| 11. |
- Magnuson, Martin, 1965-, et al.
(author)
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Interface bonding of Zr1−xAlxN nanocomposites investigated by x-ray spectroscopies and first principles calculations
- 2020
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In: Physical Review Research. - College Park, MD, United States : American Physical Society. - 2643-1564. ; 2:1
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Journal article (peer-reviewed)abstract
- The electronic structure, chemical bonding, and interface component in ZrN-AlN nanocomposites formed byphase separation during thin film deposition of metastable Zr1−xAlxN (x = 0.0, 0.12, 0.26, 0.40) are investigatedby resonant inelastic x-ray scattering, x-ray emission, and x-ray absorption spectroscopy and compared to firstprinciples calculations including transitions between orbital angular momentum final states. The experimentalspectra are compared with different interface-slab model systems using first principles all-electron full-potentialcalculations where the core states are treated fully relativistically. As shown in this work, the bulk sensitivity andelement selectivity of x-ray spectroscopy enables one to probe the symmetry and orbital directions at interfacesbetween cubic and hexagonal crystals. We show how the electronic structure develops from local octahedralbond symmetry of cubic ZrN that distorts for increasing Al content into more complex bonding. This results inthree different kinds of bonding originating from semicoherent interfaces with segregated ZrN and lamellar AlNnanocrystalline precipitates. An increasing chemical shift and charge transfer between the elements takes placewith increasing Al content and affects the bond strength and increases resistivity.
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| 12. |
- Marten, Tobias, 1979-, et al.
(author)
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Ab initio study of disorder broadening of core photoemission spectra in random Cu-Pd and Ag-Pd alloys
- 2005
-
In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 72:5
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Journal article (peer-reviewed)abstract
- A first-principles study of the effect of local environment on the electronic structure of random face-centered cubic Ag-Pd and Cu-Pd alloys is presented. The core-level shift for each atom in the equiatomic alloys is calculated and compared to experimental data. It is shown how the initial-state and final-state distributions contribute to the total broadening. We find that the initial-state and the final-state contributions together increase the broadening for the investigated core levels in Cu and Ag, whereas they cancel each other to a large degree for Pd. We also demonstrated how local lattice relaxations influence the binding energy shift. We find that relaxation does not influence the average shift, though it is able to affect the broadening of the simulated x-ray photoelectron spectroscopy spectra. © 2005 The American Physical Society.
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| 13. |
- Mizoguchi, T., et al.
(author)
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Excitonic, vibrational, and van der Waals interactions in electron energy loss spectroscopy
- 2017
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In: Ultramicroscopy. - : ELSEVIER SCIENCE BV. - 0304-3991 .- 1879-2723. ; 180, s. 93-103
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Journal article (peer-reviewed)abstract
- The pioneer, Ondrej L. Krivanek, and his collaborators have opened up many frontiers for the electron energy loss spectroscopy (EELS), and they have demonstrated new potentials of the EELS method for investigating materials. Here, inspired by those achievements, we show further potentials of EELS based on the results of theoretical calculations, that is excitonic and van der Waals (vdW) interactions, as well as vibrational information of materials. Concerning the excitonic interactions, we highlight the importance of the two-particle calculation to reproduce the low energy-loss near-edge structure (ELNES), the Na-L-2,L-3 edge of Nal and the Li-K edge of LiCI and LiFePO4. Furthermore, an unusually strong excitonic interaction at the O-K edge of perovskite oxides, SrTiO3 and LaAlO3, is shown. The effect of the vdW interaction in the ELNES is also investigated, and we observe that the magnitude of the vdW effect is approximately 0.1 eV in the case of the ELNES from a solid and liquid, whereas its effect is almost negligible in the case of the ELNES from the gaseous phase owing to the long inter-molecular distance. In addition to the static information, the influence of the dynamic behavior of atoms in materials to EELS is also investigated. We show that measurements of the infrared spectrum are possible by using a modern monochromator system. Furthermore, an estimation of the atomic vibration in core-loss ELNES is also presented. We show the acquisition of vibrational information using the ELNES of liquid methanol and acetic acid, solid Al2O3, and oxygen gas. (C) 2017 Elsevier B.V. All rights reserved.
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| 14. |
- Monteseguro, V, et al.
(author)
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Phase stability and electronic structure of iridium metal at the megabar range
- 2019
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In: Scientific Reports. - : Nature Publishing Group. - 2045-2322. ; 9
-
Journal article (peer-reviewed)abstract
- The 5d transition metals have attracted specific interest for high-pressure studies due to their extraordinary stability and intriguing electronic properties. In particular, iridium metal has been proposed to exhibit a recently discovered pressure-induced electronic transition, the so-called core-level crossing transition at the lowest pressure among all the 5d transition metals. Here, we report an experimental structural characterization of iridium by x-ray probes sensitive to both long- and short-range order in matter. Synchrotron-based powder x-ray diffraction results highlight a large stability range (up to 1.4 Mbar) of the low-pressure phase. The compressibility behaviour was characterized by an accurate determination of the pressure-volume equation of state, with a bulk modulus of 339(3) GPa and its derivative of 5.3(1). X-ray absorption spectroscopy, which probes the local structure and the empty density of electronic states above the Fermi level, was also utilized. The remarkable agreement observed between experimental and calculated spectra validates the reliability of theoretical predictions of the pressure dependence of the electronic structure of iridium in the studied interval of compressions.
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| 15. |
- Mosyagin, Igor, et al.
(author)
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Highly Efficient Free Energy Calculations of the Fe Equation of State Using Temperature-Dependent Effective Potential Method
- 2016
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In: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 120:43, s. 8761-8768
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Journal article (peer-reviewed)abstract
- Free energy calculations at finite temperature based on ab initio molecular dynamics (AIMD) simulations have become possible, but they are still highly computationally demanding. Besides, achieving simultaneously high accuracy of the calculated results and efficiency of the computational algorithm is still a challenge. In this work we describe an efficient algorithm to determine accurate free energies of solids in simulations using the recently proposed temperature-dependent effective potential method (TDEP). We provide a detailed analysis of numerical approximations employed in the TDEP algorithm. We show that for a model system considered in this work, hcp Fe, the obtained thermal equation of state at 2000 K is in excellent agreement with the results of standard calculations within the quasiharmonic approximation.
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| 16. |
- Olovsson, Weine, et al.
(author)
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Core-level shifts in complex metallic systems from first principle
- 2006
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In: Physica status solidi. B, Basic research. - : Wiley. - 0370-1972 .- 1521-3951. ; 243:11, s. 2447-2464
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Journal article (peer-reviewed)abstract
- We show that core-level binding energy shifts (CLS) can be reliably calculated within density functional theory. The scheme includes both the initial (electron energy eigenvalue) as well as final state (relaxation due to core-hole screening) effects in the same framework. The results include CLS as a function of composition in substitutional random bulk and surface alloys. Sensitivity of the CLS to the local chemical environment in the bulk and at the surface is demonstrated. A possibility to use the CLS for structural determination is discussed. Finally, an extension of the model is made for Auger kinetic energy shift calculations.
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| 17. |
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| 18. |
- Olovsson, Weine, et al.
(author)
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First principle calculations of core-level binding energy and Auger kinetic energy shifts in metallic solids
- 2010
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In: Journal of Electron Spectroscopy and Related Phenomena. - : Elsevier BV. - 0368-2048 .- 1873-2526. ; 178-179:C, s. 88-99
-
Journal article (peer-reviewed)abstract
- We present a brief overview of recent theoretical studies of the core-level binding energy shift (CLS) in solid metallic materials. The focus is on first principles calculations using the complete screening picture, which incorporates the initial (ground state) and final (core-ionized) state contributions of the electron photoemission process in X-ray photoelectron spectroscopy (XPS), all within density functional theory (DFT). Considering substitutionally disordered binary alloys, we demonstrate that on the one hand CLS depend on average conditions, such as volume and overall composition, while on the other hand they are sensitive to the specific local atomic environment. The possibility of employing layer resolved shifts as a tool for characterizing interface quality in fully embedded thin films is also discussed, with examples for CuNi systems. An extension of the complete screening picture to core-core-core Auger transitions is given, and new results for the influence of local environment effects on Auger kinetic energy shifts in fcc AgPd are presented.
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| 19. |
- Olovsson, Weine, 1975-
(author)
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Influence of Global Composition and Local Environment on the Spectroscopic and Magnetic Properties of Metallic Alloys
- 2005
-
Doctoral thesis (other academic/artistic)abstract
- Theoretical investigations of spectroscopic and magnetic properties of metallic systems in the bulk, as well as in nanostructured materials, have been performed within the density functional theory. The major part of the present work studies the differences between binding energies of electrons tightly bound to the atoms, the so-called core electrons (in contrast with the valence electrons), that is, core-level binding energy shift (CLS). By comparison between corresponding elemental core-levels for atoms situated in different chemical environments we obtain fundamental understanding of bonding properties of materials. The method of choice was the complete screening picture, which includes initial and final state effects on the same footing. The usefulness of CLS stems from that it is sensitive to differences in the chemical environment of an atom, which can be affected on one hand by the global composition of e.g. disordered materials, surfaces and interfaces, and on the other hand by the very local environment around an atom. Here CLSs have been obtained for both components in the fcc random alloys AgPd, CuPd, CuNi, CuPt, CuAu, PdAu, NiPd and NiPt. Moreover the model was extended to the Auger kinetic energy shift for the LMM Auger transition in AgPd alloys. Studies were also applied to the near surface and interface regions of PdMn nano structures on Pd(100), thin CuPd and AgPd films on inert Ru(0001), and at interfaces. The disorder broadening on CLS due to local environment effects was calculated in selected alloys.A part of the thesis concern investigations related to the magnetic ordering in Invar alloys, including the influence of local environment effects. A study was made for the dependence of effective exchange parameter on the electron concentration, volume and local chemical composition.
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| 20. |
- Olovsson, Weine, et al.
(author)
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Interface core-level shifts as a probe of embedded thin-film quality
- 2011
-
In: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 84:8, s. 085431-
-
Journal article (peer-reviewed)abstract
- We use first-principles calculations of layer-resolved core-level binding energy shifts (CLSs) within density functional theory as away to characterize the interface quality and thickness in embedded thin-film nanomaterials. A closer study of interfaces is motivated as properties specific to nanostructures can be related directly to the interface environment or indirectly as interference effects due to quantum confinement. From an analysis based on the Cu 2p(3/2) CLS for Cu embedded in Ni and Co fcc (100) and Fe bcc (100), with the interfaces represented by intermixing profiles controlled by a single parameter, we evaluate layer-resolved shifts as a probe of the thin-film quality. The core-level shifts in the corresponding disordered alloys, as well as local environment effects, are studied for comparison. We also discuss the possibility of detecting interface states by means of core-level shift measurements.
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