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- Guo, J. H., et al.
(författare)
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X-ray spectroscopic study of the charge state and local ordering of room-temperature ferromagnetic Mn-doped ZnO
- 2007
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Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 19:17
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Tidskriftsartikel (refereegranskat)abstract
- The charge state and local ordering of Mn doped into a pulsed laser deposited single-phase thin film of ZnO are investigated by using x-ray absorption spectroscopy at the O K-edge, Mn K-edge and L-edge, and x-ray emission spectroscopy at the O K-edge and Mn L-edge. This film is ferromagnetic at room temperature. EXAFS measurement shows that Mn2+ replaces the Zn site in tetrahedral symmetry, and there is no evidence for either metallic Mn or MnO in the film. Upon Mn doping, the top of O 2p valence band extends into the bandgap, indicating additional charge carriers being created.
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| 5. |
- Kvashnina, Kristina, et al.
(författare)
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Changes in electronic structure of copper films in aqueous solutions
- 2007
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Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 19:22, s. 226002-
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Tidskriftsartikel (refereegranskat)abstract
- The possibilities for using x-ray absorption spectroscopy (XAS) and resonant inelastic x-ray scattering (RIXS) to probe the Cu oxidation state and changes in the electronic structure during interaction between copper and ground-water solutions were examined. Surface modifications induced by chemical reactions of oxidized 100 Å Cu films with Cl−, SO42− and HCO3− ions in aqueous solutions with various concentrations were studied in situ using liquid cells. Copper corrosion processes in ground water were monitored for up to nine days. By comparing Cu 2p–3d, 4s transitions for a number of reference substances previously measured, changes in electronic structure of the Cu films were analysed. The XAS and RIXS spectral shape at the Cu edge, the chemical shift of the main line for Cu2+, and the energy positions of the observed satellites served as a tool for monitoring the changes during the reaction. It was found that the pH value and the Cl− concentration in solutions strongly affect the speed of the corrosion reaction.
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- Kvashnina, Kristina O., et al.
(författare)
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In situ X-ray absorption study of copper films in ground water solutions
- 2007
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Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614 .- 1873-4448. ; 447:1-3, s. 54-57
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Tidskriftsartikel (refereegranskat)abstract
- This study illustrates how the damage from copper corrosion can be reduced by modifying the chemistry of the copper surface environment. The surface modification of oxidized copper films induced by chemical reaction with Cl− and in aqueous solutions was monitored by in situ X-ray absorption spectroscopy. The results show that corrosion of copper can be significantly reduced by adding even a small amount of sodium bicarbonate. The studied copper films corroded quickly in chloride solutions, whereas the same solution containing 1.1 mM prevented or slowed down the corrosion processes.
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- Kvashnina, Kristina, et al.
(författare)
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Resonant inelastic x-ray scattering of curium oxide
- 2007
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 75:11, s. 115107-
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Tidskriftsartikel (refereegranskat)abstract
- The measurements on radioactive actinide isotopes (curium-248) were performed using very small sample quantities (micrograms) to minimize the sample activity. Resonant inelastic x-ray scattering (RIXS) spectra of curium oxide at the Cm 5d edge were measured for the first time. RIXS data are compared with theoretical calculations using atomic multiplet theory. The results indicate that isotope curium -248 in the curium oxide sample has oxidation state III due to the best agreement with RIXS calculations for Cm (III) instead of those for Cm (IV).
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- Magnuson, Martin, 1965-, et al.
(författare)
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Large magnetic circular dichroism in resonant inelastic x-ray scattering at the Mn L-edge of Mn-Zn ferrite
- 2006
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 74
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Tidskriftsartikel (refereegranskat)abstract
- Wereport resonant inelastic x-ray scattering (RIXS) excited by circularly polarizedx rays on Mn-Zn ferrite at the Mn L2,3 resonances.We demonstrate that crystal-field excitations, as expected for localized systems,dominate the RIXS spectra and thus their dichroic asymmetry cannotbe interpreted in terms of spin-resolved partial density of states,which has been the standard approach for RIXS dichroism. Weobserve large dichroic RIXS at the L2 resonance which weattribute to the absence of metallic core hole screening inthe insulating Mn ferrite. On the other hand, reduced L3-RIXSdichroism is interpreted as an effect of longer scattering timethat enables spin-lattice core hole relaxation via magnons and phononsoccurring on a femtosecond time scale.
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- Magnuson, Martin, 1965-, et al.
(författare)
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Uranium oxides investigated by X-ray absorption and emission spectroscopies
- 2006
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Ingår i: Applied Surface Science. - : Elsevier BV. - 0169-4332 .- 1873-5584. ; 252:115, s. 5615-6518
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Tidskriftsartikel (refereegranskat)abstract
- X-ray absorption and resonant X-ray emission measurements at the O 1s edge of the uranium oxides UO2, U3O8 and UO3 are presented. The spectral shapes of the O Kα X-ray emission spectra of UO3 exhibit significant excitation energy dependence, from an asymmetric to a symmetric form, which differs from those of UO2 and U3O8. This energy dependence is attributed to a significant difference in the oxygen–uranium hybridization between two different sites in the crystal structure of UO3. The spectral shapes of UO2 and U3O8 are also found to be different but without significant energy dependence. The experimental spectra of the valence and conduction bands of the uranium oxides are compared to the results of electronic structure calculations available in the literature.
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| 11. |
- Modin, A., et al.
(författare)
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Electronic structure of Cu3N films studied by soft x-ray spectroscopy
- 2008
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Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 20:23
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Tidskriftsartikel (refereegranskat)abstract
- Soft x- ray emission spectroscopy was used to characterize the electronic structure of seven copper nitride films, one synthesized with atomic layer deposition ( ALD) and six grown with chemical vapor deposition ( CVD) at different preparation temperatures. Interpretation of the x- ray emission spectra was supported by calculations of the electronic structure for bulk pure Cu3N and Cu3N with: an excess of Cu atoms, oxygen or carbon impurities, and N vacancies. The calculations are shown to describe the experimental spectra quite well. Analysis of the x- ray spectra suggests that films grown in copper rich environments and above a cut- off temperature of approximately 360 degrees C have a growing fraction of copper enriched areas, while films prepared below this temperature do not have these areas with excess copper.
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- Modin, Anders, 1975-
(författare)
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Resonant Soft X-ray Spectroscopic Studies of Light Actinides and Copper Systems
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Light actinides and copper systems were studied using resonant soft X-ray spectroscopy.An instrumental and experimental setup for soft X-ray spectroscopy meeting the requirements of a closed source for radioactivity was developed and described in detail. The setup was used for studies of single-crystal PuO2 oxidation. The existence of higher oxidation state than Pu(IV) in some surface areas of the single crystal were found from O 1s X-ray absorption measurements. Furthermore, from comparison with first principles calculations it was indicated that plutonium oxide with Pu fraction in a higher oxidation state than Pu(IV) consists of inequivalent sites with Pu(IV)O2 and Pu(V)O2 rather than a system where the Pu oxidation state is constantly fluctuating between Pu(IV) an Pu(V).It was shown that a combination of resonant O Kα X-ray emission and O 1s X-ray absorption spectroscopies can be used to study electron correlation effects in light-actinide dioxides.The electronic structure of copper systems was studied using resonant inelastic soft X-ray scattering and absorption spectroscopy. It was found that X-ray absorption can be used to monitor changes in the oxidation state but as differences between systems with the same oxidation state are in many cases small, speciation is uncertain. Therefore, a method utilizing resonant inelastic X-ray scattering as fingerprint to characterize complex copper systems was developed. The data recorded at certain excitation energies revealed unambiguous spectral fingerprints for different divalent copper systems. These specific spectral fingerprints were then used to study copper films exposed to different solutions. In particular, it was shown that resonant inelastic X-ray scattering can be used in situ to distinguish between CuO and Cu(OH)2, which is difficult with other techniques.
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