| 1. |
- Butorin, Sergei, et al.
(author)
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Effect of Ag Doping on Electronic Structure of Cluster Compounds AgxMo9Se11 (x = 3.4, 3.9)
- 2018
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In: ACS Applied Energy Materials. - : American Chemical Society (ACS). - 2574-0962. ; 1:8, s. 4032-4039
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Journal article (peer-reviewed)abstract
- The electronic structure of AgxMo9Se11 as a potential material for thermoelectric applications was studied using high-energy-resolution fluorescence-detection X-ray absorption spectroscopy (HERFD-XAS) and the resonant inelastic X-ray scattering (RIXS) technique. The experiments were supported by first-principle calculations using density functional theory (DFT). The analysis of obtained spectra indicate the presence of subvalent (less than 1+) Ag in AgxMo9Se11. The advanced HERFD-XAS measurements allowed us to resolve the contribution of the electronic states at the Fermi level of AgxMo9Se11 and to monitor its dependence on the x value. A comparison of the experimental data with the results of the DFT calculations suggests the importance of the Ag2-type sites with the shortest Ag–Se distance for affecting the properties of AgxMo9Se11.
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| 2. |
- Kapaklis, Vassilios, et al.
(author)
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Temperature dependence of the electrical resistivity and electronic structure of amorphous Fe100-xZrx films and multilayers
- 2012
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In: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 24:49, s. 495402-
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Journal article (peer-reviewed)abstract
- The electrical resistivity of amorphous Fe100-xZrx metal alloy films and multilayers has been investigated in a wide temperature and composition range. The overall behavior of the resistivity is consistent with bulk measurements, exhibiting prominent semiconductor-like changes at low temperatures. The transition from positive (metallic) to negative temperature coefficient of resistivity behavior is accompanied by minute changes in magnetoresistance and we can therefore rule out magnetic phase changes as being the cause for the observed changes in the resistivity. Using x-ray absorption and emission spectroscopies we are able to probe the unoccupied and occupied electronic densities of states. The corresponding spectra are found to significantly overlap, as expected for a metallic-like electronic structure and the absence of a band gap. Besides a broadening of the x-ray emission lines expected from an amorphous material, remarkably small differences are observed in the electronic structures when changing the amount of Zr. The resistivity data were modeled and agreement with the Mott variable range hopping model was found, indicating localized electronic states due the disordered structure of the Fe100-xZrx alloys.
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| 3. |
- Kotani, A., et al.
(author)
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Spectator and participator processes in the resonant photon-in and photon-out spectra at the Ce L-3 edge of CeO2
- 2012
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In: European Physical Journal B. - : Springer Science and Business Media LLC. - 1434-6028 .- 1434-6036. ; 85:8, s. 257-
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Journal article (peer-reviewed)abstract
- We study both theoretically and experimentally the photon-in and photon-out spectra of CeO2, which are caused by the Ce 2p to Ce 5d excitation followed by the three different de-excitation channels: (i) Ce 3d to Ce 2p (denoted by 3d-RXES), (ii) O 2p to Ce 2p (v-RXES), and (iii) Ce 5d to Ce 2p (RIXS). In 3d- and v-RXES, the 5d electron plays a role of a spectator, but in RIXS it is a participator. By extending our single impurity Anderson model (SIAM), which was used recently for our calculations of v-and 3d-RXES spectra of CeO2, we study the polarization dependence in the spectator and participator spectra, and we perform more detailed calculations for 3d- and v-RXES spectral features, as well as new calculations for the RIXS spectrum with charge transfer excitations. The polarization dependence is different for the spectator and participator spectra; we have no polarization correlation between the incident and emitted photons for the spectator spectra but a strong polarization correlation for the participator spectrum. The theoretical calculations predict that the charge transfer excitations in RIXS occur in the transfer-energy range overlapped with v-RXES, but the RIXS and v-RXES spectra can be discriminated by taking advantage of the different polarization dependence. The overlapped RIXS and v-RXES spectra are observed successfully by our experiments and well reproduced by our SIAM calculations.
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| 4. |
- Kvashnina, K. O., et al.
(author)
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Chemical State of Complex Uranium Oxides
- 2013
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In: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 111:25, s. 253002-
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Journal article (peer-reviewed)abstract
- We report here the first direct observation of U(V) in uranium binary oxides and analyze the gradual conversion of the U oxidation state in the mixed uranium systems. Our finding clarifies previous contradicting results and provides important input for the geological disposal of spent fuel, recycling applications, and chemistry of uranium species.
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| 5. |
- Kvashnina, K.O., et al.
(author)
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Electronic structure of complex copper systems probed by resonant inelastic X-ray scattering at Cu L3 edge
- 2009
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In: Physica. B, Condensed matter. - : Elsevier B.V.. - 0921-4526 .- 1873-2135. ; 404:20, s. 3559-3566
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Journal article (peer-reviewed)abstract
- We have used X-ray absorption (XA) and resonant inelastic X-ray scattering (RIXS) spectroscopies to study a series of copper compounds, namely Cu2O, CuO, Cu(OH)2, CuCl2, Cu2S, CuSO4, malachite (Cu2(CO3)2(OH)2) and atacamite (CuCl2·3Cu(OH)2). Cu 2p XA spectra provide information about oxidation states. Divalent copper gives a single narrow line due to excitations into the empty 3d state, whereas monovalent copper gives a broad band at higher energy due to transitions to 4s states. Chemical shifts of the main line in the Cu2+ XA spectra of different compounds are observed but in some cases they are too small to make a clear distinction between the species. It is shown that RIXS at the Cu 2p edge has a great potential to distinguish between the species due to large differences in spectral shapes for the same energy of the incident photon beam. First evidence for the possibility of detecting chemical composition of copper compounds is presented and discussed in details.
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| 6. |
- Kvashnina, K. O., et al.
(author)
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Role of resonant inelastic X-ray scattering in high-resolution core-level spectroscopy of actinide materials
- 2014
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In: Journal of Electron Spectroscopy and Related Phenomena. - : Elsevier BV. - 0368-2048 .- 1873-2526. ; 194, s. 27-36
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Journal article (peer-reviewed)abstract
- This paper provides a brief overview of applications of advanced X-ray spectroscopic techniques that take advantage of the resonant inelastic X-ray scattering (RIXS) in the hard and tender X-ray range and have recently become available for studying the electronic structure of actinides. We focus here on the high-energy-resolution X-ray absorption near edge structure (XANES) and core-to-core and core-to-valence RIXS spectroscopies at the U L and M edges of uranium compounds. The spectral features are analyzed using a number of theoretical methods, such as the Anderson impurity model, density functional theory in the local density approximation with an added Coulomb interaction (LDA + U), and full multiple scattering (FEFF) and ab initio finite difference method near-edge structure (FDMNES) codes. In connection with presented results, the capabilities and limitations of the experimental techniques and theoretical methods are discussed. (C) 2014 Elsevier B.V. All rights reserved.
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| 7. |
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| 8. |
- Modin, A., et al.
(author)
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Electronic structure of Cu3N films studied by soft x-ray spectroscopy
- 2008
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In: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 20:23
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Journal article (peer-reviewed)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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| 9. |
- Safdari, Majid, et al.
(author)
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Impact of synthetic routes on the structural and physical properties of butyl-1,4-diammonium lead iodide semiconductors
- 2017
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In: Journal of Materials Chemistry A. - : Royal Society of Chemistry. - 2050-7488 .- 2050-7496. ; 5:23, s. 11730-11738
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Journal article (peer-reviewed)abstract
- We report the significant role of synthetic routes and the importance of solvents in the synthesis of organic-inorganic lead iodide materials. Through one route, the intercalation of dimethylformamide in the crystal structure was observed leading to a one-dimensional (1D) [NH3(CH2)4NH3]Pb2I6 structure of the product. This product was compared with the two-dimensional (2D) [NH3(CH2)4NH3]PbI4 recovered from aqueous solvent based synthesis with the same precursors. UV-visible absorption spectroscopy showed a red-shift of 0.1 eV for the band gap of the 1D network in relation to the 2D system. This shift primarily originates from a shift in the valence band edge as determined from photoelectron-and X-ray spectroscopy results. These findings also suggest the iodide 5p orbital as the principal component in the density of states in the valence band edge. Single crystal data show a change in the local coordination around iodide, while in both materials, lead atoms are surrounded by iodide atoms in octahedral units. The conductivity of the one-dimensional material ([NH3(CH2)4NH3]Pb2I6) was 50% of the two-dimensional material ([NH3(CH2)4NH3]PbI4). The fabricated solar cells reflect these changes in the chemical and electronic structure of both materials, although the total light conversion efficiencies of solar cells based on both products were similar.
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| 10. |
- Vegelius, J. R., et al.
(author)
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Cu K beta(2,5) X-ray emission spectroscopy as a tool for characterization of monovalent copper compounds
- 2012
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In: Journal of Analytical Atomic Spectrometry. - : Royal Society of Chemistry (RSC). - 0267-9477 .- 1364-5544. ; 27:11, s. 1882-1888
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Journal article (peer-reviewed)abstract
- Cu Kβ 2,5 X-ray emission and resonant inelastic X-ray scattering measurements were performed on monovalent and divalent copper compounds. The data were compared with the results of local-density- approximation calculations. The methods were found to be efficient tools for studies of Cu 4p states in the valence band and for distinguishing between different monovalent copper compounds. This is of particular importance for the debate concerning copper corrosion in oxygen-free water.
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