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  • 1
    Language: English
    In: Analytical chemistry, 03 November 2015, Vol.87(21), pp.10815-21
    Description: Grazing emission X-ray fluorescence (GEXRF) is well suited for nondestructive elemental-sensitive depth-profiling measurements on samples with nanometer-sized features. By varying the grazing emission angle under which the X-ray fluorescence signal is detected, the probed depth range can be tuned from a few to several hundred nanometers. The dependence of the XRF intensity on the grazing emission angle can be assessed in a sequence of measurements or in a scanning-free approach using a position-sensitive area detector. Hereafter, we will show that the combination of scanning-free GEXRF and fluorescence detected X-ray absorption spectroscopy (XAS) allows for depth-resolved chemical speciation measurements with nanometer-scale accuracy. While the conventional grazing emission geometry is advantageous to minimize self-absorption effects, the use of a scanning-free setup makes the sequential scanning of the grazing emission angles obsolete and paves the way toward time-resolved depth-sensitive XAS measurements. The presented experimental approach was applied to study the surface oxidation of an Fe layer on the top of bulk Si and of a Ge bulk sample. Thanks to the penetrating properties and the insensitivity toward the electric conduction properties of the incident and emitted X-rays, the presented experimental approach is well suited for in situ sample surface studies in the nanometer regime.
    Keywords: X-Rays ; Absorption Spectroscopy ; Bulk Sampling ; X-Ray Fluorescence ; Grazing ; Emission Spectroscopy ; Nanostructure ; Angles (Geometry) ; Analysis (MD) ; Chemical Analysis (Ep) ; Chemical Analysis (Ed) ; Chemical Analysis (EC);
    ISSN: 00032700
    E-ISSN: 1520-6882
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  • 2
    Language: English
    In: Analytical Chemistry, June 2, 2015, Vol.87(11), p.5632(8)
    Description: The article describes an experimental and theoretical study of phosphorus electronic structure based on high energy resolution X-ray emission spectroscopy. The Kalpha and Kbeta emission spectra of several phosphorus compounds were recorded. The results revealed clear correlation between energy position of the Kalpha emission line and the phosphorus formal oxidation state as well as DFT-calculated number of valence electrons.
    Keywords: Phosphorus Compounds – Chemical Properties ; Phosphorus Compounds – Spectra ; Density Functional Theory – Usage ; X-Ray Spectroscopy – Usage
    ISSN: 0003-2700
    Source: Cengage Learning, Inc.
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  • 3
    Language: English
    In: Analytical Chemistry, Nov 3, 2015, Vol.87(21), p.10815(7)
    Description: The article shows that the combination of scanning-free Grazing emission X-ray fluorescence (GEXRF) and fluorescence detected X-ray absorption spectroscopy (XAS) allows for depth-resolved chemical speciation measurements with nanometer-scale accuracy. The presented experimental approach is applied to study the surface oxidation of Fe layer on the top of bulk Si and of a Ge bulk sample. The insensitivity toward the electric conduction properties of the incident and emitted X-rays, the presented experimental approach is well suited for in situ sample surface studies in the nanometer regime.
    Keywords: Absorption Spectroscopy – Usage ; Fluorescence – Analysis ; Iron Compounds – Chemical Properties ; Iron Compounds – Spectra
    ISSN: 0003-2700
    Source: Cengage Learning, Inc.
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  • 4
    In: Physical Chemistry Chemical Physics, 2014, Vol.16(17), pp.7692-7696
    Description: The electronic structure of nano-NiO was determined using resonant inelastic X-ray scattering (RIXS) spectroscopy. The nanosized NiO particles were reduced in situ , leading to the formation of metallic Ni in a single step. Time-resolved RIXS elucidated in real time the changes on the occupied and unoccupied electronic structure of the material, which are dramatically affected by the reduction process.
    Keywords: Reduction ; X-Rays ; Physical Chemistry ; Inelastic Scattering ; Nickel ; Electronic Structure ; Nanoparticles ; Nanostructure ; Miscellaneous Sciences (So);
    ISSN: 1463-9076
    E-ISSN: 1463-9084
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  • 5
    In: Physical Chemistry Chemical Physics, 2015, Vol.17(28), pp.18262-18264
    Description: We report on the reactivity of grafted tantalum organometallic catalysts with molecular oxygen. The changes in the local Ta electronic structure were followed by in situ high-energy resolution off-resonant spectroscopy (HEROS). The results revealed agglomeration and formation of Ta dimers, which cannot be reversed. The process occurs independently of starting grafted complex.
    Keywords: Tantalum ; Reactivity ; Silicon-Dioxide ; Molecular-Oxygen ; Agglomeration ; Spectrometry ; Electronic-Structure ; Tantal ; Chemisches Reaktionsvermögen ; Siliciumdioxid ; Molekularer Sauerstoff ; Agglomerieren ; Spektroskopie ; Elektronische Struktur ; Chemistry;
    ISSN: 1463-9076
    E-ISSN: 1463-9084
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  • 6
    In: Physical Chemistry Chemical Physics, 2013, Vol.15(26), pp.11088-11098
    Description: The sensitivity of the 1s X-ray emission and high-energy-resolution fluorescence-detected X-ray absorption spectroscopies (XES and HERFD-XAS) to resolve the variations in the chemical state (electronic structure and local coordination) of Br has been investigated for a selected set of compounds including NaBrO 3 , NH 4 Br and C 2 H 4 Br 2 (1,2-dibromoethane). For the Br K-edge XAS, employing the HERFD mode significantly increases the energy resolution, which demonstrates that with a crystal spectrometer used as a detector the absorption technique becomes a more powerful analytical tool. In the case of XES, the experimental results as well as the density functional theory (DFT) modeling both show that the chemical sensitivity of the main 1s diagram emission lines (K 1,2 and K 1,3 ) is rather limited. However, the valence-to-core (K 2 ) region of XES displays significant shape and intensity variations, as expected for transitions having the same final states as those of photoemission spectroscopy. The spectra are in good agreement with the molecular orbital description delivered by DFT calculations. Calculations for an extended series of Br compounds confirm that valence-to-core XES can serve as a probe for chemical analysis, and, being a hard X-ray photon-in/photon-out technique, it is particularly well-suited for in situ investigations of molecular transformations, even on the ultrafast time scales down to femtosecond time resolution.
    Keywords: X-Rays ; Mathematical Models ; Transformations ; Emission Spectroscopy ; Electronic Structure ; Femtosecond ; Tools ; Spectrometers ; Miscellaneous Sciences (So);
    ISSN: 1463-9076
    E-ISSN: 1463-9084
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  • 7
    In: CrystEngComm, 2013, Vol.15(14), pp.2583-2587
    Description: In this communication, we present an elegant and cost effective strategy for the rational design of novel materials used in the conversion of solar energy into chemical bonds. The strategy relies on the combination of theory and the latest developments in high-resolution XAS/XES at synchrotrons, which are able to map the material electronic structure with high precision, requiring a very limited amount of sample (experimental work) or none (theory).
    Keywords: Chemical Bonds ; Conversion ; Electronic Structure ; Oxynitrides ; Solar Energy ; Strategy ; Synchrotrons ; Atomic and Molecular Structure (So);
    ISSN: 1466-8033
    E-ISSN: 1466-8033
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  • 8
    Language: English
    In: Journal of the American Chemical Society, 26 December 2013, Vol.135(51), pp.19071-4
    Description: We report an in situ time-resolved high-energy resolution off-resonant spectroscopy study with subsecond resolution providing insight into the oxidation and reduction steps of a Pt catalyst during CO oxidation. The study shows that the slow oxidation step is composed of two characteristic stages, namely, dissociative adsorption of oxygen followed by partial oxidation of Pt subsurface. By comparing the experimental spectra with theoretical calculations, we found that the intermediate chemisorbed O on Pt is adsorbed on atop position, which suggests surface poisoning by CO or surface reconstruction.
    Keywords: Natural Sciences ; Chemical Sciences ; Physical Chemistry ; Naturvetenskap ; Kemi ; Fysikalisk Kemi;
    ISSN: 00027863
    E-ISSN: 1520-5126
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  • 9
    Language: English
    In: Angewandte Chemie International Edition, 20 July 2015, Vol.54(30), pp.8728-8731
    Description: Identification of active species and the rate‐determining reaction steps are crucial for optimizing the performance of oxygen‐storage materials, which play an important role in catalysts lowering automotive emissions, as electrode materials for fuel cells, and as antioxidants in biomedicine. We demonstrated that active Ce species in a ceria‐supported platinum catalyst during CO oxidation are short‐lived and therefore cannot be observed under steady‐state conditions. Using time‐resolved resonant X‐ray emission spectroscopy, we quantitatively correlated the initial rate of Ce formation under transient conditions to the overall rate of CO oxidation under steady‐state conditions and showed that ceria reduction is a kinetically relevant step in CO oxidation, whereas a fraction of Ce was present as spectators. This approach can be applied to various catalytic processes involving oxygen‐storage materials and reducible oxides to distinguish between redox and nonredox catalytic mechanisms. is the active and kinetically relevant intermediate during catalytic CO oxidation on a ceria‐supported metal catalyst, whereas long‐lived Ce species are inactive spectators. This was shown by in situ resonant X‐ray emission spectroscopy and quantitative correlation between the initial rate of Ce formation under transient conditions and the overall CO oxidation rate.
    Keywords: Ceria ; Co Oxidation ; Kinetics ; Time‐Resolved Studies ; X‐Ray Spectroscopy
    ISSN: 1433-7851
    E-ISSN: 1521-3773
    Source: John Wiley & Sons, Inc.
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  • 10
    Language: English
    In: Journal of Chemical Sciences, 2014, Vol.126(2), pp.511-515
    Description: Electronic structures of rutile and anatase polymorph of TiO 2 were determined by resonant inelastic X-ray scattering measurements and FEFF9.0 calculations. Difference between crystalline structures led to shifts in the rutile Ti d -band to lower energy with respect to anatase, i.e., decrease in band gap. Anatase possesses localized states located in the band gap where electrons can be trapped, which are almost absent in the rutile structure. This could well explain the reported longer lifetimes in anatase. It was revealed that HR-XAS is insufficient to study in-depth unoccupied states of investigated materials because it overlooks the shallow traps. Graphical Abstract The resonant X-ray emission spectroscopy around Ti k-edge was applied to probe local electronic structure of TiO 2 rutile and anatase. By measuring 1s→3d excitation and 3p→1s decay channel, differences between localized and delocalized orbitals were determined. The 3d pre-edge structures were compared with ab initio multiple scattering simulations.
    Keywords: Photo-catalysis ; high-resolution RIXS ; electronic structure
    ISSN: 0974-3626
    E-ISSN: 0973-7103
    Source: Springer Science & Business Media B.V.
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