XANES

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

XAFS study of Ti-silicalite : structure of framework Ti(IV) in presence and in absence of reactive molecules (H2O, NH3)

Abstract: X-ray absorption at the Ti K edge (both XANES and EXAFS) of a very pure Ti-silicalite containing a small fraction of Ti(IV) substituting Si(IV), has been performed in order to study the effect of the presence or absence of ligands such as H2O and NH3 on the Ti(IV) coordination sphere. In particular, the effect of an outgassing treatment at 400 K and of the interaction with NH3 has been studied and described in detail. It has been found that the Ti(FV) is fourfold coordinated in the samples outgassed at 400 K and expands its coordination sphere number under the action of adsorbates.

Photoinduced Surface Oxidation and Its Effect on the Exciton Dynamics of CdSe Quantum Dots

Abstract: With increased interest in semiconductor nanoparticles for use in quantum dot solar cells there comes a need to understand the long-term photostability of such materials. Colloidal CdSe quantum dots (QDs) were suspended in toluene and stored in combinations of light/dark and N2/O2 to simulate four possible benchtop storage environments. CdSe QDs stored in a dark, oxygen-free environment were observed to better retain their optical properties over the course of 90 days. The excited state lifetimes, determined through femtosecond transient absorption spectroscopy, of air-equilibrated samples exposed to light exhibit a decrease in average lifetime (0.81 ns) when compared to samples stored in a nitrogen/dark environment (8.3 ns). A photoetching technique commonly used for controlled reduction of QD size was found to induce energetic trap states to CdSe QDs and accelerate the rate of electron–hole recombination. X-ray absorption near edge structure (XANES) analysis confirms surface oxidation, the extent of whi...

Ab initiostudy of the physical properties ofγ-Al2O3: Lattice dynamics, bulk properties, electronic structure, bonding, optical properties, and ELNES/XANES spectra

Abstract: Based on the most recently determined noncubic structure for -Al2O3 by Menendez-Proupin and Gutierrez, a comprehensive list of physical properties is investigated theoretically. These include lattice dynamics and phonon spectra, elastic constants and bulk structural parameters, electronic structure and interatomic bonding, optical properties, and x-ray absorption near-edge structure XANES spectra. Compared to similar calculations of -Al2O3, we find a smaller lowest zone-center vibrational mode at 97.6 cm −1, a lower heat capacity, a smaller bulk modulus, and a much larger thermal-expansion coefficient. The threefold bonded O ions introduce highly localized vibrational modes near 751 cm−1. The calculated thermal Gruneisen parameter indicates a strong anharmonicity in -Al2O3. The elastic tensor and the elastic wave velocities are also evaluated showing the longitudinal wave to be nearly isotropic. For the electronic structure, we find that -Al2O3 has a smaller band gap but a refractive index similar to -Al2O3. Highly localized states at the top of the valence band originating from threefold bonded O in the more covalently bonded AlO4 tetrahedra are identified. The calculated Mulliken effective charges and bond order values indicate that the structural model for -Al2O3 has a high degree of disorder. The octahedral unit AlO6 is a stronger polyhedron than the tetrahedral unit AlO4 although the latter has stronger Al–O bonds. The calculated Al-K, Al-L3, and O-K edges for Al and O in -Al2O3 show strong dependence on their local coordination and environments. These results are in good agreement with available experimental data but the effect of the -Al2O3 samples’ porosity should be properly assessed. It is argued that the traditional view that stoichiometric -Al2O3 is a defective spinel with cation vacancies or its variations should be modified. -Al2O3 is better described as an amorphous networklike structure such that the ratio of tetrahedrally coordinated Al to octahedrally coordinated Al is close to 0.6; and the O ions are bonded to Al in either a threefold or fourfold configurations in about equal proportion.

XANES study of Cu2+-binding sites in aquatic humic substances.

Abstract: The structure and composition of the inner shell of copper (II) complexes with aquatic humic substances (HS) were studied by X-ray absorption near-edge structure (XANES) spectroscopy. The interpretation of the XANES data was based on FEFF8 code real-space multiple-scattering calculations for the prototype [Cu(H2O)6]2+ complex. These calculations reproduced the tetragonal distortion of the CuO6 octahedron representing the inner shell. They also demonstrated the polarization nature of this effect's manifestations (“splitting” of the derivative) in XANES. The extension of this interpretation to the Cu−HS system confirmed suppression of the tetragonal distortion of the inner shell in these species established by independent EXAFS experiments. XANES measurements for Cu/C ratios varying from 0.0005 to 0.03 demonstrated the nonuniform nature of copper binding sites. Experiments with Cu−ethylenediamine and Cu−glycine model systems and FEFF8 calculations indicated that for low copper concentrations (Cu/C < 0.005) ...