168 research outputs found
High-Resolution X-ray Emission and X-ray Absorption Spectroscopy
In this review, high-resolution X-ray emission and X-ray absorption spectroscopy will be discussed. The focus is on the 3d transition-metal systems. To understand high-resolution X-ray emission and reso-nant X-ray emission, it is first necessary to spend some time discussing the X-ray absorption process. Section II discusses 1s X-ray absorption, i.e., the K edges, and section III deals with 2p X-ray absorption, the L edges. X-ray emission is discussed in, respectively, the L edges. X-ray emission is discussed in, respec-tively, and section V on 2p3s and 2p3d X-ray emission. Section VI focuses on magnetic dichroism effects, and in section VII selective X-ray absorption experiments are discussed. To limit the scope of this review paper, many related topics (for example, EELS, XPS, and resonant photoemission, phonon-oriented inelastic X-ray scat-tering, and X-ray microscopy) will not be discussed. In addition, many aspects of X-ray absorption, such as reflection experiments, diffraction absorption fine structure, and related experiments, will remain untouched. EXAFS will be discussed very briefly, and its X-ray emission analogue EXEFS 69,71 will not be discussed
Multiplet effects in Resonant X-ray Emission
After a short discussion of all conventional core level spectroscopies within the single
particle model, the effects of the coupling of the core and valence wave function on the x-ray
emission spectral shapes is discussed. It will be shown that these so-called multiplet effects
strongly affect all x-ray emission spectra taken around the metal 2p resonances. In case of 1s
resonances, valence band x-ray emission is not affected, but the spectral shapes of 1s2p and 1s3p
x-ray emission can only be sensibly described with the inclusion of multiplets. A special
example is the resonant excitation into the pre-edge region, which gives rise to a quadrupole
resonance
3s2p inelastic x-ray scattering of CaF 2
In this paper the 3s2p inelastic x-ray scattering (IXS) cross sections of CaF 2 are analyzed using a ligand-field
multiplet approach. All dipole matrix elements necessary for the IXS cross section are calculated and it is
shown that interference effects are not negligible. The important possibility to map out a specific character of
the 2p^5 3d^1 intermediate states is explained. The experimental results of Rubensson et al. are reproduced with
the ligand field multiplet model and the Kramers-Heisenberg equation of inelastic x-ray scattering. The values
found for the ligand-field splitting (20.91 eV) and the 3s3d exchange splitting (1.2 eV) differ from the results
fitted to experiment
Local spin-flip spectral distribution obtained by resonant x-ray Raman scattering
We show that resonant x-ray Raman (RXR) scattering can be used to study the local spin-flip excitation
spectral distribution in magnetically ordered 3d transition-metal compounds. We demonstrate with realistic
calculations on the 3p x-ray absorption edge of a Cu^2+ compound and the 2p edge of a Ni^2+ compound that
the scattered x-ray energy and intensity distribution contains the excitation spectrum resulting from a single
local spin flip, as well as dd excitations accompanied by local spin flip satellites. We develop the theory
describing this effect and discuss the polarization conditions that can be used to observe these effects
2p3s3p, 2p3p3p, and 2p3s3s resonant Auger spectroscopy from NiO
We have investigated the behavior of the 2p3s3p, 2p3p3p, and 2p3s3s Auger lines of NiO, a model
compound in the class of strongly correlated 3d systems, while varying the photon energy across the Ni L3 and
L2 absorption edges. The experimental data are discussed in comparison with a theoretical model based on a
charge-transfer multiplet approach. When the excitation energy is below the L3 resonance, we observe the
2p3p3p and 2p3s3p peaks at a constant binding energy. This behavior is typical of nonradiative resonant
Raman scattering. If the photon energy is increased further, the 2p3p3p and 2p3s3p lines rapidly transform
into constant kinetic energy features, showing a normal Auger behavior. The transition from Raman- to
Auger-like behavior takes place for photon energies lower than the ones corresponding to excitations of the
photoelectron into ligand-hole states. This might indicate the participation of inelastic processes in the recombination
of the core hole involving energies much smaller than the NiO gap, or the possible presence of
nonlocal effects. On the high photon energy side of the L3 edge, the constant kinetic energy of the 2p3p3p
and 2p3s3p peaks is systematically larger than the one observed for an excitation well above the L2,3 edges.
We attribute this behavior to the intervention of an intermediate state of 2p^5 3d^10 character, which has very
little weight but is strongly enhanced at resonance
Magnetic circular dichroism in the 2p4d x-ray emission of EuO
Magnetic circular dichroism is observed for ferromagnetic EuO (T C 569 K) in the b2,15 fluorescence at
incident photon energies resonant with the 2p 3/2 excitation. The dichroism is dominated by exchange interac-tion
between the localized 4 f electrons and the final state 4d core hole. The spectral shapes obtained by atomic
multiplet calculations for the 2p4d emission show good agreement with the experimental data
Spin-polarized x-ray emission of 3d transition-metal ions: A comparison via K a and K ß detection
This paper demonstrates that spin-polarized x-ray-excitation spectra can be obtained using K a emission as
well as K ß lines. A spin-polarized analysis of K a x-ray emission and the excitation spectra by K a detection
on a Ni compound is reported. A systematic analysis of the first-row transition-metal ions using the ligand-field
multiplet calculation is presented for K a and K ß emission spectra
Influence of the core hole on Kß emission following photoionization or orbital electron capture: a comparison using MnO and 55Fe2O3
The Mn K ß fluorescence emission in MnO after photoionization and in "Fe 2 O 3 after radioactive electron
capture decay from the K shell have been measured using a crystal array spectrometer with an instrumental
energy bandwidth of 0.7 eV (full width at half maximum). Both compounds have a 3d 5 valence electron
configuration in the ionic approximation. It is found that the spectral features after K capture in 55 Fe 2 O 3 are
shifted in emission energy and are sharper, compared to the spectra following photoionization in MnO, i.e., the
spectra exhibit a dependence on the mode of excitation. Crystal-field multiplet calculations including ligand-to-
metal charge transfer have been carried out for the 1s intermediate states as well as for the 3p to 1s (K ß)
radiative transition. The populated 1s intermediate states after photoionization are found to be spread over
several eV. In comparison, only the lowest-lying 1s intermediate states split by the weak (1s,3d) exchange
interaction are populated after K capture. It is proposed that the differences in population of the 1s intermediate
states together with a term-dependent final-state lifetime broadening can account for the changes in the spectral
shapes due to the different modes of excitation
L2,3 x-ray absorption spectroscopy and multiplet calculations for KMF3 and K2 NaMF6 (M=Ni, Cu)
The electronic structures of nickel and copper have been studied for KMF3 and K2NaMF6 compounds by a-ray absorption spectroscopy at the Ni and Cu L-2.3 edges in order to characterize the M-F chemical bond. The spectral features have been interpreted based on the mixing of two ground-state configurations \3d(n)) +\3d(n+1)](L) under bar. Multiplet calculations were used to simulate each spectrum in order to quantify the charge transfer from fluorine to the transition metal yielding a 40% ground-state contribution of the 3d(8) configuration for K2NaCuF6 and 65% of the 3d(7) configuration for K2NaNiF6
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