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Rietveld Refinement on X-Ray Diffraction Patterns of Bioapatite in Human Fetal Bones

Bioapatite, the main constituent of mineralized tissue in mammalian bones, is a calcium-phosphate-based mineral that is similar in structure and composition to hydroxyapatite. In this work, the crystallographic structure of bioapatite in human fetuses was investigated by synchrotron radiation x-ray diffraction (XRD) and microdiffraction ( micro -XRD) techniques. Rietveld refinement analyses of XRD and micro -XRD data allow for quantitative probing of the structural modifications of bioapatite as functions of the mineralization process and gestational age.

The ReflEXAFS station at the GILDA beamline (BM08) of ESRF

The experimental station for measuring X-ray absorption spectra in total reflection geometry operative at the GILDA CRG beamline of ESRF is described. The main features of the station are shown, namely: the possibility of detecting very small signals from thin (a few ML) samples, of depositing thin films under controlled conditions and thermal treating the samples in order to study dynamical processes. Case studies are reported in order to show the performances of the apparatus.

Treatment of EXAFS data taken in the fluorescence mode in non-linear conditions.

The aim of this work is to investigate the possibility of extracting correct structural parameters from fluorescence EXAFS data taken at high count rates with an energy-resolving detector. This situation is often encountered on third-generation synchrotron radiation sources which provide a high flux on the sample. Errors caused by pulse pile-up in the extraction of structural information have been quantified in a real experiment, and different approaches to the problem of data correction have been elaborated. The different approaches are discussed in a comparison of the ability of each kind of correction to recover the correct structural parameters. The result of our analysis is that it is possible to work in non-linear conditions and correct the data, if the response of the acquisition system is known. Reliable structural information can be obtained with data acquired up to a count rate equal to approximately 60% of the inverse of the dead time.

Luminescent properties of local atomic order of Er3+ and Yb3+ ions in aluminophosphate glasses

We report on an extended x-ray absorption fine structure (EXAFS) investigation on the local atomic order around rare earth (RE) ions in Er+Yb doped aluminophosphate glasses. Samples were obtained from the melt and the RE concentration ranged from 0.5 to 5 wt.u200a%. EXAFS data were analyzed within the multiple scattering formalism providing a detailed description of the atomic neighborhood in the first two shells. In particular, each RE in was found to be surrounded by ∼7 PO4 tetrahedra linked by corner O atoms. For RE concentrations below and above the luminescence “quenching” value, no detectable variations are reported leading us to exclude the formation of RE clusters within the sensitivity of the technique. From the analysis of the edge region a description of the density of free 5d states (linked to the radiative emission probability) is also obtained, which again shows no difference at the various RE concentrations.

High Yield Synthesis of Pure Alkanethiolate-Capped Silver Nanoparticles

One-phase, one-pot synthesis of Ag(0) nanoparticles capped with alkanethiolate molecules has been optimized to easily achieve a pure product in quantitative yield. We report the synthesis of dodecanethiolate-capped silver particles and the chemophysical, structural, and morphologic characterization performed by way of UV-vis, (1)H NMR, and X-ray photoelectron (XPS) spectroscopies, X-ray powder diffraction (XRD) and X-ray absorption fine structure analysis (XFAS), electron diffraction and high-resolution transmission electron microscopy (HR-TEM), and scanning and transmission electron microscopy (SEM and TEM). Depending on the molar ratio of the reagents (dodecylthiosulphate/Ag(+)), the mean Ag(0) particle size D(XRD) is tuned from 4 to 3 nm with a narrow size distribution. The particles are highly soluble, very stable in organic solvents (hexane, toluene, dichloromethane, etc.), and resistant to oxidation; the hexane solution after one year at room temperature does not show any precipitation or formation of oxidation byproducts.

Valence state and local atomic structure of copper in Cu-implanted silica glass

Copper implanted fused silica samples were investigated for the first time by depth-selective x-ray absorption techniques. X-ray absorption near-edge structure and extended x-ray absorption fine structure measurements were performed using both x-ray fluorescence yield and conversion electron yield detection configurations, with the aim to discriminate the contribution of the copper ions at different depths. The copper species were found in both oxidized and metallic states. A dependence of the oxidized copper amount on the depth was detected. Compositional analyses were made by means of secondary ion mass and Rutherford backscattering spectrometries. A matrix-damage related oxidation effect on copper atoms was confirmed.

Supported Rhodium Nanoparticles in Catalysis: the role of stabilizers on catalytic activity and structural features

Abstract Rhodium nanoparticles supported on γ-Al 2 O 3 , derived from arene-solvated Rh atoms stabilized by trioctylamine (TOA), are valuable catalysts in hydrogenation and silylformylation reactions. They are largely more active than the analogous commercial catalyst, as well as of a sample similarly prepared in the absence of TOA. HRTEM measurements, IR studies on adsorbed CO species and extended X-ray absorption fine structure analyses evidenced the role of TOA in controlling the particle growth in the preparative process and in stabilizing the resulting Rh particles against erosion by CO and oxidation.

Local structure of hole-doped manganites: influence of temperature and applied magnetic field

We report an extended x-ray absorption fine-structure investigation on the Mn K absorption edge in La1-xCaxMnO3 as a function of temperature and magnetic field. The results provide microscopic evidence that the modifications in the local structure around Mn atomic sites, as a function of temperature and applied magnetic field, are directly related to the magneto-transport properties of these materials.

Bond length variation in In0.25Ga0.75As/InP epitaxial layers thicker than the critical thickness

We address the issue of the local structure in an epitaxial semiconductor thin film undergoing strain relaxation due to extended defects when the critical thickness for their introduction is exceeded. The nearest neighbor environment is probed by x-ray absorption fine structure spectroscopy. The particular system studied is a set of In0.25Ga0.75As films grown on InP(001) of increasing thickness; the thicknesses were chosen so as to obtain a varying degree of relaxation, ranging from pseudomorphic growth to completely relaxed state. The samples have been thoroughly characterized with complementary structural techniques and the residual strain is measured by x-ray diffraction. We find that the Ga–As bond length exhibits a linear decrease with decreasing residual strain. By comparing these results with previous studies on bond lengths in pseudomorphic InxGa1−xAs films as a function of concentration we conclude that the bond lengths have an identical behavior as a function of the mean residual strain independ...

EXAFS study of Cu-ZnO/Al2O3 catalysts for the low-temperature CO shift reaction

EXAFS measurements by means of synchrotron radiation of Cuue5f8ZnOAl2O3 CO shift catalysts and various reference compounds (Cu, CuO, Cu2O, ZnO, and spinels) show the presence of CuO and ZnO in fresh catalysts and of highly dispersed Cu and ZnO after activation and reduction. The presence of Cu2O and spinels is excluded within the detection limits. The results are in agreement with previously reported XANES studies of the same catalyst samples.