scholarly journals X-Ray Absorption Spectroscopy beyond the Core-Hole Lifetime

1993 ◽  
Vol 32 (S2) ◽  
pp. 170 ◽  
Author(s):  
Keijo Hämäläinen ◽  
J. B. Hastings ◽  
D. Peter. Siddons ◽  
Lonny Berman
Keyword(s):  
Absorption Spectroscopy ◽  
Core Hole ◽  
X Ray ◽  
The Core ◽  
X Ray Absorption

Anisotropy of the core-hole relaxation in x-ray-absorption spectroscopy as probed in square planar cuprates

1992 ◽  
Vol 45 (14) ◽  
pp. 8091-8096 ◽  
Author(s):  
H. Tolentino ◽  
M. Medarde ◽  
A. Fontaine ◽  
F. Baudelet ◽  
E. Dartyge ◽  
...  
Keyword(s):  
Absorption Spectroscopy ◽  
Core Hole ◽  
X Ray ◽  
The Core ◽  
Square Planar ◽  
X Ray Absorption

CORE-HOLE EFFECT IN THE Ce L3 X-RAY ABSORPTION SPECTRA OF CeO2 AND CeFe2: NEW EXAMINATION BY USING RESONANT X-RAY EMISSION SPECTROSCOPY

2013 ◽  
Vol 27 (16) ◽  
pp. 1330012 ◽  
Author(s):  
A. KOTANI
Keyword(s):  
Absorption Spectra ◽  
Ground State ◽  
Theoretical Calculations ◽  
Emission Spectra ◽  
Core Hole ◽  
Final State ◽  
X Ray ◽  
The Core ◽  
X Ray Absorption ◽  
Hole Effect

We consider two different resonant X-ray emission spectra for Ce compounds: Ce 3d to 2p X-ray emission (denoted by 3d-RXES) and valence to 2p X-ray emission (v-RXES), both of which follow the Ce 2p to 5d resonant excitation. We propose that the comparison of the 3d- and v-RXES spectra is a new powerful method of directly detecting the core-hole effect in the final state of Ce L 3 X-ray absorption spectra (XAS). We applied this method to recent experimental RXES spectra for CeO 2 and CeFe 2, and showed unambiguously that the core-hole effect should be essential in the XAS of both materials. This result is confirmed by theoretical calculations, which reproduce well the experimental RXES and XAS spectra. We conclude that the ground state of CeO 2 is in the mixed state of 4f0 and [Formula: see text] configurations, where [Formula: see text] is a ligand hole, instead of a pure 4f0 configuration which was proposed recently by first-principles energy band calculations. Also, we conclude that the double peaks observed in L 3 XAS of CeFe 2 are caused by the 4f0 and 4f1 configurations, which are mixed in the ground state but separated in energy by the large core-hole potential in the final state of XAS.

scholarly journals Spectral weight of resonant inelastic X-ray scattering in doped cuprates: Effect of core-hole lifetime

2018 ◽  
Vol 32 (17) ◽  
pp. 1840017 ◽  
Author(s):  
Takami Tohyama ◽  
Kenji Tsutsui
Keyword(s):  
Spectral Weight ◽  
Main Peak ◽  
Core Hole ◽  
X Ray ◽  
The Core ◽  
X Ray Scattering ◽  
Spin Flip ◽  
X Ray Absorption ◽  
Magnon Excitation ◽  
Ray Scattering

We examine the effect of core-hole lifetime on the spectral weight of resonant inelastic X-ray scattering (RIXS) in hole-doped cuprates. We calculate the spectral weight by using the exact diagonalization technique for a 4 × 4 doped Hubbard lattice and find that the spin-flip channel detecting single-magnon excitation is less sensitive to the core-hole lifetime while in the non-spin-flip channel the spectral weight is strongly dependent on the lifetime. In the latter, charge and two-magnon excitations predominately contribute to RIXS for short and long core-hole lifetimes, respectively. For a realistic value of the core-hole lifetime in cuprates, both the charge and two-magnon excitations are expected to contribute to the non-spin-flip channel in RIXS when the incident-photon energy is tuned to the main peak of X-ray absorption spectrum.

scholarly journals Finite lifetime broadening of calculated X-ray absorption spectra: possible artefacts close to the edge

2018 ◽  
Vol 25 (2) ◽  
pp. 523-528 ◽  
Author(s):  
Ondřej Šipr ◽  
Jiří Vackář ◽  
Ján Minár
Keyword(s):  
Absorption Spectra ◽  
Real Axis ◽  
Absorption Edge ◽  
Spectral Features ◽  
Core Hole ◽  
Energy Component ◽  
X Ray ◽  
The Core ◽  
X Ray Absorption ◽  
Small Imaginary Part

X-ray absorption spectra calculated within an effective one-electron approach have to be broadened to account for the finite lifetime of the core hole. For methods based on Green's function this can be achieved either by adding a small imaginary part to the energy or by convoluting the spectra on the real axis with a Lorentzian. By analyzing the FeK- andL2,3-edge spectra it is demonstrated that these procedures lead to identical results only for energies higher than a few core-level widths above the absorption edge. For energies close to the edge, spurious spectral features may appear if too much weight is put on broadeningviathe imaginary energy component. Special care should be taken for dichroic spectra at edges which comprise several exchange-split core levels, such as theL3-edge of 3dtransition metals.

X-ray absorption spectroscopy studies of phase transformations and amorphicity in nanotitania powder and silica–titania core–shell photocatalysts

2008 ◽  
Vol 41 (6) ◽  
pp. 1009-1018 ◽  
Author(s):  
S. H. Lim ◽  
N. Phonthammachai ◽  
T. Liu ◽  
T. J. White
Keyword(s):  
Absorption Spectroscopy ◽  
Sol Gel ◽  
Local Environment ◽  
Core Shell ◽  
Transformation Mechanism ◽  
X Ray ◽  
Amorphous Content ◽  
Silica Substrate ◽  
The Core ◽  
X Ray Absorption

The local environment of titanium in nanocrystalline sol-gel synthesized titania, cobaltiferous titania and silica–titania core–shell photocatalysts was investigated using X-ray absorption spectroscopy (XAS). Anatase reconstructively transforms to rutileviaa persistent amorphous phase that is retained, in part, up to 1273 K. In nanotitania, temperature-dependent trends in Ti order correlation observed by XAS parallel the development of amorphous content extracted from powder X-ray diffraction patterns, such that amorphicity shows a transient maximum at ∼873 K with the onset of rutile crystallization. Cobaltiferous and core–shell materials behaved similarly, but with anatase retained to 973 and 1273 K, respectively. In the former, cobalt redox reactions may stabilize anatase to higher temperatures by ready charge-balancing during the loss of hydroxyl and the formation of oxygen vacancies. In the core–shell architecture, higher Ti coordination and interatomic distance variance in the first- and second-nearest-neighbour shells are maintained to 1273 K by interaction of a substantially aperiodic TiO6network with the glassy silica substrate, which inhibits crystallization of rutile from the amorphous intermediate. Comparisons are also drawn with the commercial P25 catalyst. The overall transformation mechanism can be summarized as gel → non-stoichiometric anatase → amorphous titania → rutile. Smaller anatase crystals and a higher average Ti—Ti coordination environment in the core–shell structure may enhance photocatalytic activity directly, by creating larger specific surface areas and hosting reactive defects, or indirectly, by inhibiting exciton annihilation in aperiodic titania and delaying the crystallization of less photoactive rutile.

STUDY OF ELECTRONIC STRUCTURE OF MgB2 BY MULTIPLE-SCATTERING CALCULATIONS OF B K-EDGE XANES

2002 ◽  
Vol 16 (11n12) ◽  
pp. 1605-1612
Author(s):  
ZIYU WU ◽  
N. L. SAINI ◽  
A. BIANCONI
Keyword(s):  
Multiple Scattering ◽  
Density Of States ◽  
Core Hole ◽  
Edge Structure ◽  
X Ray ◽  
The Core ◽  
Al Substitution ◽  
Band Structure Calculations ◽  
X Ray Absorption ◽  
Structure Calculations

The MgB 2 system is studied by self consistent multiple-scattering calculations at the B K-edge X-ray absorption near edge structure (XANES). We find that the features in the B K-edge XANES are strongly affected by medium and long range order with large influence of the core hole potential suggesting that the band structure calculations are not enough to provide a quantitative interpretation of the spectral features. We have investigated evolution of density of states in the conduction band as a function of Al substitution in place of the Mg. The results are consistent with the fact that the Al substitution influences mainly the density of states in the B σ-band and hence suppresses the superconductivity.

XAFS in the high-energy region

1998 ◽  
Vol 5 (3) ◽  
pp. 1007-1009 ◽  
Author(s):  
Y. Nishihata ◽  
O. Kamishima ◽  
Y. Kubozono ◽  
H. Maeda ◽  
S. Emura
Keyword(s):  
Fine Structure ◽  
Energy Region ◽  
High Energy ◽  
High Energy Region ◽  
Core Hole ◽  
X Ray ◽  
The Core ◽  
Absorption Fine ◽  
X Ray Absorption ◽  
Absorption Edges

XAFS (X-ray absorption fine-structure) spectra were measured near K-absorption edges of Ce (40.5 keV), Dy (53.8 keV), Ta (67.4 keV) and Pt (78.4 keV). The blunt K-edge jump due to the finite lifetime of the core hole was observed. This makes it difficult to extract EXAFS (extended X-ray absorption fine-structure) functions at low k values. Local structure parameters can be evaluated from the EXAFS spectra above K-absorption edges in the high-energy region as well as from those above L III-edges. It was found that the finite-lifetime effect of the core hole is effectively taken into the photoelectron mean-free-path term, as predicted theoretically.

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