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While intra-atomic f–d hybridization is expected, experimental confirmation of f–d hybridization in the photoemission final state leading to 4f band structure has been limited to 5f systems and compound systems with very shallow 4f levels. We demonstrate that core 4f states can contribute to the valence band structure in a wide band gap dielectric, in this case HfO 2 in the photoemission final state. In spite of the complications of sample charging, we find evidence of symmetry in the shallow 4f levels and wave vector dependent band dispersion, the latter consistent with the crystal structure of HfO 2 .

Composite Cr-containing hydrogenated amorphous diamond-like carbon (Cr-DLC) films were synthesized by a hybrid PVD/CVD plasma-assisted deposition process. In a recent study, it was found that Cr-DLC films with 1.5 at.%), Cr is present as nanoparticles (

The mineralogy of a soil susceptible to sulfate attack was investigated in detail, with particular attention paid to the sulfate and clay minerals. The soil from north Louisiana suffered sulfate attack when stabilized by Type I portland cement. A number of analytical techniques, such as x-ray diffractometry, thermal analysis (thermogravimetry and differential scanning calorimetry), Fourier transform infrared spectroscopy, scanning electron microscopy, and x-ray absorption near edge structure (XANES), were used. Thermogravimetry showed that 7.8% gypsum (CaSO\U4\N.2H\U2\NO) was present in the soil from the average of four samples. Quantitative x-ray diffractometry yielded a value of 12.9±1.1% for one soil. XANES indicated that all the sulfur in the soil was present as sulfate phases. Gypsum was found in all size fractions. The clay minerals, kaolinite (highest concentration), illite (intermediate concentration), and smectite (lowest concentration) could be identified with certainty only after the clay fraction was concentrated by removal of gypsum by acid dissolution followed by centrifugation. Kaolinite (5%) could be easily quantified by thermogravimetry but not other clay minerals.

X-ray absorption near-edge fine structure (XANES) analyses are carried out in order to study the local structure around a Cl atom of chloronaphthalene dissolved in the CH 3 I solution near the boiling point by use of full multiple scattering calculations. We find that less than six CH 3 I molecules surround the Cl atom at distance of about 4.73 A, which is larger than the sum of the van der Waals radii. CH 3 I molecules point their CI → vectors to the Cl atom. Other important information is the relative thermal fluctuation (Debye–Waller factor) between Cl and CH 3 I, which is quite large, ∼0.71 A. These features are essential to describe the intermolecular correlation in liquids, and are similar to those of supercritical fluids (SCFs).

Changes in the composition of embedded pyrite (FeS 2 ) particle electrodes in 1 M LiClO 4 propylene carbonate solutions as a function of the applied potential have been examined in situ by S K-edge fluorescence X-ray absorption near edge structure (XANES), using a specially designed cell that minimizes attenuation of low energy X-rays. Pyrite electrodes that had been scanned from 3.0 V versus Li/Li + , i.e. close to the open circuit voltage, down to 1.0 V (fully discharged state, i.e. 4e − -reduction) and then half recharged (2e − -reoxidation) by scanning the potential in the positive direction up to 2.2 V versus Li/Li + , revealed features consistent with the presence of Li 2 FeS 2 , in agreement with in situ Fe K-edge results reported earlier by this research group. Moreover, only subtle changes were discerned between the in situ S K-edge XANES of the half-, and fully-recharged electrodes. This close resemblance may reflect similarities between the spectral signatures of Li 2 FeS 2 and Fe 1− x S (pyrrhotite), which is the main product of the discharge reaction. Evidence for the formation of elemental sulfur and Li 2 S, which are believed to be minor products of the reaction, was obtained from analysis of the first differential S XANES and selected difference spectra. The compositional variations of the embedded pyrite particles throughout the course of the electrochemical processes occur in the presence of a persistent sulfate coating.

The current status of the Louisiana State University Center for Advanced Microstructures and Devices electron storage ring, beamlines, and the scientific program are described.

Amorphous silicon-containing diamond-like carbon (Si-DLC) films were deposited on silicon wafers by Ar+ Ion Beam Assisted Deposition (IBAD) at various energy conditions. The films were examined with X-ray Absorption Near Edge Structure (XANES) spectroscopy and Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy. The Si K-edge X-ray Absorption Spectroscopy (XAS) results indicate that Si-DLC films have an amorphous structure, where each Si atom is coordinated to four carbon atoms or CHn groups. This short-range order, where a Si atom is surrounded by four C atoms, was found in all Si-DLC films. The XANES spectra do not indicate Si coordination to oxygen atoms or phenyl rings, which are present in the precursor material. A structural model of Si-DLC is proposed based on XAS findings. Simulated X-ray absorption spectra of the model produced by FEFF8 show a good resemblance to the experimental data.

Dust from production of steel in an electric arc furnace (EAF) contains a mixture of elements that pose a challenge for both recovery and disposal. This paper relates the leachability of six Canadian EAF dusts in four leaching tests [distilled water, Ontario Regulation 347 Leachate Extraction Procedure, Amount Available for Leaching (AALT), and pH 5 Stat] to their mineralogy. Chromium and nickel contaminants in EAF dust are largely unleachable (

To date, the exact nature of the plasma nitriding mechanism and the role of energetic particle bombardment are not well understood. The purpose of this work has been to obtain a more detailed knowledge about the evolution of the plasma nitrided surface layer as a function of the energy of the bombarding particles. Nitrided layers were produced at the surface of pure titanium specimens at various flux energies by Intensified Plasma-Assisted Processing (IPAP), a triode plasma technique developed in our laboratory. X-ray Absorption Near Edge Structure (XANES) spectroscopy and Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy were used to characterize the local structure of the titanium nitride layers. Cross sections of the processed specimens were studied by Auger electron spectroscopy and electron microscopy. The results showed that increasing flux energy promotes the formation of a well-ordered TiN layer at the surface. Low flux energies produce significantly lower fractions of the TiN phase at the surface, as well as thinner nitrided layers. A structural model was suggested and quantitatively tested based on the XANES and EXAFS measurements.

The local structures of ‘host’ and ‘guest’ layers of MoS2 intercalated with M(OH)2 (MMn, Co and Ni) prepared via interaction of single-layer MoS2 dispersions and solutions of M2+ salts were studied by X-ray absorption spectroscopy. According to M K-edge extended X-ray absorption fine structure (EXAFS) and X-ray absorption near-edge structure (XANES) results, the electronic structure and atomic environment of the M atoms in the intercalates are similar to that of the crystalline hydroxides M(OH)2. In the Ni intercalate, Mo K-edge EXAFS revealed a structural change of the ‘host’ MoS2 layers similar to that reported for water dispersions of MoS2 single layers. S K-edge XANES data indicate that the change is associated with increased electron density on the S atoms in the matrix. SO42− and Mo″− (4

Fe and Mo K-edge EXAFS spectra of the nitrogenase Mo-Fe protein in the indigo disulfonate (IDS) oxidized form and under slow turnover conditions have been recorded. The EXAFS of the one-electron reduced form E{sub 1} was obtained as a difference spectrum between the slow turnover and resting (E{sub 0}) spectra. Average Fe-S, Fe-Fe, and Fe-Mo distances of 2.33, 2.60, and 2.66A, respectively, along with a second Fe-Fe distance at 3.72 A were found for E{sub 1}. The IDS-oxidized MoFe protein contain spartially oxidized `P-clusters`. For this sample, average Fe-S,Fe-Fe, and Fe-Mo interactions at 2.31, 2.65, and 2.71 A, respectively, were found along with the long Fe-Fe interaction at 3.74 A. Combination of the current results with previous data on resting and thionin-oxidized nitrogenase shows a general trend a significant number of the metal-metal distances tend to contract as the enzyme becomes more reduced. 52 refs., 6 figs., 2 tabs.

Component 1 (the MoFe protein) of conventional nitrogenase from Azotobacter vinelandii contains two types of metal clusters, called M-centers and P-clusters. The M-centers, or FeMo-co, are paramagnetic in the as-isolated form of the protein, exhibiting an EPR signal typical of a rhombic S=3/2 system. The P-clusters are diamagnetic in the as-isolated form of the protein but become paramagnetic upon chemical or potentiometric oxidation. We have undertaken a controlled oxidative titration of component 1 with thionine solution and observed EPR signals believed to originate from paramagnetic P-clusters. We present EPR spectra associated with half-integer S=5/2 and S=1/2 spin states and propose that these spectra arise from the 1-equiv-oxidized form of the P-cluster

The structure of the iron sites of nitrogenase in dithionite-reduced and thionine-oxidized forms of the Mo-Fe and V-Fe proteins has been investigated using Fe K-edge X-ray absorption spectroscopy. For the dithionite-reduced Azotobacter vinelandii Mo-Fe protein, the dominant EXAFS Fourier transform peaks are assigned to Fe-S and Fe-Fe interactions at approximately 2.32 and 2.64 [angstrom], as expected for Fe-S clusters. An additional Fe-Mo component at 2.73 [angstrom] is required to completely fit the EXAFS in the 1-3-[angstrom] region. In the 3-5-[angstrom] region, a 3.8-[angstrom] Fe-Fe component is identified, with an amplitude corresponding to almost one long Fe-Fe interaction, averaged over all of the iron in the sample. Features that can be explained as Fe-S and Fe-Fe interactions at 4.3 and 4.7 [angstrom] are also observed. A similar pattern of Fe interactions is observed for the reduced A. vinelandii V-Fe protein, except that the short Fe-Mo interaction is no longer required. In both Mo-Fe and V-Fe proteins, the first coordination sphere Fe-S distances contract slightly upon thionine oxidation. The long-range Fe-S and Fe-Fe interactions are very close (within 0.1 [angstrom]) to corresponding distances in Fe[sub 6]S[sub 6] prismane clusters. If the amplitudes are adjusted by assuming that only 14 of 30 nitrogenasemore » irons participate in the M center, then they are consistent with recently proposed crystallographic models. 43 refs., 7 figs., 2 tabs.« less

This paper presents the status and the operation conditions of the 1.3 GeV storage ring at the Center for Advanced Microstructures and Devices (CAMD). An overview of existing beamlines with their relevant parameters is given and four beamlines that came into operation over the last two years are discussed in some detail.

Hurricane Katrina, a Category 4 storm on the Saffir‐Simpson scale, struck the Gulf Coast of Louisiana on August 29th, 2005. The storm surge resulted in breaches of the levee system in New Orleans at least at two locations, flooding up to 80% of the city. The floodwater also brought sediment which was left behind once the water receded after a few days. The dry sediment covered large parts of the city. Much of it was made airborne by vehicular traffic and was potentially inhaled.The sediments from the Lakeview area contained an appreciable amount of clay minerals which were absent in samples from Mid City. The speciation of these metals was quantitatively different in two neighborhoods. In one location metallic copper and zinc were present. A small amount of hexavalent chromium was detected at two sites.

The local bonding environment of Ti3+-dopant atoms in NaAlH4 after decomposition to release H2 has been studied using x-ray absorption fine structure (XAFS). The titanium K-edge spectra from doped hydride samples and the standard materials TiCl3 and TiO2 were collected in ambient atmosphere at the synchrotron source at the Center for Advanced Microstructures and Devices (CAMD). Titanium valence states present in the spectra collected from Ti-doped NaAlH4 after decomposition in air are Ti3+ and Ti4+. The Ti3+ is attributed to unreacted TiCl3. The Ti4+ present in the sample is attributed to TiO2 occurring after air oxidation. Coupled with studies of the kinetics of hydrogen desorption reactions, examination of dopant ion valence states after entry into the lattice may lead to better understanding of the interrelationship between lattice doping and desorption kinetics.

Electrodes which are resistant to chemical poisoning by CO, S, and other fuel impurities are needed to replace Pt in proton exchange membrane (PEM) fuel cells. We have designed composite electrodes comprised of single walled carbon nanotubes (CNTs) within a conducting polymer matrix. A method for solubilizing single-walled carbon nanotubes (CNTs) in aqueous media using polyelectrolyte layer-by-layer (LbL) nanoassembly of polystyrene sulfonate (PSS) and polyallylamine (PAH) at the CNT surface is elucidated. Once soluble, the CNTs were assembled onto planar substrates using alternate LbL nanoassembly to form nanocomposite films. These films will later be tested for their potential as alternative anodes in proton exchange membrane fuel cells.

Solid solutions formed by mechanical alloying in the negative heat of mixing Fe-Ni system and the positive heat of mixing Fe-Cu system were studied. X-ray absorption near edge structure (XANES) spectroscopy data were analyzed to obtain the phase fractions and phase compositions for various overall compositions across the bcc/fcc two-phase region. For both systems, at each nominal composition of the powder mixture, the two solutions formed both have the same composition as the overall alloy. It is concluded that the two-phase coexistence represents an extended region of overlapping solubility for the two phases, rather than the usual two-phase region or a clear switchover at the concentration where the two phases have the same free energy. In terms of these features, the two binary systems, one with negative heat of mixing and one with positive heat of mixing, behave the same way. The external forcing action of mechanical alloying at low temperatures drives the system toward composition homogenization. There is no stable or metastable equilibrium, and the common tangent construction and lever rule are not applicable. What results is a novel two-phase coexistence which is defined by a region of overlapping solubility, rather than the normal solubility gap. That there can be two polymorphs at each composition even after the long ball-milling treatment represents a new type of steady-state two-phase coexistence that is completely different from the normal two-phase region dictated by thermodynamics.

Extended x-ray absorption fine structures, small-angle x-ray scattering, and atomistic model calculations have been employed to probe the homogeneity of the fcc solution created in Ag-Cu, a classical system demonstrating the extension of solubility across the entire miscibility gap through rapid quenching. Our results reveal that in many cases the supersaturated solutions formed have decomposition features on the scale of 1 nm. Conventional diffraction methods are inadequate in determining the level of supersaturation or the uniformity of such solid solution alloys.

EXAFS and XANES analysis have been applied in a study of ball-milled nano-crystalline iron-nickel alloys prepared with overall compositions spanning the two-phase region. EXAFS analysis was used to determine bond distances for like and unlike atom pairs in single phase face-centered cubic Fe-Ni alloys, demonstrating the presence of bond dilation for unlike neighbors. Using XANES analysis, the compositions of the two coexisting solid solutions were determined to characterize the ball-milled two-phase region. The compositions of the coexisting face-centered and body-centered cubic phases were found to be consistent with the overall composition of the mixture. The results obtained for the negative heat-of-mixing Fe-Ni system were used for comparison to the positive heat-of-mixing Fe-Cu system.

Extended x-ray absorption fine structure (EXAFS) and Raman spectroscopy measurements have been performed in a series of liquid polymer electrolytes prepared using poly(tetramethylene glycol) (PTMG), and copolymer poly(tetramethylene glycol/poly(ethylene glycol) (PTMG/PEG), as matrices, and ZnCl2or COCl2 as dopants in the concentration range of n = 30 to 90, where n is the molar ratio of Oxigen/Metal cation. EXAFS results have shown the presence of Co-O and Co-Cl coordination shells for PTMG/CoCl2 and PTMG/PEG/CoCl2 systems. Zn-based systems have shown only Zn-Cl bonds in all the concentration range studied. The presence of ZnCl2 and COCl2 species was confirmed by Raman measurements, by the presence of bands characteristic of CI-Zn-Cl and Co-Cl stretching modes.

A critical factor in the characterization of two-phase binary alloy systems is the determination of the phase fractions and compositions of the two coexisting solid solutions for any given overall composition of the two-phase mixture. In some systems, for example nanocrystalline alloys formed by high-energy ball-milling, these parameters are difficult to attain by traditional techniques like x-ray diffraction. A new technique has been developed to obtain these quantities indirectly from x-ray absorption near edge structure (XANES) data collected at the two relevant absorption edges, with the formulation of this technique presented here in detail. The technique has been tested using Fe-Ni fcc and bcc standards and the results indicate that the method is accurate to within 5%. This method has been applied to two-phase (f.c.c. and b.c.c.) binary alloys formed by ball-milling of Cu100-xFex(x = 50-80).

MoS 2 intercalated with Mn, Co, Ni, and Ru species, prepared from single layer MoS 2 dispersions in water, were studied by x-ray absorption spectroscopy. M K-edge EXAFS results (M = Mn, Co, Ni) are consistent with an alternating MoS 2 -M(OH) 2 layered structure. For the Mn and Co intercalates the MoS 2 layers were found to be very similar to that of the parent crystalline MoS 2 with trigonal prismatic coordination of the Mo atoms. For the Ni and Ru intercalates, Mo K edge EXAFS revealed structural rearrangement of MoS 2 layers similar to that observed for MoS 2 single layers, with octahedral coordination of Mo. S K edge XANES spectra reveal that the rearrangement is coupled with a change in the electronic structure of the S atoms in the matrix. These changes can be associated with charge transfer between host and guest layers. In addition, SO 4 2- and Mo 6+ were detected in some of the intercalated materials, presumably due to exposure to air, suggesting that transition metal intercalation may increase the susceptibility of the MoS 2 layers to oxidation.

The nitrogenase VFe protein of Azotobacter vinelandii (Av1') has been shown to exist in two forms called Av1'A, which has a primary alpha beta 2 trimeric structure, and Av1'B, which has an alpha 2 beta 2 tetrameric structure [Blanchard, C. Z., & Hales, B. J. (1996) Biochemistry 35, 472-478]. Both forms exhibit S = 5/2 EPR signals in the as-isolated state that may be assigned to 1-equiv-oxidized P clusters (P+). These signals are abolished by enzymatic reduction with the component 2 protein (Av2'). Stepwise oxidative titrations of enzymatically reduced Av1'B result in the restoration of the S = 5/2 P+ signals and the concurrent decrease of the S = 3/2 vanadium cofactor signal. Further oxidation results in the appearance of an integer spin signal assigned to the 2-equiv-oxidized P cluster (P2+). Unlike the analogous signal previously observed in Mo nitrogenase component 1 (Av1), which arises from an excited state, the integer spin P2+ signal in Av1'B originates from a ground-state doublet. Similar oxidative titrations of enzymatically reduced Av1'A show redox behavior dramatically different from that of Av1'B, as monitored by EPR spectroscopy. We observed spectral evidence for a redox-induced intramolecular electron transfer between the reduced P cluster and the oxidized FeV cofactor cluster during the titrations.

CTAB (Cetyltrimethylammonium bromide) stabilized cobalt nanoparticles of three different sizes between 5.5 and 11 nm diameter were prepared using reverse-micelle method. Their geometric and electronic structure was characterized using X-ray Absorption Spectroscopy (XAS) at the Co-K-edge and Transmission Electron Spectroscopy (TEM). The as-prepared nanoparticles appear to have a cobalt core that is a mixture of the Co-α and β-phase and a shell, possibly, made of a cobalt(III) octahedral complex. The shell disappears when the particles are annealed to 250 °C and the particles are transformed into the standard hcp (α) phase. The short time stability of the particles against oxidation supports the presence of a core-shell structure with a Co core and a protective shell. A longer exposure to air leads to a more or less complete oxidation of the entire particle to CoO.