In situ time-resolved X-ray absorption near-edge structure (XANES) and X-ray diffraction (XRD) measurements are applied to track the phase transition processes of LixNi0.5Mn1.5O4, which is one of the most promising positive electrode materials for lithium ion batteries with its high redox potential
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. ...
TY - JOUR. T1 - An extended x-ray absorption fine structure spectroscopy investigation of cadmium sorption on cryptomelane (KMn8O16). AU - Randall, SR. AU - Sherman, DM. AU - Ragnarsdottir, KV. PY - 1998. Y1 - 1998. M3 - Article (Academic Journal). VL - 151. SP - 95. EP - 106. JO - Chemical Geology. JF - Chemical Geology. SN - 0009-2541. ER - ...
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TY - JOUR. T1 - Local structure of LiCoO 2 nanoparticles studied by Co K-edge x-ray absorption spectroscopy. AU - Maugeri, L.. AU - Iadecola, A.. AU - Joseph, B.. AU - Simonelli, L.. AU - Olivi, L.. AU - Okubo, M.. AU - Honma, I.. AU - Wadati, H.. AU - Mizokawa, T.. AU - Saini, N. L.. PY - 2012/8/22. Y1 - 2012/8/22. N2 - We have studied the local structure of LiCoO 2 nanoparticles by Co K-edge x-ray absorption spectroscopy as a function of particle size. Extended x-ray absorption fine structure data reveal substantial changes in the near neighbor distances and the associated mean square relative displacements with decreasing particle size. X-ray absorption near edge structure spectra show clear local geometrical changes with decreasing particle size, similar to those that appear in the charging (delithiation) process. The results suggest that the LiCoO 2 nanoparticles are characterized by a large atomic disorder confined to the Co-O octahedra, similar to the distortions generated during the ...
Heptacene was generated by surface-assisted didecarbonylation of an α-diketone precursor on a Ag(111) surface. Monitoring of the surface reaction and characterization of the adsorbed heptacene was performed with scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), near-edge X-ray absorption fine structure (NEXAFS) spectroscopy, and density functional theory (DFT) calculations. The surface-assisted formation of heptacene occurs around 460 K. Both the heptacene and the precursor molecules are oriented along the high-symmetry directions of the (111) surface and their molecular π systems face towards the substrate. The interaction with the Ag(111) substrate is not laterally uniform, but appears to be strongest on the central part of the molecule, in line with the expectations from Clars rule. In the STM images, heptacene shows a dumbbell shape, which may correspond to the substantial out-of-plane deformations of heptacene on Ag(111). As revealed by DFT, the center of the ...
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In situ X-ray absorption spectroscopy has afforded detailed structural and electronic characterization of a newly developed stabilized Pt-skin/PtCo alloy nanoparticle catalyst for CO-tolerant H2 oxidation. The X-ray absorption near-edge structure (XANES) results show the significant effects of H and CO adsorption o
Sulfur and iron concentrations in wood from three 17th century shipwrecks in the Baltic Sea, the Ghost wreck, the Crown and the Sword, were obtained by X-ray fluorescence (XRF) scanning. In near anaerobic environments symbiotic microorganisms degrade waterlogged wood, reduce sulfate and promote accumulation of low-valent sulfur compounds, as previously found for the famous wrecks of the Vasa and Mary Rose. Sulfur K-edge X-ray absorption near-edge structure (XANES) analyses of Ghost wreck wood show that organic thiols and disulfides dominate, together with elemental sulfur probably generated by sulfur-oxidizing Beggiatoa bacteria. Iron sulfides were not detected, consistent with the relatively low iron concentration in the wood. In a museum climate with high atmospheric humidity oxidation processes, especially of iron sulfides formed in the presence of corroding iron, may induce post-conservation wood degradation. Subject to more general confirmation by further analyses no severe conservation ...
The safety and feasibility of industrial electrochemical production of sodium chlorate, an important chemical in the pulp and paper industry, depend on the selectivity of the electrode processes. The cathodic reduction of anodic products is sufficiently suppressed in the current technology by the addition of chromium(VI) to the electrolyte, but due to the high toxicity of these compounds, alternative pathways are required to maintain high process efficiency. In this paper, we evaluate the electrochemical hydrogen evolution reaction kinetics and selectivity on thermally formed manganese oxide-coated titanium electrodes in hypochlorite and chlorate solutions. The morphology and phase composition of manganese oxide layers were varied via alteration of the annealing temperature during synthesis, as confirmed by scanning electron microscopy, X-ray diffraction, synchrotron radiation X-ray photoelectron spectroscopy, and near-edge X-ray absorption fine structure spectroscopy measurements. As shown in ...
Changes in bioavailability of phosphorus (P) during pedogenesis and ecosystem development have been shown for geogenic calcium phosphate (Ca-P). However, very little is known about long-term changes of biogenic Ca-P in soil. Long-term transformation characteristics of biogenic Ca-P were examined using anthropogenic soils along a chronosequence from centennial to millennial time scales. Phosphorus fractionation of Anthrosols resulted in overall consistency with the Walker and Syers model of geogenic Ca-P transformation during pedogenesis. The biogenic Ca-P (e.g., animal and fish bones) disappeared to 3% of total P within the first ca. 2,000 years of soil development. This change concurred with increases in P adsorbed on metal-oxides surfaces, organic P, and occluded P at different pedogenic time. Phosphorus K-edge X-ray absorption near-edge structure (XANES) spectroscopy revealed that the crystalline and therefore thermodynamically most stable biogenic Ca-P was transformed into more soluble forms ...
Bioaccessibility tests and mineralogical analyses were performed on arsenic-contaminated tailings and soils from gold mine districts of Nova Scotia, Canada, to examine the links between soil composition, mineralogy, and arsenic bioaccessibility. Arsenic bioaccessibility ranges from 0.1% to 49%. A weak correlation was observed between total and bioaccessible arsenic concentrations, and the arsenic bioaccessibility was not correlated with other elements. Bulk X-ray absorption near-edge structure analysis shows arsenic in these near-surface samples is mainly in the pentavalent form, indicating that most of the arsenopyrite (As1−) originally present in the tailings and soils has been oxidized during weathering reactions. Detailed mineralogical analyses of individual samples have identified up to seven arsenic species, the relative proportions of which appear to affect arsenic bioaccessibility. The highest arsenic bioaccessibility (up to 49%) is associated with the presence of calcium−iron ...
The valence states of Mn in mixed-valent layer and tunnel structure manganese dioxides (MnO2), usually referred to as phyllomanganates and tectomanganates, can be measured by X-ray absorption near-edge structure (XANES) spectroscopy with a precision and accuracy that are difficult to estimate owing to the paucity of well-characterized standards. A compilation of the Mn K-edge XANES spectra of most naturally occurring manganates, synthetic analogs of known structure and chemical composition, and pure-valence phase species is presented and made available as an open source. We intend this compilation to serve as a basis for the spectroscopic determination of the fractions of the Mn 2+, 3+, and 4+ valences in mixed-valent manganates and phase mixtures. The XANES derivatives of tectomanganates and phyllomanganates with no or little Mn3+ in the MnO2 layer exhibit intensities, shapes, and relative energy positions of the main features characteristics of a particular valence composition. For these ...
SEE PDF Full Length Article Writers: Ariadne C. Catto, Luís F. da Silva, Maria Inês B. Bernardi, Sandrine Bernardini, Khalifa Aguir, Elson Longo, and Valmor R. Mastelaro. Keywords: cobalt; gas sensor; ozone; XANES spectroscopy; XPS; zinc oxide. Abstract: A detailed study of the structural, surface, and gas-sensing properties of nanostructured CoxZn1-xO films is presented. X-ray diffraction (XRD) analysis revealed a decrease in the crystallization degree with increasing Co content. The X-ray absorption near-edge structure (XANES) and X-ray photoelectron spectroscopies (XPS) revealed that the Co2+ ions preferentially occupied the Zn2+ sites and that the oxygen vacancy concentration increased as the amount of cobalt increased. Electrical measurements showed that the Co dopants not only enhanced the sensor response at low ozone levels (ca. 42 ppb) but also led to a decrease in the operating temperature and improved selectivity. The enhancement in the gas-sensing properties was attributed to the ...
X-ray absorption spectroscopy (XAS). -EXAFS (extended X-ray absorption fine structure) for determination of metal site fine structures (metal-metal and metal-ligand distances at ~0.02 Å resolution, chemical nature and number of metal ligands).. -XANES (X-ray absorption near edge structure) for determination of metal oxidation state and site geometry. ...read more, for example here or here X-ray absorption linear dichroism spectroscopy (XALDS) for determination of orientations of interatomic vectors within, for example, the protein matrix, in crystals and partially oriented systems (such as proteins in biological membranes). ...read more, for example here or here. XAS under elevated gas pressure ...read more, for example here. X-ray emission spectroscopy (XES) for probing metal oxidation state, spin state, site geometry, electronic configuration, ligand structures, etc. ...read more, for example here or here. Time-resolved XAS/XES to follow structural changes and redox transitions at metal ...
Fujisawa et al. studied the electronic structures of CuFeS2 and CuAl0.9Fe0.1S2 by observing the phenomenon and analyzing the data of the states of Fe and Cu, and the valence-band of unit cell. The S 3p-Fe 3d bonding is found covalent base on the obvious tail of DAPT the XPS spectra of Cu 2p and S 2p [43]. Mikhlin et al. compared and analyzed the abraded chalcopyrite. and bornite in a vacuum chamber by X-ray absorption near-edge structure (XALES) to exam the electronic structure [44]. The result showed the Cu L3-edge had a strong pre-edge peak and a small post-edge peak, the Fe L2,3-edge energy was consistent with the Fe2+ oxidation state and S L-edge spectra was clearly observed [44]. It is widely accepted that the Neel temperature of CuFeS2 is extremely high, at 823 K [45] and [46]. Edelbro et al. proposed that the energy bands (−13.8 to 12.5 eV), which is lower than Fermi level, selleck chemical is similar to that of sphalerite. Woolley et al. demonstrated that, at temperature above 50 K and ...
Polarization-dependent grazing incidence X-ray Absorption Spectroscopy (XAS) measurements were completed on oriented single crystals of magnesite [MgCO3] and brucite [Mg(OH)2] reacted with aqueous uranyl chloride above and below the solubility boundaries of schoepite (500, 50, and 5 ppm) at pH 8.3 and at ambient (PCO2 = 10-3.5) or reduced partial pressures of carbon dioxide (PCO2 = 10-4.5). X-ray Absorption Near Edge Structure (XANES) spectra show a striking polarization dependence ( = 0° and  = 90° relative to the polarization plane of the incident beam) and consistently demonstrated that the uranyl molecule was preferentially oriented with its Oaxial=U(VI)=Oaxial linkage at high angles (60-80º) to both magnesite () and brucite (0001). Extended X-ray Absorption Fine Structure (EXAFS) analysis shows that the "effective" number of U(VI) axial oxygens is the most strongly affected fitting parameter as a function of polarization. Furthermore, axial tilt in the surface thin films (thickness ...
TY - JOUR. T1 - Local fivefold symmetry in liquid and undercooled Ni probed by x-ray absorption spectroscopy and computer simulations. AU - Di Cicco, A.. AU - Iesari, F.. AU - De Panfilis, S.. AU - Celino, M.. AU - Giusepponi, S.. AU - Filipponi, A.. PY - 2014/2/12. Y1 - 2014/2/12. N2 - Presence and significance of fivefold configurations in liquid metals are investigated by combining x-ray absorption spectroscopy and computer simulations (molecular dynamics and reverse Monte Carlo) in liquid and undercooled liquid nickel. We show that icosahedral short-range ordering (ISRO), probed by common-neighbor (CNA) and spherical invariant (Wî6) analysis, involves a limited fraction (14-18% in undercooled nickel for different structural models) of local atomic configurations. The emerging picture for the liquid structure is that of a mixture of nearly icosahedral structures embedded in a disordered network mainly composed of fragments of highly distorted icosahedra (40-45% of the total), structures ...
2010.12.13 The reseach article" Noradrenaline and a Thiol Analogue on Gold Surfaces: an IRAS, XPS and NEXAFS Study. " was published in Journal of Physical Chemistry C. Self-assembled monolayers and multilayers of a noradrenaline analogue (Nor-Pt) on gold substrates as well as multilayers of noradrenaline have been investigated by means of the molecular orientation, the molecule−surface interaction, the molecular composition and the functional group availability for further biointeraction processes, using X-ray photoelectron spectroscopy (XPS), infrared reflection−absorption spectroscopy (IRAS), and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy ...
Macromolecular arrays containing Zn-diethynylporphyrin coordinated to platinum tethers were studied using near-edge X-ray absorption fine structure (NEXAFS) spectroscopy at the N K-edge. Porphin (Pf), 2,8,12,18-tetraethyl-5,15-diethynyl-3,7,13,17-tetramethylporphyrin (PfNH) and 2,8,12,18-tetraethyl-5,15-diethynyl-3,7,13,17-tetramethylporphyrinatozinc(II) (Zn-Pf2), have been taken as experimental models. The resonances assignment is supported by static-exchange (STEX) calculations for the porphin (Pf) and Zn-porphin (Zn-Pf1) molecules. By calculation, four pi* resonances occur for porphin (Pf) and two for Zn-Pf1. Experimentally we detect four resonances for porphin and PfNH, and two for the Zn-complexed ones. They can be assigned to core excitations to a couple of energy split pi* orbitals for each not equivalent N atom. Our calculations justify the observed low pi* intensity as due to an extended delocalization of the pi* orbitals. The NEXAFS investigations on platinum complex/Zn-porphyrinato ...
We have calculated the N 1s near-edge X-ray absorption fine structure (NEXAFS) spectra of nitrogen-doped monolayer graphene (NG) using density functional theory (DFT) with the equivalent core hole approximation. The hexavacancy (6V) defect and its dependence on the nitrogen-doping concentration have been analyzed in detail via both N 1s -, pi* and N 1s -, sigma* transitions. The NEXAFS spectra are sensitive to the doping concentration of N in the pi* region: diluted doping weakens the main pi* peak and smears the oscillations in this region. The vacancy defect leads to a red-shift in both the pi and sigma spectra. A pyridinic nitrogen at the 6V defect center exhibits a sharp pi* peak at 398.4 eV, which agrees well with the experimental pre-edge structure at 398.6 eV. The sigma* peak is split in two, which can serve as the fingerprint to reveal the nature of the defect. A structural change from pyridinic to pyrrolic NG results in a distinctive difference in the spectral shape. The ground-state ...
Controlling molecular orientation is of great importance in organic thin films due to the fact that the fundamental properties of functional nanomaterials depend on molecular orientation at the nanoscale. However, controlling molecular orientation cannot be achieved without having an extensive understanding about the controlling factors in the organic film growth processes. Most previous studies have been devoted to monolayer structures. The structure of multilayer films has not been well investigated. This study was performed using a phenomenological approach, in which the morphology and orientation of n-alkane thin films were studied as a function of substrate identity, interface treatment, substrate temperature and deposition rate. The experimental techniques that were used include IR-spectroscopy, polarized optical microscopy, and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy and X-ray microscopy. The kinetic and thermodynamic factors that govern the orientation of organic ...
High-resolution C 1s near-edge x-ray absorption fine structure (NEXAFS) spectra of naphthalene are investigated. By comparing the spectral signatures of condensed naphthalene molecules with those of naphthalene in the gas phase, we are able to unambiguously identify spectral features which are affected by the intermolecular interactions in the condensed phase. With the help of calculations using time-dependent density-functional theory and the second-order algebraic-diagrammatic construction scheme for the polarization propagator, resonances in the relevant energy range can be assigned to valence and Rydberg-like excitations. Thus, we obtain a more detailed identification of NEXAFS resonances beyond the present literature.. ...
The increasing uses of rare-earth-doped upconversion nanoparticles (UCNPs) have obviously caused many concerns about their potential toxicology on live organisms. In addition, the UCNPs can be released into the environment, then transported into edible crop plants, and finally entered into food chain. Here, the soybean is chosen as a model plant to study the subchronic phytotoxicity, translocation, and biotransformation of NaYF4 UCNPs. The incubation with UCNPs at a relative low concentration of 10 mu g mL(-1) leads to growth promotion for the roots and stems, while concentration exceeding 50 mu g mL(-1) brings concentration-dependent inhibition. Upconversion luminescence imaging and scanning electron microscope characterization show that the UCNPs can be absorbed by roots and parts of the adsorbed UCNPs are then transported through vessels to stems and leaves. The near-edge X-ray absorption fine structure spectra reveal that the adsorbed NaYF4 nanoparticles are relatively stable during a 10 d ...
The electronic properties of Au crystal and nano Au have been investigated by theory and experiment. Molecularly capped nano-Au was synthesized using the two-phase method. Au nano-particles have been characterized by X-Ray Diffraction (XRD) and Transmission Electron Microscopy (TEM). They retain the fcc crystal structure. Their sizes have been determined to be in a range from 5.5 nm to 1.7 nm. The L3 X-ray Absorption Near Edge Structure (XANES) of nano-Au and Au foil have been recorded using synchrotron radiation, and examined by theoretical calculation [1] based on the first principles [2,3]. Both theory and experiment show that the nano-Au particles have essentially all the Au L3 XANES features of bulk Au in the near edge region with less pronounced resonance peaks. It is also shown that nano Au exhibits lower 4f binding energy than bulk Au in good agreement with quantum confined Au systems reported previously [3,4].
A broad range of chemical reactions are triggered by the absorption of light. Examples include photosynthesis and charge transfer in semiconductors and molecules. Electronic dynamics which evolve on the few femtosecond to attosecond timescale are expected to play an important role in these processes. We aim to investigate these dynamics with transient X-ray absorption near edge structure (XANES) spectroscopy. XANES spectroscopy uses resonant excitation of particular atoms in a molecule to provide a highly localised probe of electronic structure. By employing attosecond soft x-ray pulses generated via high harmonic generation for XANES spectroscopy this atomic scale spatial resolution can in principle be combined with the attosecond temporal resolution required for tracking electronic dynamics. I shall present development of a beamline for transient XANES spectroscopy and progress towards visible pump, soft x-ray probe experiments in the organic polymer poly(hexylthiophene ...
Micro-X-ray absorption near-edge structure (μ-XANES) spectroscopy has been used by several recent studies to determine the oxidation state and coordination of iron in silicate glasses. Here, we present new results from Fe μ-XANES analyses on a set of 19 Fe-bearing felsic glasses and 9 basaltic glasses with known, independently determined, iron oxidation state. Some of these glasses were measured previously via Fe XANES (7 rhyolitic, 9 basaltic glasses; Cottrell et al. 2009), while most felsic reference glasses (12) were analyzed for the first time. The main purpose of this study was to understand how small changes in glass composition, especially at the evolved end of silicate melt compositions occurring in nature, may affect a calibration of the Fe μ-XANES method.. We performed Fe μ-XANES analyses at different synchrotron radiation sources [Advanced Photon Source (APS), Argonne, U.S.A., and Angströmquelle Karlsruhe (ANKA), Germany] and compared our results to existing calibrations obtained ...
X-ray Absorption Spectroscopy (XAS) is a technique to analyze the elemental properties of a material. It can also allow one to understand the chemistry on a molecular level and whether the material is amorphous or crystalline. XAS has dignificant advantages compared to other methods since it is element specific, no high vacuum required, and no specific sample preparation is required. The XAS experiments can be either static (before and/or after reactions) or dynamic (in situ reactions) while the materials can be in solid, liquid, or gaseous states. ...
Ecosystems throughout the world are experiencing significant biogeochemical perturbation from anthropogenic activities. As one example, manganese (Mn) is enriched in surface soils at the Susquehanna Shale Hills Critical Zone Observatory (SSHCZO) in Pennsylvania due to past atmospheric inputs from industrial sources. At the SSHCZO, large quantities of Mn that are leached from soil components into solution are taken up by vegetation each year; as a result, only relatively small quantities of Mn are transferred from hillslopes into the stream. Here, we combined mass balance models at the containerized seedling (mesocosm) and pedon-scales with synchrotron-source spectroscopies (X-ray fluorescence and X-ray absorption near edge structure) to examine Mn geochemistry in the soil-plant system and the impact of vegetation on Mn transport in forested catchments.. Manganese uptake into vegetation exceeded Mn losses in soil leachate, and net Mn loss from soils decreased in the presence of vegetation due to ...
We propose an asymmetric bilayer structure in which the magnetic remanence (MR) is controlled by the in-plane strain of the top NiFe2O4 (NFO) layer epitaxially constrained by the bottom Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) substrate. In this asymmetric structure, an electric-field-induced giant piezoelectric strain from the bottom PMN-PT layer is effectively transferred to the top NFO layer. We have shown that the room-temperature magnetic remanence (MR) of the 100-nm-thick NFO layer is enhanced by 46% when an electric-field-induced in-plane compressive strain is about -0.1%. Synchrotron x-ray absorption near edge structure study supports a scenario of the cation-charge redistribution between Ni2+ and Fe3+ ions under the condition of an electric-field-induced in-plane compressive strain ...
Copper powder was introduced into the lithium sulfur battery system to capture intermediate polysulfides and Cu xS (x = 1 or 2) species was generated depending on the chain length of polysulfides. This phenomenon was verified by X-ray absorption near edge structure technique. The results indicated that copper can be oxidized to CuS by Li 2S x (x ≥ 6), and a mixture of Cu 2S and CuS was obtained when x ranges from 3 to 6. While Cu 2S is eventually formed in the presence of Li 2S 3. After several cycles activation, the polysulfide-shuttle effect and self-discharge phenomenon which hinder the application of lithium sulfur batteries are found nearly eliminated Further experiments demonstrated that in the case of Cu 2S generation, a high specific sulfur capacity of 1300 mAh g -1 could be delivered, corresponding to 77.6% sulfur utilization, while the Coulombic efficiency approximates around 100%. As a result, self-discharge experiment further demonstrated that polysulfides almost disappear in the ...
Hexane selenol (CH3(CH2)(5)SeH) was adsorbed from gas phase in ultra-high vacuum on polycrystalline Cu and studied with synchrotron radiation based photoelectron spectroscopy (PES) and Near edge X-ray absorption fine structure spectroscopy (NEXAFS). Adsorption was done on a bare copper surface at room temperature (RT), on a thin oxide on Cu at room temperature, and on a thin layer of water on Cu at 140 K.. ...
A means for intracavity sum frequency generation is described in which a er operates simultaneously, cw, at two wavelengths where the net gain at one wavelength is substantially lower than that at the other. The optical alignment of the resonator provides a region where both fundamental wavelengths are overlapped, and another region where both feedback paths are spatially distinct. An active feedback mirror is located in the path of the lower net gain laser transition to provide optical amplification at that wavelength. The laser resonator further contains a sum frequency generating crystal for intracavity sum frequency generation of the two fundamental wavelengths. The sum frequency generating crystal is placed near a laser resonator cavity mode waist in the region where both wavelengths are spatially superimposed, producing the sum frequency of the two wavelengths. An intracavity polarization rotator provides the appropriate orientation of the polarization of the two fundamental wavelengths in the
Very small, thioglycerol (TG)-capped CdS nanoparticles were synthesized by a wet chemical technique and investigated in the framework of this thesis. Also glutathione-capped particles were investigated for a comparison of the capping agents. High-resolution photoelectron spectroscopy using high-brilliance synchrotron radiation was applied as the major tool for the characterization of these particles. Additionally, the particles were investigated with UV-VIS absorption spectroscopy, XPS using a laboratory source, valence band photoemission spectroscopy (VBPES), near-edge x-ray absorption spectroscopy (NEXAFS), and micro-Raman spectroscopy to address various aspects of the particles. In the beginning, an overview on size quantization effects is given to create a theoretical background behind the work presented in this thesis. Furthermore, an overview of various conventional techniques for size determination is presented. Exact information about size, shape and size distribution of nanoparticles is ...
As shown in Figure 122, the subnanometric Pt species are finely dispersed in the MCM-22 crystallites. The size of the Pt species and their location in the crystallites was determined with the help of aberration-corrected electron microscopy. The Pt atoms and clusters are located both in the surface "cups" of MCM-22 and within the zeolite framework. In particular, a large proportion of the subnanometric Pt species are located in the internal space of the structure.. A [email protected] sample has been studied at beamline BM23 using X-ray absorption spectroscopy (XAS) to examine the local environment of Pt and to estimate the coordination number of Pt species. The Fourier transform of extended X-ray absorption fine structure (EXAFS) spectra of [email protected] and the Pt and PtO2 reference are shown in Figure 123a. Considering the first shell, the [email protected] spectrum is dominated by a peak centred around 2.65 Å with a smaller contribution at 2.08 Å (both distances are not phase corrected). Comparing with ...
The site-specific magnetic properties of thin films of the Heusler compound Mn2RuxGa, 0.6 ,x, 1.0, are studied using x-ray absorption and dichroism spectroscopy. There is evidence of half metallicity up to x = 0.7, and compensation of the Mn 4a and 4c moments in this range, leading to a zero-moment half metal. We also also discuss the effect of substrate-induced strain on the magnetic properties. By tuning the biaxial strain, simultaneous perfect magnetic compensation and half-metallic character is achievable at, below, or above room temperature ...
The use of hydrothermal methods has allowed the synthesis of a new silver copper mixed oxide, Ag2CuMnO4, the first example of a quaternary oxide containing both elements. It crystallizes with the delafossite 3R structure, thus being the first delafossite to contain both Ag and Cu. Synthesis conditions affect the final particle size (30-500 nm). Powder X-ray diffraction Rietveld refinement indicates a trigonal structure and cell parameters and , where Cu and Mn are disordered within the octahedral B positions in the plane and linearly coordinated Ag occupies de A position between layers. X-ray absorption near edge spectroscopy (XANES) for copper and manganese, and XPS for silver evidence +2, +4, and +1 oxidation states. The microstructure consists of layered particles that may form large twins showing 5 nm nanodomains. Finally, magnetic measurements reveal the existence of ferromagnetic coupling yielding in-plane moments that align antiferromagnetically at lower temperatures. The singularity of ...
To explore the capability of basaltic glass to support the growth of chemosynthetic microorganisms, complementary in situ and in vitro colonization experiments were performed. Microbial colonizers containing synthetic tholeitic basaltic glasses, either enriched in reduced or oxidized iron, were deployed off-axis from the Mid Atlantic Ridge on surface sediments of the abyssal plain (35°N; 29°W). In situ microbial colonization was assessed by sequencing of the 16S rRNA gene and basaltic glass alteration was characterized using Scanning Electron Microscopy, micro-X-ray Absorption Near Edge Structure at the Fe-K-edge and Raman microspectroscopy. The colonized surface of the reduced basaltic glass was covered by a rind of alteration made of iron-oxides trapped in a palagonite-like structure with thicknesses up to 150 μm. The relative abundance of the associated microbial community was dominated (39% of all reads) by a single operational taxonomic unit (OTU) that shared 92% identity with the iron-oxidizer
This work reports on the structure of Fe containing, Co2-based Heusler compounds that are suitable for magnetoelectronic applications. The compounds Co2FeZ where Z=Al, Si, Ga, and Ge were investigated using the x-ray diffraction XRD and extended x-ray absorption fine structure EXAFS techniques. Using XRD, it was shown conclusively that Co2FeAl crystallizes in the B2 structure whereas Co2FeSi crystallizes in the L21 structure. For compounds containing Ga or Ge, the XRD technique cannot be used to easily distinguish between the two structures. For this reason, the EXAFS technique was used to elucidate the structure of these two compounds. Analysis of the EXAFS data indicated that both compounds crystallize in the L21 structure ...
Highly dense CaMn1-xRexO3 (0 ≤ x ≤ 0.04) samples were prepared by solid-state synthesis. The effect of Re doping was assessed by the characterisation of crystal structure, oxygen content, and electrical and thermal transport properties. The oxidation state of the substituted Re was determined by X-ray absorption near edge spectra to be Re(7+), and led to expansion of the lattice and an increase in electron carrier concentration due to the formation of Mn(3+). The thermal behaviour of the electrical conductivity and the thermopower over a wide temperature range allowed identification of different conduction mechanisms: (1) below 110 K, 3D variable range hopping, (2) between 110 and 650 K, small polaron transport, and (3) above 650 K, activation of carriers over a mobility edge ...
Fontenot EB, DiTusa SF, Kato N, Olivier DM, Dale R, Lin WY, Chiou TJ, Macnaughtan MA, Smith AP. Increased phosphate transport of Arabidopsis thaliana Pht1;1 by site-directed mutagenesis of tyrosine 312 may be attributed to the disruption of homomeric interactions. Plant Cell &Environ. In press. Smith AP, Fontenot EB, Zahraeifard S, and DiTusa SF. Molecular components that drive phosphorus-remobilization during leaf senescence. In: Phosphorus metabolism in plants. Plaxton W and Lambers H eds. Wiley Blackwell. In press. Smith AP (2013) Systemic signaling in the maintenance of phosphate homeostasis. In: Long-distance systemic signaling and communication in plants. Baluška F ed. Springer Berlin Heidelberg, 149-166. Bovenkamp GL, Prange A, Schumacher W, Ham K, Smith AP, and Hormes J. (2013) Lead uptake in diverse plant families: a study applying X-ray Absorption Near Edge Spectroscopy. Env Sci & Tech. 47, 4375-82. LeBlanc MS, McKinney EC, Meagher RB, and Smith AP. (2013) Hijacking membrane ...
The predominant forms of arsenic (As) in anoxic and oxic environments are As(III) and As(V), respectively, and the fate of these forms is influenced by interactions with mineral surfaces and organic matter (OM). Interactions between As(V) and OM are believed to occur mainly via iron(Fe)-bridges in ternary Fe-arsenate complexes, but direct evidence for these interactions are scarce. Furthermore, since the speciation of Fe in the presence of organic matter varies as a function of pH and Fe concentration, a central question is how different chemical conditions will affect the As-Fe-OM interactions. In order to answer this, the As(V)-Fe(III)-OM system have been studied under a large range of experimental conditions (6485-67,243 ppm Fe(III) and Fe(III):As(V) ratios of 0.5-20 at pH 3-7), with Suwannee River natural organic matter and Suwannee River fulvic acid as sources of OM, using Fe and As K-edge X-ray absorption spectroscopy (XAS), infrared (IR) spectroscopy and chemical equilibrium modeling. Our ...
Time-resolved XAS is available in either film mode (time resolution down to few microseconds) or pump/probe mode.. Single bunch aquisition is available for specific applications. Large-spot endstation: beam size from 10 x 100 μm to 200 x 200 μm (HxV).. Small-spot endstation: beam size from 3 x 3 μm to 10 x 100 μm (HxV).. ...
Scientists at Stanford and in Sweden used x-ray absorption spectroscopy to study the chemistry of decay of the wooden beams of the Vasa. Photo: Hans Hammarskiöld/The Vasa Museum. The conservators called an emergency meeting with colleagues and chemists from Sweden, Denmark and Australia to seek solutions to a problem that threatens the Vasa and other famous finds including the Skuldelev Viking ships, the Bremen Cog, the Mary Rose and the Batavia.. Collaborators in Sweden and at Stanford have analyzed the chemistry of wood decay in the Vasa using a new technique -- x-ray absorption spectroscopy. It employs high-intensity synchrotron beams, produced when electrons accelerate around rings, to make chemical "fingerprints" that identify different oxidation states in a sample. Their findings, published in the Feb. 21 issue of Nature, may help conservators worldwide preserve wooden artifacts retrieved from the deep, many of which are displayed in museums.. The findings explain "the important role that ...
Harpham MR, Nguyen SC, Hou Z, Grossman JC, Harris CB, Mara MW, Stickrath AB, Kanai Y, Kolpak AM, Lee D, Liu DJ, Lomont JP, Moth-Poulsen K, Vinokurov N, Chen LX, Vollhardt KP. X-ray transient absorption and picosecond IR spectroscopy of fulvalene(tetracarbonyl)diruthenium on photoexcitation. Angew Chem Int Ed Engl. 2012 Jul 27; 51(31):7692-6 ...
Blackburn, N. J., Hasnain, S. S., Binsted, N., Diakun, G. P., Garner, C. D. & Knowles, P. F. (1984) An extended X-ray-absorption-fine-structure study on bovine erythrocyte superoxide dismutase in aqueous solution. Direct evidence for three-coordinate copper(I) in reduced enzyme. Biochem. J. 219, 985-990 ...
We have recently completed studies using X-ray Absorption Spectroscopy (XAS) on the B18 beamline provided by the Diamond Light Source Facility. Here we spent an exciting 24 hours taking in-situ measurements to understand the behaviour the catalyst.. By analysing the X-ray signal we were able to determine the changes in chemical form of the active species of our customers catalyst over a range of temperatures at which the catalyst would normally operate.. For more information on this particular case study and how we may be able to help you with a similar problem please see the case study.. ...
A combination of hard X-ray photoelectron spectroscopy (HAXPES) and near edge X-ray absorption fine structure (NEXAFS) are here used to investigate the presence and chemical state of crossover manganese deposited on Li-ion battery anodes. The synchrotron- based experimental techniques?using HAXPES and NEXAFS analysis on the same sample in one analysis chamber?enabled us to acquire complementary sets of information. The Mn crossover and its influence on the anode interfacial chemistry has been a topic of controversy in the literature. Cells comprising lithium manganese oxide (LiMn2O4, LMO) cathodes and lithium titanate (Li4Ti5O12, LTO) anodes were investigated using LP40 (1MLiPF6, EC:DEC 1:1) electrolyte. LTO electrodes at lithiated, delithiated, and open circuit voltage (OCV-stored) states were analyzed to investigate the potential dependency of the manganese oxidation state. It was primarily found that a solid surface layer was formed on the LTO electrode and that this layer contains deposited ...
Atomistic computer modelling and Extended X-ray Absorption Fine Structure (EXAFS) measurements were used to study the mode of solution and defects in Sr2+-doped La2O3. The computer modelling indicates that the most energetically favourable mode of solution is cation substitution with the formation of charge-compensating anion vacancies. This is confirmed by the EXAFS measurements. The EXAFS results also indicate that at high levels of Sr2+ there is the formation of the defect clusters with impurities and anion vacancies on adjacent sites, although the precise structure of the clusters could not be unambiguously identified.. ...
The fate of iron (Fe) in freshwaters is largely influenced by chemical interactions with natural organic matter (NOM). However, the knowledge about the molecular structure of the Fe species formed in association with aquatic NOM is still limited. In this work we have studied the interactions between Fe(III) and aquatic organic matter from the Suwannee River at a range of pH values and Fe concentrations (6489-55,659 μg g− 1 dry weight, pH 3.0-6.8) by means of extended X-ray absorption fine structure (EXAFS) and infrared (IR) spectroscopy. Our results showed that Fe(III) formed stable complexes with aquatic NOM, and that carboxylates were the predominant functional group involved in these interactions. At low Fe concentrations (6489-11,953 μg g− 1; pH 3.0-6.7) mononuclear Fe(III)-NOM complexes dominated the speciation while at higher pH values and Fe concentrations (~ 23,000 μg g− 1 pH 5.0-6.2 and 55,659 μg g− 1 pH 3.1-6.7) we detected mixtures of mononuclear Fe(III)-NOM complexes and ...