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| 2. |
- Kikas, A., et al.
(författare)
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Resonant inelastic x-ray scattering at the F 1s photoabsorption edge in LiF : Interplay of excitonic and conduction states, and Stokes' doubling
- 2004
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 70:8
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Tidskriftsartikel (refereegranskat)abstract
- The excitation-decay processes at the F 1s photoabsorption edge in LiF crystal are studied using resonant inelastic x-ray scattering spectroscopy. The Raman-type linear dispersion and the narrowing of the x-ray fluorescence peak are observed at resonant excitation. A theoretical model based on the Kramers-Heisenberg formula describes well the main features in fluorescence spectra and allows one to separate the contributions of the exciton and the conduction states in the scattering spectra. At the same time, the role of the shape of the spectral distribution within the incident radiation is emphasized as being critically sensitive to the number, kind, and onset of the spectral features which finally appear in the scattering spectra at a particular incident photon energy, particularly in the subthreshold excitation region.
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| 3. |
- Käämbre, Tanel, 1970-
(författare)
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Resonant Soft X-ray Spectroscopic Studies of C60 and Related Materials
- 2002
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis addresses the electronic structure of molecular and correlated solids using resonant inelastic soft X-ray scattering (RIXS), non-resonant X-ray emission, photoemissionand X-ray absorption spectroscopies. The use of monochromatised synchrotron radiation and improved energy resolution for X-ray emission have made it possible to elucidate the normal state transport properties and to get further insight into the electron-vibration coupling in fullerenes and the related compounds. The latter is particularly important in order to understand the physical mechanism of superconductivity in fullerene materials. The characteristic intermolecular charge transfer times in K3C60 are found to be longer than the X-ray scattering time-scale (a few femtoseconds). The slow intermolecular charge transport emphasizes that the reduced fullerene compounds can not be treated as simple metals, but rather as systems with strong electron correlation. The electron structure and the bonding character of the more covalent transition metal (V, Ti, Nb) fullerides have been addressed. Evidence indicating the existence of chemical bond between the metal atom(s) and C60 is presented, and the nature of the bond is discussed by comparing RIXS spectroscopic measurements and theoretical predictions. The (crystal) momentum conservation is discussed by comparing the spectroscopic data of a quasi-1D (carbon nanotubes) and quasi-2D (graphite) systems. Finally, the intra-atomic electron-electron correlation is discussed in the case of double core-hole state photo-excitation and de-excitation processes. RIXS including intermediate states with two core vacancies has been observed for the first time in the soft X-ray region.
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| 4. |
- Magnuson, Martin, 1965-, et al.
(författare)
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Magnetic circular dichroism in X-ray fluorescence of Heuseler alloys at threshold excitation
- 2001
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Ingår i: Solid State Communications. - 0038-1098 .- 1879-2766. ; 117:2, s. 79-82
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Tidskriftsartikel (refereegranskat)abstract
- The results of fluorescence measurements of magnetic circular dichroism (MCD) in Mn L2,3 X-ray emission and absorption for Heusler alloys NiMnSb and Co2MnSb are presented. Very intense resonance Mn L3 emission is found at the Mn 2p3/2 threshold and attributed to a peculiarity of the threshold excitation in materials with a half-metallic character of the electronic structure. The excitation energy dependence of Mn L2,3 X-ray emission spectra (XES) was measured at beamline ID12B at the European Synchrotron Radiation Facility (ESRF, Grenoble) using 83% circularly polarized X-rays. A very large MCD effect found in XES is attributed to strong exchange splitting of spin-up and spin-down Mn 3d states. The anomalously high ratio of L2 emission intensity to L3 emission intensity is found.
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