XANES

About: XANES is a research topic. Over the lifetime, 7737 publications have been published within this topic receiving 188032 citations.

Ultrathin Bi2S3 nanowires: surface and core structure at the cluster-nanocrystal transition.

Abstract: Herein, we present the structural characterization of the core and surface of colloidally stable ultrathin bismuth sulfide (Bi(2)S(3)) nanowires using X-ray Absorption Spectroscopy (EXAFS and XANES), X-ray Photoelectron Spectroscopy (XPS), and Nuclear Magnetic Resonance (NMR). These three techniques allowed the conclusive structural characterization of the inorganic core as well as the coordination chemistry of the surface ligands of these structures, despite the absence of significant translational periodicity dictated by their ultrathin diameter (1.6 nm) and their polycrystallinity. The atomic structure of the inorganic core is analogous to bulk bismuthinite, but Bi atoms display a remarkably higher coordination number than in the bulk. This can be only explained by a model in which each bismuth atom at the surface (or in close proximity to it) is bound to at least one ligand at any time.

Synthesis and microstructure of manganese ferrite colloidal nanocrystals

Abstract: The atomic level structure of a series of monodisperse single crystalline nanoparticles with a magnetic core of manganese ferrite was studied using X-ray absorption fine structure (EXAFS) and X-ray absorption near edge structure (XANES) techniques at both the Fe and Mn K-edges, and conventional and high resolution transmission electron microscopy (TEM and HRTEM). In particular, insights on the non-stoichiometry and on the inversion degree of manganese ferrite nanocrystals of different size were obtained by the use of complementary structural and spectroscopic characterization techniques. The inversion degree of the ferrite nanocrystals, i.e. the cation distribution between the octahedral and tetrahedral sites in the spinel structure, was found to be much higher (around 0.6) than the literature values reported for bulk stoichiometric manganese ferrite (around 0.2). The high inversion degree of the nanoparticles is ascribed to the partial oxidation of Mn2+ to Mn3+ which was evidenced by XANES, leading to non-stoichiometric manganese ferrite.

In situ transient FTIR and XANES studies of the evolution of surface species in CO oxidation on Au/TiO2.

Abstract: The adsorption of CO and its reaction with oxygen were investigated using a combination of in situ Fourier transform infrared spectroscopy, step response measurements in a microreactor, 18O isotopic labeling, and X-ray absorption near edge structure spectroscopy. An as-prepared sample in which Au is present as a surface oxyhydroxy complex does not adsorb CO. On an activated sample in which only metallic Au is detected, 0.18 ± 0.03 mol CO/(mol Au) are adsorbed on Au at −60 °C, which shows an IR band at 2090 cm-1. When oxygen is present in the gas phase, this species reacts with a turnover rate of 1.4 ± 0.2 mol CO(mol Au min)-1, which is close to the steady-state turnover rate. In contrast, there is a very small quantity of adsorbed oxygen on Au. A small IR peak at 1242 cm-1 appears when an activated sample is exposed to CO. It reacts rapidly with oxygen and is shifted to 1236 cm-1 if 18O is used. It is assigned to the possible intermediate hydroxycarbonyl.

Near Edge X-ray Absorption Fine Structure Spectroscopy Studies of Single-Crystalline V2O5 Nanowire Arrays

Abstract: Near edge X-ray absorption fine structure (NEXAFS) spectroscopy is used to precisely probe the alignment, uniformity in crystal growth direction, and electronic structure of single-crystalline V2O5 nanowire arrays prepared by a cobalt-catalyzed vapor transport process. The dipole selection rules operational for core-level electron spectroscopy enable angle-dependent NEXAFS spectroscopy to be used as a sensitive probe of the anisotropy of these systems and provides detailed insight into bond orientation and the symmetry of the frontier orbital states. The experimental spectra are matched to previous theoretical predictions and allow experimental verification of features such as the origin of the split-off conduction band responsible for the semiconducting properties of V2O5 and the strongly anisotropic nature of vanadyl−oxygen-derived (V═O) states thought to be involved in catalysis. The strong anisotropy observed across thousands of nanowires in the NEXAFS measurements clearly demonstrates the uniformity ...

Sulfur k-edge xanes spectroscopy: chemical state and content of sulfur in silicate glasses

Abstract: The chemical state and local environment of sulfur in basaltic glasses from the eastern Galapagos rift and quenched laboratory experiments have been investigated by synchrotron-radiation S K-edge X-ray absorption near-edge structure (XANES) spectroscopy, using an energy-selective fl uorescence detector. We have also investigated sulfur in melts in the system 6NaAlSiO4–CaS– CaSO4 quenched from 1500°C and various reference compounds, using conventional fl uorescence yield and total-electron yield (TEY) recording modes. The S K-edge XANES spectrum of CaS dissolved in Na-aluminosilicate glass is dominated by a broad singlet edge-feature near 2475 eV, consistent with isolated SCan coordination polyhedra in the melt, whereas that of quenched end-member CaSO4-bearing melt is similar to XANES spectra of crystalline sulfates. The linear correlation between relative XANES area and wt% content of sulfur has been used to estimate the content of sulfur in samples of lazurite (5.6–6.3 wt% by EPMA), scapolite-group minerals (0.4 wt%) and the basaltic glasses (0.04–0.15 wt%). The S K-edge XANES spectra of basaltic glasses synthesized under reducing (WM and IQF solid oxygen-buffer) conditions are dominated by a single broad absorption peak at 2470–2482 eV in combination with a weak peak or shoulder at 2470–2471 eV, and are reproduced by mixing XANES spectra of FeS and alkaline-earth monosulfi des. The S K-edge XANES spectra for glasses from the eastern Galapagos rift are also dominated by S 2– , but one TEY spectrum shows possible thiosulfate and another, trace sulfate.