XANES

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

Reaction of NH3 with titania: N-doping of the oxide and TiN formation

Abstract: The thermal nitridation of titania powder (anatase and P25) by reaction with ammonia has been investigated by in-situ reaction studies and ex-situ characterizations using X-ray photoelectron spectroscopy (XPS), near-edge X-ray absorption fine structure (NEXAFS), and X-ray diffraction (XRD). At temperatures below 750 °C, the formation of TiN from the reaction of NH3 with the titania sample was negligible. Above 750 °C, in-situ reaction studies using XRD revealed a smooth phase transition from anatase or P25 to cubic TiN. On the basis of comprehensive characterizations, the crystalline structure of nitrogen-doped TiO2 is in general similar to that of TiO2. Incorporation of nitrogen into the interstitial sites of TiO2 anatase is supported by Rietveld refinement of XRD data. Interstitial nitrogen may form N2-like species bound to either oxygen vacancies or the cavity-framework atoms with various degrees of bond strength. N 1s XPS and N K-edge NEXAFS spectra support the idea that nitrogen present in titania as...

Electronic and molecular structure of photoexcited [Ru-II(bpy)(3)](2+) probed by picosecond X-ray absorption spectroscopy

Abstract: L(2,3) X-ray absorption spectra of aqueous [Ru(II)(bpy)3]2+ have been recorded in its ground and excited states, 50 ps after short pulse laser excitation. Significant changes in both the XANES (X-ray Near-Edge Absorption Structure) and the EXAFS (Extended X-ray Absorption Fine Structure) regions of the excited state complex are detected. The XANES line shapes have been quantitatively simulated using a crystal field multiplet code in trigonal symmetry. In addition, spectral changes in the EXAFS region of both ground and excited states are analyzed in order to extract structural parameters of their corresponding molecular structures. We obtain a Ru-N bond contraction by approximately 0.03 angstroms in the excited-state complex, as compared to the ground-state compound. This contraction results from electrostatic and polarization contributions, limited by steric constraints on the bpy ligands.

Molecular Structural Dynamics Probed by Ultrafast X-Ray Absorption Spectroscopy

Abstract: The ability to visualize molecular structure in the course of a chemical reaction or a biological function has been a dream of scientists for decades. X-ray absorption spectroscopy (XAS) is ideal in this respect because it is chemically selective and can be implemented in any type of medium. Furthermore, using X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) in laser pump/X-ray probe experiments allows the retrieval of not only the local geometric structure of the system under study, but also the underlying electronic structure changes that drive the structural dynamics. We review recent developments in picosecond and femtosecond XAS applied to molecular systems in solution. Examples on ultrafast photoinduced processes such as intramolecular electron transfer, low-to-high spin change, and bond formation are presented.

A novel Li2FeSiO4/C composite: Synthesis, characterization and high storage capacity

Abstract: A Li2FeSiO4/C composite material has been prepared via a solution-polymerization approach. The composite is characterized by X-ray diffraction (XRD), X-ray absorption near edge structure (XANES), scanning electron microscope (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), and superconducting quantum interference device (SQUID). The electrochemical performance of the Li2FeSiO4 is greatly enhanced and the initial discharge capacity is ∼220 mA h g−1, when it is cycled between 1.5–4.8 V. This indicates that more than one lithium ion can be extracted out of the Li2FeSiO4 lattice. At high current densities, the Li2FeSiO4/C also exhibits excellent rate capability and cycling stability. This indicates that it is a very promising cathode material for next generation lithium-ion batteries.