DANTE is a new Digital Pulse Processor (DPP) developed for fluorescence detectors, like Silicon Drift Detectors (SDDs) or High Purity Germanium detectors (HPGe), used in X-ray Fluorescence (XRF) and X-ray Absorption Spectroscopy (XAS) experiments at synchrotron facilities. Its main features are its optimal energy resolution and peak stability for detector count rate values up to 1-2 Mcps, and its enhanced rejection of pile-up events. In this paper, we present the first complete evaluation of DANTE performance in SOLEIL synchrotron facility. DANTE has been tested in laboratory with an X-ray generator source and in different experiments at LUCIA and PUMA beamlines at SOLEIL.

High temperature cation mobilities, based on the multicomponent diffusion method, have been coupled with a structural investigation in the Na2O-CaO-Al2O3-SiO2-ZrO2 (NCASZ) system at 1200 degrees C and 1250 degrees C. From structural investigation using X-ray absorption spectroscopy (XANES), zirconium was determined in six-fold coordinated sites in the reduced glass composition range of our study and no significant structural changes have been evidenced compared to a quaternary Na2O-CaO-Al2O3-SiO2 (NCAS) glass with a similar composition. Additionally, the diffusion experiments revealed that adding zirconium in the quaternary melt has no influence on the dominant eigen-vectors that correspond to exchange between calcium and sodium. Despite the expected mobility decrease resulting from a viscosity increase upon the addition of zirconium, the dominant eigen-value calculated in this study is higher when Zr is introduced in the melt structure. This result strongly suggests that the sodium mobility is enhanced by the presence of Zr, which is explained by a change in the structural role of sodium from network modifier associated to Q(3)(Si) sites in NCAS melts to charge compensator associated with [ZrO6](2-) sites in NCASZ melts. This modification generates lower bond strengths between sodium and other cations in the melt, thus favoring an enhancement in mobility. Moreover, the diffusion matrix was applied to predict diffusion profiles between zirconium-bearing crystals and melts. We observed that even far from the composition field used for the matrix determination, predictions of zirconium diffusion profiles may be relevant and demonstrate the potential of this approach to evaluate crystal/melt dissolution behavior. (C) 2019 Elsevier Ltd. All rights reserved.

We report a detailed structural investigation of Ca-Na aluminosilicate glasses containing 0–20 wt% ZrO2 using X-ray absorption spectroscopy, Raman spectroscopy and 27Al and 29Si NMR. The X-ray absorption spectroscopy data reveal that Zr is predominantly present in ZrO6 octahedra but a significant Zr coordination change occurs with increasing ZrO2 content. Though Al and Zr are competing to be surrounded by charge balancing cations, 27Al NMR data do not show the presence of high-coordinated Al species; thus charge-balancing cations are preferentially localized close to AlO4 tetrahedra rather than Zr polyhedra, explaining the increase in Zr coordination number that ultimately leads to limit Zr solubility in glasses. Raman and 29Si NMR data indicates that Zr atoms are linked to the silicate network with a trend for higher degree of network connectivity at high zirconia content. Change in network connectivity and in Zr environment provide insights to understand chemical durability or crystallization in glasses.

Structural and electronic transformation taking place in α-FeOOH goethite have been studied by Fe K-edge x-ray absorption spectroscopy at pressures up to 50 GPa. These studies have shown the symmetrization of FeO6 octahedra coinciding with the Fe3+ high to low spin transition at pressure above ~45 GPa. Our data are in excellent agreement with the results of recent single crystal XRD and Mössbauer spectroscopy studies (Xu et al 2013 Phys. Rev. Lett. 111 175501), supporting the H-bonds symmetrization in iron oxyhydroxide, resulting from the Fe3+ high-to-low spin crossover at above 45 GPa. Our study shows an applicability of the x-ray absorption spectroscopy in a further study of the H-bonds symmetrization phenomenon.

Rods of low alloy carbon steel were corroded under anoxic conditions in compact clay at 90 degrees C. Gravimetrically-assessed corrosion damage equalled 8.5 mu m at 7 months, then slowly increased to 29.5 mu m at 76 months. The corrosion damage was heterogeneous at 7 months, and two distinct aspects coexisted: steel was replaced by (Fe,Si,O) corrosion products in some areas, and by Si-poor hydroxide and covered by akaganeite (FeO(OH,Cl)) in others, indicating corrosion in suboxic conditions. A magnetite fringe contacted the steel surface. For greater reaction times, akaganeite disappeared, and only (Fe,Si,O) corrosion products containing Fe sulfide and chukanovite were detected.

Borosilicate glasses containing 1 to 8 mol% ZrO2 were leached at pH 9, 7 and 1 until complete alteration. The Zr coordination in the bulk and at the gel surface is quantified using Zr L2- XANES spectra in fluorescence and total electron yield mode, respectively. This provides evidence of a single layer at pH 9 whereas a second alteration layer develops at the gel surface at pH 7 and at pH 1. The surface layer, a witness of the first stages of glass alteration, exhibits larger structural variations than the bulk of the gel. This is related with the alteration conditions, from incipient alteration of pristine glasses to chemical diffusion controlled by the gels formed at a later stage. In all gels investigated, a majority of Zr occurs in [6]Zr sites. However, at neutral and acidic pH, the gels contain a high fraction of 7- and 8-coordinated Zr ([7]Zr and [8]Zr, respectively) sites, and only 6-coordinated ([6]Zr) sites at pH 9. The Zr local environment in the gels, determined by Zr K-edge EXAFS, is similar to that in the pristine glasses, with some additional contribution of Zr second neighbors. Both Zr-site geometry and medium-range structure of the alteration gel bring direct evidence that, under the experimental conditions used, glass dissolution is driven by an in situ hydrolysis/condensation mechanism. This allows the gel structure to mimic that of the pristine glass, including the [6]Zr site distortion or the linkage to the silicate gel framework. The pH has a greater influence on the structure of gels than does their Zr content. The structural evolution around Zr is mainly governed by the pH during alteration, while the [6]Zr site symmetry is controlled by the Zr content of the gel. Certain gels contain more octahedral sites than expected from the concentration of charge compensating cations (Ca, Na), a situation similar to that observed in SiO2ZrO2 xerogels.

μ-XANES is used to study the modifications in the alkali and alkaline-earth environments induced by the Na+/K+ ion-exchange process in various Na –silicate glasses. The results indicate that the ion-exchange process induces a shortening of the NaO, CaO and MgO bond distances. The contraction of the NaO, CaO and MgO coordination shell allows a better accommodation of the K+ cations in the glass network and thereby leads to partial relaxation of the stress developed by the Na+/K+ ion-exchange. Nevertheless, despite the stress relaxation process, the K+ environment in the ion-exchanged glass is not equivalent to the one in Na,K–silicate as-melted glasses. Hence, this study clearly shows that the ion swapping forced K+ cations to occupy smaller sites which are not achievable via the melt quench route for glasses with the same K amount.

The role of microorganisms in the geochemical cycle of P has received great interest in the context of enhanced biological phosphorus removal and phosphorite formation. Here, we combine scanning and transmission electron microscopies, confocal laser scanning microscopy and synchrotron-based x-ray microfluorescence to analyse the distribution of P at the oxic-anoxic interface in the water column of the ferruginous Lake Pavin. We show that magnetotactic bacteria of the Magnetococca-ceae family strongly accumulate polyphosphates and appear as P hotspots in the particulate fraction at this depth. This high accumulation may be characteristic of this family and may also relate to the chemical conditions prevailing in the lake. As a result, these magneto-tactic cocci can be considered as new models playing a potentially important role in the P geochemical cycle, similar to sulphide oxidising bacteria such as Thiomargarita and Beggiatoa but thriving in a ferruginous, poorly sulphidic environment.

The local structure around the silicon atoms of silicene deposited onto Ag(1 1 0) and Ag(1 1 1) has been determined by extended x-ray absorption fine structure spectroscopy at the silicon K-edge. This study shows that silicon atoms are not in a flat honeycomb network locally buckled, but that this structure mimics the double Si(1 1 1)-plane of crystalline silicon with almost the same first and second interatomic distances (2.35 and 3.83 Å) on a regularly buckled geometry. Moreover the results evidence silver atoms at a well-defined distance from the silicon ones, a signature for an interaction between the silicene sheet and silver atoms released from the substrate.

Commissioned in May 2004 on the SLS machine, the LUCIA beamline was moved to the synchrotron SOLEIL during the summer of 2008. To take advantage of this new setting several changes to its design were introduced. Here, a review of the various improvements of the mechanics and, mostly, of the optics is given. Described in detail are the results of a new multilayer grating monochromator implemented on the Kohzu vessel already holding the two-crystal set-up. It consists of a grating grooved onto a multilayer (replacing the first crystal) associated to a multilayer (as a second crystal). It allows a shift of the low-energy limit of the beamline to around 500 eV with an energy resolution and a photon flux comparable with those of the previous couples of crystals (KTP and beryl).

We have investigated the role of ZrO2 on the nucleation/crystallization properties of aluminosilicate glasses. A comparison between Zr-free and Zr-bearing glasses shows that adding ZrO2 favors nucleation in Li-, Mg-, Ca- and Zn-bearing glasses and has no effects in Na-bearing glasses. The Zr environment has been elucidated coupling X-ray absorption spectroscopy at both Zr K- and L2,3-edges. The Zr environment corresponds to six-fold coordinated sites (Li and Na glasses) and seven-fold coordinated sites (Mg, Ca and Zn glasses), indicating the coordination number has little influence on the ability to crystallize. Direct Zr–Zr polyhedral linkages are observed for all glasses except the Na-bearing one. Since no correlation between the local Zr site and its ability to promote nucleation can be observed, the origin of the nucleating role of Zr has been interpreted as resulting from the Zr distribution with in the aluminosilicate matrix. The poor crystallization ability for Na-bearing glasses is due to the lack of direct Zr–Zr linkages. Medium range ordering appears as a key parameter to explain properties of Zr-bearing glasses.

Electronic core levels in molecules are highly localized around one atomic site. However, in single-photon ionization of symmetric molecules, the question of core-hole localization versus delocalization over two equivalent atoms has long been debated as the answer lies at the heart of quantum mechanics. Here, using a joint experimental and theoretical study of core-ionized carbon disulfide (CS2), we demonstrate that it is possible to experimentally select distinct molecular-fragmentation pathways in which the core hole can be considered as either localized on one sulfur atom or delocalized between two indistinguishable sulfur atoms. This feat is accomplished by measuring photoelectron angular distributions within the frame of the molecule, directly probing entanglement or disentanglement of quantum pathways as a function of how the molecule dissociates.

S1s photoionization in carbonyl sulfide (OCS), followed by multiple Auger decay is investigated both experimentally and theoretically, by means of photoelectron-ion coincidences. A strong influence of post-collision interaction is observed in the energy shift and the distortion of the photoelectron spectra. The magnitude of this effect depends on the total charge of the ionic fragments, i.e., on the number of electrons emitted during the decay of the inner vacancy. A satisfactory agreement is found between experiment and theory, which allows us to estimate the lifetimes of the various two-hole states of the intermediate OCS2+ ion.

The short- and medium-range local environment of zirconium was determined by Zr L2,3-edge and K-edge XANES and by Zr K-edge EXAFS in borosilicate glasses with 1 to 8mol% ZrO2. Regardless of the ZrO2 content of the glass, Zr is six-coordinated in octahedra with ZrO distances of 2.09Å. In the glasses containing 8mol% ZrO2, the octahedra are more distorted than at lower ZrO2 content. Enhanced resolution in the real space is achieved by recording Zr K-edge EXAFS spectra over a broad energy range, enabling to get access k-values up to 20Å−1 with a high signal to noise ratio. This allows discriminate between the various second neighbor contributions. A correct fit is based on four Si and two B. This local structure around Zr derived from that of zirconosilicates such as elpidite, in which two Si are replaced by two B. The ZrSi distances increase from 3.63±0.02 to 3.67±0.01Å, as ZrB distances remain constant within uncertainties, as ZrO2 content increases. Two Na are situated at 3.64±0.03Å from Zr, ensuring charge compensation of the ZrO6 sites. Increasing the CaO content from 4 to 8mol% does not lead to any structural change around Zr.

We have developed a new momentum spectrometer dedicated to momentum vector correlations in the context of deep core photoionization of atomic and molecular species in the gas phase. In this article, we describe the design and operation of the experimental setup. The capabilities of the apparatus are illustrated with a set of measurements done on the sulphur core 1s photoionization of gas-phase CS2.

After a review of temperature-dependent experimental x-ray absorption near-edge structure (XANES) and related theoretical developments, we present the Al K-edge XANES spectra of corundum and beryl for temperature ranging from 300K to 930K. These experimental results provide a first evidence of the role of thermal fluctuation in XANES at the Al K-edge especially in the pre-edge region. The study is carried out by polarized XANES measurements of single crystals. For any orientation of the sample with respect to the x-ray beam, the pre-edge peak grows and shifts to lower energy with temperature. In addition temperature induces modifications in the position and intensities of the main XANES features. First-principles DFT calculations are performed for both compounds. They show that the pre-edge peak originates from forbidden 1s to 3s transitions induced by vibrations. Three existing theoretical models are used to take vibrations into account in the absorption cross section calculations: i) an average of the XANES spectra over the thermal displacements of the absorbing atom around its equilibrium position, ii) a method based on the crude Born-Oppenheimer approximation where only the initial state is averaged over thermal displacements, iii) a convolution of the spectra obtained for the atoms at the equilibrium positions with an approximate phonon spectral function. The theoretical spectra so obtained permit to qualitatively understand the origin of the spectral modifications induced by temperature. However the correct treatment of thermal fluctuation in XANES spectroscopy requires more sophisticated theoretical tools.

Molecular-frame photoelectron angular distributions (MFPADs) in carbonyl sulfide at selected photon energies above the sulfur 1s ionization threshold have been measured using a recently developed vector-correlation experimental setup and theoretically calculated using the time-dependent DFT method. For this linear molecule, the selection of the fragmentation channel CO+ + S+ is an effective method to fix the molecular frame. The experimental results are found in good agreement with the calculated MFPADs.

Argon 1s photoionization followed by multiple Auger decays is investigated both experimentally, by means of photoelectron-ion coincidences, and theoretically. A strong influence of the different Auger decays on the photoelectron spectra is observed through postcollision interaction which shifts the maximum of the energy distribution and distorts the spectral shape. A good agreement between the calculated and measured spectra for selected Ar(n+) ions (n=1-5) allows one to estimate the widths (lifetimes) of the intermediate states for each specific decay pathway.

We report a X-ray absorption study at Ti K- and L2,3-edges to determine the role of TiO2 content as a nucleating agent in glass ceramics. It is found that the local Ti environment is not modified with TiO2 addition, indicating that medium range organization is responsible for its ability to promote internal versus bulk nucleation. We have identified a Ti coordination change between the nucleation front and the crystallized part of the glass ceramic. These changes correspond to conversion from 5-fold coordinated to 4-fold coordinated Ti in the remaining glassy part, resulting from compositional changes. This reveals that active sites for nucleation could be experimentally detected and that reorganization of the glass matrix during nucleation has a major influence on the ongoing nucleation processes.