (Cu,Zn)-pMMO were still capable of supporting the activation of dioxygen when reduced, and that the 14N-superhyperfine features associated with one of the type 2 Cu(II) centers in the hydroxylation C-cluster remained unperturbed. The replacement of the E-cluster copper ions by Zn ions did compromise the ability of the protein to mediate the transfer of reducing equivalents from exogenous reductants to the C-clusters. These observations provide strong support for the electron transfer and catalytic roles for the E-cluster and C-cluster copper ions, respectively. PMID:15541502

  7. Polar atomic displacements in multiferroics observed via anomalous x-ray diffraction

    NASA Astrophysics Data System (ADS)

    Azimonte, C.; Granado, E.; Terashita, H.; Park, S.; Cheong, S.-W.

    2010-01-01

    The minute polar atomic displacements in multiferroics are shown to be within the reach of crystallography. A nonconventional methodology with anomalous x-ray diffraction is employed to investigate such displacements in DyMn2O5 with giant magnetoelectric coupling and two distinct Mn3+ and Mn4+ sites. Intensity differences of a selected Bragg reflection were measured as the direction of electric polarization is switched by a poling field. A significant differential effect, which is strongly enhanced at energies near and above the MnK edge, was observed near and below the ferroelectric transition temperature, Tc˜40K . The direct participation of ionic displacements in the ferroelectric polarization, particularly the Mn3+ sublattice, is demonstrated, dismissing a purely electronic mechanism for the multiferroicity.

  8. Polar Glaciology

    NASA Technical Reports Server (NTRS)

    Robin, G. D.

    1984-01-01

    Two fields of research on polar ice sheets are likely to be of dominant interest during the 1990s. These are: the role of polar ice sheets in the hydrological cycle ocean-atmosphere-ice sheets-oceans, especially in relation to climate change; and the study and interpretation of material in deep ice cores to provide improved knowledge of past climates and of the varying levels of atmospheric constituents such as CO2, NOx, SO2, aerosols, etc., over the past 200,000 years. Both topics require a better knowledge of ice dynamics. Many of the studies that should be undertaken in polar regions by Earth Observing System require similar instruments and techniques to those used elsewhere over oceans and inland surfaces. However to study polar regions two special requirements need to be met: Earth Observing System satellite(s) need to be in a sufficiently high inclination orbit to cover most of the polar regions. Instruments must also be adapted, often by relatively limited changes, to give satisfactory data over polar ice. The observational requirements for polar ice sheets in the 1990s are summarized.

  9. Charge-Transfer Excitations in the Model Superconductor HgBa2CuO4+δ

    NASA Astrophysics Data System (ADS)

    Lu, L.; Chabot-Couture, G.; Zhao, X.; Hancock, J. N.; Kaneko, N.; Vajk, O. P.; Yu, G.; Grenier, S.; Kim, Y. J.; Casa, D.; Gog, T.; Greven, M.

    2005-11-01

    We report a Cu K-edge resonant inelastic x-ray scattering (RIXS) study of charge-transfer excitations in the 2-8 eV range in the structurally simple compound HgBa2CuO4+δ at optimal doping (Tc=96.5K). The spectra exhibit a significant dependence on the incident photon energy which we carefully utilize to resolve a multiplet of weakly dispersive (<0.5eV) electron-hole excitations, including a mode at 2 eV. The observation of this 2 eV excitation suggests the existence of a remnant charge-transfer gap deep in the superconducting phase. Quite generally, our results, which include additional data for the Mott insulator La2CuO4, demonstrate the importance of exploring the incident photon-energy dependence of the RIXS cross section.

  10. Local structure investigation of (Co, Cu) co-doped ZnO nanocrystals and its correlation with magnetic properties

    NASA Astrophysics Data System (ADS)

    Tiwari, N.; Doke, S.; Lohar, A.; Mahamuni, Shailaja; Kamal, C.; Chakrabarti, Aparna; Choudhary, R. J.; Mondal, P.; Jha, S. N.; Bhattacharyya, D.

    2016-03-01

    Pure, Co doped and (Co, Cu) co-doped ZnO nanocrystals have been prepared by wet chemical route at room temperature to investigate the effect of Cu doping in Co doped ZnO nanocrystals . The nanocrystals have initially been characterized by X-ray diffraction, FTIR, Raman, optical absorption and EPR spectroscopy and the results were corroborated with DFT based electronic structure calculations. Magnetic properties of the samples have been investigated by studying their magnetic hysteresis behavior and temperature dependence of susceptibilities. Finally the local structure at the host and dopant sites of the nanocrystals have been investigated by Zn, Co and Cu K edges EXAFS measurements with synchrotron radiation to explain their experimentally observed magnetic properties.

  11. Polarizing cues.

    PubMed

    Nicholson, Stephen P

    2012-01-01

    People categorize themselves and others, creating ingroup and outgroup distinctions. In American politics, parties constitute the in- and outgroups, and party leaders hold sway in articulating party positions. A party leader's endorsement of a policy can be persuasive, inducing co-partisans to take the same position. In contrast, a party leader's endorsement may polarize opinion, inducing out-party identifiers to take a contrary position. Using survey experiments from the 2008 presidential election, I examine whether in- and out-party candidate cues—John McCain and Barack Obama—affected partisan opinion. The results indicate that in-party leader cues do not persuade but that out-party leader cues polarize. This finding holds in an experiment featuring President Bush in which his endorsement did not persuade Republicans but it polarized Democrats. Lastly, I compare the effect of party leader cues to party label cues. The results suggest that politicians, not parties, function as polarizing cues. PMID:22400143

  12. Polar motion

    NASA Technical Reports Server (NTRS)

    Kolenkiewicz, R.

    1973-01-01

    Tracking of the Beacon Explorer-C satellite by a precision laser system was used to measure the polar motion and solid earth tide. The tidal perturbation of satellite latitude is plotted as variation in maximum latitude in seconds of arc on earth's surface as a function of the date, and polar motion is shown by plotting the variation in latitude of the laser in seconds of arc along the earth's surface as a function of date

  13. Characterization of Binary Ag-Cu Ion Mixtures in Zeolites: Their Reduction Products and Stability to Air Oxidation

    SciTech Connect

    Fiddy, Steven; Petranovskii, Vitalii; Ogden, Steve; Iznaga, Inocente Rodriguez

    2007-02-02

    A series of Ag+-Cu2+ binary mixtures with different Ag/Cu ratios were supported on mordenite with different Si/Al ratios and were subsequently reduced under hydrogen in the temperature range 323K - 473K. Ag and Cu K-edge X-ray Absorption Spectroscopy (XAS) was conducted on these systems in-situ to monitor the reduction species formed and the kinetics of their reduction. In-situ XANES clearly demonstrates that the formation of silver particles is severely impeded by the addition of copper and that the copper is converted from Cu(II) to Cu(I) during reduction and completely reverts back to Cu(II) during cooling. There are no indications at any stage of the formation of bimetallic Ag-Cu clusters. Interestingly, the Ag/Cu ratio appears to have no influence of the reduction kinetics and reduction products formed with only the highest Si/Al ratio (MR = 128) investigated during this study having an influence on the reduction and stability to air oxidation.

  14. Polar Stratigraphy

    NASA Technical Reports Server (NTRS)

    1999-01-01

    These three images were taken on three different orbits over the north polar cap in April 1999. Each shows a different part of the same ice-free trough. The left and right images are separated by a distance of more than 100 kilometers (62 miles). Note the similar layers in each image.

  15. Political polarization

    PubMed Central

    Dixit, Avinash K.; Weibull, Jörgen W.

    2007-01-01

    Failures of government policies often provoke opposite reactions from citizens; some call for a reversal of the policy, whereas others favor its continuation in stronger form. We offer an explanation of such polarization, based on a natural bimodality of preferences in political and economic contexts and consistent with Bayesian rationality. PMID:17452633

  16. Growth control, structure, chemical state, and photoresponse of CuO-CdS core-shell heterostructure nanowires.

    PubMed

    El Mel, A A; Buffière, M; Bouts, N; Gautron, E; Tessier, P Y; Henzler, K; Guttmann, P; Konstantinidis, S; Bittencourt, C; Snyders, R

    2013-07-01

    The growth of single-crystal CuO nanowires by thermal annealing of copper thin films in air is studied. We show that the density, length, and diameter of the nanowires can be controlled by tuning the morphology and structure of the copper thin films deposited by DC magnetron sputtering. After identifying the optimal conditions for the growth of CuO nanowires, chemical bath deposition is employed to coat the CuO nanowires with CdS in order to form p-n nanojunction arrays. As revealed by high-resolution TEM analysis, the thickness of the polycrystalline CdS shell increases when decreasing the diameter of the CuO core for a given time of CdS deposition. Near-edge x-ray absorption fine-structure spectroscopy combined with transmission x-ray microscopy allows the chemical analysis of isolated nanowires. The absence of modification in the spectra at the Cu L and O K edges after the deposition of CdS on the CuO nanowires indicates that neither Cd nor S diffuse into the CuO phase. We further demonstrate that the core-shell nanowires exhibit the I-V characteristic of a resistor instead of a diode. The electrical behavior of the device was found to be photosensitive, since increasing the incident light intensity induces an increase in the collected electrical current. PMID:23732175

  17. Full Polarization Analysis of Resonant Superlattice and Forbidden x-ray Reflections in Magnetite

    SciTech Connect

    Wilkins, S.B.; Bland, S.R.; Detlefs, B.; Beale, T.A.W.; Mazzoli, C.; Joly, Y.; Hatton, P.D.; Lorenzo, J.E.; Brabers, V.A.M.

    2009-12-02

    Despite being one of the oldest known magnetic materials, and the classic mixed valence compound, thought to be charge ordered, the structure of magnetite below the Verwey transition is complex and the presence and role of charge order is still being debated. Here, we present resonant x-ray diffraction data at the iron K-edge on forbidden (0, 0, 2n+1){sub C} and superlattice (0, 0, 2n+1/2)C reflections. Full linear polarization analysis of the incident and scattered light was conducted in order to explore the origins of the reflections. Through simulation of the resonant spectra we have confirmed that a degree of charge ordering takes place, while the anisotropic tensor of susceptibility scattering is responsible for the superlattice reflections below the Verwey transition. We also report the surprising result of the conversion of a significant proportion of the scattered light from linear to nonlinear polarization.

  18. 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.

  19. Calculated Performance Of The Variable-Polarization Undulator Upgrade To The Daresbury SRS Soft X-Ray Undulator Beamline

    NASA Astrophysics Data System (ADS)

    Roper, Mark D.; Bird, Daniel T.

    2004-05-01

    The soft x-ray beamline 5U1 on the Daresbury Laboratory SRS currently uses a planar undulator, producing linearly polarized radiation in the range 100 to 1000 eV. The undulator is soon to be replaced by a variable-polarization device of the Apple II design. The aim is to produce circularly polarized light in the energy range 265 to 1000 eV, covering the K-edges of C, N & O, and the first row transition element L-edges. This will greatly enhance the provision of circularly polarized soft-x-rays on the SRS and open up new opportunities for experimenters. The device will also produce linear polarization with a selectable angle of polarization with respect to the orbit plane, which is currently unavailable on the SRS. In order to provide the coverage over this energy range, we are exploiting the relatively large emittance of the SRS to allow us to use the second and third harmonics even in circular polarization mode. This paper presents the expected beamline output in various polarization modes and the predicted degree of polarization.

  20. Investigation of the H-Cu and Cu-Cu bonds in hydrogenated Cu

    NASA Astrophysics Data System (ADS)

    Shuttleworth, I. G.

    2013-01-01

    The pure and hydrogenated copper system CuHn (n=0, 0.25, 0.50, 0.75 and 1) has been investigated using LCAO-DFT. The average H-Cu (Cu-Cu) bonding interaction increases (decreases) with n whilst concurrent orbital-resolved studies of the H-Cu interactions showed that the (non-)directional H-Cu bonds become more (less) bonding. This preference for directional bonds is reflected in the Cu-Cu interactions. CuH0.25 is shown to have an unusually localized electronic structure compared to the more hydrogenated systems, and the origins of this structure are discussed.

  1. Cell polarity

    PubMed Central

    Romereim, Sarah M

    2011-01-01

    Despite extensive genetic analysis of the dynamic multi-phase process that transforms a small population of lateral plate mesoderm into the mature limb skeleton, the mechanisms by which signaling pathways regulate cellular behaviors to generate morphogenetic forces are not known. Recently, a series of papers have offered the intriguing possibility that regulated cell polarity fine-tunes the morphogenetic process via orienting cell axes, division planes and cell movements. Wnt5a-mediated non-canonical signaling, which may include planar cell polarity, has emerged as a common thread in the otherwise distinct signaling networks that regulate morphogenesis in each phase of limb development. These findings position the limb as a key model to elucidate how global tissue patterning pathways direct local differences in cell behavior that, in turn, generate growth and form. PMID:22064549

  2. Phase transition from fcc to bcc structure of the Cu-clusters during nanocrystallization of Fe85.2Si1B9P4Cu0.8 soft magnetic alloy

    NASA Astrophysics Data System (ADS)

    Nishijima, Masahiko; Matsuura, Makoto; Takenaka, Kana; Takeuchi, Akira; Ofuchi, Hironori; Makino, Akihiro

    2014-05-01

    A role of Cu on the nanocrystallization of an Fe85.2Si1B9P4Cu0.8 alloy was investigated by X-ray absorption fine structure (XAFS) and transmission electron microscopy (TEM). The Cu K-edge XAFS results show that local structure around Cu is disordered for the as-quenched sample whereas it changes to fcc-like structure at 613 K. The fcc Cu-clusters are, however, thermodynamically unstable and begin to transform into bcc structure at 638 K. An explicit bcc structure is observed for the sample annealed at 693 K for 600 s in which TEM observation shows that precipitated bcc-Fe crystallites with ˜12 nm are homogeneously distributed. The bcc structure of the Cu-clusters transforms into the fcc-type again at 973 K, which can be explained by the TEM observations; Cu segregates at grain boundaries between bcc-Fe crystallites and Fe3(B,P) compounds. Combining the XAFS results with the TEM observations, the structure transition of the Cu-clusters from fcc to bcc is highly correlated with the preliminary precipitation of the bcc-Fe which takes place prior to the onset of the first crystallization temperature, Tx1 = 707 K. Thermodynamic analysis suggests that an interfacial energy density γ between an fcc-Cu cluster and bcc-Fe matrix dominates at a certain case over the structural energy between fcc and bcc Cu, ΔGfcc - bcc, which causes phase transition of the Cu clusters from fcc to bcc structure.

  3. Polar Textures

    NASA Technical Reports Server (NTRS)

    2005-01-01

    [figure removed for brevity, see original site] Context image for PIA03646 Polar Textures

    This VIS image shows part of the south polar region. The ejecta from the relatively young crater covers the rougher textured polar surface.

    Image information: VIS instrument. Latitude 81S, Longitude 54.5E. 17 meter/pixel resolution.

    Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

    NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is led by Dr. Philip Christensen at Arizona State University. Lockheed Martin Astronautics, Denver, is the prime contractor for the Odyssey project, and developed and built the orbiter. Mission operations are conducted jointly from Lockheed Martin and from JPL, a division of the California Institute of Technology in Pasadena.

  4. Inducing electric polarization in ultrathin insulating layers

    NASA Astrophysics Data System (ADS)

    Martinez-Castro, Jose; Piantek, Marten; Persson, Mats; Serrate, David; Hirjibehedin, Cyrus F.

    Studies of ultrathin polar oxide films have attracted the interest of researchers for a long time due to their different properties compared to bulk materials. However they present several challenges such as the difficulty in the stabilization of the polar surfaces and the limited success in tailoring their properties. Moreover, recently developed Van der Waals materials have shown that the stacking of 2D-layers trigger new collective states thanks to the interaction between layers. Similarly, interface phenomena emerge in polar oxides, like induced ferroelectricity. This represents a promising way for the creation of new materials with customized properties that differ from those of the isolated layers. Here we present a new approach for the fabrication and study of atomically thin insulating films. We show that the properties of insulating polar layers of sodium chloride (NaCl) can be engineered when they are placed on top of a charge modulated template of copper nitride (Cu2N). STM studies carried out in ultra-high vacuum and at low temperatures over NaCl/Cu2N/Cu(001) show that we are able to build up and stabilize interfaces of polar surface at the limit of one atomic layer showing new properties not present before at the atomic scale.

  5. Probing absolute spin polarization at the nanoscale.

    PubMed

    Eltschka, Matthias; Jäck, Berthold; Assig, Maximilian; Kondrashov, Oleg V; Skvortsov, Mikhail A; Etzkorn, Markus; Ast, Christian R; Kern, Klaus

    2014-12-10

    Probing absolute values of spin polarization at the nanoscale offers insight into the fundamental mechanisms of spin-dependent transport. Employing the Zeeman splitting in superconducting tips (Meservey-Tedrow-Fulde effect), we introduce a novel spin-polarized scanning tunneling microscopy that combines the probing capability of the absolute values of spin polarization with precise control at the atomic scale. We utilize our novel approach to measure the locally resolved spin polarization of magnetic Co nanoislands on Cu(111). We find that the spin polarization is enhanced by 65% when increasing the width of the tunnel barrier by only 2.3 Å due to the different decay of the electron orbitals into vacuum. PMID:25423049

  6. Continuous control of spin polarization using a magnetic field

    NASA Astrophysics Data System (ADS)

    Gifford, J. A.; Zhao, G. J.; Li, B. C.; Tracy, Brian D.; Zhang, J.; Kim, D. R.; Smith, David J.; Chen, T. Y.

    2016-05-01

    The giant magnetoresistance (GMR) of a point contact between a Co/Cu multilayer and a superconductor tip varies for different bias voltage. Direct measurement of spin polarization by Andreev reflection spectroscopy reveals that the GMR change is due to a change in spin polarization. This work demonstrates that the GMR structure can be utilized as a spin source and that the spin polarization can be continuously controlled by using an external magnetic field.

  7. Influence of ligands on the electronic and magnetic properties of Fe porphyrin in gas phase and on Cu(001)

    SciTech Connect

    Brena, Barbara; Herper, Heike C.

    2015-05-07

    A study of the adsorption of different axial ligands on Fe porphyrin (FeP), both isolated and adsorbed on Cu(001), was performed by means of Density Functional Theory. The electronic and magnetic properties of the adsorbed FeP resulted to be strongly influenced by the axial ligands considered, Cl and O. Cl induces an enhancement of the overall molecular magnetic moment of 3.0 μ{sub B} while O or O{sub 2} leave the spin state of the molecule unchanged. The influence of the Cl in the electronic states was moreover studied by means of theoretical NEXAFS N K-edge, where the spectra of isolated FeP and FeP with Cl ligand were calculated. The adsorption of the FeP molecules on Cu(001) leads in case of Cl to a further increase of the magnetic moment due to strong deformation of the Fe-N bond.

  8. Influence of ligands on the electronic and magnetic properties of Fe porphyrin in gas phase and on Cu(001)

    NASA Astrophysics Data System (ADS)

    Brena, Barbara; Herper, Heike C.

    2015-05-01

    A study of the adsorption of different axial ligands on Fe porphyrin (FeP), both isolated and adsorbed on Cu(001), was performed by means of Density Functional Theory. The electronic and magnetic properties of the adsorbed FeP resulted to be strongly influenced by the axial ligands considered, Cl and O. Cl induces an enhancement of the overall molecular magnetic moment of 3.0 μB while O or O2 leave the spin state of the molecule unchanged. The influence of the Cl in the electronic states was moreover studied by means of theoretical NEXAFS N K-edge, where the spectra of isolated FeP and FeP with Cl ligand were calculated. The adsorption of the FeP molecules on Cu(001) leads in case of Cl to a further increase of the magnetic moment due to strong deformation of the Fe-N bond.

  9. Quasi-zero dimensional CuB2O4: a resonant inelastic X-ray scattering case study

    SciTech Connect

    Hancock, J.N.

    2010-04-29

    We explore the general phenomenology of resonant inelastic scattering (RIXS) using CuB{sub 2}O{sub 4}, a network of CuO{sub 4} plaquettes electronically isolated by B{sup +3} ions. Spectra show a small number of well-separated features, and we exploit the simple electronic structure to explore RIXS phenomenology by developing a calculation which allows for intermediate-state effects ignored in standard approaches. These effects are found to be non-negligible and good correspondence between our model and experiment leads to a simple picture of such phenomenology as the genesis of d {yields} d excitations at the K edge and intermediate-state interference effects.

  10. Ni-induced local distortions in La1.85Sr0.15Cu1-yNiyO4 and their relevance to Tc suppression: An angular-resolved XAFS study

    NASA Astrophysics Data System (ADS)

    Haskel, Daniel; Stern, Edward A.; Polinger, Victor; Dogan, Fatih

    2001-09-01

    We present results from angular-resolved x-ray-absorption fine-structure (XAFS) measurements at the Ni, La, and Sr K edges of oriented powders of La1.85Sr0.15Cu1-yNiyO4, with y=0.01, 0.03, 0.06. A special magnetic alignment procedure allowed us to measure pure ĉ- and ab-oriented XAFS at the Ni K edge in identical fluorescence geometries. Both the x-ray-absorption near-edge structure and the XAFS unequivocally show that the NiO6 octahedra are contracted along the c axis by ~0.32 Å relative to CuO6 octahedra while the in-plane distances of NiO6 and CuO6 octahedra are the same within 0.01 Å. The NiO6 octahedral contraction drives the average ĉ axis contraction measured by diffraction with increasing content of Ni. The local ĉ axis shows strong spatial fluctuations, due to the different NiO6 and CuO6 octahedral configurations and the stronger bonding of a La3+ ion than a Sr2+ ion to the O(2) apical oxygens of such octahedra. We discuss the relevance of these findings to the mechanisms of loss of superconductivity at y~0.03 and hole localization above y~0.05 by Ni dopants.

  11. Suppression of superconductivity in La1.85Sr0.15Cu1-yNiyO4: The relevance of local lattice distortions

    NASA Astrophysics Data System (ADS)

    Haskel, D.; Stern, E. A.; Polinger, V.; Dogan, F.

    2001-02-01

    The effect of Ni substitution upon the local structure of La1.85Sr0.15Cu1-yNiyO4 is commonly neglected when addressing the Ni-induced destruction of the superconducting state at y≈0.03 and a metal-insulator transition at y≈0.05. It is also sometimes assumed that direct substitution of a dopant into the CuO2 planes has a detrimental effect on superconductivity due to in-plane lattice distortions around the dopants. We present here results from angular-dependent x-ray absorption fine structure (XAFS) measurements at the Ni, La and Sr K-edges of oriented powders of La1.85Sr0.15Cu1-yNiyO4 with y=0.01, 0.03, 0.06. A special magnetic alignment geometry allowed us to measure pure ĉ and ab̂ oriented XAFS at the Ni K-edge in identical fluorescence geometries. Both the near-edge absorption spectra (XANES) and the XAFS unequivocally show that the NiO6 octahedra are largely contracted along the c-axis, by ≈ 0.16 Å. Surprisingly, the Ni-O planar bonds and the Ni-O-Cu/Ni planar buckling angle are nearly identical to their Cu counterparts. The NiO6 octahedral contraction drives the macroscopic ĉ-axis contraction observed with Ni-doping. The local ĉ-axis strongly fluctuates, due to the different NiO6 and CuO6 octahedral configurations and the much stronger bonding of a La+3 ion than a Sr+2 ion to the O(2) apical oxygens. We discuss the relevance of these findings to the mechanisms of Tc suppresion and hole-localization by Ni dopants.

  12. High-Tc superconductivity at the interface between the CaCuO2 and SrTiO3 insulating oxides

    DOE PAGESBeta

    Di Castro, D.; Cantoni, C.; Ridolfi, F.; Aruta, C.; Tebano, A.; Yang, N.; Balestrino, G.

    2015-09-28

    At interfaces between complex oxides it is possible to generate electronic systems with unusual electronic properties, which are not present in the isolated oxides. One important example is the appearance of superconductivity at the interface between insulating oxides, although, until now, with very low Tc. We report the occurrence of high Tc superconductivity in the bilayer CaCuO2/SrTiO3, where both the constituent oxides are insulating. In order to obtain a superconducting state, the CaCuO2/SrTiO3 interface must be realized between the Ca plane of CaCuO2 and the TiO2 plane of SrTiO3. Only in this case can oxygen ions be incorporated in themore » interface Ca plane, acting as apical oxygen for Cu and providing holes to the CuO2 planes. In addition, a detailed hole doping spatial profile can be obtained by scanning transmission electron microscopy and electron-energy-loss spectroscopy at the O K edge, clearly showing that the (super)conductivity is confined to about 1–2 CaCuO2 unit cells close to the interface with SrTiO3. The results obtained for the CaCuO2/SrTiO3 interface can be extended to multilayered high Tc cuprates, contributing to explaining the dependence of Tc on the number of CuO2 planes in these systems.« less

  13. Polar Landforms

    NASA Technical Reports Server (NTRS)

    2005-01-01

    10 August 2005 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows eroded remnants of carbon dioxide ice in the south polar residual cap of Mars. The scarps that outline each small mesa have retreated about 3 meters (10 feet) per Mars year since MGS began orbiting the red planet in 1997.

    Location near: 87.0oS, 31.9oW Image width: width: 3 km (1.9 mi) Illumination from: upper left Season: Southern Spring

  14. Speciation and mobility of Zn, Cu and Pb in a truck farming soil contaminated by sewage irrigation

    NASA Astrophysics Data System (ADS)

    Kirpichtchikova, T.; Manceau, A.; Lanson, B.; Marcus, M. A.; Jacquet, T.

    2003-05-01

    The forrns and mobility of Cu (290 mg/kg), Zn (1103 mg/kg), and Pb (535 mg/kg) in a soil used for intensive truck farining from the Region Ile-de-France, and which has been irrigated for more than a century with sewage water ftom the city of Paris, have been studied by chemical treatments and advanced x-ray techniques. Elemental associations and forms of metals were determined qualitatively and quantitatively by a combination of physical techniques, including μPIXE (Cu, Zn, Pb), μSXRF (Cu, Zn), μEXAFS (Zn) and powder EXAFS (Zn). The nature, number, and relative proportion of Zn species were obtained by principal component analysis and decomposition of Zn K-edge EXAFS spectra. These data collectively indicate that Cu is associated mainly with organic matter, and that Zn and Pb are bound essentially to mineral constituents. Four Zn-containing species were positively identified: Zn-phosphate and phyllosilicate as dominant species, and Zn-Fe oxyhydroxide and willemite (Zn2SiO4) as minor species. Studies are underway to determine the structural forms of Cu and Pb. Depending on the chemical treatment, up to 70% Cu, ~50% Zn, and ~85% Pb can be removed in a few days with citrate and EDTA. Citrate is generally at least as efficient as EDTA, and it has the advantage ofbeing easily biodegradable and, hence, less harmful to ecosystems.

  15. Polar ozone

    NASA Technical Reports Server (NTRS)

    Solomon, S.; Grose, W. L.; Jones, R. L.; Mccormick, M. P.; Molina, Mario J.; Oneill, A.; Poole, L. R.; Shine, K. P.; Plumb, R. A.; Pope, V.

    1990-01-01

    The observation and interpretation of a large, unexpected ozone depletion over Antarctica has changed the international scientific view of stratospheric chemistry. The observations which show the veracity, seasonal nature, and vertical structure of the Antarctic ozone hole are presented. Evidence for Arctic and midlatitude ozone loss is also discussed. The chemical theory for Antarctic ozone depletion centers around the occurrence of polar stratospheric clouds (PSCs) in Antarctic winter and spring; the climatology and radiative properties of these clouds are presented. Lab studies of the physical properties of PSCs and the chemical processes that subsequently influence ozone depletion are discussed. Observations and interpretation of the chemical composition of the Antarctic stratosphere are described. It is shown that the observed, greatly enhanced abundances of chlorine monoxide in the lower stratosphere are sufficient to explain much if not all of the ozone decrease. The dynamic meteorology of both polar regions is given, interannual and interhemispheric variations in dynamical processes are outlined, and their likely roles in ozone loss are discussed.

  16. Polar Markings

    NASA Technical Reports Server (NTRS)

    2006-01-01

    [figure removed for brevity, see original site] Context image for PIA02155 Polar Markings

    These bright and dark markings occurred near the end of summer in the south polar region. The dark material is likely dust that has been freed of frost cover.

    Image information: VIS instrument. Latitude -76.3N, Longitude 84.9E. 17 meter/pixel resolution.

    Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

    NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is led by Dr. Philip Christensen at Arizona State University. Lockheed Martin Astronautics, Denver, is the prime contractor for the Odyssey project, and developed and built the orbiter. Mission operations are conducted jointly from Lockheed Martin and from JPL, a division of the California Institute of Technology in Pasadena.

  17. Polar Layers

    NASA Technical Reports Server (NTRS)

    2006-01-01

    [figure removed for brevity, see original site] Context image for PIA02153 Polar Layers

    This image of the south polar region shows layered material. It is not known if the layers are formed yearly or if they form over the period of 10s to 100s of years or more.

    Image information: VIS instrument. Latitude -80.3N, Longitude 296.2E. 17 meter/pixel resolution.

    Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

    NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is led by Dr. Philip Christensen at Arizona State University. Lockheed Martin Astronautics, Denver, is the prime contractor for the Odyssey project, and developed and built the orbiter. Mission operations are conducted jointly from Lockheed Martin and from JPL, a division of the California Institute of Technology in Pasadena.

  18. Polar Ridges

    NASA Technical Reports Server (NTRS)

    2006-01-01

    [figure removed for brevity, see original site] Context image for PIA03662 Polar Ridges

    This ridge system is located in the south polar region.

    Image information: VIS instrument. Latitude -81.7N, Longitude 296.5E. 17 meter/pixel resolution.

    Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

    NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is led by Dr. Philip Christensen at Arizona State University. Lockheed Martin Astronautics, Denver, is the prime contractor for the Odyssey project, and developed and built the orbiter. Mission operations are conducted jointly from Lockheed Martin and from JPL, a division of the California Institute of Technology in Pasadena.

  19. Polar Textures

    NASA Technical Reports Server (NTRS)

    2005-01-01

    [figure removed for brevity, see original site] Context image for PIA03638 Polar Textures

    This image illustrates the variety of textures that appear in the south polar region during late summer.

    Image information: VIS instrument. Latitude 80.5S, Longitude 57.9E. 17 meter/pixel resolution.

    Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

    NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is led by Dr. Philip Christensen at Arizona State University. Lockheed Martin Astronautics, Denver, is the prime contractor for the Odyssey project, and developed and built the orbiter. Mission operations are conducted jointly from Lockheed Martin and from JPL, a division of the California Institute of Technology in Pasadena.

  20. Polar Terrains

    NASA Technical Reports Server (NTRS)

    2005-01-01

    [figure removed for brevity, see original site] Context image for PIA03577 Polar Terrains

    The region surrounding the South Polar Cap contains many different terrain types. This image shows both etched terrain and a region of 'mounds'.

    Image information: VIS instrument. Latitude 75S, Longitude 286.5E. 17 meter/pixel resolution.

    Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

    NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is led by Dr. Philip Christensen at Arizona State University. Lockheed Martin Astronautics, Denver, is the prime contractor for the Odyssey project, and developed and built the orbiter. Mission operations are conducted jointly from Lockheed Martin and from JPL, a division of the California Institute of Technology in Pasadena.

  1. Bonding, Backbonding, and Spin-Polarized Molecular Orbitals:Basis for Magnetism and Semiconducting Transport in V[TCNE]x~;;2

    SciTech Connect

    Kortright, Jeffrey B; Kortright, Jeffrey B; Lincoln, Derek M; Edelstein, Ruth Shima; Epstein, Arthur J

    2008-05-20

    X-ray absorption spectroscopy (XAS) and magnetic circular dichroism (MCD) at the V L2,3 and C and N K edges reveal bonding/backbonding interactions in films of the 400 K magnetic semiconductor V[TCNE]x~;;2. In V spectra, dxy-like orbitals are modeled assuming V2+ in an octahedral ligand field, while dz2 and dx2-y2 orbitals involved in strong covalent bonding cannot be modeled by atomic calculations. C and N MCD, and differences in XAS from neutral TCNE molecules, reveal spin-polarized molecular orbitals in V[TCNE]x~;;2 associated with backbonding interactions that yield its novel properties.

  2. Polar Barchans

    NASA Technical Reports Server (NTRS)

    2004-01-01

    20 July 2004 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows dark, barchan sand dunes of the north polar region of Mars. Barchan dunes are simple, rounded forms with two horns that extend downwind. Inequalities in local wind patterns may result in one horn being extended farther than the other, as is the case for several dunes in this image. The image also shows several barchans may merge to form a long dune ridge. The horns and attendant slip faces on these dunes indicate wind transport of sand from the upper left toward the lower right. The image is located near 77.6oN, 103.6oW. The picture covers an area about 3 km (1.9 mi) wide; sunlight illuminates the scene from the lower left.

  3. Polar Polygons

    NASA Technical Reports Server (NTRS)

    2004-01-01

    26 December 2003 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) picture displays polygons outlined by cracks in the martian south polar region. This southern summer view was acquired in October 2003 and is located near 86.9oS, 170.6oW. Polygons similar in size and shape to these are common in the arctic and antarctic regions of Earth. On Earth, they indicate the presence (or the past presence) of ground ice and the freeze-thaw cycles that accompany this ice. On Mars, whether ground ice was responsible for these landforms is uncertain, but their presence is suggestive that ground ice may exist or may once have existed in this region. The picture covers an area 3 km (1.9 mi) wide. Sunlight illuminates the scene from the upper left.

  4. Behavior of CuP and OFHC Cu anodes under electrodeposition conditions

    SciTech Connect

    Frankel, G.S.; Schrott, A.G.; Horkans, J.; Andricacos, P.C.; Isaacs, H.S.

    1992-08-01

    Films formed on CuP (with 0.05 wt % P) and OFHC Cu anodes in electroplating solutions were studied by X-ray Photoelectron Spectroscopy, X-ray Absorption Spectroscopy, electrochemical methods, and a newly developed gravimetric technique. The black film formed on CuP in Cl-containing solutions was found to resemble a porous sponge composed of CuCl but laden/with concentrated CuSO{sub 4} solution. The difference between the buoyancy-corrected measured mass change and the charge-equivalent mass change was found to have two components: a reversible part that comes and goes as the current is turned on and off, and an irreversible part that remains on the surface and increase in mass with time. The irreversible part results from the anodic film, which increases linearly with charge density but independent of current density. The reversible part of the mass change arises from the weight of the diffusion layer. In contrast to CuP, OFHC Cu releases much more Cu{sup +1} during anodic polarization and forms a poorly-adherent anodic film that is considerably heavier than the black film for a given charge density.

  5. Behavior of CuP and OFHC Cu anodes under electrodeposition conditions

    SciTech Connect

    Frankel, G.S.; Schrott, A.G.; Horkans, J.; Andricacos, P.C. . Thomas J. Watson Research Center); Isaacs, H.S. )

    1992-01-01

    Films formed on CuP (with 0.05 wt % P) and OFHC Cu anodes in electroplating solutions were studied by X-ray Photoelectron Spectroscopy, X-ray Absorption Spectroscopy, electrochemical methods, and a newly developed gravimetric technique. The black film formed on CuP in Cl-containing solutions was found to resemble a porous sponge composed of CuCl but laden/with concentrated CuSO{sub 4} solution. The difference between the buoyancy-corrected measured mass change and the charge-equivalent mass change was found to have two components: a reversible part that comes and goes as the current is turned on and off, and an irreversible part that remains on the surface and increase in mass with time. The irreversible part results from the anodic film, which increases linearly with charge density but independent of current density. The reversible part of the mass change arises from the weight of the diffusion layer. In contrast to CuP, OFHC Cu releases much more Cu{sup +1} during anodic polarization and forms a poorly-adherent anodic film that is considerably heavier than the black film for a given charge density.

  6. X-Ray Absorption Spectroscopic And Theoretical Studies on (L)(2)[Cu-2(S-2)N](2+) Complexes: Disulfide Versus Disulfide(Center Dot 1-) Bonding

    SciTech Connect

    Sarangi, R.; York, J.T.; Helton, M.E.; Fujisawa, K.; Karlin, K.D.; Tolman, W.B.; Hodgson, K.O.; Hedman, B.; Solomon, E.I.; /Stanford U., Chem. Dept. /SLAC, SSRL /Minnesota U. /Johns Hopkins U. /Tsukuba U.

    2009-04-30

    Cu K-, Cu L-, and S K-edge X-ray absorption spectroscopic (XAS) data have been combined with density functional theory (DFT) calculations on [{l_brace}(TMPA)Cu{r_brace}{sub 2}S{sub 2}](ClO{sub 4}){sub 2} (1), [{l_brace}Cu[HB(3,5-Pr{sub 2}{sup i}pz){sub 3}]{r_brace}{sub 2}(S{sub 2})] (2), and [{l_brace}(TMEDA)Cu{r_brace}{sub 2}(S{sub 2}){sub 2}](OTf){sub 2} (3) to obtain a quantitative description of their ground state wavefunctions. The Cu L-edge intensities give 63 and 37% Cu d-character in the ground state of 1 and 2, respectively, whereas the S K-pre-edge intensities reflect 20 and 48% S character in their ground states, respetively. These data indicate a more than 2-fold increase in the total disulfide bonding character in 2 relative to 1. The increase in the number of Cu?S bonds in 2 ({mu}-{eta}{sup 2}:{eta}{sup 2} S{sub 2}{sup 2-} bridge) compared to 1 ({mu}-{eta}{sup 1}:{eta}{sup 1} S{sub 2}{sup 2-} bridge) dominantly determines the large increase in covalency and Cu-disulfide bond strength in 2. Cu K- and L- and S K-pre-edge energy positions directly demonstrate the Cu{sup II}/(S{sub 2}{sup -}){sub 2} nature of 3. The two disulfide({center_dot}1?)'s in 3 undergo strong bonding interactions that destabilize the resultant filled antibonding {pi}* orbitals of the (S{sub 2}{sup -}){sub 2} fragment relative to the Cu 3d levels. This leads to an inverted bonding scheme in 3 with dominantly ligand-based holes in its ground state, consistent with its description as a dicopper(II)-bis-disulfide({center_dot}1?) complex.

  7. Effect of injected spins with different polarized orientations on the vortex phase transition in La0.7Sr0.3MnO3/La1.85Sr0.15CuO4 heterostructure

    NASA Astrophysics Data System (ADS)

    Zhang, M. J.; Teng, M. L.; Hao, F. X.; Yin, Y. W.; Zeng, Z.; Li, X. G.

    2015-05-01

    The current-voltage (I-V) characteristics with spin injection were investigated for the epitaxial La0.7Sr0.3MnO3/La1.85Sr0.15CuO4 heterostructure rotated from H//c to H//ab in magnetic fields up to 14 T. It is found that all the I-V curves in various magnetic fields can be scaled with a three dimensional (3D) vortex glass model, and the spin injection can induce a better 3D scaling behavior, which is closely related to the decrease of the anisotropy parameter. A vortex phase diagram for the evolution of vortex glass transition field (Hg) and upper critical field (Hc2) indicates that both Hg and Hc2 are suppressed by spin injection, and this effect becomes more obvious in the case of H//ab, which probably originates from the different suppression on the superconducting pairing strength by different injected spins' orientations.

  8. Atomic structure of glassy Mg{sub 60}Cu{sub 30}Y{sub 10} investigated with EXAFS, x-ray and neutron diffraction, and reverse Monte Carlo simulations

    SciTech Connect

    Jovari, Pal; Saksl, Karel; Pryds, Nini; Lebech, Bente; Bailey, Nicholas P.; Mellerga ring rd, Anders; Delaplane, Robert G.; Franz, Hermann

    2007-08-01

    Short range order of amorphous Mg{sub 60}Cu{sub 30}Y{sub 10} was investigated by x-ray and neutron diffraction, Cu and Y K-edge x-ray absorption fine structure measurements, and the reverse Monte Carlo simulation technique. We found that Mg-Mg and Mg-Cu nearest neighbor distances are very similar to values found in crystalline Mg{sub 2}Cu. The Cu-Y coordination number is 1.1{+-}0.2, and the Cu-Y distance is {approx}4% shorter than the sum of atomic radii, suggesting that attraction between Cu and Y plays an important role in stabilizing the glassy state. Thermal stability and structure evolution upon annealing were also studied by differential scanning calorimetry and in situ x-ray powder diffraction. The alloy shows a glass transition and three crystallization events, the first and dominant one at 456 K corresponding to eutectic crystallization of at least three phases: Mg{sub 2}Cu and most likely cubic MgY and CuMgY.

  9. 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.

  10. 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.

  11. Polarization-dependent infrared reflectivity study of Sr2.5Ca11.5Cu24O41 under pressure: Charge dynamics, charge distribution, and anisotropy

    SciTech Connect

    Frank, S.; Huber, A.; Ammerahl, U.; Hücker, M.; Kuntscher, C. A.

    2014-12-18

    We present a polarization-dependent infrared reflectivity study of the spin-ladder compound Sr₂̣₅Ca₁₁̣₅Cu₂₄O₄₁ under pressure. The optical response is strongly anisotropic, with the highest reflectivity along the ladders/chains (E∥c) revealing a metallic character. For the polarization direction perpendicular to the ladder plane, an insulating behavior is observed. With increasing pressure the optical conductivity for E∥c shows a strong increase, which is most pronounced below 2000cm⁻¹. According to the spectral weight analysis of the E∥c optical conductivity the hole concentration in the ladders increases with increasing pressure and tends to saturate at high pressure. At ~7.5 GPa the number of holes per Cu atom in the ladders has increased by Δδ=0.09(±0.01), and the Cu valence in the ladders has reached the value +2.33. Thus, the optical data suggest that Sr₂̣₅Ca₁₁̣₅Cu₂₄O₄₁ remains electronically highly anisotropic up to high pressure, also at low temperatures.

  12. Local structure and polarization resistance of Ce doped SrMnO{sub 3} using extended x-ray fine structure analysis

    SciTech Connect

    Ryu, Jiseung; Lee, Heesoo

    2014-09-15

    Changes to the local structure of Sr and Mn atoms in Sr{sub 1−x}Ce{sub x}MnO{sub 3} (SCM) according to increasing Ce content and the effect of the structural change on the polarization resistance of SCM were investigated. The reduction of manganese was confirmed by the absorption edge shift of the Mn K-edge toward lower energies. The noise of oscillation in extended X-ray absorption fine structure k{sup 3}χ data at Mn K-edge reveals the distortion of the local structure of Mn atoms, and the peak that indicates the bonding length of Mn-O, Sr/Ce, and -Mn decreased with the addition of Ce content in Fourier transformations of the Mn K-edge. The distortion of the local structure at Mn atoms was affected by the reduced manganese ions having larger ionic radii than Mn{sup 4+}. Meanwhile, few distortions of local atomic structures of Sr atoms occurred, and the average nearest neighboring distances of Sr-O and Sr-Mn are ∼2.13 Å and ∼2.95 Å, respectively. The average bonding lengths of the Ce-O and Ce-Mn increased because the ionic radius of substituted Ce ion with 12 coordination number is smaller than that of Sr ion, which leads the reduction of Mn ions and the distortion of local structure at the substituted A-site. Therefore, we reasoned that the distortion of the local atomic structure at Mn atoms in MnO{sub 6} and Ce atoms in A-site is one of the causes for interrupting oxygen ion transfers as a geometric factor, which results in an increase in the polarization resistance of SCM within the Ce composition range from 10 mol. % to 30 mol. %.

  13. Adsorption of Cu(II) to ferrihydrite and ferrihydrite-bacteria composites: Importance of the carboxyl group for Cu mobility in natural environments

    NASA Astrophysics Data System (ADS)

    Moon, Ellen M.; Peacock, Caroline L.

    2012-09-01

    Bacterially associated iron (hydr)oxide composites are widespread in natural environments, and by analogy with isolated iron (hydr)oxides and bacteria, are important scavengers of dissolved trace-metals. We precipitated ferrihydrite via rapid Fe(III) hydrolysis in the absence and presence of the non-Fe metabolising, Gram-positive bacterium Bacillus subtilis, commonly found in natural waters, soils and sediments. We combined XRD, SEM, BET and Fe K-edge EXAFS to examine the mineralogy, morphology and crystallinity of the ferrihydrite composites. We find that the mineral fraction of the composites is unaltered in primary mineralogy, morphology and crystallinity compared to pure ferrihydrite. We then measured the adsorption of Cu to ferrihydrite and the ferrihydrite-B. subtilis composites as a function of pH and the ferrihydrite:bacteria mass ratio of the composites, and used EXAFS to determine the molecular mechanisms of Cu adsorption. We determine directly for the first time that Cu uptake by ferrihydrite-B. subtilis composites is the result of adsorption to both the ferrihydrite and B. subtilis fractions. Adsorption of Cu by the B. subtilis fraction results in significant Cu uptake in the low pH regime (pH ˜4, ˜20% of [Cu]total) and significantly enhanced Cu uptake in the mid pH regime. This composite sorption behaviour is in stark contrast to pure ferrihydrite, where Cu adsorption is negligible at low pH. Overall, for composites dominated by either ferrihydrite or B. subtilis, the bacterial fraction is exclusively responsible for Cu adsorption at low pH while the ferrihydrite fraction is predominantly responsible for adsorption at high pH. Furthermore, with an increased mass ratio of bacteria, the dominance of Cu adsorption to the bacterial fraction persists into the mid pH regime and extends significantly into the upper pH region. As such, the distribution of the total adsorbed Cu between the composite fractions is a function of both pH and the ferrihydrite

  14. Electrochemical Corrosion Behavior of TiN-Coated Biomedical Ti-Cu Alloy Foam in Fluoride Containing Artificial Saliva

    NASA Astrophysics Data System (ADS)

    Mutlu, Ilven

    2014-07-01

    Highly porous Ti-Cu alloy foams were produced by powder metallurgy method for implant applications. Ti-Cu alloys were prepared with 3, 5, 7, and 10 wt pct Cu contents in order to determine optimum Cu addition. Cu addition enhances sinterability, and the Ti-Cu compacts were sintered at lower temperatures and times than pure Ti. Specimens were coated with a TiN film to enhance wear and corrosion resistance. Sintered specimens were precipitation hardened (aged) in order to increase mechanical properties. Corrosion properties of foams were examined by electrochemical techniques, such as potentiodynamic polarization, cyclic polarization, Tafel extrapolation, linear polarization resistance, and open-circuit potential measurement. Effect of Cu content, TiN coating, pH, and fluoride content of artificial saliva on electrochemical corrosion behavior of specimens was investigated.

  15. Polarized internal target apparatus

    DOEpatents

    Holt, R.J.

    1984-10-10

    A polarized internal target apparatus with a polarized gas target of improved polarization and density (achieved by mixing target gas atoms with a small amount of alkali metal gas atoms, and passing a high intensity polarized light source into the mixture to cause the alkali metal gas atoms to become polarized which interact in spin exchange collisions with target gas atoms yielding polarized target gas atoms) is described.

  16. Polarized internal target apparatus

    DOEpatents

    Holt, Roy J.

    1986-01-01

    A polarized internal target apparatus with a polarized gas target of improved polarization and density achieved by mixing target gas atoms with a small amount of alkali metal gas atoms, and passing a high intensity polarized light source into the mixture to cause the alkali metal gas atoms to become polarized which interact in spin exchange collisions with target gas atoms yielding polarized target gas atoms.

  17. Polar Color

    NASA Technical Reports Server (NTRS)

    2004-01-01

    [figure removed for brevity, see original site]

    Released 3 May 2004 This nighttime visible color image was collected on January 1, 2003 during the Northern Summer season near the North Polar Troughs.

    This daytime visible color image was collected on September 4, 2002 during the Northern Spring season in Vastitas Borealis. The THEMIS VIS camera is capable of capturing color images of the martian surface using its five different color filters. In this mode of operation, the spatial resolution and coverage of the image must be reduced to accommodate the additional data volume produced from the use of multiple filters. To make a color image, three of the five filter images (each in grayscale) are selected. Each is contrast enhanced and then converted to a red, green, or blue intensity image. These three images are then combined to produce a full color, single image. Because the THEMIS color filters don't span the full range of colors seen by the human eye, a color THEMIS image does not represent true color. Also, because each single-filter image is contrast enhanced before inclusion in the three-color image, the apparent color variation of the scene is exaggerated. Nevertheless, the color variation that does appear is representative of some change in color, however subtle, in the actual scene. Note that the long edges of THEMIS color images typically contain color artifacts that do not represent surface variation.

    Image information: VIS instrument. Latitude 79, Longitude 346 East (14 West). 19 meter/pixel resolution.

    Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with

  18. Penta prism laser polarizer.

    PubMed

    Lotem, H; Rabinovitch, K

    1993-04-20

    A novel type of laser prism polarizer is proposed. The polarizer is characterized by a high transmission efficiency, a high optical damage threshold, and a high extinction ratio. The polarizer is shaped like a regular penta prism and, thus, it is a constant deviation angle device. Polarization effects occur upon the two internal cascade reflections in the prism. Anisotropic and Isotropic types of the polarizer are discussed. The isotropic polarizer is a prism made of a high refractive-index glass coated by multilayer polarization-type dielectric coatings. Efficient s-state polarization is obtained because of p-state leakage upon the two internal cascade reflections. The anisotropic polarizer is made of a birefringent crystal in which angular polarization splitting is obtained by the bireflectance (double-reflection) effect. Fanning of a laser beam into up to eight polarized beams is possible in a prism made of a biaxial crystal. PMID:20820335

  19. 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.

  20. Uracil on Cu(110): A quantitative structure determination by energy-scanned photoelectron diffraction

    NASA Astrophysics Data System (ADS)

    Duncan, D. A.; Unterberger, W.; Kreikemeyer-Lorenzo, D.; Woodruff, D. P.

    2011-07-01

    The local adsorption site of the nucleobase uracil on Cu(110) has been determined quantitatively by energy-scanned photoelectron diffraction (PhD). Qualitative inspection of the O 1s and N 1s soft x-ray photoelectron spectra, PhD modulation spectra, and O K-edge near-edge x-ray adsorption fine structure indicate that uracil bonds to the surface through its nitrogen and oxygen constituent atoms, each in near atop sites, with the molecular plane essentially perpendicular to surface and aligned along the close packed [1overline 1 0] azimuth. Multiple scattering simulations of the PhD spectra confirm and refine this geometry. The Cu-N bondlength is 1.96 ± 0.04 Å, while the Cu-O bondlengths of the two inequivalent O atoms are 1.93 ± 0.04 Å and 1.96 ± 0.04 Å, respectively. The molecule is twisted out of the [1overline 1 0]direction by 11 ± 5°.

  1. 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.

  2. Polarized Light in Astronomy.

    ERIC Educational Resources Information Center

    King, D. J.

    1983-01-01

    The application of very sensitive electronic detecting devices during the last decade has revolutionized and revitalized the study of polarization in celestial objects. The nature of polarization, how polaroids work, interstellar polarization, dichroic filters, polarization by scattering, and modern polarimetry are among the topics discussed. (JN)

  3. Linearly polarized fiber amplifier

    DOEpatents

    Kliner, Dahv A.; Koplow, Jeffery P.

    2004-11-30

    Optically pumped rare-earth-doped polarizing fibers exhibit significantly higher gain for one linear polarization state than for the orthogonal state. Such a fiber can be used to construct a single-polarization fiber laser, amplifier, or amplified-spontaneous-emission (ASE) source without the need for additional optical components to obtain stable, linearly polarized operation.

  4. Nondiffracting transversally polarized beam.

    PubMed

    Yuan, G H; Wei, S B; Yuan, X-C

    2011-09-01

    Generation of a nondiffracting transversally polarized beam by means of transmitting an azimuthally polarized beam through a multibelt spiral phase hologram and then highly focusing by a high-NA lens is presented. A relatively long depth of focus (∼4.84λ) of the electric field with only radial and azimuthal components is achieved. The polarization of the wavefront near the focal plane is analyzed in detail by calculating the Stokes polarization parameters. It is found that the polarization is spatially varying and entirely transversally polarized, and the polarization singularity disappears at the beam center, which makes the central bright channel possible. PMID:21886250

  5. Phase transition from fcc to bcc structure of the Cu-clusters during nanocrystallization of Fe{sub 85.2}Si{sub 1}B{sub 9}P{sub 4}Cu{sub 0.8} soft magnetic alloy

    SciTech Connect

    Nishijima, Masahiko; Matsuura, Makoto; Takenaka, Kana; Takeuchi, Akira; Makino, Akihiro; Ofuchi, Hironori

    2014-05-15

    A role of Cu on the nanocrystallization of an Fe{sub 85.2}Si{sub 1}B{sub 9}P{sub 4}Cu{sub 0.8} alloy was investigated by X-ray absorption fine structure (XAFS) and transmission electron microscopy (TEM). The Cu K-edge XAFS results show that local structure around Cu is disordered for the as-quenched sample whereas it changes to fcc-like structure at 613 K. The fcc Cu-clusters are, however, thermodynamically unstable and begin to transform into bcc structure at 638 K. An explicit bcc structure is observed for the sample annealed at 693 K for 600 s in which TEM observation shows that precipitated bcc-Fe crystallites with ∼12 nm are homogeneously distributed. The bcc structure of the Cu-clusters transforms into the fcc-type again at 973 K, which can be explained by the TEM observations; Cu segregates at grain boundaries between bcc-Fe crystallites and Fe{sub 3}(B,P) compounds. Combining the XAFS results with the TEM observations, the structure transition of the Cu-clusters from fcc to bcc is highly correlated with the preliminary precipitation of the bcc-Fe which takes place prior to the onset of the first crystallization temperature, T{sub x1} = 707 K. Thermodynamic analysis suggests that an interfacial energy density γ between an fcc-Cu cluster and bcc-Fe matrix dominates at a certain case over the structural energy between fcc and bcc Cu, ΔG{sub fcc} {sub −} {sub bcc}, which causes phase transition of the Cu clusters from fcc to bcc structure.

  6. Crossed elliptical polarization undulator

    SciTech Connect

    Sasaki, Shigemi

    1997-05-01

    The first switching of polarization direction is possible by installing two identical helical undulators in series in a same straight section in a storage ring. By setting each undulator in a circular polarization mode in opposite handedness, one can obtain linearly polarized radiation with any required polarization direction depending on the modulator setting between two undulators. This scheme can be used without any major degradation of polarization degree in any low energy low emittance storage ring.

  7. Polarization-balanced beamsplitter

    DOEpatents

    Decker, D.E.

    1998-02-17

    A beamsplitter assembly is disclosed that includes several beamsplitter cubes arranged to define a plurality of polarization-balanced light paths. Each polarization-balanced light path contains one or more balanced pairs of light paths, where each balanced pair of light paths includes either two transmission light paths with orthogonal polarization effects or two reflection light paths with orthogonal polarization effects. The orthogonal pairing of said transmission and reflection light paths cancels polarization effects otherwise caused by beamsplitting. 10 figs.

  8. Polarization-balanced beamsplitter

    DOEpatents

    Decker, Derek E.

    1998-01-01

    A beamsplitter assembly that includes several beamsplitter cubes arranged to define a plurality of polarization-balanced light paths. Each polarization-balanced light path contains one or more balanced pairs of light paths, where each balanced pair of light paths includes either two transmission light paths with orthogonal polarization effects or two reflection light paths with orthogonal polarization effects. The orthogonal pairing of said transmission and reflection light paths cancels polarization effects otherwise caused by beamsplitting.

  9. Skeletal Ru/Cu catalysts prepared from crystalline and quasicrystalline ternary alloy precursors: characterization by X-ray absorption spectroscopy and CO oxidation.

    PubMed

    Highfield, James; Liu, Tao; Loo, Yook Si; Grushko, Benjamin; Borgna, Armando

    2009-02-28

    The Ru/Cu system is of historical significance in catalysis. The early development and application of X-ray absorption spectroscopy (XAS) led to the original 'bimetallic cluster" concept for highly-immiscible systems. This work explores alkali leaching of Al-based ternary crystalline and quasicrystalline precursors as a potential route to bulk Ru/Cu alloys. Single-phase ternary alloys at 3 trial compositions; Al(71)Ru(22)Cu(7), Al(70.5)Ru(17)Cu(12.5), and Al(70)Ru(10)Cu(20), were prepared by arc melting of the pure metal components. After leaching, the bimetallic residues were characterized principally by transmission XAS, "as-leached" and after annealing in H(2) (and passivation) in a thermobalance. XRD and BET revealed a nanocrystalline product with a native structure of hexagonal Ru. XPS surface analysis of Ru(22)Cu(7) and Ru(17)Cu(12.5) found only slight enrichment by Cu in the as-leached forms, with little change upon annealing. Ru(10)Cu(20) was highly segregated as-leached. XANES data showed preferential oxidation of Cu in Ru(22)Cu(7), implying that it exists as an encapsulating layer. TG data supports this view since it does not show the distinct two-stage O(2) uptake characteristic of skeletal Ru. Cu K-edge EXAFS data for Ru(22)Cu(7) were unique in showing a high proportion of Ru neighbours. The spacing, d(CuRu) = 2.65 A, was that expected from a hypothetical (ideal) solid solution at this composition, but this is unlikely in such a bulk-immiscible system and Ru K-edge EXAFS failed to confirm bulk alloying. Furthermore its invariance under annealing was more indicative of an interfacial bond between bulk components, although partial alloying with retention of local order cannot entirely be ruled out. The XAS and XPS data were reconciled in a model involving surface and bulk segregation, Cu being present at both the grain exterior and in ultra-fine internal pores. This structure can be considered as the 3-dimensional analogue of the classical type

  10. Perpendicularly magnetized spin filtering Cu/Ni multilayers

    SciTech Connect

    Shirahata, Yasuhiro; Wada, Eiji; Itoh, Mitsuru; Taniyama, Tomoyasu

    2014-01-20

    Spin filtering at perpendicular magnetized Cu/Ni multilayer/GaAs(001) interfaces is demonstrated at remanence using optical spin orientation method. [Cu(9 nm)/Ni(t{sub Ni} nm)]{sub n} multilayers are found to show a crossover from the in-plane to out-of-plane magnetic anisotropy at the Cu/Ni bilayer repetition n = 4 and the Ni layer thickness t{sub Ni} = 3. For a perpendicularly magnetized Cu/Ni multilayer/n-GaAs(001) interface, circular polarization dependent photocurrent shows a clear hysteretic behavior under optical spin orientation conditions as a function of magnetic field out-of-plane while the bias dependence exhibits a substantial peak at a forward bias, verifying that Cu/Ni multilayers work as an efficient spin filter in the remanent state.

  11. Polarization of the Sigma Minus Hyperon Produced by a Polarized Neutral Particle Beam

    NASA Astrophysics Data System (ADS)

    Nguyen, An Nhatton

    A spin transfer technique has been tried in an attempt to produce a beam of polarized hyperons. The method makes use of a two-stage targeting scheme where unpolarized protons from Fermilab's Tevatron incident on target number one (Cu) at production angles of +/-2.0 mrad would produce a beam of particles containing polarized Lambdas and Xis as well as neutrons and Ks. This secondary beam would then be swept magnetically to retain only neutral particles and brought to bear on target number two (Cu) at 0.0 mrad, producing a tertiary beam of hyperons. The polarization of some 1.3 millions reconstructed Sigma^{-} to npi^{-} events in this tertiary beam (the Sigma^{ -} having been produced in the inclusive reaction neutrals + Cu to Sigma^{ -} + X) has been measured at average Sigma^{-} momenta 320 GeV/c (1.14 millions events) and 410 GeV/c (135,000 events) and found to be |P| = 3.9 +/- 3.2 +/- 1.8% and |P| = 13.9 +/- 8.1 +/- 2.0% respectively, where the first uncertainty is statistical and the second systematic. These polarizations are small and consistent with zero, and preclude a meaningful measurement of the Sigma^{-} magnetic moment by the spin precession method. The sign of the polarizations at the target is ambiguous, giving rise to two possible different solutions for the magnetic moment--one of which distinctly disagrees with the world average value for the moment. However, this solution fits the data slightly better than the other. This inconsistency would not exist if the polarization is, in fact, zero.

  12. Neutron polarizers based on polarized ^3He

    NASA Astrophysics Data System (ADS)

    Gentile, T. R.; Jones, G. L.; Thompson, A. K.; Fei, X.; Keith, C. D.; Rich, D.; Snow, W. M.; Penttila, S.

    1997-10-01

    Research is underway at NIST, Indiana Univ., and LANL to develop neutron polarizers and analyzers based on polarized ^3He. Such devices, which rely on the strong spin dependence of the neutron capture cross section by polarized ^3He, have applications in weak interaction physics and materials science. In addition, the technology for polarized ^3He production is directly applicable to polarized gas MRI of lungs, and polarized targets. Our program, which includes both the spin-exchange and metastability-exchange optical pumping methods, will be reviewed. Spin-exchange has been used to analyze a polarized cold neutron beam at NIST, and also for lung imaging in collaboration with the Univ. of Pennsylvania. In the metastable method, the ^3He is polarized at low pressure, and must be substantially compressed. A piston compressor has been designed for this goal at Indiana Univ. and is under construction. At NIST we have compressed polarized gas using an apparatus that is based on a modified commercial diaphragm pump.

  13. Redox chemistry of a binary transition metal oxide (AB2O4): a study of the Cu(2+)/Cu(0) and Fe(3+)/Fe(0) interconversions observed upon lithiation in a CuFe2O4 battery using X-ray absorption spectroscopy.

    PubMed

    Cama, Christina A; Pelliccione, Christopher J; Brady, Alexander B; Li, Jing; Stach, Eric A; Wang, Jiajun; Wang, Jun; Takeuchi, Esther S; Takeuchi, Kenneth J; Marschilok, Amy C

    2016-06-22

    Copper ferrite, CuFe2O4, is a promising candidate for application as a high energy electrode material in lithium based batteries. Mechanistic insight on the electrochemical reduction and oxidation processes was gained through the first X-ray absorption spectroscopic study of lithiation and delithiation of CuFe2O4. A phase pure tetragonal CuFe2O4 material was prepared and characterized using laboratory and synchrotron X-ray diffraction, Raman spectroscopy, and transmission electron microscopy. Ex situ X-ray absorption spectroscopy (XAS) measurements were used to study the battery redox processes at the Fe and Cu K-edges, using X-ray absorption near-edge structure (XANES), extended X-ray absorption fine structure (EXAFS), and transmission X-ray microscopy (TXM) spectroscopies. EXAFS analysis showed upon discharge, an initial conversion of 50% of the copper(ii) to copper metal positioned outside of the spinel structure, followed by a migration of tetrahedral iron(iii) cations to octahedral positions previously occupied by copper(ii). Upon charging to 3.5 V, the copper metal remained in the metallic state, while iron metal oxidation to iron(iii) was achieved. The results provide new mechanistic insight regarding the evolution of the local coordination environments at the iron and copper centers upon discharging and charging. PMID:27292604

  14. The Amyloid-β Peptide of Alzheimer’s Disease Binds CuI in a Linear Bis-His Coordination Environment: Insight into a Possible Neuroprotective Mechanism for the Amyloid-β Peptide

    SciTech Connect

    Shearer, J.; Szalai, V

    2008-01-01

    Oxidative stress has been suggested to contribute to neuronal apoptosis associated with Alzheimer's disease (AD). Copper may participate in oxidative stress through redox-cycling between its +2 and +1 oxidation states to generate reactive oxygen species (ROS). In vitro, copper binds to the amyloid-? peptide of AD, and in vivo, copper is associated with amyloid plaques characteristic of AD. As a result, the A?CuI complex may be a critical reactant involved in ROS associated with AD etiology. To characterize the A?CuI complex, we have pursued X-ray absorption (XAS) and electron paramagnetic resonance (EPR) spectroscopy of A?CuII and A?CuI (produced by ascorbate reduction of A?CuII). The A?CuII complex Cu K-edge XAS spectrum is indicative of a square-planar CuII center with mixed N/O ligation. Multiple scattering analysis of the extended X-ray absorption fine structure (EXAFS) data for A?CuII indicates that two of the ligands are imidazole groups of histidine ligands, indicating a (NIm)2(N/O)2 CuII ligation sphere for A?CuII. After reduction of the A?CuII complex with ascorbate, the edge region decreases in energy by 4 eV. The X-ray absorption near-edge spectrum region of A?CuI displays an intense pre-edge feature at 8984.1(2) eV. EXAFS data fitting yielded a two-coordinate geometry, with two imidazole ligands coordinated to CuI at 1.877(2) A in a linear geometry. Ascorbate reduction of A?CuII under inert atmosphere and subsequent air oxidation of A?CuI to regenerate A?CuII was monitored by low-temperature EPR spectroscopy. Slow reappearance of the A?CuII EPR signal indicates that O2 oxidation of the A?CuI complex is kinetically sluggish and A? damage is occurring following reoxidation of A?CuI by O2. Together, these results lead us to hypothesize that CuI is ligated by His13 and His14 in a linear coordination environment in ??, that A? may be playing a neuroprotective role, and that metal-mediated oxidative damage of A? occurs over multiple redox cycles.

  15. NO dissociation on Cu(111) and Cu2O(111) surfaces: a density functional theory based study

    NASA Astrophysics Data System (ADS)

    Padama, A. A. B.; Kishi, H.; Arevalo, R. L.; Moreno, J. L. V.; Kasai, H.; Taniguchi, M.; Uenishi, M.; Tanaka, H.; Nishihata, Y.

    2012-05-01

    NO dissociation on Cu(111) and Cu2O(111) surfaces is investigated using spin-polarized density functional theory. This is to verify the possibility of using Cu-based catalyst for NO dissociation which is the rate limiting step for the NOx reduction process. The dissociation of molecularly adsorbed NO on the surface is activated for both cases. However, from the reaction path of the NO-Cu2O(111) system, the calculated transition state lies below the reference energy which indicates the possibility of dissociation. For the NO-Cu(111) system, the reaction path shows that NO desorption is more likely to occur. The geometric and electronic structure of the Cu2O(111) surface indicates that the surface Cu atoms stabilize themselves with reference to the O atom in the subsurface. The interaction results in modification of the electronic structure of the surface Cu atoms of Cu2O(111) which greatly affects the adsorption and dissociation of NO. This phenomenon further explains the obtained differences in the dissociation pathways of NO on the surfaces.

  16. Dielectric response of Cu/amorphous BaTiO3/Cu capacitors

    NASA Astrophysics Data System (ADS)

    Gonon, P.; El Kamel, F.

    2007-04-01

    Cu/amorphous BaTiO3/Cu capacitors were tested for their dielectric properties in the 0.1Hz -100kHz range, from room temperature to 350°C. The amorphous barium titanate dielectric layer was deposited by rf sputtering on water-cooled copper electrodes. The room-temperature dielectric constant is around 18 and the dissipation factor is 3×10-3 at 100kHz. When increasing temperature the dielectric response displays an important frequency dispersion with the appearance of a marked loss peak at low frequencies. This dispersion is ascribed to electrode polarization effects, as evidenced by measurements performed on various film thicknesses and by using different electrodes. The electrode polarization phenomenon is discussed using a simple space charge model and is shown to be related to mobile oxygen vacancies.

  17. Polarized Light Corridor Demonstrations.

    ERIC Educational Resources Information Center

    Davies, G. R.

    1990-01-01

    Eleven demonstrations of light polarization are presented. Each includes a brief description of the apparatus and the effect demonstrated. Illustrated are strain patterns, reflection, scattering, the Faraday Effect, interference, double refraction, the polarizing microscope, and optical activity. (CW)

  18. Polarization at SLAC

    SciTech Connect

    Woods, M.

    1995-01-01

    A highly polarized electron beam is a key feature. for the Current physics program at SLAC. An electron beam polarization of 80% can now be routinely achieved for typically 5000 hours of machine operation per year. Two main Physics programs utilize the polarized beam. Fixed target experiments in End Station A study the collision of polarized electrons with polarized nuclear targets to elucidate the spin structure of the nucleon and to provide an important test of QCD. Using the SLAC Linear Collider, collisions of polarized electrons with unpolarized positrons allow precise measurements of parity violation in the Z-fermion couplings and provide a very precise measurement of tile weak mixing angle. This paper discusses polarized beam operation at SLAC, and gives an overview of the polarized physics program.

  19. A Translational Polarization Rotator

    NASA Technical Reports Server (NTRS)

    Chuss, David T.; Wollack, Edward J.; Pisano, Giampaolo; Ackiss, Sheridan; U-Yen, Kongpop; Ng, Ming wah

    2012-01-01

    We explore a free-space polarization modulator in which a variable phase introduction between right- and left-handed circular polarization components is used to rotate the linear polarization of the outgoing beam relative to that of the incoming beam. In this device, the polarization states are separated by a circular polarizer that consists of a quarter-wave plate in combination with a wire grid. A movable mirror is positioned behind and parallel to the circular polarizer. As the polarizer-mirror distance is separated, an incident liear polarization will be rotated through an angle that is proportional to the introduced phase delay. We demonstrate a prototype device that modulates Stokes Q and U over a 20% bandwidth.

  20. Impact of Cu Electrode on Switching Behavior in a Cu/HfO2/Pt Structure and Resultant Cu Ion Diffusion

    NASA Astrophysics Data System (ADS)

    Haemori, Masamitsu; Nagata, Takahiro; Chikyow, Toyohiro

    2009-06-01

    In a newly proposed switching device using polycrystalline HfO2 thin film with ion diffusion path, we have found that a Cu electrode could contribute to improved switching performance. Current-voltage measurements at room temperature revealed clear resistive switching, not accompanied by a forming process, in our Cu/HfO2/Pt structure. The current step difference from one state to the other one was in the order of 103-104, giving a sufficient on/off ratio. Voltage sweep polarity suggested that filamentary Cu paths were formed due to Cu ion diffusion and annihilated at the HfO2/Pt interface at reversed bias. This filament path formation and annihilation was the origin of the switching device performance.

  1. Polar Ozone Workshop. Abstracts

    NASA Technical Reports Server (NTRS)

    Aikin, Arthur C.

    1988-01-01

    Results of the proceedings of the Polar Ozone Workshop held in Snowmass, CO, on May 9 to 13, 1988 are given. Topics covered include ozone depletion, ozonometry, polar meteorology, polar stratospheric clouds, remote sensing of trace gases, atmospheric chemistry and dynamical simulations.

  2. Hybrid polarization control

    NASA Astrophysics Data System (ADS)

    Gray, George R.; Ibragimov, Edem; Sluz, Joseph; Sova, Raymond

    2005-05-01

    We demonstrate a novel method of polarization control that combines rotatable waveplates (angle control) and variable retarders (retardance control). Such a "hybrid" polarization controller performs far better than conventional controllers, allowing nearly perfect arbitrary-to-arbitrary polarization transformations. We show theoretically that the two control parameters augment one another because they tend to result in orthogonal movements on the Poincaré sphere.

  3. Graphing Polar Curves

    ERIC Educational Resources Information Center

    Lawes, Jonathan F.

    2013-01-01

    Graphing polar curves typically involves a combination of three traditional techniques, all of which can be time-consuming and tedious. However, an alternative method--graphing the polar function on a rectangular plane--simplifies graphing, increases student understanding of the polar coordinate system, and reinforces graphing techniques learned…

  4. Playing with Polarizers.

    ERIC Educational Resources Information Center

    Hecht, Jeff

    1991-01-01

    Discussed is how polarized sunglasses block glare, help spot subtle differences in surfaces, and give a clearer view under water. Information on unpolarized and polarized light is provided. The reasons causing glare to occur and how polarizers decrease glare are discussed. (KR)

  5. Polarity at Many Levels

    ERIC Educational Resources Information Center

    Flannery, Maura C.

    2004-01-01

    An attempt is made to find how polarity arises and is maintained, which is a central issue in development. It is a fundamental attribute of living things and cellular polarity is also important in the development of multicellular organisms and controversial new work indicates that polarization in mammals may occur much earlier than previously…

  6. Physics with Polarized Nuclei.

    ERIC Educational Resources Information Center

    Thompson, William J.; Clegg, Thomas B.

    1979-01-01

    Discusses recent advances in polarization techniques, specifically those dealing with polarization of atomic nuclei, and how polarized beams and targets are produced. These techniques have greatly increased the scope of possible studies, and provided the tools for testing fundamental symmetries and the spin dependence of nuclear forces. (GA)

  7. Bumblebees Learn Polarization Patterns

    PubMed Central

    Foster, James J.; Sharkey, Camilla R.; Gaworska, Alicia V.A.; Roberts, Nicholas W.; Whitney, Heather M.; Partridge, Julian C.

    2014-01-01

    Summary Foraging insect pollinators such as bees must find and identify flowers in a complex visual environment. Bees use skylight polarization patterns for navigation [1–3], a capacity mediated by the polarization-sensitive dorsal rim area (DRA) of their eye [4, 5]. While other insects use polarization sensitivity to identify appropriate habitats [6], oviposition sites, and food sources [7], to date no nonnavigational functions of polarization vision have been identified in bees. Here we investigated the ability of bumblebees (Bombus terrestris) to learn polarization patterns on artificial “flowers” in order to obtain a food reward. We show that foraging bumblebees can learn to discriminate between two differently polarized targets, but only when the target artificial “flower” is viewed from below. A context for these results is provided by polarization imaging of bee-pollinated flowers, revealing the potential for polarization patterns in real flowers. Bees may therefore have the ability to use polarization vision, possibly mediated by their polarization-sensitive DRA, both for navigation and to learn polarization patterns on flowers, the latter being the first nonnavigational function for bee polarization vision to be identified. PMID:24909321

  8. Polarization feedback laser stabilization

    DOEpatents

    Esherick, Peter; Owyoung, Adelbert

    1988-01-01

    A system for locking two Nd:YAG laser oscillators includes an optical path for feeding the output of one laser into the other with different polarizations. Elliptical polarization is incorporated into the optical path so that the change in polarization that occurs when the frequencies coincide may be detected to provide a feedback signal to control one laser relative to the other.

  9. Calculation of polarization effects

    SciTech Connect

    Chao, A.W.

    1983-09-01

    Basically there are two areas of accelerator applications that involve beam polarization. One is the acceleration of a polarized beam (most likely a proton beam) in a synchrotron. Another concerns polarized beams in an electron storage ring. In both areas, numerical techniques have been very useful.

  10. Pulse electro-deposition of copper on molybdenum for Cu(In,Ga)Se2 and Cu2ZnSnSe4 solar cell applications

    NASA Astrophysics Data System (ADS)

    Bi, Jinlian; Yao, Liyong; Ao, Jianping; Gao, Shoushuai; Sun, Guozhong; He, Qing; Zhou, Zhiqiang; Sun, Yun; Zhang, Yi

    2016-09-01

    The issues of rough surface morphology and the incorporated additives of the electro-deposited Cu layers, which exists in electrodeposition-based processes, is one of the major obstacles to improve the efficiency of Cu(In,Ga)Se2 (CIGSe) and Cu2ZnSnSe4 (CZTSe) solar cells. In this study, the pulse current electro-deposition method is employed to deposit smooth Cu film on Mo substrate in CuSO4 solution without any additives. Grain size of the deposited Cu film is decreased by high cathode polarization successfully. And the concentration polarization, which results from high pulse current density, is controlled successfully by adjusting the pulse frequency. Flat Cu film with smooth surface and compact structure is deposited as pulse current density @ 62.5 mA cm-2, pulse frequency @100,000 Hz, and duty cycle @ 25%. CIGSe and CZTSe absorber films with flat surface and uniform elemental distribution are prepared by selenizing the stacking metal layers electro-deposited by pulse current method. Finally, the CIGSe and CZTSe solar cells with conversion efficiency of 10.39% and 7.83% respectively are fabricated based on the smooth Cu films, which are better than the solar cells fabricated by the rough Cu film deposited by direct current electro-deposition method.

  11. Thermochemical process for recovering Cu from CuO or CuO.sub.2

    DOEpatents

    Richardson, deceased, Donald M.; Bamberger, Carlos E.

    1981-01-01

    A process for producing hydrogen comprises the step of reacting metallic Cu with Ba(OH).sub.2 in the presence of steam to produce hydrogen and BaCu.sub.2 O.sub.2. The BaCu.sub.2 O.sub.2 is reacted with H.sub.2 O to form Cu.sub.2 O and a Ba(OH).sub.2 product for recycle to the initial reaction step. Cu can be obtained from the Cu.sub.2 O product by several methods. In one embodiment the Cu.sub.2 O is reacted with HF solution to provide CuF.sub.2 and Cu. The CuF.sub.2 is reacted with H.sub.2 O to provide CuO and HF. CuO is decomposed to Cu.sub.2 O and O.sub.2. The HF, Cu and Cu.sub.2 O are recycled. In another embodiment the Cu.sub.2 O is reacted with aqueous H.sub.2 SO.sub.4 solution to provide CuSO.sub.4 solution and Cu. The CuSO.sub.4 is decomposed to CuO and SO.sub.3. The CuO is decomposed to form Cu.sub.2 O and O.sub.2. The SO.sub.3 is dissolved to form H.sub.2 SO.sub.4. H.sub.2 SO.sub.4, Cu and Cu.sub.2 O are recycled. In another embodiment Cu.sub.2 O is decomposed electrolytically to Cu and O.sub.2. In another aspect of the invention, Cu is recovered from CuO by the steps of decomposing CuO to Cu.sub.2 O and O.sub.2, reacting the Cu.sub.2 O with aqueous HF solution to produce Cu and CuF.sub.2, reacting the CuF.sub.2 with H.sub.2 O to form CuO and HF, and recycling the CuO and HF to previous reaction steps.

  12. Enhanced electrochemical performance of Si-Cu-Ti thin films by surface covered with Cu3Si nanowires

    NASA Astrophysics Data System (ADS)

    Xu, Kaiqi; He, Yu; Ben, Liubin; Li, Hong; Huang, Xuejie

    2015-05-01

    Si-Cu-Ti thin films with Cu3Si nanowires on the surface and voids in the Cu layer are fabricated for the first time by magnetron sputtering combined with atomic layer deposition (ALD) of alumina. The formation of the surface Cu3Si nanowires is strongly dependent on the thickness of the coated alumina and cooling rate of the thin films during annealing. The maximum coverage of the surface Cu3Si nanowires is obtained with an alumina thickness of 2 nm and a cooling rate of 1 °C min-1. The electrode based on this thin film shows an excellent capacity retention of more than 900 mAh g-1 and a high columbic efficiency of more than 99% after 100 cycles. The improvement of the electrochemical performance of Si-Cu-Ti thin film electrode is attributed to the surface Cu3Si nanowires which reduce the polarization and inhomogeneous lithiation by formation of a surface conductive network, in addition to the alleviation of volume expansion of Si by voids in the Cu layer during cycling.

  13. Nanoscale coherent intergrowthlike defects in a crystal of La1.9Ca1.1Cu2O6 +δ made superconducting by high-pressure oxygen annealing

    NASA Astrophysics Data System (ADS)

    Hu, Hefei; Zhu, Yimei; Shi, Xiaoya; Li, Qiang; Zhong, Ruidan; Schneeloch, John A.; Gu, Genda; Tranquada, John M.; Billinge, Simon J. L.

    2014-10-01

    Superconductivity with Tc=53.5 K has been induced in a large La1.9Ca1.1Cu2O6 (La-2126) single crystal by annealing in a high partial pressure of oxygen at 1200 °C. Using transmission electron microscopy techniques, we show that a secondary Ca-doped La2CuO4 (La-214) phase, not present in the as-grown crystal, appears as a coherent intergrowthlike defect as a consequence of the annealing. A corresponding secondary superconducting transition near 13 K is evident in the magnetization measurement. Electron energy-loss spectroscopy reveals a pre-edge peak at the O-K edge in the superconducting La-2126 phase, which is absent in the as-grown crystal, confirming the hole doping by interstitial oxygen.

  14. Incorporation of C in Cu for the Fabrication of Transparent Electrodes

    NASA Astrophysics Data System (ADS)

    Isaacs, Romaine; Zhu, Hongli; Preston, Colin; Zavali, Peter; Mansour, Azzam; Lemieux, Melbs; Hu, Liangbing; Salamanca-Riba, Lourdes

    2015-03-01

    The incorporation of carbon nanostructures into the copper lattice has the potential to improve the current density of copper to meet the ever-increasing demands of nanoelectronic devices. We report on the structure and properties of a new material formed by the incorporation of carbon in concentrations up to 10 wt% into the crystal structure of copper that we refer to as ``Cu covetic''. The carbon does not phase separate after subsequent melting and re-solidification despite the absence of a predicted solid solution at such concentrations in the binary phase diagram. Bulk samples, as well as thin films grown at room temperature and high temperature are investigated. X-ray photoelectron spectroscopy (XPS) confirmed that C incorporates in the bulk of the Cu. Transmission Electron Microscopy (TEM) shows that C forms a modulated structure in the crystal lattice, and Electron Energy Loss Spectroscopy (EELS) indicates that C-K edge has graphitic nature with sp2 bonding. Copper covetic films exhibit greater transparency, higher conductivity, and resistance to oxidation than pure copper films of the same thickness, making them a suitable choice for transparent conductors. Supported by DARPA/ARL under Grant No. W911NF-13-1-0058 and ONR under Grant N000141410042.

  15. Electronic properties of CuPc and H2Pc: an experimental and theoretical study.

    PubMed

    Nardi, Marco Vittorio; Detto, Francesca; Aversa, Lucrezia; Verucchi, Roberto; Salviati, Giancarlo; Iannotta, Salvatore; Casarin, Maurizio

    2013-08-21

    Phthalocyanine (H2Pc) and its open-shell copper complex (CuPc) deposited on amorphous gold films have been studied by combining the outcomes of several synchrotron based spectroscopic tools (X-ray photoelectron spectroscopy, UV photoelectron spectroscopy and near-edge X-ray absorption fine structure, NEXAFS, spectroscopy) with those of density functional theory (DFT) calculations. The assignment of experimental evidence has been guided by the results of DFT numerical experiments carried out on isolated molecules. With specific reference to CuPc NEXAFS data collected at the N K-edge, they have been assigned by using the open-shell time-dependent DFT (TDDFT) in the framework of the zeroth order regular approximation (ZORA) scalar relativistic approach. The agreement between theory and experiment has been found to be satisfactory, thus indicating that the open-shell TDDFT (F. Wang and T. Ziegler, Mol. Phys., 2004, 102, 2585) may be used with some confidence to look into the X-ray absorption spectroscopy results pertinent to transition metal complexes. As far as the metal-ligand interaction is concerned, the combined use of NEXAFS spectroscopy and DFT outcomes ultimately testified the significant ionic contribution characterizing the bonding between the metal centre and the nitrogen atoms of the phthalocyanine coordinative pocket. PMID:23807700

  16. Composition law for polarizers

    NASA Astrophysics Data System (ADS)

    Lages, J.; Giust, R.; Vigoureux, J.-M.

    2008-09-01

    The polarization process when polarizers act on an optical field is studied. We give examples for two kinds of polarizers. The first kind presents an anisotropic absorption—as in a Polaroid film—and the second one is based on total reflection at the interface with a birefringent medium. Using the Stokes vector representation, we determine explicitly the trajectories of the wave light polarization during the polarization process. We find that such trajectories are not always geodesics of the Poincaré sphere as is usually thought. Using the analogy between light polarization and special relativity, we find that the action of successive polarizers on the light wave polarization is equivalent to the action of a single resulting polarizer followed by a rotation achieved, for example, by a device with optical activity. We find a composition law for polarizers similar to the composition law for noncollinear velocities in special relativity. We define an angle equivalent to the relativistic Wigner angle which can be used to quantify the quality of two composed polarizers.

  17. The Physics of Polarization

    NASA Astrophysics Data System (ADS)

    Degl'Innocenti, Egidio Landi

    2015-10-01

    The introductory lecture that has been delivered at this Symposium is a condensed version of an extended course held by the author at the XII Canary Island Winter School from November 13 to November 21, 2000. The full series of lectures can be found in Landi Degl'Innocenti (2002). The original reference is organized in 20 Sections that are here itemized: 1. Introduction, 2. Description of polarized radiation, 3. Polarization and optical devices: Jones calculus and Muller matrices, 4. The Fresnel equations, 5. Dichroism and anomalous dispersion, 6. Polarization in everyday life, 7. Polarization due to radiating charges, 8. The linear antenna, 9. Thomson scattering, 10. Rayleigh scattering, 11. A digression on Mie scattering, 12. Bremsstrahlung radiation, 13. Cyclotron radiation, 14. Synchrotron radiation, 15. Polarization in spectral lines, 16. Density matrix and atomic polarization, 17. Radiative transfer and statistical equilibrium equations, 18. The amplification condition in polarized radiative transfer, and 19. Coupling radiative transfer and statistical equilibrium equations.

  18. Defect-induced Nonpolar-to-polar Transition at the Surface of Chalcopyrite Semiconductors

    SciTech Connect

    Jaffe, John E.; Zunger, Alex

    2001-12-15

    In contrast to zinc-blende semiconductors, where the nonpolar (110) surface has the lowest energy, our first-principles calculations on the chalcopyrite semiconductor CuInSe2 reveal that facets terminated by the (112)-cation and (-1-1-2)-Se polar surfaces are lower in energy than the unfaceted (110) plane, despite the resulting increased surface area. This explains the hitherto puzzling existence of polar microfacets on nominally nonpolar (110) chalcopyrite surfaces. The extraordinary stability of these polar facets originates from the effective neutralization of surface charge by low-energy ordered CuIn antisite or Cu vacancy surface defects, while the relaxed but defect-free (112) surface is metallic and much higher in energy. We explain the low carrier density of the observed faceted surface in terms of autocompensation between opposite-polarity facets.

  19. Structural and Optical Properties of In-Free Cu2ZnSn(S,Se)4 Solar Cell Materials

    NASA Astrophysics Data System (ADS)

    Gao, Feng; Yamazoe, Seiji; Maeda, Tsuyoshi; Nakanishi, Koji; Wada, Takahiro

    2012-10-01

    We prepared a Cu2ZnSn(SxSe1-x)4 (CZTSSe) solid solution from elemental powders. The CZTSSe solid solutions were synthesized by heating the elemental mixtures at 550 °C for 5 h in an N2 gas. All CZTSSe materials were analyzed by Rietveld analysis using the kesterite structure with a space group of Ibar 4 (No. 82). Rietveld analysis showed that the lattice parameters, a and c, monotonically decreased with increasing S content. Moreover, the local structures of the Cu and S atoms were investigated by X-ray absorption near edge structure (XANES). Although the local structure of the S atom in CZTSSe hardly changed in relation to the S/Se ratio, we found that the surface of CZTSSe powders became slightly oxidized. On the other hand, Cu K edge XANES showed that the S/Se ratio could be easily determined from the XANES spectra. The band gap energies of the CZTSSe materials were determined by transmittance and diffuse-reflectance spectra. The transmittance spectra were recorded using CZTSSe films fabricated by a printing and high-pressure sintering (PHS) process. The band gap energy, Eg, monotonically increased from 1.05 eV for CZTSe to 1.51 eV for CZTS.

  20. Device For Viewing Polarized Light

    NASA Technical Reports Server (NTRS)

    Noever, David A.

    1995-01-01

    Technique for detection of polarized light based on observation of scene through two stacked polarizing disks. No need to rotate polarizers to create flicker indicative of polarization. Implemented by relatively simple, lightweight apparatus. Polarization seen as bow-tie rainbow pattern. Advantageous for detecting polarization in variety of meteorological, geological, astronomical, and related applications.

  1. Consecutive polarizers arrangement producing maximum polarized light intensity

    NASA Astrophysics Data System (ADS)

    Wirjawan, Johannes V. D.

    2016-03-01

    Polarizer mainly functions as a specific filter that blocks or transmits lights of certain polarization. Malus' law predicts the average intensity of polarized light passing a polarizer that transmits certain polarization direction will be proportional to the squared cosine of angle between the two polarization directions. Arranging several polarizers consecutively with various transmission directions will produce various final intensity as well as final polarized direction. Specific arrangement of an arbitrary number (N > 3) of polarizers producing maximum intensity of polarized light will be discussed in this paper. In addition, interesting pattern of maximum values of some trigonometric functions that are difficult to be solved analytically can be obtained from this discussion.

  2. Singlet-Triplet Splittings in the Luminescent Excited States of Colloidal Cu(+):CdSe, Cu(+):InP, and CuInS2 Nanocrystals: Charge-Transfer Configurations and Self-Trapped Excitons.

    PubMed

    Knowles, Kathryn E; Nelson, Heidi D; Kilburn, Troy B; Gamelin, Daniel R

    2015-10-14

    The electronic and magnetic properties of the luminescent excited states of colloidal Cu(+):CdSe, Cu(+):InP, and CuInS2 nanocrystals were investigated using variable-temperature photoluminescence (PL) and magnetic circularly polarized luminescence (MCPL) spectroscopies. The nanocrystal electronic structures were also investigated by absorption and magnetic circular dichroism (MCD) spectroscopies. By every spectroscopic measure, the luminescent excited states of all three materials are essentially indistinguishable. All three materials show very similar broad PL line widths and large Stokes shifts. All three materials also show similar temperature dependence of their PL lifetimes and MCPL polarization ratios. Analysis shows that this temperature dependence reflects Boltzmann population distributions between luminescent singlet and triplet excited states with average singlet-triplet splittings of ∼1 meV in each material. These similarities lead to the conclusion that the PL mechanism in CuInS2 NCs is fundamentally different from that of bulk CuInS2 and instead is the same as that in Cu(+)-doped NCs, which are known to luminesce via charge-transfer recombination of conduction-band electrons with copper-localized holes. The luminescence of CuInS2 nanocrystals is explained well by invoking exciton self-trapping, in which delocalized photogenerated holes contract in response to strong vibronic coupling at lattice copper sites to form a luminescent excited state that is essentially identical to that of the Cu(+)-doped semiconductor nanocrystals. PMID:26389577

  3. Interfacial Reactions in Cu/Ga and Cu/Ga/Cu Couples

    NASA Astrophysics Data System (ADS)

    Lin, Shih-kang; Cho, Cheng-liang; Chang, Hao-miao

    2014-01-01

    Cu-to-Cu bonding to connect through-silicon vias in three-dimensional integrated-circuit packaging is the most important interconnection technology in the next-generation semiconductor industry. Soldering is an economic and fast process in comparison with diffusion bonding methods. Ga has high solubility of up to 20 at.% in the Cu-rich face-centered cubic (FCC) phase and high mobility at moderate temperatures. In this work, an attempt has been made to evaluate Ga-based Cu-to-Cu interconnection by transient liquid-phase (TLP) bonding. The Cu/Ga interfacial reactions at temperatures ranging from 160°C to 300°C were examined. For reactions at temperatures lower than 240°C, the reaction path is Cu/ γ 3-Cu9Ga4/ θ-CuGa2/liquid, where the γ 3-Cu9Ga4 and θ-CuGa2 phases are thin planar and thick scalloped layers, respectively, while for the reactions at 280°C and 300°C, the scalloped γ 3-Cu9Ga4 phase is the only reaction product. The phase transformation kinetics, reaction mechanisms, and microstructural evolution in the Cu/Ga couples are elaborated. In addition, reactions of Cu/Ga/Cu sandwich couples at 160°C were investigated. The original Cu/liquid/Cu couples isothermally transformed to Cu/ γ 3-Cu9Ga4/ θ-CuGa2/ γ 3-Cu9Ga4/Cu couples as the reaction progressed. However, cracks were observed in the θ-CuGa2 phase regions after metallographic processing. The brittle θ-CuGa2 phase is undesirable for Ga-based TLP bonding.

  4. Automatic Bayesian polarity determination

    NASA Astrophysics Data System (ADS)

    Pugh, D. J.; White, R. S.; Christie, P. A. F.

    2016-07-01

    The polarity of the first motion of a seismic signal from an earthquake is an important constraint in earthquake source inversion. Microseismic events often have low signal-to-noise ratios, which may lead to difficulties estimating the correct first-motion polarities of the arrivals. This paper describes a probabilistic approach to polarity picking that can be both automated and combined with manual picking. This approach includes a quantitative estimate of the uncertainty of the polarity, improving calculation of the polarity probability density function for source inversion. It is sufficiently fast to be incorporated into an automatic processing workflow. When used in source inversion, the results are consistent with those from manual observations. In some cases, they produce a clearer constraint on the range of high-probability source mechanisms, and are better constrained than source mechanisms determined using a uniform probability of an incorrect polarity pick.

  5. Automatic Bayesian polarity determination

    NASA Astrophysics Data System (ADS)

    Pugh, D. J.; White, R. S.; Christie, P. A. F.

    2016-04-01

    The polarity of the first motion of a seismic signal from an earthquake is an important constraint in earthquake source inversion. Microseismic events often have low signal-to-noise ratios, which may lead to difficulties estimating the correct first-motion polarities of the arrivals. This paper describes a probabilistic approach to polarity picking that can be both automated and combined with manual picking. This approach includes a quantitative estimate of the uncertainty of the polarity, improving calculation of the polarity probability density function for source inversion. It is sufficiently fast to be incorporated into an automatic processing workflow. When used in source inversion, the results are consistent with those from manual observations. In some cases, they produce a clearer constraint on the range of high-probability source mechanims, and are better constrained than source mechanisms determined using a uniform probability of an incorrect polarity pick.

  6. A dual polarized antenna system using a meanderline polarizer

    NASA Technical Reports Server (NTRS)

    Burger, H. A.

    1978-01-01

    Certain applications of synthetic aperture radars require transmitting on one linear polarization and receiving on two orthogonal linear polarizations for adequate characterization of the surface. To meet the current need at minimum cost, it was desirable to use two identical horizontally polarized shaped beam antennas and to change the polarization of one of them by a polarization conversion plate. The plate was realized as a four-layer meanderline polarizer designed to convert horizontal polarization to vertical.

  7. Polarization feedback laser stabilization

    DOEpatents

    Esherick, P.; Owyoung, A.

    1987-09-28

    A system for locking two Nd:YAG laser oscillators includes an optical path for feeding the output of one laser into the other with different polarizations. Elliptical polarization is incorporated into the optical path so that the change in polarization that occurs when the frequencies coincide may be detected to provide a feedback signal to control one laser relative to the other. 4 figs.

  8. Plastic Deformation Modes of CuZr/Cu Multilayers

    NASA Astrophysics Data System (ADS)

    Cui, Yan; Abad, Oscar Torrents; Wang, Fei; Huang, Ping; Lu, Tian-Jian; Xu, Ke-Wei; Wang, Jian

    2016-03-01

    We synthesized CuZr/Cu multilayers and performed nanoindentation testing to explore the dependence of plastic deformation modes on the thickness of CuZr layers. The Cu layers were 18 nm thick and the CuZr layers varied in thickness from 4 nm to 100 nm. We observed continuous plastic co-deformation in the 4 nm and 10 nm CuZr ‑ 18 nm Cu multilayers and plastic-induced shear instability in thick CuZr layers (>20 nm). The plastic co-deformation is ascribed to the nucleation and interaction of shear transformation zones in CuZr layers at the adjacent interfaces, while the shear instability is associated with the nucleation and propagation of shear bands in CuZr layers. Shear bands are initialized in the CuZr layers due to the accumulated glide dislocations along CuZr-Cu interfaces, and propagate into adjacent Cu layers via slips on {111} plane non-parallel to the interface. Due to crystallographic constraint of the Cu layers, shear bands are approximately parallel to {111} plane in the Cu layer.

  9. Plastic Deformation Modes of CuZr/Cu Multilayers.

    PubMed

    Cui, Yan; Abad, Oscar Torrents; Wang, Fei; Huang, Ping; Lu, Tian-Jian; Xu, Ke-Wei; Wang, Jian

    2016-01-01

    We synthesized CuZr/Cu multilayers and performed nanoindentation testing to explore the dependence of plastic deformation modes on the thickness of CuZr layers. The Cu layers were 18 nm thick and the CuZr layers varied in thickness from 4 nm to 100 nm. We observed continuous plastic co-deformation in the 4 nm and 10 nm CuZr - 18 nm Cu multilayers and plastic-induced shear instability in thick CuZr layers (>20 nm). The plastic co-deformation is ascribed to the nucleation and interaction of shear transformation zones in CuZr layers at the adjacent interfaces, while the shear instability is associated with the nucleation and propagation of shear bands in CuZr layers. Shear bands are initialized in the CuZr layers due to the accumulated glide dislocations along CuZr-Cu interfaces, and propagate into adjacent Cu layers via slips on {111} plane non-parallel to the interface. Due to crystallographic constraint of the Cu layers, shear bands are approximately parallel to {111} plane in the Cu layer. PMID:26984537

  10. Plastic Deformation Modes of CuZr/Cu Multilayers

    PubMed Central

    Cui, Yan; Abad, Oscar Torrents; Wang, Fei; Huang, Ping; Lu, Tian-Jian; Xu, Ke-Wei; Wang, Jian

    2016-01-01

    We synthesized CuZr/Cu multilayers and performed nanoindentation testing to explore the dependence of plastic deformation modes on the thickness of CuZr layers. The Cu layers were 18 nm thick and the CuZr layers varied in thickness from 4 nm to 100 nm. We observed continuous plastic co-deformation in the 4 nm and 10 nm CuZr − 18 nm Cu multilayers and plastic-induced shear instability in thick CuZr layers (>20 nm). The plastic co-deformation is ascribed to the nucleation and interaction of shear transformation zones in CuZr layers at the adjacent interfaces, while the shear instability is associated with the nucleation and propagation of shear bands in CuZr layers. Shear bands are initialized in the CuZr layers due to the accumulated glide dislocations along CuZr-Cu interfaces, and propagate into adjacent Cu layers via slips on {111} plane non-parallel to the interface. Due to crystallographic constraint of the Cu layers, shear bands are approximately parallel to {111} plane in the Cu layer. PMID:26984537

  11. Asymptotes in Polar Coordinates.

    ERIC Educational Resources Information Center

    Fay, Temple H.

    1986-01-01

    An old way to determine asymptotes for curves described in polar coordinates is presented. Practice in solving trigonometric equations, in differentiation, and in calculating limits is involved. (MNS)

  12. Polarization at SLC

    SciTech Connect

    Swartz, M.L.

    1988-07-01

    The SLAC Linear Collider has been designed to readily accommodate polarized electron beams. Considerable effort has been made to implement a polarized source, a spin rotation system, and a system to monitor the beam polarization. Nearly all major components have been fabricated. At the current time, several source and polarimeter components have been installed. The installation and commissioning of the entire system will take place during available machine shutdown periods as the commissioning of SLC progresses. It is expected that a beam polarization of 45% will be achieved with no loss in luminosity. 13 refs., 15 figs.

  13. Polarized negative ions

    SciTech Connect

    Haeberli, W.

    1981-04-01

    This paper presents a survey of methods, commonly in use or under development, to produce beams of polarized negative ions for injection into accelerators. A short summary recalls how the hyperfine interaction is used to obtain nuclear polarization in beams of atoms. Atomic-beam sources for light ions are discussed. If the best presently known techniques are incorporated in all stages of the source, polarized H/sup -/ and D/sup -/ beams in excess of 10 ..mu..A can probably be achieved. Production of polarized ions from fast (keV) beams of polarized atoms is treated separately for atoms in the H(25) excited state (Lamb-Shift source) and atoms in the H(1S) ground state. The negative ion beam from Lamb-Shift sources has reached a plateau just above 1 ..mu..A, but this beam current is adequate for many applications and the somewhat lower beam current is compensated by other desirable characteristics. Sources using fast polarized ground state atoms are in a stage of intense development. The next sections summarize production of polarized heavy ions by the atomic beam method, which is well established, and by optical pumping, which has recently been demonstrated to yield very large nuclear polarization. A short discussion of proposed ion sources for polarized /sup 3/He/sup -/ ions is followed by some concluding remarks.

  14. Polarization In Remote Sensing

    NASA Astrophysics Data System (ADS)

    Egan, Walter G.

    1988-06-01

    Various aspects of polarization in remote sensing are presented including mathematical treatments and selected experimental observations. The observations are of the percent polarization from Haleakala volcanic ash, basalt powder, rhyolytic oumice. rose quartz, niccolite, ilmenite, black oak leaves. dried red pine needles, a New Haven red pine stand, moist soil, the sky above Mauna Loa Observatory, the sky above Long Island in summer and winter, and cirrus clouds. Also, space based shuttle photographic observations of polarization are described. Instrumental polarization from a Cassegrainian telescope is described as well as the design of an imaging soectropolarimeter for remote sensing. A list is presented of twelve polarimetric properties associated with remote sensing.

  15. Spectral characterization and in vitro microbiological activity of new bis-1,8-naphthalimides and their Cu(II) complexes

    NASA Astrophysics Data System (ADS)

    Ottaviani, Maria Francesca; Yordanova, Stanislava; Cangiotti, Michela; Vasileva-Tonkova, Evgenia; Coppola, Concetta; Stoyanov, Stanimir; Grabchev, Ivo

    2016-04-01

    Two novel bis-1,8-naphthalimide derivatives with different substituents at C-4 position, termed L1 and L2, were synthesized and their photophysical properties in organic solvents with different polarity were investigated. Their Cu(II) complexes were also synthesized to be used as antimicrobial agents. The structural properties of [Cu(L1) (NO3)2] and [Cu(L2) (NO3)2] complexes were studied by nuclear magnetic resonance (NMR) and Fourier transform - infrared (FT-IR) spectroscopies. Cu(II) - ligands complexation at different Cu(II)/ligand molar ratios was studied by means of UV-Vis, fluorescence and electron paramagnetic resonance (EPR) spectroscopies. The results indicate the formation of Cu-N4 and Cu-N2O2 coordinations with different structure and stability conditions for the L1 and L2 derivatives. A different solvent at different polarity also affects the structural properties and the range of stability. L1 provided more stable Cu-N4 complexes than L2. [Cu(L1) (NO3)2] also showed stronger antibacterial and antifungal abilities than those of [Cu(L2) (NO3)2]. These results indicate that [Cu(L1) (NO3)2] works as antimicrobial agent to be used in biomedical and agrochemical applications.

  16. RHIC Polarized proton operation

    SciTech Connect

    Huang, H.; Ahrens, L.; Alekseev, I.G.; Aschenauer, E.; Atoian, G.; Bai, M.; Bazilevsky, A.; Blaskiewicz, M.; Brennan, J.M.; Brown, K.A.; Bruno, D.; Connolly, R.; Dion, A.; D'Ottavio, T.; Drees, K.A.; Fischer, W.; Gardner, C.; Glenn, J.W.; Gu, X.; Harvey, M.; Hayes, T.; Hoff, L.; Hulsart, R.L.; Laster, J.; Liu, C.; Luo, Y.; MacKay, W.W.; Makdisi, Y.; Marr, G.J.; Marusic, A.; Meot, F.; Mernick, K.; Michnoff, R,; Minty, M.; Montag, C.; Morris, J.; Nemesure, S.; Poblaguev, A.; Ptitsyn, V.; Ranjibar, V.; Robert-Demolaize, G.; Roser, T.; J.; Severino, F.; Schmidke, B.; Schoefer, V.; Severino, F.; Smirnov, D.; Smith, K.; Steski, D.; Svirida, D.; Tepikian, S.; Trbojevic, D.; Tsoupas, N.; Tuozzolo, J. Wang, G.; Wilinski, M.; Yip, K.; Zaltsman, A.; Zelenski, A.; Zeno, K.; Zhang, S.Y.

    2011-03-28

    The Relativistic Heavy Ion Collider (RHIC) operation as the polarized proton collider presents unique challenges since both luminosity(L) and spin polarization(P) are important. With longitudinally polarized beams at the experiments, the figure of merit is LP{sup 4}. A lot of upgrades and modifications have been made since last polarized proton operation. A 9 MHz rf system is installed to improve longitudinal match at injection and to increase luminosity. The beam dump was upgraded to increase bunch intensity. A vertical survey of RHIC was performed before the run to get better magnet alignment. The orbit control is also improved this year. Additional efforts are put in to improve source polarization and AGS polarization transfer efficiency. To preserve polarization on the ramp, a new working point is chosen such that the vertical tune is near a third order resonance. The overview of the changes and the operation results are presented in this paper. Siberian snakes are essential tools to preserve polarization when accelerating polarized beams to higher energy. At the same time, the higher order resonances still can cause polarization loss. As seen in RHIC, the betatron tune has to be carefully set and maintained on the ramp and during the store to avoid polarization loss. In addition, the orbit control is also critical to preserve polarization. The higher polarization during this run comes from several improvements over last run. First we have a much better orbit on the ramp. The orbit feedback brings down the vertical rms orbit error to 0.1mm, much better than the 0.5mm last run. With correct BPM offset and vertical realignment, this rms orbit error is indeed small. Second, the jump quads in the AGS improved input polarization for RHIC. Third, the vertical tune was pushed further away from 7/10 snake resonance. The tune feedback maintained the tune at the desired value through the ramp. To calibrate the analyzing power of RHIC polarimeters at any energy above

  17. The Polar Insulation Investigation

    ERIC Educational Resources Information Center

    Urban-Rich, Juanita

    2006-01-01

    In this article, the author developed an activity called "The Polar Insulation Investigation." This activity builds on students' natural interest in "things polar" and introduces them to animal adaptations in a unique way. The aim of the exploration is to determine the role of animal coverings (e.g., blubber, fur, and feathers) and to see which is…

  18. Our Polar Past

    ERIC Educational Resources Information Center

    Clary, Renee; Wandersee, James

    2009-01-01

    The study of polar exploration is fascinating and offers students insights into the history, culture, and politics that affect the developing sciences at the farthest ends of Earth. Therefore, the authors think there is value in incorporating polar exploration accounts within modern science classrooms, and so they conducted research to test their…

  19. Polar Science Is Cool!

    ERIC Educational Resources Information Center

    Weeks, Sophie

    2012-01-01

    Children are fascinated by the fact that polar scientists do research in extremely cold and dangerous places. In the Arctic they might be viewed as lunch by a polar bear. In the Antarctic, they could lose toes and fingers to frostbite and the wind is so fast it can rip skin off. They camp on ice in continuous daylight, weeks from any form of…

  20. Polarized Light: Three Demonstrations.

    ERIC Educational Resources Information Center

    Goehmann, Ruth; Welty, Scott

    1984-01-01

    Describes three demonstrations used in the Chicago Museum of Science and Industry polarized light show. The procedures employed are suitable for the classroom by using smaller polarizers and an overhead projector. Topic areas include properties of cellophane tape, nondisappearing arrows, and rope through a picket fence. (JN)

  1. Mechanism of lunar polarization.

    PubMed

    Hopfield, J J

    1966-03-18

    A theoretical model to explain the negative polarization of moonlight at small lunar phase angles is developed. The model is based on the polarization of light in the diffraction region bordering the geometric shadow of an opaque dielectric obstacle. PMID:17817298

  2. Polarization and polarization fatigue in ferroelectrics

    NASA Astrophysics Data System (ADS)

    Du, Xiaofeng

    This thesis addresses some fundamental issues in ferroelectricity and its applications through a computational and experimental effort. It focuses on a variety of perovskite-type ferroelectric oxides and investigates the physical basis for spontaneous polarization, domain wall dynamics, and texture development in thin film applications. The dipole-dipole interactions between ionic species in perovskite-type materials have been calculated to determine the local field and the lattice instability. Different ferroelectric and anti-ferroelectric polarization transitions can be realized by taking into account the structure distortion of the parent perovskites. We find the local field is enhanced by short range disorder and its nature varies from disorder to disorder, causing polarization transitions in non-(100) directions. The molecular field theory has also been extended to layered perovskites, which favors in-plane polarization over c-polarization. These theoretical predictions are in agreement with the experimental observations of various perovskites and layered perovskites in both single crystal and thin film forms. Domain switching in PZT has been studied by probing the frequency dependency of polarization hysteresis. A picture of thermally activated domain wall movement is established from the frequency spectra of coercive field. The field dependence of domain wall bulging and the nature of the binding between pinning obstacles and the walls are inferred from such a study. Consistent with this picture, polarization fatigue can be defined as a process of increasing the resistance from pinning defects to domain wall motion. The chemical species that act as pinning defects have been identified through model experiments that control carrier injection, electrode interfaces, and film compositions. Based on these observations, a methodology is proposed to evaluate and predict the fatigue damage of both PZT and layered perovskite thin films. Processing of layered

  3. Parallel Polarization State Generation

    PubMed Central

    She, Alan; Capasso, Federico

    2016-01-01

    The control of polarization, an essential property of light, is of wide scientific and technological interest. The general problem of generating arbitrary time-varying states of polarization (SOP) has always been mathematically formulated by a series of linear transformations, i.e. a product of matrices, imposing a serial architecture. Here we show a parallel architecture described by a sum of matrices. The theory is experimentally demonstrated by modulating spatially-separated polarization components of a laser using a digital micromirror device that are subsequently beam combined. This method greatly expands the parameter space for engineering devices that control polarization. Consequently, performance characteristics, such as speed, stability, and spectral range, are entirely dictated by the technologies of optical intensity modulation, including absorption, reflection, emission, and scattering. This opens up important prospects for polarization state generation (PSG) with unique performance characteristics with applications in spectroscopic ellipsometry, spectropolarimetry, communications, imaging, and security. PMID:27184813

  4. Polarization of clouds

    NASA Astrophysics Data System (ADS)

    Goloub, Philippe; Herman, Maurice; Parol, Frederic

    1995-12-01

    This paper reports the main results concerning polarization by clouds derived from POLDER (polarization and directionality of earth's reflectances) airborne version. These results tend to confirm the high information content in the polarization (phase, altimetry). The preliminary results of EUCREX'94 (European Cloud Radiation Experiment) evidenced the drastically different polarized signatures for ice crystals and water droplets. Here we report systematic and statistically significative observations over the whole EUCREX data set. The results show that the cirrus exhibit their own signature. Preliminary observations performed during CLEOPATRA'91 (Cloud Experiment Ober Pfaffenhofen And Transport) and EUCREX'94 campaigns have shown the feasibility of cloud altimetry using spectral information (443 nm and 865 nm) of the polarized light over liquid water droplets clouds. Altimetry technique has been generalized on ASTEX-SOFIA'92 and EUCREX'94 data sets. All these results are presented and discussed in this paper.

  5. Precision Polarization of Neutrons

    NASA Astrophysics Data System (ADS)

    Martin, Elise; Barron-Palos, Libertad; Couture, Aaron; Crawford, Christopher; Chupp, Tim; Danagoulian, Areg; Estes, Mary; Hona, Binita; Jones, Gordon; Klein, Andi; Penttila, Seppo; Sharma, Monisha; Wilburn, Scott

    2009-05-01

    Determining polarization of a cold neutron beam to high precision is required for the next generation neutron decay correlation experiments at the SNS, such as the proposed abBA and PANDA experiments. Precision polarimetry measurements were conducted at Los Alamos National Laboratory with the goal of determining the beam polarization to the level of 10-3 or better. The cold neutrons from FP12 were polarized using optically polarized ^3He gas as a spin filter, which has a highly spin-dependent absorption cross section. A second ^ 3He spin filter was used to analyze the neutron polarization after passing through a resonant RF spin rotator. A discussion of the experiment and results will be given.

  6. Parallel Polarization State Generation

    NASA Astrophysics Data System (ADS)

    She, Alan; Capasso, Federico

    2016-05-01

    The control of polarization, an essential property of light, is of wide scientific and technological interest. The general problem of generating arbitrary time-varying states of polarization (SOP) has always been mathematically formulated by a series of linear transformations, i.e. a product of matrices, imposing a serial architecture. Here we show a parallel architecture described by a sum of matrices. The theory is experimentally demonstrated by modulating spatially-separated polarization components of a laser using a digital micromirror device that are subsequently beam combined. This method greatly expands the parameter space for engineering devices that control polarization. Consequently, performance characteristics, such as speed, stability, and spectral range, are entirely dictated by the technologies of optical intensity modulation, including absorption, reflection, emission, and scattering. This opens up important prospects for polarization state generation (PSG) with unique performance characteristics with applications in spectroscopic ellipsometry, spectropolarimetry, communications, imaging, and security.

  7. Parallel Polarization State Generation.

    PubMed

    She, Alan; Capasso, Federico

    2016-01-01

    The control of polarization, an essential property of light, is of wide scientific and technological interest. The general problem of generating arbitrary time-varying states of polarization (SOP) has always been mathematically formulated by a series of linear transformations, i.e. a product of matrices, imposing a serial architecture. Here we show a parallel architecture described by a sum of matrices. The theory is experimentally demonstrated by modulating spatially-separated polarization components of a laser using a digital micromirror device that are subsequently beam combined. This method greatly expands the parameter space for engineering devices that control polarization. Consequently, performance characteristics, such as speed, stability, and spectral range, are entirely dictated by the technologies of optical intensity modulation, including absorption, reflection, emission, and scattering. This opens up important prospects for polarization state generation (PSG) with unique performance characteristics with applications in spectroscopic ellipsometry, spectropolarimetry, communications, imaging, and security. PMID:27184813

  8. Cell polarity: mechanochemical patterning.

    PubMed

    Goehring, Nathan W; Grill, Stephan W

    2013-02-01

    Nearly every cell type exhibits some form of polarity, yet the molecular mechanisms vary widely. Here we examine what we term 'chemical systems' where cell polarization arises through biochemical interactions in signaling pathways, 'mechanical systems' where cells polarize due to forces, stresses and transport, and 'mechanochemical systems' where polarization results from interplay between mechanics and chemical signaling. To reveal potentially unifying principles, we discuss mathematical conceptualizations of several prototypical examples. We suggest that the concept of local activation and global inhibition - originally developed to explain spatial patterning in reaction-diffusion systems - provides a framework for understanding many cases of cell polarity. Importantly, we find that the core ingredients in this framework - symmetry breaking, self-amplifying feedback, and long-range inhibition - involve processes that can be chemical, mechanical, or even mechanochemical in nature. PMID:23182746

  9. Molecular content of polar-ring galaxies

    NASA Astrophysics Data System (ADS)

    Combes, F.; Moiseev, A.; Reshetnikov, V.

    2013-06-01

    We have searched for CO lines in a sample of 21 new morphologically determined polar-ring galaxies (of which nine are kinematically confirmed), obtained from a wide search in the Galaxy Zoo project by Moiseev and collaborators. Polar-ring galaxies (PRGs) are a unique class of objects, tracing special episodes in the galaxy mass assembly: they can be formed through galaxy interaction and merging, but also through accretion from cosmic filaments. Furthermore, they enable the study of dark matter haloes in three dimensions. The polar ring itself is a sub-system rich in gas, where molecular gas is expected, and new stars are formed. Among the sample of 21 PRGs, we have detected five CO-rich systems, that can now be followed up with higher spatial resolution. Their average molecular mass is 9.4 × 109M⊙, and their average gas fraction is 27% of their baryonic mass, with a range from 15 to 43%, implying that they have just accreted a large amount of gas. The position of the detected objects in the velocity-magnitude diagram is offset from the Tully-Fisher relation of normal spirals, as was already found for PRGs. This work is part of our multi-wavelength project to determine the detailed morphology and dynamics of PRGs, test through numerical models their formation scenario, and deduce their dark matter content and 3D-shape. Based on observations carried out with the IRAM 30 m telescope. IRAM is supported by INSU/CNRS (France), MPG (Germany), and IGN (Spain).Spectra of detections are available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (ftp://130.79.128.5">130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/554/A11

  10. Bis(mu-oxo)dicopper in Cu-ZSM-5 and its role in the decomposition of NO: a combined in situ XAFS, UV-vis-near-IR, and kinetic study.

    PubMed

    Groothaert, Marijke H; van Bokhoven, Jeroen A; Battiston, Andrea A; Weckhuysen, Bert M; Schoonheydt, Robert A

    2003-06-25

    In situ XAFS combined with UV-vis-near-IR spectroscopy are used to identify the active site in copper-loaded ZSM-5 responsible for the catalytic decomposition of NO. Cu-ZSM-5 was probed with in situ XAFS (i) after O(2) activation and (ii) while catalyzing the direct decomposition of NO into N(2) and O(2). A careful R-space fitting of the Cu K-edge EXAFS data is presented, including the use of different k-weightings and the analysis of the individual coordination shells. For the O(2)-activated overexchanged Cu-ZSM-5 sample a Cu.Cu contribution at 2.87 A with a coordination number of 1 is found. The corresponding UV-vis-near-IR spectrum is characterized by an intense absorption band at 22 700 cm(-1) and a relatively weaker band at 30 000 cm(-1), while no corresponding EPR signal is detected. Comparison of these data with the large databank of well-characterized copper centers in enzymes and synthetic model complexes leads to the identification of the bis(mu-oxo)dicopper core, i.e. [Cu(2)(mu-O)(2)](2+). After dehydration in He, Cu-ZSM-5 shows stable NO decomposition activity and the in situ XAFS data indicate the formation of a large fraction of the bis(mu-oxo)dicopper core during reaction. When the Cu/Al ratio of Cu-ZSM-5 exceeds 0.2, both the bis(mu-oxo)dicopper core is formed and the NO decomposition activity increases sharply. On the basis of the in situ measurements, a reaction cycle is proposed in which the bis(mu-oxo)dicopper core forms the product O(2) on a single active site and realizes the continuous O(2) release and concomitant self-reduction. PMID:12812505

  11. Spectroscopic, computational, and kinetic studies of the mu4-sulfide-bridged tetranuclear CuZ cluster in N2O reductase: pH effect on the edge ligand and its contribution to reactivity.

    PubMed

    Ghosh, Somdatta; Gorelsky, Serge I; George, Serena DeBeer; Chan, Jeannine M; Cabrito, Inês; Dooley, David M; Moura, José J G; Moura, Isabel; Solomon, Edward I

    2007-04-01

    A combination of spectroscopy and density functional theory (DFT) calculations has been used to evaluate the pH effect at the CuZ site in Pseudomonas nautica (Pn) nitrous oxide reductase (N2OR) and Achromobacter cycloclastes (Ac) N2OR and its relevance to catalysis. Absorption, magnetic circular dichroism, and electron paramagnetic resonance with sulfur K-edge X-ray absorption spectra of the enzymes at high and low pH show minor changes. However, resonance Raman (rR) spectroscopy of PnN2OR at high pH shows that the 415 cm-1 Cu-S vibration (observed at low pH) shifts to higher frequency, loses intensity, and obtains a 9 cm-1 18O shift, implying significant Cu-O character, demonstrating the presence of a OH- ligand at the CuICuIV edge. From DFT calculations, protonation of either the OH- to H2O or the mu4-S2- to mu4-SH- would produce large spectral changes which are not observed. Alternatively, DFT calculations including a lysine residue at an H-bonding distance from the CuICuIV edge ligand show that the position of the OH- ligand depends on the protonation state of the lysine. This would change the coupling of the Cu-(OH) stretch with the Cu-S stretch, as observed in the rR spectrum. Thus, the observed pH effect (pKa approximately 9.2) likely reflects protonation equilibrium of the lysine residue, which would both raise E degrees and provide a proton for lowering the barrier for the N-O cleavage and for reduction of the [Cu4S(im)7OH]2+ to the fully reduced 4CuI active form for turnover. PMID:17352474

  12. Interplanetary magnetic sector polarity inferred from polar geomagnetic field observations

    NASA Technical Reports Server (NTRS)

    Friis-Christensen, E.; Lassen, K.; Wilcox, J. M.; Gonzalez, W.; Colburn, D. S.

    1971-01-01

    In order to infer the interplanetary sector polarity from polar geomagnetic field diurnal variations, measurements were carried out at Godhavn and Thule (Denmark) Geomagnetic Observatories. The inferred interplanetary sector polarity was compared with the polarity observed at the same time by Explorer 33 and 35 magnetometers. It is shown that the polarity (toward or away from the sun) of the interplanetary magnetic field can be reliably inferred from observations of the polar cap geomagnetic fields.

  13. Electron correlation and relativistic effects in the coinage metal compounds. II. Heteronuclear dimers: CuAg, CuAu, and AgAu

    NASA Astrophysics Data System (ADS)

    Kellö, Vladimir; Sadlej, Andrzej J.

    1995-08-01

    Electric properties of heteronuclear dimers of the coinage metals are calculated at the level of the CCSD(T) approximation applied to 38 electrons of the valence and next-to-valence atomic shells. The relativistic effects are accounted for by using the scalar approximation to the Pauli hamiltonian. Both the pure relativistic and mixed relativistic-correlation contributions to energies and electric properties are computed. All calculations have been carried out by using the recently developed first-order polarized basis sets of the coinage metal atoms. In the non-relativistic approximation all studied dimers show only a moderate degree of polarity; the non-relativistic CuAg turns out to be the most polar dimer with the Cu(-)Ag(+) polarity. The relativistic effects considerably reduce the negative value of the CuAg dipole moment, change the sign of the CuAu dipole moment, and make the AgAu molecule the most polar species in the series. Simultaneously, the parallel component of the dipole polarizability shows only a small relativistic contraction. The calculated quasirelativistic interaction potentials have a correct behavior in the vicinity of their minima and give the Re and ωe values in complete agreement with experiment. Much less satisfactory are the dissociation energy data which seem to suffer from the single reference configuration approximation.

  14. Neutron Polarizers Based on Polarized 3He

    SciTech Connect

    William M. Snow

    2005-05-01

    The goal of this work, which is a collaborative effort between Indiana University, NIST, and Hamilton College, is to extend the technique of polarized neutron scattering into new domains by the development and application of polarized 3He-based neutron spin filters. After the IPNS experiment which measured Zeeman sp[litting in surface scattered neutrons using a polarized 3He cell as a polarization analyzer transporterd by car from Bloomington to Chicago, the Indiana work focused on technical developments to improve the 3He polarization of the Indiana compression system. The compression system was rebuilt with a new valve system which allows gas trapped in the dead volume of the compressors at the end of the piston stroke to be exhausted and conducted back to the optical pumping cell where it can be repolarized. We also incorporated a new intermediate storage volume made at NIST from 1720 glass which will reduce polarization losses between the compressors. Furthermore, we improved the stability of the 1083 nm laser by cooling the LMA rod. We achieved 60% 3he polarization in the optical pumping cell and 87% preservation of the polarization during compression. In parallel we built a magnetically-shielded transport solenoid for use on neutron scattering instruments such as POSY which achieves a fractional field uniformity of better than 10-3 per cm. The field was mapped using an automated 3D field mapping system for in-situ measurement of magnetic field gradients Diluted magnetic semiconductors offer many exciting opportunities for investigation of spintronic effects in solids and are certain to be one of the most active areas of condensed matter physics over then next several years. These materials can act as efficient spin injectors for devices that make use of spin-dependent transport phenomena. We just (late July 2002) finished a neutron reflectivity experiment at NIST on a GaMnAs trilayer film. This material is a ferromagnetic semiconductor which is of interest

  15. Polarization at the SLC

    SciTech Connect

    Moffeit, K.C.

    1988-10-01

    The Stanford Linear collider was designed to accommodate polarized electron beams. Longitudinally polarized electrons colliding with unpolarized positrons at a center of mass energy near the Z/sup 0/ mass can be used as novel and sensitive probes of the electroweak process. A gallium arsenide based photon emission source will provide a beam of longitudinally polarized electrons of about 45 percent polarization. A system of bend magnets and a superconducting solenoid will be used to rotate the spins so that the polarization is preserved while the 1.21 GeV electrons are stored in the damping ring. Another set of bend magnets and two superconducting solenoids orient the spin vectors so that longitudinal polarization of the electrons is achieved at the collision point with the unpolarized positrons. A system to monitor the polarization based on Moller and Compton scattering will be used. Nearly all major components have been fabricated and tested. Subsystems of the source and polarimeters have been installed, and studies are in progress. The installation and commissioning of the entire system will take place during available machine shutdown periods as the commissioning of SLC progresses. 8 refs., 16 figs., 1 tab.

  16. Review of Polarized Ion Sources

    NASA Astrophysics Data System (ADS)

    Zelenski, A.

    2016-02-01

    Recent progress in polarized ion sources development is reviewed. New techniques for production of polarized H‑ ion (proton), D‑ (D+) and 3He++ ion beams will be discussed. A novel polarization technique was successfully implemented for the upgrade of the RHIC polarized H‑ ion source to higher intensity and polarization. In this technique, a proton beam inside the high magnetic field solenoid is produced by ionization of the atomic hydrogen beam (from an external source) in the He-gas ionizer cell. Polarized electron capture from the optically-pumped Rb vapor further produces proton polarization (Optically Pumped Polarized Ion Source technique). The upgraded source reliably delivered beam for the 2013 polarized run in RHIC at S = 510 GeV. This was a major factor contributing to RHIC polarization increase to over 60 % for colliding beams. Feasibility studies of a new polarization technique for polarized 3He++ source based on BNL Electron Beam Ion Source is also discussed.

  17. North Polar Dunes

    NASA Technical Reports Server (NTRS)

    2006-01-01

    23 January 2006 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows dark sand dunes in the north polar region of Mars. Surrounding much of the north polar ice cap are fields of sand dunes. In this case, the strongest winds responsible for the dunes blew off the polar cap (not seen here), from the north-northwest (upper left).

    Location near: 76.5oN, 63.7oW Image width: 3 km (1.9 mi) Illumination from: lower left Season: Northern Summer

  18. GUIDE FOR POLARIZED NEUTRONS

    DOEpatents

    Sailor, V.L.; Aichroth, R.W.

    1962-12-01

    The plane of polarization of a beam of polarized neutrons is changed by this invention, and the plane can be flipped back and forth quicitly in two directions in a trouble-free manner. The invention comprises a guide having a plurality of oppositely directed magnets forming a gap for the neutron beam and the gaps are spaced longitudinally in a spiral along the beam at small stepped angles. When it is desired to flip the plane of polarization the magnets are suitably rotated to change the direction of the spiral of the gaps. (AEC)

  19. Strong coupling between the spin polarization of Mn and Tb in multiferroic TbMnO3 determined by x-ray resonance exchange scattering

    NASA Astrophysics Data System (ADS)

    Voigt, J.; Persson, J.; Kim, J. W.; Bihlmayer, G.; Brückel, Th.

    2007-09-01

    We report on an x-ray resonance exchange scattering (XRES) study of multiferroic TbMnO3 . Magnetic scattering is observed close to the MnK edge and the TbLIII and LII edges. Surprisingly, Tb shows XRES also in the paraelectric phase, where neutron diffraction results suggested the 4f moments to be disordered. The temperature dependence of the XRES intensities shows a distinct kink close to the ferroelectric transition temperature TC for all absorption edges. We were able to model the temperature dependence for all edges, assuming a strong coupling of Mn and Tb magnetism via the spin polarized 5d conduction band. We argue that the hybridization between Mn and Tb states is a prerequisite for the multiferroic effect in this material.

  20. Characterization of a chiral phase in an achiral bent-core liquid crystal by polarization studies of resonant x-ray forbidden reflections

    NASA Astrophysics Data System (ADS)

    Ponsinet, V.; Barois, P.; Pan, Lidong; Wang, Shun; Huang, C. C.; Wang, S. T.; Pindak, R.; Baumeister, U.; Weissflog, W.

    2011-07-01

    The chiral antiferroelectric structure of an achiral bent-core liquid crystal is characterized by resonant x-ray scattering at chlorine K edge. The “forbidden” reflections resulting from the glide or screw symmetry elements are restored by the anisotropy of the tensor structure factor, which we calculate for two possible structural models. A careful analysis of the polarization states of the restored “forbidden” reflections enables an unambiguous identification of a chiral structure (i.e., the so-called anticlinic, antiferroelectric smectic-C or Sm-CAPA) coexisting with the achiral synclinic antiferroelectric smectic-C or Sm-CSPA. The method proves to be quite powerful as it identifies the chiral structure within coexisting phases despite an imperfect orientation of the sample. The volume fraction of the chiral phase and the distribution of alignment are extracted from the data.

  1. Characterization of a chiral phase in an achiral bent-core liquid crystal by polarization studies of resonant x-ray forbidden reflections

    SciTech Connect

    Ponsinet, V.; Pindak, R.; Barois, P.; Pan, L.; Wang, S.; Huang, C.C.; Wang, S.T.; Baumeister, U. and Weissflog, W.

    2011-07-15

    The chiral antiferroelectric structure of an achiral bent-core liquid crystal is characterized by resonant x-ray scattering at chlorine K edge. The 'forbidden' reflections resulting from the glide or screw symmetry elements are restored by the anisotropy of the tensor structure factor, which we calculate for two possible structural models. A careful analysis of the polarization states of the restored 'forbidden' reflections enables an unambiguous identification of a chiral structure (i.e., the so-called anticlinic, antiferroelectric smectic-C or Sm-C{sub A}P{sub A}) coexisting with the achiral synclinic antiferroelectric smectic-C or Sm-C{sub S}P{sub A}. The method proves to be quite powerful as it identifies the chiral structure within coexisting phases despite an imperfect orientation of the sample. The volume fraction of the chiral phase and the distribution of alignment are extracted from the data.

  2. A sulfur-based transport pathway in Cu+-ATPases

    PubMed Central

    Mattle, Daniel; Zhang, Limei; Sitsel, Oleg; Pedersen, Lotte Thue; Moncelli, Maria Rosa; Tadini-Buoninsegni, Francesco; Gourdon, Pontus; Rees, Douglas C; Nissen, Poul; Meloni, Gabriele

    2015-01-01

    Cells regulate copper levels tightly to balance the biogenesis and integrity of copper centers in vital enzymes against toxic levels of copper. PIB-type Cu+-ATPases play a central role in copper homeostasis by catalyzing the selective translocation of Cu+ across cellular membranes. Crystal structures of a copper-free Cu+-ATPase are available, but the mechanism of Cu+ recognition, binding, and translocation remains elusive. Through X-ray absorption spectroscopy, ATPase activity assays, and charge transfer measurements on solid-supported membranes using wild-type and mutant forms of the Legionella pneumophila Cu+-ATPase (LpCopA), we identify a sulfur-lined metal transport pathway. Structural analysis indicates that Cu+ is bound at a high-affinity transmembrane-binding site in a trigonal-planar coordination with the Cys residues of the conserved CPC motif of transmembrane segment 4 (C382 and C384) and the conserved Met residue of transmembrane segment 6 (M717 of the MXXXS motif). These residues are also essential for transport. Additionally, the studies indicate essential roles of other conserved intramembranous polar residues in facilitating copper binding to the high-affinity site and subsequent release through the exit pathway. PMID:25956886

  3. Magnetoelectric effects in the skyrmion host material Cu2OSeO3

    PubMed Central

    Ruff, E.; Lunkenheimer, P.; Loidl, A.; Berger, H.; Krohns, S.

    2015-01-01

    Insulating helimagnetic Cu2OSeO3 shows sizeable magnetoelectric effects in its skyrmion phase. Using magnetization measurements, magneto-current analysis and dielectric spectroscopy, we provide a thorough investigation of magnetoelectric coupling, polarization and dielectric constants of the ordered magnetic and polar phases of single-crystalline Cu2OSeO3 in external magnetic fields up to 150 mT and at temperatures below 60 K. From these measurements we construct a detailed phase diagram. Especially, the skyrmion phase and the metamagnetic transition of helical to conical spin order are characterized in detail. Finally we address the question if there is any signature of polar order that can be switched by an external electric field, which would imply multiferroic behaviour of Cu2OSeO3. PMID:26446514

  4. Magnetoelectric effects in the skyrmion host material Cu2OSeO3

    NASA Astrophysics Data System (ADS)

    Ruff, E.; Lunkenheimer, P.; Loidl, A.; Berger, H.; Krohns, S.

    2015-10-01

    Insulating helimagnetic Cu2OSeO3 shows sizeable magnetoelectric effects in its skyrmion phase. Using magnetization measurements, magneto-current analysis and dielectric spectroscopy, we provide a thorough investigation of magnetoelectric coupling, polarization and dielectric constants of the ordered magnetic and polar phases of single-crystalline Cu2OSeO3 in external magnetic fields up to 150 mT and at temperatures below 60 K. From these measurements we construct a detailed phase diagram. Especially, the skyrmion phase and the metamagnetic transition of helical to conical spin order are characterized in detail. Finally we address the question if there is any signature of polar order that can be switched by an external electric field, which would imply multiferroic behaviour of Cu2OSeO3.

  5. Magnetism in zigzag and armchair CuO nanotubes: Ab-initio study

    NASA Astrophysics Data System (ADS)

    Paudel, Samir; Dandeliya, Sushmita; Chaurasiya, Rajneesh; Srivastava, Anurag; Kaphle, Gopi Chandra

    2016-05-01

    The structural stability, electronic band structure and magnetic properties of zigzag (4≤n≤12) and armchair (3≤n≤8) copper oxide nanotubes have been analyzed by employing a standard Density Functional Theory based ab-intio approach using spin polarized generalized gradient approximation with revised Perdew Burke Ernzerhoff type parameterization. The binding energy of both zigzag as well as armchair CuO nanotubes increases with increasing diameter. Whereas, calculated total magnetic moment decreases with increasing diameter. Among the considered chiralities, (5, 5) armchair (diameter 9.08 Å) and (9, 0) zigzag (diameter 9.47 Å) CuO nanotubes show highest degree of spin polarization, however total magnetic moment is found to be highest for (4, 0) zigzag and (3, 3) armchair CuO nanotubes. The computed electronic properties of considered CuO Nanotube, confirms the metallic nature of these nanotubes.

  6. First-principles study on electronic structure and optical properties of Cu-doped β-Ga2O3

    NASA Astrophysics Data System (ADS)

    Yan, Huiyu; Guo, Yanrui; Song, Qinggong; Chen, Yifei

    2014-02-01

    The electronic and optical properties of the Cu-doped and intrinsic β-Ga2O3 are studied by using the first-principles calculation method. Results show that Cu-doped β-Ga2O3 can be fabricated in experiments. Two acceptor impurity levels are introduced near the top of the valence band by Cu dopant, indicating that Cu-doped gallium oxide is a promising p-type semiconductor. Cu-doped β-Ga2O3 can be used as intermediate band semiconductor in solar cell. Cu dopant induced 100% spin polarization near the Fermi level. The analysis results of optical properties reveal that Cu-doped β-Ga2O3 is a promising potential candidate for p-type ultraviolet (UV) transparent semiconductor.

  7. Polar Environmental Monitoring

    NASA Technical Reports Server (NTRS)

    Nagler, R. G.; Schulteis, A. C.

    1979-01-01

    The present and projected benefits of the polar regions were reviewed and then translated into information needs in order to support the array of polar activities anticipated. These needs included measurement sensitivities for polar environmental data (ice/snow, atmosphere, and ocean data for integrated support) and the processing and delivery requirements which determine the effectiveness of environmental services. An assessment was made of how well electromagnetic signals can be converted into polar environmental information. The array of sensor developments in process or proposed were also evaluated as to the spectral diversity, aperture sizes, and swathing capabilities available to provide these measurements from spacecraft, aircraft, or in situ platforms. Global coverage and local coverage densification options were studied in terms of alternative spacecraft trajectories and aircraft flight paths.

  8. Mercury's South Polar Region

    NASA Video Gallery

    This animation shows 89 wide-angle camera (WAC) images of Mercury’s south polar region acquired by the Mercury Dual Imaging System (MDIS) over one complete Mercury solar day (176 Earth days). Thi...

  9. Interferometric polarization control

    SciTech Connect

    Chuss, David T.; Wollack, Edward J.; Moseley, S. Harvey; Novak, Giles

    2006-07-20

    We develop the Jones and Mueller matrices for structures that allow control of the path length difference between two linear orthogonal polarizations and consider the effect of placing multiple devices in series. Specifically, we find that full polarization modulation (measurement of Stokes Q, U, and V) can be achieved by placing two such modulators in series if the relative angles of the beam-splitting grids with respect to the analyzer orientation are appropriately chosen. Such a device has several potential advantages over a spinning wave plate modulator for measuring astronomical polarization in the far infrared through millimeter: (i) The use of small, linear motions eliminates the need for cryogenic rotational bearings; (ii) the phase flexibility allows measurement of circular as well as linear polarization; and (iii) this architecture allows for both multiwavelength and broadband modulation. We also present initial laboratory results.

  10. Polarization contrast vision

    NASA Astrophysics Data System (ADS)

    Pugh, Edward N.

    1990-05-01

    An attempt is made to establish the possibility that the geometry of certain classes of vertebrate photoreceptors results in a birefringence that allows the animals to utilize the state of polarization of light striking their retinas as a meaningful stimulus parameter. Simulate the photoreceptors as dielectric waveguides using a simple physical model, and augment this theoretical work with empirical measurements of the light guiding properties of photoreceptors in isolated pieces of retina from a green sunfish (Lepomis cyanellus). With a classical conditioning paradigm, this fish's sensitivity to light is modulated by the orientation of the plane of polarization of linearly polarized light. This functional dependence was predicted by a hypothetical antagonistic mechanism between twin cones of two orientations in the animal's retinal mosaic. Further study is planned for the nature of the stimulus to which the fish is sensitive by creating a camera that will generate images based purely upon the contrast between orthogonal polarizations at each point in space.

  11. EDITORIAL: Polarization Optics

    NASA Astrophysics Data System (ADS)

    Turunen, Jari; Friesem, Asher A.; Friberg, Ari T.

    2004-03-01

    This special issue on Polarization Optics contains one review article and 23 research papers, many of which are based on presentations at the International Commission for Optics Topical Meeting on Polarization Optics, held in Polvijärvi, Finland, between 30 June and 3 July 2003. While this issue should not in any sense be considered as a `proceedings' of this meeting, the possibility of submitting papers to it was widely advertised during the meeting, which was attended by a large fraction of prominent scientists in the field of polarization optics. Thus the quality of papers in this special issue is high. In announcing both the meeting and this special issue, we emphasized that the concept of `polarization optics' should be understood in a wide sense. In fact, all contributions dealing with the vectorial nature of light were welcome. As a result, the papers included here cover a wide range of different aspects of linear and nonlinear polarization optics. Both theoretical and experimental features are discussed. We are pleased to see that the conference and this special issue both reflect the wide diversity of important and novel polarization phenomena in optics. The papers in this special issue, and other recently published works, demonstrate that even though polarization is a fundamental property of electromagnetic fields, interest in it is rapidly increasing. The fundamental relations between partial coherence and partial polarization are currently under vigorous research in electromagnetic coherence theory. In diffractive optics it has been found that the exploitation of the vectorial nature of light can be of great benefit. Fabrication of sophisticated, spatially variable polarization-control elements is becoming possible with the aid of nanolithography. Polarization singularities and the interplay of bulk properties and topology in nanoscale systems have created much enthusiasm. In nonlinear optics, the second harmonic waves generated on reflection and

  12. Cluster formation, evolution and size distribution in Fe-Cu alloy: Analysis by XAFS, XRD and TEM

    NASA Astrophysics Data System (ADS)

    Cammelli, S.; Degueldre, C.; Cervellino, A.; Abolhassani, S.; Kuri, G.; Bertsch, J.; Lützenkirchen-Hecht, D.; Frahm, R.

    2010-03-01

    Fe-Cu alloys containing 1.3 at.% copper were studied as model systems for cluster formation in reactor pressure vessel steels. The samples were annealed at 775 K for different times and subsequently analyzed using X-ray absorption fine structure spectroscopy at the Cu-K-edge, X-ray diffraction and transmission electron microscopy. The results show that copper cluster formation might occur even with short annealing times. These clusters of about 1 nm size can switch easily from bcc iron-like structures to fcc copper, if the local copper concentration is high enough. While a short annealing time of 2.5 h at 775 K maintains a good dilution of copper in the bcc iron matrix, annealing for 312 h leads to large fcc copper precipitates. A linear combination analysis suggests that in the sample annealed 8 h, copper clusters are mostly formed with the same structure as the matrix. A co-existence of bcc and fcc clusters is obtained for 115 h of annealing. Transmission electron microscopy indicates the presence of precipitates as large as 60 nm size for an annealing time of 312 h, and X-ray diffraction provided complementary data about the clusters size distributions in all of the four samples.

  13. Active polarization descattering.

    PubMed

    Treibitz, Tali; Schechner, Yoav Y

    2009-03-01

    Vision in scattering media is important but challenging. Images suffer from poor visibility due to backscattering and attenuation. Most prior methods for scene recovery use active illumination scanners (structured and gated), which can be slow and cumbersome, while natural illumination is inapplicable to dark environments. The current paper addresses the need for a non-scanning recovery method, that uses active scene irradiance. We study the formation of images under widefield artificial illumination. Based on the formation model, the paper presents an approach for recovering the object signal. It also yields rough information about the 3D scene structure. The approach can work with compact, simple hardware, having active widefield, polychromatic polarized illumination. The camera is fitted with a polarization analyzer. Two frames of the scene are taken, with different states of the analyzer or polarizer. A recovery algorithm follows the acquisition. It allows both the backscatter and the object reflection to be partially polarized. It thus unifies and generalizes prior polarization-based methods, which had assumed exclusive polarization of either of these components. The approach is limited to an effective range, due to image noise and illumination falloff. Thus, the limits and noise sensitivity are analyzed. We demonstrate the approach in underwater field experiments. PMID:19147870

  14. Fusion of a polarized projectile with a polarized target

    SciTech Connect

    Christley, J.A.; Johnson, R.C.; Thompson, I.J.

    1995-07-15

    The fusion cross sections for a polarized target with both unpolarized and polarized projectiles are studied. Expressions for the observables are given for the case when both nuclei are polarized. Calculations for fusion of an aligned {sup 165}Ho target with {sup 16}O and polarized {sup 7}Li beams are presented.

  15. Cued recall in depression.

    PubMed

    Watts, F N; Sharrock, R

    1987-05-01

    An experiment is reported in which a depressed and a control group were tested on free recall, cued recall and recognition memory for a prose passage. As expected from previous work the depressives tended to show less impairment on recognition than on free recall. However, contrary to what some theories would predict, cued recall performance was no better than free recall. The implications of this finding for the nature of the depressive memory deficit for neutral materials are discussed. It seems that neither the amount of verbal output required, nor the need to generate retrieval cues, are critical factors. PMID:3580652

  16. Raman and x-ray absorption spectroscopy characterization of Zr-doped MOCVD YBa2Cu2O6+delta.

    SciTech Connect

    Maroni, V. A.; Kropf, Arthur J; Aytug, Tolga; Paranthaman, Mariappan Parans

    2010-01-01

    Metal organic chemical vapor deposited YBa2Cu3O6+ (YBCO) films (about 0.9 m thick) containing varying amounts of added zirconium were examined by Raman microscopy and synchrotron x-ray absorption spectroscopy. The self-field and in-field (1 T, B c) Jc performance of the YBCO films at 77 K (reported by the group at Oak Ridge National Laboratory that fabricated the samples) exhibited an increase on going from 0 mol% (m/o) Zr-added to 2.5 m/o Zr-added but then decreased sharply with increasing Zr content. Raman measurements on these films showed that the added Zr had little effect on YBCO cation disorder up to about 7.5 m/o Zr-added. Cation disorder increased while Ba Cu O content remained relatively constant for Zr additions 7.5 m/o. In the region of sharpest descent of Jc with increasing Zr content (2.5 7.5 m/o Zr-added) neither the cation disorder nor the Ba Cu O content showed a systematic variation with Jc. Zirconium K edge x-ray absorption near-edge spectroscopy revealed that virtually all of the added Zr in each sample was present as a BaZrO3-like phase (BZO). The Jc performance of the Zr-added films showed a high correlation with the variations in the next-nearest-neighbor Zr M (M = Zr, Y) scattering path amplitude from the extended x-ray absorption fine structure (EXAFS) and the critical temperature over the full range of Zr additions and with cation disorder at the higher Zr-added levels (>7.5 m/o). There was no obvious correlation with the amount of residual barium cuprate or CuO. Approximate ranges for the BZO particle dimensions estimated from the EXAFS data indicated that the mean particle size gets larger with increasing Zr addition.

  17. Morphology and electrochemical behavior of Ag-Cu nanoparticle-doped amalgams.

    PubMed

    Chung, Kwok-Hung; Hsiao, Li-Yin; Lin, Yu-Sheng; Duh, Jenq-Gong

    2008-05-01

    The aim of this study was to introduce Ag-Cu phase nanopowder as an additive to improve the corrosion behavior of dental amalgams. A novel Ag-Cu nanopowder was synthesized by the precipitation method. An amalgam alloy powder (World-Cap) was added and mixed with 5 wt.% and 10 wt.% of Ag-Cu nanopowders, respectively, to form experimental amalgam alloy powders. The original alloy powder was used as a control. Alloy powders were examined using X-ray diffraction, transmission electron microscopy (TEM), scanning electron microscopy and electron probe microanalysis. Amalgam disk specimens of metallurgically prepared were tested in 0.9% NaCl solution using electrochemical methods. The changes in the corrosion potential and anodic polarization characteristics were determined. Corrosion potential data were analyzed statistically (n=3, analysis of variance, Tukey's test, p<0.05). The diameters of lamellar structure Ag-Cu nanoparticles were measured to be approximately 30 nm. The composition of the Ag-Cu nanoparticles determined by TEM-energy-dispersive spectroscopy was 56.28 at.% Ag-43.72 at.% Cu. A light-shaded phase was found mixing with dark Cu-Sn reaction particles in the reaction zones of Ag-Cu nanoparticle-doped amalgams. The Ag-Cu nanoparticle-doped amalgams exhibited zero current potentials more positive than the control (p<0.05) and no current peak was observed at -325mV that related to Ag-Hg phase and Cu6Sn5 phase in anodic polarization curves. The results indicated that the corrosion resistance of high-copper single-composition amalgam could be improved by Ag-Cu nanoparticle-doping. PMID:18321799

  18. PRR performance of Cu- and CuBr-vapor lasers

    NASA Astrophysics Data System (ADS)

    Fedorov, V. F.; Evtushenko, Gennadiy S.; Klimkin, Vladimir M.; Polunin, Yu. P.; Soldatov, Anatoly N.; Sukhanov, Viktor B.

    1998-06-01

    Results obtained from comparative analysis of the pulse repetition rate performance of Cu- and CuBr-vapor lasers operated at high pump pulse repetitions (approximately 100 kHz) are reported. For a CuBr laser with a 8 mm diameter discharge tube the laser pulse repetition rate as high as 270 kHz was realized.

  19. Colour, polarity, disparity, and texture contributions to motion segregation.

    PubMed

    Poom, Leo; Börjesson, Erik

    2005-01-01

    We measured how different cues are combined in motion-segregation processes by using motion stimuli where randomly distributed target dots were organised in global revolving motion while the remaining noise dots performed random motion. Target dots were cued with a different colour, polarity, disparity depth, or texture orientation than the noise dots, or they were the same as the noise dots. The stimuli were presented with a prolonged static cue preview which provided position cues to target dots or, briefly with static pre-target and post-target noise frames, which provided false position cues (no preview). All cues efficiently facilitated global motion segregation in cued-preview conditions. Colour completely failed to facilitate global motion segregation in no-preview conditions. Polarity and disparity facilitated segregation in no-preview conditions, although sensitivities were lower than in the preview conditions. Remarkably, texture orientation largely facilitated motion segregation by the same amount in both cued-preview and no-preview conditions. So, colour provides only position cues to the motion-segregation task whereas texture orientation, disparity, and to a lesser extent polarity are integrated with the segregation process. PMID:16309114

  20. Polarization transfer of bremsstrahlung arising from spin-polarized electrons.

    PubMed

    Märtin, R; Weber, G; Barday, R; Fritzsche, Y; Spillmann, U; Chen, W; DuBois, R D; Enders, J; Hegewald, M; Hess, S; Surzhykov, A; Thorn, D B; Trotsenko, S; Wagner, M; Winters, D F A; Yerokhin, V A; Stöhlker, Th

    2012-06-29

    We report on a study of the polarization transfer between transversely polarized incident electrons and the emitted x rays for electron-atom bremsstrahlung. By means of Compton polarimetry we performed for the first time an energy-differential measurement of the complete properties of bremsstrahlung emission related to linear polarization, i.e., the degree of linear polarization as well as the orientation of the polarization axis. For the high-energy end of the bremsstrahlung continuum the experimental results for both observables show a high sensitivity on the initial electron spin polarization and prove that the polarization orientation is virtually independent of the photon energy. PMID:23004992

  1. Rectilinear lattices of polarization vortices with various spatial polarization distributions.

    PubMed

    Fu, Shiyao; Zhang, Shikun; Wang, Tonglu; Gao, Chunqing

    2016-08-01

    In this paper, we propose a type of rectilinear lattices of polarization vortices, each spot in which has mutually independent, and controllable spatial polarization distributions. The lattices are generated by two holograms under special design. In the experiment, the holograms are encoded on two spatial light modulators, and the results fit very well with theory. Our scheme makes it possible to generate multiple polarization vortices with various polarization distributions simultaneously, for instance, radially and azimuthally polarized beams, and can be used in the domains as polarization-based data transmission system, optical manufacture, polarization detection and so on. PMID:27505812

  2. The role of magnetism in the formation of the two-phase miscibility gap in β Cu-Al-Mn

    NASA Astrophysics Data System (ADS)

    Lanzini, Fernando; Alés, Alejandro

    2015-12-01

    A theoretical study of the ground state properties of alloys with compositions along the pseudobinary line Cu3Al-Cu2AlMn is presented. Cohesive energies, lattice parameters and magnetic moments of the two limiting compounds and three intermediate compositions are calculated by means of density functional theory. In order to evaluate the role of magnetism, both the spin-polarized (SP) and the non spin-polarized (NSP) cases have been considered. It is shown that magnetism plays a central role on the stabilization of the L21 crystal structure in Cu2AlMn, and in the formation of the miscibility gap in Cu3Al-Cu2AlMn. The considerable lattice mismatch between the end compounds can be attributed also to magnetic effects.

  3. First-principles study on the electronic, magnetic and spin transport properties of CU(6bpyNO)Cl2

    NASA Astrophysics Data System (ADS)

    Sun, Guoliang; Ding, J. F.

    2015-11-01

    The electronic structure and magnetic properties of organic Cu(6bpyNO)Cl2 have been studied by using the first-principles calculations based on density-functional theory. It is shown that the total spin magnetic moment per molecule is about 2.00 μB, which mainly comes from the Cu2+. Cu(6bpyNO)Cl2 has a semiconductor characteristic. We also calculate the spin transport properties of Cu(6bpyNO)Cl2 connected with gold electrodes by using the density-functional theory combined with the nonequilibrium Green's function, and find it exhibits nearly 100% spin polarization and obvious negative differential resistance effect, which are explained by the calculated spin-polarized transmission spectra. These studies indicate that Cu(6bpyNO)Cl2 should be useful in organic spintronic applications.

  4. Electronic structure and conductivity of nanocomposite metal (Au,Ag,Cu,Mo)-containing amorphous carbon films

    SciTech Connect

    Endrino, Jose L.; Horwat, David; Gago, Raul; Andersson, Joakim; Liu, Y.S.; Guo, Jinghua; Anders, Andre

    2008-05-14

    In this work, we study the influence of the incorporation of different metals (Me = Au, Ag, Cu, Mo) on the electronic structure of amorphous carbon (a-C:Me) films. The films were produced at room temperature using a novel pulsed dual-cathode arc deposition technique. Compositional analysis was performed with secondary neutral mass spectroscopy whereas X-ray diffraction was used to identify the formation of metal nanoclusters in the carbon matrix. The metal content incorporated in the nanocomposite films induces a drastic increase in the conductivity, in parallel with a decrease in the band gap corrected from Urbach energy. The electronic structure as a function of the Me content has been monitored by x-ray absorption near edge structure (XANES) at the C K-edge. XANES showed that the C host matrix has a dominant graphitic character and that it is not affected significantly by the incorporation of metal impurities, except for the case of Mo, where the modifications in the lineshape spectra indicated the formation of a carbide phase. Subtle modifications of the spectral lineshape are discussed in terms of nanocomposite formation.

  5. Polarized nuclear target based on parahydrogen induced polarization

    SciTech Connect

    D. Budker, M.P. Ledbetter, S. Appelt, L.S. Bouchard, B. Wojtsekhowski

    2012-12-01

    We discuss a novel concept of a polarized nuclear target for accelerator fixed-target scattering experiments, which is based on parahydrogen induced polarization (PHIP). One may be able to reach a 33% free-proton polarization in the ethane molecule. The potential advantages of such a target include operation at zero magnetic field, fast ({approx}100 HZ) polarization oscillation (akin to polarization reversal), and operation with large intensity of an electron beam.

  6. Polarized nuclear target based on parahydrogen induced polarization

    NASA Astrophysics Data System (ADS)

    Budker, D.; Ledbetter, M. P.; Appelt, S.; Bouchard, L. S.; Wojtsekhowski, B.

    2012-12-01

    We discuss a novel concept of a polarized nuclear target for accelerator fixed-target scattering experiments, which is based on parahydrogen induced polarization (PHIP). One may be able to reach a 33% free-proton polarization in the ethane molecule. The potential advantages of such a target include operation at zero magnetic field, fast (˜100 Hz) polarization oscillation (akin to polarization reversal), and operation with large intensity of an electron beam.

  7. Valence band orbital polarization in III-V ferromagnetic semiconductors

    NASA Astrophysics Data System (ADS)

    Freeman, A. A.; Edmonds, K. W.; van der Laan, G.; Campion, R. P.; Rushforth, A. W.; Farley, N. R. S.; Johal, T. K.; Foxon, C. T.; Gallagher, B. L.; Rogalev, A.; Wilhelm, F.

    2008-02-01

    The element-specific technique of x-ray magnetic circular dichroism (XMCD) is used to directly determine the magnitude and character of the valence band orbital magnetic moments in (III,Mn)As ferromagnetic semiconductors. A distinct dichroism is observed at the AsK absorption edge, yielding an As4p orbital magnetic moment of around -0.1μB per valence band hole, which is strongly influenced by strain, indicating its crucial influence on the magnetic anisotropy. The dichroism at the GaK edge is much weaker. The K edge XMCD signals for Mn and As both have positive sign, which indicates the important contribution of Mn4p states to the MnK edge spectra.

  8. Distinct oxygen hole doping in different layers of Sr₂CuO4-δ/La₂CuO₄ superlattices

    DOE PAGESBeta

    Smadici, S.; Lee, J. C. T.; Rusydi, A.; Logvenov, G.; Bozovic, I.; Abbamonte, P.

    2012-03-28

    X-ray absorption in Sr₂CuO4-δ/La₂CuO₄ (SCO/LCO) superlattices shows a variable occupation with doping of a hole state different from holes doped for x≲xoptimal in bulk La2-xSrxCuO₄ and suggests that this hole state is on apical oxygen atoms and polarized in the a-b plane. Considering the surface reflectivity gives a good qualitative description of the line shapes of resonant soft x-ray scattering. The interference between superlattice and surface reflections was used to distinguish between scatterers in the SCO and the LCO layers, with the two hole states maximized in different layers of the superlattice.

  9. Polar low dynamics

    SciTech Connect

    Montgomery, M.T.; Farrell, B.F. )

    1992-12-15

    Polar lows are intense subsynoptic-scale cyclones that form over high-latitude oceans in association with deep cumulus convection and strong ambient baroclinicity. Recent observations indicate that polar lows are generally initiated by a nonaxisymmetric interaction between a surface disturbance and an upper-level mobile trough. Extant theories of polar low formation preclude study of such a process since they either constrain their models to be axisymmetric, or do not explicitly account for his transient interaction. In this work the physics of interacting upper- and lower-level potential vorticity structures is studied as an initial-value problem using a three-dimensional nonlinear geostrophic momentum model that incorporates moist processes and includes strong baroclinic dynamics. Model results illustrate the rapid formation of an intense small-scale cyclone whose structure is consistent with observations of mature polar lows. A conceptual model of polar low development is proposed. In the first stage of development, called induced self-development, a mobile upper trough initiates a rapid low-level spinup due to the enhanced omega response in a conditionally neutral baroclinic atmosphere. A secondary development follows, called diabatic destabilization, that is associated with the production of low-level potential vorticity by diabatic processes. Diabatic destabilization represents a simple mechanism for maintaining the intensity of polar lows until they reach land. In exceptional instances of negligible upper-level forcing, the latter may also describe the gradual intensification of small-scale cyclones in regions of sustained neutrality and surface baroclinicity. Ideas regarding polar low equilibration and prospects for a unified theory of arctic and midlatitude cyclones are discussed. 75 refs., 4 figs., 1 tab.

  10. Sequential Polarity-Reversing Circuit

    NASA Technical Reports Server (NTRS)

    Labaw, Clayton C.

    1994-01-01

    Proposed circuit reverses polarity of electric power supplied to bidirectional dc motor, reversible electro-mechanical actuator, or other device operating in direction depending on polarity. Circuit reverses polarity each time power turned on, without need for additional polarity-reversing or direction signals and circuitry to process them.

  11. Cylindrically polarized nondiffracting optical pulses

    NASA Astrophysics Data System (ADS)

    Ornigotti, Marco; Conti, Claudio; Szameit, Alexander

    2016-07-01

    We extend the concept of radially and azimuthally polarized optical beams to the polychromatic domain by introducing cylindrically polarized nondiffracting optical pulses. In particular, we discuss in detail the case of cylindrically polarized X-waves, both in the paraxial and nonparaxial regime. The explicit expressions for the electric and magnetic fields of cylindrically polarized X-waves are also reported.

  12. Cu - Sc (Copper - Scandium)

    NASA Astrophysics Data System (ADS)

    Predel, B.

    This document is part of Volume 12 Phase Equilibria, Crystallographic and Thermodynamic Data of Binary Alloys', Subvolume B 'B - Ba … Cu - Zr, Supplement to Subvolumes IV/5B, IV/5C and IV/5D', of Landolt-Börnstein - Group IV 'Physical Chemistry'.

  13. Cu - Ti (Copper - Titanium)

    NASA Astrophysics Data System (ADS)

    Predel, B.

    This document is part of Volume 12 Phase Equilibria, Crystallographic and Thermodynamic Data of Binary Alloys', Subvolume B 'B - Ba … Cu - Zr, Supplement to Subvolumes IV/5B, IV/5C and IV/5D', of Landolt-Börnstein - Group IV 'Physical Chemistry'.

  14. Cu - W (Copper - Tungsten)

    NASA Astrophysics Data System (ADS)

    Predel, B.

    This document is part of Volume 12 Phase Equilibria, Crystallographic and Thermodynamic Data of Binary Alloys', Subvolume B 'B - Ba … Cu - Zr, Supplement to Subvolumes IV/5B, IV/5C and IV/5D', of Landolt-Börnstein - Group IV 'Physical Chemistry'.

  15. Cu - Y (Copper - Yttrium)

    NASA Astrophysics Data System (ADS)

    Predel, B.

    This document is part of Volume 12 Phase Equilibria, Crystallographic and Thermodynamic Data of Binary Alloys', Subvolume B 'B - Ba … Cu - Zr, Supplement to Subvolumes IV/5B, IV/5C and IV/5D', of Landolt-Börnstein - Group IV 'Physical Chemistry'.

  16. Cu - Zr (Copper - Zirconium)

    NASA Astrophysics Data System (ADS)

    Predel, B.

    This document is part of Volume 12 Phase Equilibria, Crystallographic and Thermodynamic Data of Binary Alloys', Subvolume B 'B - Ba … Cu - Zr, Supplement to Subvolumes IV/5B, IV/5C and IV/5D', of Landolt-Börnstein - Group IV 'Physical Chemistry'.

  17. Cu - Te (Copper - Tellurium)

    NASA Astrophysics Data System (ADS)

    Predel, B.

    This document is part of Volume 12 Phase Equilibria, Crystallographic and Thermodynamic Data of Binary Alloys', Subvolume B 'B - Ba … Cu - Zr, Supplement to Subvolumes IV/5B, IV/5C and IV/5D', of Landolt-Börnstein - Group IV 'Physical Chemistry'.

  18. Cu - Si (Copper - Silicon)

    NASA Astrophysics Data System (ADS)

    Predel, B.

    This document is part of Volume 12 Phase Equilibria, Crystallographic and Thermodynamic Data of Binary Alloys', Subvolume B 'B - Ba … Cu - Zr, Supplement to Subvolumes IV/5B, IV/5C and IV/5D', of Landolt-Börnstein - Group IV 'Physical Chemistry'.

  19. Polarization twist in perovskite ferrielectrics

    PubMed Central

    Kitanaka, Yuuki; Hirano, Kiyotaka; Ogino, Motohiro; Noguchi, Yuji; Miyayama, Masaru; Moriyoshi, Chikako; Kuroiwa, Yoshihiro

    2016-01-01

    Because the functions of polar materials are governed primarily by their polarization response to external stimuli, the majority of studies have focused on controlling polar lattice distortions. In some perovskite oxides, polar distortions coexist with nonpolar tilts and rotations of oxygen octahedra. The interplay between nonpolar and polar instabilities appears to play a crucial role, raising the question of how to design materials by exploiting their coupling. Here, we introduce the concept of ‘polarization twist’, which offers enhanced control over piezoelectric responses in polar materials. Our experimental and theoretical studies provide direct evidence that a ferrielectric perovskite exhibits a large piezoelectric response because of extended polar distortion, accompanied by nonpolar octahedral rotations, as if twisted polarization relaxes under electric fields. The concept underlying the polarization twist opens new possibilities for developing alternative materials in bulk and thin-film forms. PMID:27586824

  20. Polarization twist in perovskite ferrielectrics.

    PubMed

    Kitanaka, Yuuki; Hirano, Kiyotaka; Ogino, Motohiro; Noguchi, Yuji; Miyayama, Masaru; Moriyoshi, Chikako; Kuroiwa, Yoshihiro

    2016-01-01

    Because the functions of polar materials are governed primarily by their polarization response to external stimuli, the majority of studies have focused on controlling polar lattice distortions. In some perovskite oxides, polar distortions coexist with nonpolar tilts and rotations of oxygen octahedra. The interplay between nonpolar and polar instabilities appears to play a crucial role, raising the question of how to design materials by exploiting their coupling. Here, we introduce the concept of 'polarization twist', which offers enhanced control over piezoelectric responses in polar materials. Our experimental and theoretical studies provide direct evidence that a ferrielectric perovskite exhibits a large piezoelectric response because of extended polar distortion, accompanied by nonpolar octahedral rotations, as if twisted polarization relaxes under electric fields. The concept underlying the polarization twist opens new possibilities for developing alternative materials in bulk and thin-film forms. PMID:27586824

  1. Polar low monitoring

    NASA Astrophysics Data System (ADS)

    Bobylev, Leonid; Zabolotskikh, Elizaveta; Mitnik, Leonid

    2010-05-01

    Polar lows are intense mesoscale atmospheric low pressure weather systems, developing poleward of the main baroclinic zone and associated with high surface wind speeds. Small size and short lifetime, sparse in-situ observations in the regions of their development complicate polar low study. Our knowledge of polar lows and mesocyclones has come almost entirely during the period of satellite remote sensing since, by virtue of their small horizontal scale, it was rarely possible to analyse these lows on conventional weather charts using only the data from the synoptic observing network. However, the effects of intense polar lows have been felt by coastal communities and seafarers since the earliest times. These weather systems are thought to be responsible for the loss of many small vessels over the centuries, although the nature of the storms was not understood and their arrival could not be predicted. The actuality of the polar low research is stipulated by their high destructive power: they are a threat to such businesses as oil and gas exploration, fisheries and shipping. They could worsen because of global warming: a shrinking of sea ice around the North Pole, which thawed to its record minimum in the summer of 2007, is likely to give rise to more powerful storms that form only over open water and can cause hurricane-strength winds. Therefore, study of polar lows, their timely detection, tracking and forecasting represents a challenge for today meteorology. Satellite passive microwave data, starting from Special Sensor Microwave Imager (SSM/I) onboard Defense Meteorological Satellite Program (DMSP) satellite, remain invaluable source of regularly available remotely sensed data to study polar lows. The sounding in this spectral range has several advantages in comparison with observations in visible and infrared ranges and Synthetic Aperture Radar (SAR) data: independence on day time and clouds, regularity and high temporal resolution in Polar Regions. Satellite

  2. Polarization of Starlight

    NASA Astrophysics Data System (ADS)

    Whittet, D. C. B.

    The polarization of starlight is universally attributed to directional extinction arising when dust grains along the line of sight are aligned in the presence of a magnetic field. This phenomenon provides a powerful tool for studying the optical properties of the dust (size, shape, refractive index) and for charting the galactic magnetic field. Current observational constraints at all wavelengths are consistent with a picture in which only the larger grains in the size range responsible for extinction are efficient polarizers. Small grains are much less well aligned and/or more isotropic in shape than large grains. The polarizing grains include silicates, but it is not clear whether they contain appreciable quantities of carbon. The degree of alignment is highly sensitive to ambient physical conditions as well as to particle size. The polarization efficiency per unit extinction declines with increasing density within dark clouds, hindering attempts to map the intracloud magnetic field. However, spectropolarimetric studies of interstellar ice absorption features seen in deeply embedded YSOs indicate that mantled grains within dense molecular clouds can be surprisingly efficient polarizers, suggesting that a qualitatively different alignment mechanism is operating compared with diffuse regions of the ISM. This talk will present a brief overview of key observations and their interpretation, highlight areas of uncertainty, and suggest avenues of future research. The physics of grain alignment is reviewed elsewhere in this meeting (see paper by Roberge).

  3. POLARBEAR CMB Polarization Experiment

    NASA Astrophysics Data System (ADS)

    Nishino, H.; Ade, P.; Akiba, Y.; Anthony, A.; Arnold, K.; Barron, D.; Boettger, D.; Borrill, J.; Chapmann, S.; Chinone, Y.; Dobbs, M. A.; Errard, J.; Fabbian, G.; Feng, C.; Flanigan, D.; Fuller, G.; Ghribi, A.; Grainger, W.; Halverson, N.; Hasegawa, M.; Hattori, K.; Hazumi, M.; Holzapfel, W. L.; Howard, J.; Hyland, P.; Inoue, Y.; Jaffe, A.; Jaehnig, G.; Kaneko, Y.; Katayama, N.; Keating, B.; Kermish, Z.; Kimura, N.; Kisner, T.; Lee, A. T.; Le Jeune, M.; Linder, E.; Lungu, M.; Matsuda, F.; Matsumura, T.; Miller, N. J.; Morii, H.; Moyerman, S.; Myers, M. J.; O'Brient, R.; Okamura, T.; Paar, H.; Peloton, J.; Quealy, E.; Reichardt, C. L.; Richards, P. L.; Ross, C.; Shimizu, A.; Shimon, M.; Shimmin, C.; Sholl, M.; Siritanasak, P.; Spieler, H.; Stebor, N.; Steinbach, B.; Stompor, R.; Suzuki, A.; Suzuki, J.; Tanaka, K.; Tomaru, T.; Tucker, C.; Yadav, A.; Zahn, O.

    POLARBEAR is a ground-based experiment in the Atacama desert in hile, measuring the polarization of the Cosmic Microwave Background (CMB) radiation. One of the science goals of POLARBEAR is to detect the B-mode polarization pattern of the CMB produced by primordial gravitational waves from the epoch of inflation. The detection of the B-mode polarization provides strong evidence for inflationary cosmological models. POLARBEAR is expected to reach a sensitivity to the tensor-to-scalar ratio r = 0.025 at 95% confidence level, using the data from two years of observation. With a beam size of 3.5 arcminutes, POLARBEAR is also sensitive to B-mode polarization signals at small-angular scales produced by weak gravitational lensing of large-scale structure. POLARBEAR is expected to provide a constraint on the sum of neutrino masses because of their effect on the large-scale structure. POLARBEAR was deployed in late 2011 and started observing in early 2012 at 150 GHz with an array of 1,274 polarization sensitive antenna-coupled Transition Edge Sensor (TES) bolometers. The current status of the POLARBEAR experiment is reported.

  4. Polarized protons at RHIC

    SciTech Connect

    Makdisi, Y.

    1992-10-01

    The approval for construction of the Relativistic Heavy Ion Collider (RHIC) provides a potential opportunity to collide polarized proton beams at energies up to 500 GeV in the center of mass and high luminosities approaching 2 {times} 10{sup 32}/cm{sup 2}/sec. This capability is enhanced by the fact that the AGS has already accelerated polarized protons and relies on the newly completed Accumulator/Booster for providing the required polarized proton intensity and a system of spin rotators (Siberian snakes) to retain the polarization. The RHIC Spin Collaboration was formed and submitted a Letter of Intent to construct this polarized collider capability and utilize its physics opportunities. In this presentation, I will discuss the plans to upgrade the AGS, the proposed layout of the RHIC siberian snakes, and timetables. The physics focus is the measurement of the spin dependent parton distributions with such accessible probes including high p(t) jets, direct photons, and Drell Yan. The attainable sensitivities and the progress that has been reached in defining the detector requirements will be outlined.

  5. Polarized protons at RHIC

    SciTech Connect

    Makdisi, Y.

    1992-01-01

    The approval for construction of the Relativistic Heavy Ion Collider (RHIC) provides a potential opportunity to collide polarized proton beams at energies up to 500 GeV in the center of mass and high luminosities approaching 2 {times} 10{sup 32}/cm{sup 2}/sec. This capability is enhanced by the fact that the AGS has already accelerated polarized protons and relies on the newly completed Accumulator/Booster for providing the required polarized proton intensity and a system of spin rotators (Siberian snakes) to retain the polarization. The RHIC Spin Collaboration was formed and submitted a Letter of Intent to construct this polarized collider capability and utilize its physics opportunities. In this presentation, I will discuss the plans to upgrade the AGS, the proposed layout of the RHIC siberian snakes, and timetables. The physics focus is the measurement of the spin dependent parton distributions with such accessible probes including high p(t) jets, direct photons, and Drell Yan. The attainable sensitivities and the progress that has been reached in defining the detector requirements will be outlined.

  6. A Compact Polarization Imager

    NASA Technical Reports Server (NTRS)

    Thompson, Karl E.; Rust, David M.; Chen, Hua

    1995-01-01

    A new type of image detector has been designed to analyze the polarization of light simultaneously at all picture elements (pixels) in a scene. The Integrated Dual Imaging Detector (IDID) consists of a polarizing beamsplitter bonded to a custom-designed charge-coupled device with signal-analysis circuitry, all integrated on a silicon chip. The IDID should simplify the design and operation of imaging polarimeters and spectroscopic imagers used, for example, in atmospheric and solar research. Other applications include environmental monitoring and robot vision. Innovations in the IDID include two interleaved 512 x 1024 pixel imaging arrays (one for each polarization plane), large dynamic range (well depth of 10(exp 6) electrons per pixel), simultaneous readout and display of both images at 10(exp 6) pixels per second, and on-chip analog signal processing to produce polarization maps in real time. When used with a lithium niobate Fabry-Perot etalon or other color filter that can encode spectral information as polarization, the IDID can reveal tiny differences between simultaneous images at two wavelengths.

  7. Artificial polarization components

    NASA Astrophysics Data System (ADS)

    Cescato, L.; Gluch, Ekkehard; Stork, Wilhelm; Streibl, Norbert

    1990-07-01

    High frequency surface relief structures are optically anisotropic and show interesting polarisation properties 1 . These properties can be used to produce polarizations components such as wave plates polarizers. polarizing beamsplitters etc. Our experimental results show that even gratings with relatively low spatial frequency ( periods A ) exhibit a strong phase retardation and can be used as quarter-wave plates. k INTRODUC11ON The artificial birefringence exhibited by ultrahigh frequency gratings of dielectric materials can be used to produce various polarization components2 . Such components have applications in integrated optics as well as in free space optics. In order to produce the high spatial frequencies complex processes such as electron-beam lithography and reactive ion etching are needed. We show in this paper that sinusoidal holographic gratings in photoresist exhibit also a strong phase ret even at relatively long periods. L EXPERIMENTAL MEASUREMENTS To obtain the phase retardation of a lower frequency ( period A ) grating a simple setup as used by Enger and 2 can be applied. In our case however there are three measurements necessary to obtain the phase retardation because transmission of the two perpendicularly polarized beams is different from each other. I GRATING PRODUCTION grating 2 3 4 5 6 7 8 9 period (pmj 0. 74 0. 74 0. 61 0. 54 0. 46 0. 32 0. 54 0. 54 0. 54 ne (sec) 60

  8. Raman analysis of monoclinic Cu2SnS3 thin films

    NASA Astrophysics Data System (ADS)

    Berg, Dominik M.; Djemour, Rabie; Gütay, Levent; Siebentritt, Susanne; Dale, Phillip J.; Fontane, Xavier; Izquierdo-Roca, Victor; Pérez-Rodriguez, Alejandro

    2012-05-01

    Secondary phases like Cu2SnS3 are major obstacles for kesterite thin film solar cell applications. We prepare Cu2SnS3 using identical annealing conditions as used for the kesterite films. By x-ray diffraction, the crystal structure of Cu2SnS3 was identified as monoclinic. Polarization-dependent Raman investigations allowed the identification of the dominant peaks at 290 cm-1 and 352 cm-1 with the main A' symmetry vibrational modes from the monoclinic Cu2SnS3 phase. Furthermore, micro-resolved Raman investigations revealed local variations in the spectra that are attributed to a secondary phase (possibly Cu2Sn3S7). This exemplifies the abilities of micro-resolved Raman measurements in the detection of secondary phases.

  9. Polarized beams at RHIC

    SciTech Connect

    Roser, T.

    1995-11-01

    The Relativistic Heavy Ion Collider (RHIC) at Brookhaven allows for the unique possibility of colliding two 250 GeV polarized proton beams at luminosities of up to 2 {times} 10{sup 32} cm{sup {minus}2} s{sup {minus}1}. A partial Siberian Snake in the AGS has recently been successfully tested and full Siberian Snakes, spin rotators, and polarimeters for RHIC are being developed to make the acceleration of polarized beams to 250 GeV possible. High energy polarized beam collisions will open up the unique physics opportunities of studying spin effects in hard processes, which will allow the study of the spin structure of the proton and also the verification of the many well documented expectations of spin effects in perturbative QCD and parity violation in W and Z production.

  10. A lunar polar expedition

    NASA Technical Reports Server (NTRS)

    Dowling, Richard; Staehle, Robert L.; Svitek, Tomas

    1992-01-01

    Advanced exploration and development in harsh environments require mastery of basic human survival skill. Expeditions into the lethal climates of Earth's polar regions offer useful lessons for tommorrow's lunar pioneers. In Arctic and Antarctic exploration, 'wintering over' was a crucial milestone. The ability to establish a supply base and survive months of polar cold and darkness made extensive travel and exploration possible. Because of the possibility of near-constant solar illumination, the lunar polar regions, unlike Earth's may offer the most hospitable site for habitation. The World Space Foundation is examining a scenario for establishing a five-person expeditionary team on the lunar north pole for one year. This paper is a status report on a point design addressing site selection, transportation, power, and life support requirements.

  11. South Polar Layers

    NASA Technical Reports Server (NTRS)

    2003-01-01

    MGS MOC Release No. MOC2-516, 17 October 2003

    This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows eroded, stair-stepped layers in the south polar region of Mars. These layers have been considered, for the past three decades, to consist of a mixture of dust and ice. The Mars Polar Lander (MPL) mission was designed to test this hypothesis. However, sadly, MPL was lost during descent in December 1999. This exposure of south polar layered material is located near 86.3oS, 187.7oW. The image covers an area 3 km (1.9 mi) wide and is illuminated by sunlight from the upper left.

  12. Polarized Light from Jupiter

    NASA Technical Reports Server (NTRS)

    2001-01-01

    These images taken through the wide angle camera near closest approach in the deep near-infrared methane band, combined with filters which sense electromagnetic radiation of orthogonal polarization, show that the light from the poles is polarized. That is, the poles appear bright in one image, and dark in the other. Polarized light is most readily scattered by aerosols. These images indicate that the aerosol particles at Jupiter's poles are small and likely consist of aggregates of even smaller particles, whereas the particles at the equator and covering the Great Red Spot are larger. Images like these will allow scientists to ascertain the distribution, size and shape of aerosols, and consequently, the distribution of heat, in Jupiter's atmosphere.

  13. South Polar Scarps

    NASA Technical Reports Server (NTRS)

    2003-01-01

    MGS MOC Release No. MOC2-438, 31 July 2003

    The terrain of the south polar residual ice cap, made up mostly of frozen carbon dioxide, has come to be known by many as 'swiss cheese terrain,' because many areas of the cap resemble slices of swiss cheese. However, not all of the south polar cap looks like a tasty lunch food. This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows a series of curving scarps formed by erosion and sublimation of carbon dioxide from the south polar cap. This area is located near 86.3oS, 51.2oW. The image is illuminated by sunlight from the upper left; the area is about 1.5 km (0.9 mi) wide.

  14. Diurnal polar motion

    NASA Technical Reports Server (NTRS)

    Mcclure, P.

    1973-01-01

    An analytical theory is developed to describe diurnal polar motion in the earth which arises as a forced response due to lunisolar torques and tidal deformation. Doodson's expansion of the tide generating potential is used to represent the lunisolar torques. Both the magnitudes and the rates of change of perturbations in the earth's inertia tensor are included in the dynamical equations for the polar motion so as to account for rotational and tidal deformation. It is found that in a deformable earth with Love's number k = 0.29, the angular momentum vector departs by as much as 20 cm from the rotation axis rather than remaining within 1 or 2 cm as it would in a rigid earth. This 20 cm separation is significant in the interpretation of submeter polar motion observations because it necessitates an additional coordinate transformation in order to remove what would otherwise be a 20 cm error source in the conversion between inertial and terrestrial reference systems.

  15. Spring polar ozone behavior

    NASA Technical Reports Server (NTRS)

    Aikin, Arthur C.

    1992-01-01

    Understanding of the springtime behavior of polar stratospheric ozone as of mid 1990 is summarized. Heterogeneous reactions on polar stratospheric clouds as hypothesis for ozone loss are considered and a simplified description of the behavior of Antarctic ozone in winter and spring is given. Evidence that the situation is more complicated than described by the theory is produced. Many unresolved scientific issues remain and some of the most important problems are identified. Ozone changes each spring since 1979 have clearly established for the first time that man made chlorine compounds influence stratospheric ozone. Long before important advances in satellite and in situ investigations, it was Dobson's decision to place a total ozone measuring spectrometer at Halley Bay in Antarctica during the International Geophysical Year and subsequent continuous monitoring which led to the discovery that ozone was being destroyed each spring by chlorine processed by polar stratospheric clouds.

  16. Electromigration induced Kirkendall void growth in Sn-3.5Ag/Cu solder joints

    SciTech Connect

    Jung, Yong; Yu, Jin

    2014-02-28

    Effects of electric current flow on the Kirkendall void formation at solder joints were investigated using Sn-3.5Ag/Cu joints specially designed to have localized nucleation of Kirkendall voids at the Cu{sub 3}Sn/Cu interface. Under the current density of 1 × 10{sup 4} A/cm{sup 2}, kinetics of Kirkendall void growth and intermetallic compound thickening were affected by the electromigration (EM), and both showed the polarity effect. Cu{sub 6}Sn{sub 5} showed a strong susceptibility to the polarity effect, while Cu{sub 3}Sn did not. The electromigration force induced additional tensile (or compressive) stress at the cathode (or anode), which accelerated (or decelerated) the void growth. From the measurements of the fraction of void at the Cu{sub 3}Sn/Cu interface on SEM micrographs and analysis of the kinetics of void growth, the magnitude of the local stress induced by EM was estimated to be 9 MPa at the anode and −7 MPa at the cathode.

  17. POLARIZED NEUTRONS IN RHIC

    SciTech Connect

    COURANT,E.D.

    1998-04-27

    There does not appear to be any obvious way to accelerate neutrons, polarized or otherwise, to high energies by themselves. To investigate the behavior of polarized neutrons the authors therefore have to obtain them by accelerating them as components of heavier nuclei, and then sorting out the contribution of the neutrons in the analysis of the reactions produced by the heavy ion beams. The best neutron carriers for this purpose are probably {sup 3}He nuclei and deuterons. A polarized deuteron is primarily a combination of a proton and a neutron with their spins pointing in the same direction; in the {sup 3}He nucleus the spins of the two protons are opposite and the net spin (and magnetic moment) is almost the same as that of a free neutron. Polarized ions other than protons may be accelerated, stored and collided in a ring such as RHIC provided the techniques proposed for polarized proton operation can be adapted (or replaced by other strategies) for these ions. To accelerate polarized particles in a ring, one must make provisions for overcoming the depolarizing resonances that occur at certain energies. These resonances arise when the spin tune (ratio of spin precession frequency to orbit frequency) resonates with a component present in the horizontal field. The horizontal field oscillates with the vertical motion of the particles (due to vertical focusing); its frequency spectrum is dominated by the vertical oscillation frequency and its modulation by the periodic structure of the accelerator ring. In addition, the magnet imperfections that distort the closed orbit vertically contain all integral Fourier harmonics of the orbit frequency.

  18. Nanoscale coherent intergrowthlike defects in a crystal of La1.9Ca1.1Cu2O6+δ made superconducting by high-pressure oxygen annealing

    DOE PAGESBeta

    Hu, Hefei; Zhu, Yimei; Shi, Xiaoya; Li, Qiang; Zhong, Ruidan; Schneeloch, John A.; Gu, Genda; Tranquada, John M.; Billinge, Simon J. L.

    2014-10-28

    Superconductivity with Tc = 53.5 K has been induced in a large La₁.₉Ca₁.₁Cu₂O₆ (La-2126) single crystal by annealing in a high partial-pressure of oxygen at 1200°C. Using transmission electron microscopy (TEM) techniques, we show that a secondary Ca-doped La₂CuO₄ (La-214) phase, not present in the as-grown crystal, appears as a coherent “intergrowth” as a consequence of the annealing. A corresponding secondary superconducting transition near 13 K is evident in the magnetization measurement. In this study, electron energy loss spectroscopy (EELS) reveals a pre-edge peak at the O K edge in the superconducting La-2126 phase, which is absent in the as-grownmore » crystal, confirming the hole-doping by interstitial oxygen.« less

  19. Growth structure and superconductivity of Bi1.7Bi0.3Sr2Ca2Cu3O10+δ ceramics synthesized from glass-crystal precursors processed in solar type ovens

    NASA Astrophysics Data System (ADS)

    Acrivos, J. V.; Gulamova, D. D.; Chigvinadze, J. G.; Loy, D.

    2010-03-01

    The growth structure as well as the superconductivity of Bi/Pb2223 alloys is reported. Periodic lattice distortions (PLD) along the ab plane diagonal, direction of superconducting transport at the transition temperature, Tc=107K are found to dominate the growth. Trransport induced by the PLD may be responsible for the sharp Tc transitions, and the bursts of frequency and Abrikosov oscillations observed above the transition temperature up to 150K. Chemical synthesis in a heliostat oven was followed by fast quenching of the melt and annealing at 840-850K, XRD near the Cu K-edge, and Tc measured by axial-torsional vibrations in transverse magnetic fields. Tc and phaase purity obtained by green solid state chemistry, in a solar spectrum, will be discussed.

  20. Microwave Frequency Polarizers

    NASA Technical Reports Server (NTRS)

    Ha, Vien The; Mirel, Paul; Kogut, Alan J.

    2013-01-01

    This article describes the fabrication and analysis of microwave frequency polarizing grids. The grids are designed to measure polarization from the cosmic microwave background. It is effective in the range of 500 to 1500 micron wavelength. It is cryogenic compatible and highly robust to high load impacts. Each grid is fabricated using an array of different assembly processes which vary in the types of tension mechanisms to the shape and size of the grids. We provide a comprehensive study on the analysis of the grids' wire heights, diameters, and spacing.