Search results for "X-ray absorption fine structure"
showing 10 items of 220 documents
Local structural investigation of hafnia-zirconia polymorphs in powders and thin films by X-ray absorption spectroscopy
2019
Björn Matthey (Fraunhofer IKTS, Dresden) is acknowledged for providing HfO2 and ZrO2 powders on short notice after DESY’s renowned customs office punished us. Parts of this research were carried out at Petra III at DESY, a member of the Helmholtz Association (HGF). The experiments on single Si:HfO2 thin film samples were performed at the CLAESS beamline at ALBA Synchrotron with the collaboration of ALBA staff. We would like to thank Edmund Welter for assistance (in using beamline P65) and DESY for enabling this research for proposal no. 20160591 and for travel support. T.S. acknowledges the German Research Foundation (DFG) for funding this work in the frame of the project “Inferox” (project…
Short and Medium Range Order in Se1-xTexGlasses
1997
Complementary XAFS measurements (LURE and NSLS) of Se 1 - x Te x glasses have been carried out on both the Se and Te K-edges at low and room temperatures. Using a multi-shell best fit analysis procedure, we have reconstructed the Se and Te local environment: (i) first shell intrachain nearest neighbors (Se-Se 1 , Se-Te 1 , Te-Se 1 ,and Te-Te 1 ); (ii) second shell intrachain (Se-Se 2 and Se-Te 2 ) and interchain next nearest neighbors (Se⇔Se 3 single scattering in the chains Se-Se 1 -Se 3 and Se-Te 1 -Se 3 ). For the first and second coordination shells we suggest that the intrachain chemical order increases with Te content. On the other hand, we propose a model of random distribution of Se…
Quantum chemical modelling of polarons and perovskite solid solutions
2001
Abstract Following our previous study [J. Phys.: Condens. Matter 10 (1998) 6271] of a single Nb impurity and Nb clusters in KTaO 3 , we present results of the calculations for a series of perovskite KNb x Ta 1− x O 3 (KTN) solid solutions ( x =0, 0.125, 0.25, 0.75, 1). The quantum chemical method of the intermediate neglect of the differential overlap (INDO) combined with the large unit cell (LUC) periodic model is used. According to the INDO calculations, Nb impurity becomes off-center in KTaO 3 already at the lowest studied concentrations ( x =0.125), in a good agreement with XAFS measurements. We compare our results with previous ab initio FP-LMTO calculations. Quantum chemical calculati…
Influence of metal–support interaction on the surface structure of gold nanoclusters deposited on native SiOx/Si substrates
2014
The structure of small gold nanoclusters (R ~ 2.5 nm) deposited on different silica on silicon substrates is investigated using several characterization techniques (AFM, XRD, EXAFS and GISAXS). The grain morphology and the surface roughness of the deposited gold clusters are determined by AFM. The in-plane GISAXS intensity is modelled in order to obtain information about the cluster size and the characteristic length scale of the surface roughness. AFM and GISAXS results are in excellent agreement and show that the surface morphology of the deposited clusters depends on whether defect-rich (native) or defect-free (thermal) silica is used as a substrate. Gold clusters show a strong tendency …
Photochemical Synthesis of Water-Soluble Gold Nanorods: The Role of Silver Ions in Assisting Anisotropic Growth
2009
The role of Ag+ ions in the ultraviolet-driven photochemical synthesis of Au nanorods (NRs) in aqueous surfactant mixtures has been investigated in order to elucidate the mechanism that drives anisotropic nanoparticle growth. The samples, grown in the presence of varying amounts of Ag+ ions for scheduled irradiation times, have been characterized by ultraviolet−visible−near infrared (UV−vis−NIR) absorption spectroscopy, analytical transmission electron microscopy (ATEM), inductively coupled plasma atomic emission spectroscopy (ICP-AES), and extended X-ray absorption fine structure (EXAFS) measurements. Moreover, the time evolution of size and shape distribution has been investigated by stat…
Disappearance of correlations in the atom motion upon hydrogen intercalation into ReO3lattice
2016
The influence of hydrogen intercalation on the local structure of rhenium trioxide is studied in-situ by the Re L3-edge EXAFS spectroscopy and analysed using a novel approach, based on the use of evolutionary algorithm and wavelet transform. The proposed method allows us to perform accurate EXAFS analysis within the multiple-scattering approach taking into account contributions from outer coordination shells and to access the information on correlations in atomic thermal motion.
Interpretation of EXAFS in scheelite-type AWO4(A = Ca, Sr, Ba) compounds using molecular dynamics simulations
2013
In this work we successfully interpret the W L3-edge EXAFS spectra in scheelite-type AWO4 (A = Ca, Sr, Ba) compounds using a combination of classical NVT molecular dynamics (MD) and ab initio multiple-scattering (MS) theory. The configuration-averaged EXAFS spectra show good agreement with our room temperature experimental data supporting the reliability of the developed force-field models. The contributions from all coordination shells up to 6 A are elucidated. The contribution of the MS effects into the total EXAFS signal in AWO4 compounds is small, being around 10%.
Effect of the capping agents on cobalt nanoparticles
2009
The achievement of high information density and fast recording rate in memory devices crucially depends on the structure of magnetic domains. In this paper cobalt nanoparticles are synthesised using two capping agents (TOA, ODA) and two different preparation routes: thermal decomposition (TD) and Solvated Metal Atom Dispersion (SMAD). The interaction of capping agents with free metal clusters and their influence on Co nanoparticles size, atomic structure and oxidation state is investigated by means of X-ray diffraction and X-ray absorption spectroscopy.
Interpretation of the U L3-edge EXAFS in uranium dioxide using molecular dynamics and density functional theory simulations
2016
X-ray absorption spectroscopy is employed to study the local structure of pure and Cr-doped UO2 at 300 K. The U L3-edge EXAFS spectrum is interpreted within the multiplescattering (MS) theory using the results of the classical and ab initio molecular dynamics simulations, allowing us to validate the accuracy of theoretical models. The Cr K-edge XANES is simulated within the full-multiple-scattering formalism considering a substitutional model (Cr at U site). It is shown that both unrelaxed and relaxed structures, produced by ab initio density functional theory (DFT) calculations, fail to describe the experiment.
Ab initio molecular dynamics simulations of the Sc K-edge EXAFS of scandium trifluoride
2016
Scandium fluoride ScF3 has a simple cubic structure and attracts attention due to its large negative thermal expansion (NTE) over a wide range of temperatures (0-1100 K). In this study we present ab initio molecular dynamics (AIMD) simulations of ScF3 and their validation using the Sc K-edge EXAFS spectra in the temperature range from 300 K to 1000 K measured at the XAFS beamline of ELETTRA. The obtained results allow an assessement of the employed AIMD model and provide insight into the local structure and the lattice dynamics of ScF3 beyond the harmonic approximation. A strong anisotropy of the fluorine atom vibrations in the direction orthogonal to the -Sc-F-Sc- chain is observed. An exp…